Chemical force microscopy: applications in surface characterisation of natural hydroxyapatite

Detailed mapping of surface chemistry with nanometer resolution has application throughout the physical and life sciences. The atomic force microscope (AFM) has provided a tool that, when using functionalised probes, is capable of providing chemical information with this level of spatial resolution. Here, we describe the technique of chemical force microscopy (CFM) and demonstrate the sensitivity of the technique using chemical force titrations against pH. We describe in detail the specific application of mapping the surface charge on natural hydroxyapatite from skeletal tissue and show that this new information leads to a better understanding of the binding of matrix proteins to the mineral surface.     

Direct determination of thickness of sea surface microlayer using a pH microelectrode at original location

The sea surface microlayer (SML) is the interface layer between seawater and atmosphere, which is a new study field developed from the intersecting and infiltration of ocean science and atmosphere science, including the SML physics, the SML chemistry, the SML biology etc. It in-volves the recip rocity of sea-air, the globe cycle and flux of substances, so it is a key item of the global cooperative research on ocean science[1,2]. It should also be an important research field of SOLAS (sur…     

Chitosan Bio‐Based Organic–Inorganic Hybrid Aerogel Microspheres

Recently, organic–inorganic hybrid materials have attracted tremendous attention thanks to their outstanding properties, their efficiency, versatility and their promising applications in a broad range of areas at the interface of chemistry and biology. This article deals with a new family of surface‐reactive organic–inorganic hybrid materials built from chitosan microspheres. The gelation of chitosan (a renewable amino carbohydrate obtained by deacetylation of chitin) by pH inversion affords highly dispersed fibrillar networks shaped as self‐standing microspheres. Nanocasting of sol–gel processable monomeric alkoxides inside these natural hydrocolloids and their subsequent CO₂ supercritical drying provide high‐surface‐area organic–inorganic hybrid materials. Examples including chitosan–SiO₂, chitosan–TiO₂, chitosan–redox‐clusters and chitosan–clay‐aerogel microspheres are described and discussed on the basis of their textural and structural properties, thermal and chemical stability and their performance in catalysis and adsorption.     

Chitosan bio-based organic-inorganic hybrid aerogel microspheres

Recently, organic-inorganic hybrid materials have attracted tremendous attention thanks to their outstanding properties, their efficiency, versatility and their promising applications in a broad range of areas at the interface of chemistry and biology. This article deals with a new family of surface-reactive organic-inorganic hybrid materials built from chitosan microspheres. The gelation of chitosan (a renewable amino carbohydrate obtained by deacetylation of chitin) by pH inversion affords highly dispersed fibrillar networks shaped as self-standing microspheres. Nanocasting of sol-gel processable monomeric alkoxides inside these natural hydrocolloids and their subsequent CO(2) supercritical drying provide high-surface-area organic-inorganic hybrid materials. Examples including chitosan-SiO(2), chitosan-TiO(2), chitosan-redox-clusters and chitosan-clay-aerogel microspheres are described and discussed on the basis of their textural and structural properties, thermal and chemical stability and their performance in catalysis and adsorption.     

Reactions of Organic Ions at Ambient Surfaces in a Solvent-Free Environment

Solvent-free ion/surface chemistry is studied at atmospheric pressure, specifically pyrylium cations, are reacted at ambient surfaces with organic amines to generate pyridinium ions. The dry reagent ions were generated by electrospraying a solution of the organic salt and passing the resulting electrosprayed droplets pneumatically through a heated metal drying tube. The dry ions were then passed through an electric field in air to separate the cations from anions and direct the cations onto a gold substrate coated with an amine. This nontraditional way of manipulating polyatomic ions has provided new chemical insights, for example, the surface reaction involving dry isolated 2,4,6-triphenylpyrylium cations and condensed solid-phase ethanolamine was found to produce the expected N-substituted pyridinium product ion via a pseudobase intermediate in a regiospecific fashion. In solution however, ethanolamine was observed to react through its N-centered and O-centered nucleophilic groups to generate two isomeric products via 2H-pyran intermediates. The O-centered nucleophile reacted less rapidly to give the minor product. The surface reaction product was characterized in situ by surface enhanced Raman spectroscopy, and ex situ using mass spectrometry and H/D exchange, and found to be chemically the same as the major pyridinium solution-phase reaction product.     

The quality of pH measurements 100 years after its definition

Analytical chemistry is a scientific discipline based on the search of qualitative and quantitative information embodied in unknown samples which are representative of targeted systems. A. Lavoisier measured masses, S. Arrhenius discovered ions, namely hydrogen ions, S. Sørensen introduced pH and the chemical community has been dealing abundantly with them, first in the frame of classical analysis and later by means of instrumental methods of analysis responsible for large amount of data. Although statistical treatment of measurement results became part of the procedures, it took a few decades of thinking and globalization of the economy to realize that more was needed for the sake of evidence of quality; and this was found in the bases of the science of measurement and on the metrological approach. At the dawn of the twenty-first century, the most measured chemical parameter, pH, set the example of such hierarchical targeting of measurement results fit for a certain purpose, which is worth noticing particularly because 100 years have elapsed since its first definition and initial recommendation of the measurement procedure.     

Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes

A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric points of these membranes range from 3.0 to 5.2. The curves of zeta potential versus solution pH for all membranes display a shape characteristic of amphoteric surfaces with acidic and basic functional groups. Results with salts containing divalent ions (CaCl₂, Na₂SO₄, and MgSO₄) indicate that divalent cations more readily adsorb to the membrane surface than divalent anions, especially in the higher pH range. Three sources of humic acid, Suwannee River humic acid, peat humic acid, and Aldrich humic acid, were used to investigate the effect of dissolved natural organic matter on membrane surface charge. Other solution chemistries involved in this investigation include an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (dodecyltrimethylammonium bromide). Results show that humic substances and surfactants readily adsorb to the membrane surface and markedly influence the membrane surface charge.     

Ionic strength effects on silicic acid (H4SiO4) sorption and oligomerization on an iron oxide surface: an interesting interplay between electrostatic and chemical forces

The effect of ionic strength on reactions at aqueous interfaces can provide insights into the nature of the chemistry involved. The adsorption of H(4)SiO(4) on iron oxides at low surface silicate concentration (Γ(Si)) forms monomeric silicate complexes with Fe-O-Si linkages, but as Γ(Si) increases silicate oligomers with Si-O-Si linkages become increasingly prevalent. In this paper, the effect of ionic strength (I) on both Γ(Si) and the extent of silicate oligomerization on the ferrihydrite surface is determined at pH 4, 7, and 10, where the surface is, respectively, positive, nearly neutral, and negatively charged. At pH 4, an increase in ionic strength causes Γ(Si) to decrease at a given H(4)SiO(4) solution concentration, while the proportion of oligomers on the surface at a given Γ(Si) increases. At pH 10, the opposite is observed; Γ(Si) increases as I increases, while the proportion of surface oligomers at a given Γ(Si) decreases. Ionic strength has only a small effect on the surface chemistry of H(4)SiO(4) at pH 7, but at low Γ(Si) this effect is in the direction observed at pH 4 while at high Γ(Si) the effect is in the direction observed at pH 10. The pH where the surface has zero charge decreases from ≈8 to 6 as Γ(Si) increases so that the surface potential (Ψ) is positive at pH 4 for all Γ(Si) and at pH 7 with low Γ(Si). Likewise, Ψ < 0 at pH 10 for all Γ(Si) and at pH 7 with high Γ(Si). The diffuse layer model is used to unravel the complex and subtle interactions between surface potential (Ψ) and chemical parameters that influence interfacial silicate chemistry. This analysis reveals that the decrease in the absolute value of Ψ as I increases causes Γ(Si) to decrease or increase where Ψ is, respectively, positive or negative. Therefore, at a given Γ(Si), the solution H(4)SiO(4) concentration changes with I, and because oligomerization has a higher H(4)SiO(4) stoichiometry coefficient than monomer adsorption, this results in the observed dependence of the extent of silicate oligomerization on I.     

共沸蒸馏法制备表面化学改性氢氧化镁纳米颗粒

首次将表面改性剂如硬脂酸、硬脂酸锌或稀土偶联剂加入到传统的共沸蒸馏体系中,使Mg(OH)2纳米颗粒的表面改性和干燥过程同时完成。 通过 XRD、TEM、FT-IR、TG和CAM（接触角测试）等技术手段对样品的结构、形貌和性质进行了表征。 结果表明,表面改性剂不但能够和Mg(OH)2纳米颗粒的表面的OH-离子发生化学反应形成表面修饰层, 减少硬团聚现象,而且还使纳米颗粒表面由亲水性变为疏水性。 另外,对共沸蒸馏法制备表面改性纳米颗粒的机理进行了讨论,为纳米颗粒表面改性提供了一种新思路。     

In-situ infrared spectroscopic studies of adsorption processes on boehmite particle films: exchange of surface hydroxyl groups observed upon chelation by acetylacetone

Adsorption processes on poorly crystalline boehmite (PCB) particle films have been studied using attenuated total reflection infrared spectroscopy. This method allows the in-situ investigation of wet surface chemical processes. Thin films of aggregated particles of PCB that are stable between pH 4 and 11 have been prepared by drying aqueous PCB dispersions. Carbonate adsorbs to the PCB films during the film formation process but can be removed without impact on the film by washing with alkali at pH 10. The adsorption of acetylacetone (acac) to the surface of PCB has been studied at the solid/liquid and solid/gas interfaces. The concomitant changes in the OH deformations of hydroxyl groups present on the surface has been observed. The IR absorption of surface hydroxyl groups involved in adsorption of a bidentate chelating ligand have been spectroscopically isolated through their interaction with acac.     

The Research of Biomedical Intelligent Polymer Materials

The properties of biomedical intelligent polymer materials can be changed obviously when there is a little physical or chemical change caused by external condition. They are in the forms of solids, solutions and the polymers on the surface of carrier, and include water solution of hydrophilic polymers, cross-linking hydrophilic polymers(i.e. hydrogels) and the polymers on the surface of carrier. The environmental stimulating factors are temperature, pH value, composition of solution, ionic intention, light intention, electric field, stress field and magnetic field etc.. The properties of intelligent polymer are those of phase, photics, mechanics, electric field, surface energy,reaction ratio, penetrating ratio and recognition etc..Stimulation-response of intelligent water-soluble polymerWater-soluble intelligent polymer can be separated out from solution under special external condition. It can be used as the switch of temperature or pH indicator. When water-soluble intelligent polymer is mixed with soluble-enzyme matter or cell suspension, the polymer can bring phase separation and react with soluble-enzyme matter or cell membrane through accepting some external stimulation. Other water-soluble intelligent polymer is that can make the main chemical group of some natural biomolecular recognition sequence section to arrange on skeleton of polymer at random. It is the same ratio as natural biomolecules.Stimulation-response of intelligent polymer of carrier surface Intelligent polymer can be fixed on the surface of solid polymer carrier through chemical grafting or physical adsorption. When the external conditions are changed, the thickness, humidity and electric field of the surface layer will be changed. Intelligent polymer can be preparated the permanence switch by precipitating into the hole of porous surface, and it can control on-off state of the hole. When protein or cell interacts with intelligent polymer surface to be placed in to open or close, they can be selectively absorbed on hydrophobic surface.Stimulation-response of intelligent polymer hydrogelIntelligent polymer hydrogel's construction, physical property, and chemical property can change with the changing of external environmental conditions. When environmental stimulation signal, for example, solution composition, pH value, ionic intention, temperature, light intention, electric field,magnetic field and substance etc. changes, the intelligent polymer will occur to break of volume.This is the intelligence of polymer hydrogel.The intelligence of these polymers will be widely applied in biomedical fields.     

Conversion Natural Gas to Ci Hydrocarbons via Cold Plasma Reaction

Natural gas is not only an increasing important role in energy and chemicals supplies in 21st century but also the second most important of the greenhouse gases^[1]. For the past 200 years atmospheric methane concentrations have increased from 0.8 to 1.65ppm. This change in methane concentration had been led to an estimated increase in radiative forcing of climate of 0.47 W/m² compared to the increase of 1.56 W/m² due to the change in carbon dioxide concentration over a comparable time period^[2]. With large increases in natural gas reserves proven worldwide, it can be expected that natural gas will play an increasing important role in humanity future. Cold plasma chemical processing is a promising route for synthesis of chemicals that have high activation energies, because electric field can be excite reactant to the plasma and many kinds of reactive particles, electrons, free radicals, ions metastable species and photons are produced in a plasma chemical processing system.     

Metabolomics method based on ultra high performance liquid chromatography with time‐of‐flight mass spectrometry to analyze toxins in fresh and dried toad venom

Drying is a critical step to prolong the storage time in natural medicine processing but it changes the chemical characteristics of the product. In this study, research was performed to characterize the metabolomic changes in toad venom induced by vacuum‐drying at 60°C and air‐drying at room temperature by ultra high performance liquid chromatography coupled with pattern recognition approaches. In total 52 metabolites, down‐regulated or up‐regulated, were identified as potential chemical markers. Compared with fresh toad venom, vacuum‐drying at 60°C succeeded in raising the conjugated‐type bufadienolide content significantly, while the content of free‐type bufadienolides were slightly reduced. On the other hand, toad venom air‐dried at room temperature presented a relatively low amount of bufadienolides compared with fresh venom. For example, the content of several known anti‐tumor components (gamabufotalin, bufotalin, cinobufagin, etc.) were significantly reduced. The 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide bioassay further showed that venom air‐dried at room temperature had weaker anti‐tumor activity on human hepatocellular carcinoma SMMC‐7721 proliferation in vitro than samples vacuum‐dried at 60°C. These results showed that the great metabolomic changes of toad venom occurred during the drying process, suggesting that a proper drying procedure is important for sustaining the chemical quality of natural medicines.     

Development of metrology for pH measurement in Thailand

It has not been long that metrology is well accepted as an important part in analytical chemistry since it helps the chemists to receive the best measurement and accurate results with traceability. The National Institute of Metrology Thailand (NIMT), which is a public agency under the supervision of the Ministry of Science and Technology, not only focuses on physical standards but also provides and maintains standards in chemical field. pH measurement is one of the most widely used in the laboratories including industries and medical area in Thailand. The chemical laboratory starts working on the project with the objective of disseminating an accurate result in routine pH measurement. In 2002, the laboratory provided a service in calibration of pH meter and organized the first local interlaboratory comparison program (NIMT–C-ILC-1: pH buffer) in pH measurement. There were three buffer solution samples in the range of acid, neutral, and base. A total of 44 laboratories participated in this program. The NIMT chemical laboratory also participated in the proficiency testing program that was conducted by PSB Corporation Testing Group in Singapore. In 2003, NIMT started research in preparation of secondary buffers by using highly accurate pH meters with glass electrode systems. The laboratory produced three secondary buffers, which were pH 4.01, 6.86, and 9.18 with uncertainty 0.020 pH at 25°C. The competence of the laboratory was shown by the measurement results of the pilot study (APMP.QM-P06), which was organized by the APMP electrochemical analysis working group (EAWG/TCQM) in 2005. The title of this study was “pH determination of two phosphate buffers by Harned cell method and glass electrode method”. NIMT aims to achieve for establishment of the primary method for pH measurement in the near future. Presented at -- “BERM-10” -- April 2006, Charleston, SC, USA     

Personal reflections on receiving the Roger Adams Award in organic chemistry

The author reflects on his early experiences as a chemist, and on the subsequent shift in emphasis that his research has undergone from mechanistic and synthetic organic chemistry to natural products chemistry. Finally, the extension of the field of natural products chemistry into the emerging discipline of chemical ecology is noted. This essay concludes with a consideration of the importance of including science in the curricula of all college and university students.     

Adsorption and Chemical Modification of Phenols on a Silver Surface

The adsorption of phenols of different natures on silver colloidal particles is studied here by surface-enhanced Raman spectroscopy (SERS). The studied compounds can be classified in three groups: (a) cinnamic acic derivatives: caffeic and isoferulic acids; (b) catechol; and (c) the phenols derived from benzoic acid: m- and p-hydroxybenzoic acids and salicylic, vanillic, and gallic acids. The interest of these compounds lies in the fact that they are naturally occurring molecules with significant importance in relation to plant metabolism, soil chemistry, and vegetal food stability. In addition, many of these compounds have antioxidant properties derived from their high affinity toward atmospheric oxygen. They exhibit high reactivity that may be enhanced in the presence of a metal surface such as those employed for SERS spectroscopy. From the SERS results it can be deduced that a clear chemical change of caffeic and gallic acid and catechol occurred. The chemical modification consists mainly of polymerization connected to existence in the molecule of o-diphenol moieties. In the case of m-hydroxybenzoic acid the chemical change may occur at low pH at which a reorientation of the molecule on the surface takes place, while in the o-hydroxybenzoic acid the only chemical change seems to be the internal H bond breakdown induced by the complexation with the metal. Finally, isoferulic and p-hydroxybenzoic acids do not show any chemical modification upon adsorption on the metal, which takes place through the carboxylate group adopting the molecule a standing up orientation. The case of vanillic acid is not so clear, although possible chemical modification is also possible for this adsorbate. From the results found in this work it can be inferred that the factors influencing possible chemical modification are the chemical structure of the adsorbate and its orientation and interaction with the surface. Copyright 2000 Academic Press.     

Effect of KOH activation on the formation of oxygen structure in activated carbons synthesized from polymeric precursor

In this work, the influence of KOH activation on the surface chemistry of activated carbons (ACs) synthesized from polystyrene-based cation exchangeable resin (PSI) has been investigated. The surface chemistry of ACs has been characterized by using Fourier transformed infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), pH measurement, and Boehm's titration method. As a result, PSI can be successfully converted into ACs with high porosities. The total oxygen content on the ACs studied increases with increasing the KOH-to-PSI ratio. FT-IR and XPS analyses show that the resulting carbons possess a number of oxygen surface functional groups, such as carbonyl, quinone, phenol, ether, and carboxylic acid groups. The highest oxygen content and acid value are observed at a KOH-to-PSI ratio of 4 (KPS-4). However, its pH and surface basicity are higher than those of a KOH-to-PSI ratio of 2 (KPS-2), indicating the formation of basic species, such as quinone and pyrone groups. Although the oxygen-containing groups with basic character exist in the resulting carbons, all the samples are still acidic in character.     

Surface Modification by Atmospheric Pressure Air Plasma Treatment to Improve Dyeing with Natural Dyes: An Environment Friendly Approach for Leather Processing

The present study describes surface modification of leather using environment friendly atmospheric pressure dielectric barrier discharge (DBD) process to improve dyeing with natural dyes. Leather samples were exposed to dielectric barrier discharge produced in air. DBD plasma treatment changes morphology and chemical composition of the surface of leather samples. The chemical changes at leather surface are confirmed by Fourier transform infrared spectrometer. The morphology and chemical composition of leather surface is studied using scanning electron microscope and X-ray photoelectron spectroscopy. We observed significant improvement in dye uptake properties after air plasma treatment. Different species formed in plasma are identified using optical emission spectroscopy. Untreated and plasma treated samples were dyed with Eco-Garnet Brown, Eco-Hill Brown III, Eco-Turkey Red and Eco-Smoke Grey natural dyes. Dyeing behavior was assessed by spectroscopic measurement and by measuring fastness (wash and rub) properties. This has clearly indicated an increase in color intensity of plasma exposed leather as well as an increase in the dye uptake as compared to the untreated leather. Best results were obtained with Eco-Hill Brown III and Eco-Smoke Grey dyes. The study reveals that atmospheric pressure plasma has potential to become dry and eco-friendly process to modify leather surface to improve dye uptake properties with natural dyes.     

Metal Ion Coordination at the Water-Manganite (gamma-MnOOH) Interface

The local structure of Zn(II) adsorbed at the water-manganite (gamma-MnOOH) interface has been investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy. Adsorption experiments were carried out within the pH range 6.17-9.87 and surface coverages of 0.9 to 9.7 μmol/m(2)cZn(II) coordination was observed to change from six to four as pH was increased. This was indicated by a change in Zn-O distance from 2.04 to 1.96 ? and by a decrease in the obtained coordination numbers. Two higher shells were detected at about 3.08 and 3.33 ?, at all pH values and surface coverage investigated. As the backscattering phase and amplitude functions of Mn and Zn are similar, we used structural and chemical considerations to assign the backscattering at 3.08 ? to Mn neighbors, and the one at 3.33 ? to Zn atoms. Indeed the size of the Zn polyhedra, especially of ZnO(4), does not quite match the structure of the manganite surface. We conclude that Zn(II) forms multinuclear hydroxo-complexes or a zinc hydroxide phase at the surface, as it might be easier for an additional Zn(II) to bond to an already sorbed Zn. These results were compared to our previous EXAFS study of Cd(II) adsorption onto manganite, where mononuclear inner-sphere complexes bound to the surface via edges were found. Copyright 2000 Academic Press.     

Developments in accurate and traceable chemical measurements

In recent years there has been considerable interest in the application of the principles of measurement science to chemistry. This has led to the recognition of 'metrology in chemistry' as an area of relevance to analytical chemistry research. This tutorial review describes the benefits to chemistry of the implementation of the principles of measurement science and explains how they are able to improve the reliability and accuracy of chemical measurements.