Capillary liquid chromatographic fingerprint used for discrimination of Zingiber montanum from related species

Fingerprint analysis using capillary liquid chromatography (CLC) has been developed for discrimination of Zingiber montanum (ZM) from related species, for example Z. americans (ZA) and Z. zerumbet (ZZ). By comparing the fingerprint chromatograms of ZM, ZA, and ZZ we could identify ZM samples and discriminate them from ZA and ZZ by using their marker peaks. We also combined CLC fingerprint with multivariate analysis, including principal-component analysis (PCA) and canonical variate analysis (CVA); all three species were discriminated successfully. This result indicates that CLC fingerprint analysis in combination with PCA and CVA can be used for discrimination of ZM samples from samples of related species.

Two‐dimensional replica‐exchange method for predicting protein–ligand binding structures

We have developed a two‐dimensional replica‐exchange method for the prediction of protein–ligand binding structures. The first dimension is the umbrella sampling along the reaction coordinate, which is the distance between a protein binding pocket and a ligand. The second dimension is the solute tempering, in which the interaction between a ligand and a protein and water is weakened. The second dimension is introduced to make a ligand follow the umbrella potential more easily and enhance the binding events, which should improve the sampling efficiency. As test cases, we applied our method to two protein‐ligand complex systems (MDM2 and HSP 90‐alpha). Starting from the configuration in which the protein and the ligand are far away from each other in each system, our method predicted the ligand binding structures in excellent agreement with the experimental data from Protein Data Bank much faster with the improved sampling efficiency than the replica‐exchange umbrella sampling method that we have previously developed. © 2013 Wiley Periodicals, Inc.     

Synthesis and Biological Evaluation of the Forssman Antigen Pentasaccharide and Derivatives by a One‐Pot Glycosylation Procedure

The synthesis and biological evaluation of the Forssman antigen pentasaccharide and derivatives thereof by using a one‐pot glycosylation and polymer‐assisted deprotection is described. The Forssman antigen pentasaccharide, composed of GalNAcα(1,3)GalNAcβ(1,3)Galα(1,4)Galβ(1,4)Glc, was recently identified as a ligand of the lectin SLL‐2 isolated from an octocoral Sinularia lochmodes. The chemo‐ and α‐selective glycosylation of a thiogalactoside with a hemiacetal donor by using a mixture of Tf₂O, TTBP and Ph₂SO, followed by activation of the remaining thioglycoside, provided the trisaccharide at the reducing end in a one‐pot procedure. The pentasaccharide was prepared by the α‐selective glycosylation of the N‐Troc‐protected (Troc=2,2,2‐trichloroethoxycarbonyl) thioglycoside with a 2‐azide‐1‐hydroxyl glycosyl donor, followed by glycosidation of the resulting disaccharide at the C3 hydroxyl group of the trisaccharide acceptor in a one‐pot process. We next applied the one‐pot glycosylation method to the synthesis of pentasaccharides in which the galactosamine units were partially and fully replaced by galactose units. Among the three possible pentasaccharides, Galα(1,3)GalNAc and Galα(1,3)Gal derivatives were successfully prepared by the established method. An assay of the binding of the synthetic oligosaccharides to a fluorescent‐labeled SLL‐2 revealed that the NHAc substituents and the length of the oligosaccharide chain were both important for the binding of the oligosaccharide to SLL‐2. The inhibition effect of the oligosaccharide relative to the morphological changes of Symbiodinium by SLL‐2, was comparable to their binding affinity to SLL‐2. In addition, we fortuitously found that the synthetic Forssman antigen pentasaccharide directly promotes a morphological change in Symbiodinium. These results strongly indicate that the Forssman antigen also functions as a chemical mediator of Symbiodinium.     

18O/16O-Encoding Strategy for Microscale Stereochemical Determination of Peptidic Natural Products

The demand for more efficient methods of establishing the undetermined stereochemistries of peptidic natural products continues unabated. A new method for microscale stereochemical determination was devised by integrating solid-phase synthesis, split-and-mix randomization, ¹⁸O/¹⁶O-encoding of d /l -configurations, tandem mass spectrometry, and biological evaluation. Here we applied gramicidin A as the molecule for a blind test. Gramicidin A and its 31 diastereomers were randomly prepared in microgram scale with ¹⁸O/¹⁶O-stereochemical encoding and subjected to MS/MS-structural determination and cytotoxicity assay. Only the parent gramicidin A was selected from among the 32 stereoisomers, validating the high reliability of the present strategy.     

Electrochemical Determination of Organic Compounds in Automotive Fuels

This article critically reviews the electroanalytical methods devoted for the determination of organic compounds in automotive fuels that can range from contaminants to additives typically introduced into liquid biofuels and liquid fossil fuels. Contaminants such as aldehydes and ketones in bioethanol, free fatty acids and glycerol in biodiesel, and sulfur and nitrogen organic compounds in gasoline and diesel fuel, and additives such as colour markers and antioxidants added to fuels were determined by electroanalytical methods. Special focus is given to electrodes, electrochemical techniques, and sample preparation strategies. Future directions of research on electroanalysis of liquid fuels are presented.     

Coherent Vibration and Femtosecond Dynamics of the Platinum Complex Oligomers upon Intermolecular Bond Formation in the Excited State

Femtosecond time-resolved absorption and picosecond time-resolved emission measurements were carried out for highly concentrated aqueous solutions of K₂[Pt(CN)₄] to investigate excited-state dynamics of the [Pt(CN)₄²⁻] oligomers formed with metallophilic interactions. Time-resolved absorption spectra exhibit complicated dynamics that are represented with five time constants. Among them, the 90-ps and 400-ps dynamics were assigned to the S₁ → T₁ intersystem crossing of the trimer and tetramer coexisting in the solution by comparison with the fluorescence decays. Clear oscillations of transient absorption were observed in the first few picoseconds, and the frequency-detected-wavelength 2D analysis revealed that the 135-cm⁻¹ and 65-cm⁻¹ oscillations arise from the Pt–Pt stretch motions of the S₁ trimer and S₁ tetramer, respectively. The obtained time-resolved spectroscopic data provide a clear view of the excited-state dynamics of the [Pt(CN)₄²⁻] oligomers in the femto-/picosecond time region.