Relationships between charge density response functions, exchange holes and localized orbitals

The charge density response function and the exchange hole are closely related to each other via the fundamental fluctuation-dissipation theorem of physics. A simple approximate model of the static response function is visually compared on several examples in order to demonstrate this relationship. This study is completed by illustrating the well-known isomorphism between the exchange hole and the square of the dominant localized orbital lying in the space region of the reference point of the exchange hole function. The implications of these relationships for the interpretation of common chemical concepts, such as delocalization, are discussed.Comment: 10 two-columns pages, including 3 figure

Selected Physical Characteristics of Medical Students

The purpose of this study was to measure selected anthropometrical characteris-tics, motor abilities and cardiorespiratory functions of medical students. Eighty-seven students were involved in this investigation. The students were categorized into five groups: (1) recreational, doing sport activities irregularly, (2) basketball and (3) handball players, having training at least two times per week, as well as men (4) and women (5) students entering medical school. In all groups the mean body mass index and waist-to-hip ratio were at the upper level of the normal range, while body fat percentage was similar to standards for sedentary subjects. Better motor per-formances were obtained from the basketball and handball players than from the other groups. Static strength for the sample was somewhat above the normal sedentary level. The resting blood pressure and heart rate for most subjects were in the normal. Cardiovascular risk factors were found in six students. Their systolic blood pressure was above 140 mm Hg. There were no sub-jects identified with low blood pressure. The heart rate was elevated for three students from the recreational group, and in the women. Bradycardia did not occur. The vital capacity and the ability to hold one’s breath was at the upper level of the normal range. The present results emphasis the need to improve the students` prevention oriented life style through participation in exercising

Methyl 2,2-dimeth­oxy-5,5-bis­(methyl­sulfan­yl)-3-oxopent-4-enedithio­ate

In the title mol­ecule, C10H16O3S4, a short intra­molecular S⋯O(=C) distance [2.726 (2) Å] indicates the presence of a nonbonding attractive inter­action. In the crystal, mol­ecules are linked into centrosymmetric dimers via weak inter­molecular C—H⋯O and S⋯S [3.405 (3) Å] inter­actions. These dimers are linked by further weak C—H⋯O inter­actions into columns along the a axis

Are proposed early genetic codes capable of encoding viable proteins?

Proteins are elaborate biopolymers balancing between contradicting intrinsic propensities to fold, aggregate or remain disordered. Assessing their primary structural preferences observable without evolutionary optimization has been reinforced by the recent identification of de novo proteins that have emerged from previously non-coding sequences. In this paper we investigate structural preferences of hypothetical proteins translated from random DNA segments using the standard genetic code and three of its proposed evolutionarily predecessor models encoding 10, 6 and 4 amino acids, respectively. Our only main assumption is that the disorder, aggregation and transmembrane helix predictions used are able to reflect the differences in the trends of the protein sets investigated. We found that the 10-residue code encodes proteins that resemble modern proteins in their predicted structural properties. All of the investigated early genetic codes give rise to proteins with enhanced disorder and diminished aggregation propensities. Our results suggest that an ancestral genetic code similar to the proposed 10-residue one is capable of encoding functionally diverse proteins but these might have existed under conditions different from today's common physiological ones. The existence of a protein functional repertoire for the investigated earlier stages which is quite distinct as it is today can be deduced from the presented results

CoNSEnsX: an ensemble view of protein structures and NMR-derived experimental data

<p>Abstract</p> <p>Background</p> <p>In conjunction with the recognition of the functional role of internal dynamics of proteins at various timescales, there is an emerging use of dynamic structural ensembles instead of individual conformers. These ensembles are usually substantially more diverse than conventional NMR ensembles and eliminate the expectation that a single conformer should fulfill all NMR parameters originating from 10¹⁶- 10¹⁷molecules in the sample tube. Thus, the accuracy of dynamic conformational ensembles should be evaluated differently to that of single conformers.</p> <p>Results</p> <p>We constructed the web application CoNSEnsX (Consistency of NMR-derived Structural Ensembles with eXperimental data) allowing fast, simple and convenient assessment of the correspondence of the ensemble as a whole with diverse independent NMR parameters available. We have chosen different ensembles of three proteins, human ubiquitin, a small protease inhibitor and a disordered subunit of cGMP phosphodiesterase 5/6 for detailed evaluation and demonstration of the capabilities of the CoNSEnsX approach.</p> <p>Conclusions</p> <p>Our results present a new conceptual method for the evaluation of dynamic conformational ensembles resulting from NMR structure determination. The designed CoNSEnsX approach gives a complete evaluation of these ensembles and is freely available as a web service at <url>http://consensx.chem.elte.hu</url>.</p