Infrared study of alkali tri- and hexavanadates as formed from their melts

Alkali tri- and/or hexavanadates, formed by slow cooling and rapid quenching from melts, were analized by ir spectrometry and X-ray diffractometry. The trivanadate (MV₃O₈) was confirmed to be formed from melts by these procedures in both Li and Na samples and the hexavanadate (M₂V₆O₁₆) in both Rb and Cs samples but neither tri- nor hexavanadate in the K sample. The frequencies of the VO stretching bands of the tri- and hexavanadates were observed to shift toward the lower region of 1005-955 cm^?1 relative to the corresponding band at 1022 cm^?1 for pure V₂O₅. By connecting the band shifts with Bond-Strength-Bond-Length parameters of Brown-Shannon, the VO bond lengths for LiV₃O₈, NaV₃O₈, Rb₂V₆O₁₆, and Cs₂V₆O₁₆ were exactly evaluated. Based on the relative intensities of the bands, furthermore, the local structures in the sequences of the VO₄, VO₆, and V₂O₈ polyhedral units for the alkali vanadates were favorably discussed.     

Structures of [(CO2)n(H2O)m]- (n=1-4, m=1,2) cluster anions. I. Infrared photodissociation spectroscopy

The infrared photodissociation spectra of [(CO(2))(n)(H(2)O)(m)](-) (n=1-4, m=1, 2) are measured in the 3000-3800 cm(-1) range. The [(CO(2))(n)(H(2)O)(1)](-) spectra are characterized by a sharp band around 3570 cm(-1) except for n=1; [(CO(2))(1)(H(2)O)(1)](-) does not photodissociate in the spectral range studied. The [(CO(2))(n)(H(2)O)(2)](-) (n=1, 2) species have similar spectral features with a broadband at approximately 3340 cm(-1). A drastic change in the spectral features is observed for [(CO(2))(3)(H(2)O)(2)](-), where sharp bands appear at 3224, 3321, 3364, 3438, and 3572 cm(-1). Ab initio calculations are performed at the MP2/6-311++G(**) level to provide structural information such as optimized structures, stabilization energies, and vibrational frequencies of the [(CO(2))(n)(H(2)O)(m)](-) species. Comparison between the experimental and theoretical results reveals rather size- and composition-specific hydration manner in [(CO(2))(n)(H(2)O)(m)](-): (1) the incorporated H(2)O is bonded to either CO(2) (-) or C(2)O(4) (-) through two equivalent OH...O hydrogen bonds to form a ring structure in [(CO(2))(n)(H(2)O)(1)](-); (2) two H(2)O molecules are independently bound to the O atoms of CO(2) (-) in [(CO(2))(n)(H(2)O)(2)](-) (n=1, 2); (3) a cyclic structure composed of CO(2) (-) and two H(2)O molecules is formed in [(CO(2))(3)(H(2)O)(2)](-).     

Regression analysis of enzyme reaction. O-methylation of catechol derivatives by catechol-O-methyltransferase

The electronic structures of catechol derivatives, 3,4-dihydroxy-1-substituted benzenes, including epinephrine and norepinephrine, were calculated by means of the CNDO /2 and the MINDO /3 methods. Correlation between the maximum velocities divided by the molecular weight, as between the inverse of Michaelis–Menten constants in the O-methylation reaction catalyzed by catechol-O-methyltransferase and the electronic indices calculated on the basis of the frontier electron theory was found. The correlation coefficient between the observed maximum velocities divided by the molecular weight and the calculated ones was 0.873. The regression analysis showed that the Coulombic forces at the C₃ and C₄ positions and the electron acceptable indices at C₆ and meta-O positions represented the best correlation with the biological activities (V_max and K_m). The electronic indices of the catechol moieties represent the rate-limiting factor of the O-methylation reaction.     

Thin film composite optical waveguides for sensor applications: a review

We review the design and fabrication of thin-film composite optical waveguides (OWG) with high refractive index for sensor applications. A highly sensitive optical sensor device has been developed on the basis of thin-film, composite OWG. The thin-film OWG was deposited onto the surface of a potassium-ion-exchanged (K⁺) glass OWG by sputtering or spin coating (5–9 mm wide, and with tapers at both ends). By allowing an adiabatic transition of the guided light from the secondary OWG to the thin-film OWG, the electric field of the evanescent wave at the thin film was enhanced. The attenuation of the guided light in the thin film layer was small, and the guided light intensity changed sensitively with the refractive index of the cladding layer. Our experimental results demonstrate that thin-film, composite OWG gas sensors or immunosensors are much more sensitive than sensors based on other technologies.     

Imidazole‐Aided Native Chemical Ligation: Imidazole as a One‐Pot Desulfurization‐Amenable Non‐Thiol‐Type Alternative to 4‐Mercaptophenylacetic Acid

Various bioactive proteins have been synthesized by native chemical ligation (NCL) and its combination with subsequent desulfurization (e.g., conversion from Cys to Ala). In NCL, excess 4‐mercaptophenylacetic acid (MPAA) is generally added to facilitate the reaction. However, co‐elution of MPAA with the ligation product during preparative high‐performance liquid chromatography sometimes reduces its usefulness. In addition, contamination of MPAA disturbs subsequent desulfurization. Here, we report for the first time that imidazole can be adopted as an alternative to MPAA in NCL using a peptide‐alkylthioester. The efficiency of the imidazole‐aided NCL (Im‐NCL) is similar to that of traditional MPAA‐aided NCL. As model cases, we successfully synthesized adiponectin(19‐107) and [Ser(PO₃H₂)⁶⁵]‐ubiquitin using Im‐NCL with a one‐pot desulfurization.     

Structure of hydrated clusters of dibenzo-18-crown-6-ether in a supersonic jet--encapsulation of water molecules in the crown cavity

The structure of dibenzo-18-crown-6-ether (DB18C6) and its hydrated clusters has been investigated in a supersonic jet. Two conformers of bare DB18C6 and six hydrated clusters (DB18C6-(H(2)O)(n)) were identified by laser-induced fluorescence, fluorescence-detected UV-UV hole-burning and IR-UV double-resonance spectroscopy. The IR-UV double resonance spectra were compared with the IR spectra obtained by quantum chemical calculations at the B3LYP/6-31+G* level. The two conformers of bare DB18C6 are assigned to "boat" and "chair I" forms, respectively, among which the boat form is dominant. All the six DB18C6-(H(2)O)(n) clusters with n = 1-4 have a boat conformation in the DB18C6 part. The water molecules form a variety of hydration networks in the boat-DB18C6 cavity. In DB18C6-(H(2)O)(1), a water molecule forms the bidentate hydrogen bond with the O atoms adjacent to the benzene rings. In this cluster, the water molecule is preferentially hydrogen bonded from the bottom of boat-DB18C6. In the larger clusters, the hydration networks are developed on the basis of the DB18C6-(H(2)O)(1) cluster.     

An IR study of (CO2)(+)n (n=3-8) cluster ions in the 1000-3800 cm-1 region

Infrared photodissociation (IRPD) spectra of carbon dioxide cluster ions, (CO(2))(n) (+) with n=3-8, are measured in the 1000-3800 cm(-1) region. IR bands assignable to solvent CO(2) molecules are observed at positions close to the vibrational frequencies of neutral CO(2) [1290 and 1400 cm(-1) (nu(1) and 2nu(2)), 2350 cm(-1) (nu(3)), and 3610 and 3713 cm(-1) (nu(1)+nu(3) and 2nu(2)+nu(3))]. The ion core in (CO(2))(n) (+) shows several IR bands in the 1200-1350, 2100-2200, and 3250-3500 cm(-1) regions. On the basis of previous IR studies in solid Ne and quantum chemical calculations, these bands are ascribed to the C(2)O(4) (+) ion, which has a semicovalent bond between the CO(2) components. The number of the bands and the bandwidth of the IRPD spectra drastically change with an increase in the cluster size up to n=6, which is ascribed to the symmetry change of (CO(2))(n) (+) by the solvation of CO(2) molecules and a full occupation of the first solvation shell at n=6.     

Hetero-double-helix formation by an ethynylhelicene oligomer possessing perfluorooctyl side chains

Monomeric to pentameric (P)-ethynylhelicene oligomers possessing perfluorooctyl side chains were synthesized. The circular dichroism (CD) and vapor pressure osomometry (VPO) studies indicated the formation of a helix-dimer for the (P)-pentamer, for example, in trifluoromethylbenzene at 5 degrees C at concentrations above 2 x 10(-6) M. Compared with a (P)-pentamer possessing decyloxycarbonyl side chains, the perfluorooctyl (P)-pentamer exhibited lower solubilities in organic solvents, formed a thermodynamically more stable helix-dimer, and exhibited a mirror image CD spectrum. The perfluorooctyl (P)-pentamer formed a hetero-helix dimer with a decyloxycarbonyl (M)-pentamer but not with a (P)-pentamer. It indicated higher stability of the hetero-helix dimer over the homo-helix dimers.     

Selective photocatalytic reduction of nitrate to nitrogen molecules in an aqueous suspension of metal-loaded titanium(IV) oxide particles

Nitrate was photocatalytically reduced to nitrogen molecules with a high selectivity in a basic aqueous suspension of palladium and copper-loaded titanium(IV) oxide powders in the presence of oxalate anion as a hole scavenger.