Capillary electrophoretic and nuclear magnetic resonance studies of interactions between halophenols and ionic liquid or tetraalkylammonium cations.

Aqueous capillary electrophoretic studies were performed to investigate interactions between halophenols and 1-ethyl-3-methylimidazolium tetrafluoroborate or tetraethylammonium tetrafluoroborate electrolytes. In both cases, increased halogen size correlated with increased affinity for the electrolyte cation. For isomers, the ortho substituted isomer exhibited higher affinity than the para isomer. Irreproducible CE results for analyte pairs in the presence of the ionic liquid stimulated investigations of the interactions between halophenols as well as with the cations of the electrolyte. These interactions were explored by proton and fluorine one-dimensional NMR. The NMR results indicated differences in the interactions between tetraethylammonium/iodophenols and imidazolium/iodophenols. The NMR results indicate hydrophobic stacking interactions between the iodophenols and possible similar interaction among phenols and imidazolium.

Pneumocysterol [(24Z)-ethylidenelanost-8-en-3beta-ol], a rare sterol detected in the opportunistic pathogen Pneumocystis carinii hominis: structural identity and chemical synthesis.

Pneumocystis carinii pneumonia (PcP) remains among the most prevalent opportunistic infections among AIDS patients. Currently, drugs used clinically for deep mycosis act by binding ergosterol or disrupting its biosynthesis. Although classified as a fungus, P. carinii lacks ergosterol. Instead, the pathogen synthesizes a number of distinct Delta7, 24-alkylsterols, despite the abundance of cholesterol, which it can scavenge from the lung alveolus. Thus, the pathogen-specific sterols appear vital for organism survival and proliferation. In the present study, high concentrations of a C32 sterol were found in human-derived P. carinii hominis. The definitive structural identities of two C-24 alkylated lanosterol compounds, previously not reported for rat-derived P. carinii carinii, were determined by using GLC, MS, and NMR spectroscopy together with the chemical syntheses of authentic standards. The C31 and C32 sterols were identified as euphorbol (24-methylenelanost-8-en-3beta-ol) and pneumocysterol [(24Z)-ethylidenelanost-8-en-3beta-ol], respectively. The identification of these and other 24-alkylsterols in P. carinii hominis suggests that (i) sterol C-24 methyltransferase activities are extraordinarily high in this organism, (ii) 24-alkylsterols are important components of the pathogen's membranes, because the addition of these side groups onto the sterol side chain requires substantial ATP equivalents, and (iii) the inefficacy of azole drugs against P. carinii can be explained by the ability of this organism to form 24-alkysterols before demethylation of the lanosterol nucleus. Because mammals cannot form 24-alkylsterols, their biosyntheses in P. carinii are attractive targets for the development of chemotherapeutic strategies against this opportunistic infection.

Characterization of a GM1-dependent surface interaction for alcohol with DPPC membranes.

A unique surface interaction for perdeuterated ethanol and 1-butanol with dipalmitoylphosphatidylcholine (DPPC)/monosialoganglioside (GM1) multilamellar vesicles can be detected from the fast exchange averaging of the nuclear quadrupole coupling constant of the alcohol in the free and bound states using deuterium NMR. At 1.0% perdeuterated ethanol or 0.5% perdeuterated 1-butanol, a small splitting of the alcohol resonance(s) was detected in the liquid-crystalline phase, but not in the gel phase of the bilayer. The observed splitting is proportional to the fraction of alcohol bound and is dependent on temperature, alcohol, and GM1 concentrations. The splitting was only observed in the presence of negatively charged GM1 but not neutral asialoganglioside (asialo-GM1) in DPPC multilamellar vesicles. The observed splitting decreased with the addition of Ca2+ or Mg2+ ions. This effect was reversed upon the addition of chelating agents. It is proposed that the unique surface interaction for alcohol may result from small surface perturbations of the phosphatidylcholine head groups by the negatively charged sialic moieties of neighboring GM1 molecules in the bilayer.

Ethanol disordering of GM1-enriched short-sleep synaptosomal plasma membranes.

The Long-Sleep (LS) and Short-Sleep (SS) mouse synaptosomal plasma membranes differ in ethanol sensitivity at superficial membrane regions, which corresponds with the behavioral response of the mice to ethanol hypnosis. The only significant difference between these synaptosomal plasma membranes is the synaptosomal monosialoganglioside (GM1) content, LS > SS. Here, GM1 was examined as a parameter for increasing membrane sensitivity to ethanol effects in the ethanol-resistant SS membranes. Synaptosomal plasma membranes from SS mice were allowed to incorporate exogenous GM1. Membrane order was then studied at the surface, intermediate, and interior regions of the membranes by delayed Fourier transform proton NMR in the presence and absence of perdeuterated ethanol. Differences in membrane order were observed in all three membrane regions with increasing perdeuterated ethanol concentrations depending on the synaptosomal GM1 content.

Synaptic plasma membrane structure and polarity of long-sleep and short-sleep mice.

Membrane dielectric as a primary basis for effects of ethanol was examined in synaptic plasma membranes (SPM) of genetically selected ethanol-sensitive long-sleep (LS) and ethanol-resistant short-sleep (SS) mice. Multifrequency phase and modulation of fluorometry of diphenylhexatriene (DPH) was used to resolve structural and dielectric differences in the membrane interior core. Fluorescence spectral peak ratios, fluorescence lifetime analysis, and initial rates of photoreaction of DPH in SPM provided sensitive measures of SPM interior core dielectric properties. The membrane microenvironment sensed by DPH was more polar in SPM from SS mice than in SPM from LS mice. Physiological concentrations of ethanol in vitro (25-75 mM) increased the SPM interior core dielectric and potentiated photoreaction of DPH with other membrane components of SPM from LS, but not SS, mice. These effects of ethanol in vitro were maximal by 75 mM ethanol and/or exacerbated at higher ethanol. In addition, ethanol in vitro increased the fraction of DPH associated with photoreaction products with lipids from SPM of ethanol-sensitive LS mice. The data were consistent with ethanol in vitro increasing the polar molecules (ethanol and/or water) of SPM from LS but not SS mice. It is suggested that ethanol alters the polarity and increases reactivity of the interior core lipid-protein interface.

pH homeostasis in Leishmania donovani amastigotes and promastigotes.

Intracellular pH and pH gradients of Leishmania donovani amastigotes and promastigotes were determined over a broad range of extracellular pH values. Intracellular pH was determined by 31P NMR and by equilibrium distribution studies with 5,5-dimethyloxazolidine-2,4-dione or methylamine. Promastigotes maintain intracellular pH values close to neutral between extracellular pH values of 5.0 and 7.4. Amastigote intracellular pH is maintained close to neutral at external pH values as low as 4.0. Both life stages maintain a positive pH gradient to an extracellular pH of 7.4, which is important for active transport of substrates. Treatment with ionophores, such as nigericin and carbonyl cyanide m-chlorophenylhydrazone and the ATPase inhibitor dicyclohexylcarbodiimide, reduced pH gradients in both stages. Maintenance of intracellular pH in the physiologic range is especially relevant for the survival of the amastigote in its acidic in vivo environment.

Ethanol-induced changes in neuronal membrane order. An NMR study.

The effects of ethanol-d6 on the lipid matrix of rat brain neuronal membranes were investigated by delayed Fourier transform 1H-NMR techniques. At 24 degrees C, neither 0.1 nor 0.2% (v/v) ethanol-d6 measurably affected the methylene resonance intensity. However, 0.4 and 1.0% ethanol-d6 increased resonance intensity, 35 and 51%, respectively. With increasing temperature, a decrease in resonance intensity for 0.1% ethanol-d6 was observed reaching a maximum of 20% at 42 degrees C. Furthermore, increasing temperature attenuated the increases in resonance intensity seen with 0.4 and 1.0% ethanol-d6. At 24 degrees C, no concentration of ethanol-d6 had a significant effect on the choline methyl resonance. However, with increasing temperature both 0.1 and 0.2% ethanol-d6 decreased this resonance's intensity. The intensity of the terminal methyl resonance was increased in a dose related fashion by ethanol-d6, reaching a maximum of +41% at 1.0% (24 degrees C). Increasing temperature attenuated this effect, but no concentration of ethanol-d6 significantly decreased resonance intensity. The increases and decreases in resonance intensity induced by ethanol-d6 are interpreted in terms of a decrease and an increase in membrane order, respectively. It is proposed that ethanol-d6 exerts two effects on neuronal membranes, an ordering effect on the membrane surface and a disordering effect in the membrane interior. A higher enthalpy of ethanol binding to the surface as compared to the interior of the membrane leads to an attenuation of the ethanol disordering effect with increasing temperature.

Cyanogen-induced gamma-glutamyl to imidazole cross-link in carbonic anhydrase. A unique mode of inhibition.

The irreversible inhibition of carbonic anhydrase by cyanogen occurs by a unique mechanism. Cyanogen is an affinity label: it behaves like a carbodiimide and produces an intra-molecular cross-link without being incorporated. The nucleophile-labile cross-link is formed between a gamma-COOH of a Glu and an imidazole of a His with a 1:1:1 stoichiometry with the enzyme. The deletion of approximately 1 Glu and approximately 1 His was noted by amino acid analysis of enzymatically hydrolyzed carbonic anhydrase. The modified Glu was converted to 2,4-diaminobutanoic acid and quantitated by amino acid analysis. The presence and quantity of modified His was supported through high-resolution proton NMR analysis.

1H-NMR spectra of rat synaptic plasma membranes: effect of temperature and comparison with fluorescence polarization.

1H-NMR spectra of rat synaptic plasma membranes obtained over the temperature range of 24-46 degrees C are presented. The data illustrate that a transition occurs from a more ordered to less ordered state at approximately 37 degrees C. This phenomenon was not related to using D2O as the solvent and was replicated, although with less sensitivity, using fluorescence polarization methodology.

Determination of ethanol partition coefficients to the interior and the surface of dipalmityl-phosphatidylcholine liposomes using deuterium nuclear magnetic resonance spectroscopy.

The binding of ethanol-d6 to dipalmityl-phosphatidylcholine liposomes (DPPC) can be separated into two processes, namely, ethanol in the bilayer and on the surface of the bilayer. For the deuterons of the methylene group, the T2 of both bound states is shorter than the respective preexchange lifetime (tau beta) and therefore the amount of ethanol bound to both sites can be determined from the decrease in the methylene intensity resonance in the presence of DPPC. For the methyl resonance, however, only the T2 of deuterons on ethanol bound to the surface is less than its tau beta and the amount of surface bound ethanol-d6 can be determined. Subtraction yields the amount of ethanol bound within the bilayer. The partition coefficient for internally bound ethanol remains constant from 0 to 3.5 m ethanol. Surface binding is, however, highly cooperative.

Detection of a bulk water structure related conformational change in horse heart cytochrome c in Cl- -H2O solutions utilizing spectrofluoroelectrochemical techniques.

Utilizing the ratio of the fluorescence intensities of the reduced and oxidized forms of horse heart cytochrome c (cyt c), it is possible to monitor conformational changes of the protein upon reduction. The temperature dependence from 25 to 50 degrees C of the ratio is sigmoidal in nature, indicative of a conformational transition with the midpoint being 43 degrees C in 0.10 M NaCl, 0.10 M PO4 buffer, pH 7.0, solution. This transition is consistent with the previously postulated biphasic model used to explain the nonlinearity in E0' vs T in Cl- -H2O solutions [C.W. Anderson, H.B. Halsall , W.R. Heineman , and G.P. Kreishman (1977) Biochem. Biophys. Res. Commun. 76, 339-344]. In addition, the chemical shift of the bulk water proton in tetramethylammonium chloride solution shows a nonlinearity at 42 degrees C and it is postulated that the conformational changes of cyt c are the result of the behavior of the bulk water structure.

Determination of the formal reduction potential, the electron stoichiometry, and the magnitude of the conformational change upon reduction for cytochrome c from potential-dependent fluorescence spectra.

A long-optical-path electrochemical cell was used to determine the formal reduction potential (E0') and the electron stoichiometry (n) for 1 microM horse heart cytochrome c solutions from Nernst plots of the fluorescence spectrum of the tryptophan-59. Various concentration ratios of the oxidized to the reduced forms of the protein were generated by application of different potentials. The fluorescence spectrum was found to decrease with increasing concentrations of reduced cytochrome c. This decrease is interpreted in terms of a movement of the tryptophan toward the heme upon reduction, resulting in an increase in the rate of energy transfer to the heme. The magnitude of the conformational change is compared for cytochrome c in NaCl-H2O and NaBr-H2O solutions with the latter being larger.

The salt-induced destacking of purine in aqueous NaCl systems and its implications on life at elevated temperatures.

Aqueous purine solutions in the absence and presence of NaCl have been studied by vapor-pressure osmometry and high-resolution proton-magnetic-resonance spectroscopy. The presence of NaCl causes a marked change in the temperature dependence of the molal osmotic coefficient and the chemical shift of the purine resonances when compared with the corresponding quantities in purine solutions containing no added salt. In the absence of salt, the destacking of the purine is gradual as the temperature is increased, whereas there is a sharp decrease in purine stacking at approximately 42 degrees C in the presence of NaCl. This salt-induced destacking of purine is consistent with the previously noted salt-induced bulk water destructuring at temperatures above approximately 42 degrees C. This effect has been deduced from considerations of species profiles in acid-water systems as a function of temperature (Leifer, L., and Inoue, K., manuscript in preparation). The implications of this phenomenon on biological systems at elevated temperatures will be discussed.