			Home About us Contact

Complex Studies (complex + studies)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Intra- versus intermolecular hydrogen bonding equilibrium in 2-hydroxy- N,N -diethylbenzamide,

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 2 2009
P. Majewska
Abstract Complex studies of the intramolecular versus intermolecular hydrogen bond equilibrium and internal rotation of the N,N -diethylamine group in 2-hydroxy- N,N -diethylbenzamide were conducted. The intramolecular versus intermolecular process in 2-hydroxy- N,N -diethylbenzamide was studied by UV,Vis, NMR, IR and Vapour Pressure Osmometric (VPO) methods as a function of temperature and concentration in non-polar, basic and protic solvents. The unequal positions of the ethyl groups were analysed and the energy barrier to the re-orientation was defined by the NMR method. This paper presents a study into a complicated nature of competitive interaction 2-hydroxy- N,N -diethylbenzamide with the environment by means of the aforesaid methods. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Large scale wildlife monitoring studies: statistical methods for design and analysis

ENVIRONMETRICS, Issue 2 2002
Kenneth H. Pollock
Abstract Techniques for estimation of absolute abundance of wildlife populations have received a lot of attention in recent years. The statistical research has been focused on intensive small-scale studies. Recently, however, wildlife biologists have desired to study populations of animals at very large scales for monitoring purposes. Population indices are widely used in these extensive monitoring programs because they are inexpensive compared to estimates of absolute abundance. A crucial underlying assumption is that the population index (C) is directly proportional to the population density (D). The proportionality constant, ,, is simply the probability of ,detection' for animals in the survey. As spatial and temporal comparisons of indices are crucial, it is necessary to also assume that the probability of detection is constant over space and time. Biologists intuitively recognize this when they design rigid protocols for the studies where the indices are collected. Unfortunately, however, in many field studies the assumption is clearly invalid. We believe that the estimation of detection probability should be built into the monitoring design through a double sampling approach. A large sample of points provides an abundance index, and a smaller sub-sample of the same points is used to estimate detection probability. There is an important need for statistical research on the design and analysis of these complex studies. Some basic concepts based on actual avian, amphibian, and fish monitoring studies are presented in this article. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Gas-phase behavior of noncovalent transmembrane segment complexes

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2008
Linda M. M. Weigang
Specific helix oligomerization between transmembrane segments (TMSs) is often promoted by motifs like GxxxG. Disruption of this motif in the transmembrane segments of vesicular stomatitis virus G-protein and of glycophorin A results in a reduced dimerization level studied by in vivo systems like ToxR. This paper reports the influence of sequence motifs like GxxxG in solution and the gas phase. The transmembrane segments may behave differently in the gas and liquid phase, because of the absence of surrounding solvent molecules in the gas phase. Comparison of experiments depending on peptide properties performed in the gas and liquid phase discloses that the peptides retain ,some memory' of their liquid-phase structure in the gas phase. A direct correlation has been found between helicity in solution as determined by circular dichroism and dimerization in the gas phase monitored by electrospray mass spectrometry. These results show that a proper folding in solution is required for oligomerization. On the other hand, sequence-specific oligomerization depending on the GxxxG motif was not observed with the mass spectrometric detection. Further on, neither concentration-dependent complex studies nor studies regarding complex stability in the gas phase , via collision-induced dissociation (CID) , led to sequence-specific differences. Finally, the findings show that in mass spectrometric measurements noncovalent interactions of studied TMSs is rather more dependent on the secondary structure and proper folding than on their primary structure. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Human radiolabeled mass balance studies: objectives, utilities and limitations

BIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 4 2009
Natalia Penner
Abstract The determination of metabolic pathways of a drug candidate through the identification of circulating and excreted metabolites is vitally important to understanding its physical and biological effects. Knowledge of metabolite profiles of a drug candidate in animals and humans is essential to ensure that animal species used in toxicological evaluations of new drug candidates are appropriate models of humans. The recent FDA final guidance recommends that human oxidative metabolites whose exposure exceeds 10% of the parent AUC at steady-state should be assessed in at least one of the preclinical animal species used in toxicological assessment. Additional toxicological testing on metabolites that have higher exposure in humans than in preclinical species may be required. The metabolite profiles in laboratory animals and humans are generally accomplished by mass balance and excretion studies in which radiolabeled drugs are administered to these species. The biological fluids are collected, analysed for total radioactivity and evaluated for a quantitative profile of metabolites. Thus, these studies not only determine the rates and routes of excretion but also provide very critical information on the metabolic pathways of drugs in preclinical species and humans. In addition, these studies are required by regulatory agencies for the new drug approval process. Despite the usefulness of these radiolabeled mass balance studies, there is little concrete guidance on how to perform or assess these complex studies. This article examines the objectives, utilities and limitations of these studies and how these studies could be used for the determination of the metabolite exposure in animals and humans. Copyright © 2009 John Wiley & Sons, Ltd. [source]