David J. Cardin

Intensity-dependent absorption and resonant optical nonlinearity of C60 and C70 solutions

We present the optical response of solutions of C60 and C70 fullerenes to high-intensity visible laser pulses. A decrease of the transmission with increasing input intensity is observed at different wavelengths. The measurements are compared with simulations using a rate equation model. Excited-state absorption cross sections are evaluated and used to calculate the imaginary part of the resonant nonlinear susceptibility χ(3).

Photocatalytic degradation of humic acid in saline waters. Part 1. Artificial seawater: influence of TiO2, temperature, pH, and air-flow

We report the first systematic study on the photocatalytic oxidation of humic acid (HA) in artificial seawater (ASW). TiO(2) (Degussa P25) dispersions were used as the catalyst with irradiation from a medium-pressure mercury lamp. The optimum quantity of catalyst was found to be between 2 and 2.5 gl(-1); while the decomposition was fastest at low pH values (pH 4.5 in the range examined), and the optimum air-flow, using an immersion well reactor with a capacity of 400 ml, was 850 ml min(-1). Reactivity increased with air-flow up to this figure, above which foaming prevented operation of the reactor. Using pure oxygen, an optimal flow rate was observed at 300 ml min(-1), above which reactivity remains essentially constant. Following treatment for 1 h, low-salinity water (2700 mg l(-1)) was completely mineralised, whereas ASW (46000 mg l(-1)) had traces of HA remaining. These effects are interpreted and kinetic data presented. To avoid problems of precipitation due to change of ionic strength humic substances were prepared directly in ASW, and the effects of ASW on catalyst suspension and precipitation have been taken into account. The Langmuir-Hinshelwood kinetic model has been shown to be followed only approximately for the catalytic oxidation of HA in ASW. The activation energy for the reaction derived from an Arrhenius treatment was 17 (+/-0.6) kJ mol(-1).

Non-linear optical properties of Group 10 metal alkynyls and their polymers

Conjugated diacetylene and phenylacetylene systems incorporating Group 10 transition-metal complexes have been obtained via lithium acetylide intermediates. In the UV–VIS spectra, the positioning of the longest-wavelength absorption shows a strong dependence on the incorporated metal. Polymers of both the trans-nickel and the trans-platinum bisphosphine diacetylide [M(PR3)2(CC–CCH)2](M = Ni, or Pt; R = alkyl group) were synthesised. UV absorption spectra show a significant shift of the absorption maxima from those of the monomers, towards longer wavelengths, consistent with an increase in the degree of electron delocalisation per monomer unit. The third-order non-linear optical properties of these materials in solution were examined using the method of self-diffraction from laser-induced gratings with 70 ps pulses of wavelength 1.064 µm. In the case of the monomer solutions, intensity dependences of the diffraction efficiencies show the influence of the proximity of a three-photon resonance at low concentrations. At higher concentration the influence of this resonance is not apparent. Among the materials synthesised, a clear trend, down the group, is seen, the hyperpolarisabilities decreasing with increasing atomic number of the metal. Measured hyperpolarisabilities are compared with those of enyne oligomer solutions and are found to be substantially higher. Metal-containing polymeric systems show an intensity dependence that is characteristic of a pure third-order process. Molecular hyperpolarisabilities show trends similar to those of the monomeric species. Both polymers possess a non-linearity higher than that of equivalent polydiacetylene solutions.

Photocatalytic degradation of humic acid in saline waters: Part 2. Effects of various photocatalytic materials

Abstract The present study explores for the first time, the effectiveness of photocatalytic oxidation of humic acid (HA) in the increasingly important highly saline water. TiO 2 (Degussa P25), TiO 2 (Anatase), TiO 2 (Rutile), TiO 2 (Mesoporous) and ZnO dispersions were used as catalysts employing a medium pressure mercury lamp. The effect of platinum loading on P25 and zinc oxide was also investigated. The zinc oxide with 0.3% platinum loading was the most efficient catalyst. The preferred medium for the degradation of HA using ZnO is alkaline, whereas for TiO 2 it is acidic. In addition, a comparative study of HA decomposition in artificial seawater (ASW) and natural seawater (NSW) is reported, and the surface areas and band gaps of the catalysts employed were also determined. A spectrophotometric method was used to estimate the extent of degradation of HA.

X‑ray crystal structure of rac-[Ru(phen)2dppz]2+ with d(ATGCAT)2 shows enantiomer orientations and water ordering

We report an atomic resolution X-ray crystal structure containing both enantiomers of rac-[Ru(phen)2dppz](2+) with the d(ATGCAT)2 DNA duplex (phen = phenanthroline; dppz = dipyridophenazine). The first example of any enantiomeric pair crystallized with a DNA duplex shows different orientations of the Λ and Δ binding sites, separated by a clearly defined structured water monolayer. Job plots show that the same species is present in solution. Each enantiomer is bound at a TG/CA step and shows intercalation from the minor groove. One water molecule is directly located on one phenazine N atom in the Δ-enantiomer only.

‘Ship-in-a-Bottle’ Synthesis and Photochromism of Spiropyrans Encapsulated within Zeolite Y Supercages

Abstract The ship-in-a-bottle synthesis of three spiropyrans inside the NaY supercages was carried out by the condensation of 2-methylene-1,3,3-trimethylindoline with the appropriate substituted benzaldehyde. After the reaction, spiropyrans were detected in the supernatant and the zeolites became coloured. Combustion chemical and thermogravimetric analyses confirmed the presence of organic material within the solid. UV–Vis and Raman spectroscopies are compatible with the formation of the merocyanine form of the spiropyran photochromic system. Upon visible irradiation the solids bleach, and in some cases the coloration is regained upon standing in the dark for long periods. This abnormal photochromic behaviour is the reverse of that observed for the spiropyran/merocyanine system in ethanol and illustrates the possibility of zeolites as media to alter the molecular properties of incorporated guests.

Monitoring one-electron photo-oxidation of guanine in DNA crystals using ultrafast infrared spectroscopy

To understand the molecular origins of diseases caused by ultraviolet and visible light, and also to develop photodynamic therapy, it is important to resolve the mechanism of photoinduced DNA damage. Damage to DNA bound to a photosensitizer molecule frequently proceeds by one-electron photo-oxidation of guanine, but the precise dynamics of this process are sensitive to the location and the orientation of the photosensitizer, which are very difficult to define in solution. To overcome this, ultrafast time-resolved infrared (TRIR) spectroscopy was performed on photoexcited ruthenium polypyridyl-DNA crystals, the atomic structure of which was determined by X-ray crystallography. By combining the X-ray and TRIR data we are able to define both the geometry of the reaction site and the rates of individual steps in a reversible photoinduced electron-transfer process. This allows us to propose an individual guanine as the reaction site and, intriguingly, reveals that the dynamics in the crystal state are quite similar to those observed in the solvent medium.

Metal cluster expansion by addition of low valent group 14 reagents: III. Reaction of bis[bis(trimethylsilyl)methyl]tin with M3(CO)12 or its derivatives (M = Fe, Ru, or Os): the crystal and molecular structures of M3(μ-SnR2)2(CO)10(R = CH(SiMe3)2; M = Ru or Os)☆

The stannylene [SnR2] (R = CH(SiMe3)2) reacts in different ways with the three dodecacarbonyls of the iron triad: [Fe3(CO)12] gives [Fe2(CO)8(μ-SnR2)], [Ru3(CO)12] gives the planar pentametallic cluster [Ru3(CO)10(μ-SnR2)2], for which a full structural analysis is reported, while [Os3(CO)12] fails to react. Different products are also obtained from three nitrile derivatives: [Fe3-(CO)11(MeCN)] gives [Fe2(CO)6(μ-SnR2)2], which has a structure significantly different from that of known Fe2Sn2 clusters, [Ru3(CO)10(MeCN)2] gives the pentametallic cluster described above, while [Os3(CO)10(MeCN)2] gives the isostructural osmium analogue, which shows the unusual feature of a CO group bridging two osmium atoms.

The synthesis and properties of [Fe3(CO)11(RCN)] derivatives, and a high-yield general route to mono- and di-substituted derivatives of [Fe3(CO)12]; the crystal and molecular structure of [Fe3(CO)11(NCC6H4-2-Me)]

The clusters [Fe3(CO)11(RCN)] (1: R = Me, C3H5, C6H5, or C6H4-2-Me) have been prepared at low temperature from [Fe3(CO)12] and RCN in the presence of Me3NO. Compounds 1 react essentially quantitatively with a wide range of two-electron donors, L, (viz.: CO, PPh3, P(OMe)3, PPh2H, PPh2Me, PF3, CyNC (Cy = cyclohexyl), P(OEt)3, SbPh3, PBu3, AsPh3, or SnR2 (R = CH(SiMe3)2)) to give [Fe3(CO)11L] (2). In some cases (2), on treatment with Me3NO and then L′ (L′ = a second two-electron donor) yields [Fe3(CO)10LL′] in high yield. The crystal and molecular structures of 1 (L = NCC6H4Me-2) have been determined by a full single crystal structure analysis, and shown to have an axial nitrile coordinated at the unique iron atom, with two CO groups bridging the other two metal atoms.

trans/cis-isomerism and isomerisation of PdII and PtII carbene complexes; The crystal and molecular structures of cis- and trans-PtCl2 [C(NPhCH2)2]PEt3

Abstract trans-PtII or trans-PdII carbene complexes are isomerised to the thermodynamically more stable cis compounds; cis- and trans-isomeric pairs are compared with respect to reactivity and physical properties, including spectroscopic and X-ray data.