Raman spectrum of dimethyl sulfoxide (DMSO) and the influence of solvents

The Raman spectrum of DMSO is recorded with a Hilger two-prism spectrograph andλ 4358 Å excitation. In addition to all the Raman lines reported earlier, six new lines at 898, 925, 1223, 1309, 2811 and 2871 cm.−1 are observed and tentative assignments are given. The influence of solvents (CCl4, CHCl3, CH3COOH) on the S=O bond is also studied. A shift from the liquid phase value,i.e., 1043 cm.−1 to 1054, 1052 and 1009 cm.−1 in the respective solvents is observed. The possibilities of association effects and hydrogen bonding are discussed.

Enhanced Pair Hydrophobicity in the Water-Dimethylsulfoxide (DMSO) Binary Mixture at Low DMSO Concentrations

We observe a surprisingly sharp increase in the pair hydrophobicity in the water climethylsulfoxide (DMSO) binary mixture at small DMSO concentrations, with the mole fraction of DMSO (x(D)) in the range 0.12-0.16. The increase in pair hydrophobicity is measured by an increase in the depth of the first minimum in the potential of mean force (PMF) between two methane molecules. However, this enhanced hydrophobicity again weakens at higher DMSO concentrations. We find markedly unusual behavior of the pure binary mixture (in the same composition range) in the diffusion coefficient of DMSO and in the local composition fluctuation of water, We find that, in the said composition range, the average coordination number of the methyl groups (of distinct DMSO) varies between 2.4 and 2.6, indicating the onset of the formation of a chain-like extended connectivity in an otherwise stable tetrahedral network comprising of water and DMSO molecules. We propose that the enhanced pair hydrophobicity of the binary mixture at low DMSO concentrations is due to the participation of the two methane molecules in the local structural order and the emerging molecular associations in the water-DMSO mixture.

Theoretical and Computational Analysis of Static and Dynamic Anomalies in Water-DMSO Binary Mixture at Low DMSO Concentrations

Experiments have repeatedly observed both thermodynamic and dynamic anomalies in aqueous binary mixtures, surprisingly at low solute concentration. Examples of such binary mixtures include water-DMSO, water-ethanol, water-tertiary butyl alcohol (TBA), and water-dioxane, to name a few. The anomalies have often been attributed to the onset of a structural transition, whose nature, however, has been left rather unclear. Here we study the origin of such anomalies using large scale computer simulations and theoretical analysis in water-DMSO binary mixture. At very low DMSO concentration (below 10%), small aggregates of DMSO are solvated by water through the formation of DMSO-(H2O)(2) moieties. As the concentration is increased beyond 10-12% of DMSO, spanning clusters comprising the same moieties appear in the system. Those clusters are formed and stabilized not only through H-bonding but also through the association of CH3 groups of DMSO. We attribute the experimentally observed anomalies to a continuum percolation-like transition at DMSO concentration X-DMSO approximate to 12-15%. The largest cluster size of CH3-CH3 aggregation clearly indicates the formation of such percolating clusters. As a result, a significant slowing down is observed in the decay of associated rotational auto time correlation functions (of the S = O bond vector of DMSO and O-H bond vector of water). Markedly unusual behavior in the mean square fluctuation of total dipole moment again suggests a structural transition around the same concentration range. Furthermore, we map our findings to an interacting lattice model which substantiates the continuum percolation model as the reason for low concentration anomalies in binary mixtures where the solutes involved have both hydrophilic and hydrophobic moieties.

Anomalous Behavior of Linear Hydrocarbon Chains in Water-DMSO Binary Mixture at Low DMSO Concentration

We find that at a mole fraction 0.05 of DMSO (x(DMSO) = 0.05) in aqueous solution, a linear hydrocarbon chain of intermediate length (n = 30-40) adopts the most stable collapsed conformation. In pure water, the same chain exhibits an intermittent oscillation between the collapsed and the extended coiled conformations. Even when the mole fraction of DMSO in the bulk is 0.05, the concentration of the same in the first hydration layer around the hydrocarbon of chain length 30 (n = 30) is as large as 17%. Formation of such hydrophobic environment around the hydrocarbon chain may be viewed as the reason for the collapsed conformation gaining additional stability. We find a second anomalous behavior to emerge near x(DMSO) = 0.15, due to a chain-like aggregation of the methyl groups of DMSO in water that lowers the relative concentration of the DMSO molecules in the hydration layer. We further find that as the concentration of DMSO is gradually increased, it progressively attains the extended coiled structure as the stable conformation. Although Flory-Huggins theory (for binary mixture solvent) fails to predict the anomaly at x(DMSO) = 0.05, it seems to capture the essence of the anomaly at 0.15.

Fluctuation quench and hydrophobic collapse of polymers and biopolymers in water-DMSO binary mixture at low DMSO concentration

Binary mixtures have strong influence on activities of polymers and biopolymers even at low cosolvent concentration. Among the several aqueous binary mixtures studied, water-DMSO especially stands out for its unusual behavior at certain specific concentrations of DMSO. In the present work, we study the effect of water-DMSO binary mixture on polymers and biopolymers by taking a simple linear hydrocarbon chain of intermediate length (n = 30) and the protein lysozyme, respectively. We find that at a mole fraction of 0.05 of DMSO (x(DMSO) = 0.05) in aqueous solution, the hydrocarbon chain adopts the collapsed conformation as the most stable and rigid state. In this case of 0.05 mole fraction of DMSO in bulk, the DMSO concentration in the first hydration layer around the polymer is found to be as large as 17%. Formation of such hydrophobic environment around the polymer is the reason for the collapsed state gaining so much stability. Interestingly, similar quench of conformational fluctuation is also observed for the protein investigated. It is observed that in the case of alkane polymer chains, long wavelength fluctuation gets easily quenched, the polymer being purely hydrophobic. However, in case of the protein, quench of fluctuation is prominent only at the hydrophobic surface, and quench of long wavelength fluctuation becomes insignificant for the full protein. As protein contains both hydrophobic and hydrophilic moieties, the extent of quench of conformational fluctuation with respect to that in pure water is almost half for the biopolymer complex (16.83%) than the same for pure hydrophobic polymer chain (32.43%).

Unusual Structural Isomerization Of Monopropiophenone Thiocarbonohydrazone

Monopropiophenone thiocarbonohydrazone has been isolated in both linear and cyclic isomeric forms. Each form has been shown to isomerize and exist in equilibrium with the other in DMSO-d6 solution by 1H and 13C NMR spectroscopy. The kinetics of this transformation show attainment of equilibrium in approximately 6 h, with a linear to cyclic configuration ratio of 40:60.

Metal Chelates in Vinyl Polymerization: Kinetics and Mechanism of Acrylonitrile Polymerization Initiated by Cu(I1) Imine Complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(I1) 4-anilino 3-pentene 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(I1) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCld), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were 22 at two different temperatures and in different solvents. The square-root dependence of R, on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formatign was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.

Behaviour of methylmethacrylate-acrylonitrile random copolymers in dilute solution

Studies on the dilute solution properties of methylmethacrylate-acrylonitrile random copolymers of three different compositions, 0.236, 0.5 and 0.74 mole fraction (m.f.) of acrylonitrile (AN) designated as MAa, MAb and MAc, respectively, have been made in good solvents and theta solvents. MAa has been studied in benzene (Bz) and ethylacetate (EAc). MAb in acetonitrile (MeCN), dimethyl sulphoxide (DMSO) and a binary solvent mixture of Bz and dimentyl formamide (DMF) in the volume ratio 6.5:1 designated as BM1 and MAc in MeCN, DMSO and Bz + DMF in the volume ratio 1.667:1 designated as BM2. The Mark-Houwink exponent ‘a’ reveals that Bz is a theta solvent for MAa at 20°C. For MAb and MAc, BM1 and BM2, respectively have ‘a’ values of 0.5 at all three temperatures studied (30°, 40° and 50°C). It is not clear whether they represent theta states or preferential adsorption plays a role complicating the behaviour in solution. The values of A2 are very low in MeCN considering that it is a very good solvent for the copolymer, ‘a’ values for MAb and MAc being 0.75 and 0.7, respectively.

Molecular structure of Boc-Aib-Aib-Phe-Met-NH2·DMSO. A fragment of a biologically active enkephalin analogue

The tetrapeptide t-butyloxycarbonyl--aminoisobutyryl--aminoisobutyryl-L- phenylalanyl-L-methionyl amide crystallizes in the orthorhombic space group P212121 with a= 9.096, b= 18.067, c= 21.701 Å and Z= 4. The crystals contain one molecule of dimethyl sulphoxide (DMSO) associated with each peptide. The structure has been solved by direct methods and refined to an R value of 0.103 for 2 672 observed reflections. The peptide adopts a distorted 310 helical structure stabilized by two intramolecular 4 1 hydrogen bonds between the Boc CO and Aib(1) CO groups and the NH groups of Phe(3) and Met(4), respectively. A long hydrogen bond (N O = 3.35 Å) is also observed between Aib(2) CO and one of the terminal amide hydrogens. The DMSO molecule is strongly hydrogen bonded to the Aib(1) NH group. The solid-state conformation agrees well with proposals made on the basis of n.m.r. studies in solution.

Metal chelates in vinyl polymerization: Kinetics and mechanism of acrylonitrile polymerization initiated by Cu(II) imine complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(II) 4-anilino 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(II) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCl4), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were 2 at two different temperatures and in different solvents. The square-root dependence of Rp on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formation was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.

Synthesis of 4,6-(and 5,7-)dimethoxy-3,3-dimethyl-1-indanones

Grignard reaction of ethyl 3-(3,5-dimethoxyphenyl)-propionate (4) followed by cyclodehydration of the carbinol (5) with conc H2SO4 gave 4,6-dimethoxy-3,3-dimethylindane (6). Oxidation of the indane (6) with CrO3-pyridine complex in methylene chloride gave 4,6-dimethoxy-3,3-dimethylindan-1- one (1) in high yield. Conjugate addition of methyl magnesium iodide to methyl α-cyano-β-methyl-3,5-dimethoxycinnamate (11), prepared from 3,5-dimethoxyacetophenone (10) by Knoevenagel condensation, resulted in methyl 2-cyano-3-(3,5-dimethoxyphenyl)-3,3-dimethylpropionate (12). Refluxing the ester (12) with aq DMSO containing sodium chloride gave the corresponding nitrile (15) which underwent Höesch reaction to yield 5,7-dimethoxy-3,3-dimethylindan-1-one (2).

Synthesis, spectral characterization, in-vitro microbiological evaluation and cytotoxic activities of novel macrocyclic bis hydrazone

A macrocyclic hydrazone Schiff base was synthesized by reacting 1,4-dicarbonyl phenyl dihydrazide with 2,6-diformyl-4-methyl phenol and a series of metal complexes with this new Schiff base were synthesized by reaction with Co(II), Ni(II) and Cu(II) metal salts. The Schiff base and its complexes have been characterized by elemental analyses, IR, H-1 NMR, UV-vis, FAB mass, ESR spectra, fluorescence, thermal, magnetic and molar conductance data. The analytical data reveal that the Co(II), Ni(II) and Cu(II) complexes possess 2:1 metal-ligand ratios. All the complexes are non-electrolytes in DMF and DMSO due to their low molar conductance values. Infrared spectral data suggest that the hydrazone Schiff base behaves as a hexadentate ligand with NON NON donor sequence towards the metal ions. The ESR spectral data shows that the metal-ligand bond has considerable covalent character. The electrochemical behavior of the copper(II) complex was investigated by cyclic voltammetry. The Schiff base and its complexes have also been screened for their antibacterial (Escherichia coli, Staphylococcus aureus, Shigella dysentery, Micrococcus, Bacillus subtilis, Bacillus cereus and Pseudomonas aeruginosa) and antifungal activities (Aspergillus niger, Penicillium and Candida albicans) by MIC method. The brine shrimp bioassay was also carried out to study their in-vitro cytotoxic properties. (C) 2009 Elsevier Masson SAS. All rights reserved.

Tuning the beta-turn segment in designed peptide beta-hairpins: Construction of a stable type I ' beta-turn nucleus and hairpin-helix transition promoting segments

Designed octapeptides Boc-Leu-Val-Val-Aib-(D)Xxx-Leu- Val-Val-OMe ((D)Xxx = (D)Ala, 3a; (D)Val, 3c and (D)Pro, 5a) and Boc-Leu-Phe-Val-Aib-DAla-Leu-Phe-Val-OMe (3b) have been investigated to construct models of a stable type I' beta-turn nucleated hairpin and to generate systems for investigating helix-hairpin conformational transitions. Peptide 5a, which contains a central Aib-(D)Pro segment, is shown to adopt a stable type I' beta-turn nucleated hairpin structure, stabilized by four cross-strand hydrogen bonds. The stability of the structure in diverse solvents is established by the observation of all diagnostic NOEs expected in a beta-hairpin conformation. Replacement of (D)Pro5 by (D)Ala/(D)Val (3a-c) results in sequences that form beta-hairpins in hydrogen bonding solvents like CD3OH and DMSO-d(6). However, in CDCl3 evidence for population of helical conformations is obtained. Peptide 6b (Boc-Leu-Phe-Val-Aib-Aib-Leu-Phe-Val-OMe), which contains a centrally positioned Aib-Aib segment, provides a clear example of a system, which exhibits a helical conformation in CDCl3 and a significant population of both helices and hairpins in CD3OH and DMSO-d(6). The coexistence of multiple conformations is established by the simultaneous observation of diagnostic NOEs. Control over stereochemistry of the central beta-turn permits generation of models for robust beta-hairpins and also for the construction of systems that may be used to probe helix-hairpin conformational transitions. (c) 2006 Wiley Periodicals, Inc.

Monoclinic polymorph of Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-OMe(anhydrous). Parallel packing of 3(10)-/alpha-helices and a transition of helix type

The structures of two crystal forms of Boc-Trp-Ile-Ala-Aib-Ile-Val-Aib-Leu-Aib-Pro-OMe have been determined. The triclinic form (P1, Z = 1) from DMSO/H2O crystallizes as a dihydrate (Karle, Sukumar & Balaram (1986) Proc, Natl, Acad. Sci. USA 83, 9284-9288). The monoclinic form (P2(1), Z = 2) crystallized from dioxane is anhydrous. The conformation of the peptide is essentially the same in both crystal system, but small changes in conformational angles are associated with a shift of the helix from a predominantly alpha-type to a predominantly 3(10)-type. The r.m.s. deviation of 33 atoms in the backbone and C beta positions of residues 2-8 is only 0.29 A between molecules in the two polymorphs. In both space groups, the helical molecules pack in a parallel fashion, rather than antiparallel. The only intermolecular hydrogen bonding is head-to-tail between helices. There are no lateral hydrogen bonds. In the P2(1) cell, a = 9.422(2) A, b = 36.392(11) A, c = 10.548(2) A, beta = 111.31(2) degrees and V = 3369.3 A for 2 molecules of C60H97N11O13 per cell.

Synthesis and characterization of polyaniline salts with phenoxy acetic acids by emulsion polymerization

Polyaniline salts have been synthesized by chemical oxidative polymerization of aniline in the presence of phenoxy acetic acid and its two derivatives using emulsion method at room temperature and characterized by different techniques such as infrared, H-1 and C-13 NMR, UV-visible spectroscopy, SEM, wide angle X-ray diffractograms and conductivity measurements. These polyaniline salts have the desirable property of high solubility for processibility in solvents such as DNIF, DMSO and a mixture of CHCl3 and acetone and they exhibit fairly good conductivity of similar to 3.0 x 10(-3) S cm(-1). The variations in solubility, conductivity and morphology with the protonating strength of the dopants are examined.