Hydroxyl Group Of Ligand Research Articles

SYNTHESIS AND STRUCTURE OF BINUCLEAR GERMANIUM(IV)-THULIUM(III) COMPLEX WITH 1,3-DIAMINO-2-PROPANOLTETRAACETIC ACID

New heteronuclear Germanium(IV)‑ Thulium (III) complex with 1,3‑diamino‑2‑propanoltetraacetic acid (H5hpdta) was synthesized for the first time. Comparative analysis of IR‑spectrum of complex and ligand proved the absence of free COOH‑groups in the structure of compound – there are no ν(СООН) absorption bands in the IR‑spectra of complex. The significant shift of the ν(С‑N) absorption band (about 45 cm-1), ν(СН) (about 5 cm-1) and presence of ν(Ge‑N) and ν(Tm‑N) bands evidences that protonized nitrogen atoms form coordination bonds with metals. Two pairs of νas(СОО) and νs(СОО) absorption bands of carboxylate ions together with stretching vibrations of Ge‑O and Tm‑O bonds confirm their coordination to metals. There are also presented νas(Ge‑O‑Tm), νs(Ge‑O‑Tm), δ(OH) and δ(Ge‑OH) absorption bands in the IR‑spectrum of complex that indicates the bridging nature of deprotonated hydroxy and hydroxyl group of ligand and also hydrolyzed form of germanium in the structure of compound. During thermal decomposition of the complex in the temperature range of 90‑150 °С as a result of the endothermic effect, two molecules of crystallization water are removed into the gas phase. The further endoeffects at around 150‑220° C are seen with the removal of three coordinated water molecules. The oxidative destruction of the complexes is accompanied by the three exoeffects in temperature range 220‑800 °С. The products of final thermal destruction at 1000°C are GeO2 and Tm2O3. According to the X‑Ray diffraction data of complex [Ge(ОН)(μ‑hpdta)(μ‑OH) Tm(H2O)3]*2H2O, the six‑coordinated atom of Germany and octa‑coordinated atom of Thulium are bound by the bridging oxygen atom of hydroxyl group and hydroxyl-anion. Thecoordination polyhedron of Ge(1) atom is a distorted octahedron formed by three O atoms of deprotonated carboxyl and hydroxyl groups, the nitrogen atom of the hpdta5– and two O atoms of two hydroxyl-anions. The coordination polyhedron of octa-coordinated atom of Thulium is formed by of the O atoms of deprotonated carboxyl, deprotonated hydroxyl groups of the hpdta5–, the bridging oxygen atom of hydroxyl‑anion, three O atoms of coordinated water molecules and one N‑atom of the hpdta5–.

Sonochemical synthesis of amphoteric Cu0-Nanoparticles using Hibiscus rosa-sinensis extract and their applications for degradation of 5-fluorouracil and lovastatin drugs

Recent studies reported the detection of numerous emerging and active pharmaceutical constituents in the ground and surface water. To address these issues, the present study reported the ultrasound-assisted synthesis of zero-valent copper (Cu0) nanoparticles using Hibiscus rosa-sinensis extract as reducing and stabilizing agent. The catalyst was characterized using XRD, SEM, EDX, PSA, BET, etc., and the results revealed that sonochemical synthesis technique influenced the crystallinity with controlled growth of Cu0. While the hard ligand hydroxyl group (−OH) reduces the Cu2+ to Cu0 and soft ligand carbonyl group (CO) present in the oxidized polyphenols helps in capping and stabilizing the Cu0-nanoparticles. During the ultrasound application, continuous release of Cu+ from Cu0 promoted the degradation by producing OH and O2•− radicals. Approx. 91.3 % and 93.2 % degradation efficiencies were achieved for 5-fluorouracil and lovastatin. The results showed that Cu0 nanoparticles were amphoteric in nature and the synergy calculation revealed that ultrasound has a direct influence on degradation of drugs which are difficult to degrade/mineralize using conventional techniques. Based on the results, a possible degradation mechanism of drug molecules in the presence of oxidants, zero-valent copper and ultrasound has been proposed.

Spectroscopic and Theoretical Studies of Some Bivalent Metal Complexes of a Quinoline Schiff Base Derivative

Interaction of M(II) ions, M=Co, Ni, Cu, Zn, and Pd, with a Schiff base ligand (HL), derived from the condensation of 2-hydroxy-5-nitrobenzaldehyde and 8-aminoquinoline, gave the complexes [Co(L)2(H2O)2], [Ni(L)2(H2O)2], [Cu(L)(H2O)]CH3COO, [Zn(L)(H2O)]CH3COO, and [Pd(HL)Cl2]. The ligand and its complexes were characterized by means of elemental and thermal analyses, molar conductance, and magnetic moment measurements along with the different spectroscopic techniques. Theoretical calculations based on DFT were carried out to verify the optimized structures of ligand and complexes. The relative reactivity of the compounds was estimated from chemical descriptors analysis using the HOMO and LUMO frontier orbitals. Molecular docking of ligand and its zinc complex revealed that the interaction of Zn(L) with DNA is comparable to that of HL due to the presence of water OH groups instead of the hydroxyl group of ligand.

Effect of Noncanonical Amino Acids on Protein-Carbohydrate Interactions: Structure, Dynamics, and Carbohydrate Affinity of a Lectin Engineered with Fluorinated Tryptophan Analogs.

Protein–carbohydrate interactions play crucial roles in biology. Understanding and modifying these interactions is of major interest for fighting many diseases. We took a synthetic biology approach and incorporated noncanonical amino acids into a bacterial lectin to modulate its interactions with carbohydrates. We focused on tryptophan, which is prevalent in carbohydrate binding sites. The exchange of the tryptophan residues with analogs fluorinated at different positions resulted in three distinctly fluorinated variants of the lectin from Ralstonia solanacearum. We observed differences in stability and affinity toward fucosylated glycans and rationalized them by X-ray and modeling studies. While fluorination decreased the aromaticity of the indole ring and, therefore, the strength of carbohydrate–aromatic interactions, additional weak hydrogen bonds were formed between fluorine and the ligand hydroxyl groups. Our approach opens new possibilities to engineer carbohydrate receptors.

Effects of arginine on multimodal anion exchange chromatography

The effects of arginine on binding and elution properties of a multimodal anion exchanger, Capto adhere, were examined using bovine serum albumin (BSA) and a monoclonal antibody against interleukin-8 (mAb-IL8). Negatively charged BSA was bound to the positively charged Capto adhere and was readily eluted from the column with a stepwise or gradient elution using 1M NaCl at pH 7.0. For heat-treated BSA, small oligomers and remaining monomers were also eluted using a NaCl gradient, whereas larger oligomers required arginine for effective elution. The positively charged mAb-IL8 was bound to Capto adhere at pH 7.0. Arginine was also more effective for elution of the bound mAb-IL8 than was NaCl. The results imply that arginine interacts with the positively charged Capto adhere. The mechanism underlying the interactions of arginine with Capto adhere was examined by calculating the binding free energy between an arginine molecule and a Capto adhere ligand in water through molecular dynamics simulations. The overall affinity of arginine for Capto adhere is attributed to the hydrophobic and π–π interactions between an arginine side chain and the aromatic moiety of the ligand as well as hydrogen bonding between arginine and the ligand hydroxyl group, which may account for the characteristics of protein elution using arginine.

Polarizable Water Networks in Ligand–Metalloprotein Recognition. Impact on the Relative Complexation Energies of Zn-Dependent Phosphomannose Isomerase with d-Mannose 6-Phosphate Surrogates

Using polarizable molecular mechanics, a recent study [de Courcy et al. J. Am. Chem. Soc., 2010, 132, 3312] has compared the relative energy balances of five competing inhibitors of the FAK kinase. It showed that the inclusion of structural water molecules was indispensable for an ordering consistent with the experimental one. This approach is now extended to compare the binding affinities of four active site ligands to the Type I Zn-metalloenzyme phosphomannose isomerase (PMI) from Candida albicans. The first three ones are the PMI substrate β-D-mannopyranose 6-phosphate (β-M6P) and two isomers, α-D-mannopyranose 6-phosphate (α-M6P) and β-D-glucopyranose 6-phosphate (β-G6P). They have a dianionic 6-phosphate substituent and differ by the relative configuration of the two carbon atoms C1 and C2 of the pyranose ring. The fourth ligand, namely 6-deoxy-6-dicarboxymethyl-β-D-mannopyranose (β-6DCM), is a substrate analogue that has the β-M6P phosphate replaced by the nonhydrolyzable phosphate surrogate malonate. In the energy-minimized structures of all four complexes, one of the ligand hydroxyl groups binds Zn(II) through a water molecule, and the dianionic moiety binds simultaneously to Arg304 and Lys310 at the entrance of the cavity. Comparative energy-balances were performed in which solvation of the complexes and desolvation of PMI and of the ligands are computed using the Langlet-Claverie continuum reaction field procedure. They resulted into a more favorable balance in favor of β-M6P than α-M6P and β-G6P, consistent with the experimental results that show β-M6P to act as a PMI substrate, while α-M6P and β-G6P are inactive or at best weak inhibitors. However, these energy balances indicated the malonate ligand β-6DCM to have a much lesser favorable relative complexation energy than the substrate β-M6P, while it has an experimental 10-fold higher affinity than it on Type I PMI from Saccharomyces cerevisiae. The energy calculations were validated by comparison with parallel ab initio quantum chemistry on model binding sites extracted from the energy-minimized PMI-inhibitor complexes. We sought to improve the models upon including explicit water molecules solvating the dianionic moieties in their ionic bonds with the Arg304 and Lys310 side-chains. Energy-minimization resulted in the formation of three networks of structured waters. The first water of each network binds to one of the three accessible anionic oxygens. The networks extend to PMI residues (Asp17, Glu48, Asp300) remote from the ligand binding site. The final comparative energy balances also took into account ligand desolvation in a box of 64 waters. They now resulted into a large preference in favor of β-6DCM over β-M6P. The means to further augment the present model upon including entropy effects and sampling were discussed. Nevertheless a clear-cut conclusion emerging from this as well as our previous study on FAK kinase is that both polarization and charge-transfer contributions are critical elements of the energy balances.

High-resolution steady-state and time-resolved luminescence studies on the complexes of Eu(III) with aromatic or aliphatic carboxylic acids

Eu(III) luminescence spectroscopy, both in the steady-state and the time-resolved mode, is an appropriate technique to study the properties of complexes between heavy metal ions and humic substances (HS), which play a key role in the distribution of metal species in the environment. Unfortunately, room temperature luminescence spectra of Eu(III) complexes with aromatic and aliphatic carboxylic acids – model compounds of HS binding sites – are too broad to fully exploit their potential analytical information content. It is shown that under cryogenic conditions fluorescence-line-narrowing (FLN) is achieved, and the highly resolved spectra provide detailed information on the complexes. Ten model ligands were investigated. Total luminescence spectra (TLS) were recorded, using the 5D 0 ← 7F 0 transition for excitation and the 5D 0 → 7F 1 and 5D 0 → 7F 2 transitions for emission. The energy of the excitation transition depends on the ligand involved and the structure and composition of the complex. For most ligands, discontinuities in the high-resolution TLS indicated that more species, i.e. distinct complex structures, coexisted in the sample. Selective excitation was performed to measure the species-associated luminescence decay times τ. The latter strongly depend on nearby OH oscillators from coordinating water molecules or ligand hydroxyl groups. Furthermore, the asymmetry ratios r, defined as the intensity ratio of the 5D 0 → 7F 2 and 5D 0 → 7F 1 transitions, were calculated and the variation of the excitation energy E exc with the splitting of the 7F 1 triplet (Δ E) was determined, which yielded the crystal field strength parameter N ν( B 2 q ), as well as the crystal field parameters B 20 and B 22. An in-depth analysis of the results is presented, providing detailed information on the number of coexisting complexes, their stoichiometry, the number of water molecules in the first coordination sphere and their geometry (symmetry point group).

The structure of N,N′-bis(2-hydroxyethyl)ethane-1,2-diamine and its complexes with Zn(ii) and Cd(ii)

The crystal structure of the nitrate salt of N,N'-bis(2-hydroxyethyl)-ethane-1,2-diamine (BHEEN), and its complex with Zn(II) and Cd(II) are reported. (H(2)BHEEN)(NO(3))(2) packs in a layered structure with a herringbone pattern within each layer arising from H-bonding between amino and alcohol protons and NO(3)(-) counterions. In [Zn(BHEEN)(2)]Cl(2), each ligand coordinates to Zn(II) through its two N-donors producing a distorted tetrahedral geometry at the metal centre. The two hydroxyethyl arms of each ligand are trans to each other and the crystals obtained contained a racemic mixture of the bis-trans-R,R and the bis-trans-S,S isomers. All four hydroxyl groups are H-bonded to chloride counter ions, creating a layered structure. Whilst distant from the metal ion (average 3.00 A), the four O atoms of the pendent hydroxylamino groups appear positioned to interact with the metal. The orientation of the arms is preserved in a B3LYP gas phase calculation of the structure. An analysis using Bader's Atoms in Molecules indicates that the Zn-N bonds are predominantly ionic with some covalent character and that there is a weak interaction between the metal and the hydroxyl groups. Several other weak interactions including four O...HN, five O...HC and a H-H dihydrogen bond were identified. The Cd(II) complex of BHEEN crystallised as a dimer [(mu-Cl)(2)(Cd(BHEEN)Cl)(2))] with two asymmetrically-bound bridging Cl(-) ligands and a terminally-coordinated Cl(-) on each metal ion. One hydroxyl group of each ligand is coordinated to the metal and the uncoordinated hydroxyl group is H-bonded to the H atom of the coordinated hydroxyl group of the second ligand in the complex. The ESI-MS spectrum shows the presence of di-cadmium complexes, but the most intense peaks are due to mono-cadmium complexes. The gas phase B3LYP structure of the dimer energy-minimises into two monomers and the longer bond between Cd(II) and bridging Cl(-) breaks. Hence, dimerisation may be a consequence of the crystallisation process and the dimer may not be the predominant species in solution.

Gemini metallomicellar catalysis: Hydrolysis of p-nitrophenyl picolinate catalyzed by Cu(II) and Ni(II) complexes of macrocyclic ligands in gemini surfactant micelles

Cu(II) and Ni(II) complexes of two hexaaza macrocyclic ligands with and without pendant hydroxyl groups, 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane ( 1) and 3,10-bis(2-ethyl)-1,3,5,8,10,12-hexaazacyclotetradecane ( 2), were synthesized. Effects of these complexes on the hydrolysis of p-nitrophenyl picolinate (PNPP) in micelles of cationic gemini surfactants with different spacer lengths, alkanediyl-α,ω-bis(dimethyl dodecylammonium bromide) (designated as 12- s-12, s = 2, 3 and 6), have been investigated at 25 °C. The results showed that metallomicelle systems containing gemini surfactants exhibited more efficient activities for hydrolysis of PNPP than those containing the corresponding single-chained conventional surfactant dodecyltrimethyl-ammonium bromide (DTAB). For gemini surfactants, it was found that catalytic activity of the metallomicellar systems containing the surfactant 12-2-12 was lower than those of surfactants 12-3-12 and 12-6-12. In addition, metal complexes of microcyclic ligand 1 bearing pendant hydroxyl groups showed higher catalytic activities than corresponding metal complexes of 2 without hydroxyl group, indicating that ligand hydroxyl groups play an important role for catalyzed hydrolysis of PNPP in metallomicellar systems.

Accelerated Hydrolysis of p‐Nitrophenyl Picolinate Catalyzed by Metallomicelle Made from a Novel Macrocyclic Polyamine Copper(II) Complex

AbstractA copper(II) complex 1 of a novel macrocyclic polyamine ligand with hydroxylethyl pendant groups, 4,11‐bis(hydroxylethyl)‐5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane (L) has been synthesized and characterized. Rate enhancement for hydrolysis of p‐nitrophenyl picolinate (PNPP) catalyzed by 1 was studied kinetically under Brij35 micellar condition. For comparision, the catalytic activity of corresponding copper(II) complex 2 of non‐substituted macrocyclic polyamine ligand, 5,7,7,12,14,14‐hexamethyl‐1,4,8,11‐tetraaza‐cyclote‐ tradecane (L′) toward the hydrolysis of PNPP was also investigated. The results indicate that the macrocyclic polyamine copper(II) complex 1 effectively catalyzed the hydrolysis of PNPP, and the pendant ligand hydroxyl group or deprotonated pendant ligand hydroxyl group can act as catalytically active species in the reaction. A ternary complex kinetic model involving metal ion, ligand and substrate has been proposed, and the results confirmed the reasonability of such kinetic model.

Addition of carbon tetrachloride to olefins in the presence of copper complexes with polyfunctional ligands chemically immobilized on the surface of silica

Homogeneous and heterogeneous catalysts containing copper complexes with amino alcohols and hydroxy amino acids were synthesized. Heterogenized systems were immobilized on the surface of silica by covalent bonding of the hydroxyl groups of ligands to the silanol groups of silica. The resulting complexes were active in the reactions of CCl4 addition to multiple bonds of olefins. In the case of 1-octene, the activity of heterogeneous catalysts was an extremal function of metal concentration on the surface, whereas a symbatic relationship was observed for a chlorinated olefin (allyl chloride). The above effects were explained by the participation of different copper complexes, in particular, of different nuclearity, in reactions with different olefins.

Enhanced Hydrolysis of Carboxylic Acid Esters Catalyzed by Metallomicelles Made of Cu(II) and Zn(II) Complexes

Rate enhancement for hydrolysis of p-nitrophenyl picolinate (PNPP) and p-nitrophenyl acetate (PNPA) at 25°C in the pH range 6.5–8.5 have been measured kinetically in the presence of Cu(II) and Zn(II) complexes of substituted long alkyl pyridine ligand (L) under buffered co-micellar conditions with cationic surfactant CTAB. The results indicate that the activated ligand hydroxyl group can act as effective nucleophilic species in the reactions, and the complexes, especially that with Zn(II), effectively catalyze the hydrolysis of PNPP, which can be explained by the higher nucleophilicity of alkoxyl anion in Zn(II) complex than that in Cu(II) complex. A ternary complex kinetic model involving metal ion, ligand, and substrate and a bimolecular micellar reaction model have been proposed for the catalytic hydrolysis of PNPP and PNPA, respectively. Relative kinetic and thermodynamic parameters have been obtained, and the results confirmed the reasonability of such kinetic models.

Hydrolytic Metalloenzyme Models. Metal Ion Dependent Site-Selective Acylation of Hydroxyl Groups of Bis-Imidazole Ligands Catalyzed by Zn2+ and Cu2+ in the Reaction with p-Nitrophenyl 2-Pyridinecarboxylate in a Cationic Surfactant Micelle

Abstract Co-micelles of hexadecyltrimethylammonium bromide and a lipophilic bis-imidazole ligand, 1-dodecyl-4-hydroxymethyl-α-(1-dodecyl-2-imidazolyl)-2-imidazolemethanol (4) having two primary and secondary hydroxyl groups, together with the co-micelles of the related lipophilic ligands, were investigated for their catalytic activities in the hydrolysis of p-nitrophenyl 2-pyridinecarboxylate (PNPP) in the presence of Zn2+ or Cu2+. The kinetic and product analyses indicated that the reaction proceeds through the transacylation from PNPP to the hydroxyl group of ligand : metal ion complexes and that the active complexes undergoing transacylation are a 2 : 1 and a 1 : 1 complex for Zn2+ and a 1 : 1 complex for Cu2+, respectively. As for the ligand 4, the transacylation was found to be highly site-selective, i.e. it occurred predominantly on the secondary hydroxyl group with Zn2+, while on the primary hydroxyl group with Cu2+, respectively. Such selectivity was discussed in terms of the coordination structures of the active complexes.

Hydrolytic Metalloenzyme Models. Effects of AOT Reverse Micelles on the Hydrolysis of p-Nitrophenyl Picolinate Catalyzed by Zn2+ and Cu2+ Complexes of N-Alkyl-2-hydroxymethylimidazoles

Abstract The catalytic effects of bivalent metal ion (Zn2+ and Cu2+) complexes of N-alkyl-2-hydroxymethylimidazoles on the hydrolysis of p-nitrophenyl picolinate (PNPP) have been studied kinetically in the reverse micelles of AOT/hexane/water at 25 °C. The results were compared with those obtained in the non-micellar aqueous media and aqueous micelles. The hydrolysis was observed to occur through the acyl group transfer from PNPP to the ligand hydroxyl group in both cases of Zn2+ and Cu2+ ions and in all three non-micellar and micellar systems. However, the ligand:metal ion ratio in the kinetically active complexes was found to differ significantly in the three systems: there seems to exist general trends of 1 : 1, 2 : 1, and 4 : 1 stoichiometry in the ligand:metal ion ratio, depending on non-micellar aqueous media, aqueous micelles and reverse micelles, respectively. It was also noticed that the hydrolysis is always faster in micellar systems than in non-micellar aqueous media. Furthermore, a lipophilic ligand (N-dodecyl, Lig-12) was found to be more active than a hydrophilic ligand (N-methyl, Lig-1) under two micellar conditions.

Hydrolytic Metalloenzyme Models. Metal Ion Dependent Site-selective Acylations of Hydroxyl Groups of Bis-imidazole Ligands Promoted by Zn2+ and Cu2+ Ions in Cationic Micelles

Abstract Co-micelles of cetyltrimethylammonium bromide and lipophilic bis-imidazole ligands having primary and secondary hydroxyl groups in their side chains were investigated for their catalytic activities in the hydrolysis of p-nitrophenyl picolinate in the presence of Zn2+ and Cu2+ at 25 °C. The kinetic and product analyses strongly suggested that the site-selective acylation of hydroxyl groups of ligands occurs via the formation of a tetrahedral for Zn2+ ion and a square planar complex for Cu2+ ion.

A multinuclear ( 1H, 13C, 113Cd) nuclear magnetic resonance and magnetic circular dichroism spectroscopic study of thiolate complexes of cadmium

Appropriate combinations of 1H, 13C and 113Cd NMR have been used to study ca. 0.05 M solutions of a wide range of 113Cd-enriched thiolatocadmates formed from the corresponding poorly soluble cadmium thiolates in the presence of excess thiolate. In addition, MCD spectra have been recorded for dilute, ca. 10 −5 M, solutions of a representative set of thiolate complexes of cadmium. Cadmium-113 chemical shifts are given for the complexes formed by 31 different thiolates individually in water at ambient probe temperature, and slow-exchange 1H and/or 13C and/or 113Cd NMR spectra are reported for several typical complexes at reduced temperature in CD 3OD. In aqueous solution at ambient probe temperature, ligands with vicinal thiolate groups ▪ and −SCH 2CHRS − (R = H, Me, Et, CH 2OH, CH 2SO − 3 or CH 2S −)) form bis(chelate) complexes which have δ Cd ⪖ 778 ppm, less shielded than the range for tetrahedral cd(SR) 2− 4 (R = Me, Et, Pr, Me 2CH, Bu, EtMeHC, Ph, PhCH 2, CH 2CH 2X (X = OH, NH 2, or CO − 2, CH 2CH(OH)Me, CH 2CH(OH)CH 2OH, LCH 2CH(NH 2)CO − 2, or CH 2CO − 2 for which δ Cd < 666 ppm. Increasing alkyl substitution kin the α-position causes increasing shielding of the cadmium resonance for both the chelate complexes and the complexes of monodentate thiolates. Separate 113Cd and, in some cases, 1H resonances have been found for members of the series [Cd(SR) n(SR′) 4−n] 2− (R = Me, R′ = CHMe 2; R = Ph, R′ = CH 2Ph; n = 0−4) and [Cd(S(CH 2 2S) n/2(SCHMe 2) 4−n 2− (n = 0,2, or 4) at low temperature: 113Cd chemical shifts change additively or near-additively in these series. The MCD data indicate that in most of the complexes formed at the ca. 10 −5 M concentrations used for the optical studies, the local microsymmetry about the cadmium approaches tetrahedral. Specifically, the complexes [Cd(SR) 2.5] 0.5n− n (R = Me, Et, or Pr) exhibited well-resolved, symmetric A terms under the S → Cd charge transfer band in the 250 nm region. Complexes of the dithiolates −S(CH 2 nS − (n = 2,3, or 4) and −SCH 2CHMeS − gave MCD spectra which were much broader and less well-resolved. The spectra of the systems containing the vicinal dithiolates showed the formation of two complexes, as the band centre of the MCD signal blue-shifted when L/M was increased from 1 to 2; at L/M = 2, bis(dithiolate) complexes are most likely formed. With the ligand −SCH 2CHCH 2OH (BAL), the corresponding S − spectra were similar at L/M = 2 but quite different at L/M = 1. A B term centred on the 250 nm charge transfer band was observed for the solution where BAL/Cd = 1, demonstrating loss of tetrahedral symmetry about cadmium, probably due to ligation by the ligand hydroxyl group. These studies provide 113Cd NMR and MCD ‘fingerprint’ data necessary for the interpretation of the corresponding spectra of related and more complicated, biologically important cadmium complexes.

Stability Order in Metal Chelate Compounds. IV. 2-Pyridylmethanol Complexes

Abstract The complexing behavior of 2 - pyridylmethanol with magnesium(II), manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) has been studied in aqueous media at 25.0±0.1°C and an ionic strength of 0.10 m (KNO3). The stability constants for the 1 : 1 (ligand to metal) complexes of manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) with the neutral 2-pyridylmethanol and also for the 2 : 1 complexes of nickel(II) and copper(II) have been evaluated. The resulting stability order with respect to the bivalent metals has been found to follow the sequence: Cd(II)&amp;lt;Mn(II)&amp;lt;Zn(II)&amp;lt;Co(II)&amp;lt;Ni(II)&amp;lt;Cu(II) The higher stability of the present complexes relative to the corresponding pyridine complexes may be ascribed to the formation of a chelate ring which involves the hydroxyl group of the ligand. After the complex formation between metal ions and the neutral ligand has proceeded to a certain extent, the liberation of a hydroxyl proton from the complex was observed to occur in several metal complex systems. This tendency was greatest for the copper complex, followed by the zinc, nickel and cobalt complexes in this order. Acid dissociation constants for the 1:1 and 2:1 copper complexes have also been evaluated. Several pieces of evidence have been obtained in support of the coördination ability of the hydroxyl group of the present ligand in its anionic form. The neutral copper chelate, bis(2-pyridylmethanolato)copper(II), as well as other various copper 2-hyridylmethanolate chelates which involve acetate, chloride, iodide, nitrite and thiocyanate ions as the third component, has been isolated. Acetato(2-pyridylmethanolato)-copper(II) has been found to exist as the tetrameric form in chloroform.

Reaction of iron III with hydroxyaminoacids : N,N-dihydroxyethylglycineiron II

The stoichiometry and equilibrium for the reaction of iron III with N,N-dihydroxyethylglycine in aqueous medium has been investigated. Iron III is shown to'form only a 1:1 complex with the ligand; previous reports of a 2:3 complex are demonstrated to be erroneous, and probably resulted from non-equilibrium titration measurements. Using a modified Bjerrum titration procedure, the equilibrium constant for. the formation of the 1:1 complex at 25° has been determined to be 3.8 × 10 −6 moles 2 litre 2 . Attempts to differentiate between alternative structures for the complex are inconsequential, because the complex exists only in aqueous medium, where the ligand hydroxyl groups exchange rapidly with solvent water.