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  • 1
    Electronic Resource
    Electronic Resource
    Density, structural lifetime, and entropy of H-bond cages promoted by monohydric alcohols in normal and supercooled water (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6816-6826 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Density data for aqueous solutions of monohydric alcohols down to supercooling are presented and combined with data concerning viscosity of the same systems, and with available data on pure water. Two conceptually different families of longer-lived, high-connectivity H-bond structures can be sorted out in the irregular, frequently restructured network of H bonds: spontaneous structures, as in pure water, and alcohol-induced structures. Molar volumes for both are obtained and compared, allowing microscopic conclusions which agree quantitatively with available thermodynamic data. For the three alcohols studied, the well-known negative excess entropy of mixing shows a strict proportionality to the fraction of water molecules sorted out in our study as taking statistically part in alcohol-promoted cages. The remarkable proportionality extends to all alcohols, all concentrations, and all temperatures studied. Apparent (and expected) geometric distortions of alcohol-promoted cages do not affect this proportionality. However, they can be related to disturbing effects on the singular behavior of several properties of cold and supercooled water. These results are further combined with the only available quantitative data on the modulation by alcohols of the hydrophobic contribution to the functional conformational switching of a biomolecule. This allows for the first time deriving, from experiments on a protein solution, the statistical number of water molecules and associate entropy change directly involved in a specific protein function (oxygen uptake/release by human hemoglobin HbA in the specific case). Compared to the bare protein, this functional unit is largely stabilized as a consequence of the remarkably higher dimensionality in its phase space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460260
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  • 2
    Electronic Resource
    Electronic Resource
    Solvent-induced forces between solutes: A time- and space-resolved molecular dynamics study (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2407-2420 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A molecular dynamics statistical mechanical simulation study of solvent-induced forces (SIFs) acting between two fixed model solutes in a bath of 727 water molecules is reported. Simulations were run up to 500 ps on a multiprocessor system, involving 60 T800-20 transputers. Results are discussed within the statistical mechanical approach of inherent structures. It is shown that SIFs are associated with the occurrence of nonpermanent, but longer-lived statistically relevant solvent configurations promoted by solutes. Their size and sign are shown to be critically dependent on the type of solute, solute–solute distance, and mutual orientation. These features give SIFs the specificity character crucially required for functional interactions and for functional conformation and dynamics of biomolecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467681
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  • 3
    Electronic Resource
    Electronic Resource
    COOPERATIVE ONSET OF A DIFFERENT STATE OF WATER IN THE PRESENCE OF MACROMOLECULES (1973)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 204 (1973), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1973.tb30776.x
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  • 4
    Electronic Resource
    Electronic Resource
    Anomalies in the temperature dependence of the 1.2-μ absorption of liquid water (1975)
    Springer
    Journal of solution chemistry 4 (1975), S. 215-224 
    Details
    ISSN: 1572-8927
    Keywords: Liquid water ; overtone bands ; thermal anomalies ; IR profile synthesis ; temperature effects ; water structure ; water models ; solute-water interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The weakly absorbed 1.2-μ combination band of water was accurately studied as a function of temperature, in both its profile and first derivative, to obtain information on the bulk properties of liquid water. Arrhenius plots of integrated component intensity ratios showed well aligned experimental points, except for a neatly defined break occurring in the 30 to 40°C temperature interval for pure water A similar break, shifted by some 18°C towards lower temperature, was found in the case of 1M NaClO4 aqueous solutions. The breaks are tentatively assumed to result from abrupt though subtle changes involving low-frequency modes. This tentative, assumption appears independent of specific models and assignments and, although in agreement with available neutron-scattering and NMR data, needs more direct verification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00646558
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  • 5
    Electronic Resource
    Electronic Resource
    The role of solvent-induced forces in biomolecular function and stability (1993)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 15 (1993), S. 443-450 
    Details
    ISSN: 0392-6737
    Keywords: Molecular biophysics ; Thermodynamics of solutions ; Liquid-liquid transitions ; Macromolecular and polymer solutions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Solvent-induced forces (SIFs) have been for a long time erroneously related to the presence of more or less uniform “hydration shells”, consisting of more or less permanently bound water molecules. As such misconceptions fade away, it becomes clear that hydration should be viewed statistically and in terms of topological rather than geometric order, and that minor changes (due to solutes) in the structural-rearrangement times of the solvent can reflect major effects in SIFs. Recent work on SIFs at our laboratory, here critically summarized, shows: i) Precisely localized average intramolecular SIFs adjusting the operation of a protein to just what is physiologically required. ii) The involvement of SIFs in the thermodynamic stability of biomelecular solutions and “soups” and related fluctuation behaviour. Sustained, undamped fluctuations occurring in the instability region, and also subcritical ones, occurring close to (yet, not in) the instability region, have been shown to be capable of triggering important concentration- dependent biomolecular processes, iii) The involvement of large numbers of water molecules (of the order of 100) in intra- and interbiomolecular SIFs. This dramatically expands the dimensionality and extension of the functional phase space and helps understand for the first time the extraordinary thermodynamic functional stability of biomolecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456926
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  • 6
    Electronic Resource
    Electronic Resource
    Near-i.r. Absorption of H2O and D2O in the liquid and supercooled range (1983)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 2 (1983), S. 1239-1253 
    Details
    ISSN: 0392-6737
    Keywords: Studies of specific liquid structures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si riportano risultati sugli spettri di assorbimento i.r. di H2O e D2O fino alla regione di temperature del liquido sopraraffreddato. L'andamento dell'assorbanza a frequenza costante in funzione della temperatura non mostra alcuna indicazione di comportamento anomalo. Al contrario, quando gli spettri sono analizzati con metodo di deconvoluzione, si osserva un comportamento di tipo esponente critico, che correla straordinariamente bene con quello mostrato dalle proprietà di trasporto. I risultati sono discussi anche in relazione ai piú recenti modelli di struttura dell'acqua, derivanti dai risultati di simulazione e dai calcoli di connettività.
    Abstract: Резюме Приводятся результаты для спектров инфракрасного поглощения H2O и D2O для температур переохлажденной жидкости. Не обнаружено аномального поведения, когда поглощательная способность при заданной частоте изучается как функция темпетатуры. Напротив, при анализе спектров с помощью спектральных методов конволюции наблюдается поведение типа критической экспоненты, которое коррелирует с поведением, определяемым транспортыми свойствами. Полученные результаты обсуждаются в связи с недавними моделями структуры воды, полученными на основе моделирования молекулярной динамики и нычислений связности.
    Notes: Summary Results are reported on near-i.r. absorption spectra of H2O and D2O down to the temperature region of supercooled liquid. No anomalous behaviour is observed when the absorbance at any given frequency is studied as a function of temperature. A critical-exponent behaviour strikingly correlating with that exhibited by transport properties is instead observed when spectral deconvolution methods are used. Results are discussed in relation with current views on water structure, based on molecular-dynamics simulation results and connectivity calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02460209
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  • 7
    Electronic Resource
    Electronic Resource
    Physics and biophysics of solvent induced forces: hydrophobic interactions and context-dependent hydration (1998)
    Springer
    European biophysics journal 27 (1998), S. 183-196 
    Details
    ISSN: 1432-1017
    Keywords: Key words Protein folding/unfolding ; Charge-apolar solute interaction ; Molecular dynamics ; Protein coagulation ; Detergents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Solvent induced forces (SIFs) among solutes derive from solvent structural modification due to solutes, and consequent thermodynamic drive towards minimization of related free energy costs. The role of SIFs in biomolecular conformation and function is appreciated by observing that typical SIF values fall within the 20–200 pN interval, and that proteins are stable by only a few kcal mol–1 (1 kcal mol–1 corresponds to 70 pN Å). Here we study SIFs, in systems of increasing complexity, using Molecular Dynamics (MD) simulations which give time- and space-resolved details on the biologically significant scale of single protein residues and sidechains. Of particular biological relevance among our results are a strong modulability of hydrophobic SIFs by electric charges and the dependence of this modulability upon charge sign. More generally, the present results extend our understanding of the recently reported strong context-dependence of SIFs and the related potential of mean force (PMF). This context-dependence can be strong enough to propagate (by relay action) along a composite solute, and to reverse SIFs acting on a given element, relative to expectations based on its specific character (hydrophobic/ philic, charged). High specificity such as that of SIFs highlighted by the present results is of course central to biological function. Biological implications of the present results cover issues such as biomolecular functional interactions and folding (including chaperoning and pathological conformational changes), coagulation, molecular recognition, effects of phosphorylation and more.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002490050125
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  • 8
    Electronic Resource
    Electronic Resource
    Experimental studies of the rheological behavior of a demixing biopolymeric sol (1995)
    Springer
    International journal of thermophysics 16 (1995), S. 363-370 
    Details
    ISSN: 1572-9567
    Keywords: scaling behavior ; shear viscosity ; solvent-induced forces ; solvent perturbation ; spinodal demixing ; water structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Experimental data are presented concerning a large transient viscosity surge occurring in the course of spinodal demixing of agarose aqueous solutions. The study includes the effects of water perturbation by minor proportions of compatible cosolutes. Three observations are noteworthy. One concerns an upward or downward shift of the spinodal temperature, caused by cosolutes, which agrees with their expected modulation of solvent-induced forces. The second concerns the time of appearance of the viscosity surge. This is observed to follow a critical law, with an exponent independent of polymer concentration and solvent perturbation. The third concerns the inverse-power-law dependence of the viscosity peak value on shear. When the shear is scaled with an appropriate relaxation time, related to the overall interdomain structure generated by spinodal demixing, all data fall on a master curve, independent of polymer concentration, quenching depth, and solvent perturbation. This allows assigning the observed viscosity behavior to distortion and rupture of the overall interdomain structure generated by spinodal demixing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01441902
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  • 9
    Electronic Resource
    Electronic Resource
    Time-Resolved study of network self-organization from a biopolymeric solution (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 859-868 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Time-resolved studies of network self-organization from homogeneous solutions of the representative biostructural polymer agarose are presented. Solutions are temperature quenched and observed by several techniques. Consistent with previous suggestions by the authors, experiments at concentrations up to about 1.75% w/v provide direct kinetic evidence for the occurrence of at least two distinct processes, leading, in sequence, to self-assembly. These are as follows: (a) a liquid-liquid phase separation of the solution occurring via spinodal demixing and resulting in two sets of regions that have, respectively, higher and lower than average concentrations of random-coiled polymers; and (b) the subsequent 2 coils → double helix transition and accompanying cross-linking and gelation (due to branching of double helices), occurring in the high-concentration regions. The size of the high-concentration regions depends upon agarose concentration and quenching temperature, and is in the range from a fraction of micrometers to a few micrometers, in agreement with earlier experiments. Bundling of the double-helical segments is known to follow self-assembly and can be considered as a third step (gel curing). This follows from the thermo-dynamic instability of the helical segments in the solvent, behaving as a system of rod-like particles connected by more or less flexible joints.The two processes leading in succession to self-assembly are discussed in terms of a phase diagram consistent with available data. Their time scales differ remarkably. At the end of the first process, all polymers remain random coiled and freely drifting. Much later coil-helix transition is observed, always in coincidence with polymer cross-linking and gelation. The enhancement of concentration of random-coiled polymers in specific regions of the sol caused by spinodal demixing is thus a prerequisite for self-assembly of these biostructural gels in the concentration interval studied. Conceptually, concentration enhancements of this type can provide a new pathway for promotion of functional biomolecular interactions even at very low average concentrations. The mechanism will work identically if the region of instability is reached by varying the polymer concentration (e.g., by biosynthesis), rather than by temperature quenching.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360310706
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  • 10
    Electronic Resource
    Electronic Resource
    Molecular interactions in aqueous solutions: The role of random fluctuations of external parameters and of thermodynamic instabilities (1989)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 35 (1989), S. 113-124 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A biological system usually operates under nonstable values of relevant parameters, such as pH, temperature, and ionic strength. The question therefore poses whether such fluctations do affect its relevant processes. Experimental studies on the role of random temperature fluctuations on functional encounters of biostructural polymer molecules, and consequent self-assembly of supramolecular structures, have evidenced an additional, noise-induced order of these structures. This type of effect is the result of nonlinearity in physical systems, and the case of a biosystem is especially interesting. As recent experiments have shown, spinodal decomposition resulting from thermodynamic instability may favor the onset of the supramolecular ordering process. If the random fluctuations of temperature are imposed in such conditions of thermodynamic instability, their ordering effect is further enhanced.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560350106
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