Spelling suggestions: "subject:"covalent"" "subject:"covalente""
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Neklasické nekovalentní interakce v proteinech a jejich význam pro návrh nových specifických inhibitorů virových enzymů / Nonclassical noncovalent interactions in proteins and their importance for design of novel specific viral enzyme inhibitorsKříž, Kristian January 2016 (has links)
Noncovalent interactions are vital for functioning of biological systems. For instance, they facilitate DNA base pairing or protein folding. Recently, in addition to classical noncovalent interactions such as hydrogen bond, nonclassical noncovalent interactions have been discovered. An example of these interactions is halogen bond belonging to the class of σ-hole interactions, the knowledge of which is already being useful for medical compound design. The aim of this work is to find out if the chalcogen bond, also a σ-hole interaction, plays a role in the binding of existing viral inhibitors, too. Following that, we are also interested whether or to what extent can these existing chalcogen bonds be optimized for a greater affinity of the inhibitor binding. Several protein-ligand crystal structures exhibiting geometrical properties favoring a chalcogen bond have been found in the PDB database. We examined the interaction energies and the interaction energy geometrical dependencies of model systems derived from these crystal structures by means of quantum chemical calculations. Further we have optimized their strength by a series of substitutions. We thus propose that chalcogen bond can become a player in rational design of inhibitors of viral enzymes and their protein target. Keywords: Noncovalent...
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Contribution de la spectrométrie de masse à l'étude des interactions entre les protéines salivaires riche en proline et les tanins. / Study of the interactions occurring between the human salivary proline rich proteins and tannins by a mass spectrometry approach.Canon, Francis 30 September 2010 (has links)
L'astringence résulte de l'interaction des tanins, polyphénols abondants dans les végétaux, avec les protéines salivaires et plus particuliÈrement les protéines salivaires riches en proline (PRP), appartenant à la famille des protéines peu structurées. Les tanins participent aux mécanismes de défense des végétaux et présentent des effets antinutritionnels dus à leur capacitè à inhiber les enzymes digestives. La synthÈse de PRP salivaires constitue un mècanisme d'adaptation à la consommation d'aliments riches en tanins. Ce travail vise à caractèriser les complexes ètablis en solution entre les PRP et les tanins, par une approche basèe sur la spectromètrie de masse (MS). Pour cela, les protèines salivaires humaines IB5, PRP basique, et II-1, PRP glycosylèe, ont ètè produites par voie hètèrologue. AprÈs purification, les deux protèines ont ètè caractèrisèes par MS avec une source d'electronèbullisation (ESI-MS) et avec une source MALDI (Matrix-Assisted Laser Desorption/Ionisation). L'ètude des interactions par ESI-MS a confirmè la prèsence en solution de complexes non-covalents IB5tanin et permis de prèciser leurs stchiomètries. Des expèriences de compètition entre diffèrents tanins et de dissociation des complexes IB5tanin ont mis en èvidence l'influence des principales caractèristiques structurales des tanins sur cette interaction. L'ètude structurale des èdifices IB5tanin, par diffèrentes techniques de MS/MS (Collision Induced Dissociation, Electron Capture Dissociation et photodissociation) et par mobilitè ionique couplèe à la MS, a mis en èvidence la prèsence de plusieurs sites d'interaction sur IB5 ainsi que des changements conformationnels liès à l'interaction / Astringency is an important organoleptic property of plant-based food. It is attributed to interactions of tannins, which are polyphenolic compounds, with salivary proteins and especially proline rich proteins (PRPs), which belong to the group of intrinsically unstructured protein (IUP). Tannins play an important part in plant defence mechanisms. Indeed, they have an antinutritional effect as they inhibit digestive enzymes. Production of salivary PRP is thus an adaptation process to tannin-rich diets. The purpose of this work is to provide a closer look at PRPtannin supramolecular edifices in solution, using a mass spectrometry (MS) approach. The human salivary proteins IB5, a basic PRP, and II-1, a glycosylated PRP, have been produced by heterologous expression. After purification, both proteins have been characterized by MS using electrospray (ESI) and Matrix-Assisted Laser Desorption/Ionisation (MALDI) sources. The study of the interaction between IB5 and model tannins by ESI-MS confirmed the presence of IB5tannin non covalent complexes in solution and provided new information on their stoichiometries. Competitive interaction experiments between IB5 and two tannins, along with IB5tannin complexes dissociation studies revealed the impact of the main tannin chemical features on this interaction. Structural studies performed on IB5tanin edifices by Collision induced dissociation (CID), Electron Capture Dissociation (ECD) and photodissociation MS/MS experiments and by ion mobility coupled with MS showed the presence of several interaction sites on IB5 and conformational changes arising from the interaction.
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Kvantovo-chemické štúdium nekovalentných interakcií / Quantum-chemical study of noncovalent interactionsSedlák, Róbert January 2014 (has links)
The aim of this thesis is to investigate strength and origin of the stabilization for various types of noncovalent interactions. As this knowledge could lead to a deeper understand- ing and rationalization of the binding phenomena. Further, to participate on the de- velopment of new noncovalent data sets, which are nowadays inevitable in the process of parametrization and validation of new computational methods. In all the studies, different binding motifs of model complexes, which represent usually crystal structures, structures from unrelaxed scans or the local minima, were investi- gated. The calculations of the reference stabilization energies were carried out at ab initio level (e.g. CCSD(T)/CBS, QCISD(T)/CBS). Further, the accuracy of more ap- proximate methods (e.g. MP2.5, DFT-D or SQM methods) toward reference method, was tested. In order to obtain the nature of the stabilization the DFT-SAPT decompo- sition was frequently utilized. In the first part of the thesis, the importance and basic characteristics of different types of noncovalent interactions (e.g. halogen bond, hydrogen bond, π· · · π interaction etc.), are discussed. The second part provides the description of computational methods which were essential for our investigation. The third part of the thesis provides an overview for part...
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Tailoring Nanoscopic and Macroscopic Noncovalent Chemical Patterns on Layered Materials at Sub-10 nm ScalesJae Jin Bang (5929496) 20 December 2018 (has links)
<p></p><p></p><p>The unprecedented
properties of 2D materials such as graphene and MoS2 have been researched
extensively [1,2] for a range of applications including nanoscale electronic and
optoelectronic devices [3–6]. Their unique physical and electronic properties
promise them as the next generation materials for electrodes and other
functional units in nanostructured devices. However, successful incorporation
of 2D materials into devices entails development of high resolution patterning
techniques that are applicable to 2D materials. Patterning at the sub-10 nm
scale is particularly of great interest as the next technology nodes require
patterning of (semi)conductors and insulators at 7 nm and 5 nm scales for
nanoelectronics. It will also benefit organic photovoltaic cells as phase
segregation of p/n-type semiconducting polymers on 2D electrodes at
length scales smaller than the typical exciton diffusion length (10 nm)</p>
<p>is expected to improve
the charge separation efficiency [7].</p><br><p></p><p></p><p>Characterizing locally
modulated properties of non-ovalently functionalized 2D materials requires
high-resolution imaging techniques capable of extracting measurements of
various physical/chemical properties. One such method is scanning probe
microscopy (SPM) [18–21]. In Chapter 1, we present a brief review of SPM
modalities, some of which are used to characterize interfacial properties, such
as conductivity and local contact potential differences that can be modulated
by amphiphilic assemblies [17, 22]. Atomic force microscopy (AFM) is one of
main techniques that we use to determine topography. All imaging in this work
were performed in attractive AC mode [23,24] in order to minimize disruption to
the self-assembly of the amphiphiles by the scanning tip.</p><br><p></p><p></p><p>One challenge of using
SAMs for locally modulated functionalization is that the proximity to the
nonpolar interface can modify the behavior of the functionalities present on
the surface in conjunction with the steric hindrance of 2D molecular
assemblies. For instance, ionizable functional groups, one of the strongest
local modulators of surface chemistry, undergo substantial pKa shifts (in some
cases, > 5 units) at nonpolar interfaces, limiting their ability to ionize.
In order to apply molecular assembly to create 2D chemical patterns, we needed
to design alternative structures that can avoid such penalties against the
intrinsic properties of functionalities present in the assemblies. Among
amphiphiles, we observed that the chiral centers of phospholipids have the
potential of elevating the terminal functional group in the head from the surface
for improved accessibility. We refer to this type of assembly as a ’sitting’
phase. Chapter 2 describes sitting phase assembly of phospholipids; the
projection of the terminal functionality allows it to maintain solution
phase-like behavior while the dual alkyl tails provide additional stabilizing
interactions with the substrates. Given the diversity of phospholipid
architecture [25], the sitting phase assembly suggests the possibility of
greatly diversifying the orthogonality of the chemical patterns, allowing
highly precise control over surface functionalities.</p><br><p></p><p></p><p>While a variety of
methods including drop-casting [26–28] and microcontact printing [29] have been
used previously by others for noncovalent assembly of materials on the surface,
they mostly address patterning scale in the sub-μm range. Here, we utilize
Langmuir-Schaefer(LS) transfer, which has been historically used to transfer
standing phase multilayers [30], and lying-down domains of PCDA at < 100 nm
scales in the interest of molecular electronics [14, 31–33], as our sample
preparation technique. LS transfer is remarkable in that the transferred
molecules relinquish their pre-existing interactions in the standing phase at
air-water interface to undergo ∼ 90◦
rotation and assemble into the striped phase on a substrate. This introduces
the possibility of modulating local transfer rate across the substrate by
manipulating local environment of the molecules. Thus, LS transfer has the
potential to offer spatial control over the noncovalent chemical
functionalization of the 2D substrate, essential in device applications.</p><br><p></p><p></p><p>In Chapter 3 and 4, We
make comparative studies of various experimental factors such as surface pressure,
temperature and molecular interactions that affect the efficiency of LS
conversion. Considering the energetics of the transfer process, we predicted
that the rate of transfer from the air-water interface to the substrate should
be the highest from the regions around defects, which would be the
energetically</p>
<p>least stable regions of
the Langmuir film [34, 35]. In Langmuir films, two phases of lipid
assemblies—liquid expanded (LE) and liquid condensed (LC)—often coexist at the
low surface pressures (< 10 mN/m) used for sample preparation. Hence, we
hypothesized that the microscale structural heterogeneity of Langmuir films
could be translated into microscale patterns in the transferred film on HOPG.
We compare the transfer rates between LE and LC phases and investigate the
impacts of physical conditions during LS transfer such as temperature, packing
density, dipping rate and contact time to conclude that local destabilization
of Langmuir films leads to increased transfer efficiency. (Chapter 3)</p><p><br></p><p></p><p>As in the case of lipid
membranes that reorganize routinely based on the structure of the constituent
molecules [36–38], the structure of Langmuir films is strongly dependent on the
molecular structures of the constituent molecules [39–43]. Accordingly, we
expected the molecular structures/interactions to provide additional control
over the LS transfer process. In Chapter 4, we compare domain morphologies and
the average coverages between three single chain amphiphiles and two
phospholipids, each</p><p></p><p>
</p><p>of which contain
hydrogen bonding motifs of varying strengths. We show that by influencing the
adsorption and diffusion rates, molecular architecture indeed influences LS
conversion efficiency and subsequent assembly on the substrate. The presence of
strong lateral interactions limits transfer and diffusion, forming vacancies in
the transferred films with smaller domain sizes while weaker intermolecular
interactions enabled high transfer efficiencies.</p><p></p><p><br></p><p></p>
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Electrospray Ionization Mass Spectrometry for Determination of Noncovalent Interactions in Drug DiscoveryBenkestock, Kurt January 2008 (has links)
Noncovalent interactions are involved in many biological processes in which biomolecules bind specifically and reversibly to a partner. Often, proteins do not have a biological activity without the presence of a partner, a ligand. Biological signals are produced when proteins interact with other proteins, peptides, oligonucleotides, nucleic acids, lipids, metal ions, polysaccharides or small organic molecules. Some key steps in the drug discovery process are based on noncovalent interactions. We have focused our research on the steps involving ligand screening, competitive binding and ‘off-target’ binding. The first paper in this thesis investigated the complicated electrospray ionization process with regards to noncovalent complexes. We have proposed a model that may explain how the equilibrium between a protein and ligand changes during the droplet evaporation/ionization process. The second paper describes an evaluation of an automated chip-based nano-ESI platform for ligand screening. The technique was compared with a previously reported method based on nuclear magnetic resonance (NMR), and excellent correlation was obtained between the results obtained with the two methods. As a general conclusion we believe that the automated nano-ESI/MS should have a great potential to serve as a complementary screening method to conventional HTS. Alternatively, it could be used as a first screening method in an early phase of drug development programs when only small amounts of purified targets are available. In the third article, the advantage of using on-line microdialysis as a tool for enhanced resolution and sensitivity during detection of noncovalent interactions and competitive binding studies by ESI-MS was demonstrated. The microdialysis device was improved and a new approach for competitive binding studies was developed. The last article in the thesis reports studies of noncovalent interactions by means of nanoelectrospray ionization mass spectrometry (nanoESI-MS) for determination of the specific binding of selected drug candidates to HSA. Two drug candidates and two known binders to HSA were analyzed using a competitive approach. The drugs were incubated with the target protein followed by addition of site-specific probes, one at a time. The drug candidates showed predominant affinity to site I (warfarin site). Naproxen and glyburide showed affinity to both sites I and II. / QC 20100705
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Developments and applications in computer-aided drug discoveryIbrahim, Mahmoud Arafat Abd el-hamid January 2012 (has links)
Noncovalent interactions are of great importance in studies on crystal design and drug discovery. One such noncovalent interaction, halogen bonding, is present between a covalently bound halogen atom and a Lewis base. A halogen bond is a directional interaction caused by the anisotropic distribution of charge on a halogen atom X covalently bound to A, which in turn forms a positive region called σ-hole on the A–X axis. Utilization of halogen bonds in lead optimization have been rarely considered in drug discovery until recently and yet more than 50% of the drug candidates are halogenated. To date, the halogen bond has not been subjected to practical molecular mechanical-molecular dynamics (MM-MD) study, where this noncovalent interaction cannot be described by conventional force fields because they do not account for the anisotropic distribution of the charge density on the halogen atoms. This problem was solved by the author and, for the first time, an extra-point of positive charge was used to represent the σ-hole on the halogen atom. This approach is called positive extra-point (PEP) approach. Interestingly, it was found that the performance of the PEP approach in describing halogen bond was better than the semiempirical methods including the recent halogen-bond corrected PM6 (PM6-DH2X) method. The PEP approach also gave promising results in describing other noncovalent halogen interactions, such as C–X···H and C–X···π-systems. The PEP resulted in an improvement in the accuracy of the electrostatic-potential derived charges of halogen-containing molecules, giving in turn better dipole moments and solvation free energies compared to high-level quantum mechanical and experimental data.With the aid of our PEP approach, the first MM-molecular dynamics (MM-MD) study of inhibitors that form a halogen bond with a receptor was performed for tetrahalobenzotriazole inhibitors complexed to cyclin-dependent protein kinase (CDK2). When the PEP approach was used, the calculated MM-generalized Born surface area (MM-GBSA)//MM-MD binding energies for halobenzimidazole and halobenzotriazole inhibitors complexed with protein kinase CK2 were found to correlate well with the corresponding experimental data, with correlation coefficients R2 of greater than 0.90. The nature and strength of halogen bonding in halo molecule···Lewis base complexes were studied in terms of molecular mechanics using our PEP approach. The contributions of the σ-hole (i.e., positively charged extra-point) and the halogen atom to the strength of this noncovalent interaction were clarified using the atomic parameter contribution to the molecular interaction approach. The molecular mechanical results revealed that the halogen bond is electrostatic and van der Waals in nature. The strength of the halogen bond increases with increasing the magnitude of the extra-point charge. The van der Waals interaction’s contribution to the halogen bond strength is most favorable in chloro complexes, whereas the electrostatic interaction is dominant in iodo complexes.The failure of the PM6 semiempirical method in describing noncovalent halogen interactions —not only halogen bonds, but also hydrogen bonds involving halogen atoms— was reported and corrected by the introduction of a second and third generation of noncovalent halogen interactions correction. The developed correction yielded promising results for the four examined noncovalent halogen interactions, namely: C–X···O, C–X···N, C–X···π-system, and C–X···H interactions.
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Application of the Correlation Consistent Composite Approach to Biological Systems and Noncovalent InteractionsRiojas, Amanda G. 05 1900 (has links)
Advances in computing capabilities have facilitated the application of quantum mechanical methods to increasingly larger and more complex chemical systems, including weakly interacting and biologically relevant species. One such ab initio-based composite methodology, the correlation consistent composite approach (ccCA), has been shown to be reliable for the prediction of enthalpies of formation and reaction energies of main group species in the gas phase to within 1 kcal mol-1, on average, of well-established experiment, without dependence on experimental parameterization or empirical corrections. In this collection of work, ccCA has been utilized to determine the proton affinities of deoxyribonucleosides within an ONIOM framework (ONIOM-ccCA) and to predict accurate enthalpies of formation for organophosphorus compounds. Despite the complexity of these systems, ccCA is shown to result in enthalpies of formation to within ~2 kcal mol-1 of experiment and predict reliable reaction energies for systems with little to no experimental data. New applications for the ccCA method have also been introduced, expanding the utility of ccCA to solvated systems and complexes with significant noncovalent interactions. By incorporating the SMD solvation model into the ccCA formulation, the Solv-ccCA method is able to predict the pKa values of nitrogen systems to within 0.7 pKa unit (less than 1.0 kcal mol-1), overall. A hydrogen bonding constant has also been developed for use with weakly interacting dimers and small cluster compounds, resulting in ccCA interaction energies for water clusters and dimers of the S66 set to within 1.0 kcal mol-1 of well-established theoretical values.
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Controlled Interfacial Adsorption of AuNW Along 1-Nm Wide Dipole Arrays on Layered Materials and The Catalysis of Sulfide OxygenationAshlin G Porter (6580085) 12 October 2021 (has links)
<p>Controlling the
surface chemistry of 2D materials is critical for the development of next
generation applications including nanoelectronics and organic photovoltaics
(OPVs). Further, next generation nanoelectronics devices require very specific
2D patterns of conductors and insulators with prescribed connectivity and
repeating patterns less than 10 nm. However, both top-down and bottom-up
approaches currently used lack the ability to pattern materials with sub 10-nm
precision over large scales. Nevertheless, a class of monolayer chemistry
offers a way to solve this problem through controlled long-range ordering with
superior sub-10 nm patterning resolution. Graphene is most often functionalized
noncovalently, which preserves most of its intrinsic properties (<i>i.e.,</i> electronic conductivity) and
allows spatial modulation of the surface. Phospholipids such as
1,2-bis(10,12-tricsadiynoyl)-<i>sn</i>-glycero-3-phosphoethanolamine
(diyne PE) form lying down lamellar phases on graphene where both the
hydrophilic head and hydrophobic tail are exposed to the interface and resemble
a repeating cross section of the cell membrane. Phospholipid is made up of a complex
headgroup structure and strong headgroup dipole which allows for a diverse
range of chemistry and docking of objects to occur at the nonpolar membrane,
these principals are equally as important at the nonpolar interface of 2D
materials. A key component in the development of nanoelectronics is the
integration of inorganic nanocrystals such as nanowires into materials at the
wafer scale. Nanocrystals can be integrated into materials through templated
growth on to surface of interest as well as through assembly processes (i.e.
interfacial adsorption). </p>
<p>In this work, I
have demonstrated that gold nanowires (AuNWs) can be templated on striped
phospholipid monolayers, which have an orientable headgroup dipoles that can
order and straighten flexible 2-nm diameter AuNWs with wire lengths of ~1 µm. While AuNWs in
solution experience bundling effects due to depletion attraction interactions,
wires adsorb to the surface in a well separated fashion with wire-wire
distances (e.g. 14 or 21 nm) matching multiples of the PE template pitch. This
suggests repulsive interactions between wires upon interaction with dipole
arrays on the surface. Although the reaction and templating of AuNWs is
completed in a nonpolar environment (cyclohexane), the ordering of wires varies
based on the hydration of the PE template in the presence of excess oleylamine,
which forms hemicylindrical micelles around the hydrated headgroups protecting
the polar environment. Results suggest that PE template experience
membrane-mimetic dipole orientation behaviors, which in turn influences the
orientation and ordering of objects in a nonpolar environment.</p>
<p>Another
promising material for bottom-up device applications is MoS<sub>2 </sub>substrates
due to their useful electronic properties. However, being able to control the
surface chemistry of different materials, like MoS<sub>2</sub>, is relatively
understudied, resulting in very limited examples of MoS<sub>2 </sub>substrates
used in bottom-up approaches for nanoelectronics devices. Diyne PE templates adsorb
on to MoS<sub>2 </sub>in an edge-on conformation in which the alkyl tails
stack on top of each other increasing the overall stability of the monolayer. A
decrease in lateral spacing results in high local concentrations of orientable
headgroups dipoles along with stacked tails which could affect the interactions
and adsorption of inorganic materials (i.e. AuNW) at the interface. </p>
<p>Here, I show
that both diyne PE/HOPG and diyne PE/MoS<sub>2</sub> substrates can template
AuNW of various lengths with long range ordering over areas up to 100 µm<sup>2</sup>. Wires on
both substrates experience repulsive interactions upon contact with the
headgroup dipole arrays resulting in wire-wire distances greater than the
template pitch (7 nm). As the wire length is shortened the measured distance
between wires become smaller eventually resulting in tight packed ribbon
phases. Wires within these ribbon phases have wire-wire distances equal to the
template. Ribbon phases occur on diyne
PE/HOPG substrates when the wire length is ~50 nm, whereas wire below ~600 nm
produce ribbon phases on diyne PE/MoS<sub>2 </sub>substrates. </p>
<p>Another
important aspect to future scientific development is the catalysis of organic
reactions, specifically oxygenation of organic sulfides. Sulfide oxygenation is
important for applications such as medicinal chemistry, petroleum
desulfurization, and nerve agent detoxification. Both reaction rates and the
use of inexpensive oxidants and catalysts are important for practical
applications. Hydrogen peroxide and <i>tert</i>-butyl
hydroperoxide are ideal oxidants due to being cost efficient and
environmentally friendly. Hydrogen peroxide can be activated through transition
metal base homogeneous catalysts. Some of the most common catalysts are homo-
and hetero-polyoxometalates (POMs) due their chemical robustness. Heptamolybdate
[Mo<sub>7</sub>O<sub>24</sub>]<sup>6-</sup><sub> </sub>is a member of the
isopolymolybdate family and its ammonium salt is commercially available and low
in cost.<sup>22</sup> Heteropolyoxometalates have
been widely studied as a catalyst for oxygenation reactions whereas heptamolybdate
has been rarely studied in oxygenation reactions. </p>
<p> Here
I report sulfide oxygenation activity of both heptamolybdate and its peroxo
derivate [Mo<sub>7</sub>O<sub>22</sub>(O<sub>2</sub>)<sub>2</sub>]<sup>6-</sup>.
Sulfide oxygenation of methyl phenyl sulfide (MPS) by H<sub>2</sub>O<sub>2 </sub>to
sulfoxide and sulfone occurs rapidly with 100 % utility of H<sub>2</sub>O<sub>2</sub>
in the presence of [Mo<sub>7</sub>O<sub>22</sub>(O<sub>2</sub>)<sub>2</sub>]<sup>6-</sup>,
suggesting the peroxo adduct is an efficient catalyst. However, heptamolybdate
is a faster catalyst compared to [Mo<sub>7</sub>O<sub>22</sub>(O<sub>2</sub>)<sub>2</sub>]<sup>6-</sup>
for MPS oxygenation and all other sulfides tested under identical conditions.
Pseudo-first order <i>k</i><sub>cat</sub>
constants from initial rate kinetics show that [Mo<sub>7</sub>O<sub>24</sub>]<sup>6-</sup><sub>
</sub>catalyzes sulfide oxygenation faster. The significant difference in the <i>k</i><sub>cat</sub> suggests differences in
the active catalytic species, which was characterized by both UV-Vis and
electrospray ionization mass spectrometry. ESI-MS suggest that the active
intermediate of [Mo<sub>7</sub>O<sub>24</sub>]<sup>6-</sup><sub> </sub>under
catalytic reaction conditions for sulfide oxygenation by H<sub>2</sub>O<sub>2</sub>
is [Mo<sub>2</sub>O<sub>11</sub>]<sup>2-</sup>. These results show that
heptamolybdate is a highly efficient catalyst for H<sub>2</sub>O<sub>2 </sub>oxygenation
of organic sulfides.</p>
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Exploring Multiple Hydrogen Bonding and Ionic Bonding in the Design of Supramolecular PolymersChen, Xi 03 June 2020 (has links)
Supramolecular polymers represent a family of polymeric materials that are held together with dynamic, noncovalent interactions. In contrast to conventional functional polymers that usually have high melt-viscosity due to their covalent nature and chain entanglement, supramolecular polymers combine excellent physical properties with low melt-viscosity, allowing for less energy-intensive processability and recyclability. Dynamic bonding with multiple binding sites, such as multiple hydrogen bonding or multiple ionic bonding, exhibits much stronger binding strength compared to the counterparts containing only a single binding site, thereby allowing for enhanced mechanical integrity to the polymers and facilitate self-assembly. This dissertation focuses on the design of novel supramolecular polymers building from the doubly-charged or quadruple hydrogen bonding (QHB) scaffolds utilizing chain-growth polymerization or step-growth polymerization, as well as elucidate the structure-property-morphology relationships of the polymers.
A 2-step nucleophilic substitution reaction afforded a series of 1,4-diazabicyclo[2.2.2]octane (DABCO)-based styrenic monomers with two pairs of charged groups. An optimized 2-step reversible-addition-fragmentation chain-transfer (RAFT) polymerization synthesized ABA triblock thermoplastic elastomers (TPEs) with a low Tg poly (n-butyl acrylate) central block and a high Tg external charged blocks. Strong ionic interactions between doubly-charged units drove molecular self-assembly to form densely packed, hierarchical microstructures, which contributed to a robust, crosslinked physical network that allows the polymer to retain thermomechanical integrity until degradation. High-resolution single-crystal X-ray diffraction (SCXRD) coupled with powder X-ray diffraction (PXRD) further disclosed a detailed 3-D structural information of molecular arrangement and ion distribution within the charged phase through comparing DABCO-salt monomer single-crystal structure and the corresponding homopolymer XRD pattern. It was found that the physical properties of the DABCO-salt copolymers not only relied on their charge content and architectures but also dependent on their electrostatically-bonded counterions. The size and structure of the counterion determined the strength of dipole-dipole interaction, which significantly impact on thermal property, (thermo)mechanical performance, water affinity, and microstructure.
A cytosine-functionalized monomer, cytosine acrylate (CyA), allowed the synthesis of acrylic ABA triblock TPEs with pendant nucleobase moieties in the external blocks and a low Tg central polymer matrix through RAFT polymerization. Post-functionalization of cytosine (Cyt) bidentate hydrogen bonding sites with alkyl isocyanate, allowed the formation of ureido-cytosine (UCyt) groups in the external block that were readily dimerized through QHB interactions. The UCyt units in the external block enhanced mechanical strength and induced stronger phase-separation of the block copolymers compared to the corresponding Cyt-containing TPE analogs. Facile conventional free-radical polymerization using CyA and subsequent post-functionalization enabled accessibility to random copolymers containing pendant UCyt QHB moieties in the soft polymer matrix. The synergy of the flexible polymer matrix and the dynamic character of QHB groups contributed to the ultra-high elasticity of the polymer and rapid self-healing properties. QHB interactions enabled efficient mechanical recovery upon deformation by facilitating elastic chain retraction to regenerate the original physical network. Finally, one-pot step-growth polymerization through chain extending a novel bis-Cyt monomer and a commercially available polyether diamine using a di-isocyanate extender afforded segmented polyurea series for extrusion additive manufacturing. The molecular design of the polyureas featured soft segments containing flexible polyether chain and a relatively weak urea hydrogen bonding sites in the soft segment and rigid UCyt hydrogen bonding groups in the hard segment. The reversible characteristics of QHB enabled low viscosity at the processing temperature while providing mechanical integrity after processing and reinforced bonding between the interlayers, which contributed to the remarkable strength, elasticity, toughness, and interlayer adhesion of the printed parts. / Doctor of Philosophy / This dissertation focuses on designing supramolecular thermoplastic elastomers containing strong noncovalent interactions, i.e., quadruple hydrogen bonds or double ionic bonds. Inspired from noncovalent interactions in our mother nature, a series of bio-inspired monomers functionalized with nucleobase or ionic units were synthesized through scalable reactions with minimal purification steps. Polymerization of the functional monomers through step-growth or chain-growth polymerization techniques affords a variety of supramolecular thermoplastic elastomers with well-defined structures and architectures. These thermoplastic elastomers comprise soft and hard constituents; the former contains low glass transition polymer chains that provide elasticity while the latter contains strong noncovalent units to impart mechanical strength. Varying the soft/hard component ratios enables polymers with tunable physical properties to address different needs.
Systematic characterizations of these supramolecular polymers revealed their distinct properties from the polymers containing the covalent or weak noncovalent interactions and facilitate molecular-level understanding of the polymers. Generally, incorporating strong noncovalent interactions increases the temperature for polymer segmental motion and extends thermomechanical plateau windows. Additionally, the strong association strength of those non-covalent interactions promotes microphase separation and self-assembly, contributing to a high degree of structural ordering of the polymers. Moreover, the dynamic characteristics of the noncovalent interactions offer the polymers with reversible properties, which not only enables melt-processability and recyclability of the polymer but also contributes to a series of smart properties, including self-healing, shape-memory, and recoverability. Thus, the molecular design using supramolecular chemistry provides promising avenues to developing functional materials with enhanced mechanical properties, processability, and stimuli-responsiveness for emerging applications.
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A Study of Weak Noncovalent InteractionsXue, Xiaowen 20 September 2005 (has links)
No description available.
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