An in vitro study of initial adsorption from human parotid and submandibular/sublingual resting saliva at solid/liquid interfaces

The influence of saliva concentration, saliva total protein content and the wetting characteristics of exposed solids on in vitro film formation was studied by the technique of in situ ellipsometry. The rates and plateau values of adsorption (45 min) at solid/liquid interfaces (hydrophilic silica and hydrophobic methylated silica surfaces) were determinated for human parotid (HPS) and submandibular/sublingual (HSMSLS) resting saliva solutions (0.1 and 1.0%, (v/v), saliva in phosphate buffered saline). Adsorption rates were related to a model assuming mass transport through an unstirred layer adjacent to the surface. The results showed that the adsorption was rapid, concentration dependent and higher on hydrophobic than on hydrophilic surfaces. Analysis of the influence of protein concentration on the adsorbed amounts demonstrated an interaction between protein concentration and the two surfaces for HPS and HSMSLS, respectively. This may indicate differences in binding mode. Inter‐individual differences were found not to be significant at the 1% level of probability. Comparison of the observed adsorption and calculated diffusion rates suggest that on hydrophilic surfaces initial adsorption of proteins diffusing at rates corresponding to those of statherin and aPRPs takes place, whereas on hydrophobic surfaces lower molecular mass compounds appear to be involved.     

Interaction between tissue-type plasminogen activator and ligands grafted onto hydrogel

Tissue-type plasminogen activator (t-PA) has shown significant effects on the treatment of common thrombosis. In this work, molecular dynamics simulations are used in protein–ligand interaction analysis to investigate the affinity of ligands for affinity chromatography. A hydrogel matrix grafted with amine (positively charged), carboxyl (negatively charged) and hydroxyl (neutral) ligands separately is designed, and its adsorption–desorption dynamics are studied in detail. The residues on the surface of t-PA, on which the S1 pocket is located, could be more easily adsorbed by charged ligands grafted onto the hydrogel matrix than neutral ligands. The findings offer new insights into the affinity of various ligands for t-PA, and could be of potential use in t-PA purification.     

Monte Carlo Simulation Study of Adsorption Characteristics in Slit-Like Micropores Under Supercritical Conditions

Abstract

Adsorption characteristics of a solute diluted in supercritical fluids has been investigated by using the Monte Carlo simulation techniques. The Lennard-Jones potential function is used for describing interactions for a model system of CO₂ + benzene in slit-like micropores with infinite graphitic carbon walls. A modified μVT ensemble method with particle exchange proposed by Cracknell, Nicholson and Quirke (1993) is found to be much superior to the conventional μVT ensemble method especially for dense mixtures in a pore. Adsorption isotherms of CO₂ and benzene, in equilibrium with a dilute benzene mixture in CO₂ (mole fraction of benzene = 0.001), are computed by varying pressure, temperature, the benzene–surface interaction potential, and the slitwidth. Adsorption isotherm curve of CO₂ increases with an increase in pressure while that of benzene shows a maximum at a pressure far below the critical pressure of CO₂ and then it decreases with increasing pressure. The decrease in benzene adsorption with increasing pressure is attributable to both the enhanced solubility in supercritical CO₂ and the competitive adsorption of CO₂. The isotherm curves of each component at two temperatures, 313.2 K and 323.2 K, show to cross at a pressure near the critical pressure due to the “density effect” on the chemical potentials of a solute at supercritical fluid conditions. When the interaction between a solute and a surface increases, the adsorption isotherm increases. Narrowing the slitwidth results in the increase in the adsorption of solute since the external potential from two walls becomes deeper.     

The dynamic behaviours of protein BMP-2 on hydroxyapatite nanoparticles

The interaction between proteins and nanoscale inorganic particles is one of the most important topics in many fields. In this study, the dynamic behaviours of protein bone morphogenetic protein-2 (BMP-2) (with six different orientations) on hydroxyapatite (HAP) (001) surface were studied using the molecular dynamics and steered molecular dynamics simulation. The results show that the orientation of protein BMP-2 has obvious influence on its adsorption–desorption behaviours. Among the six systems studied in this article, system I exhibits the strongest interaction with the HAP (001) surface, and the number of the adsorbed residues is more than any one of the other five systems correspondingly. These findings suggest that there will be a preferential orientation when a protein is adsorbed onto a nanoscale interface. For protein BMP-2 interacting with the HAP (001) surface, the preferential orientation is the orientation in system I.     

Simulation Study of Sorption of CO2 and N2 with Application to the Characterization of Carbon Adsorbents

Abstract

The Monte Carlo method was used in its grand ensemble variant (GCMC) in combination with CO₂ and N₂ experimental isotherm data at low (77 and 195.5 K) and ambient temperatures (298 and 308 K), in order to characterize microporous carbons and obtain the corresponding pore size distribution (PSD). In particular, the CO₂ and N₂ densities and the isosteric heats of adsorption inside single, slit shaped, graphitic pores of given width were found on the basis of GCMC for pre-defined temperatures and different relative pressures. In a further step, we determined the optimal PSD for which the best match is obtained between computed and measured isotherms. Comparisons were made between the PSDs found for the same carbon sample at low and ambient temperatures for different gases, and conclusions concerning the applicability of the method and the reliability of the resulting micropore size distributions were drawn.     

Prediction of adsorption equilibria of water–methanol mixtures in zeolite NaA by molecular simulation

Predictions for the adsorption of mixtures of water and methanol in zeolite NaA are reported. The pressure dependence of the adsorption properties such as equilibrium amounts of adsorption and isosteric heats of adsorption are calculated at 378 K by molecular simulations using effective pair potential models. These data are also determined for the adsorption from liquid mixtures. The models predict selectivity inversion in the investigated range of pressure. The change in adsorption ratios can partly be explained by the structural characteristics of the system.     

Analysis of force fields and BET theory for polymers of intrinsic microporosity

A detailed force field analysis for polymers of intrinsic microporosity (PIMs) was carried out in this study. The generalised amber force field (GAFF) with united atom transferable potential for phase equilibria (TraPPE-UA), and the atomistic polymer consistent force field were evaluated. Analysis carried out with PIM-1 showed that the use of GAFF for bonded interactions and TraPPE-UA for non-bonded interactions yielded a simulated sample that compared best with available experimental data (wide-angle X-ray scattering and nitrogen adsorption at 77 K). In addition, Brunauer–Emmett–Teller surface areas, calculated from simulated nitrogen isotherms as pseudo-experimental data, showed that this common method failed to measure the geometric surface area of this type of material. These findings are expected to facilitate the predictive screening of different PIM functionalities.     

Surface modification of polypyrrole/biopolymer composites for controlled protein and cellular adhesion

The ability to control the interaction between proteins and cells with biomaterials is critical for the effective application of materials for a variety of biomedical applications. Herein, the surface modification of the biological dopant dextran sulphate-doped polypyrrole (PPy-DS) with poly(ethylene glycol) to generate a biomaterial interface that is highly resistant to protein and cellular adhesion is described. Thiolated poly(ethylene glycol) (PEG-thiol) was covalently bound to PPy-DS backbone via a thiol-ene reaction. The surface resistance to an extracellular matrix protein fibronectin increased with increasing molecular weight and concentration of PEG-thiol, and was further optimised via increasing the reaction temperature and the pH of the reactant aqueous solution. Optimised surface modification conditions substantially reduced interfacial protein adsorption, with the complete inhibition of adhesion and colonisation by primary mouse myoblasts. PEG-thiol-modified inherently conducting polymers are highly protein resistant multifunctional materials that are promising compounds for a range of biomedical and aquatic applications.     

Novel Camptothecin Analogue (Gimatecan)‐Containing Liposomes Prepared by the Ethanol Injection Method

Small‐sized liposomes have several advantages as drug delivery systems, and the ethanol injection method is a suitable technique to obtain the spontaneous formation of liposomes having a small average radius. In this paper, we show that liposomal drug formulations can be prepared in situ, by simply injecting a drug‐containing lipid(s) organic solution into an aqueous solution. Several parameters should be optimized in order to obtain a final suitable formulation, and this paper is devoted to such an investigation. Firstly, we study the liposome size distributions determined by dynamic light scattering (DLS), as function of the lipid concentration and composition, as well as the organic and aqueous phases content. This was carried out, firstly, by focusing on POPC (1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine) then on the novel L‐carnitine derivative PUCE (palmitoyl‐(R)‐carnitine undecyl ester chloride), showing that it is possible to obtain monomodal size distributions of rather small vesicles. In particular, depending on the conditions, it was possible to achieve a population of liposomes with a mean size of 100 nm, when a 50 mM POPC ethanol solution was injected in pure water; in the case of 50 mM PUCE the mean size was around 30 nm, when injected in saline (0.9% NaCl). The novel anticancer drug Gimatecan, a camptothecin derivative, was used as an example of lipophilic drug loading by the injection method. Conditions could be found, under which the resultant liposome size distributions were not affected by the presence of Gimatecan, in the case of POPC as well as in the case of PUCE. To increase the overall camptothecin concentration in the final liposomal dispersion, the novel technique of “multiple injection method” was used, and up to a final 5 times larger amount of liposomal drug could be reached by maintaining approximately the same size distribution. Once prepared, the physical and chemical stability of the liposome formulations was satisfactory within 24, as judged by DLS analysis and HPLC quantitation of lipids and drug. The Gimatecan‐containing liposomes formulations were also tested for in vitro and in vivo activity, against the human nonsmall cell lung carcinoma NCI‐H460 and a murine Lewis lung carcinoma 3 LL cell lines. In the in vitro tests, we did not observe any improvement or reduction of the Gimatecan pharmacological effect by the liposomal delivery system. More interestingly, in the in vivo Lewis lung carcinoma model, the intravenously administration of liposomal Gimatecan formulation showed a mild but significant increase of Tumor Volume Inhibition with respect to the oral no‐liposomal formulation (92% vs. 86 %, respectively; p < 0.05). Finally, our study showed that the liposomal formulation was able to realize a delivery system of a water‐insoluble drug, providing a Gimatecan formulation for intravenous administration with a preserved antitumoral activity.     

Purification,Crystallization and Properties of Primary Alcohol Dehydrogenase from a Methanol-oxidizing Pseudomonas sp. No. 2941

A simple method for purification and crystallization of primary alcohol dehydrogenase (EC 1.1.99.8) is reported. The purification procedures consisted of four steps: protamine sulfate treatment, ammonium sulfate fractionation, passage through a column of DEAE-cellulose at pH 8.0 and Sephadex G-200 gel filtration. Crystallization was performed by the addition of ammonium sulfate at 65 % saturation with an overall yield of 39 %. The crystalline enzyme had an isoelectric point of pH 7.38 and a sedimentation coefficient 8.44s. A molecular weight of 128,000 was estimated, and the enzyme consisted of two subunits each having a molecular weight of 62,000. The enzyme showed an affinity toward the lower primary alcohols, methanol to n-pentanol. Formaldehyde was also oxidized by the crystalline enzyme. The Km values for methanol and formaldehyde were found to be 20 μm and 70 μm, respectively. Ammonium ions were required for enzyme activity.