Sandwich-like complexes

Bismuth phthalocyanines of the type PcBiX can be prepared in solution by the reaction of bismuth(III) halides with PcLi2 or in a molten mixture of phthalonitrile and bismuth(III) halide.166 The sandwich-like complex [Pc2Bi]- can be obtained by slowly adding potassium methoxide to a melt of bismuth(III) oxonitrate and phthalonitrile.167... 

Lanthanides form phthalocyanines PcMX, sandwich-like complexes of the type Pc2M, and triple-decker complexes of the type Pc3M2. 

The crown ethers and the related cryptates (cryptates were first reported by J-M Lehn (J ) of France in 1969 (Figure 3)), have been used in a variety of synthetic procedures primarily because of their ability to solvate ionic materials in organic solvents (1, 14). Recently, it has been shown that crown ethers in the solid state form "sandwich" like complexes with most metals and that the counterion is also tightly bound (1 ). It is this evidence that suggested their use as ion traps in silicone RTV formulations. 

Another interesting point is the positive NOE-effect on the maleate protons observed by-irradiation of internal protons in the P-CD. Although a simultaneous inclusion of both p-bromphenyl and maleate residues is impossible in the cavity of the same CD the formation of sandwich-like complexes with the 2 1 stoichiometry of P-CD to brompheniramine is possible. This hipotetic structure is somewhat supported also with x-ray experiments performed on the single monociystals obtained from the solution of P-CD and brompheniramine. 

We have developed nanoparticle label-based electrochemical immunoassay of OP exposure biomarkers, OP-ChE (44). The principle and procedure of this method is shown in Figure 5. Here, zircomia (Zr02) NPs, electrochemically deposited on the electrode surface, which functioned as the capture antibodies in the sandwich immunoassay. The zirconia- NP- modified electrode is then exposed to the sample solution and the ChE-OP in the sample is captured by the Zr02 nanoparticles. The QD-tagged, anti-AChE conjugate is introduced to form the sandwich-like complex on the sensor surface. The captured QDs are then dissolved by a drop of acid to release cadmium ions. This is followed by square wave voltammetric (SWV) [abbreviation already introduced but unexplained] detection of the released cadmium ions at an in situ plated mercury/bismuth film electrode. 

The Lewis-acidic uranyl dication, UOi, center has been used by Reinhoudt and his group to build up receptors based on uranyl-salen complexes and crown ether units, 12. In particular, the two benzo[15]crown-5 units form a sandwich-like complex with potassium while the metal binds to the dihydrogen phosphate counterion. ... 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

Detection of pyrophosphate has also been demonstrated by a simple selfassembling system A-10 (Figure 10.32) with a pyrene-functionalized monoguani-dinium receptor. This receptor was found to self-assemble to form a 2 1 (host -guest) complex with high selectivity for biologically important pyrophosphate ions in methanol. A sandwich-like ground-state pyrene dimer is formed. The character-... 

The more elegant route—which we call for simplicity the method of [1 + l]-addition —may also be used to prepare other binuclear complexes containing either two allyl groups, or one allyl group and one halogen in the bridging positions. The results so far obtained are summarized in Eqs. (9) and (10). Compounds 45-47 are the first allyl-transition metal complexes in which not one metal atom but a dimetal unit is coordinated sandwich-like by two i73-bonded allylic ligands (75, 79). 

By introducing a crown ether unit at the C-terminal region of hydrophobic helical peptides, Otoda et al.19 were able to demonstrate increased stabilization of the peptide aggregate in the membrane by the formation of sandwich-type complexes with large cations. Ion channel activity was also increased due to the ability of the crown peptide to bind ions to the terminal portion of the hydrophobic helix bundle at the water-lipid interface. Ueda et al.20 considered the problem of insolubility of hydrophobic peptides which restricts the distribution of peptides in water to a phospholipid bilayer membrane. In consequence they constructed a hydrophobic helix bundle shielded by hydrophilic peptides that acts rather like an umbrella. 

Complexes with porphyrins, porphyrinogens,17 and phthalocyanine18 are known, with the latter being sandwich-like, Li[(Pc)Ln(Pc)]. 

The association constant for ion binding of Cyclo-(Pro-Gly)3 b nearly the same as that of antamanide, but the selectivity for Ca of Cydo-(Pro-Gly)3 is inferior to that for Na" " of antamanide (144). Cyclo-(Pro-Gly)3 resembles the K -specific cyclic hexadepdpeptide aiitibiotic enniatin (145), in the aspect that both cycUc compounds form sandwich-type comjdexes with ions. It is very likely that Cyclo-(Pro y)3 transports ions across a membrane vb the formation of a club sandwich-type complex. The metal-ion complex of Cyclo-(Pro<]tly)3 is extractable with water from organic phase. A specific behavior of clo-(Pro-Gly)3 in the ion tran rt throu a membrane b expected from fhb property. 

Quite remarkable is the low entropy of activation AS of 10.9 e.u. for the dissociation of meso-59 in contrast to AS sss (31.1 0.8 e.u.) for the complete dissociation into free radicals. In the activated complex of the dissociation of 39 the central C—C bond is no doubt almost completely broken but the system has gained only little additional freedom of mobility as compared to the ground state dimer. This strongly supports the formation of a sandwich-like arrangement of the two radicals in the activated complex as discussed above K According to the principle of microscopic... 

Fig. 8. Electron transfer from ground state phenol to benzene radical cation via a sandwich-like charge transfer complex [calculated at B3LYP/6-31G(d) level].

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