Synthesis and characterization of zinc sensors based on a monosubstituted fluorescein platform

The synthesis of a new fluorescein carboxaldehyde asymmetrically substituted on the xanthene (top) ring is reported. This molecule is a key precursor for two of three monofunctionally derivatized fluorescein-based Zn(II) sensors presented in this work. Detailed preparative routes to, and photophysical characterization of, these sensors are described. The sensors are based on the previously reported ZP4 motif (Burdette, S. C.; Frederickson, C. J.; Bu, W.; Lippard, S. J. J. Am. Chem. Soc. 2003, 125, 1778-1787) and incorporate a di(2-picolyl)amine-containing aniline-derivatized ligand framework. By varying the nature of the substituent (X) para to the aniline nitrogen atom, which is responsible for PET quenching of the unbound ZP dye, we investigated the extent to which such electronic tuning might improve the fluorescent properties of asymmetrical ZP sensors. Although a comparison of probes with X = H, F, Cl, OMe reveals that the photophysical behavior of these dyes is not readily predictable, our methodology illustrates the ease with which aniline-based ligands may be linked to fluorescein dyes.     

Rapid separation of antimicrobial metabolites by microchip electrophoresis with UV linear imaging detection

This research examines microchip electrophoresis with linear imaging UV detection for the analysis of antimicrobial metabolites, monoacetylphloroglucinol (MAPG) and 2,4-diacetylphloroglucinol (2,4-DAPG) from Pseudomonas fluorescens F113. Initial results show the separation of MAPG, 2,4-DAPG and resorcinol in less than 20 s. This was achieved using a quartz microchip with a separation channel length of 25 mm. In order to quantitate the amount of MAPG and 2,4-DAPG in a microbial cultured supernatant sample, on-chip sample introduction in a methanol/buffer matrix was investigated. Sample introduction/injection parameters were optimized to improve sensitivity and thus decrease the limit of detection (LOD). The amount of antimicrobial metabolites present was quantitated with a separation time of 15 s. A previously developed capillary electrophoretic method was compared to the microchip method in relation to speed, efficiency, precision, linear range and limit of detection. This investigation shows the fastest separation so far of these antimicrobial metabolites with high efficiency.     

RELATIONSHIP BETWEEN SURVIVAL, PHOTOPRODUCT PRODUCTION AND REPAIR CAPACITY IN A VARIANT OF BACILLUS CEREUS

Abstract —As sporulation progresses, there is an increased resistance to UV irradiation of the cells of Bacillus cereus var. alesti. This progressive increase is independent of post-irradiation treatment and appears to be a property of the stage of sporulation. In addition, the proportion of photoproducts formed is different for each stage of sporulation. Cells irradiated at Stage I (axial filament) of sporulation display relatively large amounts of spore photoproduct 'c' and less of photoproduct 'b'. As sporulation proceeds, UV irradiation results in the production of more spore photoproduct 'b' and less 'c', suggesting a progressive change in configuration of the DNA within the sporulating cell. If irradiated early in the process (Stage II), large amounts of cyclobutane-type dimers are also produced which, with the 'spore-specific' photoproducts, may be retained in the resultant spore. Although no excision-repair was detectable during germination of these spores, both vegetative and 'spore-specific' damage is reduced during this period. The 'spore-specific' repair mechanism may be able to remove vegetative damage from germinating spores.     

Preparation of polymeric amines from poly(schiff bases)

A study was made of the preparation of aromatic polymeric amines in order to test their thermal stability. The most useful method was the hydrogenation of polymeric Schiff bases by the dimethylamine—borane reagent or the borane—tetrahydrofuran reagent. The Schiff bases were prepared by the solution polymerization of terephthalaldehyde with various aromatic diamines, including 4,4′-methylenedianiline, benzidine, and p-phenylenediamine, and for comparison, 1,6-hexanediamine. The Schiff bases and the polyamines from the aromatic diamines were found to be dimers or trimers, not high polymers: the polymers from the aliphatic diamine had a degree of polymerization of about 14. Thermogravimetric analyses of the aromatic polyamines under nitrogen showed that the initial temperatures of marked degradation were 350–400°C.     

The effects of individual amino acids on the fast folding dynamics of alpha-helical peptides

Nanosecond temperature jump experiments coupled to time-resolved infrared spectroscopy were carried out on a series of alanine-based peptides containing different guest amino acids to study the effects of residues with different helix propensities on the helix-coil dynamics.     

Acylation of purine-8-thione and benzimidazole-2-thione: A reinvestigation of the site of acylation

Purine-8-thione ( 1 ) is acylated on nitrogen, not on sulfur as was previously reported. Thus, the reactions of 1 with ethyl chloroformate and with acetic anhydride yield, respectively, ethyl purine-8-thione-9( 7 )-carboxylate ( 3 ) and 9 ( 7 )acetylpurine-8-thione ( 7 ) as shown by independent synthesis and spectra. In like manner, benzimidazole-2-thione ( 10 ) reacts with acetic anhydride, ethyl chloroformate, benzoyl chloride, and cyclohexyl isocyanate to yield the corresponding N-acylated derivatives. In addition, 10 yields 1,3-dibenzoylbenzimidazole-2-thione on treatment with 2 equivalents of benzoyl chloride.     

Quinazolines. XI. Synthesis of 2,4-diamino-5, 10-diliydrobenzo[g] quinazolines

An unequivocal synthesis of 2,4-diamino-5,10-dihydrobenzo[g]quinazolines is described, starting from methyl 2-tetralone-3-carboxylates. Condensation with guanidine yielded 2-amino-4-hydroxy derivatives, which were thiated with phosphorus pentasulfide and S-alkylated with dimethyl sulfate. The resultant 2-amino-4-methylthio compounds were converted into 2,4-diamino derivatives by amination at elevated temperature and pressure. Attempted synthesis from 3-cyano-1,4-dihydro-2-methoxynaphthalene and guanidine was unsuccessful.     

Estimates of the ab initio limit for sulfur-pi interactions: the H2S-benzene dimer

The interaction between aromatic rings and sulfur atoms in the side chains of amino acids is a factor in the formation and stabilization of alpha-helices in proteins. We studied the H(2)S-benzene dimer as the simplest possible prototype of sulfur-pi interactions. High-quality potential energy curves were obtained using coupled-cluster theory with single, double, and perturbative triple substitutions (CCSD(T)) and a large, augmented quadruple-zeta basis set (aug-cc-pVQZ). The equilibrium intermonomer distance for the hydrogens-down C(2)(v) configuration is 3.8 A with an interaction energy of -2.74 kcal mol(-1). Extrapolating the binding energy to the complete basis set limit gives -2.81 kcal mol(-1). This binding energy is comparable to that of H(2)O-benzene or of the benzene dimer, and the equilibrium distance is in close agreement with experiment. Other orientations of the dimer were also considered at less complete levels of theory. A considerable reduction in binding for the sulfur-down configuration, together with an energy decomposition analysis, indicates that the attraction in H(2)S-benzene is best thought of as arising from a favorable electrostatic interaction between partially positive hydrogens in H(2)S with the negatively charged pi-cloud of the benzene.