Influences of fatty acid moiety and esterification of polyglycerol fatty acid esters on the crystallization of palm mid fraction in oil-in-water emulsion

We examined the crystallization of palm mid fraction (PMF) in oil-in-water (O/W) emulsion, after adding polyglycerol fatty acid esters (PGFEs). We employed ultrasonic velocity measurements and DSC techniques, with special emphases on the influences of fatty acid moiety and esterification of PGFE. Twelve types of PGFEs were examined as additives. PGFEs have a large hydrophilic moiety composed of 10 glycerol molecules to which palmitic, stearic and behenic acids were esterified as the fatty acid moiety with different degrees of esterification. Crystallization temperature (T(c)) of PMF remarkably increased with increasing concentrations of the PGFEs as the chain length of the fatty acid moiety increased, and the PGFE became more hydrophobic in accordance with increasing degree of esterification. We observed that the heterogeneous nucleation of PMF in the O/W emulsion was activated at the oil-water interface, where the template effect of very hydrophobic long saturated fatty acid chains of the PGFE might play the main role of heterogeneous nucleation.     

522—Catalytic oxydation of biological components on platinum electrodes modified by adsorbed metals: Anodic oxidation of glucose

The catalytic oxidation of glucose on Pt electrodes modified by adsorbed metals was studied in 1 M HClO₄ by linear sweep voltammetry. The adsorbed metals (denoted as M_ad, such as Bi_ad and Pb_ad) formed on Pt in the potential region more positive than the reversible potential of an M⁼⁺/M^o couple, lead to a marked increase in the anodic c?urrent of glucose by about one order of magnitude. The catalytic activity depends on the surface coverage by the M_ad. The strongly adsorbed species of lactone type, which are responsible for blocking the successive oxidation, are formed on the electrode surface in the anodic processes of glucose on a bare Pt electrode. The formation of such poisonous species is accelerated in the presence of adsorbed hydrogen on Pt. The effects of M_ad were discussed on the basis that M_ad plays its major role on the Pt electrode surface in removal of the adsorbed hydrogen which initiates the formation of the poisonous species.     

NMR study on the photoresponsive DNA tethering an azobenzene. Assignment of the absolute configuration of two diastereomers and structure determination of their duplexes in the trans-form

Two diastereomers of a photoresponsive oligodeoxyribonucleotide tethering a trans-azobenzene, based on the chirality of the central carbon of a diol linker, were separated by reversed-phase HPLC. On the basis of 2D NMR analysis, absolute configurations of the diastereomers alpha and beta (tentatively designated from differences in their retention time) were determined as R- and S-forms, respectively. For both diastereomers, their NMR-determined duplex structure showed that trans-azobenzene intercalates between base pairs, because distinct NOEs were observed between the protons of azobenzene and those of the adjacent base pairs, such as with the imino protons and methyl protons of thymine. The melting temperatures of both duplexes were higher than that of the corresponding native duplex, which contained no azobenzene residue, due to the intercalated trans-azobenzene stabilizing the duplex by a stacking interaction. Between these two diastereomers, differences in T(m) were also found: the melting temperature of the R-form duplex (alpha-isomer) was higher than that of the S-form (beta-isomer). On the basis of the NMR-determined structure, this difference was attributed to the fact that the S-form (beta isomer) causes more stress forming the duplex than does the R-form (alpha isomer) due to disturbances of the right-hand helix.     

Catalytic effects of metal submonolayers formed by faradaic adsorption on the anodic oxidation of ascorbic acid at a platinum electrode

The catalytic effects of metal ions on the anodic oxidation of ascorbic acid on a Pt electrode in 1 M HClO₄ were studied by linear sweep voltammetry. The anodic peak due to a two-electron oxidation of ascorbic acid shifts to the negative potential side on the addition of Bi³⁺. This indicates the accelerating effect of Bi³⁺ on the oxidation of ascorbic acid. The presence of other metal ions, such as Pb²⁺, Hg²⁺, Tl⁺, Ag⁺ and Sb³⁺, also exerts similar effects. These metal ions were adsorbed on a Pt electrode at underpotentials and the adsorbed metals (denoted as M_ad) still remain on the electrode surface until the electrode potential goes up to and beyond the peak potential of the oxidation of ascorbic acid. On the other hand, metal ions forming no adsorbed layer on Pt, such as Co²⁺, Zn²⁺, Fe³⁺ and Ni²⁺, exhibit no catalytic effect. These facts suggest that the presence of a M_ad on Pt is essential for the promotion of the anodic oxidation of ascorbic acid. However, there is a difference in the catalytic action among the M_ad, for example, Cu_ad, Cd_ad, In_ad, Sn_ad and Mo_ad display no catalytic action.The catalytic activity depends on the degree of surface coverage by the M_ad. The maximal effect of the M_ad is attained in the submonolayer region. The effects of metal ions were discussed on the basis that the M_ad plays its major role in the removal of the adsorbed ascorbic acid occupying active sites on the electrode surface, and provides effective sites for the activation of adjacent water molecules. Furthermore, from the ¹³C NMR spectra for the oxidation products, the adsorbed water on the M_ad appears to function by promoting the subsequent hydration steps, following the electron-transfer step of ascorbic acid.     

A cationic 24-MC-8 manganese cluster with ring metals possessing three oxidation states [Mn(II)4Mn(III)6Mn(IV)2(mu4-O)2(mu3-O)4(mu3-OH)4(mu3-OCH3)2(pko)12](OH)(ClO4)3

Reaction of Mn(ClO4)2 with di-pyridyl ketone oxime, (2-py)2C=NOH, gives the novel cluster [Mn(II)4Mn(III)6Mn(IV)2(mu4-O)2(mu3-O)4(mu3-OH)4(mu3-OCH3)2(pko)12](OH)(ClO4)3 1. It is the only example of a 24-MC-8, and the first metallacrown with ring metal ions in three different oxidation states. Magnetic measurements show antiferromagnetic behavior.     

Synthesis of a digermane-containing tricylic nonadecadienedione incorporating an equivalent of ring-opened THF

The combination of 2 equiv of bis[bis(trimethylsilyl)amide]germylene (5) with 2 equiv of 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) in tetrahydrofuran (THF) results in the ring-opening of 1 equiv of THF to form 2,2,8,8-tetrakis(1,1,1,3,3,3-hexamethyl-disilazan-2-yl)-5,16-diphenyl-7,9,14-trioxa-1,3,5,16,18,19-hexaaza-2,8-digerma-tricyclo[13.2.1.13,6]nonadeca-6(19),15(18)-diene-4,17-dione (6). This fast and nearly quantitative reaction builds a 15-membered ring from five different molecules. The new ring, structurally assigned by X-ray crystallography, contains a flexible methylene chain that moves rapidly on the NMR time scale.     

Ab initio study of (13)C(alpha) chemical shift anisotropy tensors in peptides

This study reports magnitudes and the orientation of the (13)C(alpha) chemical shift anisotropy (CSA) tensors of peptides obtained using quantum chemical calculations. The dependency of the CSA tensor parameters on the energy optimization of hydrogen atom positions and hydrogen bonding effects and the use of zwitterionic peptides in the calculations are examined. Our results indicate that the energy optimization of the hydrogen atom positions in crystal structures is necessary to obtain accurate CSA tensors. The inclusion of intermolecular effects such as hydrogen bonding in the calculations provided better agreement between the calculated and experimental values; however, the use of zwitterionic peptides in calculations, with or without the inclusion of hydrogen bonding, did not improve the results. In addition, our calculated values are in good agreement with tensor values obtained from solid-state NMR experiments on glycine-containing tripeptides. In the case of peptides containing an aromatic residue, calculations on an isolated peptide yielded more accurate isotropic shift values than the calculations on extended structures of the peptide. The calculations also suggested that the presence of an aromatic ring in the extended crystal peptide structure influences the magnitude of the delta(22) which the present level of ab initio calculations are unable to reproduce.     

Synthesis and characterization of three novel perfluoro-oligothiophenes ranging in length from the trimer to the pentamer

In this Article, we report on the synthesis and full characterization of three perfluorinated oligothiophenes, ranging in length from the trimer to the pentamer (PF-nT, with n = 3, 4, or 5). The differential pulse voltammetry (DPV) analysis of the compounds showed that they can be both oxidized and reduced (i.e., they display a dual or amphoteric electrochemical behavior), with the reduction peaks positively shifted relative to those of the corresponding unsubstituted oligothiophenes. The electrochemically determined energy gaps are in agreement with those measured from the UV-vis-NIR absorption spectra in solution. The conjugational properties have been investigated by means of FT-Raman spectroscopy, both as pure solids and as dilute solutes in CH(2)Cl(2), revealing that: (i) pi-conjugation does not still reach saturation with chain length for the longest oligomer, and (ii) conformational distortions from a nearly coplanar arrangement of the successive thiophene units upon solution are not too large. DFT and TDDFT quantum chemical calculations have been performed, at the B3LYP/6-31G level, to assess information about the optimized molecular structure, equilibrium atomic charges distribution, energies and topologies of the frontier molecular orbitals (MO) around the gap, vibrational normal modes associated with the most outstanding Raman scatterings, and vertical one-electron excitations that give rise to the main optical absorptions.     

2-Oxo-1,3-dioxoles as specific substrates for measurement of arylesterase activity

Various 4-arylthiomethyl-2-oxo-1,3-dioxole derivatives IIIa-o were synthesized. Their hydrolysis rates by arylesterase (EC 3.1.1.2) and cholinesterase (EC 3.1.1.8) in human serum were evaluated. Some of them were not hydrolyzed by cholinesterase, but were hydrolyzed easily by arylesterase. Among the substrates, sodium 4-((5-methyl-2-oxo-1,3-dioxol-4-yl)methylthio)benzenesulfonate (IIIg) was selected for its substrate reactivity toward arylesterase and its good water solubility. In addition, neither aliesterase (EC 3.1.1.1), acetylesterase (EC 3.1.1.6) nor cholesterol esterase (EC 3.1.1.13) hydrolyzed the compound. IIIg is thus concluded to be a specific substrate for arylesterase. Our assay system for serum arylesterase using IIIg can be readily applied to an automatic analyzer in the diagnosis of liver cirrhosis.     

Photochemical study of [3(3)](1,3,5)cyclophane and emission spectral properties of [3n]cyclophanes (n = 2-6)

Thephotochemical reaction of [3(3)](1,3,5)cyclophane 2, which is a photoprecursor for the formation of propella[3(3)]prismane 18, was studied using a sterilizing lamp (254 nm). Upon photolysis in dry and wet CH2Cl2 or MeOH in the presence of 2 mol/L aqueous HCl solution, the cyclophane 2 afforded novel cage compounds comprised of new skeletons, tetracyclo[6.3.1.0.(2,7)0(4,11)]dodeca-5,9-diene 43, hexacyclo[6.4.0.0.(2,6)0.(4,11)0.(5,10)0(9,12)]dodecane 44, and pentacyclo[6.4.0.0.(2,6)0.(4,11)0(5,10)]dodecane 45. All of these products were confirmed by the X-ray structural analyses. A possible mechanism for the formation of these photoproducts via the hexaprismane derivative 18 is proposed. The photophysical properties in the excited state of the [3n]cyclophanes ([3n]CP, n = 2-6) were investigated by measuring the emission spectra and determining the quantum yields and lifetimes of the fluorescence. All [3n]CPs show excimeric fluorescence without a monomeric one. The lifetime of the excimer fluorescence becomes gradually longer with the increasing number of the trimethylene bridges. The [3n]CPs also shows excimeric phosphorescence spectra without vibrational structures for n = 2, 4, and 5, while phosphorescence is absent for n = 3 and 6. With an increase in symmetry of the benzene skeleton in the [3(3)]- and [3(6)]CPs, the probability of the radiation (phosphorescence) process from the lowest triplet state may drastically decrease.