Preparation and photolysis of polyamides having coumarin dimer component

The ring-opening polyaddition reaction of anti and syn head-to-head Coumarin dimers with diamines and the photocleavage behavior of the resulting polyamides were investigated. Anti head-to-head Coumarin dimer successfully reacted with aliphatic and aromatic diamines in an aprotic polar solvent to give corresponding high molecular weight polyamides. The polyamides showed good film forming ability and exhibited solubility behavior typical of polyelectrolytes. Furthermore, these polyamides were found to undergo exclusively asymmetric photocleavage on the cyclobutane rings in the polymer main chain to give a fumaramide unit with elimination of 2,2′-dihydroxystilbene. On the other hand, syn head-to-head Coumarin dimer gave only low molecular weight polyamides. These polymerization and photocleavage behaviors were elucidated in comparison with those of model reactions.     

Electron-density-dependent fused-sphere surfaces derived from pseudopotential calculations

Fused-sphere surfaces can be used to mimic a molecular boundary associated with a constant value of the electron density. The simplest of such fused-sphere models are constructed by using the atomic radii for the spherical isodensity surfaces of individual atoms. In this work, we discuss the extension of this model to molecules containing atoms beyond the second row. In these many- electron systems, the computation of electron densities is usually simplified by adopting a pseudopotential (or effective-core potential) approach. Here, we discuss the performance of large- and small-core pseudo-potential calculations as a tool to derive atomic radii. Our results provide an optimum set of variable radii that can be used to build fused-sphere surfaces. This continuum of surfaces provides a simple approximation to the low-electron-density regions around molecules with heavy atoms.     

Changeable reactivity of ketyl radicals derived from 2-bromomethyl-2-(3-butenyl)benzocyclic-1-alkanones depending on electron transfer conditions employed

Photoinduced electron transfer reaction of 2-bromomethyl-2-(3-butenyl)benzocyclic-1-alkanones with amines afforded 5-exo radical cyclization products while electron transfer reaction with samarium diiodide produced cyclopropanols.     

Pulsed versus continuous laser multiphoton dissociation of iodobenzene cations

In the two-photon visible dissociation of the iodobenzene cation, laser pulse shape is unimportant when collisional relaxation is slow compared to the time between pulses but becomes important when the relaxation rate is comparable to time between pulses. The dissociation can be simulated using an internal energy-governed computer model.     

Valency states of radioactive antimony in hydrochloric acid solutions. Preparation and stability of antimony tracer for radioanalytical use

Variations of¹²⁵Sb valency states in HCl solutions were investigated by the use of the N-benzoyl-N-phenyl-hydroxylamine (BPHA) extraction method.¹²⁵Sb(V) is completely reduced to Sb(III) by one hour refluxing in conc. HCl.¹²⁵Sb(III) is gradually oxidized to Sb(V) in solutions of low HCl concentrations by the effects of their own radiations. Natural light promotes such oxidation reactions. By utilizing such oxidation-reduction effects¹²⁵Sb(V) can be easily prepared from¹²⁵Sb(III) and also¹²⁵Sb(III) can be prepared by the reduction of Cl _aq ⁻ . Their valency states were stable on keeping them in brown-colored bottles at 6M HCl concentrations.     

Inclusion of cut and as-grown single-walled carbon nanotubes in the helical superstructure of schizophyllan and curdlan (beta-1,3-glucans)

We have found that single-chain schizophyllan and curdlan (s-SPG and s-curdlan, respectively) can dissolve as-grown and cut single-walled carbon nanotubes (ag-SWNTs and c-SWNTs, respectively) in aqueous solution. The vis-NIR spectra of the composites suggest that c-SWNTs are dissolved as a bundle, whereas ag-SWNTs exist as one or only a few pieces in the tubular hollow constructed by the helical structure inherent to these beta-1,3-glucans. EDX and CLSM measurements and TEM observation established that the distribution map of these polysaccharides overlaps well with the image of SWNTs, indicating that these two components form a composite. Very interestingly, when c-SWNTs were dissolved with the aid of s-SPG or s-curdlan in water, a clear periodical structure with inclined stripes, as detected by AFM, appeared on the fibrous composite surface. Because this periodical structure has never been recognized for the composites with other water-soluble polymers, one can regard that s-SPG or s-curdlan wraps c-SWNTs constructing a helically twined structure. High-resolution TEM observation of an ag-SWNTs/s-SPG composite gave a clearer image in that two s-SPG chains twine one ag-SWNT and the helical motif is right-handed. When this sample was subjected to the AFM measurement, the composite showed the 2-3 nm height. This height implies that one piece of ag-SWNT is included in the s-SPGs helical structure. As a summary, it has been established that beta-1,3-glucans such as s-SPG and s-curdlan not only dissolve SWNTs but also create a novel superstructure on the surface.     

Novel methyl helianthrones as photosensitizers: synthesis and biological evaluation

A combination of light, oxygen and a photosensitizer is used to induce death of cancer cells by photodynamic therapy. In this study, we have synthesized several new methyl helianthrone derivatives and compared their phototoxicity with that of hypericin. In contrast to hypericin, methyl helianthrones are soluble in aqueous solutions and have a broad range of light absorbance, which allows the use of polychromatic light. Structural modifications of methyl helianthrone demonstrated that substitution of hydrogen atoms of methyl helianthrone at Positions 2 and 5 with Br atoms or methylation of its phenolic hydroxyls, significantly increases the corresponding singlet oxygen quantum yield and their phototoxicity toward alphaT3-1, M2R and LNCaP cells. The phototoxicity of some of these compounds was similar to that of hypericin. Methyl helianthrones, like hypericin, accumulated mainly in the perinuclear region as evident by confocal microscopy. Irradiation of cells pretreated with methyl helianthrone derivatives generates intracellular reactive oxygen species and lipid free radicals, as shown by a fluorescentic probe and electron paramagnetic resonance methods, respectively. The phototoxicity of these methyl helianthrones as well as their ability to oxidize membrane lipids were significantly decreased on addition of specific Type-II inhibitors, suggesting the involvement of singlet oxygen as the main oxidant.     

NMR and MO Studies on the Molecular Structure of a Fluoranthene-Benzene Complex

Summary. Fluoranthene (FA) forms a 1:1 van der Waals complex with benzene in cyclohexane. The ¹H NMR spectrum of this complex shows that the FA moiety in the complex state has five kinds of hydrogen atoms and that the ¹H NMR peaks assigned to the protons attached to the naphthalene skeleton are largely shifted to higher magnetic field on complex formation with benzene. These observations indicate that the complex takes the structure of C_S symmetry, in which the benzene molecule mainly interacts with the electronic system localized on the naphthalene moiety of FA. The present ab initio calculations reproduce well the ¹H NMR spectral shifts mentioned above and the experimentally predicted C_S structure of the complex. According to the PPP calculations for the electronic absorption spectral changes on the complex formation, the FA-benzene complex is considered to take a sandwich type structure.     

Novel alignment method of small molecules using the Hopfield Neural Network

Molecular alignment is an important step in three-dimensional quantitative structure-activity relationship (3D-QSAR) such as comparative molecular field analysis (CoMFA). A reasonable molecular alignment is necessary for building a 3D-QSAR model. In this paper, a novel method for molecular alignment using the Hopfield Neural Network (HNN) is introduced. Four kinds of chemical properties are assigned to each atom of a molecule. Then, those properties between two molecules correspond to each other using HNN. To validate our method, HNN was applied to 12 pairs of enzyme inhibitors cited from the Protein Data Bank (PDB). As a result, our method could successfully reproduce the real molecular alignments obtained from X-ray crystallography.     

Tandem radical reactions and ring-closing metathesis. Application in the synthesis of cyclooctenes

[reaction: see text] Fumarate- and acrylate-substituted oxazolidinones undergo tandem radical reaction to form dienes in moderate to good yields. The resulting dienes provide cyclooctenes in moderate to good yields after ring-closing metathesis (RCM). The role of the carbon backbone substituents and other variables in the efficiency of the eight-membered ring formation is discussed.