Structure, Dynamics and Reactivity in the Organic Solid State: Anthracene Derivatives and Charge Transfer Crystals

The work presented in this thesis tackles some important points concerning the collective properties of two typical categories of molecular crystals, i.e., anthracene derivatives and charge transfer crystals. Anthracene derivatives have constituted the class of materials from which systematical investigations of crystal-to-crystal photodimerization reactions started, developed and have been the subject of a new awakening in the recent years. In this work some of these compounds, namely, 9-cyanoanthacene, 9-anthacenecarboxylic acid and 9-methylanthracene, have been selected as model systems for a phenomenological approach to some key properties of the solid state, investigated by spectroscopic methods. The present results show that, on the basis of the solid state organization and the chemical nature of each compound, photo-reaction dynamics and kinetics display distinctive behaviors, which allows for a classification of the various processes in topochemical, non topochemical, reversible or topophysical. The second part of the thesis was focused on charge transfer crystals, binary systems formed by stoichiometric combinations of the charge donating perylene (D) and the charge accepting tetracyano-quinodimethane (A), this latter also in its fluorinated derivatives. The work was focused on the growth of single crystals, some of which not yet reported in the literature, by PVT technique. Structural and spectroscopic characterizations have been performed, with the aim of determining the degree of charge transfer between donor and acceptor in the co-crystals. An interesting outcome of the systematic search performed in this work is the definition of the experimental conditions which drive the crystal growth of the binary systems either towards the low (1:1) or the high ratio (3:1 or 3:2) stoichiometries.

Beyond simple proton transfer processes: domino reactions between 4-substituted indoles and nitroethene as a new gateway to ergot alkaloids

The multimodal biology activity of ergot alkaloids is known by humankind since middle ages. Synthetically modified ergot alkaloids are used for the treatment of various medical conditions. Despite the great progress in organic syntheses, the total synthesis of ergot alkaloids remains a great challenge due to the complexity of their polycyclic structure with multiple stereogenic centres. This project has developed a new domino reaction between indoles bearing a Michael acceptor at the 4 position and nitroethene, leading to potential ergot alkaloid precursors in highly enantioenriched form. The reaction was optimised and applied to a large variety of substrate with good results. Even if unfortunately all attempts to further modify the obtained polycyclic structure failed, it was found a reaction able to produce the diastereoisomer of the polycyclic product in excellent yields. The compounds synthetized were characterized by NMR and ESIMS analysis confirming the structure and their enantiomeric excess was determined by chiral stationary phase HPLC. The mechanism of the reaction was evaluated by DFT calculations, showing the formation of a key bicoordinated nitronate intermediate, and fully accounting for the results observed with all substrates. The relative and absolute configuration of the adducts were determined by a combination of NMR, ECD and computational methods.

Synthesis and organocatalyzed enantioselective transfer-hydrogenation of beta-amino nitroolefins

The importance of the β-amino nitroalkanes is due to their high versatility allowing a straightforward entry to a variety of nitrogen-containing chiral building blocks; furthermore obtaining them in enantiopure form allows their use in the synthesis of biologically active compounds or their utilization as chiral ligands for different uses. In this work, a reaction for obtaining enantiopure β-amino nitroalkanes through asymmetric organocatalysis has been developed. The synthetic strategy adopted for the obtainment of these compounds was based on an asymmetric reduction of β-amino nitroolefins in a transfer hydrogenation reaction, involving an Hantzsch ester as hydrogen source and a chiral thiourea as organic catalyst. After the optimization of the reaction conditions over the β-acyl-amino nitrostyrene, we tested the reaction generality over other aromatic compound and for Boc protected substrate both aromatic and aliphatic. A scale-up of the reaction was also performed.

Molecular Charge-Transfer Cross Sections and Their Correlation with Reactant Ion Structures

Charge-transfer cross sections have been obtained by using time-of-flight techniques, and results correlated with reaction energetics and theoretical structures computed by self-consistent field-molecular orbital methods. Ion recombination energies, structures, heats of formation, reaction energy defects, and 3.0-keV charge-transfer cross sections are presented for reactions of molecular and fragment ions produced by electron bombardment ionization of CH30CH, and CH$l molecules. Relationships between experimental cross sections and reaction energetics involving different ion structures are discussed.

Sensitivity of charge transfer reactions to hydrocarbon ion structures

Charge transfer reactivities of hydrocarbon ions have been measured with time-of-flight techniques, and results correlated with theoretical structures computed by self-consistent field molecular orbital methods. Recombination energies, ion structures, heats of formation, reaction energetics and relative charge transfer cross-sections are presented for molecular and fragment ions produced by electron bombardment ionization of CH4, C2H4, C2H6, C3H8 and C4H10 molecules. Even-electron bridged cations have low ion recombination energies and relatively low charge transfer cross-sections as compared with odd-electron hydrocarbon cations.

Synthesis of Macrocyclic Polymers Formed via Intramolecular Radical Trap-Assisted Atom Transfer Radical Coupling

The synthesis of cyclic polystyrene (Pst) with an alkoxyamine functionality has been accomplished by intramolecular radical coupling in the presence of a nitroso radical trap Linear alpha,omega-dibrominated polystyrene, produced by the atom transfer radical polymerization (ATRP) of styrene using a dibrominated initiator, was subjected to chain-end activation via the atom transfer radical coupling (ATRC) process under pseudodilute conditions in the presence of 2-methyl-2-nitrosopropane (MNP). This radical trap-assisted, intramolecular ATRC (RTA-ATRC) produced cyclic polymers in greater than 90% yields possessing < G > values in the 0.8-0.9 range as determined by gel permeation chromatography (GPC). Thermal-induced opening of the cycles, made possible by the incorporated alkoxyamine, resulted in a return to the original apparent molecular weight, further supporting the formation of cyclic polymers in the RTA-ATRC reaction. Liquid chromatography-mass spectrometry (LC-MS) provided direct confirmation of the cyclic architecture and the incorporation of the nitroso group into the macrocycle RTA-ATRC cyclizations carried out with faster rates of polymer addition into the redox active solution and/or in the presence of a much larger excess of MNP (up to a 250:1 ratio of MNP:C-Br chain end) still yielded cyclic polymers that contained alkoxyamine functionality.

One Pot, Two Step Sequence Converting Atom Transfer Radical Polymerization Directly to Radical Trap-Assisted Atom Transfer Radical Coupling

Monobrominated polystyrene (PStBr) chains were prepared using standard atom transfer radical polymerization (ATRP) procedures at 80 °C in THF, with monomer conversions allowed to proceed to approximately 40%. At this time, additional copper catalyst, reducing agent, and ligand were added to the unpurified reaction mixture, and the reaction was allowed to proceed at 50 °C in an atom transfer radical coupling (ATRC) phase. During this phase, polymerization continued to occur as well as coupling; expected due to the substantial amount of residual monomer remaining. This was confirmed using gel permeation chromatography (GPC), which showed increases in molecular weight not matching a simple doubling of the PStBr formed during ATRP, and an increase in monomer conversion after the second phase. When the radical trap 2-methyl-2-nitrosopropane (MNP) was added to the ATRC phase, no further monomer conversion occurred and the resulting product showed a doubling of peak molecular weight (Mp), consistent with a radical trap-assisted ATRC (RTA-ATRC) reaction.

One Pot, Two Step Sequence Converting Atom Transfer Radical Polymerization Directly to Radical Trap-Assisted Atom Transfer Radical Coupling

Monobrominated polystyrene (PStBr) chains were prepared using standard atom transfer radical polymerization (ATRP) procedures at 80 degrees C in THF, with monomer conversions allowed to proceed to approximately 40%. At this time, additional copper catalyst, reducing agent, and ligand were added to the unpurified reaction mixture, and the reaction was allowed to proceed at 50 degrees C in an atom transfer radical coupling (ATRC) phase. During this phase, polymerization continued to occur as well as coupling; expected due to the substantial amount of residual monomer remaining. This was confirmed using gel permeation chromatography (GPC), which showed increases in molecular weight not matching a simple doubling of the PStBr formed during ATRP, and an increase in monomer conversion after the second phase. When the radical trap 2-methyl-2-nitrosopropane (MNP) was added to the ATRC phase, no further monomer conversion occurred and the resulting product showed a doubling of peak molecular weight (M-p), consistent with a radical trap-assisted ATRC (RTA-ATRC) reaction. (C) 2013 Elsevier Ltd. All rights reserved.

Vibrational spectroscopic monitoring of CO2-O energy transfer: cooling processes in atmospheres of Venus & Mars

The vibrational excitation of CO2 by a fast-moving O atom followed by infrared emission from the vibrationally excited CO2 has been shown to be an important cooling mechanism in the upper atmospheresof Venus, Earth and Mars. We are trying to determine more precisely the efficiency (rate coefficient) of the CO2-O vibrational energy transfer. For experimental ease the reverse reaction is used, i.e. collision of a vibrationally excited CO2 with atomic O, where we are able to convert to the atmospherically relevant reaction via a known equilibrium constant. The goal of this experiment was to measure the magnitudes of rate coefficients for vibrational energy states above the first excited state, a bending mode in CO2. An isotope of CO2, 13CO2, was used for experimental ease. The rate coefficients for given vibrational energy transfers in 13CO2 are not significantly different from 12CO2 at this level of precision. A slow-flowing gas mixture was flowed through a reaction cell: 13CO2 (vibrational specie of interest), O3(atomic O source), and Ar (bath gas). Transient diode laser absorption spectroscopy was used to monitor thechanging absorption of certain vibrational modes of 13CO2 after a UV pulse from a Nd:YAG laser was fired. Ozone absorbed the UV pulse in a process which vibrationally excited 13CO2 and liberated atomic O.Transient absorption signals were obtained by tuning the diode laser frequency to an appropriate ν3 transition and monitoring the population as a function of time following the Nd:YAG pulse. Transient absorption curves were obtained for various O atom concentrations to determine the rate coefficient of interest. Therotational states of the transitions used for detection were difficult to identify, though their short reequilibration timescale made the identification irrelevant for vibrational energy transfer measurements. The rate coefficient for quenching of the (1000) state was found to be (4 ± 8) x 10-12 cm3 s-1 which is the same order of magnitude as the lowest-energy bend-excited mode: (1.8 ± 0.3) x 10-12 cm3 s-1. More data is necessary before it can be certain that the numerical difference between the two is real.

The recoil transfer chamber - An interface to connect the physical preseparator TASCA with chemistry and counting setups

Performing experiments with transactinide elements demands highly sensitive detection methods due to the extremely low production rates (one-atom-at-a-time conditions). Preseparation with a physical recoil separator is a powerful method to significantly reduce the background in experiments with sufficiently long-lived isotopes (t1/2≥0.5 s). In the last years, the new gas-filled TransActinide Separator and Chemistry Apparatus (TASCA) was installed and successfully commissioned at GSI. Here, we report on the design and performance of a Recoil Transfer Chamber (RTC) for TASCA—an interface to connect various chemistry and counting setups with the separator. Nuclear reaction products recoiling out of the target are separated according to their magnetic rigidity within TASCA, and the wanted products are guided to the focal plane of TASCA. In the focal plane, they pass a thin Mylar window that separates the ∼1 mbar atmosphere in TASCA from the RTC kept at ∼1 bar. The ions are stopped in the RTC and transported by a continuous gas flow from the RTC to the ancillary setup. In this paper, we report on measurements of the transportation yields under various conditions and on the first chemistry experiments at TASCA—an electrochemistry experiment with osmium and an ion exchange experiment with the transactinide element rutherfordium.

The Synthesis of Macrocyclic Polystyrene by Sequential Atom Transfer Radical Reactions

A method for the production of macrocyclic polystyrene via ring closing of a linear !,"-dibrominated polystyrene by an Atom Transfer Radical Coupling (ATRC) reaction is described. The dibrominated polystyrene chain was produced from two simultaneous atom transfer radical polymerizations (ATRPs) originating from a dibrominated benzal bromide initiator. To ensure the retention of the halogen end groups polymerization was allowed to proceed to less than 50% conversion. Using this precursor in an intramolecular ATRC (ring closing) reaction was found to yield in excess of 90% cyclic product based on refractive index-gel permeation chromatography (GPC) analysis. The cyclic architecture of the polymer was verified by GPC, Nuclear Magnetic Resonance (NMR), and mass spectrometry analysis. The utility of this method has been expanded by the addition of 2-methyl-2-nitrosopropane to the coupling reaction, which allows for the coupling to proceed at a faster rate and to yield macrocycles with incorporated alkoxyamine functionality. The alkoxyamine functionality allows for degradation of the cycles at high temperatures (>125° C) and we hypothesize that it may allow the macrocycles to act as a macroinitiator for a ring expansion polymerization in future studies.

Gold Phosphonates as Transfer Agents in Palladium Catalyzed Hirao Reactions

Through a cross-coupling reaction, aryl phosphonates are produced in high yields when the corresponding aryl bromides are reacted with a gold phosphorylating agent in the presence of a palladium catalyst and an appropriate ligand. To the best of our knowledge, this transformation is the first example involving the transfer of a phosphonate functional group from a gold complex to palladium that has been reported. Throughout the investigation, three gold phosphorylating agents were screened for activity towards the phosphorylation of aryl bromides. Aryl bromides with electrondonating and electron-withdrawing groups were successfully employed in the crosscoupling reactions. All cross-coupling reactions were carried out in THF at room temperature (25ºC) or in a microwave reactor (CEM Discover) at 60ºC for 30 or 60 minutes. The effects of changing reaction parameters such as time, temperature, catalyst and free ligand loading have been investigated. All aryl bromide substrates tested in the cross-coupling reactions produced phosphorylated products.

Dimerization of Poly(methyl methacrylate) Chains Using Radical Trap-Assisted Atom Transfer Radical Coupling

End-brominated poly(methyl methacrylate) (PMMABr) was prepared by atom transfer radical polymerization (ATRP) and employed in a series of atom transfer radical coupling (ATRC) and radical trap-assisted ATRC (RTA-ATRG) reactions. When coupling reactions were performed in the absence of a nitroso radical trap-traditional ATRC condition-very little coupling of the PMMA chains was observed, consistent with disproportionation as the major termination pathway for two PMMA chain-end radicals in our reactions. When 2-methyl-2-nitrosopropane (MNP) was used as the radical trap, coupling of the PMMA chains in this attempted RTA-ATRC reaction was again unsuccessful, owing to capping of the PMMA chains with a bulky nitroxide and preventing further coupling. Analogous reactions performed using nitrosobenzene (NBz) as the radical trap showed significant dimerization, as observed by gel permeation chromatography (GPC) by a shift in the apparent molecular weight compared to the PMMABr precursors. The extent of coupling was found to depend on the concentrion of NBz compared to the PMMABr chain ends, as well as the temperature and time of the coupling reaction. To a lesser extent, the concentrations of copper(I) bromide (CuBr), nitrogen ligand (N,N,N',N',N"-pentamethyldiethylenetriamine = PMDETA), and elemental copper (Cu) were also found to play a role in the success of the RTA-ATRC reaction. The highest levels of dimerization were observed when the coupling reaction was carried out at 80 degrees C for 0.5h, with ratio of 1:4:2.5:8:1 equiv of NBz: CuBr:Cu:PMDETA:PMMABr.

Reaction Control in Quiescent Systems of Free-Radical Retrograde-Precipitation Polymerization

Free-radical retrograde-precipitation polymerization, FRRPP in short, is a novel polymerization process discovered by Dr. Gerard Caneba in the late 1980s. The current study is aimed at gaining a better understanding of the reaction mechanism of the FRRPP and its thermodynamically-driven features that are predominant in controlling the chain reaction. A previously developed mathematical model to represent free radical polymerization kinetics was used to simulate a classic bulk polymerization system from the literature. Unlike other existing models, such a sparse-matrix-based representation allows one to explicitly accommodate the chain length dependent kinetic parameters. Extrapolating from the past results, mixing was experimentally shown to be exerting a significant influence on reaction control in FRRPP systems. Mixing alone drives the otherwise severely diffusion-controlled reaction propagation in phase-separated polymer domains. Therefore, in a quiescent system, in the absence of mixing, it is possible to retard the growth of phase-separated domains, thus producing isolated polymer nanoparticles (globules). Such a diffusion-controlled, self-limiting phenomenon of chain growth was also observed using time-resolved small angle x-ray scattering studies of reaction kinetics in quiescent systems of FRRPP. Combining the concept of self-limiting chain growth in quiescent FRRPP systems with spatioselective reaction initiation of lithography, microgel structures were synthesized in a single step, without the use of molds or additives. Hard x-rays from the bending magnet radiation of a synchrotron were used as an initiation source, instead of the more statistally-oriented chemical initiators. Such a spatially-defined reaction was shown to be self-limiting to the irradiated regions following a polymerization-induced self-assembly phenomenon. The pattern transfer aspects of this technique were, therefore, studied in the FRRP polymerization of N-isopropylacrylamide (NIPAm) and methacrylic acid (MAA), a thermoreversible and ionic hydrogel, respectively. Reaction temperature increases the contrast between the exposed and unexposed zones of the formed microgels, while the irradiation dose is directly proportional to the extent of phase separation. The response of Poly (NIPAm) microgels prepared from the technique described in this study was also characterized by small angle neutron scattering.

Hydroxylation of naphthalene by aromatic peroxygenase from Agrocybe aegerita proceeds via oxygen transfer from H2O2 and intermediary epoxidation

Agrocybe aegerita peroxidase/peroxygenase (AaP) is an extracellular fungal biocatalyst that selectively hydroxylates the aromatic ring of naphthalene. Under alkaline conditions, the reaction proceeds via the formation of an intermediary product with a molecular mass of 144 and a characteristic UV absorption spectrum (A(max) 210, 267, and 303 nm). The compound was semistable at pH 9 but spontaneously hydrolyzed under acidic conditions (pH<7) into 1-naphthol as major product and traces of 2-naphthol. Based on these findings and literature data, we propose naphthalene 1,2-oxide as the primary product of AaP-catalyzed oxygenation of naphthalene. Using (18)O-labeled hydrogen peroxide, the origin of the oxygen atom transferred to naphthalene was proved to be the peroxide that acts both as oxidant (primary electron acceptor) and oxygen source.