Erik Bründermann

Long-Range Influence of Carbohydrates on the Solvation Dynamics of Water-Answers from Terahertz Absorption Measurements and Molecular Modeling Simulations

We present new terahertz (THz) spectroscopic measurements of solvated sugars and compare the effect of two disaccharides (trehalose and lactose) and one monosaccharide (glucose) with respect to the solute-induced changes in the sub-picosecond network dynamics of the hydration water. We found that the solute affects the fast collective network motions of the solvent, even beyond the first solvation layer. For all three carbohydrates, we find an increase of 2-4% in the THz absorption coefficient of the hydration water in comparison to bulk water. Concentration-dependent changes in the THz absorption between 2.1 and 2.8 THz of the solute-water mixture were measured with a precision better than 1% and were used to deduce a dynamical hydration shell, which extends from the surface up to 5.7 +/- 0.4 and 6.5 +/- 0.9 A for the disaccharides lactose and trehalose, respectively, and 3.7 +/- 0.9 A for the glucose. This exceeds the values for the static hydration shell as determined, for example, by scattering, where the long-range structure was found to be not significantly affected by the solute beyond the first hydration shell. When comparing all three carbohydrates, we found that the solute-induced change in the THz absorption depends on the product of molar concentration of the solute and the number of hydrogen bonds between the carbohydrate and water molecules. We can conclude that the long-range influence on the sub-picosecond collective water network motions of the hydration water is directly correlated with the average number of hydrogen bonds between the molecule and adjacent water molecules for carbohydrates. This implies that monosaccharides have a smaller influence on the surrounding water molecules than disaccharides. This could explain the bioprotection mechanism of sugar-water mixtures, which has been found to be more effective for disaccharides than for monosaccharides.

Solvation Dynamics of Model Peptides Probed by Terahertz Spectroscopy. Observation of the Onset of Collective Network Motions

We have studied the solvation of model peptides at low hydration levels by terahertz absorption spectroscopy. We have recorded the concentration-dependent terahertz absorption coefficients of N-acetyl-glycine-amide (NAGA), N-acetyl-glycine-methylamide (NAGMA), N-acetyl-leucine-amide (NALA), N-acetyl-leucine-methylamide (NALMA), and N-acetyl-tryptophan-amide (NATA) in aqueous solution. We find a dramatic decrease in the THz absorption, if the number of water molecules per solute is less than 18-20. This change is taken as a signature for the breakdown of peptide-water network motions, which supports the hypothesis that a minimum number of hydration waters is required to activate these motions. This is well below a monolayer coverage of the model peptides. It is interesting to note that the required hydration level corresponds to the number of water molecules which are required for biological functionality.

Four-wave mixing and direct terahertz emission with two-color semiconductor lasers

We have observed four-wave mixing in a semiconductor laser configured to emit on two wavelengths simultaneously. The four-wave mixing sidebands exist up to 4 THz stemming from a modulation of the carrier plasma at the difference frequency of the two laser modes. In addition, we were able to generate and detect tunable THz radiation at this difference frequency from the laser device itself suggesting a scheme for a tunable THz source.

Communications: Polarity fluctuations of the protic ionic liquid ethylammonium nitrate in the terahertz regime

We have measured the complex dielectric function of the protic ionic liquid ethylammonium nitrate in the frequency range between 0.15 and 1.8 THz with a terahertz time domain spectrometer. The experiments reveal a terahertz mode which can be described as a damped harmonic oscillator with a central frequency of 1.3 THz. The terahertz mode is assigned to an intermolecular vibration, presumably associated with hydrogen-bond dynamics. The data are combined with microwave data to represent the dielectric spectrum from quasistatic conditions up to 1.8 THz.

New p-Ge THz laser spectrometer for the study of solutions: THz absorption spectroscopy of water

We present the development of a high power, tunable far-infrared p-germanium laser spectrometer for the study of dissolved biomolecules in the THz range. As a first application we report on the measurement of the absorption coefficient α for liquid water in the frequency range from 81to96cm−1. Using the p-Ge laser spectrometer we were able to penetrate through layers of up to 100μm thickness. We discuss the advantages and the limitations of this THz spectrometer. We present an analysis of the experimental data based on a χ2 test to provide an objective procedure to minimize the influence of systematic effects, for example of interference due to multiple reflections within the sample chamber. The measured absorption coefficient α lies between (410±6) and (490±6)cm−1 at 81 and 96cm−1, respectively.

High duty cycle and continuous terahertz emission from germanium

We measured laser emission from Be-doped Ge crystals with intercontact distances as small as 0.5 mm. An improved heat sink allowed a twofold increase of the laser duty cycle to 5%. We also report the measurements of THz emission from small Be-doped Ge crystals under continuous excitation with volumes as small as 0.5 mm3.

Narrow linewidth intervalence-band emission from germanium terahertz lasers

We demonstrate narrow linewidth emission from p-Ge terahertz lasers at low magnetic fields where intervalence-band emission dominates. The volume of these laser crystals is 32 mm3, which is one order of magnitude smaller than the lasers for which the emission spectrum has been measured previously. The frequencies emitted are shown to be selected by the optical cavity and do not shift with the magnetic field, as has been observed for larger laser crystals.

DOUBLE ACCEPTOR DOPED GE : A NEW MEDIUM FOR INTER-VALENCE-BAND LASERS

We report on intervalence‐band laser emission from Be‐ and Zn‐doped germanium crystals. The duty cycle of 10−3 at a repetition rate of 1 kHz is one order of magnitude larger than the highest duty cycle reported for p‐Ge lasers doped by group II acceptors. This improvement is due to the much larger hole binding energy of double acceptors Be and Zn which results in a strong reduction of the internal absorption of the generated far‐infrared radiation. Laser action has been achieved with crystal volumes as small as 0.04 cm−3, and a laser pulse length of 25 μs has been reached. Germanium crystals doped with these acceptors may offer an opportunity for achieving the ultimate goal of continuous wave operation.

Miniaturization of p ‐Ge lasers: Progress toward continuous wave operation

We have observed intervalence band laser action in Al‐doped germanium crystals with volumes as small as 0.03 cm3, one order of magnitude smaller than previously studied p‐Ge laser crystals. A duty cycle of 1.5×10−4 was achieved. We show evidence that crystal heating plays a key role in the duration of the emission pulse and have measured a maximum pulse length of 11 μs for a 0.43 cm3, Ga‐doped germanium crystal. Such progress in the understanding and performance of p‐Ge hot hole lasers marks a significant step toward continuous wave operation.

Nanoscale depth resolution in scanning near-field infrared microscopy

We have recorded nanoscale topography and infrared chemical fingerprints of attomole layered lipids consisting of dimyristoylpho-sphatidylcholine on silicon and mica. Lipids deposited on mica built stacks consisting of up to 25 bilayers, each approximately 5 nm thick, spanning a range from 5-125 nm in height. Contrast evaluation as a function of layer thickness provides the near-field depth resolution.