Sterols from Sargassum oligocystum, a brown algae from the Persian Gulf, and their bioactivity

Sargassum oligocystum (Heterokontophyta) is one of the most abundant algae distributed in the Persian Gulf. In this study, the cytotoxic effects of this algae on brine shrimp larvae were evaluated and the main sterols of the algae identified. Separation and purification of the compounds was carried out using silica gel column chromatography and HPLC to obtain eight pure compounds, 1-8. Structural elucidation of the constituents was based on the data obtained from (1)H-NMR, (13)C-NMR, HSQC, HMBC, DEPT and EI-MS. The compounds separated from S. oligocystum were identified as 22-dehydrocholesterol (1), cholesterol (2), fucosterol (3), 29-hydroperoxystigmasta-5,24(28)-dien-3β-ol (4), 24-hydroperoxy-24-vinylcholesterol (5), a mixture of 24(S)-hydroxy-24-vinylcholesterol (6) and 24(R)-hydroxy-24-vinylcholesterol (7), and ostreasterol (8) based on their spectral data and from comparison with those previously reported in the literature.     

COMPARATIVE STUDIES ON THE LETHAL, MUTAGENIC, AND RECOMBINOGENIC EFFECTS OF ULTRAVIOLET-A,-B,-C, AND VISIBLE LIGHT WITH AND WITHOUT 8-METHOXYPSORALEN IN Saccharomyces cerevisiae

Genetic effects of UV-A, UV-B, UV-C, and the combination of 8-methoxypsoralen (8-MOP) with UV-A or visible light were studied in the haploid strain XV185-14C and diploid strain D5 of Saccharomyces cerevisiae. The induction of his+, lys+, and hom+ reverse mutations was measured in strain XV185-14C. In strain D5 we measured the induction of genetically altered colonies, particularly twin spot colonies arising from a mitotic crossing-over. UV-C and UV-B induced point mutations at the three loci in the haploid strain and mitotic crossing-over and other genetic alterations in the diploid strain. UV-C was more mutagenic and recombinogenic than UV-B. UV-A or visible light alone did not induce genotoxic effects at the doses tested. However, UV-A plus 8-MOP produced lethal and mutagenic effects in the haploid strain XV185-14C, although mutagenic activity was less than that of UV-B. Visible light plus 8-MOP also induced genotoxic effects in strain XV185-14C. In the diploid strain D5, UV-A plus 8-MOP induced a higher frequency of genetic alterations than UV-B at comparative doses. Visible light plus 8-MOP was also genetically active in strain D5. The haploid strain was more sensitive to the lethal effects of UV-C, UV-B, UV-A, and impure visible light plus 8-MOP than the diploid strain.     

A new family of bis-tetrazole (BIZOL) BINOL-type ligands

The synthesis and characterization of 5-(1-(2-(1H-tetrazole-5-yloxy)naphthalen-1-yl)naphthalen-2-yloxy)-1H-tetrazole (BIZOL) as the first bis-tetrazole BINOL-type ligands is described.     

One-step Synthesis of PCL-Urethane Networks using a Crosslinking/de-crosslinking Agent

Thermally reversible cross-linked polycaprolactone-urethane (PCL-U) was prepared in one-step procedure. The PCL-U networks were synthesized from a di-isocyanate (4,4′-methylene bis(cyclohexylisocyanate) (HMDI) and hydroxyl bearing macromers and monomers: hydroxy-terminated PCL, glycerol and a di-alcohol Diels-Alder (DA) adduct. This adduct was used to introduce both diene and dienophile functions in the structure and also to protect the maleimide functions from polymerization. The thermoresponsive behavior of the material was characterized by commonly used methods such as solubility tests at different temperatures and differential scanning calorimetry analyses to highlight rDA reactions and also by rheological analysis. The effects of the cooling rate, the molar mass of polycaprolactone as well as the molar ratio [di-Isocyanate]/[PCL-diol] on the cross-linking/de-cross-linking temperatures were also analyzed. The reversible networks obtained have a self-healing behavior.     

A study of the charge propagation in nanoparticles of Fe2O3 core-cobalt hexacyanoferrate shell by chronoamperometry and electrochemical impedance spectroscopy

A composite electrode comprised of graphite, Nujol, and nanoparticles of Fe₂O₃ core–cobalt hexacyanoferrate shell was prepared and the charge transport processes in the bulk of this composite were studied. The electrode/solution interface was assumed as a binary electrolyte whose charge transport occurred between redox sites of the nanoparticles present in the composite and counter cations present in the solution. Using cyclic voltammetry, the diffusion of counter cation in the shell was investigated. Using chronoamperometry, an effective diffusion coefficient and its dependency on the applied potential was obtained. In the Nyquist diagrams, different time constants were appeared with relation to different physical and electrochemical processes. Percolation of electron in the shell of the nanoparticles appeared at very high frequencies and exhibited the feature of a diffusion process with a transmissive boundary condition at interface of core–shell structure/graphite particles. The diffusion coefficients of electron and counter cation and the standard rate constants of each individual electrochemical reaction were obtained.     

Electrochemical oxidation and determination of ceftriaxone on a glassy carbon and carbon-nanotube-modified glassy carbon electrodes

The electrochemical behavior of ceftriaxone was investigated on a carbon-nanotube-modified glassy carbon (GC-CNT) electrode in a phosphate buffer solution, pH = 7.40, and the results were compared with those obtained using the unmodified one [glassy carbon (GC) electrode]. During oxidation of ceftriaxone, an irreversible anodic peak appeared, using both modified and unmodified electrodes. Cyclic voltammetric studies indicated that the oxidation process is irreversible and diffusion-controlled. The number of electrons exchanged in the electrooxidation process was obtained, and the data indicated that ceftriaxone is oxidized via a one-electron step. The results revealed that carbon nanotube promotes the rate of oxidation by increasing the peak current. In addition, ceftriaxone was oxidized at lower potentials, which thermodynamically is more favorable. These results were confirmed by impedance measurements. The electron-transfer coefficients and heterogeneous electron-transfer rate constants for ceftriaxone were reported using both the GC and GC-CNT electrodes. Furthermore, the diffusion coefficient of ceftriaxone was found to be 2.74 × 10⁻⁶ cm² s⁻¹. Binding of ceftriaxone to human serum albumin forms a kind of electroreactive species. The percentage of interaction of ceftriaxone with protein was also addressed. A sensitive, simple, and time-saving differential-pulse voltammetric procedure was developed for the analysis of ceftriaxone, using the GC-CNT electrode. Ceftriaxone can be determined with a detection limit of 4.03 × 10⁻⁶ M with the proposed method.     

Investigating the interaction of juglone (5-hydroxy-1, 4-naphthoquinone) with serum albumins using spectroscopic and in silico methods

The interaction between juglone at the concentration range of 10–110 µM and bovine serum albumin (BSA) or human serum albumin (HSA) at the constant concentration of 11 µM was investigated by fluorescence and UV absorption spectroscopy under physiological-like condition. Performing the experiments at different temperatures showed that the fluorescence intensity of BSA/HSA was decreased in the presence of juglone by a static quenching mechanism due to the formation of the juglone–protein complex. The binding constant for the interaction was in the order of 10³ M^?1, and the number of binding sites for juglone on serum albumins was determined to be equal to one. The thermodynamic parameters including enthalpy (ΔH), entropy (ΔS) and Gibb’s free energy (ΔG) changes were obtained by using the van’t Hoff equation. These results indicated that van der Waals force and hydrogen bonding were the main intermolecular forces stabilizing the complex in a spontaneous association reaction. Moreover, the interaction of BSA/HSA with juglone was verified by UV absorption spectra and molecular docking. The results of synchronous fluorescence, UV–visible and CD spectra demonstrated that the binding of juglone with BSA/HSA induces minimum conformational changes in the structure of albumins. The increased binding affinity of juglone to albumin observed in the presence of site markers (digoxin and ibuprofen) excludes IIA and IIIA sites as the binding site of juglone. This is partially in agreement with the results of molecular docking studies which suggests sub-domain IA of albumin as the binding site.     

Droplet deformation of a strongly shear thinning dense suspension of polymeric micelles

We investigated the deformation of a strong shear thinning droplet undergoing simple shear flow in a Newtonian liquid. The droplet was an aqueous solution of poly(ethylene oxide) end capped with an alkyl group that forms spherical micelles in aqueous solution. At high concentrations and below a critical temperature, the jammed micelles showed strong shear thinning behaviour, and neither a yield stress nor a Newtonian viscosity was observed. At small shear rates, the droplet rotated and aligned in the flow, but did not deform or only very weakly. At high shear rates, the droplet deformation increased with increasing shear rate. The deformed droplet did not relax after the shear was stopped except for a modest rounding of the edges. For each shear rate, an apparent viscosity, η _ad, of the equivalent Newtonian droplet was calculated assuming affine deformation. η _ad showed a power law dependence on the capillary number Ca with an exponent of − 1.8 and was larger than the shear viscosity of the micelle suspension at the same shear rates. The results were explained by the existence of a strong gradient of the viscosity inside the droplet leading to a very low viscosity fluid layer near the droplet/matrix interface.     

用于大肠杆菌消毒的负载型和悬浮型TiO_2催化剂的动力学和催化效率（英文）

TiO2‐mediated photocatalysis is widely used in a variety of applications and products in the envi‐ronmental and energy fields, including photoelectrochemical conversion, self‐cleaning surfaces, and especially water purification systems. The dimensionality of the structure of a TiO2 material can affect its properties, functions, and more specifically, its photocatalytic performance. In this work, the photocatalytic inactivation of Gram‐negative Escherichia coli using three photocatalysts, differ‐ing in their structure and other characteristics, was studied in a batch reactor under UVA light. The aim was to establish the disinfection efficiency of solid TiO2 compared with that of suspended cata‐lysts, widely considered as reference cases for photocatalytic water disinfection. The bacterial inac‐tivation profiles obtained showed that: (1) the photoinactivation was exclusively related to the quantity of photons retained per unit of treated volume, irrespective of the characteristics of the photocatalyst and the emitted light flux densities;(2) across the whole UV light range studied, each of the photocatalytic solids was able to achieve more than 2 log bacterial inactivation with less than 2 h UV irradiation;(3) none of the used catalysts achieved a total bacterial disinfection during the treatment time. For each of the catalysts the quantum yield has been assessed in terms of disinfec‐tion efficiency, the 2D material showed almost the same performance as those of suspended cata‐lysts. This catalyst is promising for supported photocatalysis applications.