NMR Characterization (nmr + characterization)

Distribution by Scientific Domains

Selected Abstracts

NMR Characterization of Complex p- Oligophenyl Scaffolds by Means of Aliasing Techniques to Obtain Resolution-Enhanced Two-Dimensional Spectra

Damien Jeannerat
The usefulness of computer-assisted aliasing to secure maximal resolution of signal clusters in 1H- and 13C-NMR spectra (which is essential for structure determination by HMBC 2D NMR spectroscopy) in minimal acquisition time is exemplified by the complete characterization of the two complementary p -octiphenyls 1 and 2 with complex substitution patterns. The need for digital resolution near 1,Hz/pt to dissect the extensive signal clusters in the NMR spectra of these refined oligomers excluded structure determination under routine conditions. High resolution was secured by exploiting the low signal density in the 13C dimension of HMBC spectra by using computer-assisted aliasing to maximize signal density. Based on the observed shifts in DEPT and 1H-decoupled 13C-NMR spectra of 1 and 2, computer-assisted aliasing allowed to reduce the number of required time increments by a factor of 20 to 30 compared to full-width spectra with identical resolution. Without signal-to-noise constraints, this computer-assisted aliasing reduced the acquisition time for high-resolution NMR spectra needed for complete characterization of refined oligomers 1 and 2 by the same factor (e.g., from over a day to about an hour). With resolved signal clusters in fully aliased HSQC and HMBC spectra, unproblematic structure determination of 1 and 2 is demonstrated by unambiguous assignment of all C- and H-atoms. These findings demonstrate that computer-assisted aliasing of the underexploited 13C dimension makes extensive molecular complexity accessible by conventional multidimensional heteronuclear NMR experiments without extraordinary efforts. [source]

Solid-State NMR Characterization of the Multiphase Structure of Polypropylene In-reactor Alloy

Haijin Zhu
Abstract A variety of solid-state NMR techniques were used to characterize the chain dynamics, miscibility and the micro-phase structure of a polypropylene (PP) in-reactor alloy system. The alloy was physically separated into three fractions, and the molecular dynamics and relaxation behavior of the pure fractions was then compared with the components in the alloy to achieve comprehensive understanding of the phase structure of the PP in-reactor alloy. The miscibility among different components of the alloy was studied by the rotational frame spin-lattice relaxation time. Proton spin-diffusion methods were used to quantify the domain thicknesses of different regions in the alloy. The results show that the alloy is composed of three phases, namely, a homo-polyethylene (HPE) matrix, a homo-polypropylene (HPP) dispersed phase, and a linear low-density polyethylene (LLDPE) interphase. The thickness of the LLDPE interphase is estimated to be 7.7,nm at room temperature, and changes dramatically with temperature. Finally, based on all the solid-state NMR results, a model for the micro-phase-structure of the PP in-reactor alloy is proposed, and a correlation between the micro-phase structure and the excellent mechanical property is established. [source]

NMR Characterization of Carbazole-Substituted Norbornene Comonomer 9-(Bicyclo[2.2.1.]hept-5-en-2-ylmethyl)-9H -carbazole (BHMCZ) and Poly(ethylene- co -BHMCZ) Copolymer

Ilpo Mustonen
Abstract Carbazole-substituted norbornene comonomer 9-(bicyclo[2.2.1.]hept-5-en-2-ylmethyl)-9H -carbazole (BHMCZ) can be copolymerized with ethylene using the [Ph2C(Ind)(Cp)ZrCl2] catalyst and methylaluminoxane (MAO) cocatalyst system. The microstructures of BHMCZ comonomer and of ethylene,BHMCZ copolymer containing 4.6 mol-% BHMCZ units in the chain were characterized by one-dimensional 13C DEPT and two-dimensional homonuclear 1H- 1H COSY and heteronuclear 1H- 13C HXCO NMR spectroscopy. The BHMCZ comonomer appears as endo and exo stereoisomers, which were identified on the basis of chemical shifts, signal multiplicities, and coupling in the 2D NMR spectra. The NMR information on the BHMCZ isomers was used to assist in the determination of the chemical shifts and microstructure of ethylene,BHMCZ copolymer. The NMR analysis of ethylene,BHMCZ copolymer indicated that exo -BHMCZ polymerizes with ethylene slightly more readily than does endo -BHMCZ under the polymerization conditions employed. Isolated segments of exo(2)- exo(5)- exo(6) and endo(2)- exo(5)- exo(6) ethylene-BHMCZ copolymer showing carbon atom numbering. [source]

ChemInform Abstract: Synthesis, Structure and NMR Characterization of a New Monomeric Aluminophosphate [dl-Co(en)3]2 [Al(HPO4)2(H1.5PO4)2 (H2PO4)2] (H3PO4)4 Containing Four Different Types of Monophosphates.

CHEMINFORM, Issue 23 2009
Peng Chen
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

2D NMR Characterization of the La@C82 Anion.

CHEMINFORM, Issue 32 2005
Takahiro Tsuchiya
No abstract is available for this article. [source]

ChemInform Abstract: Solid-State NMR Characterization of the Mineral Searlesite and Its Detection in Complex Synthesis Mixtures.

CHEMINFORM, Issue 52 2001
Colin A. Fyfe
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Unsymmetrical ,-diimine nickel (II) complex with rigid bicyclic ring ligand: Synthesis, characterization, and ethylene polymerization in the presence of AlEt2Cl

Ting Li
Abstract Unsymmetrical ,-diimine ligand 1 was successfully synthesized via condensation of trimethylaluminum (TMA) metalated 2-methyl-6-isopropyl-aniline with rigid bicyclic aliphatic diketone camphorquinone. Syn- and anti-stereoisomers were detected by 13C NMR in the condensation product. The corresponding ,-diimine nickel (II) complex 1 was prepared from the exchange reaction of (DME)NiBr2 with the ligand 1, and displayed high activity for ethylene polymerization in the presence of diethylaluminum chloride (AlEt2Cl). The resultant polymers were confirmed by gel permeation chromatography and 13C NMR characterization to be broad molecular weight distribution polyethylene with various branches, and high degree of branching, even at low polymerization temperature ,10C. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Sulfoalkyl ether-alkyl ether cyclodextrin derivatives, their synthesis, NMR characterization, and binding of 6,-methylprednisolone

Serena Tongiani
Abstract The objective of this study is to see if random alkyl ethers of various sulfoalkyl ether cyclodextrins can be synthesized and characterized. The purpose of the alkylation was to test the hypothesis that an increase in the "height" of a cyclodextrins cavity would help in the binding/complexation of larger more structurally complex molecules. The synthesis of new cyclodextrin derivatives comprising a mixture of sulfoalkyl ether and alkyl ether substituents on the same cyclodextrin ring was performed in aqueous alkaline solutions using various sultones and alkylsulfates. The method presented provided an easy and efficient way to modify cyclodextrins avoiding the use of organic solvents and high quantities of alkylating agents and could be carried out in either a two step or "one pot" single step process. Purification was by neutralization followed by ultrafiltration. The derivatives were characterized by 1D, (1H and 13C), and a 2D NMR technique (HMQC, Heteronuclear Multiple Quantum Coherence). The combination of these techniques allowed an analysis of the degree of substitution and the site of substitution on the cyclodextrin (CD) nucleus. For both ,- and ,-CD, sulfoakylation was preferred on the 2,>,3,>,6 hydroxyls while alkylation was preferred 6,>,2,>,3. Due to the simultaneous presence of short alkyl ether chains and negatively charged sulfoalkyl ether chains, these mixed water-soluble cyclodextrin derivatives, especially those of ,-cyclodextrin, should be able to bind more complex drugs. The improved binding capacity of these new modified CDs with the model drug 6,-methylprednisolone is reported. 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2380-2392, 2005 [source]

Pharmaceutical impurity identification: A case study using a multidisciplinary approach

Karen M. Alsante
Abstract A multidisciplinary team approach to identify pharmaceutical impurities is presented in this article. It includes a representative example of the methodology. The first step is to analyze the sample by LC-MS. If the structure of the unknown impurity cannot be conclusively determined by LC-MS, LC-NMR is employed. If the sample is unsuitable for LC-NMR, the impurity needs to be isolated for conventional NMR characterization. Although the technique of choice for isolation is preparative HPLC, enrichment is often necessary to improve preparative efficiency. One such technique is solid-phase extraction. For complete verification, synthesis may be necessary to compare spectroscopic characteristics to those observed in the original sample. Although not widely practiced, an effective means of getting valuable structural information is to conduct a degradation study on the purified impurity itself. This systematic strategy was successfully applied to the identification of an impurity in the active pharmaceutical ingredient 1-(1,2,3,5,6,7-hexahydro-s-indacen-4-yl)-3-[4-(1-hydroxy-1-methyl-ethyl)-furan-2-sulphonylurea. Identification required the use of all of the previously mentioned techniques. The instability of the impurity under acidic chromatographic conditions presented an additional challenge to purification and identification. However, we turned this acidic instability to an advantage, conducting a degradation study of the impurity, which provided extensive and useful information about its structure. The following discussion describes how the information gained from each analytical technique was brought together in a complementary fashion to elucidate a final structure. 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2296,2309, 2004 [source]

Grafting of commercially available amines bearing aromatic rings onto poly(vinylidene- co -hexafluoropropene) copolymers

A. Taguet
Abstract The grafting of poly(VDF- co -HFP) copolymers with different amines containing aromatic rings, such as aniline, benzylamine, and phenylpropylamine, is presented. 19F NMR characterization enabled us to show that the sites of grafting of aromatic-containing amines were first difluoromethylene of vinylidene fluoride (VDF) in the hexafluoropropene (HFP)/VDF/HFP triad and then that of VDF adjacent to HFP. The kinetics of grafting of benzylamine, monitored by 1H NMR spectroscopy, confirmed those sites of grafting and showed that all VDF units located between two HFPs were grafted in the first 150 min, whereas those adjacent to one HFP unit were grafted in the remaining 3000 min. Parameters such as the temperature or the molar percentage of HFP in the copolymer had an influence on the maximum rate of grafted benzylamine. The higher the temperature, the higher the molar percentage of grafted benzylamine. Furthermore, the higher the molar percentage of HFP in the copolymer, the higher the molar percentage of VDF in the HFP/VDF/HFP triad, and the higher the molar percentage of grafted benzylamine. The spacer length between the aromatic ring and the amino group had an influence on the kinetics of grafting: aniline (pKa = 4.5) could not add onto the polymeric backbone, whereas phenylpropylamine was grafted in the first 150 min, and benzylamine required 3000 min to reach the maximum amount of grafting. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1855,1868, 2006 [source]

13C NMR determination of the microstructure of polypropylene obtained with the DADNi(NCS)2/methylaluminoxane catalyst system

Griselda Barrera Galland
Abstract A complete 13C NMR characterization of a polymer synthesized with a new Ni-diimine complex [DADNi(NCS)2, where DAD = 2,6 - iPrC6H3NC(Me)C(Me) N2,6 - iPrC6H3] activated by methylaluminoxane by homopolymerization of propylene is presented. The amorphous material was made up mainly of blocks of syndiotactic polypropylene and ethylene,propylene copolymer. Some degree of propylene inversion (<1.2 mol %) and of long isobutyl and 2-methyl hexyl branching (<1 mol %) were assigned and quantified. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2171,2178, 2004 [source]

13Carbon nuclear magnetic resonance of ethylene,propylene,1-decene terpolymers

Fernanda F. Nunes Escher
Abstract Many studies have been reported on the 13C NMR characterization of ethylene,,-olefin copolymers, but only a few have been reported on terpolymers. The incorporation of an ,-olefin into the polyethylene chain changes the structure and, consequently, the properties of the polymer obtained. Looking for new products, we obtained a series of ethylene,propylene,1-decene terpolymers with the metallocenic system rac -ethylene bisindenyl zirconium dichloride/methylaluminoxane. We performed a complete 13C NMR characterization of these terpolymers qualitatively and quantitatively. Here we present a detailed study of the 13C NMR chemical shifts, triad sequence distributions, monomer average sequence lengths, and reactivity ratios for these terpolymers. 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2531,2541, 2003 [source]

High-pressure NMR characterization of triacetyl-,-cyclodextrin in supercritical carbon dioxide

G. I. Ivanova
Abstract Cyclodextrins are used in many drug formulations since their cavities provide microenvironments where drug molecules can enter and form inclusion complexes for controlled drug delivery. Supercritical carbon dioxide (scCO2) is an alternative to organic solvents and a very attractive medium for the preparation of these inclusion complexes. The potential ability of triacetyl-,-cyclodextrin (TA-,-CD) to form inclusion complexes in addition to its high miscibility in liquid and scCO2 could offer a chance for an economical and environmental friendly chemical processing. In this work, high-pressure NMR studies were performed in order to obtain information on the molecular structure and dynamics of TA-,-CD in scCO2 at 313.15 K and 20 MPa and its ability to form inclusion complexes under these conditions was studied. The influence of scCO2 on a number of NMR spectral parameters, such as chemical shifts, spin-spin coupling constants, nuclear Overhauser effect (NOE) and spin-lattice relaxation (T1) has been studied. We unequivocally show for the first time structural changes of TA-,-CD in scCO2, like acetyl chain orientation and overall shape distortions that can affect its inclusion capability in this medium. The possibility of cavity self-closure is discussed and the results of two inclusion studies that support cavity self-closure, with the angiotensin-converting enzyme inhibitor, captopril, and the nonsteroid anti-inflammatory drug, flufenamic acid, are presented. Copyright 2008 John Wiley & Sons, Ltd. [source]

Characterization of nonderivatized plant cell walls using high-resolution solution-state NMR spectroscopy,

Daniel J. Yelle
Abstract A recently described plant cell wall dissolution system has been modified to use perdeuterated solvents to allow direct in-NMR-tube dissolution and high-resolution solution-state NMR of the whole cell wall without derivatization. Finely ground cell wall material dissolves in a solvent system containing dimethylsulfoxide- d6 and 1-methylimidazole- d6 in a ratio of 4:1 (v/v), keeping wood component structures mainly intact in their near-native state. Two-dimensional NMR experiments, using gradient-HSQC (heteronuclear single quantum coherence) 1-bond 13C1H correlation spectroscopy, on nonderivatized cell wall material from a representative gymnosperm pinus taeda (loblolly pine), an angiosperm Populus tremuloides (quaking aspen), and a herbaceous plant Hibiscus cannabinus (kenaf) demonstrate the efficacy of the system. We describe a method to synthesize 1-methylimidazole- d6 with a high degree of perdeuteration, thus allowing cell wall dissolution and NMR characterization of nonderivatized plant cell wall structures. Copyright 2008 John Wiley & Sons, Ltd. [source]

Solid-state NMR characterization of 69Ga and 71Ga in crystalline solids

Jason T. Ash
Abstract Gallium model systems containing four- and six-coordinate gallium sites have been investigated using solid-state NMR. Measurement of the isotropic chemical shift and electric field gradient (EFG) have been performed at 9.4 T on ,-Ga2O3, ,-Ga2O3, LiGaO2, NaGaO2, KGaO2, Ga2(SO4)3, and LaGaO3 using a variety of techniques on both NMR active nuclei (69Ga and 71Ga) including static, high speed magic-angle spinning (MAS), satellite transition (ST) spectroscopy, and rotor-assisted population transfer (RAPT). The chemical shift is found to correlate well with the coordination number, with four-coordinate gallium having values of approximately 50 ppm and six-coordinate gallium having values near 225 ppm (referenced to 1 M gallium nitrate solution). The magnitude of the EFG is found to be correlated to the distortion of the gallium polyhedra, with the strained systems having EFGs of 3 1021 Vm,2 or more, while the less strained systems have values of 1.5 1021 Vm,2 or less. A plot of chemical shift versus EFG suggests that solid-state NMR of gallium oxyanions can be more discriminating than liquid state NMR chemical shifts alone. Copyright 2006 John Wiley & Sons, Ltd. [source]

NMR characterization of new 10-membered-ring macrolactones and dihydrobenzophenazine-5-one, oxidized derivatives of benzo[a]phenazines

Marlia O. F. Goulart
Abstract Peroxidation of the phenazine of ,-lapachone using m -ClC6H4CO3HCH2Cl2 furnished a macrolactone with a rigid 10-membered ring, and the corresponding N -oxide, along with a dihydrobenzophenazine-5-one. All of the new compounds were fully characterized by spectroscopic methods, with the unambiguous assignment of the hydrogens and carbon NMR signals for the N -oxide, with the aid of 2-D NMR, mainly COSY, HMQC, HSQC and HMBC. For the other two compounds some signals could not be assigned owing to their own intrinsic features. Copyright 2004 John Wiley & Sons, Ltd. [source]

Characterization of N-methyl-L-methionine sulfoxide and isethionic acid from the red alga Grateloupia doryphora

Christelle Simon-Colin
SUMMARY Isethionic acid (2-hydroxyethane sulfonic acid) and N-methyl-L-methionine sulfoxide (4-methane sulfinyl-2-methylamino butyric acid) were isolated from the red alga Grateloupia doryphora (Cryptonemiales) collected from Brittany (France); they were identified as major organic solutes together with floridoside (,-D-galacto-pyranosyl-(1,2)-glycerol). The presence of isethionic acid has recently been reported in certain red algae, however, the occurrence of N-methyl-L-methionine sulfoxide is still very rare. This report deals with the first isolation of isethionic acid and N-methyl-L-methionine sulfoxide from G. doryphora and their subsequent NMR characterization. [source]

Synthesis and NMR characterization of 6-Phenyl-6-deoxy-2,3-di- O -methylcellulose,

Dr Navzer (Nozar) D. Sachinvala
Abstract Cellulose (1) was converted for the first time to 6-phenyl-6-deoxy-2,3-di- O -methylcellulose (6) in 33% overall yield. Intermediates in the five-step conversion of 1 to6 were: 6- O -tritylcellulose (2), 6- O -trityl-2,3-di- O -methylcellulose (3), 2,3-di- O -methylcellulose (4); and 6-bromo-6-deoxy-2,3-di- O -methylcellulose (5). Elemental and quantitative carbon-13 analyses were concurrently used to verify and confirm the degrees of substitution in each new polymer. Gel permeation chromotography (GPC) data were generated to monitor the changes in molecular weight (DPw) as the synthesis progressed, and the compound average decrease in cellulose DPw was , 27%. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize the decomposition of all polymers. The degradation temperatures (,C) and percent char at 500,C of cellulose derivatives 2 to 6 were 308.6 and 6.3%, 227.6,C and 9.7%, 273.9,C and 30.2%, 200.4,C and 25.6%, and 207.2,C and 27.0%, respectively. The glass transition temperature (Tg) of6- O -tritylcellulose by dynamic mechanical analysis (DMA) occurred at 126.7,C and the modulus (E,, Pa) dropped 8.9 fold in the transition from ,150,C to,+,180,C (6.6,,109 to 7.4,,108 Pa). Modulus at 20,C was 3.26,,109 Pa. Complete proton and carbon-13 chemical shift assignments of the repeating unit of the title polymer were made by a combination of the HMQC and COSY NMR methods. Ultimate non-destructive proof of carbon,carbon bond formation at C6 of the anhydroglucose moiety was established by generating correlations between resonances of CH26 (anhydroglucose) and C1,, H2,, and H6, of the attached aryl ring using the heteronuclear multiple-bond correlation (HMBC) method. In this study, we achieved three major objectives: (a) new methodologies for the chemical modification of cellulose were developed; (b) new cellulose derivatives were designed, prepared and characterized; (c) unequivocal structural proof for carbon,carbon bond formation with cellulose was derived non-destructively by use of one- and two-dimensional NMR methods. Copyright 2002 John Wiley & Sons, Ltd. [source]

NMR characterization of a pH-dependent equilibrium between two folded solution conformations of the pheromone-binding protein from Bombyx mori

Fred Damberger
Abstract NMR spectroscopic changes as a function of pH in solutions of the pheromone-binding protein of Bombyx mori (BmPBP) show that BmPBP undergoes a conformational transition between pH 4.9 and 6.0. At pH below 4.9 there is a single "acid form" (A), and a homogeneous "basic form" (B) exists at pH above 6.0. Between pH 5 and 6, BmPBP exists as a mixture of A and B in slow exchange on the NMR chemical shift time scale, with the transition midpoint at pH 5.4. The form B has a welldispersed NMR spectrum, indicating that it represents a more structured, "closed" conformation than form A, which has a significantly narrower chemical shift dispersion. Conformational transitions of the kind observed here may explain heterogeneity reported for a variety of odorant-binding proteins, and it will be of interest to further investigate possible correlations with pH-dependent regulation of ligand binding and release in the biological function of this class of proteins. [source]

Inhibition of ,-synuclein fibrillization by dopamine analogs via reaction with the amino groups of ,-synuclein

FEBS JOURNAL, Issue 14 2005
Implication for dopaminergic neurodegeneration
Fibrillization of ,-synuclein (,-Syn) is closely associated with the formation of Lewy bodies in neurons and dopamine (DA) is a potent inhibitor for the process, which is implicated in the causative pathogenesis of Parkinson's disease (PD). To elucidate any molecular mechanism that may have biological relevance, we tested the inhibitory abilities of DA and several analogs including chemically synthetic and natural polyphenols in vitro. The MS and NMR characterizations strongly demonstrate that DA and its analogs inhibit ,-Syn fibrillization by a mechanism where the oxidation products (quinones) of DA analogs react with the amino groups of ,-Syn chain, generating ,-Syn,quinone adducts. It is likely that the amino groups of ,-Syn undergo nucleophilic attack on the quinone moiety of DA analogs to form imino bonds. The covalently cross-linked ,-Syn adducts by DA are primarily large molecular mass oligomers, while those by catechol and p -benzoquinone (or hydroquinone) are largely monomers or dimers. The DA quinoprotein retains the same cytotoxicity as the intact ,-Syn, suggesting that the oligomeric intermediates are the major elements that are toxic to the neuronal cells. This finding implies that the reaction of ,-Syn with DA is relevant to the selective dopaminergic loss in PD. [source]