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PubMed2006

Effect of intrinsic properties of metals on the adsorption behavior of molecules: benzene adsorption on Pt group metals.

Investigation of benzene adsorption on different metal surfaces closer to a practical system appears to be a very important intermediate stage to utilize the conclusion obtained on single-crystal surfaces. In this paper, we studied the electrochemical adsorption behaviors of benzene on roughened Pt group electrodes using surface enhanced Raman spectroscopy (SERS). The effects of potential, surface roughness, and benzene concentration were investigated. Significant difference in surface Raman spectra of benzene on Ru, Rh, Pd, and Pt surfaces were found. On Pt surfaces, the parallel-chemisorbed benzene, the vertical dissociated chemisorbed benzene, and the physisorbed benzene were observed, evidenced by the ring vibration mode appearing at 872, 1012, and 991 cm(-1), respectively. On Pd, only parallel-chemisorbed benzene and physisorbed benzene were found. On Rh and Ru, the SERS signals were mainly from the parallel-chemisorbed benzene, with an extremely weak signal from the physisorbed benzene. The potential dependent study reveals that the parallel-chemisorbed species interacts strongest with the substrate, while the physisorbed species can be easily removed at positive potentials. The models for the adsorbed benzene were given to account for the different types of benzene on these Pt group metals. The difference in the atomization heat of the four metals was used to interpret the different interaction strength of benzene with Pt group metals.

Journal Article↗
PubMed2006

Adsorption of pentacene on filled d-band metal surfaces: long-range ordering and adsorption energy.

The growth of pentacene on suitable metallic templates is studied by means of low-energy electron diffraction and ultraviolet photoelectron spectroscopy. Highly ordered pentacene single layers can be prepared by deposition on filled d-band metal templates kept at 370 K. The presence of the steps for the Cu(119) vicinal surface and of the Au troughs for the Au(110)-(1 x 2) surface allows the formation of commensurate long-range ordered structures with (3 x 7) and (3 x 6) periodicities, respectively. A detailed analysis of the molecular induced electronic states evolution is performed for different growth morphologies. The adsorption energy of the ordered molecular single layers on the Au(110) surface is lower (1.90 eV) than on the Cu vicinal surface (2.36 eV), where the steps enhance the molecule adsorption energy.

Journal Article↗
PubMed2004

Comparative analysis between dextran sulfate adsorption and direct adsorption of lipoproteins in their capability to reduce erythrocyte adhesiveness/aggregation in the peripheral blood.

The purpose of this study was to compare the degree of erythrocyte adhesiveness/aggregation (EAA) reduction of two low-density lipoprotein (LDL) apheretic procedures, namely direct adsorption of lipoproteins (DALI) and dextran sulfate adsorption (DSA). A significant (P < 0.001) reduction of EAA was noted in six hypercholesterolemic patients who underwent a total of 40 apheretic sessions and no difference was noted in the degree of EAA reduction by the two techniques. Thus. being a real-time and point-of-care test, the erythrocyte adhesiveness/aggregation test can be applied in relevant situations of acute ischemia, where therapeutic LDL apheresis could improve the hemorheology of individuals with increased concentrations of cholesterol and inflammatory sensitive proteins.

Adult↗
PubMed1976

[Compartmental model of the adsorption of a dye by proteins. The possible role of adsorption in the hepatic excretion of bromosulphophthalein].

A compartmental model was suggested for the study of the hepatic excretion of bromosulphophthalein (BSP). By using a hypothesis concerning the adsorption of the BSP compound by proteins, one derives from the equations of the model several known experimental results, viz. form of concentration curves that vary in accordance with the strength of the injection, existence of a limiting Tm value, etc. An explicit formula is given for calculating Tm.

Adsorption↗
PubMed2002

Adsorption and adsorption mechanism of rice bran for chloroform from tap water.

We have found that rice bran effectively adsorbed chloroform from tap water. The amount of chloroform adsorbed was plotted against the equilibrium concentration of chloroform in solution on a logarithmic scale. A linear relationship was obtained, indicating that the adsorption reaction was a Freundlich type. The removal of chloroform by rice bran was attributed to the uptake into intracellular particles called spherosomes.

Adsorption↗
PubMed2004

Heterogeneous adsorption of 1-indanol on cellulose tribenzoate and adsorption energy distribution of the two enantiomers.

The distributions of the adsorption energies (AED) of two enantiomers, (R)-1- indanol and (S)-1-indanol, on a chiral stationary phase were measured and the results are discussed. The chiral phase used is made of cellulose tribenzoate coated on porous silica. The AEDs were determined using the expectation maximization method, a numerical method that uses directly the raw experimental isotherm data, inverts this set of data into an AED, and introduces no arbitrary information in the calculation. However, it uses the Langmuir equation as the local isotherm. The experimental data fit very well to the bi-Langmuir isotherm model for the more retained enantiomer. Our results show that the AEDs of these two enantiomers have no energy modes that would be identical (same mean energy, mode profile, and mode area), in contrast to numerous cases previously studied, e.g., that of the beta-blockers on a Cel7A column. This indicates a significantly different retention mechanism.

Adsorption↗
PubMed2003

Modeling and CFD prediction for diffusion and adsorption within room with various adsorption isotherms.

This paper presents physical models that are used for analyzing numerically the transportation of volatile organic compounds (VOCs) from building materials in a room. The models are based on fundamental physicochemical principles of their diffusion and adsorption/desorption (hereafter simply sorption) both in building materials and in room air. The performance of the proposed physical models is examined numerically in a test room with a technique supported by computational fluid dynamics (CFD). Two building materials are used in this study. One is a VOC emitting material for which the emission rate is mainly controlled by the internal diffusion of the material. The other is an adsorptive material that has no VOC source. It affects the room air concentration of VOCs with its sorption process. The floor is covered with an emission material made of polypropylene styrene-butadiene rubber (SBR). An adsorbent material made of coal-based activated carbon is spread over the sidewalls. The results of numerical prediction show that the physical models and their numerical simulations explain well the mechanism of the transportation of VOCs in a room.

Adsorption↗
PubMed2005

Direct adsorption of lipoproteins from whole blood by direct adsorption of lipoprotein apheresis: first experience in two hypercholesterolemic children.

Low density lipoprotein (LDL) cholesterol apheresis, combined with lipid lowering drugs, provides a safe and effective means of improving the prognosis of patients with homozygote familial hypercholesterolemia, especially if started before the age of seven. The direct adsorption of lipoprotein (DALI) is the first extracorporeal low density lipoprotein removing system compatible with whole blood. The purpose of the present study was to clarify the efficacy and safety of DALI in children with homozygous familial hypercholesterolemia. Two boys, aged 9 and 15 years, with familial hypercholesterolemia, who were highly resistant to dietary regimes and to drug therapy, were treated with the low density lipoprotein adsorber DALI apheresis once every 2 weeks for 24 weeks. The treated blood volumes for each procedure were 2911 mL (493 +/- SD) and 5982 mL (1129 +/- SD), respectively. In our patients, the acute mean LDL cholesterol reductions were 44.7 +/- 8.9% and 58.8 +/- 4.5%. The corresponding reductions were 42.5 +/- 7.2% and 56 +/- 4.3% for total cholesterol, and 46.5 +/- 17.1% and 55 +/- 7.5% for very low density lipoprotein cholesterol (VLDL-C). There were insignificant losses of high density lipoprotein (12.2 +/- 5.7%, 8.3 +/- 5.5%). Treatment was well tolerated in general, and neither patient suffered from irreversible or long-lasting adverse effects. Our experience with DALI apheresis is encouraging. The present report is the first on the use of DALI in children. Based on this short-term evaluation we think that DALI might be safe and effective in children with homozygote familial hypercholesterolemia, however further evaluation of long-term effects is needed.

Adolescent↗
PubMed1996

Adsorption of Beta-Blockers onto Poly(isobutylcyanoacrylate) Nanoparticles: Adsorption Model and Dielectric Interpretation

The objective of this report is to understand the boundary mechanism of a model drug, propranolol hydrochloride, onto poly(isobutylcyanoacrylate) nanoparticles stabilized with a mixture of dextran and dextran sulfate, and to explain the similarity between depletion isotherms and the curves obtained with the dielectric method. The dramatic influence of the sulfate groups has been demonstrated by the dosage of the dextran sulfate in the bulk aqueous medium as well as by the interpretation of the propranolol hydrochloride adsorption isotherm. Due to its sulfate groups, dextran sulfate is able to bind to propranolol hydrochloride by an ion exchange process and the resulting complex moves toward the nanoparticle surface. It is the first time that such a model is proposed. In addition, this model supports and explains the dielectric answer: indeed, we had demonstrated that the dielectric method makes it possible to determine the amount of drug loaded onto the nanoparticles, without any ultracentrifugation or assay of the drug. Finally, the application field of the dielectric method may be enlarged to other areas such as ionic resins.

Journal Article↗
PubMed2006

Adsorption of water-soluble polymers with surfactant character. Adsorption kinetics and equilibrium properties.

A comparative study between Langmuir and Gibbs monolayers of a hyperbranched polyol, poly(propylene glycol) homopolymers, and poly(propylene glycol)-poly(ethylene glycol) copolymers with different structure and molecular weight, is reported. Dynamic surface tension (DST) and surface pressure measurements have been carried out to characterize these amphiphilic water-soluble polymers. The adsorption kinetics results are consistent with a rapid diffusion stage followed by a slow reorganization at the air-water interface. The characteristic times of these steps, calculated by the Joos model, point out differences among the polymers in the diffusion rate and rearrangement mechanisms for diluted solutions. Short time analysis of DST data leads to diffusion coefficients in qualitative agreement with the diffusion times calculated with Joos' model. Spread monolayers remain stable for long periods of time. The desorption process seems quite inoperative. As a consequence, the surface pressure of the spread monolayers can be studied over a broad surface concentration range. 2D first-order phase transitions have been evidenced from plateaux observed in Langmuir and Gibbs isotherms. It has been found that Gibbs monolayers lead to lower surface tension states than the Langmuir ones.

Journal Article↗
PubMed2005

Effect of omega-hydrogenation on the adsorption of fluorononanols at the hexane/water interface: pressure effect on the adsorption of fluorononanols.

The interfacial tension gamma of the hexane solution of 1H,1H-perfluorononanol (FDFC(9)OH) and its omega-hydrogenated analogue, 1H,1H,9H-perfluorononanol (HDFC(9)OH), against water was measured as a function of pressure and concentration at 298.15 K in order to clarify the effect of omega-dipole on the orientation of fluorononanol molecules from the viewpoint of volume. The adsorbed films of both alcohols exhibit two kinds of phase transitions among three different states: the gaseous, expanded, and condensed states. The partial molar volume changes of adsorption - in the expanded and condensed states were evaluated and compared between the two systems. The - values of both alcohols are negative, and thus the alcohol molecules have smaller volume in the adsorbed film than in the bulk solution. Furthermore, the value was obtained through the evaluation of by the density measurement of the bulk hexane solution. It was found that the value of HDFC(9)OH is smaller than that of FDFC(9)OH in the condensed state. On the basis of three matters concerning the molecular structure of alcohols, the occupied area at the interface, and the orientation of FDFC(9)OH in the adsorbed film deduced from the earlier results of X-ray reflectivity measurement, the mean tilt angle of HDFC(9)OH from the interface normal in the condensed film was estimated to be 15 degrees . The thermodynamic estimation demonstrated here is highly valuable one to provide structure information on an adsorbed film.

Journal Article↗
PubMed2004

Adsorption of poly(ethyleneimine) on silica surfaces: effect of pH on the reversibility of adsorption.

The role of polymer charge density in the kinetics of the adsorption and desorption, on silica, of the polyelectrolyte poly(ethyleneimine) (PEI) was investigated by stagnation-point flow reflectometry. In the first series of experiments, PEI solutions were introduced at the same ionic strength and pH as the background solvent. It was found that the adsorbed amount of PEI increased by increasing pH. In the second series of investigations, several PEI solutions with ascending pH were introduced consecutively into the cell. In these cases, a stepwise buildup of the adsorbed amount was observed and the "final" adsorbed amounts were observed to be roughly equal with the adsorbed amounts of the first series of measurements at the same pH. Finally, adsorption/desorption experiments were performed where the preadsorption of PEI was followed by the introduction of PEI solutions of descending pH. No desorption was detected when the pH changed from pH = 9.7 to pH = 5.8. However, when there was a 9.7 --> 3.3 or 5.8 --> 3.3 decrease in the pH, the kinetic barriers of desorption seemed to completely disappear and roughly the same adsorbed amount as in the first series of experiments at pH = 3.3 was quickly attained by desorption of the PEI. This study reveals the high impact of pH, affecting parameters such as charge density of the surface and polyelectrolyte as well as the structure of the adsorbed macromolecules, on the desorption properties of weak polyelectrolytes. The observed interfacial behavior of PEI may have some important consequences for the stability of alternating polyelectrolyte multilayers containing weak polyelectrolytes.

Journal Article↗
PubMed1999

Neutron reflectivity studies of critical adsorption: the correspondence between a critical adsorption profile and specular neutron reflection.

For interfacial order parameter profiles which decay as Az(-mu), such as the composition profile of the noncritical interface of a binary liquid mixture at a critical end point, there is a reported one-to-one correspondence between the profile and the reflectivity which can be described by an analytical theory [S. Dietrich and R. Schack, Phys. Rev. Lett. 58, 140 (1987)]. Evidence for mu=0.53+/-0.02 for adsorption at the hydrophilic silicon/liquid surface of the mixture (2-butoxyethanol+deuterium oxide) near its lower critical end point, determined from neutron reflectivity measurements, is presented. This value is in good agreement with the theoretical prediction of mu=0.516+/-0.004. Further examination of the data permits the determination of the asymptotic surface enrichment scaling factor amplitude P0 approximately 0.11, which is not in agreement with the theoretical value P(0) = 0.94+/-0.05 and values determined by other experimental methods.

Journal Article↗
PubMed2006

"Textbook" adsorption at "nontextbook" adsorption sites: halogen atoms on alkali halide surfaces.

Density-functional theory and second order Møller-Plesset perturbation theory calculations indicate that halogen atoms bond preferentially to halide substrate atoms on a series of alkali halide surfaces, rather than to the alkali atoms as might be anticipated. An analysis of the electronic structures in each system reveals that this novel adsorption mode is stabilized by the formation of textbook two-center three-electron covalent bonds. The implications of these findings to, for example, nanostructure crystal growth, are briefly discussed.

Journal Article↗
PubMed1987

[Parameters of adsorption chromatography. 5. Adsorption parameters of potential pyrimidine-type antimycotics and their correlation with biological activity].

The RF-values of 19 fungicidal pyrimidine derivatives were determined by means of thin-layer chromatography (aluminium oxide layers) in some solvent systems and the relating parameters of adsorption chromatography were calculated. Furthermore the retention times of HPLC were determined. Both of the parameters were correlated with experimentally determined biological values.

Antifungal Agents↗