Biomedical subjects

Timm Lankau

Publications and source records attributed to Timm Lankau.

5 recordsLinked to original sources

PubMed2006

(H2O)10 and (H2O)12 on a virtual metal surface: the growth of ice.

(H2O)10 and (H2O)12 are used to investigate the growth of ice on metal surfaces with hexagonal symmetry. The model of the virtual metal surface was used to separate the electronic structure of the metal from that of the water cluster while maintaining the geometric constraints imposed by the metal surface on the water cluster. To complement the ab initio calculations on the water cluster, an additional multicenter analysis was done to analyze the hydrogen bonds within the clusters. These calculations suggested that the water bilayer structure adjacent to the virtual metal surface effectively shields the growing ice crystal from the metal surface.

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PubMed2006

Correlated proton motion in hydrogen bonded systems: tuning proton affinities.

The theorem of matching proton affinities (PA) has been widely used in the analysis of hydrogen bonds. However, most experimental and theoretical investigations have to cope with the problem that the variation of the PA of one partner in the hydrogen bond severely affects the properties of the interface between both molecules. The B3LYP/d95+(d,p) analysis of two hydrogen bonds coupled by a 5-methyl-1H-imidazole molecule showed that it is possible to change the PA of one partner of the hydrogen bond while maintaining the properties of the interface. This technique allowed us to correlate various properties of the hydrogen bond directly with the difference in the PAs between both partners: it is possible to tune the potential energy surface of the bonding hydrogen atom from that of an ordinary hydrogen bond (localized hydrogen atom) to that of a low barrier hydrogen bond (LBHB, delocalized hydrogen atom) just by varying the proton affinity of one partner. This correlation shows clearly that matching PAs are of lesser importance for the formation of a LBHB than the relative energy difference between the two tautomers of the hydrogen bond.

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PubMed2005

Solubility of methane in water: the significance of the methane-water interaction potential.

The influence of the methane-water interaction potential on the value of the Henry constant obtained from molecular dynamics simulations was investigated. The SPC, SPC/E, MSPC/E, and TIP3P potentials were used to describe water and the OPLS-UA and TraPPE potentials for methane. Nonbonding interactions between unlike atoms were calculated both with one of four mixing rules and with our new methane-water interaction potential. The Henry constants obtained from simulations using any of the mixing rules differed significantly from the experimental ones. Good agreement between simulation and experiment was achieved with the new potential over the whole temperature range.

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PubMed2003

How harmful is the first law?

In his First Law (of thermodynamics), Clausius emphasized the equivalence of heat and work-conservation of energy was mentioned only indirectly. Today, the main emphasis is put on energy conservation, but the equivalence of heat and work has proven not only to be superfluous, but also highly destructive. Because of this emphasis, heat is no longer considered an independent entity. In the guise of the quantity Q heat acts in a strange double role-an entity equivalent to work, but also as something fundamentally different. The place formerly occupied by heat is now filled with an abstract quantity, the entropy S-a phantom without macroscopically relevant properties. By using a phenomenological approach to entropy, it can be shown that entropy S does indeed have easily comprehensible macroscopic properties. This approach can be used to simplify thermodynamic reasoning and to reduce the calculus of thermodynamics to a fraction of its usual extent.

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PubMed2003

Symmetry in basic physical laws.

Recent physical experiments suggest that chirality is not a purely chemical phenomenon, but seems to be an inherent feature of basic physical laws. A fundamental physical principle (the CPT theorem) connects asymmetry in space with the "arrow of time," and shows that such an arrow exists even on the level of mesons.

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