Recently, a novel enzymatic method was developed for determination of homocysteine. This method utilizes the electrochemical hydrogen sulfide sensor along with methionine α,γ‐lyase to accomplish the fast, accurate, sensitive and selective measurements. As a continuation of this work, another enzyme, homocysteine α,γ‐lyase, was used and the parallel experiments of using both enzymes were carried out against the effect of pH, sensitivity, linearity, and interferences, in an intended comparison between these two enzymes. The excellent linearity of amperometric currents against homocysteine concentrations, high sensitivities and low detection limits for both enzymes reconfirmed that the electrochemical method is superior over other analytical means. The high enzymatic activity of methionine α,γ‐lyase surpassing homocysteine α,γ‐lyase endowed the former higher sensitivity, lower detection limit and faster response than the latter, suggesting methionine α,γ‐lyase a better candidate for homocysteine measurement by electrochemical method. The differences between these two enzymes on the trends of response time and sensitivity at different pH environments, reactivity toward several forms of homocysteine as well as on the interference from several agents were also addressed and discussed. 相似文献
The mass spectra of a series of N‐aryl α,β‐unsaturated γ‐lactams were studied. Besides the molecular ion, the three characteristic fragments such as [M+‐29], [M+‐55], and [M+‐82] were commonly found in a series of N‐Aryl α,β‐unsaturated γ‐lactams in EI/MS. Further more the mechanism for the interpretation of these fragments is also de scribed. 相似文献
Research in the field of low-molecular weight, oligomeric and polymeric α,ω-diisocyanatocarbodiimides and -polycarbodiimides has been fruitful, not only in connection with these compounds themselves, but also—as so often happens in chemistry—with quite different problems. Novel synthetic methods, discoveries concerning the properties of low-molecular weight carbodiimides and phosphane imide derivatives, as well as results on the fragmentation reactions of four-membered heterocyclic compounds containing oxygen, phosphorus, and nitrogen, and a better understanding of the diisocyanate polyaddition process are among the many by-products of this research. The “high- and low-temperature formation” of polycarbodiimides and the homogeneous and heterogeneous catalysis of this process are described, and the fundamental importance of four-membered ring fragmentation mechanisms resulting in the formation of phosphane imide derivatives is outlined. Interesting building blocks for the diisocyanate polyaddition and polycondensation processes can be synthesized by many derivatization reactions of oligomeric and high-molecular weight polycarbodiimides and polyuretonimines. The in situ production of polycarbodiimides via matrix reactions in flexible polyurethane foams leads to a cellular arrangement of the material due to the pronounced symmetrical growth processes. Combination-foams with increased carbonation tendencies are formed in this way. Attention is drawn to several industrial applications of α,ω-diisocyanatopolycarbodiimides, of high-molecular weight cross-linked polyuretonimines, and of polycarbodiimide foams. 相似文献
The intrinsic features of (hetero‐arene)–metal interactions have been elusive mainly because the systematic structure analysis of non‐anchored hetero‐arene–metal complexes has been hampered by their labile nature. We report successful isolation and systematic structure analysis of a series of non‐anchored indole–palladium(II) complexes. It was revealed that there is a σ–π continuum for the indole–metal interaction, while it has been thought that the dominant coordination mode of indole to a metal center is the Wheland‐intermediate‐type σ‐mode in light of the seemingly strong electron‐donating ability of indole. Several factors which affect the σ‐ or π‐character of indole–metal interactions are discussed. 相似文献
Semihydrogenation of α,β‐unsaturated ynoates and ‐ynones bearing a γ‐alkoxy group can be performed using triphenylphosphine and water. α,β‐Unsaturated ynoates were reduced to a mixture of cis and trans α,β‐unsaturated enoates, whereas, ynones were reduced to trans α,β‐unsaturated enones as the only products. 相似文献
Olive oil contains powerful antioxidant compounds which impart stability, contribute to various properties of it, and are valuable from the nutritional point of view. Their extraction with as mild conditions as possible led to its investigation using cyclodextrins as a tool. The inclusion ability of α-, β-, and γ-CD was estimated, and it has been demonstrated that the small cavity of α-CD as well as the wide one of γ-CD could enclose less effectively the antioxidant compounds of olive oil than the intermediate in shape cavity of β-CD. The highest yields of antioxidant compounds were achieved when olive oil was mixed with a 2%aqueous solution of β-CD and the resulting precipitate was treated with ethyl alcohol.__________Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 18–21, January–February, 2005. 相似文献
The first σ complexes were found in the 1960s and 1970s, but they did not attract more than passing attention. Only now are we beginning to recognize their key role in the chemical reactions of σ bonds, and this has encouraged more detailed study. In contrast with the more familiar π-donor complexes such as M? (CH2?CH2) and complexes like M? NH3, in which the one pair of electrons on the N atom is bound to the metal atom, in a σ complex an X? H group binds to the transition metal atom; the X? H σ-bonding electron pair acts as a 2e donor to give an (X-H)-M type complex. Dihydrogen complexes (X = H) are one important group of σ complexes. C-H-M complexes (X = R3C) with an agostic C-H-M interaction have not only been found in the ground state but also implicated in the transition states of many important organometallic transformations such as Ziegler–Natta catalysis and sigma bond metathesis. The importance of X? H bond activation will encourage continued growth in this field. 相似文献
Even though the blood–brain barrier (BBB) is compromised for angiogenesis, therapeutic agents for glioblastoma multiforme (GBM) are particularly inefficient due to the existence of a blood–tumor barrier (BTB), which hampers tumor accumulation and uptake. Integrin αvβ3 is overexpressed on glioblastoma U87 cells and neovasculture, thus making its ligands such as the RGD motif target glioblastoma in vitro and in vivo. In the present work, we have designed a modified polyethylene glycol–polyethylenimine (PEG–PEI) gene carrier by conjugating it with a cyclic RGD sequence, c(RGDyK) (cyclic arginine‐glycine‐aspartic acid‐D ‐tyrosine‐lysine). When complexed with plasmid DNA, this gene carrier, termed RGD–PEG–PEI, formed homogenous nanoparticles with a mean diameter of 73 nm. These nanoparticles had a high binding affinity with U87 cells and facilitated targeted gene delivery against intracranial glioblastoma in vivo, thereby leading to a higher gene transfer efficiency compared to the PEG–PEI gene carrier without RGD decoration. This intracranial glioblastoma‐targeted gene carrier also enhanced the therapeutic efficacy of pORF‐hTRAIL, as evidenced by a significantly prolonged survival of intracranial glioblastoma‐bearing nude mice. Considering the contribution of glioblastoma neovasculature to the BBB under angiogenic conditions, our results demonstrated the therapeutic feasibility of treating a brain tumor through mediation of integrin αvβ3, as well as the potential of using RGD–PEG–PEI as a targeted gene carrier in the treatment of intracranial glioblastoma. 相似文献
Acyl- and Alkylidenephosphanes. XXXV. Bis[ N -(trimethylsilyl)iminobenzoyl]phosphanides of Lithium and Zinc – Syntheses as well as NMR Spectroscopic, Structural, and Quantumchemical Studies From the reaction of bis(tetrahydrofuran)lithium bis(trimethylsilyl)phosphanide with two equivalents of benzonitrile in 1,2-dimethoxyethane, the yellow dme complex ( 2 a ) of lithium bis[N-(trimethylsilyl)iminobenzoyl]phosphanide ( 2 ) was obtained in 69% yield. However, the intermediate {1-[N-lithium-N-(trimethylsilyl)amido]benzylidene}trimethylsilylphosphane ( 1 ), formed by an analogous 1 : 1 addition in diethyl ether, turned out to be unstable and as a consequence could be characterized by nmr spectroscopic methods only; attempts to isolate the compound failed, but small amounts of the neutral complex 2 b , with the ligands benzonitrile and tetrahydrofuran coordinated to lithium, precipitated. The reaction of compound 2 with zinc(II) chloride in diethyl ether gives the orange-red spiro-complex zinc bis{bis[N-(trimethylsilyl)iminobenzoyl]phosphanide} ( 3 ); this complex is also formed from bis[N-(trimethylsilyl)iminobenzoyl]phosphane ( 4 ), easily amenable by a lithium hydrogen exchange of 2 a with trifluoroacetic acid [18], and zinc bis[bis(trimethylsilyl)amide]. As derived from nmr spectroscopic studies and x-ray structure determinations, compounds 2 a {δ31P +63.3 ppm; P21/n; Z = 4; R1 = 0.067}, 2 b {δ31P +63.3 ppm; P21/c; Z = 4; R1 = 0.063}, 3 {δ31P +58.2 ppm; C2/c; Z = 4; R1 = 0.037} and 4 {δ31P +58.1 ppm [18]} exist as cyclic 3-imino-2λ3σ2-phosphapropenylamides and -propenylamine, respectively, in solution as well as in the solid state. Unlike hydrogen derivative 4 the bis[N-(trimethylsilyl)iminobenzoyl]phosphanide fragments N,N′-coordinating either a lithium or a zinc cation are characterized by almost completely equalized bond lengths; typical mean distances and angles are: PC 180.3 and 178.7; CN 130.5 and 131.8; N–Si 175.3 and 179.3; N–Li 202.3; N–Zn 203.5 pm; CPC 108.8° and 110.5°; PCN 130.9° and 132.9°; CN–Li 113.0°, CN–Zn 117.4°; N–Li–N 104.6°; N–Zn–N 108.8°. Alterations in the shape of the six membered chelate rings, caused by an exchange of the 3-imino-2λ3σ2-phosphapropenylamide or related 2λ3σ2-phospha-1,3-dionate units for the corresponding phosphorus free ligands, are discussed in detail. The results of quantumchemical DFT-B3LYP calculations coincide very well with the experimentally obtained findings. 相似文献
α-Methylene-γ-butyrolactones [dihydro-3-methylene-2(3H)furanones] constitute an important group of natural products and possess wide-ranging biological activities. Progress in the synthesis of the heterocycle and the classification of the synthetic methods are not only of practical interest, but also fundamentally important as a current example for the construction of an unusual 1,4-functionality distance and an α-substituted acrylic ester moiety which is susceptible to nucleophilic attack. 相似文献
γ‐Acryloyloxyethyl‐γ‐butyrolactone is formed as a byproduct when the polymerization of γ‐acryloyloxy‐ε‐caprolactone is initiated with aluminium isopropoxide in toluene. The extent of this side reaction decreases with decreasing temperature and is dependent on whether the reaction is stopped as soon as monomer conversion is complete or not. A two‐step backbiting mechanism is proposed for this intramolecular transesterification reaction. 相似文献
P,P′-(2,5-Dimethoxy-3,6-dimethyl-2,5-dioxo-2λ5,5λ5-[1,4,2,5]dioxadiphosphinane-2,5-diyl)-bis-phosphonic acid tetramethylester The title compound 1 is formed by reaction of the corresponding phosphonic acid 2 and orthoformicacidmethylester as a mixture of four stereoisomeres. The RRSS isomer was separated. It crystallizes in the triclinic space group P ?1 with a = 649.2 pm, b = 976.1 pm, c = 1 571.7 pm, α = 80.9°, β = 88.1°, γ = 78.6° and Z = 2. The 31P and 13C NMR spectra (4 and 5 spin systems) are discussed. 相似文献
Synthesis, Crystal Structures, and Vibrational Spectra of [(Mo6X)Y]2–; Xi = Cl, Br; Ya = NO3, NO2 By treatment of [(Mo6X)Y]2–; Xi = Ya = Cl, Br with AgNO3 or AgNO2 by strictly exclusion of oxygene in acetone the hexanitrato and hexanitrito cluster anions [(Mo6X)Y]2–, Ya = NO2, NO3 are formed. X-ray structure determinations of (Ph4As)2[(Mo6Cl)(NO3)] · 2 Me2CO ( 1 ) (monoclinic, space group P21/n, a = 12.696(3), b = 21.526(1), c = 14.275(5) Å, β = 115.02(2)°, Z = 2), (n-Bu4N)2[(Mo6Br)(NO3)] · 2 CH2Cl2 ( 2 ) (monoclinic, space group P21/n, a = 14.390(5), b = 11.216(5), c = 21.179(5)Å, β = 96.475(5)°, Z = 2) and (Ph4P)2[(Mo6Cl)(NO2)] (3) (monoclinic, space group P21/n, a = 11.823(5), b = 13.415(5), c = 19.286(5) Å, β = 105.090(5)°, Z = 2) reveal the coordination of the ligands via O atoms with (Mo–O) bond lengths of 2.11–2.13 Å, and (MoON) angles of 122–131°. The vibrational spectra of the nitrato compounds show the typical innerligand vibrations νas(NO2) (∼ 1500), νs(NO2) (∼ 1270) and ν(NO) (∼ 980 cm–1). The stretching vibrations ν(N=O) at 1460–1490 cm–1 and ν(N–O) in the range of 950–1000 cm–1 are characteristic for nitrito ligands coordinated via O atoms. 相似文献
Silicon-Containing Spirocyclic Phosphorus(V) Hydrazine Heterocycles In the reaction of 1,1-dichlorosilacyclohexane with dihydrazido thiophosphoric acid O-phenylester in a 1:1 molar ratio in THF as solvent and in the presence of triethylamine mainly the expected spirocyclic system of inorganic and organic heterocycle is formed with the Si atom as spirocenter (ms, nmr). In addition and in low yield crystalls of a dimeric compound are isolated. A single crystall x-ray analysis reveals this compound to consist of a dispiro system with a central centrosymmetric eightmembered inorganic heterocycle connected with two silacyclohexanes via Si spirocenters. 相似文献