High-resolution NMR Studies Research Articles

Reaction of ninhydrin with β‐dicarbonyl compounds

AbstractThe reactions of ninhydrin (1) with β‐ketoesters and β‐diketones were studied. Two kinds of products were observed, which were either simple adducts of the dicarbonyl compounds to the center carbonyl group of ninhydrin, or tricyclic indeno[1,2‐b]furans. Treatment of methyl 3‐aminocrotonate (2) with ninhydrin led in analogous fashion to an indeno[1,2‐b]pyrrole (3) which was reduced to a complex tetracyclic dihydropyridine 12. A mechanism for the production of 12 is presented. Structures for the novel heterocycles are supported by high resolution nmr studies and X‐ray crystallography.

Studies of [Ag(PPh3)2]NO3, [Ag{P(CH2CH2CN)3}2]NO3and [Ag{P(C6H4Me–m)3}2]NO3by X-ray diffraction and solid-state nuclear magnetic resonance

Solid-state magic angle spinning (MAS)31P NMR spectra of [Ag(PPh3)2]NO31, [Ag{P(CH2CH2CN)3}2]NO32 and [Ag{P(C6H4Me-m)3}2]NO33 have been obtained. In addition, the crystal structures for 2 and 3 have been determined. The results from the high-resolution NMR study are consistent with the known structure of 1 and the structures of 2 and 3. In each case the 31P NMR spectra exhibit resolved splittings arising from 107Ag and 109Ag with 1J(109Ag31P) values of 524, 564 and 517 Hz for 1, 2 and 3, respectively. In 1 the two phosphorus nuclei are crystallographically non-equivalent, thus analysis of the 31P NMR spectrum indicates two chemically shifted phosphorus nuclei, δA 9.50 and δB 7.67, with 2J(31PA31PB)= 125 Hz. The two phosphorus nuclei of 2 are crystallographically and magnetically equivalent in the solid state as evident from the cross polarization/MAS 31P NMR spectrum, δ–9.56. Crystals of 2 are trigonal, space group Rca= 12.204(2), c= 26.418(5)A, Z= 6. The Ag and P atoms are located on a, three-fold rotation axis with Ag at the centre of inversion. The Ag–P bond distance is 2.383(1)A. The conformation of the cyanoethylphosphine ligands in 2 is analogous to the ribs of an umbrella in which the silver atom is encapsulated by the six cyano groups with an Ag ⋯ N separation of 3.439(2)A. The two phosphorus nuclei in 3 are crystallographically equivalent but magnetically non-equivalent since the molecule sits on a two-fold axis but lacks a centre of inversion. As a consequence of this symmetry the two phosphorus nuclei have identical chemical shifts, δ 11.2; however, 2J(31P31P) can be determined from slow MAS experiments. For 3 the space group is orthorhombic Aba2, a= 15.142(1), b= 24.917(2), c= 10.2536(7)A, Z= 4. The two phosphorus atoms are related by a crystallographically imposed two-fold axis. The nitrate group is chelated symmetrically to the Ag atom.

Sequential 1H NMR assignment of the complex of aponeocarzinostatin with ethidium bromide and investigation of protein-drug interactions in the chromophore binding site.

Two-dimensional 1H NMR spectroscopy has been used to investigate the binding site, binding interactions, and the conformation of a 1:1 complex of aponeocarzinostatin (apo-NCS) with ethidium bromide in solution. The protein component in the complex has been sequence-specifically assigned using information derived from coherence transfer and two-dimensional homonuclear 1H NOESY experiments. The conformation of the protein in the complex has been found to be similar to the free form of the apoprotein, and intermolecular NOEs between the residues of the protein to protons on the ethidium bromide suggest that the ethidium bromide is bound to the protein in the same cleft in which the neocarzinostatin chromophore binds. Protons on ethidium show NOE interactions to the following protein residues: Trp-39, Leu-45, Cys-47, and Gln-94 which interact with the phenanthridine ring system of ethidium, Gly-102 and Asn-103 which interact with the alkyl chain of ethidium, and Phe-52 which interacts with the phenyl ring of ethidium. The orientation of ethidium in the cleft of apo-NCS is compared and contrasted to orientation of the chromophore as determined by high-resolution NMR and X-ray diffraction studies.

High-Resolution 13C NMR Study of Liquid 2-Ethylhexyl Benzoate Confined to Porous Silica Glasses

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHigh-Resolution 13C NMR Study of Liquid 2-Ethylhexyl Benzoate Confined to Porous Silica GlassesJing Zhang and Jiri JonasCite this: J. Phys. Chem. 1994, 98, 27, 6835–6839Publication Date (Print):July 1, 1994Publication History Published online1 May 2002Published inissue 1 July 1994https://doi.org/10.1021/j100078a028RIGHTS & PERMISSIONSArticle Views72Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (554 KB) Get e-Alerts

Lewis Acid Sites and Surface Aluminum in Aluminas and Zeolites: A High-Resolution NMR Study

It was the main purpose of this work to study the nature of Lewis acidity in various catalysts (aluminas and zeolites) pretreated under controlled atmosphere at different temperatures. Isotopically enriched ammonia [sup 15]NH[sub 3] chemisorption was employed to probe the surface active sites and to allow for magnetization transfer to surface and close-to-surface Al nuclei. A special deconvolution procedure was applied to obtain [sup 27]Al spectral parameters for different Al sites in partially resolved spectra. The procedure accounted for the normal distribution of electric field gradient tensor components at a particular site. It is shown that there are two kinds of Lewis sites on aluminas: namely, a tetrahedral site with isotropic shift of about 58 ppm and quadrupolar coupling constant QCC [approx equal] 6 MHz and a pentagonal site with a isotropic shift of about 40 ppm and a slightly smaller QCC. In zeolites the same kinds of sites exist in the nonframework aluminum debris, and in addition, the Broensted sites are associated with framework aluminum. 32 refs., 8 figs., 5 tabs.

Rigid-Rod Polyesters with Flexible Side Chains Based on 1,4-Dialkyl Esters of Pyromellitic Acid and 4,4'-Biphenol. 5. High-Resolution 13C NMR Studies for Crystalline and Liquid Crystalline Layered Phases

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRigid-Rod Polyesters with Flexible Side Chains Based on 1,4-Dialkyl Esters of Pyromellitic Acid and 4,4'-Biphenol. 5. High-Resolution 13C NMR Studies for Crystalline and Liquid Crystalline Layered PhasesMasato Sone, Brian R. Harkness, Hiromichi Kurosu, Isao Ando, and Junji WatanabeCite this: Macromolecules 1994, 27, 10, 2769–2777Publication Date (Print):May 1, 1994Publication History Published online1 May 2002Published inissue 1 May 1994https://doi.org/10.1021/ma00088a018RIGHTS & PERMISSIONSArticle Views165Altmetric-Citations33LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (877 KB) Get e-Alerts Get e-Alerts

High-Resolution Proton NMR Studies of Lymphocyte Extracts

Anatomic imaging is now a well-developed application of magnetic resonance. Greater capabilities for physiologic characterization should become possible by concomitant application of spectroscopic methods. High-resolution in vitro spectroscopy must first provide a framework upon which in vivo and diagnostic interpretation may be based. Biochemical profiles consisting of quantitation of extracted aqueous metabolites and lipids of particular cells or organs establish an in vitro glossary for what may be found in the intact cell or living subject. A large variety of amino acids, intermediary metabolites, membrane precursors, and nucleotides are detectable in extracts of human peripheral blood lymphocytes, and significant changes in intracellular concentrations have been monitored after lectin-induced activation. Corresponding changes in lipid profile have also been noted. An increasing variety of other cells and tissues are being similarly characterized. Despite its limitations, NMR analysis possesses the unique prospect of providing a noninvasive and nondestructive source of biochemical information.

Conformational properties of monosubstituted cyclohexane guest molecules constrained within zeolitic host materials. A solid-state NMR investigation

The conformational properties of monosubstituted cyclohexane guest molecules (C6H11X with X = CH3, OH, Cl, Br and I) included within microporous solid host materials (silicalite-I, H-ZSM-5, NH4-mordenite and zeolite NH4-Y) have been elucidated via high-resolution solid-state 13C NMR spectroscopy. For all of the inclusion compounds investigated, the fraction of monosubstituted cyclohexane molecules in the equatorial conformation is similar to that in solution, suggesting that these host materials do not impose any significant constraints upon the conformational properties of the monosubstituted cyclohexane guest molecules. For the monohalogenocyclohexane guest molecules (C6H11X with X = Cl, Br and I), this result is in marked contrast to the situation for the same guest molecules in the thiourea host structure, for which the conformational properties of the guest molecules are substantially different from those of the same molecules in solution. For cyclohexanol (C6H11OH) in H-ZSM-5, some amount of dicyclohexyl ether (C6H11OC6H11) is observed, and is analogous to the proposed production of dimethyl ether in the first stage of methanol-to-gasoline conversion on this zeolite. The comparatively low temperature (ambient temperature) at which this conversion from cyclohexanol to dicyclohexyl ether occurs is noteworthy. In addition to our high-resolution solid-state 13C NMR studies of these materials, 1H MAS and 27AI MAS NMR spectra have also been recorded, and are discussed.

High-resolution NMR studies of (diphosphine)(diene) rhodium complexes in the solid state

Well-resolved resonances are observed in the 31P-CPMAS NMR spectra of (2S,4S)-2,4-bis(diphenylphosphino)pentane or ( S, S)-BDPP ( 1) and its cationic complexes [(Rh{( S, S)-BDPP}(NBD)]BF 4 ( 2a), [Rh{( S, S)-BDPP}(NBD)]PF 6 ( 2b), [Rh{( S, S)-BDPP}(NBD)]ClO 4 ( 2c) and [Rh{( S, S)-BDPP}(COD)]BF 4 ( 3). Packing forces split the single resonance observed for these systems in solution. The spectral parameters depend remarkably on the counterion in 2a, 2b, and 2c. Complex 3 showed a splitting of every resonance due to the presence of two independent molecules in the unit cell. The complex [Rh{( S, S)-BDPP}(NBD)Cl] ( 4) showed two broad 31P resonances which are ascribed to a number of closely related structures based on the expected trigonal bipyramidal geometry.

Solution Conformation of a Pentapeptide by NMR and Molecular Modeling Studies

Abstract High resolution NMR studies and molecular modeling calculations were performed on a linear pentapeptide BOC-Tyr-Gly-Gly-Pro-Leu-OMe. This molecule exhibits two conformations in the solution state. While the 13C spectrum in nonpolar solvents such as acetonitrile shows only one form, in DMSO-d6 and MeOD there are two forms. The appearance of the major (M) and minor (m) resonances is attributed to cis-trans isomerization about the X-Pro bond. The assignments of several proton resonances for the major conformer were made through the combined analysis of two dimensional (2D) homonuclear correlated spectroscopy (COSY) and available data on similar peptides. The solution conformation of the major moiety was probed using the distance constraints obtained from 2D-NOE spectroscopy (NOESY). In addition, other information such as presence of internal hydrogen bonds and dihedral angle values from coupling constants for the amide protons were also used.

Comparative high resolution NMR studies of n- and p-type doped polyacetylene films

High resolution NMR provides unique abilities to study either properties of the polymer chains or behavior of the doping agent in the conducting polymers. Magic angle spinning proton decoupled 13C NMR was applied to n-type sodium doped, (CHNa y) x (y ≤ 0.3), and p-type iodine doped, [CH(I 3) y] x (y ≤ 0.19), polyacetylene films prepared by Shirakawa's method. Also 2-dimensional nutation spectra of half-integer spin ( I = 3 2 ) quadrupolar 23Na nuclei were measured. All the spectra were studied as a function of the dopant content, y, determined by weight uptake after doping. The films were controlled by measurement of the conductivity which was about 10 and 50 Ω −1 cm −1 for heavily iodine and sodium doped material, respectively. We discuss our results on: (i) formation of the extended polycarbonium ions (charged solitons), (ii) doping induced cis/trans isomerization, (iii) partial compensation of (CHNa) x films by oxygen and moisture, (iv) intersite electron-electron correlations on the polymer chain, and (v) ordering of the sodium ions and occurrence of at least two different crystal phases of the polyacetylene-sodium system.

High-resolution Solid-state NMR Studies on Proteins.

A brief account is made for applications of a high-resolution solid-state NMR spectroscopy to reveal the three-dimensional structure of a variety of membrane proteins, proteins of higher molecular weight and their complexes, with emphasis on introduction of new experimental techniques. Some illustrative examples were also demonstrated to this end.

High-resolution NMR study of a synthetic oligoribonucleotide with a tetranucleotide GAGA loop that is a substrate for the cytotoxic protein, ricin.

Ricin is a cytotoxic protein that inactivates ribosomes by hydrolyzing the N-glycosidic bond at position A4324 in eukaryotic 28S rRNA. Its substrate domain forms a double helical stem and a 17-base loop that includes the sequence GAGA, the second adenosine of which corresponds to A4324. Recently, studies of mutant RNAs have shown that the four-nucleotide loop, GAGA, can function as a substrate for ricin. To investigate the structure that is recognized by ricin, we studied the properties of a short synthetic substrate, the dodecaribonucleotide r-CUCAGAGAUGAG, which forms a RNA hairpin structure with a GABA loop and a stem of four base pairs. The results of NMR spectroscopy allowed us to construct the solution structure of this oligonucleotide by restrained molecular-dynamic calculations. We found that the stem region exists as an A-form duplex. 5G and 8A in the loop region form an unusual G:A base pair, and the phosphodiester backbone has a turn between 5G and 6A. This turn seems to help ricin to gain access to 6A which is the only site of depurination in the entire structure. The overall structure of the GAGA loop is similar to those of the GAAA and GCAA loops that have been described but that are not recognized by ricin. Therefore, in addition to the adenosine at the depurination site, the neighboring guanosine on the 3' side (7G) may also play a role in the recognition mechanism together with 5G and 8A.

A high-resolution solid-state NMR study of the miscibility, morphology, and toughening mechanism of polystyrene with poly(2,6-dimethyl-1,4-phenylene oxide) blends

An extended Goldman-Shen pulse sequence was used to observe indirectly the proton spin diffusion in the blends of polystyrene (PS) with poly(2,6-dimethyl-1,4-phenylene oxides) (PPO). The results indicate that the average distance between PS and PPO is less than 5 angstrom in the intimately mixed phase, but there are heterogeneous domains on a 100-angstrom scale. The data of spin relaxation of carbons, T1(C), for homopolymers and their blends suggest that there is a strong pi-pi electron conjugation interaction between the aromatic rings of PS and those of PPO, while the aromatic rings of PPO drive the aromatic rings of PS to move cooperatively. It is the cooperative motion that markedly improves the impact strength of PS.

High-resolution NMR study of the pressure-induced unfolding of lysozyme.

The pressure-induced reversible unfolding of lysozyme was investigated by high-resolution proton magnetic resonance spectroscopy by following the proton spectra of the following residues: His-15 epsilon 1, Trp-28 epsilon 3, Leu-17 delta 2, Cys-64 alpha, and Trp-108 epsilon 3. The experiments were performed at pH 3.9 and 68.5 degrees C in the pressure range from 1 bar to 5 kbar both in the absence and presence of tri-N-acetylglucosamine (tri-NAG). From the pressure-induced changes of the equilibrium between the native and denatured forms of lysozyme, the reaction volumes (delta V) were calculated for each residue. Small but statistically significant differences in delta V were found for residues located in different regions of the protein. For example, delta V for the disulfide bonded Cys-64 alpha is smaller than the delta V's found for the other residues. In particular, the effect of tri-NAG binding to lysozyme was a change of delta V from -10.3 +/- 0.6 cm3/mol to -18.1 +/- 1.7 cm3/mol for the Trp-108 epsilon 3 residue which is located close to the active site. It is important to note that the Cys-64 alpha residue also senses the binding of the substrate analog. The ability to detect statistically significant differences for delta V of individual residues located in different regions of lysozyme represents the main result of these experiments.

Glycation and oxidation of proteins in diabetes & aging: Role of oxygen in crosslinking of proteins by glucose

The Pro23 to Thr (P23T) mutation in human γD-crystallin (HGD) shows several cataract phenotypes. We found earlier [A. Pande, O. Annunziata, N. Asherie, O. Ogun, G.B. Benedek, J. Pande, Decrease in protein solubility and cataract formation caused by the Pro23 to Thr mutation in human gamma D-crystallin, Biochemistry 44 (2005) 2491–2500] that the mutation dramatically lowers the solubility of P23T but the overall protein fold is maintained. Recently we observed that solutions of P23T showed liquid–liquid phase transition behavior similar to that of HGD but the liquid–protein crystal phase transition was altered, suggesting an asymmetric distribution of “sticky” patches on the protein surface [J.J. McManus, A. Lomakin, O. Ogun, A. Pande, M. Basan, J. Pande, G.B. Benedek, Altered phase diagram due to a single point mutation in human gammaD-crystallin, Proc. Natl. Acad. Sci. USA 104 (2007) 16856–16861]. Here we present high-resolution NMR studies of HGD and P23T in which we have made nearly complete backbone assignments. The data provide a structural basis for explaining the retrograde solubility of P23T by (a) identifying possible “sticky” patches on the surface of P23T and (b) highlighting their asymmetric distribution.

High-resolution solid state 13C NMR studies of ferrocene as a function of magic angle sample spinning frequency

High-resolution solid state 13C NMR spectra of polycrystalline ferrocene have been recorded, at room temperature, under conditions of magic angle sample spinning and high power 1H decoupling. It is shown that, contrary to naive expectations, the linewidth of the isotropic peak in the spectrum increases as the magic angle sample spinning frequency is increased. It is demonstrated, via experiments with variable decoupler field strength and experiments on ferrocene- d 10, that this effect results from the efficiency of the 1H decoupling being modulated by magic angle sample spinning. The fact that narrower linewidths are obtained at low magic angle sample spinning frequency for this material has important implications in the wider context of establishing optimum conditions for recording high-resolution 13C NMR spectra of solids, particularly when there is appreciable molecular motion in the solid.

Observation of nitrogen-14, carbon-13 indirect spin-spin coupling in high-resolution 13C [formula omitted] spectra of solids

The 13C CP MAS NMR spectrum of [( n-C 3H 7) 4N][Cd(SCN) 3], 1, indicates the presence of three non-equivalent thiocyanate ligands, in agreement with the results of a recent single-crystal X-ray diffraction study. Examination of the 13C MAS line shapes allows direct measurement of the indirect spin-spin coupling constants, 1J ( 14N, 13C) = 16 ± 1 Hz and 2J( 111 113 Cd, 13C) = 75 ± 5 Hz , for the unique N-bonded thiocyanate ligand. This is the first reported measurement of 1J ( 14N, 13C) and 2J( 111 113 Cd, 13C) in the solid state. Possible reasons for the failure to observe 1J ( 14N, 13C) values in previous high-resolution 13C CP MAS NMR studies are summarized.

An implantable dosage form for the treatment of bone infections.

The object of this investigation was the development of an implantable sustained-release dosage form, for the treatment of bone infections. Cross-linked polydimethylsiloxane (PDMS) was used as the matrix material. The drug delivery system was prepared by incorporating tobramycin, as a free base (C18H37N5O9.H2O) or as a sulfate salt [(C18H37N5O9)2.5H2SO4], into the matrix and molding into spherical beads. Following in vitro studies, the cumulative amount of drug released when plotted as a function of the square root of time was linear for both the base and the salt. The addition of glycerol to the matrix substantially accelerated the rate of drug release and the plots of cumulative amount of drug released continued to be linear as a function of the square root of time. The glycerol-incorporated beads swelled in contact with the aqueous medium but a negligible amount of glycerol was released even after exposure to the medium for 20 days. 13C solid-state and high-resolution NMR studies indicated that a fraction of the added glycerol participated in the cross-linking reaction of the polymer. The effect of the initial molecular weight of PDMS and the effect of the concentration of the cross-linker on the kinetics of drug release were investigated.

One- and two-dimensional high-resolution solid-state NMR studies of zeolite lattice structures

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOne- and two-dimensional high-resolution solid-state NMR studies of zeolite lattice structuresC. A. Fyfe, Y. Feng, H. Grondey, G. T. Kokotailo, and H. GiesCite this: Chem. Rev. 1991, 91, 7, 1525–1543Publication Date (Print):November 1, 1991Publication History Published online1 May 2002Published inissue 1 November 1991https://doi.org/10.1021/cr00007a013RIGHTS & PERMISSIONSArticle Views1308Altmetric-Citations199LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-Alerts Get e-Alerts