Phase-resolved fluorescence study of mono-L-aspartyl chlorin E6

The properties of a photosensitizer for photodynamic therapy, mono-L-aspartyl chlorin e6 (NPe6), were investigated using phase-resolved fluorescence. NPe6 was analyzed in water solution at concentrations ranging from 3.13x10(-7) to 8.00x10(-5) M. The photophysical parameters of the lowest singlet excited state of NPe6 molecules were experimentally determined. It was confirmed that NPe6 molecules were in the isolated molecular state at concentrations below 1.00x10(-5) M. It was also confirmed that the fluorescence in this concentration range was ascribable to the electronic transition of isolated NPe6 molecules from the lowest singlet excited state to the ground state. At concentrations above 1.00x10(-5) M, some of the NPe6 molecules formed dimers in water solution, which caused a red shift of the fluorescence spectrum and an enhancement of fluorescence in the 700-750 nm wavelength region. Semiempirical molecular orbital calculation revealed that the sodium aspartate attached to the tetrapyrrole ring through the ethanoic group was remarkably bent with respect to the tetrapyrrole plane. This bending appeared to hinder the formation of NPe6 dimers at concentrations up to 1.00x10(-5) M.     

A Mn12 single-molecule magnet [Mn12O12(OAc)12(dpp)4] (dppH = diphenyl phosphate) with no coordinating water molecules

The preparation and physical characterization are reported for a novel single-molecule magnet [Mn(12)O(12)(OAc)(12)(dpp)(4)] (dppH = diphenyl phosphate) with no coordinating water molecules. The crystal structure analysis reveals that there are four five-coordinate Mn(III) ions with Mn.H approaches. Addition of water in CD(2)Cl(2) solution was monitored by (1)H NMR, which showed that H(2)O could coordinate to a vacant site of a five-coordinate Mn(III) ion in solution. The measurements and analyses of magnetization hysteresis and ac magnetic susceptibility indicate that the title complex is a single-molecule magnet with a quantum tunneling behavior, whose ground state was tentatively assigned to S = 10 with g = 1.78 and D = -0.60 K.     

Synthesis and molecular recognition of pyrenophanes with polycationic or amphiphilic functionalities: artificial plate-shaped cavitant incorporating arenes and nucleotides in water

Water-soluble pyrenophanes possessing polycationic or amphiphilic side chains have been developed as synthetic host molecules to investigate hydrophobic and/or pi-stacking interactions. By utilizing omega-acetalic alkyl side chains to retain solubility and versatility, water-soluble macrocyclic pyrenophanes could be easily obtained by Stille coupling, followed by conversion of the acetal groups to hydrophilic substituents. Among the pyrenophanes synthesized, hexaammonium-, bis(diazoniacrown)-, and tetrakis[octa(oxyethylene)]-derived ones showed enough solubility in pure water. The former two cationic pyrenophanes strongly recognized anionic arenes including nucleotides, while the latter neutral one associated with monopyrenyl guests regardless of their electric natures. The strength of recognition for nucleotides by bis(diazoniacrown)pyrenophane depended on the number of phosphate moieties, decreasing in the following order: triphosphate > diphosphate approximately monophosphate.     

Control of photoreaction of amphiphilic spiropyran/n-alkane Langmuir and Langmuir-Blodgett films using the phase transition of n-alkane

The structures and photoreactions of Langmuir and Langmuir-Blodgett (LB) films of an amphiphilic spiropyran, 1',3'-dihydro-3',3'-dimethyl-6-nitro-1'-octadecyl-8-(docosanoyloxymethyl)spiro[2H-1-benzopyran-2,2'-(2H)-indole] (SP), mixed with n-alkane are investigated. The mixing ratio was fixed at 1/2 for SP/n-alkane. The surface pressure-area isotherms of SP/octadecane are categorized into two regimes: a low-temperature regime where octadecane is packed with the alkyl chains of SP, and a high-temperature regime where the addition of octadecane does not influence the isotherms significantly. The temperature dividing the two regimes is related with the melting point of the n-alkane mixed with SP in the bulk. UV irradiation of the Langmuir film in the high-temperature regime gives rise to light-induced J-aggregation, whereas that in the low-temperature regime causes only the isomerization of SP to the corresponding merocyanine, indicating that J-aggregation is hindered by the presence of n-alkane in the low-temperature regime. IR external reflection spectroscopy of the Langmuir films shows that n-alkane is released from the film during J-aggregation. The structural changes of the mixed Langmuir and LB films during J-aggregation are almost the same with those of the films of pure SP.     

Novel catalysis of dendrimer-bound Pd(0) complexes: sterically steered allylic amination and the first application for a thermomorphic system

Phosphinated dendrimer-bound Pd(0) complex catalysts show high stereoselectivity for allylic amination due to the surface congestion of dendrimers and can be easily recycled without loss of activity under thermomorphic conditions.     

A new strategy toward the total synthesis of stachyflin,a potent anti-influenza A virus agent: concise route to the tetracyclic core structure

[reaction: see text] A new strategy directed toward the total synthesis of stachyflin, a potent and novel anti-influenza A virus agent isolated from a microorganism, has been presented through the enantioselective synthesis of the tetracyclic core structure. The synthetic method features a BF(3) x Et(2)O-induced domino epoxide-opening/rearrangement/cyclization reaction as the key step.     

Oxidative aromatization of 1,3,5-trisubstituted pyrazolines and Hantzsch 1,4-dihydropyridines by Pd/C in acetic acid

[formula: see text] 1,3,5-Trisubstituted pyrazolines and Hantzsch 1,4-dihydropyridines were converted to the corresponding pyrazoles and pyridines effectively by the treatment of a catalytic amount of Pd/C in acetic acid.