Zinc cation, interactions with coordinating

Intermetallic distances are in the range of 3.63 - 3.69 A. The nickel and copper complexes have square planar coordination as can be expected for salen and salophen type tetradentate ligands [ref 10]. In the case of zinc a square pyrimidal coordination was found with the salophen unit forming the ground-plane and a DMF molecule at the apical position. The hard cation interacts with all oxygens of the polyether cavity and the coordination sphere is completed by counter anions and/or solvent molecules. In an analogous way the dinuclear complexes 7 with two (alkylated) oxime bonds were synthesized in 55-82% yield [ref 11]. 

The possibility that Mn generally favors tetrahedral coordination as its valence approaches +2 (i.e., d ) is unlikely given that MnO has a rock-salt structure not zinc blende or some other structure with Mntet. Instead, the driving force for Mn movement out of the octahedral sites of 7-Lii/2Mn02 into neighboring Li layer tetrahedral sites appears to be due to the unique cationic ordering and associated cationic interactions that are present in 7-Lii/2Mn02. 

For example, in 1963 the photochemistry of magnesium phthalocyanine with coordinated uranium cations was studied in pyridine and ethanol and indicated the occurrence of PET to the uranium complex . A rapid photoinduced electron transfer (2-20 ps) followed by an ultrafast charge recombination was shown for various zinc and magnesium porphyrins linked to a platinum terpyridine acetylide complex . The results indicated the electronic interactions between the porphyrin subunit and the platinum complex, and underscored the potential of the linking para-phenylene bisacetylene bridge to mediate a rapid electron transfer over a long donor-acceptor distance. 

Figure 37 Pc-Ceo ensemble 57 formed by a zinc crown-ether phthalocyanine supramolecular dimer similar to 54 (Figure 35a) coordinated to a pyridyl-functionalized Cgo component bearing an alkylammonium cation that is able to further interact with one of the crown ether.

The second mode of toxicity is postulated to involve the direct interaction of the epidithiodiketopiperazine motif with target proteins, forming mixed disulfides with cysteine residues in various proteins. Gliotoxin, for example, has been demonstrated to form a 1 1 covalent complex with alcohol dehydrogenase [13b, 17]. Epidithiodi-ketopiperazines can also catalyze the formation of disulfide bonds between proxi-mally located cysteine residues in proteins such as in creatine kinase [18]. Recently, epidithiodiketopiperazines have also been implicated in a zinc ejection mechanism, whereby the epidisulfide can shuffle disulfide bonds in the CHI domain of proteins, coordinate to the zinc atoms that are essential to the tertiary structure of that domain, and remove the metal cation [12d, 19],... 

When the guest used is p-nitrophenylcholine carbonate (PNPCC) the Lewis acid zinc(n) activates the well-positioned carbonyl group in the P PCC Zn-cavitand towards reactions with external nucleophiles. The energy minimized structure of the PNPCC Zn-cavitand complex shows that cation-n interactions and C —O -Zn coordination bond occurs simultaneously. 

Both thiourea (tu) and thiosemicarbazide (tsc) are bifunctional ligands, containing a DD face in addition to one or two co-ordination sites. The reaction of [Zn(tu)4]2+ with a dicarboxylate normally occurs with displacement of thiourea to give coordination polymers of the type [Zn(tu)2(p-dicarboxylate)] in which the chains are cross-linked by DD-AA interactions [157]. The fumarate derivative contains identical inter-plane hydrogen bonding to that observed in (NEt4)2 [fumarate] 2tu [158], in which the zinc atom has formally been replaced by two tetraethylammonium cations. 

H.A. Tajmir-Riahi, Carbohydrate adducts with zinc group metal ions. Interaction of p-D-fructose with Zn(ll), Cd(ll) and Hg(II) cations and the effects of metal-ion coordination on the sugar isomer binding. Carbohydr. Res., 172(198) 1. 

No matter what kind of interaction exists between A and B in, for example, the zinc-blende structure type with a coordination number of four (see Figure 1.1(c)), the atoms (or ions) can be expected to minimize their interatomic A-B distance because of energy optimization so shorter distances should indicate stronger interaction. For a purely electrostatic one (see Section 1.2), this is particularly easy to calculate the distance between A and B can then be approximated by the sum of the ionic radii of the cation and anion, Vc and Va. 

The interaction of bare monovalent (alkah metals and coinage metals) and divalent (alkaline earth and zinc group metals) cations with the N7 site of piuine NA bases was examined in gas phase using MP2/6-31G(d,p)//HF/6-31G(d,p) level of theory (Burda et al. 1996). A graphical illustration of the dependence of the coordination distance on the atomic number of the cations is displayed in O Fig- 36-1. The intermolecular M-N7 distance monotonicaUy increase with the atomic numbers for the alkali metals and metals of alkaline earths (cf. O Fig. 36-1). This increase of the distances is more pronounced for the alkali metals where it exceeds 1 A. The calculated M-N7 distances for both types of metals correlate well with the known ionic radii, e.g.. Tide (1977). The influence of the relativity for the 5s and 5p electrons (Cs, Ba ) is not as pronounced as for the 5d electrons (Au, Hg ) (Pyykko 1988). 

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