Quinoidal Azaacenes: 99 % Diradical Character

Quinoidal azaacenes with almost pure diradical character (y=0.95 to y=0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR and NMR spectroscopy, and SQUID measurements, revealing thermally populated triplet states with an extremely low‐energy gap ΔE_ST′ of 0.58 to 1.0 kcal mol^?1. The species are persistent in solution (half‐life≈14–21 h) and in the solid state they are stable for weeks.     

Exchange interactions through π-π stacking in the lamellar compound [{Cu(bipy)(en)}{Cu(bipy)(H2O)}{VO3}4]n

Structural, magnetic, and powder and single-crystal electron paramagnetic resonance (EPR) studies were performed on [{Cu(bipy)(en)}{Cu(bipy)(H(2)O)}{VO(3)}(4)](n) (bipy = 2,2'-bipyridine, en = ethylenediamine), which is a new copper-vanadium hybrid organic-inorganic compound containing Cu(II) and V(V) centers. The oxovanadium units provide an anionic scaffolding to the structure, where two types of Cu(II) coordination modes, octahedral (Cu1) and square pyramidal (Cu2), contribute to the magnetic properties. The crystal structure contains layers including Cu1 and Cu2 ions, separated by stacked arrangements of 2,2'-bipyridine molecules. Each type of Cu(II) ion in these layers forms parallel spin chains described by exchange coupling parameters J(1) and J(2) for Cu1 and Cu2, respectively (exchange couplings defined as H(ex)(i,j) = -J(ij)S(i)S(j)), which, for necessity, are assumed to be equal to J. These chains are coupled by much weaker Cu1-Cu2 exchange interactions J(3) connecting neighbor Cu1 and Cu2 ions within a layer, through paths acting as rungs of a ladder chain structure. The average coupling J, which is antiferromagnetic (J < 0), according to the susceptibility data, is estimated with similar results with a mean field approximation (J = -1.4 cm(-1)), and with a uniform chain model (J = -1.7 cm(-1)). The EPR spectra of powdered samples and oriented single crystals are shown to be independent of J(1) and J(2), but are dependent on the weak coupling J(3), and the data allow a lower limit to be established: |J(3)| > 0.04 cm(-1). The spectra are also strongly sensitive to extremely weak coupling interactions with average magnitude J(4) between copper atoms in neighboring layers, separated by ～10 ?, using the stacked 2,2'-bipyridine molecules, which produce a 2D-to-3D quantum phase transition. This is observed in single-crystal samples when the energy levels are changed with the orientation of the magnetic field. From the characteristics of these transitions, we estimate a value of |J(4)| = 0.0034 ± 0.0004 cm(-1) between Cu(II) ions in neighboring layers. This work emphasizes the important possibilities of EPR to evaluate extremely small exchange couplings between metal ions in a solid material, even in the presence of other much larger couplings.     

Synthesis of new polydentate pyrazolyl‐ethene ligands by interaction of 1H‐pyrazole and 1,1,2,2‐tetrabromoethane in a superbasic medium

Reaction of pyrazole and 1,1,2,2‐tetrabromoethane in a superbasic medium dimethylsulfoxide‐potassium hydroxide was investigated, and a number of pyrazolyl‐ and bromo‐substituted ethenes, which are the products of concurrent substitution and elimination reactions, were identified. Carrying out the reaction using different reagent mole ratios allowed to selectively isolate Z‐1,2‐bis(pyrazol‐1‐yl)ethene, 1,1,2‐tris(pyrazol‐1‐yl)ethane, and 1,1,2,2‐tetrakis(pyrazol‐1‐yl)ethane. Crystal structure of {Z‐1,2‐bis (pyrazol‐1‐yl)ethene}dichlorozinc was established using X‐ray diffraction method. J. Heterocyclic Chem., (2011).     

Chemical modification of nanocrystalline cellulose for improved interfacial compatibility with poly(lactic acid)

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Immunopharmacological Properties of Methacrylic Acid Polymers as Potential Polymeric Carrier Constituents of Anticancer Drugs

Cytostatic chemotherapeutics provide a classical means to treat cancer, but conventional treatments have not increased in efficacy in the past years, warranting a search for new approaches to therapy. The aim of the study was, therefore, to obtain methacrylic acid (MAA) (co)polymers and to study their immunopharmacological properties. 4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl] pentanoic acid (CDSPA) and 2-cyano-2-propyl dodecyl trithiocarbonate (CPDT) were used as reversible chain transfer agents. Experiments were carried out in Wistar rats. The MTT assay was used to evaluate the cytotoxic effect of the polymeric systems on peritoneal macrophages. An experimental tumor model was obtained by grafting RMK-1 breast cancer cells. Serum cytokine levels of tumor-bearing rats were analyzed. The chain transfer agents employed in classical radical polymerization substantially reduced the molecular weight of the resulting polymers, but a narrow molecular weight distribution was achieved only with CDSPA and high CPDT concentrations. Toxicity was not observed when incubating peritoneal macrophages with polymeric systems. In tumor-bearing rats, the IL-10 concentration was 1.7 times higher and the IL-17 concentration was less than half that of intact rats. Polymeric systems decreased the IL-10 concentration and normalized the IL-17 concentration in tumor-bearing rats. The maximum effect was observed for a MAA homopolymer with a high molecular weight. The anion-active polymers proposed as carrier constituents are promising for further studies and designs of carrier constituents of drug derivatives.     

The preparation of dicyano-1,3,4-thiadiazole and tricyanothiazole via 1,2,3-dithiazole chemistry

Treatment of 1,2-bis(4-chloro-5H-1,2,3-dithiazol-5-ylidene)hydrazine 4 with benzyltriethylammonium iodide (1 equiv) affords dicyano-1,3,4-thiadiazole 3 and 5-cyano-1,3,4-thiadiazole-2-carboxamide 5 in 79 and 21% yields, respectively. By using polymer bound triphenylphosphine instead of benzyltriethylammonium iodide the dicyano-1,3,4-thiadiazole 3 can be isolated in 70% yield without chromatography. The reaction of DAMN with Appel salt 8 gave 2-(4-chloro-5H-1,2,3-dithiazol-5-ylideneamino)-2-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)acetonitrile 7 (14%), 2,3-bis-(4-chloro-5H-1,2,3-dithiazol-5-ylideneamino)fumaronitrile 10 (14%), and 2,3-bis(4-chloro-5H-1,2,3-dithiazol-5-ylideneamino)maleonitrile 11 (24%) together with other products. The maleonitrile 11 isomerizes into the fumaronitrile 10 on irradiation at 365 nm. Reaction of aminoacetonitrile with Appel salt 8 gives the (dithiazolylidene)acetonitrile 7 in 33% yield. Treatment of (dithiazolylidene)acetonitrile 7 with polymer bound triphenylphosphine gives tricyanothiazole 6 in 76% yield. A rational general mechanism for the transformation of bisdithiazoles to percyanoheteroles is proposed.     

Optical properties of binuclear zinc (II) macrocyclic complexes derived from 4-methyl-2,6-diformylphenol and 1,2-diaminobenzene

In this work, we present the synthesis and optical study of the binuclear zinc(II) macrocyclic complexes, derived from 4-methyl-2,6-diformylphenol and 1,2-diaminobenzene (H₂L). Two zinc macrocyclic complexes with different anions were prepared and characterized: [Zn₂LCl₂]·H₂O (1) and [Zn₂L](NO₃)₂ (2).     

Sharp decay estimates for hyperbolic balance laws

We consider strictly hyperbolic and genuinely nonlinear systems of hyperbolic balance laws in one-space dimension. Sharp decay estimates are derived for the positive waves in an entropy weak solution. The result is obtained by introducing a partial ordering within the family of positive Radon measures, using symmetric rearrangements and a comparison with a solution of Burgers's equation with impulsive sources as well as lower semicontinuity properties of continuous Glimm-type functionals.