Total surface areas of Group IVA organometallic compounds: Predictors of toxicity to algae and bacteria

There is a high correlation between molecular surface area (TSA) of triorganotin and triorganolead compounds and their toxicity towards a bacterium (Escherichia coli) and an alga (Selenastrum capricornutum). Parallel attempts to correlate other Group IVA organometals incorporating silicon or germanium were unsuccessful. It was further demonstrated, however, that a high correlation was obtainable between certain series of compounds with the same organic substituent but different metal centers involving all Group IVA elements. In both instances, the inability to obtain a quantitative structure-activity relationship (QSAR) for all systems studied appears to be a function of the solubility of the compounds. While organotin TSA values have been found to correlate well with their toxicities toward various organisms, this study clearly suggests that this type of QSAR can be readily extended to include other organometal systems, provided that there is no solubility problem and the toxicity is a function of the hydrophobicity of the organometal compounds.     

Synthesis and characterization of fluorenone-, anthraquinone-, and phenothiazine-labeled oligodeoxynucleotides: 5'-probes for DNA redox chemistry

A facile and automated procedure for the synthesis of oligodeoxynucleotides possessing derivatives of 9-fluoreneone, 9,10-anthraquinone, and phenothiazine is described. The phosphoramidite approach is used to attach these redox and spectroscopic probes to the 5'-terminus of oligodeoxynucleotides in high yield (>95%). Thermal denaturation studies of labeled oligodeoxynucleotides show a slight enhancement in duplex stability relative to the unlabeled control, and circular dichroism spectra confirm B-form helical DNA structure in solution.     

The formation of 2,3-disubstituted thiazolidin-4-ones from s-α'-aminomercaptoacetic acid derivatives

Variously substituted N-benzylidineanilines rapidly react with thioglycolic acid to generate S-α'-aminomercaptoacetic acid derivatives. The latter subsequently cyclize to the corresponding 2,3-diarylthiazolidin-4-ones. Kinetics for the first order cyclization reaction in the solvents toluene, carbon tetrachloride and nitrobenzene have been obtained over the temperature range 333 K to 383 K and are in accord with a neutral, but geometrically complex transition state.     

Template-directed intramolecular C-glycosidation. cation-mediated synthesis of ketooxetanes from thioglycosides

Bicyclic ketooxetanes may be assembled using cation-mediated cyclisation reactions of thioglycosides possessing silyl enol ether-containing side-chains.     

Multivariate dynamic modeling for Bayesian forecasting of business revenue

Forecasting enterprise-wide revenue is critical to many companies and presents several challenges and opportunities for significant business impact. This case study is based on model developments to address these challenges for forecasting in a large-scale retail company. Focused on multivariate revenue forecasting across collections of supermarkets and product categories, hierarchical dynamic models are natural: these are able to couple revenue streams in an integrated forecasting model, while allowing conditional decoupling to enable relevant and sensitive analysis together with scalable computation. Structured models exploit multi-scale modeling to cascade information on price and promotion activities as predictors relevant across categories and groups of stores. With a context-relevant focus on forecasting revenue 12 weeks ahead, the study highlights product categories that benefit from multi-scale information, defines insights into when, how, and why multivariate models improve forecast accuracy, and shows how cross-category dependencies can relate to promotion decisions in one category impacting others. Bayesian modeling developments underlying the case study are accessible in custom code for interested readers.     

Spontaneous transmission of chirality through multiple length scales

The hierarchical transfer of chirality in nature, from the nano‐, to meso‐, to macroscopic length scales, is very complex, and as of yet, not well understood. The advent of scanning probes has allowed chirality to be monitored at the single molecule or monolayer level and has opened up the possibility to track enantiospecific interactions and chiral self‐assembly with molecular‐scale detail. This paper describes the self‐assembly of a simple, model molecule (naphtho[2,3‐a]pyrene) that is achiral in the gas phase, but becomes chiral when adsorbed on a surface. This polyaromatic hydrocarbon forms a stable and reversibly ordered system on Cu(111) in which the transmission of chirality from single surface‐bound molecules to complex 2D chiral architectures can be monitored as a function of molecular packing density and surface temperature. In addition to the point chirality of the surface‐bound molecule, the unit cell of the molecular domains was also found to be chiral due to the incommensurate alignment of the molecular rows with respect to the underlying metal lattice. These molecular domains always aggregated in groups of three, all of the same chirality, but with different rotational orientations, forming homochiral “tri‐lobe” ensembles. At a larger length scale, these tri‐lobe ensembles associated with nearest‐neighbor tri‐lobe units of opposite chirality at lower packing densities before forming an extended array of homochiral tri‐lobe ensembles at higher converges. This system displayed chirality at a variety of size scales from the molecular (≈1 nm) and domain (≈5 nm) to the tri‐lobe ensemble (≈10 nm) and extended array (>25 nm) levels. The chirality of the tri‐lobe ensembles dictated how the overall surface packing occurred and both homo‐ and heterochiral arrays could be reproducibly and reversibly formed and interchanged as a function of surface coverage. Finally, these chirally templated surfaces displayed remarkable enantiospecificity for naphtho[2,3‐a]pyrene molecules adsorbed in the second layer. Given its simplicity, reversibility, and rich degree of order, this system represents an ideal test bed for the investigation of symmetry breaking and the hierarchical transmission of chirality through multiple length scales.     

Mechanistic studies of the O2-dependent aliphatic carbon-carbon bond cleavage reaction of a nickel enolate complex

The mononuclear nickel(II) enolate complex [(6-Ph(2)TPA)Ni(PhC(O)C(OH)C(O)Ph]ClO(4) (I) was the first reactive model complex for the enzyme/substrate (ES) adduct in nickel(II)-containing acireductone dioxygenases (ARDs) to be reported. In this contribution, the mechanism of its O(2)-dependent aliphatic carbon-carbon bond cleavage reactivity was further investigated. Stopped-flow kinetic studies revealed that the reaction of I with O(2) is second-order overall and is ～80 times slower at 25 °C than the reaction involving the enolate salt [Me(4)N][PhC(O)C(OH)C(O)Ph]. Computational studies of the reaction of the anion [PhC(O)C(OH)C(O)Ph](-) with O(2) support a hydroperoxide mechanism wherein the first step is a redox process that results in the formation of 1,3-diphenylpropanetrione and HOO(-). Independent experiments indicate that the reaction between 1,3-diphenylpropanetrione and HOO(-) results in oxidative aliphatic carbon-carbon bond cleavage and the formation of benzoic acid, benzoate, and CO:CO(2) (～12:1). Experiments in the presence of a nickel(II) complex gave a similar product distribution, albeit benzil [PhC(O)C(O)Ph] is also formed, and the CO:CO(2) ratio is ～1.5:1. The results for the nickel(II)-containing reaction match those found for the reaction of I with O(2) and provide support for a trione/HOO(-) pathway for aliphatic carbon-carbon bond cleavage. Overall, I is a reasonable structural model for the ES adduct formed in the active site of Ni(II)ARD. However, the presence of phenyl appendages at both C(1) and C(3) in the [PhC(O)C(OH)C(O)Ph](-) anion results in a reaction pathway for O(2)-dependent aliphatic carbon-carbon bond cleavage (via a trione intermediate) that differs from that accessible to C(1)-H acireductone species. This study, as the first detailed investigation of the O(2) reactivity of a nickel(II) enolate complex of relevance to Ni(II)ARD, provides insight toward understanding the chemical factors involved in the O(2) reactivity of metal acireductone species.     

ENDOR studies of the ligation and structure of the non-heme iron site in ACC oxidase

Ethylene is a plant hormone involved in all stages of growth and development, including regulation of germination, responses to environmental stress, and fruit ripening. The final step in ethylene biosynthesis, oxidation of 1-aminocyclopropane-1-carboxylic acid (ACC) to yield ethylene, is catalyzed by ACC oxidase (ACCO). In a previous EPR and ENDOR study of the EPR-active Fe(II)-nitrosyl, [FeNO],(7) complex of ACCO, we demonstrated that both the amino and the carboxyl moieties of the inhibitor d,l-alanine, and the substrate ACC by analogy, coordinate to the Fe(II) ion in the Fe(II)-NO-ACC ternary complex. In this report, we use 35 GHz pulsed and CW ENDOR spectroscopy to examine the coordination of Fe by ACCO in more detail. ENDOR data for selectively (15)N-labeled derivatives of substrate-free ACCO-NO (E-NO) and substrate/inhibitor-bound ACCO-NO (E-NO-S) have identified two histidines as protein-derived ligands to Fe; (1,2)H and (17)O ENDOR of samples in D(2)O and H(2)(17)O solvent have confirmed the presence of water in the substrate-free Fe(II) coordination sphere (E-NO). Analysis of orientation-selective (14,15)N and (17)O ENDOR data is interpreted in terms of a structural model of the ACCO active site, both in the presence (E-NO-S) and in the absence (E-NO) of substrate. Evidence is also given that substrate binding dictates the orientation of bound O(2).     

Stable polythiophene semiconductors incorporating thieno[2,3-b]thiophene

This work describes a new design methodology that allows the preparation of air stable, semiconducting thiophene polymers with high charge carrier mobilities. The incorporation of thieno[2,3-b]thiophene into a polythiophene backbone introduces cross-conjugated double bonds that disfavor full delocalization, leading to high ionization potential in comparison to a fully conjugated polythiophene, with no reduction in charge carrier mobility. The resulting solution processable polymers exhibit charge carrier mobilities up to 0.15 cm2/V s and on/off ratios greater than 105 when measured in air. Transistors exhibit lifetimes of several months in air with no encapsulation necessary.