Author: Zhenzhen Dong
Publisher: ProQuest
ISBN: 9780549408833
Category : Polyimides
Languages : en
Pages :
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Book Description
A strategy for creating two-dimensional, ordered arrays of linear, conjugated organic molecules on polyimide scaffolds is described. The design takes advantage of the enforcement of consecutive 90° twist angles along the polyimide backbone. Rod-shaped conjugated molecules are held parallel and in the same plane on the scaffolds, and have optical properties similar to those of monomeric analogues. As supporting evidence for the structure of the polymers, a series of model compounds were synthesized and characterized by x-ray crystallography. The polymeric materials are soluble in common organic solvents and have been characterized by 1 H NMR, 13 C NMR, MALDI-TOF, Gel Permeation Chromatography (GPC) and UV-vis spectroscopy. The average molecular weight was determined by end group analysis. Kinetic VT-NMR study of the model compound shows that single bond rotate through the polyimide backbone only at high temperature (>90°C). Because rotation is slow at room temperature, it is expected that these polymers will serve as excellent scaffolds for aligning second order non-linear optical materials, as NLO chromophores can be poled at high temperature, but will not realign at room temperature. Ni-salophen derived foldamers were designed, synthesized and studied. The absolute sense of helicity is effectively controlled via secondary sphere chirality, through which peripheral stereocenters control the asymmetric environment. Three-center hydrogen bonds and steric interactions were utilized to bias the absolute sense of helicity. The strong bias was supported by chiroptical data and low temperature NMR studies. The helical structure in solid state was confirmed by x-ray crystallography and the solution geometry was confirmed by a series of NMR spectroscopic studies. Chiral metal-salen complexes are widely employed as asymmetric catalysts and helicity has been proposed to play a role in asymmetric induction by metal salen catalysts. A tool for measuring the ability of chiral diamine to induce asymmetry in metal-salen complexes was developed. This was accomplished by juxtaposing competing elements of chirality within Ni(salen) complexes that are predisposed to fold. The chiral end group biases for the formation of the (M)-helix, whereas the diamine biases for the diastereomeric metallofoldamer of (P)-helicity. Spectroscopic and crystallographic studies of these complexes show that the trans -cyclohexanediamine is only a weak director of absolute helicity in Ni(salen) complexes. The bias of the diamine is completely overridden by the chiral end group. An implication of this study for asymmetric catalysis is that both helical diastereomers must be considered in any models that invoke helicity to explain asymmetric induction with chiral salens. To create metal salen-based foldamers that are appropriate for asymmetric catalysis, a small foldamer was designed and synthesized. The ends of this foldamer do not wrap. The complex retains the virtue of peripheral stereocenter control over catalyst helicity. A new steric interaction is created in the design to bias the absolute sense of helicity. The helical structure of the minimalist foldamer in solid state was confirmed by x-ray crystallography and the strong bias of absolute helicity in solution was determined by chiroptical data and low temperature NMR studies.
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Category :
Languages : en
Pages : 8
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Book Description
Two-dimensional (2D) materials have attracted much attention in the past decade. They offer high specific surface area, as well as electronic structure and properties that differ from their bulk counterparts due to the low dimensionality. Graphene is the best known and the most studied 2D material, but metal oxides and hydroxides (including clays), dichalcogenides, boron nitride (BN), and other materials that are one or several atoms thick are receiving increasing attention. They may deliver a combination of properties that cannot be provided by other materials. The most common synthesis approach in general is by reacting different elements or compounds to form a new compound. However, this approach does not necessarily work well for low-dimensional structures, since it favors formation of energetically preferred 3D (bulk) solids. Many 2D materials are produced by exfoliation of van der Waals solids, such as graphite or MoS2, breaking large particles into 2D layers. However, these approaches are not universal; for example, 2D transition metal carbides cannot be produced by any of them. An alternative but less studied way of material synthesis is the selective extraction process, which is based on the difference in reactivity and stability between the different components (elements or structural units) of the original material. It can be achieved using thermal, chemical, or electrochemical processes. Many 2D materials have been synthesized using selective extraction, such as graphene from SiC, transition metal oxides (TMO) from layered 3D salts, and transition metal carbides or carbonitrides (MXenes) from MAX phases. Selective extraction synthesis is critically important when the bonds between the building blocks of the material are too strong (e.g., in carbides) to be broken mechanically in order to form nanostructures. Unlike extractive metallurgy, where the extracted metal is the goal of the process, selective extraction of one or more elements from the precursor materials releases 2D structures. In this Account, in addition to graphene and TMO, we focused on MXenes as an example for the use of selective extraction synthesis to produce novel 2D materials. About 10 new carbides and carbonitrides of transition metals have been produced by this method in the past 3 years. They offer an unusual combination of metallic conductivity and hydrophilicity and show very attractive electrochemical properties. We hope that this Account will encourage researchers to extend the use of selective extraction to other layered material systems that in turn will result in expanding the world of nanomaterials in general and 2D materials in particular, generating new materials that cannot be produced by other means.
Author: Galia Maayan
Publisher: John Wiley & Sons
ISBN: 1118517431
Category : Science
Languages : en
Pages : 446
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Book Description
Metallofoldamers are oligomers that fold into three-dimensional structures in a controlled manner upon coordination with metal ions. Molecules in this class have shown an impressive ability to form single-handed helical structures and other three-dimensional architectures. Several metallofoldamers have been applied as sensors due to their selective folding when binding to a specific metal ion, while others show promise for applications as responsive materials on the basis of their ability to fold and unfold upon changes in the oxidation state of the coordinated metal ion, and as novel catalysts. Metallofoldamers: From Helicates to Biomimetic Architectures describes the variety of interactions between oligomers and metal species, with a focus on non-natural synthetic molecules. Topics covered include: the major classes of foldamers and their folding driving force metalloproteins and metalloenzymes helicates: self-assembly, structure and applications abiotic metallo-DNA metallo-PNA and iDNA metallopeptides interactions of biomimetic oligomers with metal ions applications of metallofoldamers
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Category : Dissertations, Academic
Languages : en
Pages : 1006
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Book Description
Author: José A. Pomposo
Publisher: John Wiley & Sons
ISBN: 3527806393
Category : Technology & Engineering
Languages : en
Pages : 504
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Book Description
This first book on this important and emerging topic presents an overview of the very latest results obtained in single-chain polymer nanoparticles obtained by folding synthetic single polymer chains, painting a complete picture from synthesis via characterization to everyday applications. The initial chapters describe the synthetics methods as well as the molecular simulation of these nanoparticles, while subsequent chapters discuss the analytical techniques that are applied to characterize them, including size and structural characterization as well as scattering techniques. The final chapters are then devoted to the practical applications in nanomedicine, sensing, catalysis and several other uses, concluding with a look at the future for such nanoparticles. Essential reading for polymer and materials scientists, materials engineers, biochemists as well as environmental chemists.
Author: Zhang Ye
Publisher: World Scientific
ISBN: 9811201048
Category : Technology & Engineering
Languages : en
Pages : 220
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Book Description
Soft materials with nanometer scale aspects have been heavily used in biomedical science. Instead of providing a broad introduction of soft materials and their biomedical applications, this book focuses on the preparation of molecular assemblies of biotechnologically relevant biomimetic systems with an emphasis on medical applications.
Author: Cláudio M. Gomes
Publisher: CRC Press
ISBN: 1439809658
Category : Medical
Languages : en
Pages : 302
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Book Description
The role of metal ions in protein folding and structure is a critical topic to a range of scientists in numerous fields, particularly those working in structural biology and bioinorganic chemistry, those studying protein folding and disease, and those involved in the molecular and cellular aspects of metals in biological systems. Protein Folding an
Author: Paul S. Pregosin
Publisher: John Wiley & Sons
ISBN: 3527680292
Category : Science
Languages : en
Pages : 406
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Book Description
The first and ultimate guide for anyone working in transition organometallic chemistry and related fields, providing the background and practical guidance on how to efficiently work with routine research problems in NMR. The book adopts a problem-solving approach with many examples taken from recent literature to show readers how to interpret the data. Perfect for PhD students, postdocs and other newcomers in organometallic and inorganic chemistry, as well as for organic chemists involved in transition metal catalysis.
Author: Koichi Fukase
Publisher: Springer Nature
ISBN: 9811624585
Category : Science
Languages : en
Pages : 357
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Book Description
This book highlights recently discovered aspects of “middle-size molecules,” focusing on (1) their unique bio-functions on the basis of derivatives and conjugates of natural products, saccharides, peptides, and nucleotides; (2) the synthesis of structurally complex natural products; (3) special synthetic methods for π-conjugated functional molecules; and (4) novel synthetic methods using flow chemistry. Given its scope, the book is of interest to industrial researchers and graduate students in the fields of organic chemistry, medicinal chemistry, and materials science.
Author: Hai-Bo Yang
Publisher: Royal Society of Chemistry
ISBN: 1782628584
Category : Science
Languages : en
Pages : 304
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Book Description
A comprehensive overview of metallomacrocycles from designing complex functional metallosupramolecular systems to their applications.
