摘要:

AbstractIn the present work, the synthesis of the three primary oligomers of α‐L‐glutamic acid is described; the general formula is the following:[I]The choice of protective groups at the both ends of the chain allows for the good solubility in the water and the liberation of free carboxyl groups on the side chain. Thus, models are obtained for the study of thermodynamic properties of solutions and especially of the interactions between polyanions and cations. The prepared products are characterized by different techniques such as mass spectrometry potentiometry, tonometry, and thin‐layer chromatography. The results are in agreement and lead to the conclusions that the molecules have the general formula of [I] and are stereor

ISSN:0006-3525    

DOI:10.1002/bip.1973.360121002

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractPotentiometric neutralization of oligomers represented by the general formula shown was studied.The intrinsic pKof carboxyl function was found to be 4.40 at 25°C; the variation of the apparent pKa, ΔK(α), was studied as a function of the degree of neutralization: the influence of the degree of neutralization on the accumulation of ionic sites along the chain is clearly shown.The experimental curves of polyglutamic acid allowed us to deduce the sequence of ionic selectivity and the energy of conformational transition. The theoretical interpretation of the results was proposed in terms of the rod like model from Katchalsky's theory. The intrinsic pKofor the polymer was set equal to the value experimentally obtained on oligomers. By activity measurements on Na+and Ca2+counterions in salt‐free solutions, the free fraction of counterions was deduced on the different samples. The results were interpreted with the electrostatic model previously proposed; in this view, the oligomers are assimilated to imaginary polyelectrolytes. This allowed us to determine the values of ΔpKand the fraction of free ions at the same

ISSN:0006-3525    

DOI:10.1002/bip.1973.360121003

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractPMR investigations on the diastereomeric phosphate methyl protons of the dinucleoside ethyl phosphotriesters Tp(C2H5)T, dA, and dIp(C2H5)dI have been used to study the conformational changes of these dimersin solution. In D2O (273°K), the diastereomeric phosphate‐methly groups of Tp(C2H5)T appear as a triplet. The methyl resonances of dIp(C2H5)dI and dAp(C2H5)dA appear as two sets of triplets and their chemical shift differences (δ1− δ2), decrease with increasing temperature, finally becoming zero at 292°K and 333°K, respectively. The same phenomenon is observed for dAp(C2H5)dA in CD3OD; in this detacking solvent, the difference (δ1− δ2) diminishes to zero at a lower temperature (261°K). At room temperature in D2O, the chemical shift of the phosphate methyl of Tp(C2H5)T appears at lower field than those of dIp(C2H5)dI or dAp(C2H5)dA. The differences between the chemical shifts of these groups (δI− δTor δA− δT) increase with increasing temperature, and reach maximal values at 301°K and 333°K, respectively. The results suggest that at low temperature the largest fraction of the dimer population exists in a stacked state, with the phosphate‐ethyl groups outside the stack. Increasing temperature causes an oscillation of the bases and a shift in the dimer population away from the stacked state. Finally at high temperature, the planar bases rorate with respect to one another and in the case of dIp(C2H5)dI and dAp(C2H5)dA, the ethyl groups experience shielding by the anisotropic ring current of the five‐membered ring of the bases. Thus, the current pmr studies and those reported earlier from our laboratory support an “oscillation‐rotation model” for the unstacking process of the dimers. The relationship of this model and t

ISSN:0006-3525    

DOI:10.1002/bip.1973.360121004

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe cooperative nature of the binding between polycytidylate and the oligoinosinates I(pI)5–10has been determined. Using the data of Tazawa, Tazawa, and Ts'o, it is shown that knowledge of the slope of the adsorption isothern allows one to determine the oligomer‐polymer binidng constant, the oligomer–oligomer interaction constant, and the average degree of association (cooperative clustering) of the oligomers on the polymer. Knowledge of the above equilibrium constants as a function of temperature yields the respective thermodynamic parameters; no assumptions need to be made about the nature of the equilibrium constants or the thermodynamic parameters. For very long chains of polycytidylate, simple, explicit relations are given for the determination of the equilibrium constants involved. For finite chains of polycytidylate, the calculation of a single graph for each oligomer and polymer size allows the equilibrium constants to be determined for all experimental conditions of temperature and concentration. We find that the enthalpy and entropy of binding an oligomern, bases to be δHn= ±13.7 −n(6.65) and δSn= +32.5 −n(18.8) given, respectively, in kcal/mole and e.u.; these parameters predict a melting temperature of 81°C for the poly(I)·poly(C) complex compared with the experimental value of 75°C. If the enthalpy is interpreted as arising from a sum of hydrogen bonding and stacking interactions, then the enthalpy of stacking is −13.7 kcal/mole while the enthalpy of hydrogen bonding is +7 ± 4 kcal/mole; the positive enthalpy of hydrogen bonding presumably is a result of the fact that in the inosine‐cytosine base pair, only two of the three sites on cytosine can hydrogen bond, the third being blocked from hydrogen bonding with water. The enthalpy of interaction between neighboring bound oligomers is found to be −10.4 kcal/mole while the corresponding entropy is −26.1 e.u. The binding is bound to be cooperative, though the extent of clustering varies markedly with temperature; the average number of oligomers in a cluster on the polymer is found to about five at a melting temperature of 25°C. The approach and equations given have generally applicability to olig

ISSN:0006-3525    

DOI:10.1002/bip.1973.360121005

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractIn continuation of our studies on the effect of the base and the phosphate groups on the glycosyl and the sugar‐phosphate backbone conformation, we have carried out semi‐empirical potential energy calculations on the common 5′‐ and 3′5′‐ribopyrimidine mono‐ and diphosphates by considering simultaneous rotations about the glycosyl (χ) and the C(4′)–C(5′) (ψ) bonds. This calculation provides an assessment of the nature and orientation of the base on the sugar–phosphate backbone conformation of nucleotides and polynucleotides. It is found that the attractive inetractions between the 5′‐phosphate group and the base mutually stabilize theantiand thegauche‐gauche(gg) conformations about χ and ψ, respectively, in 5′‐ribopyrimidine nucleotides. The introduction of the 3′‐phosphate group as in 3′,5′‐ribopyrimidine diphosphates, still leaves theanti‐ggas the most favored conformation with the important difference that the probability of occurrence of theanti,gauche‐trans(gt) is how substantially increased. This is dependent to a large extent on the sugar conformation and to a lesser extent on the base. Uracil and thymine show a greater probability for theanti‐gtthan cytosine. Thesynconformation is considerably less likely and its occurrence is also dependent on the base type, cytosine showing a lesser tendency than uracil and thymine. For thesynbase, the most favourec conformation for ψ isgt, sinceggis sterically disallowed andtgis destabilized by electrostatic repulsive interactions between the 3′ and 5′‐phosphate groups. Thus, there is a striking correlation between the glycoysl and the backbone C(4′)–C(5′) bond conformations. The rest of the bonds of the backbone are considerable less dependent on the glycosyl conformation. These studies reveal that in poly‐ribopyrimidine nucletides the majority of the

ISSN:0006-3525    

DOI:10.1002/bip.1973.360121006

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe rate of hemoglobin deoxygenation is measured as a function of inorganic phosphate concentration, pH, and temperature. Isokinetic relationships (enthalpy‐entropy compensation) are searched for by applying the method of O. Exner and, for comparative purposes, the conventional method of plotting the energy of activation (E*) versus the natural log of the pre‐exponentional factor of the Arrhenious equation (InA). Both plots indicate compensation between the activation parameters. However, unlike the conventional plot, the Exner treatment is able to distinguish between two types of compensation. Furthermore, when extrapolated rate constants based on all the data in an Exner plot are transposed intoE* vs. InAplots, so‐called “turn‐around” behavior is predicted for the effect of increasing phosphate concentration at constant pH. Such “turn‐around” behavior inE* vs. InAplots has been observed experimentally by Beetlestone and co‐workers for anion binding to human hemoglobin as a functin of pH. Lastly, the compensation temperatures obtained from these data all fall within the Vaslow‐Doherty compensation range (250–350°K) which is thought to indicate that the solvent, water, is involved in the reaction mechanism. Thus, Exner plots appear to further resolve isokinetic temperatures of the Vaslow‐Doherty type. Differences in the electrostriction of solvent in the activated state is suggested as one possible physical source for the Vaslow‐Doherty type compen

ISSN:0006-3525    

DOI:10.1002/bip.1973.360121007

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe electrical conductivity of bovine Achilles tendon with various amounts of adsorbed water was measuredas a function of temperature. The conduction appeared to be fully determined by the water of hydration. The current is probably primarily carried by protons at water contents up to 45% and by small ions at water contents beyond 65%. In both ranges of water content, a linear relation between activation energy and water and content was found. As to the lower range, this is explained by the action of Coulombic forces during the separation of proton–hydroxyl ion pairs. In two regions of water content a linear relation between the logarithm of the pre‐exponential factor and the activation energy was found. There are, however, indications that at certain water contents the dissociation constant of the adsorbed water is several orders of magnitude higher than in liquid wa

ISSN:0006-3525    

DOI:10.1002/bip.1973.360121008

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractDeterminations of the amount of bound water in hydrated proteins yield strongly diverging values. The cause of this is the continuity of the transition from bound to free water, and the diffeernt sensitivities to water structure of the measuring techniques. Only the methods that aim at the determination of the amount of water, whose phase remians unchanged duing freezing, yield similar values. The value for collagen as deduced from conductivity data is about 50% water of the dry weight. It is believed that this water interacts with adsorptive groups on the macromolecules, whereas the freezable water occurs in capillaries.

ISSN:0006-3525    

DOI:10.1002/bip.1973.360121009

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe helix–coil transition of poly‐L‐lysine (PLL) in water–isopropanol solvent mixtures has been investigated at room temperature by circular dichroism measurements. Within the range of 70%–80% isopropanol concentration (by volume), the polymer undergoes a sharp transition, characterized by the formation of a fully charged α‐helical structure. On the basis of some experimental evidence the role of the organic component in solution appears more complicated than that of strengthening the intramolecular hydrogen bonds in the polymer. By analogy with the distribution of the components of alcohol–water mixtures in simple ionic systems, it is thought that only an high co‐solvent concentration brings about an extensive and possible cooperative depletion of the clusters of firmly‐bound water molecules in the domain of the polylelectrolyte, favoring the transition to the α‐helical structure. On the other hand, CD spectral patterns show that the addition of NaCl in the alcohol‐rich–water mixtures of charged poly‐L‐lysine gives rise to a transition from the α‐helical to a β‐structures conversion obeys a first‐order rate law at all times, with a rate constant dependent on solvent composition and ionic strength. In these conditions, the rate of the process is close to that found for the thermally induced α–β transition. Higher polymer concentration and/or ionic strength cause a phase separation of β‐PLL, suggesting that in this case interchain reactions (where hydrogen bonding should play the major role) predominate. Titration experiments on charged α‐helical poly‐L‐lysine in 85% or 90% isopropanol mixtures confirm the occurrence of a conformational transition, which takes place within a degree of dissociation α of 0.2–0.75. The transition is accompanied by a visible turbidity, which increases as the titration proceeds. Implications of the solvent distribution around the macroion on th

ISSN:0006-3525    

DOI:10.1002/bip.1973.360121010

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe effects of two salts, MgCl2and MgSO4on the wide‐line nmr spectrum of D2O in oriented, undernatured collagen fibers have been examined at four different D2O contents. MgCl2was found to decrease the nmr doublet splitting, as compared with equal quantities of pure D2O while the major effect of MgSO4was to inhibit the adsorption of D2O without significantly affecting its nmr spectrum. The results, together with a few observations of KCl and LiCl solutions, indicate that even fairly high concentrations of salt have only small effects on the nmr spectrum of D2O in fibrous collagen. It is considered unlikely that either “two‐state” or “structured‐water” models can satisfactorily account for the D2O‐nmr doublet spectrum or the effects of salts on it, over the entire range of obser

ISSN:0006-3525    

DOI:10.1002/bip.1973.360121011

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY