IR,NMR, XPS study of 1-(d-3-mercapto-2-methylpropionyl)-l-proline and its zinc complexes

Two Zn(II) complexes of captopril were prepared and characterized with different analytical methods: IR, NMR and XPS. Captopril is a molecule which has been proven to be very effective in reducing blood pressure. The ligand chelates via the OCO group to a zinc ion and via S and amidic oxygen atoms to another zinc ion when the ZnL complex is obtained. The sulphur atom and the amidic CO group are the only atoms involved in the coordination when the sodium—zinc complex, Na₂ZnL₂, is synthesized.     

Salen型双肟锌(Ⅱ)超分子配合物的合成及晶体结构

合成了一种含有Salen型双肟螯合配体4,4′,6,6′-四氯-2,2′-[乙二氧双(氮次甲基)]二酚(H₂L)的超分子锌(Ⅱ)配合物[ZnL(H₂O)₂]_n,并通过元素分析,红外光谱和X-射线单晶结构测定等对其结构进行了表征。该配合物由1个锌(Ⅱ)离子、1个L^2-配位单元和2个配位水分子组成。在配合物[ZnL(H₂O)₂]中,Salen-     

Mechanisms of formation of 8-oxoguanine due to reactions of one and two OH* radicals and the H2O2 molecule with guanine: A quantum computational study

Mechanisms of formation of the mutagenic product 8-oxoguanine (8OG) due to reactions of guanine with two separate OH* radicals and with H2O2 were investigated at the B3LYP/6-31G, B3LYP/6-311++G, and B3LYP/AUG-cc-pVDZ levels of theory. Single point energy calculations were carried out with the MP2/AUG-cc-pVDZ method employing the optimized geometries at the B3LYP/AUG-cc-pVDZ level. Solvent effect was treated using the PCM and IEF-PCM models. Reactions of two separate OH* radicals and H2O2 with the C2 position of 5-methylimidazole (5MI) were investigated taking 5MI as a model to study reactions at the C8 position of guanine. The addition reaction of an OH* radical at the C8 position of guanine is found to be nearly barrierless while the corresponding adduct is quite stable. The reaction of a second OH* radical at the C8 position of guanine leading to the formation of 8OG complexed with a water molecule can take place according to two different mechanisms, involving two steps each. According to one mechanism, at the first step, 8-hydroxyguanine (8OHG) complexed with a water molecule is formed ,while at the second step, 8OHG is tautomerized to 8OG. In the other mechanism, at the first step, an intermediate complexed (IC) with a water molecule is formed, the five-membered ring of which is open, while at the second step, the five-membered ring is closed and a hydrogen bonded complex of 8OG with a water molecule is formed. The reaction of H2O2 with guanine leading to the formation of 8OG complexed with a water molecule can also take place in accordance with two different mechanisms having two steps each. At the first step of one mechanism, H2O2 is dissociated into two OH* groups that react with guanine to form the same IC as that formed in the reaction with two separate OH* radicals, and the subsequent step of this mechanism is also the same as that of the reaction of guanine with two separate OH* radicals. At the first step of the other mechanism of the reaction of guanine with H2O2, the latter molecule is dissociated into a hydrogen atom and an OOH* group which become bonded to the N7 and C8 atoms of guanine, respectively. At the second step of this mechanism, the OOH* group is dissociated into an oxygen atom and an OH* group, the former becomes bonded to the C8 atom of guanine while the latter abstracts the H8 atom bonded to C8, thus producing 8OG complexed with a water molecule. Solvent effects of the aqueous medium on certain reaction barriers and released energies are appreciable. 5MI works as a satisfactory model for a qualitative study of the reactions of two separate OH* radicals or H2O2 occurring at the C8 position of guanine.     

Electrosynthesis and studies of adducts of 2-amino-1-methylbenzimidazole with metal chelates based on 2-tosylamino-N-salicylideneaniline

For the first time the adducts of 2-amino-I-methylbenzimidazole (L) with cobalt, copper, and zinc chelates based on 2-tosylamino-N-salicylideneaniline were electrochemically synthesized, and the properties and structures of these adducts were studied. According to the IR and₁H NMR spectral data on the adducts obtained and X-ray structural analysis of the copper complex, the adducts of composition mL · ML' · nH₂O (m = 1 or 2; n = 0, 1, or 2) contain the L moiety bonded to the metal atom through the pyridine-type N atom of the imidazole ring.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2093–2097, August, 1996.     

Bond Character of β-Diketone Metal Chelates

The vibrational spectra of molecules labeled with ²H, ¹³C, and ¹⁸O show that delocalization of double and single bonds in the six-membered ring is complete in all the metal chelates investigated of 2,4-pentanedione (acetylacetone), but not in 2,4-pentanedione itself. Mercury, on the other hand, is bonded to the central C atom of the ligands. The NMR spectra of the metal chelates of 3-mesityl-2,4-pentanedione and 3-anthryl-2,4-pentanedione show that the chelate rings have no magnetic anisotropy comparable with that of benzene. A critical appraisal is made of the questions whether it is at all justifiable to attribute any “aromatic character” to such molecules and why all comparisons with the chemical reactivity of benzene have so far led to controversial conclusions concerning the character of the bonding in the metal chelates of 2,4-pentanedione.     

Synthesis of copper(II) coordination compounds with benzoxazine derivatives

Copper(II) complexes with 1,2-dihydro-4H-3,1-benzoxazine (HL) derivatives, CuLOH, were prepared by anodic electrosynthesis. The use of an amalgamated copper anode resulted in an increase in the electrosynthesis rate. It follows from the IR spectra of the products that the benzoxazine ring in the ligand molecule is opened upon complexation, while a six-membered chelate ring involving the oxygen atom of the deprotonated phenol group and the imine nitrogen atom is formed.     

Nucleophilic substitution reactions in chromium arene phosphite dicarbonyl chelate complexes

Conclusions An F atom and PhO group on a coordinated P atom in chromium arene phosphite dicarbonyl chelate complexes undergo nucleophilic substitution when treated with PhLi without ring opening to give the corresponding arene diphenylphosphinite chelates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1900–1902, August, 1981.     

Structural Features of Uranyl Hydroxylaminate and Oximate Complexes

On the basis of the currently available uranyl complexes with hydroxylamine and its N-substituted derivatives and oximes, the coordination modes of the ligands and structural features of such complexes have been considered with the aim of determining general trends for this new family of uranium(VI) compounds. All the uranyl oximate and hydroxylaminate complexes contain a deprotonated ligand coordinated to the central atom through the nitrogen and oxygen atoms to form a stable three-membered chelate ring. Depending on the composition, these compounds can be divided into two large groups: complexes with tris(chelate) and bis(chelate) structural moieties.     

Positron lifetime diagnostics of β-diketonates of bivalent metals

Positron lifetime diagnostics was used to study manganese(II), cobalt(II), nickel(II), copper(II), and zinc(II) acetylacetonates, γ-chloro and γ-bromo chelate complexes of cobalt and nickel, and similar halo and nitro chelate complexes of copper. The dependences of the annihilation lifetime τ₂ on the metal nature and the stability constant of the metal chelate ring were established. The annihilation lifetime and intensity were found to depend not only on the electronic effect of the γ-substituent in the chelate ring but also on the structure of the complex. A comparison of the dependences of the frequencies of the C-O and M-O stretching vibrations on τ₂ revealed that a positron interacts simultaneously with the γ-carbon atoms and the O atoms of the chelate ring, whose accessibilities are determined by the structures of bis(chelates). The plots of the ionization potentials of the n-orbitals of the bis(chelates) vs. τ₂ were similar to the plots of the quenching rate constant of the benzophenone triplet vs. τ₂ in the presence of the bis(chelates).     

Rhenium chemistry of azooximes: oxygen atom transfer, azoimine chelation, and imine-oxime contrast

The concerned azooximes (L1OH, 1) are of type p-X-C6H4C(N2Ph)(NOH) (X = H, Me, Cl). The reaction of [Re(MeCN)Cl3(PPh3)2] with [Ag(L1OH)(L1O)] in cold dichloromethane-acetonitrile solvent has furnished the green colored ionized azoimine complex [ReV(O)Cl(PPh3)2(L1)](PF6), 2. In effect L1O- has undergone oxidative addition, the oxygen atom being transferred to the metal site. Upon treatment of [ReV(NPh)Cl3(PPh3)2] with L1OH in solution, the neutral azoimine complex [ReV(NPh)Cl3(L1H)], 3, resulted due to the spontaneous transfer of the oxime oxygen atom to a PPh3 ligand, which is eliminated as OPPh3. In contrast, the oxime of 2-acetylpyridine (L2OH, 4) did not undergo oxygen atom transfer and simply afforded the imine-oxime complex [ReV(NC6H4Y)Cl2(PPh3)(L2O)], 5, upon reacting with [ReV(NC6H4Y)Cl3(PPh3)2] (Y = H, Me, Cl). The spectral and electrochemical properties of 2, 3, and 5 and the structures of three representative compounds are reported. In the cation of 2 (X = H) the two PPh3 ligands lie trans to each other and the equatorial plane is defined by the five-membered azoimine chelate ring and the oxo and chloro ligands. The oxo ligand which forms a model triple bond (Re-O length 1.616(6) A) lies cis to the imine-N atom. In 3 (X = Cl) the ReCl3 fragment has meridional geometry and the imido nitrogen lies trans to the imine nitrogen of the planar azoimine chelate ring. In 5 x H2O (Y = Me), the Cl, oximato-N, and P atoms define an equatorial plane and the pyridine-N lies trans to the imido-N. The water of crystallization is hydrogen bonded to the oximato oxygen atom (O...O, 2.829(5) A). Reaction models in which chelation of the azooxime precedes oxygen atom transfer are proposed on the basis of oxophilicity of trivalent rhenium, Lewis acid activity of pentavalent rhenium, electron withdrawal by the azo group, and observed relative disposition of ligands in products.     

Preparation and characterization of cellulose acetate complexes

Summary Metal chelates of secondary cellulose acetate (SCA) with chromium(III), copper(II), cobalt(II), nickel(II) and UO ₂ ²⁺ were prepared and characterized by elemental analyses, magnetic moments and spectral studies. SCA acts as a uninegatively charged bidentate ligand and reacts with the metal ion via the oxygen atom of the secondary unacetylated hydroxyl group in the glucose subunit of the polymer, plus the oxygen atom of the vicinal ester group, to form a five-membered chelate ring.     

Synthesis and Crystal Structure of a Novel Two-dimensional Layered Polymer [Zn（μ-O2CCH=CHCO2）（C3H4N2）（H2O）]n

1 INTRODUCTION More than 200 known metalloenzymes of a wide variety of types have been shown to contain zinc centers at their active sites (such as hydrolases, ligases and anhydrases)[1～3]. The active zinc centers in biological systems are usually surro…     

Boron chelates and boron-metal chelates. XI. Constitution of Diphenylboron Chelates from Salicylaldehyde and amino compounds with functional groups

The chelates 1 — 5 were synthesized from salicylaldehyde, an amine component, and diphenylboric anhydride. Their elementary analytic and spectroscopic investigation showed that diphenylboron chelates were formed and not monophenylboron chelates (BC₆H₅ group belongs to two chelate rings). The ¹H-NMR spectroscopic investigation of the thermal decomposition products of 3 shows that, in addition to the release of the ethanol bonded by intermolecular hydrogen bridges, benzene is eliminated while the monophenylboron chelate is formed. By means of UV, IR, and NMR data (¹H, ¹³C and ¹¹B) it has been proved that 1 — 3 and 5 show ring closures in the “salicylaldehyde” part of the azomethine chelating agent.     

Crystal Structures of DOTMA Chelates from Ce3+ to Yb3+: Evidence for a Continuum of Metal Ion Hydration States

The crystal structures of chelates formed between each stable paramagnetic lanthanide ion and the octadentate polyamino carboxylate ligand DOTMA are described. A total of 23 individual chelates structures were obtained; in each chelate the coordination geometry around the metal ion is best described as a twisted square antiprism (torsion angle −25.0°–−31.4°). Despite the uniformity of the general coordination geometry provided by the DOTMA ligand, there is a considerable variation in the hydration state of each chelate. The early Ln³⁺ chelates are associated with a single inner sphere water molecule; the Ln-OH₂ interaction is remarkable for being very long. After a clear break at gadolinium, the number of chelates in the unit cell that have a water molecule interacting with the Ln³⁺ decreases linearly until at Tm³⁺ no water is found to interact with the metal ion. The Ln-OH₂ distance observed in the chelates of the later Ln³⁺ ions are also extremely long and increase as the ions contract (2.550–2.732 Å). No clear break between hydrated and dehydrated chelates is observed; rather this series of chelates appear to represent a continuum of hydration states in which the ligand gradually closes around the metal ion as its ionic radius decreases (with decreased hydration) and the metal drops down into the coordination cage.     

Selective imidazolidine ring opening during complex formation of iron(III), copper(II), and zinc(II) with a multidentate ligand obtained from 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine

The condensation of 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine yields a product with two imidazolidine rings, as proven by a solid-state X-ray structure analysis as well as by NMR solution spectra. This ligand, L1, undergoes a ring-opening reaction on complex formation with Cu(II), yielding [CuL2]2+ where L2 functions as a pentadentate ligand, containing only one imidazolidine ring. On complexation with Zn(II) and Fe(III), both rings are opened and the complexes [ZnL3]2+ and [FeL3]3+ with a hexadentate L3 ligand are formed. The recrystallization of [ZnL3]2+ from DMSO solution results in the complex [ZnL1(DMSO)2]2+ in which L1 behaves as a tetradentate ligand. Thus L1, L2, and L3 are structural isomers with two, one, or no imidazolidine rings, as confirmed by X-ray structure analyses. The intramolecular ring formation is the result of the nucleophilic addition of the N(amino) group to the electrophilic sp2-hybridized -HC delta+=N site. Owing to the absence of the chelate effect on the sp3-hybridized carbon atom belonging to the imidazolidine ring, the ring opening is facilitated and readily observed upon complex formation with Cu(II), Zn(II), and Fe(III).     

Synthesis and Study of Copper(II) Complexes with Aspartic Acid,Serine, and Valine

Binary and ternary copper(II) complexes with aspartic acid (H₂Asp), serine (HSer), and valine (HVal) were prepared by electrochemical and chemical procedures. The purity of the compounds was confirmed by elemental and thermogravimetric analyses. According to the IR spectra, all the complexes contain a five-membered chelate ring in which the Cu(II) atom is bonded with the oxygen atom of the carboxy group and nitrogen atom of the amino group. This is also confirmed by the ESR spectra.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 4, 2005, pp. 541–544.Original Russian Text Copyright © 2005 by Kryukova, Frolov, Kolokolov, Bolotin, Panyushkin.     

Radicals produced by gamma-irradiation of hyperquenched glassy water containing 2'-deoxyguanosine-5'-monophosphate

Hyperquenched glassy water (HGW) has been suggested as the best model for liquid water, to be used in low-temperature studies of indirect radiation effects on dissolved biomolecules (Bednarek et al. J. Am. Chem. Soc. 1996, 118, 9387). In the present work, these effects are examined by X-band electron spin resonance spectroscopy (ESR) in gamma-irradiated HGW matrix containing 2'-deoxyguanosine-5'-monophosphate. Analysis of the complex ESR spectra indicates that, in addition to OH(*) and HO2(*) radicals generated by water radiolysis, three species are trapped at 77 K:(i) G(C8)H(*) radical, the H-adduct to the double bond at C8; (ii) G(- *) radical anion, the product of electron scavenging by the aromatic ring of the base; and (iii) dR(-H)(*) radicals formed by H abstraction from the sugar moiety, predominantly at the C'5 position. We discuss the yields of the radicals, their thermal stability and transformations, as well as the effect of photobleaching. This study confirms our earlier suggestion that in HGW the H atom addition/abstraction products are created at 77 K in competition with HO2(*) radicals, in a concerted process following ionization of water molecule at L-type defect sites of the H-bonded matrix. The lack of OH(*) reactivity toward the solute suggests that the H-bonded structure in HGW is much more effective in recombining OH(*) radicals than that of aqueous glasses obtained from highly concentrated electrolyte solutions. Furthermore, complementary experiments for the neat matrix have provided evidence that HO2(*) radicals are not the product of H atom reaction with molecular oxygen, possibly generated by ultrasounds used in the process of sample preparation.     

Carbohydrates Containing Nitrogen or Sulfur in the “Hemiacetal” Ring

In 5-amino-5-deoxy-and 5-thioaldoses, a 6-membered hemiacetal ring can be formed by incorporation of a nitrogen or sulfur atom into the ring instead of the oxygen present in pyranoses. In the case of 5-(N-acylamido) -5- deoxyaldoses, the nucleophilic strength of the amide grouping is lowered, with the result that ring closure occurs only when sterically favored, or when a side reaction with formation of furanose is not possible. On the other hand, 5-amino-5-deoxyaldoses containing a free amino group readily from 6-membered “hemiacetal” rings. The resulting piperidinoses possess properties that are unusual in sugars, since they contain the 2-hydroxypiperidine ring system. Piperidinoses are stable to alkalis and labile to acids; they rearrange in the presence of acids to give Amadori compounds, or lose three molecules of water to give derivatives of β-hydroxypyridines. Owing to the high reactivity of the mercapto group, 5-thioaldoses from only sugars with rings containing sulfur, the behavior of which resembles that of the oxygen analogues. 4-Amino-4-deoxy- and 4-thioaldoses can form 5-membered rings containing nitrogen and sulfur.     

碱金属萃取化学的研究 III:弱酸性偶氮螯合剂化学结构对萃取锂的性能研究

The synergistic extractic extraction of lithium with a solution of o-phenylazophenols (HAX) and trioctylphosphine oxide (TOPO) or other trialkylphosphine oxide (TRPO, R = C8-10) in o-dichlorobenzene from aqueous solution of lithium hydroxide was reported. The structural effect of o-phenylazophenols on extraction of lithium has been examined. In the case of 1-(p-X-phenylazo)-2-naphthols, the HMO calculation shows that the charge density of azo nitrogen atom(the donor atom, denote azo N) and hydroxyl oxygen atom does not very apparently, so that the stability of their chelates with lithium has no obvious variations as well. In this case their ability to extract lithium is chiefly governed by the pKa. of the compound. The results of extraction prove that there is a linear correlation between the extraction constant Kex and pKa. However, for the second group of chelating agents, the change of their structure leads to the change of the change of both pKa and stability of chelates. The results of extraction and HMO calculation show that the stability of chelates is mainly influenced by the strength of the coordination bond, i.e. the larger the charge density of azo N (qN), the more stable the chelate will be. Therefore, their ability to extract lithium is roughly directly proportional to the stability of chelates and inversely to the pKa. the strength of coordination bond for the chelates can be experimentally measured by means of the strength of intramolecular hydrogen bond of chelating agent, ΔδOH (the diference of chemical shift of hydroxyl proton in free and bonded state). Therefore, the ratio, ΔδOH/pKa, can be used to evaluate the extraction ability of chelating agents to lithium. We find that it is approximately proportional to the distribution ratio (D).     

Synthesis and spectral study of chelate alkenylarenedicarbonyl complexes of Cr,Mo and W

Irradiation of alkenylarene tricarbonyl-chromium, -molybdenum, and -tungsten compounds in which the double bond is separated from the arene moiety by a two- or three-atom bridge results in intramolecular cyclization to give stable chelate alkenylarenedicarbonylmetal complexes. Chelate complexes containing four-atom bridges have low stabilities, and those with monoatomic bridges were not formed at all. Irradiation of styrenetricarbonyl-chromium and -molybdenum leads to dinuclear tricarbonylmetal—dicarbonylmetal complexes. The chelate complexes obtained have been studied by IR, proton NMR, and ¹³C NMR spectroscopy. The electron density distributions and the stereochemistry of the complexes are discussed. With nonsymmetric arenes, diastereoisomers are formed; the predominant isomers have been isolated in the pure form. According to the proton NMR data the double bond in alkenylarenechromium chelates is parallel of nearly parallel to the arene ring plane.