Techn. University, Diss., 2007--Darmstadt.

No description available.

The emergence of complex, carefully designed, molecular architectures incorporating either a lanthanide ion or the porphyrinic macrocycle have stimulated significant interest of late, particularly in the fields of molecular switches, molecular machines and data storage systems. The integration of these emissive species has been shown to permit the analysis of conformational, coordinative, or electronic change, and employed, in the case of the porphyrinic macrocycle, to acquire a deeper understanding of the natural process of photosynthesis, thus opening up the possibility of developing more efficient and inexpensive photovoltaic cells. This thesis begins by providing insight into the generation of cathodic photocurrent density within both monophasic and biphasic self-assembled monolayers, before documenting how the magnitude of such photoelectochemical output can be gated upon the integration of an electron relay moiety, both at the interface and into solution. The introduction of an electron relay moiety into solution has been shown to bring about increases of up to 283 % in the magnitude of the cathodic photocurrent density acquired, whilst optimisation of the distances between the metallic interface, the electron relay moiety and the porphyrinic macrocycle has also proven beneficial. Greatest photoelectrochemical output (5.1 x 1014 nA mol-1 cm-2) is realised when the porphyrinic macrocycle is covalently tethered at a distance of 4.6 nm from the quenching, metallic interface, and the relay moiety integrated at a distance of 1.7 nm from the interface and 2.9 nm from the porphyrinic macrocycle, respectively. However, greatest variation (94 %) in the magnitude of the cathodic photocurrent densities acquired is observed when the distance between the porphyrinic macrocycle and the gold surface is kept at 3.3 nm, and the relay moiety situated at either 1.2 nm or 1.7 nm from the interface, respectively. Research then moved towards trying to integrate this established conformational ruler within a porphyrin-appended, bistable [2]rotaxane. Its implementation served to try to ensure that photoelectrochemical differentiation of the ground state coconformation (GSCC) and the metastable state co-conformations (MSCC) was viable, thus enabling the efficient resolution of anion-induced molecular motion within a dynamic supramolecular architecture by means of a novel approach. The focus of this thesis then shifts to the assembly of novel, optically switchable, ternary complexes exhibiting charge-transfer based on the donor-acceptor interaction between an electron-rich naphthalene derivative (EuNap) and MV2+, an electron-poor, redox-addressable moiety. Prior to the deposition of (MV, EuNap)-CB[8] at the interface, the homoternary analogue ((MV+.)2-CB[8]) was acquired upon one electron reduction of (MV, EuNap)-CB[8] in the presence of excess MV2+. This process was revealed to be reversible upon the application of a stream of oxygen, and the relative concentration of each complex present in solution quantified upon mathematical manipulation of the biexponential decay curve acquired; upon the addition of sodium thiosulfate (Na2S2O3), the percentage of uncomplexed EuNap (τ = 0.60 ms cf. τ = 0.1 ms (MV, EuNap)-CB[8]) present in solution increased in accordance with the generation of ((MV+.)2-CB[8]) and loss of the charge-transfer interaction (λmax = 390, 490 nm), of which has been shown to quench lanthanide luminescence (Eu3+, Yb3+, Nd3+). Thus, the assembly of a molecular switch is documented which may be followed qualitatively at higher concentration by a visible colour change, and at low concentrations quantitatively by virtue of luminescence spectroscopy. No optical output (λex = 227 nm, λem = 616 nm) was acquired upon the deposition of (MV, EuNap)CB[8]) due to the occurrence of surface energy transfer (SET). As a result, 1-(10-mercaptodecyl)-1'methyl-[4,4'-bipyridine]-diium bromide and 1-methyl-1'-(10-(naphthalen-2yloxy)decyl)-[4,4'bipyridine]-1,1'-diium bromide iodide were synthesised and the assembly of a molecular film envisaged in which the molecular recognition properties of CB[n] were maintained and significant optical output from the lanthanide ion (Eu3+, λem 616 nm) detected; the assembly of such a film centred on the formation of 1:2 intermolecular heteroternary complexes and the recruitment of EuNap at a distance ≥ 3.2 nm from the gold substrate. It was envisaged that the modulation of any emissive output would be brought about upon manipulating the oxidation state of a surface-confined metallocene. This thesis ends by summarising the research conducted and assessing how the inclusion chemistry of cucurbit[8]uril and the photophysical properties of the porphyrinic macrocycle can be combined in order to fabricate a dynamic, photoresponsive molecular assembly. The electrical energy generated from the efficient harvesting of light energy could be used in a multitude of applications, most notably as a nanoscale power supply to drive and control molecular and supramolecular actuations.

In this research, the use of gold nanostructures (AuNS) was explored to evaluate the interaction between molecules and the nanoparticle (NP) surface. In that way, three different projects were developed; one project using fluorescence and two projects using Raman spectroscopy as measuring technique. The fluorescence spectroscopy project used the fluorescence lifetime imaging microscope (FLIM) to evaluate the relative position of the molecules methylene blue (MB) and cucurbit[7]uril (CB) on the gold nanoparticle (AuNP) surface. Although the inclusion complex is favored in solution, it was found that MB forms an exclusion complex with CB, when CB is attached to the AuNP surface. The first project utilizing Raman spectroscopy, specifically surface enhanced Raman scattering (SERS), took advantage of a confined system (a reverse micelle) to evaluate the Raman signal of water molecules in close proximity to the AuNP surface. It was observed that the SERS water signal had a big shift to higher energies compared with the Raman signal of the bulk water; indicating the water molecules in the system are subjected to different bond-stretching energies. The second Raman project studied the modification of two different AuNS (specifically AuNP and gold nanorod -AuNR) with thiols. Different thiols were used to evaluate the kinetics of the modification of the AuNS surface, also the different AuNS presented different ligands on their surface. In general, and considering the difference in the bonding strength of the ligands present on the AuNS surface (by synthesis) and the size of the thiol, at least 2 h are required to modify the complete AuNS surface.

No description available.

Host-guest interactions have been well studied in the new century to obtain fundamental insights into supramolecular chemistry. Most of the pioneering works have been done using techniques such as NMR, X-ray crystallography, IR spectroscopy and so on. However, none of these techniques is universal for the investigation of all types of supramolecules, and usually they have one or more limiting factors such as relatively large sample consumption, matrix effects from solvents, etc. Electrospray mass spectrometry has been widely used to investigate host-guest interactions in the gas phase. A particular advantage of gas phase host-guest research is that the experimental results can be directly compared to computational results because complicating interferences from solvents are not present. Thus electrospray mass spectrometry coupled with high-level computational methods becomes a powerful tool to elucidate binding behavior in host-guest complexes. With rigid, symmetric structures available in a range of sizes, cucurbiturils have been ideal prototypical host molecules in host-guest chemistry since they were characterized in 1980s. Recent research in my group has shown cucurbiturils can form various complexes with positive ions in the gas phase, such as molecular containers trapping small neutral guest molecules inside or wheel-and-axle architectures with linear molecules threaded through. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is an ideal technique for investigation of host-guest supramolecular complexes due to its ultra-high mass resolving power, ultra-high mass accuracy, and high sensitivity. Moreover it has the capability of trapping ions for ion chemistry, and versatile tandem mass spectrometry capabilities. This dissertation focuses on the characterization of cucurbituril complexes in the gas phase using electrospray ionization FT-ICR mass spectrometry. Chapter 1 describes FTICR mass spectrometry techniques including principles, performance, instrumentation and applications. Electrospray ionization methods are also discussed in this chapter. Chapter 2 introduces structures, properties, synthesis and host-guest chemistry of the cucurbituril family. Chapters 3 investigate cucurbituril complexation behavior with amino acids and peptides. Chapter 4 investigates the alkali metal ions “lids removal” from cucurbit[5]uril molecular box. Chapter 5 characterizes the cucurbit[6]uril pseudorotaxanes in the gas phase. Chapter 6 characterizes the complexes formed by cucurbit[6]uril and α,ω-alkyldiammonium cations in the gas phase, using energy-resolved SORI-CID method. High-level computational methods were also performed to explain the experimental results.

This thesis focuses on using mass spectrometry-based techniques for characterizing the structure and behavior of cucurbituril complexes in the gas phase. Both solvent and counter ion effects can be completely eliminated in the gas phase and the intrinsic interactions in the system are directly shown in the experimental results. Chapter 1 introduces the structures, properties and host-guest chemistry of cucurbituril, and FTICR mass spectrometry including instrumentation, performance and working principles. Two mass spectrometry-based methods for supramolecular characterization, sustained off-resonance irradiation collision induced dissociation (SORI CID) and ion molecule equilibrium measurements, are also discussed in this chapter. Chapter 2 characterizes the dissociation and reaction behaviors of the complexes formed by cucurbit[5]uril (CB5) and primary monoamines [CH3(CH2)nNH2, n = 0-7] as well as similar studies of decamethylcucurbit[5]uril (mc5) in the gas phase. This study probes host-guest interactions between the neutral cucurbituril host and alkyl chains of varying length. All the cucurbit[5]uril and decamethylcucurbit[5]uril complexes have external binding. The dissociation thresholds of the complexes suggest that the optimum monoammonium chain length for binding CB5 in the gas phase occurs for n = 2, whereas for mc5 the optimum is n = 0. Reactivity studies of CB5 and mc5 complexes indicate the highest binding affinity appears at n = 6 for CB5 and n = 5 for mc5. Chapter 3 investigates the complexes formed by cucurbit[6]uril and primary monoamines using energy resolved SORI CID methods and ion molecule equilibrium measurements. The fragmentation data, branching ratios for the various channels, and the reactivities of the complexes suggest the complexes have the monoammonium threaded through the cavity of CB6 forming a pseudorotaxane architecture. Reactivity studies of complexes of cucurbit[7]uril reveal behaviors distinctive from CB5, mc5 or CB6, which suggests both internally-bound and externally-bound structures are present in CB7 complexes.

This thesis covers combination of two independent works accomplished throughout the study. One part research is about the unexpected cyclization of Dipyridyl-glycoluril, and the other part is about synthesis of precursor calix[4]arene derivatives. In an attempted synthesis of peripherally pyridine substituted cucurbituril, an unexpected cyclized product was obtained. A careful NMR analysis followed by mass spectrometry and preliminary crystallographic analyses, helped us in resolving the structure. The structure has two quaternized pyridine functionalities and a groove suitable as a potential receptor site. In addition, just like the parent glycoluril structure, two remaining urea-derived nitrogens can be alkylated by alkyl halides. Thus, we believe this high yielding reaction may become an entry point to a new class of anion receptors. In the second work, certain important calix[4]arene derivatives were synthesized. They are the building blocks of important potential molecular, anion and cation sensing, and enzyme mimics. For these precursor molecules, functionalizations both on lower and upper rim have been studied. A careful study on NMR data has been performed and detailed investigation on the NMR data was discussed herein. Applying further one or two step procedures produces important target molecules having potential as sensors or artificial enzymes.

The enzyme spermidine/spermine N1-acetyltransferase (SSAT) is a candidate biomarker for various cancers as its activity in cancerous tissues is significantly increased. An artificial molecule, amantadine, is exclusively acetylated by SSAT to acetylamantadine (AcAm), levels of which in urine can serve as a proxy biomarker for malignancy. Current method of AcAm detection is laborious, time-consuming, and lacks the possibility of transforming to a point-of-care device. In this thesis, two different approaches were applied to detect AcAm in deionized water and in human urine using optical methods. The first one was fluorescence-based indicator displacement assay using cucurbit[7]uril as the receptor molecule. The second was programmed gold nanoparticle disaggregation with cucurbit[7]uril as a molecular linker. / Graduate

This thesis studies the different ways in which the localized plasmon heating effect of gold nanostructures -activated by plasmon excitation via visible and/or NIR irradiation- can be used to obtain different outcomes following the nanofabrication of applicable devices. Both spatial and temporal control were obtained for each one of the systems developed upon the incorporation of plasmonic gold nanostructures. Spatial control was enabled in hybrid mesoporous drug delivery systems fabricated in this thesis through the localized surface plasmon heating effect that allowed the modification of the dynamics of diffusion of the cargo being delivered, thus giving rise to different rates of release that can be controlled by plasmon excitation. At the same time, the plasmon heating effect proved to be capable of controlling the start of the release by dismantling thermo-responsive gates previously incorporated, thus enabling also a wavelength-controlled feature that enhances the versatility of these systems. Spatial control was also conferred to the photo-patterning applications presented in this dissertation by influencing the degree of motility of gold nanorods (AuNRs) embedded in polymer matrices allowing them to self-assemble when the longitudinal plasmon of the incorporated nanostructures was excited; the patterns generated were quite robust and persisted for extended periods of time. Finally, the feature of spatial heating control was also conferred to catalysis. The Friedel-Crafts alkylation of anisole by benzyl chloride using spherical gold nanoparticles (AuNPs) supported on Nb2O5-based catalysts was performed at bulk temperatures below those necessary for the reaction to occur when using bare or modified Nb2O5; this was the result of the combination of bulk and localized plasmon heating produced -both- via plasmon excitation. This also demonstrates the possibility of using plasmon excitation as an alternative heat source in this type of reactions. By combining the plasmonic properties of metallic nanostructures with those granted by mesoporous materials, polymer matrices and Nb2O5-based materials it was possible to obtain light-activated systems endowed also with temporal control and wavelength control while preserving the original properties of each systems' components. Overall, the content of this thesis describes in detail the practical aspects of combining gold nanostructures with different materials and the rationale behind the development of systems with customized and controllable properties.