Structure and dynamics of [3.3]paracyclophane as studied by nuclear magnetic resonance and density functional theory calculations.

Strained cyclophanes with small (-CH(2)-)(n) bridges connecting two benzene rings are interesting objects of basic research, mostly because of the nonplanarity of the rings and of interference of π-electrons of the latter. For title [3.3]paracyclophane, in solutions occurring in two interconverting cis and trans conformers, the published nuclear magnetic resonance (NMR) data are incomplete and involve its partially deuterated isotopomers. In this paper, variable-temperature NMR studies of its perprotio isotopomer combined with DFT quantum chemical calculations provide a complete characterization of the solution structure, NMR parameters, and interconversion of the cis and trans isomers of the title compound. Using advanced methods of spectral analysis, total quantitative interpretation of its proton NMR spectra in both the static and dynamic regimes is conducted. In particular, not only the geminal but also all of the vicinal J(HH) values for the bridge protons are determined, and for the first time, complete Arrhenius data for the interconversion process are reported. The experimental proton and carbon chemical shifts and the (n)J(HH), (1)J(CH), and (1)J(CC) coupling constants are satisfactorily reproduced theoretically by the values obtained from the density functional theory calculations.

NMR parameters of two tricyclododecadienes--strained hydrocarbons with close distance between perpendicularly or parallelly arranged double bonds.

Quantum chemical calculations of the hypothetical tricyclo[5.5.0.0(4, 10)]dodeca-1(7),4(10)-diene with a perpendicular arrangement of double bonds and of the known tricyclo[4.2.2.2(2, 5)]dodeca-1,5-diene isomer with the parallel arrangement yield, in agreement with expectations, greater stability of the latter molecule. They reproduce the available experimental results for chemical shifts and coupling constants for the latter molecule. Large calculated values of sigma(Csp2) and those of (1)J(C=C) for both dienes are not due to nonplanar distortions on the double bonds but due to the close distances between them. The calculated NMR parameters of the hypothetical diene could be useful for its future identification as the calculated values of the parameters for 1 are larger than those for 2.

Surface-Related Features Responsible for Cytotoxic Behavior of MXenes Layered Materials Predicted with Machine Learning Approach.

To speed up the implementation of the two-dimensional materials in the development of potential biomedical applications, the toxicological aspects toward human health need to be addressed. Due to time-consuming and expensive analysis, only part of the continuously expanding family of 2D materials can be tested in vitro. The machine learning methods can be used-by extracting new insights from available biological data sets, and provide further guidance for experimental studies. This study identifies the most relevant highly surface-specific features that might be responsible for cytotoxic behavior of 2D materials, especially MXenes. In particular, two factors, namely, the presence of transition metal oxides and lithium atoms on the surface, are identified as cytotoxicity-generating features. The developed machine learning model succeeds in predicting toxicity for other 2D MXenes, previously not tested in vitro, and hence, is able to complement the existing knowledge coming from in vitro studies. Thus, we claim that it might be one of the solutions for reducing the number of toxicological studies needed, and allows for minimizing failures in future biological applications.