共查询到20条相似文献,搜索用时 31 毫秒
1.
Brian E. Hingerty Raymond S. Brown Aaron Klug 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1982,697(1):78-82
The sites of three [Co(NH3)6]3+ ions bound to the phenylalanine tRNA of yeast have been determined by X-ray diffraction analysis. [Co(NH3)6]3+ binds to purine-purine sequences in yeast tRNAPhe. It is different from the binding of Co2+, which binds to the base and phosphate of residue G15. There are no direct metal-nucleotide bonds, although hydrogen bonding of the coordinated ammines to double-helical guanylguanosine sequences in the major groove and to phosphate oxygens in neighboring polynucleotide strands increases the stability of the structure. Hydrogen-bonding appears to be via cis ammine ligands to N(7) and O(6) positions of adjacent purine bases. 相似文献
2.
A. Saha N. Saha L.-n. Ji Jing Zhao Fridrich Gregáň S. Ali A. Sajadi B. Song H. Sigel 《Journal of biological inorganic chemistry》1996,1(3):231-238
The acidity constants of methyl phosphoric acid, CH3OPO(OH)2, and orthophosphoric acid, HOPO(OH)2, and the stability constants of the 1 : 1 complexes formed between Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, or Cd2+ and methyl phosphate, CH3OPO3
2–, or hydrogen phosphate, HOPO3
2–, were determined by potentiometric pH titration in aqueous solution (25 °C;I = 0.1 M, NaNO3). On the basis of previously established log K versus pK
a straight-line plots for the complexes of simple phosphate monoesters and phosphonate derivatives, R-PO3
2–, where R is a noncoordinating residue, it is shown that the stability of the M(CH3OPO3) complexes is solely determined (as one might expect) by the basicity of the –PO3
2– residue. It is emphasized that the mentioned reference lines may also be used to reveal increased complex stabilities, for
example, for certain complexes formed with 8-quinolyl phosphate the occurrence of 7-membered chelates can be proven in this
way; the same procedure is also applicable to complexes of nucleotides, etc. The M(HOPO3) complexes are slightly more stable (on average by 0.08 log unit) than it is expected from the basicity of HPO4
2–; this observation is attributed to a more effective solvation, including hydrogen bonding, than is possible with CH3OPO3
2– species.
Received: 9 November 1995 / Accepted: 5 February 1996 相似文献
3.
trans -[PtCl4(NH3)(thiazole)] (1), trans-[PtCl4(cha)(NH3)] (2), cis-[PtCl4(cha)(NH3)] (3) (cha =cyclohexylamine), and cis-[PtCl4(NH3)2] (4) has been investigatedat 25 °C in a 1.0 M aqueous medium at pH 2.0–5.0 (1) and 4.5–6.8 (2–4) using stopped-flow spectrophotometry. The redox reactions follow the second-order rate law , where k is a pH-dependent rate constant and [GSH]tot the total concentration of glutathione. The reduction takes place via parallel reactions between the platinum(IV) complexes
and the various protolytic species of glutathione. The pH dependence of the redox kinetics is ascribed to displacement of
these protolytic equilibria. The thiolate species GS− is the major reductant under the reaction conditions used. The second-order rate constants for reduction of compounds 1–4 by GS− are (1.43±0.01)×107, (3.86±0.03)×106, (1.83±0.01)×106, and (1.18±0.01)×106 M−1 s−1, respectively. Rate constants for reduction of 1 by the protonated species GSH are more than five orders of magnitude smaller. The mechanism for the reductive elimination
reactions of the Pt(IV) compounds is proposed to involve an attack by glutathione on one of the mutually trans coordinated chloride ligands, leading to two-electron transfer via a chloride-bridged activated complex. The kinetics results
together with literature data indicate that platinum(IV) complexes with a trans Cl-Pt-Cl axis are reduced rapidly by glutathione as well as by ascorbate. In agreement with this observation, cytotoxicity
profiles for such complexes are very similar to those for the corresponding platinum(II) product complexes. The rapid reduction
within 1 s of the platinum(IV) compounds with a trans Cl-Pt-Cl axis to their platinum(II) analogs does not seem to support the strategy of using kinetic inertness as a parameter
to increase anticancer activity, at least for this class of compounds.
Received: 8 December 1999 / Accepted: 15 February 2000 相似文献
4.
J. S. Singh 《Journal of biological physics》2008,34(6):569-576
Infrared (IR) and Raman spectra of 5-aminouracil were recorded in the region 200–4,000 cm − 1. Assuming under the Cs point group that the distribution of the normal mode of vibrations between the two species are planar (a′) and non-planar
(a″), given by 25a′ + 11a″ of which 30 modes (21a′ + 9a″) correspond to the uracil moiety and six modes (4a′ + 2a″) correspond
to the NH2 group, with a comparison of theoretically ab initio calculated frequencies, the results are in reasonably good agreement
with the experimental IR and Raman spectra. Consistent assignments have been made for the internal modes of the NH2 group, especially for the anti-symmetric NH2 stretching and bending modes. The non-equivalence of the two NH bonds of the NH2 group suggests a difference in the strength of the two hydrogen bonds on the pyrimidine ring. Symmetry and anti-symmetry
NH stretching modes of the NH2 group show the invalidity of the empirical relationship. These two NH2 stretching frequencies are distinctly separated from the CH/NH ring stretching frequencies. A strong and sharp IR band that
acts at 3,380 cm − 1 could be identified as the anti-symmetric NH2 mode whereas the band at 3,290 cm − 1 smaller density could be identified as the symmetric NH2 stretching mode. 相似文献
5.
A series of crown ethers containing the azobenzene moiety incorporated into crowns of various sizes [Cr(O6), Cr(O7) and Cr(O8)] and their corresponding alkali metal cation (Li+, Na+, K+, Rb+) complexes have been studied theoretically. The density functional theory (DFT) method was employed to elucidate the stereochemical
structural natures and thermodynamic properties of all of the target molecules at the B3LYP/6-31 G(d) and LANL2DZ level for
the cation Rb+. The fully optimized geometries had real frequencies, thus indicating their minimum-energy status. In addition, the bond
lengths between the metal cation and oxygen atoms, atomic torsion angles and thermodynamic energies for complexes were studied.
Natural bond orbital (NBO) analysis was used to explore the origin of the internal forces and the intermolecular interactions
for the metal complexes. The calculated results show that the most significant interaction is that between the lone pair electrons
of electron-donating oxygens in the cis-forms of azobenzene crown ethers (cis-ACEs) and the LP* (1-center valence antibond lone pair) orbitals of the alkali-metal cations (Li+, Na+, K+ and Rb+). The electronic spectra for the cis-ACEs [cis-Cr(O6), cis-Cr(O7) and cis-Cr(O8)] are obtained by the time-dependent density functional theory (TDDFT) at the B3LYP/6-31 G(d) level. The spectra of the cis-isomers show broad π → π* (S0 → S2) absorption bands at 310–340 nm but weaker n → π* (S0 → S1) bands at 480–490 nm. The calculated results are in good agreement with the experimental results. 相似文献
6.
Silver carboxylate coordination with the tetrachlorophthalate anion, in combination with neutral donor ligands, has been found to deviate from other known poly-carboxylate complexes. Both complexes reported here, bis-[tetrachlorophthalato-silver phthalazine] and bis-[ammino-tetrachlorophthato-silver di-ammino-silver], utilize mixed carboxylate bonding types for silver coordination. In the case of the phthalazine ligand, both chelating and monodentate carboxylates form the framework for the oligomeric structure. In the case of the ammine ligand, one carboxylate forms a monodentate connection to a silver-ammine group, while the other is simply involved with hydrogen bonding to lock in a [(Ag-NH3)2-Ag-NH3] substructure with an adjacent tetrachlorophthalato-silver unit. Both structures exhibit supramolecular connections via hydrogen bonding and π-π interactions. 相似文献
7.
The synthesis, spectroscopic, and electrochemical properties of trans-[L(Pyr)(NH3)4RuII/III] (Pyr=py, 3-phpy, 4-phpy, 3-bnpy, or 4-bnpy; L=H2O, Guo, dGuo, 1MeGuo, Gua, Ino, or G7-DNA) are reported. As expected, the Pyr ligand slows DNA binding by trans-[(H2O)(Pyr)(NH3)4RuII]2+ relative to [(H2O)(NH3)5RuII]2+ and favors reduction of RuIII by about 150 mV. The pyridine ligand also promotes the disproportionation of RuIII to afford the corresponding complexes of RuII and, presumably, RuIV. For L=Ino, disproportionation follows the rate law: d[RuII]/dt=k
0[RuIII]+k
1[OH–][RuIII], k
0=(2.7±0.7)×10–4 s–1 and k
1=70±1 M–1 s–1.
Received: 11 May 1998 / Accepted: 3 March 1999 相似文献
8.
Karhánek D Kacer P Kuzma M Splíchalová J Cervený L 《Journal of molecular modeling》2007,13(9):1009-1016
Theoretical investigation of Pt(0)-olefin organometallic complexes containing tertiary phosphine ligands was focused on the
strength of platinum-olefin electronic interaction. DFT theoretical study of electronic effects in a substantial number of
ethylene derivatives was evaluated in terms of the Pt-olefin binding energy using MP2 correlation theory. Organometallics
bearing coordinated olefins with general formula (R1R2C = CR3R4)Pt(PH3)2 [R = various substituents] had been selected, including olefins containing both electron-donor substituents as well as electron-withdrawing
groups. The stability of the corresponding complexes increases with a strengthening electron-withdrawal ability of the olefin
substituents.
Figure Representation of (CH2 = CHR)Pt(PPh3)2 and the stability chart 相似文献
9.
A series of metallopeptides based on the amino terminal copper/nickel (ATCUN) binding motif have been evaluated as classical inhibitors and catalytic inactivators of both rabbit and human angiotensin-converting enzyme (hACE), and human endothelin-converting enzyme 1 (hECE-1). The cobalt complex [KGHK–Co(NH3)2]2+, where KGHK is lysylglycylhistidyllysine, displayed similar K
I and IC50 values to those found for [KGHK–Cu]+, in spite of the enhanced charge, and so either the influence of charge is offset by the steric influence of the axially coordinated ammine ligands, or binding is dominated by contributions from the amino acid side chains, especially the C-terminal lysine that mimics the binding pattern observed for lisinopril. Moreover, the inhibition observed for [KGHK–Co(NH3)2]2+ contrasts with the activation of hACE by Co2+(aq), reflecting the stimulation of enzyme activity following replacement of the catalytic zinc cofactor by cobalt ion at each of the two active sites. Quantitative analysis of the dose-dependent stimulation of activity by Co2+(aq) yielded apparent affinities of 1.3 ± 0.2 and 56 ± 8 μM for the two sites in the presence of saturating Zn2+ (10 μM). Catalytic inactivation of hACE by [KGHK–Cu] + at subsaturating concentrations had previously been characterized, with k
obs = 2.9 ± 0.5 × 10−2 min−1. Under similar conditions, the same complex is found to catalytically inactivate hECE-1, with k
obs = 2.12 ± 0.16 × 10−2 min−1, demonstrating the potential for dual-action activity against two key drug targets in cardiovascular disease. Irreversible inactivation of a drug target represents a novel mechanism of drug action that complements existing classical inhibitor strategies that underlie current drug discovery efforts.Electronic Supplementary Material Supplementary material is available to authorized users in the online version of this article at . 相似文献
10.
M.-A. Elizondo-Riojas Florence Gonnet Jean-Claude Chottard Jean-Pierre Girault Jiří Kozelka 《Journal of biological inorganic chemistry》1998,3(1):30-43
d(TpG)– reacts with cis-[Pt(NH3)2(H2O)2]2+ in two steps to yield the platinum chelate cis-[Pt(NH3)2{d(TpG)-N3(1),N7(2)}]. In the latter, hindered rotation of the bases leads to an equilibrium between two rotamers interconverting slowly on
the NMR time scale. The structure of the two rotameric chelates was studied by means of 1H NMR and molecular modeling techniques. The major and minor rotamers could be assigned unambiguously to the two head-to-head
conformational domains which are characterized by syn/anti and anti/anti sugar-base orientations, respectively. Molecular models derived for both rotamers show that the orientations of the bases
are mutually quasi-enantiomeric. The interconversion between the two rotamers (k ≈ 1 s–1 at 293 K) is approximately 104 times faster than the analogous rotamer interconversion observed in cis-[Pt(NH3)2{r(CpG)-N3(1),N7(2)}]+ [Girault J-P, Chottard G, Lallemand J-Y, Huguenin F, Chottard J-C (1984) J Am Chem Soc 106 : 7227–7232], suggesting that
the steric clash of the exocyclic amino group of the platinum-bound cytosine with the ligands in cis position is more severe than that of the two thymine oxo groups.
Received: 23 June 1997 / Accepted: 30 September 1997 相似文献
11.
Active excretion of ammonia across the gills of the shore crab Carcinus maenas and its relation to osmoregulatory ion uptake 总被引:1,自引:0,他引:1
D. Weihrauch W. Becker U. Postel S. Riestenpatt D. Siebers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(5):364-376
The mechanism of transbranchial excretion of total ammonia of brackish-water acclimated shore crabs, Carcinus maenas was examined using isolated, perfused gills. Applying physiological gradients of NH4Cl (100–200 μmol · l−1) directed from the haemolymph space to the bath showed that the efflux of total ammonia consisted of two components. The
saturable component (excretion of NH4
+) greatly exceeded the linear component (diffusion of NH3). When an outwardly directed gradient (200 μmol · l−1) was applied, total ammonia in the perfusate was reduced by more than 50% during a single passage of saline through the gill.
Effluxes of ammonia along the gradient were sensitive to basolateral dinitrophenol, ouabain, and Cs+ and to apical amiloride. Acetazolamide (1 mmol · l−1 basolateral) or Cl−-free conditions had no substantial effects on ammonia flux, which was thus independent of both carbonic anhydrase mediated
pH regulation and osmoregulatory NaCl uptake. When an inwardly directed gradient (200 μmol · l−1) was employed, influx rates were about 10-fold smaller and unaffected by basolateral ouabain (5 mmol · l−1) or dinitrophenol (0.5 mmol · l−1). Under symmetrical conditions (100 μmol · l−1 NH4Cl on both sides) ammonia was actively excreted against the gradient of total ammonia, which increased strongly during the
experiment and against the gradient of the partial pressure of NH3. The active excretion rate was reduced to 7% of controls by basolateral dinitrophenol (0.5 mmol · l−1), to 44% by basolateral ouabain (5 mmol · l−1), to 46% by Na+-free conditions and to 42% by basolateral Cs+ (10 mmol · l−1), indicating basolateral membrane transport of NH4
+ via the Na+/K+-ATPase and K+-channels and a second active, apically located, Na+ independent transport mechanism of NH4
+. Anterior gills, which are less capable of active ion uptake than posterior gills, exhibited even increased rates of active
excretion of ammonia. We conclude that, under physiological conditions, branchial excretion of ammonia is a directed process
with a high degree of effectiveness. It even allows active extrusion against an inwardly directed gradient, if necessary.
Accepted: 11 March 1998 相似文献
12.
M.J. Clarke S. Bitler D. Rennert M. Buchbinder A.D. Kelman 《Journal of inorganic biochemistry》1980,12(1):79-87
The reduction of Cl(NH3)5Ru(III) and subsequent binding of heterocyclic ligands by the resultant (H2O)(NH3)5Ru(II) ion is shown to be catalyzed by components of rat-liver cells. The presence of air significantly decreases the rate of heterocyclic ligand binding. In the case of microsome and soluble component catalysis, this is probably due to oxidation of the Ru(II) ion prior to complexation. Various inhibitors of electron-transfer proteins were employed in an effort to determine the preferred reducing species. These results lend support to the hypothesis that the antitumor activity of acido ruthenium(III) ammine complexes involves activation by reduction in vivo prior to metal coordination to nucleic acids. Anticancer drugs functioning by this mechanism may be preferentially toxic to or may localize in hypoxic areas of tumors. 相似文献
13.
Wilson B. Knight Su-Jen Ting Suzan Chuang Debra Dunaway-Mariano Tuli Haromy Muttaiya Sundaralingam 《Archives of biochemistry and biophysics》1983,227(1):302-309
Monodentate Co(NH3)5PPi was determined not to be a substrate for yeast inorganic pyrophosphatase while P1,P2-bidentate Co(NH3)4PPi was turned over by the enzyme at a rate of 7.5 min?1. A kinetic analysis of the substrate activities of the P1,P2-bidentate complexes, Co(en)2PPi, Cr(NH3)4PPi, Cr(H2O)(NH3)3PPi, Cr(H2O)2(NH3)2PPi, and Cr(H2O)4PPi was carried out in order to access the potential role of the metal-water ligands in productive binding. While substitution of the H2O ligands with NH3 ligands had a minimal affect on the Km for Mg2+, the binding affinity of the complexes decreased with an increasing ligand ratio as did the turnover number of the corresponding central complexes. The Co(en)2PPi complex was hydrolyzed at a rate approximately 0.6% of that for the Co(NH3)4PPi complex. The substrate activities of β,γ-bidentate Co(NH3)4PPPi and α,β,γ-tridentate Co(NH3)3PPP with pyrophosphatase were also tested. While both complexes were shown to bind tightly to the Mg2+-activated enzyme neither was hydrolyzed. On the other hand, in the presence of the Zn2+-activated enzyme the tridentate complex was turned over at a rate of 0.17 min?1 while the bidentate complex remained inert to hydrolysis. 相似文献
14.
Michael J. Clarke Katherine F. Coffey Holly J. Perpall John Lyon 《Analytical biochemistry》1982,122(2):404-411
A number of ammine complexes of transition metals in the platinum group exhibit antitumor and mutagenic activities, which probably result from in vivo metal ion coordination to nucleic acids. Coordination at N-7 purine sites on nucleic acids may induce depurination through a general acid-catalyzed cleavage of the sugar-purine bond. This possibility was tested by observing the hydrolysis of [dGuo)(NH3)5Ru]3+ under physiological conditions. Since multiple products result from this reaction, a high-pressure liquid chromatography technique was developed for separating various ammineruthenium(III) complexes with purine, pyrimidine, and nucleoside ligands. Using this technique it was possible to identify and follow the relative concentrations of several of the hydrolysis products. These data were used to develop a preliminary reaction scheme for the decomposition of (dGuo)(NH3)5Ru(III). The net rate constant (1.8 × 10?6 s?1) for the disappearance of this complex yields an upper limit for the rate of metal-induced sugar hydrolysis. While the half-life () for the sugar hydrolysis reaction is substantially shorter than that for the free nucleoside under the same conditions, it cannot be concluded that this represents a major contribution to the mutagenicity of Ru(III) complexes. 相似文献
15.
The crystal structures of [Cr(NO)(NH3)5](PF6)2 (red) and [Cr(NO)(NH3)5]Cl(PF6) (brown) have been determined. The [Cr(NO)(NH3)5]2+(A) complex cations in these compounds have a slightly distorted octahedral geometry with a strictly linear Cr-N-O arrangement (from symmetry). The short interatomic distances (2.399 Å × 4) between the O (nitrosyl) and H (ammonia in adjacent complex cations) atoms in A(PF6)2 indicate the existence of hydrogen bonds, while the interatomic distances (3.258 Å × 8) between those in ACl(PF6) are much longer, and the hydrogen bonds should be weak in spite of the presence of the smaller counter anion of chloride ion in ACl(PF6). Comparisons of the five crystal structures of A(PF6)2, ACl2, ACl(ClO4), ACl(PF6), and A(ClO4)2 have led to the conclusion that the existence of the strong hydrogen bonds gives red crystals of A(PF6)2, while the absence of hydrogen bonds results in the formation of green crystals of A(ClO4)2 (O ? H, 3.595 Å × 2). The color change of the crystals (from red to green) with the change of outer sphere anions is attributed to the change of the strength of the hydrogen bonding between the complex cations. 相似文献
16.
Müller F Aschenbach JR Gäbel G 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(4):337-343
This study sought to investigate effects of short-chain fatty acids and CO2 on intracellular pH (pHi) and mechanisms that mediate pHi recovery from intracellular acidification in cultured ruminal epithelial cells of sheep. pHi was studied by spectrofluorometry using the pH-sensitive fluorescent indicator 2′,7′-bis (carboxyethyl)-5(6′)-carboxyfluorescein
acetoxymethyl ester (BCECF/AM). The resting pHi in N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid (HEPES)-buffered solution was 7.37 ± 0.03. In HEPES-buffered solution,
a NH4
+/NH3-prepulse (20 mM) or addition of butyrate (20 mM) led to a rapid intracellular acidification (P < 0.05). Addition of 5-(N-ethyl-N-isopropyl)-amiloride (EIPA; 10 μM) or HOE-694 (200 μM) inhibited pHi recovery from an NH4
+/NH3-induced acid load by 58% and 70%, respectively. pHi recovery from acidification by butyrate was reduced by 62% and 69% in the presence of EIPA (10 μM) and HOE-694 (200 μM),
respectively. Changing from HEPES- (20 mM) to CO2/HCO3
−-buffered (5%/20 mM) solution caused a rapid decrease of pHi (P < 0.01), followed by an effective counter-regulation. 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS; 100 μM) blocked
the pHi recovery by 88%. The results indicate that intracellular acidification by butyrate and CO2 is effectively counter-regulated by an Na+/H+ exchanger and by DIDS-sensitive, HCO3
−-dependent mechanism(s). Considering the large amount of intraruminal weak acids in vivo, both mechanisms are of major importance
for maintaining the pHi homeostasis of ruminal epithelial cells.
Accepted: 8 March 2000 相似文献
17.
Gerda Oswald Ingo Rombeck B. Song H. Sigel B. Lippert 《Journal of biological inorganic chemistry》1998,3(3):236-245
The synthesis of cis-Pt(NH3)2(dCMP) is reported and by various physico-chemical methods it is demonstrated that it is a macrochelate in which Pt(II) is
bound simultaneously to the N3 site of cytosine in dCMP2– and to a phosphate-oxygen atom. According to the NOESY spectra (cross-peaks between cytosine H6 and H2′ and H3′) the cytosine
ring adopts an anti orientation. Highly unusual is the significant (1 ppm) downfield shift of the sugar proton H5″ in the 1H-NMR spectrum and the sensitivity of the cytosine H6 resonance on the protonation state of the phosphate group. Based on
these three features a geometry for the macrochelate is proposed. The compound is a major product of the reaction of cis-[Pt(NH3)2(H2O)2]2+ with dCMP2– at neutral pH, but it even forms at pH 5. By applying pD-dependent NMR spectroscopy (1H, 31P) and potentiometric pH titration, it is demonstrated that the Pt-coordinated phosphate group can be protonated (pK
a/1=3.21±0.10 and 3.31±0.05, respectively), and 1H- and 31P-NMR spectra also indicate deprotonation (pK
a/2=13.35±0.25) of the exocyclic amino group of the cytosine moiety. The metal ion binding affinity of cis-Pt(NH3)2(dCMP) is very small, as shown for Cu2+ (log K<0.6). The cis-Pt(NH3)2(dCMP) complex reacts with nucleosides and nucleotides (L′) by losing its chelate structure and forming mixed ligand complexes,
cis-Pt(NH3)2(dCMP)(L′); this means that the phosphate group is released from the coordination sphere of Pt(II), indicating that the Pt(II)-O(phosphate)
bond is not very strong.
Received: 23 October 1997 / Accepted: 17 February 1998 相似文献
18.
DNA binding by trans-[(H2O)(Pyr)(NH3)4RuII]2+ (Pyr=py, 3-phpy, 4-phpy, 3-bnpy, 4-bnpy) is highly selective for G7 with K
G=1.1×104 to 2.8×104, with the more hydrophobic Pyr ligands exhibiting slightly higher binding. A strong dependence on ionic strength indicates
that ion-pairing with DNA occurs prior to binding. At μ=0.05, d[RuII-DNA]/dt=k[RuII][DNA], where k=0.17–0.21 M–1 s–1 with the various Pyr ligands. The air oxidation of [(py)(NH3)4RuII]
n
-DNA to [(py)(NH3)4RuIII]
n
-DNA at pH 6 occurs with a pseudo-first-order rate constant of k
obs=5.6×10–4 s–1 at μ=0.1, T=25 °C. Strand cleavage of plasmid DNA appears to occur by both Fenton/Haber-Weiss chemistry and by base-catalyzed routes,
some of which are independent of oxygen. Base-catalyzed cleavage is more efficient than O2 activation at neutral pH and involves the disproportionation of covalently bound RuIII and, in the presence of O2, Ru-facilitated autoxidation to 8-oxoguanine. Disproportionation of [py(NH3)4RuIII]
n
-DNA occurs according to the rate law: d[RuII–GDNA]/dt=k
0[RuIII–GDNA]+k
1[RuIII–GDNA][OH–], where k
0=5.4×10–4 s–1 and k
1=8.8 M–1 s–1 at 25 °C, μ=0.1. The appearance of [(Gua)(py)(NH3)4RuIII] under argon, which occurs according to the rate law: d[RuIII–G]/dt=k
0[RuIII–GDNA]+k
1[OH–][RuIII–GDNA] (k
0=5.74×10–5 s–1, k
1=1.93×10–2 M–1 s–1 at T=25 °C, μ=0.1), is consistent with lysis of the N-glycosidic bond by RuIV-induced general acid hydrolysis. In air, the ratio of [Ru-8-OG]/[Ru-G] and their net rates of appearance are 1.7 at pH 11,
25 °C. Small amounts of phosphate glycolate indicate a minor oxidative pathway involving C4′ of the sugar. In air, a dynamic
steady-state system arises in which reduction of RuIV produces additional RuII.
Received: 11 November 1998 / Accepted: 3 March 1999 相似文献
19.
Staniek H Krejpcio Z Iwanik K Szymusiak H Wieczorek D 《Biological trace element research》2011,143(3):1564-1575
Chromium(III) is considered as an essential element playing a role in carbohydrate and lipid metabolism, and various chemical
forms of this element are widely used in dietary supplements. A new trinuclear chromium(III) glycinate complex [Cr3O(NH2CH2CO2)6(H2O)3]+NO3− (CrGly), an analogue of Cr3 (trinuclear Cr(III) propionate complex) has been synthesized as a potential source of supplementary
Cr. In this study, we evaluated the acute toxicity class of CrGly in Wistar rats applying the OECD 423 procedure. Male and
female Wistar rats (n = 12, 6 ♀ and 6 ♂) were given by gavage either a single dose of CrGly 2,000 mg/kg body mass (equals to 300 mg Cr(III)/kg
body mass; in aqueous solution) or equivalent volumes of distilled water and fed ad libitum commercial Labofeed B diet, and observed carefully for 14 days, then sacrificed to collect blood and internal organs for biochemical and histologic
examination. No death cases were detected. No abnormalities in animal behavior, body mass gains, gross organ histology, or
blood morphology and biochemistry were observed. The results demonstrate that LD50 of CrGly is greater than 2,000 mg/kg when administrated orally to rat; thus, this compound appears to belong to the fifth
category in the GHS system or the fourth class (“unclassified”) in the EU classification system. 相似文献
20.
Igor S. Ignatyev Manuel Montejo Pilar Gema Rodríguez Ortega Juan Jesús López González 《Journal of molecular modeling》2013,19(4):1819-1834
DFT (B3LYP and M06L) as well as ab initio (MP2) methods with Dunning cc-pVnZ (n?=?2,3) basis sets are employed for the study of the binding ability of the new class of protease inhibitors, i.e., silanediols, in comparison to the well-known and well-studied class of inhibitors with hydroxamic functionality (HAM). Active sites of metalloproteases are modeled by [R3M-OH2]2+ complexes, where R stands for ammonia or imidazole molecules and M is a divalent cation, namely zinc, iron or nickel (in their different spin states). The inhibiting activity is estimated by calculating Gibbs free energies of the water displacement by metal binding groups (MBGs) according to: [R3M-OH2]2+ + MBG → [R3M-MBG]2+ + H2O. The binding energy of silanediol is only a few kcal mol?1 inferior to that of HAM for zinc and iron complexes and is even slightly higher for the triplet state of the (NH3)3Ni2+ complex. For both MBGs studied in the ammonia model the binding ability is nearly the same, i.e., Fe2+(t) > Ni2+(t) > Fe2+(q) > Ni2+(s) > Zn2+. However, for the imidazole model the order is slightly different, i.e., Ni2+(t) > Fe2+(t) > Fe2+(q) > Ni2+(s) ≥ Zn2+. Equilibrium structures of the R3Zn 2+ complexes with both HAM and silanediol are characterized by the monodentate binding, but the bidentate character of binding increases on going to iron and nickel complexes. Two types of intermediates of the water displacement reactions for [(NH3)3M-OH2]2+ complexes were found which differ by the direction of the attack of the MBG. Hexacoordinated complexes exhibit bidentate bonding of MBGs and are lower in energy for M=Ni and Fe. For Zn penta- and hexacoordinated complexes have nearly the same energy. Intermediate complexes with imidazole ligands have only octahedral structures with bidentate bonding of both HAM and dimethylsilanediol molecules. 相似文献