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The reaction of carbon dioxide with a mixture of a superbase and alcohol affords a superbase alkylcarbonate salt via a process that can be reversed at elevated temperatures. To utilize the unique chemistry of superbases for carbon capture technology, it is essential to facilitate carbonation and decarbonation at desired temperatures in an easily controllable manner. Here, we demonstrate that the thermal stabilities of the alkylcarbonate salts of superbases in organic solutions can be tuned by adjusting the compositions of hydroxylic solvent and polar aprotic solvent mixtures, thereby enabling the best possible performances to be obtained from the various carbon dioxide capture agents based on these materials. The findings provides valuable insights into the design and optimization of organic carbon dioxide absorbents.

A new series of 1-[2-(4-ethoxycarbonylpiperazine-1-yl)acetyl]-2,6-diarylpiperidin-4-ones (3a-3j) has been synthesized by conventional method and were characterized by IR, elemental analysis, mass spectral, 1 H NMR, 13 C NMR, and single crystal X-ray diffraction analysis. The synthesized compounds were evaluated for their antituberculosis activity against Mycobacterium tuberculosis H37Rv (ATCC-27294) and also its antimicrobial activity were examined against five familiar bacterial and fungal strains. Among the synthesized compounds, compounds 3e-3j exhibit higher inhibition potency (16 lg/ml) against M. tuberculosis H37Rv. Furthermore, compounds containing fluoro substituent in the phenyl ring at C-2 and C-6 positions of the piperidin-4-one motif (compounds 3c, 3d, and 3i) exerted better antibacterial and antifungal activity than the other phenyl-substituted compounds.

The (1)H and (13)C NMR spectra of 2,4,6,8-tetraaryl-3,7-diazabicyclo[3.3.1]nonan-9-ones (1-2), oximes (3-8) and O-benzyl oximes (9-12) were recorded. The chemical shifts were unambiguously assigned using 1D and 2D NMR spectral data. The results clearly indicate that the compounds exist in chair-boat conformation with equatorial and axial orientation of the aryl groups in the chair and boat forms, respectively. Since the molecules are flexible and dynamic in solution, the chair and boat forms are mutually interconvertible. In 3-12, because of the effect of oximation/oximination, all the protons in the heterobicyclic systems gave distinct signals except the benzylic protons of the boat form. In all synthesized compounds, the aryl group protons at C-6,8 are shielded by the aryl groups at C-2,4 and therefore appear in the lower frequency region than the aryl groups at C-2,4.

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