Green solid-phase peptide synthesis 4. γ-Valerolactone and N-formylmorpholine as green solvents for solid phase peptide synthesis

Herein, we report the use of γ-valerolactone (GVL) and N-formylmorpholine (NFM) as DMF substitutes in polystyrene based SPPS. The solubility of selected amino acids and coupling reagents were studied in GVL and NFM, followed by their use in the successful synthesis of Aib-enkephalin pentapeptide (H-Tyr-Aib-Aib-Phe-Leu-NH₂) and Aib-ACP decapeptide (H-Val-Gln-Aib-Aib-Ile-Asp-Tyr-Ile-Asn-Gly-NH₂).     

Promoter effect on the CO2-H2O formation during Fischer-Tropsch synthesis on iron-based catalysts

The effects of Mg, La and Ca promoters on primary and secondary CO_2 and H_2O formation pathways during Fischer-Tropsch synthesis on precipitated Fe/Cu/SiO_2 catalysts are investigated. The chemisorbed oxygen atoms in the primary pathway formed in the CO dissociation steps reacted with co-adsorbed hydrogen or carbon monoxide to produce H_2O and CO_2 , respectively. The secondary pathway was the water-gas shift reaction. The results indicated that the CO_2 production led to an increase in both primary and secondary pathways, and H_2 O production decreased when surface basicity of the catalyst increased in the order Ca >Mg >La.     

Extraction of biogenic amines using sorbent materials containing immobilized crown ethers

Three sorbent materials (A18C6-MS, DA18C6-MS and AB18C6-MS) based on the crown ether ligands, 1-aza-18-crown-6, 1,4,10,13-tetraoxa-7,16-diazacyclo octadecane and 4′-aminobenzo-18-crown-6, respectively, were prepared by the chemical immobilization of the ligand onto mesoporous silica support. The sorbents were characterized by FT-IR, scanning electron microscopy-energy dispersive X-ray microanalysis, elemental analysis and nitrogen adsorption-desorption test. The applicability of the sorbents for the extraction of biogenic amines by the batch sorption method was extensively studied and evaluated as a function of pH, biogenic amines concentration, contact time and reusability. Under the optimized conditions, all the sorbents exhibited highest selectivity toward spermidine (SPD) compared to other biogenic amines (tryptamine, putrescine, histamine and tyramine). Among the sorbents, AB18C6-MS offer the highest capacity and best selectivity towards SPD in the presence of other biogenic amines. The AB18C6-MS sorbent can be repeatedly used three times as there was no significant degradation in the extraction of the biogenic amines (%E > 85). The optimized procedure was successfully applied for the separation of SPD in food samples prior to the reversed-phase high performance liquid chromatography separation.     

Simultaneous Analysis of Fluoxetine, Norfluoxetine, Citalopram, and Haloperidol in Plasma by LC–ESI-IT-MS

A reliable and simple method has been developed for simultaneous analysis of fluoxetine, its metabolite norfluoxetine, citalopram, and haloperidol with lamotrigine as internal standard. The method is based on solid-phase extraction on mixed-mode cation-exchange cartridges followed by LC separation on a C₁₈ column at ambient temperature with a gradient prepared from acetonitrile and 5 mM ammonium acetate in 0.1% (v/v) aqueous formic acid. The flow rate was 0.5 mL min^?1. Eluted compounds were ionized by the electrospray ionization ion source of an ion-trap mass spectrometer and were detected by selected ion monitoring. Co-extracted endogenous compounds from plasma were eluted in the first 5 min and discarded by valve-switching. The target drugs were eluted in the period 5.5–11 min. Calibration plots were linear in the ranges 5 (or 10)–400 ng mL^?1 with correlation coefficients >0.999. Other statistical and validation results were within accepted ranges for clinical analysis.     

Biochemical Properties of α-Amylase from Peel of <Emphasis Type="Italic">Citrus sinensis</Emphasis> cv. Abosora

α-Amylase activity was screened in the peel, as waste fruit, of 13 species and cultivars of Egyptian citrus. The species Citrus sinensis cv. Abosora had the highest activity. α-Amylase AI from Abosora peel was purified to homogeneity using anion and cation-exchange, and gel filtration chromatographies. Molecular weight of α-amylase AI was found to be 42 kDa. The hydrolysis properties of α-amylase AI toward different substrates indicated that corn starch is the best substrate. The α-amylase had the highest activity toward glycogen compared with amylopectin and dextrin. Potato starch had low affinity toward α-amylase AI but it did not hydrolyze β-cyclodextrin and dextran. Apparent Km for α-amylase AI was 5 mg (0.5%) starch/ml. α-Amylase AI showed optimum activity at pH 5.6 and 40 °C. The enzyme was thermally stable up to 40 °C and inactivated at 70 °C. The effect of mono and divalent metal ions were tested for the α-amylase AI. Ba²⁺ was found to have activating effect, where as Li⁺ had negligible effect on activity. The other metals caused inhibition effect. Activity of the α-amylase AI was increased one and half in the presence of 4 mM Ca²⁺ and was found to be partially inactivated at 10 mM Ca²⁺. The reduction of starch viscosity indicated that the enzyme is endoamylase. The results suggested that, in addition to citrus peel is a rich source of pectins and flavanoids, α-amylase AI from orange peel could be involved in the development and ripening of citrus fruit and may be used for juice processing.     

Novel multicolor fluorescently labeled silica nanoparticles for interface fluorescence resonance energy transfer to and from labeled avidin

Fluorescent silica nanoparticles (SiNPs) were prepared by covalent attachment of fluorophores to the amino-modified surface of SiNPs with a typical diameter of 15 nm. The SiNPs are intended for use in novel kinds of fluorescence resonance energy transfer (FRET)-based affinity assays at the interface between nanoparticle and sample solution. Various labels were employed to obtain a complete set of colored SiNPs, with excitation maxima ranging from 337 to 659 nm and emission maxima ranging from 436 nm to the near infrared (710 nm). The nanoparticles were characterized in terms of size and composition using transmission electron microscopy, thermogravimetry, elemental analysis, and dynamic light scattering. The surface of the fluorescent SiNPs was biotinylated, and binding of labeled avidin to the surface was studied via FRET in two model cases. In the first, FRET occurs from the biotinylated fluorescent SiNP (the donor) to the labeled avidin (the acceptor). In the second, FRET occurs in the other direction. Aside from its use in the biotin–avidin system, such SiNPs also are believed to be generally useful fluorescent markers in various kinds of FRET assays, not the least because the fluorophore is located on the surface of the SiNPs (and thus always much closer to the second fluorophore) rather than being doped deep in its interior.     

Cetyltrimethylammonium bromide-coated magnetite nanoparticles as highly efficient adsorbent for rapid removal of reactive dyes from the textile companies’ wastewaters

The utilization of modified magnetite nanoparticles (Fe₃O₄ NPs) with a cationic surfactant (cetyltrimethylammonium bromide (CTAB)) as an efficient adsorbent was successfully carried out to remove reactive black 5 (RBBA), reactive red 198 (RRR) and reactive blue 21 (RTB) dyes from aqueous solutions. First, a reactor was designed to be simple, repeatable and efficient in its synthesis of Fe₃O₄ NPs via co-precipitation method. Then, an orthogonal array design (OAD), four factor-four level (4⁴) matrix was applied to assign affecting factors on removing of the dyes from aqueous solutions. The obtained results from ANOVA showed that the amount of CTAB and NaCl% significantly affect the adsorption of RBBA, RRR and RTB dyes. The sorption kinetics of the dyes were best described by a second-order kinetic model, suggesting chemisorptions mechanism. Also, dye adsorption equilibrium state data were fitted well to the Langmuir isotherm rather than Freundlich isotherm. Also, the maximum monolayer capacity, q_max, obtained from the Langmuir was 312.5, 163.9 and 556.2 mg g^-1 for RBBA, RRR and RTB, respectively. The obtained results in the present study indicated that the CTAB-coated Fe₃O₄ NPs can be an efficient adsorbent material for removal of reactive dyes form aqueous solutions.     

One-pot synthesis of benzochromeno-pyrazole derivatives

Abstract  

One-pot synthesis of different benzochromeno-pyrazole derivatives has been reported via reaction of aldehydes, 3-methyl-1H-pyrazol-5(4H)-one and α-naphthol/β-naphthol in the presence of sulfamic acid.     

TiO<Subscript>2</Subscript> nanotube height effect on the efficiency of dye-sensitized solar cells

Performance of dye-sensitized solar cells (DSSCs) based on TiO₂ nanotubes (NTs) filled with TiO₂ nanoparticles (NPs) was studied as a function of NT height (h). The NT height was varied in the range of 1.5–7.0 μm, while the NT diameter was kept constant at ~80 nm. The studies showed that DSSC efficiency, current density, and fill factor linearly increased with h and ranged in 1.76–6.5%, 3.62–13.2 mA/cm², and 0.66–0.76, respectively, within the h range studied. The electrochemical impedance spectroscopy was also performed to study DSSC electron transport properties. Based on both photovoltaic and electrochemical impedance spectroscopy data, the results were explained as being due to the increased dye loading that led to higher light-harvesting efficiency.     

Effect of Ge4+ and Mg2+ doping on superconductivity,fluctuation induced conductivity and interplanar coupling of TlSr2CaCu2O7−δ superconductors

Substitution of Ge⁴⁺ in place of Cu in Tl_0.85Cr_0.15Sr₂CaCu_2?xGe_xO_7?δ (x = 0–0.6) showed initial increase in zero critical temperature value, T_{c zero} from 98 K (x = 0) to 100 K (x = 0.1) and in the range of 85–86 K for x = 0.2–0.3. The slow decrease in T_{c zero} is unexpected as tetravalent Ge⁴⁺ substitution is expected to strongly reduce hole concentration in the samples and suppress T_{c zero}. Excess conductivity analyses of resistance versus temperature data based on Asmalazov–Larkin (AL) theory revealed that the substitution induced 2D-to-3D transition of fluctuation induced conductivity with the highest transition temperature, T_2D–3D observed at x = 0.1. FTIR spectroscopy analysis indicates Ge⁴⁺ substitution cause reduction in CuO₂/GeO₂ interplanar distance while our calculation based on Lawrence–Doniach model revealed highest superconducting coherence length, ξ_c(0) and interplanar coupling, J at x = 0.3. On the other hand, substitution of divalent Mg²⁺ for Ca²⁺ in (Tl_0.5Pb_0.5)(Sr_1.8Yb_0.2)(Ca_1?yMg_y)Cu₂O₇ (y = 0–1.0), which is not expected to directly vary hole concentration, surprisingly caused T_{c zero} to increase from 89.6 K (y = 0) to an optimum value of 95.9 K (y = 0.6) before decreasing with further increase in y. Excess conductivity analyses showed 2D-to-3D transition of fluctuation induced conductivity for all samples where the highest T_2D–3D was at y = 0.4. Similar calculation revealed highest values of ξ_c(0) and J also at y = 0.4. FTIR analysis of the samples indicates inequivalent Cu(1)O(2)Pb/Tl lengths and possible tilting of CuO₂ plane as a result of Mg²⁺ substitution. The increased ξ_c(0) and J as a result of the Ge⁴⁺ and Mg²⁺ substitutions are suggested to contributed to sustenance of superconductivity above 80 K in the samples.