Specific and non-specific interactions of procaine with activated carbon surfaces

The adsorption of procaine on eight activated carbon surfaces from simulated intestinal fluid (SIF) was evaluated using a rotating bottle method and isoperibol calorimetry. The adsorption data were fit using the modified Langmuir-like equation to calculate the non-specific and specific adsorption capacities. The surface atomic compositions were determined by X-ray photoelectron spectroscopy (XPS). A linear relationship was found between the relative non-specific adsorption capacity and the unoxidized hydrocarbon content of the activated carbon surfaces, which indicated that the non-specific adsorption site for procaine is the bare carbon surface. The apparent area occupied per procaine molecule, calculated from the specific capacity, was linearly correlated to the sum of the relative percentages of the C-O and O-C=O functional states on the surfaces. This suggested that the primary adsorption sites for procaine on the activated carbon surfaces were the oxygen-containing functional states of C-O and O-C=O, where procaine was adsorbed via hydrogen bonding. The differential heats of displacement for procaine on the four activated carbon surfaces are approximately equal to each other, which indicated that the interactions between procaine and the functional states on all surfaces are energetically equivalent.     

Electromagnetic interactions with rough metal surfaces

When surfaces are structured on the scale of the wavelength, we can expect incident light to be strongly modified by the surface. This is especially the case when the surface is metallic. We have developed a formalism for computing these modifications, closely analogous to electron scattering theory, which we briefly review and present some results for optical properties of, and electron energy loss in, colloids. Our main theme is another effect associate with rough or structured metallic surfaces: Surface Enhanced Raman Scattering, or SERS. We model the rough surface by a periodic array of spheres and obtain the correct magnitude for the enhancement and for the frequency shifts observed.     

Inelastic interactions of tunnel electrons with surfaces

Inelastic interactions of electrons emitted from the tip of a scanning tunnelling microscope (STM) are used to desorb individual hydrogen atoms from a Ge(111) surface. It is observed that the inelastic interactions depend not only on the electron energy and the current intensity but also on the electron emission regime of the STM tip. Quite surprisingly, it is found that tunnel electrons interact inelastically much less efficiently than field emitted electrons even though the electrons are in resonance with the Ge-H unoccuppied orbital.     

Protein interactions with negatively charged inorganic surfaces

Protein adsorption on charged inorganic solid materials has recently attracted enormous interest owing to its various possible applications, including drug delivery and biomaterial design. The need to combine experimental and computational approaches to get a detailed picture of the adsorbed protein properties is increasingly recognised and emphasised in this review. We discuss the methods frequently used to study protein adsorption and the information they can provide. We focus on model systems containing a silica surface, which is negatively charged and hydrophilic at physiological pH, and two contrasting proteins: bovine serum albumin (BSA) and lysozyme (LSZ) that are both water soluble. At pH 7, BSA has a net negative charge, whereas LSZ is positive. In addition, BSA is moderately sized and flexible, whereas LSZ is small and relatively rigid. These differences in charge and structural nature capture the role of electrostatics and hydrophobic interactions on the adsorption of these proteins, along with the impact of adsorption on protein orientation and function. Understanding these model systems will undoubtedly enhance the potential to extrapolate our knowledge to other systems of interest.     

Importance of structural and chemical heterogeneity of activated carbon surfaces for adsorption of dibenzothiophene

The performance of various activated carbons obtained from different carbon precursors (i.e., plastic waste, coal, and wood) as adsorbents for the desulfurization of liquid hydrocarbon fuels was evaluated. To increase surface heterogeneity, the carbon surface was modified by oxidation with ammonium persulfate. The results showed the importance of activated carbon pore sizes and surface chemistry for the adsorption of dibenzothiophene (DBT) from liquid phase. Adsorption of DBT on activated carbons is governed by two types of contributions: physical and chemical interactions. The former include dispersive interactions in the microporous network of the carbons. While the volume of micropores governs the amount physisorbed, mesopores control the kinetics of the process. On the other hand, introduction of surface functional groups enhances the performance of the activated carbons as a result of specific interactions between the acidic centers of the carbon and the basic structure of DBT molecule as well as sulfur-sulfur interactions.     

Uranium association with corroding carbon steel surfaces

We investigated the association of uranium with clean and corroded surfaces of 1010 carbon steel. Studying steel contaminated by uranium species will have an important effect on the development of methods used to clean radioactively contaminated metal waste. X‐ray photoelectron spectroscopy, synchrotron infrared microspectroscopy and laboratory‐based Fourier transform infrared analysis of steel surfaces exposed to uranyl nitrate showed the presence of crystallized hydrated uranyl oxides, uranyl hydroxides, iron oxyhydroxides and iron oxides. In general, heavily corroded areas physically shield the uranium species, which tended to associate spatially with hydroxyl groups and lepidocrocite. Lightly corroded areas contained uranium species with stronger axial U–O bonding. Infrared spectroscopy, Rutherford backscattering spectroscopy and energy‐dispersive spectroscopy mapping analysis revealed that the uranium species are well distributed within the upper micron of the thick corrosion layer and associated more with areas of high hydroxide content. Parameters such as the concentration of uranyl nitrate solution used to expose the carbon steel coupons, the method of contamination (dipped or sprayed with dilute uranyl nitrate solution) and the degree of corrosion (accelerated corrosion before and/or after contamination) played significant roles in the distribution and nature of the uranyl hydroxide/iron oxyhydroxide corrosion products found on the surface of all coupons. These factors must be considered in the development and optimization of decontamination processes for metal waste. Copyright © 2003 John Wiley & Sons, Ltd.     

Adsorption behavior of propylamine on activated carbon fiber surfaces as induced by oxygen functional complexes

In this study, the surfaces of activated carbon fibers (ACFs) were modified by nitric acid to introduce surface oxygen complexes and to observe the influence of those complexes on the propylamine adsorption of the ACFs. It was found that the oxygen complexes including carboxylic and phenolic groups were predominantly increased, resulting in the increase of total surface acidity. However, the specific surface areas and the total pore volumes of the modified ACFs were decreased by 5-8% due to the increased blocking (or demolition) of micropores in the presence of newly introduced complexes. Despite the decrease of textural properties, it was found that the amount of propylamine adsorbed by the modified ACFs was increased by approximately 17%. From the XPS results, it was observed that propylamine reacted with strong or weak acidic groups, such as COOH or OH, on the ACF surfaces, resulting in the formation of pyrrolic-, pyridonic-, or pyridine-like structures.     

Kinetics of the gas-phase chlorination of activated carbon with carbon tetrachloride

The chlorination of activated charcoals KAU and SCN with CCl₄ vapor in the temperature range 300–600 °C and also the thermal stability of the added chlorine has been studied. It is shown that chlorination with CCl₄ vapor led to the addition of up to 22 mass % (6.2 mmol/g) of chlorine to the surface layer of the carbon. The added chlorine is desorbed from the surface with formation of HCl, while at temperatures above 500 °C desorption of chlorine goes practically to completion. The effective rate constants and the energies of activation of the processes of chlorination and desorption have been found.     

Towards quantitative analysis of intermolecular interactions with Hirshfeld surfaces

Enhancements to the properties based on Hirshfeld surfaces enable quantitative comparisons between contributions to crystal packing from various types of intermolecular contacts.     

Scalable synthesis of activated carbon with superparamagnetic properties

Magnetic activated carbons were obtained by in situ formation of coated superparamagnetic iron nanoparticles in the pores of carbons initially impregnated with ferric salt solution.     

Interaction of monochlorinated phenols with granular activated carbon

The validity of an empirical model to estimate the adsorption affinity of a solute from its acidity constant (pKa) was confirmed through study of the adsorption of monochlorinated phenols on granular activated carbon.Neglecting possible adsorbate fragmentation, simplified desorption kinetic data were obtained for the massive thermal release of the investigated solutes. The resulting non-isothermal kinetic parameters confirm that thermal cleaning of the adsorbent surface is a phase-boundary controlled process involving the interruption of physical interactions according to the calculated activation energy values.

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Zusammenfassung Die Gültigkeit eines empirischen Modells zur Abschätzung der Adsorptionsaffinität eines gelösten Stoffes auf Grund der Aciditätskonstante (pKa) wurde durch Untersuchung der Adsorption von monochlorierten Phenolen an granulierter Aktivkohle bestätigt. Unter Vernachlässigung einer möglichen Adsorbatfragmentierung wurden vereinfachte kinetische Daten für die thermische Desorption der untersuchten gelösten Stoffe erhalten. Die erhaltenen, nichtisothermen kinetischen Parameter zeigen, daß die thermische Säuberung der Adsorbentoberfläche ein phasengrenzflächenkontrollierter Prozeß ist, bei dem physikalische Wechselwirkungen entsprechend den berechneten Werten der Aktivierungsenergie aufgehoben werden.

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Barothermal modification of activated carbon with maleic anhydride

We have used the barothermal treatment method (heat and pressure) to modify the surface of activated charcoal with maleic anhydride. As a result of the modification, about 1 mmol/g of thermally stable carboxyl groups are formed on the surface with a decomposition temperature range of 330–470°C. We show that the proposed procedure makes it possible to obtain materials with a uniform coverage of functional groups.     

Intermolecular noncovalent interactions with carbon in solution

One of the most familiar carbon-centered noncovalent interactions (NCIs) involving an antibonding π*-orbital situated at the Bürgi–Dunitz angle from the electron donor, mostly lone pairs of electrons, is known as n → π* interactions, and if it involves a σ* orbital in a linear fashion, then it is known as the carbon bond. These NCIs can be intra- or inter-molecular and are usually weak in strength but have a paramount effect on the structure and function of small-molecular crystals and proteins. Surprisingly, the experimental evidence of such interactions in the solution phase is scarce. It is even difficult to determine the interaction energy in the solution. Using NMR spectroscopy aided with molecular dynamics (MD) simulation and high-level quantum mechanical calculations, herein we provide the experimental evidence of intermolecular carbon-centered NCIs in solution. The challenge was to find appropriate heterodimers that could sustain room temperature thermal energy and collisions from the solvent molecules. However, after several trial model compounds, the pyridine-N-oxide:dimethyltetracyanocyclopropane (PNO–DMTCCP) complex was found to be a good candidate for the investigation. NBO analyses show that the PNO:DMTCCP complex is stabilized mainly by intermolecular n → π* interaction when a weaker carbon bond gives extra stability to the complex. From the NMR study, it is observed that the NCIs between DMTCCP and PNO are enthalpy driven with an enthalpy change of −28.12 kJ mol⁻¹ and dimerization energy of ∼−38 kJ mol⁻¹ is comparable to the binding energies of a conventional hydrogen-bonded dimer. This study opens up a new strategy to investigate weak intermolecular interactions such as n → π* interaction and carbon bonds in the solution phase.

NMR spectroscopy combined with MD simulation and electronic structure calculations enabled us to quantify the energetics of the intermolecular n → π* interaction and carbon-bonding (n → σ* interaction) in solution.     

Protein interactions with solid surfaces following contact with plasma and blood

Two aspects of blood protein interactions with solid surfaces are discussed. The first is competitive adsorption among the many proteins in the blood. The general factors which determine the composition of the adsorbed layer in any multicomponent protein system are considered and then related to current knowledge of competitive adsorption in blood. The latter pertains largely to the so-called Vroman effect whereby proteins are adsorbed and displaced from the surface in an ordered sequence. Secondly the possible transformation of adsorbed enzyme precursors into active enzymes by the agency of the surface is discussed. The example of the plasminogen-plasmin system is used to illustrate this discussion.     

Measurements of the solubilities of derivatized amino acids in supercritical carbon dioxide

The solubilities of phenylalanine and tyrosine in supercritical carbon dioxide (SCCO₂) were measured after derivatization as the N-acetyl amino acid ethyl ester, N-carbobenzoxy amino acid and N-acetyl amino acid. Using an SCCO₂ flow system, a measuring method of the saturated solubilities of the derivatized amino acids was established in which the contact height of the extraction cell, i.e. a packed column, is increased till the concentration of a derivatized amino acid at the exit of the cell reaches a plateau. The solubilities of N-acetyl phenylalanine ethyl ester (APEE) exceeded 0.001 mole fraction, which is higher than those of caffeine produced in industrial SCCO₂ processes. A possible way of separating the amino acid mixtures using polarity differences in different amino acid side chains was demonstrated using the solubility data of the N-acetyl-amino acid ethyl esters in SCCO₂, as the solubilities of APEE are higher than those of N-acetyl tyrosine ethyl ester by two orders of magnitude.     

吸汞载银活性炭纤维和吸汞活性炭纤维的热脱附特性研究

70℃下分别对载银活性炭纤维(载银量14.07%)和活性炭纤维的片状吸附体进行气态汞吸附实验,测定出载银活性炭纤维汞饱和吸附量为192.3 mg/g,活性炭纤维汞饱和吸附量为29.4 mg/g,分别为普通活性炭的48倍～192倍和7倍～29倍.采用热重分析法(TGA)研究了两种吸附剂汞饱和后的热脱附再生特性.结果表明,汞饱和载银活性炭纤维的汞脱附发生在100℃～650℃,在70 min内从50℃升温至650℃,才乏脱附率为94.73%;汞饱和活性炭纤维的汞脱附发生在100℃～230℃,在40 min内从50℃升温至350℃ ,汞脱附率为69.93%.扫描电镜分析发现,载银活性炭纤维因吸附汞而富集的银,经热脱附后变成均匀弥散于纤维表面的亚微米级和纳米级球状银颗粒;吸汞活性炭纤维经热脱附后物理吸附汞基本消失,而氧化汞颗粒反而变多,说明物理吸附的汞易于脱附,氧化汞难以脱附,同时在热脱附过程中存在金属汞向氧化汞的转化.     

Direction specific interactions of 1,4-dicarboxylic acid with calcite surfaces

Interactions of succinic acid (SUC) with the {104} cleavage faces of calcite show a strong preference in crystallographic directions. In situ atomic force microscopy revealed that the morphology of etch pits on the crystal surfaces experienced a transition from the common rhombus to a hexagon upon the introduction of SUC. The pit shape further evolved from 6-sided to 7-sided and eventually to 5-sided with increasing concentrations of SUC. Analysis indicates that the morphology changes may result from SUC preferentially binding to the [42] and [010] edges of the (104) plane to selectively slow down their step speed.     

Polymer-tethered ligand-receptor interactions between surfaces II

In this paper, we analyze the thermodynamics of interactions between surfaces mediated by polymer-tethered ligand-receptor binding. From statistical thermodynamics calculations, we obtain an effective two-dimensional binding constant reflecting contributions from the microscopic binding affinity as well as from the conformation entropy of the polymer tethers. The total interaction is a result of the interplay between attractive binding and repulsion due to confinement of the polymer chains. We illustrate the differences between three scenarios when the binding molecules are (1) immobile, (2) mobile with a fixed density, and (3) mobile with a fixed chemical potential (connected to a reservoir), which correspond to different biological or experimental situations. The key features of interactions, including the range of adhesion (onset of binding) and the equilibrium separation, can be obtained from scaling analysis and are verified by numerical solutions. In addition, we also extend our method of treating the quenched case with immobile ligands and receptors developed in a previous paper [Martin, J. I.; Zhang, C.-Z.; Wang, Z.-G. J. Polym. Sci., Part B: Polym. Phys. 2006, 44, 2621-2637] as a density expansion in terms of both ligand and receptor densities. Finally, we examine several cases having ligand-receptor pairs with different tether lengths and binding affinities, and/or nonbinding linear polymers as steric repellers. Such systems can exhibit complex interactions such as a double-well potential, or a bound state with an adjustable barrier (due to the repellers), which have both biological and bioengineering relevance.     

NMR Wool Tube: a novel method for NMR solution analysis of derivatized glass surfaces

Glass wool was placed within an NMR tube as a solid support for the covalent attachment of a molecule to allow for a simple one-dimensional 1H FT NMR solution analysis. This novel procedure avoids the use of expensive sample tubes or platforms, as required for magic angle or fast spinning, exotic pulse sequences, isotopic labeling or the use of a large number of scans to provide the ability to analyze the structure, mobility, ligand binding, and solvent interactions of the surface bound molecule.