J. de Mendoza

Palladium(II) coordination and cyclometallated complexes derived from 3- and 5-aryl-substituted pyrazoles

Palladium(II) coordination complexes of nine 3- or 5-arylpyrazoles (phenyl, 2-bromophenyl, or 3-methoxyphenyl), as well as of 3,5-diphenylpyrazole, are reported. A cis-trans mixture of [PdL2Cl2] isomers is found in the case of 3-aryl-1-methylpyrazoles, the cis-isomers being transformed into trans by heating. Only trans isomers are isolated with the other ligands. Cyclopalladation of 3-ary]-1-methylpyrazoles can be performed with palladium(II) acetate, and the resultant μ-acetate bridged dimers can be transformed into μ-chloro bridged dimers or acetylacetonate monomers. The structures of the complexes have been characterized by 1H- and 13C-NMR spectroscopy.

Palladium(II) coordination and cyclometallated complexes derived from 1-tert-butylpyrazole

The synthesis and characterization of a number of new coordination compounds of PdII with the nitrogen donor 1-tert-butylpyrazole (tBuPzH) are described. Compounds are trans-[Pd(tBuPzH)2Cl2] and the cyclometallated structures [Pd2(tBuPz)2(AcO)2] and [Pd3(tBuPz)2(AcO)4]. All these complexes are mixtures of syn and anti isomers. Also, the chloro-bridged complex [Pd2(tBuPz)2Cl2] has been isolated as an equilibrium mixture of cis and trans isomers. The compounds have been studied by variable temperature 1H- and 13C-NMR spectroscopy.

EXTRACTION OF CHIRAL AMMONIUM CATIONS AND TRANSPORT THROUGH SUPPORTED LIQUID MEMBRANES MEDIATED BY 1,2,4-TRIAZOLE-CONTAINING PODANDS AND MACROCYCLES

Abstract Extraction of chiral primary alkylammonium salts was achieved in the presence of 1,2,4-triazole-containing macrocycles and podands with moderate enantioselectivities. Although preferential transport of ( R )-1-naphthylethylammonium salts was always observed, significant differences in both rates and selectivities were found when bulk (CHCl 3 CCl 4 ) or supported (microporous polypropylene film) membranes were employed. The preparation of new protonionizable chiral bistriazolo-18-crown-6 macrocycles 3c , d is described.

Protonated amine transport and chiral recognition by 1,2,4-triazole podands and macrocycles

Abstract Transport of ammonium salts across a bulk liquid membrane with chiral macrocycles and podands containing a 1,2,4-triazole subunit takes place with moderate enantioselectivity. Good transport rates were found for both podands and macrocycles, but chiral recognition was less effective with podands.

Preparation and electrochemical switching of novel bis(anthraquinone)diazacrown ethers

Novel bis (anthraquinone)diazacrown ethers 1 and 2 were prepared by nucleophilic displacement reactions on 1-fluoro-9,10-anthraquinone by diazacrown ethers. The electrochemically switched enhanced sodium binding capabilities of these compounds with Na+ were evaluated. Both compounds exhibited enhanced sodium binding properties upon electrochemical reduction.

Protein surface recognition

Molecular recognition is at the core of the design of any supramolecular system. Proteins, because of their biological relevance and structural complexity, provide us with exquisite examples of molecular recognition in a natural setting. Most of the effort reported in the literature towards the design of artificial compounds able to bind proteins with high affinity and selectivity has been targeted to rather hydrophobic areas: the design of enzyme inhibitors could be the paradigm of such studies, the inhibitor being designed to occupy a groove on the protein surface where the active center of the enzyme is located [1].

Symmetry: Friend or Foe?

While symmetry in molecules or supramolecular complexes is desirable from the design point of view and affords simpler NMR spectra, the study of symmetrical species by NMR is often subject to ambiguities resulting from signal degeneracy. In this paper we shall discuss different ways of breaking symmetry in order to obtain additional structural information by NMR.

Molecular Recognition of Dinucleotides and Amino Acids by Artificial Receptors Containing a Bicyclic Guanidinium Subunit

Detailed molecular models have been generated for the complexes of 2′-deoxyadenylyl(3′→ 5′)-2′-deoxyadenosine and 2′-deoxyadenylyl(3′→ 5′)-2′-deoxyguanosine with a synthetic receptor for dinucleotides, and of L-phenylalanine and L-tryptophan with an enantioselective receptor for aromatic L-amino acids. The structures have been optimized by energy minimization techniques and further subjected to molecular dynamics simulations at room temperature. The resulting trajectories have provided valuable information about the relative stability of the complexes and the conformational preferences of host and guest molecules in the bound state. The relative contributions of each constitutive block to the binding enthalpies have been dissected. This knowledge should aid in our understanding of the forces involved in molecular recognition and in the design of improved novel receptors.