Packing of phospholipid vesicles studied by oxygen quenching of Laurdan fluorescence

Steady-state fluorescence oxygen quenching experiments were performed on phospholipid vesicles where 2-dimethylamino-6-lauroylnaphthalene (Laurdan) was inserted. The quenching efficiency was found to be much higher in vesicles in the liquid-crystalline phase with respect to the gel phase, by a factor of about 50. Since the oxygen solubility in the two phospholipid phases can differ at most by a factor of 4 based on literature values, we concluded that oxygen diffusion must be responsible for the great difference in the quenching efficiency. A relatively high quenching efficiency was also found in vesicles composed of equimolar gel and liquid-crystalline phospholipids. Simulations were performed using the linear superposition of the properties of the pure phases to demonstrate that, in the case of vesicles composed of coexisting phases, the diffusional properties of oxygen in each phase are largely modified by the presence of the other. The addition of 10 mol% cholesterol to the gel phase rendered Laurdan fluorescence approximately as quenchable as in the equimolar mixture of the two phases. This result points out that molecules such as cholesterol, which introduce packing defects in the bilayer, favor oxygen diffusion. From the oxygen quenching experiments and using the properties of generalized polarization, the rate of Laurdan dipolar relaxation can be estimated.Abbreviations used Laudran 2-dimethylamino-6-lauroylnapthalene - DLPC dilauroylphosphatidylcholine - DMPC dimyristoylphosphatidylcholine - DPH 1,6-diphenyl-1,3,5-hexatriene - DPPC dipalmitoylphosphatidylcholine - TNS p-tofuidinyl-6-naphthalene sulfonic acid - PBS phosphate-buffered saline solution - GP generalized polarization - NMR nuclear magnetic resonance - EPR electron paramagnetic resonance     

Aryl sulfoxide radical cations. Generation, spectral properties, and theoretical calculations

Aromatic sulfoxide radical cations have been generated by pulse radiolysis and laser flash photolysis techniques. In water (pulse radiolysis) the radical cations showed an intense absorption band in the UV region (ca. 300 nm) and a broad less intense band in the visible region (from 500 to 1000 nm) whose position depends on the nature of the ring substituent. At very low pulse energy, the radical cations decayed by first-order kinetics, the decay rate increasing as the pH increases. It is suggested that the decay involves a nucleophilic attack of H(2)O or OH(-) (in basic solutions) to the positively charged sulfur atom to give the radical ArSO(OH)CH(3)(*). By sensitized [N-methylquinolinium tetrafluoborate (NMQ(+))] laser flash photolysis (LFP) the aromatic sulfoxide radical cations were generated in acetonitrile. In these experiments, however, only the band of the radical cation in the visible region could be observed, the UV band being covered by the UV absorption of NMQ(+). The lambda(max) values of the bands in the visible region resulted almost identical to those observed in water for the same radical cations. In the LFP experiments the sulfoxide radical cations decayed by second-order kinetics at a diffusion-controlled rate, and the decay is attributed to the back electron transfer between the radical cation and NMQ(*). DFT calculations were also carried out for a number of 4-X ring substituted (X = H, Me, Br, OMe, CN) aromatic sulfoxide radical cations (and their neutral parents). In all radical cations, the conformation with the S-O bond almost coplanar with the aromatic ring is the only one corresponding to the energy minimum. The maximum of energy corresponds to the conformation where the S-O bond is perpendicular to the aromatic ring. The rotational energy barriers are not very high, ranging from 3.9 to 6.9 kcal/mol. In all radical cations, the major fraction of charge and spin density is localized on the SOMe group. However, a substantial delocalization of charge and spin on the ring (almost 50% for the 4-methoxy derivative and around 30% for the other radical cations) is also observed. This suggests some conjugative interaction between the MeSO group and the aromatic system that may become very significant when a strong electron donating substituent like the MeO group is present. The ionization energies (IE) of the 4-X ring substituted neutral aromatic sulfoxides were also calculated, which were found to satisfactorily correlate with the experimental E(p) potentials measured by cyclic voltammetry.     

Structural and electronic characterization of the complexes obtained by the interaction between bare and hydrated first-row transition-metal ions (Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+)) and glycine

The complexes formed by the simplest amino acid, glycine, with different bare and hydrated metal ions (Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+)) were studied in the gas phase and in solvent in order to give better insight into the field of the metal ion-biological ligand interactions. The effects of the size and charge of each cation on the organization of the surrounding water molecules were analyzed. Results in the gas phase showed that the zwitterion of glycine is the form present in the most stable complexes of all ions and that it usually gives rise to an eta(2)O,O coordination type. After the addition of solvation sphere, a resulting octahedral arrangement was found around Ni(2+), Co(2+), and Fe(2+), ions in their high-spin states, whereas the bipyramidal-trigonal (Mn(2+) and Zn(2+)) or square-pyramidal (Cu(2+)) geometries were observed for the other metal species, according to glycine behaves as bi- or monodentate ligand. Despite the fact that the zwitterionic structure is in the ground conformation in solution, its complexes in water are less stable than those obtained from the canonical form. Binding energy values decrease in the order Cu(2+) > Ni(2+) > Zn(2+) approximately Co(2+) > Fe(2+) > Mn(2+) and Cu(2+) > Ni(2+) > Mn(2+) approximately Zn(2+) > Fe(2+) > Co(2+) for M(2+)-Gly and Gly-M(2+) (H(2)O)(n) complexes, respectively. The nature of the metal ion-ligand bonds was examined by using natural bond order and charge decomposition analyses.     

Mass spectrometry strategies applied to the characterization of proline-rich peptides from secretory parotid granules of pig (Sus scrofa)

Basic proline-rich proteins (bPRPs) are a class of proteins widely present in saliva of humans and other mammals. They are synthesized as preproproteins and enzymatically cleaved into small peptides before secretion from the salivary glands. Recently, we characterized two proline-rich peptides (SP-A and SP-B) in parotid secretory granules of pig (Sus Scrofa) that are derived from three isoforms of a PRP proprotein (Swiss-Prot data bank: Q95JC9-1, Q95JC9-2 and Q95JC9-3). Together the coding regions for SP-A and SP-B, which are repeated many times, account for 52-70% of the coding regions of the PRP proproteins. This study was undertaken to identify peptides encoded by unassigned regions of the PRP proproteins. RP-HPLC-ESI-IT-MS analysis of enriched granule preparations from pig parotid glands by two different analytical strategies identified ten new proline-rich peptides derived from the three proproteins. Together with the coding regions for SP-A and SP-B already identified it was possible to assign 68-75% of the proproteins coding regions. The peptide sequences indicated a number of unusual proteolytic cleavage sites suggesting the presence of unknown proprotein convertases.     

Eigenvalue estimates and critical temperature in zero fields for enhanced surface superconductivity

We derive estimates for the principal eigenvalue of the boundary value problem in Ω, on ∂Ω, with α > 0 and a bounded domain. In the context of superconductivity, our results show the increase of the critical temperature in zero fields for systems with enhanced surface superconductivity. In term of long time behavior of a Brownian motion with creation of particles at the boundary, our study gives estimates for the expected number of particles inside the domain. Tiziana Giorgi: Funding to this author was provided by the National Science Foundation-funded ADVANCE Institutional Transformation Program at NMSU, fund # NSF0123690     

Endocannabinoids and related compounds: walking back and forth between plant natural products and animal physiology

Cannabis sativa has been known, used, and misused by mankind for centuries, and yet only over the last two decades has research stemming from the chemical constituents specific to this plant, the cannabinoids, started to provide fundamental insights into animal physiology and pathology, resulting in the development of new therapeutics. The discovery of the endocannabinoid system, and its targeting with two new pharmaceutical preparations now on the market in several countries, represent the most recent example of how studies on medicinal plants and on the mechanism of their biological effects can reveal, through a chain of breakthroughs, new systems of endogenous signals and physiological phenomena that can become the source of novel strategies for unmet therapeutic challenges.     

Design, synthesis and anti flaviviridae activity of N(6)-, 5',3'-O- and 5',2'-O-substituted adenine nucleoside analogs

During a random screening of representative libraries of nucleoside analogues we discovered that the adenine derivatives FEVB28 and FEG118 were Flaviviridae inhibitors endowed with potency comparable, if not superior, to that of ribavirin. Those studies prompted us to design a new class of protected nucleoside analogs, reported herein, which displays interesting anti-bovine viral diarrhea virus (BVDV) activity and low cytotoxicity in cell-based assays (4, 23, 29 EC(50): 14, 11, 26 microM respectively, CC(50)>100 microM) and appreciable activity in enzyme assays against the RNA dependent RNA polymerase (RdRp) of BVDV (4, 23, 29, RdRp inhibition activity 27, 16, 15 microM respectively). A molecular modeling study was also carried out to highlight the possible interactions between this compounds class and the corresponding hepatitis C virus (HCV) enzyme.     

Structural characterization of triorganotin(IV) complexes with sodium fusidate and DFT calculations

Three new complexes of the steroid sodium fusidate (sodium 2-[(1S,2S,5R,6S,7S,10S,11S,13S, 14Z,15R,17R)-13-(acetyloxy)-5,17-dihydroxy-2,6,10,11-tetramethyl tetracyclo[8.7.0.0^2,7.0^11,15] heptadecan-14-ylidene]-6-methylhept-5-enoate = (NaFusidate, NaFA)]), with triorganotin(IV) moieties have been prepared and investigated by conventional techniques as FTIR, Mössbauer, ESI-MS and NMR spectroscopy. The isolated compounds showed stoichiometries organotin(IV)/fusidate 1/1, R₃Sn(IV)FA (R = Me, FA1; Bu, FA2; Ph, FA3). The ligand coordination sites were determined by FTIR spectroscopic measurements. In the complexes, the carboxylate group of the fusidate ligand behaves as monodentate monoanionic donor, binding the Sn(IV) through one oxygen atom.On the basis of C-Sn-O_COO angles, calculated through the rationalization of the ¹¹⁹Sn Mössbauer parameter nuclear quadrupole splitting, it has been confirmed that, in all the solid state complexes, the Sn(IV) was tetracoordinated in a distorted tetrahedral structure.Further data from ¹¹⁹Sn CP-MAS spectra confirmed the distorted tetrahedral arrangement.In MeOH solution, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy showed monomeric complexes, where the carboxylate group mainly acts as monodentate ester-type ligand, and the occurrence of a coordinated solvent molecule to the tin center, as validated by non-relativistic NMR DFT study.     

Steady-state and laser flash photolysis study of the carbon-carbon bond fragmentation reactions of 2-arylsulfanyl alcohol radical cations

The N-methylquinolinium tetrafluoroborate (NMQ(+))-sensitized photolysis of the erythro-1,2-diphenyl-2-arylsulfanylethanols 1-3 (1, aryl = phenyl; 2, aryl = 4-methylphenyl; 3, aryl = 3-chlorophenyl) has been investigated in MeCN, under laser flash and steady-state photolysis. Under laser irradiation, the formation of sulfide radical cations of 1-3, in the monomeric (lambda(max) = 520-540 nm) and dimeric form (lambda(max) = 720-->800 nm), was observed within the laser pulse. The radical cations decayed by first-order kinetics, and under nitrogen, the formation of ArSCH(*)Ph (lambda(max) = 350-360 nm) was clearly observed. This indicates that the decay of the radical cation is due to a fragmentation process involving the heterolytic C-C bond cleavage, a conclusion fully confirmed by steady-state photolysis experiments (formation of benzaldehyde and the dimer of the alpha-arylsulfanyl carbon radical). Whereas the fragmentation rate decreases as the C-C bond dissociation energy (BDE) increases, no rate change was observed by the replacement of OH by OD in the sulfide radical cation (k(OH)/k(OD) = 1). This suggests a transition state structure with partial C-C bond cleavage where the main effect of the OH group is the stabilization of the transition state by hydrogen bonding with the solvent. The fragmentation rate of 2-hydroxy sulfanyl radical cations turned out to be significantly slower than that of nitrogen analogues of comparable reduction potential, probably due to a more efficient overlap between the SOMO in the heteroatom and the C-C bond sigma-orbital in the second case. The fragmentation rates of 1(+*)-3(+*) were found to increase by addition of a pyridine, and plots of k(base) against base strength were linear, allowing calculation of the beta Bronsted values, which were found to increase as the reduction potential of the radical cation decreases, beta = 0.21 (3(+*)), 0.34 (1(+*)), and 0.48 (2(+*)). The reactions of 1(+*) exhibit a deuterium kinetic isotope effect with values that increase as the base strength increases: k(OH)/k(OD) = 1.3 (pyridine), 1.9 (4-ethylpyridine), and 2.3 (4-methoxypyridine). This finding and the observation that with the above three bases the rate decreases in the order 3(+*) > 1(+*) > 2(+*), i.e., as the C-C BDE increases, suggest that C-C and O-H bond cleavages are concerted but not synchronous, with the role of OH bond breaking increasing as the base becomes stronger (variable transition state). It is probable that, with the much stronger base, 4-(dimethylamino)pyridine, a change to a stepwise mechanism may occur where the slow step is the formation of a radical zwitterion that then rapidly fragmentates to products.