C − H···π interactions in the metal-porphyrin complexes with chelate ring as the h acceptor

Specific C − H···π interactions with the π-system of porphyrinato chelate ring were found in crystal structures of transition metal complexes from the CSD and statistical analysis of geometrical parameters for intramolecular and intermolecular interactions was done. DFT calculations on a model system show that energy of the interaction is 1.58 kcal/mol and that the strongest interaction occurs when the distance between hydrogen atom and the center of the chelate ring is 2.6 Å. This prediction is in good agreement with the distances for intermolecular interactions found in the crystal structures. In many cases the intramolecular interaction distances are much shorter than 2.6 Å, and these short distances appear to be caused by geometrical constrains. The C − H···π interactions with chelate ring of porphyrinato ligand can be important in biomolecules with porphyrin as they can influence the structure, contribute to the stability and play some role in function of biomolecules.Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 200

Istraživanje uticaja parametara zavarivanja trenjem sa mešanjem na dinamičku izdržljivost zavarenog spoja legure aluminijuma 2024 T351

In order to ensure a quality welded joint, and thus safe operation and high reliability of the welded part or structure achieved by friction stir welding, it is necessary to select the optimal welding parameters. The parameters of friction stir welding significantly affect the structure of the welded joint, and thus the mechanical properties of the welded joint. Investigation of the influence of friction welding parameters was performed on 6 mm thick plates of aluminum alloy AA 2024 T351. The quality of the welded joint is predominantly influenced by the number of tool revolutions speed n and the welding speed v. In this research, it was adopted that the number of tool revolutions be constant n=750 rpm, and the welding speed changed (v=73, 116 and 150 mm / min). Imperfections of the face and roots of the welded specimens were not determined on all welded work pieces by the visual method. Not a single welded sample, examined by radiographic examination, have not been founded welding defects. Experimental investigations of the macro and micro-structure of welded joints achieved by different welding parameters were performed, followed by tests of mechanical properties of welded joints: tensile testing, bending testing, Charpy impact testing, fracture mechanics parameters testing, fatigue crack growth rate and fatigue testing of welded joints. The efficiency of welded joints for welding parameter B-750/116 is almost 100%, that is the tensile strength of the welded joint is approximately equal to the tensile strength of the base metal. Welded joints are not suitable for bending stresses according to the results of bending tests under static and dynamic loading conditions. By Charpy impact testing of welded joints using an instrumented pendulum, fairly low values of impact energy were obtained for all welded joints with generated notch in different positions of the welded joint structure. By examining the parameters of fracture mechanics, for welded joints achieved by different welding parameters, the fracture toughness KIc is the highest on the retreating side of the welded joint, and the lowest in the middle of the joint. The highest fracture toughness was obtained for welding parameters B-750/116. Fatigue tests of welded joints were performed on a servo-hydraulic pulsator and on electrodynamic shaker. The best properties of fatigue strength were shown by welded joints achieved by welding parameters B-750/116. Based on extensive experimental research, in general, the best structural, and thus mechanical properties of butt welded joints of aluminum alloy AA 2024 T351 were achieved by welding parameters B-750/116, that is with the ratio of welding parameters n/v=6.47

'Tipovi' aromatičnosti

The field of aromaticity continues to be controversial. The central theme of this controversy is the definition of aromaticity itself. Today, the proliferation of 'types' of aromaticity goes far beyond the conventional confines and has been extended to include heterosystems, chelate metallacycles in which metalloaromaticity stabilizes coordinated chelate ligands, inorganic molecules, and transition metal oxides. A considerable number of prefixes joined to the term of aromaticity (anti-, non-, homo-, quasi-, pseudo-, etc.) and other 'types' of aromaticity suggested so far, such as classical aromaticity, magnetic aromaticity, Mõbius aromaticity, σ-aromaticity, local-aromaticity, 3D-aromaticity and spherical aromaticity pose additional problems. All these terms related to specific properties of the molecular system illustrate that aromaticity should take into consideration multiple structural, chemical and physical manifestations - it must be a multi-dimensional phenomenon. In the following we will briefly outline the various 'types' of aromaticity for the reader, to get insight into the complexity of the vexing and nebulous concept of aromaticity.U prethodnom broju smo već rekli da je još od Majerovog (Meyer) otkrića tiofena, koji je veoma sličan benzenu po fizičkim i hemijskim osobinama, postalo jasno da je pojam aromatičnosti mnogo širi od hemije benzena i njegovih jedinjenja. Danas postoji mnogo 'tipova' aromatičnosti, a samom pojmu aromatičnosti su dodati razni prefiksi (anti-, non-, homo-, pseudo-, kvazi-, super-, itd.). Svi ovi tipovi aromatičnosti ukazuju da se koncept aromatičnosti sastoji od mnogobrojnih strukturnih, hemijskih i fizičkih manifestacija, tj. da je aromatičnost jedan multidimenzioni fenomen. U ovom članku biće predstavljeni neki od najrasprostranjenijih tipova aromatičnosti

The Compact Formulation of Anthropodynamical Measures in Physiological Anthropology

In this paper, an interdisciplinary combination of several state-of-art methods from biomechanics, modeling and multibody dynamics of the humans is described. The description of the human figure in the motion is a very important part of biomechanical analysis. In such current methods it is necessary to us mass moment of inertia as a part of the fundamental dynamic anthropomeasure when describing this motion. The goal of this work is to use and modify existing techniques and to investigate what have to be analyzed to make them work together. First, some general definitions and descriptions of mass moment of inertia adapted to anthropometric values of our population. Second, there is also a review of some simple models by means of which it is possible to calculate distribution of the body-part masses during the motion. The results are given in the form of equations and tables which present the functions between selected body parts anthropodynamical measures and percentile distribution values of males as well as females of Croatian population

Intramolecular C-H⋯π interactions in metal-porphyrin complexes

Cambridge Structural Database (CSD) was screened in order to find intramolecular C-H⋯π interactions with a chelate ring of coordinated porphyrin. It was found 154 crystal structures with 244 intramolecular C-H⋯π interactions in transition metal complexes with derivatives of porphyrin. Comparison of interacting distances indicates that interactions of hydrogen atoms in positions 2 and 6 of axially coordinated pyridine are more favorable with ruffled than with planar porphyrin

Određena je struktura i otkriven mehanizam selektivnosti kalijumovog kanala

Potassium Channels play a central role in the function of nearly every living cell. In the nervous system they govern the frequency of nerve impulses. The Potassium Channels are highly selective-perhaps as much as 10000:1 for K+ over Na+, despite the minimal structural difference between the two. At the same time, Potassium channels promote tremendous ion flux; in some cases on the order of 108 ions per second pass through a single open channel. In little more than a decade, we have come from almost complete ignorance about the molecular nature of Potassium channels to a high-resolution structure and mechanism for its selectivity

Kratka istorija pojma aromatičnosti

One of the most used concepts in modern chemical literature is concept of aromaticity. However, aromaticity, similar to some other very useful chemical concepts, cannot be quantified and directly measured. Hence, aromaticy is more abstract concept than observable. With the time, concept of aromaticity has evolved. Nowadays, aromaticity is connected with the delocalization of the electrons in rings, and from it emerged magnetic properties of the systems, that are considered as very important

'Tipovi' aromatičnosti

The field of aromaticity continues to be controversial. The central theme of this controversy is the definition of aromaticity itself. Today, the proliferation of 'types' of aromaticity goes far beyond the conventional confines and has been extended to include heterosystems, chelate metallacycles in which metalloaromaticity stabilizes coordinated chelate ligands, inorganic molecules, and transition metal oxides. A considerable number of prefixes joined to the term of aromaticity (anti-, non-, homo-, quasi-, pseudo-, etc.) and other 'types' of aromaticity suggested so far, such as classical aromaticity, magnetic aromaticity, Mõbius aromaticity, σ-aromaticity, local-aromaticity, 3D-aromaticity and spherical aromaticity pose additional problems. All these terms related to specific properties of the molecular system illustrate that aromaticity should take into consideration multiple structural, chemical and physical manifestations - it must be a multi-dimensional phenomenon. In the following we will briefly outline the various 'types' of aromaticity for the reader, to get insight into the complexity of the vexing and nebulous concept of aromaticity.U prethodnom broju smo već rekli da je još od Majerovog (Meyer) otkrića tiofena, koji je veoma sličan benzenu po fizičkim i hemijskim osobinama, postalo jasno da je pojam aromatičnosti mnogo širi od hemije benzena i njegovih jedinjenja. Danas postoji mnogo 'tipova' aromatičnosti, a samom pojmu aromatičnosti su dodati razni prefiksi (anti-, non-, homo-, pseudo-, kvazi-, super-, itd.). Svi ovi tipovi aromatičnosti ukazuju da se koncept aromatičnosti sastoji od mnogobrojnih strukturnih, hemijskih i fizičkih manifestacija, tj. da je aromatičnost jedan multidimenzioni fenomen. U ovom članku biće predstavljeni neki od najrasprostranjenijih tipova aromatičnosti

Supplementary data for the article: Antonijević, I. S.; Janjić, G. V.; Milčić, M. K.; Zarić, S. D. Preferred Geometries and Energies of Sulfur-Sulfur Interactions in Crystal Structures. Crystal Growth and Design 2016, 16 (2), 632–639. https://doi.org/10.1021/acs.cgd.5b01058

Supplementary material for: [https://doi.org/10.1021/acs.cgd.5b01058]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2042]Related to accepted version: [http://cherry.chem.bg.ac.rs/handle/123456789/3596

Kriterijumi za karakterizaciju aromatičnosti

Because of the importance of aromaticity in chemistry, there have been many attempts to rationalize and quantify this property, and to derive a universal quantitative measure of it. However, because of its multiple manifestations, there is not yet any generally accepted single quantitative definition of aromaticity. The evaluation of aromaticity is usually based on the classical aromaticity criteria, which can roughly be divided into six categories: electronic, energetic, structural or geometrical, magnetic, reactivity-based measures and spectroscopic criteria. Which criteria one chooses the best and the relationship between these different criteria (i.e., their orthogonality or nonorthogonality) is still a matter of debate