A Selective and Sensitive Chromogenic and Fluorogenic Detection of a Sulfur Mustard Simulant

A simple and highly selective chromogenic and fluorogenic detection of sulfur mustard (SM) simulants is reported. Dithiol 1, in the presence and absence of a mustard simulant behaves differently toward a squaraine dye (SQ), and thus provides a visual and spectroscopic signal for mustard gas. The sensor responds to the SM simulant, but not to the O-analog of mustard stimulant or nerve agent mimics and other electrophilic agents. The visual and fluorescent detection with less than 50 mu M of SM simulant shows good sensitivity. The utility of the sensor was demonstrated by analysis of SM simulant on surfaces, in soil, and in the gas phase.Office of Naval Research N00014-09-1-1087Welch Foundation F-1151Department of Science and Technology, IndiaDefense Research and Development Organization, IndiaChemistr

Compositions and methods for the detection of chemical warfare agents

Compositions for detection of chemical warfare agents that comprise oximate anion reactive sites and fluorophore cores. Methods for detecting a chemical warfare agents that comprise providing a detector molecule comprising an oximate anion reactive site and a fluorophore core and detecting fluorescence from the detector molecule. Methods for enhancing the reactivity of an oximate nucleophile that comprise introducing an oxime into an aprotic solvent and deprotonating the oxime to form the oximate nucleophile with a base that creates noncoordinating anions.Board of Regents, University of Texas Syste

Determining enantiomeric excess using indicator-displacement assays

The invention includes an enantioselective indicator-displacement assay useful to determine enantiomeric excess (ee) enantiomeric samples calorimetrically. Determination may be by inspection of color with the naked eye, spectrographic measurement, or mathematical calculation. Concentration may also be determined. The assay may involve two independent absorption measurements. On suitable group of enantiomeric molecules to be assayed include α-hydroxyacids. The inherent relationship between the absorbance of the indicator-displacement ensemble and the overall concentration and ee of the analyte is established through solution equilibria. The invention also includes use of the assay in drug screening and manufacturing, high throughput screening of catalysts and kits for use in conducting assays of the invention.Board of Regents, University of Texas Syste

Enthalpy vs Entropy Driven Complexation of Homoallylic Alcohols by Rh(I) Complexes

This document is the Accepted Manuscript version of a Published Work that appeared in final form inOrganometallics, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://doi.org/10.1021/om200793p.The thermodynamics of binding between several homoallylic alcohols and simple olefinic Rh(I) compounds was examined with 1H NMR spectroscopy and ITC. 1H NMR titrations revealed moderate binding of these alcohols with [Rh(COD)2]+ (1) and [Rh(COD)(CH3CN)2]+ (3), but weaker binding with [Rh(NBD)2]+ (2). ITC indicated that the complexation with [Rh(COD)2]+ is mainly governed by enthalpy whereas binding with [Rh(COD)(CH3CN)2]+ is entirely driven by entropy. The thermodynamic parameters for the homoallylic alcohol binding of Rh(I) complexes 1–3 are consistent with crystallographic data

Preferential Control of Forward Reaction Kinetics in Hydrogels Crosslinked with Reversible Conjugate Additions

Molecular substitutions were used to demonstrate preferential control over the kinetic rate constants in a poly(ethylene glycol)-based hydrogel with two different reversible thia-conjugate addition reactions. A strong electron withdrawing nitrile group on the conjugate acceptor showed a 20-fold increase in the forward rate constant over a neutral withdrawing group, while the reverse rate constant only increased 6-fold. Rheometry experiments demonstrated that the hydrogel plateau modulus was primarily dictated by reaction equilibrium, while the stress relaxation characteristics of the hydrogel were dominated by the reverse rate constant. Furthermore, the dynamic crosslinking allowed the hydrogel to rapidly and spontaneously self-heal. These results indicate that decoupling the kinetic rate constants of bond exchange allow systematic control over dynamic covalent hydrogel bulk properties, such as their adaptability, stress relaxation ability, and self-healing properties.This research was supported by the National Science Foundation (NSF MRSEC DMR-1720595, T.M.F., E.V.A., and A.M.R) and by the Burroughs Wellcome Fund (CASI-1015895, A.M.R). The authors acknowledge the use of shared research facilities supported in part by the Texas Materials Institute, the Center for Dynamics and Control of Materials: an NSF MRSEC (DMR- 1720595), and the NSF National Nanotechnology Coordinated Infrastructure (ECCS-1542159).Center for Dynamics and Control of Material

Preferential Control of Forward Reaction Kinetics in Hydrogels Crosslinked with Reversible Conjugate Additions

Molecular substitutions were used to demonstrate preferential control over the kinetic rate constants in a poly(ethylene glycol)-based hydrogel with two different reversible thia-conjugate addition reactions. A strong electron withdrawing nitrile group on the conjugate acceptor showed a 20-fold increase in the forward rate constant over a neutral withdrawing group, while the reverse rate constant only increased 6-fold. Rheometry experiments demonstrated that the hydrogel plateau modulus was primarily dictated by reaction equilibrium, while the stress relaxation characteristics of the hydrogel were dominated by the reverse rate constant. Furthermore, the dynamic crosslinking allowed the hydrogel to rapidly and spontaneously self-heal. These results indicate that decoupling the kinetic rate constants of bond exchange allow systematic control over dynamic covalent hydrogel bulk properties, such as their adaptability, stress relaxation ability, and self-healing properties.This research was supported by the National Science Foundation (NSF MRSEC DMR-1720595, T.M.F., E.V.A., and A.M.R) and by the Burroughs Wellcome Fund (CASI-1015895, A.M.R). The authors acknowledge the use of shared research facilities supported in part by the Texas Materials Institute, the Center for Dynamics and Control of Materials: an NSF MRSEC (DMR- 1720595), and the NSF National Nanotechnology Coordinated Infrastructure (ECCS-1542159).Center for Dynamics and Control of Material

Metallacyclobutadiene versus Metallatetrahedrane Structures for CI,MoC,H, Complexes

98 Organometallics 1988, 7, [98][99][100][101][102][103][104][105] portant difference in chemical reactivity between Fe-(TMM)L3 complexes (L = PR3 (3) and L = CO): a oneelectron transfer easily occurs from 3 on attempts of alkylation and the resulting 17-electron intermediate is stabilized by the basic phosphines L, whereas Fe-(TMM)(CO), is the site of electrophilic substitutions,15 but its one-electron abstraction is difficult to perform and immediately undergoes decomposition, presumably via initial cleavage of an Fe-CO bond. This illustrates the deciding role of the nature of the ligands to modulate the behavior of complexes within the same family. Cyclic voltammetry of 6a-c showed a reversible oneelectron oxidation at negative potential corresponding to the formation of Fe(o-xylylene)L,+ (69, and an irreversible wave between 0.50 and 0.70 V was observed Conclusion Our results present an easy access to electron-rich (q4-hydrocarbon)iron complexes via FeC12(PR3)n intermediates, magnesium, and halogenated substrates. This method avoids the preliminary preparation of unstable Grignard reagents and should offer a potential for organometallic syntheses. The nature and the number of ancillary PR3 groups play a determining role for the reactivity of FeC12(PR3) with o-BrMgCH2C6H4CH3, which leads to either a C-H activation or a C-C coupling reaction. The studied Fe(q4-TMM)L3 and Fe(q4-o-xylylene)L3 complexes show at the same time a high tendency to give an electron transfer and an unexpected stability of the resulting paramagnetic species. These two characteristics, which are indicative of the electron-rich nature of the complexes, appear to be modulated by the electron-donor capability of the phosphorus groups and also by the type of interaction between the hydrocarbon ligand and the' metal. Acknowledgment. We are grateful to C. Mountassir and Dr. S. Sinbandhit for helpful assistance and discussions. Registry No. la, 55853-16-2; lb, 95911-92-5; Id, 55059-43-3; 2,1871-57-4; 3a, 95911-86-7; 3a+(CF3SOf), 95911-88-9; 3a+(N0<), 111409-15-5; 3c+(CF3S03-), 111409-17-7; 4a, 612-12-4; 5,56812-61-4; 6a, 111409-13-3; 6a+, 111409-14-4; 6b, 95911-91-4; 6d, 95911-89-0; 7,952-80-7; 8b, 111409-18-8; 9b, 110074-88-9; MeC-(CH2PMe&, 77609-83-7 The bonding and energetics in the C13MoC3H3 metallacyclobutadiene are contrasted with those in the metallatetrahedrane. The complexes are found to be within 20 kcal/mol of one another, with the metallatetrahedrane being the lower in energy. The Mo-C bonds are essentially covalent in both structures, and the metallacyclobutadiene posseseefl resonance stabilization. Charge distribution in the carbon fragments reveals no cyclopropenium character in the C3H3 ring of the metallatetrahedrane. Bonding, energetics, and charge distributions are all discussed with an emphasis on structure and reactivity

Effects of linker flexibility on phase behavior and structure of linked colloidal gels

Colloidal nanocrystal gels can be assembled using a difunctional "linker" molecule to mediate bonding between nanocrystals. The conditions for gelation and the structure of the gel are controlled macroscopically by the linker concentration and microscopically by the linker's molecular characteristics. Here, we demonstrate using a toy model for a colloid-linker mixture that linker flexibility plays a key role in determining both phase behavior and structure of the mixture. We fix the linker length and systematically vary its bending stiffness to span the flexible, semiflexible, and rigid regimes. At fixed linker concentration, flexible-linker and rigid-linker mixtures phase separate at low colloid volume fractions in agreement with predictions of first-order thermodynamic perturbation theory, but the semiflexible-linker mixtures do not. We correlate and attribute this qualitatively different behavior to undesirable "loop" linking motifs that are predicted to be more prevalent for linkers with end-to-end distances commensurate with the locations of chemical bonding sites on the colloids. Linker flexibility also influences the spacing between linked colloids, suggesting strategies to design gels with desired phase behavior, structure, and by extension, structure-dependent properties.Comment: 11 pages, 8 figures, supplementary materia

Design of Chiral Supramolecular Polymers Exhibiting a Negative Nonlinear Response.

Many synthetic and supramolecular chiral polymeric systems are known to exhibit the "majority rules effect" (MRE), a positive nonlinear response in which a small enantiomeric excess ( ee ) of the chiral building blocks leads to unproportionally large chiroptical signals near zero ee . In contrast, the opposite "racemate rules effect" (RRE), a negative nonlinear response in which the chiroptical signals are flat near zero ee , while giving large nonlinear chiroptical responses to ee at high values, has only been occasionally observed. The origin of this unusual ee dependence remains elusive largely because few systems have been established that exhibit this effect. Herein, we present a design approach that enables the development of chiral supramolecular polymers with a pronounced negative nonlinear response akin to RRE. This is achieved by in situ generating a bidentate inducer for supramolecular polymerization that exists in both meso - and homochiral forms upon reacting with chiral guests. The presence of the meso -inducer creates an aggregate structure that has a little response in the circular dichroism (CD) spectra as a function of ee at a particular wavelength, but a homochiral inducer gives large changes in response to ee at this wavelength. This allowed for an RRE-like response to be observed when the CD intensity of the supramolecular polymers was plotted against the ee of the chiral guests that generate the meso - and homochiral inducers without the necessity of the racemic guest preferentially being incorporated into the polymer