Protein adsorption behaviors onto Mn(II)-doped calcium hydroxyapatite particles with different morphologies.

Fundamental experiments on the adsorption behaviors of proteins onto plate-like and rod-like manganese-doped calcium hydroxyapatite particle (abbreviated as MnHAp) were examined. All of the obtained adsorption isotherms of bovine serum albumin (BSA) and lysozyme (LSZ) in a 1 × 10-4 mol/dm3 KCl solution were of the Langmuirian type. We found that the saturated amounts of the adsorbed BSA (nsBSA) increased with the increase in Mn/(Ca + Mn) atomic ratio (abbreviated as XMn) of the plate-like MnHAp, while the saturated amounts of adsorbed LSZ (nsLCZ) decreased. This result is explained by plate shape of the particles; the large fraction of positively charged adsorbing sites produced on the ac and bc faces (C sites) of these particles is advantageous to the adsorption of negatively charged BSA. In this case, however, the fraction of negatively charged adsorbing sites produced on the ab faces (P sites) decreased, and the (nsLCZ) values therefore decreased. In the case of the rod-like MnHAp, (nsBSA) decreased until XMn = 0.08, while the (nsLCZ) values were almost constant (ca. 0.2 mg/m2) over the whole range of XMn. This decrease in (nsBSA) values is explained by the increase in the specific surface area of rod-like particles as XMn increased. However, since the fraction of P sites on the ab faces does not depend on the particle length, the (nsLCZ) values were nearly constant. The binding effect of the Mn2+ and Ca2+ ions dissolved from rod-like particles caused the increase in (nsBSA) at XMn ≥ 0.1. The adsorption behavior of proteins onto MnHAp is therefore strongly dependent on the morphology of these particles.

Effects of Ti(IV) substitution on protein adsorption behaviors of calcium hydroxyapatite particles.

The fundamental experiments on the adsorption behaviors of proteins onto photocatalytic Ti(IV)-doped calcium hydroxyapatite (TiHap) particles with varied amounts of Ti(IV) ions doped (called as original particle) were examined comparing to those onto the calcium hydroxyapatite (CaHap) ones. The heat treated TiHaps and CaHap particles at 650°C for 1h were also examined (called as heat treated particle). The Ti/(Ca+Ti) atomic ratio (X(Ti)) of the TiHap particles was varied between 0 and 0.20. Since the surface acidity of the particles was increased by increase in X(Ti) value, the negative zeta potential (zp) of the particles was increased. All the adsorption isotherms of bovine serum albumin (BSA), myoglobin (MGB) and lysozyme (LSZ) from 1×10(-4)mol/dm(3) KCl solution were the pseudo-Langmuirian type. The saturated amounts of adsorbed LSZ (n(S)(LSZ)) values onto the original particles were increased with increase in the negative zp of the particles. However, the saturated amounts of adsorbed BSA (n(S)(BSA)) values were decreased by increase in the negative zp except at X(Ti)=0.05 where n(S)(BSA) value exhibited a maximum. In the case of MGB, the saturated amounts of adsorbed MGB (n(s)(MGB)) values were less dependent on the zp of the particles. These results were explained by changing the electrostatic forces between protein molecules and TiHap particles by doping Ti(IV) ions. On the other hand, n(S)(BSA), n(S)(LSZ) and n(s)(MGB) values onto the heat treated particles were larger than the original particles in each particle system, though no relationship to the X(Ti) value was recognized in each protein system. This result was interpreted to the formation of ß-TCP crystal phase in both the CaHap and TiHap particles by the heat treatment. The Ca(2+) ions produced by dissolution from ß-TCP phase may exert as binders between BSA and surfaces of the heat treated particles. The weak binder effects of Ca(2+) and PO(4)(3-) ions were observed for the adsorptions of LSZ and MGB.

Decomposition of proteins by photocatalytic Ti(IV)-doped calcium hydroxyapatite particles.

The decomposition of protein molecules on the surface of Ti(IV)-doped calcium hydroxyapatite (TiHap) particles with a Ti/(Ca+Ti) atomic ratio among 0-0.20 under UV irradiation of 365 nm in wavelength was disclosed. The acidic bovine serum albumin (BSA), neutral myoglobin (MGB) and basic lysozyme (LSZ) were employed as a model of pathogenic proteins. The photocatalytic activities of TiHap particles were estimated from the decomposition of each protein under 1 mW/cm(2) UV irradiation dispersed in 10 mL quartz tube. The concentrations of each protein in the supernatant after centrifugation during the UV irradiation were determined both by a HPLC and a SDS-Polyacrylamide Gel Electrophoresis (SDS-PAGE) analysis methods. No change in BSA concentration ([BSA]) by UV irradiation was observed for all the unheated original TiHap particles with low photocatalytic activity. The similar results were observed for the systems employed heat treated particles endowed a high photocatalytic activity by heat treatment at 650°C for 1h. These results indicated that the decomposition of BSA molecules is hard to take place. The heme structured MGB molecules are decomposed by UV irradiation irrespective of the presence of TiHap particles. In the case of heat treated particles, MGB molecules were further decomposed by the UV irradiation. The strongest photocatalytic activity was observed for the decomposition systems of LSZ by using heat treated particles. In this system, all the TiHap particles completely decomposed LSZ molecules after started the UV irradiation. It was concluded that the ability of decomposition of proteins is strongly related to the molecular weight and rigidity of proteins molecules. The LSZ molecule with low molecular weight and rigid structure was easily decomposed on the surface of heat treated TiHap particles under UV irradiation.

Protein adsorption behaviors onto photocatalytic Ti(IV)-doped calcium hydroxyapatite particles.

The fundamental experiments on the adsorption behaviors of proteins onto photocatalytic Ti(4+)-doped calcium hydroxyapatite (TiHap) particles were examined comparing to those onto the calcium hydroxyapatite (CaHap) and commercially available typical titanium oxide (TiO(2)) photocatalyst (TKP-101). The heat treated TiHap and CaHap particles were also used after treated these particles at 650°C for 1h (abbreviated as TiHap650 and CaHap650, respectively). All the adsorption isotherms of bovine serum albumin (BSA), myoglobin (MGB) and lysozyme (LSZ) from 1×10(-4)mol/dm(3) KCl solution were the Langmuirian type. The saturated amounts of adsorbed BSA (n(s)(BSA)) for the CaHap650 particles was higher than that for CaHap. Similar results were observed for TiHap and TiHap650. The adsorption of LSZ exhibited the same result of BSA, while the saturated amounts of adsorbed LSZ (n(s)(LSZ)) value on the TiHap were much higher than CaHap. However, the saturated amounts of adsorbed MGB (n(s)(MGB)) are almost equal to those for the CaHap and TiHap nevertheless whether these particles were heat treated at 650°C or not. The TKP-101 exhibited extremely small adsorption capacity of all proteins due to its small particle size of ca. 4nm in diameter. The independence of the n(s)(MGB) value on the zeta potential (zp) of the particles was explained by the electrostatical neutrality of MGB molecules. On the other hand, the n(s)(LSZ) values were increased with increase in the negative zp of the particles. This fact was explained by increasing the electrostatic attractive forces between negatively charged particles and positively charged LSZ. However, the n(s)(BSA) values exhibit maxima for the heat treated TiHap650 and CaHap650 particles. This result was interpreted to the formation of ß-TCP crystal phase by the heat treatment. The produced Ca(2+) ions by dissolution from ß-TCP phase may exert as binders between BSA and surfaces of the heat treated particles.

Preparation of calcium hydroxyapatite nanoparticles using microreactor and their characteristics of protein adsorption.

The calcium hydroxyapatite Ca(10)(PO(4))(6)(OH)(2) (Hap) nanoparticles were prepared by using microreactor and employed these Hap nanoparticles to clarify the adsorption behavior of proteins. The size of Hap particles produced by the microreactor reduced in the order of a hardness of the reaction conditions for mixing Ca(OH)(2) and H(3)PO(4) aqueous solutions, such as flow rates of both solutions and temperature. Finally, the size of the smallest Hap nanoparticle became 2 × 15 nm(2), similar to that of BSA molecule (4 × 14 nm(2)). It is noteworthy that the smallest Hap nanoparticles still possesses rodlike shape, suggesting that particles are grown along c-axis even though the reactants mixed very rapidly in narrow channels of the microreactors. The X-ray diffraction patterns of the Hap nanoparticles revealed that the crystallinity of the materials produced by the microreactor is low. The FTIR measurement indicated that the Hap nanoparticles produced by microreactor were carbonate-substituted type B Hap, where the carbonate ions replace the phosphate ions in the crystal lattice. All the adsorption isotherms of acidic bovine serum albumin (BSA), neutral myoglobin (MGB), and basic lysozyme (LSZ) onto Hap nanoparticles from 1 × 10(-4) mol/dm(3) KCl solution were the Langmuirian type. The saturated amounts of adsorbed BSA (n(S)(BSA)) for the Hap nanoparticles produced by microreactor were decreased with decrease in the mean particle length, and finally it reduced to zero for the smallest Hap nanoparticles. Similar results were observed for the adsorption of LSZ; the saturated amounts of adsorbed LSZ (n(S)(LSZ)) also reduced to zero for the smallest Hap nanoparticles. However, in the case of MGB, the saturated mounts of adsorbed MGB (n(S)(MGB)) are also depressed with decreased in their particle size, but about half of MGB molecules still adsorbed onto the smallest Hap nanoparticles. This difference in the protein adsorption behavior was explained by the difference in the size and flexibility of three kinds of proteins. The reduction of n(S)(BSA) is due to the decrease in the fraction of C sites on the side face of each Hap nanoparticle; i.e., there is not enough area left on the nanoparticle surface to adsorb large BSA molecules even though the BSA molecules are soft and their conformations are alterable. The reduction of n(S)(LSZ) was explained by the reduction of P sites. Further, rigidity of the LSZ molecules was given another possibility of the depression of n(S)(LSZ) for the Hap nanoparticles. However, MGB molecules with small and soft structure were adsorbed on the Hap nanoparticle surface by changing their conformation. We could control the amounts of adsorbed proteins by changing the particle size of Hap in the nanometer range and kinds of proteins. These obtained results may be useful for developing biomimetic materials for bone grafts and successful surgical devices in the biochemical field.

Effects of modification of calcium hydroxyapatites by trivalent metal ions on the protein adsorption behavior.

The effects of modification of calcium hydroxyapatites (Hap; Ca10(PO4)6(OH)2) by trivalent metal ions (Al(III), La(III), and Fe(III)) on protein adsorption behavior were examined using bovine serum albumin (BSA; isoelectric point (iep) = 4.7 and molecular mass (M(s)) = 67,200 Da). The Al(III)-, La(III)-, and Fe(III)-substituted Hap particles were prepared by the coprecipitation method with different atomic ratios, metal/(Ca + metal), abbreviated as X(metal). The particles precipitated at X(metal) = 0 (original-Hap) were rod-like and 10 x 36 nm2 in size. The short, rod-like original-Hap particles were elongated upon adding metal ions up to X(metal) = 0.10, and the extent of the particle growth was in the order of La(III) < Al(III) << Fe(III). The crystallinity of the materials was slightly lowered by increasing X(metal) for all systems. The adsorption isotherms of BSA onto the Al(III)-, La(III)-, and Fe(III)-substituted Hap particles showed the Langmuirian type. The saturated amounts of adsorbed BSA (n(s)(BSA)) values were strongly dependent on X(metal) in each system. The n(s)(BSA) values for the Fe(III)-substituted Hap system were increased with an increase in X(Fe) (X(metal) value of Hap particles substituted with Fe(III)); the n(s)(BSA) value obtained at X(Fe) = 0.10 was 2.7-fold more than that for the original-Hap particle, though those for the La(III) system were decreased to ca. 1/5. On the other hand, the n(s)(BSA) values for the Al(III) system were decreased with substitution of small amounts of Al(III), showing a minimum point at X(Al) = 0.01, but they were increased again at X(Al) over 0.03. Since the concentrations of hetero metal ions dissolved from the particles exhibited extremely low values, the possibility of binder effects of trivalent cations dissolved from the particle surface for adsorbing BSA to trivalent-ion-substituted Hap particles was excluded. The increase of n(s)(BSA) by an increase in X(Fe) was explained by elongation of mean particle length along with the production of surface hydroxo ions, such as Fe(OH)2+ or Fe(OH)2+, to induce the hydrogen bond between the Fe(III)-substituted Hap surface and BSA molecules, though the number of original C sites established by Ca(II) atoms was reduced. In the case of La(III)-substituted Hap particles, the number of original C sites established by Ca(II) atoms was reduced by La(III) substitution but the mean particle length remained almost constant. Furthermore, surface hydroxo La(III) groups were absent. Therefore, the reduction of n(s)(BSA) was explained by both the unaltered mean particle length and their low surface hydrophilicity. The change of n(s)(BSA) values by X(Al) resembled that of the mean particle length. These results implied that both the mean particle length and surface hydrophilicity of Al(III)-, La(III)-, and Fe(III)-substituted Hap particles are determining factors of the adsorption amounts of BSA.

Effects of heat treatment of calcium hydroxyapatite particles on the protein adsorption behavior.

The effects of heat treatment of calcium hydroxyapatite (Hap) on the protein adsorption behavior were examined using typical proteins 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). The TEM, XRD, and gas adsorption measurements ascertained that all of the Hap particles examined were highly crystallized and nonporous. The Hap single phase was continued up to the heat treatment temperature of 600 degrees C. However, after treatment above 800 degrees C in air, the beta-Ca3(PO4)2 (beta-TCP) phase slightly appeared. TG and ICP-AES measurements suggested that all of the Hap particles are Ca2+-deficient. Also, it was indicated from FTIR and XPS measurements that a partially dehydrated oxyhydroxyapatite (pd-OHap) was formed after treatment at high temperature. The saturated amounts of adsorbed BSA (nsBSA) did not vary on the Hap particles after heat treatment at 200 and 400 degrees C. However, nsBSA values were increased by raising the heat treatment temperature above 600 degrees C. The adsorption coverage of BSA was increased up to ca. 1.4. This adsorption coverage of BSA (thetaBSA) over unity suggests that the BSA molecules densely adsorbed and a part of BSA molecules adsorbed as end-on type on the Hap particle surface or BSA molecules became contracted. Similar adsorption behavior was observed on the LSZ system, but the adsorption coverage of LSZ (thetaLSZ) values are much less than thetaBSA. On the other hand, no effect of the heat treatment of Hap particles was observed on the adsorption of MGB. The increases of nsBSA and nsLSZ were explained by the increase of calcium and phosphate ions in the solutions dissolved from beta-TCP formed after heat treatment of Hap, especially treated at high temperature. The dissolved Ca2+ and PO(4)3 - ions may act as binders between proteins and Hap surfaces; the adsorption of Ca2+ ions on the Hap surface offers an adsorption site for BSA owing to its positive charge. In the case of adsorption of positively charged LSZ molecules, PO43- ions act as a binder in an opposite way. Since the MGB molecules are neutral, no binding effect of either ion was observed.

Synthesis of positively charged calcium hydroxyapatite nano-crystals and their adsorption behavior of proteins.

Positively charged Hap nano-crystals were prepared by using beta-alanine and clarified the adsorption affinity of these surface amide functionalized Hap nano-crystals to proteins. Colloidal surface amide functionalized Hap nano-crystals were prepared by wet method in the presence of various amounts of beta-alanine by changing molar ratio of beta-alanine/Ca (beta/Ca ratio) in the solution. The rod-like nano-crystals were lengthened with addition of beta-alanine though their width did not vary; carboxyl groups of beta-alanine are strongly coordinated to Ca2+ ions exposed on ac and/or bc faces to inhibit particle growth to a- and/or b-axis directions and enhance the particle growth along to the c-axis. No difference can be recognized on the crystal structure among the synthesized Hap nano-crystals by XRD measurements. However, the large difference was recognized by TG-DTA and FTIR measurements. Those measurements revealed that beta-alanine is incorporated on the Hap nano-crystal surface up to the beta/Ca ratio of 1.0, though they are absent in the nano-crystals synthesized at beta/Ca ratio > or = 2.0. The zeta potential (zp) of beta-alanine-Hap nano-crystals prepared at beta/Ca = 0.4 and 1.0 of those incorporating beta-alanine exhibited positive charge at pH < or = 5.9. The saturated amounts of adsorbed BSA for the positively charged beta-alanine-Hap nano-crystals were increased 2.3-2.4-fold by their electrostatic attraction force between positively charged beta-alanine-Hap nano-crystals and negatively charged BSA molecules. We were able to control the adsorption affinity of Hap nano-crystal by changing their surface charge.

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.

Protein adsorption characteristics of calcium hydroxyapatites modified with pyrophosphoric acids.

Protein adsorption characteristics of calcium hydroxyapatite (Hap) modified with pyrophosphoric acids (PP(a)) were examined. The PP(a) modified Hap particles (abbreviated as PP-Hap) possessed anchored polyphosphate (PP: P-{O-PO(OH)}(n)-OH) branches on their surfaces. The 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) were examined. The zeta potential (zp) of PP-Hap particles as a function of pH overlapped; zp-pH curves were independent of the concentration of pyrophosphoric acids (abbreviated as [PP(a)]) used for modifying Hap surface. The saturated amounts of adsorbed BSA (Delta n(ads)(BSA)) were increased three-fold by the surface modification with PP(a) though they were independent of the [PP(a)]. Furthermore, the fraction of BSA desorption was independent of the [PP(a)]. This enhancement of BSA adsorption onto the PP-Hap is due to the hydrogen bonding between oxygen and OH groups of the PP-branches and functional groups of BSA molecules. In the case of LSZ, a more higher adsorption enhancement was observed; the saturated amount of adsorbed LSZ (Delta n(ads)(LSZ)) for Hap modified at [PP(a)]=6 mmol/dm(3) was nine-fold than that for Hap unmodified. This remarkable adsorption enhancement was explained by a three-dimensional binding mechanism; LSZ molecules were trapped inside of the PP-branches. Hence, a fraction of LSZ desorption was decreased with an increase in the [PP(a)]; as more PP-branches are presented on the surface the higher retardation of LSZ desorption was induced. It was expected from their small size that MGB adsorb between the PP-branches as well as LSZ. However, the amounts of adsorbed MGB (Delta n(ads)(MGB)) did not vary and were independent of the [PP(a)] due to the small numbers of functional groups of MGB. In addition, no dependence of the fraction of MGB desorption on the [PP(a)] was observed. The results of zp for all the protein systems supported the mode of protein adsorption discussed. The anchored structure of the PP-branches developed on the Hap surface to provide three-dimensional protein adsorption spaces was proved by a comparative experiment that was elucidating the effect of pyrophosphate ions for BSA adsorption onto Hap.

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].

Control on size and adsorptive properties of spherical ferric phosphate particles.

Ferric phosphate particles were prepared by aging a solution dissolving Fe(ClO4)(3) and H3PO(4) at 40-80 degrees C for 16 h in a Teflon-lined screw-capped Pyrex test tube. The spherical or agglomerated fine particles were only precipitated with an extremely fast rate of reaction. The spherical particles were only produced at a very narrow region in fairly low pH solutions. TEM observation revealed that these particles grew in spherical structure by aggregation of primary small particles. The size of spherical particles was decreased by increase in the solute concentration or raising the aging temperature. Therefore, the formation of spherical particles was explained by a polynuclear layer mechanism proposed by Nielsen. The uniform spherical particles produced are amorphous, but they were crystallized to FePO(4) after calcining above 600 degrees C. It was suggested that the voids between the primary particles within the secondary agglomerated particles constitute mesopores. The Fe/P molar ratio determined and weight loss in TG curves gave the chemical formulas of the particles as Fe(PO4)x(H2PO4)y.nH2O (x: 0.93-1.00, y: 0-0.22, n: 2.4-2.7). The amorphous spherical ferric phosphate particles showed a high selective adsorption of H2O by penetration of H2O molecules into ultramicropores, produced after outgassing pretreatment, of that size is smaller than N2 molecule. The more particles grew, the more adsorption selectivity of H(2)O became remarkable.

Effects of amino acids on the formation of hematite particles in a forced hydrolysis reaction.

The influence of amino acids on the formation of hematite particles from a forced hydrolysis reaction of acidic FeCl3 solution was examined. The spherical particles were produced on the systems with L-phenylalanine (L-Phe), L-serine (L-Ser) and L-alanine (L-Ala), though L-glutamine (L-Gln) and L-glutamic acid (L-Glu) gave ellipsoidal hematite particles. This morphological change in hematite particles is consistent with the order of stability constant of amino acids against to Fe3+ ions (K). The hematite particles produced with L-Glu, L-Gln and L-Ser were highly porous because they are formed by aggregation of cluster particles. These particles exhibited microporous behavior by outgassing the particles below 200 degrees C while they changed to mesoporous after treating above 300 degrees C by elimination of amino acids molecules remained between the cluster particles within the hematite particles. The hematite particles strongly depended on the nature of amino acids such as alternation of solution pH and adsorption affinity to beta-FeOOH and/or polynuclear primary (PN) particles. The systems on L-Ala and L-Phe, showing very rapid phase transformation from beta-FeOOH to hematite, exhibited the Ostwald ripening. A rotational particle preparation procedure suggested that the morphology of hematite particle is governed by the mode and strength of amino acid adsorption onto beta-FeOOH and/or PN particles.

Control on shape, porosity and surface hydrophilicity of hematite particles by using polymers.

The shape, porosity, and surface hydrophilicity of hematite particles formed from a forced hydrolysis reaction of acidic FeCl3 solution were controlled by using a trace of polymers (0.001 and 0.003 wt%). The spherical particles were produced on the systems with polyvinyl alcohol (PVA) and polyaspartic acid (PAS). In the case of polyacryl amide (PAAm), slightly small spherical particles were precipitated at 0.003 wt%. However, polyacrylic acid (PAAc) and poly-γ-glutamic acid (PGA) gave ellipsoidal particles. This morphological change on hematite particles depended on the order of functional groups of polymers as -OH<-CONH2<-COOH<-COOH and ⟩C=O, corresponding to the order in extent of polymer molecules for complexation to Fe3+ ions and adsorption onto particle surface. Accompanying this order, the hematite particles produced were changed from less porous to microporous. On the other hand, only the system with 0.003 wt% of PAAm produced mesoporous hematite particles. Choosing the kinds of polymers also controlled the ultramicroporosity and surface hydrophilicity of the particles.

Preparation and characterization of carbonated barium-calcium hydroxyapatite solid solutions.

Particles of carbonated barium-calcium hydroxyapatite solid solutions (BaCaHap) with different Ba/(Ba+Ca) (X(Ba)) atomic ratios were prepared by a wet method at 100 degrees C and characterized by various means. The crystal phases and structures of the products strongly depended on the composition of the starting solution, that is, the Ba/(Ba+Ca) atomic ratio ([X(Ba)]) and H3PO4 concentration ([H3PO4]) in the solution. BaCaHap with X(Ba)0.43 could be prepared at [X(Ba)]0.7 by changing [H3PO4], but could never be obtained at [X(Ba)]=0.8-0.95 regardless of [H3PO4]. The carbonated calcium hydroxyapatite particles prepared at [X(Ba)]=0 were fine and short rod-shaped particles (ca. 14x84 nm). With increasing [X(Ba)] from 0 to 0.8, the particles obtained became large spherical agglomerates. The carbonated barium hydroxyapatite particles formed at [X(Ba)]=1 were long rod-shaped agglomerates (ca. 0.2x2 microm) of fine primary particles. The amount of CO2 adsorbed irreversibly on a series of BaCaHaps showed a minimum at (Ba+Ca)/(P+C) atomic ratio of around 1.56, which agreed well with the minimum cation/P ratio obtained for the other hydroxyapatites, as already reported.

Effects of vinyl series polymers on the formation of hematite particles in a forced hydrolysis reaction.

The influence of polymers on the formation of hematite particles from forced hydrolysis of acidic FeCl(3) solution was investigated using vinyl series polymers with different functional groups. The disk-like hematite particles were produced from forced hydrolysis of acidic FeCl(3) solution in the presence of polyvinyl alcohol (PVA: 0-1 wt%). On the other hand, spherical particles were produced by addition of very small amounts of polyacrylamide (PAAm: 0-0.004 wt%). The size of spherical particles was slightly decreased with increase in the concentration of PAAm. The ellipsoidal particles were precipitated by addition of a very low concentration of polyacrylic acid (PAAc: 0-0.004 wt%). The effect of polymers on the hematite particle formation was expressed in the order of PVA

Structure of synthetic calcium hydroxyapatite particles modified with pyrophosphoric acid.

Synthetic colloidal calcium hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2): CaHap) was treated with pyrophosphoric acid (H(4)P(2)O(7): PP) in acetone and the materials were characterized by XRD, TEM, FTIR, and N(2) and H(2)O adsorption measurements. XRD patterns and morphology of CaHap particles were essentially not changed by the modification. The additional amount of PO(4) of CaHap was increased with an increase of PP concentration and the Ca/P molar ratio of the particles decreased from 1.62 to 0.81. IR results indicated that the isolated surface POH band developed with increasing the PP concentration up to 6.0 mmol dm(-3) by the reaction of isolated surface POH groups of CaHap and pyrophosphoric acids. Above 10.2 mmol dm(-3), a hydrogen-bonding surface POH band appeared at 2913 cm(-1) and enlarged with increasing the PP concentration, while the isolated surface POH band was weakened. The results of N(2) and H(2)O adsorption measurements revealed that the modified particles aggregated compared to the unmodified ones, which would be due to the formation of hydrogen-bonding surface POH groups among the particles.

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.

Influence of hydrolyzed and nonhydrolyzed Ti, Cr, and Al ions on the formation of beta-FeOOH particles.

Beta-FeOOH particles were synthesized in the presence of Ti(IV), Al(III), and Cr(III) at metal/Fe atomic ratios of 0-0.1 by the following two methods: hydrolysis of aqueous FeCl3 solutions added to the hydrolysis products of these metal ions (subsequent hydrolysis, SH) and hydrolysis of aqueous FeCl3 solutions dissolving these metal ions (combined hydrolysis, CH). On increasing Al/Fe the particle size of the products with AlCl3 by SH method steeply rose at a low Al/Fe and then fell. The similar increase of particle size was seen in SH method with Ti(SO4)2 though the addition of TiCl4 decreased the particle size. In CH method, Ti(IV) markedly impeded the beta-FeOOH formation but Al(III) and Cr(III) showed no influence. The particles prepared by CH and SH methods contained a large amount of Ti(IV) but a few Al(III) and Cr(III). The large spindle-shaped and rod-shaped particles produced by SH method with AlCl3 and Ti(SO4)2 were highly microporous and poorly crystallized, indicating that the particles consist of fine primary particles and the aggregation of fine particles would be promoted by SO4(2-). The different influences of the metal ions on the beta-FeOOH formation were explained by their hydrolysis characteristics.

Structures of beta-FeOOH particles formed in the presence of Ti(IV), Cr(III), and Cu(II) ions.

beta-FeOOH particles were prepared by aging aqueous FeCl3 solutions containing Ti(IV), Cr(III), and Cu(II) at room temperature for 360 days. The structures of the formed particles were investigated by various techniques including TEM, XRD, XAFS, and adsorption of N2 and H2O. Ti(IV) markedly impeded the crystallization and particle growth of beta-FeOOH by coprecipitation with Fe(III) and disturbing the short-range structure of beta-FeOOH particles. In the presence of a large amount of Ti(IV), it was pronounced that the hydrolysis of Ti(IV) impeded beta-FeOOH formation by reducing the solution pH, whereas Cr(III) and Cu(II), which were hardly involved in the products, gave rise to no noticeable effects on the formation of beta-FeOOH particles. The knowledge obtained in this study can be available for interpretation of the anti-corroding function of Ti alloyed with steels in a Cl- -containing environment.