During brewing, beer obtains its bitter flavor from the bitter acids that come from hops. In the journal Angewandte Chemie, scientists now report that they have used X-ray crystallography to determine the absolute configurations of these humulones and isohumulones, as well as several of their derivatives.
Humulones are bacteriostatic bitter substances from hops (Humulus lupulus) and act as natural preservatives. When beer wort is heated together with hops, rearrangement products are formed. These bitter compounds, known as iso-alpha acids or isohumulones, give beer its characteristic flavor. In addition, extracts of hops, such as the more stable tetrahydro-iso-alpha acids used by some brewers instead of hops, have been developed.
When humulones rearrange, a ring containing six carbon atoms converts into a five-membered ring. At the end of this process, two side groups may be arranged in two different ways: They can be on the same side or on opposite sides of the plane of the ring. The former arrangement is called the cis form and the latter is the trans form. But, in the cis-isohumulones, do the two side groups point up or down? And in the trans-isohumulone, which side group points up and which points down? In the six-membered ring of the original humulone there is a carbon atom in the ring with two different side groups attached to it. What is the absolute configuration (the “handedness) at this carbon atom?
A team headed by Werner Kaminsky has successfully answered these questions by means of X-ray crystallographic analysis. This project, undertaken by scientists at KinDex Therapeutics (Seattle) and the University of Washington (Seattle), was complex, because the isomerization process of humulones results in a large number of very similar compounds that had to be separated, purified, and the acids converted into suitable salts.
The absolute configurations of the hops bitter acids found by Kaminsky and his co-workers contradict some of the results previously reported in the literature, which raises the question of how suitable the indirect methods (Horeau method, Cotton effect) used for these studies really are for such investigations. Thanks to their new insights, the researchers have now also been able to determine the mechanism of the rearrangement in detail.
Why is the configuration so interesting? Although excessive beer consumption is not recommended, there are some indications that the hops bitter acids may have positive effects on diabetes, some forms of cancer, and inflammation, as well as weight loss. However, the effects seem to vary substantially depending on the absolute configuration. In addition, the various degrees of bitterness in beer seem to depend on the different forms of the tetrahydro-iso-alpha acids. Now that their stereochemistry is definitively known, these conjectures can be seriously tested, since the binding of iso-alpha acids to proteins requires that their “handedness” be compatible—like nuts and bolts.
Symbiotic bacteria: from hitchhiker to beetle bodyguard
28.04.2017 | Johannes Gutenberg-Universität Mainz
Nose2Brain – Better Therapy for Multiple Sclerosis
28.04.2017 | Fraunhofer-Institut für Grenzflächen- und Bioverfahrenstechnik IGB
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Medical Engineering
28.04.2017 | Earth Sciences
28.04.2017 | Life Sciences