Hydrophilicity/hydrophobicity adsorbate-induced

In our work [103] the adsorption of a-chymotrypsin and bovine serum albumin at the hydrophobic surface of fluoroplast and at the hydrophilic silica has been investigated. In a tube 0.3 ml the adsorbent in an amount of 75-80 mg was induced (as a suspension in the case of hydrophobic adsorbent), than 5 ml of the protein solution of definite concentration was induced in a tube, carefully stirred during 2 hours and than centrifugated. The range of concentrations varying was 0.1-0.9 mg/ml for a-chymotrypsin and 0.2-3 mg/ml for BSA. Results are given in Table 5. 

Photocatalytic systems based on the plasmon-induced charge separation can be used for oxidation of alcohols, aldehydes, and phenol [8, 13] mineralization of carboxylic acids [14] oxidation of benzene to phenol [15] release of hydrogen from alcohols and ammonia [16] and oxidation and reduction of water (but not water splitting) [17]. The photocatalytic system can also be applied to hydrophilic/hydrophobic patterning based on photocatalytic removal of a hydrophobic thiol adsorbed on metal nanoparticles [18]. 

Taking into account that both the voltammetric maximum and the depression in drop time-potential curves were affected by the ion pair formation equilibrium of Na DPA in LM, it is concluded that Na which has been transferred from NB to W may be adsorbed at the interface from the side of W inducing the adsorption of DPA as a counterion from the NB side. At the interface, the adsorbed Na may exist as an ion pair, which is denoted as Na DPAj, hereafter. The possibility of the interfacial ion pair formation between a hydrophobic cation (or anion) in an organic phase and a hydrophilic anion (or cation) in an aqueous phase has been proposed by Girault and Schiffrin [32], and Kakiuchi et al. [33]. 

The influence of adsorption on the structure of a -chymotrypsin is shown in Fig. 10, where the circular dichroism (CD) spectrum of the protein in solution is compared with that of the protein adsorbed on Teflon and silica. Because of absorbance in the far UV by the aromatic styrene, it is impossible to obtain reliable CD spectra of proteins adsorbed on PS and PS- (EO)8. The CD spectrum of a protein reflects its composition of secondary structural elements (a -helices, / -sheets). The spectrum of dissolved a-chymotrypsin is indicative of a low content of or-helices and a high content of //-sheets. After adsorption at the silica surface, the CD spectrum is shifted, but the shift is much more pronounced when the protein was adsorbed at the Teflon surface. The shifts are in opposite directions for the hydrophobic and hydrophilic surfaces, respectively. The spectrum of the protein on the hydrophilic surface of silica indicates a decrease in ordered secondary structure, i.e., the polypeptide chain in the protein has an increased random structure and, hence, a larger conformational entropy. Adsorption on the hydrophobic Teflon surface induces the formation of ordered structural elements, notably an increase in the content of O -helices (cfi, the discussion in Sect. 3.1.4). 

The enzymatic activities of O -chymotrypsin in solution and adsorbed at the different surfaces are presented in Fig. 11, where the specific enzymatic activity (defined as activity per unit mass of protein) is plotted as a function of temperature. The enzyme loses activity due to adsorption. On the hydrophobic Teflon and PS surfaces, the activity is completely gone, whereas on the hydrophilic silica surface, or-chymotrypsin has retained most of its biological function. These differences are in agreement with the adsorption isotherms and the circular dichroism spectra. The influence of the hydrophobicity of the sorbent surface on the affinity of the protein for the sorbent surface, as judged from the rising parts of the adsorption isotherms (Fig. 8), suggests that the proteins are more perturbed and, hence, less biologically active when adsorbed at hydrophobic surfaces. Also, the CD spectra indicate that adsorption-induced structural perturbations are more severe at hydrophobic surfaces. 

A somewhat curious effect arises when additional water is dosed on top of this synthetic inner layer, in that the work function is observed to exhibit substantial further decreases. This implies that the water molecules in the multilayers above the inner layer assume some measure of preferential orientation, induced by the presence of the adsorbed bromide in the first layer. This result is probably connected to structure making and structure breaking, or hydrophobic and hydrophilic, properties of soild surfaces, but will not be discussed in detail here. 

Complementing the equilibrium measurements will be a series of time resolved studies. Dynamics experiments will measure solvent relaxation rates around chromophores adsorbed to different solid-liquid interfaces. Interfacial solvation dynamics will be compared to their bulk solution limits, and efforts to correlate the polar order found at liquid surfaces with interfacial mobility will be made. Experiments will test existing theories about surface solvation at hydrophobic and hydrophilic boundaries as well as recent models of dielectric friction at interfaces. Of particular interest is whether or not strong dipole-dipole forces at surfaces induce solid-like structure in an adjacent solvent. If so, then these interactions will have profound effects on interpretations of interfacial surface chemistry and relaxation. 

A change in the hydrophilic nature of the polymer surface on irradiation of poly-(p-phenylazoacrylanilide) (PAAn) or its copolymer with HEMA may be used to control the adsorption — desorption behavior of proteins or organic substances onto the polymer [49]. Adsorption of lysozyme onto the copolymer of p-phenylazo-acrylanilide and HEMA was foimd to decrease from 4.6 eg to 1.8 eg per gram of adsorbent on ultraviolet irradiation, which induces the isomerization from the trans to the cis form. The decrease in adsorption ability upon ultraviolet irradiation is explained by a reduction of the hydrophobic interaction between the protein and the polymer, which results from the appearance of hydrophilic cw-form azobenzene on the surface. 

The utilization of classical polystyrene particles or hydrophobic latexes for protein concentrations can induce undesirable phenomena such as protein denaturation and low concentration yields, on account of the high adsorption affinity between both species which may lead to a low desorbed amount. In addition, the use of such hydrophobic colloids in the polymerase chain reaction (PCR) of nucleic acid amplification step generally leads to total inhibition of the enzymatic reaction. The inhibition phenomena can be attributed to the denaturation of enzymes adsorbed in large numbers onto hydrophobic coUoids. The utilization of hydrophilic and highly hydrated latex particles (irrespective of temperature) is the key to solving this problem by suppressing the inhibition of enzyme activity. The purpose of this stage is then to focus on the potential apphcation of thermally responsive poly(NIPAM) particles for both protein and nucleic acid concentrations. 

It is interesting that the different delivery sites of the drugs can provide a variety of anesthetic potencies. For example, the strongest and long-lasting anesthetic effect of DBC H+ can be combined with the specific trap in zone II. The penetration of DBC H+ into the hydrophobic bilayer interior, zone III, can be a cause of the toxicity. In contrast, I ROI 11, preferentially adsorbed on the hydrophilic surface of the bilayer, zone I, and easily desorbed in the aqueous phase, cannot induce the long-lasting anesthetic effect and toxicity. 

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