Thiol-ene radical coupling is increasingly used for the biofunctionalisation of biomaterials and the formation of 3D hydrogels enabling cell encapsulation. Indeed, thiol-ene chemistry presents interesting features that are particularly attractive for platforms requiring specific reactions of peptides or proteins, in particular in situ, during cell culture or encapsulation: thiol-ene coupling occurs specifically between a thiol (from cysteine residues for example) and a non-activated alkene (unlike Michael addition); it is relatively tolerant to the presence of oxygen; it can be triggered by light, to trigger dynamic systems or for patterning. Despite such interest, little is known about the factors impacting thiol-ene chemistry in situ, under biologically relevant conditions. Here we explore some of the molecular parameters controlling photo-initiated thiol-ene coupling chemistry with a series of alkenes and thiols, including peptides, in buffered conditions. 1H NMR spectroscopy and HPLC were used to quantify the efficiency of couplings and the impact of the intensity of UV exposure, pH of the buffer, as well as the molecular structure and local microenvironment close to alkenes and thiols to be coupled. Our studies demonstrate that molecular design should be carefully selected in order to achieve high biofunctionalisation levels in biomaterials with peptides.

Thiol-ene chemistry is versatile and efficient and can be used as a powerful tool in polymer synthesis. In this thesis, the concept of thiol-ene chemistry has been central, where it has been explored as a tool for the synthesis of well-defined hydrogels and dopa-functional materials towards biomedical applications; such as hydrogels, primers for adhesive fixation of bone fractures, self-healing gels, and micelles for drug-delivery. Using thiol-ene chemistry, well-defined hydrogels were realized in order to study how the structure influences properties such as swelling, stiffness and hydrolytic degradation. It was found that all these characteristics are related to each other, as a more loosely crosslinked hydrogel experiences higher swelling, lower stiffness and higher degradation rates. Dopa-functional materials have gained a lot of interest throughout the years due to the remarkable adhesive properties they possess in wet environments. In the pursuit of new primers towards thiol-ene functional crosslinked bone adhesives, compounds with dopa moieties were proposed. Primers derived from dopamine were found to enhance the adhesion towards bone, and it was concluded that addition of NaOH was essential to achieve good adhesion. The strongest adhesion was achieved when thiol and ene-functional primers were used in combination. Most synthetic routes to dopa-functional polymers involve several protection and deprotection steps and a more simplistic synthetic route is therefore desired. The possibility of using UV-initiated thiol-ene chemistry to produce dopa-functional polymers was therefore investigated. The resulting polymers were shown to exhibit self-healing properties upon complexation with Fe3+ ions. Finally, the developed synthetic route was used to produce dopa and allyl-functional triblock-co-polymers. These triblock-co-polymers were then used to form micelles and evaluated as drug-delivery vehicles for the cancer-drug doxorubicin. The micelles were found to have high drug-loading capacities and slow release profiles and showed promising results when evaluated against breast-cancer cells. / Reaktioner mellan tioler och omättade kemiska föreningar utgör ett mångsidigt och effektivt redskap inom polymersyntes. I denna avhandling har begreppet tiol-en kemi varit centralt och kemin har använts för syntes av såväl väldefinierade hydrogeler som dopa-funktionella material. Dessa material har sedan utvärderats mot biomedicinska tillämpningar såsom hydrogeler, primers för fixering av benfrakturer, självläkande geler och kontrollerad läkemedelsleverans. Tiol-en-kemi har i denna avhandling använts för att framställa väldefinierade hydrogeler som sedan utvärderats med avseende på hur strukturen påverkar egenskaper såsom svällningsgrad, styvhet och nedbrytningshastighet. Det visade sig att alla dessa egenskaper är relaterade till varandra och att lösare tvärbundna hydrogeler uppvisar högre svällning, lägre styvhet och högre nedbrytningshastigheter. Marina musslor har en exceptionell förmåga att fästa mot olika ytor och på grund av detta har det visats en hel del intresse för dopa-funktionella material genom åren. På jakt efter en primer för att öka vidhäftningen hos benlim proponerades därför föreningar med dopafunktionella grupper. Det visade sig att dopaminderivat kunde förbättra vidhäftningen mot ben och det visade sig även att tillsats av natriumhydroxid var viktigt för att uppnå god vidhäftningsförmåga. Den starkaste vidhäftning uppnåddes när derivat med tiol och omättade bindningar användes i kombination. Syntes av dopafunktionella material involverar ofta flera reaktionssteg och en förenklad syntesväg är därför att eftersträva. UV-initierad tiol-en-kemi undersöktes därför som en möjlig syntesväg för att framställa dopafunktionella polymerer. Polymererna visade sig ha självläkande egenskaper vid komplexbildning med järnjoner. Slutligen användes denna syntesväg för att framställa blocksampolymerer. Dessa blocksampolymerer användes sedan för att bilda miceller med lovande resultat vid utvärdering för leverans av läkemedel mot bröstcancer. / <p>QC 20160125</p>

Intracellular protein-protein interactions (PPIs) play a vital role in many biological processes. Although they are viewed as of high biological interest they prove difficult to explore as potential targets for drug discovery. Numerous studies have shown α- helical peptides 'locked' in their respective bioactive structure can greatly increase their performance by increasing their target affinity, resistance to proteolysis as well as facilitating cellular uptake. A striking feature of literature to date is how few studies utilise different stapling techniques when developing inhibitors for PPIs. Current methods generally exploit ruthenium catalysed ring closing metathesis (RCM) or copper catalysed alkyne/azide click (CuAAC) chemistry to generate geometrically constrained peptides. Even though these methods have shown great potential they both share a fundamental limitation as the chemistry can only be employed on small synthetic peptides and cannot be extended to larger proteins. Thiol-ene coupling (TEC) chemistry (Chapter 1) which is often described as a 'click' reaction due to its fast reaction rates, high yields, wide functional group tolerance and insensitivity to ambient oxygen and water has the potential to solve this challenge. Thiol-ene chemistry was investigated as an alternative stapling strategy by employing the naturally occurring amino acid L-cysteine (Cys) as a source of the thiyl radical and L-homoallylglycine (Hag), a non-natural amino acid shown to act as a methionine surrogate in protein synthesis to act as a source of an alkene functionality to form a potentially expressible thioether tether in Chapter 2. However, due to unsatisfactory results from the intramolecular thiol-ene cyclisation at the molar concentrations required for peptide or protein modification, and a promising new lead, the closely related thiol-yne reaction was investigated as an alternative in Chapter 3. Using a small library of peptides (14 mers) derived from α-Synuclein (αSyn), a protein mainly found in the presynaptic terminals in the brain and is believed to be key to the pathological progress of Parkinson's disease, a successful macrocyclisation was achieved between the side chains of cysteine (Cys) and homopropargylglycine (Hpg). Although the vinyl-thioether tether did not confer any helical conformation on the stapled peptides, the results clearly demonstrate a potential route for the development of expressible staples. Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labelling (SDSL) of biomolecules has become a powerful tool for studying the structure and conformational dynamics of biomolecules. Typically, proteins are modified in a site-specific manner by utilising the side chains of cysteine residues to form disulphide bonds with spin active compounds, however, this strategy has its limitations. In Chapter 3 thiol-ene chemistry was investigated as an alternative biorthogonal method to spin label proteins and peptides. The newly synthesised sulfhydryl bearing nitroxide spin label was found to degrade upon exposure to radical promoting conditions, however, an alternative strategy was explored using more classical thiol-Michael chemistry to spin label dehydroalanine (Dha) modified peptides giving the desired spin labelled complex.

Polymer nanocomposite technology has had significant impact on material design. With the environmental advantages of photopolymerization, a research has recently focused on producing nanocomposites utilizing inexpensive clay particles based on in situ photopolymerization. In this research, novel polymerizable organoclays and thiol-ene photopolymerization have been utilized to develop advanced photopolymer clay nanocomposites and to overcome several limitations in conventional free radical photopolymers. To this end, factors important in nanocomposite processes such as monomer composition, clay dispersion, and photopolymerization behavior in combination with the evolution of ultimate nanocomposite properties have been investigated. For monomer-organoclay compositions, higher chemical compatibility of components induces enhanced clay exfoliation, resulting in photopolymerization rate increases due to an amplified clay template effect. Additionally, by affecting the stoichiometric ratio between thiol and acrylate double bond in the clay gallery, thiolated organoclays enhance thiol-ene copolymerization with increased final thiol conversion while acrylated organoclays encourage acrylate homopolymerization. In accordance with the reaction behavior, incorporation of thiolated organoclays makes polymer chains more flexible with decreased glass transition temperature due to higher formation of thio-ether linkages while adding acrylated organoclays significantly increases the modulus. Photopolymer nanocomposites also help overcome two major drawbacks in conventional free radical photopolymerization, namely severe polymerization shrinkage and oxygen inhibition during polymerization. With addition of a low level of thiol monomers, the oxygen inhibition in various acrylate systems can be overcome by addition of only 5wt% thiolated organoclay. The same amount of polymerizable organoclay also induces up to 90% decreases in the shrinkage stress for acrylate or thiol-acrylate systems. However, nonreactive clays do not reduce the stress substantially and even decreases the polymerization rate in air. Additionally, the clay morphology and polymerization behavior are closely related with evolution of ultimate nanocomposite performance. Use of polymerizable organoclay significantly improves overall toughness of nanocomposites by increasing either modulus or elongation at break based on the type of polymerizable organoclay, which demonstrates the promise of this technology as a modulation and/or optimization tool for nanocomposite properties.

Aim of this thesis was to combine the versatility of sulfur-chemistry, regarding redox-sensitivity as well as chemo- and site-specific conjugation, with multifunctionality of poly(glycidol)s as an alternative to poly(ethylene glycol). First the homo- and copolymerizations of EEGE and AGE were performed with respect to molar-mass distribution and reaction kinetics. A detailed study was given, varying the polymerization parameters such as DP, counter ion, solvent and monomer influence. It can be concluded that in general the rates for all polymerizations are higher using K+, in contrast to Cs+, as counter ion for the active alkoxide species. Unfortunately, K+ as counter ion commonly leads to a reduced control over polymer dispersity. In this thesis it was shown that the broad molar-mass distributions might be reduced by adding the monomer in a step-wise manner. In experiments with a syringe pump, for continuously adding the monomer, a significant reduction of the dispersities could be found using K+ as counter ion. In analogy to the oxyanionic polymerization of epoxides, the polymerization of episulfides via a thioanionic mechanism with various DPs was successful with thiols/DBU as initiator. In most experiments bimodality could be observed due to the dimerization, caused by oxidation processes by introduced oxygen during synthesis. Reducing this was successful by modifying the degassing procedure, e.g. repeated degassing cycles after each step, i.e. initiation, monomer addition and quenching. Unfortunately, it was not always possible to completely avoid the dimerization due to oxidation. Thiophenol, butanethiol, mercaptoethanol and dithiothreitol were used as thiol initiators, all being capable to initiate the polymerization. With the prediction and the narrow molar-mass distributions, the living character of the polymerization is therefore indicated. Homo- and copolymers of poly(glycidol) were used to functionalize these polymers with side-chains bearing amines, thiols, carboxylic acids and cysteines. The cysteine side-chains were obtained using a newly synthesized thiol-functional thiazolidine. For this, cysteine was protected using a condensation reaction with acetone yielding a dimethyl-substituted thiazolidine. Protection of the ring-amine was obtained via a mixed-anhydride route using formic acid and acetic anhydride. The carboxylic acid of 2,2-dimethylthiazolidine-4-carboxylic acid was activated with CDI and cysteamine attached. The obtained crystalline mercaptothiazolidine was subjected to thiol-ene click chemistry with allyl-functional poly(glycidol). A systematic comparison of thermal- versus photo-initiation showed a much higher yield and reaction rate for the UV-light mediated thiol-ene synthesis with DMPA as photo-initiator. Hydrolysis of the protected thiazolidine-functionalities was obtained upon heating the samples for 5 d at 70 °C in 0.1 M HCl. Dialysis against acetic acid lead to cysteine-functional poly(glycidol)s, storable as the acetate salt even under non-inert atmosphere. An oxidative TNBSA assay was developed to quantify the cysteine-content without the influence of the thiol-functionality. A cooperation partner coupled C-terminal thioester peptides with the cysteine-functional poly(glycidol)s and showed the good accessibility and reactivity of the cysteines along the backbone. SDS-PAGE, HPLC and MALDI-ToF measurements confirmed the successful coupling. / Ziel der Arbeit war es die Vielseitigkeit der Schwefelchemie, hinsichtlich der Redoxsensitivität und chemo- und seitenspezifischer Konjugation, mit der Funktionalisierbarkeit von Poly(glycidol)en, als multifunktionale PEG-Alternative zu kombinieren. Zunächst wurden die Homo- und Copolymerisationen von EEGE und AGE hinsichtlich der Molmassenverteilung und der Reaktionskinetik untersucht. Durch die Variation der Polymerisationsparameter, wie angestrebter Polymerisationsgrad, Gegenion, Lösungsmittel und Monomer, wurde der Einfluss dieser untersucht. Allgemein konnte gezeigt werden, dass die Polymerisationen schneller ablaufen, wenn K+, im Gegensatz zu Cs+, als Gegenion zum aktiven Alkoxidkettenende verwendet wird. Nachteilig bei der Verwendung von K+ als Gegenion ist der Kontrollverlust der Polymerisation, welcher mit einer Erhöhung der Dispersität einhergeht. Es konnte gezeigt werden, dass die Breite der Molmassenverteilung durch die Geschwindigkeit der Monomerzugabe kontrolliert werden kann. Tatsächlich konnte die Dispersität durch die Verwendung einer Spritzenpumpe verbessert werden, da das Monomer mit einer konstanten angepassten Flussrate hinzugefügt wurde. Analog zur oxyanionischen Polymerisation von Epoxiden, war die Polymerisation von Episulfiden mittels thioanionischer Polymerisation ebenfalls möglich. Hierzu wurden verschiedene Polymerisationsgrade von EETGE und ATGE angestrebt und mittels Thiol/DBU als Initiator auch erreicht. In den meisten Fällen war jedoch eine Dimerisierung der Polymere zu beobachten, welche durch die Oxidation der aktiven Thiolatspezies verursacht wurde. Eine Möglichkeit zur Dimerisierungsunterdrückung war die wiederholte Durchführung von Entgasungszyklen nach jedem Arbeitsschritt, z.B. nach Zugabe des Initiators, des Monomers oder nach dem Quenchen. Trotz dieses experimentellen Aufwandes konnte nicht immer ein vollständiger Ausschluss der Dimerisierung erreicht werden. Thiophenol, Butanthiol, Mercaptoethanol und Dithiothreitol wurden als Thiolinitiatoren (in Kombination mit DBU) verwendet und waren alle in der Lage die Polymerisation zu starten. Die Kontrolle des Polymerisationsgrades und die enge Molmassenverteilung der Polymere verdeutlichen, dass die thioanionische Polymerisation ebenfalls lebend verläuft. Glycidol Homo- und Copolymere wurden verwendet und die Seitenketten mit Amin-, Thiol-, Carbonsäure- und Cysteingruppen funktionalisiert. Die Cysteinseitenketten wurden durch ein neues thiolfunktionales Thiazolidin erhalten. Ausgehend von Cystein und Aceton wurde zunächst das Dimethyl-substituierte Thiazolidin erhalten, welches daraufhin am Ring-Amin mit Essigsäureanhydrid und Ameisensäure formyliert wurde. Die Carbonsäurefunktion des Thiazolidins wurde mittels CDI aktiviert und anschließend mit Cysteamin umgesetzt. Hierbei bildete sich das niedermolekulare kristalline thiolfunktionale Thiazolidin, welches mittels Thiol-En-Click Chemie an allyl-funktionales Poly(glycidol) geknüpft werden konnte. Eine systematische Untersuchungen der thermischen und UV-induzierten Thiol-En-Click Chemie zeigte, dass wesentlich höhere Umsätze und Geschwindigkeiten bei der photoinduzierten Reaktion erhalten werden. Mittels 0.1 M HCl konnte bei 70 °C innerhalb von 5 d die Hydrolyse der Thiazolidine im Anschluss erreicht werden. Nach der anschließenden Dialyse der Polymere gegen 0.1 M Essigsäure wurde erfolgreich das Acetatsalz der cysteine-funktionalen Poly(glycidol)e erhalten. Diese waren hinsichtlich der Thioloxidation unter atmosphärischen Bedingungen stabil. Ein oxidativer TNSBA-Assay wurde entwickelt, um die Menge der Cysteine zu quantifizieren und gleichzeitig den störenden Einfluss der Thiole zu unterbinden. Ein Kooperationspartner setzte die cysteinfunktionalisierten Poly(glycidol)e mit C-terminalen Thioestern um und konnte die gute Zugänglichkeit und Aktivität der Cysteine entlang des Polymerrückgrats nachweisen. SDS-PAGE, HPLC und MALDI-ToF Messungen bestätigten die erfolgreiche Konjugation im Anschluss.

Advancements in the biomedical field are driven by the design of novel materials with controlled physical and bio-interactive properties. To develop such materials, researchers rely on the use of highly efficient reactions for the assembly of advanced polymeric scaffolds that meet the demands of a functional biomaterial. In this thesis two main strategies for such materials have been explored; these include the use of off-stoichiometric thiol-ene networks and dendritic polymer scaffolds. In the first case, the highly efficient UV-induced thiol-ene coupling (TEC) reaction was used to create crosslinked polymeric networks with a predetermined and tunable excess of thiol or ene functionality. These materials rely on the use of readily available commercial monomers. By adopting standard molding techniques and simple TEC surface modifications, patterned surfaces with tunable hydrophobicity could be obtained. Moreover, these materials are shown to have great potential for rapid prototyping of microfluidic devices. In the second case, dendritic polymer scaffolds were evaluated for their ability to increase surface interactions and produce functional 3D networks. More specifically, a self-assembled dendritic monolayer approach was explored for producing highly functional dendronized surfaces with specific interactions towards pathogenic E. coli bacteria. Furthermore, a library of heterofunctional dendritic scaffolds, with a controllable and exact number of dual-purpose azide and ene functional groups, has been synthesized. These scaffolds were explored for the production of cell interactive hydrogels and primers for bone adhesive implants. Dendritic hydrogels decorated with a selection of bio-relevant moieties and with Young’s moduli in the same range as several body tissues could be produced by facile UV-induced TEC crosslinking. These gels showed low cytotoxic response and relatively rapid rates of degradation when cultured with normal human dermal fibroblast cells. When used as primers for bone adhesive patches, heterofunctional dendrimers with high azide-group content led to a significant increase in the adhesion between a UV-cured hydrophobic matrix and the wet bone surface (compared to patches without primers). / <p>QC 20140116</p>

No description available.

No description available.

Silicon nanoparticles (SiNPs) are regarded as a promising alternative of traditional II-VI quantum dots in the field of bio-applications due to their photoluminescence and bio-compatibility. <br>Chapter 1 reviews various synthetic routes and applications of SiNPs. <br>Chapter 2 describes the mechanochemical synthesis of photoluminescent SiNPs with an organic ligand shell through reactive high energy ball milling (RHEBM). The morphology and size distribution of as-prepared SiNPs were determined by TEM. The bonding modes of the ligand shell including their mole fractions were investigated based on NMR and FTIR spectra of the as-prepared SiNPs.<br>Chapter 3 introduces the removal of the iron impurities, which were introduced into the SiNPs product from the milling media, stainless steel, by a physical method (GPC) and a chemical method (washing by HCl aqueous solution). The effect of the iron impurities to the optical properties of SiNPs is discussed.<br>Chapter 4 exhibits the surface functionalization of SiNPs with various functional groups through thiol-ene click reactions of vinyl-terminated SiNPs with various thiols. In addition, SiNP nanoclusters and DNA-conjugated SiNPs were prepared through thiol-ene click reactions of vinyl-terminated SiNPs with a tetrathiol-terminated crosslinker and a thiol-functionalized DNA, respectively<br>Chapter 5 is a miscellaneous chapter which includes the preparation of SiNPs through RHEBM of silicon wafers with 2,3-dimethyl-1,3-butadiene, and the effect of UV irradiation at 254 nm to the chemical structures and optical properties of SiNPs. / acase@tulane.edu

The research described herein is aimed at exploring the thermo-mechanical properties of thiol-ene polymers in bulk form, investigating the ability of thiol-ene polymers to behave desirably as photolithographic media, and providing the first characterization of the mechanical properties of two-photon stereolithography-produced polymer structures. The thiol-ene polymerization reaction itself is well-characterized and described in the literature, but the thermomechanical properties of thiol-ene and thiol-ene/acrylate polymers still require more rigorous study. Understanding the behavior of thiol-ene networks is a crucial step towards their expanded use in bulk form, and particularly in specialized applications such as shape memory devices. Additionally, the thiol-ene polymerization reaction mechanism exhibits unique properties which make these polymers well suited to photolithography, overcoming the typical dichotomy of current materials which either exhibit excellent photolithographic behavior or have controllable properties. Finally, before two-photon stereolithography can create mechanisms and devices which can serve any mechanically functional role, the mechanical properties of the polymers they produce must be quantitatively characterized, which is complicated by the extremely small scale at which these structures are produced. As such, mechanical characterization to date has been strictly qualitative. Fourier transfer infrared spectroscopy revealed functional group conversion information and sol-fraction testing revealed the presence of unconverted monomer and impurities, while dynamic mechanical analysis and tensile testing revealed the thermomechanical responses of the systems. Nanoindentation was employed to characterize the mechanical properties of polymers produced by two-photon stereolithography. Optical and electron microscopy were exploited to provide quantitative and qualitative evaluations of thiol-ene/acrylate performance in small-scale polymerization regimes. The broad objective of the research was to explore thiol-ene polymer behavior both in bulk and at the small scale in an effort to supplement the material library currently used in these fields and to expand the design envelope available to researchers. The significance of the research is the advancement of a more complete and fundamental understanding of thiol-ene polymerization from kinetics to final properties, the quantitative establishment of the mechanical properties of materials created with two-photon stereolithography, and the comprehensive characterization of a supplementary class of photopatternable polymers with greater property tunability than is possible with currently used materials.