Hydrogen-bonded clusters of hydroperoxyl radical with ammonia: a theoretical study

Ab initio calculations at MP2/6-311++G(d,p) computational level were used to analyze the interaction between a molecule of the hydroperoxyl radical with 1 up to 4 molecules of ammonia. Three minima were found for 1:2 and 1:4 complexes of HOO and NH₃. Two complexes were located as minima on the potential energy surface of 1:3 complexes. Red shifts of the OH stretching frequency upon complex formation in the range between 560 and 1,116 cm⁻¹ are predicted. Cooperative effect in terms of stabilization energy is calculated for the studied clusters. The cooperative effect is increased with the increasing size of studied clusters. The Quantum Theory Atoms in Molecules (QTAIM) theory was also applied to explain the nature of the complexes.     

Surface and Thermodynamic Properties of Nonionic Surfactants Based on Rosin-Maleic Anhydride and Acrylic Acid Adducts

Ester-adduct derivatives of rosin were synthesized by reacting rosin maleic anhydride (RMA) or rosin acrylic acid (RAA) adducts with polyethylene glycol 600 (PEG600), 1000 (PEG1000) or 2000 (PEG2000) and at elevated temperature. These derivatives were evaluated for acid number, FTIR spectroscopy, molecular weight (Mw) and polydispersity. The surface properties of the prepared surfactants were determined by measuring the surface tension at different temperatures. The surface tension, critical micelle concentration, and surface activities were determined at different temperatures. Surface parameters such as surface excess concentration (Γmax), the area per molecule at interface (Amin) and the effectiveness of surface tension reduction (πCMC) were determined from the adsorption isotherms of the prepared surfactants. Some thermodynamic data for the adsorption process were calculated and are discussed.     

Application of SiO2-Pr-SO3H as an efficient catalyst in the Ritter reaction

Sulfonic-acid-functionalized silica was applied as an efficient heterogeneous acid catalyst in the Ritter reaction to prepare amides by reaction of various benzylic, allylic, and tertiary alcohols with various nitriles in good to excellent yields under solvent-free conditions. The simplicity of the reaction, recovery of catalyst without loss of reactivity, high yield of products, and short reaction time represent improvements over many existing methods.     

Natural products in treatment of ulcerative colitis and peptic ulcer

Ulcerative colitis is an inflammatory chronic disease that affects the mucosa and submucosa of the colon and rectum. Several types of drugs are available such as aminosalicylates. Peptic ulcer disease (PUD) is a common disorder that affects millions of individuals worldwide and it can be considered one of the most important common diseases in the world. Treatment of peptic ulcers depends on using a number of synthetic drugs that reduce the rate of stomach acid secretion (Antiacids), protect the mucous tissues that line the stomach and upper portion of the small intestine (Demulcents) or to eliminate Helicobacter pylori (H. pylori). In most cases, incidence of relapses and adverse reactions is seen in the following synthetic antiulcer therapy. Accordingly, the main concern of the current article is to introduce a safe drug (or more) of natural origin, to be used for the management of gastric ulcers without side effects.A widespread search has been launched to identify new anti-ulcer therapies from natural sources. Herbs, medicinal plants, spices, vegetables and crude drug substances are considered to be a potential source to control various diseases including gastric ulcer and ulcerative colitis. In the scientific literature, a large number of medicinal plants and their secondary metabolites with potential anti-ulcer (anti-peptic ulcer and antiulcerative colitis) activities have been reported. Treatment with natural products produces promising results and fewer side effects. Our goal is to collect the published data in the last 24 years and reviews the natural products reported in the treatment of these diseases and their mechanism of action.     

Oxidative Diels-Alder reaction of 2, 5-dihydroxybenzoic acid with 1, 3-cyclopentadiene

The electrochemical oxidation of 2,5-dihydroxybenzoic acid (1) has been studied in the presence of 1,3-cyclopentadiene (2) as a diene in water/ethanol (40/60, v/v) mixture using cyclic voltammetry and controlled-potential coulometry. A plausible mechanism for the oxidation of 1 in the presence of 2 is presented. Compound 1 was converted into bis-adduct 5 via electrooxidation, Diels-Alder reaction of 2 to anodically generated 3,6-dioxocyclohexa-1,4-dienecarboxylic acid (1ox), decarboxylation reaction, electrooxidation and Diels-Alder reaction. The electrochemical synthesis of 5 was performed in a onepot reaction, without toxic reagents, at a carbon electrode in a simple cell using an environmentally friendly method.     

Thermal inactivation and conformational lock studies on glucose oxidase

In this study, the dissociative thermal inactivation and conformational lock theories are applied for the homodimeric enzyme glucose oxidase (GOD) in order to analyze its structure. For this purpose, the rate of activity reduction of glucose oxidase is studied at various temperatures using β-d-glucose as the substrate by incubation of enzyme at various temperatures in the wide range between 40 and 70 °C using UV–Vis spectrophotometry. It was observed that in the two ranges of temperatures, the enzyme has two different forms. In relatively low temperatures, the enzyme is in its dimeric state and has normal activity. In high temperatures, the activity almost disappears and it aggregates. The above achievements are confirmed by dynamic light scattering. The experimental parameter “n” as the obvious number of conformational locks at the dimer interface of glucose oxidase is obtained by kinetic data, and the value is near to two. To confirm the above results, the X-ray crystallography structure of the enzyme, GOD (pdb, 1gal), was also studied. The secondary and tertiary structures of the enzyme to track the thermal inactivation were studied by circular dichroism and fluorescence spectroscopy, respectively. We proposed a mechanism model for thermal inactivation of GOD based on the absence of the monomeric form of the enzyme by circular dichroism and fluorescence spectroscopy.     

NaBH4/Ac2O/DOWEX(R)50WX4: A Convenient System for Fast Preparation of gem‐Diacetates from Aldehydes

Reductive‐acylalation of aldehydes has been carried out by NaBH₄/Ac₂O/DOWEX(R)50WX4 system. A variety of aldehydes (1 mmol) have been reacted with Ac₂O (0.5 mL) and NaBH₄ (1 mmol) in the presence of DOWEX(R)50WX4 (0.5 g) for the preparation of their corresponding acylals within 1 min at room temperature with excellent yields of the products (90‐95%). Ketones do not react with this system.     

Applying a Smart Technique for Accurate Determination of Flowing Oil-Water Pressure Gradient in Horizontal Pipelines

Two-phase flow of liquids in pipelines is crucial subject in many industries such as chemical and petroleum. Accurate prediction of pressure gradient will lead to a better design of an energy efficient transportation system. Although numerous studies for prediction of two-phase flowing pressure drop have been reported in the literature, the accurate prediction of this parameter has been a topic of debate in many research areas. In this article, a novel model based on least square support vector (LSSVM) was proposed for calculation of two-phase flowing pressure drop in horizontal pipes. The inputs of this model are oil and water superficial velocities, pipe diameter, pipe roughness, and oil viscosity. To develop and test the model, more than 700 experimental dataset from open literature were utilized. The results of proposed model were compared against the well-known empirical correlations. Statistical error analysis showed that the LSSVM model outperforms existing predictive models. Finally, an outlier diagnosis was performed to detect the doubtful experimental.      

Magnetic Nanoparticles Supported Ionic Liquids Improve Firefly Luciferase Properties

Ionic liquids as neoteric solvents, microwave irradiation, and alternative energy source are becoming as a solvent for many enzymatic reactions. We recently showed that the incubation of firefly luciferase from Photinus pyralis with various ionic liquids increased the activity and stability of luciferase. Magnetic nanoparticles supported ionic liquids have been obtained by covalent bonding of ionic liquids-silane on magnetic silica nanoparticles. In the present study, the effects of [γ-Fe₂O₃@SiO₂][BMImCl] and [γ-Fe₂O₃@SiO₂][BMImI] were investigated on the structural properties and function of luciferase using circular dichroism, fluorescence spectroscopy, and bioluminescence assay. Enzyme activity and structural stability increased in the presence of magnetic nanoparticles supported ionic liquids. Furthermore, the effect of ingredients which were used was not considerable on K _m value of luciferase for adenosine-5′-triphosphate and also K _m value for luciferin.     

Synthesis and thermogravimetric analysis of inclusion complexes of O2N2-donor Aza-crown macrocyclic ligands with [60]fullerene

A simple method for the formation of inclusion complex of [60]fullerene with two O₂N₂-donor aza-crown macrocyclic ligands was introduced. The products were characterized using UV–vis and IR spectroscopies as well as HPLC, and ESI mass spectrometry. The ESI mass and elemental analysis data revealed that the ratio of macroring:[60]fullerene were not the same. The binding capability of the macrorings as well as the number of the macroring addends to [60]fullerene were investigated using thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). Considering percentage mass loss in different steps of TG and the enthalpy changes in DSC found for each of these products, the number of their addends on [60]fullerene were calculated. Theoretical calculations in semi-empirical level using AM1 suggested that proper orientation of the nitrogen-donor groups on the aza-crown macrorings toward [60]fullerene could be the main factor for the observed difference in the number of macroring addends attached to [60]fullerene.