Measuring pH locally with terahertz spectroscopy

 

https://www.nanowerk.com/news2/biotech/newsid=56677.php

(Nanowerk News) Nowadays, it is easy to determine an average pH for larger quantities of liquid. It is a challenge, however, to define a local pH value.

Researchers at Ruhr-Universität Bochum have developed a new method to determine a local pH value near a specific site of a biomolecule. A reliable measurement with a pH meter is only been possible in a larger ensemble, or homogeneous bulk.

The new procedure, which is based on terahertz spectroscopy, is described by the team from the Cluster of Excellence Ruhr Explores Solvation, Resolv for short, in the journal Angewandte Chemie International Edition ("Probing local electrostatics of glycine in aqueous solution by THz spectroscopy").

The teams from the Chair of Physical Chemistry II led by Professor Martina Havenith and from the Chair of Theoretical Chemistry led by Professor Dominik Marx cooperated during the work. “There is increased evidence that biological reactions do not depend so much on the global chemical properties of a solution but rather that the local conditions in the immediate vicinity of an enzyme are crucial,” says Martina Havenith. This includes, for example, the pH value or local charge state.

“It is important for us to be able to not only measure these local properties but also to compute predictively – for instance, if we want to optimize solvation conditions for using enzymes as biocatalysts,” says Dominik Marx.

Tests with the amino acid glycine

The scientists worked with a solution of the amino acid glycine. It has two functional groups that can pick up or release protons. The acid can therefore be present in different protonation states, which can be varied by changing the pH of the solution.

The chemists examined glycine solutions using terahertz (THz) spectroscopy. They use transmit radiation in the THz frequency in the solution, which absorbs part of the radiation. The researchers present the absorption pattern in a given frequency range in the form of a spectrum. At the same time, they also simulate the THz spectra of these aqueous solutions for different pH conditions.

Different spectra depending on pH value

The spectra differed significantly depending on the protonation state of glycine. The two groups investigated why this was the case using complex computer simulations, called ab initio molecular dynamics simulations. This method allows researchers to assign certain areas of a spectrum – called bands – to the movements of different bonds in the molecule.

In this way, they showed how the different protonation states were reflected in the spectrum. While deprotonated glycine (high pH) causes almost no absorption in this part of the terahertz spectrum, protonated glycine (low pH) produces clearly visible absorption bands. The spectrum of an intermediate state, the glycine zwitterion (neutral pH), was in between.

The researchers thus obtained a kind of fingerprint of protonation, measured as a function of pH. They showed that the intensity of the spectrum in the range of 0 to 15 terahertz correlates with the pH.

In further experiments, the researchers demonstrated that the method also works for other biomolecules, i.e. the amino acid valine and for small peptides. “In the future, this fundamental finding will open up new opportunities for us to non-invasively determine local states of charge on the surface of biomolecules,” summarises Martina Havenith.

Source: Ruhr-Universität Bochum

How ions gather water molecules around them

This photo shows Gerhard Schwaab, Martina Havenith and Federico Sebastiani (from the left).

Credit: RUB, Marquard

https://www.sciencedaily.com/releases/2018/08/180809112504.htm

Charged particles in aqueous solutions are always surrounded by a shell of water molecules. However, much is still unknown about the nature of this so-called hydration shell. Using terahertz spectroscopy, chemists from Bochum have gained new insights into how an ion affects the water molecules in its environment. Prof Dr Martina Havenith, Dr Gerhard Schwaab and Dr Federico Sebastiani from the Chair of Physical Chemistry II of Ruhr-Universität Bochum (RUB) provide an overview of the results of the experiments in the journal Angewandte Chemie in July 2018.

"The hydration shell of ions is extremely important for understanding fundamental processes such as the transport of ions through membranes or batteries," says Martina Havenith, spokesperson of the Cluster of Excellence Ruhr Explores Solvation. "However, seemingly simple questions, like the size of the hydration shell or the occurrence of ion pair formation, still remain unanswered."

New spectroscopic methods developed

At the Ruhr-Universität Bochum, Martina Havenith's team approaches this question with spectroscopic methods developed in-house. The researchers send short pulses of radiation in the terahertz range, i.e. with a wavelength just under one millimetre, through the sample. The mixture absorbs the radiation to different degrees in different frequency ranges, which is made visible in the form of a spectrum. The spectrum, i.e. the absorption pattern, reveals something about the movement of certain bonds in the investigated molecules, for example about hydrogen bonds in a water network.

The Bochum group developed special techniques using low-frequency terahertz radiation to determine the size of the hydration shell, i.e. the number of water molecules that are affected by an ion. They mathematically break down the recorded absorption pattern into its components and can thus identify the parts in the spectrum that reveal something about individual ions or pairs of ions.

Resolving water molecules in hydration shell

The result: Hydration shells with a size between two and 21 water molecules were determined for more than 37 salts investigated. The number depends for instance on the size of the ion and its valency. Single-charged ions usually affect fewer water molecules than multiple-charged ions. "However, this is not entirely systematic, but also depends on the cation or anion present," explains Martina Havenith.

The researchers use their method to determine the so-called effective number of water molecules, which is the minimum number of water molecules that is affected by an ion, i.e. that cannot move as freely as the unaffected surrounding water. Due to the positive or negative charge of an ion, the water molecules with their partially positively charged hydrogen atoms or their partially negatively charged oxygen atom align themselves with the ion. "The effect of the ion on the water molecules gradually decreases with distance," Havenith explains. "Thus there is not always a clear boundary between affected and unaffected water molecules." The team therefore specifies a minimum number for the size of the hydration shell.

Ion pairs studied

However, the Bochum group dealt not only with individual ions, but also with pairs of cations and anions. The water molecules affect the formation of the ion pair. They can either form a joint hydration shell around the two partners or separate shells around cation and anion. The team is able to estimate how many water molecules these shells each consist of. "In order to know how many water molecules surround an iron chloride, it is not enough to know how many water molecules are affected by a single chloride ion and how many by a single iron ion," explains Havenith. This is not a simple additive process.

"In general, our results clearly show that cooperative effects rather than individual ion properties are decisive," sums up the researcher. It is therefore not enough to know a single ion property in order to predict how a salt will affect the water molecules in its environment. Instead, various parameters, such as the charge density or the combination of the cation-anion will determine whether an ion pair is formed.

Simulation results confirmed

The experimental data are suitable for theoretical simulations of other groups and can serve as input parameters for chemical process engineering.

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Story Source:

Materials provided by Ruhr-University Bochum. Note: Content may be edited for style and length.

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Journal Reference:

1. Martina Havenith-Newen, Gerhard Schwaab, Federico Sebastiani. Ion hydration and ion pairing as probed by THz spectroscopy. Angewandte Chemie International Edition, 2018; DOI: 10.1002/anie.201805261

EU grants €2.5 million for terahertz probe into protein reactions

Team led by Bochum's Martina Havenith develops new method to measure real time heat and energy changes at protein-solvent interface.

Prof Dr Martina Havenith from the Ruhr-Universität Bochum (RUB) http://optics.org/news/7/4/25 The European Research Council(ERC) is to finance a research team led by Prof Dr Martina Havenith from the Ruhr-Universität Bochum (RUB) with €2.5 million over five years to develop an optical procedure to investigate the behavior of proteins in biochemical reactions. In a process called time-resolved terahertz calorimetry, the RUB scientists say they will “tinker with terahertz laser spectroscopy to deduce with nanosecond precision how proteins and solvent exchange energy and rearrange themselves in biological processes”. Professor Havenith, who is Chair of the Department of Physical Chemistry II at RUB and speaker for the cluster of known as European Research Council (“Resolv”), will lead an international team with Prof Dr Irit Sagi from the Weizmann-Institute in Israel and Dr Matthias Heyden from the Max-Planck-Institute for Coal Research in Mülheim at the Ruhr, Germany. ’Underestimated role of water’ Fundamental biological processes such as protein folding, protein-protein interactions and enzymatic reactions take place in watery solutions and depend upon the ability of the reacting molecules to recognize themselves in a solvent. Molecular recognition is mediated through various chemical interactions that can be studied by calorimetry, measuring enthalpy, entropy d other associated energetic parameters. Unfortunately, current calorimetric approaches are all based on heat transfer, hence they deliver results on time scales of 1 to 100 seconds and can analyze the system only at equilibrium, that is when molecules are already bound. However, as Havenith points out, a successful reaction is the result of a dynamic interplay between the partner molecules and the solvent. "Terahertz-Calorimetry promises to investigate these processes, for the first time in real time with a million time better time resolution," the scientists claim. The new technique will use terahertz light sources to excite solvent molecules and biomolecules at the time scales of hydrogen bond dynamics in water as well as large-amplitude motions of proteins and nucleic acids. “If we are able to collect full information on these time-scale dynamics, we can deduce useful values of entropy, enthalpy, and so on associated with molecular recognition processes”, said Havenith. Time-resolved terehaertz calorimetry will also offer, the opportunity to directly access the distinct contributions of the solute entropy changes versus those of the solvent. To this end, the Bochum-based project will combine the expertise gathered in terahertz laser development with microwave technology, biophysics, calorimetry and theoretical modeling. “Interdisciplinary discussions within Resolv were crucial to inspire us the THz calorimetry idea”, added Havenith. Two grants In the latest application round for the ERC's Advanced Grants, two further researchers from the Ruhr-Universität Bochum have been successful: IT security expert Prof Dr Christof Paar also raised such a grant. Via these two projects, the RUB will receive up €5 million in total. The European Union launched the European Research Council in 2007 to fund excellent research in Europe. The ERC Advanced Grants program targets senior researchers with ground-breaking ideas that may be risky to pursue, awarding up to €2.5 million for five years. The 2015 call received almost 2000 project applications from 29 countries, but only about 14% of them were selected after a peer review process. “I received the confirmation message at Zürich airport after an 11-hour flight. I had to read it three times before I believed it. It is such a great chance to test some exciting new ideas”, said Havenith.

Manipulating transistors at terahertz frequencies

http://phys.org/news/2015-11-transistors-terahertz-frequencies.html#jCp

An interdisciplinary team at the Ruhr-Universität Bochum has found a way of accessing the interior of transistors. The researchers have manipulated the electron gas contained within by applying resonators to generate rhythmic oscillation in the terahertz range inside. They shared their findings in the magazine Scientific Reports.


Transistors can be manipulated not only with voltages

Used for switching and amplifying, transistors are fundamental elements of modern electronics. By applying a specific voltage externally to a transistor, an electric current is controlled inside, which, in turn, generates a new voltage. Compared with the externally applied voltage, the new voltage may be amplified, may oscillate or be logically connected to it. In order to interact with their surroundings via electric current and voltage, transistors contain ultra-thin electron layers, so-called 2D electron gases. The RUB team demonstrated that these gases can be controlled not only via DC and radio-frequency voltages.

Electron gas can be oscillated like jelly

"A 2D electron gas is like jelly," explains Prof Dr Andreas Wieck from the Chair for Applied Solid State Physics. "If pressure is electrically applied to the gas from above with a characteristic frequency, thickness and density oscillations are generated." Accordingly, the gas can be manipulated via electric forces, which oscillates much more rapidly than any radio or microwave frequency. As it has a thickness of just about ten nanometres, the oscillations follow the laws of quantum mechanics. This means: all occurring oscillations have a specific frequency, namely in the terahertz range, i.e. in the range of 1012 Hertz. "Pressure to the electron gas must be applied in that rapid change," elaborates Wieck. Andreas Wieck, Dr Shovon Pal, Dr Nathan Jukam and other colleagues from the workgroup Terahertz Spectroscopy and Technology as well as from the Chair of Electronic Materials and Nanoelectronics have found a way to trigger the required oscillations. Thus, a new method of accessing the interior of a transistor has been created.

Resonators generate thickness oscillations

One hundred nanometres above the electron gas, the RUB researchers evaporated an array of identical metallic resonators which can oscillate with the required fixed frequency. The electron gas was embedded in a semiconductor and could be modified via external DC voltage, namely it could be made a bit thicker or thinner. The thickness determines the frequency which makes the gas oscillate optimally. Deploying external voltage, the researchers were able to fine-tune the electron gas to the resonators, i.e. adjust the gas so that the alternating electric pressure of the resonators excites it optimally to oscillate in the terahertz range.

Sensors for chemical and environmental technology

This method could be of interest for sensors in chemical and environmental applications, as the researchers suggest. This is because molecule oscillations typically happen in the terahertz range. With modified transistors, such oscillations can be recorded and sensors can be developed that react to the frequencies of certain gases or liquids.

 Explore further: Technique makes it possible to measure the intrinsic properties of quantum dot transistors

More information: Shovon Pal et al. Ultrawide electrical tuning of light matter interaction in a high electron mobility transistor structure, Scientific Reports (2015). DOI: 10.1038/srep16812

Rapid data transfer thanks to quantum physics

In order to generate oscillating polarisation, the researchers bend the laser with a nail (left). Thus, the active material is no longer symmetrical and becomes birefringent. Generally speaking, the more strongly a laser is bent, the faster the oscillation. Credit: RUBIN, photo: Schirdewahn
http://phys.org/news/2015-02-rapid-quantum-physics.html

RUB engineers have developed a new concept for accelerating data transfer in server farms. To this end, the team at the Chair of Photonics and Terahertz Technology applies a quantum-mechanical variable, i.e. the spin. RUBIN, the science magazine published by the Ruhr-Universität Bochum, reports on how researchers optimise so-called spin lasers for data transfer.

Polarisation oscillation rather than modulation of light intensity

To date, information in server farms is transported directly between individual computers via glass fibre cables. Semiconductor lasers generate light pulses; the information is coded in the changes to light intensity. The faster light intensity is varied, the faster information is transferred. Maximum speed is limited by fundamental physical laws, however. Therefore, the RUB team headed by Prof Dr Martin Hofmann and PD Dr Nils Gerhardt does not modulate light intensity but uses light polarisation instead.

Aligning spins and generating oscillating polarisation

Using a laser, the RUB researchers generate a specific circularly polarised light, in which the polarisation direction oscillates, i.e. alternates between two rotational directions. It is possible to make this oscillation much faster than to change the laser light intensity. The reason: variation of light intensity through electric-current modulation is based on the motion of many electrons that cannot be shifted at any chosen speed. Polarisation oscillation, on the other hand, is based on a quantum-mechanical property of electrons, namely the spin, and the motion of a few electrons is sufficient therefor. By orienting the spins of a group of electrons in the laser into the same direction, the researchers generate oscillating polarisation. They have decoded the underlying effect in detail.

The team from the Chair of Photonics and Terahertz Technology wish to accelerate data transfer in server farms. Credit: RUBIN, photo: Gorczany

 Explore further: Nanoparticles break the symmetry of light

Provided by Ruhr-Universitaet-Bochum

Read more at: http://phys.org/news/2015-02-rapid-quantum-physics.html#jCp