Reactivity characteristics of squid β-chitin as compared with those of shrimp chitin: High potentials of squid chitin as a starting material for facile chemical modifications

Chemical reactivity of β-chitin isolated from squid pens has been examined in various reactions to elucidate the possibility of facile modifications in simple manners leading to the preparation of derivatives with well-defined structures. β-Chitin swelled in common solvents such as methanol and pyridine unlike the ordinary α-chitin and exhibited much higher reactivity than β-chitin. Free amino groups present in β-chitin were easily and selectively acetylated with acetic anhydride in methanol to give chitin with a uniform structure, poly(N-acetyl-D-glucosamine). When acetylation reaction was carried out in pyridine, O-acetylation proceeded smoothly besides N-acetylation. In the presence of 4-dimethylaminopyridine as the catalyst, even full acetylation was achieved under mild conditions. Tosylation was also quite efficient in pyridine without side reactions such as N-deacetylation which is unavoidable in the tosylation of α-chitin. β-Chitin also enabled direct tritylation in pyridine in the presence of 4-dimethylaminopyridine. All these reactions were quite sluggish with β-chitin, and no reactions or only very low extents of substitution were observed, indicating the high potential of β-chitin as a versatile starting material for facile modification reactions. © 1994 John Wiley & Sons, Inc.     

Examination of numerical accuracy on fragment-DFT calculations with integral values of total electron density functions

Fragment molecular orbital (FMO) method gives a powerful tool to investigate electronic structures for biological substances, and ABINIT-MP program has been developed to implement ab initio FMO calculations effectively. We introduced DFT code into ABINIT-MP and applied fragment-DFT (F-DFT) calculations to model polypeptides. The total accuracy of numerical integrations employed in those calculations was examined by the total numbers of electrons in the molecules. It is shown that the numerical integral of the total density function under the fragment approximation works as an indicator for the numerically total accuracy on the F-DFT implementation.     

Effect of additives on the photovoltaic performance of coumarin-dye-sensitized nanocrystalline TiO2 solar cells

The effects of deoxycholic acid (DCA) and 4-tert-butylpyridine (TBP) as additives on the photovoltaic performance of coumarin-dye-sensitized nanocrystalline TiO2 solar cells were investigated. DCA coadsorption improved both the photocurrent and photovoltage of the solar cells, even though it decreased the amount of dye adsorbed on the TiO2 electrode. The improved photocurrent may arise from suppression of the deactivation of the excited state via quenching processes between dye molecules or a more negative LUMO level of the dye in the presence of DCA, resulting in a high electron-injection yield from the dye into TiO2. The increased photovoltage is probably due to suppression of recombination between the injected electrons and I3- ions on the TiO2 surface (dark current). The addition of TBP to the electrolyte also markedly improved the photovoltage and fill factor of the solar cell, and consequently, the total conversion efficiency increased from 3.6% to 7.5%. FT-IR spectroscopy indicated that a large amount of TBP was adsorbed on the dye-coated TiO2 films in the presence of Li cations. This result suggests that TBP, like DCA, suppressed the dark current on the TiO2 surface, which resulted in the improved photovoltage.     

Thin metal films on quasicrystalline surfaces

Thin metal films with a thickness of one or over one monolayer formed on quasicrystalline surfaces were studied using reflection high-energy electron diffraction, X-ray photoelectron spectroscopy, X-ray photoelectron diffraction and scanning tunneling microscopy. The substrates were the 10f surface of d-Al–Ni–Co and the 5f surface of i-Al–Pd–Mn. The metals deposited were Au, Pt, Ag and In. None of these metals forms any ordered layer by deposition onto clean quasicrystalline surfaces. However, if a submonolayer of In is present atop the 10f surface, an epitaxial layer of multiply-twinned AuAl₂ crystals is formed by Au deposition and subsequent annealing. This is also the case for Pt deposition, but not for Ag deposition. Although the surfactant effect of In is also observed in the case of Au deposition on the 5f surface of i-Al–Pd–Mn, the ordered layer formed is a film of Au–Al alloy with icosahedral symmetry. No ordered films are formed by Pt or Ag deposition onto the 5f surface, regardless of the presence of an In-precovered layer. A Sn film monolayer induced by surface diffusion was also studied.     

EXCITED STATE DYNAMICS OF RETINAL PROTEINS AS STUDIED BY FOURIER TRANSFORM OF OPTICAL ABSORPTION SPECTRUM—I. DEVELOPMENT OF ANALYTICAL METHOD

Abstract— We significantly improved the analytical method for the study of excited state dynamics of pigments, by means of the time correlation function (tcf) of the vibrational wavepacket which is produced by the Fourier transform of experimentally obtained optical absorption spectra (FTOA). Applying the tcf method to the spectra of rhodopsin at 0°C and -180°C, we observed specific peaks which are slightly different between 0°C and -180°C in the early time region (1–130 fs) of the absolute value of tcf, representing a characteristic propagation of the wavepacket along a reaction coordinate pertinent to the cis-trans photoisomerization of the chromophore accompanying the motion of protein moiety. From the analysis of phase angle propagation, we obtained a rather small relaxation energy, 6–7 kcal/mol. Based on these results, we can say that FTOA analysis is useful as one of the most powerful techniques for the study of very early procedures in the excited state dynamics of pigments.     

Enzyme-mediated enantioselective hydrolysis of 1,2-diol monotosylate derivatives bearing an unsaturated substituent

We have succeeded in the easy preparation of optically active 1,2-diol monotosylates bearing an unsaturated substituent via enzymatic hydrolysis. Lipase PS quickly catalyzes the hydrolyses of 2-acetoxybut-3-enyl tosylate, which has a double bond, and 2-acetoxybut-3-ynyl tosylate, which has a triple bond, with excellent enantioselectivity to afford the corresponding optically active compounds. The reaction is also applicable to acetates with a longer chain, which has a double bond at the terminus. To demonstrate the applicability of this method, enantiomerically pure (R)-massoialactone, a natural coconut flavor, has been synthesized from racemic 2-acetoxypent-4-enyl tosylate in several steps. Furthermore, the enzyme can recognize the stereochemistry of olefins, and the (Z)-alkenyl structure is more suitable for the enantioselective hydrolysis than the (E)-isomer.     

Freezing-out of nuclear polarization in radioactive core ions of microclusters, “snowballs” in superfluid helium

A novel method was tried successfully to trap ions and to freeze out their nuclear polarization inside aggregates of helium atoms, snowballs, in superfluid helium. Spin polarized¹²B (T _1/2=20.4 ms) ions were introduced into superfluid helium and snowballs were created around the impinged impurity ions. Beta-ray asymmetry was measured to obtain the nuclear polarization of decaying¹²B. The comparison with the initial value of¹²B polarization produces that no relaxation in polarization was observed throughout lifetime of¹²B.     

Enzymatic resolution of (RS)-1-phenylalkyl β-d-glucosides to (R)-1-phenylalkyl β-primeverosides and (S)-1-phenylalkyl β-d-glucosides via plant xylosyltransferase

The stereoselective xylosylation of (RS)-1-phenylalkyl β-d-glucosides was investigated using plant xylosyltransferase isolated from cultured Catharanthus roseus cells. Enzymatic xylosylation of (RS)-1-phenylethyl β-d-glucoside afforded (R)-1-phenylethyl β-primeveroside and (S)-1-phenylethyl β-d-glucoside. The (R)-selective xylosylation of (RS)-1-phenylbutyl β-d-glucoside also occurred to give (R)-1-phenylbutyl β-primeveroside and recovered (S)-1-phenylbutyl β-d-glucoside.     

Regioselective formation of silybin-23-beta-D-glucoside by glucosylation of silybin with cultured plant cells of Eucalyptus perriniana

Time course experiment revealed that cultured plant cells of Eucalyptus perriniana regioselectively glucosylated silybin to silybin-23-beta-D-glucoside in up to 70% yield.