NMR Relaxation Parameters Research Articles

A new approach to the silica gel surface: characterization of different surface regions by silicon-29 magic angle spinning NMR relaxation parameters and consequences for quantification of silica gels by NMR [Erratum to document cited in CA112(24):223903d

A new approach to the silica gel surface: characterization of different surface regions by silicon-29 magic angle spinning NMR relaxation parameters and consequences for quantification of silica gels by NMR [Erratum to document cited in CA112(24):223903d

ChemInform Abstract: A New Approach to the Silica Gel Surface. Characterization of Different Surface Regions by 29Si Magic Angle Spinning NMR Relaxation Parameters and Consequences for Quantification of Silica Gels by NMR.

ChemInform Abstract: A New Approach to the Silica Gel Surface. Characterization of Different Surface Regions by 29Si Magic Angle Spinning NMR Relaxation Parameters and Consequences for Quantification of Silica Gels by NMR.

13C NMR studies of the polymerization mechanism and the dynamics of poly(alkyl methacrylate) grafted onto silk fibers

Abstract13C NMR was extensively used to determine the tacticity of poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(butyl methacrylate) (PBMA) grafted onto silk fibers using radiation‐induced graft copolymerization. All polymers are predominantly syndiotactic and the tacticity is virtually independent of the degree of grafting. The value of PΣ (= Pm/r + Pr/m) was calculated from the triad distribution and was found to be approximately one. This indicates that all the above polymer chains grafted onto silk fibers are syndiotactic and obey Bernoullian statistics. The number‐average sequence length of either meso or racemic additions was determined using the triad distribution. The 13C NMR relaxation parameters, spin‐lattice relaxation time, T1, and nuclear Overhauser effect, NOE, were observed and then the value of the correlation time for average segmental motion, τc, and the width parameter, p, were determined by assuming a log χ2 distribution for the correlation time. A relatively small value of p was obtained, indicating that the distribution of the correlation time is large. Taking into account the τc values of different poly(alkyl methacrylate) chains grafted onto silk fibers, the following order of segmental motion was furnished: PMMA > PEMA > PBMA.

A new approach to the silica gel surface: characterization of different surface regions by silicon-29 magic angle spinning NMR relaxation parameters and consequences for quantification of silica gels by NMR

Native and some monofunctionally derivatized silica gels have been investigated by 29Si CP MAS NMR spectroscopy with pulse and with cross-polarization (CP) excitation. Contact time variation experiments for some native materials yield results for the siloxane (Q4)g roups which cannot be described with a single set of THsi and TlpHv alues. Quantitative analyses of such silicas with CP excitation require CP curves as standards. For these samples Tlsi values measured with pulse excitation differ from those obtained by CP excitation. TlpHv alues depend on the contact time, selected for the experiment. Moreover, multiexponential Tlsi analyses for Q3 and Q4 reveal that the longitudinal relaxation process of native silica gels generally can be separated into at least three different processes, each with its characteristic average value for Tlsi. Explanations for CP behavior and Tlsi inhomogeneities are offered in terms of different forms of coexistence in silica gels of relatively mobile amorphous regions. Implications of these results for quantification of surface groups of silicas with cross-polarization MAS NMR are discussed.

13C NMR study of the overall and internal motions of a semi‐rigid hydrocarbon

AbstractAn extensive investigation has been made of the 13C NMR relaxation parameters of 2,4‐dicyclohexyl‐2‐methylpentane neat and in solution. Spin‐lattice relaxation times and nuclear Overhauser enhancements were measured as a function of temperature, concentration and radiofrequency. The results for all the carbons, except the methyls, can be interpreted by using a reduced spectral density which suggests that there is an isotropically rotating semi‐rigid backbone structure whose internal librations and vibrations reduce the amplitude of the spectral density. However, interpretation of the methyl group data required the addition of a discrete correlation time characteristic of the internal motion about a C3 axis. From dilution studies, the validity of using the two‐correlation time spectral density with S2 = 0 when the rate of overall motion approaches that of the internal motion was established, for the first time.

Interpretation of frequency-dependent nuclear magnetic resonance relaxation data from micelles formed in the 6-(dimethyleicosylammonio)hexanoate–water system

An NMR relaxation study of micelles formed in the 6-(dimethyleicosylammonio)hexanoate–water system is presented. The zwitterionic surfactant has been specifically labelled with 2H in the position adjacent to the nitrogen on the main hydrocarbon chain, and the 2H NMR relaxation parameters have been determined at nine different magnetic field strengths. In addition, 13C relaxation data for the same position in the molecule are presented for three different magnetic field strengths. All the presented NMR relaxation data depend on the magnetic field strength used. The data are analysed with the so-called two-step model, which was originally developed in order to interpret frequency-dependent NMR relaxation data for aggregated surfactant systems. Within the framework of the two-step model two different models for the aggregate motion are discussed, viz. aggregate tumbling and collective fluctuations of the director. Both models are capable of describing the data. In particular, the former model gives a consistent picture with reasonable values of the inherent parameters, provided that the internal motions that the surfactants undergo within the aggregate, have motional components in the nanosecond range. In order to characterize the micelles as regards their size and shape, we also present some small-angle X-ray and fluorescence data for the micelles.

Molecular motion in cyclic siloxanes studied by 17O, 29Si, and 13C nuclear magnetic resonance spectroscopy

NMR studies of nine cyclosiloxanes, Dn, have been carried out, and measurements made of 17O NMR line-widths and chemical shifts, and 29Si and 13C NMR relaxation parameters. The results obtained give information on the changes in molecular motion with increasing ring size. It is proposed that the smaller Dn compounds, up to D8, can be assumed to be undergoing isotropic motion as neat liquids and in solution in C6D6. At ∼ D8, in 1 mol dm–3solution, isotropic motion is no longer sufficient to describe the relaxation parameters, and for the larger rings a novel conformational process involving SiMe2: groups passing through the Dnring is proposed to account for the results.

NMR Imaging and Spectroscopy of the Mammalian Central Nervous System after Heavy Ion Radiation

NMR imaging, NMR spectroscopy, and histopathologic techniques were used to study the proton relaxation time and related biochemical changes in the rodent brain after in vivo helium beam irradiation with single doses of 10, 20, 30, and 50 Gy. Two-dimensional Fourier transform spin-echo imaging and saturation recovery with projection reconstruction were used to measure the NMR relaxation parameters. These parameters were correlated with proton spectroscopy and histopathology. Additional high resolution in vitro proton spectroscopy was performed on brain extracts to observe chemical changes that could not be seen in vivo. The major findings from these experiments were that at 4-14 days postirradiation, image intensity and T1 relaxation time decreased on the irradiated side and increased on the nonirradiated side relative to nonirradiated control animals. In vivo surface coil proton spectroscopy methods demonstrated changes in lipid and phosphatidylcholine (p-choline) peaks. In vitro studies of the aqueous fraction of brain extracts showed radiation-induced changes in lactate, 4-aminobutyric acid, and p-choline peak areas. In the organic fraction, radiation-induced changes were observed in phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine. With histology and Evans blue injections, blood-brain barrier alterations were seen as early as 4 days after a dose of 50 Gy.

Experimental animal models of viral myocarditis

Animal models of congestive heart failure and dilated cardiomyopathy following encephalomyocarditis (EMC) virus infection have been developed. Differences were found between different strains of mice in the frequency of occurrence and severity of myocarditis, and even in the character of the pathological lesions. Genetic factors may play an important role in pathogenesis. Right ventricular aneurysm and arrhythmias were seen in these models. Viral myocarditis may play a pathogenetic role in right ventricular dysplasia. Auto-antibodies against heart developed and the distribution of cardiac myosin isoenzymes was altered during the course of myocarditis. Myocardial uptake of technetium-99m pyrophosphate and changes in NMR relaxation parameters have been studied in these models. Virus vaccine, passive immunization, recombinant interferon α A/D and ribavirin protected mice from developing myocarditis. Immunosuppressive agents such as prednisolone and cyclosporinwere studied, but had no beneficial effect on these models. An animal model of perimyocarditis induced by coxsackie virus B3 is also described. Because the myocardial lesions are severe and occur frequently, our animal models are considered suitable for studying pathogenetic mechanisms and for the evaluation of diagnostic methods and prevention and therapeutic interventions of viral myocarditis.

ChemInform Abstract: Synthesis and Solution Structure of [Va13]‐HC Toxin by 1H and 13C NMR Relaxation Parameters.

AbstractThe title compound (II) is synthesized starting from the linear tetrapeptide ester (Ia) via the intermediates (Ib) and (Ic) (no yields given).

13C NMR Studies of the Molecular Flexibility of Antidepressants

The solution dynamics of a series of clinically potent antidepressants have been investigated by measuring 13C NMR relaxation parameters. Correlation times and internal motional rates were calculated from spin-lattice relaxation times and nuclear Overhauser effects for the protonated carbons in mianserin, imipramine-like antidepressants, and amitriptyline-like antidepressants. These data were interpreted in terms of overall molecular tumbling, internal rotations, and inherent flexibility of these structures. Of particular interest was the conformational variability of the tricyclic nucleus of the tricyclic antidepressants, where the data indicated a fivefold difference in mobility of the dimethylene bridge of imipramine-like antidepressants relative to amitriptyline-like compounds. The implications of such a difference in internal motions is discussed in relation to previous NMR studies and to the reported differences in pharmacological activity of these antidepressants.

Nuclear magnetic resonance probes for investigations of the virus-cell interactions.

Measuring the NMR relaxation parameters of selectively excited protons within molecules bound to the cell membrane was shown to provide a profitable way of looking at the virus-cell interaction. Such approach made it possible to delineate the virus adsorption to human red blood cells by using the NMR features of the cytoskeleton inhibitor colchicine.

Changes of relaxation times T1 and T2 in rat tissues after biopsy and fixation

NMR spectroscpical measurements of relaxation times were conducted on muscle, intestine, fatty tissue and cerebral cortex and white matter of the rat at various time intervals following removal of the tissue. It appeared that most tissues can be stored at 4°C up to 24 hours without noticeable effects on NMR relaxation parameters. Exceptions are the T 2 of muscle and the T 1 and T 2 of intestine, which tended to change in the first hour after biopsy. Relaxation parameters change considerably after fixation of the tissues. Therefore the effects of fixation have to be taken into account when carrying out NMR measurements on fixed tissues.

Fluoroquinacrine binding to nucleic acids: investigation of the 19F-NMR, optical, and fluorescence properties in the presence of DNA, poly(A), and tRNA.

AbstractThe interaction of fluoroquinacrine, 3‐fluoro‐7‐chloro‐9‐(diethylamino‐1‐methylbutyl‐amino)acridine, with poly(A), DNA, and tRNA has been investigated by monitoring changes in the 19F‐nmr properties, the fluorescence, and the optical absorbance of the drug. The changes in the properties of fluoroquinacrine in the presence of nucleic acids are similar to those observed for quinacrine and suggest that the drugs bind in a similar fashion. The molecular dynamics of fluoroquinacrine bound to nucleic acids were determined by interpreting the data from a number of different nmr relaxation experiments with a two‐correlation‐time model. The two motions are the long‐range bending motion of the drug‐nucleic acid complex and the sliding of the drug between the base pairs. Both dipolar and chemical shift anisotropy contributions to the nmr relaxation parameters were taken into consideration. The binding of fluoroquinacrine to tRNA appears to be different from that observed for binding to DNA. Optical absorbance and 19F‐nmr were also used to examine the helix‐to‐coil transitions of the drug–nucleic acid complexes. In the DNA complex, the 19F chemical shift changes parallel the absorption changes that occur during the transition. 19F‐nmr and absorption show that the drug–tRNA complexes undergo a cooperative helix‐to‐coil transition, with the drug binding sites melting when the tRNA is 70% denatured.

ChemInform Abstract: NMR RELAXATION PARAMETERS IN MOLECULES WITH INTERNAL MOTION: EXACT LANGEVIN TRAJECTORY RESULTS COMPARED WITH SIMPLIFIED RELAXATION MODELS

Chemischer InformationsdienstVolume 13, Issue 3 Physical Organic Chemistry ChemInform Abstract: NMR RELAXATION PARAMETERS IN MOLECULES WITH INTERNAL MOTION: EXACT LANGEVIN TRAJECTORY RESULTS COMPARED WITH SIMPLIFIED RELAXATION MODELS R. M. LEVY, R. M. LEVYSearch for more papers by this authorM. KARPLUS, M. KARPLUSSearch for more papers by this authorP. G. WOLYNES, P. G. WOLYNESSearch for more papers by this author R. M. LEVY, R. M. LEVYSearch for more papers by this authorM. KARPLUS, M. KARPLUSSearch for more papers by this authorP. G. WOLYNES, P. G. WOLYNESSearch for more papers by this author First published: January 19, 1982 https://doi.org/10.1002/chin.198203044Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume13, Issue3January 19, 1982 RelatedInformation

NMR relaxation parameters in molecules with internal motion: exact Langevin trajectory results compared with simplified relaxation models

NMR relaxation parameters in molecules with internal motion: exact Langevin trajectory results compared with simplified relaxation models

13C NMR relaxation parameters of solid polyethylene, measured with magic angle sample spinning

¹³C NMR relaxation parameters of solid polyethylene, measured with magic angle sample spinning

Internal motions in proteins examined by 13C NMR rotating frame spin-lattice relaxation: Chymotrypsinogen

The experimental observable for the NMR relaxation technique involving rotating frame spin-lattice relaxation in the presence of an off-resonance rf field consists of the ratio of the intensity of a resonance peak in the presence of an rf field applied off-resonance to the intensity in the absence of the applied field. The intensity ratio ( R) is related to a relaxation rate ( 1 T 1ϱ off ) produced by the off-resonance irradiation. These relaxation parameters are shown to complement the usual spin-lattice relaxation rate ( 1 T 1 ), the linewidth ( W 1 2 ), and the nuclear Overhauser effect (NOE) in studies of protein mobility. The relaxation parameters are calculated and compared for two motional models, one simply involving random isotropic rotational tumbling and the other imposing internal rotation on the isotropic tumbling. Use of all the 13C NMR relaxation parameters to study protein mobility is illustrated for α-chymotrypsinogen A. A satisfactory fit of theoretical predictions to all the experimental relaxation data for the threonine Cβ resonance is obtained only when the theoretical relaxation parameters are calculated for an overall rotational reorientation time of 35 nsec and a correlation time for the internal motion of 20 nsec.

Calculated carbon-13 NMR relaxation parameters for a restricted internal diffusion model. Application to methionine relaxation in dihydrofolate reductase

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCalculated carbon-13 NMR relaxation parameters for a restricted internal diffusion model. Application to methionine relaxation in dihydrofolate reductaseRobert E. London and John AvitabileCite this: J. Am. Chem. Soc. 1978, 100, 23, 7159–7165Publication Date (Print):November 1, 1978Publication History Published online1 May 2002Published inissue 1 November 1978https://doi.org/10.1021/ja00491a006RIGHTS & PERMISSIONSArticle Views151Altmetric-Citations95LEARN 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 (815 KB) Get e-Alerts Get e-Alerts

NMR relaxation parameters in a two-spin system by selective nuclear overhauser effects

Relaxation rate parameters in coupled spin systems can be obtained by steady-state selective saturation experiments. The overdetermined relaxation matrix is calculated from experimental intensity changes by utilizing the concept of a generalized inverse of a singular matrix. The theory is applied to the two-spin AX system of C-13-enriched sodium formate in D 2O. The simplicity of the method and its independence of specific relaxation models and motional assumptions make this type of experiment a feasible alternative to transient methods.