Hydrogen-bonding effect on C NMR chemical shifts of amino acid residue carbonyl carbons of some peptides in the crystalline state

¹³C cross polarization-magic angle spinning NMR spectra were measured for a series of peptides containing -valine, -leucine and -aspartic acid residues, for which the crystal structures were already determined by X-ray diffraction, in order to investigate the relationship between hydrogen-bond lengths (R_N…O) and ¹³C chemical shifts of amide carbonyl carbons in the peptides. From these experimental results, it was found that the isotropic ¹³C chemical shifts (δ_iso) of the amino acid residues move linearly downfield with a decrease in R_N…O within the hydrogen-bonded length range considered here and also shown in our previous work on glycine and -alanine residues as expressed by δ_iso(ppm) = a − bR_N…O(Å) where a and b are 215.4 (ppm) and 14.2 (ppm Å⁻¹) for the -valine residue, 202.2 (ppm) and 10.0 (ppm Å⁻¹) for the -leucine residue, and 199.0 (ppm) and 9.6 (ppm Å⁻¹) for the -aspartic acid residue, respectively. Using these relations, the R_N…O values of some polypeptides in the crystalline state were determined through the observation of the amide carbonyl carbon chemical shifts. These values were compared with those determined by the X-ray diffraction method. Furthermore, quantum-chemical calculation of the ¹³C shielding constant for a model compound was carried out by the finite perturbation theory INDO method in order to ascertain the ¹³C shielding behavior in the formation of hydrogen bonds.     

Temperature dependence on the binding of butyl orange by bovine serum albumin: The effect of urea

The effect of urea on the extent of the binding of butyl orange by bovine serum albumin has been examined by an equilibrium dialysis method. The first binding constants and the thermodynamic parameters for the formation of the first dye anion–protein complex have been calculated. Addition of urea to the binding system causes a marked decrease in the absolute magnitude of the free energy change. The enthalpy change during binding becomes more exothermic, and the entropy change tends to decrease with increasing concentration of urea. These results can be interpreted in terms of the concept that urea reduces the structure of the aqueous environment and hence lowers the tendency of apolar groups of the dye and the albumin to participate in the formation of hydrophobic interactions.     

Effect of sorbitol and inositol on the critical micelle concentration of nonionic surfactants in water and in aqueous urea

Summary The critical micelle concentrations (cmc) of non-ionic surfactants in water and in aqueous urea with or without hexahydric alcohols, sorbitol and inositol, were determined. In water the cmc's of the surfactants were decreased by the addition of the hexahydric alcohols. In addition, there was a remarkable difference in the decreasing ability between these two hexahydric alcohols. Inositol decreased the cmc's more markedly than sorbitol. In aqueous urea the effect of these hexahydric alcohols on the cmc's and the difference in the decreasing ability between the two alcohols were less than those in water. These results were explained in terms of the effect of the hexahydric alcohols on the structure of water.

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Zusammenfassung Es wurde die kritische Mizellbildungskonzentration nichtionogener Tenside in Wasser sowie in wäßrigen Harnstofflösungen mit und ohne Zusatz von Inosit und Sorbitol bestimmt. In Wasser wird die cmc bei Zusatz der hexahydrischen Alkohole vermindert; Inosit wirkt dabei stärker als Sorbit. In wässrigen Harnstofflösungen ist der Einfluß auf die cmc und der Unterschied zwischen den zwei Alkoholen geringer als in Wasser. Die Ergebnisse werden über die Beeinflussung der Struktur des Wassers durch die Alkohole gedeutet.

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With 5 figures and 2 tables     

Effect of sulphonic acid on the aqueous solubility of disperse dyes

Summary The solubilities of the following compounds in water andp-toluenesulphonic acid aqueous solution were determined at 5, 25 and 40 C: azobenzenep-aminoazobenzene,p-hydroxyazobenzene,p-N, N-dimethylaminoazobenzene and 1-phenylazo-4-aminonaphthalene. Prom the results the thermodynamic parameters for the transfer of one mole of the compound from water top-toluenesulphonic acid aqueous solution were calculated. It was found that the process was nearly athermal: furthermore, it was invariably accompanied by a positive unitary entropy change. The solubilizing mechanism of aromatic sulphonic acids was explained in terms of an adduct-formation with the compound to be dissolved by means of hydrophobic and nonpolarvan der Waals interactions.

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Zusammenfassung Die Löslichkeiten folgender Verbindungen in Wasser und wÄ\rigerp-ToluolsulphonsÄure-Lösung wurden bei 5, 25 und 40 C bestimmt: Azobenzol,p-Aminoazobenzol,p-Hydroxyazobenzol,p-N,N-dimethylammoazobenzol undL-Phenylazo-4-aminonaphthalin. Aus den Ergebnissen wurden die thermodynamischen Parameter für den übergang eines Mols der Verbindung von Wasser zup-ToluolsulphonsÄurewÄ\rigen Lösungen berechnet. Es wurde gefunden, da\ die Prozesse nahezu athermisch sind. Au\erdem sind sie sÄmtlich durch eine positive und gleichmÄ\ig gro\e EntropieÄnderung begleitet. Der Lösungsmechanismus aromatischer SulphonsÄuren wird in den Begriffen einer Adduktbildung mit der Komponente erklÄrt, die durch die hydrophoben unpolarenvan-der-Waals-Wechselwirkungen entsteht.

     

Counterion mixing effects on the conformational transitions of polyelectrolytes. II. Counterion binding as measured by NMR spectroscopy of alkali metal poly(acrylate)s

Bound states of counterions during the coil‐globule transition of poly(acrylic acid) in water/organic solvent mixtures were investigated by NMR spectroscopy of alkali metal cations (Li⁺, Na⁺, Cs⁺). Accompanying the transition, the line widths of the respective NMR peaks significantly increased with increasing the organic solvent composition in the medium. Although this line width broadening suggests that some specific counterion binding with desolvation is involved with the coil‐globule transition, the most marked broadening was observed in higher organic solvent compositions than those of the coil‐globule transition region detected by the viscometry. Namely, the specific counterion binding with desolvation proceeds even after the polymer chain collapsed. This means in turn that such a strong counterion binding is not a prerequisite for the coil‐globule transition, at least at the stage of the onset. For the Li⁺/Cs⁺ mixed counterion system in 60 vol % DMSO, where our previous conductivity data suggested that the specific counterion binding occurred only for Cs⁺ during the coil‐globule transition induced on mixing with Li⁺, a significant increase in the line width was also observed only for Cs⁺. The coincidence between the conductivity and the NMR results for the Li⁺/Cs⁺ mixed counterion system strongly supports a working hypothesis, “size‐fitting effect,” that has been proposed to determine the counterion specificity observed for the conformational transitions of polyelectrolytes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2132–2139, 2009     

Counterion mixing effects on the conformational transitions of polyelectrolytes. I. Volume phase transition and coil‐globule transition of alkali metal poly(acrylate)s

Counterion mixing effects on the volume phase transition and the coil‐globule transition of alkali metal poly(acrylate)s (PAAM) in aqueous organic solvents were investigated by observing the swelling behavior of PAAM gel and by measuring the solution viscosity and the conductivity as a function of the counterion mixing ratio. Marked transitions to the collapsed states were induced only for Li⁺/Cs⁺ system in most solvent systems; namely, PAA gel significantly collapsed in the presence of Li⁺ and Cs⁺ counterions irrespective of the solvent species employed, while only a slight deswelling was observed for Li⁺/K⁺ system in some aqueous organic solvents. Corresponding specific decrements in the solution viscosity and conductivity were also confirmed for the combination of Li⁺ and Cs⁺ in aqueous dimethyl sulfoxide (DMSO) system. A simple analysis of the conductivity decrement observed for Li⁺/Cs⁺ system in 60 vol % DMSO suggested that only Cs⁺ is tightly bound upon addition of Li⁺ while no restriction is induced for Li⁺ upon mixing with Cs⁺. A working hypothesis is proposed for the apparently intriguing behaviors of the counterions in the mixed system. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2122–2131, 2009     

Renormalization group approach to matrix models via noncommutative space

Journal of High Energy Physics - We provide a detailed correspondence between G 4 gauge fluxes in F-theory compactifications with SU(n) and SU(n) × U(1) gauge symmetry and their Type IIB...     

Spontaneous supersymmetry breaking in large-N matrix models with slowly varying potential

We construct a class of matrix models, where supersymmetry (SUSY) is spontaneously broken at the matrix size N infinite. The models are obtained by dimensional reduction of matrix-valued SUSY quantum mechanics. The potential of the models is slowly varying, and the large-N limit is taken with the slowly varying limit.