Biological and structural studies of phosphonium 'masked thiolate' compounds.

The ability of phosphonium cations to act as intracellular transport vectors is well-established. Phosphonioalkylthiosulfate zwitterions, and ω-thioacetylalkylphosphonium salts, which act as 'masked thiolate' ligands, are useful precursors for the formation of phosphonium-functionalised gold nanoparticles, enabling the nanoparticles to be transported into cells for diagnostic and therapeutic purposes. In this study we have completed cytotoxicity studies of ω-thioacetylpropylphosphonium salts derived from triphenylphosphine and tri(4-fluorophenyl)phosphine, which show that the compounds are only toxic towards PC3 prostate cancer cells at high concentrations and at prolonged incubation periods and display IC50 values of 67 µM and 252 µM respectively, significantly higher than those of other phosphonium salts. MALDI-TOF-MS has been used to investigate the uptake of the compounds by PC3 cells and to quantify detectable levels of the compounds inside the cells. The structures of ω-thioacetylpropyl(tri-4-fluorophenyl) phosphonium bromide and the corresponding tri(4-fluorophenyl)phosphoniopropylthiosulfate zwitterion have been investigated by single crystal X-ray crystallography. The results show that molecules of the zwitterion are held together through an extensive array of electrostatic and non-covalent interactions. The unit cell of ω-thioacetylpropyl(tri-4-fluorophenyl)phosphonium bromide contains eight cations together with eight bromide anions and two waters of crystallisation, all held together through a complex network of hydrogen bonds. The differences in the molecular packing of the two compounds may account for the lower solubility of the zwitterion in aqueous solutions, compared with that of the phosphonium salt.

Triphenylarsonium-functionalised gold nanoparticles: potential nanocarriers for intracellular therapeutics.

Two new triphenylarsonium alkylthiolate precursors, a thiosulfate zwitterion and a thioacetate salt, have been structurally characterised and their cytotoxicity evaluated against PC3 cells. The arsonium compounds have been used to prepare gold nanoparticles decorated with triphenylarsonium groups.

"Afterlife experiment": use of MALDI-MS and SIMS imaging for the study of the nitrogen cycle within plants.

As part of a project to demonstrate the science of decay, a series of mass spectrometry imaging experiments were performed. The aim was to demonstrate that decay and decomposition are only part of the story and to show pictorially that atoms and molecules from dead plants and animals are incorporated into new life. Radish plants (Raphanus sativus) were grown hydroponically using a nutrient system containing (15)N KNO3 (98% labeled) as the only source of nitrogen. Plants were cropped and left to ferment in water for 2 weeks to create a radish "tea", which was used as a source of nitrogen for radish grown in a second hydroponics experiment. After 5 weeks of growth, the radish plants were harvested and cryosectioned, and sections were imaged by positive-ion MALDI and SIMS mass spectrometry imaging. The presence of labeled species in the plants grown using (15)N KNO3 as nutrient and those grown from the radish "tea" was readily discernible. The uptake of (15)N into a number of identifiable metabolites has been studied by MALDI-MS and SIMS imaging.

Formation of T-shaped versus charge-transfer molecular adducts in the reactions between bis(thiocarbonyl) donors and Br2 and I2.

The reactions of 4,5,6,7-tetrathiocino-[1,2-b:3,4-b']-1,3,8,10-tetrasubstituted-diimidazolyl-2,9-dithiones (R(2),R'(2)-todit; 1: R=R'=Et; 2: R=R'=Ph; 3: R=Et, R'=Ph) with Br(2) exclusively afforded 1:1 and 1:2 "T-shaped" adducts, as established by FT-Raman spectroscopy and single-crystal X-ray diffraction in the case of complex 1·2Br(2). On the other hand, the reactions of compounds 1-3 with molecular I(2) provided charge-transfer (CT) "spoke" adducts, among which the solvated species 3·2I(2)·(1-x)I(2)·xCH(2)Cl(2) (x=0.94) and (3)(2)·7I(2)·xCH(2)Cl(2), (x=0.66) were structurally characterized. The nature of all of the reaction products was elucidated based on elemental analysis and FT-Raman spectroscopy and supported by theoretical calculations at the DFT level.

Phosphonioalkylthiosulfate zwitterions--new masked thiol ligands for the formation of cationic functionalised gold nanoparticles.

We report the synthesis and structural characterisation of a new family of stable phosphonioalkylthiosulfate zwitterions, R3P+ (CH2)nS2O3- (R = Ph or Bu, n = 3,4,6, 8 or 10) which behave as cationic masked thiolate ligands with applications in the functionalisation of gold nanoparticles, having potential as new diagnostic biorecognition systems. The ligands were prepared by treatment of omega-bromoalkylphosphonium salts with sodium thiosulfate. The crystal and molecular structures of the zwitterions (R = Ph, n = 3) and (R = Bu, n = 3) were determined. A series of phosphonioalkanethiolate-capped gold nanoparticles dispersed in water was prepared by borohydride reduction of potassium tetrachloroaurate in the presence of the zwitterions in a dichloromethane-water system. UV-visible spectroscopy and scanning transmission electron-microscopy indicated that capped nanoparticles of ca. 5 nm diameter were present.

Structural and magnetic properties of a novel ferrocenyl-diiodine charge transfer complex.

The reaction of 4-ferrocenyl-1,3-dithiole-2-thione with diiodine affords an unprecedented "double" charge-transfer complex; the highly ordered ferrocenium units are held by a supramolecular polyiodide chain, and the material shows evidence of the formation of zigzag magnetic chains below 2 K.