Towards a mesoscopic model of water-like fluids with hydrodynamic interactions

We present a mesoscopic lattice model for non-ideal fluid flows with directional interactions, mimicking the effects of hydrogen bonds in water. The model supports a rich and complex structural dynamics of the orientational order parameter, and exhibits the formation of disordered domains whose size and shape depend on the relative strength of directional order and thermal diffusivity. By letting the directional forces carry an inverse density dependence, the model is able to display a correlation between ordered domains and low density regions, reflecting the idea of water as a denser liquid in the disordered state than in the ordered one.     

Reformation Instability in Elastic Solids

The reformation of a body fundamentally involves the mapping of one natural reference configuration of it into another natural reference configuration. The mass and the constitutive properties of the material remain unaltered, but the overall shape of the reference configuration generally changes. If, when a natural reference configuration is distorted, there is a portion of the boundary of the body that is displacement controlled, then a reformation of the body must be such that the original displacement controlled part of the boundary and its reformation are identical. In common applications that involve reformation, the remainder of the boundary is traction-free and a reformation essentially involves a change of the morphology of this traction-free surface. For example, undulations are often a characteristic feature of the reformation of a free, plane boundary surface. Reformations are a result of a material instability and they may associate with a chemically induced diffusive processes in which particles of the body move into preferred places. Fundamentally, a reformation is generated in response to the drive to lower the total stored energy of the body. In this work we are not concerned with the physical processes that take place during reformation, but rather we are concerned with characterizing the onset of the instability. We develop a variational characterization of the reformation instability for a nonlinear elastic body and we include the effect of surface energy. As an example, we consider the axial deformation of a circular cylinder and argue that small scale nano-wires, for which the diameter-to-length ratio is sufficiently small, are expected to be stable with respect to spatial variations when extended. Moreover, we observe that if the surfacial energy function is sufficiently convex at the undistorted state such wires may also be stable with respect to spatial variations when compressed. We then show that such small scale nano-wires are unstable with respect to reformation when either extended or compressed.     

First synthesis and full characterization of mexiletine N-carbonyloxy β-d-glucuronide

A simple, convergent synthesis of the N-carbonyloxy β-d-glucuronide of mexiletine (sodium salt) in moderate yield is described. The compound is now available as an authentic reference standard for analytical studies, enabling more detailed investigation on the metabolism of mexiletine.     

Design of Liposomes Carrying HelixComplex Snail Mucus: Preliminary Studies

In recent decades liposomes have been used in different field thanks to their ability to act as a vehicle for a wide range of biomolecules, their great versatility and their easy production. The aim of this study was to evaluate liposomes as a vehicle for the actives present in the HelixComplex (HC) snail mucus for topical delivery. Liposomes composed of a mixture of phosphatidylcholine, cholesterol and octadecylamine were prepared with and without HC (empty liposomes) and their biological efficacy was tested by evaluating cell viability and migration. HC-loaded liposomes (LHC) were stable throughout 60 days of observation, and showed interesting effects on wound healing reconstitution. In particular, we observed that 25 µg/mL LHC were already able to induce a higher cell monolayer reconstitution in comparison to the untreated samples and HC treated samples after only 4 h (28% versus 10% and 7%, p = 0.03 and p= 0.003, respectively). The effect was more evident at 24 h in comparison with the untreated control (54% versus 21.2% and 41.6%, p = 0.006 and p = NS, respectively). These results represent a preliminary, but promising, novelty in the delivery strategy of the actives present in the HelixComplex mucus.     

In vivo synthesized proteins with monoexponential fluorescence decay kinetics

Tryptophan, when in a protein, typically shows multiexponential fluorescence decay kinetics. Complex kinetics prevents a straightforward interpretation of time-resolved fluorescence protein data, particularly in anisotropy studies or if the effect of a dynamic quencher or a resonance energy transfer (RET) acceptor is investigated. Here, time-resolved fluorescence data are presented of an isosteric tryptophan analogue, 5-fluorotryptophan, which when biosynthetically incorporated in proteins shows monoexponential decay kinetics. Data are presented indicating that the presence of a fluoro atom at the 5-position suppresses the electron transfer rate from the excited indole moiety to the peptide bond. This process has been related to the multiexponential fluorescence decay of tryptophan in proteins. The monoexponential decay of 5-fluorotryptophan makes it possible to measure simultaneously multiple distances between 5-fluorotryptophan and a RET acceptor. We demonstrate that for an oligomeric protein, consisting of two single-tryptophan-containing subunits, the individual distances between 5-fluorotryptophan and the single substrate binding site can be resolved using a substrate harboring a RET acceptor.     

Electronic properties of mononuclear, dinuclear, and polynuclear cobaltacarboranes: electrochemical and spectroelectrochemical studies

Electronic interactions and metal-metal communication in a wide range of cobaltacarborane-hydrocarbon complexes containing one to six metal centers, and exhibiting a variety of modes of inter-cage connectivity and molecular architectures, have been investigated via cyclic voltammetry, controlled potential coulometry, and UV-visible spectroelectrochemistry. The properties of mixed-valent Co(III)/Co(IV) and Co(II)/Co(III) species that are generated on oxidation or reduction of dinuclear and polynuclear Co(III) complexes were examined and classified as Robin-Day Class I (localized), Class II (partially delocalized), or Class III (fully delocalized) systems. The extent of metal-metal communication between metallacarborane cage units is strongly influenced by the type of intercage connection (e.g., cage B-B or Cp-Cp); the vertexes involved (equatorial vs apical); the nature of the linking unit, if any; and the presence of substituents on the carborane cages. In multi-tripledecker complexes where three CpCo(C(2)B(3)H(4))CoCp units are linked through a central triethynyl benzene connector, the data suggest that Co-Co electronic communication is extensive (Class III) within individual sandwich units while intersandwich delocalization is weak or absent. An extended Hückel study of CpCoC(2)B(4)H(6) double-decker and CpCo(C(2)B(3)H(5))CoCp triple-decker sandwich model complexes shows significant differences in the orbital contributions involved in the HOMO and LUMO of the former vs the latter type. The calculations afford additional insight into the electronic structures and properties of these systems as elucidated by the experimental studies.     

Fragment kinetic energies and modes of fragment formation

Kinetic energies of light fragments ( A相似文献   

Anti-α-Glucosidase and Antiglycation Activities of α-Mangostin and New Xanthenone Derivatives: Enzymatic Kinetics and Mechanistic Insights through In Vitro Studies

Diabetes mellitus is characterized by chronic hyperglycemia that promotes ROS formation, causing severe oxidative stress. Furthermore, prolonged hyperglycemia leads to glycation reactions with formation of AGEs that contribute to a chronic inflammatory state. This research aims to evaluate the inhibitory activity of α-mangostin and four synthetic xanthenone derivatives against glycation and oxidative processes and on α-glucosidase, an intestinal hydrolase that catalyzes the cleavage of oligosaccharides into glucose molecules, promoting the postprandial glycemic peak. Antiglycation activity was evaluated using the BSA assay, while antioxidant capacity was detected with the ORAC assay. The inhibition of α-glucosidase activity was studied with multispectroscopic methods along with inhibitory kinetic analysis. α-Mangostin and synthetic compounds at 25 µM reduced the production of AGEs, whereas the α-glucosidase activity was inhibited only by the natural compound. α-Mangostin decreased enzymatic activity in a concentration-dependent manner in the micromolar range by a reversible mixed-type antagonism. Circular dichroism revealed a rearrangement of the secondary structure of α-glucosidase with an increase in the contents of α-helix and random coils and a decrease in β-sheet and β-turn components. The data highlighted the anti-α-glucosidase activity of α-mangostin together with its protective effects on protein glycation and oxidation damage.     

Synthetic and Nanotechnological Approaches for a Diagnostic Use of Manganese

The development of multimodal imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI) allows the contemporary obtaining of metabolic and morphological information. To fully exploit the complementarity of the two imaging modalities, the design of probes displaying radioactive and magnetic properties at the same time could be very beneficial. In this regard, transition metals offer appealing options, with manganese representing an ideal candidate. As nanosized imaging probes have demonstrated great value for designing advanced diagnostic/theranostic procedures, this work focuses on the potential of liposomal formulations loaded with a new synthesized paramagnetic Mn(II) chelates. Negatively charged liposomes were produced by thin-layer hydration method and extrusion. The obtained formulations were characterized in terms of size, surface charge, efficiency of encapsulation, stability over time, relaxivity, effective magnetic moment, and in vitro antiproliferative effect on human cells by means of the MTT assay. The negatively charged paramagnetic liposomes were monodisperse, with an average hydrodynamic diameter not exceeding 200 nm, and they displayed good stability and no cytotoxicity. As determined by optical emission spectroscopy, manganese complexes are loaded almost completely on liposomes maintaining their paramagnetic properties.     

Structural and electronic properties of defective 2D transition metal dichalcogenide heterostructures

We present a first-principles study on the structure-property relationships in MoS₂ and WS₂ monolayers and their vertically stacked hetero-bilayer, with and without Sulfur vacancies, in order to dissect the electronic features behind their photocatalytic water splitting capabilities. We also benchmark the accuracy of three different exchange-correlation density functionals for both minimum-energy geometries and electronic structure. The best compromise between computational cost and qualitative accuracy is achieved with the HSE06 density functional on top of Perdew–Burke–Ernzerhof minima, including dispersion with Grimme's D3 scheme. This computational approach predicts the presence of mid-gap states for defective monolayers, in accordance with the present literature. For the heterojunction, we find unexpected vacancy-position dependent electronic features: the location of the defects leads either to mid-gap trap states, detrimental for photocatalyst or to a modification of characteristic type II band alignment behavior, responsible for interlayer charge separation and low recombination rates.