Quantum mechanical calculations of tryptophan and comparison with conformations in native proteins

We report a detailed analysis of the potential energy surface of N-acetyl-l-tryptophan-N-methylamide, (NATMA) both in the gas phase and in solution. The minima are identified using the density-functional-theory (DFT) with the 6-31g(d) basis set. The full potential energy surface in terms of torsional angles is spanned starting from various initial configurations. We were able to locate 77 distinct L-minima. The calculated energy maps correspond to the intrinsic conformational propensities of the individual NATMA molecule. We show that these conformations are essentially similar to the conformations of tryptophan in native proteins. For this reason, we compare the results of DFT calculations in the gas and solution phases with native state conformations of tryptophan obtained from a protein library. In native proteins, tryptophan conformations have strong preferences for the beta sheet, right-handed helix, tight turn, and bridge structures. The conformations calculated by DFT, the solution-phase results in particular, for the single tryptophan residue are in agreement with native state values obtained from the Protein Data Bank.     

Preconcentration of cadmium and nickel using the bioadsorbent Geobacillus thermoleovorans subsp. stromboliensis immobilized on Amberlite XAD-4

Cadmium and nickel ions have been preconcentrated on Geobacillus thermoleovorans subsp. stromboliensis, immobilized on Amberlite XAD-4, and were determined by flame atomic absorption spectrometry (FAAS). Parameters such as pH, amount of adsorbent, eluent type and volume, flow rate of solution and the matrix interference effect on retention have been studied, and extraction conditions were optimized. Elution of Cd(II) and Ni(II) from minicolumns was carried out with 1.0 M hydrochloric acid or nitric acid with recoveries from 97 to 100%. The sorption capacity is 0.0373 and 0.0557 mmol g^?1 for Cd(II) and Ni(II), respectively. The detection limits were 0.24 μg L^?1 for cadmium and 0.3 μg L^?1 for nickel. The relative standard deviations of the procedure were below 10%. The procedure was validated by analyzing certified reference materials and applied to the determination of Cd(II) and Ni(II) in natural water and food samples.     

Liquid crystalline block copolymers by sequential cationic or promoted cationic and free-radical polymerizations

The scope for the study of the synthesis and properties of liquid crystalline (LC) block copolymers is briefly outlined. While there are many approaches to the synthesis of LC block copolymers, the use of azo macroinitiators is very versatile and allows one to produce diverse block copolymer architectures. Azo macroinitiators are prepared by cationic or promoted cationic polymerization of tetrahydrofuran (1) or cyclohexene oxide (2), and are then used to initiate the free-radical polymerization of various methacrylates 3,4 or acrylates 5–9 containing mesogenic azobenzene or biphenyl units thereby yielding block copolymers. The AB or ABA block copolymers are microphase-separated and form smectic and/or nematic mesophases similar to the respective LC homopolymers.     

A Novel and Selective Methylene Blue Imprinted Polymer Modified Carbon Paste Electrode

In this study, methylene blue (MB) imprinted microbeads were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM).Differential pulse voltammetric responses of carbon paste electrodes modified with MB imprinted polymer were used to evaluate the adsorption and selectivity features of the polymer. For selectivity studies two basic dyestuffs (thionine blue and toluidine blue) which have similar structure to MB were chosen. Comparison of the voltammetric responses obtained with pure carbon paste and carbon paste modified with either imprinted or nonimprinted polymer electrodes revealed that MB imprinted polymer presented a higher selectivity to the template molecule MB in contrast to structurally similar molecules, thionine blue and toluidine blue.     

Facile assembly of Bodipy-based metal ion sensor using click chemistry

In this study, two novel 4,4′-difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPY)-based metal ion sensors were synthesised using ‘click’ chemistry. The coordination modes and binding constants of the complexes formed with a range of metal ions were calculated. Results indicate that both BODIPY molecules can potentially serve as fluorescent sensors for the studied metal cations. The results also show that the BODIPY-based sensors have more selectivity for Zn (II) ions in the presence of other metal ions.     

Electrochemical behavior of tadalafil on TiO2 nanoparticles–MWCNT composite paste electrode and its determination in pharmaceutical dosage forms and human serum samples using adsorptive stripping square wave voltammetry

A sensitive and selective electroanalytical method for the determination of tadalafil (TAD) using adsorptive stripping square wave voltammetry at multiwalled carbon nanotube paste electrode (MWCNTPE) and modified TiO₂-multiwalled carbon nanotube paste electrode (TiO₂-MWCNTPE) was presented. The calibration curves were linear in the concentration range of 3.6–8.1 and 12.7–61.1 μM on MWCNTPE, 0.27–15.2 μM on TiO₂-MWCNTPE. The recommended method was successfully applied to the determination of the drug in tablets and human serum samples with good recoveries. The selectivity of the proposed method was considered in the presence of Ca²⁺, K⁺, Na⁺, 2-mercapto benzimidazole, thiourea, and dopamine by means of recovery tests. Interfering agents did not show considerable effect on TAD determination. No electroactive interferences from the tablet excipients and endogenous substances from biological material were detected. The possible electrooxidation pathway and the number of transferred electrons were also investigated.     

Synthesis of macrocyclic polyethers and polyether diesters and preparation of their cationic complexes

New macrocyclic polyethers, 2,3,5,6-bis-[5′(5′)-chlorobenzo]-1,7,10-trioxacyclododeca-2,5-diene (I), 2,3,5,6-bis-[5′(5′)-chlorobenzo]-1,7,10,13-tetra oxacyclo pentadeca-2,5-diene (II), and 2,3,5,6-bis-[5′(5′)-chlorobenzo]-1,7,10,13,16-penta oxa cyclo octadeca-2,5-dien (III), and macrocylic lactones 2,3,5,6-bis-[5′(5′)-chlorobenzo]-1,7,10,13-tetraoxacyclopentadeca-2,5-diene-8,15-dione (IV) and 2,3,5,6-bis[5′(5′)-chlorobenzo]-1,7,10,13,16-pentaoxacyclooctadeca-2,5-diene-8,18-dione (V) were synthesized. Complexes of ligands III and V with metal cations were prepared. Furthermore, their metal-picrate extraction with some metal salts was attempted. Structures of the ligands and complexes were confirmed using spectroscopic techniques.     

Effect of molecular conformations on the adsorption behavior of gold-binding peptides

Despite extensive recent reports on combinatorially selected inorganic-binding peptides and their bionanotechnological utility as synthesizers and molecular linkers, there is still only limited knowledge about the molecular mechanisms of peptide binding to solid surfaces. There is, therefore, much work that needs to be carried out in terms of both the fundamentals of solid-binding kinetics of peptides and the effects of peptide primary and secondary structures on their recognition and binding to solid materials. Here we discuss the effects of constraints imposed on FliTrx-selected gold-binding peptide molecular structures upon their quantitative gold-binding affinity. We first selected two novel gold-binding peptide (AuBP) sequences using a FliTrx random peptide display library. These were, then, synthesized in two different forms: cyclic (c), reproducing the original FliTrx gold-binding sequence as displayed on bacterial cells, and linear (l) dodecapeptide gold-binding sequences. All four gold-binding peptides were then analyzed for their adsorption behavior using surface plasmon resonance spectroscopy. The peptides exhibit a range of binding affinities to and adsorption kinetics on gold surfaces, with the equilibrium constant, Keq, varying from 2.5x10(6) to 13.5x10(6) M(-1). Both circular dichroism and molecular mechanics/energy minimization studies reveal that each of the four peptides has various degrees of random coil and polyproline type II molecular conformations in solution. We found that AuBP1 retained its molecular conformation in both the c- and l-forms, and this is reflected in having similar adsorption behavior. On the other hand, the c- and l-forms of AuBP2 have different molecular structures, leading to differences in their gold-binding affinities.     

New metal complexes with diclofenac containing 2-pyridineethanol or 2-pyridinepropanol: synthesis,structural, spectroscopic,thermal properties,catechol oxidase and carbonic anhydrase activities

Four new neutral diclofenac-based complexes, [Co(dicl)2(2-pyet)2] 1, [Ni(dicl)2(2-pyet)2] 2, [Cu2(dicl)2(2-pyet)2] 3, and [Cu2(dicl)2(2-pypr)2] 4 have been synthesized and characterized by elemental analysis, FT-IR, thermal analysis. Complexes 1, 3, and 4 have also been characterized by X-ray single-crystal structural analysis. The compounds of Co(II) and Ni(II) have octahedral geometry with two diclofenac and two 2-pyridineethanol ligands in the coordination sphere. The compounds of Cu(II) have square-pyramidal geometry and Cu(II) ions are linked via oxygens to the bridging 2-pyridineethanol or 2-pyridinepropanol ligands. The Δν values acquired by FT-IR are in agreement with the single XRD data. Studies on the thermal properties are reported and the complexes are stable to 196, 216, 215, and 201 °C in air, respectively. Two dinuclear Cu(II) complexes have demonstrated catalytic activity on oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone showing saturation kinetics at high substrate concentrations. The diclofenac complexes are investigated as inhibitors of the human cytosolic isoforms hCA I and II. The complexes are good as hCA I inhibitors (Kis of 1.52–55.06 μM) but only moderately efficient as hCA II inhibitors (Kis of 0.23–5.61 μM).     

In vitro biological activities and fatty acid profiles of Pistacia terebinthus fruits and Pistacia khinjuk seeds

This study reports in vitro anticholinesterase, antioxidant and antimicrobial effects of the n-hexane, dichloromethane, ethanol and ethanol–water extracts prepared from Pistacia terebinthus L. fruits and Pistacia khinjuk Stocks seeds as well as their total phenolic and flavonoid contents, and fatty acid compositions. Ethanol and ethanol–water extracts of both species exhibited higher anticholinesterase activity than galanthamine. Among ABTS, DPPH and CUPRAC assays, the highest antioxidant capacity of the extracts was found in the last one. P. terebinthus ethanol extract being rich in flavonoid content showed the best cupric reducing effect. All extracts possessed no antimicrobial activity. The main fatty acid in P. terebinthus fruits (52.52%) and P. khinjuk seeds (59.44%) was found to be oleic acid. Our results indicate that P. terebinthus fruits and P. khinjuk seeds could be a good source of anticholinesterase compounds, and could be phytochemically investigated.