Resonance Raman spectroscopy characterization of single-wall carbon nanotube separation by their metallicity and diameter.

Several techniques were recently reported for the bulk separation of metallic (M) and semiconducting (S) single wall carbon nanotubes (SWNTs), using optical absorption and resonance Raman spectroscopy (RRS) as a proof of the separation. In the present work, we develop a method for the quantitative evaluation of the M to S separation ratio, and also for the SWNT diameter selectivity of the separation process, based on RRS. The relative changes in the integrated intensities of the radial-breathing mode (RBM) features, with respect to the starting material, yield the diameter probability distribution functions for M and S SWNTs in the separated fractions, accounting for the different resonance conditions of individual SWNTs, while the diameter distribution of the starting material is obtained following the fitting procedure developed by Kuzmany and coworkers. Features other than the RBM are generally less effective for characterization of the separation process for SWNTs.

Palladium and platinum famotidine complexes.

The molecule of the well-known ulceration inhibitor, famotidine, is an excellent coordinator of transition metal ions. The guanidine, amine group and thiazole nitrogen, and the thioether sulphur are preferential sites to bind metal ions. Pd(II) and Pt(II) derivatives of famotidine have been synthesized and studied structurally. There is evidence that the palladium complex is a monomer while the platinum complex forms a dimer. Due to the interesting structure of the platinum complex several assays have examined the possible antitumour activity. Changes in DNA conformation induced by both complexes have been detected by CD, interstrand crosslinking interactions and electrophoretic mobility, but studies of the cytotoxicity of the platinum compound with U937 human leukemia cells and HeLA human womb carcinoma cells show only a small antiproliferative potential.

Pd(II)- and Pt(II)-cimetidine complexes. Crystal structure of trans-[Pt(N,S-cimetidine)(2)]Cl(2)(*)12H(2)O.

The influence of cimetidine on patients under cisplatin treatment for cancer is controversial. It has moderate or no effects on several types of cancer and its effects on the nephrotoxicity induced by cisplatin are uncertain. To examine the binding properties and antiproliferative effects of the known anticancer noble metals, cimetidine (cim) was complexed to platinum(II) and palladium(II). The crystal structure of the Pt-cim compound shows two molecules of cimetidine coordinated to the metal through thioether sulfur and imidazolic nitrogen whereas spectroscopic studies in solution for Pd-cim reveal that the ratio of the metal to cimetidine is 1:1 with identical coordination environments. To determine the antitumor activity of the drugs, the interaction of the metallic complexes and free cimetidine with DNA was assessed. Their cytotoxic activity was compared with that of cisplatin.

Structural and cytotoxic study of new Pt(II) and Pd(II) complexes with the bi-heterocyclic ligand mepirizole.

Pd(II) and Pt(II) complexes of formulae [MLCl2], where L = mepirizole, were synthesized and characterized. Two complexes were obtained and studied by different techniques: IR, 1H and 13C NMR and XPS spectroscopies and mass spectrometry (electrospray). The crystal structure of the complex cis-dichloro-4-methoxy-2-(5-methoxy-3-methyl- pyrazol-1-yl)-6-methyl-pyrimidinepalladium(II), [Pd(mep)Cl2], was studied by crystal X-ray diffraction. It consists of discrete molecules with planar geometry. Pd(II) ions are four-coordinated by two mepirizole nitrogen atoms (N1 from the pyrazole ring and N4 from the pyrimidine ring) and two chlorine atoms. The geometry of the PdN2Cl2 chromophore is a distortion of the square-planar coordination. Data from powder pattern X-ray diffraction of cis-dichloro-4-methoxy-2-(5-methoxy-3-methyl-pyrazol-1-yl)-6-methyl- pyrimidineplatinum(II), [Pt(mep)Cl2], demonstrated that the two complexes are isostructural. The cytotoxic activity of both Pd and Pt complexes was checked for six different tumor cell lines and was lower than that of cisplatin. The Pt bound to DNA was also checked and only a low percentage is able to cross the cell membrane.

Study of the modifications caused by cisplatin, transplatin, and Pd(II) and Pt(II) mepirizole derivatives on pBR322 DNA by atomic force microscopy.

Modifications of the structure of pBR322 DNA caused by interaction with cisplatin, transplatin and Pd(II) and Pt(II) mepirizole derivatives were studied. The compounds were incubated with the plasmid DNA for 24 h at 37 degrees C and then observed with an atomic force microscope. Circular DNA was used because the small tertiary structural changes are easy to monitor. Likewise, its superhelical nature mimics DNA better than certain forms of intracellular DNA such as chromatin. AFM images clearly reveal that the complexes induce changes in the topological forms of fully relaxed pBR322 DNA. Most of the compounds produce a more compact DNA structure with modified writhing number. Analysis of gel migration of the relaxed pBR322 DNA incubated with the platinum complexes provides complementary information, which is in good agreement with AFM results.

Phonon-assisted excitonic recombination channels observed in DNA-wrapped carbon nanotubes using photoluminescence spectroscopy.

By using a sample of DNA-wrapped single-wall carbon nanotubes strongly enriched in the (6,5) nanotube, photoluminescence emissions observed at special excitation energy values were identified with specific mechanisms of phonon-assisted excitonic absorption and recombination processes associated with (6,5) nanotubes, including one-phonon, two-phonon, and some continuous-luminescence processes. Such detailed processes are not separately identified in three-dimensional semiconducting materials. A general theoretical framework is presented to interpret the experimentally observed phonon-assisted processes in terms of excitonic states.

Study of the interaction of DNA with cisplatin and other Pd(II) and Pt(II) complexes by atomic force microscopy.

Modifications in the structure of a 260 bp DNA (hlyM) fragment from Escherichia coli caused by interaction with Pd(II) and Pt(II) complexes were studied. Cisplatin and transplatin [cis- and trans-PtCl2(NH3)2 respectively], Pt2Cl2(Spym)4 (Spym = 2-mercaptopyrimidine anion), Pd-famotidine and Pt-famotidine were incubated with DNA for 24 h at 37 degrees C and then observed with an atomic force microscope. Atomic force microscopy (AFM) provides the opportunity for nanometer resolution in research on the interaction between nucleic acids and metal complexes. The complexes induced noticeable changes in DNA topography according to their different characteristics and structure. In the case of cisplatin a shortening in DNA strands was observed. Transplatin and Pt2Cl2(Spym)4 caused shortening and compaction, whilst an aggregation of two strands was observed for the Pt-famotidine compound but not for the Pd-famotidine compound or the metal-free famotidine.

Study of the interaction between a histidine-deoxyguanosine hybrid and cisplatin.

A histidine-2'-deoxyguanosine hybrid, Phac-Hse(p5'dG)-His-OH (I), was synthesized, and its reaction with cisplatin was monitored by reversed-phase HPLC and 1HNMR. Two new compounds, II and III, were observed to be simultaneously formed, II in larger proportion than III. These products were isolated after HPLC purification and extensively characterized. Both II and III contained platinum, had the same mass and showed a bathochromic displacement of their absorption maxima with respect to that of I. Both remained undegraded upon enzymatic digestion and yielded I when treated with NaCN. From these data and the information provided by 1HNMR analysis, we inferred that II and III were constitutional isomers, in particular chelates in which platinum was coordinated to the N7 of guanine and either the N pi or the N tau imidazole nitrogens, respectively. No preference of the metal for either of these N-donors was observed.