Biomedical subjects

C T Klein

Publications and source records attributed to C T Klein.

5 recordsLinked to original sources

PubMed2000

Threshold-based structure-activity relationships of pyrazines with bell-pepper flavor.

Quantitative structure activity relationships (QSAR) and comparative molecular field analysis (CoMFA) are applied in order to explain the aroma of 46 bell-pepper aroma compounds. Biological activities log(1/c) values are used, where c stands for the detection threshold value of the aroma compound in water. Results of conventional QSAR and CoMFA are both satisfactory in statistical significance and predictive ability. We construct a qualitative model using the graphic features of CoMFA together with the results of "classical" QSAR analysis, which is performed by multiple linear regression. Finally, the human olfactory detection threshold values of excluded pyrazines are successfully predicted. This makes CoMFA and QSAR two important tools for designing new aroma compounds and in elucidating the mechanism of odor-receptor interaction.

Humans↗

PubMed2000

Predicting the free energies of complexation between cyclodextrins and guest molecules: linear versus nonlinear models.

PURPOSE: In the present paper, linear and nonlinear models for complexation of alpha- beta- and gamma-cyclodextrin with guest molecules are developed, with the aim of free energy prediction and interpretation of the association process. METHODS: Linear and nonlinear regression is used to correlate experimental free energies of complexation with calculated molecular descriptors. Molecular modeling supports the interpretation of the results. RESULTS: Highly predictive models are obtained, although the structural variability of the compounds used for their deduction is large, reaching from synthetic heterocycles to steroids and prostaglandins. CONCLUSIONS: The scaled regression coefficients give insight to the complexation mechanisms, which appear to be different for the three types of cyclodextrins.

Cyclodextrins↗

PubMed1999

Sources for structure formation and switches in metabolic pathways.

Zonation of function, i.e. localization of metabolic activity in certain regions of histologically uniform tissues, is an often observed phenomenon. Moreover, experiments show that such metabolic patterns are highly dynamical. Since in the pathways of intermediary metabolism no autocatalytic reactions are observed, different types of metabolic regulation are sources of the non-linearities necessary for structure formation. Two models of biochemical reactions frequently encountered in metabolic pathways, namely a bisubstrate kinetics model with substrate inhibition, and an allosteric model with product regulation, are presented. It is shown, that they are well-suited to reproduce the dynamical behavior suggested by experimental findings, like their capability to act as switches, or their ability for spatio-temporal pattern formation in mature tissues.

Allosteric Regulation↗

PubMed1999

Selective assembly of cyclodextrins on poly(ethylene oxide)-poly(propylene oxide) block copolymers.

This paper presents a computational study on the formation of a molecular necklace formed by specific threading of cyclodextrins (CDs) on block copolymers. Structural as well as energetic principles for the selective complexation of alpha- and beta-cyclodextrin with poly(ethylene oxide)-poly(propylene oxide) block copolymers (PEO-PPO) are elucidated considering a diblock copolymer of equimolecular composition (PEO)4-(PPO)4 as guest. A non-statistical distribution of CDs, i.e. alpha-CDs primarily located on the PEO chain and beta-CDs on PPO blocks of the polymer, is based on a variety of structural features and energetic preferences considering both potential as well as solvation energies. This selectivity becomes already obvious considering 1:1 complexes between PEO and PPO monomers and the two CDs, but is increasingly evident when calculating higher order ensembles. Besides the host-guest interaction, docking between CDs themselves is an important, also non-statistical, prerequisite for the self-assembly of highly ordered tubes. The formation of intermolecular hydrogen bonds between adjacent CDs in a tubular aggregate gives an important contribution to the overall stability of the molecular necklace. The net effect, based on the preferential interaction between host and guest as well as between the host molecules themselves, results in the formation of a stable, highly ordered macromolecular, multicomponent aggregate.

Cyclodextrins↗

PubMed1995

Turing structures in a system with regulated gap-junctions.

In two coupled cells, each containing a bisubstrate-kinetics reaction system, the two substrates can cross the membranes through gap-junction protein channels (gating). Passing through the gap-junctions is controlled by one of the substrates, thus resulting in non-linear diffusion. Linear stability analysis gives the conditions, under which the symmetric fixpoint becomes unstable, leading to spatial asymmetry (Turing structures). The implications for morphogenesis are discussed.

Animals↗