Studies of end-groups in polystyrene using H NMR

Studies have been made by 400 MHz ¹H NMR of initiator fragments in polystyrene made by radical polymerization in solution at 60 °C. Azoisobutyronitrile, benzoyl peroxide and lauroyl peroxide have been used as initiators. The peaks arising from hydrogens in the end-groups have been recognized. They cause alterations in the ratio of “aromatic hydrogens” to “aliphatic hydrogens” for polystyrene.     

Polystyrene latex particles coated with crosslinked poly(N-isopropylacrylamide)

Thermoresponsive colloidal particles were prepared by seeded precipitation polymerization of N-isopropylacrylamide (NIPAM) in the presence of a crosslinking monomer, N,N-methylenebisacrylamide (MBA), using polystyrene latex particles (ca. 50 nm in diameter) as seeds in aqueous dispersion. Phase transitions of the prepared poly(N-isopropylacrylamide), PNIPAM, shells on polystyrene cores were studied in comparison to colloidal PNIPAM microgel particles, in H₂O and/or in D₂O by dynamic light scattering, microcalorimetry and by ¹H NMR spectroscopy including the measurements of spin–lattice (T1) and spin–spin (T2) relaxation times for the protons of PNIPAM. As expected, the seed particles grew in hydrodynamic size during the crosslinking polymerization of NIPAM, and a larger NIPAM to seed mass ratio in the polymerization batch led to a larger increase of particle size indicating a product coated with a thicker PNIPAM shell. Broader microcalorimetric endotherms of dehydration were observed for crosslinked PNIPAM on the solid cores compared to the PNIPAM microgels and also an increase of the transition temperature was observed. The calorimetric results were complemented by the NMR spectroscopy data of the ¹H-signal intensities upon heating in D₂O, showing that the phase transition of crosslinked PNIPAM on polystyrene core shifts towards higher temperatures when compared to the microgels, and also that the temperature range of the transition is broader.     

Reductive debenzylation of hexabenzylhexaazaisowurtzitane — the key step of the synthesis of polycyclic nitramine hexanitrohexaazaisowurtzitane

Main features of the reductive debenzylation of 2,4,6,8,10,12-hexabenzyl-2,4,6,8,10,12-hexaazaisowurtzitane were studied. This process is the key step of the synthesis of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0^3,11.0^5,9]dodecane (hexanitrohexaazaisowurtzitane, CL-20), a compound with unique energetic and explosive characteristics. The use of the latter is restricted so far by the high cost of the two-step process of debenzylation during which the compound is rapidly deactivated. The expensive Pd/C catalyst is deactivated in the first step of the process, which limits the use of this polycyclic nitramine. The influence of the solvent nature; loadings of the reactants, catalyst, and cocatalyst; the hydrogen pressure and reaction temperature on the general features of the process and the yield of the target precursor of CL-20 was studied. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2290–2295, December, 2007.     

CrOx/SiO2催化剂上丙烷在CO2气氛中脱氢反应的研究

采用XRD、UV-vis DRS、ESR和微分吸附量热等技术,考察了铬担载量分别为2.5、5和10wt%的CrO_x/SiO₂催化剂的结构、表面性质和氧化还原性能。结果表明,催化剂表面上存在多种Cr的氧化态和聚集形式。随着Cr担载量从2.5wt%到10wt%的逐渐增大,催化剂表面占主导地位的Cr物种由CrO₃单体转为多聚CrO₃和Cr₂O₃晶相。在CO₂气氛中催化剂对丙烷转化率和丙烯选择性的大小顺序为2.5wt%CrO_x/SiO₂>5wt%CrO_x/SiO₂>10wt%CrO_x/SiO₂,反应过程中的原位ESR和UV-visDRS测定结果表明,催化剂表面的反应活性中心为Cr⁵⁺,Cr⁵⁺可由催化剂预处理过程中Cr³⁺的氧化及丙烷反应过程中CrO₃单体的还原产生,在反应中CO₂可使Cr³⁺重新氧化为Cr⁵⁺.     

Complex macromolecular dynamics:: I. Estimation technique for time-resolved emission anisotropy ratio of chromophores incorporated into polymer chains

Time-resolved fluorescence emission anisotropy ratios of carbazolyl groups incorporated into polystyrene chains in polyethyleneoxide(PEO)/1,2-dichloroethane mixtures have been measured by the single photon counting method. The fluorescence depolarization method is very excellent to clarify various dynamical modes of polymer chains, and many theoretical and experimental researches have so far been reported in the field of polymer chain dynamics. However there are few reports about the dynamics on the polymer side chain, because the dynamical mechanism of the polymer side chain is very complicated. In this report we tried to analyze the dynamical modes of the polymer side chains by the fluorescence depolarization method. Five dynamical modes of a polymer chain based on the Wöessner model were estimated by our original analytical technique `χ²-map method'. The value of each mode of a polymer side chain was discussed above the overlap concentration (C^*) of PEO and the micro-environments were clarified in the vicinity of the chromophore attached to the polymer side chain.     

Microporous hypercrosslinked polystyrene Styrosorb as a restricted access packing in sample clean-up for high performance liquid chromatography. Part I: Evaluation of restricted access properties

Summary Styrosorb is a beaded microporous polystyrene with particle sizes between 2 and 4 m. In spite of hypercrosslinkage the material was seen to swell in organic solvents. The native material is functionalized with Tris-groups at the outer surface of the particles. The average pore diameter was determined as 1.45±0.3 nm from size exclusion data using polystyrene and polyethylene standards in THF. The reversed phase behavior of the restricted access phase Styrosorb was investigated by injection of two test mixtures. Mixture I contained five aromatic amines, mixture II consisted of Amperozide^R and four related compounds. The optimum range of mobile phase composition was assessed so that analytes were separated whilst any proteins present were eluted unretained. Due to the small particle size short columns of 29×4 mm can be used for both sample clean-up and analytical separation of Amperozide^R and its metabolite.     

新型吸附剂的合成、表征及其对Ni(II)的吸附研究

利用滴加法合成了球形含Ni^2＋交联壳聚糖, 并通过胺化引入大量活性氨基, 再经除镍制成对重金属镍离子具有较好吸附能力的新型吸附剂[P-C-CTS(Ni)]. 通过Ni^2＋吸附容量的测定, IR及XPS分析, 验证了合成技术路线的正确性. 通过研究pH值对吸附量的影响, 初步讨论了无柠檬酸根(Cit)配位体存在时, 吸附剂对Ni(II)的吸附为螯合作用. 通过Cit存在条件下(c_Ni＝c_Cit＝0.852 mmol•L^－1), 吸附剂对Ni(II)离子和Cit的吸附量随pH值的变化, 结合相应pH值下金属镍的形态分布, 探讨了其对Ni(II)的吸附机理, 研究认为不仅仅是简单的螯合作用, 其吸附机理和吸附量与溶液中金属离子的存在形式有关, 引入静电吸附原理解释了吸附剂对Ni(II)的吸附现象.     

Oxidation of C-labeled ethyl linoleate monitored and quantitatively analyzed by C NMR

The oxidation of ¹³C-labeled ethyl linoleate (¹³C-EL), a model compound for alkyd resins, was investigated by ¹³C NMR in the presence of Co(II)-2-ethylhexanoate (Co-EH), Mn(acac)₃ (acac = acetylacetonate), and Mn(acac)₃ in combination with 2,2′-bipyridine (bpy), respectively. The use of ¹³C-EL allows us, in an unprecedented way, to reveal the individual evolution of hydroperoxides (ROOH) and peroxy (ROOR) links by ¹³C NMR and to quantify the oxidation intermediates during the oxidation. Mn(acac)₃ appeared to be less effective in decomposing ROOH than Co-EH and the Mn(acac)₃/bpy combination. Quantitative analyses were attempted for a few major ¹³C peaks.     

Screening of Dowex® anion-exchange resins for invertase immobilization

Commercial yeast invertase (Bioinvert^®) was immobilized by adsorption on anion-exchange resins, collectively named Dowex^® (1×8:50–400, 1×4:50–400, and 1×2:100–400). Optimal binding was obtained at pH 5.5 and 32°C. Among different polystyrene beads, the complex Dowex-1×4–200/invertase showed a yield coupling and an immobilization coefficient equal to 100%. The thermodynamic and kinetic parameters for sucrose hydrolysis for both soluble and insoluble enzyme were evaluated. The complex Dowex/invertase was stable without any desorption of enzyme from the support during the reaction, and it had thermodynamic parameters equal to the soluble form. The stability against pH presented by the soluble invertase was between 4.0 and 5.0, whereas for insoluble enzyme it was between 5.0 and 6.0. In both cases, the optimal pH values were found in the range of the stability interval. The K _m and V _max for the immobilized invertase were 38.2 mM and 0.0489 U/mL, and for the soluble enzyme were 40.3 mM and 0.0320 U/mL.     

Ag+与Hg2+对G-四链体DNA结构的破坏及其对构筑DNA逻辑门的应用

本工作利用圆二色光谱研究了Ag+与Hg2+对4种代表性G-四链体DNA结构的破坏作用。结果表明Ag+可能通过与碱基G螯合从而破坏G-四链体结构;Hg2+能通过形成T-Hg2+-T碱基对,及其他方式破坏G-四链体结构。含巯基(-SH)的半胱氨酸与Ag+与Hg2+可以发生较强的配位作用,从而使被Ag+与Hg2+破坏后的G-四链体DNA结构得以回复。基于此,一个新颖的Ag+/Hg2+-半胱氨酸-DNA逻辑门得以构筑。     

Identification Des Produits De La Reduction Electrochimique d'Un Nouvel Antiinflammatoire: Le Piroxicam

Abstract

The electrochemical reduction of piroxicam has been investigated on a mercury pool in acidic and alcaline media.

After exhaustive electrolysis, the extraction followed by chromatographic separation of the reaction products gives the reduced compounds which have been identified by spectroscopic techniques. From the analysis of the NMR ¹H, ¹³C and IR spectra and the results of our preceding electrochemical investigation, the polarographic behaviour of piroxicam has been elucidated. The process occurs by the irreversible reduction of the double bond of the enol function over the total pH range investigated. However, in alkaline and highly acidic solutions, a preceding two-electron step occurs, giving rise to the opening of the thiazine ring.     

“NMR invisible” aluminum species in dealuminated mordenite zeolite: a1H/27 AI TRAPDOR NMR study

Various kinds of aluminum species in dealuminated mordenite were investigated in detail, and the quadrupole coupling constants (QCCs) for aluminum atoms associated with these species were obtained by means of the newly introduced¹H/²⁷ AI TRAPWR method as well as²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR). QCC values of 11.3, 15.3, 13.3 and (14.0± 0.6) MHz were determined from the TRAPDOR profiles for Lewis acid sites, Bronsted acid sites (SiOHAl) and two kinds of non-framework aluminum species Al(OH) _n , respectively. The source of the “invisible Al” is discussed on the basis of the NMR experimental results.     

Radiological characterization of drinking waters in Central Italy

Due to the importance of water in human life, its quality must be strictly controlled; for this purpose, simple and reliable analytical methods must be available. In this study, a monitoring of radioactivity content was performed in tap waters collected in a region of Central Italy to check the compliance with recent European and Italian regulations. Gross alpha and beta activities, ²³⁸U, ²³⁴U, ²²⁶Ra, ²²²Rn, and ³H concentrations were measured. Gross alpha and beta activities were determined by standard ISO 9696 and ISO 9697; for ²²⁶Ra, ²²²Rn and ³H determination, liquid scintillation was used. ²³⁸U and ²³⁴U concentrations were determined by alpha spectrometry after separation from the matrix by extraction chromatography and electroplating. The results revealed that the tritium concentration was always lower than 6.75 Bq l^− 1. The concentrations (mBq l^− 1) of ²²⁶Ra, ²²²Rn, ²³⁸U, and ²³⁴U ranged from < 1.70 to 15.31, from 0.69 to 20.3, from 0.65 to 48.77, and from 0.78 to 51.50, respectively.²³⁴U/²³⁸U ratios were higher than 1 in most cases. The results obtained revealed that, in most samples, gross alpha and gross beta were lower than the parameter value indicated in the international regulations. An attempt was also made to find a correlation between these results and the chemical parameters of waters.     

Safranal Induces Vasorelaxation by Inhibiting Ca2+ Influx and Na+/Ca2+ Exchanger in Isolated Rat Aortic Rings

Introduction: Safranal, which endows saffron its unique aroma, causes vasodilatation and has a hypotensive effect in animal studies, but the mechanisms of these effects are unknown. In this study, we investigated the mechanisms of safranal vasodilation. Methods: Isolated rat endothelium-intact or -denuded aortic rings were precontracted with phenylephrine and then relaxed with safranal. To further assess the involvement of nitric oxide, prostaglandins, guanylate cyclase, and phospholipase A₂ in safranal-induced vasodilation, aortic rings were preincubated with L-NAME, indomethacin, methylene blue, or quinacrine, respectively, then precontracted with phenylephrine, and safranal concentration–response curves were established. To explore the effects of safranal on Ca²⁺ influx, phenylephrine and CaCl₂ concentration–response curves were established in the presence of safranal. Furthermore, the effect of safranal on aortic rings in the presence of ouabain, a Na⁺-K⁺ ATPase inhibitor, was studied to explore the contribution of Na⁺/Ca²⁺ exchanger to this vasodilation. Results: Safranal caused vasodilation in endothelium-intact and endothelium-denuded aortic rings. The vasodilation was not eliminated by pretreatment with L-NAME, indomethacin, methylene blue, or quinacrine, indicating the lack of a role for NO/cGMP. Safranal significantly inhibited the maximum contractions induced by phenylephrine, or by CaCl₂ in Ca²⁺-free depolarizing buffer. Safranal also relaxed contractions induced by ouabain, but pretreatment with safranal totally abolished the development of ouabain contractions. Discussion/Conclusion: Inhibition of Na⁺-K⁺ ATPase by ouabain leads to the accumulation of Na⁺ intracellularly, forcing the Na⁺/Ca²⁺ exchanger to work in reverse mode, thus causing a contraction. Inhibition of the development of this contraction by preincubation with safranal indicates that safranal inhibited the Na⁺/Ca²⁺ exchanger. We conclude that safranal vasodilation is mediated by the inhibition of calcium influx from extracellular space through L-type Ca²⁺ channels and by the inhibition of the Na⁺/Ca²⁺ exchanger.     

Hydrolysis of Volatile Ammonium Oxofluorotitanate According to 19F, 17O, and 49Ti NMR Data

Hydrolysis of NH₄TiO_xF_5-2x (x0.4) (I) was investigated by ¹⁹F, ¹⁷O, and ⁴⁹Ti NMR. The interaction of complex I with water is accompanied by the formation of [TiF₆]^2- and multinuclear titanium forms. The composition of the main forms resulting from hydrolysis of I has been established. The bonding of titanium octahedra into dimers and other oligomers occurs by formation of hydroxyl bridges, considerably lowering the pH of the solution. Close analogy has been found between hydrolysis of the title complex and that of titanium tetrafluoride.     

Isolation of Protein-Nucleic Components of Cotton Chromatin and Investigation of Their Interaction with the Cytokinin-Receptor Complex

Cotton chromatin was fractionated into its components. Fractions of histone proteins, nonhistone proteins (NHp-1, NHp-2, NHp-3), and DNA were obtained. Their interactions with ³ H-BAP and ³ H-BAP-CBP complex were investigated. The RNA-polymerase activities of the obtained fractions were investigated. Fraction NHp-2 was shown to bind specifically hormone and its complex with the receptor. RNA-polymerase was localized in fraction NHp-2     

Synthesis of 9-substituted tetrahydrodiazepinopurines—asmarine A analogues

Asmarines are marine alkaloids, with a unique tetrahydro[1,4]diazepino-[1,2,3-g,h]purine (THDAP) structure and interesting biological properties. Three synthetic approaches were employed for the preparation of the THDAP system. Several N-9, of the purine, protecting groups were investigated. ¹⁵N-Chemical shifts measured from ¹⁵NH HMBC experiments for several compounds, that demonstrate the influence of various structural features on the ¹⁵N-resonances are reported.     

Synthesis and Hydrolysis of Hybridized Silicon Alkoxide: Si(OEt)x(OBut)4-x. Part I: Synthesis and Identification of the Si(OEt)x(OBut)4-x

Using silicon tetrachloride (SiCl₄), tert-butanol (t-BuOH), ethanol (EtOH) and NH₃, the hybridized silicon ethoxide 3-tert-butoxide (Si(OEt)_x(OBu^t)_4-x) was synthesized and the configuration of the material was investigated by FT-IR,¹ H and ¹³C NMR and gas chromatogram/mass spectrum (GC/MS) techniques. The results confirm that both the ethoxy and the tert-butoxy groups have been attached to silicon atoms. Furthermore, the alkoxy group types and their relative amounts in the alkoxide were also determined by ¹H and ¹³C NMR and GC/MS.     

The effect of silica nanoparticles on the morphology, mechanical properties and thermal degradation kinetics of PMMA

Silica-PMMA nanocomposites with different silica quantities were prepared by a melt compounding method. The effect of silica amount, in the range 1-5 wt.%, on the morphology, mechanical properties and thermal degradation kinetics of PMMA was investigated by means of transmission electron microscopy (TEM), X-ray diffractometry (XRD), dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), Fourier-transform infrared spectroscopy (FTIR), ¹³C cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy (¹³C{¹H} CP-MAS NMR) and measures of proton spin-lattice relaxation time in the rotating frame (T_1ρ(H)), in the laboratory frame (T₁(H)) and cross-polarization times (T_CH). Results showed that silica nanoparticles are well dispersed in the polymeric matrix whose structure remains amorphous. The degradation of the polymer occurs at higher temperature in the presence of silica because of the interaction between the two components.