The influence of sample area on diclofenac sodium quantification by diffuse reflectance IR spectroscopy

A procedure for the quantitative determination of diclofenac sodium (DS) in commercial capsules and tablets based on Partial Least Squares (PLS) treatment of diffuse reflectance FTIR spectroscopic (DRIFTS) data is described. Two DRIFTS accessories, a Collector II (Spectra-Tech) and a Seagull (Harrick Scientific), were used to collect the spectra. The spectrometer beam area on the surface of the sample was approximately sevenfold smaller for the Collector II accessory compared to the Seagull accessory. Spectra collection using the smaller beam spot resulted in significantly higher quantification errors for the single measurements. To reduce the errors associated with the Collector II accessory spectra were collected seven times while randomly changing the sample position. The mean spectra were used in the analysis. To compare the predictive ability of the constructed models, the relative standard errors of prediction (RSEP) were calculated. The RSEPs were 1.3-2.9% and 2.0-2.6% using the Collector II accessory and 1.0-1.5% and 1.1-1.7% using the Seagull accessory, for calibration and validation data sets, for the different PLS models. Three commercial preparations containing 20.5, 23.2 and 34.5% DS were successfully quantified using the developed models. The proposed procedure can be used as a fast, precise and economic method for DS quantification in tablets and capsules.     

Synthesis of Natural Products by C−H Functionalization of Heterocycless

Total synthesis is considered by many as the finest combination of art and science. During the last decades, several concepts were proposed for achieving the perfect vision of total synthesis, such as atom economy, step economy, or redox economy. In this context, C−H functionalization represents the most powerful platform that has emerged in the last years, empowering rapid synthesis of complex natural products and enabling diversification of bioactive scaffolds based on natural product architectures. In this review, we present an overview of the recent strategies towards the total synthesis of heterocyclic natural products enabled by C−H functionalization. Heterocycles represent the most common motifs in drug discovery and marketed drugs. The implementation of C−H functionalization of heterocycles enables novel tactics in the construction of core architectures, but also changes the logic design of retrosynthetic strategies and permits access to natural product scaffolds with novel and enhanced biological activities.     

Polyethylene green composites modified with post agricultural waste filler: thermo-mechanical and damping properties

The aim of the study was to determine thermo-mechanical properties and applicability of sunflower husk waste as a filler for ultra low density polyethylene composites. The post agricultural waste filler was milled and chemically treated with (3-aminopropyl)triethoxysilane (3-APS). The amount of filler used was 5, 10 and 20 wt%. The mechanical and thermal properties of the composites containing unmodified and modified natural fillers were determined in the course of static tensile test, rebound resilience by Schob method, and dynamic mechanic thermal analysis. The influence of filler loading and chemical modification of the filler on the morphology of natural composites was evaluated by SEM analysis.     

Langmuir evaporation from the (100), (111A), and (111B) faces of GaAs

We have measured the Langmuir evaporation of Ga and As from the (100), (111A), and (111B) faces of GaAs above and below the congruent evaporation temperature T_c. We have found that T_c is lowest for the (111B) face and highest for the (111A) face. These differences can be understood in terms of the different lifetimes of surface Ga on these faces. Furthermore, we have deduced that the evaporation processes are the rate limiting steps in the decomposition of GaAs. Below T_c, decomposition is controlled by the evaporation of Ga; above T_c it is controlled by the evaporation of As.     

Electrostatic Localization of RNA to Protocell Membranes by Cationic Hydrophobic Peptides

Cooperative interactions between RNA and vesicle membranes on the prebiotic earth may have led to the emergence of primitive cells. The membrane surface offers a potential platform for the catalysis of reactions involving RNA, but this scenario relies upon the existence of a simple mechanism by which RNA could become associated with protocell membranes. Here, we show that electrostatic interactions provided by short, basic, amphipathic peptides can be harnessed to drive RNA binding to both zwitterionic phospholipid and anionic fatty acid membranes. We show that the association of cationic molecules with phospholipid vesicles can enhance the local positive charge on a membrane and attract RNA polynucleotides. This phenomenon can be reproduced with amphipathic peptides as short as three amino acids. Finally, we show that peptides can cross bilayer membranes to localize encapsulated RNA. This mechanism of polynucleotide confinement could have been important for primitive cellular evolution.     

System size, energy, pseudorapidity, and centrality dependence of elliptic flow

This Letter presents measurements of the elliptic flow of charged particles as a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and 200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider. The elliptic flow in Cu-Cu collisions is found to be significant even for the most central events. For comparison with the Au-Au results, it is found that the detailed way in which the collision geometry (eccentricity) is estimated is of critical importance when scaling out system-size effects. A new form of eccentricity, called the participant eccentricity, is introduced which yields a scaled elliptic flow in the Cu-Cu system that has the same relative magnitude and qualitative features as that in the Au-Au system.     

2',3'-Dideoxy-3'-thionucleoside triphosphates: syntheses and polymerase substrate activities

All four 2',3'-dideoxy-3'-thio-nucleosides (ddtNTPs) function as substrates for the Y410F mutant of Deep Vent (exo-) DNA polymerase. Not only are the ddtNTPs incorporated to form the N + 1 product, but further elongations are observed in which the key step is attack of the 3'-thiol on the 5'-triphosphate. Although other polymerases are likely to differ in their use of the ddtNTPs, there does not appear to be a fundamental prohibition against using a thiol nucleophile on a phosphate anhydride electrophile. The syntheses of four ddtNTPs (C, T, A, G) are described. [structure: see text]     

Ribosomal synthesis of dehydroalanine-containing peptides

Dehydroalanine is a nonproteinogenic amino acid, but it is a component of a wide variety of natural products with therapeutic activities. Indeed, this alpha,beta-unsaturated residue is a highly versatile building block due to its rigidifying effect on peptide backbones and its electrophilicity which allows site-specific thiol ligations of peptides with small molecules or proteins. To harness such versatility in genetically encoded, combinatorial peptide libraries, we report a simple and robust method for the ribosomal synthesis of dehydroalanine-containing peptides. Selenalysine, a selenium-containing lysine analogue, was recruited as a masked dehydroalanine equivalent. This residue is efficiently incorporated by a reconstituted Escherichia coli translation system at high fidelity and efficiency despite the presence of low levels of lysine. Mild oxidative conditions were used to convert selenalysine into dehydroalanine post-translationally. Using this method, we demonstrate the preparation of polyunsaturated and highly decorated peptides. This report is an important step toward the preparation and selection of large libraries of protein-reactive compounds with potential use as novel drugs or as analytical tools.