Quantum effect on the internal proton transfer and structural fluctuation in the H+ 5 cluster

The thermal equilibrium state of H+(5) is investigated by means of an ab initio path integral molecular dynamics (PIMD) method, in which degrees of freedom of both nuclei and electrons at finite temperature are quantized within the adiabatic approximation. The second-order Moller-Plesset force field has been employed for the present ab initio PIMD. At 5-200 K, H+(5) is shown to have the structure that the proton is surrounded by the two H(2) units without any exchange of an atom between the central proton and the H(2) unit. At 5 K, the quantum tunneling of the central proton occurs more easily when the distance between the two H(2) units is shortened. At the high temperature of 200 K, the central proton is more delocalized in space between the two H(2) units, with less correlation with the stretching of the distance between the two H(2) units. As for the rotation of the H(2) units around the C(2) axis of H+(5) , the dihedral angle distribution is homogeneous at all temperatures, suggesting that the two H(2) units freely rotate around the C(2) axis, while this quantum effect on the rotation of the H(2) units becomes more weakened with increasing temperature. The influence of the structural fluctuation of H+(5) on molecular orbital energies has been examined to conclude that the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap is largely reduced with the increase of temperature because of the spatial expansion of the whole cluster.     

Development of a flow-injection analysis (FIA) enzyme sensor for fructosyl amine monitoring

An enzyme-sensor system with flow-injection analysis (FIA) has been developed for the detection of fructosyl amine compounds; the sensor utilizes fructosyl amine oxidase isolated from the marine yeast Pichia sp. N1-1 strain. With this FIA system 0.2 to 10 mmol L(-1) fructosyl valine can be determined. The sensor is approximately five times more sensitive to fructosyl valine, a model compound for glycated hemoglobin HbA1c, than to N(epsilon)-fructosyl lysine, a model compound for glycated albumin. This FIA system can also be used to detect fructosyl dipeptides. The operational stability of the sensor enabled more than 120 consecutive sample injections over a period of approximately 20 h.     

Intercalation chemistry of aluminium dihydrogentriphosphate with weak bases and polymerization of aniline between its layers

Weak bases such as 2-aminopyridine, 4-aminopyridine,o-phenylenediamine,p-phenylenediamine and aniline were intercalated into aluminium dihydrogentriphosphate (ADHP) using ultrasonic wave irradiation. The interlayer spacing of ADHP increased from 8.1 Å to 12.4–20.0 Å. From the values of the layer expansions and host/guest ratios, bilayer or monolayer structures were considered. Chemical oxidation of the aniline resulted in the formation of polyaniline in the ADHP layers.Author for correspondence.     

Second hyperpolarizability of phenalenyl radical system involving acetylene π-conjugated bridge

The static second hyperpolarizability (γ) of a singlet diradical system involving phenalenyl radicals linked with acetylene π-conjugated bridge, BPLE, is investigated as well as reference closed-shell systems, BPRY1 and BPRY2, by the hybrid density functional theory method. The γ value of BPLE with intermediate diradical character is shown to be about four times as large as that of BPRY1 with similar π-conjugation length and to be about twice as large as that of BPRY2 with longer π-conjugation length. This feature is in agreement with our prediction that the molecules with intermediate diradical characters enhance γ values compared to the closed-shell molecules.     

Phencyclone Diels-Alder adducts as a new crystalline host. Role of C---H···π and C---H···O interactions

A series of crystalline host compounds, which have a bicyclo[2.2.1]heptene-7-one system, has been synthesized and their inclusion behavior has been investigated. The cycloadduct of phencyclone and N-naphthylmaleimide forms a 1:1 crystalline inclusion complex with 2-butanone. The crystal structure indicates the presence of weak lattice forces supported by C---H···π and C---H···O interactions.     

Acid-base equilibrium of aqua-chromium-dioxolene complexes aimed at formation of oxo-chromium complexes

A series of aqua-Cr(III)-dioxolene complexes, [Cr(OH(2))(3,5-Bu(2)SQ)(trpy)](ClO(4))(2) (1s), [Cr(OH(2))(3,5-Bu(2)Cat)(trpy)]ClO(4) (1c), [Cr(OH(2))(3,6-Bu(2)SQ)(trpy)](ClO(4))(2) (2), [Cr(OH(2))(Cat)(trpy)]ClO(4) (3), [Cr(OH(2))(Cl(4)Cat)(trpy)]ClO(4) (4), [Cr(OH(2))(3,5-Bu(2)SQ)(Me(3)-tacn)](ClO(4))(2) (5), [Cr(OH(2))(Cat)(Me(3)-tacn)]ClO(4) (6), and [Cr(OH(2))(Cl(4)Cat)(Me(3)-tacn)]ClO(4) (7) (Bu(2)SQ = di-tert-butyl-o-benzosemiquinonate anion, Bu(2)Cat = di-tert-butylcatecholate dianion, Cat = catecholate dianion, Cl(4)Cat = tetrachlorocatecholate dianion, trpy = 2,2':6',2' '-terpyridine, and Me(3)-tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), were prepared. On the basis of the crystal structures, redox behavior, and elemental analyses of these complexes, dioxolene in 1c, 3, 4, 6, and 7 coordinated to Cr(III) as the catechol form, and the ligand in 1s, 2, and 5 was linked to Cr(III) with the semiquinone form. All the aqua-Cr(III) complexes reversibly changed to the hydroxo-Cr(III) ones upon dissociation of the aqua proton, and the pK(a) value of the aqua-Cr(III) complexes increased in the order 6 > 3 approximately 1c > 7 > 5 approximately 4 > 1s. Hydroxo-Cr(III)-catechol complexes derived from 1c, 3, 4, 6, and 7 did not show any signs of dissociation of their hydroxy proton. On the other hand, hydroxo-Cr(III)-semiquinone complexes were reduced to hydroxo-Cr(III)-catechol in H(2)O/THF at pH 11 under illumination of visible light.     

Primary events in dim light vision: a chemical and spectroscopic approach toward understanding protein/chromophore interactions in rhodopsin

The visual pigment rhodopsin (bovine) is a 40 kDa protein consisting of 348 amino acids, and is a prototypical member of the subfamily A of G protein-coupled receptors (GPCRs). This remarkably efficient light-activated protein (quantum yield = 0.67) binds the chromophore 11-cis-retinal covalently by attachment to Lys296 through a protonated Schiff base. The 11-cis geometry of the retinylidene chromophore keeps the partially active opsin protein locked in its inactive state (inverse agonist). Several retinal analogs with defined configurations and stereochemistry have been incorporated into the apoprotein to give rhodopsin analogs. These incorporation results along with the spectroscopic properties of the rhodopsin analogs clarify the mode of entry of the chromophore into the apoprotein and the biologically relevant conformation of the chromophore in the rhodopsin binding site. In addition, difference UV, CD, and photoaffinity labeling studies with a 3-diazo-4-oxo analog of 11-cis-retinal have been used to chart the movement of the retinylidene chromophore through the various intermediate stages of visual transduction.     

Synthesis of molybdenocene(IV) and tungstenocene(IV) tropolonato complexes: Its derivative containing calix[4]arene moiety

The cationic di-μ-hydroxo dinuclear complexes of molybdenocene and tungstenocene [Cp₂M(μ-OH)₂MCp₂]⁺ (Cp = η-C₅H₅; M = Mo or W) react with tropolone to afford corresponding tropolonato complexes [Cp₂M(trop)]⁺ (trop = C₇H₅O₂). The products were investigated by IR, ¹H NMR, and ¹³C NMR spectroscopy as well as by X-ray crystallography (M = W). The structure shows that the central metal is surrounded by a distorted tetrahedral array of the two centers of cyclopentadienyl ligands and the two oxygen atoms of tropolonato ligand. The reaction has been extended to the synthesis of calix[4]arene receptor functionalized at the 1,3-positions of the upper rim with two tropolonato-molybdenocene centers.     

Kinetics of crosslinking reactions. 1. Reaction rate of intramolecular crosslinkings by using a soluble microgel

Soluble microgels with several pendant vinyl groups were synthesized by radical copolymerization of methyl methacrylate (MMA) with p-divinyl benzene (p-DVB). The polymerization conditions used for intramolecular crosslinking of microgels were chosen from gel permeation chromatograph (GPC) measurements of the reaction products. The rate constant of intramolecular crosslinking (k_pⁱ) was estimated from the changes in the concentration of pendant vinyl groups of microgel by using photometrical measurements at 30°C assuming a unimolecular termination mechanism of polymer radicals. As a result, k_pⁱ showed larger values than k_p of styrene and depended strongly on the internal structure of the microgels.