A Thermodynamic Study of 1-Propanol–Glycerol–H2O at 25°C: Effect of Glycerol on Molecular Organization of H2O

The excess chemical potential, partial molar enthalpy, and volume of 1-propanol were determined in ternary mixtures of 1-propanol–glycerol–H₂O at 25°C. The mole fraction dependence of all these thermodynamic functions was used to elucidate the effect of glycerol on the molecular organization of H₂O. The glycerol molecules do not exert a hydrophobic effect on H₂O. Rather, the hydroxyl groups of glycerol, perhaps by forming clusters via its alkyl backbone with hydroxyl groups pointing outward, interact with H₂O so as to reduce the characteristics of liquid H₂O. The global hydrogen bond probability and, hence, the percolation nature of the hydrogen bond network is reduced. In addition, the degree of fluctuation inherent in liquid H₂O is reduced by glycerol perhaps by participating in the hydrogen bond network via OH groups. At infinite dilution, the pair interaction coefficients in enthalpy were evaluated and these data suggest a possibility that the interaction is mediated through H₂O.     

Formation of HO2 radicals from the 248 nm two-photon excitation of different aromatic hydrocarbons in the presence of O2

The excitation energy dependence of HO(2) radical formation from the 248 nm irradiation of four different aromatic hydrocarbons (benzene, toluene, o-xylene, and mesitylene) in the presence of O(2) has been studied. HO(2) has been monitored at 6638.20 cm(-1) by cw-CRDS, and the formation of a short-lived, unidentified species, showing broad-band absorption around the HO(2) absorption line, has been observed. For all four hydrocarbons, the same HO(2) formation pattern has been observed: HO(2) is formed immediately on our time scale after the excitation pulse, followed by a formation of more HO(2) on a much longer time scale. Taking into account the absorption of the short-lived species, the yields of both types of HO(2) radicals are in agreement with a formation following 2-photon absorption by the aromatic hydrocarbons. The yields do not much depend on the nature of the aromatic hydrocarbon. For practical use in past and future experiments on aromatic hydrocarbons, an empirical value is given, allowing the estimation of the total concentration of HO(2) radicals formed at 40 Torr He in the presence of around [O(2)] = 1 × 10(17)cm(-3) as a function of the 248 nm excitation energy: [HO(2)]/[aromatic hydrocarbon] ≈ 2 × 10(-6) × E(2) (with E in mJ cm(-2)).     

Vibrational spectra of chloroform, freon-11 and selected isotopomers in the terahertz region

The fundamental bands of the CCl₃ asymmetric deformation modes of selected isotopomers of chloroform (CHCl₃) and freon-11 (CFCl₃) have been measured in a static cell at ambient temperature using a laser-based source of tunable radiation in the terahertz region of the electromagnetic spectrum. The analysis of the rotational contours of the bands enabled the derivation of the fundamental frequencies with an accuracy of better than 3 GHz.     

Separation and quantitation of phycobiliproteins using phytic acid in capillary electrophoresis with laser-induced fluorescence detection

The similar electrophoretic mobilities and sizes of several of the phycobiliproteins, which are derived from the photosynthetic apparatus of cyanobacteria and eukaryotic algae, render their separation and quantitation a challenging problem. However, we have developed a suitable capillary electrophoresis (CE) method that employs a phytic acid-boric acid buffer and laser-induced fluorescence (LIF) detection with a single 594 nm He-Ne laser. This method takes advantage of the remarkably high quantum yields of these naturally fluorescent proteins, which can be attributed to their linear tetrapyrrole chromophores covalently bound to cysteinyl residues. As such, limits of detection of 1.18 x 10(-14), 5.26 x 10(-15), and 2.38 x 10(-15) mol/l were obtained for R-phycoerythrin, C-phycocyanin, and allophycocyanin proteins, respectively, with a linear dynamic range of eight orders of magnitude in each case. Unlike previously published CE-LIF methods, this work describes the separation of all three major classes of phycobiliproteins in under 5 min. Very good recoveries, ranging from 93.2 to 105.5%, were obtained for a standard mixture of the phycobiliproteins, based on seven-point calibration curves for both peak height and peak area. It is believed that this development will prove useful for the determination of phycobiliprotein content in naturally occurring cyanobacteria populations, thus providing a useful tool for understanding biological and chemical oceanographic processes.     

Determination of the chromophore structures in the photoinduced reaction cycle of phytochrome

The chromophore structures in the parent states Pr and Pfr as well as in the photocycle intermediate Lumi-R of oat phytochrome phyA are determined by comparison of the experimental resonance Raman spectra with calculated Raman spectra that have been obtained by density functional theory calculations (B3LYP) using scaled force fields. The spectra were calculated for various tetrapyrrole geometries including more than twenty different methine bridge isomers. For the parent states Pr and Pfr the best agreement in terms of vibrational frequencies, isotopic shifts, and Raman intensities was achieved with the ZZZasa and ZZEssa geometry, respectively. For the first intermediate Lumi-R, the chromophore geometry is concluded to be the ZZEasa configuration. These finding imply that the primary step of the photoactivation of phytochrome is the Z/E isomerization of the C-D methine bridge double bond, whereas the single bond remains in the anti conformation. The subsequent transition to the physiologically active state Pfr includes a (partial) single bond rotation of the A-B methine bridge.     

High-sensitivity capillary electrophoresis method for monitoring purine nucleoside phosphorylase and adenosine deaminase reactions by a reversed electrode polarity switching mode

A simple, efficient, and highly sensitive in-line CE method was developed for the characterization and for inhibition studies of the nucleoside-metabolizing enzymes purine nucleoside phosphorylase (PNP) and adenosine deaminase (ADA) present in membrane preparations of human 1539 melanoma cells. After filling the running buffer (50 mM borate buffer, 100 mM SDS, pH 9.10) into a fused-silica capillary (50 cm effective length × 75 μm), a large sample volume was loaded by hydrodynamic injection (5 psi, 36 s), followed by the removal of the large plug of sample matrix from the capillary using polarity switching (-20 kV). The current was monitored and the polarity was reversed when 95% of the current had been recovered. The separation of the neutral analytes (nucleosides and nucleobases) was performed by applying a voltage of 15 kV. An about 10-fold improvement of sensitivity for the five investigated analytes (adenosine, inosine, adenine, hypoxanthine, xanthine) was achieved by large-volume stacking with polarity switching when compared with CE without stacking. For inosine and adenine detection limits as low as 60 nM were achieved. To the best of our knowledge, this represents the highest sensitivity for nucleoside and nucleobase analysis using CE with UV detection reported so far. The Michaelis-Menten constants (K(m)) for PNP and ADA and the inhibition constants (K(i)) for standard inhibitors determined with the new method were consistent with literature data.     

On-Line Coupling of High-Performance Liquid Chromatography to Atmospheric Pressure Chemical Ionization Mass Spectrometry (HPLC/APCI-MS and MS/MS). The Pollen Analysis of Hippeastrum x hortorum (Amaryllidaceae)

A H₂O/MeOH extract of the pollen of Hippeastrum x hortorum (Amaryllidaceae) was analyzed. A mixture of different compounds (at the most 84) was found, namely the geometrically ((E,E), (E,Z), (Z,E), and (Z,Z) and structurally isomeric N,N′-dicoumaroyl (=N,N′-bis[3-(4-hydroxyphenyl)prop-2-enoyl]), N,N′-diferuloyl (=N,N′-bis[3-(4-hydroxy-3-methoxyphenyl)prop-2-enoyl]), N,N′-disinapoyl (=N,N′-bis[3-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-enoyl]), N-coumaroyl-N′-feruloyl, and N-feruloyl-N′-sinapoyl derivatives of spermidine (=4-azaoctane-1,8-diamine=N-(3-aminopropyl)butane-1,4-diamine). Their structures were proven by using on-line-coupled high-performance liquid chromatography and atmospheric-pressure chemical-ionization mass spectrometry (HPLC-UV(DAD)/APCI-MS and MS/MS), UV-induced (E)⇌(Z) photoisomerization, and catalytic hydrogenation, as well by comparing their spectra and chromatographic behavior with those of synthetic standards. According to the physicochemical properties of these natural compounds, a proposed biological function is discussed.     

Photochemical investigation of Roussin's red salt esters: Fe2(mu-SR)2(NO)4

The photochemistry of various Roussin's red ester compounds of the general formula Fe(2)(SR)(2)(NO)(4), where R = CH(3), CH(2)CH(3), CH(2)C(6)H(5), CH(2)CH(2)OH, and CH(2)CH(2)SO(3)(-), were investigated. Continuous photolyses of these ester compounds in aerated solutions led to the release of NO with moderate quantum yields for the photodecomposition of the ester (Phi(RSE) = 0.02-0.13). Electrochemical studies using an NO electrode demonstrated that 4 mol of NO are generated for each mole of ester undergoing photodecomposition. Nanosecond flash photolysis studies of Fe(2)(SR)(2)(NO)(4) (where R = CH(2)CH(2)OH and CH(2)CH(2)SO(3)(-)) indicate that the initial photoreaction is the reversible dissociation of NO. In the absence of oxygen, the presumed intermediate, Fe(2)(SR)(2)(NO)(3), undergoes second-order reaction with NO to regenerate the parent cluster with a rate constant of k(NO) = 1.1 x 10(9) M(-1) s(-1) for R = CH(2)CH(2)OH. Under aerated conditions the intermediate reacts with oxygen to give permanent photochemistry.     

Micro-homogeneity studies of boron carbide powders

We have studied the micro-homogeneity of boron carbide powders by inductively coupled plasma optical emission spectrometry (ICP-OES) and total reflection X-ray fluorescence spectrometry (TXRF) using slurry sampling. To get information on the particle size distributions of the powders, the stabilized slurries of boron carbide powders were nebulized, the aerosols were transported into a Batelle impactor and the droplets were collected on the impactor stages bearing TXRF sample holders. In a first series of measurements, parameters of the impaction like the duration of the impaction and the use of glutinous substance on the sample holders were optimized. The different mass size fractions for industrial boron carbide powders were determined by weight measurements of the fractions collected on the different stages. The established particle size distributions were in the range of 0.5 to >16 μm and found similar to those determined by laser diffraction reported elsewhere. Analyses of the mass fractions by slurry sampling TXRF showed that Ca, Ti, Cr, Mn, Fe, Ni and Cu within the measurements errors were homogeneously distributed over the mass fractions between 0.5 and 4 μm and that their concentrations agreed with the bulk composition, as determined with ICP-OES subsequent to digestion. However, light underestimates were found at the 5 (Mn) up to 150 μg g^?1 (Fe) level. Finally, boron carbide powders were washed out with nitric acid with different concentrations and leaching solutions and the residues were analyzed by ICP-OES and TXRF respectively. It is shown that up to 60% of the residual trace impurities in the powder studied can be removed by leaching with 34% (v/v) of nitric acid.

Group 4 dimethylsilylenebisamido complexes bearing the 6-[2-(diethylboryl)phenyl]pyrid-2-yl motif: synthesis and use in tandem ring-opening metathesis/vinyl-insertion copolymerization of cyclic olefins with ethylene

Two novel Zr(IV)- and Hf(IV)-based bisamido complexes bearing the 6-[2-(diethylboryl)phenyl]pyrid-2-yl motif, that is, [ZrCl(2){Me(2)Si(DbppN)(2)}(thf)] (9) and [HfCl(2){Me(2)Si(DbppN)(2)}(thf)(2)] (10) (DbppN=6-[2-(diethylboryl)phenyl]pyridine-2-amido) have been prepared. Their reactivities have been compared with that of a model precatalyst that does not bear the aminoborane motif. Upon activation with methylalumoxane, precatalysts 9 and 10 are active in the homopolymerization of ethylene (E) yielding high-density polyethylene (HDPE). In the copolymerization of E with cyclopentene (CPE), for example by the action of 9, the presence of CPE resulted in a dramatic increase in the polymerization activity of E, while CPE incorporation remained close to or at zero. In the vinyl-insertion copolymerization of norborn-2-ene (NBE) with E by the action of 9, statistical cyclic olefin copolymers of these two monomers were obtained. At higher NBE concentrations, however, 9 gave rise to reversible ring-opening metathesis (ROMP)/vinyl-insertion polymerization (VIP) of NBE with E, resulting in the formation of multi-block copolymers of the general formula poly(NBE)(ROMP)-co-poly(NBE)(VIP)-co-poly(E). This particular feature of precatalyst 9, that is, the ability to induce a reversible α-H elimination/α-H addition reaction, is attributed to the unique role of the 6-[2-(diethylboryl)phenyl]pyrid-2-yl ligand. Accordingly, a model precatalyst lacking this ligand does not have the ability to induce α-H elimination/α-H addition reactions. The different (11)B NMR shifts of various diethylborylphenylpyrid-2-ylamines and -amides permit a ranking of the strengths of the B-N bonds in these compounds. This strength of the B-N bond is correlated with the propensity of 9/MAO to produce poly(NBE)(ROMP)-co-poly(NBE)(VIP)-co-poly(E) at different temperatures.