[Show abstract][Hide abstract] ABSTRACT: The settling of marine diatoms Amphora coffeaeformis onto a photocatalytic titanium dioxide surface was monitored by ATR-IR. Attachment of the diatoms via their mucilaginous secretions was monitored via observation of protein amide I and II linkages, carboxylate linkages from a uronic acid polysaccharide, and sulfate ester groups. Exposure to UV-A light resulted in the rapid removal of the groups attached to the photocatalyst surface, demonstrating the potential antifouling capability of a TiO 2 anatase surface.
Materials Science Forum 01/2012; 700:227-230. DOI:10.4028/www.scientific.net/MSF.700.227
[Show abstract][Hide abstract] ABSTRACT: The preparation of ligand-functionalised copper(II) hydroxide (Cu(OH)(2)) particles and their conjugation with hydrophobic CdSeS quantum dots (QDs) is reported. The photoluminescence of the QDs is efficiently quenched upon their conjugation with the functionalised Cu(OH)(2) particles. Cu(OH)(2) was functionalised with 2,2'-dipyridyl (2,2-bipy) and n-octanoic acid (OcA), by adsorption of the desired ligand to Cu(OH)(2) suspended in solvent. The resulting functionalised Cu(OH)(2) substrates were characterised using infrared, UV-visible diffuse reflectance, and X-ray photoelectron spectroscopic techniques, TEM imaging, and micro- and thermogravimetric analysis. The spectral data indicated that both 2,2-bipy and OcA coordinated to Cu(OH)(2) in a bidentate manner. The functionalised Cu(OH)(2) substrates were introduced to suspensions of hydrophobic CdSeS QDs, and the resulting QD-functionalised Cu(OH)(2) conjugates were also characterised using spectroscopic and electron microscopy techniques. UV-visible diffuse reflectance spectroscopy indicated the extension of the optical absorption of the Cu(OH)(2) to longer wavelengths upon conjugate formation.
Journal of Colloid and Interface Science 03/2010; 346(2):288-95. DOI:10.1016/j.jcis.2010.03.010 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Avidin-biotin bioconjugation reactions have been carried out on CdS nanoparticle films in H2O and D2O and investigated using in situ ATR-IR spectroscopic techniques. The experimental procedure involved the sequential adsorption of mercaptoacetic acid, the protein avidin, and the subsequent binding of the ligand biotin. The IR spectra of the solution-phase species mercaptoacetic acid, avidin, and biotin, at pH=7.2 were generally found to be similar in both H2O and D2O, with some minor peak shifts due to solvation changes. The IR spectra of the adsorbed species suggested that avidin may have undergone a conformational change upon adsorption to the CdS surface. In general, adsorption-induced conformational changes for avidin are likely, but to our knowledge have not been previously reported. The conformation of adsorbed avidin appeared to change again upon the binding of biotin, with the spectral data suggesting partial reversion to its native solution conformation.
[Show abstract][Hide abstract] ABSTRACT: Adsorption and desorption kinetics at the solid/solution interface have been monitored using attenuated total reflection infrared (ATR-IR) spectroscopy to evaluate this approach as an alternative to equilibrium (adsorption isotherm) measurements of adsorption affinity. The adsorption and desorption kinetics of oxalate ion to anatase TiO2 have been measured by using aqueous 1 x 10(-4) mol L(-1) oxalic acid solutions at pH 4 and thin films of TiO2 particles deposited on an internal reflection prism. The adsorption kinetics were obtained from the absorbance versus time behavior of major adsorbed oxalate infrared absorptions with flow of oxalic acid solution followed by flow of solution not containing oxalic acid to measure the desorption kinetics. Regression analysis of the desorption data based on Langmuir kinetics yielded three distinct pseudo-first-order rate constants with desorption half-lives of 300, 14, and 2 min, indicating the presence of three adsorbed oxalate species of different adsorption affinities. The most slowly desorbing and most strongly bound adsorbate species is likely to be a bidentate chelating oxalate ion from comparisons with the IR spectra of coordination compounds involving oxalate ligands. Regression analysis of the adsorption data was unable to yield the corresponding pseudo-first-order adsorption constants and prevented the calculation from kinetics data of Langmuir adsorption affinity constants. Measurement of adsorption and desorption kinetics by ATR-IR spectroscopy is expected to provide a relatively rapid means of assessing the presence of species of different adsorption affinities in systems in which their spectra are not well differentiated.
[Show abstract][Hide abstract] ABSTRACT: The square planar Ag(I) stereochemistry is generally acknowledged as rare, with only ∼2% of all reported silver complexes possessing this stereochemistry. Many researchers reporting such complexes often mistakenly believe that their example is one of only a handful of previously reported examples. This is despite the fact that there are currently around 65 well characterised complexes containing square planar Ag(I) ions, about half of which are coordination polymers. In this review, we critically examine each example and draw attention to trends that arise in their formation. The scope is limited to ‘traditional’ coordination complexes. Inorganic complexes containing extended mineral like structures, and complexes containing silver-π or silver-arene motifs are not considered in this review.
[Show abstract][Hide abstract] ABSTRACT: Ligand exchange reactions at the surface of oleate- and trioctylphosphine oxide (TOPO)-capped CdS quantum dots have been studied with attenuated total reflection infrared (ATR-IR) spectroscopy, using thin films deposited from organic solvent suspensions. The oleate and trioctylphosphine capping ligands were found to form highly ordered and densely packed monolayers on the CdS surface. Adsorbed oleate is coordinated to CdS in a chelating bidentate manner through the carboxylate functional group, while adsorbed trioctylphosphine oxide is coordinated though the P=O functional group and appears to have numerous adsorption environments on the CdS surface. Exposure of such films to aqueous solution was found to cause partial delamination of the films from the ATR prism interface which was reversible upon redrying. Ligand exchange reactions on the oleate- and trioctylphosphine-capped CdS films were studied in situ at room temperature by allowing the films to be exposed to dilute aqueous solutions of thiol-containing ligands. Oleate and trioctylphosphine oxide are both strongly adsorbed to the CdS surface, and ligand exchange with monothiol-containing ligands has been found to be highly dependent upon experimental conditions, in particular pH, where exchange is only observed at solution pH where the exchanging ligand is uncharged. This is attributed to the inability of a charged ligand to penetrate the hydrophobic polymethylene layer on the CdS surface.
[Show abstract][Hide abstract] ABSTRACT: The adsorption of the ligands alpha-lipoic acid, dihydrolipoic acid, and dithiothreitol to films of deposited CdS nanoparticles was studied in situ by ATR-IR spectroscopy. For alpha-lipoic acid and dihydrolipoic acid, the spectra of the adsorbed species closely resemble those of the respective solution species. However, for dithiothreitol, the spectrum of the adsorbed species is significantly different from that of the solution species and is attributed to an interruption of intermolecular hydrogen bonding upon adsorption to the CdS. The S-H stretching absorption of the dihydrolipoic acid solution species at pH=8.6 is observed at 2542 cm(-1). The corresponding absorptions for dithiothreitol occur at 2578 and 2528 cm(-1) and are attributed to monomers and dimers. Adsorption of dihydrolipoic acid and dithiothreitol is found to occur via both thiol functional groups and an additional interaction between the carboxylate and the CdS surface. The adsorption of alpha-lipoic acid to CdS in the presence of light proceeds with photo-oxidation of the CdS surface and reductive cleavage of the disulfide bond of alpha-lipoic acid to produce some adsorbed dihydrolipoic acid and thiosulfate. The adsorption of alpha-lipoic acid to CdS in the absence of visible light shows no photo-oxidation and suggests that adsorption occurs via retention of the disulfide bond. The adsorption isotherm data for dihydrolipoic acid and dithiothreitol gave good fits to the Langmuir isotherm, with adsorption constants higher than those for monothiol-containing ligands on CdS. The Langmuir adsorption constant for n-octanoic acid on CdS indicates that the additional interaction between the carboxylate group of dihydrolipoic acid and the CdS is weak in comparison with the dithiol interaction with CdS.
[Show abstract][Hide abstract] ABSTRACT: CdSexSy nanocrystals were synthesized in eight solvents that have different coordinating properties, trioctylphosphine oxide, trioctylphosphine, triphenylphosphine, oleylamine, hexadecylamine, dioctylamine, trioctylamine, and 1-octadecene at 230−300 °C. These nanocrystals exhibited high photoluminescence, which could be tuned over most of the visible region by changing the Se/S ratio or the solvent. The nanocrystals were characterized using UV−vis and IR spectroscopy, TEM, EDS, XRD, and NMR. 31P NMR and IR studies provided vital information about the nanocrystal surface capping ligands, indicating that those prepared in noncoordinating solvents were stabilized in solution mainly by oleic acid while those prepared in the coordinating solvents were stabilized mainly by solvent, phosphine and phosphine sulfide ligands, and some oleic acid. The hexagonal or cubic phase of these nanocrystals can be selectively prepared at temperatures as high as 300 °C by choosing the appropriate solvent.
Chemistry of Materials 09/2007; 19(21). DOI:10.1021/cm070818k · 8.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Probing the surface chemistry of thiol ligand binding to cadmium chalcogenide nanocrystals is important to clarify factors involved in quantum dot stability and surface functionalization. Deposited CdS nanocrystal films have been used in this work as model quantum dot surfaces for ligand adsorption studies. The adsorption of mercaptoacetic acid, mercaptopropionic acid, and mercaptoethanol, from aqueous solution to CdS thin films, has been studied by in situ infrared spectroscopy. The absence of a S-H stretch absorption for the adsorbed species shows that adsorption occurs via the deprotonated thiol group, and the spectrum of the adsorbed carboxylic acid species closely resembles those of the solution ligands. Adsorption of mercaptoacetic acid and of mercaptopropionic acid resulted in pKa(COOH) decreases of 1.5 and 0.5, respectively. Significant changes in the spectrum of mercaptoethanol upon adsorption have been observed, but the present uncertainty in mercaptoethanol spectral interpretation does not provide structural inferences. Adsorption isotherms determined from the spectral data indicate strong thiol adsorption to CdS. The adsorption isotherms have been fitted to both Langmuir and Freundlich equations, with the latter providing a better fit. This may be attributed to a change in the probability of adsorption to vacant surface sites due to the increased CdS surface negative charge as the surface coverage increases.
[Show abstract][Hide abstract] ABSTRACT: The flexible ligand 4,6-bis(3‘-pyridylmethylsulfanyl)dibenzofuran (L) was synthesized in a three-step reaction sequence. This new ligand was complexed with both AgClO4 and AgNO3, in a 1:2 metal-to-ligand ratio. The isomorphous structures were one-dimensional coordination polymers each containing a rare square-planar Ag(I) connector. The X-ray structures showed numerous π interactions.