Progress in Physical Chemistry - Volume 1

1;Content;6
2;Preface;8
3;Attacking a Small Beast: Ar CO, a Prototype for Intermolecular Forces;10
3.1;1. Introduction;10
3.2;2. Quantum-mechanical description of Ar CO;15
3.2.1;2.1 The Ar CO Hamiltonian;15
3.2.2;2.2 Coriolis coupling;19
3.3;3. Theoretically predicted potential surfaces for Ar CO;20
3.4;4. Experimental results;22
3.4.1;4.1 High resolution vibrational-rotational spectroscopy;22
3.4.2;4.2 Ground state and propeller modes;24
3.4.3;4.3 Intermolecular modes: the intermolecular bending state;25
3.4.4;4.4 Coriolis decoupling;26
3.4.5;4.5 Intermolecular modes: the stretch;28
3.4.6;4.6 Intermolecular modes: combination bands;29
3.4.7;4.7 Coupling of intramolecular and intermolecular modes;30
3.5;5. Comparison between theoretical and experimental data;30
3.6;6. Semi-empirical fit of the potential surface;34
3.7;7. Perspectives;42
3.7.1;Acknowledgement;43
3.7.2;References;43
4;IR Spectroscopy of Microsolvated Aromatic Cluster Ions: Ionization- Induced Switch in Aromatic Molecule Solvent Recognition;46
4.1;1. Introduction;47
4.2;2. Experimental approach;49
4.3;3. Results and discussion;55
4.3.1;3.1 Complexes of acidic aromatic ions with nonpolar ligands;55
4.3.2;3.2 Complexes of bare aromatic hydrocarbon cations with polar ligands;70
4.4;4. Concluding remarks and outlook;82
4.4.1;Acknowledgement;84
4.4.2;References;84
5;Fluorescence Imaging of Reactive Processes;90
5.1;1. Introduction;90
5.2;2. Principles of LIF imaging;91
5.2.1;2.1 Fluorescence quenching;93
5.2.2;2.2 LIF in the gas phase;93
5.2.3;2.3 LIF in solutions;94
5.3;3. Experimental considerations;98
5.3.1;3.1 Set-up for gas phase diagnostics;98
5.3.2;3.2 Microscopic LIF imaging;102
5.4;4. Examples: gas phase chemistry;105
5.4.1;4.1 Reaction rate imaging;105
5.4.2;4.2 Turbulence/ chemistry interactions;107
5.5;5. Examples: biological applications;108
5.5.1;5.1 Protein mobility in live cells;109
5.5.2;5.2 Protein protein interactions;112
5.6;6. Conclusions;115
5.6.1;Acknowledgement;115
5.6.2;References;115
6;Modern High Resolution NMR for the Study of Structure, Dynamics and Interactions of Biological Macromolecules;118
6.1;1. Introduction;118
6.2;2. Protein structure and dynamics by conventional liquid NMR;122
6.2.1;2.1 Homonuclear 2D NMR;122
6.2.2;2.2 Heteronuclear 3D and 4D NMR;123
6.2.3;2.3 Protein structure determination;125
6.2.4;2.4 Protein dynamics;132
6.2.5;2.5 Recent technological advances;133
6.3;3. Deuteration and TROSY push the molecular weight limit of solutionNMR;135
6.4;4. Residual dipolar couplings provide global structure restraints;139
6.5;5. Exploring protein ligand interactions by solution NMR;142
6.5.1;5.1 Structure of protein complexes;142
6.5.2;5.2 Localization of interaction sites;148
6.5.3;5.3 Ligand screening by NMR;151
6.5.4;Acknowledgement;154
6.5.5;References;155
7;Time-Resolved ESCA: a Novel Probe for Chemical Dynamics;166
7.1;1. Introduction;166
7.2;2. Sources for ultrashort XUV pulses;168
7.2.1;2.1 Laser-bases sources;170
7.2.2;2.2 Synchrotron radiation sources;173
7.2.3;2.3 Free-electron lasers;174
7.3;3. Applications of XUV pulses in time-resolved studies;175
7.3.1;3.1 Electron spectroscopy with synchrotron radiation;175
7.3.2;3.2 Electron spectroscopy with high harmonics;176
7.3.3;3.3 Other time-resolved methods;179
7.4;4. Exploring the limits of temporal resolution;180
7.5;5. Summary and outlook;183
7.5.1;References;184
8;Kinetics of Electrochemical Phase Formation in Two- Dimensional Systems;188
8.1;1. Introduction;188
8.2;2. Nucleation and growth kinetics in two dimensional systems;191
8.2.1;2.1 General formalism;193
8.2.2;2.2 Nucleation;193
8.2.3;2.3 Growth kinetics;205
8.2.4;2.4 Avrami theorem;209
8.3;3. Combined adsorption and phase transformation kinetics;210
8.3.1;3.1 Parallel adsorption and phase transformation (mechanism (1));211
8.3.2;3.2 Phase transformation according to a consecutive mechanism;214
8.4;4. Summarizing;221
9;Factors

IR Spectroscopy of Microsolvated Aromatic Cluster Ions: Ionization-Induced Switch in Aromatic Molecule Solvent Recognition (S. 39-40)

By Otto Dopfer
Institut für Physikalische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

Ion Ligand Interaction / IR Spectroscopy / Cluster Ions / Ion Solvation / Aromatic Molecules

IR spectroscopy, mass spectrometry, and quantum chemical calculations are employed to characterize the intermolecular interaction of a variety of aromatic cations (A+) with several types of solvents. For this purpose, isolated ionic complexes of the type A+ Ln , in which A+ is microsolvated by a controlled number (n) of ligands (L), are prepared in a supersonic plasma expansion, and their spectra are obtained by IR photodissociation (IRPD) spectroscopy in a tandem mass spectrometer. Two prototypes of aromatic ion solvent recognition are considered: (i) microsolvation of acidic aromatic cations in a nonpolar hydrophobic solvent and (ii) microsolvation of bare aromatic hydrocarbon cations in a polar hydrophilic solvent.

The analysis of the IRPD spectra of A+ L dimers provides detailed information about the intermolecular interaction between the aromatic ion and the neutral solvent, such as ion ligand binding energies, the competition between different intermolecular binding motifs (H-bonds, p-bonds, charge dipole bonds), and its dependence on chemical properties of both the A+ cation and the solvent type L. IRPD spectra of larger A+ Ln clusters yield detailed insight into the cluster growth process, including the formation of structural isomers, the competition between ion solvent and solvent solvent interactions, and the degree of (non)cooperativity of the intermolecular interactions as a function of solvent type and degree of solvation. The systematic A+ Ln cluster studies are shown to reveal valuable new information about fundamental chemical properties of the bare A+ cation, such as proton affinity, acidity, and reactivity.

Because of the additional attraction arising from the excess charge, the interaction in the A+ Ln cation clusters differs largely from that in the corresponding neutral A Ln clusters with respect to both the interaction strength and the most stable structure, implying in most cases an ionization-induced switch in the preferred aromatic molecule solvent recognition motif. This process causes severe limitations for the spectroscopic characterization of ion ligand complexes using popular photoionization techniques, due to the restrictions imposed by the Franck Condon principle. The present study circumvents these limitations by employing an electron impact cluster ion source for A+ Ln generation, which generates predominantly the most stable isomer of a given cluster ion independent of its geometry.

1. Introduction

Many biophysical and chemical phenomena, including biomolecular recognition, protein folding, biological activity, and chemical reaction mechanisms strongly depend on the microsolvation environment [1 12]. Such solvation effects are particularly important for charged species, because of the larger strength and longer range of ion solvent interactions compared to corresponding neutral neutral interactions [13 24]. Biological molecules are often (locally) charged due to either (de-)protonation or charge separation [1 5]. Moreover, many fundamental chemical reaction mechanisms are ion molecule reactions, and their properties strongly depend on solvation due to large forces between the ionic species and the solvent molecules [6 8].