Showing papers in "Journal of the Chemical Society, Faraday Transactions in 1994"

Reduction of cerias with different textures by hydrogen and their reoxidation by oxygen

Abstract: Successive reduction steps of CeO2 particles by hydrogen between 300 and 1070 K have been followed by temperature-programmed reduction (TPR) and in situ magnetic measurements on several samples with different BET surface areas. The nature of the phases present in cerias reduced between 670 and 1270 K was determined by X-ray analysis. Finally, reoxidation by oxygen or air was studied at room temperature for all the reduced samples.Magnetic and TPR results show a direct relationship between the degree of reduction and the BET surface area. Indeed, for most of the samples, the degree of reduction at 620–670 K determined by magnetism corresponded to the creation of one layer of Ce3+ ions at the surface of the ceria. A similar relationship between the BET surface area and the extent of reduction was established using the area of the low-temperature TPR composite peak, the maximum of which was found to be constant at 810 K.When the reduction progresses further into the bulk, two main phases were evidenced: first, and expanded cubic CeO2 –x phase derived from the initial ceria by a dilatation of the whole structure and, for deeply reduced samples, the hexagonal Ce2O3 phase. A new intermediate phase, cubic Ce2O3, was also observed on samples reduced at 1070–1170 K.Complete reoxidation by oxygen occurs at room temperature, for all reduction percentages below ca. 60 %, i.e. as long as the reduced phase remained in the cubic form. When the hexagonal Ce2O3 phase has been formed, the reoxidation cannot be completed at 294 K.

Time-resolved microwave conductivity. Part 1.—TiO2 photoreactivity and size quantization

Abstract: Charge-carrier recombination dynamics after laser excitation are investigated by time-resolved microwave conductivity (TRMC) measurements of quantum-sized (Q-) TiO_2, Fe^(III)-doped Q-TiO_2, ZnO and CdS, and several commercial bulk-sized TiO2 samples. After pulsed laser excitation of charge carriers, holes that escape recombination react with sorbed trans-decalin within ns while the measured conductivity signal is due to conduction-band electrons remaining in the semiconductor lattice. The charge-carrier recombination lifetime and the interfacial electron-transfer rate constant that are derived from the TRMC measurements correlate with the CW photo-oxidation quantum efficiency obtained for aqueous chloroform in the presence of TiO_2. The quantum efficiencies are 0. 4 % for Q-TiO_2, 1. 6 % for Degussa P25, and 2. 0 % for Fe^(III)-doped Q-TiO_2. The lower quantum efficiencies for Q-TiO_2 are consistent with the relative interfacial electron-transfer rates observed by TRMC for Q-TiO_2 and Degussa P25. The increased quantum efficiencies of Fe^(III)-doped Q-TiO_2 and the observed TRMC decays are consistent with a mechanism involving fast trapping of valence-band holes as Fe^(IV) and inhibition of charge-order recombination.

Physisorption of argon, nitrogen and oxygen by MCM-41, a model mesoporous adsorbent

Abstract: Adsorption isotherms of argon, nitrogen and oxygen have been determined at 77 K on a sample of MCM-41, a novel form of aluminosilicate. All the isotherms are Type IV in the IUPAC classification. The argon and oxygen isotherms exhibit well defined hysteresis loops, whereas the nitrogen isotherm is completely reversible. This unusual character is attributed to capillary condensation taking place within a narrow range of tubular pores of effective width 3.3–4.3 nm. MCM-41 shows considerable promise as a model mesoporous adsorbent.

Synthesis of SAPO-34: high silicon incorporation in the presence of morpholine as template

Abstract: Synthesis of small pore SAPO-34 molecular sieve has been achieved under optimum conditions, elucidated by a detailed study of the kinetics of crystallization, in the presence of morpholine as a template. Incorporation of high silicon content into the framework of SAPO-34 has been observed and corroborated by physico-chemical characterization studies. Magic-angle spinning (MAS) NMR investigation points to the existence of aluminosilicate domains in the SAPO framework.

FT Raman and FTIR studies of titanias and metatitanate powders

Abstract: FT Raman and FTIR/FTFIR skeletal spectra of different TiO2 powders, of both synthetic and commercial origin, and of Sr, Ba, Co and Ni metatitanates are reported and discussed in relation to the predictions of factor group analyses. The ability of vibrational techniques to show the presence of brookite impurities in both anatase and rutile, and of rutile in anatase, as well as to give morphological and surface information is emphasized. The spectra of SrTiO3, BaTiO3, NiTiO3 and CoTiO3 are also discussed in relation to their different structures (pervoskite and ilmenite-type).

Spectroscopic properties of aromatic dicarboximides. Part1.—N—H and N-methyl-substituted naphthalimides

Abstract: The photophysical properties of the N—H and N-methyl derivatives of 1,2-, 2,3- and 1,8-naphthalimides have been studied. The shift of the fluorescence emission position as a function of the solvent polarity indicates only a weak variation of dipole moment for the excited state compared with the corresponding value in the ground state (5.7 D for 2b, 2.8 D for 3b and <2 D for 4b, 1 D ≈ 3.335 64 × 10–30 C m, and 2b, 3b and 4b are N-methyl-1,2- naphthalimide, N-methyl-2,3-napthalimide and N-methyl-1,8-naphthalimide). However, important modifications of the photophysical properties are observed which depend on the relative position of the dicarboximide moiety on the naphthalene ring: the intersystem crossing rate constant of 4b increases dramatically by three orders of magnitude compared with that of 2b; simultaneously, the fluorescence quantum yield decreases from 0.77 to 0.03, although the corresponding rate constant, kf, increases. This difference is found to arise from the energy gap between the lowest1(π, π*) singlet excited state and the upper 3(n,π*) triplet state, which is of the order of 9 kcal mol–1 for 2b and less than 2 kcal mol–1 for 4b in acetonitrile solution. Protic solvents increase the energy difference between the n,π* and π,π* states thus decreasing the mixing of the two levels; as a consequence, the lifetime of 4b is increased, i.e. from <60 ps in hexane to 2.1 ns in trifluoroethanol. A triplet–triplet annihilation process occurs with the N-methyl derivatives 3b and 4b which leads to a monomer delayed fluorescence with the former, and mainly to a delayed excimer emission with the latter.

Delft molecular mechanics: a new approach to hydrocarbon force fields. Inclusion of a geometry-dependent charge calculation

Abstract: A new hydrocarbon force fields for saturated and non-conjugated unsaturated hydrocarbons has been developed. The most important difference between this force field and existing ones is its ability to produce a realistic, geometry-dependent charge distribution, the charges being calculated by the geometry-dependent method of Mortier (W. J. Mortier, S. K. Ghosh and S. Shankear, J. Am. Chem. Soc., 1986, 108, 4315). The use of this charge the calculation means that polarization effects can be reproduced. charge–Charge interactions are used between all the atoms in the molecules.Results show that by using this method a good hydrocarbon force field can be constructed. Heats of formation for a hundred compounds are calculated with an average absolute difference from experimental values of 1.02 kJ mol–1. Geometries, IR Frequencies and conformational energies are also well reproduced.

Thermodynamic properties of 0–6 mol kg–1 aqueous sulfuric acid from 273.15 to 328.15 K

Abstract: Generalised equations are presented for an extended form of the Pitzer molality-based thermodynamic model, involving an ionic strength-dependent third virial coefficient. Compatibility with the established formulation is retained. Osmotic coefficients, emf measurements, degrees of dissociation of the HSO–4 ion, differential enthalpies of dilution and heat capacities for aqueous H2SO4 from 273.15 to 328.15 K, 0–6.1 mol kg–1 and at 1 atm pressure have been critically evaluated. Treating this solution as the mixture H+–HSO–4–SO2–4–H2O, and using hydrogen sulfate dissociation constants from the literature, the model parameters were fitted to the data yielding a self-consistent representation of activities, speciation and thermal properties together with the standard potentials of four electrochemical cells and standard-state heat capacities of the SO2–4 ion as functions of temperature. The model equations represent the experimental data accurately (without the use of mixture parameters θHSO4, SO4 and ψHSO4, SO4, H), and should yield values of the osmotic coefficient that are suitable for use as an isopiestic standard over this temperature and molality range. The new model will also enable improved prediction of the properties of mixed acidic sulfate systems.

Time-resolved microwave conductivity. Part 2.—Quantum-sized TiO2 and the effect of adsorbates and light intensity on charge-carrier dynamics

Abstract: Charge-carrier recombination dynamics after a pulsed laser excitation are investigated by time-resolved microwave conductivity (TRMC) for quantum-sized (Q-) TiO2 and P25, a bulk-phase TiO2. Adsorbed scavengers such as HNO3, HCl, HClO4, isopropyl alcohol, trans-decalin, tetranitromethane, and methyl viologen dichloride result in different charge-carrier recombination dynamics for Q-TiO2 and P25. The differences include a current doubling with isopropyl alcohol for which electron injection into Q-TiO2 is much slower than into P25 and relaxation of the selection rules of an indirect-bandgap semiconductor due to size quantization. However, the faster interfacial charge transfer predicted for Q-TiO2 due to a 0. 2 eV gain in redox overpotentials is not observed. The effect of light intensity is also investigated. Above a critical injection level, fast recombination channels are opened, which may be a major factor resulting in the dependence of the steady-state photolysis quantum yields on l–1/2. The fast recombination channels are opened at lower injection levels for P25 than for Q-TiO2, and a model incorporating the heterogeneity of surface-hole traps is presented.

Variational transition-state theory and semiclassical tunnelling calculations with interpolated corrections: a new approach to interfacing electronic structure theory and dynamics for organic reactions

Abstract: In variational transition-state theory (VTST) and semiclassical tunnelling calculations, especially those with semiempirical potential-energy surfaces, it is sometimes desirable to match the classical energies and vibration frequencies of some points (e.g. the reactant, saddle point, product, van der Waals complex, ion–molecule complex) along the minimum-energy path (MEP) and in the reaction swath with high-level results, as this can improve the accuracy. This can be accomplished by adding a correction function to the calculated energies or frequencies. In this paper, we introduce a three-point or zero-order interpolated correction method which is based on the correction at three points, in particular the saddle point and two stationary points, one on each side of the MEP. We use the corrections at these points to build a correction function for the classical energy and for each vibrational mode frequency along the MEP. The function is calibrated such that the corrected result matches the accurate values at these stationary points. The functional forms to be used depend on the shape of the MEP under consideration and the relative correction values at those points. Similar treatments are applied to the determinant of the moment of inertia tensor along the reaction path and to the potential-energy function in non-adiabatic regions of corner-cutting tunnelling paths. Once parameters in the functional forms are determined, we then use the corrected energy, frequency and moments of inertia information together with other MEP and reaction swath data, as obtained directly from the potential-energy surface, to perform new VTST calculations. Details of the implementation are presented, and applications to reaction rate calculations of the OH + CH4→ H2O + CH3 and CF3+ CD3H → CF3H + CD3 reactions are included.

The Polanyi Lecture. The colourful world of complex-forming bimolecular reactions

Abstract: The author's Polanyi Lecture 1992 is summarized, discussing experimental examples of complex-forming bimolecular reactions, their identification by pressure and temperature dependence as well as isotope labelling studies, and their theoretical analysis The still fragmentary theoretical treatment involves all ingredients of unimolecular rate theory, relying heavily on quantum-chemical characterizations of reaction pathways and of the corresponding entrance and exit transition states The reactions are often governed by rotational as well as vibrational ‘channel switching’ Ion–neutral molecule and neutral–neutral molecule reactions show analogous behaviour, although quantitative differences are observedThis Polanyi memorial lecture was given when the 1992 Polanyi medal was presented to Professor J Troe at the 12th International Gas Kinetics Symposium in July 1992 in Reading

IR studies of cerium dioxide: influence of impurities and defects

Abstract: An infrared study of CeO2 is presented which allows discrimination of the bands due to residual carbonaceous impurities from the bands arising from multiphonon absorption and electronic transitions induced by atomic defects CO adsorption experiments show the presence of coordinatively unsaturated (cus) Ce3+ or Ce4+ surface ions depending on the nature of the pretreatment The role of plasmon–phonon coupling in the infrared examination of semiconductors is also stressed

IR study of ethene and propene oligomerization on H-ZSM-5: hydrogen-bonded precursor formation, initiation and propagation mechanisms and structure of the entrapped oligomers

Abstract: The oligomerization reaction of ethene and propene on H-ZSM-5 has been studied by fast FTIR spectroscopy. Oligomerization proceeds through: (i) formation of short-lived hydrogen-bonded precursors by interaction of the alkene with the internal acidic Bronsted sites, (ii) a protonation step and (iii) a chain-growth step. The relative strength of the hydrogen bonds in the ethene–OH and propene–OH π-complexes (precursors) is estimated on the basis of the downward shift of both the ν(OH) and ν(CC) frequencies (–389 and –11 cm–1 for ethene and –539 and –19 cm –1 for propene). For both molecules, the protonation of the precursors is the rate-determining step of the oligomerization process. The chain-growth mechanism and the structure of the entrapped oligomers are discussed on the basis of computer graphic and molecular dynamics simulations. Mainly linear of low branched products are formed whose length and structure is essentially determined by the steric hindrance imposed by the zeolitic framework.

High-resolution electron microscopy studies of a microporous carbon produced by arc-evaporation

Abstract: The soot produced as a byproduct of fullerene synthesis by arc-evaporation consists of a microporous carbon with a surface area, after activation with carbon dioxide, of ca. 700 m2 g–1. Here, we investigate the structure of this material, and its appearance after electron irradiation and high-temperature heat treatment, using high-resolution electron microscopy. We show that the heat treatment transforms the new carbon into a structure containing large, tube-like pores, rather than into polycrystalline graphite. This suggests that the arc-evaporated carbon may have a novel, fullerene-related microstructure, and that it may be the precursor for nanotube formation.

Derivation of interatomic potentials for microporous aluminophosphates from the structure and properties of berlinite

Abstract: A Born model using formal oxidation states has been derived for aluminophosphates, based on the mineral berlinite, which is compatible with existing potentials for ionic materials. Empirical fitting was used to determine the phosphorus–oxygen potential, based upon the crystal structure, elastic and dielectric properties. This model is comparable to previous partial-charge models for the reproduction of the elastic, dielectric, piezoelectric and phonon properties of berlinite, while being superior for the crystal structure. The thermal expansion of berlinite within the quasi-harmonic approximation has also been determined. Calculations on MAPO-36 demonstrate the transferability of the potential model to other aluminophosphates.

Interaction of water with α,α-trehalose in solution: molecular dynamics simulation approach

Abstract: Molecular simulations of an aqueous solution of α,α-trehalose (α-D-glucopyranosylα-D-glucopyranoside) have been carried out to further the understanding of the effect of α,α-trehalose as a protecting agent against water stress in biological systems. The hydrogen-bond network and water dynamics were found to be only slightly altered compared with pure water (SPC/E model). Some internal hydrogen bonds in trehalose stabilize the conformation that was found to have glycosysidic dihedral angles of 215° and 216°. It is found that trehalose can fit into a water structure involving at least ten water molecules per trehalose. Results support the view that the ability of trehalose to protect against water stress is due to the stabilization of biological structures and not to modification of the properties of water.

Comparative IR-spectroscopic study of low-temperature H2 and CO adsorption on Na zeolites

Abstract: Extraframework cation sites in the sodium forms of the zeolites ZSM-5, mordenite, Linde-4A and faujasite-type X and Y have been investigated by using low-temperature adsorption of dihydrogen and carbon monoxide as IR spectroscopic probes. The extent of H—H and C—O bond polarization was found to be dependent not only on the cation electrostatic field, but also on the neighbouring oxygen atoms of the zeolite framework. The influence of these oxygen atoms is most keenly felt by adsorbed molecular hydrogen, but they also affect the IR frequency shift of the stretching vibration of adsorbed carbon monoxide. The Si : Al ratio of the zeolite framework modulates the basic strength of the oxygen atoms, and this was found to be reflected in the IR stretching frequency of both adsorbed molecules, H2 and CO.

Some thermodynamic properties of aqueous amino acid systems at 288.15, 298.15, 313.15 and 328.15 K: group additivity analyses of standard-state volumes and heat capacities

Abstract: Densities and heat capacities have been measured for aqueous solutions of L-aspartic acid, L-glutamic acid and α-aminobutyric acid at 288.15, 298.15, 313.15 and 328.15 K. These data have been used to calculate apparent molar volumes, V2, ϕ, and apparent molar heat capacities, Cp, 2, ϕ, which in turn have been used to calculate standard-state volumes, text-decoration:overlineV°2, and standard-state heat capacities, text-decoration:overlineC°p, 2. Helgeson, Kirkham and Flowers equations, for neutral organic species in water, have been used to model the calculated standard-state volumes and heat capacities of the amino acids as a function of temperature at constant pressure. These data, and data previously reported for amino acid systems, have been used as input for a group additivity type analysis. The merits of the additivity scheme are discussed, and attempts are made to interpret the predicted trends in the group contributions as a function of temperature.

Host–guest complexes of cucurbituril with the 4-methylbenzylammonium lon, alkali-metal cations and NH4+

Abstract: Kinetic measurements indicate the existence of two different complexes of cucurbituril with 4-methylbenzylammonium ions: (i) an association complex, where the ammonium group binds to one of the polar portals of cucurbituril and the hydrophobic part extends into the solvent, and (ii) an inclusion complex, where the hydrophobic part extends into the cavity of cucurbituril. This complex is used as an indicator for the binding of simple monovalent cations to cucurbituril. Stability constants are reported for the 1 : 1 complexes of cucurbituril with different cations.

Photocatalysts with tunnel structures for decomposition of water. Part 1.—BaTi4O9, a pentagonal prism tunnel structure, and its combination with various promoters

Abstract: Photocatalysts have been prepared by impregnating barium tetratitanate, BaTi4O9, which has a pentagonalprism tunnel structure, with aqueous solutions of CoCl2, Ni(NO3)2, In(NO3)3, RuCl3, H2IrCl6 or H2PtCl6, and then activating with either reduction or oxidation. For decomposition of water under irradiation with light from a Xe lamp, reduction caused low photocatalytic activities. Oxidation of RuCl3-impregnated BaTi4O9 at 848 K led to active photocatalysts which produce H2 and O2 in the correct stoichiometric ratio. The photocatalytic activity increased with an increase in the amount of loaded Ru until it reached 1 wt. %, and remained nearly constant up to 3 wt. %. The X-ray photoelectron spectra showed that the active Ru was in a tetravalent state, forming RuO2 on the BaTi4O9 surface. UV diffuse reflectance spectra showed that BaTi4O9 had a threshold of absorption of light at around 410 nm which reached a maximum at 320 nm. From high-resolution transmission electron microscopy and microanalysis the spherical RuO2 particles of 1.4–3.0 nm in diameter were found to be dispersed uniformly on the regular lattice of BaTi4O9. It is concluded that the pentagonal-prism tunnel structure of BaTi4O9 has a ‘nest’ effect and is responsible for the high dispersion of RuO2 particles, which leads to the high photocatalytic activity.

Adsorption on MCM-41 mesoporous molecular sieves. Part 1.—Nitrogen isotherms and parameters of the porous structure

Abstract: Nitrogen adsorption isotherms have been measured on a series of aluminosilicate and titanosilicate MCM-41 Molecular sieves, whose mean pore radius varied from ca 09 to ca 2 nm By means of comparison plots the nature of the adsorption on these materials was found to depend strongly on their pore size With pores of radius of around 1 nm multilayer coverage of the pore walls occurs If the radius is increased to 15–18 nm the mechanism of adsorption changes into a two-stage one, ie the multilayer coverage of the pore walls is suceeded by the spontaneous filling of the pore volume by capillary condensation without hysteresis In even greater pores the usual capillary condensation with hysteresis occursThe estimation of pore structure parameters was based on standard methods of adsorption isotherm processing, including the calculation of the pore size distribution from the desorption branch of the hysteresis loop With the smaller pore materials, where the Kelvin equation does not hold, the estimation was based on the cylindrical pore model A detailed knowledge of the pore structure of MCM-41 materials was thus obtained

FTIR study of carbon monoxide adsorption on ceria: CO2–2 carbonite dianion adsorbed species

Abstract: CO has been adsorbed in doses at room temperature by ceria which had been reduced with CO and then evacuated at 873 K, or only evacuated at this temperature, as well as by a Pd/CeO2 catalyst, H2-reduced and evacuated at 823 K. From comparison of the observed IR spectra with literature results concerning matrix-isolated Cs2CO2 species, the formation of two carbonite CO2–2 species adsorbed over reduced ceria may be inferred. One of these species, with C2v geometry and with IR bands at around 1300 and 1160 cm–1, was formed before the other one, with a Cs structure and characterized by IR bands at 1270, 1071 and 771 cm–1. A band at 1465 cm–1 was only tentatively assigned to a third carbonite species. CO2–2 species ultimately lead to CO2–3 species when they are heated in vacuum.

Electrosteric stabilisation of colloidal zirconia with low-molecular-weight polyacrylic acid. An atomic force microscopy study

Abstract: The adsorption of low-molecular-weight polyacrylic acid (Mr= 2000) on zirconia has been studied as a function of pH. In this study, an atomic force microscope (AFM) was used to monitor directly the changes in polymer conformation at the solid/water interface. Force–distance profiles were obtained at AFM scan rates equivalent to those expected for Brownian collision rates. The size of the steric interaction lengths between the surfaces was seen to increase as a function of increasing pH.These increases were related to the increasing size of the adsorbed polyelectrolyte owing to decreasing segment–surface affinity and increasing segment–segment repulsions at higher pH. Data at low pH were used to estimate the size of the uncharged collapsed polymer coil at the interface. Best fits of the long-range electrical double-layer interactions allowed an estimate of the effective plane of charge at each pH for the adsorbed polyelectrolyte.

Use of a neural network to determine the boiling point of alkanes

Abstract: Back-propagation neural networks (NNs) are useful for the study of quantitative structure–activity relationships or structure–property correlations. Models of relationships between structure and boiling point (bp) of 150 alkanes were constructed by means of a multilayer neural network (NN) using the back-propagation algorithm. The results of our NN were compared with those of other models from the literature, and found to be better. The boiling points of the 150 alkanes were then predicted by removing 15 compounds (test set) and using the 135 other molecules as a training set. Using the same process, all the compounds in the data bank were then predicted in groups of 15 compounds. The results obtained were satisfying.

Water adsorption in active carbons described by the Dubinin–Astakhov equation

Abstract: It is shown that the adsorption of water by a variety of active carbons can be described within the framework of Dubinin's theory. Owing to the low values of the characteristic energy, E(0.8–2.5 kJ mol–1), the Dubinin–Astakhov equation becomes S-shaped in the range 0.3 < p/po <0.7 and provides a good basis for the fit of the adsorption branch of type V isotherms near room temperature. The parameters of the equation are almost temperature invariant and consequently a good agreement is also found in many cases for the enthalpies of immersion into water, as predicted by the extension of Dubinin's theory.

Photochromism, thermochromism and solvatochromism of some spiro[indolinoxazine]-photomerocyanine systems: effects of structure and solvent

Abstract: Three spiro[indoline-naphthoxazines] and a spiro[indoline-phenanthroxazine], which exhibit photochromic and thermochromic properties, have been investigated. Solvent and structure effects on the absorption spectra of the merocyanines produced under UV irradiation and kinetic parameters for the ring-closure and ring-opening reactions were studied. Positive solvatochromism was found, indicating that the opened form is a weakly polar species. Equilibrium constants and rate constants for the forward and back reactions spiroxazine ⇄ merocyanine increase with increasing the solvent polarity and with electron-donating groups in the oxazine moiety. The reaction is endothermic by 10–20 kJ mol–1 and almost isoentropic. The activation entropy is generally negative, while the activation Gibbs energy is approximately independent of solvent and structure.

Investigation of solvent effects on pericyclic reactions by computer simulations

Abstract: A combination of quantum and statistical mechanics is being used to probe the origins of solvent effects on the kinetics of organic reactions. Ab initio molecular orbital calculations provide gas-phase reaction paths and partial charges for the reacting systems. The reaction paths are then followed by Monte Carlo simulations in periodic cells containing hundreds of solvent molecules, and the changes in Gibbs free energies of solvation are obtained. Results are provided for several prototypical pericyclic reactions : Diels–Alder cycloadditions for methyl vinyl ketone with cyclopentadiene and the dimerization of cyclopentadiene, the Claisen rearrangement of allyl vinyl ether, and the electrocyclic ring opening of cyclopropanones to oxyallyls. Detailed insights are obtained on issues such as the acceleration of the Diels–Alder reactions and Claisen rearrangement in water, and the electronic nature of oxyallyls.

Formation of two-dimensional structures from colloidal particles on fluorinated oil substrate

Abstract: We propose a new type of liquid substrate, perfluorinated oil (F-oil), for the formation of two-dimensional arrays from colloidal particles. The appropriate conditions for particle ordering (experimental cell, type and concentration of surfactants, etc.) are reported. Large and well ordered structures from µm-sized latex particles are obtained. Ordered clusters of globular protein (ferritin) macromolecules are also observed. The structures formed are directly transferred (after the F-oil evaporation) onto a solid substrate for subsequent study by means of optical and electron microscopy. The mechanism of the ordering process is studied and the advantages and disadvantages of the liquid substrates (in comparison with the solid ones) are discussed. Some possible ways for control of the ordering process and for improvement of the quality of the arrays are pointed out.

Kinetic model for serum albumin adsorption : experimental verification

Abstract: When human serum albumin is adsorbed at a hydrated metal oxide surface, the amounts which can be desorbed by replacing the protein solution with pure solvent steadily decrease. A quantitative kinetic model involving two modes of adsorption, reversible and irreversible, is inferred, and tested by allowing the adsorption and desorption to take place on the surface of planar optical waveguides, and determining the surface coverage from the shift in the mode indices of guided waves due to the adsorption. The method allows the surface coverage to be determined to a precision of ca. 1 ng cm–2 every 15–30 s. Excellent agreement with the model was obtained.

Identification of isolated Pt atoms in H-mordenite

Abstract: The state and dispersion of Pt supported on mordenite have been studied using FTIR spectroscopy, CO Chemisorption, and H–D isotope exchange of cyclopentane. Under conditions for which other criteria indicate the presence of monatomic Pt0, a characteristic IR band of adsorbed CO is identified at 2123 cm–1. The position of this band does not change with CO coverage, indicating an interaction between CO and highly dispersed Pt. A significant blue shift of the band with respect to that of CO on multiatomic Pt clusters and the disappearance of this band upon neutralizing the acidic OH groups show that the Pt atoms are electron-deficient and interact with zeolite protons. These FTIR data thus confirm the presence of extremely small Pt clusters, presumably [Pt1—Hz]z+ adducts, in H-mordenite.