Breakage of λ-DNA by inorganic tin and organotin compounds as environmental pollutants

In proportion to the environmental pollution problems caused by organotin compounds, the genotoxicities of tin compounds in the environments have become of interest so as to estimate their safety in recent years. In this work, isolated λ-DNA (double-strand DNA) was incubated with inorganic tin(II) and tin(IV) and five organotin compounds [n-butyltin trichloride, di(n-butyltin) dichloride, methyltin trichloride, dimethyltin dichloride and trimethyltin chloride] in reaction systems both with and without hydrogen peroxide (H₂O₂) content. The tin compounds tested in this study did not induce DNA breakage in the absence of hydrogen peroxide. Divalent inorganic tin (SnCl₂) and tetravalent inorganic tin (SnCl₄) caused DNA breakage in the presence of hydrogen peroxide (10 mM), and the DNA damage activity of inorganic tin was much more potent in divalent inorganic tin (SnCl₂) than in tetravalent inorganic tin (SnCl₄). Divalent inorganic tin (SnCl₂) induced DNA breakage in a concentration-dependent fashion at concentrations greater than 0.1 mM of SnCl₂ in the presence of hydrogen peroxide (10 mM). DNA breakage was not caused by n-butyltin compounds and methyltin compounds either in the presence or in the absence of hydrogen peroxide.     

5-Fluorouracil derivatives. XX. Synthesis and antitumor activity of 5'-O-unsaturated acyl-5-fluorouridines

Various kinds of 5'-O-unsaturated acyl 5-fluorouridines were synthesized to obtain 5-fluorouridine derivatives with low toxicity and high antitumor activity. Antitumor activity of the compounds against L-1210 leukemia in mice was examined, and the 5'-O-4-pentenoyl derivative showed the highest antitumor activity.     

Ca at C82 isomers: computed temperature dependency of relative concentrations

Relative concentrations of nine isomers of Ca at C82 derived from the C82 isolated-pentagon-rule satisfying cages are computed in a wide temperature interval. The computations are based on the Gibbs energy constructed from partition functions supplied with molecular parameters from density functional theory calculations. Five structures show significant populations at higher temperatures: C2v > Cs > C2 > C3v > Cs. The computed relative stabilities agree well with available observations.     

Reaction paths of some open-shell reactive intermediates

The intermolecular interaction energy for reacting systems in singlet, triplet and doublet states was partitioned by the perturbation expansion method into the chemically meaningful five interaction terms: the Coulomb, exchange-repulsion, induction, dispersion, and charge-transfer energies. In the local ZDO approximation, these energy terms were evaluated for the dimerization of methylenes (^1,3CH₂), the additions of carbenes (^1,3CH₂ and^1,3CF₂) as well as amino radicals (²NH₂ and²NF₂) toward ethylene, and the hydrogen abstractions by methylenes (^1,3CH₂), nitrene (³NH), and hydroxyl radical (²OH) from methane. It has been found that the reaction path is much influenced by the spinmultiplicity, and that the charge-transfer and exchange-repulsion terms play a dominant role in determining the course of reactions.     

Electrical Properties of Polycrystalline Lithium Chloroboracite Prepared by the Sol-Gel Method

The electrical properties of polycrystalline lithium chloroboracite, Li4B7O12Cl, prepared by the sol-gel method were investigated in connection with their structure. Li4B7O12Cl pellets were prepared with different amounts of hydrochloric acid or ammonium chloride. The kind and amount of the chlorine source affected the formation of by-products (Li2B4O7, LiCl, a glass phase) and the morphology of the Li4B7O12Cl pellets. Thus their conductivity, which is dominated by grain boundary response owing to the high porosity of the materials, was also affected. The formation of Li2B4O7 as a by-product led to a higher activation energy and lower conductivity. In those pellets in which Li2B4O7 did form, an increase of the amount of glass phase led to higher conductivities.     

Two-dimensional self-organization of phthalocyanine and porphyrin: dependence on the crystallographic orientation of Au

By immersing Au substrate into a benzene solution containing both cobalt(II) phthalocyanine (CoPc) and copper(II) tetraphenyl-21H,23H-porphine (CuTPP), a two-dimensional alternate bimolecular structure was formed on the reconstructed Au(100)-(hex) surface.     

The first example of the stereoselective synthesis of 7 beta-carbamoyl-4,5alpha-epoxymorphinan via a novel and reactive gamma-lactone

7beta-Carbamoyl-4,5alpha-epoxymorphinans 5 were stereoselectively synthesized from the 7alpha-carboxylate intermediate 3 in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and amines under reflux conditions in mesitylene via a novel and reactive gamma-lactone 7. These were the first examples of the stereoselective syntheses of 7beta-substituted 4,5alpha-epoxymorphinans. The mechanism of the reaction process was elucidated as follows: 1) epimerization of 7alpha-carboxylate 3, 2) intramolecular lactonization of 7beta-carboxylate 6, and 3) aminolysis of the resultant gamma-lactone 7. The aminolysis of the isolated reactive gamma-lactone 7 with allylamine and the alcoholysis with MeOH in the presence of NaBH(4) proceeded at room temperature. The gamma-lactone 7 can be a useful intermediate for the preparation of 7beta-substituted 4,5alpha-epoxymorphinans that would be potent selective delta opioid receptor ligands. The stereoselective syntheses of the 7alpha-carbamoyl-4,5alpha-epoxymorphinans 9 from 7alpha-carboxylate 3 via 7alpha-carboxylic acid were also successful.     

Dependence of molecular recognition of fullerene derivative on the adlayer structure of zinc octaethylporphyrin formed on Au(100) surface

Adlayers of ZnOEP were prepared on reconstructed Au(100)-(hex) and unreconstructed Au(100)-(1 x 1) surfaces by immersing into a benzene solution containing ZnOEP molecules, and the adlayer structures were characterized by scanning tunneling microscopy (STM). A hexagonally arranged ZnOEP array was formed on an Au(100)-(hex) surface, whereas a rectangularly arranged ZnOEP array was found on an Au(100)-(1 x 1) surface. The adlayer structure of ZnOEP was dependent upon the underlying Au atomic arrangements. Furthermore, an investigation of the spuramolecular assembly for these modified surfaces was carried out by using an open-cage C(60) derivative (opened C(60)). A supramolecular assembled adlayer with a 1:1 composition of opened C(60)/ZnOEP was formed on Au(100)-(hex), whereas aggregates of opened C(60) were found on the ZnOEP-modified Au(100)-(1 x 1) surface. Electrochemical responses of opened C(60) were significantly influenced by underlying ZnOEP arrays. This finding suggests that precise control of underlying ZnOEP adlayers with the Au atomic structure is important to recognize the opened C(60) on them.     

Theoretical study of endohedral metallofullerenes: Sc3−nLanN@C80 (n=0–3)

To provide theoretical insight into the structures and properties of Sc₃N@C₈₀, which has been isolated in high yield and purity as a new stable endohedral metallofullerene, density functional calculations are carried out for the Sc_3?nLa_nN@C₈₀ (n=0–3) series. Because of electron transfer from Sc₃N to C₈₀, the electronic structure of Sc₃N@C₈₀ is formally described as (Sc₃N)⁶⁺C$_{80}^{6-}$. The encapsulated Sc₃N cluster takes a planar structure with long Sc–Sc distances and is highly stabilized inside the I_h cage of C₈₀, which rotates rapidly. As the number of La atoms increases, the Sc_3?nLa_nN cluster is forced to maintain a pyramidal structure in Sc_3?nLa_nN@C₈₀. In addition, the C₈₀ cage takes an open‐shell electronic structure due to an increase in the number of electrons transferring from Sc_3?nLa_nN. These make the endohedral structure less stable and more reactive. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1353–1358, 2001     

Isolation, characterization, and theoretical study of La2@C78

A new metallofullerene, La2@C78, has been synthesized by DC arc discharge method, isolated by high-performance liquid chromatography, and characterized by laser desorption time-of-flight mass spectrometry, UV-vis-NIR absorption, differential pulse voltammetry, 13C NMR spectroscopy, and theoretical calculations. The La2@C78/CS2 solution is dark violet and presents several characteristic absorption features at 647, 561, 533, and 386 nm, with an onset around 1000 nm. With respect to empty D3-C78, the capability of La2@C78 as an electron acceptor or donor is stronger. Addition of 1,1,2,2-tetrakis(2,4,6-trimethylphenyl)-1,2-disirane to La2@C78 photochemically, as well as thermally, affords bis- and mono-adducts. Theoretical studies and 13C NMR spectroscopic analysis of La2@C78 indicate that it possesses a D3h-C78 cage (78:5).