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Solvent Shift (solvent + shift)

Distribution by Scientific Domains

Chemistry	80%

Selected Abstracts

Biophysical studies of the development of amyloid fibrils from a peptide fragment of cold shock protein B

FEBS JOURNAL, Issue 9 2000
Deborah K. Wilkins
The peptide CspB-1, which represents residues 1,22 of the cold shock protein CspB from Bacillus subtilis, has been shown to form amyloid fibrils when solutions containing this peptide in aqueous (50%) acetonitrile are diluted in water [M. Großet al. (1999) Protein Science8, 1350,1357] We established conditions in which reproducible kinetic steps associated with the formation of these fibrils can be observed. Studies combining these conditions with a range of biophysical methods reveal that a variety of distinct events occurs during the process that results in amyloid fibrils. A CD spectrum indicative of ,,structure is observed within 1 min of the solvent shift, and its intensity increases on a longer timescale in at least two kinetic phases. The characteristic wavelength shift of the amyloid-binding dye Congo Red is established within 30 min of the initiation of the aggregation process and corresponds to one of the phases observed by CD and to changes in the Fourier transform-infrared spectrum indicative of ,,structure. Short fibrillar structures begin to be visible under the electron microscope after these events, and longer, well-defined amyloid fibrils are established on a timescale of hours. NMR spectroscopy shows that there are no significant changes in the concentration of monomeric species in solution during the events leading to fibril formation, but that soluble aggregates too large to be visible in NMR spectra are present throughout the process. A model for amyloid formation by this peptide is presented which is consistent with these kinetic data and with published work on a variety of disease-related systems. These findings support the concept that the ability to form amyloid fibrils is a generic property of polypeptide chains, and that the mechanism of their formation is similar for different peptides and proteins. [source]

1H chemical shifts in NMR: Part 23,, the effect of dimethyl sulphoxide versus chloroform solvent on 1H chemical shifts

MAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2006
Raymond J. Abraham
Abstract The 1H chemical shifts of 124 compounds containing a variety of functional groups have been recorded in CDCl3 and DMSO- d6 (henceforth DMSO) solvents. The 1H solvent shift ,, = ,(DMSO) , ,(CDCl3) varies from ,0.3 to +4.6 ppm. This solvent shift can be accurately predicted (rms error 0.05 ppm) using the charge model of ,, ,, , and long-range contributions. The labile protons of alcohols, acids, amines and amides give both, the largest solvent shifts and the largest errors. The contributions for the various groups are tabulated and it is shown that for H.C.C.X ,-effects (X = OH, NH, O, NH.CO) there is a dihedral angle dependence of the ,-effect. The group contributions are discussed in terms of the possible solvent,solute interactions. For protic hydrogens, hydrogen bonding is the dominant interaction, but for the remaining protons solvent anisotropy and electric field effects appear to be the major factors. Copyright © 2006 John Wiley & Sons, Ltd. [source]

1H chemical shifts in NMR: Part 22,,Prediction of the 1H chemical shifts of alcohols, diols and inositols in solution, a conformational and solvation investigation

MAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2005
Raymond J. Abraham
Abstract The 1H NMR spectra of a number of alcohols, diols and inositols are reported and assigned in CDCl3, D2O and DMSO- d6 (henceforth DMSO) solutions. These data were used to investigate the effects of the OH group on the 1H chemical shifts in these molecules and also the effect of changing the solvent. Inspection of the 1H chemical shifts of those alcohols which were soluble in both CDCl3 and D2O shows that there is no difference in the chemical shifts in the two solvents, provided that the molecules exist in the same conformation in the two solvents. In contrast, DMSO gives rise to significant and specific solvation shifts. The 1H chemical shifts of these compounds in the three solvents were analysed using the CHARGE model. This model incorporates the electric field, magnetic anisotropy and steric effects of the functional group for long-range protons together with functions for the calculation of the two- and three-bond effects. The long-range effect of the OH group was quantitatively explained without the inclusion of either the CO bond anisotropy or the COH electric field. Differential , and , effects for the 1,2-diol group needed to be included to obtain accurate chemical shift predictions. For DMSO solution the differential solvent shifts were calculated in CHARGE on the basis of a similar model, incorporating two-bond, three-bond and long-range effects. The analyses of the 1H spectra of the inositols and their derivatives in D2O and DMSO solution also gave the ring 1H,1H coupling constants and for DMSO solution the CHOH couplings and OH chemical shifts. The 1H,1H coupling constants were calculated in the CHARGE program by an extension of the cos2, equation to include the orientation effects of electronegative atoms and the CHOH couplings by a simple cos2, equation. Comparison of the observed and calculated couplings confirmed the proposed conformations of myo -inositol, chiro -inositol, quebrachitol and allo -inositol. The OH chemical shifts were also calculated in the CHARGE program. Comparison of the observed and calculated OH chemical shifts and CH. OH couplings suggested the existence of intramolecular hydrogen bonding in a myo -inositol derivative. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Molecular Design of Superabsorbent Polymers for Organic Solvents by Crosslinked Lipophilic Polyelectrolytes,

ADVANCED FUNCTIONAL MATERIALS, Issue 24 2008
Toshikazu Ono
Abstract Molecular design of lipophilic polyelectrolyte gels as superabsorbent polymers that exhibit a high degree of swelling in less-polar and nonpolar organic solvents is demonstrated. A small amount of tetraalkylammonium tetraphenylborate with long alkyl chains as a lipopholic ion pair is incorporated into crosslinked polyacrylates with variable alkyl chain lengths to provide novel lipophilic polyelectrolyte gels. Their swelling degree becomes more than 100 times as much as their dried weights in various organic solvents. The high effectiveness of the swellable solvents shifts to the polar ones by decreasing the length of the alkyl chain. Swelling or collapsing of the lipophilic polyelectrolyte gels originates from both incompatibility of the polymer chains in the media and dissociation of ionic groups. Thus, a unique superabsorbency is observed when the polymer chains have good compatibility with the solvents and the solvents have relatively high polarities enough to dissociate the ionic groups. By varying the polarity of the neutral monomer in these polyelectrolyte gels, the design of gels that can absorb solvents of nearly any polarity is demonstrated. [source]