Felipe Medrano

Recognition of Anions and Neutral Guests by Dicationic Pyridine-2,6-dicarboxamide Receptors

Dicationic N-methylated at pyridyl or quinolyl moieties derivatives of three isomers of N,N-bis(pyridyl)pyridine-2,6-dicarboxamide (o-, m-, and p-1) and of N,N-bis(3-quinolyl)pyridine-2,6-dicarboxamide (4) strongly bind anions in MeCN (log K in the range 3.5-6.5) with pronounced selectivity for Cl(-) and also bind neutral urea and amide guests with log K in the range 1.1-2.8. Crystal structures of the triflate salts of m-1, p-1, and 4 show that amide NH and pyridinium o-CH groups are directed inside the receptor cleft with their four protons forming a circle of radius ca. 2.35 A optimal for inclusion of Cl(-). The binding of anions to these protons is evident from the crystal structure of a mixed triflate/chloride salt of p-1, calculated (DFT/B3LYP 6-31G**) structures of 1:1 complexes of all receptors with Cl(-), and results of (1)H NMR titrations. In the crystal structure of o-1 pyridinium N-Me(+) groups are directed inside the receptor cleft impeding the anion complexation, but calculations demonstrate that simple rotation of pyridinium rings in opposite directions by ca. 30 degrees creates a cavity to which the Cl(-) ion can fit forming 4 hydrogen bonds to amide NH and aliphatic CH groups of N-Me(+). The results of (1)H NMR titrations confirm this type of binding in solution. Anions quench the intense fluorescence of 4, which allows their fluorescent sensing in the muM range. A new methodology for determination of anion binding constants to strongly acidic receptors by inhibitory effects of anions on the receptor deprotonation by an external base has been developed. High affinity and selectivity of anion complexation by dicationic pyridine-2,6-dicarboxamides is attributed to the rigid preorganized structure of receptors, the high acidity of NH and CH groups, and the electrostatic charge effect.

Unusually high phosphodiesterolytic activity of La(III) hydroxide complexes stabilized by glycine derivatives.

Glycine and N,N-dimethylglycine stabilize La(III) hydroxide complexes of the type La2L2(OH)4 which possess phosphodiesterolytic activity close to that observed with most active tetravalent cations like Ce(IV).

Polyaniline alloys with poly(3-sulfonato-4-hydroxystyrene)

Oxidation of aniline with ammonium peroxodisuffate in aqueous solutions containing poly(3-sutfonato-4-hydroxystyrene) gave polymer alloys (or polymer blends) with a general composition of {(—C6H4NH—)[—CH2—CH(C6H3·OH·SO3–)—]x(H2SO4)y·zH2O}n. Their electrical conductivities depended on the composition and varied between 10–5 and 0.5 S cm–1 at 300 K. The polyaniline salts were soluble in water and exhibited an electronic absorption band characteristic of emeraldine salts at 800 nm. The corresponding alkaline solutions showed a band due to emeraldine bases at 600 nm. These bands showed a pH dependence that is a consequence of an interchain interaction between two kinds of polymer chains. A polymer with x= 04, y= 1.2 and z= 3.6 was soluble enough to observe EPR spectra, whose pH dependence showed that, with increasing pH, deprotonation occurs at polarons prior to deprotonation at bipolarons.

Molecular Recognition of Thymine and Uracil in Water by an Amino-, Amido-, and Carboxymethyl-functionalized Pyridinophane

A new water soluble 26-membered macrocyclic pyridinophane functionalized by amide and carboxymethyl groups has been synthesized in a single step reaction and characterized by elemental analysis, mass spectrometry (FAB+), UV-vis, fluorescence, and 1H NMR spectroscopy as well as single-crystal X-ray diffraction analysis. Its complexation properties with the nucleobases thymine and uracil have been explored in aqueous media by performing 1H NMR titration experiments and potentiometric studies. The binding constants of the 1:1 host-guest complexes were determined as 103 M− 1 by proton NMR and 102–103 M− 1 by potentiometry. Semiempirical molecular modelling studies have shown that the nucleobases are included within the cavity of the macrocyclic receptor and that the complexes are stabilized by hydrogen bonding.

Copolymerization of diphenylmethane andp-xylene by oxidative coupling

SummaryDiphenylmethane underwent oxidative coupling in the presence of di-t-butyl peroxide and formed 1,1,2,2-tetraphenylethane. This coupling reaction resulted in the formation of a copolymer of diphenylmethane andp-xylene. The new copolymer was soluble in common organic solvents and had a molecular weight of 32,000 (polystyrene base).

Amide-based [12]-, [12.12]- and [12.12.12.12]paracyclophanes: non-planarity of amide and phenyl groups in the [12]cyclophane

A reaction between ethylenediaminetetraacetic dianhydride and p-xylene-α,α′-diamine has given three amide-based cyclophanes with different ring sizes; the (1∶1)-reaction product is 3,10-dioxo-5,8-bis(carboxymethyl)-2,5,8,11-tetraaza[12]paracyclophane, the (2∶2)-product is 3,10,21,28-tetraoxo-5,8,23,26-tetrakis(carboxymethyl)-2,5,8,11,20, 23,26,29-octaaza[12.12]paracyclophane, and the (4:4)-product is 3,10,21,28,39,46,57,64-octaoxo-5,8,23,26,41,44, 59,62-octakis(carboxymethyl)-2,5,8,11,20,23,26,29,38,41,44,47,56,59,62,65-hexadecaaza[12.12.12.12]paracyclophane. These amide paracyclophanes have been characterized by NMR, infrared, absorption and electrospray mass spectroscopies. Ab initio calculations have shown that the amide and phenyl groups in the (1∶1)-product, i.e., amide[12]paracyclophane, are distorted from the planar structures owing to the strain of the small cyclophane ring. This unusual structure results in physical properties different from those of the other cyclophanes having larger ring sizes: for example, (1) a low acidity of the amide hydrogen and (2) a low basicity of the amino nitrogen.

Polyaniline salts of toluenesulfonate and sulfonated poly(p-vinylphenol)

Abstract Polyaniline salts of toluenesulfonate (TS) and sulfonated poly( p -vinylphenol) (SPVP) have been prepared. The polyaniline salt of TS exhibited a room-temperature electrical conductivity of 10 S cm −1 . The activation energy for electrical conduction was 0.02 eV, which was significantly smaller than the value 0.04 eV reported for other salts. The aromatic nature of the organic anion is expected to enhance the interchain diffusion of charge carriers. The electrical conductivity of the polyaniline salt of the polymer anion was of the order of 10 −4 S cm −1 . A polyaniline base derived from the SPVP salt was water-soluble in the presence of excess NaSPVP, due to complexation between the two polymers.