Intermolecular stacking of a tetranuclear cyclic Pt(II) complex: NMR characterization and X-ray crystal structure of cis-trans-cis-trans tetra[μ-2,6-diethynyl-4-nitroaniline-bis(tri(p-tolyl)phosphine)platinum(II)]

The synthesis and characterization of a tetranuclear Pt complex, cis-trans-cis-trans tetra[μ-2,6-diethynyl-4-nitroaniline-bis(tri(p-tolyl)phosphine) platinum(II)], namely [L₂Pt-DENA]₄ with L = tri-p-tolylphosphine, is reported. The complex was obtained by the dehydrohalogenative condensation of 2,6-diethynyl-4-nitroaniline (DENA) with cis-[dichlorobis(tri(p-tolyl)phosphine)platinum(II)]. The single crystal structure determination of [L₂Pt-DENA]₄ indicated the formation of a neutral molecular cycle with four alternating platinum units in cis and trans configurations, all bridged with DENA spacers with the presence of solvent (toluene) crystallization molecules. A twisted tetranuclear cyclic feature was identified. The formation of intermolecular stacks of the tetranuclear complex in solution was assessed by means of nuclear Overhauser enhancement spectroscopy (NOESY) and rotating frame Overhauser effect spectroscopy (ROESY) characterizations.     

Organic functionalization of carbon nanotubes

A very general and versatile method for functionalizing different types of carbon nanotubes is described, using the 1,3-dipolar cycloaddition of azomethine ylides. Approximately one organic group per 100 carbon atoms of the nanotube is introduced, to yield remakably soluble bundles of nanotubes, as seen in transmission electron micrographs. The solubilization of the nanotubes generates a novel, interesting class of materials, which combines the properties of the nanotubes and the organic moiety, thus offering new opportunities for applications in materials science, including the preparation of nanocomposites.     

Surface enhanced Raman scattering investigation of the halide anion effect on the adsorption of 1,2,3-triazole on silver and gold colloidal nanoparticles

The halide anion effect on the adsorption of 1,2,3-triazole on Ag and Au colloidal nanoparticles has been investigated by means of surface enhanced Raman scattering (SERS), UV-visible absorption spectroscopy, and scanning electron microscopy. To interpret the SERS spectra, the vibrational spectra of 1,2,3-triazole were assigned with the help of density functional theoretical (DFT) calculations of the two tautomers of 1,2,3-triazole, both free and bound to Ag and Au adatoms. Upon addition of halide anions, both tautomers interact with the Ag surface through one nitrogen atom. Analogous behavior is observed in the case of basified Au colloids, whereas at the usual pH of these hydrosols (approximately 6) the adsorption of 1,2,3-triazole is the same of that observed in halide-free colloids.     

Enantiomeric resolution of anti-HIV agents on a cellulose derivative chiral stationary phase

Summary Anti-HIV enantiomeric 1H, 3H-thiazolo[3, 4-a] benzimidazoles have been stereospecifically analyzed by elution on a column of cellulose tris-(4-methyl-phenylbenzoate)ester adsorbed on macroporous silica (Chiralcel^R OJ).The enantiomeric resolution of the compounds examined is linked to a complex and competitive contribution of different factors.     

Influence of organic modifier and temperature on the enantiomeric separation of γ-lactams by HPLC

Summary A high-performance liquid chromatographic method is reported for the resolution of the enantiomers of a series of fused -lactams (2,7-diaza-3-oxo[3.3.0]octan-6-ones) with probable anti-HIV and anticancer activity. Resolution was achieved on a Chiralcel^® OD column, cellulose tris-(3,5-dimethylphenyl carbamate) adsorbed on macroporous silica gel; mixtures ofn-hexane and isopropyl alcohol in different proportions were used as the mobile phase. The analysis was studied at different temperatures.     

Phenyldimethylsilyl-Substituted Ketenes and Bisketenes

The phenyldimethylsilyl-substituted monoketene PhMe(2)SiCH=C=O (1) and bisketene (PhMe(2)SiC=C=O)(2) (3) have been prepared and compared to the corresponding Me(3)Si- and t-BuMe(2)Si-substituted species. The (13)C, (17)O, and (29)Si NMR spectra fit the pattern shown by other silylketenes and provide no evidence for transmission of a substituent effect of the Ph group through the silicon to the ketenyl group, as has been proposed for PhMe(2)Si-substituted radicals. The UV spectrum of 1 does show a longer lambda and greater epsilon than for t-BuMe(2)SiCH=C=O, and this may indicate some interaction of the phenyl group with the ketene chromophore, while the greater reactivity of 1 in hydration compared to t-BuMe(2)SiCH=C=O is ascribed to the inductive effect of the phenyl. The very similar ring-opening reactivity of the bis(phenyldimethylsilyl)cyclobutenedione (6) to form 3 compared to the bis(Me(3)Si) analogues also provides no evidence of a significant interaction of the phenyl with the ketene. A new type of stabilized 1,8-bisketene based on the arylbis(dimethylsilyl) grouping, namely, 1,4-bis(ketenyldimethylsilyl)benzene (12), has been prepared for the first time.     

Solvent effects on 17O nuclear magnetic shielding: N-methylformamide in polar and apolar solutions

The solvent effect on ¹⁷O isotropic shielding was computed by different methods: the polarizable continuum model and a mixed approach, including a few real solvent molecules treated as the solute. The experimental data show that the behavior of protic and aprotic solvents is markedly different: we found that the continuum approach describes well the observed shielding at various dielectric constants for aprotic solvents, while the mixed procedure is needed when hydrogen bonds to the magnetic centre are present.Contribution to the Jacopo Tomasi Honorary Issue