J. Clayton Baum

Bis(μ-N,N′-η2-N,O-η2-N′,O′-di(o-methoxyphenyl)formamidinato)disilver(I): an interesting coordination geometry for silver(I) and room temperature fluorescence

Abstract Reported here are the synthesis, structural and spectroscopic characterization of the title disilver compound, which provides the first example of room temperature fluorescence from a d10–d10 compound. In addition to confirmation of the dinuclear nature of the compound, X-ray crystallographic analysis reveals an N2O2 (distorted) tetrahedral coordination for each silver(I) center.

Organic matter source discrimination by humic acid characterization: Synchronous scan fluorescence spectroscopy and Ferrate(VI)

In this study, seven soil and sedimentary humic acid samples were analyzed by synchronous scan fluorescence (SSF) spectroscopy. The spectra of these humic acids were compared to each other and characterized, based on three major SSF peaks centered at approximately 281, 367 and 470 nm. Intensity ratios were calculated based on these peaks that were used to numerically assist in source discrimination. All humic acid samples were then reacted with Ferrate(VI) and were again analyzed with SSF. Upon the addition of Ferrate(VI) SSF spectra were obtained which more readily differentiated humic acid source. This method will assist geochemists and water management districts in tracing sources of organic matter to receiving water bodies and may aid in the elucidation of the chemical nature of humic acids.

Semiempirical MO and voltammetric estimation of ionization potentials of organic pigments. Comparison to gas phase ultraviolet photoelectron spectroscopy

Abstract A number of organic pigments were identified by semiempirical molecular orbital calculations, using the PM3 method, as having ionization potential (IP) values of 7.0–9.5 eV. Based on photostability, solubility and commercial availability twelve (quinacridone, isoviolanthrone, indanthrone, indigo, 3,4,9,10 perylenetetracarboxylic dianhydride, bis( p -chlorophenyl)1,4-diketopyrrolo (3,4-C) pyrrole, pyranthrone, indanthrene yellow GCN, 16,17-dimethoxyviolanthrone, indanthrene gold orange, 4,4′-diamino-9,9′,10,10′-tetrone [1,1′ bianthracene], and N,N ′ ditridecyl-3,4,9,10-perlenetetracarboxylic diimide) were chosen for further study. The accuracy of the MO calculations was confirmed by experimental measurement of the ionization potentials for eight of the pigments, using gas phase ultraviolet photoelectron spectroscopy. For compounds having at least three fused rings and containing oxygen, nitrogen, or both, the theoretical and experimental IPs have a linear relationship defined by the equation IP exp =0.694IP Calc +1.9049. Lewis acid pigment solubilization (LAPS) was shown to be a viable approach to preparing electrodes for cyclic voltammetry of pigment solid films. The results of the cyclic voltammetry experiments were utilized to formulate the equation E ox (V vs. NHE)=0.5488 IP Calc −3.042, which relates the experimental oxidation potential to the theoretical IP.

Novel computational study on π-stacking to understand mechanistic interactions of Tryptanthrin analogues with DNA

Abstract Based on recently published initial experimental results on the intercalation of a class of broad spectrum antiparasitic compounds, we present a purely theoretical approach for determining if these compounds may preferentially intercalate with guanosine/cytosine (GC)-rich or adenosine/thymidine (TA)-rich regions of DNA. The predictive model presented herein is based upon utilization of density functional theory (DFT) to determine a priori how the best intercalator may energetically and sterically interact with each of the nucleoside base pairs. A potential new method using electrostatic potential maps (EPMs) to visually select the best poses is introduced and compared to the existing brute-force center of mass (COM) approach. The EPM and COM predictions are in agreement with each other, but the EPM method is potentially much more efficient. We report that 4-azatryptantrin, the best intercalator, is predicted to favor π-stacking with GC over that of TA by approximately 2–4 kcal/mol. This represents a significant difference if one takes into account the Boltzmann distribution at physiological temperature. This theoretical method will be utilized to guide future experimental studies on the elucidation of possible mechanism(s) for the action of these antiparasitic compounds at the molecular level.

Hydrazine/nitrogen dioxide fiber optic sensor

This paper outlines the development of a dual hydrazine/nitrogen dioxide (HZ/NO2) prototype fiber optic sensor utilizing an acid-base indicator that undergoes color changes depending on which gas is present. Bromothymol blue bromocresol green mixture (1/1) in hydrogel (1/1), produces a blue-green indicator for HZ and/or NO2. The sensor was tested several times over a period of eight weeks and the response was cconsistent and proved the feasibility of dual HZ/NO2 leak detection. Prototype sensor construction, the hardware, and the software of the electronic interrogator circuitry are briefly explained. The paper presents a summary of sensor response when exposed to 52 ppm and 18 ppm hydrazine and 400 ppm and 200 ppm nitrogen dioxide.

New insight into the action of tryptanthrins against Plasmodium falciparum: Pharmacophore identification via a novel submolecular QSAR descriptor

A new submolecular quantitative structure activity relationship (QSAR) descriptor was applied toward elucidating the anti-malarial pharmacophore of tryptanthrins, a class of compounds known for their anti-parasitic activities. The new descriptor is based on experimental and computational measurements of the tunneling barriers of individual lobes of the molecular orbitals. Lobe-by-lobe QSAR correlation plots revealed a single lobe of the LUMO to be strongly associated with tryptanthrins anti-malarial activity. The correlation also showed a threshold behavior wherein barriers below a particular value show low IC50 values. Above the threshold, the correlation of IC50 vs the logarithm of the barrier is linear with R2 = 0.999. This barrier threshold may be applied as a design criterion for future tryptanthrin-based anti-malarial lead optimization. The new descriptor may be broadly applicable toward other molecular systems of interest, such as catalysts, pesticides, and herbicides. The authors have named the new descriptor: submolecular tunneling analysis of barriers (STAB).

In silico simulations of tunneling barrier measurements for molecular orbital-mediated junctions: A molecular orbital theory approach to scanning tunneling microscopy

A new simulator for scanning tunneling microscopy (STM) is presented based on the linear combination of atomic orbitals molecular orbital (LCAO-MO) approximation for the effective tunneling Hamiltonian, which leads to the convolution integral when applied to the tip interaction with the sample. This approach intrinsically includes the structure of the STM tip. Through this mechanical emulation and the tip-inclusive convolution model, dI/dz images for molecular orbitals (which are closely associated with apparent barrier height, ϕap) are reported for the first time. For molecular adsorbates whose experimental topographic images correspond well to isolated-molecule quantum chemistry calculations, the simulator makes accurate predictions, as illustrated by various cases. Distortions in these images due to the tip are shown to be in accord with those observed experimentally and predicted by other ab initio considerations of tip structure. Simulations of the tunneling current dI/dz images are in strong agreeme...