Mixing-induced anisotropic correlations in molecular crystalline systems

We investigate the structure of mixed thin films composed of pentacene (PEN) and diindenoperylene (DIP) using X-ray reflectivity and grazing incidence X-ray diffraction. For equimolar mixtures we observe vanishing in-plane order coexisting with an excellent out-of-plane order, a yet unreported disordering behavior in binary mixtures of organic semiconductors, which are crystalline in their pure form. One approach to rationalize our findings is to introduce an anisotropic interaction parameter in the framework of a mean field model. By comparing the structural properties with those of other mixed systems, we discuss the effects of sterical compatibility and chemical composition on the mixing behavior, which adds to the general understanding of interactions in molecular mixtures.Comment: 5 pages, 5 figures, accepted by Phys. Rev. Let

Trimethylsilyl-, -germyl- und -stannyl-Hydrazine : eine Substanzklasse mit plastischen Eigenschaften

Derivate des Hydrazins, bei denen alle Wasserstoffatome durch Trimethylelementgruppen substituiert sind (Element = Si, Ge und Sn), geben bei Zimmertemperatur reflexarme Röntgenbeugungsdiagramme, die sich kubisch flächenzentriert indizieren lassen (Z = 4). Diese plastischen Phasen sind über weite Temperaturbereiche (T bis 250 K) stabil, wandeln sich jedoch bei Temperaturerniedrigung, nach Durchlauf einer weiteren Mesophase (primitiv kubisches Gitter, Z = 4), in Tieftemperaturphasen um, in denen die Moleküle eine normale van-der-Waals-Packung einnehmen. Vergleichende Untersuchungen an den verschiedenen Derivaten legen folgende Interpretation nahe: in der plastischen Phase führen die Moleküle (Eigensymmetrie annähernd D2d) Bewegungen um die kristallographischen 4-und 3zähligen Achsen aus, in der Mesophase reduzieren sich diese Bewegungen auf solche um die 3zählige Achse und bei tiefen Temperaturen sind die Moleküle schließlich in Ruhelage. Die Substitution einer Trimethylelementgruppierung durch die Phenylgruppe verhindert chemisch die Ausbildung der plastischen Phase

Beyond Born-Mayer: Improved Models for Short-Range Repulsion in ab Initio Force Fields

Short-range repulsion within intermolecular force fields is conventionally described by either Lennard-Jones (<i>A</i>/<i>r</i>¹²) or Born–Mayer (<i>A</i> exp­(−<i>Br</i>)) forms. Despite their widespread use, these simple functional forms are often unable to describe the interaction energy accurately over a broad range of intermolecular distances, thus creating challenges in the development of ab initio force fields and potentially leading to decreased accuracy and transferability. Herein, we derive a novel short-range functional form based on a simple Slater-like model of overlapping atomic densities and an iterated stockholder atom (ISA) partitioning of the molecular electron density. We demonstrate that this Slater–ISA methodology yields a more accurate, transferable, and robust description of the short-range interactions at minimal additional computational cost compared to standard Lennard-Jones or Born–Mayer approaches. Finally, we show how this methodology can be adapted to yield the standard Born–Mayer functional form while still retaining many of the advantages of the Slater-ISA approach

Fine-tuning of a thermosalient phase transition by solid solutions

Thermosalient crystals are solids that exhibit motion at the macroscale as a consequence of a thermally induced phase transition. They represent an interesting scientific phenomenon and could be useful as actuators for the conversion of thermal energy into motion or mechanical work. The potential utilization of these miniature transducers in real-world devices requires a controllable phase transition (i.e. a predetermined temperature). While it is difficult to control these performances with a single-component molecular crystal, “tunable” properties could be accomplished by solid solutions. To verify this hypothesis, the thermosalient material [Zn(bpy)Br2] (bpy = 2,2′-bipyridine) was selected and its synthesis was performed in the presence of chloride ions. The resulting mixed crystals ([Zn(bpy)Br2xCl2(1−x)]) show that the product undergoes the expected thermosalient phase transition, and the temperature of the onset of the phase transition and the transition enthalpy depend on the Cl/Br ratio

Construction of molecular mechanics energy functions by mathematical transformation of ab initio force fields and structures

A method is presented by which ab initio (or empirical) force fields and structures can be converted to molecular mechanics energy parameters. Using Cartesian coordinates, the effect of van der Waals and other nonquadratic interactions is eliminated from the original spectroscopic force field, and molecular mechanics force constants and reference geometry parameters are derived. The computed parameters yield molecular structure and vibrational frequencies that are identical to the original ones. The transformation produces a complete general valence force field, which in most cases is impractical, and a procedure to reduce the number of force constants is therefore described. Different ways of applying the transformation are outlined.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38283/1/540120312_ftp.pd

ЛЕЧЕНИЕ И ПРОФИЛАКТИКА АДЕНОИДИТОВ БАКТЕРИАЛЬНЫМИ ЛИЗАТАМИ У ЧАСТО БОЛЕЮЩИХ ДЕТЕЙ

We carried out the analysis of researches devoted to the treatment of children with chronic adenoiditis and hypertrophy of adenoid vegetations. We proved that the usage of topic immunomodulator IRS19 incombination with etiotropic treatment allows to sanate lymphoid tissues in nasopharynx effectively and to preserve its continuity as an important organ supplying unspecific and specific protection of the child’s organism.Проведен анализ исследований, посвященных лечению детей с хроническим аденоидитом и гипертрофией аденоидных вегетаций. Показано, что применение топического иммуномодулятора ИРС 19 в комплексе с этиотропным лечением позволяет более эффективно провести санацию лимфоидной ткани носоглотки и сохранить ее целостность как важного органа, обеспечивающего неспецифическую и специфическую защиту детского организма

Unexpected origins of the enhanced pairing affinity of 2′-fluoro-modified RNA

Various chemical modifications are currently being evaluated for improving the efficacy of short interfering RNA (siRNA) duplexes as antisense agents for gene silencing in vivo. Among the 2′-ribose modifications assessed to date, 2′deoxy-2′-fluoro-RNA (2′-F-RNA) has unique properties for RNA interference (RNAi) applications. Thus, 2′-F-modified nucleotides are well tolerated in the guide (antisense) and passenger (sense) siRNA strands and the corresponding duplexes lack immunostimulatory effects, enhance nuclease resistance and display improved efficacy in vitro and in vivo compared with unmodified siRNAs. To identify potential origins of the distinct behaviors of RNA and 2′-F-RNA we carried out thermodynamic and X-ray crystallographic analyses of fully and partially 2′-F-modified RNAs. Surprisingly, we found that the increased pairing affinity of 2′-F-RNA relative to RNA is not, as commonly assumed, the result of a favorable entropic contribution (‘conformational preorganization’), but instead primarily based on enthalpy. Crystal structures at high resolution and osmotic stress demonstrate that the 2′-F-RNA duplex is less hydrated than the RNA duplex. The enthalpy-driven, higher stability of the former hints at the possibility that the 2′-substituent, in addition to its important function in sculpting RNA conformation, plays an underappreciated role in modulating Watson–Crick base pairing strength and potentially π–π stacking interactions

Exercise engagement drives changes in cognition and cardiorespiratory fitness after 8 weeks of aerobic training in sedentary aging adults at risk of cognitive decline

BackgroundWith our aging population, many individuals are at risk of developing age-related cognitive decline. Physical exercise has been demonstrated to enhance cognitive performance in aging adults. This study examined the effects of 8 weeks of aerobic exercise on cognitive performance and cardiorespiratory fitness in sedentary aging adults at risk for cognitive decline.MethodsFifty-two participants (age 62.9 ± 6.8, 76.9% female) engaged in eight weeks of moderate-to high-intensity exercise (19 in-person, 33 remotely). Global cognition was measured by the Repeatable Battery for the Assessment of Neuropsychological Status, the Delis-Kaplan Executive Function System, and the Digit Span subtest of the Wechsler Adult Intelligence Scale (WAIS) Fourth Edition. Cardiorespiratory fitness was measured via heart rate recovery at minute 1 (HRR1) and 2 (HRR2), and exercise engagement (defined as percent of total exercise time spent in the prescribed heart rate zone). We measured pre and post changes using paired t-tests and mixed effects models, and investigated the association between cardiorespiratory and cognitive performance using multiple regression models. Cohen's d were calculated to estimate effect sizes.ResultsOverall, 63.4 % of participants demonstrated high engagement (≥ 70% total exercise time spent in the prescribed heart rate zone). There were significant pre-post improvements in verbal fluency and verbal memory, and a significant decrement in working memory, but these were associated with small effect sizes (Cohen's d &lt;0.5). Concerning cardiorespiratory fitness, there was a pre-to-post significant improvement in HRR1 (p = 0.01, d = 0.30) and HRR2 (p &lt; 0.001, d = 0.50). Multiple regressions revealed significant associations between cardiorespiratory and cognitive performance, but all were associated with small effect sizes (Cohen's d &lt; 0.5). Interestingly, there were significant between-group differences in exercise engagement (all p &lt; 0.001), with remote participants demonstrating greater exercise engagement than in-person participants.ConclusionImprovements in cognition and cardiorespiratory fitness were observed after 8 weeks of moderate to high-intensity exercise in aging adults. These results suggest that committing to a regular exercise regimen, even for a brief two-month period, can promote improvements in both cardiorespiratory fitness and cognitive performance, and that improvements are driven by exercise engagement