On mechanical waves and Doppler shifts from moving boundaries

We investigate the propagation of infinitesimal harmonic mechanical waves emitted from a boundary with variable velocity and arriving at a stationary observer. In the classical Doppler effect, X_s(t)=vt is the location of the source with constant velocity v. In the present work, however, we consider a source co‐located with a moving boundary x=X_s(t), where X_s(t) can have an arbitrary functional form. For ‘slowly moving’ boundaries (i.e., ones for which the timescale set by the mechanical motion is large in comparison to the inverse of the frequency of the emitted wave), we present a multiple‐scale asymptotic analysis of the moving boundary problem for the linear wave equation. We obtain a closed‐form leading‐order (with respect to the latter small parameter) solution and show that the variable velocity of the boundary results not only in frequency modulation but also in amplitude modulation of the received signal. Consequently, our results extend the applicability of two basic tenets of the theory of a moving source on a stationary domain, specifically that (i) for non‐uniform boundary motion can be inserted in place of the constant velocity v in the classical Doppler formula and (ii) that the non‐uniform boundary motion introduces variability in the amplitude of the wave. The specific examples of decelerating and oscillatory boundary motion are worked out and illustrated. Copyright © 2017 John Wiley & Sons, Ltd.     

RNA Cleavage Catalyzed by Amphoteric Bis(acyl)guanidinium Derivatives

Described herein are two series (twelve compounds each) of very closely related guanidinium‐based receptors and their ability to catalyze hydrolytic cleavage of a unique RNA substrate – oligo‐dT flanked t rans‐ A ctivation R esponsive region of the HIV‐1 mRNA, TAR RNA. The significant difference in activities of otherwise very similar compounds is discussed, and direct and indirect evidences supporting our interpretation are presented. The results indicate that improvements in catalytic efficiency could be achieved with little modification of the structure of a relatively weak catalyst, and that a crucial feature could be a finely calibrated interplay between anion‐binding and proton‐donating abilities.     

Copolymerization of benzoquinone with norbornene

For the first time, the conjugated dicarbonyl compound benzoquinone has been copolymerized with the strained cyclo-olefin norbornene using catalytic amounts of the Friedel-Crafts metathesis catalytic system WOCl₄+AlCl₃. All analyses reveal that the products consist of conjugated blocks originating from benzoquinone connected with spacers originating from norbornene. The products are soluble in benzene, toluene, chlorobenzene, etc. but possess properties of the conjugated polymers. They have been synthesized via a very simple one-pot procedure.     

Nickelmodifiedlarge poremesoporoussilicas ascatalysts for methanol decomposition

Summary Ni-modifiedlarge poremesoporous silicasarecharacterized by XRD, N₂physisorption and TPR with H₂. Theeffectof the supportpore structure on their catalytic behaviorin methanol decomposition to H₂, CO and CH₄is studied.     

Bottom-up driven involuntary attention modulates auditory signal in noise processing

Background  

Auditory evoked responses can be modulated by both the sequencing and the signal-to-noise ratio of auditory stimuli. Constant sequencing as well as intense masking sounds basically lead to N1m response amplitude reduction. However, the interaction between these two factors has not been investigated so far. Here, we presented subjects tone stimuli of different frequencies, which were either concatenated in blocks of constant frequency or in blocks of randomly changing frequencies. The tones were presented either in silence or together with broad-band noises of varying levels.     

Kinetics and intimate mechanism of protein crystal nucleation

Experimental and theoretical investigations on protein crystal nucleation are reviewed. Various experimental applications of the classical principle, which requires separation of the nucleation and growth stages of the crystallization process, are described. Temperature control is used most frequently, hypergravity and concentration changes being auxiliary techniques. Nucleation time-lags are measured by imposing temperature evoked supersaturation gradients. Application perspectives are revealed. Nucleation rates are measured according to the classical principle mentioned above, and energy barriers for crystal nucleation and numbers of molecules constituting the critical nuclei are calculated. Surprisingly, although requiring unusually high supersaturation, protein crystal nucleation occurs much more slowly than that with small molecule substances. On this basis novel notions are suggested for the elementary mechanism of protein crystal bond formation. Due to the selection of the crystalline bonding patches a successful collision between protein molecules, resulting in the formation of a crystalline connection, requires not only sufficiently close approach of the species, but also their proper spatial orientation. Imposing a rigid steric constraint, the latter requirement postpones the crystal nucleus formation. Besides, it was shown that cluster coalescence is not a factor, hampering the protein crystal nucleation. The comparison of the model predictions with experimental results proved that nucleation kinetics is governed by kinetic (not by energetic) factors.     

Conformational Dynamics Underlies Different Functions of Human KDM7 Histone Demethylases

The human KDM7 subfamily histone H3 Nϵ-methyl lysine demethylases PHF8 (KDM7B) and KIAA1718 (KDM7A) have different substrate selectivities and are linked to genetic diseases and cancer. We describe experimentally based computational studies revealing that flexibility of the region linking the PHD finger and JmjC domains in PHF8 and KIAA1718 regulates interdomain interactions, the nature of correlated motions, and ultimately H3 binding and demethylation site selectivity. F279S an X-linked mental retardation mutation in PHF8 is involved in correlated motions with the iron ligands and second sphere residues. The calculations reveal key roles of a flexible protein environment in productive formation of enzyme-substrate complexes and suggest targeting the flexible KDM7 linker region is of interest from a medicinal chemistry perspective.     

Heterocyclizations of hydroxyketones with two‐coordinated (trimethylsilylamino)phosphines, (Me3Si)2N?PE?SiMe3

The reaction of two‐coordinated (trimethylsilylamino)phosphines (Me₃Si)₂N PE SiMe₃ 1 (E = N) and 2 (E = CH) with hydroxycarbonyl compounds proceeded with four‐ or five‐member heterocyclization to yield derivatives of oxaphosphetane, oxaphospholanes, and oxaphospholes. The reaction rate depends on the structure of hydroxyketones as well as on the type of the two‐coordinated phosphorus compound in accordance with the polarity of the P=N and P=C bonds. Thus, reaction was completed in 30 min in the case of the ortho carbonyl phenoxy derivatives with the phosphine 1 , but required 2 h in the case of the alkyl hydroxy carbonyls. All reactions with the phosphine 2 took about 24 h. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:413–417, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20033     

Novel reactive thermosensitive polyethers – control of transition point

A new class of thermosensitive polymers based on polyethers is discussed. Using living anionic polymerisation techniques a series of homo- and block copolymers of 2,3-epoxypropanol-1 (the glycidol), ethoxy ethyl glycidol ether, its hydrophobic derivative, and ethylene oxide of different molar masses and topology (linear and comb-like) was obtained. By simple chemical modification of hydroxyl groups in polyglycidol segments hydrophobic elements were introduced into polymer chains, which allowed to control the transition point related to the lower critical solution temperature between 0 to 100°C. The relation between the transition temperature and the structure of obtained polymers is discussed.     

Rooibos Flavonoids,Aspalathin, Isoorientin,and Orientin Ameliorate Antimycin A-Induced Mitochondrial Dysfunction by Improving Mitochondrial Bioenergetics in Cultured Skeletal Muscle Cells

The current study investigated the physiological effects of flavonoids found in daily consumed rooibos tea, aspalathin, isoorientin, and orientin on improving processes involved in mitochondrial function in C2C12 myotubes. To achieve this, C2C12 myotubes were exposed to a mitochondrial channel blocker, antimycin A (6.25 µM), for 12 h to induce mitochondrial dysfunction. Thereafter, cells were treated with aspalathin, isoorientin, and orientin (10 µM) for 4 h, while metformin (1 µM) and insulin (1 µM) were used as comparators. Relevant bioassays and real-time PCR were conducted to assess the impact of treatment compounds on some markers of mitochondrial function. Our results showed that antimycin A induced alterations in the mitochondrial respiration process and mRNA levels of genes involved in energy production. In fact, aspalathin, isoorientin, and orientin reversed such effects leading to the reduced production of intracellular reactive oxygen species. These flavonoids further enhanced the expression of genes involved in mitochondrial function, such as Ucp 2, Complex 1/3, Sirt 1, Nrf 1, and Tfam. Overall, the current study showed that dietary flavonoids, aspalathin, isoorientin, and orientin, have the potential to be as effective as established pharmacological drugs such as metformin and insulin in protecting against mitochondrial dysfunction in a preclinical setting; however, such information should be confirmed in well-established in vivo disease models.