Polyacetylenes and Cumulenes,Potential Elements for Molecular Machines and Precursors of Carbon Clusters: A Theoretical Study

A recently described very simple procedure for estimating Hartree–Fock (H. F.) energy and accurate nonrelativistic energy has been used with simple hydrocarbons possessing C?C or C?C bonds and for the acetylene dimer. Experimental characteristics (heats of formation, ionization potentials, electron affinities), structural features, and reactivity have been discussed in terms of quantum‐chemistry characteristics at the H. F. level and also at a level including a part of electron correlation. Deviations from linearity with derivatives of long polyacetylenes and cumulenes are ascribed to the lowest‐energy deformation vibrations, which decrease rapidly when passing from short to long acetylenic and cumulenic chains. The role of derivatives and heteroanalogues of hydrocarbons under study in atmospheric and interstellar chemistry is briefly mentioned. Derivatives with enhanced stability represent potentially promising construction materials for molecular devices and also resources for the preparation of defined clusters of C‐atoms.     

Synthesis of a Sialyl Lewis x Mimic with Fixed Carboxylic Acid Group: Chemical Approach toward the Elucidation of the Bioactive Conformation of Sialyl Lewis x

The relation of the solution and bioactive conformation of sialyl Lewis x (sLe(x)) has been addressed by chemical means. To mimic the preferred solution conformation of sLe(x) 1, the more rigid analog 2 has been designed and synthesized. The sialic acid residue of 1 was replaced by a carboxylic acid function which is fixed in the equatorial position of a six membered ring acetal fused to galactose. Due to entropic considerations, an increased biological activity could be expected if the preferred solution conformation and bound form of sLe(x) were similar. Since mimic 2 was found to be inactive in an E-selectin binding assay, the bound form of sLe(x) most probably differs from the prevailing solution conformation.     

S(N)1-like reactions of bicyclic alpha-amino ethers with sulfur,nitrogen, and carbon nucleophiles. Synthesis of 1-azabicyclo[3.2.2]nonanes functionalized at carbon C2 and C6 with complete stereocontrol

[reaction: see text] In the presence of nucleophiles, Lewis acid mediated cleavage of alpha-amino ethers derived from quincorine and quincoridine affords a variety of C2-substituted and C6-vinylated 1-azabicyclo[3.2.2]nonanes. These are enantiopure and are formed in S(N)1-like reactions with complete stereocontrol. There is no leakage into 2-Nu en route to product 1-Nu or vice versa. Me(3)SiCN provides new Strecker-type alpha-amino nitriles. In the presence of TTMPP-BF(3).OEt(2), the ketene acetal Me(2)C=C(OMe)OSiMe(3) delivers enantiopure bicyclic beta-amino acid esters.     

Experimental and theoretical study of the adsorption of fumaramide [2]rotaxane on Au(111) and Ag(111) surfaces

Thin films of fumaramide [2]rotaxane, a mechanically interlocked molecule composed of a macrocycle and a thread in a "bead and thread" configuration, were prepared by vapor deposition on both Ag(111) and Au(111) substrates. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy were used to characterize monolayer and bulklike multilayer films. XPS determination of the relative amounts of carbon, nitrogen, and oxygen indicates that the molecule adsorbs intact. On both metal surfaces, molecules in the first adsorbed layer show an additional component in the C 1s XPS line attributed to chemisorption via amide groups. Molecular-dynamics simulation indicates that the molecule orients two of its eight phenyl rings, one from the macrocycle and one from the thread, in a parallel bonding geometry with respect to the metal surfaces, leaving three amide groups very close to the substrate. In the case of fumaramide [2]rotaxane adsorption on Au(111), the presence of certain out-of-plane phenyl ring and Au-O vibrational modes points to such bonding and a preferential molecular orientation. The theoretical and experimental results imply that the three-dimensional intermolecular configuration permits chemisorption at low coverage to be driven by interactions between the three amide functions of fumaramide [2]rotaxane and the Ag(111) or Au(111) surface.     

Electrophoretic dynamics of large DNA stars in polymer solutions and gels

We have developed a procedure for synthesizing large stable branched DNA structures that enables visualization via fluorescence microscopy. Using this procedure we have synthesized large DNA stars and observed their electrophoretic behavior in polymer solutions and gels. In dilute polyacrylamide solutions, the DNA stars move as random coils and appear to experience only brief collisions with the polymer chains in solution. The effect of polymer solution concentration on the electrophoretic mobility of stars in the dilute regime is found to be in good accord with predictions of the transient entanglement coupling (TEC) model. In semidilute polymer solutions, the star arms extend in the field direction and drag the core through the matrix. The star arms form several U-shaped conformations as they collide and engage with polyacrylamide chains. The U-shaped conformations occasionally evolve into J-shaped conformations as the star arms slide off the matrix chains they engage during electrophoretic migration. In concentrated polymer solutions, the arms of the star extend and form V-shaped structures with the core as the apex. The arms then pull the core through the matrix. These V-shaped conformations are much longer-lived than U-shaped ones and, unlike the latter, do not transform to J-shaped conformations. In polyacrylamide and agarose gels, where matrix entanglements are fixed, DNA stars become trapped when entanglements with matrix molecules prevent the core from being pulled through the matrix by the extended arms. This trapping was observed at all gel concentrations and electric fields studied.     

Chloracylierung und Bromacylierung von Carbonylverbindungen: Eine in Vergessenheit geratene Carbonylreaktion. I. Präparative Anwendungsbreite

Chloroacylation and bromoacylation of carbonyl compounds: A forgotten carbonyl reaction. I. Scope of the reaction Aliphatic, α,β-unsaturated and aromatic aldehydes as well as aliphatic ketones react with acyl halides to (α-haloalkyl)esters. These bifunctional derivates contain two leaving groups of different reactivity. The scope of this scarcely of this scarcely known carbonyl reaction is discussed.     

Antioxidant Activity of Ruthenium Cyclopentadienyl Complexes Bearing Succinimidato and Phthalimidato Ligands

In these studies, we investigated the antioxidant activity of three ruthenium cyclopentadienyl complexes bearing different imidato ligands: (η⁵-cyclopentadienyl)Ru(CO)₂-N-methoxysuccinimidato (1), (η⁵-cyclopentadienyl)Ru(CO)₂-N-ethoxysuccinimidato (2), and (η⁵-cyclopentadienyl)Ru(CO)₂-N-phthalimidato (3). We studied the effects of ruthenium complexes 1–3 at a low concentration of 50 µM on the viability and the cell cycle of peripheral blood mononuclear cells (PBMCs) and HL-60 leukemic cells exposed to oxidative stress induced by hydrogen peroxide (H₂O₂). Moreover, we examined the influence of these complexes on DNA oxidative damage, the level of reactive oxygen species (ROS), and superoxide dismutase (SOD) activity. We have observed that ruthenium complexes 1–3 increase the viability of both normal and cancer cells decreased by H₂O₂ and also alter the HL-60 cell cycle arrested by H₂O₂ in the sub-G1 phase. In addition, we have shown that ruthenium complexes reduce the levels of ROS and oxidative DNA damage in both cell types. They also restore SOD activity reduced by H₂O₂. Our results indicate that ruthenium complexes 1–3 bearing succinimidato and phthalimidato ligands have antioxidant activity without cytotoxic effect at low concentrations. For this reason, the ruthenium complexes studied by us should be considered interesting molecules with clinical potential that require further detailed research.