Pyramidalized olefins: a DFT study of bicyclo[2.1.1]-, -[3.2.1]-, and -[3.2.2]alkenes and their fused derivatives. Two rare examples of pi-facially symmetric pyramidal olefins

Density functional theory (B3LYP/6-31G) was used to study a large series of bridged polycyclic alkenes based on the bicyclo[2.1.1], -[3.2.1], and -[3.2.2] nuclei. In those compounds with pi-facial dissymmetry, butterfly bending of the strained olefinic bonds was generally predicted. Surprisingly, large pyramidalizations are calculated for the highly strained but pi-facially symmetric tetracyclo[5.1.1.1.(3,5)0(2,6)]dec-2-ene (28, psi = 19.8 degrees ) and tetracyclo[5.2.2.1.(3,5)0(2,6)]dodec-2,8,10-triene (33, psi = 14.4 degrees ). The preference for propano-directed bending in the bicyclo[3.2.1]octenes is about as strong as that for endo bending in norbornenes.     

Protein secondary structure preferencs

This paper addresses the question to what extent steric properties of sequence neighbors effect the preferences of an amino acid residue to assume the-helical or some other secondary structure conformation. We find that an amino acid has increased tendency to be in-helical conformation when its sequence neighbors are bulky. This result is an outcome of our automated method for finding conformational preferences as functions of physical parameters important for protein folding. The steric environment for a given residue in a protein is defined as an average of water-accessible surface areas of its primary structure neighbors in extended conformation for model tripeptides. For all amino acids, including non-helix formers like glycine and arginine, the preference for the helical structure increases if their primary structure neighbors form a larger steric environment.     

A note on the theorem of Johnson,Palmer and Sell

The well-known theorem of Johnson, Palmer and Sell asserts that the endpoints of the Sacker–Sell spectrum of a given cocycle \(\mathcal {A}\) over a topological dynamical system (M, f) are realized as Lyapunov exponents with respect to some ergodic invariant probability measure for f. The main purpose of this note is to give an alternative proof of this theorem which uses a more recent and independent result of Cao which formulates sufficient conditions for the uniform hyperbolicity of a given cocyle \(\mathcal {A}\) in terms of the nonvanishing of Lyapunov exponents for \(\mathcal {A}\). We also discuss the possibility of obtaining positive results related to the stability of the Sacker–Sell spectra under the perturbations of the cocycle \(\mathcal {A}\).     

Trapping Reactive Intermediates by Mechanochemistry: Elusive Aryl N‐Thiocarbamoylbenzotriazoles as Bench‐Stable Reagents

Monitoring of mechanochemical thiocarbamoylation by in situ Raman spectroscopy revealed the formation of aryl N‐thiocarbamoylbenzotriazoles, reactive intermediates deemed unisolable in solution. The first‐time isolation and structural characterization of these elusive molecules demonstrates the ability of mechanochemistry to access otherwise unobtainable intermediates and offers a new range of masked isothiocyanate reagents.     

Effects of the composition of active carbon electrodes on the impedance performance of the AC/AC supercapacitors

Journal of Solid State Electrochemistry - Considerable diversity in the preparation methodology of active electrode materials for carbon supercapacitors makes direct comparison of the results...     

Laboratory Real‐Time and In Situ Monitoring of Mechanochemical Milling Reactions by Raman Spectroscopy

Mechanistic understanding of mechanochemical reactions is sparse and has been acquired mostly by stepwise ex situ analysis. We describe herein an unprecedented laboratory technique to monitor the course of mechanochemical transformations at the molecular level in situ and in real time by using Raman spectroscopy. The technique, in which translucent milling vessels are used that enable the collection of a Raman scattering signal from the sample as it is being milled, was validated on mechanochemical reactions to form coordination polymers and organic cocrystals. The technique enabled the assessment of the reaction dynamics and course under different reaction conditions as well as, for the first time, direct insight into the behavior of liquid additives during liquid‐assisted grinding.     

Synthesis of Functionalized Polynorbornanes Employing 2,5‐Bis(trifluoromethyl)‐1,3,4‐oxadiazole

Cycloaddition reaction of 2,5‐bis(trifluoromethyl)‐1,3,4‐oxadiazole with strained olefinic bonds of norbornenes was used to synthetize functionalized polynorbornanes. This simple, one step procedure was more effective when reaction was carried out by classical heating, in comparison to microwave‐assisted reactions. Various functional groups were stable in the reaction conditions (ester, imide, phthalimide, piperidyl, and carboxylic acid), whereas anhydride, N‐Boc, or TMS functionalities do not withstand reaction conditions.     

A cascade thermal isomerisation of cyclobutane di-(carbomethoxy) Δ2-1,2,3-triazolines with intramolecular 1,3-dipolar cycloreversion as the key step

Unprecedented thermal isomerisation of the strained Δ²-1,2,3-triazolines led to the formation of products possessing a novel 1,2,7-triaza-[3.3.0]octa-2-ene ring system incorporated in a norbornane framework. Experimental evidence and quantum chemical calculations have been used to support a postulated reaction mechanism involving as the first step, a rare example of intramolecular 1,3-dipolar cycloreversion. Subsequently, several steps involving 1,3-dipolar ring closure, hydrogen shifts and an intramolecular addition are postulated leading to the observed product of this deep-seated isomerisation. The influence of changing substituents on the product outcome of this novel reaction cascade was also studied.     

Datko-Pazy conditions for nonuniform exponential stability

For linear cocycles over both maps and flows, we obtain Datko-Pazy type of conditions under which all Lyapunov exponents of a given cocycle are negative. Furthermore, by combining our results with the results on subadditive ergodic optimisation, we also present new criteria for uniform exponential stability of linear cocycles.