Peptide ligation via side-chain auxiliary

A new peptide ligation strategy based on a side-chain auxiliary was developed; the auxiliary is fairly simple and can be removed, without product isolation, under basic conditions.     

Spectrophotometric determination of H(2)-receptor antagonists via their oxidation with cerium(IV)

A simple, accurate and sensitive spectrophotometric method has been developed and validated for determination of H(2)-receptor antagonists: cimetidine, famotidine, nizatidine and ranitidine hydrochloride. The method was based on the oxidation of these drugs with cerium(IV) in presence of perchloric acid and subsequent measurement of the excess Ce(IV) by its reaction with p-dimethylaminobenzaldehyde to give a red colored product (lambda(max) at 464nm). The decrease in the absorption intensity of the colored product (DeltaA), due to the presence of the drug was correlated with its concentration in the sample solution. Different variables affecting the reaction were carefully studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9990-0.9994) were found between DeltaA values and the concentrations of the drugs in a concentration range of 1-20microgml(-1). The assay limits of detection and quantitation were 0.18-0.60 and 0.54-1.53microgml(-1), respectively. The method was validated, in terms of accuracy, precision, ruggedness and robustness; the results were satisfactory. The proposed method was successfully applied to the determination of the investigated drugs in pure and pharmaceutical dosage forms (recovery was 98.3-102.6+/-0.57-1.90%) without interference from the common excipients. The results obtained by the proposed method were comparable with those obtained by the official methods.     

Nonextractive procedure and precolumn derivatization with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole for trace determination of trimetazidine in plasma by high-performance liquid chromatography with fluorescence detection

A highly sensitive high-performance liquid chromatographic method with fluorescence detection has been developed and validated in a single laboratory for the trace determination of trimetazidine (TMZ) in human plasma. Fluoxetine (FLX) was used as the internal standard. TMZ and FLX were isolated from plasma by protein precipitation with acetonitrile and derivatized by heating with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole in pH 8 borate buffer at 70 degrees C for 30 min. Separations were performed in the isocratic mode on a Nucleosil CN column with the mobile phase acetonitrile-10 mM sodium acetate buffer (pH 3.5)-methanol (47 + 47 + 6, v/v/v) at a flow rate of 1.0 mL/min. The derivatized samples were excited at 470 nm and monitored at an emission wavelength of 530 nm. Under the optimum chromatographic conditions, a linear relationship with a good correlation coefficient (r = 0.9997, n = 5) was obtained for the peak area ratio of TMZ to FLX and for TMZ concentrations of 1-120 ng/mL. The proposed method has the lowest limits of detection and quantitation reported to date for the determination of TMZ in plasma with values of 0.3 and 0.95 ng/mL, respectively. The values for intra- and interassay precision were satisfactory; the relative standard deviations were < or =4.04%. The accuracy of the method was demonstrated; the recoveries of TMZ from spiked human plasma were 98.13-102.83 +/- 0.2-4.04%. The method has high throughput because of its simple sample preparation procedure and short run time (<10 min). The results demonstrated that the proposed method would have great value when applied in pharmacokinetic studies for TMZ.     

Polybenzimidazole‐decorated carbon nanotube: A high‐performance proton conductor

Interaction between negatively charged Nafion^® and a positively charged polybenzimidazole‐decorated carbon nanotube leads to the formation of an ionic complex with high charge density for proton conduction, which can lead to an improvement in transport properties. Here we investigate the high‐temperature and low‐humidity proton conductivity of this nanocomposite membrane as a potential membrane for fuel cell applications.

     

Plasmon enhanced light absorption in bulk heterojunction organic solar cells

Silver nanospheres (Ag NSs) buffer layers were introduced via a solution casting process to enhance the light absorption in poly (3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C61 butyric acid methyl ester (PCBM) bulk heterojunction organic solar cells. These Ag NSs, as surface plasmons, could increase the optical electric field in the photoactive layer whilst simultaneously improving the light scattering. As a result, this buffer layer improves the light absorption of P3HT:PCBM blend and consequently improves the external quantum efficiency (EQE) of organic solar cells. In this work, different sizes of Ag NSs plasmon‐enhanced layer were investigated, with the aim of optimizing the performance of devices. UV‐vis spectrometer measurement demonstrates that the total optical absorption of P3HT:PCBM blend films in the spectral range of 350–650 nm is increased by ～4 and 6% with incorporation of the 20 and 40 nm Ag NSs, respectively. The J_sc was shown to increase by ～21 and 24% for 20 and 40 nm Ag NSs, respectively. This is due to the extra photogenerated excitons by the plasmonic resonance of Ag NSs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chemistry and biology of the ubiquitin signal

Ubiquitination is one of the most utilized posttranslational modifications in eukaryotes and is involved in a wide range of cellular processes, but is mostly known as a signal for proteasomal degradation. Recently, it has become clear that the ubiquitin signal is far more complex and is dictated by the ubiquitin component and the substrate. The remarkable diversity of the ubiquitin signaling process has triggered an incredible amount of effort to investigate the role of ubiquitination on biological processes. However, despite more than three decades of studies, several important questions remain unanswered. A major hurdle is the inability to obtain homogeneous ubiquitin bioconjugates in sufficient amounts from cells or by application of the enzymatic machinery. Recent breakthroughs in chemical and semisynthetic strategies, however, offer solutions to these challenges. In this Review, we survey the fundamental biological aspects of the ubiquitin signal and present the emerging non-enzymatic approaches for overcoming these obstacles.     

Hydrodynamic Characteristics and Adsorption Particularity of Nanobiological Feedstock Along the Bed Height in a Novel Chromatography Column

Expanded bed adsorption (EBA) is a practical method for the separation of nanoparticulates. In order to analysis the local hydrodynamic and adsorption behavior of nanoparticle (NP)-based biological feedstock, a modified Nano Biotechnology Group EBA column with a 26-mm inner diameter was used to withdraw liquid from different axial positions of the column. Fabricated egg albumin (EA) NPs with an average size of 70 nm were employed as a model system and viral size/charge mimic to assess the relationship between hydrodynamic and adsorption performance of NPs at the different column regions. The effects of influential factors, including flow velocity and initial concentration of NPs, on NP hydrodynamic behavior and adsorption kinetics along the bed height were investigated. NP hydrodynamic studies confirmed that non-uniform behavior dominated the system and a decreasing trend of liquid mixing/dispersion with increase of bed height was observed in this column. The results demonstrated an increase in the mixing/dispersion at certain bed heights with the increase in both the velocity and feed initial concentration. Breakthrough curves were measured at various column points to determine the adsorption performance [dynamic binding capacity (DBC) and yield] in different bed positions/zones. Yield and DBC of NPs were improved along the bed height, whereas liquid velocity had the opposite effect. Increasing the initial concentration of NPs enhanced only the DBC. Separation of EA NPs under optimal conditions was 87 %, which is an excellent result for a one-pass frontal chromatography method.

     

Variation in antioxidant attributes at three ripening stages of guava (Psidium guajava L.) fruit from different geographical regions of Pakistan

The present investigation was carried out to appraise the levels of total phenols and vitamin C as well as antioxidant potential at three different ripening stages (un-ripe, semi-ripe and fully-ripe) of guava (Psidium guajava L.) fruit collected from three different geographical regions of Pakistan (Islamabad, Faisalabad and Bhakkar). The antioxidant potential of guava fruit extracts was assessed by means of different in-vitro antioxidant assays, namely inhibition of peroxidation in linoleic acid system, reducing power and radical scavenging capability. Overall, fruit at the un-ripe stage (G1) exhibited the highest levels of TPC, TFC, reducing power and DPPH radical scavenging activity, followed by the semi-ripe (G2) and fully-ripe (G3) stages. On the other hand, vitamin C content increased as the fruit maturity progressed, with highest value seen at the fully-ripe stage (G3) followed by the semi-ripe (G2) and un-ripe stage (G1). The concentration of vitamin C in fruits varied as: Faisalabad (136.4-247.9 mg 100 g?1), Islamabad (89.7-149.7 mg 100 g?1) and Bhakkar (73.1-129.5 mg 100 g?1). The results showed that different stages of maturation and geographical locations had profound effects on the antioxidant activity and vitamin C contents of guava fruit.     

Synthesis and Crystal Structure of a Cyanido-Bridged Bimetallic Copper(II)–Silver(I) Complex of Imidazole and [Ag(CN)<Subscript>2</Subscript>]<Superscript>−</Superscript>: [Cu(Imidazole)<Subscript>4</Subscript>{Ag(CN)<Subscript>2</Subscript>}<Subscript>2</Subscript>]

Abstract  

A cyanido-bridged Cu(II)–Ag(I) bimetallic complex, [Cu(Imidazole)₄{Ag(CN)₂}₂] has been prepared and structurally characterized. The compound crystallizes in the orthorhombic space group Pmna. The crystal structure of the complex consists of trinuclear molecules made up of one [Cu(Imidazole)₄]⁺² and two [Ag(CN)₂]⁻ units. The trinuclear molecules are interlinked to each other through N–H–N and C–H–N hydrogen bonds. The Cu(II) ions are located on mirrors and assume distorted octahedral geometry with the basal plane consisting of four imidazole N-atoms.     

Applications of enzymatic and non-enzymatic methods to access enantiomerically pure compounds using kinetic resolution and racemisation

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Different methods to access enantiomerically pure compounds.