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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: Neue technische Entwicklungen, Änderungen im Rohstoffangebot oder bei den Rohstoffpreisen, aber auch Forderungen des Umwelt- und Arbeitsschutzes führen dazu, daß die technische Herstellung von anorganischen und organischen Basisprodukten weit stärkeren Veränderungen unterworfen ist, als die Lehrbücher vermuten lassen. „Chemie in unserer Zeit“ setzt mit dem vorliegenden Beitrag eine lockere Folge von Berichten über aktuelle Verfahren zur Herstellung industrieller Basischemikalien fort.

Notes: Die Linienformanalyse der 1H- und 13C-NMR-Spektren wird zur Bestimmung der Aktivierungsparameter der Valenzisomerisierung von verschieden substituierten Spironorcaradienen zu Spirocycloheptatrienen 5 ⇌ 6 herangezogen. Während die Aktivierungsparameter bei Dibenzospironorcaradienen 5a, b vergleichbar sind mit denen der einfachen Norcaradienderivate, treten bei den Daten der Tetrachlorderivate 5c, d erhebliche Abweichungen auf.

Notes: Radikale mit Bicyclo[3.2.1]octan-Gerüst wurden ESR-spektroskopisch untersucht, um Aussagen über nichtbindende Wechselwirkungen in Radikalen zu gewinnen. Die Ähnlichkeit der Spindichteverteilung in 7 und 8 zeigt, daß 7 den Charakter eines bicyclischen Allylradikals besitzt. Eine merkliche Wechselwirkung wischen HOMO-Allyl und LUMO-Doppelbindung in 7 existiert nicht. Gleiches gilt, wenn anstelle der Doppelbindung ein Benzolrest anelliert ist. Die experimentellen Befunde werden mit INDO-Rechnungen verglichen.

Notes: Die thermische Isomerisierung von Thiophosphorsäure-O-2-butenylester-O,O-dimethylester (1b) (Schema 3) verläuft nach einem Geschwindigkeitsgesetz 1. Ordnung. Die Polarität des Mediums beeinflußt nicht die Aktivierungsparameter und übt lediglich einen minimalen Einfluß auf die Geschwindigkeitskonstanten aus. Die kinetischen Daten und der festgestellte „spezielle“ Salzeffekt lassen den Schluß zu, daß diese Isomerisierung einem intramolekularen ionischen Mechanismus folgt. Als ionische Zwischenstufe werden Ionenpaare postuliert.

Notes: 1,2-Diphenyldiphosphan (1) wird - entgegen Literaturangaben - bei der Reaktion von KHPPh mit 1,2-Dibromethan gebildet. Reines 1 ist durch Hydrolyse oder Alkoholyse von Me3Si(Ph)P - P(Ph)SiMe3 unter Lichtausschluß erhältlich und bei - 30°C beständig. Es disproportioniert bei Raumtemperatur in PhPH2, höhere Homologe der Reihe H2[PPh]n  -  insbesondere H2[PPh]3 - und cyclische Phenylphosphane [PPh]n  -  vor allem [PPh]5. Diese Umlagerungen werden durch Licht, Phosphide sowie starke Säuren und Basen beschleunigt. Mit K(Ph)P—P(Ph)K, Me3Si(Ph)P—P(Ph)SiMe3 oder P2Ph4 reagiert 1 zu den unsymmetrischen Diphosphanen K(Ph)P—P(Ph)H, Me3Si(Ph)P—P(Ph)H bzw. Ph2P—P(Ph)H. Die NMR-, IR- und Raman-Spektren von 1 werden diskutiert.

Notes: Organic Syntheses by Means of Transition Metal Complexes, 6: Synthesis of Ketenimines via Ketenimine Complexes, Isocyanide Carbene Addition and Ketenimine Carbene Rearrangement in Metal ComplexesTransition metal carbene complexes of the Fischer type, e. g. pentacarbonyl(methoxymethyl-carbene)chromium(0), add isocyanides to give ketenimine complexes (1). Ligand displacement by excess isocyanide affords ketenimines (3), which can be isolated in good yields. In contrast to free ketenimine, the nucleophilic attack on ketenimine coordinated to a metal occurs at the terminal carbon atom leading to carbene complexes. The structures of the ketenimine complexes of chromium (1) and tungsten (2), the product of isomerization (5)(2) of the chromium complex, and the products formed by addition of methanol or water (6 and 7, resp.)(2) are discussed, using 13C NMR data.

Notes: Die Hexa- und Decahydrobenz[a]anthracene 3 und 5 sind in einem einstufigen Verfahren durch Diels-Alder-Reaktionen der Tetrahydrobenzo[b]furane 2 mit 2,3-Didehydronaphthalin (1) bzw. mit dem Naphthalin-endoxid 4 zugänglich. Die Reaktionsfolgen 3 → 6, 7 und 8 sowie 5 → 9 zeigen die vielfältigen Abwandlungsmöglichkeiten der Primäraddukte 3 und 5 zu hydroxy- und oxo-substituierten (partiell hydrierten) Benz[a]anthracenen auf.

Notes: Die Vinylfluoride 5-8 wurden durch Umsetzung der entsprechenden Olefine mit BrF und sich anschließende Dehydrobromierung dargestellt und die Solvolysereaktionen in mehreren Lösungsmitteln untersucht. Die Reaktionsprodukte sowie die unter verschiedenen Bedingungen gemessenen Solvolysegeschwindigkeiten deuten auf einen Verlauf der Solvolyse über Vinylkationen.

Notes: Die Darstellung von 9-Methylentricyclo[4.2.1.02,5]nonan (3), 8-Methylentricyclo[3.2.1.02,4]octan (2) und ihrer Derivate, sowie von Methylenhomocuban (37) und 9-Methylenpentacyclo-[4.3.0.02,4.03,8.05,7]nonan (38) wird beschrieben.

Notes: Die cis-Hydroxylierung des Naphthopyrans 5 liefert als Hauptprodukt das Ketol 9. Daneben können das epimere Ketol 11 und die hydroxylierten Chinone 2 und 13 isoliert werden. Das Syntheseprodukt 2 ist die 6-Desoxy-Verbindung des Naturstoffs Cryptosporin (1). Über die Stereochemie der katalytischen Hydrierung des Ketols 9 und die Reduktion mit Natriumborhydrid und Diisobutylaluminiumhydrid wird berichtet.

Notes: Die Kinetik der Säurehydrolyse des Tetraaquamono(salicylaldehydato)chrom(III)-Kations in perchlorsaurer Lösung wurde in Abhängigkeit vom Zusatz verschiedener Anionen bei 70°C und konstanter Ionenstärke untersucht. Die Hydrolyse wird durch die Oxyanionen Sulfat und Nitrat stark beschleunigt, während die Halogenid-Ionen Chlorid und Bromid die Reaktionsgeschwindigkeit nur geringfügig erhöhen. Dieses Ergebnis wird mit dem „cis-Effekt“ der Oxyanionen erklärt. Der Reaktionsablauf wird mit einem assoziativen Interchange-Mechanismus (Ia) interpretiert.

Notes: Heterocyclotetraaromaten waren bisher unbekannt. Es wurden 4 Vertreter (6a, 7, 9, 11) mit nucleophilen aromatischen Ringgliedern und 1 Vertreter (13b) mit elektrophilen aromatischen Ringgliedern dargestellt. Mit einer Ausnahme erfolgte die Cyclisierung der Vorstufen durch oxidative Kupplung.

Notes: Dimethylhydrazone (DMH's) 6-10 von enolisierbaren Aldehyden und Ketonen können mit n-Butyllithium und/oder Lithium-diisopropylamid in Tetrahydrofuran quantitativ in α-Stellung metalliert werden. Die so erhaltenen Lithiumderivate 11-14 sind hochreaktive Kohlenstoffnucleophile. Ihre Verwendung als Enolatäquivalente wird über die Sequenz Carbonylverbindung, DMH-Derivat. Metallierung, Reaktion mit Alkylhalogeniden (→ 16, 18, 19) und Spaltung zur α-substituierten Carbonylverbindung (17) an einer Anzahl von Beispielen demonstriert. Die Alkylierungen erfolgen, von Spezialfällen abgesehen, regiospezifisch am weniger substituierten Kohlenstoffatom. Cyclohexanonderivate werden stereoselektiv axial alkyliert, was zur Darstellung von trans-disubstituierten Cyclohexanonen ausgenutzt wird. Zur quantitativen Spaltung der Dimethylhydrazone zurück zu den Carbonylverbindungen unter milden Bedingungen (pH 7, Raumtemperatur) wurde eine neue oxidative Hydrolyse entwickelt. Die Vorteile der Methode werden kurz diskutiert.

Notes: Die Lösungsmittelvariation übt auf kleine Bildungsgeschwindigkeiten der Sulfonsäureamide 3 aus Sulfonsäurechloriden 1 und Anilinen 2 einen größeren Einfluß aus als auf die rascheren Umsetzungen reaktiverer Ausgangssubstanzen (s. Tab. 1 und 2). Im Gegensatz dazu steht der Anstieg der Selektivität mit zunehmender Reaktivität, wenn in einem Solvens die Substituenten X und Y der Sulfonsäurechloride 1 und Aniline 2 variiert werden(5). Dieser Widerspruch zwischen Gültigkeit des Reaktivitäts-Selektivitätsprinzips (RSP)(1) bei Lösungsmittelwechsel und seiner Ungültigkeit bei Substituentenvariation läßt sich mit dem gegenläufigen Einfluß der Substituenten X und Y auf die Bindungsbildung und den Bindungsbruch deuten (s. Übergangszustände 4 und 5 im Reaktionsschema 1). Es wird geschlossen, daß das Versagen des RSP nicht mit einem Versagen des Hammond-Postulats einhergeht.Selektivitätsmessungen bei unterschiedlichen Temperaturen zeigen, daß die isoselektiven Temperaturen (Tis) dieser Reaktionsserien bei ca. 190°C liegen (s. Tab. 3 und 5. Abb. 2).

Notes: Aus dem Cyclosteroid 1 wie den A-Nor-Steroid-dienen 2 und 4 wurde durch HBr-induzierte, regioselektive Doppelbindungsisomerisierungen das 17α-konfigurierte A-Nor-Steroid-dien 3a dargestellt. Die Isomerisierungen (Δ8(9) bzw (Δ8(14) → Δ14) verlaufen bei 1, 2 und 4 bei Einhaltung spezieller Reaktionsbedingungen unter Konfigurationsinversion der 17β-Isopropylgruppe, vermutlich über ein spirocyclisches Zwischenprodukt. Aus 3a wurde 20-Methyl-14β,17α-pregn-4-en-3-on (9a) erhalten.

Notes: MINDO/3-Berechnungen der Konformation und der Bindungsstärken bei substituierten 1,2-Dioxetanen (3-7) zeigen, daß die O—O-Bindung durch zunehmende Alkylsubstitution gestärkt wird. Damit sollte die Stabilität des Moleküls und der Synchroncharakter des Zerfallsmechanismus zunehmen. Substituenten mit freie Elektronenpaaren (OR, F) hingegen schwächen die C—C-Bindung soweit, daß der Zerfall zu Produkten im elektronischen Grundzustand unter bevorzugtem Öffnen der C—C-Bindung möglich erscheint.

Notes: Durch Umsetzung der Grignard-Verbindung von 1 mit den α,ω-disubstituierten Alkanen 2-4, 7 unter Katalyse mit Li2CuCl4 werden die Verbindungen 6a, b, 8, 9 synthetisiert. Die Reaktion des Lithiumsalzes von 12 mit den Dihalogenalkanen 10a, 11b in THF/HMPT und nachfolgende Hydrolyse ergibt die Verbindungen 14a, b mit Ketten von 38 und 46 Kohlenstoffatomen. Durch Wiederholung dieser Reaktionsfolge werden die Alkin-Derivate 18a, b mit Ketten von 64 und 72 Kohlenstoffatomen erhalten.

Notes: Bei n→π*-Anregung mit Natrium-Licht vereinigt sich Xanthion (1) mit Acenaphthylen, Inden bzw. N-Phenylmaleinimid in guten Ausbeuten zu den Spirothietan-Derivaten 3, 7 bzw. 8. Die analogen Photoreaktionen (λ ≍ 400 nm) der 2-Thioparabansäure 4 in Gegenwart von Inden, Benzo[b]furan bzw. N-Phenylmaleinimid verlaufen unter Bildung der Spirothietane 6a, b bzw. 9. Spektroskopische Daten sichern die Konstitutionen.

Notes: Der Isothioharnstoff 1a reagiert mit den Sulfonylisocyanaten 2a-c zu den stabilen 1,4-Dipolen 3a-c, die sich spektroskopisch sowie durch Protonierung zu den Harnstoffen 7 charakterisieren lassen. An einem Beispiel (3b) wurde die Molekülstruktur durch eine Röntgenstrukturanalyse aufgeklärt. Die höher substituierten Isothioharnstoffe 1b-g setzen sich mit 2a, b in einer [2 + 2]-Cycloreversion zu den Isocyanaten 5 und den N-Sulfonylisothioharnstoffen 6 um. Mit (Thio)-Benzoylisocyanat (2d, e) entstehen nach dem gleichen Reaktionsprinzip N-(Thio)Benzoylisothioharnstoffe 8.

Notes: Aus N,N-Dimethyl-(E)-styrylamin (1) und halogensubstituierten Methansulfonylchloriden (2a-e) entstehen neben acyclischen Substitutionsprodukten (4a-e) mit hoher Selektivität die 2r-Halogen-3c-dimethylamino-4t-phenylthietan-1,1-dioxide (3a-c). Durch Cope-Eliminierung aus 3a-c erhält man ausschließlich die 2-Halogen-4-pheny-2H-thiet-1,1-dioxide (5a-c). Die nachträgliche Einführung von Halogen in die 2-Position von 4-Phenyl-2H-thiet 1,1-dioxid gelingt ebensowenig wie dessen Oxidation zum 2-Oxoderivat.

Notes: 2-Benzoyl-3-chlorbenzo[b]thiophen-1,1-dioxid (1a) reagiert mit Semicarbazid, 4-Methylbenz-amidrazon, 1,8-Diaminonaphthalin zu 1c-e, mit KSCN zu dem Senföl 1g: durch Hydrolyse von 1g erhält man 1h, zu dem man auch durch Umsetzung von 1a mit Ammoniak gelangt. 1a reagiert mit Natriumazid zu 2b, mit Hydrazin zu 2a. Saure Hydrolyse von 1d führt zur Verbindung 3. 3-Aminocrotonsäure-ethylester kondensiert mit 1a zum Pyridinderivat 4: mit Guanidin, Benzamidin und Acetamidin erhält man die Pyrimidinabkömmlinge 6a-c. 1g reagiert mit Anilin zu 5, 1a mit o-Phenylendiamin, Ethylendiamin und N-Methylethylendiamin zu Diazepinverbindungen 8a-c, mit o-Aminothiophenol zum Benzothiazol 9.

Notes: Die Folgereaktionen nach der Stickstoff-Abspaltung aus 2-Diazo-12-methyl-1-cyclododecanon (15) werden untersucht. Am intermediären 12-Ring-α-oxocarben 17 wird das erste Beispiel einer photochemisch und thermisch ausgelösten 1,2-Sauerstoffverschiebung in cyclischen α-Oxocarbenen beschrieben. Die Umlagerung verläuft über das kondensierte Oxiren-System 18. Das Auftreten der beiden isomeren α-Oxocarbene 17 und 17′ wird durch die nachfolgende 1,2-Wasserstoff-verschiebung zu isomeren α,β-ungesättigten Ketonen (19, 20 und 19′, 20′) belegt. Im Gegensatz dazu wird bei der silberoxid-katalysierten Reaktion keine Oxiren-Beteiligung gefunden.

Notes: Molecular orbital calculations indicate substantial barriers to internal rotation in thiadiborolene-Fe(CO)3 and diazaborolene-Cr(CO)3 complexes. The equilibrium geometry of the two molecules should also differ. A fragment analysis explains these results and leads to a general analysis of rotational barriers in heterocyclopentadienyl and substituted cyclopentadienyl-ML3 and -ML2 complexes. In the latter an interesting “slipping” from η5 toward η2 coordination is predicted.

Notes: 1,6-Methano[10]annulene-Cr(CO)3 and several related complexes adopt an anomalous orientation of the Cr(CO)3 unit with respect to the polyene, compared to all other hexatriene-Cr(CO)3 complexes. A theoretical analysis of this problem shows that these conformational preferences are closely related to the cycloheptatriene-norcaradiene valence tautomerism. Several strategies for influencing the barrier to internal rotation in these complexes are presented. An analysis of the conformational preference, rotational barrier, and bending of the exocyclic methylene group in fulvene-Cr(CO)3 is also discussed. This is extended to the analogous benzyl-Cr(CO)3 and cyclobutadiene-carbinyl-Fe(CO)3 cations. Finally, the orientations of these complexes are contrasted to those containing two more electrons.

Notes: N,N′-Dimethyl- (1a-c), N,N,N,N′-Tetramethyl- (9a-c) und N,N′-Dimethyl-N,N′-diphenyl-diamide werden durch Chlorierung unter UV-Bestrahlung in die entsprechenden Bis(chlormethyl)- (2a-c, 13, 14) bzw. Tetrakis(chlormethyl)diamide (10a-c) übergeführt. Chlorierung von N,N′-Dimethyldichlormalonamid (1c) mit überschüssigem Chlor führt in guter Ausbeute zum N,N′-Bis(dichlormethylen)dichlormalonamid (5). Die Verbindungen werden NMR-spektroskopisch und durch Substitutionsreaktionen charakterisiert. N-(Dichlormethylen)benzamid (15) reagiert mit Dimethylsulfoxid zum N-Benzoyl-S,S-dimethylsulfimid (17), das thermisch teilweise zu N,N′-Methylendibenzamid (19) abgebaut wird.

Notes: Nach den Gleichungen (1) und (2) wurden Komplexe des Typs cis-[Pd(C ≡ CR)2(dpe)] sowie cis-[Pd(C ≡ CC6H4C ≡ CH-o)(Cl)(dpe)] dargestellt (dpe = (C6H5)2PCH2CH2P(C6H5)2; R = H, C6H5, CH3). Die cis-Struktur dieser Verbindungen wird durch ihre IR-Spektren bzw. 31P-NMR-Daten belegt.  -  Die Komplexe cis-[Pd(C2R)2(dpe)] reagieren mit überschüssigem KC ≡ CR gemäß Gleichung (4) zu den nicht ganz reinen Tetrakis(alkinyl)palladaten(II). K2[Pd(C2R)4]. Beide Komplextypen lassen sich gemäß Gleichung (5) oder (6) zu den schon lange bekannten Palladium(0)-Verbindungen K2[Pd(C2R)2] reduzieren.

Notes: 3,4,6-Tri-O-acetyl-1,2-didesoxy-D-arabino-hex-1-enopyranose (1a) reagiert in Acetonitril mit Natriumazid, Kaliumthiocyanat und Kalium-O-ethyl-dithiocarbonat unter Bortrifluorid-Etherat-Katalyse zu den entsprechend in 1-Stellung substituierten 2,3-Didesoxy-2-enopyranosyl-Verbindungen 2a, 3a, 11a und 11b. Sie unterliegen bereits bei Raumtemperatur einer allylischen Umlagerung unter Bildung der 3-substituierten Glycale 4a, 5a, 12a und 12b. Im Falle der Azidoverbindungen sind die Umlagerungen reversibel und führen zu Gleichgewichten zwischen Glycalen und Pseudoglycalen. Ähnliche Ergebnisse werden mit anderen Glycalen erhalten. Durch Allylumlagerung an Glycalen sind auch C-verzweigte Zucker zugänglich, wie durch die Umlagerung von 14 nach 15 und die Bildung von 18 aus 17 gezeigt werden konnte.

Notes: Functional Derivatives of Trimethylphosphine. VII: Ambivalent Behaviour of Tetrakis(trimethylphosphine) iron: Reaction with CH3ITreatment of the title complex 1a ⇌ 1b with CH3I in pentane at ambient temperature yields L4(CH3)Fel(L = P(CH3)3). The reaction is shown to proceed via oxidative addition to the iron(0) isomer 1a. In ether at lower temperature, a reaction with the iron(II) isomer 1b predominates, which leaves its hydridoiron function unchanged. So, a hydridoiron iodide complex is formed, probably by attack on the Fe—C bond.

Notes: Durch Ringschluß von 2-Hydroxybenzimidsäure-Derivaten 1 und 2 mit Carbonyl-Reagenzien werden 2H-1,3-Benzoxazin-2-one 3 und 4 erhalten. Heterocyclische o-Hydroxycarboximidsäure-Derivate 5 bzw. N,N′-überbrückte Amidine 7 liefern die mehrkernigen Analoga 6 bzw. 8.

Notes: 3,5-Dimethoxy-4-phenyl-1-benzothiepin-1-oxid kristallisiert in der rhombischen Raumgruppe P212121. Die Struktur der Verbindung wurde, röntgenographisch mittels direkter Methoden bestimmt. Der Siebenring besitzt eine stark aufgewölbte Bootform mit exo-ständigem Sauerstoff der Sulfoxid-Funktion.

Notes: Synthese und thermisches Verhalten der diastereomeren 9-Methyl- und 4,9-Dimethyl-cis-bicyclo-[6.1.0]nona-2,4,6-trien-9-carbonitrile 1a,b und 10a,b werden beschrieben. Die in den Systemen 1a und 1b entartete Bicyclo[6.1.0]nonatrien ⇌ Bicyclo[6.1.0]nonatrien-Umlagerung konnte am Beispiel der Dimethylderivate 10a und 10b experimentell nachgewiesen werden. Die wechselseitige Umlagerung 10a ⇌ 11a ⇌ 12a ⇌ 13a bzw. 10b ⇌ 11b ⇌ 12b ⇌ 13b erfolgt bei 102.5°C ([D6]Benzol) stereospezifisch mit der von Woodward und Hoffmann postulierten Inversion am wandernden Kohlenstoff C-9. Außer durch das stereochemische Ergebnis wird der synchrone Charakter dieser Umlagerung durch den energetischen Parameter wahrscheinlich gemacht. Der Unterschied der Gibbs-Aktivierungsenergie für die Öffnung der Cyclopropanbindung C-1 - C-9 in der Bicyclo[6.1.0]nonatrien → Bicyclo[4.2.1]nonatrien-Isomerisierung 1a → 7a + 7b, 1b → 7a + 7b und in der Umlagerung 10a → 11a, 10b → 11b beträgt in jedem Fall ca. 7 kcal/mol und legt einen aromatischen Übergangszustand für die entartete Umlagerung nahe.

Notes: Aus den 19F-NMR-Spektren von N-(Fluorphenyl)guanidinen und ihren Salzen werden die Taftschen σ1- und σR-Werte errechnet. Die Umlagerung des N-Nitro-N′-phenylguanidins (1) in starker Säure verläuft intermolekular als Nitrierung eines N-Phenylguanidinium-Ions durch NO2⊕. Es entstehen o- und p-Nitroderivate mit relativ zu Benzol nur geringfügig reduzierter Geschwindigkeit. -- Zusammen mit 35Cl-NQR-Messungen (1) und der Beeinflussung von Redoxpotentialen bei Guanidinochinonen(2) zeigen diese Befunde, daß die Guanidinogruppe als mesomerer Elektronendonator wirkt.  -  Neben dem erwarteten  -  I-Effekt zeigt die Guanidiniumgruppe trotz ihrer positiven Ladung und der Einschränkung der Mesomerie im Guanidinsystem einen deutlichen + M-Effekt.

Notes: 3,4-Diethyl-2,5-dimethyl-Δ3-1,2,5-thiadiborolen (1) reagiert mit den Hexacarbonylen des Chroms und Molybdäns photochemisch zu den Mono- und Bis(thiadiborolen)-Komplexen 2, 3 und 4, 5. Letztere zeigen größere thermische und hydrolytische Stabilität als die Tetracarbonyl-Verbindungen. 4 entsteht auch aus 1 und (C6H6)Cr(CO)3. Aus den spektroskopischen Daten wird auf das Vorliegen von pentahapto-Thiadiborolen-Komplexen und cis-Anordnung der CO-Gruppen in 4 und 5 geschlossen.

Notes: Cyclopeptide werden in einer Sauerstoffatmosphäre photochemisch-radikalisch unter Benzophenon-Katalyse zu Mono- und Bishydroperoxiden (1, 2, 4, 6, 8, 10, 11) oxidiert. Die gleichen Produkte entstehen auch bei der Oxidation mit Hilfe von Radikalstartern.

Notes: Die elektrochemische Reduktion des 1-Methyl- (2) und 1,4-Dimethyl-2,3-dioxo-1,2,3,4-tetra-hydrochinoxalins (3) führt im sauren Medium in einer ungewöhnlichen vierelektronigen Reduktionsstufe zu 1-Methyl- (4) bzw. 1,4-Dimethyl-3-oxo-1,2,3,4-tetrahydrochinoxalin (5), die unter Autoxidation jeweils die Ausgangsverbindungen zurückbilden. Die Mechanismen der Reduktions-und Reoxidationsprozesse werden diskutiert und experimentell belegt. Es wird gezeigt, daß bei der Autoxidation die Stufe eines 1-Methyl-3-oxo-3,4-dihydrochinoxalinium-Kations (15, 16) durchlaufen wird und der eingeführte 2-Carbonylsauerstoff aus dem Wasser stammt.

Notes: Die 6,7-Dioxotetrahydropteridine 1-9 warden synthetisiert und der kathodischen Elektro-reduktion unterworfen. Die 8-unsubstituierten Derivate 1-5 werden im allgemeinen sowohl im sauren als auch alkalischen Medium in einem vierelektronigen Prozeß zu den entsprechenden 6-Oxo-5,6,7,8-tetrahydropteridinen (13-17) reduziert, wogegen bei den 8-Alkyl-Derivaten 6-9 die Reduktion nach Aufnahme von 2 Elektronen auf der 8-Alkyl-7-hydroxy-6-oxo-5,6,7,8-tetrahydro-Stufe (19-22) zum Stillstand kommt. Die 2,3-Dioxotetrahydropyrido-pyrazine 10-12 zeigen analoges Reaktionsverhalten unter formaler Reduktion einer Oxo-Funktion zu 23-26 neben der Bildung kleiner Mengen an Dimeren (27, 28). Die Konstitutionen der neu synthetisierten Verbindungen werden durch spektroskopische Untersuchungen gesichert.

Notes: Die Iminophosphorane 2a-i und 6a-c bilden mit Aminodiiminophosphoran 1 stabile Addukte, für die aufgrund der spektroskopischen Befunde und der thermolytischen Spaltung die cyclischen Strukturen 3a-i bzw. 7a,b und 8b,c vorgeschlagen werden.

Notes: 35)Cl-chemische Verschiebungen (δ35Cl) von 17 Alkylchloriden und 4 Alkenylchloriden werden mitgeteilt. Eine lineare Korrelation zwischen δ35Cl und δ19F analoger Fluoride für Alkylhalogenide des Typs CnH2n+1 X und CnH2nX2 zeigt den gleichsinnigen Einfluß des Alkylrestes auf die chemischen Verschiebungen δ35Cl und δ19 F. Bei mehr als zwei Halogenatomen pro Kohlenstoff versagt diese Beziehung, ebenso bei Alkenylhalogeniden; Gründe hierfür werden diskutiert. Zwischen der berechneten Ladungsdichte am Chlor und δ35Cl läßt sich keine lineare Korrelation herstellen.

Notes: Radikale mit Bicyclo[3.2.1]octan-Gerüst (2, 11-13) werden auf eine Umlagerung in tricyclische (3) und tetracyclische Radikale (4) untersucht. Produktanalysen und ESR-spektroskopische Studien zeigen, daß die Radikale mit Bicyclo[3.2.1]octa-2,6-dienyl-Gerüst am stabilsten sind. Dies trifft auch zu, wenn in 3-Stellung (11-13) von 2 radikalstabilisierende Gruppen eingeführt werden, welche die Konstitution 4, nicht aber 2 stabilisieren können. Auf Grund dieser Ergebnisse ist es nicht überraschend, daß die von Tricyclo[3.2.1.02,7]oct-3-en (17) und Tetracyclo[3.2.1.02,7.04,6]-octan (18) abgeleiteten Radikale sich in das Bicyclo[3.2.1]octa-2,6-dienyl-Radikal 2 umlagern. Gleiches trifft für die aus Bicyclo[2.2.2]octa-2,5-dien (25) und Bicyclo[2.2.2]oct-2-en (26) erzeugten sekundären Radikale 21 und 22 zu.

Notes: exo-Bicyclo[4.1.0]hept-2-en-7-diazonium-Ionen (16) wurden durch alkalische Spaltung des entsprechenden Nitrosoharnstoffs 15 erzeugt. In schwach alkalischem Methanol erhielten wir 7-anti-Methoxybicyclo[2.2.1]hept-2-en (17), 2-exo-Methoxybicyclo[3.2.0]hept-6-en (19) 7-exo-Methoxybicyclo[4.1.0]hept-2-en (20), 5-Methoxy-1,3-cycloheptadien (21) und 3-Methoxy-1,4-cycloheptadien (22). 22 wird durch Isomerisierung von 3-Methoxy-1(Z).4(E)-cycloheptadien (30) gebildet, das wir in Form der Furan-Addukte 25 und 26 abfangen konnten. Wir nehmen an, daß 19 aus 5-Methoxy-1(Z),3(E)-cycloheptadien (31) durch intramolekulare Cyclisierung entsteht. Die Konfiguration von 19, 20, 25 und 26 spricht für den Angriff von Methanol auf das „halbgeöffnete“ Cyclopropyl-Kation 29. - Alle in CH3OD/HCO2Na gebildeten Produkte hatten etwa gleichen D-Gehalt. Die Stellung des Deuteriums in 17 zeigt, daß Doppelbindungsbeteiligung von 16 direkt zum 7-Norbornenyl-Kation 33 führt und das tricyclische Kation 32 nicht als Zwischenstufe auftritt. In Gegenwart von Lithiummethylat entstanden überwiegend die Produkte 17 und 18 aus dem 7-Norbornenyl-Kation 33, während 19-22 nun fehlten. Die Änderung der Produktverhältnisse wird durch die Carben-Umlagerung 38 → 41 erklärt, der sich eine Protonierung von 41 zu 33 anschließt.

Notes: exo-Bicyclo[5.1.0]octa-2.4-dien-8-diazonium-Ionen (11) wurden durch alkalische Spaltung des entsprechenden Nitrosoharnstoffs (10) erzeugt. In schwach alkalischer Lösung entstanden als Hauptprodukte Derivate des Bicyclo[3.3.0]octadiens (12, 13) und des 1(Z),3(Z),6(E)-Cyclooctatriens (17). Die Reaktionsprodukte und die Verteilung einer D-Markierung in 12a, 13a weisen auf eine conrotatorische Umwandlung von 11 in das Cyclooctatrienyl-Kation 24 als erste Zwischenstufe hin. In Gegenwart von Natriummethylat wurde überwiegend 8-syn-Methoxybicyclo[3.2.1]-octa-2,6-dien (18a) gebildet. 8-Diazobicyclo[3.2.1]octa-2,6-dien (39) wurde aus dem Tosylhydrazon 38 erzeugt und als Zwischenstufe auf dem Weg von 11 zu 18 ausgeschlossen. Sehr wahrscheinlich erfolgt die 1,3-Kohlenstoffverschiebung als Umlagerung des Carbens 37 in 40.

Notes: Unter Thiazoliumsalz-Katalyse werden Aldehyde an Vinylketoester und Esteraldehyde an Vinylketone unter Bildung von Diketocarbonsäureestern addiert.

Notes: Die Bestrahlung einer äquimolaren Lösung eines organischen Disulfids (5a-d) und von Tricyclo-[4.1.0.02,7]heptan (4) lieferte als Hauptprodukt ein Stereoisomerengemisch der Bis-thioether 7 und 8, daneben in geringerer Ausbeute das Sulfid 6. Letzteres entstand nahezu ausschließlich, wenn am Disulfid sperrige Reste hafteten (5e,f).

Notes: Die beobachteten Aufspaltungen der beiden ersten Photoelektronenbanden und die berechneten Spannungsenergien der [n]Paracyclophane werden diskutiert und in einem einfachen Modell vorwiegend auf die Deformation des Benzolrings zurückgeführt. Energetische Überlegungen führen zu dem Schluß, daß der „aromatische Charakter“ der Benzoleinheit in den [n]Paracyclophanen bei n = 6 weitgehend und bei = 5 vollständig verlorengegangen ist.