The formation of excimer and exciplex in the structural investigations of lipid vesicles: deuterium isotope effect

Origin of green photoluminescence in four-ring bent-core molecules with ESIPT, selective sensing of zinc ions by turn-on emission and their liquid crystal properties

Fluorescent four-ring symmetrical/unsymmetrical molecules containing alkyl chains of a varied number of –CH₂– groups with a bent-core have been synthesized to explore their liquid crystalline (LC) and photophysical properties.

Elucidating mechanisms of thermostabilization of poliovirus by D2O and MgCl2

To understand a significant reduction in the loss of poliovirus infectivity by D2O and a combination of D2O and MgCl2 at 37-45 degrees C, this paper attempts to elucidate the mechanisms underlying the thermostabilization of poliovirus. Three serotypes of Sabin oral poliovirus vaccine strains were investigated. Temperature-dependent fluorescence emission intensity studies showed that the effects of D2O and MgCl2 on the stability and conformation of poliovirus are correlated with those of the infectivity of poliovirus. Fluorescence steady-state polarization revealed that the conformation of poliovirus capsid is sensitive to D2O medium and MgCl2 salt, and that the rigidity of poliovirus conformation is increased in their presence. The exposure of poliovirus tryptophan residues to water is modified by D2O and MgCl2, as evidenced by changes in fluorescence emission intensity excited at 295 nm. The involvement of hydrogen bonding in the D2O effect was demonstrated by the greatly increased value of relative fluorescence intensity. Conformational alteration was also shown by changes in the positive band (193-230 nm) of circular dichroism spectra. D2O and MgCl2 were also found to reduce the interaction of virus with water as examined by differential scanning microcalorimetry, leading to a decline in the extent of water penetration into the poliovirus capsid. All these observations were found to be more profound in a combination of D2O with MgCl2 than D2O or MgCl2 alone. By inducing a conformation favorable to maintaining the poliovirus assembly and by reducing virus-water interaction to decrease water penetration into the poliovirus capsid, D2O, MgCl2, or D2O-MgCl2 is able to exert its thermostabilization effect. Thus, to maintain the virus assembly and conformation of the virus and to reduce the swelling of the virus capsid are key factors in increasing the thermostability of poliovirus. These two factors are mutually complementary. The latter can provide a favorable environment for the formers and the formers, in turn, lead to the latter.

Thermodynamic elucidation of solute-induced lipid interdigitation phase: lipid interactions with hydrophobic versus amphipathic species

Comparative thermodynamic studies on the interactions of aqueous dispersions of dipalmitoyl phosphatidylcholine (DPPC) bilayer vesicles with hydrophobic and amphipathic species were conducted to elucidate the nature of the solute-induced interdigitated lipid phase. Cyclohexanol, a strong hydrophobic species, lowers the temperature (tm) of the lipid main phase transition from the gel to the liquid-crystalline phase. Unlike ethanol (an amphipathic species), as reported previously, cyclohexanol does not exert a biphasic effect on tm (lowering tm at lower concentrations and raising tm at higher concentrations). At cyclohexanol greater than or equal to 15.4 mg/ml or 0.154 M, the thermogram of DPPC vesicles exhibits a small transition adjacent to the main phase transition but at a lower temperature. In contrast, ethanol does not promote such a small transition. Furthermore, the enthalpy (delta H) of the transition is increased in the presence of cyclohexanol. The sign of the enthalpy change (delta H-delta Ho) is positive and that of the free energy change (delta G-delta Go) is negative, a characteristic of solute-solute hydrophobic interaction. In contrast, DPPC bilayer vesicles exhibit both (delta H-delta Ho) and (delta G-delta Go) greater than 0 in the presence of ethanol in a concentration range where lipid vesicles exist in an interdigitated phase. To support the above distinct thermodynamic observations, fluorescence steady-state polarization (P) measurements were also performed. At the temperature below tm, the value of P decreases as cyclohexanol concentration increases, while a biphasic effect on P was found in the presence of ethanol. These findings support the postulation that the solute-induced interdigitated lipid phase requires the solute molecule to be amphipathic in nature.