Topochemical synthesis and catalysis of metal nanoparticles exposed on crystalline cellulose nanofibers

Topochemical synthesis of gold nanoparticles (AuNPs) was achieved on crystalline cellulose single nanofibers (CSNFs), which were tailored from native cellulose. Exposed AuNPs@CSNFs composite exhibited an excellent catalytic efficiency: the turnover frequency of the AuNPs@CSNFs was up to 840 times that of conventional polymer-supported AuNPs, for a model aqueous reduction reaction. Our novel strategy provides a promising solution to realize efficient use of limited noble metals using natural bioresources.     

Transverse Relaxation of Scalar‐Coupled Protons

In a preliminary communication (B. Baishya, T. F. Segawa, G. Bodenhausen, J. Am. Chem. Soc. 2009 , 131, 17538–17539), we recently demonstrated that it is possible to obtain clean echo decays of protons in biomolecules despite the presence of homonuclear scalar couplings. These unmodulated decays allow one to determine apparent transverse relaxation rates R₂^app of individual protons. Herein, we report the observation of R₂^app for three methyl protons, four amide H^N protons, and all 11 backbone H^α protons in cyclosporin A. If the proton resonances overlap, their R₂^app rates can be measured by transferring their magnetization to neighboring ¹³C nuclei, which are less prone to overlap. The R₂^app rates of protons attached to ¹³C are faster than those attached to ¹²C because of ¹³C–¹H dipolar interactions. The differences of these rates allow the determination of local correlation functions. Backbone H^N and H^α protons that have fast decay rates R₂^app also feature fast longitudinal relaxation rates R₁ and intense NOESY cross peaks that are typical of crowded environments. Variations of R₂^app rates of backbone H^α protons in similar amino acids reflect differences in local environments.     

An efficient and regioselective iodination of electron-rich aromatic compounds using N-chlorosuccinimide and sodium iodide

An efficient and regioselective method for iodination of electron-rich aromatic compounds was found using N-chlorosuccinimide and sodium iodide in AcOH with short reaction times. This method is also applicable to non-benzenoid aromatic or heteroaromatic compounds.     

Room-temperature regioselective C-H/olefin coupling of aromatic ketones using an activated ruthenium catalyst with a carbonyl ligand and structural elucidation of key intermediates

Mechanistic studies of the ruthenium-catalyzed reaction of aromatic ketones with olefins are presented. Treatment of the original catalyst, RuH(2)(CO)(PPh(3))(3), with trimethylvinylsilane at 90 °C for 1-1.5 h afforded an activated ruthenium catalyst, Ru(o-C(6)H(4)PPh(2))(H)(CO)(PPh(3))(2), as a mixture of four geometric isomers. The activated complex showed high catalytic activity for C-H/olefin coupling, and the reaction of 2'-methylacetophenone with trimethylvinylsilane at room temperature for 48 h gave the corresponding ortho-alkylation product in 99% isolated yield. The activated catalyst was thermally robust and showed excellent catalytic activity under refluxing toluene conditions. (1)H and (31)P NMR studies of the C-H/olefin coupling at room temperature suggested that an ortho-ruthenated complex, P,P'-cis-C,H-cis-Ru(2'-(6'-MeC(6)H(4)C(O)Me))(H)(CO)(PPh(3))(2), participated in the reaction as a key intermediate. Isotope labeling studies using acetophenone-d(5) indicated that the rate-limiting step was the C-C bond formation, not the C-H bond cleavage, and that each step prior to the reductive elimination was reversible. The rate of C-H/olefin coupling was found to exhibit pseudo first-order kinetics and to show first-order dependence on the ruthenium complex concentration.     

Complex mixture analysis of organic compounds in green coffee bean extract by two‐dimensional NMR spectroscopy

A complex mixture analysis by one‐ and two‐dimensional nuclear magnetic resonance (NMR) spectroscopy was carried out for the first time for the identification and quantification of organic compounds in green coffee bean extract (GCBE). A combination of ¹H? ¹H DQF‐COSY, ¹H? ¹³C HSQC, and ¹H? ¹³C CT‐HMBC two‐dimensional sequences was used, and 16 compounds were identified. In particular, three isomers of caffeoylquinic acid were identified in the complex mixture without any separation. In addition, GCBE components were quantified by the integration of carbon signals by use of a relaxation reagent and an inverse‐gated decoupling method without a nuclear Overhauser effect. This NMR methodology provides detailed information about the kinds and amounts of GCBE components, and in our study, the chemical makeup of GCBE was clarified by the NMR results. Copyright © 2010 John Wiley & Sons, Ltd.     

Dicationic platinum porphyrin catalyzed cycloisomerization of enynes

Cycloisomerization of 1,6-enynes is successfully carried out in the presence of a dicationic platinum(IV) catalyst to afford five-membered ring systems. The use of a weakly coordinating axial ligand is the key to bringing out the catalytic activity of platinum porphyrin for the reaction.     

Effect of pyrolysis conditions on the properties of carbonaceous nanofibers obtained from freeze-dried cellulose nanofibers

Carbonaceous nanofibers (CsNFs) were produced by pyrolysis of cellulose nanofibers synthesised from wood pulp using a top-down approach. The effects of heat treatment conditions on the thermal, morphological, crystal and chemical properties of the CsNFs were investigated using TGA, SEM, XRD and FT-IR, respectively. The results showed that heat treatment conditions around the thermal decomposition temperature of cellulose greatly influence the morphology of resulting materials. Slow heating rates (1 °C/min) between 240 and 400 °C as well as prolonged isothermal heat treatment (17 h) at 240 °C were necessary to avoid destruction of the original fibrous morphology in carbonized nanofibers. On the other hand, such heat treatment had little effect on micron sized fibers. The optimized heat treatment conditions led to the release of oxygen and hydrogen from cellulose before thermal breakdown of glycosidic rings, which in turn prevented depolymerization and tar formation, resulting in the preservation of the fibrous morphology.