Biomedical subjects

Theo G M van de Ven

Publications and source records attributed to Theo G M van de Ven.

3 recordsLinked to original sources

PubMed2006

Ultrasonic characterization of proteins and blood cells.

Ultrasound changes its intensity and speed when propagating through a liquid or a suspension containing particles. In addition it generates a weak electric signal by altering the motion of ions and charged particles. Hence acoustic and electroacoustic measurements provide information about the properties of suspended particles and molecules. Here we present both acoustic and electroacoustic results on blood suspensions and protein solutions, relevant to life sciences. For blood cells a strong increase in acoustic attenuation with volume fraction is found, from which the speed of sound in an erythrocyte is found to be about 1900 m/s, assuming the attenuation is due to scattering only. A similar value of 1700 m/s is found from the increase in sound speed of the dispersion with concentration. Electroacoustic measurements on bovine serum albumin (BSA) yield a charge of about seven elementary charges per BSA molecule. These results show the power and usefulness of acoustic and electroacoustic measurement techniques for biological systems.

Acoustics↗

PubMed2006

Molecular orbital studies of gas-phase interactions between complex molecules.

Describing interactions among large molecules theoretically is a challenging task. As an example, we investigated gas-phase interactions between a linear nonionic oligomer and various model compounds (cofactors), which have been reported to associate experimentally, using PM3 semiempirical molecular orbital theory. As oligomer, we studied the hexamer of poly(ethylene oxide) (PEO), and as cofactors, we studied corilagin and related compounds containing phenolic groups (R-OH). These systems are of interest because they are models for PEO/cofactor flocculation systems, used in industrial applications. The PM3 delocalized molecular orbitals (DLMO) describe the bonding between (PEO)6 and cofactors, and some of them cover the complete complex. The DLMOs which cover the traditionally considered hydrogen bonds R-OH...O or R-CH...O show a distinct "pinch", a decrease of the electron density, between the H...O atoms. Calculations of Gibbs free energy, entropy, and enthalpy show that the PEO/cofactor complexes do not form at room temperature, because the loss of entropy exceeds the increase in enthalpy. The change in enthalpy is linearly related to the change in entropy for the different complexes. Even though bond lengths, bond angles, DLMOs, and electron densities for the PEO/cofactor complexes are consistent with the definition of hydrogen bonds, the number of intermolecular R-OH...O and R-CH...O bonds does not correlate with the enthalpy of association, indicating that the bonding mechanism for these systems is the sum of many small contributions of many delocalized orbitals.

Journal Article↗

PubMed2005

Association-induced polymer bridging by poly(ethylene oxide)-cofactor flocculation systems.

Poly(ethylene oxide) (PEO) is used in papermaking, water purification and mineral flotation as a flocculating agent. Despite the fact that PEO does not adsorb on cellulose and bleached lignin, and only poorly on calcium carbonate, it can nevertheless be used to deposit colloidal pigments on pulp fibers. PEO by itself is inefficient, but it can be made to work in combination with another compound, usually referred to as a cofactor or an enhancer. The cofactor associates with PEO and the association complex acts as an efficient bridging agent. There are two classes of cofactor: those who cause PEO to cluster and those that do not. In general PEO association-clusters are more efficient flocculating agents than non-clustered PEO. The PEO dissolution procedure has an important effect on the PEO flocculation efficiency. Before reaching thermodynamic equilibrium, PEO is in an entangled state. Cofactors that cluster PEO are likely to maintain PEO in an entangled state and, like the association-clusters, these entanglements are more efficient flocculation agents than well-dispersed PEO. Salt also affects the PEO-cofactor association. For most cofactors, salt is needed to induce the association. Calcium ions can act as bridging agents between association complexes, especially those containing carboxyl groups, thus promoting the formation of association-clusters.

Adsorption↗