S. Chandrasekhar

Bio: S. Chandrasekhar is an academic researcher from Raman Research Institute. The author has contributed to research in topics: Liquid crystal & Biaxial nematic. The author has an hindex of 31, co-authored 124 publications receiving 3368 citations. Previous affiliations of S. Chandrasekhar include Royal Institution & University of Mysore.

Dynamical theory of reflexion from cholesteric liquid crystals

Abstract: The analogy between the optical phenomena exhibited by cholesterics and the diffraction of x-rays from perfect crystals is empha-sized and some of its consequences are discussed. Difference equations similar to those formulated by Darwin in his dynamical theory lead to simple analytical expressions for the reflexion coefficient, rotatory power and circular dichroism which are shown to be in good agree-ment with the results of the rigorous electromagnetic treatment. An extension of the theory to absorbing systems at once yields the relevant formulae for the Borrmann effect in cholesterics. It is pointed out that this simple approach should be sufficient for most practical calculations.

Form and Function in Biological Macromolecules: Kinetic Stability is Key, with Oblique Roles for Intramolecularity and Hydrophobicity in Enzyme Catalysis

Abstract: Certain structure-reactivity aspects of biological macromolecules, with particular emphasis on protein folding and enzyme catalysis, are discussed herein. Furthermore, the role played by the hydrophobic effect and intramolecularity in enzymic reactivity are evaluated afresh, with new insights of much importance in chemical biology. Thus, the sum of the energies of the hydrogen bonds constituting the tertiary structures of proteins, determines the overall Gibbs energy of activation for loss of conformational integrity. As protein molecules of even modest size consist of a relatively large number of intramolecular hydrogen bonding interactions, the activation barrier to even partial unfolding of the α-helices and β-sheets forming the tertiary structure would be prohibitively high under normal conditions. The resulting kinetic stability conserves the natural conformation of a protein molecule established at the ribosomal site of synthesis, carrying the molecule through the thick-and-thin of a range of metabolic pathways during its ‘journey of life’. However, protein molecules also acquire flexibility via ‘strain delocalization’ (Ramachandran plots being relevant), thus enabling stabilization of multiple transition states along a pathway (particularly in case of covalent enzyme-substrate complexes). Two mechanistic features of enzyme catalysis that have been exhaustively studied are intramolecularity and the hydrophobic effect. Although intramolecularity has for long been touted as the origin of enzymic reactivity, this can be challenged on fundamental physical-organic grounds. Intriguingly, however, the collapse of the classical Michaelis-Menten mechanism for enzyme catalysis leads to a reconsideration of the role of intramolecularity, although not as hitherto envisaged. Thus, a majority of enzymes apparently form covalent enzyme-substrate complexes—possibly also exergonically—so the subsequent reactions at the active site may well benefit from the traditional propinquity effect: The critical caveat would be the highly exergonic formation of final products. It is argued that the hydrophobic effect—although intuitively reasonable—is difficult to pin down quantitatively, model systems (including micelles) leading to inconsistent and debatable results. However, the hydrophobic effect likely contributes to enzymic reactivity along with charge-relay via the proteinic backbone.

Significance of nucleologenesis, ribogenesis, and nucleolar proteome in the pathogenesis and recurrence of hepatocellular carcinoma

Abstract: ABSTRACT Introduction Emerging evidence suggests that enhanced ribosome biogenesis, increased size, and quantitative distribution of nucleoli are associated with dysregulated transcription, which in turn drives a cell into aberrant cellular proliferation and malignancy. Nucleolar alterations have been considered a prognostic histological marker for aggressive tumors. More recently, advancements in the understanding of chromatin network (nucleoplasm viscosity) regulated liquid–liquid phase separation mechanism of nucleolus formation and their multifunctional role shed light on other regulatory processes, apart from ribosomal biogenesis of the nucleolus. Areas covered Using hepatocellular carcinoma as a model to study the role of nucleoli in tumor progression, we review the potential of nucleolus coalescence in the onset and development of tumors through non-ribosomal biogenesis pathways, thereby providing new avenues for early diagnosis and cancer therapy. Expert opinion Molecular-based classifications have failed to identify the nucleolar-based molecular targets that facilitate cell-cycle progression. However, the algorithm-based tumor risk identification with high-resolution medical images suggests prominent nucleoli, karyotheca, and increased nucleus/cytoplasm ratio as largely associated with tumor recurrence. Nonetheless, the role of the non-ribosomal functions of nucleoli in tumorigenesis remains elusive. This clearly indicates the lacunae in the study of the nucleolar proteins pertaining to cancer.

Experimental Studies on a Terminally Non-Polar Reentrant Nematogenic Mixture

Abstract: We present here the results of our x-ray, high pressure and dielectric studies on a reentrant nematogenic mixture of n-dodecyl-4-(4-ethoxybenzylideneamino)-α-methylcinnamate and 4-n-heptyloxyphenyl-4-(4-ethylcyclohexanoyloxy)benzoate, neither of which possesses a strongly polar end group. The layer spacing measurements show that the smectic A phase is probably of the partially bilayer type. While the pressure-temperature diagram of this mixture is similar to that observed for strongly polar reentrant systems, the dielectric results show some significant differences.

Handbook of Optical Materials

Abstract: CRYSTALLINE MATERIALS Introduction Physical Properties Optical Properties Mechanical Properties Thermal Properties Magnetooptic Properties Electrooptic Properties Elastooptic Properties Nonlinear Optical Properties GLASSES Introduction Commercial Optical Glasses Specialty Optical Glasses Fused Silica Fluoride Glasses Chalcogenide Glasses Magnetooptic Properties Electrooptic Properties Elastooptic Properties Nonlinear Optical Properties Special Glasses POLYMERIC MATERIALS Optical Plastics Index of Refraction Nonlinear Optical Properties Thermal Properties Engineering Data METALS Physical Properties of Selected Metals Optical Properties Mechanical Properties Thermal Properties Mirror Substrate Materials LIQUIDS Introduction Water Physical Properties of Selected Liquids Index of Refraction Nonlinear Optical Properties Magnetooptic Properties Commercial Optical Liquids GASES Introduction Physical Properties of Selected Gases Index of Refraction Nonlinear Optical Properties Magnetooptic Properties Atomic Resonance Filters APPENDICES Safe Handling of Optical Materials Abbreviations, Acronyms, and Mineralogical or Common Names for Optical Materials Abbreviations for Methods of Preparing Optical Materials and Thin Films Fundamental Physical Constants Units and Conversion Factors

Dendron-Mediated Self-Assembly, Disassembly, and Self-Organization of Complex Systems

Abstract: Dendron-mediated self-assembly, disassembly, and self-organization of complex systems have been investigated. The most ideal building blocks would need to display shape persistence in solution and in the solid state, since only this feature provides access to the use of complementary methods of structural analysis. Most supramolecular dendrimers are chiral even when they are constructed from nonchiral building blocks and are equipped with mechanisms that amplify chirality. This poses additional challenges associated with the understanding of the structural origin of chirality in different supramolecular structures through combinations of structural analysis methods. While many supramolecular structures assembled from dendrimers and dendrons resemble some of the related morphologies generated from block-copolymers, they are much more complex and are not determined by the volume ratio between the dissimilar parts of the molecule.

Discotic Liquid Crystals: From Tailor-Made Synthesis to Plastic Electronics

Abstract: Most associate liquid crystals with their everyday use in laptop computers, mobile phones, digital cameras, and other electronic devices. However, in contrast to their rodlike (calamitic) counterparts, first described in 1907 by Vorlander, disklike (discotic, columnar) liquid crystals, which were discovered in 1977 by Chandrasekhar et al., offer further applications as a result of their orientation in the columnar mesophase, making them ideal candidates for molecular wires in various optical and electronic devices such as photocopiers, laser printers, photovoltaic cells, light-emitting diodes, field-effect transistors, and holographic data storage. Beginning with an overview of the various mesophases and characterization methods, this Review will focus on the major classes of columnar mesogens rather than presenting a library of columnar liquid crystals. Emphasis will be given to efficient synthetic procedures, and relevant mesomorphic and physical properties. Finally, some applications and perspectives in materials science and molecular electronics will be discussed.