Kinetic studies on the acid catalyzed reaction of hydroxamic acids in β-cyclodextrin/surfactant mixed systems

The acid catalyzed hydrolysis of two N-substituted hydroxamic acids (C₆H₅CON(OH)R, R = C₆H₅ (PBHA), R = C₆H₅CH₂(BBHA)) in mixed systems containing -cyclodextrin (—CD) and a surfactant (sodium dodecyl sulfate, SDS) has been studied. The reactions are inhibited by —CD. The inhibition is attributed to the formation of inclusion complex and competition between the micellization and complexation processes.This revised version was published online in December 2005 with corrections to the Cover Date.     

Simultaneous determination of betulinic acid, β-sitosterol and lupeol in fruits,leaves, root and stem bark of Dillenia pentagyna Roxb. by a validated high-performance thin-layer chromatography method

JPC – Journal of Planar Chromatography – Modern TLC - In the present investigation, a simple and effective high-performance thin-layer chromatography (HPTLC) method was developed and...     

Bayesian Approach to Hurst Exponent Estimation

Fractal investigation of a signal often involves estimating its fractal dimension or Hurst exponent H when considered as a sample of a fractional process. Fractional Gaussian noise (fGn) belongs to the family of self-similar fractional processes and it is dependent on parameter H. There are variety of traditional methods for Hurst exponent estimation. Our novel approach is based on zero-crossing principle and signal segmentation. Thanks to the Bayesian analysis, we present a new axiomatically based procedure of determining the expected value of Hurst exponent together with its standard deviation and credible intervals. The statistical characteristics are calculated at the interval level at first and then they are used for the deduction of the aggregate estimate. The methodology is subsequently used for the EEG signal analysis of patients suffering from Alzheimer disease.     

Insights into Structural Modifications of Valproic Acid and Their Pharmacological Profile

Valproic acid (VPA) is a well-established anticonvulsant drug discovered serendipitously and marketed for the treatment of epilepsy, migraine, bipolar disorder and neuropathic pain. Apart from this, VPA has potential therapeutic applications in other central nervous system (CNS) disorders and in various cancer types. Since the discovery of its anticonvulsant activity, substantial efforts have been made to develop structural analogues and derivatives in an attempt to increase potency and decrease adverse side effects, the most significant being teratogenicity and hepatotoxicity. Most of these compounds have shown reduced toxicity with improved potency. The simple structure of VPA offers a great advantage to its modification. This review briefly discusses the pharmacology and molecular targets of VPA. The article then elaborates on the structural modifications in VPA including amide-derivatives, acid and cyclic analogues, urea derivatives and pro-drugs, and compares their pharmacological profile with that of the parent molecule. The current challenges for the clinical use of these derivatives are also discussed. The review is expected to provide necessary knowledgebase for the further development of VPA-derived compounds.     

High pressure structural phase transition in uranium monochalcogenides

The pressure induced phase transition in uranium monochalcogenides, UX (X = S, Se, and Te) is studied by two-body potential approach. It is found that US, USe and UTe undergo a structural phase transition from NaCl (B1) type to CsCl (B2) type at 78.5, 21 and 9.5 GPa, respectively, which is in good agreement with the recent experimental data. In addition, second-order elastic constants (SOECs) (C ₁₁, C ₁₂ and C ₁₄) have been calculated which can be used to establish the nature of the forces in these materials. The present study shows that the considered two-body potential model can be used to predict the phase transition pressure in UX compounds provided the strength and hardness parameters in B1 and B2 phases are different.     

Selection of overwintering microhabitats used by the arctic woollybear caterpillar,Gynaephora groenlandica

In extreme environments such as the High Arctic, climatic conditions challenge physiological tolerance of insects resulting in prolonged dormancy and extended life cycles. Therefore, the selection of suitable microhabitats for overwintering is crucial. At two field sites on Ellesmere Island, we located hibernacula (silk overwintering structures) used by the Arctic woollybear caterpillar, Gynaephora groenlandica (W?cke) (Lepidoptera: Lymantriidae) during their 11 month dormancy. All hibernacula found were anchored to the base of rocks and were not associated with vegetation. Rocks may function to absorb solar radiation and re-radiate heat, accelerating localized snowmelt, thus allowing caterpillars to emerge as early as possible in spring to begin foraging. Temperatures experienced by G. groenlandica in hibernacula throughout the winter were well within their physiological tolerance range. During late summer aestivation, hibernaculum temperatures were similar to, but more stable than, nearby soil surface temperatures. Lower maximum daily hibernaculum temperatures during the warmest month (July) may reduce metabolic rates and provide some energy savings. Since hibernacula were not randomly distributed around rocks, this suggests that G. groenlandica key in on some feature of the hibernaculum site. The northeast orientation of hibernacula at Eastwind Lake corresponds to the leeward side of rocks. Therefore wind patterns may be important in hibernaculum site selection. Other potential cues that may guide selection of hibernacula sites remain unclear: no seasonal changes in preference for light or soil moisture were observed between active and dormant caterpillars, and thermotaxis could not be distinguished from thigmotaxis.