A Method of Determining Selectivity Coefficients Based on the Practical Slope of Ion Selective Electrodes

It is a problem to be solved that the experimental selectivity coefficients of ion selective electrodes( ISEs) depend on the activity. This paper studied the new method of determining selectivity coefficients. A mixed ion response equation, which was similar to Nicolsky-Eisenman (N-E) equation recommended by IUPAC, was proposed. The equation includes the practical response slope of ISEs to the primary ion and the interfering ion. The selectivity coefficient was defined by the equation instead of the N-E equation. The experimental part of the method is similar to that based on the N-E equation. The values of selectivity coefficients obtained with this method do not depend on the activity whether the electrodes exhibit the Nernst response or non-Nernst response. The feasibility of the new method is illustrated experimentally.     

Synthesis of a New Cerebroside Isolated from Typhonium giganteum Engl

The stereoselecfive synthesis of typhoniside, a new cerebroside isolated from Typhonium giganteum Engl. was accomplished.Cerebrosides are a kind of glycolipids highly enriched on the surface of myelin-producing cells and are composed by C18-4,8-sphingadienine, a-hydroxy acid and a saccharide head. It was the first time that cerebrosides were isolated from this traditional Chinese medicine (TCM) by us. In this paper, C18-4,8-sphingadienine was synthesized from D-xylose via a SN2 type reaction, α-Hydroxy acid was prepared from (R)-4-hydroxyte-trahydrofuran-2-one, which in turn could be obtained from Lascorbic acid.     

Mechanism of the Deaquation of Aquopentaaminocobalt（Ⅲ）Bromide

There are two theories,SN1 and SN2, for the mechanism of the deaquation of aquopentaamincobalt(Ⅲ） bromide(AAC-B). Both of the theories are supported by some experimental and calculated data. But there are not any experiments to determine directly the structure of the intermediates at dififferent reaction time.In this paper the structures of the intermediates at different reaction time in deaquation-anation of AACB were determined by extended X-ray absorption fine structure (EXAFS) and the reaction process was studied by the combination of X-ray powder diffraction and EXAFS.It was demonstrated that the deaquation-anation of AACB obeys the SN2 theory.     

Studies on the Preparation of Polymer Spherical Symmetry GRIN Sphere and Controlling its Gradient Index Distribution

In this paper, a polymer spherical symmetry GRIN sphere lens were prepared by the suspension-diffusion-copolymerization(SDC) technique, selecting methyl methacrylate(MMA) as monomer M1 and acrylic 2,2,2-trifluoroethyl ester(3FEA) as M2. The radial distribution of refractive index of the lens was measured by the shearing interference method, which demonstrated that the quadratic refractive-index distribution was formed in the sphere lens, and its △ n=0.019.     

Study on the Synthesis of La（3）-doped Nano-TiO_2 and Photocatalytic Degradation of Methyl Orange

In this paper,La(3)-doped Nano-TiO2(La(3)-TiO2) was synthesized via hydrothermal process.Structure and optical properties of the synthesized samples were characterized via XRD,FT-IR,DRS,etc.The results showed that the phase transformation of TiO2 from anatase to rutile was effectively prevented by La(3)-doping,which improved the thermal stability of anatase,and also suppressed particle aggregation and grain growth of TiO2.The formation of Ti-O-La bond promoted UV absorption intensity of TiO2,and provoked red shift of absorbed light.And the spectra response range of TiO2 was extended significantly to visible light by La(3)-doping,then photocatalytic performance was improved effectively.Compared with pure nano-TiO2,the performance of La(3)-TiO2 which photocatalyticly degraded methyl orange was increased significantly.     

Studies on the energy transfer system of terbium-norfloxacin chelate and its interaction with serum albumins

The energy absorbed by norfloxacin could be transferred to terbium(Ⅲ) through chela-tion of norfloxacin with terbium(Ⅲ),then the characteristic fluorescence emission could be observed.The interaction of serum albumins with norfloxacin have been investigated in this paper.The results showed that HSA could inhibit the energy transfer between norfloxacin and terbium(Ⅲ).But,BSA could not.It was shown that the binding properties of norfloxacin to HSA and BSA were totally different.     

Construction of the Skeleton of Phthalascidin,Mechanism of the Formation o the Key Tricyclic Lactam Intermediate

The mechanism of the formation of a key tricyclic lactam intermediate 3 was studied. It was found that the E-form compound 3 was transformed from the Z-form compound 4. The formation of 4 was a kinetically controlled process while the formation of 3 was a thermodynamically favorable one. A possible mechanism was given in this paper.     

Studies of Self-assembled Monolayers Formed by Imidazoline on Iron Surface by SEM and SECM

Self-assembled monolayers (SAMs) formed from organic substances can improve the inhibition of metal corrosion, because uniform and closely packed films formed on the metal surface providing an insulating layer1, 2. SAMs on the iron surface are studied so far because iron is one active metal which is easily corroded in the air. In this paper, SECM and SEM have successfully been applied in the study of SAMs inhibition corrosion for iron. SECM has been used to study the electrochemically a…     

Molecular Dynamics Simulation of the Self-assembled Monolayers of 1-Adamantanethiolate and Its Derivatives on Au（111） Surfaces

The self-assembled monolayers （SAMs） of 1-adamantanethiolate and its derivatives on Au（111） surface were investigated. Density functional theory （DFT） calculation indicates that the most stable configuration for absorption is at the face centered cubic （fcc）-bridge site. Canonical ensemble molecular dynamics （MD） simulations were carried out to study the structures and energies of the SAMs. The ordered structures of the SAMs were analyzed by means of radial distribution function and the relative stability of the SAMs was compared. It was concluded by the comparison of various contributions to the SAM formation energy that the formation of the SAMs was determined by the intermolecular nonbonding interaction and the chemical bonding interaction of sulfur and gold.     

Electrodeposition mechanism of Ni-Mo-P alloy in the solution of ammoniac citrate

The induced codeposition mechanism of Mo, P and Ni from the solution of ammoniac citrate was studied by means of steady-state polarization, AC impedance and X-ray Photoelectron Spectroscopy (XPS). The result of electrochemical measurements proved that [NiCit(NH3)2]- is the electro-active species of nickel, though nickel ions exist mainly as [NiCit(NH3)3]- in ammoniac citrate. XPS experiments proved the existence of tetravalent molybdenum corresponding to MoO2 on the surface of some deposits. The intermediate product, MoO2, was probably reduced to Mo in the alloy deposit by atomic hydrogen adsorbed on the induced metal nickel. The reduction of H2PO2- occurs through two distinctive steps with PH3 as an intermediate, which subsequently reacts with atomic hydrogen to form P in the alloy deposit. The electrodeposition mechanism was proposed in this paper.     

Chemical and thermal stability of alkanethiol and sulfur passivated InP(100)

InP(100) surfaces treated with Na2Sx9H20 and CnH(2n+1)SH are examined by contact angle measurement, X-ray photoelectron spectroscopy, and atomic force microscopy to determine the chemical and thermal behavior of these passivated surfaces. The surfaces coated by octadecanethiol (n = 18) self-assembled monolayers (SAMs) are found to be more stable toward oxidation than the S-passivated surface. The chemical stability of octadecanethiol SAMs in various environments is examined. The thiol monolayer is found to be stable in 0.1 M HCl but degrades in 0.1 M NaOH, boiling chloroform, and water. The behavior of these surfaces at elevated temperatures under a vacuum is also investigated. The octadecanethiol-coated InP(100) is stable up to 473 K, above which the films begin to degrade. Unlike other substrates on which the entire molecule including the sulfur headgroup desorbs together, on InP, the sulfur headgroup remains on the surface even after annealing to 673 K. These observations suggest that the desorption occurs by S-C bond cleavage as well as In-S bond cleavage. The sulfur of S-passivated InP is found to be more thermally stable than that of the octadecanethiol monolayer, perhaps due to their different bonding geometries and hence energies.     

Directed, selective insertion of single molecules into patterned self-assembled monolayers of alkanethiols with different chain lengths

Pd(ii) pincer adsorbate molecules (1) were inserted into self-assembled monolayers (SAMs) of alkanethiols with different chain lengths (C(8) to C(18)) on annealed gold substrates. Their presence was brought to expression by reaction of with Au nanoclusters bearing phosphine moieties (2). The surface-confined Au nanoclusters were observed only on the shorter chain SAMs (C(8)SH to C(16)SH) and not on C(18)SH SAMs. This is attributed to the longer chain length of C(18)SH preventing the insertion of pincer molecules. Microcontact printing (microCP) with C(18)SH on unannealed gold substrates and the subsequent immersion of the substrates into C(8)SH, C(10)SH, C(12)SH, or C(16)SH solutions, yielded a series of patterned SAMs that have areas of thiols of different chain lengths. Insertion of 1 followed by expression using 2, or insertion of 3 showed inserted molecules only in the shorter chain SAM areas. The absolute particle densities in the former case were higher than on the corresponding homogeneous SAMs on annealed substrates, probably due to larger numbers of defects in the SAMs on unannealed substrates.     

Measurement of the charge number per adsorbed molecule and packing densities of self-assembled long-chain monolayers of thiols

We have applied a recently developed method (Langmuir 2006, 22, 5509-5519) to determine charge numbers per adsorbed molecule and packing densities in self-assembled monolayers (SAMs) of octadecanethiol (C18SH), a representative long-chain thiol. Our method yields values of area per molecule that are physically reasonable, in contrast to the popular reductive desorption method, which gives molecular areas that are smaller than those determined by the van der Waals radii. In a nonadsorbing electrolyte, we were able to model the dependence of the charge number per adsorbed molecule on the electrode potential, taking into account that the desorption process is a substitution reaction between the solvent and the adsorbate. We have also shown that the charge number per adsorbed thiol is affected by the specific adsorption of the anion of the electrolyte. In the latter case, the thiol competes for adsorption sites at the surface not only with water but also with the anion of the electrolyte, and this competition has an effect on the measured charge number.     

Well-ordered self-assembled monolayer surfaces can be used to enhance the growth of protein crystals

A series of hydrophobic self-assembled monolayers (SAMs) was generated by the adsorption of undecanethiol, dodecanethiol, and octadecanethiol onto transparent gold-coated glass microscope slides. Protein crystallization trials using droplets deposited on the surfaces of the optically transparent SAMs were compared to those for which the droplets were deposited on the surfaces of conventional silanized glass microscope slides. For the five distinct proteins examined in the crystallization trials (i.e., lysozyme, alpha-lactalbumin, hemoglobin, thaumatin, and catalase), the SAMs generally afforded, (1) a faster rate of crystallization, (2) a larger crystal size; and (3) a broader range of crystallization conditions than that afforded by silanized glass. The greatest enhancements were observed with the highly ordered SAMs derived from octadecanethiol, which are evaluated here for the first time.     

十八硫醇自组装膜对TiO2光电氧化甲醇的敏化作用

纳米电极;甲醇光电氧化;十八硫醇自组装膜对TiO2光电氧化甲醇的敏化作用     

Comparative study of monolayers self-assembled from alkylisocyanides and alkanethiols on polycrystalline Pt substrates

This paper compares the properties of self-assembled monolayers (SAMs) derived from octadecylisocyanide (ODI) and octadecanethiol (ODT) on polycrystalline Pt substrates. Both monolayers formed at a similar rate using 1.0 mM solutions in ethanol and achieved a thickness of 22-23 A after 24 h as determined by ellipsometry measurements. The advancing contact angles of ODI and ODT monolayers were found to be 113 and 117 degrees, respectively, suggesting a slight difference in structure between them. X-ray photoelectron spectroscopy revealed that SAMs of ODT were more stable than those of ODI, which was supported by experiments that probed desorption of these layers in prewarmed hexadecane. Cyclic voltammetry measurements indicated that both monolayer systems could diminish electron-transfer rates substantially, although ODT monolayers were more effective and robust than their ODI counterparts. The resistance of the SAMs to ion penetration differed in a similar way, and a microcontact-printed monolayer of ODT could protect the underlying Pt better in an HCl/Cl2-based etch process than the one formed from ODI.     

Systematic control of the packing density of self-assembled monolayers using bidentate and tridentate chelating alkanethiols

The structural and interfacial properties of self-assembled monolayers (SAMs) on gold derived from the adsorption of a series of 1,1,1-tris(mercaptomethyl)alkanes (i.e., CH3(CH2)mC[CH2SH]3, where m = 9, 11, 13, 15) were investigated. The new SAMs, which possess uniformly low densities of alkyl chains, were characterized by ellipsometry, contact angle goniometry, and polarization modulation infrared reflection absorption spectroscopy. Additional analysis of the SAMs by X-ray photoelectron spectroscopy permitted a direct calculation of the packing densities of the SAMs on gold. The results as a whole, when compared to those obtained on SAMs generated from normal alkanethiols (CH3(CH2)m+2SH), 2-alkylpropane-1,3-dithiols (CH3(CH2)mCH[CH2SH]2), and 2-alkyl-2-methylpropane-1,3-dithiols (CH3(CH2)mC(CH3)[CH2SH]2) having analogous chain lengths, demonstrate that the 1,1,1-tris(mercaptomethyl)alkanes afford SAMs with alkyl chains having the lowest packing density and least conformational order.     

Effect of chain length of some 2D and 3D alkanethiols on gold studied by DSC and voltammetry

Striking similarities and differences in the behaviour of two-dimensional (2D) self-assembled monolayers (SAMs) on gold and corresponding three-dimensional (3D) SAMs on gold of two alkanethiols of different chain lengths, hexadecanethiol (HDM) and octadecanethiol (ODM) were investigated as a function of temperature. Cyclic Voltammetry (CV) of the 2D SAMs and Differential Scanning Calorimetry (DSC) of the 3D SAMs were used to study previously unexplained behaviour. CV revealed two transition temperatures in both the HDM and ODM 2D systems. In the DSC studies, both a lower and higher temperature transition was observed in the 3D SAMs of HDM but only one temperature transition was observed in the 3D SAMs of ODM. It was deduced that the lower temperature transitions in the gold-alkanoate nanoparticles were related to interaction between the methyl group chain ends. The lower temperature transition was observed in the 3D system of HDM but not that of ODM because the curvature in the 3D system that is absent in the 2D system reduces the interaction between the alkyl chain ends due to a longer chain resulting in an increased distance between the end groups. It was concluded that the lower transition temperature was attributed to the disordering of the alkyl chains starting from the end closest to the terminal groups.     

Binary self-assembled monolayers of alkanethiols on gold: deposition from solution versus microcontact printing and the study of surface nanobubbles

The coadsorption of alkanethiols on noble metals has been recognized for a long time as a suitable means of affording surfaces with systematically varied wettability and other properties. In this article, we report on a comparative study of the composition of the mixed self-assembled monolayers (SAMs) obtained (i) by the coadsorption of octadecanethiol (ODT) and 16-mercaptohexadecanoic acid (MHDA) from ethanol and chloroform onto gold substrates and (ii) by microcontact printing using poly(dimethyl siloxane) (PDMS) stamps. SAMs prepared by coadsorption from solution showed a preferential adsorption of ODT for both solvents, but this trend was reversed in microcontact-printed SAMs when using chloroform as a solvent, as evidenced by contact angle and Fourier transform infrared (FTIR) spectroscopy measurements. An approximately linear relationship between the static contact angle and the degree of swelling with different solvents was observed, which suggests that the surface composition can be controlled by the interaction of the solvent and the PDMS elastomer. The altered preference is attributed to the different partitioning of the two thiols into solvent-swelled PDMS, as shown by (1)H NMR spectroscopy. Finally, molecularly mixed binary SAMs on ODT and MHDA on template-stripped gold were applied to study the effect of surface nanobubbles on wettability by atomic force microscopy (AFM). With a decreasing macroscopic contact angle measured through water, the nanoscopic contact angle was found to decrease as well.     

硫醇在金电极上的SA单分子层膜的电化学研究

金基底上的硫醇自组装单分子层膜(Self-asembledmonolayers,SAMs)具有良好的稳定性和有序性,因此在基础研究及应用技术等领域都受到了广泛的重视^[1].通过电化学方法测定自组装膜对溶液中电活性物质的异向电子转移的阻碍作用.