Comment on enhanced Raman scattering from adsorbates on semiconductor surfaces

A recently published model of surface enhanced Raman scattering from adsorbed molecules on semiconductor surfaces is compared to our experimental results for amorphous carbon on PbTe. The model fails to account for the major features of the observed scattering.     

Kinetics and mechanisms of homogeneous catalytic reactions: Part 7. Hydroformylation of 1-hexene catalyzed by cationic complexes of rhodium and iridium containing PPh3

Cationic rhodium and iridium complexes of the type [M(COD)(PPh₃)₂]PF₆ (M = Rh, 1a; Ir, 1b) are efficient precatalysts for the hydroformylation of 1-hexene to its corresponding aldehydes (heptanal and 2-methylhexanal), under mild pressures (2–5 bar) and temperatures (60 °C for Rh and 100 °C for Ir) in toluene solution; the linear to branched ratio (l/b) of the aldehydes in the hydroformylation reaction varies slightly (between 3.0 and 3.7 for Rh and close to 2 for Ir). Kinetic and mechanistic studies have been carried out using these cationic complexes as catalyst precursors. For both complexes, the reaction proceeds according to the rate law r_i = K₁K₂K₃k₄[M][olef][H₂][CO]/([CO]² + K₁[H₂][CO] + K₁K₂K₃[olef][H₂]). Both complexes react rapidly with CO to produce the corresponding tricarbonyl species [M(CO)₃(PPh₃)₂]PF₆, M = Rh, 2a; Ir, 2b, and with syn-gas to yield [MH₂(CO)₂(PPh₃)₂]PF₆, M = Rh, 3a; Ir, 3b, which originate by CO dissociation the species [MH₂(CO)(PPh₃)₂]PF₆ entering the corresponding catalytic cycle. All the experimental data are consistent with a general mechanism in which the transfer of the hydride to a coordinated olefin promoted by an entering CO molecule is the rate-determining step of the catalytic cycle.     

Energetics of Water/Cyclodextrins Interactions

The heat capacities of solid -CD, 8.1 H₂O and -CD, 6.0 H₂O have been measured between 10 and 300 K by adiabatic calorimetry. Using earlier results obtained in similar experiments with anhydrous cyclodextrins and with -CD, 9.7 H₂O, a comparative analysis has been developed. The energetic behaviours of anhydrous and hydrated cyclodextrins (CDs) have been compared in order to investigate the role of water molecules in the stabilization of the cyclodextrin's rings and on their reactivities. Calculations, based on the additivity of thermodynamic properties, provide the energetic and entropic average contributions of water molecules in each cyclodextrin. From these results, we assumed that the water–water and water–CD interactions are rather different according to the cyclodextrin. In the (-CD, 9.7 H₂O) structure, the water molecules seem to be better organised in a relatively independent network. Concerning hydrated -CD and -CD, stronger water–CD interactions probably prevent an optimal organisation of the water–water bonds network. Differential scanning calorimetry was also used to follow the evolution of the thermal behaviour of -CD, nH₂O versus hydration ratio between 170 and 300 K. Our results indicate that the -CD ring needs at least 1.6 water molecules to be stabilized in the solid state.     

Effect of meta-tetra(hydroxyphenyl)chlorin (mTHPC)-mediated photodynamic therapy on sensitive and multidrug-resistant human breast cancer cells

Meta-tetra(hydroxyphenyl)chlorin (mTHPC) is in clinical trials for the photodynamic therapy (PDT) of localized-stage cancer. The PDT susceptibility of cells expressing multidrug resistance (MDR) phenotype is an attractive possibility to overcome the resistance to cytotoxic drugs observed during cancer chemotherapy. The accumulation, photocytotoxicity and intracellular localization of mTHPC were examined using the doxorubicin selected MCF-7/DXR human breast cancer cells, expressing P-glycoprotein (P-gp), and the wild-type parental cell line, MCF-7. No significant difference in mTHPC accumulation was observed between the two cell lines up to 3 h contact. The photodynamic activity of mTHPC, measured 24 h after irradiation with red laser light (lambda=650 nm), was significantly greater in MCF-7/DXR as compared to MCF-7 cells. A light dose of 2.5 J cm(-2) inducing 50% of cytotoxicity in MCF-7, resulted in 85% cytotoxicity in MCF-7/DXR. The presence of P-gp inhibitors SDZ-PSC-833 and cyclosporin A did not modify the mTHPC-induced cytotoxicity. The difference in intracellular mTHPC distribution pattern between two cell lines may contribute to different photocytotoxicity. Our results indicate that mTHPC mediated PDT could be useful in killing cells expressing MDR phenotype.     

Thermal Behaviour of Anhydrous α-, β- and γ-Cyclodextrin at Low Temperature

Heat capacities of anhydrous -and -cyclodextrin were measured by adiabaticcalorimetry between 10 K and 300 K. The thermalbehaviour of the two compounds exhibits significantdifferences. -Cyclodextrin shows an anomalousexcess heat capacity in the entire region between 70 Kand 210 K. In the case of -cyclodextrin, anendothermic effect is observed at 240K. This effect isanalysed through the study of the correspondingentropy change and discussed in terms ofintramolecular organization.Using the known heat capacity values of anhydrous-CD, a comparative analysis has been developed.For each cyclodextrin, the average behaviour of abound -D-glucopyranose has been calculated andcompared. From a thermodynamic point of view, thedegree of organization of the dehydrated macrocycliccompounds could be expressed as-CD -CD -CD.     

Diallylphosphines as New Bidentate Ligands in Iridium Complexes

Abstract

Addition of four equivalents of tButyldiallylphosphine to a solution of one equivalent of [(COE)₂Cl]₂ in CHCl₃ at low temperature produced two isomers of the metallated complex 2, formed by C-H activation. 2 evolve at 40°C to 3, by a hydride transfer from iridium to the cyclooctene (COE) ligand.