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Author: Pavel Hobza Publisher: Royal Society of Chemistry ISBN: 1847558534 Category : Science Languages : en Pages : 239
Book Description
Co-authored by an experimentalist (Klaus M3ller-Dethlefs ) and theoretician (Pavel Hobza), the aim of this book is to provide a general introduction into the science behind non-covalent interactions and molecular complexes using some important experimental and theoretical methods and approaches.
Author: Pavel Hobza Publisher: Royal Society of Chemistry ISBN: 1847558534 Category : Science Languages : en Pages : 239
Book Description
Co-authored by an experimentalist (Klaus M3ller-Dethlefs ) and theoretician (Pavel Hobza), the aim of this book is to provide a general introduction into the science behind non-covalent interactions and molecular complexes using some important experimental and theoretical methods and approaches.
Author: Terrence Chang Publisher: ISBN: Category : Languages : en Pages : 109
Book Description
The physical properties of molecules in solution, such as basicity and structure, depend on the cooperation and competition of noncovalent intra- and intermolecular interactions. Studying these interactions in the condensed phase is made difficult by the presence of competing influences from counterions and impurities. In the gas phase, however, specific ions, ion complexes and hydration states can be isolated and studied by Fourier transform mass spectrometry coupled with infrared (IR) laser spectroscopy. Using these two techniques, it is possible to isolate specific ions before inducing dissociation via absorption of IR photons. The extent of absorption at a given wavelength correlates to the relative abundance of product ions produced via dissociation, which can be measured using mass spectrometry. The absorption of IR photons only occurs at specific wavelengths depending on which functional groups are present and how their vibrational modes are influenced by interactions such as hydrogen bonding. Structural information is obtained from these spectra by interpreting the presence of certain bands and their frequencies. In addition, information can also be obtained by comparing the spectra from ions of interest to the spectra of reference ions, with known structures, or the simulated spectra of computed geometries. These types of studies provide valuable insight into how noncovalent interactions govern the structure of biomolecules and hydrogen-bonded networks. This dissertation reports experiments utilizing IR spectroscopy to study how water-ion interactions can affect both the structure of an ion solvated by an aqueous nanodrop as well as the hydrogen-bonding network of the nanodrop itself. In addition, the structural effects of ion-peptide interactions, which are relevant to understanding how ions influence biological processes, are also investigated. In order to study the ability of water to stabilize protonation sites on larger molecules, I investigated the influence of sequential hydration on the structure of protonated p-aminobenzoic acid (PABAH+), which has different preferred aqueous solution and gas-phase protonation sites. The preferred protonation site of PABA is the amine in aqueous solution, but the preferred protonation site is the carbonyl O atom of the carboxylic acid in the gas phase. The spectrum of PABAH+*(H2O)1 contains an absorption band at a particular photon energy indicating that protonation occurs at the carboxylic acid, i.e. there is a spectroscopic signature for the O-protonated structure. This absorption band persists for PABAH+*(H2O)2-6, indicating that these ions have a population of O-protonated isomers as well. Spectra for PABAH+*(H2O)6 are also consistent with presence of a second isomer, in which the amine is protonated. These results indicate that PABAH+ exists in the preferred gas-phase structure for PABAH+*(H2O)1-6, but there is a transition to the preferred solution-phase structure when the ion is solvated by six or more water molecules. In isolation, the excess charge associated with protonation at the carbonyl O atom of the carboxylic acid can be resonantly stabilized and delocalized into the phenyl ring and amine. When six or more water molecules are attached, however, a more favorable hydrogen-bonding network can be formed at the protonated amine than at the carboxylic acid. In contrast to PABAH+, protonation for m-aminobenzoic acid (MABA) occurs at the amine site even when solvated by only one water molecule due to orientation of the amine and carboxylic acid group. This orientation prevents the positive charge from being delocalized into the amine. Thus, MABAH+ serves as an ideal model for the solvation of the N- and C-termini of a protonated amino acid, for which the N- and C-termini typically interact with each other. The measured spectra for MABAH+*(H2O)1,2 are consistent with the attachment of water to a H atom of the protonated amine. For MABAH+*(H2O)3, the measured spectrum indicates that the dominant isomer has a hydrogen-bonded water bridge between the amine and carbonyl O atom of the carboxylic acid. This result indicates that the formation of this water bridge is more energetically favorable than the formation of a third ionic hydrogen bond to the amine group. The spectra for MABAH+*(H2O)n also indicate that water molecules attach to the carboxylic acid H atom, i.e. the ion is fully hydrogen-bonded when there are ≥6 water molecules attached. Ion spectroscopy can also be used to study how ion-water interactions influence hydration structures. Certain positive ions are known to induce cage-like clathrate structures when hydrated by 20 water molecules. The hydration of NH4+ as well as selected, protonated primary, secondary and tertiary amines solvated by 19 - 21 water molecules was investigated in order to elucidate details about how amines can stabilize clathrate structures. The spectra of NH4+ as well as monomethyl-, n-heptyl-, and tert-butylammonium+ with 20 water molecules attached are consistent with the nearly exclusive presence of clathrate structures, whereas nonclathrate structures are present for the more highly substituted amines. By comparison, nonclathrate structures are observed for all ions when 19 or 21 water molecules are attached. Spectroscopic evidence for clathrate structures for NH4+*(H2O)20 has been previously reported, but the location of the ion, whether at the surface or the interior, was difficult to determine based on the IR spectrum of this ion alone. Thus, the spectra of NH4+, monomethyl- and n-heptylammonium+ solvated by 20 water molecules were compared to those for Rb+ and tert-butylammonium+, which serve as references for clathrate structures with the ion located in the interior or at the surface, respectively. These comparisons indicate that NH4+ goes to the interior, whereas protonated primary amines are located at the surface, irrespective of the size of the alkyl group. In addition to ion-water interactions, ion-biomolecule interactions can also be probed by ion spectroscopy. Although there are several studies that have used ion spectroscopy to investigate cations coordinated to amino acids and peptides, there are fewer studies focused on these same biomolecules complexed with anion adducts. The ions Gly3*X-, Ala3*X- and Leu3*X- (X = Cl, Br and I) were studied in order to investigate how the size of anion adducts and alkyl side chains influence the coordination of halide anions to aliphatic peptides. The spectra of Gly3*Cl-, Ala3*Cl- and Leu3*Cl- suggest that all three complexes adopt similar structures, where Cl- coordinates to the peptides by accepting three or four hydrogen bonds from the amides as well as the N- and C-termini. These results indicate that the size of the alkyl chain does not have a significant influence on the coordination geometry of these complexes. These structures are "inverted" in comparison to previously reported structures for Gly3*Na+ and Ala3*Na+, where the Na+ coordinates to lone pair electrons of the N atom of the N-terminus, or the carbonyl O atoms of the amides and C-terminus. The spectra of Gly3*X-, Ala3*X- and Leu3*X- each appear similar to each other within each peptide, indicating that the size of the anion does not significantly affect the coordination geometry.
Author: James Stephen Prell Publisher: ISBN: Category : Languages : en Pages : 474
Book Description
Experiments investigating the role of non-covalent interactions in the structure, properties, and reactivity of gas-phase ion-biomolecule, ion-water, and water-biomolecule complexes in the gas phase are presented and discussed in this dissertation. Ions generated using electrospray ionization and trapped using Fourier transform ion cyclotron resonance mass spectrometers at the University of California, Berkeley, and the FOM Institute for Plasma Physics Rijnhuizen in Nieuwegein, The Netherlands, are probed using infrared photodissociation/infrared multiple photon dissociation (IRPD/IRMPD) spectroscopy and kinetics and electron capture dissociation. IRMPD spectra of alkali metal cationized dipeptides, protonated dipeptides, and trivalent lanthanide cationized polypeptides reported here reveal the role of ion size, formal charge site geometry, peptide sequence, gas-phase basicity, and competition between carbonyl groups and aromatic groups in the structures of these complexes. IRPD spectra of hydrated hydrophobic ions in the gas phase reveal a hydrogen bonding motif that contrasts strongly with those typically seen for more strongly hydrated ions. The role of ion charge state and size in the structures of gas-phase "nanodrops" is discussed based on their IRPD spectra and a computationally inexpensive point-charge model, as well as the dependence of these spectra on the electric field of the ion. These results show that ions can intrinsically affect the hydrogen bond structure of the water network out to three or more solvation shells, in contrast to many recent reports that only the first solvation shell is affected for ions in bulk solution. A new method using IRPD/IRMPD kinetics is demonstrated for directly measuring relative populations of spectroscopically distinguishable ion isomers, and a method for extending IRPD spectroscopic techniques to extensively hydrated ions that dissociate quickly is illustrated. This photodissociation kinetic method is demonstrated for several ion-biomolecule complexes and hydrated biomolecular ions, and relative Gibbs free energies, entropies, and enthalpies for nearly isoenergetic thermal ion populations are obtained with unprecedented precision. Ion nanocalorimetry is used to measure appearance energies for products of the exothermic reaction of a hydrated, doubly protonated dipeptide in the gas phase with a low-energy free electron, and nearly complete quenching of peptide fragmentation is achieved with a very small number of water molecules in the precursor ion complex.
Author: Steve Scheiner Publisher: Springer ISBN: 3319141635 Category : Science Languages : en Pages : 528
Book Description
Computational methods, and in particular quantum chemistry, have taken the lead in our growing understanding of noncovalent forces, as well as in their categorization. This volume describes the current state of the art in terms of what we now know, and the current questions requiring answers in the future. Topics range from very strong (ionic) to very weak (CH--π) interactions. In the intermediate regime, forces to be considered are H-bonds, particularly CH--O and OH--metal, halogen, chalcogen, pnicogen and tetrel bonds, aromatic stacking, dihydrogen bonds, and those involving radicals. Applications include drug development and predictions of crystal structure.
Author: Christoph A. Schalley Publisher: John Wiley & Sons ISBN: 0470131152 Category : Science Languages : en Pages : 593
Book Description
Details the many benefits of applying mass spectrometry to supramolecular chemistry Except as a method for the most basic measurements, mass spectrometry (MS) has long been considered incompatible with supramolecular chemistry. Yet, with today's methods, the disconnect between these two fields is not warranted. Mass Spectrometry and Gas-Phase Chemistry of Non-Covalent Complexes provides a convincing look at how modern MS techniques offer supramolecular chemists a powerful investigatory toolset. Bringing the two fields together in an interdisciplinary manner, this reference details the many different topics associated with the study of non-covalent complexes in the gas phase. The text begins with brief introductions to supramolecular chemistry and such relevant mass spectrometric methods as ionization techniques, analyzers, and tandem MS experiments. The coverage continues with: How the analyte's transition into the gas phase changes covalent bonding How limitations and pitfalls in analytical methods may produce data misinterpretations Artificial supramolecular aggregates and their examination Biomolecules, their complexes, and their examination After the general remarks making up the first section of the book, the following sections describe specific experimental procedures and are illustrated with numerous examples and short tutorials. Detailed citations end each chapter. Mass spectrometrists, supramolecular chemists, students in these fields, and interested readers from other disciplines involving the study of non-covalent bonds will all value Mass Spectrometry and Gas-Phase Chemistry of Non-Covalent Complexes as an innovative and practical resource.
Author: Pavel Hobza
Author: Pavel Hobza
Author: Jeremy Thomas O'Brien
Author: Charlotte Ann Corbett
Author: Terrence Chang
Author: Orlando Manuel Cabarcos
Author: James Stephen Prell
Author: Steve Scheiner
Author: Christoph A. Schalley
Author: Elise Ann Dennis
Author: Xin Cong