Evaluation of solute-solvent interactions from solvent blue-shifts of n → π* transitions of C=O, C=S, NO2 and N=N groups: hydrogen bond energies of various donor-acceptor systems

Effects of non-polar, polar and proton-donating solvents on the n → π* transitions of C=O, C=S, NO2 and N=N groups have been investigated. The shifts of the absorption maxima in non-polar and polar solvents have been related to the electrostatic interactions between solute and solvent molecules, by employing the theory of McRAE. In solvents which can donate protons the solvent shifts are mainly determined by solute-solvent hydrogen bonding. Isobestic points have been found in the n → π* bonds of ethylenetrithio-carbonate in heptane-alcohol and heptane-chloroform solvent systems, indicating the existence of equilibria between the hydrogen bonded and the free species of the solute. Among the different proton-donating solvents studied water produces the largest blue-shifts. The blue-shifts in alcohols decrease in the order 2,2,2-trifluoroethanol, methanol, ethanol, isopropanol and t-butanol, the blue-shift in trifluoroethanol being nearly equal to that in water. This trend is exactly opposite to that for the self-association of alcohols. It is suggested that electron-withdrawing groups not merely decrease the extent of self-association of alcohols, but also increase the ability to donate hydrogen bonds. The approximate hydrogen-bond energies for several donor-acceptor systems have been estimated. In a series of aliphatio ketones and nitro compounds studied, the blue-shifts and consequently the hydrogen bond energies decrease with the decrease in the electron-withdrawing power of the alkyl groups. It is felt that electron-withdrawing groups render the chromophores better proton acceptors, and the alcohols better donors. A linear relationship between n → π* transition frequency and the infrared frequency of ethylenetrithiocarbonate has been found. It is concluded that stabilization of the electronic ground states of solute molecules by electrostatic and/or hydrogen-bond interactions determines the solvent shifts.

A systems perspective of host-pathogen interactions: predicting disease outcome in tuberculosis

The complex web of interactions between the host immune system and the pathogen determines the outcome of any infection. A computational model of this interaction network, which encodes complex interplay among host and bacterial components, forms a useful basis for improving the understanding of pathogenesis, in filling knowledge gaps and consequently to identify strategies to counter the disease. We have built an extensive model of the Mycobacterium tuberculosis host-pathogen interactome, consisting of 75 nodes corresponding to host and pathogen molecules, cells, cellular states or processes. Vaccination effects, clearance efficiencies due to drugs and growth rates have also been encoded in the model. The system is modelled as a Boolean network. Virtual deletion experiments, multiple parameter scans and analysis of the system's response to perturbations, indicate that disabling processes such as phagocytosis and phagolysosome fusion or cytokines such as TNF-alpha and IFN-gamma, greatly impaired bacterial clearance, while removing cytokines such as IL-10 alongside bacterial defence proteins such as SapM greatly favour clearance. Simulations indicate a high propensity of the pathogen to persist under different conditions.

Towards optimum diffraction efficiency for methylene blue sensitized dichromated gelatin holograms

A systematic investigation has been carried out into the optimization of diffraction efficiency (η) of methylene blue sensitized dichromated gelatin (MBDCG) holograms. The influence of the following parameters on η have been studied: prehardener concentration (CH), concentrations of ammonium dichromate (CA) and methylene blue (CM) as photosensitizers, and exposure (E). This study revealed that with CH similar, equals 0.5, CA similar, equals 30, CM similar, equals 0.3, and E similar, equals 400–600, optimum diffraction efficiency of over 80%, can be easily achieved in MBDCG holograms.

A systems perspective of host-pathogen interactions: predicting disease outcome in tuberculosis

The complex web of interactions between the host immune system and the pathogen determines the outcome of any infection. A computational model of this interaction network, which encodes complex interplay among host and bacterial components, forms a useful basis for improving the understanding of pathogenesis, in filling knowledge gaps and consequently to identify strategies to counter the disease. We have built an extensive model of the Mycobacterium tuberculosis host-pathogen interactome, consisting of 75 nodes corresponding to host and pathogen molecules, cells, cellular states or processes. Vaccination effects, clearance efficiencies due to drugs and growth rates have also been encoded in the model. The system is modelled as a Boolean network. Virtual deletion experiments, multiple parameter scans and analysis of the system's response to perturbations, indicate that disabling processes such as phagocytosis and phagolysosome fusion or cytokines such as TNF-alpha and IFN-gamma, greatly impaired bacterial clearance, while removing cytokines such as IL-10 alongside bacterial defence proteins such as SapM greatly favour clearance. Simulations indicate a high propensity of the pathogen to persist under different conditions.

Role of juvenile hormone in the synthesis and sequestration of vitellogenins in the red cotton stainer, Dysdercus koenigii (Heteroptera : Pyrrhocoridae)

Investigations were carried out to determine the role of juvenile hormone (JH) and 20-hydroxy ecdysone in the synthesis and uptake of vitellogenins, which were earlier identified, purified and characterised, in Dysdercus koenigii. The concentration(s) of vitellogenin(s) in fat body, haemolymph and that of vitellin(s) in ovary were significantly lower after chemical allatectomy at eclosion. In addition, at 70 h after emergence, chemical allatectomy reduced ovarian vitellin concentration, but vitellogenin levels remained normal in the fat body and haemolymph. The haemolymph vitellogenins were not incorporated into oocytes in such insects. Administration of JH-III at 20 h after allatectomy restored vitellogenin levels in the fat body and haemolymph, but the ovary failed to incorporate the available vitellogenins from haemolymph in such insects. However, when JH-III was administered twice, one at 20 h and then at 70 h after allatectomy, vitellogenin concentrations in fat body and haemolymph and also vitellin concentrations in ovary approached control levels. It is suggested that JH has two separate roles, one in vitellogenin synthesis and the other in uptake. 20-hydroxy ecdysone had no apparent role in either vitellogenin synthesis or uptake in D. koenigii. (C) 2000 Elsevier Science Inc. All rights reserved.

Interaction of 3-hydroxybenzoate-6-hydroxylase with cibacron blue

Cibacron blue is a potent inhibitor of 3-HBA-6-hydroxylase at a concentration < 1 mu M. Kinetic analyses revealed that at a concentration below 0.5 mu M the dye behaves as an uncompetitive inhibitor with respect to 3-HBA and competes with NADH for the same site on the enzyme. The alteration of the near-UV CD spectrum and quenching of the emission fluorescence of the enzyme by cibacron blue indicates a significant alteration in the environment of aromatic amino acid residues due to a stacking interaction and subtle conformatiodnal changes in the enzyme. The concentration-dependent quenching of the intrinsic fluorescence of the enzyme by cibacron blue was employed to determine the binding parameters such as association constant (K-a) and stoichiometry (r) for the enzyme-dye complex.

Characterization of foot-and-mouth disease virus types Ο and Asia 1 RNA

Foot-and-mouth disease is an acute and highly contagious febrile disease affecting cloven-footed animals. Identification of the foot-and-mouth disease virus (FMDV), the causative agent of the disease, posed problems because of the occurrence of many types and subtypes of the virus. A molecular approach based on oligonucleotide mapping of FMDV RNA has been used for the identification and characterization of virus isolates obtained in a disease outbreak (King et al., 1981). One-dimensional oligonucleotide mapping was used for rapid analysis of FMDV RNA (LaTorre et al., 1982). FMDV types Ο and Asia 1 of Indian origin are being routinely used for vaccine production in India. This report presents the differences between FMDV types Ο and Asia 1 at molecular level based on one-dimensional oligonucleotide mapping of virus-induced poly (A) RNA.

Role of external electron donor in methylene blue sensitized dichromated gelatin holograms:an experimental study

An experimental study to ascertain the role of external electron donor in methylene blue sensitized dichromated gelatin (MBDCG) holograms has been carried out. The required volume holographic transmission gratings in MBDCG have been recorded using 633-nm light from a He-Ne laser. Three well-known electron donors, namely, N, N-dimethylformamide (DMF); ethylenediaminetetraacetic acid (EDTA); triethanolamine (TEA), were used in this study. The variation of diffraction efficiency (η) as a function of light exposure (E) and concentration (C) of the electron donor under consideration was chosen as the figure of merit for judging the role of external electron donor in MBDCG holograms. A self-consistent analysis of the experimental results was carried out by recalling the various known facts about the photochemistry and the hologram formation in DSDCG and also DCG. The important findings and conclusions are as follows: (i) Each η vs E graph is a bell-shaped curve and its peak height is influenced in a characteristic manner by the external electron donor used. (ii) High diffraction efficiency/recording speed can be achieved in pure MBDCG holograms. (iii) The diffraction efficiency/recording speed achieved in electron donor sensitized MBDCG holograms did not show any significant improvement at all over that observed in pure MBDCG holograms. (iv) In electron donor sensitized MBDCG holograms, the electron donor used, depending on its type and concentration, appears to promote the process of cross-linking of gelatin molecules in a manner to either retain or deteriorate the refractive-index modulation achieved using pure MBDCG.

Methylene blue sensitized dichromated gelatin holograms: a study of their storage life and reprocessibility

The results of an experimental investigation on the storage life and reprocessibility of methylene blue sensitized dichromated gelatin (MBDCG) holograms are reported. The major conclusions of the investigation are: (i) Storage of MBDCG holograms in normal laboratory conditions for long periods is possible and it diminishes somewhat their diffraction efficiency. (ii) The results on short time storage and long time storage are almost similar, thus indicating that the diffraction efficiency can be stabilized through storage in a relatively short period of time. (iii) The deterioration in the diffraction efficiency on storage is less [D(eta) < 20%] for gratings of low/medium initial efficiency (eta < 70%) and it is more for gratings of high initial efficiency. (iv) About 65-95% restoration of the diffraction efficiency can be accomplished through reprocessing. (v) The restoration of diffraction efficiency is almost perfect [R(eta) > 80%] for gratings of low/medium initial efficiency (eta <75%) whereas it is rather imperfect for gratings having high initial efficiency.

Facile hydrothermal synthesis and observation of bubbled growth mechanism in nano-ribbons aggregated microspherical Covellite blue-phosphor

Well uniform microspheres of phase pure Covellite were synthesized through a simple hydrothermal approach using poly vinyl pyrrolidone (PVP) as surfactant. The micro-spheres were constituted of numerous self-organized knitted nano-ribbons of similar to 30 nm thickness. The effect of conc. PVP in the hydrothermal precursor solution on the product morphology was investigated. Based on the out-coming product micro-architecture a growth mechanism was proposed which emphasized bubbled nucleation inside the hydrothermal reactor. In a comparative study on linear optical properties, enhancement of luminescent intensity was observed for nano-ribbon clung microspheres rather than that of agglomerates of distorted particles, which may be attributed to better crystallinity as well as reduced surface defects and ionic vacancies for ribbon-like nano-structures.

Modelling studies on neurodegenerative disease causing triplet repeat sequences d(CGG/GCC) and d(CAG/CTG): Duplexes vs Quadruplexes

Model building and molecular mechanics studies have been carried out to examine the potential structures for d(GGC/GCC)5 and d(CAG/CTG)5 that might relate to their biological function and association with triplet repeat expansion diseases. Model building studies suggested that hairpin and quadruplex structures could be formed with these repeat sequences. Molecular mechanics studies have demonstrated that the hairpin and hairpin dimmer structures of triplet repeat sequences formed by looping out of the two strands are as favourable as the corresponding B-DNA type hetero duplex structures. Further, at high salt condition, Greek key type quadruplex structures are energetically comparable with hairpin dimer and B-DNA type duplex structures. All tetrads in the quadruplex structures are well stacked and provide favourable stacking energy values. Interestingly, in the energy minimized hairpin dimer and Greek key type quadruplex structures, all the bases even in the non-G tetrads are cyclically hydrogen bonded, even though the A, C and T-tetrads were not hydrogen bonded in the starting structures.