1,721,194 research outputs found
A Selective and Sensitive Chromogenic and Fluorogenic Detection of a Sulfur Mustard Simulant
No full textA 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
Mechanistic Studies on Covalent Assemblies of Metal-Mediated Hemi-Aminal Ethers
No full textThe use of reversible covalent bonding in a four-component assembly incorporating chiral alcohols was recently reported to give a method for determining the enantiomeric excess of the alcohols via CD spectroscopy. Experiments that probe the mechanism of this assembly, which consists of 2-formylpyridine (2-PA), dipicolylamine (DPA), Zn(II) and alcohols to yield zinc complexes of tren-like ligands, are presented. The studies focus upon the mechanism of conversion of a hemi-aminal (1) to a hemi-aminal ether (3), thereby incorporating the fourth component. It was found that molecular sieves along with 3 to 4 equivalents of alcohol are required to drive the conversion of 1 to 3. Attempts to isolate an intermediate in this reaction via addition of strong Lewis acids led to the discovery of a five-membered ring pyridinium salt (5), but upon exposure to Zn(II) and alcohols gave different products to the assembly. This was interpreted to support the intermediacy of an iminium species. Kinetic studies reveal that the conversion of 1 to 3 is zero-order in alcohol in large excesses of alcohol, supporting rate-determining formation of an intermediate prior to reaction with alcohol. Further, the magnitudes of the rate constants for interconversion of 1 and 3 are similar, supporting the notion that there are similar rate-determining steps (rds) for the forward and reverse reactions. Hammett plots show that the rds involves creation of a negative charge (interpreted as the loss of positive charge), supporting the notion that the decomplexation of Zn(II) from the assemblies to generate apo-forms of 1 and 3 is rate-determining. The individual mechanistic conclusions are combined to create a qualitative reaction coordinate diagram for the interconversion of 1 and 3.National Institutes of Health R01GM077437Welch Foundation F-1151, F-1390National Science Foundation CHE-1212971NIH GM059802Chemistr
Reaction-based Indicator displacement Assay (RIA) for the selective colorimetric and fluorometric detection of peroxynitrite
No full textUsing the self-assembly of aromatic boronic acids with Alizarin Red S (ARS), we developed a new chemosensor for the selective detection of peroxynitrite. Phenylboronic acid (PBA), benzoboroxole (BBA) and 2-(N,N-dimethylaminomethyl)phenylboronic acid (NBA) were employed to bind with ARS to form the complex probes. In particular, the ARS-NBA system with a high binding affinity can preferably react with peroxynitrite over hydrogen peroxide and other ROS/RNS due to the protection of the boron via the solvent-insertion B-N interaction. Our simple system produces a visible colorimetric change and on-off fluorescence response towards peroxynitrite. By coupling a chemical reaction that leads to an indicator displacement, we have developed a new sensing strategy, referred to herein as RIA (Reaction-based Indicator displacement Assay).</p
Circular dichroism of multi-component assemblies for chiral amine recognition and rapid ee determination
No full textUpon mixing a chiral amine, enantiopure BINOL, and o-formyl phenyl boronic acid, the three components assemble efficiently and rapidly into chiral host-guest structures that produce distinct circular dichroism signals for each enantiomer of the amine. Employing BINOL and two derivatives to create an array of receptors, the CD signals resulting from several a-chiral primary amines were processed by principal component analysis and linear discriminant analysis to give satisfactory discrimination of the amines studied. Not only was the system able to differentiate the analytes chemoselectively and enantioselectively, but it also allowed for the rapid determination of chiral amineNational Institutes of Health GM77437Welch Foundation F-1151Chemistr
Exploration of Plasticizer and Plastic Explosive Detection and Differentiation with Serum Albumin Cross-Reactive Arrays
No full textPlastic explosives, such as Semtex and C4, are commonly used explosive mixtures. The differentiation and detection of the plasticizers within these mixtures could provide information for anti-terrorism and combat activities. In this study, we demonstrate a strategy of using cross-reactive serum albumin proteins to differentiate and detect the plasticizers found within these explosive mixtures. With our sensing ensemble, comprised of serum albumins, fluorescent indicators and an additive, we successfully classified the five plasticizers found within Semtex and C4 using linear discriminate analysis, and differentiated simulated Semtex and C4 mixtures based on surrogates of the explosive material(s) and the plasticizer composition in these samples. Finally, we have shown the utility of this type of cross-reactive array for real life use in a battlefield setting by examining these mixtures in the presence of soil contamination.Office of Naval Research N00014-09-1-1087Welch Foundation F-1151Chemistr
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Synthesis and Structural Analyses of Phenylethynyl-Substituted Tris(2-Pyridylmethyl)Amines and their Copper(II) Complexes
No full textThree new tris(2-pyridylmethyl) amine-based ligands possessing phenylethynyl units have been prepared using Sonogashira couplings and substitution reactions. Copper(II) complexes of those tetradentate ligands have also been synthesized. Solid-state structures of the six new compounds have been determined by single-crystal X-ray diffraction analyses. Examination of the molecular structures of the ligands revealed the expected triangular geometries with virtually undeformed carbon-carbon triple bonds. While the tertiary nitrogen of the free ligands seem to be prevented from participation in supramolecular non-covalent interactions by the pyridyl hydrogen at the 3-position, the pyridyl nitrogens play a crucial role in the packing mode of the crystal structure. The nitrogens form weak hydrogen bonds, varied in length between 2.32 and 2.66 angstrom, with the pyridyl hydrogen of its neighbouring molecule. The [N center dot center dot center dot H-C] contacts enforce one-dimensional columnar assemblies on ligands that organize into wall-like structures, which in turn assemble into three-dimensional structures through CH-pi interactions. Structural analyses of Cu(II) complexes of the ligands revealed propeller-like structures caused by steric crowding of three pyridine ligands. The copper complexes of the ligands having three phenylethynyl substituents showed a remarkably deformed carbon-carbon triple bond enforced by a steric effect of the three phenyl groups. Most significantly, a total of seventy non-covalent interactions, classified into twelve types of hydrogen-involving short contacts, were identified in this study. The phenylethynyl substituent participated in forty-two interactions as a hydrogen bond acceptor, and its role was more distinctive in the crystal structures of the Cu(II) complexes.National Science Foundation CHE-1212971Welch Foundation F-0046Chemistr
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Case studies on the aspects of molecular signaling: binding forces, signal generation, and a mature receptor
No full texttextThe field of molecular and atomic sensing has seen a vast growth over the last
few decades. Yet many advances still remain to be made. This dissertation takes an in
depth look at the two major aspects in a molecular sensing or signaling scaffold—namely
the binding of a target followed by the transduction of an observable signal. Chapter 1
will deal with intermolecular binding forces in the form of a case study on electrophilic
coordination to carbonyl compounds. Computational studies are performed to determine
the optimal geometry of an electrophile interacting with a carbon acid to affect the
greatest enhancement in the acidity at the α-carbon. We find that partial interaction
through the π-system of the carbonyl and the resulting enolate affords the greatest acidity
enhancement. Chapter 2 then switches to studies on the development of a novel signaling
method for a molecular signaling assay. Two novel elements—transition metal catalytic
signal amplification and peroxyoxalate chemiluminescence—are utilized to generate a
signaling motif incorporating two new methodologies for signal generation. The first
uses of catalytic signal amplification for the detection of small organic analytes and
peroxyoxalate chemiluminescence for signal generation in a molecular recognition event
are described. Finally, both elements are brought together in Chapter 3, which describes
a mature ionophoric chemodosimeter with both highly sensitive binding and strong signal
output. The use of a squaraine dye as a signaling unit for the detection of palladium(II)
salts is described in which an aliphatic thiol acts as the theoretical “host” in a covalent
displacement type assay. Palladium(II) and other transition metal detection is of
importance both industrially and environmentally, and the assay described is sensitive to
levels desired in both arenas.Chemistry and BiochemistryChemistr
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Sequenceable Sequence-Defined Oligourethanes as a Medium for Information Storage
No full textPhysical data storage is an increasingly active field of research. Potential storage media such as DNA or RNA can encode sufficient information to be viable, but they are not stable in the long term. A potential alternative to these heavily studied polymers presented itself in plastics, especially the linear polymers of oligourethanes. These plastics demonstrate both the information density and stability necessary for long-term storage of encoded data, so long as individual units can be decoded and read at a later time. Previous work determined appropriate sequencing conditions for stepwise degradation of the oligourethanes, allowing for the reverse engineering of the sequence-defined polymer. With this proof of concept of information storage, focus was shifted toward solid phase synthesis, labeling, and sequencing of polyurethanes with diverse monomers bearing variable functionalities, to assess stability in the degradation conditions. Interest in the inclusion of Tunable Orthogonal Reversible Covalent (TORC) bonds served as the impetus for the synthesis of a Lysine-based monomer capable of “click” reactions. This monomer was successfully synthesized, integrated into a sequence-defined oligourethane, and modified with a TORC functionality using click chemistry. Moving forward, the project will focus on the sequencing of sequence-defined oligourethanes containing this and other monomers bearing variable functionalities, as well as investigating the capability of TORC-functionalized oligourethanes to form higher-ordered structures akin to DNA.Chemistr
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TORC Bonding Pairs as an Alternative to Nucleobases in Self Replicating Polymers
No full textThe search for life on other planets is limited due to having only an incomplete knowledge of the origins of life on Earth as reference. While genetic information is stored and replicated by RNA and DNA using nucleobase chemistry here on Earth, this may not be the case on other planets with different environmental conditions. Tunable Orthogonal Reversible Covalent (TORC) bonds have promise in the creation of sequence-specific replicators because their orthogonality allows for the TORC bonding pairs to function similarly to nucleotide bases, defining and replicating the sequence, while their reversibility allows for duplexes to be separated for replication and their increased strength as covalent bonds would make these replicators more suitable to hot environments than the hydrogen bonding interactions observed in DNA replicators. This project represents the first step in the creation of sequence-specific TORC replicators by demonstrating the templating and synthesis of short peptide strands from a template strand using the hydrazone TORC bonding pair. In addition to this, macrocyclic products were also produced using these templates. This unexpected result holds promise for the creation of macrocyclic TORC replicators. The creation of macrocycles also has therapeutic applications, as macrocyclic peptides have useful properties but are generally difficult to synthesize, and the templates created in this project can quantitatively produce macrocyclic peptide products without any unwanted side products.Chemistr
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Fluorescent sensors for the detection of analytes in solution
No full texttextThis dissertation describes work aimed at the development of fluorescent
sensors for various analytes in solution. In chapter 1, an introduction to molecular
recognition and sensing is presented to provide background information
pertaining to research discussed in the later chapters. Here, topics such as
molecular interactions in solution, single-analyte sensing using preorganized
scaffolds, installation of signaling groups for detection of binding, analytical
techniques for complexation and sensing using multiple component sensing
ensembles are reviewed.
Chapter 2 describes a project to develop a molecular sensor with a Noxide-bipyridine
complex as a binding site and for signaling the association. The
project progressed through the synthesis towards three different sensor designs,
until 2.60 was obtained containing a bis-bipyridine-tetra-N-oxide europium
complex and two ammonium groups as binding sites.
Binding studies were performed using a target guest, 2,3-
bisphosphoglycerate (2.1), a glycolytic intermediate involved in oxygen transport
regulation. A 1:1 host-guest complex was observed in 50% methanol /
acetonitrile solution with a Ka of 6.70 x 105
M-1. Related glycolytic intermediates
lacking a second phosphate (2.2, 2.3, 2.63), however, showed 2:1 guest to 2.60
binding. Phenylphosphate bound 1:1 with a Ka of 2.0 x 105
M-1. Finally, all
compounds showed 2:1 guest to host binding with model host 2.61, which lacks
the ammonium groups. The data shows that of similar glycolytic intermediates,
only 2.1 undergoes 1:1 binding with 2.60 and indicates the importance of the
second phosphate on the guest and the host ammoniums in forming this complex.
In chapter 3, work towards the development of multiple differential
sensors for small metal cations is presented. Approaches included random
derivitization of resin beads with fluorophores and azacrown ethers and two
attempts at synthesizing resin bound azacrown ethers and cryptands with
covalently attached coumarins. Finally, in chapter 4, work concerning the
construction of a Brønsted plot using compounds which could potentially form
low-barrier hydrogen bonds is presented. Determination of the kinetics and
acidity of a series of compounds with varying electronics at hydrogen bonding
locations is discussed.Chemistry and BiochemistryChemistr
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