End-to-end azide-bridged manganese(III) chain compounds: field-induced magnetic phase transitions and variation of T(C) to 38 K depending on the side groups of the Schiff bases

Three one-dimensional coordination polymers [Mn(L)(N(3))](n) [L = L1 (1), L2 (2), L3 (3); L1H(2) = N,N'-bis(5-chlorosalicylideneiminato)-1,3-diaminopentane, L2H(2) = N,N'-bis(5-bromosalicylideneiminato)-1,3-diaminopentane, L3H(2) = N,N'-bis(5-bromosalicylideneiminato)-1,3-diamino-2-dimethylpropane] bridged by end-to-end azides were prepared. The crystal systems differ according to the Schiff bases used. Each Mn atom adopts a typical Jahn-Teller distortion. The helicity of the chains occurs in a racemic manner only for 2. No noncovalent forces are relevant in 2, while π-π contacts are visible in 1 and 3. Magnetic measurements show the presence of apparent spin canting. Complexes 1 and 3 exhibit a field-induced metamagnetic transition from an antiferromagnetic state to a weak ferromagnetic phase, whereas 2 embraces a field-induced two-step magnetic phase transition. The critical temperature is observed at 38 K for 2, which is relatively higher than those for 1 (11 K) and 3 (10 K). The pronounced long-range order may contribute from intrachain exchange couplings and through-space dipolar interactions between adjacent chains.     

Regioselectivity of enzymatic and photochemical single electron transfer promoted carbon-carbon bond fragmentation reactions of tetrameric lignin model compounds

New types of tetrameric lignin model compounds, which contain the common β-O-4 and β-1 structural subunits found in natural lignins, have been prepared and carbon-carbon bond fragmentation reactions of their cation radicals, formed by photochemical (9,10-dicyanoanthracene) and enzymatic (lignin peroxidase) SET-promoted methods, have been explored. The results show that cation radical intermediates generated from the tetrameric model compounds undergo highly regioselective C-C bond cleavage in their β-1 subunits. The outcomes of these processes suggest that, independent of positive charge and odd-electron distributions, cation radicals of lignins formed by SET to excited states of sensitizers or heme-iron centers in enzymes degrade selectively through bond cleavage reactions in β-1 vs β-O-4 moieties. In addition, the findings made in the enzymatic studies demonstrate that the sterically large tetrameric lignin model compounds undergo lignin peroxidase-catalyzed cleavage via a mechanism involving preliminary formation of an enzyme-substrate complex.     

Kaempferol and kaempferol rhamnosides with depigmenting and anti-inflammatory properties

The objective of this study was to examine the biological activity of kaempferol and its rhamnosides. We isolated kaempferol (1), a-rhamnoisorobin (2), afzelin (3), and kaempferitrin (4) as pure compounds by far-infrared (FIR) irradiation of kenaf (Hibiscus cannabinus L.) leaves. The depigmenting and anti-inflammatory activity of the compounds was evaluated by analyzing their structure-activity relationships. The order of the inhibitory activity with regard to depigmentation and nitric oxide (NO) production was kaempferol (1) > a-rhamnoisorobin (2) > afzelin (3) > kaempferitrin (4). However, a-rhamnoisorobin (2) was more potent than kaempferol (1) in NF-kB-mediated luciferase assays. From these results, we conclude that the 3-hydroxyl group of kaempferol is an important pharmacophore and that additional rhamnose moieties affect the biological activity negatively.     

Congruential Inventory Model for Two-Echelon Distribution Systems

Large-scale inventory-distribution systems typically comprise a hierarchy of warehouses that stock goods for distribution to retailers at which demand for these goods originates. This paper develops an inventory model for two-echelon distribution systems under the assumption that the central warehouse and retailers order periodically. Characteristics of the optimal policy are described. An iterative solution procedure is presented to find optimal or near optimal operating-policy variables. Solutions of the model to a large number of test examples show that the model outperforms other existing models in the literature without sacrificing the computation time. Tested against the lower bounds on the optimal average annual variable cost obtained by removing some of the ordering costs, the solutions of the present model are found to be near optimal.     

Synthesis of conjugated copolymers containing phenothiazinylene vinylene moieties and their electrooptic properties

Four different types of conjugated copolymers, consisting of alternating structures of phenothiazinylene vinylene and phenylene vinylene derivatives such as phenylene vinylene, 1,1′‐biphenyl‐4,4′‐ylene vinylene, 2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene, and 9,10‐anthrylene vinylene, were prepared by Horner–Emmons condensation between appropriate diphosphonates and dialdehydes. Single‐layer and double‐layer light‐emitting diodes were fabricated with the synthesized conjugated polymers, and their electroluminescent properties were investigated. Poly(N‐2‐ethylhexyl‐3,6‐phenothiazinylene vinylene‐alt‐9,10‐anthrylene vinylene), containing phenothiazinylene vinylene and anthrylene vinylene as repeat units, emitted a reddish‐orange color with Commission Internationale de l'Eclairage coordinates of x = 0.6173 and y = 0.3814 that was very similar to the National Television System Committee standard red, and it showed a bipolar carrier‐injection/transporting capability caused by electron‐withdrawing anthracene and electron‐donating amino groups. Poly[N‐2‐ethylhexyl‐3,6‐phenothiazinylene vinylene‐alt‐2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene], containing phenothiazinylene vinylene and dialkoxy phenylene vinylene moieties, showed excellent hole‐injection/transporting capability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2502–2511, 2003     

Effects of pressure on the compressibility and crystallization of fiber-forming polymers

The effects of pressure on the compressibility and crystallization of three fiber-forming polymers, poly(tetramethylene terephthalate), nylon 66, and Qiana® nylon, have been studied. The Instron capillary rheometer was adapted as a high-pressure dilatometer for all the high-pressure experiments. The compressibility results reaffirmed that polymers are highly compressible, and their compressibilities are nonlinear at temperatures above the glass transition temperatures. Polymer melts show higher compressibility than do polymers in the solid state. The kinetics of crystallization of these polymer melts under high pressures were studied. Analysis of the data revealed low Avrami exponents at high pressures. It seems that the kinetics of crystallization of these polymers from the melt under high pressure are different from those at normal pressure. Crystallization temperatures of these polymers were also measured. The crystallization temperatures are considerably higher at higher pressures.     

Graphite catalyzed reduction of aromatic and aliphatic nitro compounds with hydrazine hydrate

Aromatic and aliphatic nitro compounds were readily reduced to amino compounds in excellant yields with graphite and hydrazine hydrate.     

Absorption and gain of laser dyes with picosecond pumping

Using a passively mode-locked Nd:YAG laser, the absorption and gain of oxazine 1 and 9 were examined. Picosecond pumping is shown to have better gain efficiency and wavelength tunability than nanosecond pumping.     

Photoinduced electron transfer processes in 1,8-naphthalimide-linker-phenothiazine dyads

Photoinduced electron transfer (PET) processes of 1,8-naphthalimide-linker-phenothiazine (NI-L-PTZ) dyads have been investigated using the nanosecond- and picosecond-transient absorption measurements. Two kinds of linker were introduced, i.e., polymethylene-linked dyad (NI-C8-PTZ and NI-C11-PTZ) and a poly(ethyl ether)-linked one (NI-O-PTZ). The 355 nm pulsed laser excitation of NI-C8-PTZ, NI-C11-PTZ, and NI-O-PTZ in acetonitrile produced NI radical anion (NI*-) and PTZ radical cation (PTZ*+) with the absorption bands around 420 and 520 nm, respectively, through charge transfer from PTZ to NI in the singlet excited state (NI(S1)) as well as in the triplet excited states (NI(T1)) in acetonitrile. On the other hand, the charge transfer process occurred only from NI(S1) in nonpolar solvents. The rates of charge transfer and charge recombination processes largely depended on the solvent polarity and they are affected by the length of linkers and electronic coupling through polyether linker. The PET mechanism is discussed in terms of the free energy change for the charge transfer.