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NMR Study (nmr + study)

Distribution by Scientific Domains

Chemistry	79%
Polymers and Materials Science	7%
Life Sciences	5%
Physics and Astronomy	3%
2 Other Domains	6%

Distribution within Chemistry

Analytical Chemistry	51%
Organic Chemistry	16%
10 Other Subdomains	33%

Selected Abstracts

NMR Study of L-Shaped (Quinoxaline)platinum(II) Complexes , Crystal Structure of [Pt(DMeDPQ)(bipy)](PF6)2

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2004
Enrico Rotondo
Abstract A 1H and 13C NMR study of nine PtII complexes of DMeDPQ [6,7-dimethyl-2,3-bis(2-pyridyl)quinoxaline] and BDPQ [2,3-bis(2-pyridyl)benzo[g]quinoxaline], and the crystal structure of one of them, are reported. The results are consistent with Cs symmetry of "L-shaped square-planar complexes". The rigid seven-membered chelated quinoxaline ligand holds the fused aromatic rings nearly perpendicular to the PtII coordination plane, generating the peculiar L-shaped structure. Ancillary ligands in the residual coordination sites are: a) bidentate flexible-planar 2,2,-bipyridine (bipy; complexes 1 and 2); b) bidentate rigid-planar dipyrido[3,2- a:2,3,- c]phenazine (dppz) or benzo[b]dipyrido[3,2- h:2,,3,- j]phenazine (bdppz; complexes 3,6); or c) 3-substituted monodentate pyridines (3-Rpy; complexes 7,9). The L-shaped geometry has been exploited to gain insight into the steric and dynamic features that regulate the noncovalent interactions of these square-planar complexes with DNA. We have shown previously, for [Pt(bipy)(n -Rpy)2]2+, that bipy twisting can be frozen out on the NMR timescale below 260 K. Preservation of the Cs symmetry at low temperature indicates a lack of bipy fluxionality within these L-shaped structures. The static butterfly-like symmetric orientation of the quinoxaline pyridyl rings accounts for the hampered twisting of Pt(bipy), which is otherwise assisted by the synchronous "windscreen wiper" conrotatory rocking of the ancillary pyridine rings. The L-geometry can also be used to monitor the ancillary n -Rpy rotation by NMR spectroscopy. The quasi-vertical quinoxaline pyridyl rings alignment leave room in the coordination plane for the crossing of the opposite pyridine rings, thereby reducing their rotational barriers about the Pt,N bond. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Kinetics of Demixing and Remixing Transitions in Aqueous Solutions of Poly(N -isopropylacrylamide): A Temperature-Jump 1H NMR Study

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 21 2006
Pavel V. Yushmanov
Abstract Summary: The time course of the coil-to-globule collapse and intermolecular aggregation of poly(N -isopropylacrylamide) in aqueous solution upon exceeding the lower critical solution temperature (LCST) are investigated by temperature-jump 1H NMR spectroscopy. After the temperature jump, we record the time dependences of (i) the mobile fraction of the polymer chain as revealed by the intensity of the liquid-like NMR signal, (ii) the local mobility of those chains as revealed by the transverse relaxation time T2, and (iii) their self-diffusion coefficient D. The same data are also reported at their temperature-dependent long-time limits. The results suggest a sudden, faster than one second, collapse and intermolecular aggregation into globules and a slower reorganization/redistribution of the individual chains among and within the globular and mobile states. We found that all molecular changes are reversible if the temperature remains less than ca. 6,8 K above the LCST for less than a few minutes; under those conditions, experiments upon sudden temperature quench below the LCST show that the aggregates disintegrate and swell into coils in less than a few seconds. 1H NMR signal intensity of the methyl groups of 1 wt.-% PNIPAM dissolved in 0.1 M NaCl solution in D2O in a temperature-jump experiment from 300 to 312 K. The data were recorded by the 90°,,,(180°,2, -)n -detection of the CPMG pulse sequence. [source]

A Morphological and 13C NMR Study of the Extramandibular Fat Bodies of the Striped Dolphin (Stenella coeruleoalba)

THE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 7 2007
C. Maxia
Abstract The molecular and histological structure of the fat bodies covering externally the posterolateral region of the jaw of the striped dolphin (Stenella coeruleoalba) was investigated by means of morphological and nuclear magnetic resonance techniques. The analyses of samples belonging to adult and juvenile individuals were performed with the aim of seeking the presence of age-related differences. In our study, the level of isovalerate (iso5:0) in the extramandibular fat of the juvenile individuals is comparable with those of the adult counterparts; conversely, longer isobranched fatty acids were detected in lower quantities in the juveniles together with a higher degree of unsaturation. The morphologic analyses revealed that, in both adults and juveniles, this fatty tissue is similar to univacuolar adipose tissue. However, in the juveniles, a muscular component was present, whereas only in adult subjects, enlarged and irregularly shaped cavities may be seen within the adipose tissue. These cavities, structurally organized as veins, may regulate blood flow in response to changing water temperature and stabilize thermal gradient within the jaw lipids. These data suggest that the molecular components and the histological organization can indicate a maturation of the organ with age that probably may reflect different sound reception properties. Anat Rec, 2007. © 2007 Wiley-Liss, Inc. [source]

A MAS NMR Study of the Bacterial ABC Transporter ArtMP

CHEMBIOCHEM, Issue 4 2010
Vivien Lange Dr.
Abstract ATP-binding cassette (ABC) transport systems facilitate the translocation of substances, like amino acids, across cell membranes energised by ATP hydrolysis. This work describes first structural studies on the ABC transporter ArtMP from Geobacillus stearothermophilus in native lipid environment by magic-angle spinning NMR spectroscopy. The 2D crystals of ArtMP and 3D crystals of isolated ArtP were prepared in different nucleotide-bound or -unbound states. From selectively 13C,15N-labelled ArtP, several sequence-specific assignments were obtained, most of which could be transferred to spectra of ArtMP. Residues Tyr133 and Pro134 protrude directly into the ATP-binding pocket at the interface of the ArtP subunits, and hence, are sensitive monitors for structural changes during nucleotide binding and hydrolysis. Distinct sets of NMR shifts were obtained for ArtP with different phosphorylation states of the ligand. Indications were found for an asymmetric or inhomogeneous state of the ArtP dimer bound with triphosphorylated nucleotides. With this investigation, a model system was established for screening all functional states occurring in one ABC transporter in native lipid environment. [source]

ChemInform Abstract: Variable-Temperature 17O NMR Study of Oxygen Motion in the Anionic Conductor Bi26Mo10O69.

CHEMINFORM, Issue 35 2008
Lesley Holmes
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]

Multinuclear High-Resolution NMR Study of Compounds from the Ternary System NaF,CaF2,AlF3: From Determination to Modeling of NMR Parameters.

CHEMINFORM, Issue 9 2007
C. Martineau
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, please click on HTML or PDF. [source]

Synthesis and Dynamic NMR Study of Fluorinated Dialkyl 2-[(tert-Butylimino)-methylene]-3- [(2-alkoxy-2-oxoacetyl)-2-fluoroanilino]-succinates.

CHEMINFORM, Issue 2 2006
Issa Yavari
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Topotactic Transformations of Sodalite Cages: Synthesis and NMR Study of Mixed Salt-Free and Salt-Bearing Sodalites.

CHEMINFORM, Issue 40 2002
Henning Trill
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Confinement and Step-Wise Reopening of Channels in an Artificial Cell/Inorganic Capsule: A 7Li NMR Study

CHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2008
Erhard
Lifting the quarantine for cations: The 20 pores of a spherical molybdenum oxide based capsule, dissolved in dimethyl sulfoxide and containing encapsulated Li+ ions, can be plugged completely with formamidinium cations/guests; however, it can be re-opened stepwise by adding water. Exchange/communication between internal and external Li+ and the blockage thereof have been studied by 7Li NMR spectroscopy (see graphic), also with reference to the use of paramagnetic additives. [source]

Soft Metal Ion-Selective Electrodes Based on ,-Coordinate Calixarene Derivatives

ELECTROANALYSIS, Issue 15-16 2003
Setsuko Yajima
Abstract Calix[4]arene derivatives incorporating ,-unsaturated alkenyl groups or saturated alkyl groups and their monomeric analogues were used as ,-coordinate neutral carriers for ion-selective electrodes (ISEs) of soft metals [silver and thallium(I)] ions. The EMF responses were excellent for most of the ISEs, among which there was no significant difference in the response. The ion selectivities of the ISEs depend on the structure of neutral carriers employed. 1H NMR study explains the difference in the ion selectivity. In the metal-ion complexation by the ,-coordinate calixarene derivatives, thallium ion is likely to interact with the calixarene skeleton, while silver ion tends to interact with both of the calixarene skeleton and the ,-unsaturated alkenyl groups. [source]

Separation of propranolol enantiomers by CE using sulfated ,-CD derivatives in aqueous and non-aqueous electrolytes: Comparative CE and NMR study,

ELECTROPHORESIS, Issue 9 2010
Anne-Catherine Servais
Abstract Separations using CE employing non-aqueous BGE are already as well established as separations in aqueous buffers. The separation mechanisms in achiral CE with non-aqueous BGEs are most likely similar to those in aqueous buffers. However, for the separation of enantiomers involving their interaction with chiral buffer additives, the interaction mechanisms might be very different in aqueous and non-aqueous BGEs. While the hypothesis regarding distinct mechanisms of enantiomer separations in aqueous and non-aqueous BGEs has been mentioned in several papers, no direct proof of this hypothesis has been reported to date. In the present study, the enantiomers of propranolol were resolved using CE in aqueous and non-aqueous methanolic BGEs with two single isomer sulfated derivatives of ,-CD, namely heptakis (2,3-diacetyl-6-sulfo)-,-CD and heptakis (2,3-dimethyl-6-sulfo)-,-CD. The enantiomer migration order of propranolol was inverted when an aqueous BGE was replaced with non-aqueous BGE in the case of heptakis (2,3-dimethyl-6-sulfo)-,-CD but remained the same in the case of heptakis (2,3-diacetyl-6-sulfo)-,-CD. The possible molecular mechanisms leading to this reversal of enantiomer migration order were studied by using nuclear overhauser effect spectroscopy in both aqueous and non-aqueous BGEs. [source]

NMR Study of L-Shaped (Quinoxaline)platinum(II) Complexes , Crystal Structure of [Pt(DMeDPQ)(bipy)](PF6)2

Synthesis of Pyrazoles by Treatment of 3-Benzylchromones, 3-Benzylflavones and Their 4-Thio Analogues with Hydrazine,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2006
Albert Lévai
Abstract The synthesis of pyrazoles 13,24 has been accomplished by treatment of 3-benzylchromones 1,5, 3-benzylflavones 6,12 and their 4-thio analogues 25,29 with hydrazine hydrate in hot pyridine. A plausible reaction mechanism for the formation of pyrazoles 13,24 is discussed. A 1H NMR study in [D6]DMSO allowed the presence of both pyrazole annular tautomers to be observed, due to the presence of intramolecular hydrogen bonds in each tautomer (OH--N and NH--O). GIAO/B3LYP/6-311++G** calculations were carried out on some model pyrazoles to provide a theoretical basis for the NMR experimental observations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Rapid decomposition of phytate applied to a calcareous soil demonstrated by a solution 31P NMR study

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2010
A. L. Doolette
myo -Inositol hexakisphosphate (phytate) is widely regarded as an abundant form of soil organic phosphorus (P) in many soils. Its abundance is believed to be because of its resistance to microbial degradation. We examined the fate of phytate added to a calcareous soil as a solution at a concentration of 58 mg P kg,1, with and without the addition of wheat straw. The soil was incubated for 13 weeks, with phytate concentrations determined at 0, 1, 4, 7 and 13 weeks using NaOH-EDTA soil extraction followed by 31P nuclear magnetic resonance (NMR) spectroscopy. The phytate concentration declined rapidly, with 18% (phytate + wheat straw) and 12% (phytate) of the initial phytate remaining after 13 weeks. This coincided with an increase in the proportion of orthophosphate relative to total NaOH-EDTA extractable P (from 65 to 81%) and a small increase in , - and , -glycerophosphate concentration, providing evidence for the microbial degradation of phytate. The decrease in phytate concentration was consistent with a first-order decay with a half-life for phytate of 4,5 weeks. This study demonstrates that in the calcareous soil examined, phytate was not highly stable, but a potentially biologically available form of P. In order to quantify the concentration of P species, we developed an improved method of spectral deconvolution. This method accounted for a broad signal (3.5,6.5 ppm) in the monoester region of the spectra that represented up to 23% of the total extractable P. We found that when this broad signal was not included, phytate concentrations were over-estimated by up to 54%. [source]

NMR Studies of Proton Transport in Anhydrous Polymer Electrolytes for High Temperature Fuel Cells,

FUEL CELLS, Issue 3-4 2008
H. A. Every
Abstract This paper presents an NMR study of the dynamic processes related to proton transport in a new polymer consisting of two blocks , poly(2,6-diphenylphenol) (P3O) and an imidazole functionalised poly(2,6-dimethylphenol) (imi-PPE) , and subsequently doped with polyphosphoric acid (PPA). From 1H and 31P NMR relaxation and diffusion measurements of the individual homopolymers and block copolymer, it was observed that addition of PPA significantly enhanced the mobility of imi-PPE and the imi-block copolymer, but not of P3O. The similarity in 1H T2 values between imi-PPE and the imi-block copolymer suggests that the relaxation behaviour in the block copolymer is dominated by the imi-PPE phase. 1H diffusion in P3O and the imi-block copolymer were comparable to pure PPA, suggesting that the proton diffusion is similar in each case. For imi-PPE, the diffusion coefficients were several orders of magnitude lower, reflecting a restricted diffusion process that is not indicative of the proton mobility. For all three polymers, the 31P T2 relaxation behaviour and inability to measure 31P diffusion coefficients imply hindered translational motion of the phosphonate groups. From these results, it can be concluded that hydrogen bonds between the phosphoric acid and the polymer form a network that facilitates proton transport via a hopping mechanism. [source]

Novel tetracyclic imidazole derivatives: Synthesis, dynamic NMR study, and anti-inflammatory evaluation

JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 3 2010
Renata Rup
A series of tetracyclic imidazole derivatives 9a,9v and 10a,10h are prepared by multistep route starting from the known tricyclic diketones 2a,2d. Intermediary dibenzooxepin[4,5- d]imidazoles (3a, 3c) and dibenzothiepin[4,5- d]imidazoles (3b, 3d) are N -protected to 4e, 4f and to the isomeric compounds 5a, 5b and 6a, 6b. The isomeric compounds 5 and 6 are separated. Compounds 4, 5, and 6 are formylated at C(2) to afford 7a,7j. In the last steps, aldehyde group is reduced, then alkylated to the two sets of isomeric ,-dimethylaminoalkyl derivatives 9a,9v. N -deprotection of 9i,9v led to the compounds 10a,10h. Assignment of the syn/anti structure to 5a and 6a was supported by 1D selective ROESY NMR spectra, whereas conformational mobility for the selected representatives 8a and 8b is studied by dynamic NMR. Activation energies (energy barriers for interconversion) are determined to be ,11.5 and 16.2 kcal/mol, respectively. A series of derivatives 9 and 10 were tested in vitro for their anti-inflammatory activity. J. Heterocyclic Chem., (2010). [source]

Structural motifs in the maturation process of peptide hormones.

JOURNAL OF PEPTIDE SCIENCE, Issue 2 2002
The somatostatin precursor.
Abstract Synthetic peptides reproducing both the native domain around the dibasic cleavage site of pro-somatostatin, and mutated sequences thereof, previously assayed in site-directed mutagenesis experiments, have been studied by CD in different solvent systems, such as water, TFE/H2O, MeCN/H2O and aqueous SDS, in order to ascertain the ability of each solvent to stabilize secondary structural motifs. A combination of deconvolution methods and empirical calculations, that allow subtraction of the contributions due to unordered structures from the spectra, suggests that mainly two distinct families of ordered conformers containing ,-helix and/or structurally different ,-turns are present in solution, the relative stability of the different conformers depending on the nature of the solvent. The presence of ,-turns is in line with a previous NMR study in DMSO and DMSO/H2O. Comparison of the CD spectra in aqueous SDS of peptides undergoing processing with a sequence not processed in vivo shows that only the latter possesses a stable and detectable ,-helix population. This observation suggests that the structuration involving ,-turns but no ,-helix, which was observed by CD both in SDS and organic solvent/H2O mixtures at high water contents, might be of biological significance. The similarity of this structuration to molecular models obtained from NMR data in DMSO and DMSO/H2O is discussed. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd. [source]

A solid-state NMR study of phase structure, molecular interactions, and mobility in blends of citric acid and paracetamol

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2009
S. Schantz
Abstract Citric acid anhydrate (CAA) and paracetamol (PARA), prepared as crystalline physical mixtures and as amorphous blends, were studied using 13C solid-state cross polarization magic angle spinning (CPMAS) NMR. Amorphous blends showed significant line broadening from the conformational distribution as compared to the crystalline samples. Also, chemical shift variations were observed between crystalline and amorphous blends, which were attributed to differences in intermolecular interactions. Averaging of proton rotating-frame spin-lattice relaxation times (T1,) probed via different 13C sites in the amorphous blends confirmed molecular level mixing. For some, initially amorphous, sample compositions the onset of crystallization was evident directly from spectra and from the significantly longer T1, relaxations. Thus, crystallization caused phase separation with properties of the two phases resembling those of pure CAA and PARA, respectively. 13C spectra of amorphous 50/50 (w/w, %) CAA/PARA recorded from above the glass transition temperature broadened as the temperature increased to a maximum at T,,,Tg,+,33 K. This was the result of a dynamic interference between the line narrowing techniques being applied and the time scale of molecular reorientation in the miscible melt. The derived average correlation time was found to correspond well with previous results from melt rheology. We conclude that the underlying reasons for physical instability (i.e., crystallization from the miscible melt, including molecular interactions and dynamics) of this class of amorphous binary mixtures can be effectively evaluated using NMR spectroscopy. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:1862,1870, 2009 [source]

1H and 13C NMR study of a series of C-9-substituted 19-norsteroids

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2002
Laurence Dallery
Abstract The 1H and 13C NMR spectra of a series of 9-substituted 19-norsteroids were completely assigned using a series of 2D NMR experiments, which included 1H,1H COSY, NOESY and 1H,13C heteronuclear HETCOR and HMQC. For second-order spin systems, chemical shifts and coupling constants were obtained by simulation of the experimental spectrum. Criteria were deduced to characterize the stereochemistry of these different compounds (multiplet pattern of H-8, and variation of chemical shifts). The results allow the easy determination of the configuration at C-9. Conformational changes resulting from the substitution were studied by NMR and molecular modeling calculations (AM1). Copyright © 2001 John Wiley & Sons, Ltd. [source]

pH-independent hydrolysis of 4-nitrophenyl 2,2-dichloropropionate in aqueous micellar solutions: relative contributions of hydrophobic and electrostatic interactions

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2001
Omar A. EI Seoud
Abstract The pH-independent hydrolysis of 4-nitrophenyl 2,2-dichloropropionate (NPDCP) in the presence of aqueous micelles of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, alkyltrimethylammonium chlorides, alkyldimethylbenzylammonium chlorides (alkyl,=,cetyl and dodecyl) and polyoxyethylene(9) nonylphenyl ether was studied spectrophotometrically. The observed rate constants, kobs, decrease in the following order: bulk water >cationic micelles >anionic micelles >non-ionic micelles. This order is different from that observed for pH-independent hydrolysis of 4-nitrophenyl chloroformate (NPCF), whose reaction is faster in cationic micelles than in bulk water. A proton NMR study on solubilization of a model ester, 4-nitrophenyl 2-chloropropionate, showed that the methylene groups in the middle of the surfactant hydrophobic chain are most affected by the solubilizate. Lower polarity and high ionic strength of interfacial water decrease the rates of hydrolysis of both NPCF and NPDCP, but the fraction of the former ester that diffuses to the interface is probably higher than that of the latter. Therefore, whereas the (negatively charged) transition state of NPCF is stabilized by cationic interfaces and destabilized by anionic interfaces, that of NPDCP is negligibly affected by ionic interfaces, which explains the observed rate retardation by all ionic micelles. Calculated activation parameters corroborate our explanation. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Solid-state 13C and 129Xe NMR study of poly(vinyl alcohol) and poly(vinyl alcohol)/lactosilated chitosan gels

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2003
Simona Lai
Abstract Dry and hydrated poly(vinyl alcohol) (PVA) gels with 55% (a-PVA) and 61% (s-PVA) syndiotacticity and related PVA/lactyl chitosan (LC) blends have been investigated with 129Xe and cross-polarization/magic-angle-spinning 13C NMR techniques. Although the dry gels exhibit two broad 129Xe resonances in the slow-to-intermediate exchange limit, both hydrated gels show three resonances. The corresponding dry blends exhibit two signals, the chemical shifts and line widths of which change with respect to those of pure PVA, whereas one (a-PVA/LC) or two (s-PVA/LC) signals appear in the spectra of the hydrated blends. A comparative analysis of the data demonstrates that LC rearranges the domains of the polymeric matrix in both the dry and hydrated blends according to the syndiotacticity of the PVA chains. Information on the molecular motions of the amorphous and swollen polymeric domains in the kilohertz range has been obtained from an analysis of the spin-lattice relaxation times. These data indicate that the dynamics and arrangement of the PVA chains in the gels are strongly affected by their tacticity and the addition of the copolymer LC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3123,3131, 2003 [source]

1H-HRMAS NMR study of smoked Atlantic salmon (Salmo salar)

MAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2010
David Castejón
Abstract High-resolution magic angle spinning (HRMAS) NMR spectroscopic data of smoked Atlantic salmon (Salmo salar) were fully assigned by combination of one- and two-dimensional-HRMAS experiments. Complete representative spectra, obtained after few minutes of analysis time, revealed a large number of minor and major compounds in the sample. The methodology is limited by the low sensitivity of NMR, and therefore HRMAS only enables the determination of the most relevant components. These were fatty acids (FAs), carbohydrates, nucleoside derivatives, osmolytes, amino acids, dipeptides and organic acids. For the first time, spectra were resolved sufficiently to allow semiquantitative determination in intact muscle of the highly polyunsaturated FA 22:6 ,-3. Additionally, the feasibility of 1H-HRMAS NMR metabolite profiling was tested to identify some bioactive compounds during storage. This profiling was carried out by the non-destructive and direct analysis (i.e. without requiring sample preparation and multiple step procedures) of intact salmon muscle. The proposed procedure can be applied to a large number of samples with high throughput due to the short time of analysis and quick evaluation of the data. Copyright © 2010 John Wiley & Sons, Ltd. [source]

31P Solid state NMR study of structure and chemical stability of dichlorotriphenylphosphorane

MAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2009
Nina C. Gonnella
Abstract Solid state 31P NMR spectroscopy was used to examine, monitor and quantify the compound integrity of the chemical reagent dichlorotriphenylphosphorane. Comparison was also made with solution 31P NMR spectra which showed that this highly reactive species could be observed in dry benzene prior to conversion to the hydrolyzed product. This is the first reported solid state NMR study of the stability and reactivity of dichlorotriphenylphosphorane and the first account of its observation and comparison in the solution state. In the solid state, the ionic and covalent forms for dichlorotriphenylphosphorane were observed along with hydrolyzed products, however, the degree of hydrolysis was dependent upon the rotor packing conditions. Calculation of the relative percent composition of dichlorotriphenylphosphorane with hydrolyzed product was made for samples prepared in air versus under nitrogen atmosphere. This information was critical in adjusting the amount of reagent used in chemical development syntheses and scale up laboratories. All hydrolyzed products were identified, based upon chemical comparisons with spectra of pure materials. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Predicting the NMR spectra of nucleotides by DFT calculations: cyclic uridine monophosphate

MAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2008
Alessandro Bagno
Abstract We present an experimental and quantum chemical NMR study of the mononucleotide cyclic uridine monophosphate in water. Spectral parameters (1H and 13C chemical shifts and 1H1H, 13C1H, 31P13C and 31P1H spin-spin coupling constants) have been carefully obtained experimentally and calculated using DFT methods including the solvent effect and the conformational flexibility of the solute. This study confirms that the 1H and 13C spectra of polar, flexible molecules in aqueous solution can be predicted with a high level of accuracy, comparable to that obtained for less complex systems. Copyright © 2008 John Wiley & Sons, Ltd. [source]

A solid-state 23Na NMR study of monovalent cation binding to double-stranded DNA at low relative humidity

MAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2008
Alan Wong
Abstract We report a solid-state 23Na NMR study of monovalent cation (Li+, Na+, K+, Rb+, Cs+ and NH4+) binding to double-stranded calf thymus DNA (CT DNA) at low relative humidity, ca 0,10%. Results from 23Na31P rotational echo double resonance (REDOR) NMR experiments firmly establish that, at low relative humidity, monovalent cations are directly bound to the phosphate group of CT DNA and are partially dehydrated. On the basis of solid-state 23Na NMR titration experiments, we obtain quantitative thermodynamic parameters concerning the cation-binding affinity for the phosphate group of CT DNA. The free energy difference (,G° ) between M+ and Na+ ions is as follows: Li+ (,1.0 kcal mol,1), K+ (7.2 kcal mol,1), NH4+ (1.0 kcal mol,1), Rb+ (4.5 kcal mol,1) and Cs+ (1.5 kcal mol,1). These results suggest that, at low relative humidity, the binding affinity of monovalent cations for the phosphate group of CT DNA follows the order: Li+ > Na+ > NH4+ > Cs+ > Rb+ > K+. This sequence is drastically different from that observed for CT DNA in solution. This discrepancy is attributed to the different modes of cation binding in dry and wet states of DNA. In the wet state of DNA, cations are fully hydrated. Our results suggest that the free energy balance between direct cation,phosphate contact and dehydration interactions is important. The reported experimental results on relative ion-binding affinity for the DNA backbone may be used for testing theoretical treatment of cation-phosphate interactions in DNA. Copyright © 2008 John Wiley & Sons, Ltd. [source]

1H NMR study of internal motions and quantum rotational tunneling in (CH3)4NGeCl3

MAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2008
K. J. Mallikarjunaiah
Abstract (CH3)4NGeCl3 is prepared, characterized and studied using 1H NMR spin lattice relaxation time and second moment to understand the internal motions and quantum rotational tunneling. Proton second moment is measured at 7 MHz as function of temperature in the range 300,77 K and spin lattice relaxation time (T1) is measured at two Larmor frequencies, as a function of temperature in the range 270,17 K employing a homemade wide-line/pulsed NMR spectrometers. T1 data are analyzed in two temperature regions using relevant theoretical models. The relaxation in the higher temperatures (270,115 K) is attributed to the hindered reorientations of symmetric groups (CH3 and (CH3)4N). Broad asymmetric T1 minima observed below 115 K down to 17 K are attributed to quantum rotational tunneling of the inequivalent methyl groups. Copyright © 2007 John Wiley & Sons, Ltd. [source]

A nitrogen-15 NMR study of hydrogen bonding in 1-alkyl-4-imino-1,4-dihydro-3-quinolinecarboxylic acids and related compounds

MAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2006
Laurence Carlton
Abstract The title compounds contain groups (amine, amide, imine, carboxylic acid) that are capable of forming intramolecular hydrogen bonds involving a six-membered ring. In compounds where the two interacting functional groups are imine and carboxylic acid, the imine is protonated to give a zwitterion; where the two groups are imine and amide, the amide remains intact and forms a hydrogen bond to the imine nitrogen. The former is confirmed by the iminium 15N signal, which shows the coupling of 1J(15N,1H) ,85 to ,86.8 Hz and 3J(1H,1H) 3.7,4.2 Hz between the iminium proton and the methine proton of a cyclopropyl substituent on the iminium nitrogen. Hydrogen bonding of the amide is confirmed by its high 1H chemical shift and by coupling of the amide hydrogen to (amide) nitrogen [(1J(15N,1H) ,84.7 to ,90.7 Hz)] and to ortho carbons of a phenyl substituent. Data obtained from N,N -dimethylanthranilic acid show 15N1H coupling of (,)8.2 Hz at 223 K (increasing to (,)5.3 Hz at 243 K) consistent with the presence of a N··· HO hydrogen bond. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Theoretical and experimental NMR study of protopine hydrochloride isomers

MAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2005
Jaromír Tou
Abstract The 1H and 13C NMR chemical shifts of cis - and trans -protopinium salts were measured and calculated. The calculations of the chemical shifts consisted of conformational analysis, geometry optimization (RHF/6,31G** method) and shielding constants calculations (B3LYP/6,31G** method). Based on the results of the quantum chemical calculations, two sets of experimental chemical shifts were assigned to the particular isomers. According to the experimental results, the trans -isomer is more stable and its population is ,68%. Copyright © 2005 John Wiley & Sons, Ltd. [source]

17O NMR in room temperature phase of La2Mo2O9 fast oxide ionic conductor

MAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2005
Joel Emery
Abstract A room temperature 17O NMR study of La2Mo2O9, a fast oxide ionic conductor exhibiting a phase transition at 580 °C between a low-temperature ,-phase and a high-temperature ,-phase, is presented. Four partly overlapping quasi-continuous distributions of oxygen sites are evidenced from 1D magic angle spinning (MAS) and 2D triple quantum MAS NMR experiments. They can be correlated with the three oxygen sites O1, O2 and O3 of the high-temperature crystal structure. The low-temperature phase is characterized by two distributed sites of type O1, which proves that the symmetry is lower than in the cubic high-temperature phase. Two-dimensional experiments show that there is no dynamic exchange process, on the NMR time-scale, between the different oxygen sites at room temperature, which agrees well with conductivity results. Copyright © 2005 John Wiley & Sons, Ltd. [source]

NMR study of quinolizidine alkaloids: relative configurations, conformations,

MAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2005
Phuong Mai Le
Abstract Extracts of fruits and leaves of Connarus paniculatus afford six quinolizidine alkaloids which were identified as piptanthine, 18-epipiptanthine, ormosanine, homoormosanine, podopetaline (monohydrochloride) and homopodopetaline on the basis of high-field NMR studies. 1D and 2D NMR experiments provide complete assignments of the 1H and 13C spectra. In conjunction with detection of nuclear Overhauser effects (NOESY), these results allow detailed structure characterization including determination of relative configurations for the chiral sites and conformational analysis. Exchange phenomena involving nitrogen inversion were detected. Copyright © 2005 John Wiley & Sons, Ltd. [source]