Specific rearrangement reactions of acetylated lysine containing peptide bn (n = 4–7) ion series

Characterization of ε‐N‐acetylated lysine containing peptides, one of the most prominent post‐translational modifications of proteins, is an important goal for tandem mass spectrometry experiments. A systematic study for the fragmentation reactions of b ions derived from ε‐N‐acetyllysine containing model octapeptides (K_AcYAGFLVG and YAK_AcGFLVG) has been examined in detail. Collision‐induced dissociation (CID) mass spectra of b_n (n = 4–7) fragments of ε‐N‐acetylated lysine containing peptides are compared with those of N‐terminal acetylated and doubly acetylated (both ε‐N and N‐terminal) peptides, as well as acetyl‐free peptides. Both direct and nondirect fragments are observed for acetyl‐free and singly acetylated (ε‐N or N‐terminal) peptides. In the case of ε‐N‐acetylated lysine containing peptides, however, specific fragment ions (m/z 309, 456, 569 and 668) are observed in CID mass spectra of b_n (n = 4–7) ions. The CID mass spectra of these four ions are shown to be identical to those of selected protonated C‐terminal amidated peptides. On this basis, a new type of rearrangement chemistry is proposed to account for the formation of these fragment ions, which are specific for ε‐N‐acetylated lysine containing peptides. Consistent with the observation of nondirect fragments, it is proposed that the b ions undergo head‐to‐tail macrocyclization followed by ring opening. The proposed reaction pathway assumes that b_n (n = 4–7) of ε‐N‐acetylated lysine containing peptides has a tendency to place the K_Ac residue at the C‐terminal position after macrocyclization/reopening mechanism. Then, following the loss of CO, it is proposed that the marker ions are the result of the loss of an acetyllysine imine as a neutral fragment. Copyright © 2014 John Wiley & Sons, Ltd.     

New version of Bäcklund transformations in Euclidean 3‐space

In this paper, we study the Bäcklund transformations for the adjoint curve in the Euclidean 3‐space. Firstly, it is obtained some essential equations of the Bäcklund transformation. After this, we give a new theorem, the Bäcklund transformations for the adjoint curve in Euclidean 3‐space.     

Three Tyrosinase Inhibitors and Antioxidant Compounds from Salsola foetida

Phytochemical investigation on the whole plant of Salsola foetida resulted in the isolation of three new phenolic compounds 1, 2 , and 3 , which exhibit tyrosinase inhibition with moderate antioxidant activity. Compounds 1 – 3 inhibited tyrosinase with IC₅₀ 2.61, 1.85, and 0.40 μM , while exhibiting DPPH radical scavenging activity with IC₅₀ 383, 427 and 378 μM , respectively. The structures of 1, 2 , and 3 were determined by modern spectroscopic techniques.     

Predicting points of zero charge of oxides and hydroxides

Pauling's electrostatic valence principle has been applied to describe the surface-charging mechanism of oxides in an aqueous environment. This approach has led to the development of an equation with which one can predict the points of zero charge (PZC) of oxides and hydroxides from crystallographic data. The equation proposed in the present work is an improved version of Parks' PZC equation. The improvements are the following: (i) The equation does not incorporate correction terms to take the cation coordination numbers into account; (ii) the PZC of a complex oxide can be predicted directly from crystallographic data instead of from “assumed” PZCs of its component oxides; and (iii) one can use the mean metal-oxygen bond distance of a crystal instead of the ionic radii tabulated by Parks, which are not consistent with the up-to-date values.     

Surface diffusive motion in a periodic and asymmetric potential

9,10-Dithioanthracene adsorbed on Cu(111) diffuses exclusively along the high-symmetry axis of the molecule-substrate system. Further reduction of the symmetry of the system by asymmetric methylation does not reduce the symmetry of the motion although it has a substantial effect on the diffusion rate (100-fold reduction) and renders the diffusion barrier asymmetric. This is in contrast to the behavior expected of a classical particle, and it provides a direct single-molecule-scale vista on the validity of The Principle of Microscopic Reversibility first formulated by Tolman in 1924, which despite its fundamental role has attracted little visualization.     

Cationic palladium(II) catalysts on O-carboxymethyl chitosan Schiff base for Suzuki coupling reactions

In this study, catalytic activity of two different cationic O-Carboxymethyl chitosan Schiff base palladium (II) complexes in Suzuki coupling reactions and synthesis of biarlys having different functional groups, and reusability of the catalysts were tested. Chemical structures of the synthesized biaryls were elucidated by GC-MS and ¹H-NMR; and no by-products were observed in the spectra. Cationic palladium (II) catalysts high turnover numbers and selectivity were recorded for the reactions. Mercury test demonstrated that the reaction mechanism proceed a homogeneous route. Reusability tests of cationic biocatalysts showed that their catalytic activity were still highly efficient even after six cycles.     

Free radical scavenging phenylethanoid glycosides from Leucas indica Linn

A new phenylethanoid glycoside, 2-(3,4-dihydroxyphenyl)-ethyl-O-alpha-L-rhamnopyranosyl-(1 --> 3)-O-alpha-L-rhamnopyranosyl-(1 --> 6)-4-O-E-feruloyl-beta-D-glucopyranoside (3-O-methyl poliu-moside, 1) along with five known phenylethanoid glycosides (2-6) were isolated from the aerial parts of Leucas indica Linn. The structure of compound 1 has been elucidated on the basis of spectral data. Compounds 1-6 exhibited significant antioxidant activity in 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay method. These compounds were also found to be moderate inhibitors of xanthine oxidase (XO) enzyme.     

A new method for fast chitin extraction from shells of crab,crayfish and shrimp

A new method for quick chitin isolation from the shells of crab, crayfish and shrimp is described. The main difference between the new method and the conventional method is two sodium hypochlorite (NaClO) treatments for 10 min each before the processes of demineralisation and deproteinisation. After the NaClO treatment, only 15 min is adequate for the demineralisation and 20 min for the deproteinisation processes. Newly extracted chitin from crab, crayfish and shrimp shells and commercial chitin were characterised using FT-IR, TGA, X-ray diffractometry and elemental analysis. From the results, it was observed that the chitins isolated with the new method and the commercial chitin had almost the same physicochemical properties. The advantage of the new method compared to traditional methods is the relatively rapid chitin extraction. When compared to the traditional chitin extraction method, the proposed method appears to be promising regarding its time and energy saving nature.