Nuclear Magnetic Resonance Spectral Studies Research Articles

Electronic, infrared and proton magnetic resonance spectral studies on some azo and azo-azomethine derivatives

Electronic, infrared and proton magnetic resonance spectral studies on some azo and azo-azomethine derivatives

Synthesis, crystal structure and nuclear magnetic resonance spectral study of the (+)-(R,R,R*,S*)- and (–)-(S,S,R*,S*)-enantiomers of the chiral diphosphine [C6H4(PPhCH2CHO)2CMe2]-1,2

Treatment of the dilithiodiphosphide [Li(tmen)]2[C6H4(PPh)2-1,2](tmen =N,N,N′,N′-tetramethylethylenediamine) with (–)-(R,R)- or (+)-(S,S)-Me2C(OCHCH2OSO2C6H4Me-p)2 afforded the enantiomeric chiral diphosphine (+)-(R,R,R*,S*)- or (–)-(S,S,R*,S*)-[C6H4(PPhCH2CHO)2CMe2]-1,2, respectively. Their crystal structures have been determined which show them to be isostructural; hence they are enantiomers rather than diastereoisomers. Thus the original chirality of Me2C(OCHCH2OSO2C6H4Me-p)2 induces a preferred chirality at the P atoms of the product diphosphines. A 1H and 31P NMR spectral study of (+)-(R,R,R*,S*)-[C6H4(PPhCH2CHO)2CMe2]-1,2 has been carried out, involving selective decoupling and nuclear Overhauser experiments, Karplus curves for both 3JHH and 2JPH couplings and ring current shielding effects. This allows assignments to be made of the 31P and non-aromatic 1H signals, and demonstrates that the structure determined by X-ray crystallography in the solid state is not significantly changed in solution.

Synthesis and Characterization of Novel Ruthenium(II) Chelates with Some Schiff Bases Derived from 4-Benzoyl-3-Methyl-1-Phenyl-2-Pyrazolin-5-One and Sulpha Drugs

Abstract Three novel ruthenium(II) complexes with the neutral bidentate O,N-donor Schiff bases L-L (where L-L is the Schiff base prepared from sulphadiazine, sulphamerazine or sulphamethazine and 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one) have been synthesized by the interaction of K2RuCl5. H2O and the Schiff bases in aqueous ethanol. The complexes, which have been characterized on the basis of elemental analyses, molar conductances, cyclic voltammetry, infrared, electronic and proton nuclear magnetic resonance spectral studies, have the general formula [Ru(L-L)2(Cl)2]. Ethanol reduces ruthenium(III) to ruthenium(II) during reflux. An octahedral structure is proposed for these diamagnetic complexes. Referee I: W. E. Rudzinski Referee II: T. G. Richmond

Nuclear magnetic resonance spectral study of 2-acetylpyridine4 N-alkylthiosemicarbazones and their cobalt(III) complexes

1H and13C n.m.r. spectra are reported for a series of 2-acetylpyridine4 N-alkylthiosemicarbazones in order to study the effect of increased size of the alkyl function on the ratio of isomers present in solution. Similarly, n.m.r. data for the bis(thiosemicarbazone)cobalt(III) complexes are included, as well as these complexes' ligand field parameters.

Melt‐polymerizable bisimido‐bisphthalonitriles containing silicon, fluoro, and ether groups: Synthesis, characterization, and NMR study

AbstractVarious melt‐polymerizable bisimido‐bisphthalonitrile polymer precursors were synthesized by the reaction of 4‐aminophthalonitrile (4‐APN) with bis(3,4‐dicarboxyphenyl) dimethylsilane dianhydride (SIDA), 4,4′‐hexafluoroisopropylidene diphthalic anhydride (6FDA), bis(3,4‐dicarboxyphenyl)ether dianhydride (ODPA), and 3,3′, 4,4′‐tetracarboxylichenzophen+ne dianhydride (BTDA) in an aprotic solvent. The synthesized monomers showed crystalline melting at 269 and 271°C. Elemental analysis, differential thermal analysis (DTA), infrared (IR), nuclear magnetic resonance (1H‐NMR) and mass spectral studies were carried out to characterize the synthesized monomers. Thermogravimetric analysis (TGA) of the synthesized monomers showed their thermal stability at 410–400°C. A detailed study and NMR investigation of the first step of condensation reaction was carried out and indicated the formation of a transient charge transfer complex. Thermal cyclization of the formed intermediate, however, gave the required monomers. A preliminary study demonstrated that melt‐polymerization of the synthesized monomers gave thermallystable, tough polymers.

Isolation and structure of cribrostatins 1 and 2 from the blue marine sponge Cribrochalinasp

The blue marine sponge cribrostatins 1 (1, 8.8 × 10−6% yield) and 2 (2, 3.1 × 10−6% yield) active against the P388 lymphocytic leukemia cell line (ED50 1.58 and 2.73 μg/mL respectively) have been isolated. The previously known isoquinolinequinones mimosamycin (3), renierone (4), and O-demethylrenierone (5) were also isolated and shown to display activity against the P388 cell line (ED50 0.73, 2.75, and 8.36 μg/mL, respectively). Importantly, both cribrostatin 1 and mimosamycin showed selective activity against all of the nine human melanoma cell lines employed by the U.S. National Cancer Institute. Structural determinations were accomplished utilizing high field nuclear magnetic resonance (400 MHz) and mass spectral studies. Confirmation of the cribrostatin 1 structure was achieved by X-ray crystallographic techniques.

New aspects of the chemistry and mechanism of electrochemical reduction of kynurenine at mercury electrodes in aqueous media

New features of the chemistry of kynurenine in aqueous media over the pH range of 0 to 12 have been obtained using a combination of spectroscopic and electrochemical techniques at mercury electrodes. While 13C nuclear magnetic resonance (NMR) spectroscopic data show exchange averaged spectra over the pH range examined, polarographic techniques reveal the presence of three kynurenine reduction processes which are predominant at close to the 100% level at pH 2, 7 and 10 respectively. Thus, the various forms of kynurenine exchange rapidly on the NMR time scale, but not at a diffusion controlled rate, so that the species present in solution can be studied individually by electrochemical methods. The protonated form(s) of kynurenine present at low pH is adsorbed at mercury electrodes in an orientation which is parallel to the electrode surface and obeys a Frumkin adsorption isotherm. At higher concentrations of the acidic form and at all concentrations of the neutral and basic forms, the reduction processes are diffusion controlled in the limiting current region of polarograms and involve an overall irreversible two electron-two proton reduction process at the carbonyl group, with the chemical steps rather than the charge transfer process being rate determining. NMR, infra-red and mass spectral studies of the products of bulk electrolysis at a mercury pool electrode are consistent with the formation of diastereoisomers of γ( o-aminophenyl)homoserine and in the analytical context, pH 2 offers the most sensitive response towards kynurenine with limits of detection being 3.1×10 −8 M with conventional differential pulse polarography and 1.7×10 −8 M with a modified pulse method which discriminates against the overlapping hydrogen ion reduction wave.

The reorientation of t-butyl groups in butylated hydroxytoluene: A deuterium nuclear magnetic resonance spectral and relaxation time study

Deuterium nuclear magnetic resonance (NMR) spectra and spin–lattice relaxation times were determined in order to study the dynamics of t-butyl groups in butylated hydroxytoluene. The results are consistent with a model first proposed by Beckmann et al. [J. Magn. Reson. 36, 199 (1979)], where there is an inequivalence between the methyl groups within each t-butyl group. While two methyl groups reorient rapidly relative to the whole t-butyl rotation, the remaining methyl group is more restricted in its motion, reorienting at a rate comparable to that of the t-butyl group itself. The spin–lattice relaxation data show two T1 minima, the high temperature minimum (40 °C) corresponding to the combined t-butyl and ‘‘slow’’ methyl rotations, and the low temperature minimum corresponding to ‘‘fast’’ methyl group rotation. Using an explicitly defined T1 fitting function, the T1 data yield activation energies of 2.2 and 6.0 kcal/mol for the fast methyl and t-butyl rotations, respectively, both in agreement with Beckmann’s values obtained from proton T1 experiments. It was also possible to simulate the low temperature deuterium NMR spectra from T=−160 °C to T=−80 °C using the aforementioned dynamical inequivalence between the t-butyl methyl groups. While the fast methyl group rotation was in the motional narrowing region for T>−160 °C, it was possible, from the simulations, to determine the t-butyl exchange rates to within 10%. The jump rates are remarkably close to the values predicted from the T1 results. Above −80 °C, the spectra could not be simulated, implying that a third motion must be present to further alter the high temperature line shapes. The effective axial asymmetry of the T>−20° spectra indicates that the additional motion involves a two site exchange.

Lactoperoxidase-catalyzed oxidation of thiocyanate by hydrogen peroxide: nitrogen-15 nuclear magnetic resonance and optical spectral studies

To establish the agent(s) responsible for the activity of the lactoperoxidase (LPO)/SCN-/H2O2 system, the oxidation of thiocyanate with hydrogen peroxide, catalyzed by lactoperoxidase, has been studied by 15N NMR and optical spectroscopy at different concentrations of thiocyanate and hydrogen peroxide and at different pHs. The formation of hypothiocyanite ion (OSCN-) as one of the oxidation products correlated well with the activity of the LPO/SCN-/H2O2 system and was maximum when the concentrations of the H2O2 and SCN- were nearly the same and the pH was less than 6.0. At [H2O2]/[SCN-] = 1, OSCN- decomposed very slowly back to thiocyanate. When the ratio [H2O2]/[SCN-] was above 2, formation of CN- was observed, which was confirmed by 15N NMR and also by changes in the optical spectrum of LPO. The oxidation of thiocyanate by H2O2 in the presence of LPO does not take place at pH greater than 8.0. Since thiocyanate does not bind to LPO above this pH, the binding of thiocyanate to LPO is considered to be prerequisite for the oxidation of thiocyanate. Maximum inhibition of oxygen uptake by Streptococcus cremoris 972 bacteria was observed when hydrogen peroxide and thiocyanate were present in equimolar amounts and the pH was below 6.0.

The use of thermal and spectrometric analyses for the structure investigation ofarylhydrazoneacetoacetylaminopyridines and their copper chelates

A series of α-arylhydrazoneacetoacetylaminopyridine ligands and their copper(II) complexes have been isolated and characterized. Characterization involves elemental and thermal analyses together with UV, visible, proton magnetic resonance and IR spectral studies. Based on these physicochemical studies, the structural formulae for the obtained ligands and their complexes have been suggested. The suggested formulae of these complexes are CuL·X (L = ligands, X = H 2O or acetate group). Thermal analysis of the ligands and of their isolated complexes have already indicated hydrogen bonding within the ligand molecule and different modes of interaction between the ligands and the central copper(II) metal ions. UV, visible, IR and 1H NMR spectral studies have also been used to investigate the nature of the hydrogen bonding within the ligands and have indicated that their coordination to the central metal ion is via oxygen- and nitrogen-containing groups. This work is relevant to the applications of these dyes and their complexes in different fields of industry.

A novel flavonol glycoside in the leaves of Epimedium sempervirens.

A new flavonol glycoside with two acetyl groups, sempervirenoside A, was isolated from the leaves of Epimedium sempervirens NAKAI. The structure of sempervirenoside A was established to be 3-O-[3-O-acetyl-β-D-xylopyranosyl-(1→3)-4-O-acetyl-α-L-rhamnopyranosyl]-7-O-β-D-glucopyranosyl-3, 5, 7-trihydroxy-4'-methoxy-8-(3-methyl-2-butenyl) flavone by ultraviolet, fast atomic bombardment mass, and proton and carbon-13 nuclear magnetic resonance spectral studies.

Synthesis and characterization of dioxomolybdenum complexes of semicarbazones

Six-coordinate dioxomolybdenum(VI) complexes of the type [MoO2(SCZ)2] (HSCZ=semicarbazone) were prepared and characterized by elemental analyses, molecular weight determinations and conductance and magnetic measurements. On the basis of electronic, i.r., proton magnetic resonance, and13C nuclear magnetic resonance spectral studies, an octahedral geometry withcis-MoO2 is proposed.

ChemInform Abstract: Synthesis and Characterization of Mixed Azomethine Derivatives of Silicon(IV).

Abstract Synthesis and characterization of mixed azomethine derivatives of silicon(IV) with anils and thio-anils have been described. Such derivatives of the type (ONO)Si(ONS) in which ONO and ONS represent the donor sets of two different bifunctional tridentate azomethines, have been prepared by 1:1:1 molar reactions of silicon tetraacetace with equimolar amounts of the ligands. These are obtained as coloured solids and behave as non-electrolytes in dry DMF. Suitable hexa-coordinated structures based on elemental analysis, molecular weight determinations, conductance measurements and infrared and proton magnetic resonance spectral studies have been indicated for these derivatives.

13C nuclear magnetic resonance spectral study on the distribution of substituents in relation to the preparation method of partially acetylated dextrans

Abstract 13C nuclear magnetic resonance (n.m.r.) spectra of partially modified dextrans with acetyl groups prepared by reaction with acetyl chloride or acetic anhydride in the homogeneous phase were analysed at 75.4 MHz. It was found that the distribution of substituents in the anhydroglucose units of these partially acetylated dextrans can be estimated from their ring carbon spectra. The results showed that for acetylated dextrans prepared by reaction with acetyl chloride, the reactivity of individual secondary hydroxyl groups decreases in the order C-2 > C-4 > C-3. For those modified dextrans prepared with acetic anhydride, the ease of acetylation was C -2⋍ C -3 > C -4 . The results were explained by considering the formation of intramolecular hydrogen bonds as well as by steric considerations.

Cell growth inhibitory dihydrophenanthrene and phenanthrene constituents of the african tree Combretum caffrum

Combretum caffrum, a tree in the family Combretaceae, has been found to contain three 9,10-dihydrophenanthrenes (6,7-dihydroxy-2,3,4-trimethoxy; 7-hydroxy-2,3,4,6-tetramethoxy; and 2,7-dihydroxy-3,4,6-trimethoxy) that inhibit (ED50 2.2, 2.8, and 2.6 μg/mL) growth of the murine lymphocytic leukemia cell line. One phenanthrene (7-hydroxy-2,3,4,6-tetramethoxy) was also isolated with similar (ED50 2.0 μg/mL) activity. Structures for each of these substances, including a dihydrophenanthrene (2-hydroxy-3,4,6,7-tetramethoxy-9,10-dihydrophenanthrene), were determined by detailed high resolution nuclear magnetic resonance and mass spectral studies and (or) X-ray crystal structure analysis.

Synthesis and Characterization of Mixed Azomethine Derivatives of Silicon(IV)

Abstract Synthesis and characterization of mixed azomethine derivatives of silicon(IV) with anils and thio-anils have been described. Such derivatives of the type (ONO)Si(ONS) in which ONO and ONS represent the donor sets of two different bifunctional tridentate azomethines, have been prepared by 1:1:1 molar reactions of silicon tetraacetace with equimolar amounts of the ligands. These are obtained as coloured solids and behave as non-electrolytes in dry DMF. Suitable hexa-coordinated structures based on elemental analysis, molecular weight determinations, conductance measurements and infrared and proton magnetic resonance spectral studies have been indicated for these derivatives.

Synthesis and Structural Studies of Cxovanadium(V) Complexes of Semicarbazones

Abstract 1:1 and 1:2 mole ratio reactions of trichlorooxovanadium(V) with the sodium salt of semicarbazones derived from different heterocyclic aldehydes result in the formation of five- and six-coordinated oxovanadium(v) complexes, respectively. These have been isolated and characterised by elemental analysis, molecular weight determinations and conductance and magnetic measurements. Based on electronic, infrared and proton magnetic resonance spectral studies, distorted trigonal bipyramidal and octahedral geometries have been suggested for the mono- and bis-Schiff base complexes, respectively.

Oxotitanium(IV) and titanium(IV) complexes with thiocarbohydrazones

Oxotitanium(IV) complexes were prepared by treating oxotitanium(IV) perchlorate with thiocarbohydrazone in a methanolic medium. The complexes are orange-yellow in colour and have 1:1 stoichiometry of the type TiO · L. Titanium(IV) complexes were prepared by reacting titanium(IV) chloride (anhydrous) with thiocarbohydrazone in an anhydrous chloroform medium. These are reddish brown in colour and conform to a 1:1 stoichiometry of the type TiL · Cl 2. L in both cases stands for a doubly deprotonated ligand. IR and proton magnetic resonance (PMR) spectral studies suggest that the oxotitanium(IV) complexes have a coordination number of five whereas titanium(IV) complexes have a coordination number of six.

Synthesis of Biologically Active Lead (II and IV) Complexes of Schiff Bases Derived from Sulpha Drugs

Abstract The present paper describes the synthesis and structural features of the lead complexes with Schiff bases derived from sulpha drugs. The resulting complexes have been subjected to elemental analyses, conductance measurements, molecular weight determination and electronic, infra-red and proton nuclear magnetic resonance spectral studies and their plausible structures have been discussed. A few representative complexes have also been screened for their fungicidal as well as bactericidal activity and found to be quite active in this respect.

Synthesis, spectroscopic studies and the mechanism of formation of 4,5‐dihydro‐1,2,4‐oxadiazoles

AbstractNine 4,5‐dihydro‐1,2,4‐oxadiazoles, 2a‐i, were synthesized by the reaction of benzamidoximes, 1a‐i, with aliphatic and aromatic aldehydes. None of these compounds were encountered in the literature. The ultraviolet, infrared and proton magnetic resonance spectral studies supported the cyclic structure. Structure determination of a chloral‐benzamidoxime adduct, 15, by X‐ray crystallography helped us to suggest the mechanism of formation of 4,5‐dihydro‐1,2,4‐oxadiazole from benzamidoxime and an aldehyde. Substances 2a,b,d,e,g,h, showed some activity against fungus Neurospora crassa. Compound 2e also presented growth inhibition in Mycobacterium smegmatis.