Expected and unexpected results from combined beta-hairpin design elements

A model beta-hairpin dodecapeptide [EFGWVpGKWTIK] was designed by including a favorable D-ProGly Type II' beta-turn sequence and a Trp-zip interaction, while also incorporating a beta-strand unfavorable glycine residue in the N-terminal strand. This peptide is highly folded and monomeric in aqueous solution as determined by combined analysis with circular dichroism and 1H NMR spectroscopy. A peptide representing the folded conformation of the model beta-hairpin [cyclic(EFGWVpGKWTIKpG)] and a linear peptide representing the unfolded conformation [EFGWVPGKWTIK] yield unexpected relative deviations between the CD and 1H NMR spectroscopic results that are attributed to variations in the packing interactions of the aromatic side chains. Mutational analysis of the model beta-hairpin indicates that the Trp-zip interaction favors folding and stability relative to an alternate hydrophobic cluster between Trp and Tyr residues [EFGYVpGKWTIK]. The significance of select diagonal interactions in the model beta-hairpin was tested by rearranging the cross-strand hydrophobic interactions to provide a folded peptide [EWFGIpGKTYWK] displaying evidence of an unusual backbone conformation at the hydrophobic cluster. This unusual conformation does not appear to be a result of the glycine residue in the beta-strand, as replacement with a serine results in a peptide [EWFSIpGKTYWK] with a similar and seemingly characteristic CD spectrum. However, an alternate arrangement of hydrophobic residues with a Trp-zip interaction in a similar position to the parent beta-hairpin [EGFWVpGKWITK] results in a folded beta-hairpin conformation. The differences between side chain packing of these peptides precludes meaningful thermodynamic analysis and illustrates the caution necessary when interpreting beta-hairpin folding thermodynamics that are driven, at least in part, by aromatic cross strand interactions.     

Dually responsive multiblock copolymers via RAFT polymerization: Synthesis of temperature- and redox-responsive copolymers of PNIPAM and PDMAEMA

We report synthesis of temperature- and redox-responsive multiblock copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization. Well-defined α,ω-bis(dithioester)-functionalized poly(N-isopropylacrylamide) (PNIPAM) and poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) were prepared using 1,4-bis(thiobenzoylthiomethyl)benzene and 1,4-bis(2-(thiobenzoylthio)prop-2-yl)benzene as RAFT agents, respectively. Dually responsive multiblock copolymers were synthesized in a single aminolysis/oxidation step from the α,ω-bis(dithioester)-terminated PNIPAM and PDMAEMA. The copolymers and their stimulus-responsive behavior were characterized by size exclusion chromatography, NMR, light scattering and atomic force microscopy. Due to the presence of redox-sensitive disulfide bonds between the blocks, the copolymers were readily reduced to the starting polymer blocks. The presence of temperature-responsive PNIPAM blocks provided the copolymers with the ability to assemble into core-shell nanostructures with hydrophobic PNIPAM as a core and cationic PDMAEMA as stabilizing shell when above the phase transition temperatures of PNIPAM. The temperature-induced assembly of the copolymers also showed substantial pH sensitivity. The phase transition temperature increased with decreasing pH, while molecular weight of the assemblies decreased.     

Green Synthesis and Characterization of Hybrid Collagen–Cellulose–Albumin Biofibers from Skin Waste

Collagen (C) and cellulose are prominent biopolymers from the animal and plant kingdom and widely used in bioengineering. Albumin, on the other hand, is the most abundant plasma protein present in mammalian blood. In this work, collagen extracted from animal skin waste was blended with hydroxyethyl cellulose (HEC) and bovine serum albumin (A) and wet-spun to form hybrid biodegradable C/HEC/A fibers. They were further cross-linked with glutaraldehyde vapors and analyzed. X-ray diffraction and infra-red spectroscopic studies of the hybrid fibers display peaks corresponding to collagen, cellulose, and albumin. Incorporation of cellulose into the biopolymeric matrix leads to a reasonable improvement in mechanical, swelling, and thermal properties of hybrid fibers. Addition of albumin improves the regularity of fiber surface without altering the porosity as observed under a microscope. Hence, the formed hybrid biofibers can be potentially used as a suture material as well as for different biomedical applications due to their improved properties.     

Novel Synthesis of (E)-3-Arylidene-2,3-dihydrobenzo[b][1,4]oxazepin-4(5H)-ones Using Baylis–Hillman Derivatives via Reductive Cyclization

A simple synthesis of novel (E)-3-arylidene-2,3-dihydrobenzo[b][1,4]oxazepin-4(5H)-ones from bromides of the Baylis--Hillman adducts using Fe/AcOH for the in situ reduction of nitro group, into an amino group, followed by the cyclization as a key step, has been described.     

Development of fish gelatin-based artificial fish baits incorporating bioattractants from seafood processing waste

The study dealt with evolving an artificial fish bait by incorporating bioattractant concentrates derived from seafood processing wastes by enzymatic hydrolysis namely fish waste concentrate (FWC), squid waste concentrate (SWC), and shrimp processing concentrate (SPWC). They were characterized based on amino acid content and presence of different functional groups using FTIR. Among them, SWC was found to have the highest amino acid content of 60.85mg/100 mg followed by FWC (42.21mg/100 mg) and SPWC (24.82mg/100 mg). The developed artificial fish baits were subjected to protein leaching, solubility in seawater besides testing for acceptability by the red snapper. The study revealed that the bait incorporated with SWC at 3% level was found be the most ideal, with the protein leaching rate of 24.82 mg/g/h, solubility rate of 36.6 mg/g/h and the attractability score of 29/30. The amino acid leaching rate was 3.11 mg/h/100 mg and it was found to contain five amino acids such as glycine, proline, glutamic acid, alanine and serine. The study revealed that the hydrolyzed squid waste concentrate can be incorporated at 3% (w/w) with fish gelatin based biomatrix during gelation to prepare artificial bait.     

Optical and redox properties of a series of 3,4-ethylenedioxythiophene oligomers

The optical and redox properties of a series of 3,4-ethylenedioxythiophene oligomers (EDOTn, n=1-4) and their beta,beta'-unsubstituted analogues (Tn, n=1-4) are described. Both series are end capped with phenyl groups to prevent irreversible alpha-coupling reactions during oxidative doping. Absorption and fluorescence spectra of both series reveal a significantly higher degree of intrachain conformational order in the EDOTn oligomers. Oxidation potentials (E(PA1) and E(PA2)) determined by cyclic voltammetry reveal that those of EDOTn are significantly lower than the corresponding Tn oligomers as a consequence of the electron-donating 3,4-ethylenedioxy substitution. Linear fits of E(PA1) and E(PA2) versus the reciprocal number of double bonds reveal significantly steeper slopes for the EDOTn than for the Tn oligomers. This could indicate a more effective conjugation for the EDOTn series, confirmed by the fact that coalescence of E(PA1) and E(PA2) is reached already at relatively short chain lengths ( approximately 5 EDOT units) in contrast to the Tn series (>10 thiophene units). The stepwise chemical oxidation of the EDOTn and Tn oligomers in solution was carried out to obtain radical cations and dications. The energies of the optical transitions of the radical cations and dications as determined by UV/Vis/NIR spectroscopy were similar for the two series. These spectroscopic observations are consistent with quantum-chemical calculations performed on the singly charged molecules. Cooling solutions containing T2.+, T3.+, EDOT2.+, and EDOT3.+ revealed the reversible formation of dimers, albeit with a somewhat different tendency, expressed in the values for the dimerization enthalpy.     

Introduction of bis-discotic and bis-calamitic mesogenic addends to C 60

The synthesis and characterization of four C 60 Bingel cyclopropanation adducts incorporating bis-biphenylene (three adducts) and bis-triphenylene (one adduct) moieties are described. The thermal analysis (POM and DSC) of these materials reveals that they are not liquid crystalline. However, two of the precursor bis-biphenylene malonate esters possess monotropic mesophases. Furthermore, each of the corresponding C 60 adducts is miscible in the melts of the precursor malonate ester, and at low dopings, retains the liquid crystalline monotropic mesophases of the precursor.     

Influence of the Oxide Content in the Catalytic Power of Raney Nickel in Hydrogen Generation

The influence of oxides in the hydrogen evolution on Raney nickel electrocatalysts was characterized by electrochemical impedance measurements. In addition, these materials show competitive overpotentials for hydrogen evolution with a modified Watts bath as a binder for the Raney nickel. The optimum result was ?190?mV of overpotential at 100?mA?cm^?2. Oxygen in the Raney Ni catalyst affects its electroactivity toward hydrogen evolution. The source of oxygen is related to the presence of chloride ions in the modified Watts bath. A Watts bath binds Raney Ni particles to the surface of the catalysts and chloride regulates the oxygen content in the nickel binder during electrodeposition. High oxygen content increases the hydrogen evolution overpotential of the electrode. The electroactivity of the synthesized porous coatings was evaluated by polarization curves and impedance plots. In addition, surface characterization by X-ray diffraction, field emission–scanning electron microscopy equipped with energy-dispersive analysis, and X-ray photoelectron spectroscopy is reported.     

Sonoassisted Microbial Reduction of Chromium

This study presents sonoassisted microbial reduction of hexavalent chromium (Cr(VI)) using Bacillus sp. isolated from tannery effluent contaminated site. The experiments were carried out with free cells in the presence and absence of ultrasound. The optimum pH and temperature for the reduction of Cr(VI) by Bacillus sp. were found to be 7.0 and 37 °C, respectively. The Cr(VI) reduction was significantly influenced by the electron donors and among the various electron donors studied, glucose offered maximum reduction. The ultrasound-irradiated reduction of Cr(VI) with Bacillus sp. showed efficient Cr(VI) reduction. The percent reduction was found to increase with an increase in biomass concentration and decrease with an increase in initial concentration. The changes in the functional groups of Bacillus sp., before and after chromium reduction were observed with FTIR spectra. Microbial growth was described with Monod and Andrews model and best fit was observed with Andrews model.