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1.
A series of dihydroxamic acid ligands of the formula [RN(OH)C(O)] 2(CH 2) n, ( n = 2, 4, 6, 7, 8; R = CH 3, H) has been studied in 2.0 M aqueous sodium perchlorate at 25.0 °C. These ligands may be considered as synthetic analogs to the siderophore rhodotorulic acid. Acid dissociation constants (p Ka) have been determined for the ligands and for N-methylacetohydroxamic acid (NMHA). The p Ka1 and p Ka2 values are: n = 2, R = CH 3 (8.72, 9.37); N = 4, R = CH 3 (8.79, 9.37); N = 6, R = CH 3; N = 7, R = CH 3 (8.95, 9.47); N = 8, R = CH 3 (8.93, 9.45); N = 8, R = H (9.05, 9.58). Equilibrium constants for the hydrolysis of coordinated water (log K) have been estimated for the 1:1 feeric complexes of the ligands n = 2, 4, 8; R = CH 3. The N = 8 ligand forms a monomeric complex with Fe(III) while the n = 2 and 4 ligands form dimeric complexes. For hydrolysis of the n = 8 monomeric complex, log K1 = −6.36 and log K2 = −9.84. Analysis of the spectrophotometric data for the dimeric complexes indicates deprotonation of all four coordinated waters. The successive hydrolysis constants, log K1–4, for the dimeric complexes are as follows: n = 2 (−6.37, −5.77, −10.73, −11.8); n = 4 (−5.54, −5.07, −11.57, −10.17). The log K2 values for the dimers are unexpectedly high, higher in fact than log K1, inconsistent with the formation of simple ternary hydroxo complexes. A scheme is proposed for the hydrolysis of the ferric dihydroxamate dimers, which includes the possible formation of μ-hydroxo and μ-oxo bridges. 相似文献
2.
The shear piezoelectricity was observed in oriented films of poly-β-hydroxybutyrate (PHB) and copolymers of β-hydroxybutyrate (HB) and β-hydroxyvalerate (HV). The piezoelectric stress constant 3 14 = e′ 14 − ie″ 14 (polarization/strain), the piezoelectric strain constant d14 = d′ 14 − id″ 14 (polarization/stress), the elastic constant c = c′ + ic″ and the dielectric constant = ′ − i″ were determined at a frequency of 10 Hz over a temperature range from −150° to +150°C. Piezoelectric relaxations as well as elastic and dielectric relaxations were clearly observed at the glass transition temperature of about 15°C. In order to evaluate the piezoelectric constants ( e2 and d2) for the piezoelectric phase which consists of the crystalline region and the oriented non-crystalline region, a spherical dispersion two phase model was utilized. Assuming the appropriate fixed values for the elastic and dielectric constants in the piezoelectric phase, d2 and d2 were calculated as a function of temperature. For a PHB and a copolymer (17 HV/83 HB), e2 and d2 showed relaxations, leading to a conclusion that the instantaneous piezoelectric constant in the crystalline phase is constant independent of temperature but the piezoelectric constant in the oriented non-crystalline phase is relaxational and has the opposite sign. For a copolymer (25 HV/75 HB) and a chloroform treated copolymer (17 HV/83 HB), e2 and d2 were constant independent of temperature, indicating that the oriented non-crystalline phase has disappeared owing to the increased molecular flexibility due to copolymerization or annealing in chloroform vapour. 相似文献
3.
Due to contradictions in the literature we have redetermined the acid-base properties of riboflavin (=RiFl; vitamin B 2), i.e. 7,8-dimethyl-10-ribityl-isoalloxazine, and of flavin mononucleotide (FMN 2−), also known as riboflavin 5′-phosphate, via potentiometric pH titrations ( I = 0.1 M, NaNO 3; 25 °C). In contrast to various claims, the isoalloxazine ring cannot be protonated at pH > 1, a result in agreement with an early study (p Ka = −0.2; L. Michaelis, M.P. Schubert and C.V. Smythe, J. Biol. Chem., 116 (1936) 587–607); deprotonation of the ring system occurs in both compounds with p Ka 10. The p Ka value of 0.7 determined for the deprotonation of H 2(FMN) must be attributed to the release of the first proton from the fully protonated phosphate group; its second proton is released with p Ka = 6.18 in agreement with the acidity constants of various other monoprotonated monophosphate esters. The stability constants of the 1:1 complexes formed between Mg 2+, Ca 2+, Sr 2+, Ba 2+, Mn 2+, Co 2+, Ni 2+, Cu 2+, Zn 2+ or Cd 2+ (---M 2+) and FMN 2− were determined by potentiometric pH titrations in aqueous solution ( I = 0.1 M, NaNO 3; 25 °C). The log stability constants of all these M(FMN) complexes are about 0.2 log units higher than expected from the basicity of the phosphate group. This slight stability increase cannot be attributed to the formation of a seven-membered chelate involving the ribit-hydroxy group at C-4′ as the stability constants for the M 2+ 1:1 complexes of glycerol 1-phosphate (G1P 2−) demonstrate: G1P 2− contains the same structural unit which would also allow in this case the formation of the mentioned seven-membered chelate; however, the stability of the M(G1P) complexes is solely determined by the basicity of the phosphate group. Hence, in agreement with earlier conclusions (J. Bidwell, J. Thomas and J. Stuehr, J. Am. Chem. Soc., 108 (1986) 820–825) regarding Ni(FMN) one must conclude that the slight stability increase of the M(FMN) complexes has to be attributed to the isoalloxazine ring. The equality of the stability increase of the complexes for all the mentioned ten metal ions precludes its attribution to an interaction with an N site and makes a specific interaction with an O site also somewhat unlikely. In addition, carbonyl oxygens appear as not very favorable for the formation of macrochelates by a further interaction with already phosphate-coordinated metal ions. Therefore, we propose that the slight but significant stability increase originates from M(FMN) species (with a formation degree of about 30%) in which the hydrophobic flavin residue is close to the metal ion, thereby lowering the ‘effective’ dielectric constant in the microenvironment of the metal ion and thus indirectly promoting the −PO 32−/M 2+ interaction. 相似文献
4.
The relationship between the p Ka of 8-quinolinol derivatives {8-quinolinol (Hqn), 2-methyl- (H2-Meqn), 2,4-dimethyl- (H2,4-diMeqn), 5-chloro- (H5-Clqn) and 5,7-dichloro-8-quinolinols (H5,7-diClqn)} and a π-donor ability of the 8-quinolinolato oxygens has been investigated by the identification of the structures of the major products, [RuCl(QN)(QN′)NO] (HQN=8-quinolinol derivative; HQN′=different 8-quinolinol derivatives), obtained by the reaction of [RuCl 3(QN or QN′)NO] − with HQN′ or HQN. The results obtained clearly showed that the oxygen of the 8-quinolinol derivative that has a higher p Ka predominantly coordinates in the trans position to the NO ligand and is a better π-electron donor. The order of the π-electron donor ability for the oxygen of the 8-quinolinol derivatives is as follows: H2-Meqn≥H2,4-diMeqn>Hqn≥H5-Clqn>H5,7-diClqn, almost agreeing with the magnitude of the p Ka values of the corresponding 8-quinolinols. The structures of cis-1 [RuCl(5,7-diClqn) 2NO] and cis-1 [RuCl(5,7-diClqn)(2-Meqn)NO] were determined by X-ray diffraction. 相似文献
5.
Disc electrophoretically homogeneous spinach-chloroplast cytochrome b6 was found to be a lipoprotein whose redox potential was essentially unchanged during isolation. These results further support the hypothesis of Triton X-100/4 M urea, pH 8, as a useful extracting medium for membrane lipoproteins. Cytochrome b6 was found to have a heme equivalent dry weight of 1 mol of heme per 60 000 g. Of this, 20 000 g was lipid-extractable. The molecular weight was 60 000 with a partial specific volume of 0.84 ml/g. The protein portion of the molecule (40 000) consisted of 1 polypeptide chain of 20 000 daltons, 1 of 9600 daltons and 2 of 6600 daltons. A simple lipid composition (relative to the original membrane) was found consisting of 7 mol of chlorophyll a and 6 mol of cardiolipin per mol of cytochrome; these two lipids thus account for about 75–80% of the lipid content. An unidentified minor neutral lipid and minor polar lipid were also detected. At pH 7.0 in the presence of 0.5% Triton X–100, E′0 was −0.080 V, and in the absence of Triton X–100, E′0 was −0.120 V. At pH 8 in 0.5% Triton X–100, E′0 was −0.084 V, thus indicating that the redox potential is independent of pH in the region 7–8. The redox reaction proceeded via a one-electron-transfer. 相似文献
6.
The stability constants of the 1:1 complexes formed between Mg 2+, Ca 2+, Sr 2+, Ba 2+, Mn 2+, Co 2+, Ni 2+, Cu 2+, Zn 2+ or Cd 2+ (M 2+) and the simple, sterically unhindered imidazole-type ligands, imidazole, 1-methylimidazole, 5-chloro-1-methylimidazole, N-(2,3,5,6-tetrafluorophenyl)imidazole or 4′-(imidazol-1-yl)acetophenone (L), were determined by potentiometric pH titrations in aqueous solution (25°C; I = 0.5 M, NaNO 3). The construction of log KMLM versus p KHLH plots results in straight lines; the equations for the least-squares lines are calculated and listed. These data allow calculation of the expected stability constant for a complex of any imidazole-type ligand, provided its p KHLH value (in the p Ka range 4–8) is known. For the stabilities of Fe 2+ complexes with imidazole-type ligands an estimation procedure is provided. It is shown further that the complex formation between 1-methylbenzimidazole (MBI) and Mn 2+, Ni 2+, Cu 2+ or Zn 2+ is s sterically hindered, i.e. the data points for these M(MBI) 2+ complexes do not fall on the straight lines defined by the imidazole-type ligands. 相似文献
7.
The Dmt-Tic pharmacophore exhibits potent δ-opioid receptor antagonism. Analogues with substitutions in the second pharmacophore with (1, 1′) or without a COOH function (2–9) were synthesized: several had high δ affinity (1′, 2, 7, and 9), but exhibited low to non-selectivity toward μ receptors similar to H-Dmt-Tic-amide and H-Dmt-Tic-ol. Functional bioactivity indicated high δ antagonism (p A2 7.4–7.9) (1′, 2, and 9) and modest μ agonism, pEC 50 (6.1–6.3) (1′, 2, 8, and 9), but with Emax values analogous to dermorphin. These Dmt-Tic analogues with mixed δ antagonist/μ agonist properties would appear to be better candidates as analgesics than pure μ agonists. 相似文献
8.
1. In membranes prepared from dark grown cells of Rhodopseudomonas capsulata, five cytochromes of b type ( E′ 0 at pH 7.0 +413±5, +270±5, +148±5, +56±5 and −32±5 mV) can be detected by redox titrations at different pH values. The midpoint potentials of only three of these cytochromes ( b148, b56, and b−32) vary as a function of pH with a slope of 30 mV per pH unit. 2. In the presence of a Co/N2 mixture, the apparent E′0 of cytochrome b270 shifts markedly towards higher potentials (+355 mV); a similar but less pronounced shift is apparent also for cytochrome b150. The effect of CO on the midpoint potential of cytochrome b270 is absent in the respiration deficient mutant M6 which possesses a specific lesion in the CO-sensitive segment of the branched respiratory chain present in the wild type strain. 3. Preparations of spheroplasts with lysozyme digestion lead to the release of a large amount of cytochrome c2 and of virtually all cytochrome cc′. These preparations show a respiratory chain impaired in the electron pathway sensitive to low KCN concentration, in agreement with the proposed role of cytochrome c2 in this branch; on the contrary, the activity of the CO-sensitive branch remains unaffected, indicating that neither cytochrome c2 nor the CO-binding cytochrome cc′ are involved in this pathway. 4. Membranes prepared from spheroplasts still possess a CO-binding pigment characterized by maxima at 420.5, 543 and 574 nm and minima at 431, 560 nm in CO-difference spectra and with an band at 562.5 nm in reduced minus oxidized difference spectra. This membrane-bound cytochrome, which is coincident with cytochrome b270, can be classified as a typical cytochrome “o” and considered the alternative CO-sensitive oxidase. 相似文献
9.
Deuterium magnetic resonance ( 2H-NMR) and Raman spectroscopy are used to investigate order and fluidity at the terminal methyl position in 16- d3, 16′- d3 dipalmitoylphosphatidylcholine (16- d6 DPPC) multibilayers. These methods reveal substantial motion and disorder in the gel phase, 5–10°C below the gel-liquid crystal phase transition temperature ( Tm). The phase transition is sensed in the 2H-NMR spectrum as a reduction in the quadrupole splitting from 14 kHz to 3 kHz. In contrast, the Raman parameter used to characterize the CD 3 vibrations is quite insensitive to the melting process, although an analogous parameter does sense disordering at Tm at the 10 and 10′ position in 10- d2, 10′- d2 DPPC. The difference in the response of the NMR and Raman parameters may arise because the vibrational spectrum of the CD 3 group is inhomogenously broadened and is therefore quite sensitive to alterations in the local environment around the methyl group. In contrast, the NMR quadrupole splitting is sensitive to both local motion of the methyl group and, near Tm, to motions of the CD 2 group induced by transgauche isomerizations further up the chain. The difficulties that arise when results from different spectroscopic techniques are compared are demonstrated. 相似文献
10.
The effect of incorporation of 1-palmitoyl- sn-glycero-3-phosphocholine (PLPC) on the structure of the P β′ ripple mesophase in aqueous dispersions of 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) has been studied by differential scanning calorimetry (DSC) and scanning dilatometry (SD). For samples containing 34 wt. % 2H 2O and 0–15 wt. % PLPC, a pretransition was observed by DSC. The pretransition disappears at 15 wt. % PLPC. The behavior of thermodynamic functions at the pretransition and main transition gives new insights on the structural changes produced by PLPC on bilayers of DPPC. 相似文献
11.
We describe the syntheses, physicochemical properties and biological evaluation of a novel series of complexones containing bis- or biazoles moieties and two iminodiacetic acid units as novel ligands for paramagnetic lanthanides. The complexones were prepared by reaction of the corresponding 1,1′-bishaloethylbi- or bispyrazoles with methyl iminodiacetate and subsequent NaOH hydrolysis. 1,1′-Bisbromoethyl precursors were obtained by direct alkylation with an excess of 1,2-dibromoethane, or by heating the corresponding alcohol in HCl. Sigmoidal binding isotherms and MO calculations supported as most stable structures in solution, those containing two Gd(III) atoms bound per molecule of complexone with half saturation values S 0.5 (M −1, 22 °C, pH 7.2) in the range 6.5 10 −60.5<36.1 10−6. Relaxivity properties [r1, r2, s−1 mM−1 Gd(III)] determined at 1.5 Tesla gave values (12.0<r1<17.7, 12.2<r2<20), improving significantly the relaxivities of reference compounds such as Gd(III)EDTA (5.2, 5.6) or Gd(III)DTPA (4.30, 4.30). These improvements involve mainly increased hydration and slower rotational motions. In vitro toxicity experiments are reported. 相似文献
12.
The kinetics and equilibria of complex formation by Ga(III) with NCS − in aqueous solution have been measured over a range of acidities and temperatures, the contributing paths to the reaction resolved, and their rate constants and activation parameters determined. The hydrolysis equilibria required to carry out this resolution of kinetic behaviour have also been measured. Unlike the other reported complexation reactions of Ga(III) in aqueous solution, the separate reaction pathways can be assigned with no ambiguity. At 25 °C and ionic strength 0.5 M, the observed forward rate constant for the complex formation is described by {k1 + k2K1h/[H+] + k3K1hK2h/[H+]2} M−1 s−1. For these conditions, the first and second successive hydrolysis constants of Ga(H2O)63+ are given by pK1h = 3.69 ± 0.01 and pK2h = 3.74 ± 0.04. The rate constants corresponding to the reactions of the species Ga(H2O)63+, Ga(H2O)5(OH)2+ and Ga(H2O)4(OH)2+ with NCS− are k1 = 57 ± 4 M−1 −1, k2 = (1.08 ± 0.01) × 105 M−1 s−1 and k3 = 3 × 106 M−1 s−1 respectively. The complexation equilibrium quotient [GaNCS2+]/([Ga3+][NCS−]) has been independently determined by spectrophotometric titration to be 20.8 ± 0.3 M−1 at 25 °C and ionic strength 0.5 M. These kinetic results lead to an interpretation of the data, and a reinterpretation of other data for aquo-Ga(III) complex formation kinetics from the literature which support the assignment of a dissociative interchange mechanism for these reactions rather than the associative activation mode sometimes proposed. 相似文献
13.
This paper investigates the polyelectrolyte behaviour of welan in aqueous solution. From conductivity and activity measurements it is demonstrated that a double-helical conformation is adopted irrespective of pH and ionic strength. The intrinsic p K of its carboxylic groups is found to be abnormally low (p K0 = 2.2) and no conformational transition was observed during neutralization. The viscometric behaviour was studied as a function of degree of neutralization, polymer concentration, shear rate and ionic strength. The linear relation [η]= f( Cs−1/2) allows the determination of B, the stiffness parameter from Smidsrod, whose value characterizes a very stiff molecule. 相似文献
14.
The stability constants of the 1:1 complexes formed between Cu(Arm) 2+, where Arm = 2,2′-bipyridyl or 1,10-phenanthroline, and methyl phosphate, CH 3OPO 32−, or hydrogen phosphate, HOPO 32−, were determined by potentiometric pH titration in aqueous solution (25°C; l = 0.1 M, NaNO 3). On the basis of previously established log K versus p Ka straight-line plots (D. Chen et al., J. Chem. Soc., Dalton Trans. (1993) 1537–1546) for the complexes of simple phosphate monoesters and phosphonate derivatives, R-PO 32−, where R is a non-coordinating residue, it is shown that the stabilities of the Cu(Arm) (CH 3OPO 3) complexes are solely determined by the basicity of the -PO 32− residue. In contrast, the Cu(Arm) (HOPO 3) complexes are slightly more stable (on average by 0.15 log unit) than expected on the basicity of HPO 42−; this is possibly due to a more effective solvation including hydrogen bonding, an interaction not possible with coordinated CH 3OPO 32− species. Regarding biological systems the observation that HOPO 32− is somewhat favored over R-PO 32− species in metal ion interactions is meaningful. 相似文献
15.
1. 1. Cyanide inhibits the catalytic activity of cytochrome aa3 in both polarographic and spectrophotometric assay systems with an apparent velocity constant of 4·103 M−1·s−1 and a Ki that varies from 0.1 to 1.0 μM at 22 °C, pH 7·3. 2. 2. When cyanide is added to the ascorbate-cytochrome c-cytochromeaa3−O2 system a biphasic reduction of cytochrome c occurs corresponding to an initial Ki of 0.8 μM and a final Ki of about 0.1 μM for the cytochrome aa3−cyanide reaction. 3. 3. The inhibited species (a2+a33+HCN) is formed when a2+a33+ reacts with HCN, when a2+a32+HCN reacts with oxygen, or when a3+a33+HCN (cyano-cytochrome aa3) is reduced. Cyanide dissociates from a2+a33+HCN at a rate of 2·10−3 s−1 at 22 °C, pH 7.3. 4. 4. The results are interpreted in terms of a scheme in which one mole of cyanide binds more tightly and more rapidly to a2+a33+ than to a3+a33+.
Abbreviations: TMPD, N,N,N′,N′-tetramethyl-p-phenylenediamine 相似文献
16.
3-[3-(Piperidinomethyl)phenoxy]alkyl, N-cyano- N′-[ω-[3-(1-piperidinylmethyl)phenoxy]alkyl]guanidine and 2-(5-methyl-4-imidazolyl)methyl thioethyl derivatives containing fluorescent functionalities were synthesized and the histamine H 2 receptor affinity was evaluated using the H 2 antagonist [ 125I]-aminopotentidine. The compounds exhibited weak to potent H 2 receptor affinity with p Ki values ranging from <4 to 8.85. The highest H 2 receptor affinity was observed for N-cyano- N′-[ω-[3-(1-piperidinylmethyl)phenoxy]alkyl]guanidines substituted with methylanthranilate (13), cyanoindolizine (6) and cyanoisoindole (11) moieties via an ethyl or propyl linker. 相似文献
17.
A range of related adenosines and 5′-N-ethylcarboxamidoadenosines bearing oxygenated substituents in the N 6 position have been synthesised and evaluated as A 1-adenosine receptor ligands. Compound 9 emerged with potent affinity ( EC50 = 1.1 nM). 相似文献
18.
The complexes [Ln(pytpy)(NO 3) 2(μ-OCH 3)] 2 (Ln = Eu(III), Tb(III), Dy(III), pytpy=4′-( n-pyridyl)-2,2′:6′,2″-terpyridine, n = 2, 3) were synthesized and characterized by IR, elemental analyses, UV–Vis and luminescent spectroscopy. Three complexes crystallized in monoclinic system, P21/ n space group. Lanthanide ions are nine-coordinated by three nitrogen atoms from tridentate pytpy ligands, four oxygen atoms from two bidentate nitrate groups and two oxygen atoms from two methoxo groups, forming distorted tricapped trigonal prismatic geometries. The dimethoxo-bridges connect two metal ions in asymmetric fashion into dimeric structures with short LnLn distances of 3.767(1), 3.740(1) and 3.720(1) Å for Eu(III), Tb(III) and Dy(III) complexes, respectively. Photoluminescence measurement indicates that 1 and 3 emit the characteristic luminescence of Tb(III) and Eu(III) ions in the solid state, respectively. The luminescent spectrum of Eu(III) complex in solvents was also investigated. 相似文献
19.
The first examples of binary palladium(II) derivatives of unsaturated carboxylic acids are reported. It was found that the interaction of Pd 3(μ-OAc) 6 with the ,β-unsaturated 1-methylcrotonic (tiglic) and crotonic acids leads to the corresponding carboxylates of composition Pd 3[μ-O 2CC(R′) = CHMe] 6, where R′ = Me (1) or H (2). The new compounds have been characterized by elemental analysis, solid and solution IR, 1H and 13C NMR, and ESI mass spectrometry. The crystal structure of 1 has been determined. This molecule displays a central Pd 3 cyclic core with Pd–Pd distances of 3.093–3.171 Å. Each Pd–Pd bond is bridged by a pair of carboxylate ligands, one above and the other below the Pd 3 plane, providing a square planar coordination for each Pd atom in an approximate D3h overall symmetry arrangement. Solution spectroscopic data show that the bridging η 1:η 1:μ 2 interaction of the carboxylates of 1 and 2 is readily displaced, with a change of the ligand to the terminal (η 1) coordination mode. 相似文献
20.
A number of N, N′-bis(4-substituted phenyl)-1,7-diaza-12-crown-4 and N, N′-bis(4-substituted phenyl)-1, 10-diaza-18-crown-6 (where the substituents are OCH 3, CH 3, H, Cl, respectively) have been prepared by cyclization reaction of a ditosylate with the appropriately substituted diol. These new macrocyclic ligands have been characterized by means of elemental analysis, IR, 1H NMR and MS spectra. The crystal structures of N, N′-bis(4-chlorophenyl)-1,10-diaza-18-crown-6 (21) and its complex with barium thiocyanate Ba(SCN) 2 (22) have been determined by single crystal X-ray diffraction. The crystallographic data are as follows: 21: C 24H 32Cl 2N 2O 4, orthorhombic, P2 12 12 1, A=4.852(1), B=11.989(2), C=41.231(8) Å, V=2398.7(8) Å 3, Z=4; 22: C 26H 32Cl 2N 4O 4S 2Ba, monoclinic, P2 1/ c, A=8.801(2), B=11.653(9), C=15.756(6) Å, ß=105.96(3)°, V=1553.7(14) Å 3, Z=2. In the complex, the Ba atom is eight-coordinate (O(1), O(2), O(1)′, O(2)′, N(1), N(1)′, N(21), N(21)′) to form a distorted D6h geometry with the Ba atom at the center of crystallographic symmetry. 相似文献
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