Nuclear Overhauser Enhancement Measurements Research Articles

Carbon 13 spin-lattice relaxation, linewidth, and nuclear Overhauser enhancement measurements of nucleosome length DNA.

Carbon 13 NMR data were obtained at four magnetic fields for double-stranded DNA samples 120 and 160 nucleotide pairs long. Spectral linewidths are several-fold smaller than predicted for overall rigid rod rotation and increase with increasing field, indicating significant chemical shift dispersion contributions to high field linewidths. Spin-lattice relaxation times are short (e.g. T1 values for CH carbon atoms are approximately 0.5 s at 67.9 MHz), and increase with increasing field. Nuclear Overhauser effects of 0.6 to 0.8 (theoretical maximum = 2.0) were measured for the same protonated carbon atoms at 100.6 MHz. These short T1 values nd relatively large nuclear Overhauser effects show that double-stranded DNA undergoes rapid internal motions with effective correlation times of a few nanoseconds. Preliminary data indicate that DNA base carbon motions occur on essentially the same time scale as sugar motions, thus arguing against independent flexibility of the DNA backbone. Linewidths decreased 2- to 5-fold and nuclear Overhauser effects doubled, upon heat denaturation of DNA, as expected for increased motion. On the other hand, NT1 values of native and denatured DNA were nearly identical, suggesting insensitivity of spin-lattice relaxation times to motions in the nanosecond range in these relatively stiff chains.

ChemInform Abstract: NUCLEAR MAGNETIC RESONANCE SPECTRA OF SOME SILYL AND TRIMETHYLSILYL PSEUDOHALIDES

Proton, 13C, 15N, and 29Si n.m.r. spectra have been recorded for SiH3(CN), SiH3(NCY)(Y = O, S, or Se), and SiMe3(CN) at room temperature or below, as has the 77Se spectrum of SiH3(NCSe). The spectra show no sign of the presence of other isomers, nor of any intermolecular exchange that is fast on the n.m.r. time scale. The n.m.r. parameters are given, together with T1 and nuclear Overhauser enhancement measurements, for SiMe3(CN) at three different temperatures. The spin-rotation contribution to relaxation appears to be dominant.

Comparison of the heme electronic and molecular structure of soybean leghemoglobin and sperm whale myoglobin by proton NMR

The proton nuclear magnetic resonance spectra of soybean ferric leghemoglobin a in the low-spin cyanide and nicotinate complexes have been assigned by specific deuteration of heme methyl groups. The assignments differ from those obtained solely from nuclear Overhauser enhancement measurements and are indicative of a proximal histidyl imidazole-hemin interaction which is very similar to that found in sperm whale myoglobin. The absence of a hyperfine shifted exchangeable NH peak for the distal histidine in leghemoglobin suggests either a very different orientation for this distal ligand or a significantly faster exchange rate with bulk solvent than found in myoglobin.

Melittin bound to dodecylphosphocholine micelles 1H-NMR assignments and global conformational features

Assignments have been obtained for most of the 1H-NMR lines of melittin bound to fully deuterated dodecylphosphocholine micelles by combined use of two-dimensional spin echo correlated spectroscopy and one-dimensional NMR methods. Nuclear Overhauser enhancement measurements showed that the mobility of the entire polypeptide chain is reduced by binding of melittin to the detergent micelle and that the amino-terminal and carboxy-terminal halves of the primary structure constitute separate, compact domains within the conformation of micelle-bound melittin. p 2H titration experiments showed that the presence of positive charges on the four amino groups of melittin had little influence on the conformation of the micelle-bound polypeptide. Titration of tetrameric melittin with detergent provided evidence that melittin assumes similar conformations as a self-aggregated tetramer and as a monomer bound to micelles.

Conformation and dynamic structure of poly(inosinic acid) in neutral aqueous solution by 1 H-, 2 H-, 13 C-, and 31 P-NMR spectroscopy.

The conformation and dynamic structure of single-stranded poly(inosinic acid), poly(I), in aqueous solution at neutral pH have been investigated by nmr of four nuclei at different frequencies: 1 H (90 and 250 MHz), 2 H (13.8 MHz), 13 C (75.4 MHz), and 31 P (36.4 and 111.6 MHz). Measurements of the proton-proton coupling constants and of the 1 H and 13 C chemical shifts versus temperature show that the ribose is flexible and that base-base stacking is not very significant for concentrations varying from 0.04 to 0.10M in the monomer unit. On the other hand, the proton T1 ratios between the sugar protons, T1 (H1 ')/T1 (H3 '), indicate a predominance of the anti orientation of the base around the glycosidic bond. The local motions of the ribose and the base were studied at different temperatures by measurements of nuclear Overhauser enhancement (NOE) of protonated carbons, the ratio of the proton relaxation times measured at two frequencies (90 and 250 MHz), and the deuterium quadrupolar transverse relaxation time T2 . For a given temperature between 22 and 62°C, the 13 C-{1 H} NOE value is practically the same for seven protonated carbons (C2 , C8 , C1' , C2' , C3' , C4' , C5' ). This is also true for the T1 ratio of the corresponding protons. Thus, the motion of the ribose-base unit can be considered as isotropic and characterized by a single correlation time, τc , for all protons and carbons. The τc values determined from either the 13 C-{1 H} NOE or proton T1 ratios, T1 (90 MHz)/T1 (250 MHz), and/or deuterium transverse relaxation time T2 agree well. The molecular motion of the sugar-phosphate backbone (O-P-O) and the chemical-shift anisotropy (CSA) were deduced from T1 (31 P) and 31 P-{1 H} NOE measurements at two frequencies. The CSA contribution to the phosphorus relaxation is about 12% at 36.4 MHz and 72% at 111.6 MHz, corresponding to a value of 118 ppm for the CSA (σ = σ∥ - σ⟂). Activation energies of 2-6 kcal/mol for the motion of the ribose-base unit and the sugarphosphate backbone were evaluated from the proton and phosphorus relaxation data.

Nuclear magnetic resonance spectra of some silyl and trimethylsilyl pseudohalides

Proton, 13C, 15N, and 29Si n.m.r. spectra have been recorded for SiH3(CN), SiH3(NCY)(Y = O, S, or Se), and SiMe3(CN) at room temperature or below, as has the 77Se spectrum of SiH3(NCSe). The spectra show no sign of the presence of other isomers, nor of any intermolecular exchange that is fast on the n.m.r. time scale. The n.m.r. parameters are given, together with T1 and nuclear Overhauser enhancement measurements, for SiMe3(CN) at three different temperatures. The spin-rotation contribution to relaxation appears to be dominant.

A two-dimensional nuclear Overhauser enhancement (2D NOE) experiment for the elucidation of complete proton-proton cross-relaxation networks in biological macromolecules

The recently developed technique of two-dimensional (2D) cross-relaxation spectroscopy is utilized for systematic measurements of selective nuclear Overhauser enhancements (NOE) in the high resolution 1H nuclear magnetic resonance (NMR) spectra of biological macromolecules in solution. Compared to conventional one-dimensional NOE studies, the 2D NOE experiment has the principal advantage that it avoids detrimental effects arising from the limited selectivity of preirradiation in crowded spectral regions. Furthermore, it yields with a single instrument setting a complete network of NOE's between all the protons in the macromolecule. The resulting information on intramolecular proton-proton distances provides a new avenue for studies of the spatial structures of biopolymers.

Stereochemistry of the hexosulose in cardenolide glycosides of the asclepiadaceae

The 4,6-dideoxyhexosulose moiety of gomphoside (1) and afroside (2) has been shown to have the 1′S,2′S,3′R,5′R configuration, Formation of 2′,3′-OO-isopropylidene derivatives establishes that the hydroxy-group at C-3′, which is axial, is cis to that at C-2′. The latter group is cis to the anomeric C-1′ hydrogen, as shown by nuclear Overhauser enhancement measurements. Chemical and 1H and 13C n.m.r. data have been used to show that the same chirality at carbons 1′, 2′, and 5′ is present in the following glycosides from plants of the Ascepiadaceae family: calactin (3), syriobioside (10), desglucosyrioside (11), syrioside (12), uscharidin (5), calotoxin (9), uscharin (7), and voruscharin (8).

Individual assignments of the methyl resonances in the proton nuclear magnetic resonance spectrum of the basic pancreatic trypsin inhibitor

In earlier work the resonances of the 20 methyl groups in the basic pancreatic trypsin inhibitor (BPTI) had been identified in the 360-MHz 1H nuclear magnetic resonance (NMR) spectra and most of the methyl lines had from spin-decoupling experiments been assigned to the different types of amino acid residues. The assignments to the different amino acid types were now completed by studies of the saturation transfer between the denatured and the globular forms of the inhibitor and by spin-decoupling experiments in nuclear Overhauser enhancement (NOE) difference spectra. These distinguished between the methyl resonances of Ala and Thr. Furthermore, for most of the methyl resonances, individual assignments to specific residues in the amino acid sequence were obtained from measurements of intramolecular proton-proton NOE's, use of lanthanide NMR shift and relaxation probes, and comparative studies of various chemically modified forms of BPTI. These data provide the basis for individual assignments of the methyl 13C NMR lines in BPTI and for detailed investigations of the relations between the spatial structure of the protein and the chemical shifts of the methyl groups. The methyl groups in BPTI are of particular interest since they are located almost exclusively on the surface of the protein and thus represent potential natural NMR probes for studies of the protein-protein interactions in the complexes formed between BPTI and a variety of proteases.

Conformations of 3-Deazaadenosine, 3-Deaza-8-azaadenosine, and Benzimidazole-1-β-ᴅ-riboside in Solution: HRNMR-, Proton-Relaxation-Time-, and Nuclear-Overhauser- Effect Studies

The solution conformations of 3-deazaadenosine, 3-deaza-8-azaadenosine, and benzimidazole-1-β- ᴅ-riboside have been determined by nuclear magnetic resonance methods in aqueous and ammonia solutions. The two-state S ⇄ N model of Altona and Sundaralingam is used to analyse the ribose moiety. In order to characterize the orientation of the base relative to the ribose, longitudinal proton relaxation time and nuclear Overhauser enhancement measurements have been carried out. It is shown that 3-deazaadenosine and benzimidazole-1-β-ᴅ-riboside exist preferentially in the S- syn-g+/t (70%) and the N-anti-g+/t (30%) conformation families. In the case of 3-deaza-8-aza- adenosine, some destabilization of the g+ rotamer occurs. In this case, the pulsed methods seem to indicate a preference of the base for the anti range.

8-Alkylaminoadenyl nucleotides as probes of dehydrogenase interactions with nucleotide analogs of different glycosyl conformation.

The nucleotides 8-amino-, 8-methylamino-, and 8-dimethylaminoadenylic acid have been synthesized and their preferred conformations about the glycosyl bond in qaueous solution have been determined by 1H nuclear magnetic resonance spectroscopy. Paramagnetic relaxation studies, nuclear Overhauser enhancement measurements, chemical shifts, and coupling constant comparisons indicate that their is rotation about the glycosyl bond and that preference for either the anti or syn conformation depends on the extent of alkyl substitution on the 8-amino group. The primary and secondary amines 8-amino- and 8-methylaminoadenylic acid adopt a perferential anti conformation about the glycosyl bond, while the tertiary amine 8-dimethylaminoadenylic acid exists predominantly in the syn form. These three analogs provide a system to study interactions of a dehydrogenase with coenzyme inhibitors having different glycosyl conformer populations. All three analogs are competitive inhibitors of NADH in reaction with chicken muscle lactate dehydrogenase, and the Ki values show little dependence on the nature of the amino substitution. This demonstrates that the distribution of conformations about the nucleotide glycosyl bond does not effect the competition of the nucleotide for lactate dehydrogenase apoenzyme. Several models for enzyme-coenzyme binding are discussed. The available data cannot distinguish whether the enzyme binds nucleotide in both the anti and syn conformations or in purely the anti conformation. However, at some stage of the enzyme-coenzyme interaction, there appears to be a strong stabilization of the nucleotide in the anti conformation about the glycosyl bond.

ChemInform Abstract: CARBON‐13 AND NITROGEN‐15 SPIN‐LATTICE RELAXATION (T1) AND NUCLEAR OVERHAUSER ENHANCEMENT (NOE) MEASUREMENTS FOR ACETAMIDE AND N,N‐DIMETHYLACETAMIDE

Nitrogen-15 spin-lattice relaxation times (T_1's) and nuclear Overhauser enhancement (NOE) values are found to vary over a range of concentrations for acetamide. Our data indicate that intermolecular amide-amide hydrogen bonds are broken on dilution in water. Carbon-13 spin-lattice relaxation times and nuclear Overhauser enhancement measurements are given for acetamide and N,N-dimethylacetamide at 5.3 M. There is good agreement between experimental and calculated relaxation rates assuming rapid rotation of the α methyl group and slow rotation about the amide bond.

Carbon-13 and nitrogen-15 spin-lattice relaxation (T1) and nuclear Overhauser enhancement (NOE) measurements for acetamide and N,N-dimethylacetamide

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCarbon-13 and nitrogen-15 spin-lattice relaxation (T1) and nuclear Overhauser enhancement (NOE) measurements for acetamide and N,N-dimethylacetamideDonald D. Giannini, Ian M. Armitage, Harry Pearson, David M. Grant, and John D. RobertsCite this: J. Am. Chem. Soc. 1975, 97, 12, 3416–3419Publication Date (Print):June 1, 1975Publication History Published online1 May 2002Published inissue 1 June 1975https://doi.org/10.1021/ja00845a023RIGHTS & PERMISSIONSArticle Views197Altmetric-Citations23LEARN 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 (473 KB) Get e-Alerts Get e-Alerts

Determination of rotational mobilities of backbone and side-chain carbons of poly(gamma-benzyl L-glutamate) in the helical and random-coil states from measurements of carbon-13 relaxation times and nuclear Overhauser enhancements.

Determination of rotational mobilities of backbone and side-chain carbons of poly(gamma-benzyl L-glutamate) in the helical and random-coil states from measurements of carbon-13 relaxation times and nuclear Overhauser enhancements.