(+)-7-Bromotrypargine: an antimalarial β-carboline from the Australian marine sponge Ancorina sp.

Mass-directed isolation of the CH₂Cl₂/MeOH extract from the Australian marine sponge Ancorina sp. resulted in the purification of a new antimalarial β-carboline, (+)-7-bromotrypargine 1, along with the previously isolated natural product, 6-bromotryptamine 2. The structure of 1 is determined by extensive 1D/2D NMR and MS data analyses. Comparison of the chiro-optical data for 1 with literature values of related natural products is used to determine the absolute stereochemistry of (+)-7-bromotrypargine as 1R. Antimalarial activity data for 1 and 2 against a chloroquine-resistant (Dd2) and chloroquine-sensitive (3D7) Plasmodium falciparum strain are also provided.     

Botryllamides K and L, new tyrosine derivatives from the Australian ascidian Aplidium altarium

Chemical investigation of the Australian ascidian Aplidium altarium led to the isolation of two new tyrosine derivatives, botryllamides K (1) and L (2), together with six known metabolites, botryllamides A-C (3-5), botryllamide G (6) and perspicamides A (7) and B (8). The structures of these compounds were elucidated by spectroscopic analysis. This is the first reported chemistry from this species. Compounds 1-8 were evaluated for their cytotoxicity towards the tumour cell lines, MCF-7 (breast), H460 (lung) and SF268 (central nervous system).     

Benchmarking Transfer Entropy Methods for the Study of Linear and Nonlinear Cardio-Respiratory Interactions

Transfer entropy (TE) has been used to identify and quantify interactions between physiological systems. Different methods exist to estimate TE, but there is no consensus about which one performs best in specific applications. In this study, five methods (linear, k-nearest neighbors, fixed-binning with ranking, kernel density estimation and adaptive partitioning) were compared. The comparison was made on three simulation models (linear, nonlinear and linear + nonlinear dynamics). From the simulations, it was found that the best method to quantify the different interactions was adaptive partitioning. This method was then applied on data from a polysomnography study, specifically on the ECG and the respiratory signals (nasal airflow and respiratory effort around the thorax). The hypothesis that the linear and nonlinear components of cardio-respiratory interactions during light and deep sleep change with the sleep stage, was tested. Significant differences, after performing surrogate analysis, indicate an increased TE during deep sleep. However, these differences were found to be dependent on the type of respiratory signal and sampling frequency. These results highlight the importance of selecting the appropriate signals, estimation method and surrogate analysis for the study of linear and nonlinear cardio-respiratory interactions.     

Isolation,structure determination,and biological activity of a novel alkaloid,perophoramidine, from the Philippine ascidian Perophora namei

Chemical investigation of the Philippine ascidian Perophora namei has resulted in the isolation of a novel polycyclic alkaloid, perophoramidine (1). The structure of 1 was determined by the interpretation of 1D/2D NMR and MS data. Dehalogenation of perophoramidine (1) by ammonium formate catalyzed transfer hydrogenation confirmed the type and number of halogen atoms present in 1.     

Path-independent integrals for the direct determination of stress intensity factors in certain classical crack problems

Stress intensity factors have been determine directly for certain special crack problems with the help of J or other path-independent integrals. Such procedures have not been used successfully in what are perhaps the most classical of all crack problems: those in two dimensions involving a crack of finite length in an infinite medium with loading at infinity of either Mode I, Mode II or Mode III type. We give a new class of path-independent integrals which are suitable for this purpose.     

A lattice-based model of the kinetics of twin boundary motion

In this paper we derive a macroscopic kinetic law for twin boundary motion from a lattice dynamical model. The model is developed for compound and type-1 twins and it is explicitly illustrated for a Cu-Al-Ni shape memory alloy. The governing multiple-well energy is calculated using an effective interatomic potential; a Frenkel-Kontorowa type model is developed for the dynamics at the lattice scale; and a quasi-continuum approximation is used to determine the continuum-scale kinetics. The model predicts that compound twins in the Cu-Al-Ni shape memory alloy are an order of magnitude more mobile than type-1 twins which is consistent with experimental observations.     

Discontinuous deformation gradients away from the tip of a crack in anti-plane shear

Summary This paper examines the finite elastostatic problem for a crack under anti-plane shear conditions. A class of incompressible, homogeneous, isotropic, elastic materials is considered for which the governing displacement equation of equilibrium is elliptic at both sufficiently small and sufficiently large shearing strains but is hyperbolic at an intermediate level of strains. The small-scale nonlinear crack problem is considered and an exact solution is found through use of the hodograph method.The principal feature of the solution is the presence of two pairs of curves issuing from points on the crack-faces, different from the crack-tips, across which the displacement gradients and stresses suffer jump discontinuities.The results communicated in this paper were obtained in the course of an investigation supported by the NSF Materials Research Laboratory at Brown University.     

An approach to skeletal diversity using functional group pairing of multifunctional scaffolds

Diversification of enantioenriched Michael adducts through functional group pairing to gain access to a range of five- to ten-membered complex fused and bridged ring systems is described.     

Fluorescence based strategies for genetic analysis

Synthetic chemistry has been central to the design of modern methods of genetic analysis. In this article, we discuss the underlying chemistry and biophysical principles that have been used in the development of robust methods for the analysis of DNA in the diagnostic laboratory.