NMR Spectroscopic Techniques (nmr + spectroscopic_techniques)

Distribution by Scientific Domains

Selected Abstracts

Water-borne melamine,formaldehyde-cured epoxy,acrylate corrosion resistant coatings

Sarvat Zafar
Abstract Organic protective coatings are widely used in corrosion control. However, environmental standards establish that the volatile organic compounds either must be removed or controlled at the lowest possible levels. The carcinogenic environmental impact of volatile organic compounds has led to the substitution of solvent-borne coatings by water-borne coating systems. Among recently developed water-borne coatings, epoxy- and acrylic-based coatings have a special significance over other reported water-borne systems. Keeping in mind, the importance of water-borne coatings in the present work, we report the synthesis of water-borne epoxy,acrylate (EpAc) and melamine,formaldehyde (MF) as well as formulation of their anticorrosive coatings. The structural elucidation of MF-cured EpAc was carried out by FTIR, 1H NMR, and 13C NMR spectroscopic techniques. The coatings of EpAc-MF were applied on mild steel strips and were evaluated for physicochemical, physicomechanical characterization, and the anticorrosive performance under different environmental conditions. The present coating system EpAc coatings exhibited superior performance as compared to the reported water-borne epoxy,acrylatecoatings. The presence of melamine,formaldehyde in the resin increases the scratch hardness, impact resistance, alkali resistance, and thermal stability of these coatings. EpAc-MF-1 was found to cure at ambient temperature and exhibit good physicomechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Substituent effects of phthalimide-based nucleoside analogs on binding a CG Watson,Crick base pair

Z. Xiao
Abstract Five differently substituted phthalimide nucleosides were studied by NMR spectroscopic techniques for their ability to recognize and bind a cytosine,guanosine (CG) Watson,Crick base pair in CD2Cl2. Whereas only rather weak binding was observed for analogs with an amino, acetamido, or benzamido substituent, strong binding was observed with the analogs carrying an ureido and n -butyl ureido residue. 2D NOE measurements at low temperatures confirm the proposed binding mode for the high-affinity ligands but indicate binding interactions for the weakly bound analogs different from the expected geometry. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Synthesis and characterization of water-soluble barbiturate- and thiobarbiturate-functionalized polystyrene

S. Raja
Abstract The synthesis and characterization of barbiturate- and thiobarbiturate-functionalized polystyrene from polystyrene homopolymer by polymer-modification reactions is discussed. Polystyrene homopolymer quantitatively functionalized at the para postion with diethyl oxomalonate functionality was subjected to a condensation reaction with urea and thiourea in the presence of sodium methoxide in methanol. This reaction proceeded essentially to quantitative conversion to the barbiturate- (BAPS) and thiobarbiturate-functionalized polystyrenes (TBAPS) as estimated by 1H NMR, UV, and IR spectroscopies. Thus, several copolymers of styrene with barbiturate- and thiobarbiturate-functionalized styrene were synthesized. The detailed characterizations of quantitatively functionalized polystyrene using gel permeation chromatographic, IR, UV, and 1H NMR spectroscopic techniques as well as thermogravimetric analysis are discussed. An application of the newly synthesized polymer in removing Cu(II) ions from aqueous solution is demonstrated. This is the first report on the synthesis of BAPS and TBAPS by the polymer-modification route or otherwise. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 731,737, 2002; DOI 10.1002/pola.10154 [source]

NMR spectroscopic analysis of new spiro-piperidylrifamycins

Eduardo Rubio
Abstract New spiro-piperidylrifamycin derivatives are presented. These compounds were synthesized from the reaction of 3-amino-4-iminorifamycin S and enantiomerically pure 4-piperidones, which generate diasteroisomeric rifabutin analogues with a new stereocentre at the spiranic carbon. The 1H and 13C NMR spectra of these new compounds, and also the configuration of the new stereogenic centres, were assigned using 2D NMR spectroscopic techniques. A preliminary study of the 1H and 13C NMR spectra of the starting compounds rifamycin S, 3-amino-4-iminorifamycin S and the related rifabutin was also carried out and as a result, their previously published 13C NMR data were corrected. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A new bioactive steroidal saponin from Sansevieria cylindrica

Alexandra da Silva Antunes
Abstract A new steroidal saponin was isolated from the leaves of Sansevieria cylindrica. Its structure was established as (3,,12,,15,,25S)-26-(,- D -glucopyranosyloxy)-22-hydroxyfurost-5-en-3-yl 12- O - (6-deoxy-,- L -mannopyranosyl)-15- O -(6-deoxy-,- L -mannopyranosyl)-,- D -glucopyranoside. The structural identification was performed using detailed analyses of 1H and 13C NMR spectra including 2D NMR spectroscopic techniques (COSY, HETCOR, HMBC and HMQC) and chemical conversions. The steroidal saponin showed no haemolytic effects in the in vitro assays and demonstrated inhibition of the capillary permeability activity. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Electrochemical behaviour and electrochemical polymerization of fluoro-substituted anilines

Atilla Cihaner
Abstract The electrochemical behaviour of three fluoro-substituted aniline monomers, 2-fluoroaniline (2FAN), 3-fluoroaniline (3FAN) and 4-fluoroaniline (4FAN), was investigated in aqueous acidic and organic media by means of cyclic voltammetry (CV) studies. Constant potential electrolysis (CPE) of the monomers in acetonitrile,water mixture (1:1 by volume) using NaClO4 as supporting electrolyte yielded soluble polymers. The mechanism of electrochemical polymerization was investigated using in situ electron spin resonance (ESR) and in situ UV,VIS spectroscopic techniques for one of the monomers (4FAN). Both CV and in situ UV,VIS measurements indicated that the polymers obtained are in the emeraldine base form. In situ ESR studies indicated that electrochemical polymerization involves a radical-cation as an intermediate. Characterization of polymer products have been carried out using FTIR and NMR spectroscopic techniques, and thermal behaviour was studied using differential scanning calorimetry (DSC). It was found that conductivity can be imparted to as-synthesized polyfluoroanilines via iodine doping. © 2002 Society of Chemical Industry [source]

Synthesis, crystal structure and electrochemical properties of three isocloso eleven-vertex ferrocenecarboxylate ruthenaborane clusters

Jianmin Dou
Abstract The reaction of [RuCl2(PPh3)3] with closo -[B10H10]2, and C5H5FeC5H4COOH (FcCO2H) in refluxing CH2Cl2 solution affords three ruthenaborane clusters: [PPh3(H2O)(FcCO2)RuB10H8Cl] (1), [(PPh3)2ClRu(PPh3)(FcCO2)RuB10H9]·0.5CH2Cl2 (2 × 0.5CH2Cl2) and [PPh3(FcCO2)2RuB10H8] (3). All of these compounds are characterized by FT-IR, NMR spectroscopic techniques, elemental analysis and single-crystal X-ray analysis. They are all based on a closo -type 1:2:4:2:2 {RuB10} stack with the metal occupying the unique six-connected apical position and can be considered as having isocloso structures derived from the complete capping of the open face of an arachano geometry to give a completely closed deltahedral cluster. Compounds 1 and 2 both have an exo -polyhedral ferrocenecarboxylate that is attached with one {RuO} and one {BO} bond each, resulting in one exo -cyclic five-membered RuOCOB ring. There is in addition one exo -polyhedral ruthenium atom bonded to the center {RuB10} cluster via one {RuRu} linkage and two {RuHµB} bridges, which forms a closed exo -polyhedral tetrahedron configuration in compound 2. Compound 3 has two exo -polyhedral ferrocenecarboxylates to form two five-membered RuOCOB rings engendering a symmetrical conformation. All of these new 11-vertex ruthenaboranes can be considered as having isocloso structures derived from the complete capping of the open face of an arachano geometry to give a completely closed deltahedral cluster. Copyright © 2006 John Wiley & Sons, Ltd. [source]