Presented here are several convergent synthetic routes to conjugated oligo(phenylene ethynylene)s. Some of these oligomers are free of functional groups, while others possess donor groups, acceptor ...groups, porphyrin interiors, and other heterocyclic interiors for various potential transmission and digital device applications. The syntheses of oligo(phenylene ethynylene)s with a variety of end groups for attachment to numerous metal probes and surfaces are presented. Some of the functionalized molecular systems showed linear, wirelike, current versus voltage (I(V)) responses, while others exhibited nonlinear I(V) curves for negative differential resistance (NDR) and molecular random access memory effects. Finally, the syntheses of functionalized oligomers are described that can form self‐assembled monolayers on metallic electrodes that reduce the Schottky barriers. Information from the Schottky barrier studies can provide useful insight into molecular alligator clip optimizations for molecular electronics.
Functionalized conjugated oligo(phenylene ethylene)s with donor groups, acceptor groups, porphyrin interiors, and heterocycle interiors (see scheme) have been synthesized by several convergent synthetic routes. These compounds have potential for wire and digital device applications: some showed linear, wirelike, current versus voltage (I(V)) responses, while others exhibited nonlinear I(V) curves for negative differential resistance (NDR) and molecular random access memory effects.
An ion-selective electrode for acetate based on (α,α,α,α)-5,10,15,20-tetrakis2-(4-fluorophenylureylene)phenylporphyrin as an ionophore that has no metal center and forms hydrogen bonds to the analyte ...is described. At pH 7.0 (0.1 M HEPES−NaOH buffer), the electrode based on this ionophore and cationic sites (50 mol % relative to the ionophore) responds to acetate in a linear range from 1.58 × 10-4 to 1.58 × 10-2 M with a slope of −54.8 ± 0.8 mV/decade and a detection limit of (3.06 ± 1.15) × 10-5 M. Selectivity coefficients determined with the separate solution method (SSM) indicate that interferences of hydrophobic inorganic anions are relatively small (log (SSM): NO3 -, +0.68; SCN-, +0.60; NO2 -, +0.22; I-, +0.20; ClO4 -, +0.12; Br-, −0.13). Responses to anions that are good hydrogen bond acceptors, i.e., Cl-, HSO3 -, and HCO3 -, were Nernstian and were weaker than the response to acetate (log (SSM): −0.54, −0.56, and −1.34, respectively). Negligibly small responses were observed for very hydrophilic anions, i.e., F-, SO4 2-, and H2PO4 -/HPO4 2-. While aliphatic carboxylates such as formate, propanoate, pyruvate, and lactate gave Nernstian responses similar to acetate, interferences of salicylate and benzoate were considerably decreased in comparison with electrodes based on cationic sites only. Concentrations of acetic acid in vinegar samples were determined by direct potentiometry and agreed with values determined by a standard enzymatic method.
A series of neutral, urea-appended, free-base porphyrins and their Zn(II) complexes have been synthesized and characterized. The (α,α,α,α)-5,10,15,20-tetrakis(2-(arylurea)phenyl)porphyrins bind ...strongly (K (M-1) > 103−105) to chloride anion in DMSO-d 6 and also in the more competitive solvent system DMSO-d 6/D2O (88:12, v/v) and bromide anion in DMSO-d 6, as revealed by 1H NMR titration studies. The porphyrin derivatives exhibited significant binding selectivity since they complexed with the spherical Cl- and Br- to a much greater extent than with the tetrahedral H2PO4 - and HSO4 - and the trigonal NO3 - anions in DMSO-d 6. Indeed, the selectivity trend Cl- > Br- ≫ H2PO4 - > HSO4 - > NO3 - is novel for any neutral urea-anion binding system. On the other hand, the corresponding metalloporphyrins exhibited a decrease in binding strength and selectivity in DMSO-d 6. The stoichiometry of binding for the anions and porphyrins was determined to be 1:1. The enthalpy of complexation was determined to be highly favorable and the entropy of complexation determined to be unfavorable from a variable-temperature 1H NMR experiment with a 1:1 tetrabutylammonium bromide/porphyrin complex. X-ray crystallography revealed (α,α,α,α)-5,10,15,20-tetrakis(2-(4-chlorophenylurea)phenyl)porphyrin to be the first coordination complex of an anion (chloride and bromide) bound by a neutral free-base porphyrin. The binding motif consisted of the halide, buried deep within the porphyrin pocket, bound by two adjacent urea functional groups via four hydrogen bonds, with the two remaining urea functional groups involved in hydrogen bonding to solvent molecules. The crystal structure of the tetrabutylammonium halide−porphyrin complex showed additional Coulombic interaction between the electron-poor sulfur of a pocket-bound, hydrogen-bonded DMSO and halide anion.
A route to porphyrins bearing trans-thiols is described using a thioacetyl-containing aldehyde or a thioacetyl-containing dipyrromethane in the presence of catalytic BF3·OEt2 followed by oxidation. ...Metal complexation and ammonium hydroxide induced acetyl removal provides a route to these important molecular systems for future electronics experiments in which the thiols would serve as the adhesion points to gold probes.
As part of a research initiative to evaluate food crops for their nutritional and herbal
values, the antimicrobial activity of the n-C6H14, CH2C12 and CH3CH20H extract of Brassica
rapa chinensis, ...Artocarpus altilis, Solanum melongena fruits and leaves of Moringa oleifera were
investigated. Each plant part was subjected to selective extraction using the above solvents.
Antimicrobial activity was investigated asceptically, using the Disc Diffusion Assay at a
concentrations of 0.025g/ml, 0.05g/ml and O.lg/ml against pathogens: E. coli, S. aureus, Bacillus
subtilis, K. pneumoniae and C. albicans for Brassica rapa chinensis and Artocarpus altilis. Also,
the combined CH3CH20H and n-C6H14 extracts of A. altilis and Brassica rapa chinensis were
investigated. The n-C6H14 and CH3CH20H extract of Solanum melongena fruit and leaves of
Moringa oleifera were tested for their antimicrobial activity at concentrations of 5%, 10% and 20%
of crude extracts. The diameter of the zone of inhibition, DZOI was used as the food crop
antimicrobial potency. The highest AZOI of 209.34 mm2 was induced by the CH3CH20H extract
of Brassica rapa chinensis against E. coli at a concentration of 0.025g/ml. The lowest AZOI of
12.56 mm2 was induced by Brassica rapa chinensis against Bacillus subtilis at a concentration of
0.025g/ml. Both the n-C6H14 and CH3CH20H extracts of Solanum melongena fruit and Moringa
oleifera leaves showed greater antibacterial activity at a higher concentration of 20% of crude
extract. The order of bacteria susceptibility to Moringa oleifera extract being S. aureus > K.
pneumoniae > E.coli, whereas that for Solanum Melongena extract being S. aureus > E.coli > K.
pneumoniae. The area of zone of inhibition ranged from 44.15 mm2 to 53.55 mm2. Selective
antimicrobial activity were observed for all four food crop extracts. Thus, the above food crops
can be used as antibacterial agents in addition to their nutritional values.
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