Albumin and fibrinogen adsorption onto phosphatidylcholine monolayers investigated by Fourier transform infrared spectroscopy

Dipalmitoylphosphatidylcholine (DPPC) monolayers were deposited onto a germanium attenuated total reflectance (ATR) crystal using the Langmuir–Blodgett technique. The DPPC-coated crystal was then exposed to human serum albumin or human fibrinogen solutions while measuring the protein adsorption by recording FTIR spectra. The effect of the zwitterionic nature of the DPPC polar headgroup towards protein adsorption has been ascertained by exposing either the phospholipid headgroup or the acyl chains to the protein solution; this was possible by the use of a silanized or a bare germanium crystal. Calibration curves have been made to measure the protein surface concentrations. After 3 h, the albumin surface concentration on DPPC monolayers was about three times higher when the proteins were exposed to the lipid acyl chains instead of the polar headgroups (e.g. 3 vs. 1 μg cm⁻²). As for fibrinogen (FGN) adsorption, when the lipid polar headgroups were exposed to the protein solution, the FGN adsorption was low reaching a maximum value of 0.5 μg cm⁻². When interacting with the lipid acyl chains, the FGN adsorption reached a plateau at a value of 2.1 μg cm⁻² after 3 h. Clearly, both albumin and FGN showed a low tendency to adsorb on surfaces where the lipid polar headgroups are exposed toward the protein solution.     

Determination of adsorption heats of individual adsorption complex by combination of microcalorimetry and FTIR spectroscopy

Adsorption of CO as a probe molecule on K-FER zeolites differing in Si/Al ratio was investigated. Successful determination of adsorption heats of individual adsorption complexes formed upon adsorption of CO molecules on K-FER zeolites at 300 K by combination of IR spectroscopy with adsorption microcalorimetry is reported. Adsorption heat of bridged carbonyl complexes, where CO molecule interacts with two nearby extraframework K⁺ cations, was experimentally determined for the first time. It was found that bridged complexes on dual cationic sites exhibit adsorption heat of 34.8 kJ mol^?1, whereas monodentate carbonyls on single isolated K⁺ cation exhibit adsorption heat of only 26.2 kJ mol^?1 and adsorption heat of isocarbonyls was 21.5 kJ mol^?1.     

Investigation of the factors affecting organic cation adsorption on some silicate minerals

In this study, the effects of some factors on the adsorption of a basic dye (methylene blue) on bentonite and sepiolite samples were studied. These factors are cation (Na(+) and Ca(2+)) saturation of the samples and pH and ionic strength of the dye solution. The adsorption data were found to conform to the Langmuir equation within the concentration range studied and Langmuir constants were determined for each of the samples. The adsorption capacities of the samples were found to increase with cation saturation. Changes in the pH of the dye solution had no significant influence on the adsorption capacity and adsorption capacities were found to decrease with increasing ionic strength. The maximum sorption capacity of methylene blue exceeded the cation exchange capacity of bentonite and sepiolite.     

A study of the factors affecting the adsorption of cobalt ions onto Pakistani coal powder from solutions

Large deposits of coal are abundantly available in Pakistan. An attempt has been made to check its efficacy for the cobalt ions from aqueous solutions in order to exploit the locally available naturally occurring cheaper material for the decontamination/removal of metal ions from nuclear and industrial effluents. The adsorption behavior of cobalt ions on coal powder has been studied as a function of various physicochemical parameters i.e., stirring speed, shaking time, pH, concentration of cobalt ions, temperature, etc. Conditions for the uptake of cobalt ions were established. Adsorption dynamics models such as intra-particle diffusion model, pseudo-first order kinetic model (Lagergren’s equation) and pseudo-second order kinetic model were applied to the adsorption data to elucidate the adsorption process and its mechanism. Results reveal that the adsorption mechanism is predominantly diffusion and both intra-particle and boundary layer diffusion seem significant in the rate controlling step. The adsorption process is best accounted for using pseudo second order kinetic model and the overall rate of adsorption process appears to be controlled by more than one step, namely the external mass transfer and intra-particle diffusion mechanism. The existence of two slopes in the Freundlich plot also confirms the surface diffusion and intra-particle diffusion modes of adsorption. The Langmuir isotherm equation was obeyed well in the whole range of cobalt ions concentration with high value of correlation coefficient (r ²  = 0.999). The adsorption energy (E _a) calculated from D–R isotherm was 6.756 kJ/mol indicating physical nature of adsorption. The adsorption of cobalt ions increased with the increase of temperature and thermodynamic parameters such as ΔH, ΔS and ΔG were calculated. Results suggested that the cobalt ions adsorption on coal powder is endothermic (ΔH 33.90 kJ/mol) and spontaneous (negative ΔG values) process. The adsorption of other metal ions on coal powder was studied at optimized condition for cobalt ions to check its selectivity. Consequently, cobalt ions can be removed from Zr, Ru Eu, Er, Sm, Gd, Dy, Ce, U, and Th ions, where as Cs, Cr and Sr ions reduces the adsorption of cobalt ions by co-adsorption and their reducing affect is in the order of Sr > Cr > Cs.     

The nature of lyophobic coating and the adsorption of organic molecules and water on modified silicas

The protective properties of lyophobic layers of various natures chemically grafted to a silica carrier were comparatively studied. The modifiers were silanes with the compositions CF₃(CH₂)₂Si(CH₃)₂Cl (CF₃), C₈H₁₇Si(CH₃)₂Cl (C₈H₁₇), and ClSi(CH₃)₂[OSi(CH₃)₂]₂Cl (OMS). The differences between the surface properties of chemically modified silicas observed in adsorption, chromatographic, and IR spectroscopic measurements were shown to be related to a nonuniform electron density distribution in CF₃ grafted radicals and the special features of the structure of CF₃ and OMS grafted layers caused by the possibility of interaction between the terminal groups of these radicals and the surface of the carrier. Modified silicas possessed low surface energy and were superhydrophobic materials. The sample with grafted octyl groups C₈H₁₇ had the highest stability with respect to water.     

Acidity and surface behaviour of alumina-boria catalysts studied by adsorption microcalorimetry of probe molecules

Acidity and basicity of alumina-boria catalysts supported on porous or non-porous alumina have been studied by adsorption microcalorimetry of probe molecules (ammonia, pyridine and sulphur dioxide). Despite decreasing in initial heats, the total acidity as determined by ammonia adsorption increased in number and strength as a function of percentage of boron oxide. Ammonia, as a strong base, was shown to cover all types sites from strong to weak acid sites. Pyridine, as a weaker probe, was shown to dose only the stronger sites of the samples which stay nearly constant after B₂O₃ coverage approaching the monolayer. The basic sites of the amphoteric alumina support are neutralized by 10 wt% of boron oxide on non-porous alumina and 20 wt% of B₂O₃ on porous alumina. The catalytic activity for partial oxidation of ethane increased with acidity and reached a maximum constant value above 20 wt% of boron oxide.     

Investigation of Mg modified mesoporous silicas and their CO2 adsorption capacities

CO₂ adsorption properties on Mg modified silica mesoporous materials were investigated. By using the methods of co-condensation, dispersion and ion-exchange, Mg²⁺ was introduced into SBA-15 and MCM-41, and transformed into MgO in the calcination process. The basic MgO can provide active sites to enhance the acidic CO₂ adsorption capacity. To improve the amount and the dispersion state of the loading MgO, the optimized modification conditions were also investigated. The XRD and TEM characteristic results, as well as the CO₂ adsorption performance showed that the CO₂ adsorption capacity not only depended on the pore structures of MCM-41 and SBA-15, but also on the improvement of the dispersion state of MgO by modification. Among various Mg modified silica mesoporous materials, the CO₂ adsorption capacity increased from 0.42 mmol g⁻¹ of pure silica SBA-15 to 1.35 mmol g⁻¹ of Mg–Al–SBA-15-I1 by the ion-exchange method enhanced with Al³⁺ synergism. Moreover, it also increased from 0.67 mmol g⁻¹ of pure silica MCM-41 to 1.32 mmol g⁻¹ of Mg–EDA–MCM-41-D10 by the dispersion method enhanced with the incorporation of ethane diamine. The stability test by 10 CO₂ adsorption/desorption cycles showed Mg–urea–MCM-41-D10 possessed quite good recyclability.     

Factors affecting the adsorption of ethoxylated nonyl phenol onto synthetic rubber

Adsorption of non‐ionic surfactant (ethoxylated nonyl phenol; ENP) from aqueous solution is studied at 30 °C using butyl rubber (II R) mixed with two types of carbon black: high abrasion furnace (HAF) and general purpose furnace (GPF) as fillers with different concentrations. The results indicate that butyl loaded with HAF is more efficient as adsorbent surface than that loaded with GPF irrespective of the carbon black concentration and the adsorption increases as the immersion time increases. The experimental data of adsorption isotherms could be fitted to the Langmuir equation below the critical micelle concentration (CMC) of ENP. Copyright © 2003 John Wiley & Sons, Ltd.     

Flow microcalorimetry of adsorption of anionic alkyl surfactants at the solid/liquid interface

Flow microcalorimetry was used to study the adsoption of anionic alkyl surfactants from aque--ous solutions onto silica. It is found that for alkyl sulfate systems the strength of adsorption interactionincreases with increases of the alkyl chain length and decreases as temperature rises. The adsorptiondepends only on monomer concentration of the solution even above the critical micelle concentration(cmc). The assumption is made that the adsorption involves only a transfer of monomers from bulkto surface phase. A different adsorption mechanism is operative for the alkyl carboxylate.     

Effect of the surface condition of silicas with grafted monofunctional polyfluoroalkylsilanes on the adsorption of polar molecules

Lyophobized silicas containing relatively small numbers of grafted perfluorohexyl (1.1 nm^?2) and perfluorobutyl (1.7 nm^?2) groups are studied by means of gas chromatography, adsorption under static conditions, and IR spectroscopy. The results are compared to those obtained by us previously for a series of samples with dense polyfluoroalkyl monolayers (≥2.0 nm^?2). Effects related to the influence of the grafting density and the size of fluorine-containing groups on the adsorption of polar compounds and the hydrophobicity of the surface are discussed.     

Investigation of the mechanism of protein adsorption on ordered mesoporous silica using flow microcalorimetry

The adsorption of bovine serum albumin (BSA) and lysozyme (LYS) on siliceous SBA-15 with 24 nm pores was studied using flow microcalorimetry; this is the first attempt to understand the thermodynamics of protein adsorption on SBA-15 using flow microcalorimetry. The adsorption mechanism is a strong function of protein structure. Exothermic events were observed when protein–surface interactions were attractive. Entropy-driven endothermic events were also observed in some cases, resulting from lateral protein–protein interactions and conformational changes in the adsorbed protein. The magnitudes of the enthalpies of adsorption for primary protein–surface interactions decrease with increased surface coverage, indicating the possibility of increased repulsion between adsorbed protein molecules. Secondary exothermic events were observed for BSA adsorption, presumably due to secondary adsorption made possible by conformational changes in the soft BSA protein. These secondary adsorption events were not observed for lysozyme, which is structurally robust. The results of this study emphasize the influence of solution conditions and protein structure on conformational changes of the adsorbed protein and the value of calorimetry in understanding protein–surface interactions.     

Hydrogen bonding of 2,4-pentanediol and related molecules studied by infrared and 1H-NMR spectroscopy

Intermolecular self-associations of 2,4-pentanediol, 2-methyl-2,4-pentanediol and 1,3-butanediol in carbon tetrachloride solution have been studied by i.r. and ¹H-NMR spectroscopy. The spectrophotometric data have been analyzed by the least squares method to obtain the association constants and thermodynamic parameters. It turned out that 2,4-pentanediol, 2-methyl-2,4-pentanediol and 1,3-butanediol all take a cyclic trimer structure through hydrogen bonding. The association constants for trimerization were obtained as 330 and 810 mol⁻² dm⁶ at 30°C, and the enthalpy changes were −34 and −38 kJ mol⁻¹ and entropy changes were −62 and −68 J K⁻¹ mol⁻¹, for 2,4-pentanediol and 2-methyl-2,4-pentanediol, respectively.     

A comparison of the adsorption of KF and NH4F onto silica gel

Silica gel has been fluorinated with KF, Na₂SiF₆, NH₄F and (NH₄)₂SiF₆, and the resulting reagents have been analysed by ¹⁹F and ²⁹Si magic angle spinning NMR and infrared spectroscopy. Fluorination with NH₄F and (NH₄)₂SiF₆ results in the formation of (SiO)₃SiF groups at the surface, where F has replaced OH, whereas the anion SiF²⁻₆ is formed when silica is fluorinated with KF.     

The adsorption of KCN,KOCN and KSCN onto silica gel: Chemisorption vs. physisorption

²⁹Si magic angle spinning NMR, and i.r. spectroscopy have been used to study the adsorption of KCN, KOCN and KSCN onto silica gel. KCN and KOCN chemisorb, forming Si-OCN groups at the silica surface, whereas KSCN is physisorbed. KCN-silica and KOCN-silica show a peak at −99 ppm in the ²⁹Si NMR spectrum, and a broad band at 2300 cm⁻¹ in the i.r. spectrum; these features are absent in the spectra of KSCN-silica.     

H2 adsorption on 3d transition metal clusters: a combined infrared spectroscopy and density functional study

The adsorption of H2 on a series of gas-phase transition metal (scandium, vanadium, iron, cobalt, and nickel) clusters containing up to 20 metal atoms is studied using IR-multiple photon dissociation spectroscopy complemented with density functional theory based calculations. Comparison of the experimental and calculated spectra gives information on hydrogen-bonding geometries. The adsorption of H2 is found to be exclusively dissociative on Sc(n)O+, V(n)+, Fe(n)+, and Co(n)+, and both atomic and molecularly chemisorbed hydrogen is present in Ni(n)H(m)+ complexes. It is shown that hydrogen adsorption geometries depend on the elemental composition as well as on the cluster size and that the adsorption sites are different for clusters and extended surfaces. In contrast to what is observed for extended metal surfaces, where hydrogen has a preference for high coordination sites, hydrogen can be both 2- or 3-fold coordinated to cationic metal clusters.     

Fourier transform infrared spectroscopy study of the effect of pH on anion and cation adsorption onto poly(acrylo‐amidino diethylenediamine)

The role of hydrogen bonding in the chemistry of transition‐metal complexes remains a topic of intense scientific and technological interest. Poly(acrylo‐amidino diethylenediamine) was synthesized to study the effects of hydrogen bonding on complexes at different pHs. The polymer was synthesized through the coupling of diethylene triamine with polyacrylonitrile fiber in the presence of AlCl₃ · 6H₂O addition. The adsorption capacity of this polymer was 11.4 mequiv/g. The ions used for the adsorption test were CrO, PO, Cu²⁺, Ni²⁺, Fe²⁺, and Ag⁺. All experiments were confirmed with Fourier transform infrared. In the study of anion adsorption, at low pHs, only ionic bonds existed, whereas at high pHs, no bonds existed. However, in the middle pH region, both ionic bonds and hydrogen bonds formed between poly(acrylo‐amidino diethylenediamine) and the chromate ion or phosphate ion. When poly(acrylo‐amidino diethylenediamine) and metal ions (Cu²⁺, Ni²⁺, Fe²⁺, and Ag⁺) formed complexes, a hydrogen‐bonding effect was not observed with Fourier transform infrared. The quantity of metal ions adsorbed onto poly(acrylo‐amidino diethylenediamine) followed the order Ag⁺ > Cu²⁺ > Fe²⁺ > Ni²⁺. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2010–2018, 2004     

染料在纳米TiO2薄膜表面吸附性能的研究

采用溶胶－凝胶法制备纳米TiO2薄膜，并通过吸附染料形成染料／TiO2复合薄膜。分析了染料与TiO2薄膜的相互关系，利用紫外可见、比表面等技术研究染料在纳米TiO2薄膜表面的吸附性能，并计算出TiO2薄膜对染料的最大吸附率。研究表明，染料溶液浓度、温度以及TiO2薄膜浸泡时间对染料吸附量有着显著的影响，染料的吸附性能直接影响着太阳能电池的光电转换效率。