Cyclic amines can be encapsulated in a water-soluble self-assembled supramolecular host upon protonation. The hydrogen-bonding ability of the cyclic amines, as well as the reduced degrees of rotational freedom, allows for the formation of proton-bound homodimers inside of the assembly that are otherwise not observable in aqueous solution. The generality of homodimer formation was explored with small N-alkyl aziridines, azetidines, pyrrolidines, and piperidines. Proton-bound homodimer formation is observed for N-alkylaziridines (R = methyl, isopropyl, tert-butyl), N-alkylazetidines (R = isopropyl, tert-butyl), and N-methylpyrrolidine. At high concentration, formation of a proton-bound homotrimer is observed in the case of N-methylaziridine. The homodimers stay intact inside the assembly over a large concentration range, thereby suggesting cooperative encapsulation. Both G3(MP2)B3 and G3B3 calculations of the proton-bound homodimers were used to investigate the enthalpy of the hydrogen bond in the proton-bound homodimers and suggest that the enthalpic gain upon formation of the proton-bound homodimers may drive guest encapsulation.

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Encapsulation and characterization of proton-bound amine homodimers in a water-soluble, self-assembled supramolecular host

Publisher Summary This chapter deals with conformational equilibria: (1) in piperidines, (2) in piperidine derivatives, in which ring methylenes are replaced by nitrogen, oxygen, and sulfur atoms, and (3) in systems incorporating these rings in fused ring structures, in which the additional rings are also six-membered. Fused-ring structures with other sizes of rings are generally not included, except for tropane. The chapter illustrates the principal methods available for the investigation of heterocyclic conformational analysis. Then follows a treatment of individual ring systems, in which the discussion centers on the conformational preferences of substituents on tertiary nitrogen and on ring carbon atoms, the energetics of nitrogen inversion, and phenomena arising from the presence of two or more heteroatoms in one ring. Emphasis is placed on simply the substituted free bases. The chapter deals with ring reversal equilibria and kinetics in the conformational analysis of six-membered rings. The problems of conformational equilibria in N-alkylpiperidinium salts and N-quaternization reactions, and the relationships of these to conformational equilibria in the free bases are not covered since this area is a large one requiring separate treatment.

Conformational Equibria in Nitrogen-Containing Saturated Six-Membered Rings

A number of new ionic titanocene compounds have been isolated and characterised, which exhibit excellent cytotoxicity against different human tumour cell lines including a defined cisplatin resistant cell line A range of biological assays have been carried out to determine levels of cytotoxicity and levels of DNA interstrand crosslinking

Functionalised cyclopentadienyl titanium compounds as potential anticancer drugs.

https://pubs.acs.org/doi/pdf/10.1021/acs.orglett.5b02195

Lewis Acid Catalyzed Annulation of Nitrones with Oxiranes, Aziridines, and Thiiranes

2.19 – 1,2,4-Triazines and their Benzo Derivatives

The synthesis and conformational analysis of tetrahydro-1,2,4-oxadiazines

Conformational equilibria and barriers to ring and nitrogen inversion are determined by 1H and 13C n.m.r. for 13 1-oxa-3-azacyclohexanes and correlated with recent work on the conformational analysis of saturated heterocycles.

The conformational analysis of saturated heterocycles. Part 100. 1-Oxa-3-azacyclohexanes

Conformational equilibria and barriers to ring and nitrogen inversion, determined by 1H and 13C n.m.r. for the title compounds, are correlated with other recent work on ring-1,3-diheteroatom-substituted cyclohexanes.

The conformational analysis of saturated heterocycles. Part 101. 1,3-Diazacyclohexanes and 1-thia-3-azacyclohexanes

Proton and 13C n.m.r. spectra indicate that 4,5-dimethyl- and 4,5-diethyl-1,2-dioxa-4,5-diazacyclohexanes exist very predominantly in the equilibrating ax–eq and/or ax–ax conformations: for the di-isopropyl analogue this co-exists with ca. 20% of the eq–eq conformer.

The conformational analysis of saturated heterocycles. Part 92. Conformational equilibria of 1,2-dioxa-4,5-diazacyclohexanes

2-Oxa-4a,8a-diazadecalin (2) shows bands of the predominant αα and a minor Iµα form. 1,2,4-Trimethyl-1,2,4-triaza-(3) and 3,4-dimethyl-1-thia-3,4-diaza-cyclohexane (4) probably exist in the αIµα and Iµα conformations, respectively. These conclusions are in good agreement with those from solution measurements, as are those for four 1,2,4,5-tetra-azacyclohexanes.

Conformational analysis of saturated heterocycles. Part 94. Applications of photoelectron spectroscopy to molecular properties. Part 3. Photoelectron spectroscopic studies of some 1-oxa-3,4-diaza-, 1-thia-3,4-diaza-, 1,2,4-triaza-, and 1,2,4,5-tetra-aza-cyclohexanes

Fernando M. S. Brito-Palma

Papers

The synthesis and conformational analysis of tetrahydro-1,2,4-oxadiazines

The conformational analysis of saturated heterocycles. Part 100. 1-Oxa-3-azacyclohexanes

The conformational analysis of saturated heterocycles. Part 101. 1,3-Diazacyclohexanes and 1-thia-3-azacyclohexanes

The conformational analysis of saturated heterocycles. Part 92. Conformational equilibria of 1,2-dioxa-4,5-diazacyclohexanes

Conformational analysis of saturated heterocycles. Part 94. Applications of photoelectron spectroscopy to molecular properties. Part 3. Photoelectron spectroscopic studies of some 1-oxa-3,4-diaza-, 1-thia-3,4-diaza-, 1,2,4-triaza-, and 1,2,4,5-tetra-aza-cyclohexanes