A study of the nature of plasma protein adsorption on the surface of perfluorocarbon emulsions stabilized by different triblock copolymers

The composition of plasma proteins adsorbed on the surface of perfluorocarbon emulsions stabilized by different triblock copolymers and their quantitative ratio were analyzed. The results allowed us to describe three types of protein adsorption on the surface of emulsion droplets. Opsonin proteins prevailed during the first type of adsorption. Their adsorption occurred on a dense and inactive layer of triblock copolymers. The second type of adsorption occurred due to the hydrophobic effect on a dense and mobile layer, with low-molecular-weight proteins being predominantly adsorbed (monoadsorption). The third type of adsorption occurred on a loose layer of triblock copolymers. In this case, the adsorption of a large amount of proteins with a molecular weight of 10–500 kDa was observed, while the total molecular weight was distributed over a large number of proteins.     

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.     

Adsorption of phenol and aniline on natural and organically modified montmorillonite: experiment and molecular modelling

Natural and intercalated Wyoming montmorillonite (MMT) with the tetramethylammonium (TMA) cations were used for the adsorption of phenol and aniline. Laboratory experiments characterised by adsorption isotherms were compared with the results of molecular modelling simulations. Aniline adsorbed itself strongly on MMT; while using the TMA intercalates (TMA-MMT), its adsorption decreased. On the contrary, the adsorption of phenol on TMA-MMT was moderately higher than on the MMT surface. The MMT surface models were described by empirical force field used in molecular mechanics and dynamics. The Burchart–Universal force field was used in the Cerius² modelling environment. The modelling results revealed the important role of water forming a moderately concentrated layer on the pure MMT surface. Water molecules enable the adsorption of aniline on MMT and, on the contrary, repel phenol molecules from MMT. In the case of TMA-MMT, lower amount of water near a silicate layer caused decrease in the aniline adsorption and, on the contrary, increase in the phenol adsorption.     

Osmotic pressure measurements on insulin: anomalous results indicate that the monomer is preferentially adsorbed

The concentration dependence of the number average molecular weight of insulin at pH 2, ionic strength 0.05, and 20 degrees C as determined by osmotic pressure measurements indicates that the hormone is a homogeneous protein of molecular weight close to that of the dimer. Since sedimentation equilibrium experiments confirm what is well known, namely that insulin is a self-associating protein dissociating to monomer under these conditions, an explanation for the anomaly was sought in the possible loss of protein from solution by adsorption. Analysis of the results strongly supports this conclusion and consideration of the adsorption properties of insulin in terms of hydrophobic interactions shows them to be consistent with the behaviour of insulin as a self-associating protein. The monomer appears to be the primary molecular species responsible for insulin adsorption.     

Enhancing Protein Adsorption Simulations by Using Accelerated Molecular Dynamics

The atomistic modeling of protein adsorption on surfaces is hampered by the different time scales of the simulation ( s) and experiment (up to hours), and the accordingly different ‘final’ adsorption conformations. We provide evidence that the method of accelerated molecular dynamics is an efficient tool to obtain equilibrated adsorption states. As a model system we study the adsorption of the protein BMP-2 on graphite in an explicit salt water environment. We demonstrate that due to the considerably improved sampling of conformational space, accelerated molecular dynamics allows to observe the complete unfolding and spreading of the protein on the hydrophobic graphite surface. This result is in agreement with the general finding of protein denaturation upon contact with hydrophobic surfaces.     

硝酸铵水凝胶分子印迹聚合物的制备

目的：目前安全问题成为世界各国的首要问题,尤其是对炸药分子的检测。硝酸铵是硝铵炸药的主要成分。研究水凝胶分子印迹法对硝铵炸药分子的检测。方法：水凝胶分子印迹方法制备硝酸铵水凝胶分子印迹聚合物,运用静态结合实验对其结合率进行了测定。结果：聚合物对硝酸铵具有良好的识别和吸附性能。印迹聚合物的解离常数为4.08g/L,最大吸附量为3.51mg/g。结论：水凝胶分子印迹法可合成水溶性炸药分子印迹聚合物,并且识别及吸附性能良好。     

Integrated bioprocesses

Integrated bioprocesses have been developed to optimise yield and cost-effectiveness of production of low and high molecular weight molecules. Low molecular weight products are removed from the cultivation medium with in situ extraction, in situ adsorption or crystallisation to avoid product inhibition. One-pot processes are being developed to replace two-stage reactions. Recent developments in the integrated purification of high molecular weight products focus mainly on the integration of solid/liquid separation and initial product recovery such as expanded bed adsorption or extraction in aqueous two-phase systems. Additionally, new approaches for a more efficient processing of inclusion bodies have been developed.     

Insulin adsorption on functionalized silica surfaces: an accelerated molecular dynamics study

We study the influence of surface functionalization of a silica surface on insulin adsorption using accelerated molecular dynamics simulation. Three different functional groups are studied, CH₃, OH, and COOH. Due to the partial charges of these groups, the surface polarity of silica is strongly altered. We find that the adsorption energies of insulin change in agreement with the decreasing surface polarity. Conformational changes in the adsorbed protein and the magnitude of the molecular dipole moment in the adsorbed state are consistent with this result. We conclude that protein adsorption on functionalized polar surfaces is governed by the induced changes in surface polarity.     

Amino acid side chain interaction with chelate-liganded crosslinked dextran, agarose and TSK gel. A mini review of recent work.

Protein adsorption and retention data collected from recent chromatographic studies on hydrophilic gels substituted with chelate-bonded metal ions are discussed. Attempts are made to interpret the adsorption behavior in terms of molecular events caused by the affinity for the immobilized metal ions.     

Adsorption chromatography of Schardinger dextrins on Sephadex G-15

Both α- and β-Schardinger dextrins and their α-1 → 6-substituted glucosyl derivatives behave anomalously on Sephadex G-15 column chromatography in that they are retarded well beyond their expected elution volumes. It would appear that they are fractionated by adsorption chromatography rather than by molecular sieving. The separations are superior to those on the molecular sieve Bio-Gel P-2, where adsorption does not occur, and offer a useful preparative method for the glucosyl dextrins.     

Fluorination of BC3 nanotubes: DFT studies

We have studied the adsorption of atomic and molecular fluorines on a BC₃ nanotube by using density functional calculations. It was found that the adsorption of atomic fluorine on a C atom of the tube surface is energetically more favorable than that on a B atom by about 0.97 eV. The adsorption of atomic fluorine on both C and B atoms significantly affects the electronic properties of the BC₃ tube. The HOMO-LUMO energy gap is considerably reduced from 2.37 to 1.50 and 1.14 eV upon atomic F adsorption on B and C atoms, respectively. Molecular fluorine energetically tends to be dissociated on B atoms of the tube surface. The associative and dissociative adsorption energies of F₂ were calculated to be about ?0.42 and ?4.79 eV, respectively. Electron emission density from BC₃ nanotube surface will be increased upon both atomic and molecular fluorine adsorptions due to work function decrement.     

Protein adsorption at air-water interfaces: a combination of details

Using a variety of spectroscopic techniques, a number of molecular functionalities have been studied in relation to the adsorption process of proteins to air-water interfaces. While ellipsometry and drop tensiometry are used to derive information on adsorbed amount and exerted surface pressure, external reflection circular dichroism, infrared, and fluorescence spectroscopy provide, next to insight in layer thickness and surface layer concentration, molecular details like structural (un)folding, local mobility, and degree of protonation of carboxylates. It is shown that the exposed hydrophobicity of the protein or chemical reactivity of solvent-exposed groups may accelerate adsorption, while increased electrostatic repulsion slows down the process. Also aggregate formation enhances the fast development of a surface pressure. A more bulky appearance of proteins lowers the collision intensity in the surface layer, and thereby the surface pressure, while it is shown to be difficult to affect protein interactions within the surface layer on basis of electrostatic interactions. This work illustrates that the adsorption properties of a protein are a combination of molecular details, rather than determined by a single one.     

Protein recovery from enzyme‐assisted aqueous extraction of soybean

Enzyme‐assisted aqueous oil extraction from soybean is a “green” alternative to hexane extraction that must realize potential revenues from a value‐added protein co‐product. Three technologies were investigated to recover protein from the skim fraction of an aqueous extraction process. Ultrafiltration achieved overall protein yields between 60% and 64%, with solids protein content of 70%, and was effective in reducing stachyose content, with fluxes between 4 and 10 L/m² hr. Protein content was limited because of high retention of lipids and the loss of polypeptides below 13.6 kDa. Isoelectric precipitation was effective in recovering the minimally hydrolyzed proteins of skim, with a protein content of 70%, again limited by lipid content. However, protein recovery was only 30% because of the greater solubility of the hydrolyzed proteins. Recovery by the alternative of protein capture on dextran‐grafted agarose quaternary‐amine expanded bed adsorption resins decreased with decreasing polypeptide molecular weight. Proteins with molecular mass greater than 30 kDa exhibited slow adsorption rates. Expanded bed adsorption was most effective for recovery of proteins with molecular weight between 30 and 12 kDa. Overall, adsorption protein yields were between 14% and 17%. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

A compendium of potential energy maps of zeolites and molecular sieves

We present potential maps of xenon in 20 different zeolites and molecular sieves. The potential maps reveal both the accessible pore volume and localized adsorption sites and so are important in understanding adsorption and diffusion processes in nanoporous materials. We examine zeolites and molecular sieves with one-dimensional channel-like nanopores (zeolite-Theta 1, AlPO₄-5, zeolite-Omega, zeolite-L, ZSM-12, AlPO₄-8, and VPI-5), with two-dimensional intersecting channel-like nanopores (ZSM-5 [silicalite], ZSM-11, ferrierite, mordenite, and zeolite-Beta), and with three-dimensionally connected cagelike nanopores (zeolite-A, zeolite-Rho, zeolite-Y, sodalite, chabazite, cloverite, cation-poor zeolite-A, and cation-rich zeolite-A). We report the fraction of pore volume accessible, the maximum energy well depth at the adsorption sites, and the activation energy to move between sites. We note several examples of surprising similarities and differences between various molecular sieves. In several instances, we show that these potential profiles are relevant for other small Lennard-Jones-like molecules. By comparison with published Monte Carlo and molecular dynamics simulations, we show that the density distributions of adsorbates at low density are well predicted by the potential maps.     

Immunoaffinity purification and identification of the molecular chaperone calnexin.

We have developed a method for the immunoaffinity purification of calnexin, an endoplasmic reticulum molecular chaperone, and analyzed the molecular weight of purified calnexin using matrix-assisted laser adsorption ionization time of flight mass spectrometry (MALDI TOF-MS). Calnexin was thereby found to have a molecular weight of 66.1 x 10(3), which is nearly identical to the molecular weight estimated from the protein sequence.     

New, highly efficient formulation of diclofenac for the topical, transdermal administration in ultradeformable drug carriers, Transfersomes

Unmodified and polyethylene glycol (PEG) modified neutral and negatively charged liposomes were prepared by freeze-thaw and extrusion followed by chromatographic purification. The effects of PEG molecular weight (PEG 550, 2000, 5000), PEG loading (0-15 mol%), and liposome surface charge on fibrinogen adsorption were quantified using radiolabeling techniques. All adsorption isotherms increased monotonically over the concentration range 0-3 mg/ml and adsorption levels were low. Negatively charged liposomes adsorbed significantly more fibrinogen than neutral liposomes. PEG modification had no effect on fibrinogen adsorption to neutral liposomes. An inverse relationship was found between PEG loading of negatively charged liposomes and fibrinogen adsorption. PEGs of all three molecular weights at a loading of 5 mol% reduced fibrinogen adsorption to negatively charged liposomes. Protein adsorption from diluted plasma (10% normal strength) to four different liposome types (neutral, PEG-neutral, negatively charged, and PEG-negatively charged) was investigated using gel electrophoresis and immunoblotting. The profiles of adsorbed proteins were similar on all four liposome types, but distinctly different from the profile of plasma itself, indicating a partitioning effect of the lipid surfaces. alpha2-macroglobulin and fibronectin were significantly enriched on the liposomes whereas albumin, transferrin, and fibrinogen were depleted compared to plasma. Apolipoprotein AI was a major component of the adsorbed protein layers. The blot of complement protein C3 adsorbed on the liposomes suggested that the complement system was activated.     

Kinetics of protein adsorption and desorption on surfaces with grafted polymers

The kinetics of protein adsorption are studied using a generalized diffusion approach which shows that the time-determining step in the adsorption is the crossing of the kinetic barrier presented by the polymers and already adsorbed proteins. The potential of mean-force between the adsorbing protein and the polymer-protein surface changes as a function of time due to the deformation of the polymer layers as the proteins adsorb. Furthermore, the range and strength of the repulsive interaction felt by the approaching proteins increases with grafted polymer molecular weight and surface coverage. The effect of molecular weight on the kinetics is very complex and different than its role on the equilibrium adsorption isotherms. The very large kinetic barriers make the timescale for the adsorption process very long and the computational effort increases with time, thus, an approximate kinetic approach is developed. The kinetic theory is based on the knowledge that the time-determining step is crossing the potential-of-mean-force barrier. Kinetic equations for two states (adsorbed and bulk) are written where the kinetic coefficients are the product of the Boltzmann factor for the free energy of adsorption (desorption) multiplied by a preexponential factor determined from a Kramers-like theory. The predictions from the kinetic approach are in excellent quantitative agreement with the full diffusion equation solutions demonstrating that the two most important physical processes are the crossing of the barrier and the changes in the barrier with time due to the deformation of the polymer layer as the proteins adsorb/desorb. The kinetic coefficients can be calculated a priori allowing for systematic calculations over very long timescales. It is found that, in many cases where the equilibrium adsorption shows a finite value, the kinetics of the process is so slow that the experimental system will show no adsorption. This effect is particularly important at high grafted polymer surface coverage. The construction of guidelines for molecular weight/surface coverage necessary for kinetic prevention of protein adsorption in a desired timescale is shown. The time-dependent desorption is also studied by modeling how adsorbed proteins leave the surface when in contact with a pure water solution. It is found that the kinetics of desorption are very slow and depend in a nonmonotonic way in the polymer chain length. When the polymer layer thickness is shorter than the size of the protein, increasing polymer chain length, at fixed surface coverage, makes the desorption process faster. For polymer layers with thickness larger than the protein size, increases in molecular weight results in a longer time for desorption. This is due to the grafted polymers trapping the adsorbed proteins and slowing down the desorption process. These results offer a possible explanation to some experimental data on adsorption. Limitations and extension of the developed approaches for practical applications are discussed.     

Differences in the adsorption and diffusion behaviour of water and non-polar gases in nanoporous carbon: role of cooperative effects of pore confinement and hydrogen bonding

We investigate the effect of pore confinement and molecular geometry on the adsorption and self-diffusion of H₂O, CO₂, Ar, CH₄, C₃H₆, SF₆ and C₅H₁₂, in a realistic model of nanoporous silicon carbide derived carbon (SiC-DC), constructed using hybrid reverse Monte Carlo simulation. Adsorption isotherms, adsorbate–adsorbate and adsorbate–adsorbent contributions to the isosteric heat of adsorption are determined to study the effect of pore confinement, microporosity and molecular geometry on adsorption of these gases. We describe the cooperative effect of pore confinement and hydrogen bonding on the formation of water clusters and anomalous adsorption behaviour of water compared with non-polar gases. We find that, in contrast to literature results based on the slit-pore model, pore-filling does not occur below the saturation pressure in hydrophobic amorphous carbon materials such as SiC-DC and activated carbon fibre. We also compare self-diffusivities and activation energy barriers of water and non-polar gases in the microporous structure of SiC-DC to identify underlying correlations with molecular properties. We demonstrate that the self-diffusivity of water deviates considerably from the correlation between diffusivity and molecular kinetic diameter observed for non-polar gases. This is attributed to the reduced diffusivity of water, and its relatively large energy barrier at high loadings despite its small kinetic diameter, which is due to the blocking effect of water clusters at pore entries.