Electronic interactions in tertiary oligophenylureas

The syntheses, structures, and spectroscopy of a series of oligomeric tertiary oligophenylureas possessing one to five phenyl rings are reported. A convergent synthetic method employing tertiary monoamine and diamine building blocks is employed. NMR and molecular modeling are indicative of folded structures for all of the oligophenylureas in which adjacent phenyl rings have a splayed face-to-face geometry. NMR chemical shifts, absorption and emission maxima, and electrochemical oxidation potentials are all dependent upon the number of phenyl rings. The addition of a first inner phenyl has a pronounced effect on the chemical shifts, while a second and third inner phenyl have diminished effects. The oxidation potentials of the oligophenylureas display an abrupt decrease upon the addition of the second inner phenyl. The absorption and emission spectra are relatively insensitive to the addition of one to three inner phenyl rings. The electronic structures of the oligophenylureas possessing one to eight rings have been analyzed using ZINDO calculations. The frontier orbitals of the ureas with one to three phenyl rings are localized on a single phenyl ring (the inner ring for the three-ring urea), whereas the frontier orbitals of the higher oligomers are delocalized over two phenyl rings. In all cases, urea-localized n,pi* transitions are lower in energy than the phenyl-localized pi,pi* transitions. The changes in properties with added phenyl rings parallel those previously observed for multilayered cyclophanes; however, they are less pronounced because of weaker coupling between the phenyl rings of the oligophenylureas.     

Superoxide radical anion adduct of 5,5-dimethyl-1-pyrroline N-oxide (DMPO). 2. The thermodynamics of decay and EPR spectral properties

The formation of the superoxide radical anion (O2*-) adduct of the nitrone 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as detected by electron paramagnetic resonance (EPR) spectroscopy is one of the most common techniques for O2*- detection in chemical and biological systems. However, the nature of DMPO-O2H has confounded spin-trapping investigators over the years, since there has been no independently synthesized DMPO-O2H to date. A density functional theory (DFT) approach was used to predict the isotropic hyperfine coupling constants arising from the N, beta-H, and gamma-H nuclei of DMPO-O2H using explicit interactions with water molecules as well as via a bulk dielectric effect employing the polarizable continuum model (PCM). Theoretical calculation on the thermodynamics of DMPO-O2H decay shows favorable intramolecular rearrangement to form a nitrosoaldehyde and a hydroxyl radical as products, consistent with experimental observations. Some pathways for the bimolecular decomposition of DMPO-O2H and DMPO-OH have also been computed.     

Electrical properties of mobile site ion exchange membranes with interfacial permselectivity breakdown: Non-zero current properties

Equations are derived which describe the current-voltage behavior of thick, mobile site ion exchangers with Donnan extraction of co-ions. The equations are transcendental in nature and are solved numerically. Passing current results in distance-dependent, site profiles and variation in interfacial permselectivity with current. An impedance diagram is digitally simulated for a membrane under current polarization and inductive behavior is seen. Effects of co-ion mobility and bathing salt activity variation are investigated. Equations for membrane resistance and current-voltage curves for this system are compared with fixed site, perm-selective mobile site, and non-permselective membrane properties.     

Direct probing of zwitterion formation in unsolvated peptides

Molecular beam electric deflection measurements have been used to determine electric susceptibilities for small unsolvated alanine-based peptides. The electric susceptibility provides information about the charge distribution within the peptide and can be used to distinguish between zwitterionic and canonical forms. Measured electric susceptibilities for WAn peptides (n = 1-5) are similar to those for capped Ac-WAn-NH2 peptides (which cannot form zwitterions). Susceptibilities calculated using a simulated tempering-based approach are substantially larger for the zwitterionic form than for the canonical form. The measured susceptibilities are in good agreement with those calculated for the canonical form. For the larger peptides, the lowest potential energy structure found in the simulations is hairpin-like, while the lowest free energy structure found at room temperature is extended. The zwitterionic form is constrained by intramolecular interactions which make it entropically unfavorable.     

Diisophorone and related compounds—II: 1-Alkoxy- and 1-carboxy-diisophorane derivatives

The acid catalysed interaction in dioxan of trialkyl orthoformates with diisophor-2(7)-en-ol-3-one, diisophor-2(7)-en-ol, and their bisnor-homologues, provides the corresponding 1-alkoxy-compounds. Their structure is established by the identity of -methoxydiisophor-2(7)-en-3-one obtained by this method, and by the action of sodium methoxide on 1-chlorodiisophor-2(17)-en-3-one. The latter is regenerated from 1-methoxy(or ethoxy) diisophor-2(7)-en-3-one by the action of stannic chloride-acetyl chloride. Catalytic hydrogenation reduces the 3-keto-function in 1-alkoxydiisophor-2(7)-en-3-ones to a methylene unit; simultaneous removal of the 1-alkoxy-group in the case of the 1-isopropoxy-homologue yields the penultimate parent hydrocarbon of this series, diisophor-2(7)-ene.The combined action of silver sulphate and formic acid in concentrated sulphuric acid on 1-chlorodiisophor-2(7)-en-3-one (and its bisnor-homologue) produces the corresponding 1-carboxylic acids. These are also obtainable by the hydrolysis of the 1-cyano-compound, and are esterifiable by the standard methods.     

SYNTHESIS OF POSITIVELY CHARGED PHTHALOCYANINES and THEIR ACTIVITY IN THE PHOTODYNAMIC THERAPY OF CANCER CELLS

Positively charged zinc containing or metal free phthalocyanines 6a-c and 7a-c were prepared via a three step procedure starting from 4-nitrophthalonitrile. The phthalocyanines contain alkyl chains of different length in order to influence the hydrophilic vs lipophilic character of the compounds. The partition between a hydrophilic (water) and lipophilic (octanol-1) phase was determined, and the photoredox activities were investigated. Initial results on the photodynamic activity of these compounds were compared with those of Dougherty's Photofrin II on different malignant and non-malignant cell lines (XP 29MAmal, CX1, HeLa, S180 and NO17). Positively charged phthalocyanines in vitro showed a higher photodynamic activity than Photofrin II.     

Synthesis, structure, and theoretical study of the nonclassical [CuTe(7)](3-) anion

The compound [PPh(4)](2)[NEt(4)][CuTe(7)] has been synthesized from the reaction of CuCl with a polytelluride solution in dimethylformamide at room temperature. The compound crystallizes with two formula units in the triclinic space group P(-)1 in a cell with dimensions a = 8.9507(18) A, b = 14.714(3) A, and c = 23.277(5) A and alpha= 86.32(3) degrees, beta= 80.17(3) degrees, and gamma= 75.63(3) degrees (T = -120 degrees C). Ab initio calculations indicate that the nonclassical [CuTe(7)](3)(-) anion is the result of joining Te(3)(2-) and [CuTe(4)](1-) fragments through donor-acceptor interactions.     

Changes in calmodulin main-chain dynamics upon ligand binding revealed by cross-correlated NMR relaxation measurements

The fast dynamics of protein backbones are often investigated by nuclear magnetic relaxation experiments that report on the degree of spatial restriction of the amide bond vector. By comparing calmodulin in the peptide-bound and peptide-free states with these classical methods, we observe little difference in the dynamics of the polypeptide main chain (average order parameter decrease of 0.01 unit upon binding). However, when using NMR methods that monitor the mobility of the CO-Calpha bond vector, we reveal a significant reduction of dynamics of the protein main chain (average order parameter decrease of 0.048 units). Previous investigations have suggested that the side-chain dynamics is reduced by an average of 0.07 order parameter units upon ligand binding (Lee, A. L.; Kinnear, S. A.; Wand, A. J. Nat. Struct. Biol. 2000, 7, 72-77). The current findings suggest that the change of the CO-Calpha bond vector dynamics is intermediate between the changes in NH and side-chain dynamics and report a previously undetected loss of main-chain entropy. Weak site-to-site correlations between the different motional indicators are also observed.     

Synthesis of a homotrifunctional conjugation reagent based on maleimide chemistry

A novel homotrifunctional conjugation reagent, 1,3,5-tris-(N-maleimidomethyl)benzene has been synthesized in high yield with minimum purification. The reactivity of this compound was examined by using l-cysteine as a nucleophile.     

High electron mobility in solution-cast and vapor-deposited phenacyl-quaterthiophene-based field-effect transistors: toward N-type polythiophenes

New carbonyl-functionalized quaterthiophenes, 5,5' '-diperfluorophenylcarbonyl-2,2':5',2' ':5' ',2' '-quaterthiophene [DFCO-4T], 5,5' '-diphenyl-2,2':5',2' ':5' ',2' '-quaterthiophene [DPCO-4T], and a polymer having the same basic motif as DFCO-4T, poly{1,4-bis[(3'-n-octyl-2,2'-dithiophene)carbonyl]-2,3,5,6-tetrafluorobenzene} [P(COFCO-4T)], have been synthesized, characterized, and the crystal structures of the molecules determined. Field-effect transistors fabricated with vapor-deposited and solution-cast films of DFCO-4T exhibit very high Ion:Ioff current ratios (up to 108) and electron mobilities up to approximately 0.51 and approximately 0.25 cm2.V-1.s-1, respectively. Solution-cast blends of P(COFCO-4T) and DFCO-4T (1:1 weight ratio) exhibit an electron mobility of approximately 0.01 cm2.V-1.s-1 (Ion:Ioff = 104).