Pressure dependence of the Davydov splitting in tetracene single crystals

The reflection spectrum of the OO component of the first singlet transition of tetracene single crystal has been measured as a function of pressure in the range 1 atm–6.5 kbar. A discontinuous change in the Davydov splitting occurs near 3 kbar confirming the existence of a pressure-induced first order phase transition discovered recently by measurements of the magnetic field anisotropy in the single crystal tetracene fluorescence. The pressure-induced spectral red-shifts are larger in the low-pressure (LP) phase than those in the high-pressure (HP) crystal structure. The Davydov splitting of the OO band however increases with increasing pressure at a larger rate of 57 cm^?1/kbar for the HP phase as compared with 46 cm^?1/kbar for the LP phase.     

A novel synthesis of racemic and enantiomeric forms of prostaglandin B1 methyl ester

3-(Dimethoxyphosphorylmethyl)cyclopent-2-enone was converted into (+/-)-prostaglandin B1 methyl ester in two steps involving regioselective alkylation at C(2) with methyl 7-iodoheptanoate and subsequent Horner-Wittig reaction with dimer of 2-hydroxyheptanal (42% overall yield). The use of (R)- and (S)-2-(tert-butyldimethylsilyloxy)heptanal for the Horner olefination reaction gave, after deprotection of the hydroxy group, the enantiopure forms of the title compound in 28% overall yield.     

Surface Aggregation of Candida albicans on Glass in the Absence and Presence of Adhering Streptococcus gordonii in a Parallel-Plate Flow Chamber: A Surface Thermodynamical Analysis Based on Acid-Base Interactions

Adhesive interactions between yeasts and bacteria are important in the maintenance of infectious mixed biofilms on natural and biomaterial surfaces in the human body. In this study, the extended DLVO (Derjaguin-Landau-Verwey-Overbeek) approach has been applied to explain adhesive interactions between C. albicans ATCC 10261 and S. gordonii NCTC 7869 adhering on glass. Contact angles with different liquids and the zeta potentials of both the yeasts and bacteria were determined and their adhesive interactions were measured in a parallel-plate flow chamber.Streptococci were first allowed to adhere to the bottom glass plate of the flow chamber to different seeding densities, and subsequently deposition of yeasts was monitored with an image analysis system, yielding the degree of initial surface aggregation of the adhering yeasts and their spatial arrangement in a stationary end point. Irrespective of growth temperature, the yeast cells appeared uncharged in TNMC buffer, but yeasts grown at 37 degrees C were intrinsically more hydrophilic and had an increased electron-donating character than cells grown at 30 degrees C. All yeasts showed surface aggregation due to attractive Lifshitz-van der Waals forces. In addition, acid-base interactions between yeasts, yeasts and the glass substratum, and yeasts and the streptococci were attractive for yeasts grown at 30 degrees C, but yeasts grown at 37 degrees C only had favorable acid-base interactions with the bacteria, explaining the positive relationship between the surface coverage of the glass by streptococci and the surface aggregation of the yeasts. Copyright 1999 Academic Press.     

Anion driven ionic liquid crystals: The effect of the connecting group in [closo-1-CB9H10]- derivatives on mesogenic properties

Replacement of the connecting CH₂ group in ionic liquid crystal 1a[Pyr] with an oxygen atom in 1b[Pyr] resulted in significant destabilisation of the nematic and, to a greater extent, smectic A (SmA) phases, as established from binary mixture studies in 2a[Pyr]. Density functional theory (DFT) modelling of both anions suggests that the destabilisation results from the difference in charge distribution rather than conformational changes. Binary mixture studies demonstrated that all three ionic liquid crystals are compatible with a non-ionic benzoate nematic host 3a.     

Flow-through partial-filling affinity capillary electrophoresis using a crossreactive antibody for enantiomeric separations

It is demonstrated that the separation of diastereoisomers and enantiomers can be accomplished by the flow-through partial-filling affinity CE using a crossreactive mAb. This approach revealed differences in the binding strength of the (+/-)-cis- and (+/-)-trans-benzo[a]pyrene tetrols with the anti-polycyclic aromatic hydrocarbon mAb and demonstrated that (+)-enantiomers are more strongly immunocomplexed than their (-)-counterparts. It is proposed that crossreactive monoclonal antibodies (i.e. mAb raised against achiral molecule and possessing limited selectivity) could be effectively utilized for specific stereoisomeric differentiation and chiral separations.     

High resolution spectral differentiation of enantiomers: benzo[a]pyrene tetrols complexed with a promiscuous antibody

The interaction of the highly cross-reactive anti-PAH monoclonal antibody with four diastereomeric benzo[a]pyrene tetrols (BPTs) is studied by means of fluorescence line-narrowing spectroscopy. It is shown that the interaction of enantiomers of cis-BPT and trans-BPT with the antibody involves different complex geometries. These spatially different ligand-protein interactions alter the relative intensities of the excited-state vibrational frequencies of immunocomplexed molecules allowing for unambiguous spectroscopic resolution of all four enantiomeric isomers. This study represents the first example of a high-resolution, fluorescence-based spectroscopic method capable of enantiospecific differentiation.     

Nonphotochemical hole-burning study of selectively stained normal and cancerous human ovarian tissues

Results are presented of nonphotochemical hole-burning (HB) experiments on cancerous ovarian and analogous normal peritoneal in vitro tissues stained with the mitochondrial-selective dye rhodamine 800. A comparison of fluorescence excitation spectra, hole-growth kinetics data, and external electric field (Stark) effects on the shape of spectral holes burned in cancerous and normal tissues stained with rhodamine 800 revealed significant differences only in the dipole moment change (fDeltamu) measured by a combination of HB and Stark spectroscopies. It is shown that the permanent dipole moment change for the S0--> S1 transition of the rhodamine 800 molecules in cancerous tissue is higher than that of normal tissue by a factor of about 1.4. The finding is similar to the HB results obtained earlier for human ovarian surface epithelial cell lines, i.e., OV167 carcinoma and OSE(tsT)-14 normal cells stained with the same mitochondria-specific dye (Walsh et al. Biophys. J. 2003, 84, 1299). We propose that the observed difference in the permanent dipole moment change in cancerous ovarian tissue is related to a modification in mitochondrial membrane potential.     

Temperature dependence of hole growth kinetics in aluminum-phthalocyanine-tetrasulfonate in hyperquenched glassy water

The temperature (T) dependence of hole growth kinetics (HGK) data that span more than four decades of burn fluence are reported for aluminum-phthalocyanine tetrasulfonate (APT) in fresh and annealed hyperquenched glassy water (HGW) for temperatures between 5 and 20 K. The highly dispersive HGK data are modeled by using the "master" equation based on the two level system (TLS) model described in 2000 by Reinot and Small [J. Chem. Phys. 2000, 113, 10207]. We have demonstrated that thermal line broadening is not enough to account for temperature-dependent HGK for temperatures greater than 10 K. To overcome the discrepancy, the hole growth model must account for thermal hole filling (THF) processes. For the first time, the "master" equation used for HGK simulations is modified to take into account both the temperature dependence of the (single site) absorption spectrum and THF processes, effectively turning off those TLS which do not participate in the hole burning process at higher temperatures. A single set of parameters, some of which were determined directly from the hole spectra, was found to provide satisfactory fits to the HGK data for APT in fresh and annealed HGW for holes burned in the 679.7-676.9 nm range from the high to low energy sides of the Qx absorption band. Furthermore, we propose that HGK modeling at high burn fluences requires that the TLS model be further modified to take into account the existence of extrinsic multiple level systems.     

High-spin structure of yrast-band in 78Kr

Lifetime of levels up to 22⁺, have been measured in ⁷⁸Kr and an oblate shape is assigned to the ground state using the CSM and the configuration dependent shell correction calculations. Calculations further show that ⁷⁸Kr is highly γ-soft nucleus. The experimental Q _t values coupled with theoretical calculations indicate an oblate shape for ⁷⁸Kr at low spins and triaxial shape at higher spins     

Structure of 72,74Se at high spin

Lifetimes of high spin states up to { }=22⁺ in the yrast positive parity bands have been measured to investigate the shape evolution with increasing spin in ^{72, 74}Se. The Q _t values derived from these measurements indicate that prolate shape stabilizes for ⁷²Se, while a triaxial shape develops for ⁷⁴Se at higher spins. Comparison of the observed trend in Q _t with spin for ^{72, 74}Se with that of the corresponding kryptones isotones emphasizes the stability provided by N=38 prolate shell gap even at high rotational frequency.