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This research explores the links between the structure and dissociation energetics of ionized non-covalent complexes. In chapter 3, a large series of similar non-covalent complexes were probed using electrospray tandem mass spectrometry (ESI-MS/MS) and RRKM modelling in order to identify any trends in the dissociation energetics based on charge state, overall size of the complex, or size of the substrate. Ion mobility spectrometry (IMS) in conjunction with molecular mechanics/molecular dynamics (MM/MD) was used to study the conformations of these non-covalent complexes in order to determine if the same trends identified in the energetics could be corroborated independently based on structure. The system of study consisted of varying lengths of the synthetic polymer, polymethylmethacrylate (PMMA) complexed with singly or doubly protonated diaminoalkanes (DAA) of varying length. The critical energies of dissociation (E0) increased as the length of the polymer increased and was not significantly affected by the length of the singly protonated DAA substrates. The E0 of dissociation of doubly protonated complexes was strongly influenced by the length of the DAA; longer DAA substrates had greater separation of charge which decreased coulombic repulsion within the complex resulting in higher E0 values. MM/MD low energy structures of all complexes were validated with experimental IMS measurements and showed that the arrangement between the polymer and DAA were similar for different singly protonated DAAs. When doubly protonated, the length of DAA was the most important factor in determining the overall structure of the complex. In chapter 4, a direct link is shown between the observed E0 dissociation energies and the molecular conformations for eight different peptide–saccharide complexes containing either a tri-saccharide (d-(+)-raffinose and d-panose) or tetra-saccharide (stachyose and maltotetraose) with a small peptide (FLEEL and FLEEV). The E0 values were highly related to the overall conformation adopted by the non-covalent complex in the gas phase. Complexes containing peptide FLEE(L/V) with the tri-saccharide raffinose or panose had similar E0 of dissociation (∼0.64 eV) and similar conformations based on MM/MD simulations and IMS drift times. Conversely, for complexes containing a FLEE(L/V) peptide with one of the isomeric tetra-saccharides; stachyose had a E0 ∼0.08 eV greater than maltotetraose. This difference of intermolecular interaction was also reflected by the IMS drift times; maltotetraose in complex with FLEEV or FLEEL had a 5.9% and 2.3% faster IMS drift time than stachyose respectively. This indicated that the molecular arrangement between maltotetraose and the peptides was more compact than the stachyose-peptide complexes. In chapter 5, RRKM modelling of breakdown diagrams is not possible when the reactant ion signal is overlapped by other isobaric species. Trimeric, non-covalent complexes that contained two PMMA molecules and a doubly protonated DAA, [(PMMAa)(DAA+2H)(PMMAb)]+2, have m/z signals that contain multiple different complexes having the same total number of polymer repeat units but differ in the length of the each polymer. In this situation, the applicability of using the simple kinetic method to gain insight into relative binding energies was explored. The major factors which determined the suitability of the kinetic method for this system were identified as the structural arrangement of the reactant ion complex, possible reverse activation barriers, and the evaluations of Δ(ΔS‡). MM/MD simulations coupled with IMS suggests that within the reactant ion, the DAA is almost equally shared between two PMMA oligomers and that the two PMMA oligomers interact predominately with the DAA, and not with each other. MS/MS of the trimeric reactant complexes proceeds by neutral loss of one polymer and is suggested to proceed with little or no reverse activation barrier based on the low coulombic repulsion factors. The IMS drift times of [(PMMAa)(DAA+2H)]+2 complexes that were generated directly by ESI-MS or by dissociation of a trimeric, [(PMMAa)(DAA+2H)(PMMAb)]+2 complex were found to be identical. This provides some evidence that Δ(ΔS‡) ≈ Δ(ΔS) and using a statistical mechanics approach, Δ(ΔS) ≈ 0. The effective temperature (Teff) variable in the kinetic method expression was found to decrease as a function of the size of the trimeric complex, suggesting that the population distribution of the dissociating ensemble of complexes narrows as size increases. Overall, when RRKM fitting is not possible, the simple kinetic method could provide relative energetic ranking of competing dissociations reactions however the Teff term contributed to the greatest uncertainty in obtaining absolute quantities. Fitting MS/MS breakdown diagrams of non-covalent complexes with multiple dissociation channels is difficult due to the number of total fitting variables. Building from the simple kinetic method, chapter 6 shows that the relationship between the natural logarithm of competing fragment ions and reciprocal collision energy yields a branching relationship that allows for the sign of Δ(ΔS‡) and Δ(E0) between the channels to be obtained. Furthermore, the relationships between the fitting variables of RRKM modelling are empirically related to the theoretical branching relationship characteristics. This allowed for the fitting variables of all dissociation channels to be expressed as a function of a single channel so that the theoretical branching relationship matches the experimental branching relationship. Using this method, RRKM fitting of a MS/MS breakdown diagram for APCI ionized anthracene determined the E0 and ∆S‡ was 4.69 ± 0.29 eV and -3 ± 17 J K-1; 4.21 ±0.29 eV and -19 ±15 J K-1; and 4.81 ± 0.29 eV and 36 ±22 J K-1 for hydrogen loss, acetylene loss and diacetylene loss respectively. With one exception, these values are within experimental error of the iPEPICO derived energetic values. In chapter 7, MS/MS of ammoniated triacylglycerides at multiple collision energies and computational analysis are used to explain the cause of uneven dissociation rates of the FAs from different positions on the glycerol backbone. The loss of sn-1 and sn-3 FAs are found to have lower activation energies than the loss of the sn-2 position FA, however the loss of the FA from the sn-2 position is more entropically favourable. Theoretical MS/MS breakdown curves were fit to experimental values using RRKM theory to estimate the E0 of dissociation of FAs from the three glycerol positions. The E0 values for cleavage from the sn-1 and sn-3 positions were found to be approximately 1.52 eV, while that for the sn-2 position was highly dependent on the identity of the FA at that position. Computational structures and energy analysis suggest that an important step in the dissociation of [TAG+NH4]+ is the loss of ammonia. In a model system, glyceryl tributyrate, the loss of NH3 produced two distinct [TAG+H]+ product structures sitting 148 kJ and 160 kJ in energy above the ammoniated structure. The [TAG+H]+ structure that leads to the loss of the sn-1(3) is 12 kJ lower than the [TAG+H]+ structure that leads to the loss of the sn-2 FA. From this, the loss of a neutral FA that follows sits only an additional 35–48 kJ above the [TAG+H]+ structures. In Chapter 8, singly deprotonated β-cyclodextrin monomers, [(β-CD-H+]-1, and doubly deprotonated dimers, [(β-CD)2-2H+]-2, are both present following ESI-MS and have the same monoisotopic m/z. Similar to chapter 5, this makes it difficult to generate an MS/MS breakdown diagrams that can be modelled with RRKM theory. IMS was used to mobility separate [(β-CD-H+]-1 and [(β-CD)2-2H+]-2 and was followed by MS/MS of the [(β-CycD)2-2H+]-2 ion. A second problem when generating a MS/MS breakdown diagram of non-covalent complexes that contain identical components is that the fragment ions could have an identical monoisotopic m/z as the reactant ion. MS/MS of [(β-CycD)2-2H+]-2 results in two [(β-CD-H+]-1 fragments. To overcome this, breakdown diagrams were then generated by monitoring the changes in the isotopic profile. The RRKM derived E0 for dissociation of [(β-CycD)2-H+]-1 and [(β-CycD)2-2H+]-2 were 1.85 ± 0.11eV and 1.79 ± 0.09eV, respectively, corresponding to a slight decrease in complex stability due to increased charge-charge repulsion in the dianion.

O estudo da reatividade de íons em fase gasosa é bem diversificado e têm sido extensivamente explorado com técnicas de espectrometria de massas. Essa tese apresenta resultados experimentais e teóricos em três áreas distintas da química de íons em fase gasosa. Os processos iônicos foram experimentalmente estudados em um espectrômetro de massa por transformada de Fourier (FTMS ou FT-ICR), método de alta resolução que possibilita um acompanhamento temporal de reações de íons em -fase gasosa. Em vários momentos são apresentados resultados de cálculos teóricos, necessários para a elucidação do mecanismo das reações observadas e das estruturas de espécies envolvidas. Um dos assuntos estudados se refere à obtenção de dados termoquímicos a partir da dissociação de íons induzida por radiação infravermelha. O método desenvolvido anteriormente no laboratório, que utiliza como fonte de radiação um filamento aquecido, foi comparado com a dissociação induzida por laser de CO2.Os resultados indicam que o primeiro método é capaz de diferenciar íons através das suas energias de dissociação enquanto que o segundo mostrou ser pouco sensível às variações de energias de dissociação para os íons estudados (derivados de acetofenona e alguns alquilbenzenos). Um outro tema abordado é a reação de substituição nucleofílica aromática em fase gasosa. As reações de nucleófilos como F-, OH- e alguns alcóxidos com nitrobenzeno e halobenzenos foram detalhadas. O mecanismo da reação e a atuação de complexos íon-molécula foram caracterizados. Foi possível estabelecer que reações de substituição nucleofílica aromática podem ser muito rápidas em fase gasosa mesmo na ausência de grupos ativadores no anel aromático. Reações SNAr podem ocorrer em fase gasosa em competição com abstração de próton, ou como reação secundária do produto desprotonado através da formação de um complexo íon-molécula de tempo de vida suficiente para sofrer rearranjos. O último assunto apresentado é a reação de íons de caráter eletrofílico, CF3+,CCl3+ e CClF2<SUP+, com acetofenona e derivados. Vários caminhos de reação foram observados experimentalmente, o que proporcionou um amplo estudo para a elucidação das estruturas e dos mecanismos das reações. Os resultados obtidos com substratos deuterados e os resultados de cálculos teóricos indicam que os diferentes produtos de reação observados são devidos a um ataque inicial do eletrófilo no oxigênio carbonílico da acetofenona. / The study of ionic reactivity in the gas-phase has been widely explored with mass spectrometry techniques. This thesis reports experimental and theoretical results in three different areas of gas-phase ion chemistry. The ionic processes were experimentally studied by Fourier transform mass spectrometry (FTMS or FT-ICR), a high resolution method that allows for the observation of ion/molecule reactions. For almost all cases, extensive theoretical calculations were necessary to clarify the mechanisms of the observed reactions and to establish the structures of the ions. The first part of the thesis deals with the possibility of deriving termochemical data from ion dissociation processes induced by infrared radiation. The method previously developed in our laboratory, which uses a heated tungsten wire as the infrared source, was compared with the dissociation induced by a CO2 laser. The results show that the former method can readily differentiate ions by their dissociation energy while the second one proved to be insensitive for the ions studied in this thesis (acetophenones derivatives and some alkylbenzenes). The second part deals with gas-phase nucleophilic aromatic displacement reactions. Reactions of gas-phase nucleophiles such as F-, OH- and some alcoxides with nitrobenzene and halobenzenes were extensively studied. The reaction mechanism and the role of ion-molecule complexes were established. Nucleophilic aromatic displacement can be very fast in the gas-phase even in the absence of activating groups in the ring. Gas-phase Sn Ar reactions may occur in competition with proton abstraction, or may N result from a secundary reaction following proton abstraction through a ion-molecule complex with life time enough to suffer rearrangements. The last part of the thesis deals with the reaction of eletrophilc ions, such as CFSUB>3+ , CCl3+ e CClF2+ , with acetophenone and substituted 3 3 2 acetophenones. Several reaction paths were experimentally observed, wich motivated a thorough investigation of these reactions to establish the structures of the ions and the mechanisms of the reactions. The combination of experimental results obtained with deuterated substrates and theoretical calculations suggest that all the different products observed result from initial attack of the eletrophilic ion on the carbonyl oxygen atom of acetophenone.

O estudo da reatividade de íons em fase gasosa é bem diversificado e têm sido extensivamente explorado com técnicas de espectrometria de massas. Essa tese apresenta resultados experimentais e teóricos em três áreas distintas da química de íons em fase gasosa. Os processos iônicos foram experimentalmente estudados em um espectrômetro de massa por transformada de Fourier (FTMS ou FT-ICR), método de alta resolução que possibilita um acompanhamento temporal de reações de íons em -fase gasosa. Em vários momentos são apresentados resultados de cálculos teóricos, necessários para a elucidação do mecanismo das reações observadas e das estruturas de espécies envolvidas. Um dos assuntos estudados se refere à obtenção de dados termoquímicos a partir da dissociação de íons induzida por radiação infravermelha. O método desenvolvido anteriormente no laboratório, que utiliza como fonte de radiação um filamento aquecido, foi comparado com a dissociação induzida por laser de CO2.Os resultados indicam que o primeiro método é capaz de diferenciar íons através das suas energias de dissociação enquanto que o segundo mostrou ser pouco sensível às variações de energias de dissociação para os íons estudados (derivados de acetofenona e alguns alquilbenzenos). Um outro tema abordado é a reação de substituição nucleofílica aromática em fase gasosa. As reações de nucleófilos como F-, OH- e alguns alcóxidos com nitrobenzeno e halobenzenos foram detalhadas. O mecanismo da reação e a atuação de complexos íon-molécula foram caracterizados. Foi possível estabelecer que reações de substituição nucleofílica aromática podem ser muito rápidas em fase gasosa mesmo na ausência de grupos ativadores no anel aromático. Reações SNAr podem ocorrer em fase gasosa em competição com abstração de próton, ou como reação secundária do produto desprotonado através da formação de um complexo íon-molécula de tempo de vida suficiente para sofrer rearranjos. O último assunto apresentado é a reação de íons de caráter eletrofílico, CF3+,CCl3+ e CClF2<SUP+, com acetofenona e derivados. Vários caminhos de reação foram observados experimentalmente, o que proporcionou um amplo estudo para a elucidação das estruturas e dos mecanismos das reações. Os resultados obtidos com substratos deuterados e os resultados de cálculos teóricos indicam que os diferentes produtos de reação observados são devidos a um ataque inicial do eletrófilo no oxigênio carbonílico da acetofenona. / The study of ionic reactivity in the gas-phase has been widely explored with mass spectrometry techniques. This thesis reports experimental and theoretical results in three different areas of gas-phase ion chemistry. The ionic processes were experimentally studied by Fourier transform mass spectrometry (FTMS or FT-ICR), a high resolution method that allows for the observation of ion/molecule reactions. For almost all cases, extensive theoretical calculations were necessary to clarify the mechanisms of the observed reactions and to establish the structures of the ions. The first part of the thesis deals with the possibility of deriving termochemical data from ion dissociation processes induced by infrared radiation. The method previously developed in our laboratory, which uses a heated tungsten wire as the infrared source, was compared with the dissociation induced by a CO2 laser. The results show that the former method can readily differentiate ions by their dissociation energy while the second one proved to be insensitive for the ions studied in this thesis (acetophenones derivatives and some alkylbenzenes). The second part deals with gas-phase nucleophilic aromatic displacement reactions. Reactions of gas-phase nucleophiles such as F-, OH- and some alcoxides with nitrobenzene and halobenzenes were extensively studied. The reaction mechanism and the role of ion-molecule complexes were established. Nucleophilic aromatic displacement can be very fast in the gas-phase even in the absence of activating groups in the ring. Gas-phase Sn Ar reactions may occur in competition with proton abstraction, or may N result from a secundary reaction following proton abstraction through a ion-molecule complex with life time enough to suffer rearrangements. The last part of the thesis deals with the reaction of eletrophilc ions, such as CFSUB>3+ , CCl3+ e CClF2+ , with acetophenone and substituted 3 3 2 acetophenones. Several reaction paths were experimentally observed, wich motivated a thorough investigation of these reactions to establish the structures of the ions and the mechanisms of the reactions. The combination of experimental results obtained with deuterated substrates and theoretical calculations suggest that all the different products observed result from initial attack of the eletrophilic ion on the carbonyl oxygen atom of acetophenone.