Complete NMR elucidation of a novel trishomocubane hydantoin and its mono- and bis-t-Boc protected derivatives

The syntheses of a novel trishomocubane hydantoin and its mono- and bis-protected t-Boc derivatives are described. The less nucleophilic N-3' nitrogen of the hydantoin ring is protected first when treated with di-tert-butyl dicarbonate (t-Boc anhydride), possibly owing to steric hindrance by the bulky trishomocubane cage skeleton. More basic conditions were required to form the bis-protected t-Boc hydantoin with the same reagent. The structures of these novel compounds were elucidated with 2D NMR techniques. The proton spectrum of the trishomocubane skeleton is complex owing to major overlap of proton signals. A high-level DFT calculation was used to determine some of the crucial interatomic positions, which assisted with the elucidation of the structures. The assignment of proton and carbon signals of the three structures is described and it differs significantly from each other and also from the trishomocubanol precursor. The bis-Boc hydantoin is required for a more facile hydrolysis to the corresponding trishomocubane amino acid at room temperature.     

Generalized Isothermal Universes

We present a simple nonstatic generalization of the isothermal universe. The cosmological fluid obeys a barotropic equation of state of the form p=. We employ a causal heat transport equation of the Maxwell–Cattaneo form to study the thermodynamical behavior of our model.     

An Analytical Solution for Fully Developed Flow in a Curved Porous Channel for the Particular Case of Monotonic Permeability Variation

A theoretical analysis of the Dean problem in heterogenous porous media is presented for the specific case of monotonic permeability variation in the vertical direction. The solutions are presented in terms of the curvature ratio η which is shown to affect the flow patterns. No multiple vortex solutions were noted for all values of the curvature ratio η.     

Stability of Gravity Driven Convection in a Cylindrical Porous Layer Subjected to Vibration

The linear stability theory is used to investigate analytically the effects of gravity modulation on convection in a homogeneous cylindrical porous layer heated from below. The linear stability results show that increasing the frequency of vibration stabilizes the convection. In addition the aspect ratio of the porous cylinder is shown to influence the stability of convection for all frequencies analysed. It was also observed that only synchronous solutions are possible in cylindrical porous layers, with no transition to subharmonic solutions as was the case in Govender (2005a) [Transport Porous Media 59(2), 227–238] for rectangular layers or cavities.     

Coriolis Effect on the Stability of Centrifugally Driven Convection in a Rotating Anisotropic Porous Layer Subjected to Gravity

We investigate natural convection in a fluid saturated rotating anisotropic porous layer subjected to centrifugal gravitational and Coriolis body forces. The Darcy model (including the centrifugal, gravitational and Coriolis terms; and permeability anisotropy effects) and a modified energy equation (including the effects of thermal anisotropy) is used in the current analysis. The linear stability theory is used to evaluate the critical Rayleigh number for the onset of convection in the presence of thermal and mechanical anisotropy. It is shown that the preferred solution comprises roll cells aligned parallel to the vertical z-axis. As a result, it is found that the Coriolis acceleration (or Taylor number) and the gravitational term play no role in the stability of convection.     

An analogy between a gravity modulated porous layer heated from below and the inverted pendulum with an oscillating pivot point

The governing equations for the inverted pendulum is developed and shown to be analogous to the gravity modulated porous layer heated from below. In particular the temperature in a gravity modulated porous layer heated from below (R>0-unstable) is likened to the motion of an inverted pendulum (unstable). As gravity modulation stabilizes convection, Transport Porous Med. 57 (2004), 113, it is found that oscillating the pivot point of an unstable, inverted pendulum stabilizes the motion.     

Three-Dimensional Convection in an Inclined Porous Layer Heated from below and Subjected to Gravity and Coriolis Effects

The linear stability theory is used to investigate analytically the effects of Coriolis acceleration on gravity driven convection in a rotating porous layer. The stability of a basic solution is analysed with respect to the onset of stationary convection. It was discovered that increasing the Taylor number caused degeneracy to polyhedric cells for a specific range of inclination angles. The effects of the magnitude of the horizontal wavenumber is discussed in relation to the magnitude of the Taylor number.     

Anti-Diabetic Potential of Plant-Based Pentacyclic Triterpene Derivatives: Progress Made to Improve Efficacy and Bioavailability

Diabetes mellitus (DM) results from the inability of the pancreas to produce sufficient insulin or weakened cellular response to the insulin produced, which leads to hyperglycemia. Current treatments of DM focus on the use of oral hypoglycemic drugs such as acarbose, alpha-glucose inhibitors, sulphonylureas, thiazolidinediones, and biguanides to control blood glucose levels. However, these medications are known to have various side effects in addition to their bioavailability, efficacy, and safety concerns. These drawbacks have increased interest in the anti-diabetic potential of plant-derived bioactive compounds such as oleanolic and maslinic acids. Although their efficacy in ameliorating blood glucose levels has been reported in several studies, their bioavailability and efficacy remain of concern. The current review examines the anti-diabetic effects of oleanolic, maslinic, asiatic, ursolic, and corosolic acids and their derivatives, as well as the progress made thus far to enhance their bioavailability and efficacy. The literature for the current review was gathered from leading academic databases—including Google Scholar and PubMed—the key words listed below were used. The literature was searched as widely and comprehensively as possible without a defined range of dates.     

Novel Polyelectrolyte Carboxymethyl Konjac Glucomannan–Chitosan Nanoparticles for Drug Delivery

Summary: Carboxymethyl Konjac Glucomannan–Chitosan (CKGM‐CS) nanoparticles, which are well dispersed and stable in aqueous solution, were spontaneously prepared under very mild conditions by polyelectrolyte complexation. Investigations of the physicochemical properties of these nanoparticles were undertaken. This study showed that the nanoparticulate system driven by complex formation has potential as an advanced drug‐delivery system for water‐soluble drugs.

Preparation mechanism of CS–CKGM nanoparticles.     

GPU-enhanced DEM analysis of flow behaviour of irregularly shaped particles in a full-scale twin screw granulator

During twin screw granulation (TSG),small particles,which generally have irregular shapes,agglomer-ate together to form larger granules with improved properties...