Effect of amino,hydroxyl, and carboxyl terminal groups of alkyl chains of self-assembled monolayers on the adsorption pattern of gold nanoparticles

The adsorption pattern of gold nanoparticles (AuNPs) on functionalized self-assembled monolayers (SAMs) produced on a Au(111) surface was characterized. The Au(111) was modified with 11-amino-1-undecanethiol hydrochloride (AUT), 11-mercapto-1-undecanol (MUT), or 11-mercaptoundecanoic acid (MUA) at an elevated temperature and pressure. The AuNPs aggregated on the AUT-SAM surface, whereas they were well dispersed on the MUT-SAM surface and localized on the MUA-SAM surface. The results suggest that interactions between AuNPs differ according to the degree of peeling of citrate-layer-capped AuNPs. The degree of peeling, which is related to both the surface randomness of the SAMs and the functional characteristics of the terminal group of each SAM, was discussed on the basis of scanning tunneling microscopy observations, X-ray photoelectron spectroscopic analyses, and contact angle measurements. Our study shows that AuNP patterns can be controlled by changing the terminal group of the alkyl thiol SAM on a Au(111) surface.     

Mechanistic studies of the formation of different states of oxygen on irradiated ZrO2 and the photocatalytic nature of photoprocesses from determination of turnover numbers

The photoadsorption of oxygen (photoreduction on electron surface-active centers) and the photoadsorption of hydrogen (photooxidation on hole surface-active centers) as well as the photooxidation of hydrogen in the presence of oxygen were examined over irradiated zirconia (ZrO2) specimens by thermoprogrammed desorption spectroscopy (TPD) and kinetically to assess the states (forms) of oxygen species formed on the surface of zirconia. The three TPD spectral maxima observed inferred three oxygen species of varying activity in the photooxidation of hydrogen. The number of surface-active sites on the zirconia surface were quantitatively estimated (ca. 1 x 10(16) centers), thereby permitting an estimate of the turnover numbers (TON) for the photooxidation of hydrogen (TON > 14.5) and for the photoreduction of oxygen (TON > 6.6). These demonstrate for the first time that a photoreaction occurring on the surface of a metal-oxide photocatalyst is truly photocatalytic.     

Reaction of SO2 with AuCeO2(111): importance of O vacancies in the activation of gold

Synchrotron-based high-resolution photoemission was used to study the adsorption and chemistry of SO(2) on AuCeO(2)(111) and AuO(x)CeO(2) surfaces. The heat of adsorption of the molecule on Au nanoparticles supported on stoichiometric CeO(2)(111) was 4-7 kcalmol larger than on Au(111). However, there was negligible dissociation of SO(2) on the AuCeO(2)(111) surfaces. The full decomposition of SO(2) was observed only after introducing O vacancies in the ceria support. AuO(x)CeO(2) surfaces were found to be much less chemically active than AuCeO(2)(111) or AuCeO(2-x)(111) surfaces. The active sites in {Au + AuO(x)}ceria catalysts should involve pure gold nanoparticles in contact with O vacancies.     

Calculations of pH-dependent binding of proteins to biological membranes

Binding of proteins to membranes is often accompanied by titration of ionizable residues and is, therefore, dependent on pH. We present a theoretical treatment and computational approach for predicting absolute, pH-dependent membrane binding free energies. The standard free energy of binding, DeltaG, is defined as -RTln(P(b)/P(f)), where P(b) and P(f) are the amounts of bound and free protein. The apparent pK(a) of binding is the pH value at which P(b) and P(f) are equal. Proteins bind to the membrane in the pH range where DeltaG is negative. The components of the binding free energy are (a) the free energy cost of ionization state changes (DeltaG(ion)), (b) the effective energy of transfer from solvent to the membrane surface, (c) the translational/rotational entropy cost of binding, and (d) an ideal entropy term that depends on the relative volume of the bound and free state and therefore depends on lipid concentration. Calculation of the first term requires determination of pK(a) values in solvent and on the membrane surface. All energies required by the method are obtained from molecular dynamics trajectories on an implicit membrane (IMM1-GC). The method is tested on pentalysine and the helical peptide VEEKS, derived from the membrane-binding domain of phosphocholine cytidylyltransferase. The agreement between the measured and the calculated free energies of binding of pentalysine is good. The extent of membrane binding of VEEKS is, however, underestimated compared to experiment. Calculations of the interaction energy between two VEEKS helices on the membrane suggest that the discrepancy is mainly due to the neglect of protein-protein interactions on the membrane surface.     

Study and analytical application of rare earth inhibition of laccase

The effect of metal ions on the laccase-catalyzed redox reaction of 5,6-dibromo-2,3-dicyanohydroquinone to 5,6-dibromo-2,3-dicyanosemiquinone was studied. The results show that rare earth ions strongly inhibited the reaction, while most of the common elements such as Ca(2+), Mg(2+), Cu(2+), Zn(2+), Al(3+) and Fe(3+), etc. had no inhibition on the reaction. Further experimental results reveal that the inhibition of lanthanum (III) on laccase activity was of the comparative type and the degree of inhibition of La(3+) on laccase activity was proportional to the concentration of La(3+). Based on this, a simple, rapid and new stopped-flow enzyme-catalyzed analytical kinetic method for determination of rare earth was proposed and applied to the determination of trace amounts of rare earth in water.     

Effects of bulk impurity concentration on the reactivity of metal surface: sticking of hydrogen molecules and atoms to polycrystalline Nb containing oxygen

Nonmetallic impurities segregated onto metal surfaces are able to drastically decrease the chemical reactivity of metals. In the present paper, effects of bulk impurities on the reactivity of metallic surfaces were investigated in a wide temperature range on an example of the sticking of hydrogen molecules and atoms to Nb [polycrystalline, with mainly (100)] containing solute oxygen. At all the investigated surface temperatures, T(S) (300-1400 K), we found the bulk oxygen concentration C(O) to have a strong effect on the integral probability, alpha(H(2) ), of dissociative sticking of H(2) molecules followed by hydrogen solution in the metal lattice: alpha(H(2) ) monotonically decreased by orders of magnitude with increasing C(O) from 0.03 to 1.5 at. %. The sticking coefficient alpha(H(2) ) was found to depend on T(S) but not on the gas temperature. The effect of C(O) on alpha(H(2) ) is explained by the presence of oxygen-free sites (holes in coverage) serving as active centers of the surface reaction in the oxygen monolayer upon Nb. In contrast to H(2) molecules, H atoms were found to stick to, and be dissolved in, oxygen-covered Nb with a probability comparable to 1, depending neither on C(O) nor on T(S). This proves that, unlike H(2) molecules, H atoms do stick to be dissolved mainly through regular surface sites covered by oxygen and not through the holes in coverage.     

Dependence of molecular recognition of fullerene derivative on the adlayer structure of zinc octaethylporphyrin formed on Au(100) surface

Adlayers of ZnOEP were prepared on reconstructed Au(100)-(hex) and unreconstructed Au(100)-(1 x 1) surfaces by immersing into a benzene solution containing ZnOEP molecules, and the adlayer structures were characterized by scanning tunneling microscopy (STM). A hexagonally arranged ZnOEP array was formed on an Au(100)-(hex) surface, whereas a rectangularly arranged ZnOEP array was found on an Au(100)-(1 x 1) surface. The adlayer structure of ZnOEP was dependent upon the underlying Au atomic arrangements. Furthermore, an investigation of the spuramolecular assembly for these modified surfaces was carried out by using an open-cage C(60) derivative (opened C(60)). A supramolecular assembled adlayer with a 1:1 composition of opened C(60)/ZnOEP was formed on Au(100)-(hex), whereas aggregates of opened C(60) were found on the ZnOEP-modified Au(100)-(1 x 1) surface. Electrochemical responses of opened C(60) were significantly influenced by underlying ZnOEP arrays. This finding suggests that precise control of underlying ZnOEP adlayers with the Au atomic structure is important to recognize the opened C(60) on them.     

Effect of metals on melt oxidation of polyethylene

Oxidation of polyethylene (PE) melts in contact with metals (Cu, Pb, Au, Al, Zn, Ag) has been studied by infrared spectroscopy and differential thermal analysis (DTA). These metals may be divided into two groups, depending on their activity for oxidizing PE: namely, high-activity metals (Cu, Pb, Ag, Zn) and low-activity metals (Al, Au). During the oxidation of PE in contact with high-activity metals dissolution of the surface layer of metal is observed with accumulation of metal-containing compounds (salts of carboxylic acids) in the bulk of the polymer. With low-activity metals these phenomena are not observed. The rate of oxidation of PE on low-activity metals approaches the oxidation rate of nonmetals (polytetrafluoroethylene and inorganic glass). With certain high-activity metals (Cu, Pb) the process of oxidation is accelerated only in the early stage of oxidation; then the oxidation rate slows down and the oxidation process ceases. PE films separated from metal after being oxidized on it possess chemical memory, i.e., their oxidation rate depends on the nature of the metal with which they had been in contact, and on the duration of the contact oxidation. The effect of salts of carboxylic acids (metal stearates) on the oxidation of PE melts was also studied. Based on the data obtained, it is concluded that the rate of oxidation of PE melts on high-activity metals is controlled by metal-containing compounds which are the products of contact reactions.     

Effect of Co doping on catalytic activity of small Pt clusters

Platinum is the most widely used catalyst in fuel cell electrodes. Designing improved catalysts with low or no platinum content is one of the grand challenges in fuel cell research. Here, we investigate electronic structures of Pt(4) and Pt(3)Co clusters and report a comparative study of adsorption of H(2), O(2), and CO molecules on the two clusters using density functional theory. The adsorption studies show that H(2) undergoes dissociative chemisorption on the tetrahedral clusters in head on and side on approaches at Pt centers. O(2) dissociation occurs primarily in three and four center coordinations and CO prefers to adsorb on Pt or Co atop atoms. The adsorption energy of O(2) is found to be higher for the Co doped cluster. For CO, the Pt atop orientation is preferred for both Pt(4) and Pt(3)Co tetrahedral clusters. Adsorption of CO molecule on tetrahedral Pt(3)Co in side on approach leads to isomerization to planar rhombus geometry. An analysis of Hirshfeld charge distribution shows that the clusters become more polarized after adsorption of the molecules.     

The effect of pharmaceuticals on the nanoscale structure of PEO-PPO-PEO micelles

We present results on the effects of various hydrophobic drugs and additives on the micellar structure of Pluronic F127 solutions. Small-angle neutron scattering experiments on 5wt% F127 solutions were used to measure micelle core size (R(1)), micelle corona size (R(2)), intermicellar interaction distance (R(int)), polydispersity (sigma), and aggregation number (N(agg)); dynamic light scattering was used to measure critical micelle concentration (CMC); and ultraviolet spectroscopy was used to measure drug solubility and apparent micelle-water partition coefficient (K(mw)). The core and corona size were found to generally increase in the presence of the drugs, as did R(int). Both sigma and N(agg) were found to decrease in the presence of most of the drugs, and the CMC was found to vary considerably with no clear correlation. A design of experiments (DOE) approach was used to analyze the results and build empirical correlations. All of the parameters from the SANS experiments were found to depend strongly on drug solubility, with a weak dependence on K(mw) in most cases. The aggregation number, however, was found to depend strongly on both K(mw) and solubility. The correlations can be used to roughly predict the structural parameters of F127 micelles for other hydrophobic drugs.     

First-principles studies of chiral step reconstructions of Cu(100) by adsorbed glycine and alanine

Adsorption of amino acids on Cu(100) is known experimentally to induce surface reconstructions featuring intrinsically chiral Cu(3,1,17) facets, but no information about the geometry of the molecules on these chiral facets is available. We present density-functional theory calculations for the structure of glycine and alanine at moderate coverages on Cu(3,1,17). As might be expected, molecules prefer to bind at the step edges on this surface rather than on the surface's (100)-oriented terraces. The adsorption of enantiopure alanine on Cu(3,1,17) is predicted to be weakly enantiospecific, with S-alanine being more stable on Cu(3,1,17)(S) than R-alanine. By comparing the surface energies of Cu(100) and Cu(3,1,17) in the presence of adsorbed glycine or alanine, our calculations provide insight into the driving force for chiral reconstructions of Cu(100) by amino acids.     

Effects of magnetite nanoparticles on the thermorheological properties of carrageenan hydrogels

The influence of magnetite (Fe(3)O(4)) nanoparticles on the rheological properties of kappa-, iota- and lambda-carrageenan gels has been investigated. Small amplitude oscillatory shear measurements were performed to study the effect of the presence of Fe(3)O(4) nanoparticles with particle sizes of ca. 10 nm on the gel properties, as a function of carrageenan type, carrageenan concentration and magnetite load. The formation of Fe(3)O(4) nanoparticles on the presence of biopolymer was observed to promote the gelation process and lead to stronger gels as indicated by an increase in the gel viscoelastic moduli and of the gelation temperature. This effect was more marked for kappa-carrageenan than for iota- and lambda-carrageenan and has been proposed to depend not only on Fe(3)O(4) concentration but also on the concentration of potassium ions. A mechanism based on the combined effect of Fe(3)O(4) nanoparticles and potassium ions was suggested, involving the adsorption of potassium ions on the negatively charged surface of the Fe(3)O(4) nanoparticles, thus leading to an increase of the potassium ion concentration within the "carrageenan cages" containing the magnetite. This would, therefore, promote more extensive biopolymer helical aggregation, thus resulting in the formation of a stronger kappa-carrageenan gel in the presence of Fe(3)O(4), as observed. Since iota- and lambda-carrageenan gels are known to be less sensitive to potassium ions concentration, the effect of precipitating Fe(3)O(4) within these biopolymers is reduced.     

Am(III) adsorption on oxides of aluminium and silicon: effects of humic substances,pH, and ionic strength

The adsorption of Am(III) (total concentration 10(-9) mol/l) on alumina, silica, and hematite was studied by a batch technique. The effects of pH, ionic strength, and humic substances on the adsorption of Am(III) on alumina and silica were investigated, and the adsorption isotherms of Am(III) on alumina and silica at different pH values were determined. It was found that compared with the adsorption of Am(III) on alumina, the adsorbability of silica on the basis of mass is less, the relative adsorption rate on silica is slower, the sensitivity of adsorption on silica to ionic strength is less, the dependence of adsorption on silica on pH is gentler, and consequently that the adsorption characteristics of Am(III) on alumina and silica are distinctly different. The negative effect of fulvic acid on the adsorption on silica and the positive effect of humic acid on the adsorption on alumina were found. In contrast to the Am(III) adsorption on alumina and silica, a tremendously high adsorbability of Am(III) on hematite was found. The sequence of adsorbabilities of Am(III) on the basis of mass is Fe2O3 > Al2O3 > SiO2.     

First-principles study of some factors controlling the rate of ammonia decomposition on Ni and Pd surfaces

Using the plane-wave pseudopotential method within the density-functional theory with the generalized gradient approximation for exchange and correlation potential, we have calculated adsorption energies (E(ad)), diffusion barrier, and the first dissociation barrier (E(1)) for NH(3) on Ni and Pd surfaces. While the top site is found to be preferred for NH(3) adsorption on both Ni(111) and Pd(111), its calculated diffusion barrier is substantially higher for Pd(111) than for Ni(111). We also find that during the first dissociation step (NH(3)-->NH(2)+H), NH(2) moves from the top site to the nearest hollow site on Ni(111) and Pd(111) and on the stepped surfaces, Ni(211) and Pd(211), it moves from the initial top site at the step edge to the bridge site in the same atomic chain. Meanwhile H is found to occupy the hollow sites on all four surfaces. On Ni(111), E(1) is found to be 0.23 eV higher than E(ad), while at the step of Ni(211), E(1) and E(ad) are almost equal, suggesting that the probability for the molecule to dissociate is much on the step of Ni(211). In the case of Pd(211), however, we find that the dissociation barrier is much higher than E(ad). These trends are in qualitative agreement with the experimental finding that ammonia decomposition rate is much lower on Pd than on Ni.     

On the clarification of the IR stretching vibration assignment of adsorbed N2 on Rh0 and Rhdelta+ surface atoms of supported Rh crystallites

The low-temperature adsorption of N(2) on Rh/SiO(2) samples of various particle-size distributions was followed by FTIR. The addition of O(2) pulses on Rh(0) surfaces saturated with chemisorbed N(2) allowed us to reassign stretching frequencies attributed originally to N(2)-Rh(0) to N(2)-Rh(delta+). The formation of the latter oxidized Rh species is assumed to be induced by an electron withdrawal from adsorbed oxygen species on Rh surface centers neighboring those onto which N(2) species are chemisorbed. The present work, thus, enables us to delimit ranges of frequencies for which the adsorption of N(2) can be considered to occur on either Rh(0) or Rh(delta+) centers for nu(N2) lower or higher than 2243 cm(-1), respectively. The N(2)-FTIR experiments performed on the studied catalysts also suggest a lattice plane selectivity for N(2) adsorption on metallic Rh planes of different natures which, to our knowledge, has not been reported yet for Rh.     

Study of hydration of two cements of different strengths

Main hydration products of two cement pastes, i.e. CSH-gel, portlandite (P) (and specific surface S) were studied by static heating, and by SEM, TEM and XRD, as a function of cement strength (C-33 and C-43) hydration time (th) and subsequent hydration in water vapour.Total change in mass on hydration and air drying, M_o, increased with strength of cement paste and with hydration time. Content of water escaping at 110 to 220°C, defined as water bound with low energy, mainly interlayer and hydrate water, was independent on cement strength but its content increased with (th). Content of chemically bound (zeolitic) water in CSH-gel, escaping at 220-400°C, was slightly dependent on strength and increased with (th). It was possibly derived from the dehydroxylation of CSH-gel and AFm phase. Portlandite water, escaping at 400-500°C, was independent on cement strength and was higher on longer hydration. Large P crystals were formed in the weaker cement paste C-33. Smaller crystals were formed in C-43 but they increased with (th). Carbonate formated on contact with air (calcite, vaterite and aragonite), decomposed in cement at 600-700^oC. It was high in pastes C-33(1 month) and C-43(1 month), i.e. 5.7 and 3.3%, respectively; it was less than 1% after 6 hydration months (low sensitivity to carbonation) in agreement with the XRD study showing carbonates in the air dry paste (1month), and its absence on prolonged hydration (6 months) and on acetone treatment. Water vapour treatment of (6 months) pastes or wetting-drying increased this sensitivity.Nanosized P-crystals, detected by TEM, could contribute to the cement strength; carbonate was observed on the rims of gel clusters.This revised version was published online in November 2005 with corrections to the Cover Date.     

Polymer-assisted preparation of nanoscale films of thermoelectric PbSe and PbTe and of lead chalcogenide-polymer composite films

Polymer films of polyethyleneoxide (PEO) or poly(L-lactide) (PLLA) containing a single-source precursor for either PbSe or PbTe were used to produce films of nanoparticles of these thermoelectric materials. The monomeric homoleptic chalcogenolates lead(II) bis-(2,4,6-trifluoromethylphenylselenolate) Pb[SeC(6)H(2)(CF(3))(3)](2) and lead(II) bis-[tris(trimethylsilyl)silyl-tellurolate] Pb[TeSi(SiMe(3))(3)](2) were used as single-source precursors for the thermolytic formation of the lead chalcogenides. The thickness and the quality of as-obtained thin films depended decisively on the spin-coating conditions, on the polymer, on the precursor concentration in the composite film before thermolysis and on the annealing time. Thin layers of particles of 30-50 nm size and high crystallinity were obtained. They were characterized by X-ray diffraction, thermal analysis and electron microscopy.     

Synthesis of dendron-protected porphyrin wires and preparation of a one-dimensional assembly of gold nanoparticles chemically linked to the pi-conjugated wires

A one-dimensional assembly of gold nanoparticles chemically bonded to pi-conjugated porphyrin polymers was prepared on a chemically modified glass surface and on an undoped naturally oxidized silicon surface by the following methods: pi-conjugated porphyrin polymers were prepared by oxidative coupling of 5,15-diethynyl-10,20-bis-((4-dendron)phenyl) porphyrin (6), and its homologues (larger than 40-mer) were collected by analytical gel permeation chromatography (GPC). The porphyrin polymers (>40-mer) were deposited using the Langmuir-Blodgett (LB) method on substrate surfaces, which were then soaked in a solution of gold nanoparticles (2.7 +/- 0.8 nm) protected with t-dodecanethiol and 4-pyridineethanethiol. The topographical images of the surface observed by tapping mode atomic force microscopy (AFM) showed that the polymers could be dispersed on both substrates, with a height of 2.8 +/- 0.5 nm on the modified glass and 3.1 +/- 0.5 nm on silicon. The height clearly increased after soaking in the gold nanoparticle solution, to 5.3 +/- 0.5 nm on glass and 5.4 +/- 0.7 nm on silicon. The differences in height (2.5 nm on glass and 2.3 nm on silicon) corresponded to the diameter of the gold nanoparticles bonded to the porphyrin polymers. The distance between gold nanoparticles observed in scanning electron microscopic images was ca. 5 nm, indicating that they were bonded at every four or five porphyrin units.     

Acid catalysed novel rearrangement of bicyclic dienone

The dienone (4) on heating with methanolic hydrochloric acid underwent ring cleavage yielding the aromatic ketal (6) which on acid hydrolysis produced the aldehyde (7). Similar treatment of the dienone (4) with acetic anhydride and p-toluenesulfonic acid furnished the ester (8) which on alkaline hydrolysis afforded the dimeric product (10). The structure of the products (6), (7), (8) and (10) are defined on the basis of the spectral evidence.     

蛋白质在离子交换色谱上选择性和非吸附特性

对蛋白质在离子交换柱上选择民性和非吸附特性进行了研究。蛋白质在有机磷酸锆阳离子色谱柱上,其保留作用随流动相ｐＨ值在离子强度的增加而减小;蛋白质在强阳离子和强阴离子色谱柱上的保留作用,即是流动相中的ｐＨ值等于蛋白质的等当点,其净电荷为零。不册蛋白质仍有不同程度的保留,这主要是由于蛋白质的三维结构使电荷 密度的大小和分布的不均匀以及离子交换填料表面性质的影响。