Showing papers in "Journal of the Chemical Society, Faraday Transactions in 1998"
TL;DR: In this article, a self-consistent field approach is used to model the adsorbed layers of casein-based emulsion gels and to understand the excellent stabilizing properties of the caseins.
Abstract: Physical properties of oil-in-water emulsions stabilized by milk proteins are determined largely by the nature of the adsorbed layer at the surface of the dispersed droplets. There are two distinct classes of protein: the disordered caseins (especially αs1-casein and β-casein) and the globular whey proteins (especially β-lactoglobulin). Substantial differences exist between these two classes in terms of adsorbed layer structure and surface rheological properties at the oil/water interface. Theoretical modelling of adsorbed layers of αs1-casein and β-casein with a simple self-consistent-field approach is useful for understanding the excellent stabilizing properties of the caseins, and in interpreting the aggregation behaviour of casein-based emulsions as a function of ionic strength and pH. The creaming behaviour and droplet flocculation are sensitive also to the concentration of non-adsorbed casein. In systems containing milk protein and small-molecule surfactant, competitive adsorption has a strong influence on orthokinetic emulsion stability, and on the viscoelasticity of heat-set β-lactoglobulin-stabilized emulsion gels. Computer simulation of model particle gel networks shows considerable promise for providing new insight into the relationship between interparticle interactions and the structure and rheology of emulsion gels.
352 citations
TL;DR: Cavity ring-down spectroscopy (CRDS) is a laser-based absorption spectrograph that is starting to find extensive application as a consequence of the very high sensitivity of the method compared with more traditional infrared spectrograms as discussed by the authors.
Abstract: Cavity ring-down spectroscopy (CRDS) is a laser-based absorption spectroscopy technique that is starting to find extensive application as a consequence of the very high sensitivity of the method compared with more traditional absorption spectroscopy techniques. We describe the experimental implementation of CRDS and its application to a number of areas of research including laser diagnostics of hostile environments, reaction kinetics and spectroscopy, with particular emphasis on our ongoing studies of the fast (sub-nanosecond) predissociation of electronically excited states of small molecules and radicals.
343 citations
TL;DR: The application of small and weakly interacting probe molecules for the characterization of acidic and basic properties by FTIR spectroscopy is exemplified by using H- and alkali cation-exchanged zeolites as typical solid Bronsted and Lewis acids and Lewis bases as discussed by the authors.
Abstract: The application of small and weakly interacting probe molecules for the characterization of acidic and basic properties by FTIR spectroscopy is exemplified by using H- and alkali cation-exchanged zeolites as typical solid Bronsted and Lewis acids and Lewis bases. Criteria for the selection of probe molecules are given. Bronsted acidity can be characterized by the H-bonding method when CO and N2 are used as molecular probes. Quantum chemical calculations are shown to provide important additional information on the electronic nature of the adsorption interaction and the vibrational behaviour of the probe molecule. Lewis acidity dominates in cation-exchanged zeolites for small cations (Li+, Na+) whereas basic properties develop with increasing cation radius. CO, CO2, N2 and CH4 interact with cation centers, the interaction energy decreasing with increasing cation radius. CO at very low equilibrium pressures permits a siting of Na+, and the Al distribution in six-rings (SII-sites) can be probed. CH4 interacts with cations in the M+···H3CH configuration having C3v symmetry. CH-acids such as Cl3CH(D), acetylene and methylacetylene, are shown to be potentially suitable probe molecules for basic properties using the H-bonding method. All three molecules undergo Oz2−···H–C H-bonding and the induced red-shift of the C–H stretching frequency permits a ranking of the base strength of a given series of materials.
322 citations
TL;DR: In this paper, the textural and structural properties of high specific surface area (HS) CexZr1-xO2 mixed oxides (CeZrMO) and their modification upon thermal aging have been investigated.
Abstract: The textural and structural properties of high specific surface area (HS) CexZr1-xO2 mixed oxides (CeZrMO) and their modification upon thermal aging have been investigated. Results from BET area determination and complete porosity analysis, as well as high-resolution electron microscopy, XRD, Raman and FTIR spectroscopies are presented. Some relationships between the molar composition of the binary systems and their textural and structural properties are presented. In addition, it has been possible to propose an explanation for structural features of the mixed oxides (solid-solution structures and possible phase segregation) as a function of Ce content, a point of great interest for the knowledge of phase composition and stability of CeZrMO.
189 citations
TL;DR: In this article, a review of recent quasi-classical trajectory calculations of the dynamics of some prototypic elementary reactions, from state-resolved differential cross-sections (DCS) to thermal rate constants, are reviewed.
Abstract: Recent quasi-classical trajectory (QCT) calculations of the dynamics of some prototypic elementary reactions, from state-resolved differential cross-sections (DCS) to thermal rate constants, are reviewed. The reactions studied are H + H2, F + H2, Cl + H2 and O(1D) + H2, for which reliable potential-energy surfaces (PES) are available. The QCT results are analysed in the light of the most recent quantum mechanical (QM) calculations and experimental findings. In general, QCT integral, differential reaction cross-sections and rate constants are found to be in good agreement with their QM and experimental counterparts, indicating that, for the systems considered, the motion of the nuclei during reactive encounters is largely classical and that quantum effects, such as tunnelling, play a relatively minor role in the overall dynamics. The importance of the zero-point energy of the transition state is highlighted as one of the most important deficiencies of the QC treatment. The need for precise QC and quantal simulations of the actual laboratory measurements, in order to identify experimental quantum effects clearly, is emphasized. Finally, the importance of the calculation and measurement of vector correlations in chemical reactions is stressed and some examples are presented.
186 citations
TL;DR: In this paper, the ionic structure of organic electrolyte solutions was investigated by means of Raman spectroscopy for mixed aprotic solvents that dissolve lithium salts, and the results showed that the number of EC molecules interacting with the lithium cation (Li+) was higher than that of DMC in a mixed EC+DMC (50:50 by volume) system.
Abstract: The ionic structure of organic electrolyte solutions has been investigated, by means of Raman spectroscopy for mixed aprotic solvents that dissolve lithium salts. The solutions consisted of binary solvent systems of a high permittivity solvent (ethylene carbonate, EC) mixed with low viscosity alkyl carbonates (dimethyl carbonate, DMC, and diethyl carbonate, DEC) or a linear alkyl ether (1,2-dimethoxyethane, DME) and of LiCF3SO3, LiPF6 and LiN(C2F5SO2)2 as the solute. The Raman shifts based on the solvents varied with the sort of dissolved lithium salts and their concentration. The ion solvation was estimated from the side-bands of the Raman scattering for the C–O stretch of single bonds of the carbonate groups and for the symmetric ring deformation of EC. The number of EC molecules interacting with the lithium cation (Li+) was higher than that of DMC in a mixed EC+DMC (50:50 by volume) system. The apparent solvation number of Li+ in 1.5 mol dm-3 LiCF3SO3 solution was about 2.8 in EC+DMC, whereas that in 1.5 M LiPF6 solution was about 3.9. Specific solvation of Li+ was distinguished in EC+DME (50:50), where DME predominantly coordinates to Li+. However, it was also confirmed that EC, which has a lower donicity, interacts with Li+ even in the EC+DME system. That is, the solvation number of EC in LiCF3SO3/(EC+DME) remained ca. 1.0 even in high salt concentrations.
184 citations
TL;DR: In this paper, three perylene derivatives with fluorescent quantum yields of 100% were suggested as new useful standards for the determination of fluorescence quantum yields, which are N,N′-bis(1-hexylheptyl)-3,4:9,10-perylenebis(dicarboximide) and perylene-3, 4, 9, 10-tetracarboxylictetramethyl ester which dissolve in organic solvents.
Abstract: Three perylene derivatives with fluorescent quantum yields of 100% are suggested as new useful standards for the determination of fluorescence quantum yields. The compounds are N,N′-bis(1-hexylheptyl)-3,4:9,10-perylenebis(dicarboximide) and perylene-3,4,9,10-tetracarboxylictetramethyl ester which dissolve in organic solvents, and the water-soluble perylene-3,4,9,10-tetracarboxylic acid tetrapotassium salt. All compounds are easily handled, very photostable, and show only minor quenching by oxygen under normal experimental conditions.
179 citations
TL;DR: In this paper, two photocatalytic reactions on suspended titanium dioxide particles were combined via platinum electrodes and cation-exchange membranes, and water was continuously split into hydrogen and oxygen under photoirradiation.
Abstract: Photochemical splitting of water was achieved by combining two photocatalytic reactions on suspended titanium dioxide particles, namely, the reduction of water to hydrogen using bromide ions, which were oxidized to bromine and the oxidation of water to oxygen using FeIII ions, which were reduced to FeII ions. These two reactions were carried out in separate compartments and combined via platinum electrodes and cation-exchange membranes. At the electrodes, FeII ions were oxidized by bromine, and protons were transported through the membranes to maintain the electric neutrality and pH of the solutions in the two compartments. As a result, water was continuously split into hydrogen and oxygen under photoirradiation. Reversible reactions on photocatalysts often suffer from the effects of back reactions, unless the products are removed. In the present system the problem is largely prevented, because the concentrations of the products in solution are automatically maintained at a low level.
173 citations
TL;DR: A graph set approach was used to classify the structural differences and similarities of the polymorphs, the results of which indicated packing motifs common to three of the four known crystal structures as discussed by the authors.
Abstract: Sulfathiazole, a compound that forms four known crystal structures, has been examined with a view to understanding its polymorphism. A graph set approach was used to classify the structural differences and similarities of the polymorphs, the results of which indicated packing motifs common to three of the four structures. By combining this analysis with experimental morphological data, it has been possible to examine the origins of the observed solvent dependence of polymorph appearance in this system. In particular, the possible link between the observed hydrogen-bond motifs of each form and the associated processes of nucleation and crystal growth from n-propanol, nitromethane, ethanol, water and ammonia solution, have been considered.
161 citations
TL;DR: In this article, the 2 A structure of glucoside bound concanavalin-A was reported and compared with the 2A structure of the mannoside complex, and the interaction energies of the substrate in each crystallographic subunit were calculated by molecular mechanics and found to be essentially the same for both sugars.
Abstract: Crystallographic and computational methods have been used to study the binding of two monosaccharides (glucoside and mannoside) to concanavalin-A. The 2 A structure of glucoside bound concanavalin-A is reported and compared with the 2 A structure of the mannoside complex. The interaction energies of the substrate in each crystallographic subunit were calculated by molecular mechanics and found to be essentially the same for both sugars. Further energy minimisation of the active site region of the subunits did not alter this conclusion. Information from crystallographic B-factors was interpreted in terms of mobility of the sugars in the combining site. Molecular dynamics (MD) was employed to investigate mobility of the ligands at the binding sites. Switching between different binding states was observed for mannoside over the ensemble in line with the crystallographic B-factors. A calculated average interaction energy was found to be more favourable for mannoside than glucoside, by 4.9±3.6 kcal mol-1 (comparable with the experimentally determined binding energy difference of 1.6±0.3 kcal mol-1). However, on consideration of all terms contributing to the binding enthalpy a difference is not found. This work demonstrates the difficulty in relating structure to thermodynamic properties, but suggests that dynamic models are needed to provide a more complete picture of ligand–receptor interactions.
152 citations
TL;DR: In this paper, the authors discuss the origin of electrochemical oscillations and argue that most of the currently known electromagnetic oscillators belong to one of two different classes, i.e., spontaneous oscillations of current or potential, complex and chaotic oscillations, and associated bifurcation scenarios.
Abstract: Many electrochemical systems are known to exhibit complex non-linear behaviour such as spontaneous oscillations of current or potential, complex and chaotic oscillations and associated bifurcation scenarios and spatial pattern formation when maintained far from thermodynamic equilibrium. We discuss the origin of electrochemical oscillations and argue that most of the currently known electrochemical oscillators belong to one of two different classes. These classes are distinguished by the different types of electrical control under which oscillations are observable and are characterized by qualitatively different impedance spectra. The possibility of observing electrochemical oscillations under truly potentiostatic conditions is discussed briefly, as well as the role of global coupling, due to the electroneutrality condition in the formation of spatiotemporal patterns on the electrode surface.
TL;DR: The microscopic structure observed through the mass-spectrometric analysis of clusters isolated from solution also shows good contrast between these binary mixtures as follows: methanol molecules have substitutional interaction with water clusters, while acetonitrile molecules have additional interaction with the water clusters as discussed by the authors.
Abstract: Water–methanol and water–acetonitrile, which show exothermic and endothermic mixing, respectively, represent good contrast in non-ideality of a binary mixture. The microscopic structure observed through the mass-spectrometric analysis of clusters isolated from solution also shows good contrast between these binary mixtures as follows: (1) methanol molecules have substitutional interaction with water clusters, while acetonitrile molecules have additional interaction with water clusters; (2) the clustering of methanol molecules are promoted in the presence of water; on the contrary, the acetonitrile clusters are disintegrated in the presence of water. Such findings could partially explain the non-ideality of these binary mixtures on the basis of the cluster structures.
TL;DR: Neutron reflection is one of the few newly developed techniques capable of probing structure at wet surfaces, i.e. air/liquid, solid/liquid and liquid/liquid interfaces as mentioned in this paper.
Abstract: Neutron reflection is one of the few newly developed techniques capable of probing structure at wet surfaces, i.e. air/liquid, solid/liquid and liquid/liquid interfaces. Although neutron scattering is not intrinsically sensitive to surfaces, the grazing incidence geometry of neutron reflection and the possibility of varying neutron refractive indices by isotopic substitution, particularly H/D substitution, make reflection extremely sensitive to selected parts of many interfacial layers. The technique is able to probe the average structure along the surface normal in a number of situations where the layer is too disordered or complex to be investigated by other methods. The application of neutron reflection to small molecules, surfactants, polymers and polymer–surfactant mixtures at the air/water interface, and examples of the behaviour of surfactants, proteins and polymers at the buried solid/liquid interface are described. Where appropriate the scope of neutron reflection relative to other new techniques is assessed.
TL;DR: In this article, the equilibrium constant for reaction (1) has been determined in neutral solution to be (1.4±0.1)×105 d mol-1, with forward and reverse rate constants, k1 and k-1.
Abstract: The equilibrium constant for reaction (1) has been determined in neutral solution to be (1.4±0.1)×105 d mol-1, with forward and reverse rate constants, k1 and k-1, of (8.5±0.7)×109 d mol-1 s-1 and (6.0±0.5)×104 s-1, respectively. At 25°C the rate constants for the reactions of ClNsbd and Cl2- were measured to be (2.5±0.3)×105 s-1 and (1.3±0.1)×103 s-1 with water and (6.5±0.6)×108 d mol-1 s-1 and ca. 0, within experimental error, with 2-methyl-propan-2-ol. Deviation from the equilibrium values of [ClNsbd] and [Cl2-] in the early stages of the reactions was investigated and shown to account for the discrepancy between the value of K1 determined here and a previous estimate from our laboratory.
TL;DR: In this paper, a reaction mechanism has been proposed in which a pair of adjacent oxide ion vacancies serves as the active site, the reaction starts with the successive adsorption of two NO molecules at the active sites, and the release of oxygen is equilibrated with the gas phase.
Abstract: Kinetics of NO decomposition have been investigated over La0.8Sr0.2CoO3 and La0.4Sr0.6Mn0.8Ni0.2O3 perovskite-type oxides. The NO decomposition reaction was practically first-order for NO in the range 0.1–0.5 vol.% NO. The activity was decreased by the presence of gaseous oxygen up to 9 vol.% with the reaction order between −0.16 and −0.82 depending on temperature, contact time and catalyst. A reaction mechanism has been proposed in which a pair of adjacent oxide ion vacancies serves as the active site, the reaction starts with the successive adsorption of two NO molecules at the active site, and the release of oxygen is equilibrated with the gas phase. The derived rate equation satisfactorily explains the experimental results.
TL;DR: In this article, a dual-beam diode array spectrometer was used to measure the UV-VIS absorption spectra of CH2Br2, CH2I2 and Ch2BrI.
Abstract: The UV–VIS absorption spectra of CH2Br2, CH2I2 and CH2BrI have been measured over the wavelength range 215–390 nm using a dual-beam diode array spectrometer. The spectra consist of broad continuous absorption bands. CH2Br2 exhibits its maximum cross-section of σ=2.71(±0.16)×10-18 cm2 molecule-1 at λ=219 nm. The magnitude of the peak cross-sections for the iodine-containing molecules above λ=210 nm are σ=1.62(±0.10)×10-18 cm2 molecule-1 at λ=248 nm and σ=3.78(±0.23)×10-18 cm2 molecule-1 at λ=288 nm for CH2I2, and σ=5.67(±0.34)×10-18 cm2 molecule-1 at λ=215 nm and σ=2.34(±0.14)×10-18 cm2 molecule-1 at λ=267 nm for CH2BrI. The temperature dependence of the absorption cross-sections was investigated over the temperature range 348–250 K. A decline in the cross-sections with decreasing temperature was observed in the tail of the spectra. At the peaks the opposite effect was observed. All three gases have been found in the atmosphere and the atmospheric photolysis rates of CH2Br2, CH2I2 and CH2BrI were calculated as a function of altitude and solar zenith angle using the measured cross-sections. Model calculations show that, during sunlit hours, CH2I2 and CH2BrI will be photolysed within minutes and hours, respectively. The photolysis of CH2Br2 is much slower and reaction with the OH radical is the dominant atmospheric loss process.
TL;DR: In this article, the authors showed that some specific Bronsted acid sites observed in steamed Y zeolites were also present in silica-alumina samples, allowing them to relate them to silica alumina debris.
Abstract: Progressive CO adsorption has been studied by IR spectroscopy, at low temperature on acid-leached steamed Y zeolites and on two silica–alumina samples with different Si/Al ratios. The IR spectra of the steamed Y zeolites are complex in the ν(OH) range. After CO adsorption only some perturbed ν(OH) and ν(CO) bands had previously been assigned. This study showed that some specific Bronsted acid sites observed in steamed Y zeolites were also present in silica–alumina samples, allowing us to relate them to silica–alumina debris. On the silica–alumina samples, the more acidic site strength [characterized by a perturbed ν(OH) band near 3450 cm-1] was found to be close to that of the high-frequency (HF)OH groups of non-dealuminated HY zeolites. A quantitative estimation of such sites was obtained by determination of the molar absorption coefficient e(CO) of the corresponding perturbed ν(CO) band.
TL;DR: The adsorption of chicken egg white lysozyme at the air/water interface has been studied by specular neutron reflection as mentioned in this paper, where the signal is only from the adsorbed protein layer.
Abstract: The adsorption of chicken egg white lysozyme at the air/water interface has been studied by specular neutron reflection. The variation of the total thickness of the lysozyme layer at the surface of water under varying solution conditions has been determined. The use of mixed H2O and D2O allowed the determination of the extent of immersion of the layer in water at all concentrations. The measured layer thickness combined with the globular dimensions of lysozyme suggests that the adsorbed lysozyme molecules retain their globular structure with no significant denaturation. Measurements were made over a lysozyme concentration range of 9×10-4 g dm-3 to 4 g dm-3 at pH 7 and at an ionic strength of 0.02 M. The thickness of the layer was determined by measuring neutron reflectivities in null reflecting water (NRW) where the signal is only from the adsorbed protein layer. Below 0.1 g dm-3 the surface coverage increases with bulk concentration but the thickness of the layer is constant at 30±3 A, suggesting that lysozyme is adsorbed sideways-on. As the bulk concentration increases, the layer thickness gradually increases to a value of 47±3 A2 at a bulk concentration of 1 g dm-3, suggesting that the molecules switch from sideways-on to longways-on orientations. The area per molecule at 1 g dm-3 was found to be 950±50 A2 which is close to the limit of 30×30 A2 for a saturated layer of longways-on molecules. The extent of mixing of the layer with water was determined directly by measuring reflectivity profiles in mixed H2O and D2O. A two layer model was found to be appropriate with an upper layer in air and a lower layer fully immersed in water. The thickness of the layer in air was found to vary from 15±5 Aat the lowest bulk concentration to 9±3 Aat the highest concentration studied. The results show that as the total layer thickness increases with bulk concentration the fraction of the layer immersed in water increases from 50 to 85%. At the highest concentration of 4 g dm-3 the adsorbed layer is better described by a two layer model consisting of a close packed top layer of thickness 47±3 Aand a loosely packed sublayer of 30±3 A.
TL;DR: In this article, the photoexcited states properties of N-methylpyrrolidinofullerenes C60[(C3H6N)R] were investigated.
Abstract: Steady-state absorption/fluorescence spectra and time-resolved absorption/fluorescence spectra were measured to investigate the photoexcited states properties of N-methylpyrrolidinofullerenes C60[(C3H6N)R] [R=H (1), p-C6H4CHO (2), p-C6H4NO2 (3), p-C6H4OMe (4), p-C6H4NMe2 (5)]. Functionalization causes bandshifts to longer wavelength for absorption and fluorescence spectra, accompanied by enhancements in the fluorescence quantum yields in nonpolar solvents. The triplet (T) states of these derivatives show very similar properties (quantum yields, molar absorption coefficients and O2 quenching) to C60 whereas T–T absorption bands shift to short wavelength and the lowest triplet energies decrease compared with those of C60. Derivative 5, which has a strong electron-donating group, shows a prominent solvent polarity effect on the fluorescent quantum yield and lifetime, and triplet formation, suggesting that intramolecular charge transfer takes place.
TL;DR: In this paper, the incorporation of CO2 into CaHAP during the preparation was investigated mainly by FTIR spectroscopy, and it was shown that the inclusion of CO32− ions in PO43− sites is maximum for CAHAP formed at pH 5.94 and that in OH− sites increases as the solution pH rises.
Abstract: Calcium hydroxyapatite (CaHAP) particles were prepared by precipitation reactions of Ca(OH)2 and H3PO4 at different pH. Incorporation of CO2 into CaHAP during the preparation was investigated mainly by FTIR spectroscopy. The amount of CO32− ions contained in the formed CaHAP was increased by raising the solution pH. IR bands of the CO32− ions incorporated into CaHAP were assigned by means of CO2 adsorption. The 1414, 1447 and 1500 cm−1 bands were assignable to CO32− ions in OH− sites of the CaHAP crystals and the 1457 and 1550 cm−1 bands to CO32− ions in PO43− sites. This assignment is different from those in the literature. FTIR results demonstrated that the inclusion of CO32− ions in PO43− sites is maximum for CaHAP formed at pH 5.94 and that in OH− sites increases as the solution pH rises.
TL;DR: In this paper, the authors compared the results of ethene, propene and isobutene chemisorption at an aluminosilicate Bronsted-acid site in the zeolite chabazite.
Abstract: Quantum-chemical studies of ethene, propene and isobutene chemisorption at an aluminosilicate Bronsted-acid site in the zeolite chabazite are reported. Comparison of the results using different cluster models and a qm/mm (quantum mechanical/molecular mechanical) embedded cluster approach are compared and contrasted. As in previous studies, the activation barriers for the chemisorption process leading to a surface alkoxide are found to follow a carbenium ion trend, i.e. ethene>propene>isobutene. In contrast to previous studies, however, results indicate that the stability of the alkoxide is also very sensitive to a number of factors, the dominant one being steric interactions with the acid site, i.e. the stability order is ethene>propene>isobutene. This steric effect and other, less dominant, contributions are only observed when host environment effects are included in the model, in the present case via constraints on the cluster boundaries and via the qm/mm embedded-cluster approach. The possible formation of stable carbenium ions in the pores of acidic zeolites is discussed.
TL;DR: A series of iron-containing mesoporous silicas (Fe-HMS) with Fe contents up to 5.7 wt.% have been prepared at room temperature using the neutral hexadecylamine as surfactant molecule as discussed by the authors.
Abstract: A series of iron-containing mesoporous silicas (Fe-HMS) with Fe contents up to 5.7 wt.% have been prepared at room temperature using the neutral hexadecylamine as surfactant molecule. Characterization of these materials by a variety of spectroscopic techniques, including EXAFS, EPR, Mossbauer and UV–Vis spectroscopies, suggests that Fe species are tetrahedrally coordinated in as-made materials. Tetrahedra are highly distorted with two long and two short Fe–O bond distances due to hydrogen-bonding type interactions with the organic molecules. Removal of the amines by solvent extraction does not modify the chemical environment around the Fe species. Subsequent calcination leads to mainly 3-coordinated Fe species, readily converting to 4-coordinated species in the presence of water. The solvent extraction appears to be a key step to prevent the formation of extraframework iron oxide species, which are formed in large amount when the surfactant is directly removed from as-made materials by calcination in air at high temperature.
TL;DR: In this paper, the atomistic structure of an extensive set of ceria surfaces are predicted using four different inter-atomic potential models and the dependence of the results on the parameters is discussed in detail.
Abstract: The atomistic structure of an extensive set of ceria surfaces are predicted using four different inter-atomic potential models. The dependence of the results on the parameters is discussed in detail. For example, we find that while absolute surface energies vary considerably, relative energies do not. As such, an octahedral crystallite morphology can be predicted with confidence. However, for one model the predicted surface ion relaxations are large and very different compared to those of the other three models. This is due, in part, to the difficulties of applying shell model parameters derived from bulk calculations to surface studies.
TL;DR: In this article, a 1:1 tetradentate complex of B(OH)4- with the N-methylglucamine group was found to have 104.0±0.1 binding constant.
Abstract: N-Methylglucamine resin has been shown to be a good adsorbent for borate or boric acid. Above ca. pH 6, the boron adsorbability of this resin increased with a maximum around pH 9. The maximum distribution ratio was higher than 106, however, further increase in pH resulted in a decrease in the distribution ratio. The combination of distribution and 11B MAS NMR measurements revealed the formation of a 1:1 tetradentate complex of B(OH)4- with the N-methylglucamine group. The calculated pH-dependence of boron adsorption agreed well with the experimental results with respect to the -log [H+] values in the resin phase (not in the external solution) estimated by 31P NMR measurements. The maximum adsorption around pH 9 of the equilibrated solution is due to the fact that the pH in the resin phase remains higher than that in the external solution. Therefore, B(OH)3/B(OH)4- is selectively concentrated into the resin phase and by the dehydration condensation B(OH)4- forms the 1:1 tetradentate complex with the anchor group. The overall formation constant of the complex was estimated to be 104.0±0.1, which was almost the same magnitude as that of the 1:1 monochelate complex with an α,β-diol site of N-methyl-D-glucamine (which is an analogue of the functional group of the resin) in aqueous solutions of pH 5.1–7.4. However, the binding structures of each 1:1 complex with the N-methyl-D-glucamine group are quite different in the aqueous solution and in the crosslinked polymer.
TL;DR: In this article, carbon nanotubes were produced in large amounts by catalytic decomposition of acetylene over a Co incorporated zeolite NaY support and the quality of the resulting carbon was characterized by means of transmission electron microscopy.
Abstract: Carbon nanotubes were produced in large amounts by catalytic decomposition of acetylene over a Co incorporated zeolite NaY support. Purification of multi-wall nanotubes was required in order to eliminate catalyst and amorphous carbon produced by thermal decomposition of hydrocarbon. First, separation of nanotubes and catalyst particles was carried out by hydrofluoric acid treatment. Then, two ways of removing amorphous carbon were studied: permanganate oxidation and air oxidation. The quality of nanotubes was characterized by means of transmission electron microscopy and the yield of pure nanotubes was quantitatively determined. Changes caused by treatment of the nanotubes were investigated by high resolution electron microscopy and a comparison was made between the nanotubes produced by this method and those synthesized by an arc discharge process after oxidation treatment.
TL;DR: In this article, the Raman spectra of the following rare earth halide-alkali halide binary molten salt systems have been measured: LnBr3-KBr (Ln=La, Nd, Gd) and NdCl3-ACl (A=Li, Na, K, Cs).
Abstract: Raman spectra of the following rare earth halide–alkali halide binary molten salt systems have been measured: LnBr3–KBr (Ln=La, Nd, Gd) and NdCl3–ACl (A=Li, Na, K, Cs). The complete composition range has been studied at temperatures up to 850°C. The spectral changes occurring upon melting the elpasolite compounds Cs2NaLnBr6 (Ln=La, Nd, Gd) and Cs2NaNdCl6 and the pure crystalline solids LnBr3 (Ln=La, Nd, Gd) and NdCl3 were also measured. The data indicate that the behavior of these melt mixtures is similar to those of the YX3–KX (X=F, Cl, Br) binaries studied before. In molten mixtures rich in alkali halide with lanthanide halide mole fractions less than 0.25, the predominant species are the LnX63- octahedra giving rise to two main bands P1 (polarized) and D1 (depolarized) which are assigned to the ν1(A1g) and ν5(F2g) octahedral modes. In molten mixtures rich in LnX3 the spectra are characterized by the P1 and D1 bands plus two new bands D2 (depolarized) and P2 (polarized). The P2 band shifts continuously to higher frequencies with increasing LnX3 content. These four bands are attributed to the D3 distortions of the LnX63- octahedra bound by edges in the melt. The room temperature Raman spectra of the LnX3 solid compounds were characterized by bands due to the vibrational modes of the different crystalline structures: hexagonal for LaBr3 and NdCl3, orthorhombic for NdBr3 and rhombohedral for GdBr3 having the Ln3+ coordination number (CN) or 9, 8 and 6, respectively. With increasing temperature the spectra of the GdBr3 solid are dominated by six Raman bands which are assigned to the vibrational modes of a triple layer of ions consisting of distorted octahedra GdBr63- (CN=6) which share edges with neighboring octahedra. Upon melting, the molar volume of GdBr3 does not change much and the spectra are characterized by the above-mentioned P1, P2, D1 and D2 bands and can be correlated to the triple layer modes of the solid. The high temperature spectra of the hexagonal LaBr3, NdCl3 and the orthorhombic NdBr3 show that the structure and CN remain the same up to melting. However, upon melting, the compact orthorhombic (CN=8) and hexagonal (CN=9) forms increase drastically their molar volume and give spectra similar to those of molten GdBr3, YBr3 and YCl3 where the Ln3+ is in a six-fold coordination (CN=6). It appears that the structures of all the LnX3 melts are similar and independent of the structure of the solids. The frequency changes upon melting the LnX3 solids, the presence and assignment of the P1, P2, D1 and D2 bands in the spectra, the continuous shift of the P2 band with composition in the LnX3–AX binaries and the correlation of the high temperature modes of the rhombohedral LnX3 solid (CN=6) to the liquid suggest that the loose network structure proposed for the LnX3 melts is more likely to arise from ‘triple layer’ like structures composed of distorted octahedra. The rigidity of the network is related to the splitting of the P1 and P2 band and increases with increasing distortion of the octahedra in the sequence La–Y; F–Br. Fast interchange of ions leads to short lifetimes for the octahedra and weak intralayer interactions.
TL;DR: In this article, the authors show that the experimental data can be reproduced well by means of Lee's theory of hydrophobic hydration, and demonstrate that the purely structural reorganization of H-bonds in the hydration shell of a nonpolar solute is a compensating process.
Abstract: The solubility in water of noble gases, at room temperature, increases with their size, whereas that of gaseous aliphatic hydrocarbons decreases on increasing their size. This puzzling experimental observation is a unique feature of water as solvent. No real explanation of the phenomenon exists, even though it has been suggested that it is evidence of clathrate-type structure formation around nonpolar molecules. In this paper, we show that the experimental data can be reproduced well by means of Lee's theory of hydrophobic hydration. A fundamental ingredient of this theory is the demonstration that the purely structural reorganization of H-bonds in the hydration shell of a nonpolar solute is a compensating process. The solubility is determined by the balance of two contrasting factors: the excluded volume entropy change due to cavity creation in the solvent, and the direct solute–solvent van der Waals interactions. The work of cavity creation is dominant, determining the poor solubility of nonpolar compounds in water. However, for noble gases, on increasing the hard-sphere diameter, the van der Waals interactions increase, in absolute value, more rapidly than the work of cavity creation, enhancing the solubility. On the contrary, for aliphatic hydrocarbons, on increasing the hard-sphere diameter the van der Waals interactions increase, in absolute value, less rapidly than the work of cavity creation, lowering the solubility. The experimental data of hydration Gibbs energies, therefore, can be accounted for without invoking an enhancement of water structure in the hydration shell of a nonpolar solute.
TL;DR: In this article, the authors investigated the interactions between CuO and the TiO2 (anatase) support, in samples prepared by impregnating the support with an aqueous solution of Cu(NO3)2·6H2O.
Abstract: In this paper, Brunomer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) are used to investigate the interactions between CuO and the TiO2 (anatase) support, in samples prepared by impregnating the TiO2 support with an aqueous solution of Cu(NO3)2·6H2O. The results indicate that the surface structure of the TiO2 support has not been changed by supported CuO, and the dispersion capacity of CuO is about 6.98 Cu2+ nm (TiO2)−2. The structure of the supported copper oxide species is strongly dependent on the amount of CuO loaded. At low CuO loading, only a highly dispersed surface CuO species is formed on the support and when the CuO loading exceeds its dispersion capacity, crystalline CuO is formed as all the vacant surface sites of the TiO2 support are occupied by Cu2+ ions. In addition, it is found that both the reduction behavior and the crystalline-structure transition of the TiO2 support are related to the interactions between TiO2 and CuO.
TL;DR: In this article, the proton affinities of the four oxygen lone pairs and of the two nitrogen atoms and the deprotonation energies PA(A-) of the NH bonds of uracil are calculated by density functional theory (DFT) using the 6-31G(d,p) and 6- 31G++(d-p) basis set.
Abstract: The proton affinities PA(B) of the four oxygen lone pairs and of the two nitrogen atoms and the deprotonation energies PA(A-) of the two NH bonds of uracil are calculated by density functional theory (DFT) using the 6-31G(d,p) and 6-31G++(d,p) basis set. The PAs are also calculated by abinitio MO theory (MP4) using 6-31G(d,p) for comparison. The DFT/B3LYP energies and the frequency shifts of the ν(OH) stretching vibrations are calculated with the 6-31++G(d,p) basis for the three cyclic structures of the uracil–water complexes. The usual correlations between energies of frequency shifts and the PAs do not hold in the case of closed structures. The most stable cyclic complex is formed at the oxygen lone pair characterized by the lowest basicity and at the NH bond characterized by the highest acidity. The energy of the complex decreases with increasing value of the difference PA(A-)-PA(B).
TL;DR: In this paper, the formation of isocyanate species has been studied over Ag/Al2O3 by IR spectroscopy and mass spectrometry, and it has been shown that the NCO species are highly reactive toward NO+O2 at room temperature, being converted into N2, CO 2, CO and a small amount of N2O.
Abstract: The formation of the reactivity of isocyanate species have been studied over Ag/Al2O3 by IR spectroscopy and mass spectrometry. Adsorbed CxHyNOz and NO3− species are produced by reaction among NO, O2 and C3H6 at room temperature. Thermal decomposition of adsorbed CxHyNOz species leads to the formation of two types of NCO species (NCO on Ag and NCO on Al2O3) above 423 K. These NCO species are thermally stable in vacuum at 673 K, while adsorbed NO3− species decompose completely. The NCO species are highly reactive toward NO+O2 at room temperature, being converted into N2, CO2, CO and a small amount of N2O. The NCO species are less active in NO or O2 alone than in the mixture of NO and O2. Thus, excess oxygen added in the NO reduction by C3H6 plays an important role in the formation of adsorbed CxHyNOz species and in the reaction of adsorbed NCO with NO. It is suggested that the formation of adsorbed CxHyNOz and adsorbed NCO is essential for the progress of the NO reduction with C3H6 in the presence of O2 under the present experimental conditions.