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The elucidation of the molecular mechanism of the interaction of denaturing and stabilizing agents with proteins is a problem of eminent fundamental and practical consequences. In the present study we provide strong evidence by dielectric relaxation studies on RNase A–glycerol–water solutions that the protein creates for itself an aqueous environment in its immediate vicinity by attracting water molecules from the bulk solvent, thereby increasing the glycerol concentration of the bulk solution. This finding provides direct spectroscopic support for the thermodynamic results of Gekko and Timasheff (K. Gekko and S. N. Timasheff, Biochemistry, 1981, 20, 4668; K. Gekko and S. N. Timasheff, Biochemistry, 1981, 20, 4677) who reported preferential exclusion of glycerol from the protein domain.

Dielectric loss spectra between 1 MHz and 36 GHz have been measured at 20°C for solutions of hexadecyl trimethylammonium bromide and chloride, tetrahexylammonium bromide and tetrabutylam-monium bromide in chloroform and 1-octanol (three solutes per solvent) at moderate and high concen-trations. The discussion is aimed at identifying relaxation processes involving ions. Describing the relax -ational part of the spectra (after subtraction of the conductivity contribution) by a sum of spectral com-ponents, the lowest frequency component can be attributed to the solute in all cases. Its concentration dependence is indicative of two ionic relaxation processes differing in physical nature. The solvent is partly involved in those processes; moreover a structure breaking effect is likely to occur in case of the alcoholic solvent. The results are also discussed in comparison with a molten alkylammonium salt and with solutions of this and of inorganic salts.

Dielectric spectra have been measured up to 72 GHz at 20°C for solutions of β-cyclodextrin (CD) in the following solvents over the whole solubility range of CD: dimethylsulfoxide (DMSO), DMSO/ 1,4-dioxane mixture (2:1 molar ratio), DMSO/water mixtures (2:1 and 1:2). The spectra are analyzed into a sum of Debye type spectral components. These are likely to be caused by different physical pro-cesses. The discussion shows (i) that there is a preferential CD-DMSO interaction, by far exceeding the CD-water interaction, and (») that, concerning CD-DMSO, a loose interaction can be distinguished from the formation of an inclusion complex.

Dielectric spectra up to 72 GHz have been measured at 20 °C for binary mixtures of a monohydric and a dihydric alcohol, composed from the following groups of substances. Monoalcohols: 1-butanol and tert -butanol. Diols: Ethanediol, 1,2- and 1,3-propanediol, 1,2- and 1,4-butanediol, 1,2- and 1,5-pentanediol. The spectra are rather similar in shape. They are formally described by four Debye type spectral components. The principal (lowest frequency) component, which is related to the dynamics of self and/or hetero-association, is discussed with respect to steric conditions. In mixtures of 1-butanol with longer chain 1,2-diols, the principal relaxation time passes through a minimum on increasing the diol content. In mixtures of tert -butanol (which has a weaker self-association tendency) with longer chain 1, n -diols, on the other hand, it passes through a maximum. With regard to the principal relaxation strength, longer chain 1,2-diols tend to resemble monohydric alcohols of full diol chain length while 1, n -diols tend to resemble monohydric alcohols of half the diol chain length.

The results of viscosity measurements for mixtures of 1-propanol, 2-propanol, 3-amino-1-propanol and (±)i-amino-2-propanol with 1,4-dioxane at 20, 30 and 40°C are presented and comparatively discussed. From the temperature dependence of viscosity, activation energies are determined.

Dielectric spectra have been measured for the title systems up to 72 GHz at 20 °C with salt concentrations ≤1 mol/1 and DMSO mole fractions of the mixed solvent in the 0.3 to 0.6 range. Results can be described by a superposition of two Debye terms (at lower frequencies) plus one Cole-Davidson term (at higher frequencies). The discussion is particularly focused on the lowest frequency term, which is related to ionic species. These are likely to consist in nonsymmetrically solvated cations rather than ion pair complexes. While Cu, Ni and Mg nitrates behave similarly, the Zn salt shows some differences which possibly are due to a change of the coordination number with increasing salt content.

The pure 1-alkanols C4 to C12 and seven of their short/long chain binary equimolar mixtures are in-vestigated by static and dynamic dielectric measurements up to 36 GHz at 20, 30 and 40 °C. The apparent dipole moment and the relaxation parameters from a three Debye term analysis of the spectra are discussed. The mixtures are found to behave like a one component alcohol of mean chain length. An odd-even effect is revealed by comparison of mixtures containing C11 with those containing C12 as long chain mixture component.

Dielectric spectra have been measured for the title systems up to 72 GHz at 20 °C with salt concentrations ≤ 1 mol/l. The results are described by a superposition of Debye terms. Two terms are sufficient for binary water/DMSO mixtures, while two additional lower frequency ones are required when salt is added. The results for both halides differ only little. The relaxation strengths of a term ascribable to ionic complexes and a term ascribable to water/DMSO (2:1) complexes vary in opposing sense, demonstrating the competition between those complexes.

The dielectric spectra of the following liquid mixture systems have been measured over the whole absorption region: Glycerol (Gly)/n-butanol, Gly/t-butanol (both at 20°C) and Gly/guaiacol (20,40 and 60°C). The results are comparatively discussed with regard to hetero-interactions, taking into consideration the possibility of internal hydrogen bonding in the case of guaiacol and, generally, of steric constraints.

The dielectric spectra up to 72 GHz have been measured at 20 °C for solutions of glucose and sorbitol (max. 1 mol/1) in the mixed solvent water/tetrahydrofuran (THF) as a function of the THF content (max. volume fraction 0.4). There is no significant difference in the relaxation behaviour of corresponding glucose and sorbitol systems. The spectra of binary water/THF as well as hydroxy compound/water systems show that the respective minor components influence the structure and dynamics of water. The ternary systems hydroxy compound/water/THF, however, exhibit merely a superposition of those effects, thus there is no evidence for an interaction between the hydroxy compound and THF in aqueous environment.

The dielectric spectra of aqueous solutions of ribonuclease A (RNase) have been measured in the frequency domain over the whole absorption region between 2 MHz and 72 GHz at 20°C in two solvents, pure water and 8 mol/1 urea solution. These environmental conditions promote the native and unfolded state of the protein, respectively. The results are discussed with regard to (i) the low and (ii) the high frequency part of the spectra. The contribution to (i) which is attributable to the tumbling motion of RNase is changed by the presence of urea, indicating that the RNase moieties are increased in polarity, but only insignificantly in size. From (ii) it is concluded that addition of urea leads to a change in the overall water structure and dynamics which is accompanied by an increased fraction of non-associated solvent molecules. These are likely to be instrumental in the denaturation process.

Electron paramagnetic resonance (EPR) spectra of Mn2+ centers in 11 langbeinites, A2 +B2 2+ (SO4)3 2-, with A+ = NH4 +, K+, Rb+ or Tl+ and B2+ = Mg2+, Ca2+, Zn2+ or Cd2+, are measured over relatively large temperature ranges chosen to cover phase transitions, if any. For 7 langbeinites which do not contain Mg2+, phase transitions are observed, but no more than one low temperature phase is distinguishable by EPR. Except for the K-Zn langbeinite, only one defect center is noticeable in that phase. The low temperature EPR parameters are reported, and their temperature dependence is discussed with respect to correlations between structure and phase transition characteristics and to the trigger mechanism.

The dielectric spectrum of guaiacol in toluene solution (mole fraction 0.3 to 1) has been measured over the whole absorption region at 20, 40 and 60 °C. The results are discussed with regard to intra and intermolecular hydrogen bonding effects. Intramolecular interactions appear to be predominant. Only the ‘anomalous’ relation between relaxation time and viscosity is indicative of intermolecular interactions which, however, remain comparably weak even in the pure liquid.

The dielectric spectra of binary liquid mixtures of the following alcohols with N, N-dimethylformamide (DMFA) have been measured between 5 MHz and 72 GHz at 20°C:l-Hexanol, 1,2-hexanediol and 1,4-butanediol. The analysis of the spectra, which is particularly aimed at information on hetero-associ-ation, gives evidence for the formation of mixed aggregations, indicated by a minimum in the ‘free’ DMFA relaxation contribution at a mixture ratio of about 1:1 for hexanol/DMFA and about 1:2 in case of the dihydric alcohol/DMFA systems.

The static permittivities and the dielectric spectra (frequencies ranging between some MHz and 72 GHz) are measured for the following liquids in the pure state and in mixtures with 1,4-dioxane at 20 °C: 2-amino-1-ethanol, 3-amino-1-propanol, 4-amino-1-butanol, 5-amino-1-pentanol, (±)1-amino-2-propanol, (±)2-amino-1-propanol, (±)2-amino-1-butanol, 2-amino-2-methyl-1-propanol. The dielectric loss spectra of these aminoalcohols resemble those of dihydric alcohols but are generally broader. This finding is discussed with respect to the different kinds of hydrogen bonds feasible with the present substances, taking into consideration the relative weight of relaxation contributions ascribable to associates in relation to molecular structure.

The dielectric spectra of the title systems (with moderate to high salt concentrations) have been measured between MHz frequencies and 72 GHz at 20, 40 and 60 °C (EtAc only 20 °C). Apart from the conductivity contribution, there are two evidently discernible relaxation contributions. These are ascribed to unaffected solvent (at higher frequencies) and, on the other hand, to affected solvent and to ionic species (at lower frequencies). The nature of the latter and their relaxation mechanism are discussed by comparing the respective relaxation parameters with those of other liquid systems.

The static permittivity has been investigated for the ternary mixtures of 1,6-hexanediol/n-dodecanol/heptane, 1,2-ethanediol/n-dodecanol/heptane, and 1,6-hexanediol/n-hexanol/heptane. In addition, the static properties of pure n-hexanol and binary solutions of n-hexanol, cyclohexanol and n-heptanol in n-heptane have been studied together with the binary mixture hexanediol/hexanol. The results are discussed. Broadband dielectric relaxation spectra (at 20 to 40 °C) are reported for the three ternary systems. The concentration of the polar substances ranges from alcohol mole fraction x = 0.1 to 1. The dependence of relaxation parameters on concentration and temperature of the ternary mixtures is discussed.

X-band ESR spectra of liquid solutions of Cu(II)nitrate and Cu(II)chloride in N-methyl-formamide and four N,N-disubstituted amides are reported and discussed with respect to the occurrence of ion pairs or higher ionic aggregations. Nitrate solutions allow to distinguish two complex types of moderate asymmetry at most. Chloride solutions indicate a succession of at least three complex types with strongly increasing asymmetry.

The dielectric spectrum has been measured between some MHz and 72 GHz for the following 14 pure liquids at 20°C: N, N-Di(methyl-, ethyl-, isopropyl-, butyl-, isobutyl) formamide, 1-formylpiperidine, N-methylformanilide, N,N-di(methyl-, ethyl-, isopropyl) acetamide, N-acetylcaprolactam, N, N-dimethylacrylamide, N,N-dimethylpropionamide, and N, N-diethyl-m-toluamide. Moreover, diisobutylformamide and diethyltoluamide have been studied in mixtures with n-hexane over the whole concentration range down to very dilute solutions. The relaxation parameters of all these systems are reported. Particular attention is given to the discussion of the two mixture systems since these exhibit a peculiar concentration dependence of the relaxation strengths of the Debye type spectral components used to describe their spectrum. This behaviour is likely to relate to a flexibility effect which is remarkably intensified on dilution.

With regard to the interpretation of dielectric relaxation spectra of associating liquids such as alcohols, a two state model for the rotational tumbling motion of a dipole is considered: The moment (of constant magnitude) is assumed to undergo stochastic tumbling during a "free" state, alternating with an "associated" state where for a certain residence time the rotational motion can be neglected. One particle autocorrelation functions according to that model are calculated numerically. In any case, they can well be described as sum of (at most) two exponentials. The corresponding parameters are given as function of "association" probability and residence time

The results o f a dielectric relaxation study (in the frequency region from about 1 kHz to 1 GHz) of the liquid crystalline title com pound (C3H7-Cyhx-Ph-NCS , 3-CHBT) in the isotropic and the nematic phase (measurements with electric field parallel to alignment) are presented. The spectra of both phases can be described by two relaxation processes of Debye-type, possibly related to rotation around the long and short molecular axes.

The static and dynamic dielectric properties o f the title system are reported for a concentration series from about 8 mmol/1 up to 2.3 mol/I at 20 °C. The apparent moment (4.2 D , extrapolated to infinite dilution) decreases with increasing concentration, the relaxation time increases proportional to viscosity, that is, somewhat steeper than usually observed. Com parison with other molecules suggests that these features are mainly due to the high dipole moment rather than being specifically related to the prolate shape o f the molecule. The broadening o f the spectrum toward the high frequency side, on the other hand, may be due to the molecular shape.

Broadband dielectric relaxation spectra (at 20 to 40 °C) are reported for three liquid alcohol/non­ polar solvent systems: Binary hexanol/mesitylene mixtures and two corresponding ternary mixtures, where 5 percent of hexanol are replaced by a dihydric alcohol, namely resorcinol (1,3-dihydroxyben­ zene) or 2,2´-dihydroxydiphenyl. The concentration of the polar substance(s) ranges from dilute solutions to pure alcohol(s). The lower frequency relaxation contribution, which generally is the more dominating the higher the alcohol concentration, is additionally enhanced by the diol admixture in the case of low and moderate concentrations. This can be understood as a hetero-association effect, the diol molecules playing a bridging role, which also leads to an increase in the mean lifetime of associated states.

The dielectric absorption spectra of the following hydrated salts dissolved in acetonitrile are measured between 30 MHz and 72 GHz at 20 °C: Mn(NO 3 ) 2 ·4H 2 O, Cu(NO 3 ) 2 ·3H 2 O, Zn(NO 3 ) 2 ·4H 2 O, Y(NO 3 ) 3 ·4H 2 O and La(NO 3 ) 3 ·6H 2 O. Concentrations are up to 4 mol/l (Mn salt) or 1.5 mol/l (other salts). At sufficiently high concentrations, two absorption maxima are revealed after correction for the conductivity contribution in all cases, which are likely to relate to ion-pair species (in a generalized sense) and solvent. A formal description is possible by using three Debye type terms (including an intermediate one of, in most cases, relatively weak intensity). The concentration dependence of the corresponding relaxation parameters is discussed with respect to structure and dynamics of ion-pair species and solvent.

The dielectric relaxation spectrum is measured at 20°C at frequencies up to 72 GHz for the following alcohols and their aqueous mixtures over the whole mixture range: 1,2-ethanediol; 1,2- and 1,3-propanediol; 1,2-, 1,3-, 1,4- and 2,3-butanediol; for comparison moreover: ethanol; diethyleneglycol and 1,2,3-propanediol. It is found possible to analyze the spectra into discrete spectral components according to one and the same scheme in all cases. Three mixture ranges can be distinguished on the volume fraction scale, the parameters of the intermediate and, particularly, the water rich region being rather insensitive to the nature of the alcoholic component.

The dielectric spectra of diethylsulfoxide (DESO)/tetrachloromethane mixtures have been measured from 0.5 to 72 GHz at 20 °C. On the basis of the relation between the relaxation time and the DESO concentration a complex formation between DESO and tetrachloromethane is suggested.

Powder and single crystal X-band EPR spectra are measured of the cubic (high temperature) phase of eleven langbeinites, A2+B (SO4)3, doped with Fe3+. One center of axial symmetry is observed, the ZFS parameter B of which is discussed in comparison with corresponding results on manganese-doped langbeinites. Very probably Fe3+ forms a substitutional center in the more spacious of the two non-equivalent B sites, which leads to local relaxation depending on ionic radii. Charge compensation by an A site vacancy is likely. Die Pulver- und Einkristall-EPR-Spektren der kubischen (Hochtemperatur-)Phase von elf Fe3+-dotierten Langbeiniten (A+2B (SO4)3) werden gemessen. Sie zeigen alle ein axiales Zentrum, dessen Nullfeldaufspaltungsparameter B im Vergleich mit entsprechenden Ergebnissen fur Mn2+-dotierte Langbeinite diskutiert wird. Die substitutionelle Besetzung des groseren der beiden nichtaquivalenten B-Platze ist wahrscheinlich, wobei die Umgebung in Abhangigkeit von der Ionengrose relaxiert. Der Ladungsausgleich erfolgt vermutlich durch eine A-Leerstelle.

The cubic (high temperature) phase of some langbeinites, A+ 2 B2 2+(SO4)3 with 11 different combinations of A and B type cations, doped with Mn2+, is investigated by EPR. Powder or single crystal spectra are measured at X-band. They indicate centers of axial symmetry in all cases. In 6 of the langbeinites two centers are found which differ considerably in intensity. Both centers are substitutional defects (Mn in the crystallographically nonequivalent divalent B ion sites). For the more intense one the zero field splitting parameter is proved to be negative in all cases. That center is assigned to the more spacious site which, depending on the cation size, allows for local relaxation. It is shown by comparison with predictions of the superposition model that relaxation appears to be effective

Dielectric relaxation spectra are measured (in the range from some MHz to 72 GHz, at 20 °C) of LiClO 4 , LiCl, LiNO 3 , CuCl 2 · 2H 2 O and Cu(NO 3 ) 2 ·3H 2 O solutions using the title solvents (salt concentrations up to 2 mol/l). Several related sytems are studied for comparison. After correction for the conductivity contribution, broad, unstructured spectra are left which are in particular discussed with respect to a reasonable separation into solute and solvent contribution. A low frequency contribution can be ascribed to quasi rigid, solvated ion pairs (occuring except for LiClO 4 ), and a broad high frequency contribution is due to the solvent as affected by the ionic solute. A separatete consideration is devoted to the general question as to whether in conducting liquids the dipolar relaxation parameters might appear inluenced by conductivity.

The dielectric spectrum of PVP 1200 in pyrrolidone solution is measured between 2 MHz and 72 GHz at temperatures of 20, 40, and 60°C. Polymer concentrations are up to a monomole fraction of 0.5. The results are described in terms of Debye type components. For pure pyrrolidone two components are required which are probably caused by associated and monomeric solvent. Additional low frequency components ascribable to the polymer appear with PVP solutions. Here the solvent contributions can be distinguished into unaffected, loosely affected and tightly bound solvent. As a peculiar feature there is direct evidence of the interchange of solvent-solvent to solvent-polymer interaction.

The dielectric spectrum is measured up to 72 GHz of solutions of polyvinylpyrrolidone (PVP) in tetramethylurea (TMU), dimethylethylene urea and dimethylpropylene urea. Concentrations are up to a monomole fraction of 0.65 (PVP 1200) or 0.5 (PVP 40 000). Measuring temperatures are 20CC for all systems and additionally 40 and 60°C for the TMU solutions. For the description of the results a superposition of Debye type components is used, which are discussed in particular with respect to the solvent contributions. These can be distinguished into three regions: (i) Unaffected bulk-type; (ii) loosely affected, relaxation time and activation enthalpy increasing with increasing polymer content; (iii) quasi bound and moving together with the polymer. The solvation numbers (total of affected solvent per repeat unit of polymer) are about 1.5 to 2.

The permittivity of the following mixtures has been measured at 20°C between 30 MHz and 72 GHz: PEG 400 with toluene or PEG 400 dimethylether (PEGDM); PEG 200 with ethyleneglycolmonomethylether, ethyleneglycol, ethanol, methanol or water. The description of the dielectric spectra ranges from an apparently unperturbed superposition of contributions from both mixture components (PEGPEGDM) to the occurance of strong additional contributions (PEGH2O) which are ascribable to heteroassociation.

The real part of conductivity was measured for a number of salt solutions in different polar (nonaqueous) solvents over a broad frequency range up to 72 GHz at 20°C. The slope of the double log representation of conductivity versus frequency decreases with increasing salt concentration and solution viscosity. An extrapolation to infinite viscosity yields slope values similar to those found with vitreous systems which are claimed to exhibit “universal” behaviour.

The dynamic dielectric properties of the title substances are measured at 20 °C at frequencies up to 72 GHz in the pure liquid state and in mixtures (x = 0.4–1) with benzene and tetrachloromethane. Rotational tumbling motion of single (non-associated) molecules is likely to be the main relaxation process. Peculiarities are found with two out of the six systems, namely mixtures of cyanopiperidine and cyanopyrrolidine with tetrachloromethane. These are discussed as possibly due to a concentration dependent conformational equilibrium.

The dielectric relaxation of water rich aqueous solutions of ethanol, ehtylene glycol, glycerol, diethylene glycol, 1,2-butanediol, 1,3-butanediol and 1,4-butanediol has been measured at 20 °C. In all cases the fitting of the data by a sum of Debye type spectral components allows for two description modes which can be interpreted as a collective alteration of the water relaxation or, on the other hand, as formation of a microheterogenous solution where "affected" and "unaffected" water becomes discernible

Frequency domain dielectric spectroscopy (30 MHz to 72 GHz) is utilized to study solvation in polyethylene glycol (PEG) — methyl pyrrolidone (MPy) mixtures over the whole mixture range at 20 °C, in particular with PEG 200. Further pure PEGs (200 to 400) and butyl glycol (in the pure state and in benzene and n-hexane solution) are considered for comparison to facilitate the assessment of PEG relaxational behavior. It turns out that the PEG-MPy mixtures can be described in terms of a simple solvation model which takes into account only the bulk and the solvating solvent state. The solvation number per repeat unit is about 0.85 in the dilute solution limit. It decreases gradually with increasing PEG concentration in accordance with a solvation equilibrium model.

The dielectric relaxation behavior of the title solutions of PVP 40000 is measured in the frequency domain (50 MHz to 36 GHz) at 20 °C. The polymer content of the solutions (up to 0.25 mole fraction of monomer units) is such that it does not yet contribute significantly to dielectric loss. The solvent relaxation shows in all cases a bulk and a slowed down contribution, both characterized by concentration-independent relaxation times. The slow contribution is ascribed to the solvate. Solvation numbers for dilute solutions roughly range between 2 and 4 per PVP repeat unit.

Tumor necrosis factor receptor (TNFR) family members such as glucocorticoid-induced TNFR (GITR) control T cell activation, differentiation, and effector functions. Importantly, GITR functions as a pivotal regulator of physiologic and pathologic immune responses by abrogating the suppressive effects of T regulatory cells and costimulating T effector cells. However, the molecular mechanisms underlying GITR-triggered signal transduction pathways remain unclear. Interestingly, GITR-induced stimulation of TNFR-associated factor (TRAF) 5-deficient T cells resulted in decreased activation of nuclear factor kappaB as well as the mitogen-activated protein kinases p38 and extracellular signal-regulated protein kinase, whereas activation of c-Jun N-terminal kinase was less affected. Consistent with impaired signaling, costimulatory effects of GITR were diminished in TRAF5-/- T cells. In sum, our studies indicate that TRAF5 plays a crucial role in GITR-induced signaling pathways that augment T cell activation.

The static and broadband dynamic dielectric properties of the title mixtures, which contain the diol to an only minor fraction, are reported for the whole concentration range (al-cohol mole fraction 0.1 to 1). As with similar systems, the diol leads to increased association effects.

The frequency dependent complex permittivity of LiClO4 solutions in tetraethyleneglycol dimethylether (tetraglyme) with concentrations up to 1.5 mol/1 is measured at 20 °C over a broad frequency range (5 MHz to 72 GHz). Apart from the conductivity contribution, there are two distinguishable absorption regions. The relaxation at higher frequencies is due to the solvent. The lower frequency feature is due to ionic processes. It comprises two spectral components, which both are unlikely to be caused by rotational tumbling motion of well-defined ionic species (e.g. ion pairs) but rather seem to involve some other processes such as confined translational modes of ionic motion.

The dielectric spectrum of the title substance ('neohexanol') in its pure liquid state is reported for 293 K up to 71 GHz and, for a restricted frequency range, also for lower temperatures (down to 253 K). The room temperature spectrum resembles that of alicyclic alcohols, in particular cyclopentanol, with respect to spectral shape, main relaxation time and the relation of the latter to viscosity, which similarity may be connected with the fact that these alcohols are able to form 'plastic crystals'.

The dielectric spectra of liquid cyclopentanol, cyclohexanol, cycloheptanol and cyclooctanol are reported for frequencies up to 72 GHz and temperature 20 (cyclohexanol solid), 30 and 40 °C. The absorption spectra are peculiar in exhibiting a remarkably developed high frequency shoulder which is attributed to single molecule and internal motion, while the principal absorption is due to association as with other alcohols

The dielectric relaxation spectrum of the title substance in mixtures with 1,4-dioxane or benzene (pure liquid to moderate mixture ratios) is measured between 5 MHz and 36 GHz at 20°C. The static permittivity is determined over the whole mixture range. The results are discussed in particular with respect to the possibility that different types of hydrogen bonded aggregations may contribute to the main relaxation