Browsing by Subject "Supramolecular chemistry"
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Item Aromatic electron donor-acceptor interactions in novel supramolecular assemblies(2006) Reczek, Joseph James; Iverson, Brent L.Item Boronic acid and guanidinium based synthetic receptors: new applications in differential sensing(2003) Wiskur, Sheryl Lynn; Anslyn, Eric V.In the field of supramolecular chemistry a common goal is to design a receptor that is highly selective for a targeted analyte. While this is a worthwhile goal, many of these synthetic receptors are less selective than their natural counterparts such as enzymes or antibodies. Many aspects of the work shown herein demonstrate that these less selective synthetic receptors are still useful chemosensors. Just as Nature utilizes differential receptors in our sense of taste and smell, synthetic sensor arrays can be developed to achieve similar results. Chapter 1 is an overview of the development of a sensor. It begins with the aspects of binding carboxylates and diols, specifically by guanidiniums and boronic acids. Next, signaling motifs of a sensor are discussed, leading to the advantages of using an indicator displacement assay. Finally, differential sensors are discussed, introducing the idea of incorporating non-selective synthetic sensors for the detection of multiple analytes with the use of pattern recognition. Chapter 2 discusses the use of non-selective synthetic receptors in a number of sensing schemes. First a receptor was used to bind a class of age related analytes found in scotch whiskies. A correlation was found between the age of the scotch and the sensing ensemble’s response to the beverage. In another sensing application, a high degree of selectivity was achieved by using two receptors and two indicators together in solution. Due to the differential response of the receptors to the indicators and the guests, the simultaneous quantification of tartrate and malate was achieved with the aid of pattern recognition. Finally, initial efforts were put forth for incorporating the receptor into a differential sensing array by immobilizing the receptor on a solid support. The selectivity of the receptor was investigated, showing that the receptor still had a higher affinity for tartrate over malate. Chapter 3 investigated the thermodynamics of guanidiniums and boronic acids binding carboxylates and diols, respectively. Four hosts were investigated with a variety of guests. The association constants were determined through UV/vis analysis, while the entropy and enthalpy were determined with isothermal titration calorimetry. The binding of boronic acids to more than just aliphatic diols was also investigated. Chapter 4 discussed the development of new sensor for catechol containing analytes. The sensor’s design is based on iron binding siderophores. The iron is both the binding site and the signaling motif for the sensor. Upon addition of catechol guests, a signal modulation did occur.Item Design and synthesis of artificial receptors for selective and differential sensing(2007-12) Zhang, Tianzhi, 1973-; Anslyn, Eric V., 1960-This dissertation consists of four chapters. The first chapter provides an in-depth background of synthetic receptors for recognitions of phosphorylated molecules. This chapter covers synthetic receptors developed within the last two decades, and it focuses on the diverse functionalities and detection techniques involved in the receptor design. Chapter 2 discusses the synthesis and employment of a metalated receptor for the selective recognition of organic phosphates and phospho-amino acids, and describes a receptor with a pseudo tetrahedral cavity, which was found to be selective to phosphate, was synthesized utilizing a new and efficient synthetic route. UV-Vis titrations were used to determine binding constants for various organic phosphates and phospho-amino acids. The receptor:Cu(II) complex was found to differentiate the degree and size of phosphate substitutions. Chapter 3 describes the synthesis and application of a type of differential receptors for the recognition of phosphorylated tri-peptides from regular tri-peptides. The tri-peptide couples described in this chapter were part of sequences in protein Filamentous R-synuclein, which was discovered to have a close relation to Parkinson's disease. Extensive Ser129 phosphorylation was observed in diseased brains. Both solid phase and solution phase differential receptors were obtained in the investigations of peptide differentiation. A series of screening methods were applied to narrow down the system combinations. Linear discrimant analysis (LDA) statistical analysis generated a large spatial separation among six tripeptides. Chapter 4 describes the synthesis of a boronic acid based receptor for carboxy and phospho sugars recognition. Due to the large affinity to gluconic acid, which is the only product of enzyme catalyzed glucose oxidation, this receptor was successfully applied in determination of glucose concentration in human serum.Item Electron transfer within tetrathiafulvalene calix[4]pyrrole supramolecular ensembles(2014-12) Davis, Christina Marie; Sessler, Jonathan L.; Krische, Michael J; Siegel, Dionicio R; Hoffman, David W; Brodbelt, Jennifer S; Anslyn, Eric VOver the last decade, the ecological need for clean and renewable energy sources has resulted in considerable resources being directed toward the development of systems capable of converting light energy into chemical energy. This has led to a focus on artificial photosynthetic systems and solar cell devices. These types of devices are desirable since they do not contribute to greenhouse gas emissions, as compared with fossil fuels. Organic solar cells (OSCs) are able to convert solar energy into chemical energy via photon absorption that creates a potential difference in the medium and results in electron transfer. The evolution and lifetime of the charge-separated state produced upon this electron transfer has proved difficult to mimic with synthetic materials. One well recognized problem is that to achieve efficient electron transfer, the rate of back electron transfer must be slower than that of forward electron transfer. Creating a molecular dyad that undergoes rapid electron transfer and results in a long lifetime is a key step in the creation of an organic solar cell that permits efficient solar energy conversion. One such way to achieve these systems is to employ supramolecular interactions to pre-organize the donors and acceptors in solution. The goal of the studies depicted in this dissertation was to explore whether tetrathiafulvalene substituted calix[4]pyrroles (TTF–C4Ps) paired with suitable electron acceptors would lead to systems that undergo electron transfer, either thermal or photoinduced, followed by the formation of stable charge-separated states. We chose to employ fullerenes (Chapter 2) and a porphyrin substituted with a carboxylate functional group (Chapter 3) as the acceptors in the putative electron transfer complexes since both are well known as photoabsorbers that have been extensively studied in photosynthetic model systems. The electron transfer from a TTF moiety of the calix[4]pyrrole to either fullerene or porphyrin was studied via UV-Vis-NIR, fluorescence, and electron spin resonance spectroscopies as well as with laser flash photolysis measurements and theoretical calculations. Chapter 4 details work in which TTF oxidation states were used to create a stable TTF mixed-valence dimer as well as a redox switched “on—off—on” fluorescent system.Item Experimental contributions to the theory and application of molecular recognition(2008-05) Hughes, Andrew Dike, 1980-; Anslyn, Eric V., 1960-Molecular recognition is a major branch of modern organic chemistry, and it resides at the forefront of supramolecular chemistry. Supramolecular chemistry refers to the study of the noncovalent intermolecular interaction that are crucial for biological processes, catalytic systems, the organization of crystalline or solution phase superstructures, and molecular recognition to name a few examples. The following dissertation reports research efforts from the Anslyn group into three topics of fundamental interest to the molecular recognition community: cooperativity, array sensing, and the development of highly selective sensors for minimally functionalized analytes. Chapter 1 is a review of the most fundamental points of molecular recognition as it applies to the experimental work that follows. Intermolecular association phenomena are driven by multiple discrete, noncovalent interactions, and cooperativity is a measure of the efficiency with which these interactions are employed in a given system. Cooperativity is poorly understood despite its ubiquity in biological and molecular recognition contexts. The first synthetic hostguest system exhibiting positive cooperativity in water is reported in Chapter 2. The utility of sensitive but unselective sensors when applied in an array format has recently come to light. Chapter 3 details an array of polyaromatic fluorophores dissolved in an aqueous surfactant solution that was used to sense nitrated explosives. This exceptionally unselective quenching process was able to detect and discriminate nitrated explosives such as RDX and TNT at concentrations as low as 19 [mu]M. Finally, Chapters 4 and 5 report different approaches to the sensing of enantiomeric excess in [alpha]-chiral alcohols using an indicator displacement paradigm. Chapter 4 explores unprecedented efforts to convert the Sharpless catalytic epoxidation system to the first Ti[superscript IV]-based molecular recognition system. Chapter 5 focuses upon a two-stage approach of derivatization of the [alpha]-chiral alcohol to a metal chelating ligand followed by employment of the derivative in an indicator displacement assay.Item Exploring chemistry of tetrathiafulvalene-calix[4]pyrroles : supramolecular ion mediated electron transfer(2010-12) Park, Jung Su; Sessler, Jonathan L.; Anslyn, Eric V.; Crooks, Richard M.; Siegel, Dionicio R.; Dodabalapur, AnanthMolecular recognition exploiting non-covalent interactions mediates the structure and function of many critical biological and synthetic molecules. There has thus been continuing and intense efforts in the design and synthesis of supramolecular systems with the capability of recognizing specific chemical species. Among various guest species, Prof. Sessler's group has been focused on the study of artificial anion receptors. Calix[4]pyrrole is a tetrapyrrolic macrocycle that is capable of binding anions via concerted and directional hydrogen bonding. Recently, a tetrathiafulvalene (TTF) functionalized calix[4]pyrrole (TTF-C4P) was synthesized and studied as a receptor for various guest species such as anions, electron deficient guest species, and C₆₀. This dissertation focuses on the recent discovery in supramolecular chemistry of TTF-calix[4]pyrrole derivatives. Chapter 1 provides a brief overview of the historical perspective, redox properties, and uses of TTF derivatives as functional building blocks for supramolecular assemblies, as well as previous findings involving the supramolecular chemistry of TTF-C4P. Chapter 2, as the major focus of this dissertation, describes ion mediated supramolecular and reversible electron transfer processes between TTF-C4P and bisimidazolium salts (BIQ²⁺2X⁻). We discovered that the electron transfer processes between these redox couples could be controlled reversibly by ion binding. Specifically, we found that anion binding to the TTF-C4P receptor promotes the forward ET processes. In contrast, cation complexation to the cavity of TTF-C4P causes the reverse ET processes. Such ion mediated ET processes play an essential role in biological ET systems including photosynthesis and respirations. These reversible ET processes were mapped out by spectroscopic (¹H-NMR, UV-Vis NIR titrations, and EPR analysis) and X-ray single crystallographic analyses of both the intermediate and products. Chapter 3 describes the synthesis of aromatic (thiophene and benzene) annulated TTF-calix[4]pyrroles as new and significantly improved receptors for poly-nitroexplosives. The resulting electronic modulations of the parent TTF-pyrrole structure result in significantly enhanced binding affinities for the corresponding TTF-C4Ps toward polynitro-explosives. This is reflected in a high level of positive homotropic allosterism. The degree of the cooperative effect was found to vary depending on the nature of both the receptors and guest species. The origin of the cooperative binding can be explained by conformational locking and an inductive effect of binding the first nitroaromatic guest.Item New Calixarene and Cyclophane Macrocycles(2011-05) Son, Pillhun; Bartsch, Richard A.; Mayer, Michael F.; Fuertes, Michael J.; Niwayama, SatomiThe design, synthesis and analysis of new supramolecular hosts are rapidly developing areas of chemistry. This dissertation research presents the synthesis of new calix[4]arene ligands, new cyclophane derivatives and a new type of crown ether corrals accompanied by fluorescence binding analysis. A variety of calix[4]arene ligands have been developed in the past for various applications. Novel di-ionizable tetrabutoxycalix[4]arenes in four different conformations have been synthesized in this dissertation research. In contrast with the tetrabutoxycalix[4]arene ligands which are conformationally fixed, a conformationally mobile methoxy-tributoxy-calix[4]arene was synthesized. The synthetic exploration of calix[4]arene ligands was expanded into multicalix[4]arenes and cyclophane-bridged calix[4]arenes. Cyclophanes have been applied to diverse areas of supramolecular chemistry. A cyclophane with rigid α,α’-bis[(4-hydroxyphenyl]-1,4-diisopropyl-benzene components has been previously termed “corrals”. New synthetic routes, methods, techniques and ring-closure components have been applied to achieve 77 new corral derivatives, which selectively possess attractive properties, such as chirality, selective functionalization, asymmetry, and fluorescence. For some of the new cyclophane hosts synthesized fluorescence binding analysis was conducted. A total of 75 metal salt species was tested with two crown ether corrals resulting in interesting cation recognition, anion effects and selective fluorescence effects on shaking.Item Progress towards a highly efficient and accurate platform for enantiomeric excess determination(2016-05) Lin, Chung-Yon; Anslyn, Eric V., 1960-; Sessler, Jonathan L; Keatinge-Clay, Adrian; Jones, Richard AEnantiomeric excess (ee) determination remains as the bottleneck for high throughput screening of asymmetric catalysts. The work described herein sought to expand on two previously developed ee sensing assays from our lab– an iron based amine assembly and a zinc based multicomponent assembly. To start, the substituent effect of the zinc multicomponent dynamic assembly for secondary chiral alcohol ee determination was investigated. A new assembly with a higher dynamic range and smaller error was observed. Additionally, potential cooperative binding to the multicomponent assembly was investigated. Furthermore, this work included some preliminary results for a concurrent sensing platform for molecules with chiral amine and alcohol moieties.Item Sensing approaches for the discrimination of small molecules and multivalent analytes(2014-12) Gade, Alexandra Moore; Anslyn, Eric V., 1960-; Sessler, Jonathan; Ellington, Andrew; Hoffman, David; Aldrich, RichardDifferential arrays, composed of receptors that are capable of generating unique patterns of responses, have been shown to be useful for discrimination of molecular analytes. Herein, differential arrays have been developed and utilized for the discrimination of small molecule and multivalent biological analytes using cross-reactive receptors. A variety of carboxylate-binding guanidinium-based receptors were tested for their ability to discriminate carboxylate enantiomers. Lanthanide complexes showed the most promising enantiodifferentiation. A dynamic receptor for multivalent biological analytes was developed using self-assembling components designed to target cancer cell lines in a cross-reactive manner. Using this differential array, cancer cell lines of different tissue origin were classified using principal component analysis. The receptors in the array responded to targets as hypothesized but also behaved in a cross-reactive manner that allowed for analyte differentiation. The classification response of the array was reproducible. Boronic acid receptors and receptor arrays were also developed for discrimination of cell surface glycans. In this work, the success of cross-reactive receptors with designed components in differential sensing for small molecules as well as complex multivalent analytes is demonstrated.Item Studies of anion binding in pyrrole-containing supramolecular motifs(2002) Zimmerman, Rebecca Suzanne; Sessler, Jonathan L.Anions are important in a wide range of biological as well as chemical processes. In addition to their importance in the areas of medicine and catalysis, many environmental pollutants are anionic, such as phosphates, nitrates, and pertechnetate. Anions are more difficult to sense via electrostatic interactions than cations because of their lower charge to radius ratio; the majority of neutral anion receptors thus utilize hydrogen bonding as the predominant binding mode. Anions also have a wide range of geometries and require a high degree of complementarity in receptor design in order to achieve selectivity. Additionally, an anion receptor must successfully compete with the solvent environment. Anions are very strongly solvated, and the free energy gained upon binding must exceed the free energy lost as the result of dehydrating the anion. This can make binding in protic or hydroxylic solvents particularly challenging. Because of the inherent difficulties associated with anion recognition, the development of anion binding agents has lagged behind corresponding work on cation receptors. Currently, there are two general classes of synthetic anion receptors, those that are positively charged and those that are neutral. The major advantage of neutral hosts is that the absence of a positive charge generally provides for more selective binding, for the simple reason that positive charges are nondirectional and lead to electrostatic attractions that cannot by definition be selective for a particular anion. Another advantage to neutral hosts is that there is no inherent competition with a receptor associated with a counterion, which can often result in a weaker affinity for the intended guest. This dissertation focuses on the anion binding behavior of neutral, pyrrole containing supramolecular systems. The first chapter will discuss the ability of ferrocene-pyrrole conjugates to sense anions electrochemically. Chapter 2 investigates the anion binding ability of an expanded calixphyrin and a strapped calixpyrrole. Chapter 3 focuses on crown ether appended dipyrrolylquinoxalines and their effectiveness as ditopic receptors. Chapter 4 provides experimental methods and characterization data.Item Synthesis and characterization studies of novel macrocyclic compounds with CH and NH donor groups(2011-12) Cai, Jiajia; Sessler, Jonathan L.; Willson, C G.; Krische, Michael J.; Cowley, Alan H.; Fast, Walter L.The dissertation focuses on the recent discovery in supramolecular chemistry of novel macrocyclic compounds with NH and CH donor groups. Chapter 1 provides a brief overview of the anions under study, supramolecular chemistry, the relevant other anion receptors, as well as previous findings involving the use of CH donor groups as functional building blocks. Chapter 2, as the major focus of this dissertation, describes a pyrrolyl-based triazolophane, incorporating CH and NH donor groups, which acts as a receptor for the pyrophosphate anion in chloroform solution. It shows selectivity for this trianion, followed by HSO₄− > H₂PO₄− > Cl− > Br− (all as the corresponding tetrabutylammonium salts), with NH−anion interactions being more important than CH−anion interactions. In the solid state, the receptor binds the pyrophosphate anion in a clip-like slot via NH and CH hydrogen bonds. Chapter 3 describes a pyrrole–based triazolium–phane which has been prepared through “click” chemistry in moderate yield. It displays a high selectivity for tetrahedral oxyanions relative to various test monoanions and trigonal planar anions in mixed polar organic–aqueous solvent media. It was also found that the binding affinity and selectivity of the macrocycle to the anions are solvent dependent. Several crystal structures were solved. They confirm that the cationic macrocycle ring binds pyrophosphate and phosphate anions in the solid state. Finally, chapter 4 describes a novel 1,3,4-substituted 1,2,3-triazolium salt found to function as an effective precursor for the synthesis of structurally characterized cationic silver(I) and ruthenium(II) carbene complexes of overall 1:2 ligand-to-metal stoichiometry. The Ag(I) complex crystallized in the form of an eight silver atom containing cluster, whereas the Ru(II) complex proved to be a discrete species and was found to be capable of initiating the ring-opening metathesis polymerization of norbornene upon activation with (trimethylsilyl)diazomethane.Item Synthetic selective and differential receptors for the recognition of bioanalytes(2006) Wright, Aaron Todd; Anslyn, Eric V.Item The uses of supramolecular chemistry in synthetic methodology development(2009-05) Shabbir, Shagufta Hasnain; Anslyn, Eric V., 1960-Enantioselective indicator displacement assays (eIDAs), was transitioned to a high-throughput screening protocols, for the rapid determination of concentration and enantioselectivity (ee) of chiral diols and α-hydroxycarboxylic acid. To improve the design of our previously established receptor based on o-(N,N-dialkylaminomethyl)arylboronate scaffolds for eIDAs. The rigidity of the receptor, which pertinent from the formation of an intramolecular N-B dative bond was investigated. o-(Pyrrolidinylmethyl)phenylboronic acid its complexes with bifunctional substrates such as catechol, [alpha]-hydroxyisobutyric acid, and hydrobenzoin was studied in detail by x-ray crystallography and ¹¹B NMR. Our structural study predicts that the formation of an N-B dative bond, and/or solvolysis to afford a tetrahedral boronate anion, depends on the solvent and the complexing substrate present. To simplify the operation of eIDAs, we introduced an analytical method, which utilize a dual-chamber quartz cuvette, which reduces the number of spectroscopic measurements from two to one and introduced artificial neural networks (ANNs) which simplifies data analysis. In a second example a high-throughtput screening protocol for hydrobenzoin was developed. The method involves the sequential utilization of what we define herein as screening, training, and analysis plates. Several enantioselective boronic-acid based receptors were screened using 96-well plates, both for their ability to discriminate the enantiomers of hydrobenzoin and to find their optimal pairing with indicators resulting in the largest optical responses. The best receptor/indicator combination was then used to train an ANN to determine concentration and ee. To prove the practicality of the developed protocol, analysis plates were created containing true unknown samples of hydrobenzoin generated by established Sharpless asymmetric dihydroxylation reactions, and the best ligand was correctly identified. The system was extended to pattern recognition for the rapid determination of identity, concentration, and ee of chiral vicinal diols. A diverse enantioselective sensor array was generated with three chiral boronic acid receptors and pH indicators. The optical response produced by the sensor array, was analyzed by two pattern recognition algorithms: principal component analysis (PCA) and ANNs. The PCA plot demonstrated good chemoselective and enantioselective separation of the analytes, and ANNs was used to accurately determine the concentration and ee of five unknown samples.