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1.
Phase transitions of poly(N-isopropylacrylamide-co-acrylic acid) (PiPA-AA) and poly(N,N- diethylacrylamide-co-acrylic acid) (PdEA-AA) in water have been investigated by means of turbidimetry, Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The phase transition temperatures (Tp) of these copolymers increase with the degree of ionization () of the acrylic acid (AA) units, which in turn is dependent on the pH of the solutions. Apparent values of pKa for the AA units, determined from the pH dependencies of Tp, are 4.7 and 5.4 for PiPA-AA and PdEA-AA, respectively. Differences between Tp for PiPA-AA and Tp for PiPA homopolymer (Tp) are +1.5 and –0.2 °C/mol% of AA at =1 and 0, respectively. The values of Tp for PdEA-AA are +2.6 (ionic) and –0.5 (nonionic)°C/mol%, indicating that the incorporated AA units have a larger effect on PdEA than on PiPA. DSC measurements performed with each of these copolymers at different pH values show a linear relationship between Tp and the enthalpy of transition (H). IR measurements of PiPA-AA show that the profiles of IR bands from both iPA and AA units exhibit critical changes at Tp of the copolymer. Heating the solution above Tp leads to shifts of the amide II, C–H stretch, and C–H bend bands from the iPA units toward lower wavenumbers, as well as a shift of the amide I band from the iPA units toward higher wavenumbers. A decrease in the intensity of the symmetric C=O stretch IR band from carboxylate anions (1560 cm–1), and an increase in the intensity of the C=O stretch band from COOH groups (1705 cm–1) suggest that a partial protonation of the carboxylate groups (COO–+H+COOH) takes place upon the phase transition. 相似文献
2.
R. Bruce King 《Journal of mathematical chemistry》2008,44(1):5-19
The special projective linear groups PSL(2ℓ + 1) or L
2(2ℓ + 1) of order 2ℓ(2ℓ + 1)(ℓ + 1) can be used to study atomic shells of electrons with angular momentum quantum number ℓ
corresponding to the atomic p, d, f, and g shells for ℓ = 1, 2, 3, 4, respectively. For the atomic g shell the group L
2(9) is isomorphic with the alternating group A
6 on six objects of order 360 or the symmetry group of the 5-dimensional simplex, a 5-dimensional analogue of the tetrahedron
with 6 vertices and 15 edges. This leads to the subgroup chain SO(9) ⊃ SO(5) ⊃ L
2(9) for the atomic g shell analogous to the subgroup chain SO(7) ⊃ G
2 ⊃ L
2(7) ≈7
O for the atomic f shell. In the L
2(9) group only the representations of spherical harmonics or sums thereof, Γ(Yℓ), with dimensions dim Γ(Yℓ) or dim Γ(Yℓ) ± 1 divisible by 9 are found to be individually reducible to irreducible representations (irreps) or sums of irreps of L
2(9). This leads to term groupings such as S, PD, G, PF, DH, L, PK, DI, FH, M, FI, PO, DN, HK, R, etc., of increasing total
dimension for the irreps of SO(9) for various g
n
configurations in the atomic g shell. 相似文献
3.
A structure and kinetic stability study on some complexes with the general formula MN5, where M are the alkali-metal atoms, Li, Na, K, and Rb, has been carried by using hybrid density functional methods. Complex B (C2v) with two points of attachment to the N5 ring is the most energetically favored for all metals considered here. Pyramidal structures A (C5v) are kinetically unstable and they rapidly rearrange to the most stable planar structures B. At the QCISD(T)/6-311 + G*//B3LYP/6-311 + G* + ZPE (B3LYP/6-311 + G*) level, the decomposition barrier heights of LiN5-B, NaN5–B, KN5-B, and RbN5-B are predicted to be 19.9, 22.0, 22.5, and 23.0 kcal/mol, respectively. In addition, the rate constants of the decomposition reaction MN5-B MN3 + N2 (M + Li, Na, K, and Rb) are also predicted using conventional transition state theory and canonical variational transition state theory, respectively. 相似文献
4.
Dupard-Julien CL Kandlakunta B Uppu RM 《Analytical and bioanalytical chemistry》2007,387(3):1027-1032
A reversed-phase, high-performance liquid chromatography (RP-HPLC) method that allows quantitation of low levels of epoxides
has been described. The method involved derivatization of epoxides using 100- to 1,000-fold excess N,N-diethyldithiocarbamate (DTC) at 60 °C for 20 min at neutral pH. The unreacted DTC was then decomposed to CS2 and diethyl amine by acidification of the reaction mixture to pH 2 using orthophosphoric acid. The first two steps could
be performed in the same reaction vessel by sequential addition of reagents. In the final step, an aliquot (20 μL) of the
derivatized sample was analyzed for the presence of stable esters of DTC by RP-HPLC using a Supelcosil LC-18-S (150 × 4.6-mm)
column and a mobile phase consisting of 40% (v/v) acetonitrile in water at a flow of 1 mL min−1. Using UV detection at 278 nm, the epoxides gave linear responses in the concentration range of 0.25 to 50 μM. The method
is robust, and as low as 5 pmol of the analyte could be successfully detected and quantified with recoveries of ≥94%. Following
a minimal pretreatment such as ultrafiltration (molecular weight cutoff 5,000 Da), the method is suitable for analysis of
epoxides in complex physiological fluids (e.g., fetal bovine serum). The method has been rigorously evaluated and adapted
in our laboratory for routine analysis and determination of stability of epoxides of 1,3-butadiene and other alkenes added
to cell cultures. 相似文献
5.
Electrochemical measurements including cyclic voltammetry, differential capacity, and chronocoulometry have been used to characterize the adsorption behaviors of the zwitterionic surfactant
N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS) on the Au(111) electrode surface. The thermodynamics of the ideally polarized electrode have been employed to determine the Gibbs excess and the Gibbs energy of adsorption. The results show that the adsorption of DDAPS has a multistate character. The first two states are observed at potentials close to zero charge. At low bulk DDAPS concentrations, it corresponds to the formation of a film of nearly flat adsorbed molecules. At higher concentrations it is converted into a hemimicellar state. The second state is formed at negative potentials and charge densities close to 0 C cm–2. It corresponds to a film of tilted molecules oriented with the hydrocarbon tail towards the metal and the polar head toward the solution.Dedicated to Professor Zbigniew Galus on the occasion of his 70th birthday and in recognition of his many contributions to electrochemistry. 相似文献
6.
A nonlabeling electrochemical detection method for analyzing the polymerase-chain-reaction-amplified sequence-specific p16
INK4A
gene, in which the basis for the covalent immobilization of deoxyribonucleic acid (DNA) probe is described, has been developed.
The self-assembly process was based on the covalent coupling of glutaraldehyde (GA) as an arm molecule onto an amino-functional
surface. The p16
INK4A
gene was used as the model target for the methylation detection of early cancer diagnosis. An amino-modified DNA probe was
successfully assembled on the GA-coupling surface through the formation of Schiff base under potential control. The hybridization
of amino-modified DNA probes with the target was investigated by means of electrochemical measurements, including cyclic voltammetry
and square wave voltammetry. Furthermore, the functions of GA coupling for sequence-specific detection were compared with
those obtained based on mercaptopropionic acid. Hybridization experiments indicated that the covalent coupling of GA was suitable
for the immobilization of DNA probe and was sensitive to the electrochemical detection of single-base mismatches of label-free
DNA targets in hybridization. Moreover, reported probe-modified surfaces exhibited excellent stability, and the hybridization
reactions were found to be completely reversible and highly specific for recognition in subsequent hybridization processes.
The strategy provided the potential for taking full advantage of existing modified electrode technologies and was verified
in microarray technology, which could be applied as a useful and powerful tool in electrochemical biosensor and microarray
technology. 相似文献
7.
V. E. Romanov E. E. Shul’ts M. M. Shakirov G. A. Tolstikov 《Chemistry of Natural Compounds》2008,44(3):346-351
New N-acylates of the norditerpenoid alkaloid N-deacetyllappaconitine that were modified in the aromatic ring and are interesting as potential pharmacologically valuable
compounds were prepared.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 275–279, May–June, 2008. 相似文献
8.
Thermoresponsive hydrogels based on N-isopropylacrylamide, N-hydroxymethylacrylamide, and 2-hydroxyethyl methacrylate, poly(NIPAM–co-NHMAAm–co-HEMA), have been synthesized and their swelling—deswelling behavior studied as a function of NIPAM concentration, NIPAM/NHMAAm and NIPAM/HEMA mole ratio, and total monomer concentration. Copolymers varying in composition have been obtained by redox copolymerization of these three monomers. Temperature has been changed in the ranges from 4 to 70 °C at fixed pH and total ionic strength. Equilibrium swelling ratio, dynamic swelling ratio, and dynamic deswelling ratio were evaluated for all hydrogel systems. The equilibrium swelling ratios of the copolymeric gels decrease with increasing NHMAAm and HEMA content. The formation of the intermolecular hydrogen bonding between hydroxyl and amido groups decreases the hydrophilic group numbers of the gel and the affinity of the gel towards water decreases. The copolymer gels also showed rapid volume transitions with time. The time required for equilibrium shrinking increased with increasing NHMAAm and HEMA content in the gel. 相似文献
9.
Paramasivam Parthiban Mannangatty Rani Senthamaraikannan Kabilan 《Monatshefte für Chemie / Chemical Monthly》2009,49(3):287-301
Abstract A series of variously substituted N-methylpiperidin-4-one-O-benzyloximes were synthesized by three different methods. Among them, the direct conversion of 2,6-diarylpiperidin-4-ones
into the corresponding oxime ethers (method A) was proved to be better than the other two methods in the sense of good yield,
convenience, easy work-up and quick reaction time. All the synthesized compounds are characterized by IR, Mass and NMR (1H NMR, 13C NMR, 1H-1H COSY, 1H-13C COSY and HMBC) spectral studies. The conformational preference of the synthesized oxime ethers with/without alkyl and aryl
substituents at C-3/C-5 and C-2/C-6 is discussed using the spectral data. The observed chemical shifts and coupling constants
suggest that the synthesized oxime ethers adopt chair conformation with equatorial orientation of all the substituents, whereas
1-methyl-3-isopropyl-2,6-diphenylpiperidin-4-one-O-benzyloxime also exists in boat conformation. Based on the NMR data, the effects of oximination on ring carbons and their
associated protons and alkyl substituents are discussed. In addition, the effect of NMe group on the 2,6-diarylpiperidin-4-one-O-benzyloximes was also studied.
Graphical abstract
相似文献
10.
N. V. Nastapova A. S. Stepanov V. V. Yanilkin V. A. Burilov V. V. Skripacheva A. R. Mustafina S. E. Solov’eva A. I. Konovalov 《Russian Journal of Electrochemistry》2009,45(7):783-794
The electrochemical properties of n-sulfonatothiacalyx[4]arene (H4XNa4) complexes with [Co(dipy)3]3+ and Fe3+ ions were studied by means of cyclic voltammetry in aqueous solution at pH 2.5. The observed single-electron reduction of [Co(dipy)3]3+ bound extraspherically to the upper rim and Fe3+ ion bound intraspherically to the lower rim of n-sulfonatothiacalyx[4]arene in binary [Co(dipy)3]3+ · H3X5?, H3X5? · Fe3+, and ternary [Co(dipy)3]3+ · H3X5? · Fe3+ heterometal complexes was more difficult than in the free state. The reversible single-electron transfer to the metal ion results in lower binding energy ([Co(dipy)3]3+, ΔΔG 0 = 3.9 kJ/mol) or in full fast dissociation of the complex (Fe3+). The ternary complex in the solution forms the aggregates, in which inner encapsulated Fe(III) and Co(III) ions are not reduced on the electrode. Their quantitative reduction takes place by the relay mechanism of intra- and intermolecular electron transfer through electrochemically generated [Co(dipy)3]2+ outer ions. 相似文献
11.
A novel organic gel film modified electrode was simply and conveniently fabricated by casting LixMoOy and polypropylene carbonate (PPC) onto the surface of a gold electrode. The cyclic voltammetry and amperometry studies demonstrated that the LixMoOy film modified electrode has a high stability and a good electrocatalytic activity for the reduction of iodate. In amperometry, a good linear relationship between the steady current and the concentration of iodate was obtained in the range from 3×10–7 to 1×10–4 mol L–1 with a correlation coefficient of 0.9997 and a detection limit of 1×10–7 mol L–1. 相似文献
12.
Summary. The regioselective reaction of N1-benzyl-N2-(4-nitrophenyl)ethanediamide with dialkyl acetylenedicarboxylates or alkyl propiolates in the presence of triphenylphosphine
leads to dialkyl 4-benzylamino-1-(4-nitrophenyl)-5-oxo-2,5-dihydro-1H-pyrrole-2,3-dicarboxylates or alkyl 4-benzylamino-1-(4-nitrophenyl)-2-oxo-5-pyrrolidinecarboxylates in good yields. 相似文献
13.
Kershaw JA Nekrassova O Banks CE Lawrence NS Compton RG 《Analytical and bioanalytical chemistry》2004,379(4):707-713
The effect of Cu(II) on the determination of homocysteine via its electrochemically initiated reaction with N,N-diethyl-p-phenylenediamine is examined. The presence of copper inhibited the detection process for homocysteine owing to a complexation reaction occurring. This provided an indirect route for the sensitive and selective determination of Cu(II), which produced a linear response over the range from 2.5 to 500 M and a limit of detection of 2.5 M. The detection pathway was examined in the presence of metallic and inorganic ions, with negligible interference observed. 相似文献
14.
R. I. Kublashvili M. O. Labartkava K. P. Giorgadze D. Sh. Ugrekhelidze 《Chemistry of Natural Compounds》2008,44(4):413-415
N-Tolylglycosylamines were synthesized from o-, m-, and p-toluidines and aldoses (D-glucose, D-galactose, D-mannose, L-rhamnose, D-xylose, and L-arabinose). The anomeric and isomeric
compositions of the synthesized products were established using 13C NMR methods.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 333–335, July–August, 2008. 相似文献
15.
Lignocellulose copolymers with grafted lactam rings were prepared by graft copolymerization of wood with N-vinylpyrrolidone initiated by Fe2+-H2O2. The principal features of their formation were investigated as functions of reactant concentrations, temperature, and polymerization
time.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 174–176, March–April, 2008. 相似文献
16.
Starch materials of different amylose content were allowed to react with saturated and unsaturated fatty acids of varying
chain length from C14 to C18 under homogeneous conditions applying the solvent N,N-dimethyl acetamide in combination with LiCl. As reagent the corresponding acid chlorides and, alternatively, carboxylic acids
in situ activated with toluene-4-sulfonyl chloride and N,N′-carbonyldiimidazole (CDI) were studied. Using fatty acid chlorides (FACl) and toluene-4-sulfonyl chloride-activated acids
an almost complete substitution of the starch occurs. By in situ activation of the fatty acids with CDI, products with a degree of substitution up to 2 were obtained, which, in particular,
represents a simple and very mild procedure. 相似文献
17.
Amphiphilic diblock copolymers consisting of 2-(N, N-dimethylamino)ethyl methacrylate (DMAEMA, abbreviated as DMA) and stearyl methacrylate (SMA) with different degrees of polymerization
and compositions were prepared by reversible addition–fragmentation chain transfer (RAFT) copolymerization. The composition
and chemical structures of (co)polymers were confirmed by the measurements of 1H NMR spectroscopy and gel permeation chromatography (GPC). The self-aggregating structures of amphiphilic diblock copolymers
with the concentration of 0.1~0.3 wt.% in THF/water mixed solvent was investigated by transmission electron microscopy (TEM)
and dynamic light scattering (DLS). It was found that both the morphologies and aggregating particle size resulted from the
amphiphilic diblock copolymers depended on the variation of pH values, the lengths of the hydrophobic PSMA chains, and the
weight ratio of THF/water mixed solvent. 相似文献
18.
I. V. Smolyaninov N. N. Letichevskaya A. V. Kulakov Ya. B. Aref’ev K. P. Pashchenko N. T. Berberova 《Russian Journal of Electrochemistry》2007,43(10):1187-1199
The mechanisms of redox transformations of sterically hindered [1IBQ]-[3IBQ], 9,10-iminophenanthraquinone [4IFQ], and o-aminophenol [5AP] have been studied by cyclic voltammetry. It has been shown that the reduction process in tetrahydrofuran consists of two consecutive reversible steps leading to the formation of a radical anion and a dianion. In the case of acetonitrile, only the first redox process is detected, which involves the steps of protonation and electron addition resulting in the formation of a monoanion. Quantum-chemical calculations indicate a lower degree of participation of the six-membered nonaromatic carbon ring in the spin density delocalization in the o-iminosemiquinonate radical anions as compared to o-benzosemiquinonate radical anions. The oxidation of iminoquinones results in the formation of an unstable radical cation, which undergoes further chemical transformations. An increase in the acidity of a medium leads to the formation of protonated forms with the reduction potential being shifted anodically. The introduction of screening groups makes it possible to suppress side reactions of hydrolysis and cyclization of oxidized o-aminophenol [5AP] forms. Therefore, the major product of complete electrolysis is o-iminobenzoquinone [2IBQ]. 相似文献
19.
V. V. Kostrub E. B. Tsupak Yu. N. Tkachenko M. A. Shevchenko 《Russian Chemical Bulletin》2008,57(8):1754-1759
Reactions of 5-aryl- and 5,7-diaryl-1,3-dimethyl-2,4-dioxopyrano[4,3-d]pyrimidinium salts with hydrazine were studied. In the former case, the reaction products were the 6-amino-1,3-dimethyl-2,4-dioxopyrido[4,3-d]pyrimidinium salts. 5,7-Diarylpyrano[4,3-d]pyrimidinium salts were transformed into either the corresponding pyridinium salts or 1H-pyrimido-[5,4-d][1,2]diazepine-2,4(3H,9H)-diones, depending on the hydrazine concentration and the reaction time.
For Part 1, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1720–1725, May, 2008. 相似文献
20.
Eberhard Reimann Rainer Hertel Jürgen Krauss 《Monatshefte für Chemie / Chemical Monthly》2008,139(6):673-684
Alkylation of Reissert compounds derived from 3-methylisoquinolines with several 2-cyanobenzylbromides followed by hydrolytic cleavage provided the corresponding 1-benzyl-3-methylisoquinolines. Treatment of the latter with methylmagnesiumiodide caused cyclization to the title compounds rather than formation of 2-acetylbenzylisoquinolines. 相似文献