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1.
The N,N-diisopropylphosphoramidites 10a and 10b of appropriately protected chiral diastereoisomers of d(T[P-18O]-A) ( 8a and 8b , resp.), chiral by virtue of the isotope 18O at the P-atom, have been synthesized. The 18O-isotope was incorporated by oxidation of the phosphite triester 3 with H2[18O]/I2. Separation of the diastereoisomers was accomplished by flash chromatography of the O-3′-deprotected phosphate triesters 5a/b . The absolute configuration at the chiral P-atom was deduced from the methylation products of the fully deprotected diastereoisomers 8a and 8b . Phosphinylation of 5a and 5b yielded the configurationally pure phosphoramidites 10a and 10b , respectively, which were then employed in solid-phase synthesis to yield the self-complementary oligomers d(G-A-G-T-(Rp)-[P-18O]-A-C-T-C) ( 13 ) and d(G-A-G-T-(SP)-[P-18O]-A-C-T-C) ( 14 ), respectively.  相似文献   

2.
《Electroanalysis》2005,17(8):685-693
Carbon paste electrodes were modified by mixing appropriate amounts of the monomers o‐phenylendiamine, p‐phenylendiamine and m‐phenylendiamine (o‐PD, p‐PD and m‐PD) into a graphite powder‐paraffin oil matrix. The electropolymerization of the incorporated phenylendiamine was then carried out in a carbon paste electrode in acidic medium by cyclic voltammetry between ?0.30 V and +0.90 or under constant potential. The modified carbon paste electrodes (MCPEs) obtained by this electropolymerization method were found to be useful for trace determination of Pb2+ in aqueous solutions. Lead(II) was first preconcentrated on the modified electrodes by complexation with the modifier, and the electrode was then transferred to an electrochemical cell. The best results in terms of sensitivity and detection limit were obtained with poly p‐phenylenediamine (poly (p‐PD)). For a 10‐min preconcentration time, the calibration plot was linear from 5×10?8 mol L?1 to 10?5 mol L?1, with r2=0.999 and relative standard deviation equal to 5%. However, the lowest lead concentration that could be detected was 10?9 mol L?1. Interference from metal ions like Cd(II), Hg(II), Zn(II), Fe(II) and Cu(II) was also studied.  相似文献   

3.
5-Aminotetrazole trinitrophloroglucinolate ((ATZ)TNPG) was prepared and characterized by elemental analysis and FT-IR spectroscopy. The crystal structure was determined by X-ray diffraction analysis and it belonged to orthorhombic system and Pbca space group with a=0.6624(2) nm, b=1.7933(4) nm, c=2.3117(5) nm, V=2.7458(9) nm3, Z=4, and Dc=1.849 g·cm−3. The molecular formula was confirmed to be (ATZ)TNPG·2H2O. 5-Aminotetrazole cation (ATZ+) and trinitrophloroglucinol anion (TNPG) were linked into 2-D layers along b-axis and c-axis by hydrogen bonds. Then the layers were linked along a-axis by hydrogen bonds between the water molecules belonging to different layers. The thermal decomposition mechanism of the compound was studied by differential scanning calorimetry (DSC), thermogravimetry-thermogravimetric analysis (TG-DTG), and Fourier transform-infrared (FT-IR) spectroscopy techniques. Under nitrogen atmosphere with a heating rate of 10 °C·min−1, the compound experienced one endothermic process with peak temperature of 76 °C and one exothermal process with peak temperature of 203 °C. The former was confirmed to be a dehydrate process. The latter was the decomposition of TNPG and ATZ+ in the compound. The exothermic enthalpy change of this process was −212.10 kJ·mol−1. The kinetic parameter calculation from Kissinger's method were, E=132.1 kJ·mol−1, ln(A/s−1)=12.54 with r=0.9990, and the calculation results from Ozawa-Doyle's method were, E=133.1 kJ·mol−1 with r=0.9992.  相似文献   

4.
The intriguing multi‐ligand compound [Cu(IMI)4Cl]Cl ( 1 ) with the ligand imidazole (IMI) was synthesized and characterized by elemental analysis and FT‐IR spectroscopy. The crystal structure was determined by X‐ray single crystal diffraction and the crystallographic data showed that the compound belongs to the monoclinic P21/n space group [α = 8.847(2) Å, b = 13.210(3) Å, c = 13.870(3) Å, and β = 90.164(3)°]. Furthermore, the CuII ion is five‐coordinated by four nitrogen atoms from four imidazole ligands and a chlorine atom. The thermal decomposition mechanism was determined based on differential scanning calorimetry (DSC) and thermogravimetric (TG‐DTG) analysis. The non‐isothermal kinetics parameters were calculated by the Kissinger's method and Ozawa's method, respectively. The energy of combustion, enthalpy of formation, critical temperature of thermal explosion, entropy of activation (ΔS), enthalpy of activation (ΔH), and free energy of activation (ΔG) were measured and calculated.  相似文献   

5.
The syntheses of four new β-cyclodextrin-hexasiloxane copolymers from heptakis(2,3-di-O-methyl)-β-cyclodextrin (2) by multi-step processes are described. 6A,6C-Di-O-[p,p'-methylenebis(benzenesulfonyl)]hetakis(2,3-di-O-methyl)β-cyclodextrin (3) , which was prepared by the reaction of 2 with p,p'-methylenebis-(benzenesulfonyl chloride), is a key intermediate for the preparation of permethylated 6A,6C-bisalkenyl-β-cyclodextrins 5, 6 , and 9. Permethylated 6A,6C-bissulfonate ester 4 , which was obtained from 3 by a methylation reaction under mild conditions, was reacted with sodium allyloxide or sodium ω-undecenyloxide to produce permethylated 6A,6C-bisallyl- (or bis-ω-undecenyl)-β-cyclodextrin 5 or 6 or was hydrolyzed with 2% sodium amalgam in methanol to yield diol 7. Compound 7 was oxidized with periodinane, followed by Wittig's reaction with methyltriphenylphosphonium iodide to give permethylated 6A,6C-dideoxy-6A,6C-dimethylene-β-cyclodextrin (9). Treatment of 2 with p,p'-methylenebis(benzenesulfonyl chloride) or p,p'-biphenyldisulfonyl chloride gave bissulfonate esters 10 or 11 , respectively. Both of them were treated with sodium p-allyloxy-phenoxide in DMF, followed by methylation, to form permethylated 6A,6D-di-O-(p-allyloxyphenyl)-β-cyclo-dextrin (16). Bisalkenes 5, 6, 9 and 16 were copolymerized with α,ω-dioctyldecamethylhexasiloxane by a hydrosilylation process to give the cyclodextrin-containing copolymers 17–20.  相似文献   

6.
[32-14C]Chlorophyll a ( 10b ) was synthesized from pheophorbide a methyl ester ( 5a ) in a seven-step partial synthesis. The key intermediate pheophorbide d methyl ester ( 6 ) was obtained by ozonolysis of the vinyl group of 5a in 91% yield. Selective reduction of the CHO group of 6 gave the corresponding alcohol 7 , and conversion of the latter to the phosphonium bromide 8 yielded after Wittig reaction with [14C]paraformaldehyde, [32-14C]pheophorbide a methyl ester ( 5b ). The final transformation to the title compound was achieved by acid hydrolysis of 5b , esterification with natural phytol to [32-14C]pheophytin a ( 9b ), and eventual insertion of a Mg2+ ion.  相似文献   

7.
The synthesis of 2,2′-bis(bis(dimethylamino)-phosphino)-3,3′5,5′-tetra-tert-butylbiphennyl ( 5 ) is described. It was extensively studied by 1H, 13C, and 31P NMR spectroscopy. Furthermore, the X-ray analysis of 5 is reported. Crystals of 5 are tetragonal, space group P¯421c, a = b = 24.770 (3) Å, c = 12.658 (4) Å, Z = 8. The surprising reaction of 5 with proton acids leading to the formation of various phosphorus containing five- and six-membered ring compounds is discussed. On reaction of one of the six-membered ring compounds ( 9 ) with magnesium in THF, a λ3, λ5-diphosphaphenanthrene ( 19 ) was obtained.  相似文献   

8.
A 1-D chain complex, cadmium(ΙΙ) chloride thiocyanate (1), [CdCl(SCN)] n was synthesized by evaporation and characterized by single-crystal X-ray diffraction and FT-IR techniques. The compound crystallizes in the space group Pnma of orthorhombic system with cell parameter a = 9.5967(7), b = 4.2595(3), and c = 10.1789(7) Å; V = 416.08(5) Å3 and Z = 4. The cadmium(ΙΙ) is five-coordinate, surrounded by one pair of (µ-1,1-NCS) bridging NCS? and three Cl? as a µ3-linker coordinating three Cd(ΙΙ) centers, approximately a severely distorted square-pyramidal configuration. Cd(ΙΙ), Cl?, and SCN? form an infinite 1-D chain with chair-like features, a new example of mixed Cd–NCS–Cl discrete compounds. The photophysical properties of the crystals have been investigated with one emission peak at 473 nm observed for the title complex in the solid state, which exhibits blue luminescence. The mechanical properties of the crystals have been studied using Vickers microhardness tester and the hardness was 78.6 kg mm?2.  相似文献   

9.
All four stereoisomers of (E)-vitamin Kb i. e. (21E, 7R, 111R)-l (= 1a), (21E, 71 R, l11S)-1 (= 1b), (21E, 71 S, 111S) 1 ( = 1c), and (21E, 71S, 111R)-l ( = Id), have been synthesized in a state of high chemical and stereoisomeric purity. The synthesis of stereoisomers lb-d relied on the use of the optically active Cf1* and C*10-building blocks (R)- or (S)-4-(benzyloxy)-3-methylbutanal ((R)- or (S)-2) and (R)- or (S)-citronellal ((R)- or (S)- 3 ) which had been secured by the Rh1-catalyzed allylamine-to-enamine isomerization technology. For the synthesis of the natural (E)-vitamin-K1 stereoisomer 1a , a new route starting from natural phylol was developed, based on an O-alkylation/rearrangement procedure. A HPLC method was developed which separates with remarkable efficiency all four stereoisomers of (E)- as well as three out of the four stereoisomers of (Z)-vitamin K1 on optically active poly(trityl methacrylate) as the chiral stationary phase supported on Nucleosil. By this method, the stereoisomeric content of the stereoisomers 1b-d synthesized was shown to be in the range of 96-98 %, while the natural isomer 1a was configurationally uniform. The biological activity of the four (E)-vitamin-K1 stereoisomers was determined by means of the curative prothrombin time test with vitamin-K-depleted chicks. A high precision of the results was obtained with the recently introduced up-and-down organization of the test and the statistical evaluation according to an estimation procedure. With the natural (E)-vitamin-K1 stereoisomer 1a as standard (set at 1. 0), activities of 0. 93, 1. 19, and 0. 99 were found for stereoisomers 1b, 1c , and 1d , respectively. Within the confidence limits, these activity ratios can be regarded as identical, A very similar efficacy was obtained by comparison of (E, all-rac )-vitamin K1 ((21E, RS, 11′ RS)- 1 ; equimolar mixture of the four stereoisomers 1a-d) with the natural (E)-vitamin-K1 stereoisomer 1a ). A synergistic effect was not detectable, as was the case with the eight α-tocopheryl-acetate stereoisomers.  相似文献   

10.
Electrodeposition of bismuth on gold microelectrodes for determination of Pb(II) by square wave anodic stripping voltammetry (SWASV) was accomplished by an in situ procedure in alkaline solution. A linear calibration plot for Pb(II) in the concentration range 40 to 6700 nmol L?1 (r=0.998) was obtained, the detection limit was found to be 12.5 nmol L?1 (S/N=3) and the relative standard deviation in solutions containing 1 μmol L?1 Pb(II) was 4% (n=12). The analytical performance of the proposed sensor was tested by measuring the Pb(II) concentration in a wine sample. The result was in good agreement with the one obtained by GFAAS.  相似文献   

11.
A novel 1:2 proton transfer self‐associated compound LH2 , (GH+)2(pydc2—), was synthesized from the reaction of dipicolinic acid, pydcH2, (2, 6‐pyridinedicarboxylic acid), and guanidine hydrochloride, (GH+)(Cl). The characterization was performed using IR, 1H and 13C NMR spectroscopy and single‐crystal X‐ray diffraction. LH2 · H2O crystallizes in the space group C2/c of the monoclinic system and contains eight molecules per unit cell. The unit cell dimensions are: a = 26.480(5)Å, b = 8.055(2)Å, c = 14.068(3)Å. The first coordination complex (GH)2[Cd(pydc)2] · 2H2O, was prepared using LH2 and cadmium(II) iodide, and characterized by 1H and 13C NMR spectroscopy and X‐ray crystallography. The crystal system is triclinic with space group P1¯ with one molecule per unit cell. The unit cell dimensions are: a = 8.5125(7)Å, b = 11.0731(8)Å, c = 13.2404(10)Å. The cadmium(II) atom is six‐coordinated with a distorted octahedral geometry. The two pydc2— units are almost perpendicular to each other. The protonation constants of the building blocks of the pydc‐guanidine adduct, the equilibrium constants for the reaction of pydc2— with guanidine and the stoichiometry and stability of the Cd2+ complex with LH2 in aqueous solution were accomplished by potentiometric pH titration. The solution studies strongly support a self‐association between pydc2— and GH+ with a stoichiometry for the CdII complex similar to that observed for the isolated crystalline complex. In fact, the [Cd(pydc)2]2— complex was found as the most abundant species in solution (> 90 %) at a pH >5.  相似文献   

12.
The crystal structure of (±)-7,8,13β,14α-tetrahydro-N7-(13C)methylcorysaminium iodide (13C- 3a ·I) was investigated by X-ray analysis and thus the relative configuration (7S*,13S*,14S*) established (Fig. 1). The conformation of 3a was shown to have a cis-junction of the B/C rings and the rings A and D in an antiperiplanar position relative to the C(13)? C(14) bond (‘anti-cis’), a twisted half-chair for ring B, and a half-chair for ring C (Figs. 2 and 3). Conformation analysis by 1H-NMR data indicated that the crystal conformation of 3a is also the preferred one in MeOH solution.  相似文献   

13.
Thermometric titrations of lanthanum perchlorate, titanium (III)-chloride, uranium (IV)-sulfate, and uranyl sulfate with EDTA solutions were carried out by using a Keithley nanovoltmeter with a rhodium-platinum thermocouple at 25°±0.01°. The formation of LaY?, TiY?, U(IV)Y and UO2HY? ions was confirmed. The heat of reaction for the system, Ti(III)+H2Y2? = TiY?+2H+, was given by δH1 = 1.933-1.422×10 m +2.056×104m (in cal) and the limiting value was evaluated to be δH°1 = 1.9 kcal mol?1 at 25°C.  相似文献   

14.
A poly(vinyl chloride) (PVC) membrane sensor for holmium ions was fabricated based on N‐[(Z)‐1‐(2‐thienyl)‐ methylidene]‐N‐[4‐(4‐{[(Z)‐1‐(2‐thienyl)methylidene]amino} phenoxy)phenyl] amine (TPA) as a new ion carrier, acetophenon (AP) as plasticizing solvent mediator and sodium tetraphenyl borate (NaTPB) as an anion excluder. The electrode shows a good selectivity towards Ho3+ ions respect to other inorganic cations, including alkali, alkaline earth, transition and heavy metal ions. The constructed sensor displays a Nernstian behavior (19.5±0.3 mV/decade) over the concentration range of 1.0×10−6 to 1.0×10−2 mol·L−1 with the detection limit of the electrode being 4.6×10−7 mol·L−1 and very short response time (ca. 5 s). It has a useful working pH range of 3.2–9.8 for at least 8 weeks. The electrode was successfully applied as an indicator electrode for the potentiometric titration of a Ho3+ solution with EDTA and holmium determination in some alloys. The proposed sensor accuracy was studied by the determination of Ho3+ in mixtures of three different ions.  相似文献   

15.
采用新型Salen中间体合成了新型Salen Zn(II)配合物. 用紫外-可见光谱滴定法研究了主体双核Salen Zn(II)与咪唑、二胺类等含氮小分子的分子识别行为, 测定了它们的缔合常数. 对咪唑类客体的缔合常数顺序为Kθ(Im)>Kθ(2-MeIm)>Kθ(EMeIm); 对二胺类客体缔合常数顺序为Kθ(DAP)>Kθ(DAE). 主体与咪唑类和二胺类客体的配位数分别是2和1. 主体与这些客体的识别过程为放热、熵减的焓驱动反应. 利用圆二色光谱研究了识别过程的Cotton效应. 用分子力学方法研究了主客体体系的最低能量构型, 通过量化计算对实验事实做了进一步解释.  相似文献   

16.
The N′-dabcyl-N α-(9-fluorenylmethoxy)-carbonyllysine was prepared by reaction of lysine-Cu2+ complex with the N-hydroxysuccinimide (HOSu) activated ester of [4-(4'-dimethylamino)phenylazo]benzoic acid (dabcyl acid) followed by treatment with EDTA and acylation with Fmoc-OSu, and the N α-tert-butyloxycarbonyl-N′-dabcyllysine was prepared by reaction of N α-tert-butyloxycarbonyllysine with dabcyl-OSu.  相似文献   

17.
Heterodiamantanes and Structurally Related Compounds. Part III. The Pentacyclic C11-Diethers 5, 13-Dioxapentacyclo [6.5.0.02,6.03,12.04,9]tridecane, 4, 13-Dioxapentacyclo [6.4.1.02,7.03,10.05,9]tridecane, and 3, 10-Dioxapentacyclo [7.3.1.02,7.04,12.06,11]tridecane In connection with the studies on heterodiamantanes and structurally related compounds the three novel pentacyclic diethers 3 – 5 were prepared starting from the cyclopentadienone dimer 6 . All four compounds have as common features a central carbocyclic 6-membered ring with four axial alkyl substituents and two oxygen functions in 1, 4 position. The required eleventh C-atom was introduced by dichlorocarbene addition either to 6 ( → 7 ) (Scheme 2) or to 29 ( → 28 ) (Scheme 4). Diether 3 was obtained by reduction of 26 (Scheme 2), a suitable precursor prepared either by intramolecular addition ( 24 → 26 ; Scheme 2) or substitution ( 30 → 26 , 31 → 26 ; Scheme 4), as well as by direct substitution ( 44 → 3 , 42 → 3 ; Scheme 5). Diether 4 was the product of a direct substitution ( 39 → 4 , 36 → 4 ; Scheme 5). The synthesis of diether 5 was achieved from the addition product 51 (resulting from the alcohols 47 and 48 ; Scheme 6). Diether 4 is the thermodynamically least stable of the three diethers 3 – 5 . It was easily isomerized to 5 on treatment with concentrated sulfuric acid in benzene whereas 3 and 5 remained unchanged under these conditions.  相似文献   

18.
The Schiff base of all-trans-retinal was investigated in organic solution by 1H- and 13C-NMR. at high field. Complete assignment of the 1H-NMR. peaks of N-butyl-(all-trans-retinylidene)amine ( 2 ) and the N-butyl-(all-trans-retinylidene)-ammonium ion ( 3 ) was achieved by INDOR (internuclear double resonance). The vicinal proton coupling constants of the polyene chain show that the π-bond orders remain unchanged in N-butyl-(all-trans-retinylidene)amine relative to all-trans-retinal ( 1 ), but change towards larger π-delocalization in the N-butyl-(all-trans-retinylidene)ammonium ion. At ?-61° only one isomer of N-butyl-(all-trans-retinylidene)ammonium was observed. This was shown to be trans at the imine linkage and independent of the solvent. The trifluoroacetic acid counter-ion can approach the positive charge of the N-atom in the weakly polar solvent dichloromethane but not in the leveling solvent methanol. In dichloromethane the nature of the 1:1 complex is a H-bonded (O?…H-N+) ion-pair whose rate of breaking and forming is rapid at RT. Strong stabilization of the ion-pair resulted from homo-conjugation with a second molecule of trifluoroacetic acid. Excess of acid efficiently diminished the isomerization rate at the C,N-bond.  相似文献   

19.
Laser-induced time-resolved phosphorescence has been used to evaluate the quenching of gaseous biacetyl (3Au) molecules by various molecules at 25°C. The quenching of biacetyl (3Au) molecules by biacetyl itself was not detectable under our experimental conditions, and a pressure-independent lifetime of 1.70 ± 0.08 msec was found. The bimolecular rate constants (units of l/mol·sec) for quenching of the 3Au molecules by cis-2-pentene, trans-2-pentene, cis-1,3-pentadiene, trans-1,3-pentadiene, and oxygen were found to be (3.3 ± 1.9) × 103, (4.0 ± 0.2) × 104, (3.9 ± 0.1) × 108, (1.3 ± 0.1) × 108, and (5.2 ± 0.4) × 108, respectively.  相似文献   

20.
The use of lithium cation in composites of block copolymers [polyethylene‐b‐polyethylene oxide (PE‐b‐50%PEO and PE‐b‐80%PEO)] and their derivatives was tested as a modifier of the vapor sorption and impedance of these complexes. The block copolymer PE‐b‐80%PEO was modified by oxidation of its hydroxyl end group to both a carboxylic acid group (PE‐b‐80%PEO)CH2COOH and its sodium salt (PE‐b‐80%PEO)CH2COO? Na+ for the purpose of improving its compatibility and performance as a matrix for composites. These modified copolymers were characterized by FTIR, DSC, and mass spectrometry. The sorption of water of these copolymers and their composites with lithium nitrate was also compared, as well as the electrical properties of their composites were measured by electrical impedance spectroscopy. For the composites obtained with PE‐b‐80%PEO and lithium nitrate, it was found that lithium cation plays an important role increasing the sorption rate, which is maximized for the PE‐b‐80%PEO + (21% lithium nitrate) composite. For the copolymers (PE‐b‐80%PEO)CH2COOH and (PE‐b‐80%PEO)CH2COO? Na+ and their composites, the highest sorption rate was observed for salt in the following order: COO? Na+ > COOH > OH. The PE‐b‐80%PEO + (21% lithium nitrate) composite behaves as a solid polymeric ionic conductor fitting the Williams–Landel–Ferry equation. However, both (PE‐b‐80% PEO)CH2COOH and (PE‐b‐80%PEO)CH2COO? Na+ + (21% lithium nitrate) composites fitted the Variable Range Hopping equation, indicating a conductance trend with temperature governed by a thermally activated with energy of 0.482 and 0.524 eV and not by a relaxation process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1809–1817, 2010  相似文献   

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