No abstract

New platinum(II) complexes have been prepared as models for explaining the coordination of multiple β‐diketonate li‐gands to give [Pt(O,O′‐acac)(γ‐acac)L] species. The new com‐pounds containing both an O,O′‐chelated acetylacetonate ligand and a sulfoxide in the platinum coordination sphere, [PtCl(O,O′‐acac)(DMSO)] (1) and [Pt(O,O′‐acac)(γ‐acac)(DMSO)] (2), have been synthesised and characterised by 1H, 13C, 195Pt 1‐D and 2‐D NMR heteronuclear correlation spectroscopy and, in the case of 2, by X‐ray crystal structure analysis also. Moreover, a new synthetic pathway to obtain the previously reported complex K[Pt(O,O′‐acac)(γ‐acac)2] (3) has been developed. The data presented herein are consistent with a reaction mechanism which explains the subsequent steps of the coordination of multiple β‐diketonate li‐gands to platinum(II) complexes, where the first species formed contains one O,O′‐chelated acac group. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

SYP51 and 52 are the two members of the SYP5 Qc-SNARE gene family in Arabidopsis thaliana. These two proteins, besides their high level of sequence identity (85%), have shown to have differential functional specificity and possess a different interactome. Here we describe a unique and specific interaction of SYP51 with an ER aquaporin, AtNIP1;1 (also known as NLM1) indicated to be able to transport arsenite [As(III)] and previously localized on PM. In the present work we investigate in detail such localization in vivo and characterize the interaction with SYP51. We suggest that this interaction may reveal a new mechanism regulating tonoplast invagination and recycling. We propose this interaction to be part of a regulatory mechanism associated with direct membrane transport from ER to tonoplast and Golgi mediated vesicle trafficking. We also demonstrate that NIP1;1 is important for plant tolerance to arsenite but does not alter its uptake or translocation. To explain such phenomenon the hypothesis that SYP51/NIP1;1 interaction modifies ER and vacuole ability to accumulate arsenite is discussed.

The reactivity of platinum(II) complexes of the type [PtCl(O,O-acac)(L)] (1) and [Pt(O,O-acac)(gamma-acac)(L)] (2) (L = DMSO, a; DMS, b), with a range of hard and soft nucleophiles such as dimethylsulfide (DMS, b), triphenylphosphine, (PPh3, c), ethylene (eta2-C2H4, d), carbon monoxide (CO, e), pyridine (py, f), and guanosine (Guo, g) has been investigated. Interestingly, the complexes 1a and 1b undergo selective substitution of the chloro or sulfur ligand depending on the hard/soft character of the incoming nucleophile. The soft incoming ligand replaces the softer one and the hard ligand replaces the harder one, giving [PtCl(O,O'-acac)(L)] complexes (1b, 1c, 1d and 1e in the reaction of 1a with L = DMS, PPh3, eta2-C2H4, CO, respectively), and [Pt(O,O'-acac)(DMSO)(L')] (3f, 3g) and [Pt(O,O'-acac)(DMS)(L')] (4f, 4g) species in the reaction of 1a and 1b with L' = py and guo, respectively. In the cases of 2a and 2b complexes, where the pi-bonded acac (gamma-acac) replaces the chloro ligand, only in the presence of an incoming soft nucleophile substituting the soft sulfur ligand the reaction occurs. Equilibrium constants for the substitution reactions were measured by 1H NMR spectroscopy. Variable temperature 1H NMR spectroscopy studies, performed for the reaction of 1a and 2a complexes with DMS, revealed that the selective substitution of DMSO with DMS takes place in both cases, according to a second-order kinetic law. The calculated values of DeltaH++ and DeltaS++ are consistent with an associative mechanism. NMR spectroscopic characterization (1H, 13C, 195Pt, 31P) for the complexes and crystal structures of isolated complexes ([PtCl(O,O'-acac)(L)] (1) and [Pt(O,O'-acac)(gamma-acac)(L)] (2), L = DMSO, 1a and 2a; L = DMS, 1b and 2b; L = PPh3, 1c and 2c) are herein reported and discussed.

Four- and five-coordinate platinum(II) complexes, cis-[PtCl2(A2)] (1) and [PtCl2(A2)(eta2-ethylene)] (2) {A2 = 4,7-diphenyl-1,10-phenanthroline disulfonic acid disodium salt, BPS (mixture of isomers) (a); 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline disulfonic acid disodium salt, BCS (mixture of isomers) (b)} have been synthesized and characterized by 1H, 13C, and 195Pt NMR spectroscopy. The stability and high water solubility of complexes 1a, 1b and 2b, due to the presence of the polar SO3- groups on the ligands skeleton, allowed to test their in vitro cytotoxicity on HeLa tumour cells in a wide range of drug concentration. At low and medium incubation doses (<200 microM) 1a, 1b and 2b all showed similar in vitro cytotoxicity, negligible or much lower with respect to cisplatin. At doses higher than 200 microM their activity increased and 1b, the most active among the new complexes, exhibited a cytotoxicity comparable, although still lower, with respect to cisplatin. GFAAS Platinum analytical data showed that the tested compounds 1a, 1b and 2b, although carrying sulfonate charged groups, may undergo cellular uptake, which, in the case of 1b and 2b, is even higher with respect to cisplatin. Furthermore, in the case of 1b and 2b it has been possible to compare, for the first time, the cytotoxic activity for square-planar four-coordinate and trigonal-bipyramidal five-coordinate platinum(II) complexes having the same carrier ligand. The tendency of the five-coordinate species 2b to give at longer incubation time similar cytotoxicity with respect to the square-planar compound 1b suggests a possible use of the trigonal-bipyramidal five-coordinate complexes as prodrugs.