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1.
The belt-like polyphenylenes, [0n]paracyclophanes, (n = 5 and 6), have been investigated using semi-empirical, ab initio and DFT methods. The molecular structure, rotational barrier on twisting a single phenyl ring and the aromatic character within each ring as well as in the whole molecule have been evaluated. [05]Paracyclophane is predicted to have a quinonoid structure. In contrast, the equatorial pentaphenyl fragment found in C70 as well as the hexagons of the less strained [06]paracyclophane have benzenoid character. Approximate band structures have been derived for larger cycles of [0n] paracyclophanes.Electronic Supplementary Material available.  相似文献   

2.
After exposure to [U-13C3]glycerol, the liver produces primarily [1,2,3-13C3]- and [4,5,6-13C3]glucose in equal proportions through gluconeogenesis from the level of trioses. Other 13C-labeling patterns occur as a consequence of alternative pathways for glucose production. The pentose phosphate pathway (PPP), metabolism in the citric acid cycle, incomplete equilibration by triose phosphate isomerase, or the transaldolase reaction all interact to produce complex 13C-labeling patterns in exported glucose. Here, we investigated 13C labeling in plasma glucose in rats given [U-13C3]glycerol under various nutritional conditions. Blood was drawn at multiple time points to extract glucose for NMR analysis. Because the transaldolase reaction and incomplete equilibrium by triose phosphate isomerase cannot break a 13C-13C bond within the trioses contributing to glucose, the appearance of [1,2-13C2]-, [2,3-13C2]-, [5,6-13C2]-, and [4,5-13C2]glucose provides direct evidence for metabolism of glycerol in the citric acid cycle or the PPP but not an influence of either triose phosphate isomerase or the transaldolase reaction. In all animals, [1,2-13C2]glucose/[2,3-13C2]glucose was significantly greater than [5,6-13C2]glucose/[4,5-13C2]glucose, a relationship that can only arise from gluconeogenesis followed by passage of substrates through the PPP. In summary, the hepatic PPP in vivo can be detected by 13C distribution in blood glucose after [U-13C3]glycerol administration.  相似文献   

3.
There is rising interest in non-enzymatic cholesterol oxidation because the resulting oxysterols have biological activity and can be used as non-invasive markers of oxidative stress in vivo. The preferential site of oxidation of cholesterol by highly reactive species is at C7 having a relatively weak carbon–hydrogen bond. Cholesterol autoxidation is known to proceed via two distinct pathways, a free radical pathway driven by a chain reaction mechanism (type I autoxidation) and a non-free radical pathway (type II autoxidation). Oxysterols arising from type II autoxidation of cholesterol have no enzymatic correlates, and singlet oxygen (1ΔgO2) and ozone (O3) are the non-radical molecules involved in the mechanism. Four primary derivatives are possible in the reaction of cholesterol with singlet oxygen via ene addition and the formation of 5α-, 5β-, 6α- and 6β-hydroxycholesterol preceded by their respective hydroperoxyde intermediates. The reaction of ozone with cholesterol is very fast and gives rise to a complex array of oxysterols. The site of the initial ozone reaction is at the Δ5,6 –double bond and yields 1,2,3-trioxolane, a compound that rapidly decomposes into a series of unstable intermediates and end products. The downstream product 3β-hydroxy-5-oxo-5,6-secocholestan-6-al (sec-A, also called 5,6-secosterol), resulting from cleavage of the B ring, and its aldolization product (sec-B) have been proposed as a specific marker of ozone-associated tissue damage and ozone production in vivo. The relevance of specific ozone-modified cholesterol products is, however, hampered by the fact sec-A and sec-B can also arise from singlet oxygen via Hock cleavage of 5α-hydroperoxycholesterol or via a dioxietane intermediate. Whatever the mechanism may be, sec-A and sec-B have no enzymatic route of production in vivo and are reportedly bioactive, rendering them attractive biomarkers to elucidate oxidative stress-associated pathophysiological pathways and to develop pharmacological agents.  相似文献   

4.
[14C]5,6-Dihydroxytryptamine ([14C] 5,6-DHT) and [14C]5,7-dihydroxytryptamine ([14C]5,7-DHT) were deaminated to toluene-isoamylalcohol extractable products when incubated with homogenates of rat hypothalamus or pons-medulla oblongata. [14C]5,6-Dihydroxyindole acetic acid ([14C]5.6-DHIAA) and [14C]5,7-dihydroxyindole acetic acid ([14C]5,7-DHIAA) were detected as MAO metabolites by TLC besides non-identified components. The conversion of [14C]5,6-DHT and [14C]5,7-DHT obeyed, at least initially, Michaelis-Menten kinetics (Km 5,7-DHT: 0.5 × 10?3M; Km 5,6-DHT: 1.25 × 10?3M). Inhibition of the reaction by the MAO A inhibitor, clorgyline, resulted in a typical double sigmoidal inhibition curve indicating that both amines are metabolized by both types of MAO (A and B). In deprenyl inhibition studies, however, 5,7- and 5,6-DHT seemed to be preferred substrates of MAO A. Incubation of rat brain homogenates with [14C]5,6-DHT and [14C]5,7-DHT or with the MAO metabolites [14C]5,6-DHIAA and [14C]5,7-DHIAA caused a time-dependent break-down of the dihydroxylated indole compounds with subsequent binding of radioactivity to perchloric acid insoluble tissue components. 5,6-DHT inactivated MAO in rat brain homogenates parallel to its decomposition and extensive protein binding. The inactivation of MAO by 5,6-DHT and the extensive binding of radioactivity to protein were antagonized by dithiothreitol (DTT), glutathione (GSH) and L-ascorbic acid. Reduction of [O2] in the incubation medium slightly attenuated the inactivation of MAO by 5,6-DHT. Catalase or superoxide dismutase failed to prevent MAO from being inactivated by 5,6-DHT. The results suggest that oxidation products of 5,6-DHT, e.g. its corresponding o-quinone, are involved in the inactivation of MAO in vitro and mainly responsible for the binding of radioactivity to brain proteins in vitro. Similar mechanisms may also be operative in the in vivo neurotoxicity of 5,6-DHT. The lack of inactivation of MAO by 5,7-DHT in vitro correlated with a low degree of radioactivity binding (from [14C]5,7-DHT) to homogenate protein pellets; the binding to proteins was barely influenced by GSH, cysteine, DTT and l -ascorbic acid. These latter findings do not provide a plausible explanation for the mechanism(s) involved in the well known in vivo neurotoxicity of 5,7-DHT.  相似文献   

5.
E. coli ribosomes are readily photoinactivated by methylene blue in the presence of air. A variety of singlet oxygen quenchers like NaN3, 2,5-dimethylfuran, hydroquinone and ascorbic acid provide about 60% protection against this photoinactivation indicating that a major mechanism of ribosome inactivation proceeds through the formation of singlet oxygen, with small contributions (<40%) from other mechanisms. The singlet oxygen quenchers, 1,4-diazabicyclo [2.2.2] octane and triethylamine give unexpected results, in that they show no protection against photoinactivation.  相似文献   

6.
Water-soluble [60]fullerene (C60) derivatives were synthesized to examine their bioactivities. PC12 cells were used as a model of nerve cells and the bioactivities of synthesized C60 derivatives together with some reported ones were tested. Among the compounds tested, C60/(γ-CyD)2, C60-bis(γ-CyD) (5) containing C60-mono(γ-CyD) (5′), and C60/PVP were sufficiently soluble in water and showed an enhancing effect on the neurite outgrowth of NGF-treated PC12 cells.  相似文献   

7.
Ionic liquids have great potential in biological applications and biocatalysis, as some ionic liquids can stabilize proteins and enhance enzyme activity, while others have the opposite effect. However, on the molecular level, probing ionic liquid interactions with proteins, especially in solutions containing high concentrations of ionic liquids, has been challenging. In the present work the 13C, 15N-enriched GB1 model protein was used to demonstrate applicability of high-resolution magic-angle-spinning (HR-MAS) NMR spectroscopy to investigate ionic liquid–protein interactions. Effect of an ionic liquid (1-butyl-3-methylimidazolium bromide, [C4-mim]Br) on GB1was studied over a wide range of the ionic liquid concentrations (0.6–3.5 M, which corresponds to 10–60% v/v). Interactions between GB1 and [C4-mim]Br were observed from changes in the chemical shifts of the protein backbone as well as the changes in 15N ps-ns dynamics and rotational correlation times. Site-specific interactions between the protein and [C4-mim]Br were assigned using 3D methods under HR-MAS conditions. Thus, HR-MAS NMR is a viable tool that could aid in elucidation of molecular mechanisms of ionic liquid–protein interactions.  相似文献   

8.
On the basis that meta-chlorophenylpiperazine (mCPP; 1) is a nonselective 5-HT2C agonist, that benz-fused tryptamines (e.g., 5) display enhanced 5-HT2 affinity, and that certain isotryptamines 3 reportedly bind with enhanced affinity and selectivity at 5-HT2C receptors, we prepared and examined a series of isotryptamine-related analogues as potentially selective 5-HT2C agonists. None of the compounds displayed selectivity for 5-HT2C versus 5-HT2A receptors. Detailed re-examination of a compound previously reported to display 100-fold 5-HT2C selectivity [i.e., S(+)-5,6-difluoro-α-methylisotryptamine] revealed that its selectivity versus 5-HT2A receptors was, at best, only 10-fold.  相似文献   

9.
Complete chemical selectivity ( , chemospecificity) has been achieved in the homogeneous deuteration of C5---C6 and endocyclic C10---C11 prostaglandin double bonds without rearrangement or partial reduction of C13---C14 or C8---C12 double bonds. The homogeneous deuteration reaction utilizes protection of the C13---C14 double bond as the C15 O-silyl ether and protection of the carboxyl group as the methyl ester prior to reduction under molecular deuterium with tris(triphenylphosphine)chlororhodium (I) (Wilkinson's catalyst) in 60:40 acetone:benzene at 25°C. The reaction has been used to prepare six specifically deuterated prostaglandins: 5,6-dideuterio-PGF, 5,6-dideuterio-PGE1, 5,6-dideuterio-PGB1, 3,3,4,4,5,6-hexadeuterio-PGF, 5,6,10,11-tetradeuterio-11-deoxy-PGE1, and 10,11-dideuterio-11-deoxy-PGE1.  相似文献   

10.
A novel porphyrin‐C60 dyad (PCD1) is designed and synthesized to investigate and manipulate the supramolecular structure where geometrically isotropic [such as [60]fullerene (C60)] and anisotropic [such as porphyrin (Por)] units coexist. It is observed that PCD1 possesses an enantiomeric phase behavior. The melting temperature of the stable PCD1 thermotropic phase is 160 °C with a latent heat (ΔH) of 18.5 kJ mol?1. The phase formation is majorly driven by the cooperative intermolecular Por–Por and C60–C60 interactions. Structural analysis reveals that this stable phase possesses a supramolecular “double‐cable” structure with one p‐type Por core columnar channel and three helical n‐type C60 peripheral channels. These “double‐cable” columns further pack into a hexagonal lattice with a = b = 4.65 nm, c = 41.3 nm, α = β = 90°, and γ = 120°. The column repeat unit is determined to possess a 12944 helix. With both donor (D; Pro) and acceptor (A; C60) units having their own connecting channels as well as the large D/A interface within the supramolecular “double‐cable” structure, PCD1 has photogenerated carriers with longer lifetimes compared to the conventional electron acceptor [6,6]‐phenyl‐C61‐butyric acid methyl ester. A phase‐separated columnar morphology is observed in a bulk‐heterojunction (BHJ) material made by the physical blend of a low band‐gap conjugated polymer, [poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta [2,1‐b;3,4‐b′]‐dithiophene)‐alt‐4,7‐(2,1,3‐benzothia‐diazole)] (PCPDTBT), and PCD1. With a specific phase structure in the solid state and in the blend, PCD1 is shown to be a promising candidate as a new electron acceptor in high performance BHJ polymer solar cells.  相似文献   

11.
Long chain fatty acid synthesis was studied using etiolated leek seedling microsomes. In the presence of ATP, [2-14C]malonyl-CoA was incorporated into fatty acids of C16C26. The omission of ATP, even in the presence of acetyl-CoA, led to a complete loss of activity, which was restored by addition of exogeneous acyl-CoAs. Comparison of acyl-CoA (C12C24) elongation showed that stearoyl-CoA, in the presence of [2-14C]malonyl-CoA, was the more efficient precursor leading to the formation of fatty acids having a chain length of C20C26. [1-14C]C16CoA and [1-14C]C18CoA were elongated in the presence of malonyl-CoA, without degradation of the acyl chain. The time-course and the malonyl-CoA concentration curves showed that [1-14C]C18CoA was a better primer than [1-14C]C16CoA. Acyl-CoA elongation was also studied over the concentration range 4.5–45 μM [1-14C]C18CoA. Comparison of the radioactivity incorporated into the fatty acids formed using [2-14C]malonyl-CoA in the presence of C18CoA, on the one hand, and [1-14C]C18CoA in the presence of malonyl-CoA, on the other, demonstrated clearly that the acyl chain of the acyl-CoA was elongated by malonyl-CoA.  相似文献   

12.
S.A. Sholl  R.C. Wolf 《Steroids》1980,36(2):209-218
For the purpose of describing the pathway by which estrogens are synthesized in the rhesus monkey (Macacamulatta) corpus luteum (CL), CL were obtained during the midluteal phase of the menstrual cycle and fragments incubated with equimolar amounts of [7-3H]pregnenolone plus [4-14C]progesterone. Metabolites including 3H-progesterone, 3H, 14C-20α-dihydroprogesterone, 3H, 14C-17-hydroxyprogesterone, 3H-estrone and 3H-estradiol-17β appeared in the medium during the first 20 minutes of incubation, 3H, 14C-Androstenedione was not consistently noted until after 60 minutes. Despite the fact that the 14C/3H-17-hydroxyprogesterone ratio quickly approached a constant value in the medium, 14C-estrogens were not detected in the medium or tissue fragments suggesting that progesterone was not a principal precursor for estrogen synthesis. As evidenced by the observation that the 14C/3H-progesterone ratio was significantly higher in luteal fragments than the 17-hydroxyprogesterone ratio, 17-hydroxyprogesterone appeared to be synthesized from pregnenolone both by way of progesterone and by another route which did not include progesterone. C21- and C18-Steroids were more concentrated in tissue fragments after 120 minutes of incubation than in the medium indicating that these steroids were sequestered by luteal tissue.  相似文献   

13.
14.
The reaction of O2?? with H2O2 in the presence of 1,3-diphenylisobenzofuran was studied. o-Dibenzoylbenzene was obtained in 82 % yield, which decreased to 52 % when dimethoxyethane was presence. Additions of β-carotene or 1,4-diazabicyclo-[2,2,2]-octane also inhibited the production of o-dibenzoylbenezene. These results show that singlet oxygen may be a considerable species generated by the Haber-Weiss reaction.  相似文献   

15.
Gangliosides are characteristically enriched in various membrane domains that can be isolated as low density membrane fraction insoluble in detergents (detergent-resistant membranes, DRMs) or obtained after homogenization and sonication in 0.5 M sodium carbonate (low-density membranes, LDMs). We assessed the effect of the ceramide structure of four [3H]-labeled GM1 ganglioside molecular species (GM1s) taken up by HL-60 cells on their occurrence in LDMs, and compared it with our previous observations for DRMs. All GM1s contained C18 sphingosine, which was acetylated in GM1(18:1/2) or acylated with C14, C18 or C18:1 fatty acids (Fas)  相似文献   

16.
The Lewis bases triphenyl phosphine and tricyclohexyl phosphine (L) displace [60]fullerene (C60) from fac-(η2-C60)(η2-phen)W(CO)3 (phen=1,10-phenanthroline) to produce fac-(η2-phen)(η1-L)W(CO)3. Under flooding conditions, the reactions were first order with respect to fac-(η2-C60)(η2-phen)W(CO)3. The order with respect to C60 and L depends on the reaction conditions i.e., whether [C60]/[L] ≈ 0 or 0?It [C60]/[L] ≈ 1. Two limiting cases of an interchange displacement of [60]fullerene from fac-(η2-C60)(η2-phen)W(CO)3, whose relative contributions to the overall mechanism depend on the nature of the solvent, are proposed based on the rate law and on the activation parameters. The mechanism involves an initial [60]fullerene dissociation to produce (i) the electronically unsaturated intermediate (η2-phen)W(CO)3 for the dissociative displacement and (ii) the solvated intermediate fac-(solvent)(η2-phen)W(CO)3 for the solvent-assisted [60]fullerene dissociation. The W-C60 bond energy in fac-(η2-C60)(η2-phen)W(CO)3 was estimated to be in the vicinity of 105 kJ/mol based on the enthalpy of activation of the step where presumably [60]fullerene dissociates from fac-(η2-C60)(η2-phen)W(CO)3 to produce (η2-phen)W(CO)3.  相似文献   

17.
Magnetic shielding constants for an isolated fullerene C60, cucurbituril CB[9], and the host-guest complex C60@CB[9] were calculated as a function of separation of the monomers. Our results in the gas phase and water indicate a significant variation of the magnetic properties for all atoms of the monomers in the complex and after liberation of fullerene C60 from the interior of the CB[9] cavity. The interaction between the two monomers results in a charge transfer that collaborates with a redistribution of electron density to deshield the monomers.
Graphical Abstract NMR spectroscopy alteration on C60@CB[9] host-guest mutual interactions?
  相似文献   

18.
Accumulation of l -kynurenine and quinolinic acid (QUIN) in the brain occurs after either ischemic brain injury or after systemic administration of pokeweed mitogen. Although conversion of l -[13C6]tryptophan to [13C6]-QUIN has not been demonstrated in brain either from normal gerbils or from gerbils given pokeweed mitogen, direct conversion in brain tissue does occur 4 days after transient cerebral ischemia. Increased activities of enzymes distal to indoleamine-2,3-dioxygenase may determine whether l -kynurenine is converted to QUIN. One day after 10 min of cerebral ischemia, the activities of kynureninase and 3-hydroxy-3,4-dioxygenase were increased in the hippocampus, but local QUIN levels and the activities of the indoleamine-2,3-dioxygenase and kynurenine-3-hydroxylase were unchanged. By days 2 and 4 after ischemia, however, the activities of all of these enzymes in the hippocampus as well as QUIN levels were significantly increased. Kynurenine aminotransferase activity in the hippocampus was unchanged on days 1 and 2 after ischemia but was decreased on day 4, at a time when local kynurenic acid levels were unchanged. A putative precursor of QUIN, [13C6]anthranilic acid, was not converted to [13C6]-QUIN in the hippocampus of either normal or 4-day postischemic gerbils. Gerbil macrophages stimulated by endo-toxin in vitro converted l -[13C6]tryptophan to [13Ce]QUIN. Kinetic analysis of kynurenine-3-hydroxylase activity in the cerebral cortex of postischemic gerbils showed that Vmax increased, without changes in Km. Systemic administration of pokeweed mitogen increased indoleamine-2,3-dioxygenase and kynureninase activities in the brain without significant changes in kynurenine-3-hydroxylase or 3-hydroxyanthranilate-3,4-dioxygenase activities. Increases in kynurenine-3-hydroxylase activity, in conjunction with induction of indoleamine-2,3-dioxygenase, kynureninase, and 3-hydroxyanthranilate-3,4-dioxygenase in macro-phage infiltrates at the site of brain injury, may explain the ability of postischemic hippocampus to convert l -[13C6]tryptophan to [13C6]QUIN.  相似文献   

19.
N(4)-amino-and N(4)-hydroxycytosines as base analogue mutagens   总被引:2,自引:0,他引:2  
N(4)-Aminocytosine [N(4)NH2C] and N(4)-amino-2′-deoxycytidine [N(4)NH2dC] are highly mutagenic for Escherichia coli and phage φ 80 but not for T4. There is some evidence that they are incorporated into the φ 80 DNA but [14C]-N(4)NH2C could not be detected in the bacterial DNA.N(4)-Hydroxy-5,6-dihydro-6-hydroxylaminodeoxycytidine (di-NHOH-dC) is mutagenic for φ 80 and E. coli, but N(4)-hydroxydeoxycytidine [N(4)OH-dC] only has a strong inactivating effect.  相似文献   

20.
A new charge recombination layer for inverted tandem polymer solar cells is reported. A bilayer of MoOX/Al2O3:ZnO nanolaminate is shown to enable efficient charge recombination in inverted tandem cells. A polymer surface modification on the MoOX/Al2O3:ZnO nanolaminate bilayer increases the work function contrast between the two outward surfaces of the charge recombination layer, further improving the performance of tandem solar cells. An analysis of the electrical, optical, and surface properties of the charge recombination layer is presented. Inverted tandem polymer solar cells, with two photoactive layers comprising poly (3‐hexylthiophene) (P3HT):indene‐C60 bisadduct (IC60BA) for the bottom cell and poly[(4,8‐bis‐(2‐ethylhexyloxy)‐benzo[1,2‐b:4,5‐b']dithiophene)‐2,6‐diyl‐alt‐(4‐(2‐ethylhexanoyl)‐thieno[3,4‐b]thiophene))‐2,6‐diyl] (PBDTTT‐C):[6,6]‐phenyl C61 butyric acid methyl ester (PC60BM) for the top cell, yield an open‐circuit voltage of 1481 mV ± 15 mV, a short‐circuit current density of 7.1 mA cm?2 ± 0.1 mA cm?2, and a fill factor of 0.62 ± 0.01, resulting in a power conversion efficiency of 6.5% ± 0.1% under simulated AM 1.5G, 100 mW cm?2 illumination.  相似文献   

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