Ranjith Krishna Pai

Chromones as a privileged scaffold in drug discovery: A review

The chromone and its derivatives are the most important heterocyclic compounds, which is a common and integral feature of a variety of natural products and medicinal agents. These heterocycles show a variety of pharmacological properties, and change of their structure offers a high degree of diversity that has proven useful for the search of new therapeutic agents. A large volume of research has been carried out on chromone and their derivatives, which has proved the pharmacological importance of this heterocyclic nucleus. The present review focuses on the pharmacological profile of chromone derivatives in the current literature with an update of recent research findings on this nucleus and the perspectives that they hold for future research.

Divalent Cation-Induced Variations in Polyelectrolyte Conformation and Controlling Calcite Morphologies: Direct Observation of the Phase Transition by Atomic Force Microscopy

In the biomineralization process, the changes in conformation of organic matrix may be a widespread phenomenon. Investigation of the structural relationship between organic and inorganic materials is the main subject. The approach taken was to extract quantitative information of the variations in polyelectrolyte conformation during the mineralization process using atomic force microscopy. The results infer the evidence of the role of polyelectrolyte conformation in mineralization of calcium carbonate and the methods for understanding the principle that govern biomineralization.

Embedded proteins and sacrificial bonds provide the strong adhesive properties of gastroliths

The adhesive properties of gastroliths from a freshwater crayfish (Cherax quadricarinatus) were quantified by colloidal probe atomic force microscopy (AFM) between heavily demineralized gastrolith microparticles and gastrolith substrates of different composition. Combined AFM and transmission electron microscopy studies demonstrated that the sequential detachment and large adhesion energies that characterise the adhesive behaviour of a native gastrolith substrate are dominated by sacrificial bonds between chitin fibres and between chitin fibres and CaCO(3). The sacrificial bonds were shown to be strongly related to the gastrolith proteins and when the majority of these proteins were removed by ethylenediaminetetraacetic acid (EDTA), the sequential detachment disappeared and the adhesive energy was reduced by more than two orders of magnitude.

Photophysics of the Red Chromophore of HcRed: Evidence for Cis−Trans Isomerization and Protonation-State Changes

HcRed is a dimeric intrinsically fluorescent protein with origins in the sea anemone Heteractis crispa. This protein exhibits deep red absorption and emission properties. Using a combination of ensemble and single molecule methods and by varying environmental parameters such as temperature and pH, we found spectroscopic evidence for the presence of two ground state conformers, trans and cis chromophores that are in thermal equilibrium and that follow different excited-state pathways upon exposure to light. The photocycle of HcRed appears to be a combination of both kindling proteins and bright emitting GFP/GFP-like proteins: the trans chromophore undergoes light driven isomerization followed by radiative relaxation with a fluorescence lifetime of 0.5 ns. The cis chromophore exhibits a photocycle similar to bright GFPs and GFP-like proteins such as enhanced GFP, enhanced YFP or DsRed, with radiative relaxation with a fluorescence lifetime of 1.5 ns, singlet-triplet deactivation on a microsecond time scale and solvent controlled protonation/deprotonation in tens of microseconds. Using single molecule spectroscopy, we identify trans and cis conformers at the level of individual moieties and show that it is possible that the two conformers can coexist in a single protein due to the dimeric nature of HcRed.

Hexagonal columnar liquid crystals as a processing additive to a P3HT:PCBM photoactive layer

Morphology of the donor/acceptor network in the photoactive layer is critical in order to optimize the device performance. In the present study, a new trihydrazone-functionalized cyanopyridine (CPTH-D16) demonstrating an ambient temperature hexagonal columnar liquid crystalline phase is introduced into the well-known photoactive layer i.e. P3HT:PCBM as a processing additive towards the construction of an efficient solar cell. Photon absorption and emission properties of the blends in the solution/film state are systematically investigated by UV-visible and fluorescence spectroscopy. Furthermore, surface morphology, the degree of crystallinity, changes in nanostructure, and the conductivity of blend films are determined through epi-fluorescence and atomic force microscopy. It is observed that the addition of the CPTH-D16 liquid crystal drastically increases the TUNA current passing through the P3HT:PCBM film. Here, the structural anisotropic nature of CPTH-D16 material helps to obtain well-ordered morphology with nanostructured crystallite formation as well as enhanced current in the P3HT:PCBM film.

Temperature-induced formation of strong gels of acrylamide-based polyelectrolytes

Very strong physical gels have been formed by moderate temperature increases of concentrated aqueous dispersions of acrylamide-based copolymers. The results of rheometry, confocal laser scanning microscopy, and differential scanning calorimetric studies of acrylamide-based copolymers with acrylic acid (poly[AM-AA]) and the sodium salt of 2-acrylamido-2-methylpropane acid (poly[AM-NaAMPS]) suggest that the temperature-induced swelling of the polymer beads and dissolved chains creates strongly entangled polymer networks above the upper critical solution temperature. Analysis of the viscoelastic response showed that the time scale for the gelation process is about minutes to hours. The addition of high concentrations of Ca(2+) resulted in a significant reduction in the modulus.

SELECTIVE CONTROL OF CALCIUM CARBONATE CRYSTALS MORPHOLOGIES USING SULFONATED POLYMER AS ADDITIVE

ABSTRACT We report two selective morphologies of CaCO 3 crystals using poly(potassium 2-acrylamido-2-methylpropanesulfonate) [poly(KAMPS)] as template through gas diffusion method. The presence of anionic sulphonte groups on poly(KAMPS) determined the kinetic crystallization and was fundamental for stabilizing oriented triangle and tubular shape of calcite. The modified CaCO 3 were followed by SEM and XRD techniques. Inorganic architectures with hierarchically complex shape and optimized properties have great potential as agents in optical, electronic, magnetic and biomedical applications. Keywords : calcite, crystallization, gas diffusion method, polymorphs. e-mail: aneira@uchile.cl. INTRODUCTION Along the evolution, the living organisms have developed capacities to form intricate hybrid materials (biominerals) highly optimized through a complex mineralizing process called biomineralization (1-6) . For example, certain bacteria produce magnetic nanocrystals, many mollusks build CaCO 3

Light-Harvesting Antenna System for Molecular Electronics

Molecular electronics has been growing rapidly to a point where the ambition is to miniaturize conventional electronic devices down to the single-molecule scale. We construct a molecular scale electronic device based on a donor-acceptor antenna (DAA) system composed of an electron donating quantum dots (QDs) and electron accepting C60 coupled via an aminoalkanethiol bridge. The DAA system was fabricated by a self-assembly procedure, and the charge transfer (CT) rate and charge discharge (CD) efficiency are demonstrated. The CT rate that we obtained for our DAA system is 776 × 106 s-1, which is ten times greater than the reported value. Photoluminescence excitation data, PL lifetime, and intensity trajectory data show that strong CT occurs from the QD to the C60 PTA, and this thin DAA film (<;100 nm) device can hold photogenerated charges for almost 3 h before complete dissipation when not connected to an external circuit, which can have a positive impact on the application of these DAA-based device in molecular electronics. We anticipate that our findings will catalyze the development of new lightweight solar battery.

A Novel Dental Restorative Composite Fabricated With Nanostructured poly(KAMPS)/aragonite Filler

A nanostructured dental restorative composite has been fabricated with a new poly(KAMPS)/aragonite filler to investigate the use of bioinspired materials in dental applications. The composite is fabricated with a common dental light activated resin and a poly(KAMPS)/aragonite filler created by biomimetic pathways and formed entirely from dilute aqueous solutions. The aragonite nanorod filler has a nanostructure with rod widths of 120 nm and polymer-filled spacings of 10–20 nm. Nanoindentation is used to characterize the mechanical properties of the novel composite. The new bioinspired composite has application as a dental restorative material.

Effect of Crystallite Orientation on Nanomechanical Properties of a Nanostructured Poly(KAMPS)/Aragonite Composite

Nanomechanical properties of a new poly(KAMPS)/aragonite composite are investigated by nanoindentation to determine effects of crystallite orientation. The composite is fabricated using biomimetic pathways and formed entirely from dilute aqueous solutions. Nanorods of aragonite precipitate within a matrix of poly(KAMPS)-based polyelectrolyte and a nanostructured material with rod widths of 120 nm and polymer-filled spacings of 10–20 nm is created. From nanoindentation, the effect of crystallite orientation on mechanical properties is explored. The new biomimetic composite has application in the biomedical and dental fields as a restorative material.