The Experts below are selected from a list of 66 Experts worldwide ranked by ideXlab platform
Chad M Rienstra - One of the best experts on this subject based on the ideXlab platform.
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proton detected solid state nmr spectroscopy of fully protonated proteins at 40 khz magic angle spinning
Journal of the American Chemical Society, 2007Co-Authors: Donghua H Zhou, Gautam J Shah, Mircea Cormos, Charles Mullen, Dennis Sandoz, Chad M RienstraAbstract:Remarkable progress in solid-state NMR has enabled complete structure determination of uniformly labeled proteins in the size range of 5−10 kDa. Expanding these applications to larger or mass-limited systems requires further improvements in spectral sensitivity, for which Inverse Detection of 13C and 15N signals with 1H is one promising approach. Proton Detection has previously been demonstrated to offer sensitivity benefits in the limit of sparse protonation or with ∼30 kHz magic-angle spinning (MAS). Here we focus on experimental schemes for proteins with ∼100% protonation. Full protonation simplifies sample preparation and permits more complete chemical shift information to be obtained from a single sample. We demonstrate experimental schemes using the fully protonated, uniformly 13C,15N-labeled protein GB1 at 40 kHz MAS rate with 1.6-mm rotors. At 500 MHz proton frequency, 1-ppm proton line widths were observed (500 ± 150 Hz), and the sensitivity was enhanced by 3 and 4 times, respectively, versus dir...
R A T M Abbenhuis - One of the best experts on this subject based on the ideXlab platform.
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183w nmr spectroscopy of w vi imidoaryl and imidoalkyl complexes using Inverse Detection based on non specific long range interactions
Magnetic Resonance in Chemistry, 1994Co-Authors: Alceo Macchioni, Paul S Pregosin, Paul Adriaan Van Der Schaaf, Gerard Van Koten, Heinz Rüegger, R A T M AbbenhuisAbstract:183W NMR spectra for a series of octahedral W(VI) imidophenyl, ‘WNPh’ and W(VI) imidoethyl, ‘WNEt,’ complexes were obtained using Inverse Detection based on non-specific long-range interactions. The metal couples to both the ortho and para protons of the NPh moiety (four and six bonds, respectively). The 183W shift is shown to be sensitive to the nature of the ligand and the coordination number. The effect of geometric isomerism on δ183W is shown to be several hundred ppm. Some δ14N and δ15N and 1J(183W,15N) data are reported. A number of new geometric isomers, involving the position of the NR ligand with respect to the remaining ligands, have been identified.
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183w nmr spectroscopy of w vi imidoaryl and imidoalkyl complexes using Inverse Detection based on non specific long range interactions
Magnetic Resonance in Chemistry, 1994Co-Authors: Alceo Macchioni, Paul S Pregosin, Paul Adriaan Van Der Schaaf, Gerard Van Koten, Heinz Rüegger, R A T M AbbenhuisAbstract:183W NMR spectra for a series of octahedral W(VI) imidophenyl, ‘WNPh’ and W(VI) imidoethyl, ‘WNEt,’ complexes were obtained using Inverse Detection based on non-specific long-range interactions. The metal couples to both the ortho and para protons of the NPh moiety (four and six bonds, respectively). The 183W shift is shown to be sensitive to the nature of the ligand and the coordination number. The effect of geometric isomerism on δ183W is shown to be several hundred ppm. Some δ14N and δ15N and 1J(183W,15N) data are reported. A number of new geometric isomers, involving the position of the NR ligand with respect to the remaining ligands, have been identified.
H W Spiess - One of the best experts on this subject based on the ideXlab platform.
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Inverse Detection and heteronuclear editing in 1h 15n correlation and 1h 1h double quantum nmr spectroscopy in the solid state under fast mas
Journal of Magnetic Resonance, 2001Co-Authors: Ingo Schnell, B Langer, Shm Serge Sontjens, Van Mhp Marcel Genderen, Rint P Sijbesma, H W SpiessAbstract:Signal enhancement in heteronuclear correlation spectra as well as signal selection in 1H experiments can be achieved through Inverse, i.e., 1H, Detection in the solid state under fast MAS conditions. Using recoupled polarization transfer (REPT), a heteronuclear 1H–15N single-quantum correlation (HSQC) experiment is presented whose symmetrical design allows the frequency dimensions to be easily interchanged. By observing the 15N dimension indirectly and detecting on 1H, the sensitivity is experimentally found to be increased by factors between 5 and 10 relative to conventional 15N Detection. In addition, the Inverse 1H–15N REPT-HSQC scheme can be readily used as a filter for the 1H signal. As an example, we present the combination of such a heteronuclear filter with a subsequent 1H–1H DQ experiment, yielding two-dimensional 15N-edited 1H–1H DQ MAS spectra. In this way, specific selection or suppression of 1H resonances is possible in solid-state MAS experiments, by use of which the resolution can be improved and information can be unravelled in 1H spectra.
Yusuke Nishiyama - One of the best experts on this subject based on the ideXlab platform.
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fast magic angle sample spinning solid state nmr at 60 100 khz for natural abundance samples
Solid State Nuclear Magnetic Resonance, 2016Co-Authors: Yusuke NishiyamaAbstract:In spite of tremendous progress made in pulse sequence designs and sophisticated hardware developments, methods to improve sensitivity and resolution in solid-state NMR (ssNMR) are still emerging. The rate at which sample is spun at magic angle determines the extent to which sensitivity and resolution of NMR spectra are improved. To this end, the prime objective of this article is to give a comprehensive theoretical and experimental framework of fast magic angle spinning (MAS) technique. The engineering design of fast MAS rotors based on spinning rate, sample volume, and sensitivity is presented in detail. Besides, the benefits of fast MAS citing the recent progress in methodology, especially for natural abundance samples are also highlighted. The effect of the MAS rate on (1)H resolution, which is a key to the success of the (1)H Inverse Detection methods, is described by a simple mathematical factor named as the homogeneity factor k. A comparison between various (1)H Inverse Detection methods is also presented. Moreover, methods to reduce the number of spinning sidebands (SSBs) for the systems with huge anisotropies in combination with (1)H Inverse Detection at fast MAS are discussed.
Gary E Martin - One of the best experts on this subject based on the ideXlab platform.
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constant time Inverse Detection gradient accordion rescaled heteronuclear multiple bond correlation spectroscopy cigar hmbc
Magnetic Resonance in Chemistry, 2000Co-Authors: Chad E Hadden, Gary E Martin, V V KrishnamurthyAbstract:A further refinement of the recently reported IMPEACH-MBC long-range heteronuclear shift correlation experiment is described. The new experiment, CIGAR-HMBC (constant time Inverse-detected gradient accordion rescaled long-range heteronuclear multiple bond correlation), modifies the constant time variable delay of the IMPEACH-MBC experiment to allow user-determined scaling of F1 modulation. The refinement offered in the CIGAR-HMBC experiment allows the investigator to reintroduce whatever degree of F1 modulation is desired to authenticate weak long-range responses. Results obtained with the CIGAR-HMBC experiment using a range of values for Jscale are compared with results obtained with identically optimized ACCORD-HMBC and IMPEACH-MBC experiments. Copyright © 2000 John Wiley & Sons, Ltd.
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characterization of a trace by product of the synthesis of the protease inhibitor tipranavir pnu 140690
Journal of Heterocyclic Chemistry, 1999Co-Authors: Gary E Martin, Chad E Hadden, Russell H Robins, Frank W Crow, Wayne K Duholke, Jane E Guido, Brian D Kaluzny, Thomas J Thamann, Bruce A PearlmanAbstract:TipranavirTM (PNU-140690) is a protease inhibitor under clinical investigation for the treatment of human acquired immunodeficiency syndrome (AIDS). During scale-up synthesis of clinical quantities of the bulk drug, a colored, transient by-product of the final coupling reaction was observed. Quantities of this colored, transient chemical species were too low (<<0.1%) for characterization by conventional spectroscopic methods. It was, however, possible to isolate sufficient material for characterization based on mass spectrometry and submicro Inverse-Detection gradient (SMIDG) nmr methods by methanol stripping of silica gel that had been used in purification of bulk drug. This process afforded an enriched feedstock from which small quantities of this highly colored and unstable (halflife < 18 hours in methanol and < 10 minutes in acetone) trace contaminant could be isolated by semi preparative reversed phase hplc. The impurity was identified as an unstable Zincke salt formed by the condensation of two molecules of the anilino precursor and the pyridine used as a base in the final step of the synthetic process. Following identification of this impurity, efforts were undertaken to engineer it out of the synthetic process.
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low level long range 1h 15n heteronuclear shift correlation at natural abundance using submicro nmr techniques
Journal of Natural Products, 1998Co-Authors: Chad E Hadden, Gary E MartinAbstract:: Gradient Inverse-detected NMR methods have provided experimental access to long-range 1H-15N heteronuclear shift correlation data at natural abundance. When used in conjunction with newly developed submicro-Inverse-Detection gradient (SMIDG) NMR probes, sample size requirements are dramatically reduced. Long-range 1H-15N GHMBC data are shown for a 1 mg sample ( approximately 3 mmol, 0.11 M) of the alkaloid strychnine (1) dissolved in 30 mL of CDCl3. All of the correlations observed in previous studies using samples in the range of 20-40 mg in 5 mm NMR probes were observed in data acquired overnight on a 1 mg sample in a 1.7 mm SMIDG NMR probe. A previously unreported long-range correlation, 3JH-15a-N(19), was observed in data recorded over a weekend for the 1 mg sample. Data recorded over a weekend using a 1 mmol (334 mg) sample of strychnine (1) in 30 mL of CDCl3 contained the majority of the responses from the 1 mg sample. The practical limit of Detection for long-range 1H-15N heteronuclear shift correlation data at natural abundance would appear to be approximately 1 mmol with data acquisition over a weekend or longer using present submicro-NMR probe technology.
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improvements in the sensitivity of Inverse detected heteronuclear correlation spectra using micro Inverse probes and micro cells hmqc and hmbc spectra of caribbean ciguatoxin preliminary structural inferences
Tetrahedron Letters, 1995Co-Authors: Ronald C Crouch, Gary E Martin, Steven M Musser, Ray H Grenade, Robert Wayne DickeyAbstract:Abstract Ciguatoxins are extremely potent activators of voltage-dependent sodium channels and elicit gastrointestinal and neurologic dysfunction in humans. Because they are present only at extremely low levels, the acquisition of heteronuclear shift correlation nmr spectra has been very difficult. Inverse-detected heteronuclear shift correlation experiments (HMQC and HMBC) have greatly increased sensitivity relative to older, heteronuclide-detected experiments. The use of micro Inverse-Detection probes has afforded a further dramatic increase in sensitivity relative to conventional 5 mm probe technology. Micro Inverse-Detection probes employed in conjunction with Shigemi micro nmr cells are shown to afford a further significant improvement in sensitivity which was necessary to acquire spectra on a sample of
