A CNDO/2 SCF perturbation theory is presented for interpreting the form of CNDO/2 potential energy surfaces of unimolecular reactions. The analysis is performed by calculating the energy change E arising from a distortion of the molecular geometry along the reaction coordinate. E is decomposed into different perturbational contributions which are appropriate for an interpretation of the perturbation energy E. Moreover, E is resolved into energy parts arising from a single occupied orbital and contributions due to pairwise orbital interactions. In this way one evaluates numerically how the form of the occupied and unoccupied orbitals determines the magnitude of E. If the distortion occurs along a definite symmetry coordinate, group-theoretical arguments can be applied to discuss the magnitude of characteristic components of the perturbation energy. The SCF perturbation theory is used to analyze the isomerization of ethylene, cis-2-butene and cis-2-butenenitrile.This work was partially supported by Nato-Grant No. 1072 相似文献
Plasminogen is the primary zymogen in the fibrinolytic pathway, and its primary function involves degradation of fibrin. Biomaterials often show adsorption of fibrinogen and subsequent formation of fibrin. Plasminogen's function in vivo could be adapted to facilitate its activation and fibrinolytic function on a biomaterial surface. In order to elucidate plasminogen function adsorbed to a model fibrinolytic surface ligands known to affect plasminogen properties in solution were attached to model silica surfaces to study the effects of immobilized ligands as fibrinolytic activators. Model silica surfaces were synthesized which contained covalently attached lysine moieties (surface I), sulfonate moieties (surface II) or a combination of both (surface III). Lysine moieties on these model surfaces interact specifically with multiple lysine-binding sites of plasminogen and induce a number of changes in conformation and function. Sulfonate moieties interact non-specifically with accessible lysine and arginine residues of plasminogen and also affect the function of plasminogen. Inherent physico-chemical properties monitored following plasminogen adsorption were activation to plasmin, enzymatic activity, fluorescent intensity, and fluorescent polarization, monitored by total internal reflection fluorescence, each of which are affected by plasminogen conformation.
Correlations were as follows: increased fluorescent intensity and decreased fluorescent polarization were indicative of plasminogen conformational changes and are correlated to increased enzymatic activity of plasmin. Surfaces I and III showed a 20% increase in fluorescent intensity, and a 25% and 8% decrease in fluorescent polarization, respectively, in comparison to surface II. The specific activity for surfaces I and III was increased 11.3 and 1.8 fold above that found for surface II. Plasminogen incubated with sulfonate groups in solution resulted in no increase in fluorescent intensity and a slight decrease in fluorescent polarization as compared with plasminogen alone and reduced specific activity of plasmin in the presence of sulfonate as compared with plasmin alone. Lysine or ε-aminocaproic acid (ACA) incubated with plasmin in solution showed a 30% and 10% increase in fluorescent intensity, a 24% and 5% decrease in fluorescent intensity, and maximum specific activity increased 3.6 and 2.5 fold, respectively, over plasminogen alone.
Interactions of plasminogen with ligands for its lysine-binding sites produced dramatic effects both in solution and adsorbed to model fibrinolytic surfaces. The characterization of these interactions along with known fibrin interactions will allow selection of appropriate surface modifications to enhance the fibrinolysis of thrombus formed at a biomaterial interface. These modifications may lead to a native-like surface structure to protein and cellular components of blood and create a more biocompatible surface. 相似文献
Biofilm growth of Bacillus subtilis, Pseudomonas fragi, Pediococcus inopinatus and Listeria monocytogenes was studied on stainless steel surfaces at room and low temperatures to evaluate the results of traditional hygiene measures. The results were compared with those of image analysis of stainless steel surfaces in an epifluorescence microscope. Statistical analyses were carried out to determine the variations between the conventional cultivation swab method, the glycocalyx amount obtained using swabbing, and the values of the areas of the biofilm, slime and cells. As a general rule, old biofilms showed total counts at approximately the same levels as the young biofilm. The results showed that temperature affected the results for all strains except B. subtilis. The strains of Pe. inopinatus and Ps. fragi showed increased attachment at 6°C and L. monocytogenes at 25°C. The biofilm slime was more easily detached than the cells. The results indicated that the traditional swab method is not reliable for the measurement of biofilm formation on surfaces. 相似文献
In this contribution we propose a simple model of adsorption of a binary (racemic) mixture on a chiraly templated surface. As an example, the adsorption of a liquid mixture of enantiomers on a chiral stationary phase (CSP) is considered. In particular, we study the effect of the lateral interactions in the adsorbed phase on the kinetic and equilibrium isotherms of the enantiomers. Additionally, we investigate the influence of the composition of the surface on the performance of the CSP in the presence of the lateral interactions. To that end, the adsorption of the mixture is modeled by using Monte Carlo simulations as well as by applying an analytical approach involving rate equations coupled with the Mean Field Approximation (MFA). The predictions of the theory are found to be in good agreement with the results of the simulations. 相似文献
The family of all possible reaction mechanisms on a potential surface has an algebraic structure with potential applications in quantum chemical molecular design and synthesis planning.Transformation properties and equivalence relations of reaction paths on potential energy hypersurfaces lead to a topological definition of reaction mechanisms. The family of all fundamental reaction mechanisms on the hypersurface has a group structure,the fundamental group of an appropriately defined topological space. Isomorphism and homomorphism relations between fundamental groups of reaction mechanisms are used to characterize the chemically important topological properties of various subsets of a hypersurface, or those of different excited state hypersurfaces. 相似文献
Fractal dimension of a carious tooth surface was determined using an electrochemical method. The method was based on time-dependent diffusion towards electrode surfaces, which is one of the most useful and reliable methods for the determination of fractal dimension of electrode surfaces. For this purpose, the tooth was covered with a gold layer, which acted as an electrode in electrochemical experiments. It is suggested that the fractal dimension can be used as a quantitative measure of the state of dental surfaces. The method presented demonstrates the power of electrochemical techniques for the determination of fractal dimension of surface of non-conducting objects. 相似文献