RELATIVE REACTIVITIES OF THE EXCITED STATES OF FUROCOUMARINS FOR [2+2] PHOTOCYCLOADDITION REACTION WITH TETRAMETHYLETHYLENE

Abstract— The Stern-Volmer constants for fluorescence quenching by tetramethylethylene decrease in the order DMC ≫ DHP > F-2 > 8-MOP. The same order was observed for the quantum yields of [2+2] cycloaddition reaction with tetramethylethylene on direct irradiation. In [2+2] photocycloaddition of F-2 with tetramethylethylene in ethanol, the ratio of quantum yields deduced from singlet and triplet states of F-2; φ₃⁰/φ₁⁰, is about 5. The excited triplet state is the reactive state for the [2+2] photocycloaddition of F-2 with tetramethylethylene in solution but the excited singlet state of F-2 becomes very important in biological conditions.     

Surface modification of polyethylene terephthalate using PEO-polybutadiene-PEO triblock copolymers

The initial step of thrombus formation on blood-contacting biomaterials is known to be adsorption of blood proteins followed by platelet adhesion. It is generally accepted that surface modification of the biomaterials with poly(ethylene oxide) (PEO) substantially reduces protein adsorption and cell adhesion. Dacron® (polyethylene terephthalate) fabric, which is one of the biomaterials commonly used in blood-contacting devices, was grafted with PEO. A simple two-step procedure for covalent grafting of PEO onto the surface of Dacron® fabric was used. The surface was first treated with PEO-polybutadiene-PEO (PEO-PB-PEO) triblock copolymer, to introduce a layer of double bonds onto the surface. The Dacron® surface was then exposed to a solution of Pluronic® F108 (PF108), a commercially available PEO-poly(propylene oxide)-PEO (PEO-PPO-PEO) triblock copolymer. The surface with two adsorbed layers of PEO-PB-PEO and PF108 was γ-irradiated in the presence of PF108 in the bulk solution for a total radiation dose of 0.8 Mrad. The bulk concentrations of PEO-PB-PEO and PF108 were varied to maximize the efficiency of PEO grafting. Fibrinogen adsorption on PEO-grafted surfaces was reduced more than 90%, compared with that on control surfaces, irrespective of the bulk concentrations of polymers used for grafting. Platelet adhesion was also reduced substantially by PEO grafting. Only a few round platelets were able to adhere to the PEO-grafted surface, while the control surface was fully covered with aggregates of activated platelets. PEO grafting on polyethylene terephthalate using PEO-PB-PEO and PEO-PPO-PEO block copolymers is a simple approach that can be used for various other biomaterials.     

Ruthenium‐catalyzed formal alkyl group transfer: Synthesis of quinolines from nitroarenes and alkylammonium halides

Nitroarenes are reductively cyclized with an array of tetraalkylammonium halides and trialkylarnmonium chlorides in the presence of a catalytic amount of a ruthenium catalyst along with tin(II) chloride dihydrate at 180° to afford the corresponding quinolines in moderate to good yields. The addition of tin(II) chloride dihydrate is necessary for the effective formation of quinolines and toluene is the solvent of choice. A reaction pathway involving initial reduction of nitroarenes to anilines and conversion of alkylammonium halides to alkylamines, alkyl group transfer from alkylamines to anilines to form an imine, dimerization of imine, and heteroannulation is proposed for this catalytic process.     

Highly efficient Pd-catalyzed carbonylative cross-coupling reactions with tetraorganoindates

Tetraorganoindates, which were prepared easily from the reaction of 1 equiv of InCl(3) with 4 equiv of organometallics, could be employed as effective nucleophilic cross-coupling partners in Pd-catalyzed carbonylative cross-coupling reactions with a variety of organic electrophiles. The present method gave unsymmetrical ketones and 1,4-diacylbenzenes in good yields with highly efficient transfer of almost all the organic groups attached to the indium under a carbon monoxide atmosphere in THF at 60 degrees C.     

Kinetically controlled Ag+-coordinated chiral supramolecular polymerization accompanying a helical inversion

We report kinetically controlled chiral supramolecular polymerization based on ligand–metal complex with a 3 : 2 (L : Ag⁺) stoichiometry accompanying a helical inversion in water. A new family of bipyridine-based ligands (d-L1, l-L1, d-L2, and d-L3) possessing hydrazine and d- or l-alanine moieties at the alkyl chain groups has been designed and synthesized. Interestingly, upon addition of AgNO₃ (0.5–1.3 equiv.) to the d-L1 solution, it generated the aggregate I composed of the d-L1AgNO₃ complex (d-L1 : Ag⁺ = 1 : 1) as the kinetic product with a spherical structure. Then, aggregate I (nanoparticle) was transformed into the aggregate II (supramolecular polymer) based on the (d-L1)₃Ag₂(NO₃)₂ complex as the thermodynamic product with a fiber structure, which led to the helical inversion from the left-handed (M-type) to the right-handed (P-type) helicity accompanying CD amplification. In contrast, the spherical aggregate I (nanoparticle) composed of the d-L1AgNO₃ complex with the left-handed (M-type) helicity formed in the presence of 2.0 equiv. of AgNO₃ and was not additionally changed, which indicated that it was the thermodynamic product. The chiral supramolecular polymer based on (d-L1)₃Ag₂(NO₃)₂ was produced via a nucleation–elongation mechanism with a cooperative pathway. In thermodynamic study, the standard ΔG° and ΔH_e values for the aggregates I and II were calculated using the van''t Hoff plot. The enhanced ΔG° value of the aggregate II compared to that of the formation of aggregate I confirms that aggregate II was thermodynamically more stable. In the kinetic study, the influence of concentration of AgNO₃ confirmed the initial formation of the aggregate I (nanoparticle), which then evolved to the aggregate II (supramolecular polymer). Thus, the concentration of the (d-L1)₃Ag₂(NO₃)₂ complex in the initial state plays a critical role in generating aggregate II (supramolecular polymer). In particular, NO₃⁻ acts as a critical linker and accelerator in the transformation from the aggregate I to the aggregate II. This is the first example of a system for a kinetically controlled chiral supramolecular polymer that is formed via multiple steps with coordination structural change.

The nanoparticles were transformed into the supramolecular polymer as the thermodynamic product, involving a helical inversion from left-handed to right-handed helicity.     

Metabolism of eupatilin in rats using liquid chromatography/electrospray mass spectrometry

Eupatilin (5,7-dihydroxy-3',4',6-trimethoxy flavone) is an active ingredient of an ethanol extract of Artemisia asiatica (DA-9601) that is used in the treatment of gastritis. In vitro and in vivo metabolism of eupatilin in the rats has been studied by LC-electrospray mass spectrometry. Rat liver microsomal incubation of eupatilin in the presence of NADPH and UDPGA resulted in the formation of four metabolites (M1-M4). M1, M2, M3 and M4 were tentatively identified as 3'- or 4'-O-demethyl-eupatilin glucuronide, eupatilin glucuronide, 6-O-demethyleupatilin and 3'- or 4'-O-demethyl-eupatilin, respectively. Those metabolites from in vitro study were also characterized in bile, plasma or urine samples after an intravenous administration of eupatilin to rats. In rat bile, plasma and urine samples, eupatilin glucuronide (M2) was a major metabolite, whereas M3, M4 and M4 glucuronide (M1) were the minor metabolites.     

Spontaneous reduction of metal ions on the sidewalls of carbon nanotubes

Nanotube/nanoparticle hybrid structures are prepared by forming Au and Pt nanoparticles on the sidewalls of single-walled carbon nanotubes. Reducing agent or catalyst-free electroless deposition, which purely utilizes the redox potential difference between Au3+, Pt2+, and the carbon nanotube, is the main driving force for this reaction. It is also shown that carbon nanotubes act as a template for wire-like metal structures. The successful formation of the hybrid structures is monitored by atomic force microscopy (AFM) and electrical measurements.     

Cadmium(II) and mercury(II) complexes of an NO2S2-donor macrocycle and its ditopic xylyl-bridged analogue

The NO2S2-donor macrocycle (L1) was synthesised from the ring closure reaction between Boc-N-protected 2,2'-iminobis(ethanethiol) (3) and 2,2'-(ethylenedioxy)bis(benzyl chloride) (4) followed by deprotection of the Boc-group. alpha,alpha'-Dibromo-p-xylene was employed as a dialkylating agent to bridge two L1 to yield the corresponding N-linked product (L2). The X-ray structure of L2 (as its HBr salt) is described. A range of Cd(II) and Hg(II) complexes of L1 (6-9) and L2 (10-12) were prepared and characterised. Reaction of HgX2 (X = Br or I) with L1 afforded [Hg(L1)Br]2[Hg2Br6].2CH2Cl2 6 and [Hg(L1)I(2)] 7, respectively. For 6, the Hg(II) ion in the complex cation has a distorted tetrahedral coordination environment composed of S2N donor atoms from L1 and a bromo ligand. In 7 the coordination geometry is highly distorted tetrahedral, with the macrocycle coordinating in an exodentate manner via one S and one N atom. The remaining two coordination sites are occupied by iodide ions. [Hg(L1)(ClO4)]ClO4 8 was isolated from the reaction of Hg(ClO4)2 and L1. The X-ray structure reveals that all macrocyclic ring donors bind to the central mercury ion in this case, with the latter exhibiting a highly distorted octahedral coordination geometry. The O2S2-donors from the macrocyclic ring define the equatorial plane while the axial positions are occupied by the ring nitrogen as well as by an oxygen from a monodentate perchlorato ion. Reaction of Cd(NO3)(2).4H2O with L1 afforded [Cd(L1)(NO3)2](.)0.5CH2Cl2 9 in which L1 acts as a tridentate ligand, binding exo-fashion via its S2N donors. The remaining coordination positions are filled by two bidentate nitrate ions such that, overall, the cadmium is seven-coordinate. Reactions of HgX2(X = Br or I) with L2 yielded the isostructural 2 : 1 (metal : ligand) complexes, [Hg2(L2)Br4] 10 and [Hg2(L2)I(4)] 11. Each mercury ion has a distorted tetrahedral environment made up of S and N donors from an exodentate L2 and two coordinated halides. Contrasting with this, the reaction of L2 with Cd(NO3)(2).4H2O yielded a 1-D coordination network, {[Cd2(L2)(NO3)4].2CH2Cl2}n 12 in which each ring of L2 is exo-coordinated via two S atoms and one N atom to a cadmium ion which is also bound to one monodentate and one bidentate nitrate anion. The latter also has one of its oxygen atom attached to a neighboring cadmium via a nitroso (mu2-O) bridge such that the overall coordination geometry about each cadmium is seven-coordinate. The [Cd(L2)0.5(NO3)2] units are linked by an inversion to yield the polymeric arrangement.     

Synthesis of 32‐phenyl‐substituted methyl E/Z‐pyropheophorbide‐a's from methyl E/Z‐pyropehophorbide‐a 131‐ketoximes

Methyl E/Z‐pyropheophorbide‐a 13¹‐ketoximes 2a,b and their O‐acetyl derivatives 3a,b were oxidized with osmium(VIII) oxide to give aldehydes 4a,b and 5a,b , respectively. The Wittig reactions of the aldehyde chlorines 4a,b and 5a,b with benzyltriphenylphosphonium chloride were performed to form the corresponding methyl (3¹E/Z,13¹E/Z)‐3²‐phenylpyropheophorbide‐a 13¹‐ketoximes 6aa‐bb and their O‐acetyl derivatives 7aa‐bb ; hydrolysis of these ketoximes 6aa,ba and 6ab,bb in formic acid produced methyl (E/Z)‐3²‐phenylpyropheophorbide‐a's 8a,b .     

A rhodium‐catalyzed route for oxidative coupling and cyclization of 2‐aminobenzyl alcohol with ketones leading to quinolines

2‐Aminobenzyl alcohol undergoes oxidative cyclization with aryl(alkyl), alkyl(alkyl) and cyclic ketones in dioxane at 80° in the presence of a catalytic amount of RhCl(PPh₃)₃ along with KOH to afford the corresponding quinolines in good yields. The catalytic pathway seems to be proceeded via a sequence involving initial oxidation of 2‐aminobenzyl alcohol to 2‐aminobenzaldehyde by a rhodium catalyst, cross aldol reaction between 2‐aminobenzaldehyde and ketones, and cyclodehydration.