Theoretical advances in the dissolution studies of mineral–water interfaces

This article presents theoretical advances in computational modeling of dissolution at mineral–water interfaces with specific emphasis on silicates. Two different Monte Carlo methods have been developed that target equilibrium properties and kinetics in silicate–water dissolution. The equilibrium properties are explored using the combined reactive Monte Carlo and configurational bias Monte Carlo (RxMC-CBMC) method. The new RxMC-CBMC method is designed to affordably simulate the three-dimensional structure of the mineral with explicit water molecules. The kinetics of the overall dissolution process is studied using a stochastic kinetic Monte Carlo method that utilizes rate constants obtained from accurate ab initio calculations. Both these methods provide important complementary perspective of the complex dynamics involving chemical and physical interactions at the mineral–water interface. The results are compared to experimental and previous computational data available in the literature.     

Effects of dynamical couplings in hydrogen bond systems in the polarized IR spectra of 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde crystals

This paper presents the investigation results of the polarized IR spectra of 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde crystals measured at 293 and 77 K. Analysis of the results concerned the linear dichroic, H/D isotopic and temperature effects observed in the spectra of the hydrogen and deuterium bond at the frequency ranges of the ν_O–H and the ν_O–D bands, respectively. The main spectral properties of the crystals were interpreted in terms of the “strong-coupling” theory on the basis of the hydrogen bond dimer model. The spectra revealed that the strongest vibrational exciton coupling involved the closely-spaced hydrogen bonds, each belonging to a different chain of associated molecules. The reason for two different crystalline systems, are characterized by almost identical ν_O–H and ν_O–D band shapes, is explained. It was proved that a random distribution of the protons and deuterons took place in the lattices of the isotopically diluted crystals.     

Characterization of Commercial Amylases for the Removal of Filter Cake on Petroleum Wells

Drilling fluid has many functions, such as carry cuttings from the hole permitting their separation at the surface, cool and clean the bit, reduce friction between the drill pipe and wellbore, maintain the stability of the wellbore, and prevent the inflow of fluids from the wellbore and form a thin, low-permeable filter cake. Filter cake removal is an important step concerning both production and injection in wells, mainly concerning horizontal completion. The drilling fluids are typically comprised of starch, the most important component of the filter cake. A common approach to remove this filter cake is the use of acid solutions. However, these are non-specific reactants. A possible alternative is the use of enzymatic preparations, like amylases, that are able to hydrolyze starch. Wells usually operate in drastic conditions for enzymatic preparations, such as high temperature, high salt concentration, and high pressure. Thus, the main objective of this work was to characterize four enzymatic preparations for filter cake removal under open hole conditions. The results showed that high salt concentrations (204,000 ppm NaCl) in completion fluid decreased amylolytic activity. All enzymatic preparations were able to catalyze starch hydrolysis at all temperatures tested (30, 65, 80, and 95 °C). An increase of amylolytic activity was observed with the increase of pressure (100, 500 and 1,000 psi) for one commercial amylase.     

Characterization of the first beta-class carbonic anhydrase from an arthropod (Drosophila melanogaster) and phylogenetic analysis of beta-class carbonic anhydrases in invertebrates

Background

The β-carbonic anhydrase (CA, EC 4.2.1.1) enzymes have been reported in a variety of organisms, but their existence in animals has been unclear. The purpose of the present study was to perform extensive sequence analysis to show that the β-CAs are present in invertebrates and to clone and characterize a member of this enzyme family from a representative model organism of the animal kingdom, e.g., Drosophila melanogaster.

Results

The novel β-CA gene, here named DmBCA, was identified from FlyBase, and its orthologs were searched and reconstructed from sequence databases, confirming the presence of β-CA sequences in 55 metazoan species. The corresponding recombinant enzyme was produced in Sf9 insect cells, purified, kinetically characterized, and its inhibition was investigated with a series of simple, inorganic anions. Holoenzyme molecular mass was defined by dynamic light scattering analysis and gel filtration, and the results suggested that the holoenzyme is a dimer. Double immunostaining confirmed predictions based on sequence analysis and localized DmBCA protein to mitochondria. The enzyme showed high CO₂ hydratase activity, with a k_cat of 9.5 × 10⁵ s^-1 and a k_cat/K_M of 1.1 × 10⁸ M^{- 1}s^{- 1}. DmBCA was appreciably inhibited by the clinically-used sulfonamide acetazolamide, with an inhibition constant of 49 nM. It was moderately inhibited by halides, pseudohalides, hydrogen sulfide, bisulfite and sulfate (K_I values of 0.67 - 1.36 mM) and more potently by sulfamide (K_I of 0.15 mM). Bicarbonate, nitrate, nitrite and phenylarsonic/boronic acids were much weaker inhibitors (K_Is of 26.9 - 43.7 mM).

Conclusions

The Drosophila β-CA represents a highly active mitochondrial enzyme that is a potential model enzyme for anti-parasitic drug development.     

Shuangancistrotectorines A–E,Dimeric Naphthylisoquinoline Alkaloids with Three Chiral Biaryl Axes from the Chinese Plant Ancistrocladus tectorius

Five novel dimeric naphthylisoquinoline alkaloids, shuangancistrotectorines A ( 3 a ), B ( 3 b ), C ( 4 ), D ( 5 a ), and E ( 5 b ), have been isolated from the twigs of the Chinese plant Ancistrocladus tectorius. Their absolute stereostructures were determined by spectroscopic and chiroptical methods in combination with quantum chemical CD calculations. In contrast to all other known dimeric naphthylisoquinoline alkaloids, in which the central binaphthalene axis is 6′,6′′‐coupled and thus not rotationally hindered, the dimers described here are linked via the sterically more hindered 3′,3′′‐ or 1′,1′′‐positions of the naphthalene units. They are thus the first such dimers—and even the very first natural products at all—that have three consecutive stereogenic axes. Hence, including the stereogenic centers, they have up to seven stereogenic units in total. Some of the compounds, in particular shuangancistrotectorines A, B, and D ( 3 a , 3 b , and 5 a ) exhibit very good, and specific, antiplasmodial activities.     

Structural Analysis of a Helical Peptide Unfolding Pathway

The analysis of the folding mechanism in peptides adopting well‐defined secondary structure is fundamental to understand protein folding. Herein, we describe the thermal unfolding of a 15‐mer vascular endothelial growth factor mimicking α‐helical peptide (QK_L10A) through the combination of spectroscopic and computational analyses. In particular, on the basis of the temperature dependencies of QK_L10A H_α chemical shifts we show that the first phase of the thermal helix unfolding, ending at around 320 K, involves mainly the terminal regions. A second phase of the transition, ending at around 333 K, comprises the central helical region of the peptide. The determination of high‐resolution QK_L10A conformational preferences in water at 313 K allowed us to identify, at atomic resolution, one intermediate of the folding–unfolding pathway. Molecular dynamics simulations corroborate experimental observations detecting a stable central helical turn, which represents the most probable site for the helix nucleation in the folding direction. The data presented herein allows us to draw a folding–unfolding picture for the small peptide QK_L10A compatible with the nucleation–propagation model. This study, besides contributing to the basic field of peptide helix folding, is useful to gain an insight into the design of stable helical peptides, which could find applications as molecular scaffolds to target protein–protein interactions.     

Synthesis, structure and adsorption properties of nanoporous SBA-15 materials with framework and surface functionalities

Highly ordered SBA-15 nanoporous silica containing ethylene, phenylene bridges or/and amine, thiol, vinyl and phenyl surface groups were synthesized by using amphiphilic block copolymer as the structure-directing agent. The XRD data shows high degree of the order of the final structures. Obtained materials have well-developed porous structure—values of specific surface area are in the range 700–1050 m²/g and the sizes of cylindrical mesopores are in the range 6.5–9.5 nm. It was determined that size of the mesopores strongly depends even on small amounts of co-monomers co-condensing with TEOS. A new technique to introduce some amount of pendant amine groups by co-condensation of proper monomers has been proposed. Tetragonal structure was obtained when small amount of vinyl groups was introduced to the system. A new approach of determining pore size based only on the XRD measurements was compared with KJS method, confirming full usefulness of the former for calculation of the size of mesopores in SBA-15 materials. Dedicated to Professor Mietek Jaroniec on the occasion of his 60th birthday.     

Micro-solid oxide fuel cells: status,challenges, and chances

Abstract  Micro-solid oxide fuel cells (micro-SOFC) are predicted to be of high energy density and are potential power sources for portable electronic devices. A micro-SOFC system consists of a fuel cell comprising a positive electrode-electrolyte-negative electrode (i.e. PEN) element, a gas-processing unit, and a thermal system where processing is based on micro-electro-mechanical-systems fabrication techniques. A possible system approach is presented. The critical properties of the thin film materials used in the PEN membrane are discussed, and the unsolved subtasks related to micro-SOFC membrane development are pointed out. Such a micro-SOFC system approach seems feasible and offers a promising alternative to state-of-the-art batteries in portable electronics. Graphical abstract  Graphical Abstract text      

Micellization study and adsorption properties of an ionic surfactant synthesized from hydrogenated cardanol in air–water and in air–brine interfaces

A sulfonate (2,4-sodium dissulfonate-5-n-pentadecylphenol) was synthesized from hydrogenated cardanol and the micellization study was carried out using temperature and electrolyte concentration as variables. The adsorption parameters were obtained using surface tension data by the Frumkin adsorption model and the Simplex Nelder–Mead method. Values of critical micelle concentration (cmc) and surface excess (Γ) were obtained in three different temperatures (303 K, 313 K, and 323 K) and two electrolyte concentrations (NaCl solution—0.1 M and 0.25 M). It was verified that cmc decreased with increasing electrolyte concentration and temperature. The Gibbs free energy showed that the micellization process was spontaneous for all studied systems and temperatures, and also that the presence of several CH₂ groups was significant for micelle formation.     

Einige neue Thiaspirane

The synthesis of fifteen new (constitutionally nonsymmetrical) dithiaspirans having both sulfur atoms in the 7-membered ring is described. Some aspects of the conformation of the compounds are studied using¹H nmr. Conformational transmission is observed in all cases.