Proton-coupled Electron Transfer in a Three Hydrogen Bond DDA Array Capable of Binding an AAD Guest PDF Download
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Category : Electronic books
Languages : en
Pages : 71
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Proton-coupled electron transfer (PCET) reactions are essential to many of the fundamental chemical processes of life. In the Smith group we have studied a p-phenylenediamine-based urea, U(H)H, by applying PCET. In this study, the phenyl group in U(H)H is replaced by an imidazole group to form a three hydrogen bond array, UImH. Therefore, AAD arrays, such as APy, are needed as guest compounds to form three intermolecular non-covalent contacts. The initial hypothesis was that oxidation of the phenylenediamine of UImH should lead to stronger H-bonding with the guest compound, and this would make the oxidation easier leading to a negative shift in the E1/2 in the presence of the guest compound. The cyclic voltammetry (CV) of UImH has been examined in methylene chloride and acetonitrile with platinum (Pt) and glassy carbon (GC) electrodes. On both electrodes, CV shows two, closely-spaced, reversible waves of similar height, but a single wave is observed at the lowest concentration on the high scan rate (5.0 V/s). Interestingly, the single wave decreases in relative size as the concentration increases and appears to gradually split into the two smaller peaks seen at slow san rate. Based on the results of CV plus DFT calculations, it is likely that ? dimerization is occurring during the electrochemical reaction. The newest mechanism hypothesizes two electrons per UImH with one intramolecular proton transfer at low concentrations and high scan rate and two sequential one electron transfers per two UImH at high concentration, producing a net one electron oxidation per UImH at high concentration. Addition of the guest, APy, results in a slight increase in the current of the CV waves of UImH. However, very little change in the potential of the CV wave is observed upon addition of the guest, indicating that oxidation does not change binding strength. The increase in current that is observed is most likely due to hydrogen bonding interfering with the ? dimerization. Even though UImH did not show the expected behavior, the ? dimerization is arguably far more interesting, and may have applications in supramolecular chemistry, including the design of smart materials.
Author:
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 71
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Book Description
Proton-coupled electron transfer (PCET) reactions are essential to many of the fundamental chemical processes of life. In the Smith group we have studied a p-phenylenediamine-based urea, U(H)H, by applying PCET. In this study, the phenyl group in U(H)H is replaced by an imidazole group to form a three hydrogen bond array, UImH. Therefore, AAD arrays, such as APy, are needed as guest compounds to form three intermolecular non-covalent contacts. The initial hypothesis was that oxidation of the phenylenediamine of UImH should lead to stronger H-bonding with the guest compound, and this would make the oxidation easier leading to a negative shift in the E1/2 in the presence of the guest compound. The cyclic voltammetry (CV) of UImH has been examined in methylene chloride and acetonitrile with platinum (Pt) and glassy carbon (GC) electrodes. On both electrodes, CV shows two, closely-spaced, reversible waves of similar height, but a single wave is observed at the lowest concentration on the high scan rate (5.0 V/s). Interestingly, the single wave decreases in relative size as the concentration increases and appears to gradually split into the two smaller peaks seen at slow san rate. Based on the results of CV plus DFT calculations, it is likely that ? dimerization is occurring during the electrochemical reaction. The newest mechanism hypothesizes two electrons per UImH with one intramolecular proton transfer at low concentrations and high scan rate and two sequential one electron transfers per two UImH at high concentration, producing a net one electron oxidation per UImH at high concentration. Addition of the guest, APy, results in a slight increase in the current of the CV waves of UImH. However, very little change in the potential of the CV wave is observed upon addition of the guest, indicating that oxidation does not change binding strength. The increase in current that is observed is most likely due to hydrogen bonding interfering with the ? dimerization. Even though UImH did not show the expected behavior, the ? dimerization is arguably far more interesting, and may have applications in supramolecular chemistry, including the design of smart materials.
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Category : Electronic books
Languages : en
Pages : 62
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This thesis demonstrates the validity of a new strategy to create highly redox- responsive H-bond dimers based on electron transfer induced proton transfer. The underlying principle is straightforward: a reduction increases the negative charge on a H-acceptor or oxidation increases the positive charge on a H-donor will increase the strength of a H-bond. However, it is possible oxidation or reduction could also lead to full proton transfer. If this occurs across the H-bond, the primary H-bonds will remain, but the secondary H-bonds will change. This can lead to an increase in unfavorable secondary interactions, which would counteract the effect of the initial proton transfer, but, with proper design, proton transfer could lead to an increase in favorable secondary interactions, which would enhance the effect of initial transfer. For this work, a 3 H-bond DAD array (D = H donor; A = H-acceptor) that contains a N-methyl-4,4'-bipyridinium or “monoquat” redox couple, H(MQ+)H, was synthesized. 1HNMR studies show H(MQ+)H forms a three H bond dimer with the non-electroactive ADA array, O(NH)O, in CH2Cl2 with a Kassoc = 507 M−1. This modest Kassoc is typical for DAD-ADA dimers due to the three, favorable primary H-bonds being counterbalanced by four unfavorable secondary H-bonds. Cyclic voltammetry studies of H(MQ+)H in CH2Cl2 show no significant shift in the E1/2 of the first reduction with addition of O(NH)O but a significant positive shift in the second reduction upon addition of only 1 equivalent. The maximum ∆E1/2= 0.311V corresponds to a 1.8×105 increase in binding strength, giving a very large binding constant of 9.1×107 M−1 in the fully reduced state. This value is consistent with that expected for a DDD-AAA complex in which all the primary and secondary H-bonds are favorable. Such a complex would be formed if proton transfer across the central H-bond occurs upon addition of the second electron. This conclusion is supported by CV’s with monoquat itself, indicating that the fully reduced monoquat anion is sufficiently basic to deprotonate O(NH)O. Overall, this work supports the hypothesis that, with proper design, proton transfer can be used to amplify the effect of electron transfer in redox-responsive H-bonding systems.
Author: Jonathan L Sessler
Publisher: Royal Society of Chemistry
ISBN: 1847552471
Category : Science
Languages : en
Pages : 431
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Book Description
Anion recognition plays a critical role in a range of biological processes, and a variety of receptors and carriers can be found throughout the natural world. Chemists working in the area of supramolecular chemistry have created a range of anion receptors, drawing inspiration from nature as well as their own inventive processes. This book traces the origins of anion recognition chemistry as a unique sub-field in supramolecular chemistry while illustrating the basic approaches currently being used to effect receptor design. The combination of biological overview and summary of current synthetic approaches provides a coverage that is both comprehensive and comprehensible. First, the authors detail the key design motifs that have been used to generate synthetic receptors and which are likely to provide the basis for further developments. They also highlight briefly some of the features that are present in naturally occurring anion recognition and transport systems and summarise the applications of anion recognition chemistry. Providing as it does a detailed review for practitioners in the field and a concise introduction to the topic for newcomers, Anion Receptor Chemistry reflects the current state of the art. Fully referenced and illustrated in colour, it is a welcome addition to the literature.
Author: James A. Roberts
Publisher:
ISBN:
Category : Charge exchange
Languages : en
Pages : 384
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Author:
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 150
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This thesis presents a mechanistic study of two phenylenediamine derivatives. The first is a disubstituted phenylenediamine with a phenyl-urea substituted para to a dimethylamino group. The phenyl-urea moiety offers two N-H sites for hydrogen bonding and proton transfer. This is UHH. The second, is a disubstituted phenylenediamine with an isocytosine-urea moiety substituted para to a dimethylamino group. The combined isocytosine-urea-phenylenediamine forms a redox active 4-hydrogen bond array where the urea moiety offers two N-H sites for proton donation and the isocytosine offers two sites for hydrogen bond acceptance. This is UpyH. Initial cyclic voltammetry (CV) experiments for UHH show reversible CV behavior in CH2Cl2 and irreversible CV behavior in CH3CN. With the inclusion of two UHH analogs, one with both N-H sites "blocked" with methyl substituents, UMeMe, and a second analog with a single urea N-H site, UMeMe, CV analysis continued. From these studies, in addition to a UV-vis/ CV study, it was determined that the dimethylamino on a fully reduced UHH or UMeH could abstract a proton from a second radical cation urea N-H. This was immediately followed by a thermodynamically favorable second electron transfer. Thus the products at the end of the first oxidation wave from a 2 e-, 1H+ transfer are a quinoidal cation and a fully reduced/protonated UHH or UMeH. On the return scan, UHH in CH3CN and UMeH in both solvents undergo a thermodynamically non-favored back proton transfer at a more energetic reduction potential. UHH in CH2Cl2 accesses a lower energy pathway through the formation of a hydrogen bond complex as part of a wedge scheme. Both pathways are supported by results from concentration and scan rate dependent CV studies that show two return waves correlating to two pathways. UV-vis results show a protonated/reduced species, but no radical cation. In the UpyH project, by using the same CV and UV-vis analysis in addition to an 1HNMR study in CH2Cl2/NBu4PF6, we show UpyH favors a dimerized form but as the dimer undergoes oxidation it breaks apart then reforms on the return scan. To our knowledge this the first account for electrochemically breaking apart a Upy derivative.
Author: Slawomir Grabowski
Publisher: Springer Science & Business Media
ISBN: 140204853X
Category : Science
Languages : en
Pages : 536
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Book Description
This book uses examples from experimental studies to illustrate theoretical investigations, allowing greater understanding of hydrogen bonding phenomena. The most important topics in recent studies are covered. This volume is an invaluable resource that will be of particular interest to physical and theoretical chemists, spectroscopists, crystallographers and those involved with chemical physics.
Author: Bernard R. Glick
Publisher:
ISBN:
Category : Medical
Languages : en
Pages : 724
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Book Description
The second edition explains the principles of recombinant DNA technology as well as other important techniques such as DNA sequencing, the polymerase chain reaction, and the production of monclonal antibodies.
Author: Wolfgang Binder
Publisher: Springer Science & Business Media
ISBN: 3540685871
Category : Technology & Engineering
Languages : en
Pages : 215
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Book Description
Control of polymeric structure is among the most important endeavours of modern macromolecular science. In particular, tailoring the positioning and strength of intermolecular forces within macromolecules by synthetic methods and thus gaining structural control over the final polymeric materials has become feasible, resulting in the field of supramolecular polymer science. Besides other intermolecular forces, hydrogen bonds are unique intermolecular forces enabling the tuning of material properties via self-assembly processes over a wide range of interactions strength ranging from several kJmol to several tens of kJmol . Central for the formation of these structures are precursor molecules of small molecular weight (usually lower than 10 000), which can assemble in solid or solution to aggregates of defined geometry.
Author: Ivan Stibor
Publisher: Springer
ISBN: 9783642445187
Category : Science
Languages : en
Pages : 0
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Book Description
with contributions by numerous experts
Author: Joel S. Miller
Publisher: John Wiley & Sons
ISBN: 3527604502
Category : Science
Languages : en
Pages : 395
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Book Description
Combining the contemporary knowledge from widely scattered sources, this is a much-needed and comprehensive overview of the field. In maintaining a balance between theory and experiment, the book guides both advanced students and specialists to this research area. Topical reviews written by the foremost scientists explain recent trends and advances, focusing on the correlations between electronic structure and magnetic properties. The book spans recent trends in magnetism for molecules -- as well as inorganic-based materials, with an emphasis on new phenomena being explored from both experimental and theoretical viewpoints with the aim of understanding magnetism on the atomic scale. The volume helps readers evaluate their own experimental observations and serves as a basis for the design of new magnetic materials. Topics covered include: * Metallocenium Salts of Radical Anion Bis-(dichalcogenate) metalates * Chiral Molecule-Based Magnets * Cooperative Magnetic Behavior in Metal-Dicyanamide Complexes * Lanthanide Ions in Molecular Exchange Coupled Systems * Monte Carlo Simulation * Metallocene-Based Magnets * Magnetic Nanoporous Molecular Materials A unique reference work, indispensable for everyone concerned with the phenomena of magnetism.
