Crystallographic and quantum-chemical study of interactions between sulfur and disulfide bond

Показано је да сумпор-сумпор интеракције постоје у различитим молекулским системима. Геометрије и енергије сумпор-сумпор интеракција су испитиванеу великој мери применом квантнохемијских прорачуна и статистичкe анализe геометријских параметара добијених из кристалних структура. Недавно је показано да сумпор-сумпор интеракције у кристалним структурама малих молекула преферирају паралелну оријентацију [1]. У овом раду испитиване су геометрије и енергије интеракција између сумпора и дисулфидне везе применом статистичке анализе података добијених претраживањем Кембричке базе структурних података и квантнохемијских прорачуна. Резултати анализе контаката у кристалним структурама показују да сумпорима тежњу ка грађењу бифуркованих интеракција са дисулфидном везом док је тежња ка грађењу линеарних интеракција мања. Квантнохемијски прорачуни су урађени на различитим модел системима. Енергије интеракцијакао и геометрије су у складу са резултатима статистичке анализе кристалографских података. Енергија бифурковане интеракције износи - 1,54 kcal/mol, док је линеарна интеракција слабија, -1,20 kcal/mol израчунато на врло прецизном CCSD(T)/CBS нивоу. Израчунати електростатички потенцијали за интерагујуће молекуле су у сагласности са кристалографским и квантнохемијским подацима. 1 I. S. Antonijević, G. V. Janjić, M. K. Milčić, S. D. Zarić, Cryst. Growth Des., 16 (2016) 632–639.It has been demonstrated that sulfur−sulfur interactions exist in various molecular systems. Geometries and energies of sulfur-sulfur interactions have been extensively studied by quantum chemical calculations and by statistical analysis of geometrical parameters obtained from crystal structures. Recently, it was shown that sulfur-sulfur interactions in crystal structures of small molecules prefer parallel orientations 1. In this work geometries and energies of interactions between sulfur and disulfide bond were investigated using statistical analysis of data obtained by searching the Cambrige Structural Database (CSD) and quantum chemical calculations. Results of analysis of contacts found in the CSD show that sulfur atom in crystal structures have tendency towards the formation of bifurcated interaction with disulfide bond rather than linear interaction. Quantum chemical calculations are performed on different model systems. Calculated interaction energies and geometries are in accordance with the results of statistical analysis of crystalografic data. The estimated energy for bifurcated interaction is -1.54 kcal/mol while linear interaction is weaker, -1.20 kcal/mol calculated on very accurate CCSD(T)/CBS level. The calculated electrostatic potentials for interacting molecules are in agreement with both crystallographic and quantum chemical data. Acknowledgements: This work was supported by the Serbian Ministry of Education, Science and Technological Development [grant number 172065]. I. S. Antonijević would like to thank IUCr for financial support

From Brussels to Belgrade: Challenges in Conducting Research and Constructing Explanations of the Collapse of Yugoslavia

While acknowledging that it is important to examine events within their appropriate context, this article is interested in the capacity of qualitative research methods to assist us so that we can get a more accurate picture of European Community involvement in the Yugoslav federation and the decisions that terminated its existence. More precisely, the article is concerned with the extent to which archival collections and interviews with state as well as nonstate actors can shape our ideas and consequent explanations of the Yugoslav state crisis. In addition, the last section elaborates on a number of challenges one may encounter while being on such a demanding research journey. As suggested by the concluding remarks, new interpretations, apart from managing to satisfy the researcher’s own ambition to complement the existing scholarship, should also serve to encourage fresh questions and answers

Enhanced hydrogen production from thermochemical processes

To alleviate the pressing problem of greenhouse gas emissions, the development and deployment of sustainable energy technologies is necessary. One potentially viable approach for replacing fossil fuels is the development of a H2 economy. Not only can H2 be used to produce heat and electricity, it is also utilised in ammonia synthesis and hydrocracking. H2 is traditionally generated from thermochemical processes such as steam reforming of hydrocarbons and the water-gas-shift (WGS) reaction. However, these processes suffer from low H2 yields owing to their reversible nature. Removing H2 with membranes and/or extracting CO2 with solid sorbents in situ can overcome these issues by shifting the component equilibrium towards enhanced H2 production via Le Chatelier's principle. This can potentially result in reduced energy consumption, smaller reactor sizes and, therefore, lower capital costs. In light of this, a significant amount of work has been conducted over the past few decades to refine these processes through the development of novel materials and complex models. Here, we critically review the most recent developments in these studies, identify possible research gaps, and offer recommendations for future research

Effect of Bacillus licheniformis on seed germination of different weed species

The effects of Bacillus licheniformis on seed germination and seedlings growth of several weed species (Abuthilon theophrasti Medik., Ambrosia artemisiifolia L., Cuscuta campestris Yunck., Datura stramonium L. and Onopordon acanthium L.), have been tested. Seeds of each species were germinated in water solutions containing B. licheniformis, in Petri dishes, while seedlings growth tested after transfer of seeds germinated in water immediately after radicle emergence. Control (seed germination/seedlings growth in water) was also included for each weed species. Germination tests were conducted in an incubator set to 25°C, in the dark. Seeds were considered to be germinated with the emergence of the radicle. Germinated seeds were counted and percentage of germination was calculated after 7 days. Also, seedlings lengths were measured 7 days after seedling transfer to bacterial solution. The obtained results shown that B. licheniformis inhibited A. theophrasti, A. artemisiifolia, C. campestris and D. stramonium seed germination, while effect on O. acanthium was opposite. Contrary to effect on germination, bacterial solution had promotional effect on seedlings growth