Solution Depletion Method Research Articles

Adsorption studies of dodecylamine at the quartz interface using an electrode-separated piezoelectric sensor

The adsorption process of dodecylammonium chloride (DAC) from aqueous solutions onto a quartz crystal interface was investigated in situ using an electrode-separated piezoelectric sensor (ESPS). Increasing amounts of DAC adsorbed onto a quartz crystal surface resulted in linearly decreasing oscillating frequencies of the ESPS. The adsorption density can be monitored by the frequency decrease. The adsorption density obtained by calculation using the Sauerbrey equation in the ESPS method is greater than that in solution depletion method. A calibration coefficient is added into the Sauerbrey equation to correct the influence of surface roughness of the quartz crystal on the adsorption density. The influence of solution properties on the adsorption density measurement was discussed. A dependence of the adsorption density on pH was reported.

Temperature Independent Adsorbate Structure of 4-Octyl-, 4-Decyl-, and 4-Dodecylbenzenesulfonates at the Al2O3/Water Interface

In situ Fourier transform infrared (FTIR)-attenuated total reflection (ATR) spectroscopy and linear dichroism (LD) analysis were used to characterize the Gibbs' surface excess (Γ) and molecular orientation (ϑ, mean tilt from the interface normal) of sodium 4-n-octylbenzenesulfonate (SOBS), sodium 4-n-decylbenzenesulfonate (SDeBS), and purified sodium 4-n-dodecylbenzenesulfonate (SDoBS) adsorbed at the Al2O3/water interface. The Γ values were confirmed by the solution depletion method. The ϑ values were determined separately for the phenyl rings, alkyl chains, and SO3- head groups. Thin films (150−220 nm) of Al2O3 on the surface of ZnSe IR internal reflection elements allowed in situ IR ATR adsorption measurements on a model hydrophilic solid from the near IR to 950 cm-1. Both Γ and ϑ for SOBS and SDeBS were insensitive to ionic strength, but were slightly sensitive to pH and temperature. The crystal structure of SOBS·1/2H2O was determined by single-crystal X-ray diffraction and compared with polarized sin...

Thermodynamics of Micellization and Adsorption of Zwitterionic Surfactants in Aqueous Media

Titration microcalorimetry has been applied to study the micellization and adsorption of the following zwitterionic surfactants: (1) the C12 and C14 homologues of (alkyldimethylammonio)ethanoate and (alkyldimethylammonio)-1-propanesulfonate (referred to as C12N1C, C14N1C, C12N3S, and C14N3S, respectively); (2) (dodecyldimethylammonio)butanoate (C12N3C); (3) three surfactants of the [(dodecyldimethylammonio)alkyl]phenylphosphinate type with the intercharge alkanediyl group being C3H6, C6H12, and C10H20 (C12N3PPh, C12N6PPh, and C12N10PPh, respectively). In regard to the basic principles of both the micellization and the adsorption on a hydrophilic silica surface, the zwitterionic surfactants studied fall into line with polyoxyethylenated nonionics. Enthalpy of dilution measurements allowed determining the standard molar enthalpies of micellization (Δmicho) and thus, basing on the appropriate critical micelle concentration values, estimates could be made of the standard molar energies of micellization (Δmicgo) to furnish the corresponding entropy changes, Δmicso. At room temperatures, the negative free energy term is the result of an unfavorable positive enthalpy change and a favorable increase in entropy, the latter contribution dominating. The positive values of Δmicho decrease with rising temperature, addition of NaCl, decreasing hydrophilic character of the zwitterionic headgroup, and increasing length of the alkyl chain. Adsorption isotherms for the same surfactants on two hydrophilic silica surfaces, Spherosil XOB015 and precipitated silica RP 63-876, were measured using the solution depletion method. The related changes in the differential molar enthalpy of displacement (Δdplh) were detected calorimetrically as a function of surface coverage, ϑ. Adsorption of surfactant betaines is the interplay of two mechanisms: (1) ion−dipole bonding between the ionic surface sites and the zwitterionic headgroups oriented with the quaternary nitrogen group close to the surface and the anionic substituent group away from it; (2) formation of surface aggregates, induced by the hydrophobic effect. At higher coverages, Δdplh is a constant function of ϑ, the trends with changing temperature, salt content, and molecular structure of the surfactant essentially paralleling the corresponding Δmicho changes. Strong cooperativity in the adsorption phenomenon results in extended surface aggregates or even bilayers in the adsorption plateau region; otherwise the adsorbed phase is fairly fragmented.

The interaction of positively charged phospholipid vesicles with bacteria

Streptococcus sanguis strain C104 Proteovesicles (proteoliposomes) have been used for the delivery of bactericides t o several strains of oral and skinassociated bacteria adsorbed on solid surfaces (microtitre plates) I1.21. The preparation and characterisation of proteoliposomes is relatively complex 131 and simpler methods of liposomal targeting and delivery are desirable. One possible approach is t o exploit the negative charge on the surface of bacteria 141 by targeting w i th positively charged liposomes. Here positively charged liposomes were prepared by the extrusion method 151 in phosphate buffered saline (pH 7.4) from dipalmitoylphosphatidylcholine (DPPCI-cholesterol mixtures (weight ratio 1 :0.26) containing variable amounts of stearylamine (SA) in a range up t o 17 w t % of the total liposomal lipid. The liposomes, which had weight-average diameters in the range 100-140nm. were radiolabelled w i th 3H-DPPC. Two methods were used t o study the interaction of the liposomes w i th bacteria; liposome adsorption t o adsorbed biofilms on microtitre plates and adsorption t o bacterial suspensions using a solution-depletion technique. In the former method adsorbed biofilms were prepared by incubation of bacterial suspensions of specific optical absorbance (0.5) in microtitre plate wells for 18 hours. Liposome suspensions were incubated w i th the biofilms for 2 hours at 37°C. after which the liquid phase was removed and the biofilm was dispersed in 1 % w/v sodium ndodecylsulphate and analysed by scintillation counting to determine the extent of liposome adsorption. Liposome adsorption was expressed as the percentage apparent monolayer coverage (% amc) of the biofilm calculated from the projected diameter of the liposomes and the area of the biofilm. In the solution-depletion method the liposomes were incubated w i th bacterial suspensions of known cell concentration (as determined by cell counting) for 2 hours; the suspension was gently centrifuged t o pellet the bacteria (5609 for 10 minutes) and the supernatant analysed for liposomal lipid. From the bacterial cell number and depletion of liposome concentration in the supernatant, the number of liposomes adsorbed per bacterium was determined as a function of liposomal lipid concentration.

Temperature dependence of bovine serum albumin adsorption onto a poly(ethylene oxide)-grafted surface

The adsorption of bovine serum albumin (BSA) onto bare polyethylene (PE) and poly(ethylene oxide)-grafted PE particles was studied by the solution depletion method. Adsorption measurements were performed at different temperatures in the range of 25–65°C. The PE surface adsorbs high amounts of protein corresponding to a complete side-on monolayer in the temperature range 25–45°C. The considerable increase in the adsorbed amount and the shape of the isotherms at temperatures above 55°C indicate surface aggregation approaching the denaturation temperature of BSA. A lower degree of protein adsorption was obtained for PEO-grafted surfaces, and the amount of BSA adsorbed increases continuously with the temperature over the whole range studied. This is in accordance with the changing wettability of the PEO-grafted surface with temperature. The different temperature dependences of the adsorption behaviour found for PE and PEO-grafted surfaces show the joint influence of the protein properties in solution and the surface interactions on the adsorption.

Vanadium in pig iron

The solution-depletion method of measuring protein adsorption is implemented using SDS gel electrophoresis as a separation and quantification tool. Experimental method is demonstrated using lysozyme (15 kDa), α-amylase (51 kDa), human serum albumin (66 kDa), prothrombin (72 kDa), immunoglobulin G (160 kDa), and fibrinogen (341 kDa) adsorption from aqueous-buffer solution to hydrophobic octyl-sepharose and silanized-glass particles. Interpretive mass-balance equations are derived from a model premised on the idea that protein reversibly partitions from bulk solution into a three-dimensional (3D) interphase volume separating the physical-adsorbent surface from bulk solution. Theory both anticipated and accommodated adsorption of all proteins to the two test surfaces, suggesting that the underlying model is descriptive of the essential physical chemistry of protein adsorption. Application of mass balance equations to experimental data quantify partition coefficients P, interphase volumes VI, and the number of hypothetical layers M occupied by protein adsorbed within VI. Partition coefficients quantify protein-adsorption avidity through the equilibrium ratio of interphase and bulk-solution-phase w/v (mg/mL) concentrations WI and WB, respectively, such that P≡WI/WB. Proteins are found to be weak biosurfactants with 45<P<520 and commensurately low apparent free-energy-of-adsorption -6RT<(ΔGadsphobic0=-RTlnP)<-4RT. These measurements corroborate independent estimates obtained from interfacial energetics of adsorption (tensiometry) and are in agreement with thermochemical measurements for related proteins by hydrophobic-interaction chromatography. Proteins with molecular weight MW<100kDa occupy a single layer at surface saturation whereas the larger proteins IgG and fibrinogen required two layers.