Anil Kumar

Bio: Anil Kumar is an academic researcher from Kurukshetra University. The author has contributed to research in topics: Polymerization & Catalysis. The author has an hindex of 34, co-authored 335 publications receiving 8569 citations. Previous affiliations of Anil Kumar include Shri Mata Vaishno Devi University & Indian Institute of Technology Kanpur.

A two-dimensional nuclear overhauser enhancement (2d noe) experiment for the elucidation of complete proton-proton cross-relaxation networks in biological macromolecules

Abstract: 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.

Experimental techniques of two-dimensional correlated spectroscopy

Abstract: Two-dimensional (2D) homonuclear correlated spectra manifest connectivities between spin-coupled nuclei and can thus provide assignments of individual spin systems in complex 1 H NMR spectra. Two experimental techniques discussed in this paper, spin-echo correlated spectroscopy and foldover-corrected correlated spectroscopy, are particularly suitable versions for handling the large data matrices encountered in work with biological macromolecules. This paper explains the fundamental aspects of these two techniques and the relations with the conventional 2D correlated spectroscopy technique.

Buildup rates of the nuclear Overhauser effect measured by two-dimensional proton magnetic resonance spectroscopy: implications for studies of protein conformation

Abstract: It is demonstrated, by means of experiments with the basic pancreatic trypsin inhibitor, that the buildup rates of the nuclear Overhauser effect can be measured by two-dimensional NMR spectroscopy. Qualitative correlations between the buildup rates of first-order Overhauser effects, which arise from direct dipole-dipole coupling between closely spaced protons, and the proton-proton distances in the protein conformation are established. Second-order Overhauser effects due to spin diffusion by cross-relaxation between more distant protons are also identified. On the basis of these observations, potentialities and limitations of two-dimensional nuclear Overhauser enhancement spectroscopy for studies of the conformation of biological macromolecules are discussed and suggestions made for improved experimental procedures. For quantitative measurements of Overhauser effects, the use of phase-sensitive spectra and of techniques for selective suppression of J cross-peaks in data sets recorded with very short mixing times appears particularly important.

NMR Fourier zeugmatography

Abstract: A new technique of forming two- or three-dimensional images of a macroscopic sample by means of NMR is described. It is based on the application of a sequence of pulsed magnetic field gradients during a series of free induction decays. The image formation can be achieved by a straightforward two- or three-dimensional Fourier transformation. The method has the advantage of high sensitivity combined with experimental and computational simplicity.

Homonuclear two-dimensional 1H NMR of proteins. Experimental procedures

Abstract: Experimental techniques used for homonuclear 2D 1H NMR studies of proteins are described. A brief survey of the general strategy for structural studies of proteins by 2D NMR is included. The main part of the paper discusses guidelines for the selection of experimental techniques, the elimination of artifacts and unwanted peaks in protein 2D 1H NMR spectra, suppression of the solvent line in H2O solutions, experimental parameters, numerical data processing before and after Fourier transformation, and suitable presentations of complex 2D NMR spectra.

MLEV-17-based two-dimensional homonuclear magnetization transfer spectroscopy

Abstract: Recently, we have shown that net magnetization transfer among scalar coupled homonuclear spins can be obtained by the application of a spin-lock field (I), or more effectively, by the application of a phase-alternated spin-lock field (2, 3). Analogous methods to accomplish net homonuclear magnetization transfer, based on different rfirradiation schemes have previously been reported by Braunschweiler and Ernst (4). As they and others (5-9) have pointed out, the key to net magnetization transfer between two coupled spins, A and X, is to remove the Zeeman contributions, HzA and Hzx, from the Hamiltonian, or to make them identical, i.e., HzA = Hz,. This can be accomplished by suitable rf irradiation schemes or by zero-field NMR (JO). In this communication we describe a new mixing scheme that is based on the MLEV-16 composite pulse decoupling cycle (II). We have modified this cycle to make it less sensitive to pulse imperfections and it will be shown that this type of MLEV mixing provides net magnetization transfer over a substantial bandwidth with only limited rf power. More importantly, the apparent decay constant of spin-locked magnetization can be prolonged by up to a factor of two (compared to TIP) by using this new type of mixing scheme. If the Zeeman part of the Hamiltonian is eliminated, the spin system will evolve solely under the influence of scalar coupling. Magnetization can then propagate through the molecule in a way that is very similar to spin diffusion among protons in a rigid solid, where dipolar couplings are usually much larger than differences in chemical shift. For molecules consisting of only two coupled homonuclear spins, A and X, Braunschweiler and Ernst have shown that in the isotropic coupling limit there is an oscillatory exchange of the A and X magnetization, with period 1 /JAx. Explicit results for the AX2 case have very recently been presented by Chandrakumar and Subramanian (12). For larger spin systems a computer simulation program appears to be the easiest way to predict the rate at which magnetization will propagate through the molecule. AS demonstrated earlier (2), the net magnetization transfer obtained in this type of experiment permits the recording of phase-sensitive spectra, and gives in many cases enhanced resolution and sensitivity compared to the widely used COSY experiment (13-16). For short mixing times (<0.1/J), only direct connectivities will be observed. For longer mixing times, magnetization that has been transferred from spin A to spin M during the first part of the mixing period can be relayed to spin X during the second

Gradient-tailored excitation for single-quantum NMR spectroscopy of aqueous solutions.

Abstract: A novel approach to tailored selective excitation for the measurement of NMR spectra in non-deuterated aqueous solutions (WATERGATE, WATER suppression by GraAdient-Tailored Excitation) is described. The gradient echo sequence, which effectively combines one selective 180° radiofrequency pulse and two field gradient pulses, achieves highly selective and effective water suppression. This technique is ideally suited for the rapid collection of multi-dimensional data since a single-scan acquisition produces a pure phase NMR spectrum with a perfectly flat baseline, at the highest possible sensitivity. Application to the fast measurement of 2D NOE data of a 2.2. mM solution of a double-stranded DNA fragment in 90% H2O at 5 °C is presented.

Application of phase sensitive two-dimensional correlated spectroscopy (COSY) for measurements of 1H-1H spin-spin coupling constants in proteins.

Abstract: Two-dimensional correlated spectroscopy (COSY) is used for measurements of proton-proton spin-spin coupling constants in protein 1H NMR spectra. High digital resolution along the frequency axis ω2 is achieved by placing the carrier frequency in the center of the spectrum, using quadrature detection in both dimensions and presenting the spectrum in the phase sensitive mode. Compared to other techniques for studies of spin-spin coupling constants, COSY provides greatly improved spectral resolution. This is illustrated by experiments with H2O solutions of the small globular protein BUSI IIA (bull seminal inhibitor IIA).

Two‐dimensional spectroscopy. Application to nuclear magnetic resonance

Abstract: The possibilities for the extension of spectroscopy to two dimensions are discussed. Applications to nuclear magnetic resonance are described. The basic theory of two‐dimensional spectroscopy is developed. Numerous possible applications are mentioned and some of them treated in detail, including the elucidation of energy level diagrams, the observation of multiple quantum transitions, and the recording of high‐resolution spectra in inhomogenous magnetic fields. Experimental results are presented for some simple spin systems.