Search

The two coordinatively unsaturated complexes [[Cu(cyclam)].sup.2+] (cyclam: 1,4,8,11-tetraazacyclotetradecane, 1) and [[Cu([Bn.sub.4]cyclam)].sup.2+] (Bn4cyclam: 1,4,8,11-tetrabenzyl-1,4,8,11- tetraazacyclotetradecane, 2) in an MeCN solution uptake an anion [X.sup.-] (halide, pseudohalide) to give square pyramidal ternary complexes, whose stability has been determined through spectrophotometric titration experiments. The formation of a five-cordinate complex is favored by the trans-1 configuration of the [[Cu([Bn.sub.4]cyclam)].sup.2+] receptor, but it is contrasted by the severe steric repulsions exerted by the benzyl substituents on the macrocyclic framework. No significant repulsive effects have been observed in anion binding to the [[Cu(cyclam)].sup.2+] receptor, exhibiting a trans-111 configuration. The existence of a linear relationship between the magnitude of the red shift experienced by the d-d absorption band on anion binding and log K values is discussed. Key words: tetraamine macrocycles, anion recognition, five-coordinate complexes, spectroscopic properties/thermodynamic quantities linear relationships. Les complexes coordinativement insatures [[Cu(cyclam)].sup.2+] (cyclam : 1,4,8,11-tetraazacyclotetradecane, 1) et [[Cu([Bn.sub.4]cyclam)].sup.2+] (Bn4cyclam : 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclotetradecane, 2) dans une solution de MeCN solution se fixent a un anion X(halogenure, pseudo-halogenure) pour former des complexes ternaires pyramidaux a base carree dont la stabilite a ete determinee a l'aide d'experiences de titrage spectrophotometriques. La formation d'un complexe pentacoordonne est favorisee par la conformation trans-1 du recepteur [[Cu([[Bn.sub.4]cyclam)].sup.2+] mais elle est genee par les fortes repulsions steriques exercees par les substituants benzyles sur la structure macrocyclique. Aucun effet repulsif significatif n'a ete observe au niveau de la liaison de l'anion au recepteur [[Cu(cyclam)].sup.2+], qui presentait une conformation trans-111. L'existence d'une relation lineaire entre la magnitude du decalage vers le rouge que subit la bande d'absorption d-d au niveau de la liaison anionique et les valeurs de log K est analysee. [Traduit par la Redaction] Mots-cles : tetraamines macrocycliques, reconnaissance anionique, complexes pentacoordonnes, relations lineaires entre proprietes spectroscopiques et quantites thermodynamiques., Introduction Classical coordination chemistry, that involving metal ions, originated from the studies of Alfred Werner on the ammonia complexes with substitutionally inert metal ions ([Co.sup.III], [Cr.sup.III], [Pt.sup.IV]) and dates back [...]

New iron (II) bis(dimethylglyoximatoborate) complexes [Fe[[(dmgB[R.sub.2]).sub.2](MePz)L].sup.+], R = 4-methoxyphenyl and L = Nmethylpyrazinium ion (MePz), tetracyanoethylene (tcne), carbon monoxide, or pyridine are described. The dicationic bis MePz derivative is the first example of a complex containing two small cationic ligands. All adopt the [C.sub.2v] conformation in solution, which serves to sandwich one axial ligand between 4-methoxyphenyl groups. Charge transfer spectra, conformational dynamics, and electrospray mass spectrometry studies are reported. Equilibrium and rate constants for ligand substitution reactions give a binding order trans to MePz: MePz ~ CO < pyridine, C[H.sub.3]CN. Key words: iron dimethylglyoximatoborate, N-methylpyrazinium ion, cationic ligand, tetracyanoethylene. De nouveaux complexes de bis(dimethylglyoximatoborate) de fer(II) ([[Fe[(dmgB[R.sub.2]).sub.2](MePz)L].sup.+], oU R = 4-methoxyphenyl et L = N-ion methylpyrazinium (MePz), tetracyanoethylene (TCNE), monoxyde de carbone ou pyridine) sont decrits dans le present article. Le derive dicationique bis-MePz est le premier exemple de complexe contenant deux petits ligands cationiques. Tous adoptent la conformation [C.sub.2v] en solution, qui permet a un ligand axial d'etre pris en tenaille entre des groupes 4-methoxyphenyl. Le present article presente les spectres de transfert de charge, la dynamique conformationnelle et les analyses a l'aide d'un spectrometre de masse par electronebulisation. En comparant les constantes d'equilibre et de vitesse des reactions de substitution, on peut classer les liaisons en trans par rapport a MePz selon l'ordre suivant : MePz ~ CO < pyridine, C[H.sub.3]CN. [Traduit par la Redaction] Mots-cles : dimethylglyoximatoborate de fer, ion N-methylpyrazinium, ligand cationique, tetracyanoethylene., Introduction Extensive studies of a variety of low-spin iron (II) diborylated dioxime complexes Fe[([dmgBF.sub.2]).sub.2]LT and Fe[([dmgBPh.sub.2]).sub.2]LT have been described previously. (1) The axial ligands L or T include 2-aminobutane (2-BuN[H.sub.2], [...]

The acidity constants of protonated 9-[2-(phosphonomethoxy)ethyl]-2-amino-6-dimethylaminopurine ([H.sub.3] [(PME2A6DMAP).sup.+]) are considered, and the stability constants of the M[(H;PME2A6DMAP).sup.+] and M(PME2A6DMAP) complexes ([M.sup.2+] = [Mg.sup.2+], [Ca.sup.2+], [Sr.sup.2+], [Ba.sup.2+], [Mn.sup.2+], [Co.sup.2+], [Ni.sup.2+], [Cu.sup.2+], [Zn.sup.2+], or [Cd.sup.2+]) were measured by potentiometric pH titrations in aqueous solution (25°C; I = 0.1 mol/L, NaN[O.sub.3]). In the M[(H;PME2A6DMAP).sup.+] species, [H.sup.+] and [M.sup.2+] (mainly outersphere) are at the phosphonate group; this is relevant for phosphoryl-diester bridges in nucleic acids because, in the present system, there is no indication for a [M.sup.2+]- purine binding. This contrasts, for example, with the complexes formed by 9-[2-(phosphonomethoxy)ethyl]adenine, M[(H;PMEA).sup.+], where [M.sup.2+] is mainly situated at the adenine residue. Application of log [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] plots for simple phosph(on)ate ligands, [R-P[O.sub.3.sup.2-] (R being a residue that does not affect [M.sup.2+] binding), proves that all M(PME2A6DMAP) complexes have larger stabilities than what would be expected for a [M.sup.2+]-phosphonate coordination. Comparisons with M(PME-R) complexes, where R is a noncoordinating residue of the (phosphonomethoxy)ethane chain, allow one to conclude that the increased stability is due to the formation of fivemembered chelates involving the ether-oxygen of the -C[H.sub.2]-O-C[H.sub.2]-P[O.sub.3.sup.2-] residue: the percentages of formation of these [M(PME2A6DMAP).sub.cl/O] chelates, which occur in intramolecular equilibria, vary between 20% ([Sr.sup.2+], [Ba.sup.2+]) and 50% ([Zn.sup.2+], [Cd.sup.2+]), up to a maximum of 67% ([Cu.sup.2+]). Any [M.sup.2+] interaction with N3 or N7 of the purine moiety, as in the parent M(PMEA) complexes, is suppressed by the (C2)N[H.sub.2] and (C6)N [(C[H.sub.3]).sup.2-] substituents. This observation, together with the previously determined stacking properties, offers an explanation why [PME2A6DMAP.sup.2-] has remarkable therapeutic effects. Key words: acyclic nucleoside phosphonates, antivirals, intramolecular equilibria, metal-ion complexes, nucleotide analogues, stability constants. Les constantes d'acidite de la 9-[2-(phosphonomethoxy)ethyle]-2-amino-6-dimethylaminopurine protonee, [H.sub.3][ (PME2A6DMAP).sup.+], ont ete etudiees et les constantes de stabilite des complexes M[(H;PME2A6DMAP).sup.+] et M(PME2A6DMAP) ([M.sup.2+] = [Mg.sup.2+], [Ca.sup.2+], [Sr.sup.2+], [Ba.sup.2+], [Mn.sup.2+],[Co.sup.2+],[Ni.sup.2+],[Cu.sup.2+],[Zn.sup.2+] ou [Cd.sup.2+]) mesurees par titrages pH potentiometriques en solution aqueuse (25°C; I = 0.1 mol/L, NaN[O.sub.3]). Dans les complexes M[(H;PME2A6DMAP).sup.+], [H.sup.+] et [M.sup.2+] (essentiellement la sphere externe) se situent sur le groupe phosphonate; ceci est pertinent si l'on considere les ponts phosphodiesters dans les acides nucleaires car le present systeme ne presente apparemment aucune liaison [M.sup.2+]-purine, tandis que, par exemple, dans le cas des complexes formes a partir de la 9-[2- (phosphonomethoxy)ethyle] adenine, c'est a dire le complexe M[(H;PMEA).sup.+], ou [M.sup.2+] est surtout un residu d'adenine. Les representations graphiques de log [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] dans le cas des ligands phosph (on)ates simples, [R-P[O.sub.3.sup.2-], ou R est un residu qui n'a aucun effet sur la liaison avec [M.sup.2+], montrent que tous les complexes M(PME2A6DMAP) presentent une plus grande stabilite que celle a laquelle on s'attend dans le cas d'une coordination [M.sup.2+]-phosphonate unique. Des compararisons avec les complexes M(PME-R), ou R est un residu non coordinant de la chaine de (phosphonomethoxy)ethane, permettent de conclure que l'augmentation de la stabilite s'explique par la formation de chelates a cinq membres qui met en jeu la liaison ether-oxyde du residu -C[H.sub.2]_O_C[H.sub.2]_P[O.sub.3.sup.2-]. Les degres de formation de ces chelates M[(PME2A6DMAP).sub.cl/O], produits aux equilibres intramoleculaires, varient entre 20 % ([Sr.sup.2+], [Ba.sup.2+]) et 50 % ([Zn.sup.2+], [Cd.sup.2+]), et atteignent un maximum de 67 % ([Cu.sup.2+]). Toute interaction entre [M.sup.2+] et le N3 ou N7 de la portion correspondante a la purine, telle qu'elle se produit dans les complexes M(PMEA) parents, est eliminee par les substituants (C2)N[H.sup.2] et (C6)N[ (C[H.sub.3]).sub.2]. Cette observation, auxquelles s'ajoutent les proprietes liees ti l'empilement determinees precedemment, permettent d'expliquer les remarquables effets therapeutiques que presente le compose [PME2A6DMAP.sup.2-]. [Traduit par la Redaction] Mots-cles: phosphonates nucleosides acycliques, antiviraux, equilibres intramoleculaires, complexes ion-metalliques, analogues nucleotidiques, constantes de stabilite., 1. Introduction Acyclic nucleoside phosphonates (ANPs) are a group of nucleotide analogues with remarkable antiviral activities. (1-3) Their development has resulted in the approval of three drugs for human medicine: [...]

Abstract: Water channels AQP7 and AQP8 may be involved in transcellular water movement in the small intestine. We show that both AQP7 and AQP8 mRNA are expressed in rat small [...]

Subphthalocyanine-based metallosupramolecular capsules have been self-assembled employing a chiral phosphine (S-BINAP). This ligand seems to provide an arrangement of the coordination positions of platinum that inverts the known process of chiral self-discrimination of subphthalocyanines, which is typically produced between the enantiomers of the macrocycle when a nonchiral ligand is used for the self-assembly. In this article, we describe preliminary studies on the effect of S-BINAP on the self-assembly subphthalocyanine capsules. Key words: subphthalocyanines, metal-directed self-assembly, enantiomers, chiral self-discrimination, supramolecular chemistry. Resume : Des capsules metallo-supramoleculaires a base de subphthalocyanine ont ete auto-assemblees a l'aide d'une phosphine chirale (S-BINAP). Avec ce ligand, il semble que l'on obtienne un arrangement des positions de coordination du platine dans lequel le processus connu d'autodiscrimination chiral des subphthalocyanines est inverse. Celui-ci se produit generalement entre les enantiomeres du macrocycle lorsqu'un ligand non chiral est utilise pour l'auto-assemblage. Dans la presente publication, nous decrivons des etudes prealables de l'effet du S-BINAP sur l'auto-assemblage des capsules de subphthalocyanine. [Traduit par la Redaction] Mots-cles : subphthalocyanines, auto-assemblage dirige par un metal, enantiomeres, autodiscrimination chirale, chimie supramoleculaire., Introduction Subphthalocyanines (SubPcs) (1,2) (Fig. 1) are nonplanar aromatic macrocycles composed of three units of 1,3-diiminoisoindoline N-fused around a boron atom. SubPcs are synthesized by cyclotrimerization of phthalonitriles. If the [...]