Selective decomposition of proteins by photocatalytic Ti(IV)-doped calcium hydroxyapatite particles from mixed-protein systems

The decomposition of protein molecules from a mixed-protein solution on the surface of calcium hydroxyapatite (CaHap) and Ti(IV)-doped CaHap (TiHap) particles with a Ti/(Ca + Ti) atomic ratio (X _Ti) of 0.10 and 0.20 under UV irradiation of 365 nm in wavelength was investigated. Acidic bovine serum albumin (BSA) and basic lysozyme (LSZ) were employed as a model of pathogenic proteins. The photocatalytic activities of TiHap particles were estimated from the decomposition of BSA and LSZ from the BSA (2.5 mg/cm³)–LSZ(1.0 mg/cm³) mixture under 1 mW/cm² UV irradiation dispersed in a 10-mL quartz tube. No change in BSA concentration by UV irradiation was observed for all the unheated original CaHap and TiHap particles without and with low photocatalytic activities, respectively. Similar results were observed for the systems that employed heat-treated particles endowed a high photocatalytic activity by heat treatment at 650 °C for 1 h. On the other hand, a selective photocatalytic decomposition was observed for the LSZ, i.e., only LSZ molecules were decomposed completely from the BSA (2.5 mg/cm³)–LSZ(1.0 mg/cm³) mixture by using heat-treated TiHap particles with X _Ti?=?0.10 and 0.20. This selective decomposition by TiHap particles was interpreted by higher adsorption affinity of positively charged LSZ to highly negatively charged TiHap together with low molecular weight and rigid structure of LSZ molecules.     

Acceleration of protein decomposition by photocatalytic Ti(IV)-doped calcium hydroxyapatite particles and its application for reduction of pathogenic proteins

Acceleration of protein decomposition from single- and mixed-protein solutions on the surface of Ti(IV)-doped calcium hydroxyapatite (TiHap) particles with a Ti/(Ca+Ti) atomic ratio (X _Ti) of 0.10 and 0.20 under ultraviolet (UV) irradiation was investigated. The UV irradiation started immediately after dispersing the TiHap particles in protein solution in a quartz tube (0 h UV method). Lysozyme (LSZ) was steeply decomposed in a LSZ single system by the 0 h UV method. Furthermore, a selective photocatalytic decomposition of LSZ was observed on the mixed-protein system; i.e., only LSZ molecules were decomposed completely from the bovine serum albumin (BSA; 2.5 mg/cm³)???LSZ (1.0 mg/cm³) mixture using TiHap particles. The selective decomposition of pathogenic protein β₂-microglobulin (β₂-MG) from 20 μg/cm³ β₂-MG???10 mg/cm³ BSA mixture in 1.5 mL?×?10^?4 M KCl solution was also examined. The UV irradiation started at 24 h after dispersing TiHap particles in BSA–β₂-MG-mixed solution for attaining the protein adsorption equilibrium (24 h UV method). It was revealed that β₂-MG molecules were entirely destructed by the 24 h UV method by only irradiating UV light to the dispersions for 24 h. The obtained selective decomposition of β₂-MG strongly suggested that TiHap particles can be applied for a blood purification therapy using UV irradiation.     

Effects of acetonitrile on adsorption behavior of bovine serum albumin onto synthetic calcium hydroxyapatite particles

The objective of this study was to examine the effects of acetonitrile (AN) on the adsorption behavior of bovine serum albumin (BSA) onto calcium hydroxyapatite [Ca10(PO4)6(OH)2 Ca10, Hap] materials by combining the ultraviolet (UV) and circular dichroism (CD) measurements of BSA solution. The structural change of BSA molecules with addition of AN was investigated by UV and CD spectroscopy measurements prior to studying adsorption behavior of BSA onto Hap. The CD spectra revealed that the fraction of alpha-helical content of BSA is remarkably decreased at AN concentrations above 30 vol.%, while beta-sheet content is increased. On the other hand, the percentages of random coil and turn contents were decreased only slightly. In addition to this secondary structural change of BSA, the UV spectra suggested that the tertiary structure of protein molecules was also changed by the addition of large amounts of AN; BSA molecules associate to form molecular aggregates at [AN]> or =40 vol.%. From the adsorption of BSA onto Hap particles (ca. 30 nm in the particle length) from a water-AN mixed solution, it was revealed that the adsorption behavior of BSA strongly depends on the change of secondary and tertiary structures of BSA by addition of AN. The contraction of BSA molecules at low AN concentrations (10-20 vol.%) gave their small cross-sectional area, providing a large amount of adsorption (n(BSA)), although n(BSA) was decreased above 30 vol.% AN by enlargement of BSA molecules with solvation and unfolding some alpha-helix domains. The n(BSA) values of the systems with AN exhibited a maximum; n(BSA) was increased at a lower BSA concentration region, although it was decreased at a higher BSA concentration due to self-association. Accompanying the change of n(BSA) with AN addition, the maxima of electrophoretic mobility (em) of the Hap particles were observed for the systems with AN, although the em of Hap particles was normally increased and saturated with increase in protein coverage for the native structure on the system without AN. On the other hand, because the aggregated BSA molecules could be cooperatively bound, the adsorption of BSA onto the Hap particles with large size (108 nm in the particle length) was enhanced in the presence of AN.     

Effects of pyrophosphate ions on protein adsorption onto calcium hydroxyapatite

The effects of pyrophosphate ions (PP: P2O7(4-)) on the adsorption of proteins onto calcium hydroxyapatite (Hap) were examined using typical proteins of bovine serum albumin (BSA: isoelectric point (iep) = 4.7, molecular mass (M(s)) = 67 200 Da, acidic protein), myoglobin (MGB: iep = 7.0, M(s) = 17 800 Da, neutral protein), and lysozyme (LSZ: iep = 11.1, M(s) = 14,600 Da, basic protein). The UV and CD measurements determined that both the secondary and the tertiary structures of protein molecules do not vary in the presence of PP. The adsorption of BSA was strongly depressed by the addition of PP in all the methods with changing the order of PP addition. Even if BSA was pre-adsorbed on the Hap surface, PP replaced BSA molecules by strong preferential adsorption onto Hap to reduce the amounts of adsorbed BSA. A similar effect was observed with the adsorption of MGB. On the other hand, the amount of adsorbed LSZ (n(LSZ)) was increased with an increase in the concentration of PP, and the n(LSZ) value showed a maximum point in each adsorption isotherm. This fact was explained by a compression of the electric double layer (EDL) around each LSZ molecule by PP. This compression of the EDL induced the reduction of lateral electrostatic repulsions between charged LSZ molecules on the Hap surface and enhanced the formation of closed-packed monolayers to raise the n(LSZ) value. However, since the number of PPs around a LSZ molecule is decreased by an increase in the LSZ concentration in each system, the thickness of the EDL may be increased. Hence, n(LSZ) was reduced again after the maximum point in each system. Tripolyphosphate (TPP: P3O10(5-)) ions exhibited similar effects on the adsorption behaviors of all proteins, but a much more pronounced effect was observed on the LSZ system. TPP with a higher eletronegativity shielded the EDL more highly than PP to increase the n(LSZ) value. The results of the zeta potential for all the protein systems supported the modes of protein adsorption discussed.     

Adsorption of immunogamma globulin onto various synthetic calcium hydroxyapatite particles

This paper presents data on adsorption of immunogamma globulin (IgG) onto synthetic rodlike calcium hydroxyapatite particles (CaHaps) with various particle lengths and calcium/phosphate (Ca/P) atomic ratios ranging from 1.54 to 1.65 and compares the obtained results to those of acidic (bovine serum albumin, BSA), neutral (myoglobin, MGB), and basic (lysozyme, LSZ) proteins reported before. The effect of electrolyte concentration on IgG adsorption was also examined. The initial rate of IgG adsorption was similar to that of BSA and was slower than that of MGB and LSZ. This fact was interpreted by the difference in the structural stability and molecular weight of these proteins. The isotherms of IgG adsorption onto the CaHap particles were of pseudo-Langmuir type. The saturated amount of adsorbed IgG values (nsIgG) for the particles with mean particle length less than 70 nm decreased with increasing Ca/P ratio. The adsorption behavior of IgG molecules was very similar to that of basic LSZ, though IgG has zero net charge. The nsIgG value was increased with increased mean particle length of CaHaps; the relationship was less significant than that for BSA but similar to those for MGB and LSZ. The similar adsorption behavior of IgG and LSZ suggested that the Fab parts of IgG molecules preferentially adsorb onto CaHap to provide the reversed Y-shaped conformation of IgG. The change of the adsorption mode of IgG molecules from the reversed Y-shaped conformation to side-on by "spreading" the Fc part of IgG molecules onto the particle surface over a longer adsorption time was suggested. The nsIgG value was increased with increasing electrolyte concentration by screening the intra- and intermolecular electrostatic interactions of proteins.     

Synthesis of phosphate-type fluorocarbon-hydrocarbon hybrid surfactants and their adsorption onto calcium hydroxyapatite

Five novel phosphate-type hybrid surfactants, C_mF_2m+1C₆H₄CH[OPO₂(OC₆H₅)Na]C_nH_2n+1 (FmPHnPPhNa: m = 4, 6, 8; n = 3, 5), have been synthesized. When compared with sulfate-type hybrid surfactants, C_mF_2m+1C₆H₄CH(OSO₃Na)C_nH_2n+1 (C₆H₄ = p-phenylene), the new hybrid surfactants were found to have comparable abilities to lower the surface tension of water. The critical micelle concentrations of FmPHnPPhNa followed Klevens’ rule and their occupied areas per molecule increased with increasing m and n. Calcium hydroxyapatite (CaHAp) pellets modified with FmPH3PPhNa gave high hydro and lipophobic surfaces. The hybrid surfactants are expected to be useful as new dental reagents for oral hygiene.     

Synthesis of phosphate-type fluorocarbon-hydrocarbon hybrid surfactants and their adsorption onto calcium hydroxyapatite

Five novel phosphate-type hybrid surfactants, C_mF_2m+1C₆H₄CH[OPO₂(OC₆H₅)Na]C_nH_2n+1 (FmPHnPPhNa: m = 4, 6, 8; n = 3, 5; C₆H₄ = p-phenylene, C₆H₅ = phenyl), have been synthesized. When compared with sulfate-type hybrid surfactants, C_mF_2m+1C₆H₄CH(OSO₃Na)C_nH_2n+1 (C₆H₄ = p-phenylene), the new hybrid surfactants are found to have comparable abilities to lower surface tension of water. The critical micelle concentrations of FmPHnPPhNa follow Klevens rule and their occupied areas per molecule increase with increasing m and n. Calcium hydroxyapatite (CaHAp) pellets modified with FmPH3PPhNa gives high hydrophobic and lipophobic surfaces. The hybrid surfactants are expected as new dental reagents for oral hygiene.     

Synthesis and characterization of Ti(IV)-substituted calcium hydroxyapatite particles by forced hydrolysis of Ca(OH)2-Na5P3O10-TiCl4 mixed solution

Ti(IV)-substituted calcium hydroxyapatite (TiHap) particles were prepared by aging Ca(OH)₂, TiCl₄, and sodium triphosphate (sodium tripolyphosphate, Natpp: Na₅P₃O₁₀) mixed solution at 100 °C for 18 h. The ellipsoidal secondary TiHap particles with ca. 100～150 nm in length composing by aggregation of small ellipsoidal primary particles with ca. 20 nm in length were produced at atomic ratio of Ti/(Ca+Ti) [X_Ti]≦0.2. The in situ IR spectra of these TiHap particles exhibited very small bulk OH^? band at 3,570 cm^?1. This result indicated that the TiHap particles were formed by aggregation of fine primary particles and OH^? ions along with c-axis in the primary particles were disordered. The TiHap particles with Ca/P atomic ratio larger than theoretical value of 1.67 did not exhibit surface P–OH groups at 3,659 and 3,682 cm^?1. The diffuse reflectance UV spectra of TiHap particles revealed that these particles have a UV absorption property, especially fabricated at X_Ti?=?0.1. The particles prepared at X_Ti?=?0.6 and 0.8 were amorphous and nanoparticles with 5～10 nm in diameter, but those precipitated at X_Ti?=?1.0 were poorly crystallized anataze-type TiO₂ nanoparticles.     

Studies on the adsorption behaviors of Pb(II) onto an acyl-thiourea resin

In this paper, an acyl-thiourea resin (PIDTR) was synthesized and its adsorption performances to Pb(II) were investigated by adsorption tests, scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses. A pH of 6.0 was found to be the optimum pH to obtain the maximum adsorption capacity in 12 hours of equilibration time. The Langmuir model was well fitted to the adsorption data with adsorption capacity of 0.756?mmol?·?g^?1. The adsorption kinetics showed that the adsorption process experienced liquid film diffusion and chemical reaction. The thermodynamic studies indicated that the adsorption for Pb(II) was spontaneous and endothermic. The results of SEM suggested that Pb(II) adsorbed on the surface of PIDTR. The FTIR and XPS analyses further confirmed Pb(II) might chemisorb onto PIDTR surfaces and N–Pb, O–Pb, and S–Pb were formed with the breakage of C?O, C?S, and N-H bonds in the PIDTR molecule.     

Encapsulation of titanium(IV) oxide particles in hollow silica for size-selective photocatalytic reactions

A core-shell composite of TiO2 particles encapsulated in a hollow silica was fabricated, and the core-shell composite showed size-selective photocatalytic activity for decomposition of organics without reducing the intrinsic activity of the naked TiO2 core.     

The electron structure and photocatalytic activity of Ti(IV) doped Bi_2O_3

Density functional theory (DFT) plays a significant role in the development of visible light responsive photocatalysts.Based on the first-principles plane-wave ultrasoft pseudopotential (USPP) method,the crystal structures of α,β,γ,and δ-Bi2O3 were optimally calculated for the total density of states (TDOS) and the partial density of states (PDOS) of Bi,O atoms.The calculation for Ti(IV) doped Bi2O3 supercell was carried out.The effects of Ti(IV)-doping on the electron structures and light absorption proper...     

Protein adsorption on polystyrene latex particles

Protein adsorption is the net result of various types of interaction between the different components present in the system, i.e. the sorbent surface, the protein(s), the solvent and any other solutes such as low molecular weight electrolyte. In this paper methods and techniques will be discussed to study the mechanism of protein adsorption on, in particular, colloidal particles. The discussion is based on experimental data obtained with relatively simple systems that contain one well-defined protein and well-characterized polystyrene latexes. Thus, the adsorption behavior of lysozyme and α-lactalbumin are compared, emphasizing the role of structural rearrangements in the protein molecule.     

Adsorption of barium and calcium chloride onto negatively charged alpha-Fe(2)O(3) particles

Adsorption of cations (Na(+), Ca(2+), Ba(2+)) onto negatively charged (pH 10.4) hematite (alpha-Fe(2)O(3)) particles has been studied. The oxide material was carefully prepared in order to obtain monodisperse suspensions of well-crystallized, quasi-spherical particles (50 nm in diameter). The isoelectric point (IEP) is located at pH 8.5. Adsorption of barium ions onto oxide particles was carried out and the electrophoretic mobility was measured throughout the adsorption experiment. Comparison with calcium adsorption at full coverage reveals a higher uptake of Ba(2+). In both cases it shows also that chloride ions coadsorb with M(2) ions. Simultaneous uptake of the positive and negative ions explains why the electrophoretic mobility does not reverse to cationic migration. A theoretical study of the surface speciation has been carried out, using the MuSiC model. It reveals the presence of negative as well as positive sites on both sides of the point of zero charge (PZC) of the hematite particles, which may explain the coadsorption of Ba(2+) and Cl(-) at pH 10.4. The effective charge of the oxide particles, calculated from the electrophoretic mobility, is in very good agreement with the results found with the MuSiC modelization and the chloride/barium adsorption ratio. It also verifies the theory of ionic condensation. Calorimetric measurements gave a negative heat for the overall reaction occurring when Ba(2+)/Cl(-) ions adsorb onto hematite. Despite the fact that anions (Cl(-) and OH(-)) adsorption onto mineral oxides is an exothermic phenomenon, it is likely that barium and calcium adsorption is endothermic, denoting the formation of an inner-sphere complex as reported in the literature.     

Microcalorimetric study of protein adsorption onto calcium hydroxyapatites

To clarify the adsorption mechanism of proteins onto calcium hydroxyapatite (Hap), the present study measured adsorption (DeltaHads) and desorption (DeltaHdes) enthalpies of bovine serum albumin (BSA; isoelectric point (iep) 4.7, molecular mass (Ms) 67,200 Da, acidic protein), myoglobin (MGB; iep=7.0, Ms=17,800 Da, neutral protein), and lysozyme (LSZ; iep=11.1, Ms=14,600 Da, basic protein) onto Hap by a flow microcalorimeter (FMC). Five kinds of large platelike particles of CaHPO4.2H2O (DCPD) after hydrolyzing at room temperature with different concentrations of NaOH aqueous solution ([NaOH]) for 1 h were used. DCPD converted completely to Hap after treatment at [NaOH]>or=2%, and the crystallinity of Hap was increased with an increase in [NaOH] up to 10%. The amounts of protein adsorbed (Deltanads) and desorbed (Deltandes) were measured simultaneously by monitoring the protein concentration downstream from the FMC with a UV detector. The Deltanads values were also measured statically by a batch method in each system. The Deltanads values measured by the FMC and static measurements fairly agreed with each other. Results revealed that DeltaHBSAads was decreased with an increase in [NaOH]; in other words, DeltaHBSAads was decreased with the improvement of Hap's crystallinity, suggesting that the BSA adsorption readily proceeded onto Hap. This fact indicated a high affinity of Hap to protein. This affinity was further recognized by DeltaHBSAdes because its positive value was increased by increasing [NaOH]. These opposite tendencies in DeltaHBSAads and DeltaHBSAdes revealed that Hap possessed a high adsorption affinity to BSA (i.e., enthalpy facilitated protein adsorption but hindered its desorption). The fraction of BSA desorption was also decreased with an increase in [NaOH], confirming the high affinity of Hap to protein. Similar results were observed on the LSZ system, though the enthalpy values were smaller than those of BSA. In the case of neutral MGB, DeltaHBSAads also exhibited results similar to those of the BSA and LSZ systems. However, due to its weak adsorption by the van der Waals force, DeltaHBSAdes was small and almost zero at [NaOH]>or=2%. Hence, the fraction of MGB desorption was less dependent on [NaOH].     

Evaluation of electron-hole recombination properties of titanium (IV) oxide particles with high photocatalytic activity

Electron-hole recombination in nano-sized titanium(IV) oxide (TiO₂) particles with various physical properties, which have been shown to be highly active photocatalysts, was evaluated by quantitative analysis of reduced titanium species (Ti³⁺), which might be formed at crystalline defective sites in TiO₂ particles through photo-irradiation in the presence of a hole scavenger under deaerated conditions. These highly active photocatalyst samples were synthesized by hydrothermal crystallization in organic media (HyCOM method) and post-calcination. The Ti³⁺ density decreased with increasing calcination temperature (T _c), and a linear correlation was observed between the Ti³⁺ density and rate constant for electron-hole recombination evaluated by femtosecond pump-probe diffuse reflection spectroscopy. Reaction rate (R _Ag) and the amount of silver ions (Ag⁺) adsorbed on TiO₂ particles ([Ag⁺]_ads) were measured for photocatalytic silver metal deposition along with oxygen formation from an aqueous Ag⁺ solution under deaerated conditions, and the slope of the R _Ag versus [Ag⁺]_ads plot was determined. Kinetic investigation of this reaction showed that the reciprocal of the slope was approximately related to the ratio of the rates for electron-hole recombination and electron trapping (k _r/k _e ratio). The k _r/k _e ratio decreased as T _c increased, and the logarithm of the k _r/k _e ratio was linearly related with Ti³⁺ density. These two parameters were used as a measure for the recombination properties of TiO₂ photocatalysts with various physical properties.     

Evaluation of adsorption behavior for U(VI) and Th(IV) ions onto solidified Mannich type material

Treatment of aqueous solution contaminated by uranium and thorium using a new Mannich type resin was studied. Different instrumental techniques such as elemental analysis, FTIR, and thermogravimetric analysis were employed for full characterization of the synthetic resin. Adsorption behavior was studied by batch experiments to determine the optimum conditions for U(VI) and Th(IV) ion removal. The adsorption studies showed the best fit with the second order rate equation and Langmuir model. The adsorption process is endothermic, spontaneous, and of increased disorder. The regeneration of sorbent was carried out using diluted HCl and the reuse of sorbent remains appreciable.     

Removal of Reactive Yellow 84 from aqueous solutions by adsorption onto hydroxyapatite

The adsorption of a reactive dye, Reactive Yellow 84, from aqueous solution onto synthesized hydroxyapatite was investigated. The experiments were carried out to investigate the factors that influence the dye uptake by the adsorbent, such as the contact time under agitation, absorbent dosage, initial dye concentration, temperature and pH of dye solution. The experimental results show that the amount of dye adsorbed increases with an increase in the amount of hydroxyapatite. The maximum adsorption occurred at the pH value of 5. The equilibrium uptake was increased with an increase in the initial dye concentration in solution. The experimental isotherm data were analyzed using Langmuir isotherm equation. The maximum monolayer adsorption capacity was 50.25 mg/g. The adsorption has a low temperature dependency and was endothermic in nature with an enthalpy of adsorption of 2.17 kJ mol⁻¹.     

Ti(IV)-centered dynamic interconversion between Pd(II), Ti(IV)-containing ring and cage molecules

Heteronuclear, supramolecular ring and cage complexes have been constructed from a pyridyl catechol ligand, TiO(acac)2, and PdCl2(CH3CN)2. These two complexes are quantitatively interconvertible, in which Ti4+-centered coordination changes take place between a well-known Ti(catecholato)3 and a newly established TiH(catecholato)2(acetylacetonato) structures. The Ti4+-centered structural changes arise from the changes in the component fraction and basicity condition.