Ternary complexes of nickel(II) withAMP,ADP andATP as primary ligands and some biologically important polybasic oxygen acids as secondary ligands

Summary Potentiometric equilibrium measurements have been made at 25±0.1 °C (=0.1 mol dm^–3 KNO₃) for the interaction of adenosine-5-mono-, -di-, and-triphosphate (AMP,ADP, andATP) and Ni(II) with biologically important secondary ligand acids (malic, maleic, succinic, tartaric, citric and oxalic acids) in a 1:1:1 ratio and the formation of various 1:1:1 mixed ligand complex species inferred from the potentiometricpH titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants ofAMP,ADP,ATP and secondary ligand acid, have been refined with SUPERQUAD computer program. In some systems logK values are positive, i.e. the ternary complexes are found to be more stable than the corresponding binary complexes. H-bond formation seems to be most effective in deciding the stability of the ternary complexes formed in solution. Stabilities of mixed ligand complexes increases in the orderAMP<ADP<ATP. With respect to the secondary ligands, the formation constants of the mixed lignads complexes decrease in the order succinic>maleic>tartaric>malic>citric>oxalic acid.

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Ternäre Komplexe von Nickel(II) mitAMP,ADP undATP als Primärliganden und einigen biologisch wichtigen polyfunktionellen Carbonsäuren als Sekundärliganden

Zusammenfassung Es wurde die Wechselwirkung von Adenosin-5-mono-, -di- und -triphosphat (AMP,ADP undATP) und Ni(II) mit biologisch relevanten Säuren als Sekundärliganden (Äpfel-, Malein-, Bernstein-, Wein-, Zitronen- und Oxalsäure) im Verhältnis 1:1:1 mittels potentiometrischer Gleichgewichtsmessungen bei 25±0.1 °C und =0.1 mol dm^–3 KNO₃ untersucht. Aus den potentiometrischepH-Titrationen ergaben sich verschiedene 1:1:1-Komplexe mit gemischten Liganden. Zunächst abgeschätzte Komplexbildungskonstanten und Säuredissoziations-konstanten vonAMP,ADP,ATP mit den als Sekundärliganden eingesetzten Säuren wurden über das SUPERQUAD-Rechenprogramm verfeinert. In einigen Systemen sind die Werte von logK positiv, was bedeutet, daß die ternären Komplexe stabiler sind als die entsprechenden binären Komplexe. In einige ternären Komplexen scheinen die Wasserstoffbrücken zwischen den Liganden entscheidend zu sein. Die Stabilitäten der gemischten Liganden steigen in der ReiheAMP<ADP<ATP an. Bezüglich der Sekundärliganden ergibt sich die absteigende Stabilitätsreihung Bernsteinsäure>Maleinsäure>Weinsäure>Äpfelsäure>Zitronensäure>Oxalsäure.

     

Thermal properties of solid complexes with biologically important heterocyclic ligands

The stoichiometry of thermal decomposition of the complexes Ni(NCS)₂(fpy)₄ (I), Ni(NCS)₂(bfpy)₄ (II) and Ni(NCS)₂(CF₃Phfpy)₄ (III) (where fpy=furopyridine, bfpy=benzo-[2,3]furo[3,2-c]pyridine, CF₃Phfpy=2-(3-fluoromethylphenyl) furo[3,2-c]pyridine) have been investigated in nitrogen atmosphere from room temperature to 500°C by means of TG and DTG. The results revealed that release of the heterocyclic ligands occurs in two steps. IR data suggested that fpy, bfpy and CF₃Phfpy ligands were coordinated to Ni(II) through the N atom of the respective heterocyclic rings and same is the case with the anionic NCS group.     

Thermal properties of solid complexes with biologically important heterocyclic ligands

The thermal decomposition of the complexes Mg(SCN)₂(2-OHpy)₄·H₂O(I), Mg(SCN)₂(quin)₄·2H₂O(II) and Mg(SCN)(quinox)₄·5H₂O(III) (2-OHpy–2-hydroxypyridine, quin–quinoline, quinox–quinoxaline) has been investigated in static air atmosphere at 20–1000 °C by means of thermogravimetry (TG), differential thermal analysis (DTA), and infrared (IR) spectroscopy. The composition of the complexes had been identified by means of elemental analysis and complexometric titration. The possible scheme of destruction of the complexes is suggested. The final product of the thermal decomposition was MgS. IR data suggest that heterocyclic ligands were coordinated to Mg(II) through the nitrogen atom of their heterocyclic ring. Thiocyanate group is also coordinated through the nitrogen atom.     

Thermal properties of solid complexes with biologically important heterocyclic ligands

Thermogravimetry (TG), derivative thermogravimetry (DTG) and infrared (IR) spectroscopy have been applied to the investigation of the thermal behaviour and structure of the compounds [Cu(2-Clbz)₂(nia)₂(H₂O)₂] (I), [Cu(2-Clbz)₂(nia)₂]·H₂O (II), [Cu(2-Brbz)₂(nia)₂]·2H₂O (III), [Cu(2-Brbz)₂(nia)₂(H₂O)] (IV), where 2-Clbz and 2-Brbz?=?2-chloro- and 2-bromobenzoate anions, nia?=?nicotinamide, H₂O?=?water molecules. Thermal decomposition of all studied compounds proceeds in three steps. Heating the compounds first results in a release of non-coordinated and/or coordinated water molecules. The final product of thermal decomposition was CuO. The thermal stability of the complexes can be ordered in the sequence: I<IV<III<II. Nicotinamide is coordinated to Cu(II) through the nitrogen atom of the heterocyclic ring. IR data suggest the unidentate coordination of benzoate anions to Cu(II) in complexes I, IV and bidentate coordination in complexes II and III.     

Thermal properties of solid complexes with biologically important heterocyclic ligands

The stoichiometry of thermal decomposition of the complexes Co(NCS)₂(fpy)₄ (I), Co(NCS)₂(Mefpy)₄ (II) and Co(NCS)₂(bfpy)₄ (III) (where fpy = furo[3,2-c]pyridine, Mefpy = methylfuro[3,2-c]pyridine, bfpy = benzo-[2, 3]furo[3,2-c]pyridine) have been investigated in nitrogen atmosphere from room temperature (RT) to 800 °C by means of TG and DTA. The results revealed that release of heterocyclic ligands occurs in one step. Infrared data suggested that fpy, Mefpy and bfpy were coordinated to Co(II) through the nitrogen atom of the respective heterocyclic ring and anionic ligands through nitrogen atom of the NCS groups.     

Two complexes of PtIV and AuIII with 2,2′‐dipyridylamine and 2,2′‐dipyridylaminide ligands

Two noble metal complexes involving ancillary chloride ligands and chelating 2,2′‐bipyridylamine (Hdpa) or its deprotonated derivative (dpa), namely [bis(pyridin‐2‐yl‐κN)amine]tetrachloridoplatinum(IV), [PtCl₄(C₁₀H₉N₃)], and [bis(pyridin‐2‐yl‐κN)aminido]dichloridogold(III), [AuCl₂(C₁₀H₈N₃)], are presented and structurally characterized. The metal atom in the former has a slightly distorted octahedral coordination environment, formed by four chloride ligands and two pyridyl N atoms of Hdpa, while the metal atom in the latter has a slightly distorted square‐planar coordination environment, formed by two chloride ligands and two pyridyl N atoms of dpa. The difference in conjugation between the pyridine rings in normal and deprotonated 2,2′‐dipyridylamine is discussed on the basis of the structural features of these complexes. The influence of weak interactions on the supramolecular structures of the complexes, providing one‐dimensional chains of [PtCl₄(C₁₀H₉N₃)] and dimers of [AuCl₂(C₁₀H₈N₃)], are discussed.     

Thermal studies on some group VIII complexes with biologically active ligands

The mode of decomposition of complexes involving biologically important ligands such as thiouracil and xanthine coordinated to some group VIII metals has been studies by thermogravimetry. The results show that the complex tris-(dithiouracil) trichlororhodium(III) is monomeric and not polymeric as suggested previously. The decomposition behavior of the complex indicates that after the initial loss of a ligand molecule to form a four-coordinate complex, further ligand removal takes place in one sharp step. In the case of the complexes bis-(3-methylxanthine) diammineplatinum(II) and bis-(9-methylxanthine) diamminepalladium(II), ammonia comes off first, followed by rapid loss of the remaining xanthine ligands. Moreover, the activation energy determined for the main decomposition step suggests that the breakdown of the xanthine ligand involves the initial cleavage of the pyrimidine moiety, followed closely by loss of the remaining imidazole portion.

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Zusammenfassung Die Art der Zersetzung von Komplexen einiger Metalle der VIII. Gruppe mit biologisch wichtigen Liganden, wie Thiouracil and Xanthin, wurde thermogravimetrisch untersucht. Die Ergebnisse zeigen, daß der Komplex Tris-(dithiouracil) trichlororhodium(III) monomer und nicht — wie früher vermutet — polymer ist. Das Zersetzungsverhalten des Komplexes zeigt, daß nach dem zu einem tetrakoordinierten Komplex führenden Verlust eines Ligandmoleküls die Abgabe eines weiteren Liganden in einem scharfen Schritt erfolgt. Im Falle der Komplexe Bis-(3-methylxanthin) diamminplatin(II) und Bis-(9-methylxanthin) diamminpalladium(II) erfolgt zunächst eine Abspaltung von Ammoniak, der ein schneller Verlust der verbleibenden Xanthinliganden folgt. Die für die Hauptzersetzungsreaktion bestimmte Aktivierungsenergie läßt vermuten, daß der Abbau der Xanthinliganden über eine Spaltung des Pyrimidinteils verläuft, der schnell die Abgabe des verbleibenden Imidazolteils folgt.

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, , VIII . , -() (III) , , . - , . - (3-) (II) -(9 -) - (II) -(II) , . , , , , .

     

Complexes of biologically important ligands. I. Ternary complexes of nickel(II) comprising 1,10-o-phenanthrolineazosulfonamide derivatives and alkyldithiophosphates

5-[p-(R-Sulfonyl)phenylazo]-1,10-o-phenanthroline (L) and its octahedral complexes of the type [Ni(R₂dtp)₂(L)] (where R₂dtp = diethyl-or dipropyldithiophosphate) with the core NiN₂S₄ have been prepared and characterized by spectral, magnetic, and thermogravimetric methods. The thermal decomposition mechanism of the compounds was proposed and the kinetic parameters of decomposition were calculated making use of the Coats—Redfern and Horowitz—Metzger equations.     

Type I Photosensitization of 2′‐deoxyadenosine 5′‐monophosphate (5′‐dAMP) by Biopterin and its Photoproduct Formylpterin

Biopterin (Bip) and its photoproducts 6‐formylpterin (Fop) and 6‐carboxypterin (Cap) accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder where the protection against UV radiation fails because of the lack of melanin. These compounds absorb in the UV‐A inducing a potential photosensitizing action that can cause damage to DNA and other biomolecules. In this work, we have investigated the capability of these pterin derivatives (Pt) to act as photosensitizers under UV‐A irradiation for the degradation of 2′‐deoxyadenosine 5′‐monophosphate (5′‐dAMP) in aqueous solutions, as model DNA target. Steady‐state and time‐resolved experiments were performed and the effect of pH was evaluated. The results showed that photosensitized degradation of 5′‐dAMP was only observed under acidic conditions, and a mechanistic analysis revealed the participation of the triplet excited state of the pterin derivatives (³Pt*) by electron transfer yielding the corresponding pair of radical ions (Pt^?? and 5′‐dAMP^?+), with successive photosensitizer recovery by electron transfer from Pt^?? to O₂. Finally, 5′‐dAMP^?+ participates in subsequent reactions to yield degradation products.     

The mass spectra of some 5′-alkul substituted 5′-thioadenosine trimethylsilyl derivatives

Trimethylsilyl derivatives of 5′-S-alkyl substituted 5′-thioadenosines give mass spectra that are characterized by a number of highly intense ions. These ions are formed by the fragmentation of the alkyl substituted sugar moicty and are specific for the alkyl group in the substitution.     

Spectroscopic and magnetic properties of Cu(II) complexes with selected biologically important ligands

The aim of this work was to study the spectroscopic and magnetic properties of copper(II) o-, m-, p-aminobenzoates, o-, m-, p-methoxybenzoates and o-, m- and p-nitrobenzoates. The complexes were synthesized and their compositions were evaluated by elementary analysis. The infrared and Raman spectra for Cu(II) aminobenzoates, methoxybenzoates and nitrobenzoates were recorded and assigned. The obtained data were compared with those previously published for aminobenzoic, methoxybenzoic and nitrobenzoic acids and their sodium salts. The structures of Cu(II) o-, m-, p-aminobenzoates, o-, m-, p-methoxybenzoates and o-, m- and p-nitrobenzoates as well as the change in the electronic charges distribution caused by Cu(II) complex formation were discussed.     

Synthesis of 2′-Deoxyisoguanosine 5′-Triphosphate and 2′-Deoxy-5-methylisocytidine 5′-Triphosphate

The syntheses of the 5′-triphosphates of 2′-deoxyisoguanosine (=p₃isoG_d) and 2′-deoxy-5-methylisocytidine (=p₃me⁵isoC_d), two new bases for the genetic alphabet, are described. The triphosphates were synthesized from the corresponding nucleosides using a transient-protection procedure. The introduction of a methyl group at the 5-position of 2′-deoxyisocytidine remarkably improved the stability of the triphosphate. Characterization of the triphosphates included enzymatic incorporation opposite the complementary base in a template oligonucleotide.     

Ultra‐fast adenosine 5′‐triphosphate,adenosine 5′‐diphosphate and adenosine 5′‐monophosphate detection by pressure‐assisted capillary electrophoresis UV detection

Herein, we report a new CE method to measure adenine nucleotides adenosine 5′‐triphosphate, adenosine 5′‐diphosphate, and adenosine 5′‐monophosphate in red blood cells. For this purpose, 20 mmol/L sodium acetate buffer at pH 3.80 was used as running electrolyte, and the separation was performed by the simultaneous application of a CE voltage of 25 kV and an overimposed pressure of 0.2 psi from inlet to outlet. A rapid separation of these analytes in less than 1.5 min was obtained with a good reproducibility for intra‐ and inter‐assay (CV<4 and 8%, respectively) and an excellent analytical recovery (from 98.3 to 99%). The applicability of our method was proved by measuring adenine nucleotides in red blood cells.     

Crystal structure and sequential dehydration transitions of disodium guanosine 5′‐monophosphate tetrahydrate

Disodium guanosine 5′‐monophosphate was reported previously to crystallize as both the tetrahydrate and the heptahydrate. We herein report a determination of the molecular and crystal structures of the title tetrahydrated salt, 2Na⁺·C₁₀H₁₂N₅O₈P²⁻·4H₂O. It was found that the structure differs markedly from that of the heptahydrate, but greatly resembles that of disodium deoxyguanosine 5′‐monophosphate tetrahydrate. The C2′—O2′H moiety of ribose is surrounded by hydrophilic moieties and is disordered over two sites. The sugar puckering mode is O4′‐endo‐C1′‐exo at both sites and the conformation around the C4′—C5′ bond is gauche–trans. Powder X‐ray diffraction and thermal analyses revealed that the temperature‐controlled transition from the tetrahydrate to the anhydride proceeded through three intermediate phases between 40 and 60 °C at 0% relative humidity. Large induction periods were observed.     

Photophysical Properties and Photochemical Behaviour of Ruthenium(II) complexes containing the 2,2′-bipyridine and 4,4′-diphenyl-2,2′-bipyridine ligands

The temperature dependence of the emission lifetime of the series of complexes Ru(bpy)_n(4,4′-dpb) (bpy = 2,2′bipyridine, 4,4′-dpb = 4,4′-diphenyl-2,2′-bipyridine) has been studied in propionitrile/butyronitrile (4:5 v/v) solutions in the range 90–293 K. The obtained photophysical parameters show that the energy separation between the metal-to-ligand charge tranfer (³MLCT) emitting level and the photoreactive metal-centered (³MC) level changes across the series (ΔE = 3960, 4100, 4300, and 4700 cm^?1 for Ru(bpy)), Ru(bpy)2(4,4′-dpb)²⁺, Ru(bpy)(4,4′-dpb), and Ru(4,4′-dpb), respectively, where ΔE is the energy separation between the minimum of the ³MLCT potential curve and ³MLCT – ³MC crossing point. Comparison between spectral and electrochemical data indicated that the changes in ΔE are due to stabilization of the MLCT levels in complexes containing 4,4′-dpb with respect to Ru(bpy)²⁺₃. The photochemical data for the same complexes (as I^? salts) have been obtained in CH₂Cl₂ in the presence of 0.01M Cl^? upon irradiation at 462 nm. The complexes containing 4,4′-dpb are more photostable than Ru(bpy). Comparison between the data for thermal population of the ³MC photoreactive state and those for photochemistry indicated that the overall photochemical process is governed by (i) a thermal redistribution between the emitting and photoreactive excited states, and (ii) mechanistic factors, likely related to the size of the detaching ligand.     

Kinetics of the substitution reactions of some Pt(II) complexes with 5′‐GMP and L‐histidine

The reactions of platinum(II) complexes, [PtCl₂(dach)] (dach = (1R,2R)‐1,2‐diaminocyclohexane) and [PtCl₂(en)] (en = ethylenediamine) with biologically relevant ligands such as 5′‐GMP (guanosine‐5′‐monophosphate) and l ‐His (l ‐histidine) were studied by UV–vis spectrophotometry, ¹H NMR spectroscopy, and high‐performance liquid chromatography (HPLC). Spectrophotometrically, these reactions were investigated under pseudo‐first‐order conditions at 310 K in 25 mM Hepes buffer (pH 7.2) and 10 mM NaCl to prevent the hydrolysis of the complexes. The [PtCl₂(en)] complex reacts faster than [PtCl₂(dach)] in the reaction with studied nucleophiles. This confirms the fact that the reactivity of studied Pt(II) complexes depends on the structure of the inert bidentate ligand. Also, the substitution reactions with l ‐His are always faster than the reactions with nucleotide 5′‐GMP. The reactions of [PtCl₂(dach)] and [PtCl₂(en)] complexes with l ‐histidine are studied by ¹H NMR spectroscopy. The obtained rate constants are in agreement with those obtained by UV–vis. The same reactions were studied by HPLC comparing the obtained chromatograms during the reaction. The changes in intensity of signals of the free and coordinated ligand show that after a few days there is only one dominant product in the system. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 99–106, 2011     

Investigation on lanthanide binuclear complexes of 1,5-bis-(1′-phenyl-3′-methyl-5′-pyrazolone-4′)-1,5-pentanedione and 2,2′-bipyridine

The coordination of 1,5-bis-(1′-phenyl-3′-methyl-5′-pyrazolone-4′)-1,5-pentanedione (BPMPPD) and 2,2′-bipyridine (bipy) with lanthanide ions in water-alcohol solution has been studied. Binuclear complexes of the types : Ln₂(BPMPPD)₃(bipy)₂·nH₂O (n = 2 for Y, n = 4 for Eu, Gd, Dy, Ho, Er, Tm and Yb); Ln₂(BPMPPD)₃bipy·nH₂O (n = 10 for La, n = 3 for Pr, Nd, Sm and Tb) were formed. The compounds were characterized by elemental analysis, molar conductance, IR, UV, ¹H NMR spectroscopy, thermogravimetric analysis and fluorescence spectra.     

Bonding in titanocenyl complexes containing O,O′‐cyclic ligands

Density functional theory calculations show that the formal 16‐electron count of d⁰ [Cp₂Ti^IV(O,O′‐BID)]^0/1 complexes containing a O,O′‐chelated bidentate ligand O,O′‐BID of different ring size, is increased via Ti←O π bonding when both the O donor atoms carry a formal negative charge. The Ti←O π bonding occurs by symmetry lowering of the complex by either symmetrical (C_s) or unsymmetrical (C₂) folding of the O,O′‐BID ligand round the O···O axis. An NBO analysis confirms the Ti←O π charge transfer via back‐bonding. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010