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1.
The bilayer phase transitions of palmitoylstearoyl-phosphatidylcholine (PSPC), diheptadecanoyl-PC (C17PC) and stearoylpalmitoyl-PC (SPPC) which have the same total carbon numbers in the two acyl chains were observed by differential scanning calorimetry and high-pressure optical method. As the temperature increased, these bilayers exhibited four phases of the subgel (Lc), lamellar gel (Lβ′), ripple gel (Pβ′) and liquid crystal (Lα), in turn. The Lc phase was observed only in the first heating scan after cold storage. The temperatures of the phase transitions were almost linearly elevated by applying pressure. The temperature-pressure phase diagrams and the thermodynamic quantities associated with the phase transitions were compared among the lipid bilayers. For all the bilayers studied, the pressure-induced interdigitated gel (LβI) phase appeared above the critical interdigitation pressure (CIP) between the Lβ′ and Pβ′ phases. The CIPs for the PSPC, C17PC and SPPC bilayers were found to be 50.6, 79.1 and 93.0 MPa, respectively. Contribution of two acyl chains to thermodynamic properties for the phase transitions of asymmetric PSPC and SPPC bilayers was not even. The sn-2 acyl chain lengths of asymmetric PCs governed primarily the bilayer properties. The fluorescence spectra of Prodan in lipid bilayers showed the emission maxima characteristic of bilayer phases, which were dependent on the location of Prodan in the bilayers. Second derivative of fluorescent spectrum exhibited the original emission spectrum of Prodan to be composed of the distribution of Prodan into multiple locations in the lipid bilayer. The F″497/F″430 value, a ratio of second derivative of fluorescence intensity at 497 nm to that at 430 nm, is decisive evidence whether bilayer interdigitation will occur. With respect to the Lβ′/LβI phase transition in the SPPC bilayer, the emission maximum of Prodan exhibited the narrow-range red-shift from 441 to 449 nm, indicating that the LβI phase in the SPPC bilayer has a less polar “pocket” formed by a space between uneven terminal methyl ends of the sn-1 and sn-2 chains, in which the Prodan molecule remains stably. 相似文献
2.
The bilayer phase transitions of six kinds of mixed-chain phosphatidylcholines (PCs) with an unsaturated acyl chain in the sn-1 or sn-2 position, 1-oleoyl-2-stearoyl- (OSPC), 1-stearoyl-2-oleoyl- (SOPC), 1-oleoyl-2-palmitoyl- (OPPC), 1-palmitoyl-2-oleoyl- (POPC), 1-oleoyl-2-myristoyl- (OMPC) and 1-myristoyl-2-oleoyl-sn-glycero-3-phosphocholine (MOPC), were observed by means of differential scanning calorimetry (DSC) and high-pressure light transmittance measurements. Bilayer membranes of SOPC, POPC and MOPC with an unsaturated acyl chain in the sn-2 position exhibited only one phase transition, which was identified as the main transition between the lamellar gel (Lβ) and liquid crystalline (Lα) phases. On the other hand, the bilayer membranes of OSPC, OPPC and OMPC with an unsaturated acyl chain in the sn-1 position exhibited not only the main transition but also a transition from the lamellar crystal (Lc) to the Lβ (or Lα) phase. The stability of their gel phases was markedly affected by pressure and chain length of the saturated acyl chain in the sn-2 position. Considering the effective chain lengths of unsaturated mixed-chain PCs, the difference in the effective chain length between the sn-1 and sn-2 acyl chains was proven to be closely related to the temperature difference of the main transition. That is, a mismatch of the effective chain length promotes a temperature difference of the main transition between the positional isomers. Anomalously small volume changes of the Lc/Lα transition for the OPPC and OMPC bilayers were found despite their large enthalpy changes. This behavior is attributable to the existence of a cis double bond and to significant inequivalence between the sn-1 and sn-2 acyl chains, which brings about a small volume change for chain melting due to loose chain packing, corresponding to a large partial molar volume, even in the Lc phase. Further, the bilayer behavior of unsaturated mixed-chain PCs containing an unsaturated acyl chain in the sn-1 or sn-2 position was well explained by the chemical-potential diagram of a lipid in each phase. 相似文献
3.
Byers JA 《Journal of theoretical biology》2009,256(1):81-59
The effective attraction radius (EAR) of an attractive pheromone-baited trap was defined as the radius of a passive “sticky” sphere that would intercept the same number of flying insects as the attractant. The EAR for a particular attractant and insect species in nature is easily determined by a catch ratio on attractive and passive (unbaited) traps, and the interception area of the passive trap. The spherical EAR can be transformed into a circular EARc that is convenient to use in two-dimensional encounter rate models of mass trapping and mating disruption with semiochemicals to control insects. The EARc equation requires an estimate of the effective thickness of the layer where the insect flies in search of mates and food/habitat. The standard deviation (SD) of flight height of several insect species was determined from their catches on traps of increasing heights reported in the literature. The thickness of the effective flight layer (FL) was assumed to be , because the probability area equal to the height of the normal distribution,, times the FL is equal to the area under the normal curve. To test this assumption, 2000 simulated insects were allowed to fly in a three-dimensional correlated random walk in a 10-m thick layer where an algorithm caused them to redistribute according to a normal distribution with specified SD and mean at the midpoint of this layer. Under the same conditions, a spherical EAR was placed at the center of the 10-m layer and intercepted flying insects distributed normally for a set period. The number caught was equivalent to that caught in another simulation with a uniform flight density in a narrower layer equal to FL, thus verifying the equation to calculate FL. The EAR and FL were used to obtain a smaller EARc for use in a two-dimensional model that caught an equivalent number of insects as that with EAR in three dimensions. This verifies that the FL estimation equation and EAR to EARc conversion methods are appropriate. 相似文献
4.
Matthias Meier 《Biophysical journal》2010,98(8):1529-1538
The effect of nonionic detergents of the n-alkyl-β-D-glucopyranoside class on the ordering of lipid bilayers and the dynamics of membrane-embedded peptides were investigated with 2H- and 31P-NMR. 1,2-dipalmitoyl-sn-glycero-3-phosphocholine was selectively deuterated at methylene segments C-2, C-7, and C-16 of the two fatty acyl chains. Two trans-membrane helices, WALP-19 and glycophorin A71-98, were synthesized with Ala-d3 in the central region of the α-helix. n-Alkyl-β-D-glucopyranosides with alkyl chains with 6, 7, 8, and 10 carbon atoms were added at increasing concentrations to the lipid membrane. The bilayer structure is retained up to a detergent/lipid molar ratio of 1:1. The insertion of the detergents leads to a selective disordering of the lipids. The headgroup region remains largely unaffected; the fatty acyl chain segments parallel to the detergent alkyl chain are only modestly disordered (10-20%), whereas lipid segments beyond the methyl terminus of the detergent show a decrease of up to 50%. The change in the bilayer order profile corresponds to an increase in bilayer entropy. Insertion of detergents into the lipid bilayers is completely entropy-driven. The entropy change accompanying lipid disorder is equivalent in magnitude to the hydrophobic effect. Ala-d3 deuterated WALP-19 and GlycA71-97 were incorporated into bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine at a peptide/lipid molar ratio of 1:100 and measured above the 1,2-dimyristoyl-sn-glycero-3-phosphocholine gel/liquid-crystal phase transition. Well-resolved 2H-NMR quadrupole splittings were observed for the two trans-membrane helices, revealing a rapid rotation of the CD3 methyl rotor superimposed on an additional rotation of the whole peptide around the bilayer normal. The presence of detergent fluidizes the membrane and produces magnetic alignment of bilayer domains but does not produce essential changes in the peptide conformation or dynamics. 相似文献
5.
Masataka Kusube 《生物化学与生物物理学报:生物膜》2005,1668(1):25-32
In order to understand the effect of polar head group modification on the thermotropic and barotropic phase behavior of phospholipid bilayer membranes, the phase transitions of dipalmitoylphosphatidylethanolamine (DPPE), dipalmitoylphosphatidyl-N-methylethanolamine (DPMePE), dipalmitoylphosphatidyl-N,N-dimethylethanolamine (DPMe2PE) and dipalmitoylphosphatidylcholine (DPPC) bilayer membranes were observed by differential scanning calorimetry and high-pressure optical methods. The temperatures of the so-called main transition from the gel (Lβ) or ripple gel (Pβ′) phase to the liquid crystalline (Lα) phase were almost linearly elevated by applying pressure. The slope of the temperature-pressure boundary, dT/dp, was in the range of 0.220-0.264 K MPa−1 depending on the number of methyl groups in the head group of lipids. The main-transition temperatures of N-methylated DPPEs decreased with increasing size of head group by stepwise N-methylation. On the other hand, there was no significant difference in thermodynamic quantities of the main transition between the phospholipids. With respect to the transition from the subgel (Lc) phase to the lamellar gel (Lβ or Lβ′) phase, the transition temperatures were also elevated by applying pressure. In the case of DPPE bilayer the Lc/Lβ transition appeared at a pressure higher than 21.8 MPa. At a pressure below 21.8 MPa the Lc/Lα transition was observed at a temperature higher than the main-transition temperature. The main (Lβ/Lα) transition can be recognized as the transformation between metastable phases in the range from ambient pressure to 21.8 MPa. Polymorphism in the gel phase is characteristic of DPPC bilayer membrane unlike other lipid bilayers used in this study: the Lβ′, Pβ′ and pressure-induced interdigitated gel (LβI) phases were observed only in the DPPC bilayer. Regarding the bilayers of DPPE, DPMePE and DPMe2PE, the interdigitation of acyl chain did not appear even at pressures as high as 200 MPa. 相似文献
6.
The partial phase diagram and the hydration properties of the 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE)-water system, in the absence and presence of 30 mol% cholesterol, have been investigated by solid state phosphorus NMR of the lipid and deuterium NMR of heavy water. The POPE-D2O phase diagram resembles other phosphatidylethanolamine (PE)-water systems: below water-to-lipid molar ratios (Ri) of 3 the lamellar gel (L or Lc)-to-hexagonal type II (HII) phase sequence is observed on increasing the temperature. For Ri3 the thermotropic sequence (L or Lc)-L-HII is detected. On increasing hydration from Ri=3, the HII phase is detected from 40°C to 85°C whereas the gel phase is observed from 40°C to 30°C. The limiting hydrations of the gel, L and HII phases are Ri 3, 17 and 20, respectively. The number of bound water molecules per lipid is ca. 8 in both the La and HII phases. The presence of cholesterol stabilizes the hexagonal phase 20°C below temperatures at which it is observed in its absence and reduces the limiting hydration of the fluid and hexagonal phases to Ri 9 and 14, respectively. The structure and/or dynamics of the water bound to the interface are markedly modified on going from the L to the HII phase.Abbreviations NMR
Nuclear magnetic resonance
- DDPE
1,2-Didodecyl-rac-glycerol-3-phosphoethanol-amine
- DHPE
1,2-Dihexadecyl-sn-glycerol-3-phosphoethanol-amine
- DOPE
1,2-Dioleoyl-sn-glycerol-3-phosphoethanol-amine
- POPE
1-Palmitoyl-2-oleoyl-sn-glycerol-3-phosphoetha-nolamine
- DAPE
1,2-Diarachinoyl-sn-glycerol-3-phosphoethanol-amine
- DMPC
1,2-Dimyristol-sn-glycerol-3-phosphocholine
- DPPC
1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine
- Tc
lamellar gel-to-lamellar fluid transition temperature
- Th
lamellar fluid-to-hexagonal transition temperature 相似文献
7.
Gabriele Heinze-Brückner 《Inorganica chimica acta》2011,374(1):385-391
A dinuclear ferric complex with the redox-active ligand (LCl2)2- (H2LCl2 = N,N′-dimethyl-bis(3,5-dichloro-2-hydroxybenzyl)-1,2-diaminoethane), was synthesized and characterized. The two iron(III) ions are six-coordinate in a distorted octahedral environment of the donor set of one (LCl2)2− and one amine and one phenolate donor of a second (LCl2)2−, which bridges the two complex halves. The relatively low-symmetric complex 1 crystallizes in the space group R. The crystal structure contains hexagonal, one-dimensional channels parallel to the c axis with diameters of ∼13 Å. The absorption spectrum of 1 exhibits strong characteristic features of pπ → dπ∗, pπ → dσ∗, phenolate-to-metal CTs, and π → π∗ ligand transitions. Electrochemical studies on 1 reveal the redox-activity of the coordinated ligand (LCl2)2− by showing irreversible oxidative electron-transfer waves. The reductive electron transfers at negative potentials seem to originate from metal-centered processes. A detailed comparison to complexes with similar donor sets provides new insights into the electrochemical properties of these kinds of complexes. 相似文献
8.
The ligand 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane (L8) has afforded six-coordinate monomeric and dimeric complexes [(L8)CoII(H2O)2][ClO4]2 (1), [(L8)NiII(MeCN)2][BPh4]2 (2), [(L8)NiII(O2CMe)][BPh4] (3), and . The crystal structures of 1, 2 · MeCN, 3, and 4 revealed that the ligand L8 is flexible enough to expand its coordinating ability by fine-tuning the angle between the chelating fragments and hence folds around cobalt(II)/nickel(II) centers to act as a tetradentate chelate, allowing additional coordination by two trans-H2O, cis-MeCN, and a bidentate acetate affording examples of distorted octahedral , , and coordination. The angles between the two CoN2/NiN2 planes span a wide range 23.539(1)° (1), 76.934(8)° (2), and 69.874(14)° (3). In contrast, complex 4 is a bis-μ-1,3-acetato-bridged (syn-anti coordination mode) dicobalt(II) complex [Co?Co separation: 4.797(8) Å] in which L8 provides terminal bidentate pyridylpyrazole coordination to each cobalt(II) center. To our knowledge, this report provides first examples of such a coordination versatility of L8. Absorption spectral studies (MeCN solution) have been done for all the complexes. Complexes 1-3 are uniformly high-spin. Temperature-dependent (2-300 K) magnetic studies on 4 reveal weak ferromagnetic exchange coupling between two cobalt(II) (S = 3/2) ions. The best-fit parameters obtained are: Δ (axial splitting parameter) = −765(5) cm−1, λ (spin-orbit coupling) = −120(3) cm−1, k (orbital reduction factor) = 0.93, and J (magnetic exchange coupling constant) = +1.60(2) m−1. 相似文献
9.
The specific volumes of seven 1,2-diacyl-sn-glycero-3-phosphocholines with symmetric, unbranched acyl chains containing one, four, or six cis double bonds per chain, or with a saturated sn-1 chain and one, four, or six cis double bonds in the sn-2 chain were determined by the neutral buoyancy method. Experiments were conducted in the liquid crystalline lamellar phase over the temperature range from 5 to 35 °C. It is demonstrated that the molecular volume of phosphatidylcholines can be well approximated as the sum of a constant volume of the polar lipid head region and the temperature-dependent volumes of hydrocarbon chain CH2, CH, and terminal CH3 groups. A linear dependence of chain segment volumes on temperature was observed. A self-consistent set of partially temperature-dependent volumes is obtained that allows prediction of phosphatidylcholine molecular volumes within very tight error margins. 相似文献
10.
《Inorganica chimica acta》2010,363(13):3302-8934
The reactions of L1-3Li salts containing different Y,C,Y-chelating ligands L1 = 2,6-(t-BuOCH2)2C6, L2 = 2,6-(MesOCH2)2C6 and L3 = 2,6-(Me2NCH2)2C6 with PCl3 is reported. While the presence of ligands L2,3 afforded the synthesis of dichlorophosphines L2PCl2 (2) and L3PCl2 (3), the use of ligand L1 resulted to the isolation of O → P coordinated 1-chloro-7-(t-butoxymethyl)-3H-2,1-benzoxaphosphole (1) as the result of the cyclization type reaction of dichlorophosphines L1PCl2. The hydrolysis of compounds 1-3 as well as the preparation of phosphanes L2PH2 (7), L3PH2 (8), L2PH(SnMe3) (9) and L3PH(SnMe3) (10) is also discussed. The presence of N → P coordination enabled the isolation of N → P coordinated diselenoxophosphorane L3PSe2 (11). Compounds 1-11 were characterized by the help of multinuclear NMR spectroscopy, ESI mass spectrometry and the structure of compound 11 was established by X-ray diffraction analysis. 相似文献
11.
It is commonly believed that all membrane sterols are rigid all-trans ring systems with a fully extended alkyl side-chain and that they similarly influence phospholipid bilayer physical properties. Here, we report the sterol concentration-dependent, thermotropic phase behaviour of binary dipalmitoylphosphatidylcholine (DPPC)/sterol mixtures containing two similar 5α-H sterols with different functional group orientations (3α-OH or 3β-OH), which adopt an ideal all-trans planar ring conformation but lack the deformed ring B conformation of cholesterol (Chol) and epicholesterol (Echol), using differential scanning calorimetry (DSC). Our deconvolution of the DSC main phase transition endotherms show differences in the proportions of sterol-poor (sharp) and sterol-rich (broad) domains in the DPPC bilayer with increasing sterol concentration, which delineate gel/liquid-crystalline (Pβ′/Lα) and disordered gel (Lβ)/liquid-ordered (lo) phase regions. There are similarities in the DPPC main phase transition temperature, cooperativity and enthalpy for each 3β-ol and 3α-ol pair with increasing sterol concentration and differences in the parameters obtained for both the sterol-poor and sterol-rich regions. The sterol-poor domain persists over a greater concentration range in both 3α-ol/DPPC mixtures, suggesting that either those domains are more stable in the 3α-ols or that those sterols are less miscible in the sterol-rich domain. Corresponding parameters for the sterol-rich domain show that at sterol concentrations up to 20 mol%, the 5α-H,3β-ol is more effective at reducing the phase transition enthalpy of the broad component () than Chol, but is less effective at higher concentrations. Although mixtures containing Echol and 5α-cholestan-3α-ol have similar positive slopes below 7 mol% sterol, suggesting that they abolish the Lβ/lo phase transition equally effectively at low concentrations, Echol is more effective than the saturated 3α-ol at higher sterol concentrations. A comparison of obtained for the saturated and unsaturated pairs suggests that the latter sterols stabilize the lo phase and broaden and abolish the DPPC main phase transition more effectively than the saturated sterols at physiologically relevant concentrations, supporting the idea that the double bond of Chol and Echol promotes greater sterol miscibility and the formation of lo phase lipid bilayers relative to corresponding saturated sterols in biological membranes. 相似文献
12.
Using a racemic mixture of the tridentate ligand, (((2-pyridyl)ethylamine)methyl)phenolate ion (L−) and , NCS−, (NC)2N−, OAc− as coligands, complexes having the formula [Ni(L)(N3)] (1), [Ni(L)(NCS)]2 (2), [Ni2(L)2(OAc)(N(CN)2)]n (3) were prepared and structurally characterized. In 1, Ni(II) has a square planar geometry and phenolate oxygen is involved in dipolar ?Nδ+ interaction with electrophilic central nitrogen atom of coordinated azide ion. Complex 2 is dimeric in nature and nickel(II) is penta-coordinated. Compounds 1 and 2 exist as centrosymmetric dimers made up of a pair of R and S enantiomers of L. In 3, an acetate and phenoxo bridged dinickel complex is present which is further linked to a zig-zag coordination polymer by the dicyanamide ion. In a given chain of 3, both L have same enantiomeric form and either RR or SS dimers are repeated along the chain. The magnetic properties are described. 相似文献
13.
Pawlowicz NP van Grondelle R van Stokkum IH Breton J Jones MR Groot ML 《Biophysical journal》2008,95(3):1268-1284
Time-resolved visible pump/mid-infrared (mid-IR) probe spectroscopy in the region between 1600 and 1800 cm−1 was used to investigate electron transfer, radical pair relaxation, and protein relaxation at room temperature in the Rhodobacter sphaeroides reaction center (RC). Wild-type RCs both with and without the quinone electron acceptor QA, were excited at 600 nm (nonselective excitation), 800 nm (direct excitation of the monomeric bacteriochlorophyll (BChl) cofactors), and 860 nm (direct excitation of the dimer of primary donor (P) BChls (PL/PM)). The region between 1600 and 1800 cm−1 encompasses absorption changes associated with carbonyl (CO) stretch vibrational modes of the cofactors and protein. After photoexcitation of the RC the primary electron donor P excited singlet state (P*) decayed on a timescale of 3.7 ps to the state (where BL is the accessory BChl electron acceptor). This is the first report of the mid-IR absorption spectrum of ; the difference spectrum indicates that the 9-keto CO stretch of BL is located around 1670-1680 cm−1. After subsequent electron transfer to the bacteriopheophytin HL in ∼1 ps, the state was formed. A sequential analysis and simultaneous target analysis of the data showed a relaxation of the radical pair on the ∼20 ps timescale, accompanied by a change in the relative ratio of the and bands and by a minor change in the band amplitude at 1640 cm−1 that may be tentatively ascribed to the response of an amide CO to the radical pair formation. We conclude that the drop in free energy associated with the relaxation of , is due to an increased localization of the electron hole on the PL half of the dimer and a further consequence is a reduction in the electrical field causing the Stark shift of one or more amide CO oscillators. 相似文献
14.
Koichiro Takao 《Inorganica chimica acta》2010,363(4):802-806
The oxidation from to in HCl aq. was studied in situ by combining electrochemistry with XAFS spectroscopy. During the oxidation of , isosbestic points were observed in Pt LIII and LII XANES spectra as a function of time, indicating that the Pt(II/IV) redox equilibrium is the only reaction in the system. The Pt LIII and LII X-ray absorption edge energies of the initial PtIICl42− are 11562.9 and 13271.8 eV, respectively, while those of the electrolyzed species are 11564.6 and 13273.7 eV which are identical with those of a reference sample. The coordination of the electrolyzed species was characterized by structural parameters derived from the EXAFS curve fit, and identified to . 相似文献
15.
The complexes [Mn(L1)(tcc)] (1), [Mn(L2)(tcc)] · H2O · 0.5CH3OH (2), [Mn(L3)(tcc)] · CH2Cl2 (3), [Mn(L4)(tcc)] · 1.5CH2Cl2 (4), [Mn(L5)(tcc)] (5), and (HN(C2H5)3)[Mn(L6)(tcc)] · CH2Cl2 (6) have been synthesized using the ligands HL1 (2-[(bis(pyridin-2-ylmethyl)amino)methyl]phenol), HL2 (2-[[((6-methylpyridin-2-yl)methyl)(pyridin-2-ylmethyl)amino]methyl] phenol), HL3 (2-[[((6-methylpyridin-2-yl)methyl)(pyridin-2-ylmethyl)amino]methyl]-4-nitrophenol), HL4 (2-[(bis(pyridin-2-ylmethyl)amino)methyl]-4-bromophenol), HL5 (2-[(bis(pyridin-2-ylmethyl)amino)methyl]-6-methoxyphenol) and H2L6 ([(bis(2-hydroxy-5-nitrobenzyl))(pyridin-2-ylmethyl)]amine) and characterized by X-ray crystallography, mass spectrometry, IR, UV-Vis spectroscopy, cyclic voltammetry, and elemental analysis. Compounds 1 and 6 crystallize in the monoclinic space groups P21/n and P21/c, respectively, whereas the crystal structures of complexes 2, 3, and 4 were solved in the triclinic space group . Complex 5 crystallizes in the orthorhombic space group P212121. Complexes 1-6 are structural related to the proposed active site of intradiol cleaving catechol dioxygenase exhibiting a distorted octahedral N3O3 (1-5) and N2O4 (6) donor set, respectively. Complexes 1-6 can be regarded as structural manganese analogous for substituted forms of iron-containing intradiol cleaving catechol dioxygenases, where the substrate tetrachlorocatechol (tcc) is asymmetrically bound to the metal center. 相似文献
16.
The complex formation between several trivalent lanthanides (Ln) and 5-sulfosalicylate, (SSA)3−, was investigated by potentiometry, 1H NMR, and time resolved laser-induced fluorescence spectroscopy (TRLIFS). The potentiometric data were used to deduce the stoichiometry and equilibrium constants for the reactions pLn3+ + rL ? LnpH−qLr + qH+ at 298 K in an ionic medium with a constant concentration of Na+ equal to 1.00 M. Note that “L” denotes the SSA ligand where all protons are dissociated. Two mononuclear chelating complexes, LnL(aq) and , were identified. Their stability constants obtained by least-squares refinement of the potentiometric data agree well with previously published information. In addition, two additional dinuclear complexes, and , which have very different 1H NMR and fluorescence characteristics, were identified by least-squares refinement in the −log[H+] range of 6.0-10.0. 1H NMR spectra from the ligand in the complex showed separate peaks having two different rates of exchange with free ligand in the bulk solution besides a signal from the free and carboxylate-coordinated ligands. This indicates that the dinuclear complex, , consists of two different types of chelating ligands: μ-{OR}-type chelating ligands between metals to form the {Ln2L2}-type core structure and the bidentate ligands outside the {Ln2L2}-type core. This core structure is different from the An(IV)-SSA case (An(IV): tetravalent actinide), in which hydroxides play the role of forming the {An2(OH)2}-type core structure. TRLIFS measurement gave further information about the dynamics and molecular structures of the complexes. 相似文献
17.
Shu-Fei Huang Phalguni Misra Sasankasekhar Mohanta Ho-Hsiang Wei 《Inorganica chimica acta》2004,357(5):1627-1631
The syntheses, structures, and magnetic properties of two new μ-alkoxo-μ-pyrazolato heterobridged compounds, [Cu II2(L1-F)(μ-prz)] (1) and [Cu II2(L1-2OMe) (μ-prz)] · 0.5 CH3CN (2) (prz=pyrazolato; H2L1-F=1,3-bis(3-fluorosalicylideneamino)-2-propanol; H2L1-2OMe=1,3-bis(4,6-dimethoxy salicylideneamino)-2-propanol) have been reported. Compound 1 crystallizes in triclinic space group with a=8.6392(10) Å, b=10.6431(9) Å, c=11.6809(13) Å, α=85.972(8)°, β=71.492(9)°, and γ=72.221(9)°, while the unit cell parameters of 2 are as follows: space group: monoclinic C2/c, a=28.2948(5) Å, b=7.3033(2) Å, c=26.3933(5) Å, and β=96.243(1)°. The variable-temperature magnetic susceptibility measurements reveal that the metal centers in both the compounds are antiferromagnetically coupled with J=−200 cm−1 for 1 and J=−175 cm−1 for 2. The magnetic behaviors have been explained on the basis of two opposing factors, complementarity and countercomplementarity of magnetic orbitals. 相似文献
18.
Ribose 5-phosphate (R5P) is a sugar known to undergo the Maillard reaction (glycation) at a rapid rate. In a reaction with the lysines of bovine heart cytochrome c, R5P generates superoxide () that subsequently reduces ferri-cytochrome c to ferro-cytochrome c. The rate equation for the observed cytochrome c reduction is first order in respect to cytochrome c and half order in respect to R5P. The addition of amines to the cytochrome c-R5P system greatly increases the generation with rates of approximately 1.0 μM min−1 being observed with millimolar levels of R5P and amine at 37 °C. Pre-incubation of R5P with the amine prior to cytochrome c addition further enhances the rate of cytochrome c reduction approximately twofold for every 30 min of incubation. While clearly accounting for a portion of the reduction of cytochrome c, is not the sole reductant of the system as the use of superoxide dismutase only partially limits cytochrome c reduction, and the contribution of proportionally decreases with longer amine-R5P incubation times. The remainder of the cytochrome c reduction is attributed to either the Amadori product or a cross-linked Schiff base created when a Maillard reaction-derived dicarbonyl compound(s) reacts with the amine. It is believed that these compounds directly transfer electrons to ferri-cytochrome c and subsequently become stable free-radical cations. ATP, a putative regulator of cytochrome c activity, does not inhibit electron transport from or the cross-linked Schiff base but does prevent R5P from reacting with surface lysines to generate superoxide. The spontaneous reaction between R5P and amines could serve as an alternative system for generating in solution. 相似文献
19.
A series of compounds [FeIIH3LMe]Br·Y·nMeOH ( (1), (2), (3), (4); n = 0 or 1) were synthesized, where H3LMe is a hexadentate N6 tripodal ligand of the neutral form, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine, and their structures and magnetic properties were investigated. The compounds 1−3 with counter anions , , and contain methanol as a crystal solvent, and show no SCO behaviors, while the corresponding Cl− compounds have no crystal solvent and show a variety of SCO behaviors. The compound [FeIIH3LMe]Br·CF3SO3 (4) has no crystal solvent and has isomorphous structure to the Cl− compounds, and shows an abrupt spin transition between the HS (S = 2) and LS (S = 0) states with a hysteresis about 2 K and large frozen-in effect below 72 K. The T1/2↑ and T1/2↓ values are 98 and 96 K, whose values are higher than those of corresponding Cl− compound about 15 K and the width of hysteresis is narrower than that of corresponding Cl− compound about 2 K. The crystal structures of 4 were determined at 296 and 93 K, where the crystal system and space group showed no change between these temperatures. The structures at both temperatures have a same 2D layered structure, which is composed of NH?Br− hydrogen bonds between the Br− ion and the imidazole NH groups of three neighboring cations [FeIIH3LMe]2+. This network structure is the same as that of corresponding Cl− compound. The 600 nm light irradiation at 5 K induced the LIESST effect. 相似文献