Ab initio study of the tautomeric forms of some quinolinediones

7,8-dihydroquinoline-4,5 (1H,6H)-dione (1) and 7,8-dihydroquinoline-2,5-(1H,6H)-dione (2) in their tautomeric oxo and hydroxy forms have been studied by ab initio Hartree-Fock calculations; tautomerization energies predict a more stable hydroxy structure having an intramolecular hydrogen bond for compound 1, whereas the oxo form is slightly-preferred for compound 2. Fourier Transform-Infra Red (FT-IR) spectra in CHCl₃ solution indicate that the predicted most stable tautomers in the vapour phase remain as such.     

Supramolecular architectures of streptavidin on biotinylated self-assembled monolayers. Tracking biomolecular reorganization after bioconjugation

In this work we have studied the supramolecular bioconjugation of streptavidin (SAv) on biotinylated self-assembled monolayers. By using the quartz crystal microbalance technique with dissipation we were able to follow in real time the biomolecular reorganization within the film. The overall process could be described as an early stage involving a significant increase in surface coverage followed by another stage where the SAv layer slowly reached the asymptotic coverage. Finally, a reorganization process takes place in the bioconjugated film. These results on the kinetics of biomolecular reorganization can be described in terms of the Lifshitz-Slyozov law. These are the first experimental results demonstrating the complexity and the different time scales involved on the bioconjugation of SAv at solid-liquid interfaces. We consider that these findings could have strong implications on the molecular design of biosensing platforms.     

3-methylthiophene self-assembled monolayers on planar and nanoparticle Au surfaces

In this article the adsorption of 3-methylthiophene on planar and nanoparticle Au surfaces is investigated. The resulting systems are compared with a benchmark system based on 1-decanethiol. The characterization data collected evidence the formation of a packed 3-methylthiophene SAM on the planar surface. In particular, spectroscopic investigations suggest that 3-methylthiophene aromatic system is not adsorbed on the surface through the pi-electron system but rather through the S atom alone. On the other hand, the behavior of 3-methylthiophene on nanoparticle surfaces is notably different from that of the alkanethiol. Only a limited fraction of the surface of Au nanoparticles results to be actually coated after purification; this notwithstanding, the nanoparticle growth seems to be strongly influenced by the presence of such a labile encapsulating agent.     

Strong oscillations in molecular valence photoemission intensities

Photoemission from the two outermost ionizations [highest occupied molecular orbitals (HOMO and HOMO-1)] of Mg(eta(5)-C(5)H(5))(2) has been studied with synchrotron radiation in the gas phase. Strong oscillations in the HOMO-1/HOMO ratio, qualitatively similar to those well-known for fullerenes, are found. Excellent agreement with the experimental ratio is provided by accurate cross section calculations both at the density-functional theory and time-dependent density-functional theory level, indicating that a many electron response has a minor role for this effect. A comparison with the calculated values for other metal sandwich compounds indicate that the presence of oscillations is a widespread phenomenon, and a potential source of interesting information on the structural and electronic properties of the target molecule.     

Cu-catalyzed asymmetric allylic alkylations of aromatic and aliphatic phosphates with alkylzinc reagents. An effective method for enantioselective synthesis of tertiary and quaternary carbons

Efficient enantioselective Cu-catalyzed allylic alkylations of aromatic and aliphatic allylic phosphates bearing di- and trisubstituted olefins are disclosed. Enantioselective C-C bond forming reactions are promoted in the presence of 10 mol % readily available chiral amino acid-based ligand (5 steps, 40% overall yield synthesis) and 5 mol % (CuOTf)2 x C6H6. Reactions deliver tertiary and quaternary stereogenic carbon centers regioselectively and in 78-96% ee. Data regarding the effect of variations in ligand structure on the efficiency and enantioselectivity of the alkylation process, as well as a mechanistic working model, are presented. The suggested model involves a dual role for the chiral Cu complex: association of the Cu(I) center to the olefin is facilitated by a two-point binding between the carbonyl of the ligand's amide terminus and the P=O of the substrate.     

Detection of hypophosphite, phosphite, and orthophosphate in natural geothermal water by ion chromatography

Current doctrine states that phosphorus is incorporated into cells in the pentavalent(V) oxidation state as orthophosphate. However, recent studies show that microorganisms contain enzymes used to metabolize reduced forms of phosphorous, including phosphite(III) and hypophosphite(I), which suggests that there is a natural source for these chemical species. This paper will discuss suppressed conductivity ion chromatography methods developed to detect hypophosphite, phosphite, and orthophosphate in a geothermal water matrix containing fluoride, chloride, bromide, nitrate, hydrogen carbonate and sulfate. All peaks were clearly resolved, and calibrations were linear with estimated 3sigma detection limits of 0.83, 0.39, and 0.35 microM for hypophosphite, phosphite, and orthophosphate, respectively.     

Mechanisms of cytotoxicity in human ovarian carcinoma cells exposed to free Mce6 or HPMA copolymer-Mce6 conjugates

It is essential to understand cellular responses on photodynamic therapy (PDT) to design delivery systems that maximize cytotoxic effects coupled with minimal induction of side effects or protective mechanisms (or both). Here, we investigated mechanisms of toxicity in human ovarian carcinoma A2780 cells treated with structurally diverse N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer (P)-mesochlorin e6 monoethylenediamine (Mce6) conjugates that possessed differential subcellular accumulation or covalent attachments of photosensitizers (or both). Apoptosis and necrosis were observed after photoactivation, with increased apoptotic responses observed in cells exposed to conjugates possessing Mce6 linkage via a lysosomally degradable tetrapeptide spacer (HPMA copolymer-Mce6 conjugates containing Mce6 bound via glycylphenylalanylleucylglycine [GFLG] linker [P-GFLG-Mce6], HPMA copolymer-Mce6 conjugates containing Mce6 bound via a GFLG spacer and containing nuclear localization sequence, PKKKRKV132K(FITC)C [NLS(fluorescein-5-isothiocyanate [FITC])] bound via a thioether linkage [P-NLS(FITC)-GFLG-Mce6]). Furthermore, the induction of necrosis was more pronounced in cells exposed to conjugates containing both a nuclear localization sequence (NLS) and Mce6 bound by a degradable linker (P-NLS(FITC)-GFLG-Mce6). Caspase-independent mechanisms of cell death were identified in cells treated with nuclear-targeted conjugates possessing Mce6 attached using a nondegradable tether (HPMA copolymer-Mce6 conjugates containing Mce6 bound via a GG spacer and containing NLS(FITC) bound via a thioether linkage [P-NLS(FITC)-GG-Mce6]), whereas low levels of apoptosis and necrosis were detected in cells exposed to photoactivated nontargeted HPMA copolymer-Mce6 conjugates containing Mce6 coupled through a nondegradable spacer (HPMA copolymer-Mce6 conjugates containing Mce6 bound via GG linker [P-GG-Mce6]). Variations in gene expression were observed in cells on PDT. Specifically, HSP70 expression was solely detected in cells treated with P-GFLG-Mce6, whereas the loss of detection of several genes were observed in cells treated with P-NLS(FITC)-GFLG-Mce6. Variations in cellular responses on PDT using different HPMA copolymer-Mce6 conjugates will prove useful in the design of optimal HPMA copolymer PDT delivery systems.     

Cu(II) complexes with heterocyclic substituted thiosemicarbazones: the case of 5-formyluracil. Synthesis,characterization, x-ray structures,DNA interaction studies,and biological activity

Two new 5-formyluracil thiosemicarbazone (H(3)ut) derivatives, Me-H(3)ut (1) and Me(2)-H(3)ut (2), were synthesized by reacting thiosemicarbazides, mono- and dimethylated on the aminic nitrogen, with 5-formyluracil and were subsequently characterized. These ligands, treated with copper chloride and nitrate, afforded three complexes: [Cu(Me-H(3)ut)Cl(2)].H(2)O (3), [Cu(Me(2)-H(3)ut)Cl(2)].H(2)O (4), and [Cu(Me-H(3)ut)(NO(3))(OH(2))(2)]NO(3) (5). The crystal structures of these complexes have been determined by single-crystal X-ray diffraction. In 3 and 4, a similar pentacoordination is present; the copper atom is surrounded by the ligand SNO donor atoms and by two chloride ions. The structure of 5 consists of [Cu(Me-H(3)ut)(NO(3))(OH(2))(2)](+) cations and nitrate anions. The copper coordination (4 + 2) involves the SNO ligand atoms and a water oxygen in the basal plane; the apical positions are occupied by a second water oxygen and by an oxygen of a monodentate nitrate group. Two biochemical techniques, namely DNA titration in the UV-vis region and thermal denaturation, have been employed to probe the details of DNA binding of these compounds. Analysis of the results suggests that our compounds are able to interact with DNA by electrostatic and groove binding but not by intercalation. The compounds have been also tested in vitro on human leukemic cell line U937, but they are not able to inhibit significantly cell proliferation.     

Synthesis and structural characterisation of CdS nanoparticles prepared in a four-components "water-in-oil" microemulsion

Nanostructured semiconductor particles are currently under intense investigation because of their enhanced photoreactivity and photocatalytic properties due to the quantum-size effect and the dependence of the photophysical and photochemical properties on their size as it approaches the exciton diameter. This increasing interest has led to the development of several synthetic procedures to prepare and stabilise uniform crystallites. In this paper, we report a novel synthetic pathway to obtain cadmium sulphide (CdS) nanoparticles in a quaternary "water-in-oil" microemulsion formed by a cationic surfactant cetyltrimethylammonium bromide (CTAB), pentanol, n-hexane and water. The synthesis of CdS in this system is achieved by mixing two microemulsions containing Cd(NO3)2 and Na2S, respectively. The nanocrystals have been characterised by using UV--visible spectroscopy and Transmission Electron Microscopy to investigate the influence of various parameters of the particles' formation and stability in solution. Capping of nanoparticles with suitable organic molecules has been performed in order to increase their stability and afford solubility in a wide range of solvents.