Library

Notes: The contribution of the 1-6 N-terminal sequence to the conformational properties of the S-peptide (the 1-20 sequence of ribonuclease A) was assessed by determining in the ribonuclease S′ system the helical content and the binding capability of synthetic [Orn10]-S-peptide analogs, in which lysine1, glutamic2 and threonine3 were progressively deleted, alanine4 and alanine5were alternatively replaced by serine, and alanine6 was substituted by serine or proline. Both the deletion of the three N-terminal residues and the alanine6/proline replacement produces the loss of the helical structure up to lysine7. No or minor effects are found in all other cases. From the comparison of the binding data, the energy for the conformational stabilization of the N-terminal region was calculated to amount to 1.4 kcal/mol. The results are discussed in comparison with the known x-ray data of the enzyme, with some predictive rules of secondary structure which were applied to this region and with the known phylogenetic variance of the residues in this region.

Notes: In the Polymerization of phenylalanine N-carboxyanhydride (NCA) in No2Oh initiated by MeNHBzl, L-,D-, and DL-NCA As were polymerized at the same rate, and no stereoselectivity was observed. When the same experiment was carried out in HCONEt2, however, L- and D-NCA were both polymerized at a rate which was about twice as large as that of DL-NCA. In this case, the polymerization is stereoselective, ascribable to a preferable reaction between the optical enantiomorphs of the terminal residue of the growing chain and the NCA of the same chirality. On the other hand, the polymerization initiated by SarNMe2 and MeNH(CH2)2CONMe2 were stereoselective in NO2Ph and HCONEt2, but they were not stereoselective in m-(MeO)2Ph. These findings indicate that the polymerizations initiated by a strong base in highly dipolar solvents are stereoselective. Apparently, the reaction between a chiral, cyclic terminal of growing chain and a chiral, cyclic activated NCA in the activated-NCA mechanism is highly stereoselective. In addition, from a kinetic investigation on on the copolymerization between L- and D-NCAs, the penultimate chiral centers were also suggested to contribute to the stereoselection. Stereoselection by the α-helical conformation of the growing chain and by a chiral, linear terminal amine have been considered so far, and the contribution from the present type of stereoselection must have been overlooked.

Notes: Transient electric birefringence measurements of the bacteriophages T2L0 and T6 were performed under such conditions that the tail fibers are extended. The data obtained are compared to previously reported data for T4B. For all T-even phages the degree of extension of the tail fibers is a function of pH, ionic strength, and temperature. For T4B, much higher ionic strengths are needed than for T2L0 and T6 to accomplish complete tail-fiber extension. The rotational diffusion coefficients of the phages with fully extended fibers are equal to 120 ± 3 sec-1, 132 ± 5 sec-1, 157 ± 4 sec-1 for T2L0, T4B, and T6, respectively. The respective optical anistropies are - (2.66 ± 0.05) × 10-4, and - (3.07 ± 0.15) × 10-4. The differences in the rotational diffusion coefficient and optical anisotropy arise because the conformation of the fully extended tail fibers is different for the three phages. The tail fibers of T2L0 project further into the solution (away from the head) than do those of T4B and T6. The apparent permanent dipole moments of T2L0 and T6 decrease with increasing ionic strength. This decrease is caused by the screening of the surface charges on the phage body by the counter-ions in the solution. The biological relevance of this decrease is illustrated by the fact that the adsorption rate of T6 phages to E. coli B bacteria shows a similar dependence of ionic strength. Evidence is pressented that the tail fibers may move more or less independently of the phage body when an electric field is applied to the suspension.

Notes: We have measured the ultraviolet CD spectra for covalently closed and linear forms of phage PM2 DNA in solution. We find that increased concentrations of salt or ethanol (up to 50% ethanol by weight) depress the long-wavelength positive CD bands in the spectra of both forms of DNA, although the spectrum of the native covalently closed DNA always has a slightly larger magnitude of these bands than does the spectrum of the linear DNA. In addition, both DNAs are equally capable of undergoing a transition to the A conformation in 70-80% ethanol at low Na+ concentrations. Thus, the constraint imposed by the covalent closure of a DNA molecule does not seem to hinder its conformational response to these changing solution conditions. Lang [(1973) J. Mol. Biol. 78, 247-254] has found by electron microscopy that T7 DNA has an inherent ability to condense into compact particles, suggested to be supercoils of multiple order. Both covalently closed and linear forms of PM2 DNA also become condensed when the DNA, in 0.2M ammonium acetate and 1 mM EDTA, is exposed to ethanol and subsequent drying on specimen grids [Lang, D., Taylor, T. N., Dobyan, D. C. & Gray, D. M. (1976) J. Mol. Biol. 106, 97-107]. Under similar conditions, in solutions of 0.2M ammonium acetate and 1 mM EDTA to which ethanol is added, we have measured the CD spectra of both covalently closed and linear forms of DNA. Below ethanol concentrations at which the DNA obviously precipitates, the CD spectra of both forms have reduced long-wavelength positive CD bands.

Notes: The polymeric cobalt(II) porphyrin complexes were prepared from cobalt(II) protoporphyrin IX dimethyl ester(Co(II)P) and copolymers of 4-vinylpyridine and styrene(PSP), and their binding ability of molecular oxygen was studied in toluene solution. The five- and six-coordinate structure of CoP-PSP complexes were confirmed by esr spectra. The esr parameters for the CoP-PSP complexes were not affected by the molecular weight and the vinylpyridine-unit content of PSP-ligand. The 1:1 dioxygen-Co complex was reversibly formed when the solution of CoP-PSP was exposed to oxygen atmosphere at low temperature. While the visible spectra and esr parameters for the dioxygen complexes of CoP-PSP were the same as those of the CoP-pyridine complex, the equilibrium constant for the oxygen binding increased with the vinylpyridine-unit content of the PSP-ligand. The larger entropy change was observed for the oxygenation in the CoP-PSP system especially, of which the vinylpyridine-unit content was large.

Notes: The low-temperature dynamic mechanical relaxation of ox Ligamentum nuchae elastin, swollen with water and ethylene glycol at various swelling ratios, has been investigated by means of the Rheovibron DDV II viscoelastometer, at frequencies from 3.5 to 110 Hz. The peak location on the temperature scale, its intensity and activation energy have been studied as a function of solvent content and it has been found that the two solvents influence the dynamic mechanical behavior in a quite different way. A similar interaction of the solvent molecules with the backbone peptide groups is assumed for both solvents, and the differences in the mechanical spectra, which are more marked the higher the solvation degree, are explained in terms of the different size of the protein-solvent relaxing units.

Notes: The relation between the chemical structure of a protein and the physical properties of a heat-set gel of that protein has been investigated. The physical properties of the gel are determined by means of mechanical experiments in which the viscoelastic properties of the gel are determined in terms of the storage shear modulus, the loss modulus and the stress-strain curve. The storage shear modulus defined the solid (elastic) character of the gel. The chemical structure of the protein and the nature of the solvent determine the nature and number of cross-links in the gel. The cross-links in gels formed by heating concentrated solutions of ovalbumin in 6M urea solutions were found to be disulfide bridges and the mechanical properties of these ovalbumin/urea gels approximated those of an ideal rubber. The latter finding enables one to calculate the number of cross-links per ovalbumin molecule from the value of the storage modulus, using the classical theory of rubber elasticity. This theory, together with the Flory-Huggins lattice model, can also be used to calculate the number of cros-links per ovalbumin molecule from the swelling behavior of ovalbumin/urea gels. The number of cross-links per ovalbumin molecule calculated from these two types of experiments are in mutual agreement and correspond with the number of thiol groups in ovalbumin. We conclude, thereforee, that theories of polymer physics can be used to relate the chemical structure of a protein to the physical properties of its gel.

Notes: The single-strand helix-coil transition in various oligo- and polyadenylates is characterized by means of an improved cable temperature-jump technique. In all the polymers studied {poly(rA), poly(dA), poly[A(m2′)] and poly[A(e2′)]} helix-coil relaxation is observed in the time range from 30 to 1000 nsec. Relaxation-time constants observed at wavelengths λ〈280 nm (τα) are different from those found at λ 〉280 nm (τβ), indicating the presence of more than two conformational states. The time constants τα increase in the series poly(dA), poly[A(m2′)], constants τβ/τα is approximately 2.5, except in poly(dA) where τβ/τα ≈ 9. Relaxation measurements with r(A)n- oligomers show a decrease in conformational mobility with increasing chain length. The relaxation curves also demonstrate that “internal” residues have lower reaction rates than residues at the ends of the oligomer chain. Measurement in D2O reveal a solvent isotope effect for τα of +87% for poly(rA), and of +53% for poly(dA), whereas no isotope effect is found in τβ. The absence of “slow” relaxation processes in the model compound 9,9′ -trimethylenebisadenine shows that the relatively low rate of the single-strand helix-coil transitions is due to the coupling of base stacking with the folding of the sugar-phosphate chain. The absence of a seprate relaxation process (corresponding to τβ) in 9,9′-trimethylenebisadenine, as well as in the dinucleotides ApC and CpA, suggests that this relaxation process is dependent upon the presence of both the sugar-phosphate chain and of adjacent adenine bases. The experimental data provide evidence that there is more than one ordered conformation in various single-stranded oligo- and polyadenylates and that the transition between these conformations is influenced by the sugar conformation.

Notes: An algorithm has been developed that permits one to find all possible conformations of the sugar-phosphate backbone for any given disposition of DNA base pairs. For each of the conformations thus obtained, the energy of the helix was calculated by the method of atom-atom potentials. Several isolated regions in the space of the bases′ parameters (Arnott's parameters) have been found for energetically favorable helical structures. Two parameters, the distance of a base pair from the helix axis, D, and the windling angle, τ, allow one to subdivide possible conformations into the families of closely related forms. Two regions (ravines) on the (D, τ) map correspond to the know A and B families. In the B family a continuous transition has been obtained in which the double helix undergoes increasing winding, while the base pairs are moving toward the major (nonglycosidic) groove.Interrelationships between the variables, characterizing the spatial structure of the double helix, D, τ, TL and χ, when going along the bottom of the B ravine, were also obtained.Besides the Known A and B families, several new ones were found to be energetically possible. Among these the strongly underwound helices with the negative D values, as well as the forms with the C4-C5 angle in a trans position, should be mentioned.Biological roles of the different double-stranded conformations, in particular, in protein-nuclei acid interaction are discussed.

Notes: The theoretical basis for the statistical mechanical deconvolution of a thermally induced macromolecular melting profile is presented. It is demonstrated that all the thermodynamic quantities characterizing a multistate macromolecular transition can be obtained from the average excess enthalpy function, 〈ΔH〉, of the system, without any assumption of the particular model or mechanism of the reaction.Experimentally, 〈ΔH〉 is obtained from scanning calorimetric data by direct integration of the excess apparent molar heat capacity function, ΦCp. Once 〈ΔH〉 is known as a continuous function of the temperature, the partition function, Q, of the system can be calculated by means of the equation \documentclass{article}\pagestyle{empty}\begin{document}$$Q_{\left( T \right)} = \exp \smallint _{T_0}^T {\left( {\frac{{\left\langle {\Delta H} \right\rangle }} {{RT^2}}} \right)} dT $$\end{document} From the partition function all the thermodynamic quantities of the system can be obtained. It is shown that the number of discrete macroscopic energy states, the enthalpy and entropy changes between them, and the relative population of each state as a function of temperature can be calculated in a recursive form.

Notes: The high-resolution 1H-nmr study of the ferrichrome cyclohexapeptides, in d6-DMSO solutions, has been extended to the amide NH spectral region. A total of ten diamagnetic analogues of ferrichrome that differ in the coordinated metal ion (Al3+, Ga3+ or Co3+), the primary structure, the nature of the bidentate hydroxamate moiety, or the isotope compositions (14N, 15N) have been investigated. The 3JαNH values reflect regiorous conformational isomorphism throughout the complete suite of analogues, quite independent of the residue occupancy of each site. Totally resolved amide multiplets have been obtained in most cases and the four-line (doublet of doublets) appearances of glycyl NH resonances has been observed for the first times; these data enabled stereospecific assignment and accurate analysis of the NH-CαH proton spin systems. The high resolution was made possible by the use of a suitable spectral deconvolution shceme at 360 MHz. The fine structure, extraordinarily well displayed in the 15N-peptide spectra, provides a series of parameter values whose consistency has been checked by computer simulation. Since the crystallographic structure for two of the ferric peptides is known to 0.002-Å resolution, a 3J vs θ correspondence could be confidently established. A Karplus curve was derived from the combined x-ray and nmr data: \documentclass{article}\pagestyle{empty}\begin{document}$$ ^3 J_{\alpha {\rm NH}} = 5.4\cos ^2 \theta - 1.3\cos \theta + 2.2{\rm Hz} $$\end{document} It is suggested that seriously nonplanar amides can exhibit 3JαNH values higher than predicted by the ferrichrome curve.

Notes: The general formulas describing the low-angular dependence of polarized (Vv) and depolarized (Hv) light-scattering intensity by a chain macromolecule of arbitrary form with anisotropic polarizability are derived. It is shown that the value dHv/dtHvo (where t = [〈R2〉S/L]2, S being the scattering vector) is an indication of the chain-flexibility mechanism. This permits one to distinguish between the models of a wormlike chain, regular zigzag, or statistical zigzag. The results of numerical calculations useful for the interpretation of experimental data are presented.

Notes: The kinetics of the fluorescence decay of the energy donor in a homologous series of oligopeptides each containing at its ends a donor and an acceptor of electronic excitation energy was investigated in solvent mixtures of different viscosities. The repeating unit in the peptides was N5-(2-hydroxyethyl)-L-glutamine and the chromophores used as donor and acceptor were naphthalene and dansyl, respectively. The number of units in the peptides studied varied from four to nine. The solvents used were mixtures of glycerol and trifluoroethanol in various proportions. The decay rate of the donor fluorescence increases when the solvent viscosity decreases. This behavior is due to the disturbance of the equilibrium end-to-end distribution of distance of the excited molecules by the energy transfer process, which is more favorable foe short than for long distances. The subsequent rearrangement towards the equilibrium distribution by diffusion of the molecular ends relative to one another enhances the efficiency of the energy transfer. Assuming a modified Fick equation to describe this diffusion motion, the fluorescence decay data were analyzed in terms of a diffusion coefficient describing the Brownian motion of the molecular ends. The diffusion coefficients thus evaluated increase systematically upon decreasing the solvent viscosity. For example, for the oligopeptides studied it changes from unmeasurably small values in glycerol solution to values varying between 10-8 to 10-7 cm2/sec at room temperature in a glycerol trifluoroethanol solvent mixture of viscosity of 8 centipoise. The values obtained for the diffusion coefficient are smaller by about an order of magnitude than the values expected for the diffusion coefficients of the free chromophores in solvents of comparable viscosity. It is thus concluded that the backbone of the polymeric chains possesses appreciable internal friction which exerts resistance to the Brownian motion of the polymer chains. The diffusion coefficient of the end-to-end motion is systematically smaller for the shorter than for the longer chains. For example, at room temperature in a solvent mixture of 8 centipoise it is 3×10-8, 5×10-8, 7.6×10-8, and 8.5×10-8 cm2/sec for oligomers containing four, five, eight, and nine N5-(2-hydroxylethyl)-L-glutamine repeating units, respectively. The internal friction thus impedes the motion of the molecular ends more effectively in the shorter chains than in the longer ones.Analysis of the energy-transfer experiments in solvents spanning a wide range of viscosities shows that the orientational factor appearing in Förster's equation for energy transfer does not interfere perceptibly with the evaluation of the end-to-end distances from the fluorescence decay data when naphthalene and dansyl serve as donor and acceptor, respectively. This is due to the fact that both the donor emission and acceptor absorption in the range of spectral overlap are characterized by more than one transition dipole moment, as is evident from the corresponding polarization data.

Notes: Raman spectroscopic studies have been carried out on polymers of L-valine ranging in degree of polymerization (DP) from 2 to 930. The spectrum of the hexapeptide (DP = 6) is closely similar over the entire range 40-1750 cm-1 to those of polymers with much higher DP, and the structure is clearly shown to be that of the antiparallel pleated sheet (β-structure) by the amide I and III frequencies. The formation of a little α-helical structure occurs in polymers with DP above 500, although the amount does not appear to be a linear function of DP. The α-helical structure is unstable and readily destroyed in samples cast from trifluoroacetic acid solution. It is stabilized by the incorporation of L-alanine, a strong helix-former; polymers of the latter may in turn be forced into a α-structure in copolymers sufficiently rich in L-valine.

Notes: The fluorescence properties of several cooligopeptides of glycine, phenylalanine, and tryptophan, containing one or two aromatic residues, are investigated. In particular, a detailed analysis is made of the influence of pH upon the quantum yield and the position of the emission maximum (λmax) in H-Trp-Trp-OH, H-Trp-Gly-OH, H-Gly-Trp-OH, H-Gly-Trp-Gly-OH, H-Trp-Trp-OH, H-Trp-Trp-Gly-OH, H-Gly-Trp-Trp-OH, H-Phe-Trp-OH, H-Phe-Trp-Gly-OH, H-Gly-Phe-Trp-OH, and H-Gly-X-(Gly)n-Trp-Gly-OH, with X = Phe or Trp, and n = 0,1,2. It is shown that raising the pH from ca. 2 to 11 results in a red shift of λmax, and an increase in the quantum yield. These changes, mostly structure dependent, are in most cases attributable to electronic perturbations acting directly upon the λmax of the fluorophore(s) and upon the quenching efficiency of the free amino and carbonyl groups. For the compounds having two adjacent tryptophyl residues, it is shown that the two fluorophores do not appear to have the same emission properties and the quantum yield is lower than expected. The causes of this behavior are discussed in terms of conformational effects, stacking interactions, and radiationless energy transfer. Finally, an attempt is made to correlate fluorescence data with previous circular dichroism data which had indicated the occurrence of a conformationally rigid structure for some of the compounds having two adjacent aromatic residues.

Notes: Group-specific polysaccharides isolated by means of a cetavlon procedure are immunogenic in man and induce protective immunity against meningococcal meningitis. Minute quantities of the polymers in solution can act as vaccines. We now report the first characterization of a fractionated (C-1) group C polysaccharide in 0.4KM KCl and 0.05M sodium acetate by means of light-scattering spectroscopy. Independent measurements of refractive index increments, absolute scattered intensities, angular scattering intensities and line widths as a function of scattering angles and delay times at different concentrations using incident wavelengths of 632.8 nm from a He-Ne laser and of 488 nm from an argon-ion laser yield information on aggregation properties, molecular weight (Mr), radius of gyration 〈r0g〉1/2z, translational diffusion coefficient 〈D〉0z, and second virial coefficients A2 and B2 of C-1 polysaccharide.At relatively high ionic strength (0.04M KCl + 0.05M sodium acetate), we obtain for the C-1 polysaccharide in solution Mr = 5.15 × 105, 〈r2g〉1/2z = 345 Å, A2 = 1.25 × 10-4 ml/g, 〈D〉0z = 1.16 × 10-7 cm2/sec with a corresponding Stokes radius of 240 Å and B2 = 4.4 ml/g. A2 and B2 are the second virial coefficients from intensity- and diffusion-coefficient measurements. The C-1 polysaccharide aggregates in solution and behaves hydrodynamically like random coils. Viscosity and sedimentation studies further confirm our conclusions that the fractioned C-1 polysaccharide aggregates in solution and EDTA can partially break up those aggregates. However, the system remains polydisperse even after adding an excess amount of EDTA. The weight-average molecular weight of the C-1 polysaccharide in solution depends upon ionic strength and exhibits a minimum at ∼0.2M KCl. Finally, viscosity, light-scattering, and sedimentation results all show that the aggregated macromolecular system behaves like random-coiled polymers with no measurable shape factors.

Notes: We extend fluorescence correlation spectroscopy to systems that undergo translation or laminar flow in a sample cell. We include theoretical and experimental results; we consider uniform and nonuniform velocity profiles. Concentration correlation analysis extracts microscopic rate parameters from measurements of the spontaneous concentration fluctutations, which occur even at equilibrium. Fluorescence is one of the most sensitive means of monitoring these fluctuations. Analysis of flowing or translating systems (1) offers a method of measuring number concentrations of selected species, for example, of aggregates or polymers, (2) provides a nonperturbing velocity probe, (3) sometimes allows one to circumvent photolytic degradation, (4) has proved extremely helpful in testing and aliging apparatus for fluorescence correaltion measurement and in verifying theoretical analyses, and (5) may be required for interpretation of results obtained on systems in motion, even though that motion is undesired or initially unsuspected. We include both theoretical and experimental results for combined Poiseuille flow and diffusion in the geometry which is of most practical interest. Theoretical expressions for the much simpler cases of nondiffusive Poiseuille flow as well as uniform flow or translation with or without diffusion constitute limiting cases which are displayed explicitly.

Notes: In the preceding article1 we demonstrated that the partition function of a system is experimentally accessible from scanning calorimetric data. In this article the general results of the deconvolution theory are applied to the general case of cooperative transitions in macromolecules. It is demonstrated that, in the limit of very large systems, all the relevant molecular averages and molecular distribution functions can be directly obtained from the experiment. In doing this, the method of the grand partition function is used. It is shown that in the case of homopolymers, only one parameter, the stability constant, needs to be explicitly specified for a complete description of the system. Since the partition function is directly evaluated from the experiment, no special assumptions or artificial constraints directed to obtain a mathematically solvable model are required. This result offers the unique opportunity of having direct experimental access to statistical averages of systems in which the partition function cannot analytically be solved. Consequently, the theory can be extended to cooperative transitions occurring in two and three dimensions by introducing cluster distribution functions.

Notes: The pyridoxal Schiff bases of the polypeptides poly(L-lysine), poly(L-ornithine), and poly(L-α,γ-diaminobutyric acid) were prepared and investigated in water/methanol by CD spectra and equilibrium dialysis experiments. Only the poly(L-α,γ-diaminobutyric acid) derivative is characterized by a relevant optical activity similar to that found in pyridoxal enzymes. The stereospecific interactions between the pyridoxylideneimine group and the polypeptide chain prevent the hydrolysis reaction of the aldimine bond.

Notes: The protein turkey-heart cytochrome c is used as a model protein to study charge effects in sedimentation equilibrium experiments in three-component solutions. Data are given for the dependence of the apparent M (1-υρ) on ρ in solutions of KCl, RbCl, CsCl, and triethylamine hydrochloride. The results show the Donnan effect to have a significant influence on the apparent molecular weight, found by extrapolation of the data to a solution density of one. The apparent molecular weights are for protein at infinite dilution. A theoretical treatment is presented where the magnitude of this effect can be predicted accurately from the formal net charge of the protein as computed from the amino acid composition. The results are shown to be important in computing the preferential hydration of the protein in concentrated salt solutions. For such systems the Donnan effect should be subtracted from the total interaction coefficient for multicomponent system in order to obtain the preferential hydration.

Notes: The cupric complexes of poly(Nε-acetoacetyl-L-lysine), [Lys(Acac)]n′ poly(Nδ-acetoacetyl-L-ornithine), [Orn(Acac)]n′ and poly(Nγ-acetoacetyl-L-diaminobutyric acid), [A2bu-(Acac)]n, as well as of the model compound n-hexyl acetoacetamide, have been investigated by means of absorption, potentiometric, equilibrium dialysis, and CD measurements. While in the complex of the model compound, one chelating group is bound to one cupric ion, in the polymeric complexes two β-ketoamide groups are bound to Cu(II) under the same experimental conditions. The binding constant of cupric ions to the three polymers and the formation constant of the Cu(II)-nhexylacetoacetamide complex have been evluated. Investigation on the chiroptical properties of the three polymeric complexes shows that the peptide backbone does not undergo conformational transitions, remaining α-helical when up to 20% of the side chains are bound to Cu(II). The optical activity of the β-ketoamide chromophores is substantially affected by complex formation and is discussed in terms of asymmetric induction from the chiral backbone.

Notes: The Mettler/Paar precision density meter DMA-02D has been used to determine the concentration of saturated solutions of amino acids at 20.0, 25.0, and 29.8 °C. The technique has proven itself an elegant and precise method. The solubilities of all of the amino acids with the exceptions of proline, lysine, and cystine have been measured. The Gibbs free energies of transfer from saturated water solution to 1M Na2SO4 and to 1M Gu·HCL along with the van't Hoff heats and entropies have been calculated. The van't Hoff heats have been compared with the calorimetrically determined heats for some of the amino acids. The Lumry-Rajender relation between the entropy and heats has been observed. The process of transfer of the amino acids from water to the solvents is primarily enthalpic rather than entropic.

Notes: The effect of magnesium ions on the parameters of the DNA helix-coil transition has been studied for the concentration range 10-6-10-1M at the ionic strengths of 10-3M Na+. Special attention has been given to the region of low ion concentrations and to the effect of polyvalent metallic impurities present in DNA. It has been shown that binding with Mg++ increases the DNA stability, the effect being observed mainly in the concentration range 10-6-10-4M. At[Mg++]〉10-2M the thermal stability of DNA starts to decrease. The melting range extends to concentrations ∼10-5M and then decreases to 7-8°C at the ion content of 10-3M. Asymmetry of the melting curves is observed at low ionic strengths ([Na+] = 10-3M) and [Mg++] ≤ 10-5M. The results, analyzed in terms of the statistical thermodynamic theory of double-stranded homopolymers melting in the presence of ligands, suggest that the effects observed might be due to the ion redistribution from denatured to native DNA. An experimental DNA-Mg++ phase diagram has been obtained which is in good agreement with the theory. It has been shown that thermal denaturation of the system may be an efficient method for determining the ion-binding constants for both native and denatured DNA.

Notes: Studies on the cross-linking of a tripeptide (t-butyloxycarbonyl-L-alanyl-D,L-2-amino-6-heptenoyl-L-alanine methyl ester) have shown that it is possible to form specific cross-links in good yields through Schiff base formation of the ε amino group of lysine. The heptenoic acid residue has been ozonized to an aldehyde and condensed with the ε amino of lysine in the compounds alpha-t-butyloxycarbonyl-L-alanyl-L-lysine methyl ester and alpha-t-butyloxycarbonyl-L-lysine methyl ester to form the cross-link, lysinonorleucine. This compound has been stabilized by reduction with sodium borohydride and quantitated on the amino acid analyzer. This technique converts from 60 to 98% of the available aldehyde to lysinonorleucine.

Notes: The determination of structural changes in antibodies due to their specific interaction with antigenic proteins is an important problem in understanding immunological responses. The method of polarized ATR infrared spectroscopy applied to protein films adsorbed on an appropriate solid surface can give information about the conformation of the polypeptide chains, as well as their orientation with respect to the surface. The adsorption of anti-rabbit serum albumin onto monomolecular films of rabbit serum albumin, bovine serum albumin, and ovalbumin, and of anti-ovalbumin onto films of rabbit serum albumin and ovalbumin at a Ge-aqueous interface have been studied by this technique. The intensity of the amide I absorption indicates that the strengths of binding of these three albumin proteins with anti-rabbit serum albumin is, under appropriate conditions, in the order rabbit 〉 bovine ≫ ovalbumin; with anti-ovalbumin, it is ovalbumin ≫ rabbit. Since the frequencies of the amide I band appear near 1655 cm-1 for all the proteins and protein complexes studied, the major contributions to their conformation comes from α-helix and random-coil structures. The average orientation of the transition moments of the amide I and A bands has been shown to be about 75° with respect to the surface normal. This indicates that the polypeptides chains are on the average approximately parallel to the surface for all the systems studied. Consequently, the effect of the specific antibody-antigen interaction on the conformation and orientation of the former seems negligible in these films.

Notes: The Raman spectra of guanylyl (3′-5′) guanosine (GpG) in solution in H2O and D2O at pH 3-7 have been recorded at various temperatures between 0 and 80°C. The results are consistent with the existence in the lower temperature range of stable aggregates formed by the stacking of GpG tetramers. The aggregates melt cooperatively near 60°C, which results in important changes in the spectra. Among these, a large increase in intensity of some of the bands assigned to the guanine residues shows that unstacking of the bases occurs at the melting. Also apparent in the spectra are changes in the intensity and frequency of band attributable to molecular groups involved in intermolecular hydrogen bonding between adjacent molecules in the complex. The melting temperature of GpG decreases by approximately 15°C upon lowering the concentration from 5 × 10-2 to 5 × 10-4M, as shown by Raman, calorimetric, CD, and uv measurements. The experimentally determined ΔH and ΔS for the melting transition are 9 Kcal/mol and 28 e.u./mol, respectively. The aggregation of GpG in 1.5 × 10-3M solutions was found to be very slow. The half-time of the process, which roughly follows first-order kinetics, is approximately 3 min at 10°C and 21 min at 35°C. The negative energy of activation associated with this reaction (-143 Kcal) indicated that the process involves intermediates whose concentrations decrease the temperatures raised, thus slowing down the overall process. The rate of disaggregation of GpG upon dilution to very low concentration is also extremely slow, indicating that the GpG aggregates, once formed, are very stable.

Notes: The Raman spectra of poly(L-lysine) with various structures, ionized poly(L-glutamic acid), and deuterated N-methylacetamides have been observed using visible and the 257.3-nm laser lines as the light source. Most of the Raman bands with significantly enhanced intensities in the uv-excited spectra of the polymers have been assigned to the vibrations associated with the C=O and C-N stretching modes, the amide I, II, III, I′, II′, and III′, with reference to the results obtained for simple amide molecules including the deuterated N-methylacetamides. Several amide frequencies have been newly identified and the structures of the polymers have been discussed through the comparison of the Raman and ir amide frequencies.

Notes: Real and imaganiry parts of complex dielectric constant of dilute solutions of DNA in 10-3M NaCl with molecular weight ranging from 0.4 × 106 to 4 × 106 were measured at frequencies from 0.2 Hz to 30 kHz. Dielectric increments Δε were obtained from Cole-Cole plots and relaxation times τD from the loss maximum frequency. The τD of all samples agrees well with twice of the maximum viscoelastic relexation time in the Zimm theory, indicating that the low-frequency dielectric relaxiation should be ascribed to be the rotation of DNA. The rms dipole moment, which was obtained from Δε, agree well with that calculated from the counterion fluctuation theory. The dielectric increment was found to be greatly depressed in MgCl2, which is resonably interpreted in terms of a strong binding of Mg++ ions with DNA.

Notes: Ultravoilet photoelectron spectroscopy has been employed to exmamin the valence electronic structure of 5-fluorouracil, 5-chlorouracil, 5-bromouracil, and 5-iodouracil. Photoelectron bands associted with the three highest π orbitals and the two oxygen atom lone-pair orbitals were assigned by a comparison to similar bands observed in the photoelectron spectrum of uraciul. Bands arising from the halogen atom lone-pair orbitals were assigned by comparing the present results with photoelectron spectra measured for halobenzenes, and by considering the linear dependence of halogen atom lone-pair ionization potentials upon halogen atom electronegativities. The present spectroscopic results have been compared with results from studies of association constants of 5-halouracil-adenine complexes. This examination in dicates that the complex association constants incresase as the ionization potentials of the highest occupied π orbital and the halogen atom lone-pair orbitals of th halouracils decrease.

Notes: Electric dichroism measurements on poly(A) in low-ionic-strength solution demonstrate that below a molecular weight of 130,000 the double-stranded polymer is hydrodynamically rigid and above that molecular weight becomes increasingly flexible. At 500,000 it is considerably more flexible than DNA of the same molecular weight, with a mean end-to-end distance of about 1150 Å compared to approximately 1600 Å for DNA. The fully extended length for both DNA and poly(A) of this molecular weight is about 2750 Å. It is further shown that the orientation of these polyelectrolytes in an electric field is consistent with theoretical treatments of the counter-ion distribution and a preliminary model based on the additivity of classical valence charge anisotropy and counter-ion polarization is postulated for the orientation mechanism. Single-stranded pol (A) is shown not only to retain its base stacking in the presence of the electric field but to extend the persistent regions of stacked bases so that it attains a rodlike structure very similar to the one in the double-stranded polymer is found to be less than that expected from consideration of the x-ray structure. An explanation for this result is sought in the electric asymmetry of the helical polymer.

Notes: The effect of hydration on the solid-state conformation and relaxation behavior of the alkaline earth salts of poly (L-glutamic acid) has been examined. The calcium and strontium salts take the β-conformation and the magnesium salt takes the α-form. No hydration-dependent conformational transitions were observed. The amount of bound water, as measured by differential scanning calorimetry, appears to depend on the size of the cation, while conformation has little or no effect. A relative measure of the barrier to side-chain reorientation was obtained from the temperature of the side-chain (β1) relaxation. It was found that the barrier is determined by electrostatic forces and increases with increasing cation surface charge density. Side-chain motion also appears to be more hindered in the β-conformation than in the α-conformation.

Notes: An optimized potential function for base-stacking interaction is constructed. Stacking energies between the complementary pairs of a dimer are calculated as a function of the rotational angle and separation distance. Using several different sets of atomic charges, the electrostatic component in the monopole-monopole approximation (MMA) is compared to the more refined segmented multipole-multipole representation (SMMA); the general features of the stacking minima are found to be correctly reproduced with IEHT or CNDO atomic charges. The electrostatic component is observed to control the location of stacking minima. The MMA, in general, is not a reliable approximation of the SMMA in regions away from minima; however, the MMA is reliable in predicting the location and nature of stacking minima. The attractive part of the Lennard-Jones 6-12 potential is compared to and parameterized against the expression for the second-order interaction terms composed of multipole-bond polarizability for the polarization energy and transition-dipole bond polarizabilities for approximation of the dispersion energy. The repulsive part of the Lennard-Jones potential is compared to a Kitaygorodski-type repulsive function; changing the exponent from its usual value of 12 to 11.7 gives significantly better agreement with the more refined repulsive function. Stacking minima calculated with the optimized potential method are compared with various perturbation-type treatments. The optimized potential method yields results that compare as well with melting data as do any of the more recent and expensive perturbation methods.

Notes: The 1H-nmr spectra (270 MHz) of cyclic di- and tri-L-azatidine-2-carboxylic acid [cy-clo(L-Aze)2 and cyclo(L-Aze)3] were determined in CDCl3 and D2O and computer simulated. The spectral results were compared with those obtained with cyclo (L-Pro)2 and cyclo (L,-Pro)3. In CDCl3 and D2O solution, the four membered ring of cyclo (L-Aze)2 is puckered with the α-proton in a pseudo-axial position, and the φ angle is smaller in absolute value than -60°, as found for cyclo (L-Pro)2,. The puckering of the four-membered ring of cyclo(L,-Aze)3 in CDCl3 has the α-proton in a pseudo-equatorial position and φ angle larger in absolute value than -60°, in agreement with cyclo(L-Pro)3. In D2O, cyclo(L-Aze)3 was found to interconvert rapidly between different conformers. In the azetidine cyclic peptides studied, the range of values found for the φ angles was smaller than in the related proline cyclic peptides, indicating greater rigidity in the four-membered ring.

Notes: The study of the Cu(II)-hyaluronate complexes by absorption and CD spectra, as well as by acid-base titration and viscosity, provides information about the nature of ligands and the conformation of the polymer. Three different complexes have been identified. The first (complex I), which is formed between pH 3 and 6, involves mainly the carboxyl groups of the polymer as ligands and is characterized by a strong absorption band at 238 nm. In this complex formation, the CD properties of hyaluronate do not charge appreciably. The second (complex II) forms between pH 6 and 8 bad shows a major change in CD properties. The changes include (1) a new positive CD band at 250 nm and a strong negative on in the π → π* amide transition region and (2) the disappearance of the negative n → π* amide CD band near 210 nm. A sharp increase in absorbance at 238 nm from complex I to II has been attributed to a conformational transition which is also manifested in the CD features of hyaluronate. Complex II involves, in addition to the carboxyl group, the nitrogen atom of the deprotonated acetamido group coordinated to Cu(II). The absorption at 230-280 nm is associated with the optically active charge-transfer transitions involving ligands to metal ion. At higher concentrations of the polymer or at higher pH, complex II aggregates to a gel, complex III. Chondroitin, differing from hyaluronic acid in the C-4 hydroxyl group configuration of the glucosamine moiety, does not show any CD change in the presence of Cu(II).The results provide further support to our fourfold helical structure of Cu(II)-hyaluronate complex at pH between 6 and 8. Intrinsic viscosities of hyaluronate in the presence of the cupric ion is lower than in the presence of other monovalent or bivalent cations, indicating a compact conformation of the polymer when it is complexed with Cu(II).

Notes: The far-uv CD spectra of eight lectins are presented. These eight lectins, as well as others previously studied, are grouped into three classes according to their particular CD spectra. The eight lectins studied appeared to have secondary structure dominated by β-pleated sheet, which so far has been true of all lectins. An attempt was made to quantitate the three structural components (α-helix, β-pleated sheet, and aperiodic) in the lectins using the data for reference proteins given by Chen et al. [Biochemistry 13,3350 (1974)]. For lectins in two of the classes, this method proved excellent and values for the three components are given. However, for the third class of lectins, which includes most of the lectins as well as Concanavalin A, this method of analysis proved to be unsatisfactory. This inadequacy was due to two factors: (1) the reference proteins used by Chen and (2) the unusual CD spectra of these lectins manifested by considerable ellipticity above 225 nm in a region where there are no known peptide electronic transitions.

Notes: In an attempt to better our understanding of the conformational stabilities in RNAs, an intensive theoraticl study has been carried out on one of its dimeric subunits, ApA, using an improved set of atom-atom interaction energy parameters and an improved version of energy-minimization technique. The C(3′)0endo and the C(2′)-endo sugar ApA units were sperately considered and 38 probable conformations have been analyzed in each case. The total potential energy, comprising nonbonded, electrostatic, and torsional contributions, was minimized by varying all seven relevant dihedral angles simumtaneously. The result reveal that 17 conformations in the case of C(3′)-endo sugar ApA and 7 confomations in the case of C(2′)-endo sugar ApA unit, the lowest energy conformation corresponds to a nonhelical structure and the A-RNA and the Watson-Crick-yype conformations lie at energy levels of about 0.5 and 1.0 Kcal/mo., respectively, above the lowest energy found. For ApA with the lops of different types in the backbone and they all differ in energies by about 3.5 Kcal/mol with refrence to the lowest energy founs. It is noted that the order ofmprefrence of the base stacking is observed in the A-RNA and the Watson-Crick type conformers. The ApA unit with C(2′)-endo sugar is forced to assume phosphodiester conformations with large deviations fom the expected staggered conformations compared to the ApA unit with C(3′)-endo sugar. The result obtained for ApA are discussed with refrence to those previously obtained for the dApdA unit. Te theoretical predictions are compared with the experimental data on the tRNAPhe crystal, as well as those on fibrous RNAs and RNa subunitlike crystal structures. This study brings out many important aspects of the conformational stability of ApA which have been missed by studies made by others on this system.

Notes: The synthess of 18 co-oligopeptides of L-methionine and glycine is reported. A series of oligomers, Boc-Gly-Metn-OMe (n = 1-6), and six hexamers-containing five methionyl and one glycyl residue were synthesized using the mixed anhydride procedure. Polarimetric studies give evidence that oligomers in the Boc-Gly-Metn-Ome series are essentially disordered in hexafluoroacetone sesquihydrate but begin forming secondry structures at n 〉 4 in trifluorethanol. Difference in the molar rotation values found for the six hexamers in hexafluoroacetone sesquihydrate may indicate that these compounds, while primirily disordered, are present in slightly different conformations.

Notes: Monodisperesed, N-and C-Protected homo-oligopeptides [number (n) of resides from 2 to 5] of L-valine, L-isoleucine, and L-phenylalnine were studied by ir absorption spectroscopy between 1200 and 350 cm-1 at various solvents. The solvents and chain-length effects were examined for non-hydrogen-bonded peptide groups. The frequencies of the self-associated species are consistent with a model derived from the amide data. Self-association species are consistent with a model derived from the amide data. Self-association is favored by higher values of n = 2, the peptide is insoluble when more than two chains are bonded. For n = 3, 4, several chains may be associated by sliding along one another and remain soluble. For n = 2, the peptide is insoluble when more than two chains are bonded. For n = 3, 4, several chains may be associated by sliding along one another and remain slouble. For n = 5, the effect of n is to favour a model in which two chains exactly face each other so that the peptide precipitates at relatively low concentration.

Notes: Possible conformations of X-D-alanyl4-D-alanine5 and its analogs X-L-analyl4-D-alanine5 X-D-alanyl4-L-alanine5, X-D-butyl4-D-alanine5, X-D-alanyl4-D-butyric acid5, X-D-valyl4-D-alanine5, and X-D-alanyl4-D-valine5 have been analyzed by theoretical methods. These studies suggest that L-alanine and D-valine at the 4 or 5 postion of the pentapeptide moiety of peptidoglycan will drastically reduce the cross-linking in peptidoglycan biosynthesis, whereas the effect of D- butyric acid will be marked at the 4 postition and modeate at the 5 position. This is in good agreement with experimental results. The cross-linking enzyme transpeptidase requires a specific confroamation for the 4th and 5th residues for optimal binding.

Notes: Infrared dichroism measurements of oriented films of poly(dA)·poly(dT) and poly[d(A-T)]·poly[d(A-T)] have been made under the conditions of low salts content and high humidity for which the geometry is known. The angles which the transition moments make with the helix axis are compared with the orientations of the corresponding bonds. Except for the in-plane base model of poly[(A-T)]·poly[d(A-T)], there is no agreement. This may imply either that a model which assumes bonds and transition moments to be colinear is not acceptable or that x-ray data are inaccurate. These possibilities are discussed especially with respect to phosphate group orientation. An appendix gives the derivations of dichroic-ratio expressions for helical molecules of different symmetry types.

Notes: Measurements of fluorescence depolarization on fumarase labeled with the dye pyrene-butyryl were used to test for previously reported structural changes in this enzymes. These apparent conformation changes were of interest because they seemed to correlate with variation in catalytic activity provoked by changing temperature or pH, or by the presence of a competitive inhibitor. In the present studies, the bound dye pyrene-butyryl and the enzymes were investigated systematically to ensure that simple interpretation of fluorescence depolarization results would be meaningful. This analysis showed that carefully controlled experimental condition were necessary to eliminate a dye component with a short fluorescence lifetime and that it was essential to allow for small variations of lifetime with temperature. Contrary to the previous report, a constant rotational relaxation time of the magnitude expected for a nearly spherical molecule of fumarase was found. No changes were detectable by fluorescence depolarization in the size or shape of pyrene-butyryl-fumarase under the solution conditions tested that caused variation in enzyme activity.

Notes: Several cyclic hemopeptides containing L-azetidine-2-carboxylix acid (Aze) - an imino acid homologous with proline but containing one less methylene group in its cyclic side chain - have been prepared. The peptides reported include (Aze)2, cyclo(Aze)3, and cyclo(Aze)6. The synthesis and spectral characterization of these cyclic peptides are described, and the results discussed in terms of the rigidity and steric constraints attributable to Aze-containing peptides. CD spectra of these materials in several solvents are reported and compared with those of proline analogs; the similarity between the CD spectra of cyclo(Aze)3 and cyclo (Pro)3, is noted.

Notes: The application of rotating frame spin-lattice relaxtion to the determination of the intramolecular motions in peptides is discussed, and results are presented on the application of 13C T1p to peptide microdynamics in solution. The effective molecular rotational reorientation times at the amide and amino nitrogens may be derived from appropriate data onT1p of the carbons adjacent to them. We also show by theoretical caculations that 1H and 13C T1p experiments of suitable 2H and 15N substituted peptides will allow intramolecular main- and sidechain motions, characterized by times in the range 10-1-10-6 sec, to be investigated.

Notes: A Monte-Carlo method including long-range interactions is used to oligopeptide chains in random-coil state. The chains are composed of 4, 9, or 14 repeating units and are labeled with the luminopheres tyrosine or tryptophan. Interactions with a solvent (water) are taken into account in the calculations through modifications of the semiempirical potential-energy functions. The chains represent oligopeptides composed of hydrophobic or hydrophilic amino acid residues. Various properties relavent to the interpretaiton of nonradiative enrgy-transfer experiments, such as the average value of the orientation factor for dipole-dipole interaction of the luminophores, 〈k2〉, the distribution function of the distances between the luminophores f(rl), the efficiences of energy transfer in the static and dyamic averaging regimes, 〈T〉s amnd 〈T〉d, as well as the fluorescence decay I(t) of the donor luminophore in various averaging conditions, are computed. It is shown that, for all chains considered, 〈k2〉 is not vary far form 0.67 and that 〈T〉s and 〈T〉d have completely different values. Due to the small extent of correlation between the distances rl and the mutual orientations of the lumninophores, the decay kinetics 〈I(t)s corresponding to a static averaging regime can be expressed in terms of distribution functions f(rl). These results are in agrrement with those obtained previously for the unperturbed chain model.

Notes: For a better understanding of the interactions between DNA and various acridine dyes, the binding of acridine (Acr) and 10-methylacridine (MeAcr) to native and heat-denatured calf-thymus DNA was studied in the pH range between 4 and 10 by the equilibrium dialysis and spectroscopic methods. The binding between DNA and the dyes was predominantly electrostatic. The amount of bound Acr varied with pH, mixing ratio (P/D), and the DNA conformation, and reached a maximum at pH = 5.2. The amount of bound MeAcr was constant in the pH range 5-9. The apparent binding constants of these dyes were obtained at some pH, and they were found to vary with P/D for native DNA-dye complexes. The pure spectra of bound Acr and MeAcr could be unmasked. The bound Spectra were bathochromic and hypochromic relative to the spectra of free days. Acridine bound to native DNA was shown to undergo structural changes from an acridiniumlike to a neutral acridinelike form as the pH of solutions was varied. The pK value for the transition between the bound forms was evaluated to be 7.3. The extrinsic Cotton effects of the bound dyes were observed in the DNA-Acr and-MeAcr complexes and varied with pH and the conformation of DNA.

Notes: An x-ray structural study of the 1-methylcytosine H+ complex reveals asymmetrically hydrogen-bonded dimers which are further stacked such that the molecular overlaps are between charged and neutral bases. This study supports the assignment of the asymmetry in the interbase hydrogen bonding in the cytidine-cytidine H+ hydrogen-bonded complex. Furthermore, it is suggested that hemiprotonated, helical polyribocytidylic acid has as its translational repeat unit a set of highly stacked pairs of asymmetrically hydrogenbonded bases. The asymmetry in the interbase hydrogen bonding is stimulated, at least in part, by base-stacking considerations.

Notes: Diffusion data of helium, nitrogen, oxygen, and carbon dioxide through glassy cellulose triacetate were obtained and analyzed by the modified time-lag technique of DiBenedetto and Paul. Thermodynamic data were evaluated and a probable mechanism for gaseous diffusion is discussed.

Notes: Poly(phenylthiirane)s obtained by polymerization with different initiators were degraded to isomeric cyclic dimers 1, 2, 3, and 4 by treatment with cationic initiators. Analysis of the mixture of the four different isomers gives evidence of a fast transalkylation reaction when a cationic initiator is present in the polymer solution.

Notes: Rate and association constants (kf and K, respectively) for the addition of sulfite ion to three flavins (including isoalloxazines) and to four flavin-containing polymers were determined at 30°C in aqueous systems. The forward reaction rates for polymer-bound flavins at an ionic strength of μ = 0,18 mol/l were enhanced by factors of 15-37 and the association constants by factors of 7-19, compared with those of the corresponding monomeric flavins. A linear log kf - log K relationship was found for monomeric flavins. While the parameters for polymer-bound flavins deviated to the upper area by 0,5-1,0 log units. An increase in the salt concentration suppressed markedly the reaction parameters for polymer-bound flavins, and the log kf - logK plot at μ = 0,7 mol/l was involved in the linear relation for monomeric flavins.

Notes: The formation of a charge-transfer complex (CTC) between maleic anhydride and tetrahydrofuran both in bulk and in chloroform solution is proved by electronic absorption spectroscopy, and its association constant at 35°C is determined by this technique and by 1H NMR. The effect of irradiation with monochromatic 350 nm light upon the fluorescence spectrum of the CTC excited with this same radiation is studied. Significant changes are noted in the bulk system, but the changes are much smaller in the presence of methyl methacrylate which is simultaneously polymerized. The effect of oxygen on the polymerization is discussed.

Notes: Natural abundance 15N NMR spectra of various aliphatic lactams and of the corresponding polyamides were measured in trifluoroacetic acid. Cis and trans amide bonds were found to have nearly identical shifts and identical 1JNH coupling constants. Increasing chain length of the monomeric units and increasing ring size result in a downfield shift of the 15N signals. The 13C NMR spectra display, on the other hand, remarkable shift differences for lactams and Nylons. The polyamides show a monotonic downfield shift of the carbonyl signal with increasing chain length of the monomeric unit in contrast to the lactams. The 13C NMR spectra of the lactams were measured in various solvents; they show a downfield shift of the carbonyl signals with increasing acidity of the solvent. Protic solvents also favor strongly the cis-form of 1-aza-2-cyclononanone over the trans-form.

Notes: Series of polyamides were prepared from p-phenylenediamine, and aliphatic α,ω-diamines on the one hand, and fumaric acid, isophthalic acid, terephthalic acid, and aliphatic α,ω-diacids on the other hand. The natural abundance 15N NMR spectra of these polyamides were measured in trifluoroacetic acid, and relationships between the chemical shifts and the structure of the monomer units are discussed. Increasing chain length of the aliphatic diamines results in increasing downfield shift of the diamines themselves and of the polyamides derived from them. No “γ-effect” or similar deviations from the monotonic shift function are observed; however, the influence of the diacid residues on the chemical shift is less regular. The shifts of the homopolyamides are useful for assigning or predicting the shifts of copolyamides. The 15N NMR spectrum of the copolyamide “Trogamide T” is discussed.

Notes: The synthesis and the conformational studies of the following sequential polypeptides are reported: poly(alanyl-3-aminopropanoic acid), poly(alanyl-4-aminobutanoic acid), poly(alanyl-5-aminopentanoic acid), and poly(alanyl-6-aminohexanoic acid). These compounds were examined in the solid state by X-ray diffraction and in solution by circular dichroism spectroscopy. X-ray diffraction patterns indicate that all copolymers assume an antiparallel pleated-sheet conformation. The results in solution suggest that the synthetic polypeptides, in 2,2,2-trifluoroethanol (TFE)/methanol exhibit a β-conformation. The addition of water to a solution of copolymers in TFE destabilize this ordered structure except in the case of poly(alanyl-6-aminohexanoic acid).

Notes: Results of studies on the determination of the initiation rate of the copolymerization reaction of acrylonitrile with methyl methacrylate, initiated by 2,2′-azoisobutyronitrile in N,N-dimethylformamide at 60°C are reported. The inhibition method used was that involving the stable Banfield's radical (N-[1,1-dimethyl-3-(N-oxidophenyliminio)butyl]-N-phenylaminyl oxide).In the case of acrylonitrile an effect of a side reaction of initiation with the stable radical was observed along with a retarding effect due to inhibition reaction products.In the homopolymerization of methyl methacrylate there takes place a slight effect from a side initiation reaction due to the Banfield's radical, the inhibition reaction products not influencing the further course of the polymerization reaction.The overall contribution of the side initiation reaction changes in the copolymerization of acrylonitrile with methyl methacrylate for different comonomer mixtures with their composition, the actual changes being non-additive. The initiation rate depends on the composition of the monomer mixtures and may be described by the following relation: \documentclass{article}\pagestyle{empty}\begin{document}$ R_i = R_{i,{\rm AN}} \cdot X_{{\rm AN}}^{0,66} + R_{{\rm i,MM}} \cdot X_{{\rm MM}}^{{\rm 1,30}}, $\end{document} where Ri, AN=(8,20±0,15).10-7 mol.dm-3.s-1 and Ri, MM=(7,75±0,25).10-7 mol.dm-3.s-1.

Notes: The influence of antioxidants and ionic agents on Depolarization Thermocurrents (DTC) of low density polyethylene has been studied. Ionic agents increase the height of the potential barrier which + involved in the relaxation observed at highest temperature/lowest frequency at a given frequency/temperature (χ). The relaxations observed at lower temperature/higher frequency (β and γ) are not modified by ionic agents but by antioxidants: the activation energy of the relaxation time increases and the preexponential factor decreases for both β and γ modes. Some of the processes constituting the β and γ modes are non-ohmic. They may be attributed to charge motions.

Notes: The kinetics of aqueous polymerization of acrylamide, initiated by the potassium persulfate(K2S2O8)/2-mercaptoethylamine hydrochloride (MEAH) redox pair was studied under nitrogen atmosphere at 30 ± 0,1 °C. The initial rates of polymerization were found to be proportional to [K2S2O8]1,5 (in the range of 0,8 to 1,2 mmol-1), to [acrylamide]1 (in the range of 0,8.10-1 to 1,2.10-1 mol 1-1), and to [MEAH]1 (in the range of 1,0 to 7,0mmol 1-1), respectively. The overall energy of activation was found to be 9,8 kcal mol-1 (40kJ mol-1). Water miscible alcohols and common salts (NaF, NaCl, (CH3)4NI) appeared to depress both the polymerization rate and the maximum conversion. With MnSO4.4H2O the reverse influence was found.

Notes: Methylene groups of 1,4-polybutadiene were partially brominated with N-bromosuccinimide. A subsequent Grignard-Wurtz-reaction with 4-methoxyphenyl-, 3,4-dimethoxyphenyl-, and 2-thienylmagnesium bromide resulted in an exchange of the bromine atoms for 4-methoxyphenyl, 3,4-dimethoxyphenyl and 2-thienyl groups. Another type of modification was the reaction of 1,4-polybutadiene with 4-methoxytoluene and o-resp: p-toluic acid methylester in the presence of dicumyl peroxide. Thereby 4-methoxyphenylmethyl and 2- resp. 4-methoxycarbonylphenylmethyl groups were introduced into the polymer. The modified polymers were investigated by IR-spectroscopy and degraded by olefin metathesis with 4-octene using a WCl6/Sn(CH3)4 catalyst. The degradation products were separated by gas chromatography and identified by mass spectrometry.

Notes: The thermal polymerization of acrylonitrile initiated by the cerium(IV)/acetaldehyde (A) redox system was carried out at 25°C, and the rate of monomer disappearance, -d[M]/dt, was followed by gravimetry and the rate of cerium(IV) disappearance -d[Ce(IV)]/dt by titrimetry. -d[M]/dt was found to be directly proportionsl to [M]3/2, [A]1/2, and [Ce(IV)]1/2. -d[Ce(IV)]/dt was found to be directly proportional to [Ce(IV)] and [A]. A reaction scheme is given together with the kinetic expressions. The activation energy for the overall rate was found to be 67,24kJ.mol-1 (16,06kcal.mol-1), and the value of the second order rate constant kr, was obtained as 2,481.mol-1s-1.

Notes: The stepwise syntheses of cyclo{quater[(5-alkyl-2-hydroxy-1,3-phenylene)methylene]}s (5) are described and compared with a one-flask reaction procedure. The structures of the cyclic compounds 5 are analytically confirmed and their properties were compared with those of linear phenol formaldehyde condensates which have very similar structures and molecular weights.

Notes: Structural changes in an ethylene-rich ethylene-propylene-diene terpolymer (EPDM) were studied as a function of applied external stress. From its initial unstretched value of 15%, the terpolymer crystallinity increased to 73% at a tensile strain of 225%. X-ray diffraction patterns showed that, when stretched, the terpolymer assumed a hexagonal structure and an increase in the until cell a-dimension occurred. A fibre texture developed with the lamellae inclined to the tensile axis.

Notes: NMR shift reagent, tris(dipivalomethanato)europium(III), was applied to the 1H NMR measurement of isotactic and syndiotactic poly(methyl methacrylate) in solution in the temperature range 25-80°C. The solvents used were benzene (C6D6), chloroform (CDCl3), and carbon tetrachloride (CCl4). By comparing the observed values of paramagnetically induced shift with the values of geometric factor calculated for several kinds of conformational models hitherto proposed for these polymers, the possible conformations of the respective polymers in solution were eludicated. Furthermore the variation, as a function of temperature, of the carbon-13 spin-lattice relaxation times of individual carbons of isotactic and syndiotactic poly(methyl methacrylate) in benzene and chloroform solutions were measured and the correlation between the molecular motion and the conformation is discussed. It is pointed out that the conformation depends both on the stereochemical configuration and the nature of solvent, and the molecular motion depends both on the conformation and the configuration.

Notes: Polyesters and copolyesters of 2-hydroxyacetic acid (glycolic acid) and 2-hydroxypropionic acid (lactic acid) were investigated by direct pyrolysis in the ion source of a mass spectrometer. Thermal degradation of these polyesters and copolyesters at 10-6 mbar yields cyclic oligomers which are further degraded by an electron impact induced mechanism by elimination of formaldehyde or acetaldehyde and CO2 to give characteristic series of linear ions. In the pyrolysis mass spectrum of a copolyester (mole ratio of monomeric units ≈1:1) intact sequences up to 8 monomeric units can be observed.

Notes: Polymerization of mixtures of D- and L-isomers of α-amino acid N-carboxy anhydrides follow normal copolymerization behavior, and sometimes even ideal copolymerization, which is conventionally interpreted as leading to a random distribution of monomer units along the polymer chains. Equations are dereived which relate the fraction of isotactic L-diads to experimental data from the previously reported methods involving sequential and stereospecific cleavage with enzymes. The application of these equations to poly(D,L-leucines), which were prepared by polymerization of racemic leucine N-carboxy anhydride with chiral and achiral primary amines as initiators, indicated that the polymers contain between 94 and 98% isotactic diads. The poly(leucines) thus consist of long stereoblocks despite the observed ideal copolymerization behavior.

Notes: Isotactic and syndiotactic poly(alkyl methacrylate)s (R = CH3, C2H5, isoC3H7, n-C4H9 and t-C4H9) were prepared by anionic mechanism and the spin-lattice relaxation times T1 of individual carbons and protons were measured mainly in toluene-d8 by the inversion-recovery Fourier transform (IRFT) method. The T1's of the carbons in the isotactic polymers were consistently longer than those of the comparable carbons in the syndiotactic polymers. The ratios of 13C-T1's for syndiotactic and isotactic polymers were always in the range of ca. 0,4-0,6 for all types of carbons. The 13C-T1's decreased with an increase in the bulkiness of the ester group in both polymers. From the measurements of the nuclear Overhauser enhancement (NOE) it was found that the spin-lattice relaxations of carbons in polymethacrylates are dominated by 13C-1H dipolar interactions and that the extreme narrowing condition is satisfied at least above 70°C. The effect of solvent on 13C-T1 was also studied. The results of the measurements of 1H-T1's were parallel to those in the carbons' case. It was concluded that the dependence of T1 upon the configuration of the polymer is mainly caused by the configurational dependence of the segmental mobility of the polymer.

Notes: Addition of two molecules of sec-butyllithium to one molecule of m-diisopropenylbenzene produces a bifunctional initiator which is soluble in non-polar solvents. This initiator is quite efficient for the polymerization of isoprene and butadiene and allows the preparation of samples of particular interest: bifunctional polydienes with high 1,4-cis and 1,4 contents, respectively, and by using a cross-linking agent elastomeric gels even after removal of the solvent.

Notes: The olefin polymer metathesis reaction in the case of polybutadienes is influenced by the nature of the connection and the distribution of the 1,2-units.

Notes: N-(tert-Butoxycarbonyl)-L-leucyl-D-leucyl-L-leucyl-D-leucine tetrapeptide was synthesized from L- and D-leucine α-amino acids by conventional coupling methods. This tetrapeptide was transformed into an activated (polymerizable) tetrapeptide by conversion to the pentachlorophenyl ester and subsequent removal of the tert-butoxycarbonyl group. Condensation polymerizations of the activated tetrapeptide were performed in various solvents with triethylamine and N,N-diethyl-1-amino-2-propanol bases. Molar masses (“molecular weights”) of the resulting polymers were estimated to be in excess of 34000 g/mol. From optical rotation measurements in trifluoroacetic acid solution, it was found that the polymers were highly syndiotactic, although a small amount of isomerization (0,9-2,1%) occurred to yield polymers with a small excess of L-leucine residues. The degree of isomerization decreased with decreasing base strength and concentration and with decreasing polarity of the solvent; these effects were explained in terms of the simultaneous enolization and/or oxazolone-formation reactions.Preliminary studies of the conformation of syndiotactic poly(leucine) were performed with X-ray diffraction, NMR, IR and optical rotation methods. It was concluded that syndiotactic poly(leucine) most probably exists in a π-helical conformation with a preferred screw sense in both the solid state and in chloroform solution. NMR and optical rotation data on solutions in trifluoroacetic acid/chloroform showed that the polymer exhibits a conformational transition in the region of 4-10% trifluoroacetic acid content.

Notes: The two leading terms in the perturbation series expansion of the second virial coefficient A2 have been derived for a three-block copolymer. The theoretical dependences of second virial coefficients on composition of a two-block copolymers AB, b three-block copolymers ABA and c mixtures of two homopolymers A and B have been compared at low values of the excluded volume parameters zA, zB and zAB. It follows from these calculations that with increasing thermodynamic quality of the solvent (with respect to both homopolymers) the effect of repulsive interaction between unlike segments of types A and B on the second virial coefficient of the copolymer decreases. The applicability of perturbation series to block copolymers is discussed.

Notes: The change of the radial structure during the thermofixation of poly(ethylene terephthalate), [poly(oxyethyleneoxyterephthaloyl)], fibres with and without shrinkage is studied.The fibre structure is described by interferometric measurements, which allow statements about order and orientation as a function of the fibre radius. The fibre interferograms are interpreted by an analytical model, which has been developed in the first part of this series.

Notes: N-(3-Vinylphenyl)-2,5-dimethoxy-4-methylbenzamide (3) was synthesized. By copolymerization of 3 and of N-(2,5-dimethoxy-4-methylphenyl)-4-vinylbenzamide, respectively, with 4-vinylpyridine and 1,4-divinylbenzene protected redox resins were obtained. By removal of the protective groups the corresponding free redox resins were obtained. Their chemical stability and redox capacities were investigated. The influence of the anilinocarbonyl group on the midpoint potential of the hydroquinone/quinone system was studied on the model compound N-phenyl-2,5-dihydroxy-4-methylbenzamide.

Notes: Styrene was copolymerised with butyl acrylate and butyl methacrylate, resp., in a solution of benzene, conducting the reaction to various conversions (5-95%). The over-all composition of the copolymers was analysed by IR-spectroscopy and elemental analysis. At sufficiently low yields the copolymerisation parameters were determined according to Fineman-Ross and Mayo. After a slight adjustment of these parameters the integrated copolymerisation equation by Meyer and Lowry could be applied very well to describe the results, even at high yields. By using this equation, distribution curves of the chemical composition of the copolymers were calculated. Benoit's parameters P and Q of chemical heterogeneity were evaluated as a function of composition of the reaction mixture and conversion.

Notes: The solubilization of anthracene, naphthalene and Orange OT by micelles of cetyltrimethylammonium bromide (hexadecyltrimethylammonium bromide), sodium laurylsulfate (sodium dodecylsulfate) and dode-cylamine hydrochloride has been measured at 30°C. These data and others obtained from the literature are interpreted in terms of the solubilization number n and the aggregation number N by using a very simple equation relating n, N, the critical micelle concentration (CMC) and the molar solubility of the solutes. The interpretation of the solubilization leads to a new, simpler and less empirical method of finding the CMC from solubilization data. Values of n less than 1, close to 1 and much greater than 1 were found.

Notes: Cross-linking of amylose with 1-chloro-2,3-epoxypropane (epichlorohydrin) was studied in aqueous 1M NaOH solution in dependence of the amylose concentration, the mole ratio of anhydroglucose to epichlorohydrin, and the degree of polymerization of the primary chains. Structural changes which occur during the pre-gel phase were followed by chemical analysis, by viscosity and light scattering measurements, and by the optical properties of the iodine complex. The results indicate in the early stage of the process that the introduced glycerol diether groups are mainly present as intermolecular cross-links as seen from a rapid increase in the molecular weight. With further progress of the reaction a decrease of particle density may be derived from the unusual dependence of intrinsic viscosity and mean square radii of gyration on molecular weight. The results are discussed being due to association of amylose segments by hydrogen bonds in the weakly cross-linked products and a solubilizing effect of monoether substituents introduced later on.

Notes: In the asymmetric addition of 1-dodecanethiol to isopropenyl methyl ketone catalyzed by the terminal primary amino group of oligo((S)-alanine) (1c), the trimer and the tetramer in β-conformation gave much higher optical yield than the monomer and the dimer in random conformation. A similar result was obtained in the catalysis by β-alanyl-poly((S)-alanine) (3).

Notes: Synthesis of Nε,N′ε-(pyromellitoyl)dilysine (8) was carried out by reacting L-lysine with dimethyl pyromellitate (6) followed by thermal imidation. The obtained product 8 was reacted with Cu2+ ions to form a light blue chelate polymer (9). Model compounds, Nε-phthaloyllysine (4) and its copper chelate complex 5, were also synthesized by a similar process for comparison. IR spectra, optical and solubility properties of the monomer and its chelate polymer together with their corresponding model compounds were investigated. The thermal stability of chelate polymer 9 in acid solution of different pH value were also investigated.