Aged Termites Undertake Self-Destructive Defensive Behaviour

We send our young men to war, ants send their old ladies. This aphorism illustrates long-known phenomenon observed in many social insects: The most risky activities are executed by oldest members of the society, whose possible loss represents the smallest detriment to the colony. We described the defensive behaviour in workers of the termite Neocapritermes taracua, which develop an exceptional two-component suicidal apparatus consisting of copper-containing protein crystals, stored in external pouches, and internal salivary glands. Both the amount of defensive substances and the readiness to sacrifice itself increase with workers' age, along with the decrease of food-collecting ability. During aggressive encounters, worker's body ruptures and the crystals react in the hemolymph droplet with the salivary gland secretion to produce the defensive secretion. The effect of the secretion is clearly twofold: it is toxic to natural competitors, while its stickiness prevents invertebrate enemies from attacking other nestmates. This exceptional defensive strategy nicely illustrates how sociality favours the evolution of extreme adaptations, not without resemblance to kamikaze actions.

Šobotník J., Bourguignon T., Hanus R., Demianová Z., Pytelková J., Mareš M., Foltýnová P., Preisler J., Cvačka J., Krasulová J., Roisin Y.:
Explosive backpacks in old termite workers.
Science 337: 436, 2012.

Unraveling the structure of "wet" electrons helps to understand radiation processes involved in DNA damage during cancer treatment and in nuclear waste storage

The study selected by Science as Editor's Choice (Science 2012, 338, 583) aims at providing an "authoritative answer" to the question concerning structure of a key intermediate in water radiolysis - the solvated electron. This study concludes a five year research project performed in Prague in collaboration with the University of Southern California and ETH Zurich. It has been aimed at computational and experimental description of ultrafast processes following photoionization of water leading to formation of OH radicals and solvated electrons. The former play a crucial role in indirect DNA damage during radiative cancer treatment, while the latter represent a dangerous reactant in nuclear waste storage. If the solvated electrons are not efficiently neutralized, they can react in the acidic environment of aqueous nuclear waste with protons forming a potentially explosive hydrogen gas. The present computational study, performed solely at IOCB, provides a detailed view on the structure and dynamics of the solvated electron. Thanks to a state-of-the-art methodology combining quantum chemistry and molecular dynamics techniques we were able to solve a 40-year old riddle about how an electron "dissolves" in water.

Uhlig F., Maršálek O., Jungwirth P.:
Unraveling the Complex Nature of the Hydrated Electron.
Journal of Physical Chemistry Letters 3: 3071 (2012).

Uhlig F., Maršálek O., VandeVondele J., Jungwirth P.:
Structure, Dynamics, and Reactivity of Hydrated Electrons by Ab Initio Molecular Dynamics.
Accounts of Chemical Research 45: 23-32 (2012).

Novel fluorescent labelling of DNA for sensing of DNA-protein interactions

Two new fluorescent groups for DNA labelling capable of sensing of DNA-protein interactions have been developed. Sequence-specific interactions of diverse proteins (restriction enzymes, transcription factors, DNA methyltransferases etc.) with DNA play a crucial role in many biological processes. We have designed and synthesized two novel types of fluorophores for studying of these interactions. The first type is based on solvatochromic aminophthalimide which was linked to dNTPs via propargyl tether and incorporated to DNA by polymerase. The labelled DNA exerted very low fluorescence in water but, upon binding of proteins (i.e. p53 or single strand binding protein), the fluorescence was enhanced by factor of 2-3 due to changing of polarity of the microenvironment (to less polar) around the fluorophore. The second type was based on fluorophore from green fluorescence protein (GFP) and, again, the fluorophore was attached to dNTPs and incorporated to DNA. The labelled DNA enhanced the fluorescence upon binding of proteins (p53 or SSB) by the factor of 3-5 due to hindered rotation of the fluorophore. This label was also used for time resolved study of kinetics of nucleotide incorporation and primer extension by Vent(exo-) polymerase. Both labels may find practical applications in spectroscopic studies of DNA-modifying enzymes or transcription factor binding.

Riedl J., Ménová P., Pohl R., Orság P., Fojta M., Hocek M.:
GFP-like Fluorophores as DNA Labels for Studying DNA-Protein Interactions
Journal of Organic Chemistry 77: 8287-8293 (2012).

Riedl J., Pohl R., Ernsting N. P., Orság P., Fojta M., Hocek M.:
Labelling of nucleosides and oligonucleotides by solvatochromic 4-aminophthalimide fluorophore for studying DNA–protein interactions
Chemical Science 3: 2797-2806, 2012 (2012).

A General Approach to Optically Pure [5]-, [6]-, and [7]Heterohelicenes

The lack of a general methodology for the effective synthesis of nonracemic helicenes and their analogs has been a major hurdle that has limited a wider exploitation of these helically chiral aromatic systems in enantioselective catalysis, molecular recognition, self-assembly, surface science, chiral materials, and other branches of science. Ideally, a practical asymmetric synthesis should be independent of both the length of the helical backbone and the presence of functional groups. Various concepts of the asymmetric synthesis of helicenes have been explored but no general protocol for obtaining optically pure helicenes or their analogs with a wide structural diversity has yet been reported. We have developed a general methodology for the preparation of optically pure [5]-, [6]-, and [7]heterohelicenes for the first time. It is based on a CoI- or Ni0-catalyzed diastereoselective [2 + 2 + 2] cycloisomerization of centrally chiral triynes to deliver helicenes comprising two 2H-pyran rings. The major advantages of this methodology is that the stereochemical outcome (dr uniformly 100:0) depends neither on the helicene length nor the functional group(s) present. Moreover, the synthesized 2H-pyran [5]heterohelicenes exist as single helices even at higher temperature (in contrast to the parent [5]helicene that racemizes at room temperature) and both enantiomers of but-3-yn-2-ol (a key chiral building block) are commercially available. Finally, the helicity of the products can be easily predicted computationally. The 2H-pyran-modified helicenes might widely be applied to, e.g., enantioselective catalysis.

Žádný J., Jančařík A., Andronova A., Šámal M., Vacek Chocholoušová J., Vacek J., Pohl R., Šaman D., Císařová I., Stará I.G., Starý I.:
A General Approach to Optically Pure [5]-, [6]-, and [7]Heterohelicenes.
Angewandte Chemie International Edition 51: 5857-5861 (2012).