[en] The research and development programmes of the Neutron Physics Division of the Bhabha Atomic Research Centre, Bombay, for the period 1977-1978 are outlined. The fields covered include reactor (neutron) physics, fusion and plasma neutronics, biological and high precision crystallography, solid state phenomena and seismology as well as the associated workshop facilities. (K.B.)

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[en] Proteins are involved practically at every stage of biological organization and interactions. X-ray diffraction studies on protein structures are aimed at understanding and interpreting a vast majority of biological phenomena at molecular level. This subject, initiated during the second quarter of this century, has played a pivotal role in enhancing knowledge of the life processes, such as the enzyme activity, control and expression of genetic information, immune response and others. Thanks to the improved techniques of sample preparation, availability of high-intensity X-ray sources, fast digital computers with larger memories and interactive graphics systems, many new methods of structure analysis and interpretation are being attempted, and more and more complex biomolecular systems are being investigated in recent years. A reinvestigation of the phase problem, optimization of molecular models by augmenting the diffraction data with other extra-crystallographic information (energy and geometry restraints, etc.); the use of real-time graphics techniques for model interpretation and editing, etc., are some of the recent developments that need special mention. (author). 37 refs

[en] Understanding structure-property relationships of naturally occurring materials has been the aim of scientific research for centuries. The discovery of short wavelength x-rays and neutrons in the 20th century provided a means of studying molecular structure. The methodology of x-ray and neutron diffraction has been successfully applied to determine structures of molecules across disciplines of physics, chemistry, biology, biochemistry and medicine. Typical applications in physics include study of phase transformations, elasticity measurements, magnetic structure, surface scattering etc. In chemistry, the applications have ranged from routine structure determinations of reaction intermediates or natural products to refinement of quantum chemical parameters of atomic and molecular charge densities. The science of crystallography has had a profound effect on the disciplines of biology and medicine. A whole new discipline and industry was created when the structure of DNA was discovered through x-ray diffraction

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No abstract available

[en] Glycyl-L-threonine dihydrate [C₆H₁₂N₂O₄.2H₂O,NH₃⁺.CH₂.CONH.CH(CHOHCH₃).COO^-.2H₂O] crystallizes in space group P2₁2₁2₁ with Z = 4 and a = 9.592 (16), b = 10.002 (10) and c = 10.632 (11) A. Three dimensional (3D) neutron intensity data with sin theta/lambda <= 0.5 A^-1 have been collected on a computer-controlled four-circle neutron diffractometer. All 16 H atoms of the asymmetric unit have been located in a 3D neutron Fourier map. Full-matrix least-squares refinements, including anisotropic temperature factors for all atoms and an extinction factor, led to a weighted R(F²) value of 0.085 for 754 observations. Structural parameters of this dipeptide compare favourably with similar values observed in the neutron diffraction studies of amino acids and dipeptides. The peptide group is non-planar due to small but significant deviations of Δω and thetasub(c) [2.9 (5) and -2.9 (12)⁰ respectively] from zero. The two C-O bond distances of the terminal α-COO^- group are consistent with the hydrogen bonding involving this group. The crystal structure is stabilized by a 3D network of hydrogen bonds, nine such distinct hydrogen bonds being contributed by each asymmetric unit. (Auth.)

[en] The hydrogen-bond interaction can be studied using a variety of spectroscopic and crystallographic techniques, as well as theoretical studies based on quantum chemical principles, semi-empirical procedures, and statistical interpretations. A degree of specificity, along with flexibility, provides H-bonded systems with a variety of unusual and interesting physical, chemical and biological properties. Neutron diffraction is the method of choice for obtaining high-precision data on hydrogen-atom positions and hydrogen-bond stereo-chemistry in crystals. Neutron inelastic scattering can provide information on the dynamics of H-bonded systems. High-precision neutron diffraction studies on a variety of crystal hydrates, amino acids and small peptides, development of semi-empirical potential functions for bent-hydrogen bonds, and statistical analysis of H-bond populations associated with various donor and acceptor groups are some of the investigations on hydrogen bonding, carried out at Trombay during the past three decades. (author). 39 refs., 7 figs., 3 tabs

[en] Neutron beam research started in India more than four decades ago. Presently, the National Facility for Neutron Beam Research, NFNBR is located in Dhruva, a 100 MW research reactor. The entire facility, including the development of neutron detectors, is the result of indigenous efforts of the participating scientists from Bhabha Atomic Research Centre, BARC. NFNBR is accessible to national and international collaborations, and about forty research groups from various institutions have already availed this facility. Active collaboration with ISIS started since 1984, when the day-1 spectrometer, built at BARC, became operational at ISIS. The collaboration continued with the fabrication, at BARC, of parts for OSIRIS spectrometer. Many neutron beam researchers from BARC have carried out collaborative experiments using the neutron sources at USA, France, Germany, Switzerland, and Japan. (author)

[en] The two most important molecular movements which bring about the order-disorder ferroelectric phase transition in the hydrogen-bonded ferroelectric triglycine sulfate (TGS) are the swinging of the amino group (-NH₃⁺) of one of its three glycine ions, namely GI, and the tunnelling of hydrogen in the hydrogen bond between its other two glycine ions, GII and GIII (GII-H-GIII). The potential function for bent hydrogen bonds is used along with the structural parameters of the TGS crystal to model the double-well potential (U) seen by the amino group (-NH₃⁺) of GI in TGS. The ferroelectric phase transition in TGS is investigated from the point of view of the double-well instability. Results obtained are in good agreement with those obtained earlier using the Ising-type theoretical model. Correlation between the two crucial molecular movements in TGS, namely swinging of the -NH₃⁺ group of GI and tunnelling of hydrogen in the hydrogen bond GII-H-GIII of TGS, is established