Incorporation of polydimethylsiloxane into polyurethanes and characterization of copolymers

Novel copolymers of polyurethane (PU) were prepared by direct transurethanetion reaction of a commercial PU with polydimethylsiloxanes (PDMS, MW 1000, 5000, and 10,000) containing hydroxyl end-groups. Transurethanetions with different mass ratios of hydrophobic PDMS to hydrophilic PU chains (PDMS1000–PU: 43:57, 67:33, 71:29, and 80:20; PDMS5000–PU: 37:63, and 51:49; PDMS10000–PU: 51:49) were carried out in solution at 65 and 100 °C. In catalyzed reactions, dibutyltin dilaurate (SnC₃₂H₆₄O₄) was used to promote bond breaking in the PU chain and accelerate the reaction between hydroxyl end-groups of PDMS and regenerated isocyanates of PU. The chemical structures of the prepared copolymers were comprehensively characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopies. According to elemental analysis, the content of PDMS varied between 3 wt.% and 16 wt.%, and results obtained from the ¹H NMR spectroscopy were in good agreement with the results of elemental analysis. Increased length of the hydrophobic chain increased the content of PDMS in the copolymer. The GPC results showed that molar masses of the PUPDMS copolymers were lower than the molar mass of the starting PU. The glass transitions (T_g) of the copolymers were shifted to lower temperature as compared with T_g of the starting polyurethane. ATR FTIR spectroscopy showed the surface of the copolymer films to be enriched with siloxane groups and, according to electron microscopy, it was textured with microspheres. The static contact angles for copolymer films measured with deionized water ranged from 94° to 117°. The different structural, thermal and surface properties of the PUPDMS copolymers as compared with PU indicated that transurethanetion had taken place.     

Synthesis and characterization of new cyclotriphosphazene compounds

In the present study, spiro (1a), dispiro (1b, 2, 3), per-substituted spermine-bridged (6–9) and dispiroansa spermine (10) derivatives of cyclotriphosphazene have been synthesized. The structures of the novel compounds (1b, 6–10) have been characterized by elemental analysis, FTIR, mass spectrometry, ¹H and ³¹P NMR spectroscopy. The molecular structures of 1b, 2, 8, and 10 were determined by single crystal X-ray crystallography. In order to investigate the anti-tumour properties of the newly synthesized cyclotriphosphazene derivatives, in vitro cytotoxic activity test (MTT assay) has been performed using HT-29 (human colon adenocarcinoma) and Hep2 (human epidermoid larynx carcinoma) cell lines. The result of the MTT assay showed that while compound 1a has cytotoxic effect on both Hep2 and HT-29 cell lines, compound 3 has only cytotoxic effect towards the Hep 2 cells.     

A ground-state-dominated magnetic field effect on the luminescence of stable organic radicals

Organic radicals are an emerging class of luminophores possessing multiplet spin states and potentially showing spin-luminescence correlated properties. We investigated the mechanism of recently reported magnetic field sensitivity in the emission of a photostable luminescent radical, (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) doped into host αH-PyBTM molecular crystals. The magnetic field (0–14 T), temperature (4.2–20 K), and the doping concentration (0.1, 4, 10, and 22 wt%) dependence on the time-resolved emission were examined by measuring emission decays of the monomer and excimer. Quantum mechanical simulations on the decay curves disclosed the role of the magnetic field; it dominantly affects the spin sublevel population of radical dimers in the ground states. This situation is distinctly different from that in conventional closed-shell luminophores, where the magnetic field modulates their excited-state spin multiplicity. Namely, the spin degree of freedom of ground-state open-shell molecules is a new key for achieving magnetic-field-controlled molecular photofunctions.

We investigated the mechanism of the magnetic field effect (MFE) on the emission of a luminescent radical doped into host crystals. It was revealed that the spin sublevel population of radical dimers in the ground states is the key that governs the MFE.     

六(甲氧基乙氧基乙氧基)三聚磷腈的合成与表征

以六氯三聚磷腈和甲氧基乙氧基乙醇为主要原料,合成了全取代的六(甲氧基乙氧基乙氧基)三聚磷腈,并用IR、31P NMR、1HNMR、13C NMR、FABMS等现代谱学技术对其结构进行了表征。经生物活性试验证明,此化合物对腐生线虫Panagrellus redivivus具有一定的毒杀活性。     

Oligothiophenes. Part 4: Formation and characterization of stable radicals from novel bis- and tris-bithiophene methanes

Two star-shaped structures of the bis- and tris-thiophene methane types have been synthesized in a facile two-step synthesis. The resulting bis- and tris-thiophene methanes readily react with oxygen both as solids and in solution to yield stable radicals. The formed radicals, which were investigated using electron paramagnetic resonance (EPR), were found to be residing on the central carbons of the bis- and tris-thiophene methanes.     

Endor detection of conformational changes and internal rotations in organic stable free radicals in solution

The detection of conformational changes and internal rotation of the commonly used free radicals DPPH, PAC and BDPA are reported. Comparison with other spectroscopic techniques shows that ENDOR can be uniquely helpful for obtaining such information.     

Photochemistry and spectroscopy of "stable organic radicals": steric and electronic effects in intermolecular photoinduced electron transfer

The intermolecular reactivities of amino-substituted perchlorotriphenylmethyl radicals 1-3 were studied, with particular emphasis on electron transfer (ET) reactions. The natural fluorescence lifetimes and the rates of the electron-transfer quenching were studied with several electron donors and acceptors. Fluorescence quenching studies demonstrate the importance of the redox potentials of the ET pair on the observed steric and electronic properties.     

Synthesis and magnetic behavior of stable organic open-shell polymers containing phenothiazine cation radicals as spin resources

Two types of organic open-shell polymer containing phenothiazine cation radicals as spin resources were synthesized and the magnetic behaviors were investigated. The one is the 1,3-phenylene-linked polymer, and the other is the arylamine nitrogen-linked polymer. Precursor polymers were prepared by the Suzuki-Miyaura coupling and the Pd-catalyzed amination. The formation of complexes between the phenothiazine moieties in precursor polymers and antimony(V) chloride gave stable open-shell polymers. The magnetic behavior of 1,3-phenylene-linked polymer was intramolecularly ferromagnetic, but intermolecularly antiferromagnetic. Whereas, the arylamine nitrogen-linked polymer was in the S = 1 spin state in spite of low spin concentration of 0.16 spins per repeating unit.     

Structure of organized organic mono- and multi-layer films

A review is presented of some interesting structural properties of monomolecular layers at the air/water interface (Langmuir films) and of organized multilayer structures of organic molecules (Langmuir-Blodgett films). In particular multilayer films of bipolar lipids from archaebacteria and of proteins are considered, together with single-electron junction quantum effects in parallel, special emphasis is given to some recently developed experimental techniques based on X-ray scattering. supramolecular assemblies consisting of multilayers containing nanoparticles.     

Separation and identification of DMPO adducts of oxygen-centered radicals formed from organic hydroperoxides by HPLC-ESR,ESI-MS and MS/MS

Many electron spin resonance (ESR) spectra of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) radical adducts from the reaction of organic hydroperoxides with heme proteins or Fe(2+) were assigned to the adducts of DMPO with peroxyl, alkoxyl, and alkyl radicals. In particular, the controversial assignment of DMPO/peroxyl radical adducts was based on the close similarity of their ESR spectra to that of the DMPO/superoxide radical adduct in conjunction with their insensitivity to superoxide dismutase, which distinguishes the peroxyl adducts from the DMPO/superoxide adduct. Although recent reports assigned the spectra suggested to be DMPO/peroxyl radical adducts to the DMPO/methoxyl adduct based on independent synthesis of the adduct and/or (17)O-labeling, (17)O-labeling is extremely expensive, and both of these assignments were still based on hyperfine coupling constants, which have not been confirmed by independent techniques. In this study, we have used online high performance liquid chromatography (HPLC or LC)/ESR, electrospray ionization-mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) to separate and directly characterize DMPO oxygen-centered radical adducts formed from the reaction of Fe(2+) with t-butyl or cumene hydroperoxide. In each reaction system, two DMPO oxygen-centered radical adducts were separated and detected by online LC/ESR. The first DMPO radical adduct from both systems showed identical chromatographic retention times (t(R) = 9.6 min) and hyperfine coupling constants (a(N) = 14.51 G, a(H)(beta) = 10.71 G, and a(H)(gamma) = 1.32 G). The ESI-MS and MS/MS spectra demonstrated that this radical was the DMPO/methoxyl radical adduct, not the peroxyl radical adduct as was thought at one time, although its ESR spectrum is nearly identical to that of the DMPO/superoxide radical adduct. Similarly, based on their MS/MS spectra, we verified that the second adducts (a(N) = 14.86 G and a(H)(beta) = 16.06 G in the reaction system containing t-butyl hydroperoxide and a(N) = 14.60 G and a(H)(beta) = 15.61 G in the reaction mixture containing cumene hydroperoxide), previously assigned as DMPO adducts of t-butyloxyl and cumyloxyl radical, were indeed from trapping t-butyloxyl and cumyloxyl radicals, respectively.     

A disilapentalene and a stable diradical from the reaction of a dilithiosilole with a dichlorocyclopropene

The reaction of 1,1-dilithio-2,3,4,5-tetraphenylsilole (1) with 1,1-dichloro-2,3-diphenylcyclopropene (2) leads to the novel 1,4-disila-1,4-dihydropentalene (4), as well as an exceptionally stable diradical for which the structure 3 is suggested. The diradical is unreactive toward water, methanol, and chloroform; upon heating it transforms into 4. Structure 3 for the paramagnetic species is proposed on the basis of EPR data and theoretical calculations. The trans-trans isomer of diradical 3 was calculated to be more stable than its cis-cis isomer. The strong and stable EPR signal in the reaction mixture is probably due to the trans-trans isomer of diradical 3 in the triplet state. A reaction scheme describing the formation of 3 and 4 is presented.     

Incorporation of carbon and nitrogen atoms into proteins measured by protein-based stable isotope probing (Protein-SIP)

The identification of metabolically active microbial key players is fundamental for understanding the structure and functions of contaminant-degrading communities. The metabolic activity can be analysed by feeding the microbial culture with stable-isotope-labelled substrates and subsequently tracing their incorporation into the biomass. In this paper we present a method which is able to detect the incorporation of stable isotopes from the substrate into the proteins of a benzene-metabolising microorganism. Pseudomonas putida strain ML2 was grown under aerobic conditions with the substrates (12)C-benzene, (13)C-benzene or (15)N-ammonium and (12)C-benzene. Proteins of these cultures were resolved by two-dimensional gel electrophoresis (2-DE) and corresponding protein spots were subjected to matrix-assisted laser ionization/desorption mass spectrometric (MALDI-MS) analysis. The proteins of the (12)C-sample were identified by peptide mass fingerprinting (PMF) as well as by tandem mass spectrometric (MS/MS) measurements. The (13)C- or (15)N-content of the peptides from the labelling experiments was determined by MALDI-MS/MS. The incorporation of heavy isotopes into the proteins from cultures grown on (13)C-benzene and (15)N-ammonium was determined based on the mass differences between labelled and non-labelled peptides as well as on the isotopic distribution of the y(1)-ion of arginine. The method we present here principally allows the unravelling of the carbon and nitrogen flow not only in pure cultures, but also in microbial communities consisting of many microbial species. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Structure of hybrid organic–inorganic sols for the preparation of hydrothermally stable membranes

A procedure for the preparation of hybrid sols for the synthesis of organic–inorganic microporous materials and thin film membranes is reported. We describe silane reactivity and sol structure for acid-catalysed colloidal sols from mixtures of either tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES), or bis(triethoxysilyl)ethane (BTESE) and MTES. Early-stage hydrolysis and condensation rates of the individual silane precursors were followed with ²⁹Si liquid NMR and structural characteristics of more developed sols were studied with Dynamic Light Scattering. Condensation was found to proceed at more or less similar rates for the different precursors. Homogeneously mixed hybrid colloids can therefore be formed from precursor mixtures. The conditions of preparation under which clear sols with low viscosity could be formed from BTESE/MTES were determined. These sols were synthesised at moderate water/silane and acid/silane ratios and could be applied for the coating of defect-free microporous membranes for molecular separations under hydrothermal conditions.     

Synthesis and spectroscopic studies of diorganotin(IV) adducts based on cyclotriphosphazene scaffolds with exocyclic pyrazolyl substituents

Functionalized cyclotriphosphazenes with four pyrazolyl substituents have been employed for the synthesis of two new organotin complexes. These new compounds have been characterized by elemental analysis and IR, ¹H, ³¹P and ¹¹⁹Sn NMR spectroscopy. On the basis of these data, pyrazolylcyclotriphosphazene is bis-bidentate neutral ligand coordinating to two SnMe₂Cl₂ molecules in the resulting adducts. Coordination occurs only via the pyrazolyl nitrogens; cyclotriphosphazene ring nitrogens are not involved in coordination. The ¹¹⁹Sn NMR data are consistent with increasing of coordination number of tin(IV) in solution.     

Rate constants of the reaction between alkyl radicals and oxygen and stable nitroxyl radicals

Conclusions The rate constants of the reaction between the alkyl radicals of hydrocarbons (R^.) and of vinyl monomers (M^.) and O₂ and stable nitroxyl radicals were determined at 50C. The low-molecular-weight radicals react with O₂ (k₁) and the (k₃) more rapidly than the M^. do. For polar R^. and M^. k₁ and k₃ are close, and for the nonpolar ones k₁>k₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2446–2450, November, 1979.The authors express their appreciation to V. A. Golubev for submitting the nitroxyl radicals and A. P. Moravskii for help in running the experiment.     

Contributions to the chemistry of halosilane adducts: XVIII. On the nature of compounds of trimethylhalosilanes with 1,1,3,3-tetramethylguanidine and 2-trimethylsilyl-1,1,3,3-tetramethylguanidine: preparation and characterization of mono- and bis-(2-trimethylsilyl)-1,1,3,3-tetramethylguanidinium halides

1,1,3,3-Tetramethylguanidine (TMG) and 2-(trimethylsilyl)-1,1,3,3-tetramethylguanidine (TMSTMG) react with trimethylhalosilanes Me₃SiHal in equimolar ratio with ionization of the Sihalogen bond to give the stable guanidinium salts [(Me₂N)₂CNHSiMe₃]Hal (Hal  Cl (1), Br (2)) and [(Me₂N)₂CN(SiMe₃)₂]Hal (Hal  Cl (3), Br (4), I (5)), respectively, involving tetracoordinate silicon. No reaction occurs with Me₃SiF. The same ionic species are present in CHCl₃ or CH₃CN solutions (IR, ¹H, ²⁹Si NMR), thus establishing for the first time, the formation of an ionic solid derivative of Me₃SiCl stable towards dissociation. Reaction with an excess of TMG gives an equilibrium mixture of TMSTMG and TMG · HHal. The bis(silyl)guanidinium salts are less stable towards dissociation than the mono(silyl) derivatives, the stability sequence being Cl⁻ < Br⁻ < I⁻ within the series. The reactions of both types of compound have been investigated. The implications of the present and earlier results for the mechanisms of racemization and nucleophilic substitution at silicon are discussed.