The structure and function of biomolecules are strongly influenced by their hydration shells. Structural fluctuations and molecular excitations of hydrating water molecules cover a broad range in space and time, from individual water molecules to larger pools and from femtosecond to microsecond time scales. Recent progress in theory and molecular dynamics simulations as well as in ultrafast vibrational spectroscopy has led to new and detailed insight into fluctuations of water structure, elementary water motions, electric fields at hydrated biointerfaces, and processes of vibrational relaxation and energy dissipation. Here, we review recent advances in both theory and experiment, focusing on hydrated DNA, proteins, and phospholipids, and compare dynamics in the hydration shells to bulk water.

http://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.6b00765

Water Dynamics in the Hydration Shells of Biomolecules

Molecular Reaction Dynamics: Frontmatter

Active control of chemical reactions on a microscopic (molecular) level, that is, the selective breaking or making of chemical bonds, is an old dream. However, conventional control agents used in chemical synthesis are macroscopic variables such as temperature, pressure or concentration, which gives no direct access to the quantum-mechanical reaction pathway. In quantum control, by contrast, molecular dynamics are guided with specifically designed light fields. Thus it is possible to efficiently and selectively reach user-defined reaction channels. In the last years, experimental techniques were developed by which many breakthroughs in this field were achieved. Femtosecond laser pulses are manipulated in so-called pulse shapers to generate electric field profiles which are specifically adapted to a given quantum system and control objective. The search for optimal fields is guided by an automated learning loop, which employs direct feedback from experimental output. Thereby quantum control over gas-phase as well as liquid-phase femtochemical processes has become possible. In this review, we first discuss the theoretical and experimental background for many of the recent experiments treated in the literature. Examples from our own research are then used to illustrate several fundamental and practical aspects in gas-phase as well as liquid-phase quantum control. Some additional technological applications and developments are also described, such as the automated optimization of the output from commercial femtosecond laser systems, or the control over the polarization state of light on an ultrashort timescale. The increasing number of successful implementations of adaptive learning techniques points at the great versatility of computer-guided optimization methods. The general approach to active control of light–matter interaction has also applications in many other areas of modern physics and related disciplines.

Quantum control of gas-phase and liquid-phase femtochemistry.

Time-resolved infrared (IR) and Raman spectroscopy elucidates molecular structure evolution during ultrafast chemical reactions. Following vibrational marker modes in real time provides direct insight into the structural dynamics, as is evidenced in studies on intramolecular hydrogen transfer, bimolecular proton transfer, electron transfer, hydrogen bonding during solvation dynamics, bond fission in organometallic compounds and heme proteins, cis-trans isomerization in retinal proteins, and transformations in photochromic switch pairs. Femtosecond IR spectroscopy monitors the site-specific interactions in hydrogen bonds. Conversion between excited electronic states can be followed for intramolecular electron transfer by inspection of the fingerprint IR- or Raman-active vibrations in conjunction with quantum chemical calculations. Excess internal vibrational energy, generated either by optical excitation or by internal conversion from the electronic excited state to the ground state, is observable through transient frequency shifts of IR-active vibrations and through nonequilibrium populations as deduced by Raman resonances.

ULTRAFAST CHEMISTRY: Using Time-Resolved Vibrational Spectroscopy for Interrogation of Structural Dynamics

We review the progress in controlling quantum dynamical processes in the condensed phase with femtosecond laser pulses. Due to its high particle density the condensed phase has both high relevance and appeal for chemical synthesis. Thus, in recent years different methods have been developed to manipulate the dynamics of condensed-phase systems by changing one or multiple laser pulse parameters. Single-parameter control is often achieved by variation of the excitation pulse’s wavelength, its linear chirp or its temporal subpulse separation in case of pulse sequences. Multiparameter control schemes are more flexible and provide a much larger parameter space for an optimal solution. This is realized in adaptive femtosecond quantum control, in which the optimal solution is iteratively obtained through the combination of an experimental feedback signal and an automated learning algorithm. Several experiments are presented that illustrate the different control concepts and highlight their broad applicability. These fascinating achievements show the continuous progress on the way towards the control of complex quantum reactions in the condensed phase.

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Femtosecond quantum control of molecular dynamics in the condensed phase

Vibrational and vibronic relaxation and related energy redistribution play an important role in many photoinduced processes of molecules. In the condensed phase, in which collision-induced relaxation is of particular relevance, these phenomena occur on a very rapid time scale between several tens of femtoseconds and 100 ps (1, 2). Spectroscopy with ultrashort laser pulses has been widely applied to elucidate the dynamics and physical mechanisms of intraand intermolecular energy redistribution (3, 4). Indeed, time resolved experiments have provided extensive information not accessible by other experimental techniques. In this article, we present a review on vibrational and vibronic relaxation of large molecules in liquids. Photoinduced redistribution processes of molecules, which consist typically of 20 or more atoms, are considered. We discuss. femtoand picosecond spectroscopy of the intramolecular redistribution and the intermolecular energy transfer from vibrationally hot molecules to their (cold) surrounding. We focus on measurements of vibrational and vibronic lifetimes, as well as on studies of energy redis­ tribution and transport. However, we will not consider dephasing of vibranic or vibrational states, relaxation processes connected to the

Wolfgang Kaiser

Papers

VIBRATIONAL AND VIBRONIC RELAlXATION OF LARGE POL-yrATOMIC MOLECULES IN LIQUIDS

Transient States of an Intramolecular Proton Transfer Cycle Studied by Degenerate Four-Wave Mixing