A six-bowl carceplex that entraps seven guest molecules, 5.(DMSO)7, was synthesized and characterized. The dynamics of the host shell was studied in solution in the absence and presence of water. A multiple-molecule template was found to drive the formation of 5.(DMSO)x.G(7-x) (G = DMA, DMF; x = 5-7). Higher selectivity was found for species containing greater numbers of DMSO molecules.
We report a study of the template effect in the formation of tetramethylene-bridged hemicarceplex
7·guest. Two tetrol cavitands were bridged with 1,4-dibromobutane in the presence of suitable template (guest)
molecules in N-formylpiperidine as solvent. Selectivity was observed when competing templates were present
during the reaction: the relative templating abilities (template ratios) of 30 different guest molecules range by
3600-fold, and manifest a significant preference for para-disubstituted benzenes. Twenty-one of the 30
hemicarceplexes used in this templation study are new. The trend in guest selectivity is markedly different
from previous studies in which smaller cavities (e.g., carceplex 2·guest) are formed. In such studies, capsule
3·guest was a good transition state model, whereas this is not the case in the present work.
A free-standing simple enol has been generated inside a carceplex. Rates of ketonization under various conditions were determined; ketonization is extremely slow as compared to the rate in solution. Complexed water is required, and the mechanism proceeds via formation of an enolate followed by protonation at carbon by the same molecule of water that removed the proton from the enol. Acid or base retards ketonization by removing water from the cavity.
A new method, utilizing image analysis on TLC, was developed for the
determination of zygacine,
the neurotoxic steroidal alkaloid in death camas (Zigadenus
venenosus). The quantitative
detection
level of zygacine on TLC was 1 μg. Diurnal changes in zygacine
levels were not evident, nor were
there differences in zygacine levels in death camas growing at high- or
low-elevation habitats. The
image analysis method was also applied to the determination of
vanillylveracevine in Zigadenus
elegans.
Keywords: Zigadenus venenosus; death camas; steroid alkaloids;
zygacine; image analysis
Eleven self-complementary G/\C derivatives bearing hydrophobic moieties were synthesized and characterized. One representative derivative from this family was shown to self-assemble into rosette nanotubes in hexane and form Langmuir-Blodgett films at the air-water interface.
Mono-N-alkylated primary oxalamide derivatives with different sized branched alkyl tail-groups were excellent low molecular weight gelators for a variety of different organic solvents with different polarities and hydrogen-bonding abilities. Solvent-gelator interactions were analyzed using Hansen solubility parameters, while 1H NMR and FTIR spectroscopy were used to probe the driving forces for the supramolecular gelation. The molecular structures of the twin tail-groups did not significantly affect the supramolecular gelation behavior in different solvents. However, for select solvents, the molecular structures of the tail-groups did have a significant effect on gel properties such as the critical gelator concentration, thermal stability, gel stiffness, gel strength, network morphology, and molecular packing. Finally, metabolic activity studies showed that the primary alkyl oxalamide gelators had no effect on the metabolic activity of mouse immune cells, which suggests that the compounds are not cytotoxic and are suitable for use in biomedical applications.
The template effect in the formation of a trimer carceplex using 1-3 molecules as templates is explored. Thirteen different templates were studied and template ratios were measured for templates of like and unlike molecularity. Five transition-state models were studied for their binding abilities to see if these mirror the template ratios. The chemical shifts of the guests and the thermodynamic and kinetic values for templation suggest that binding is key, often tight, and that the guest determining step is formation of the last covalent bond. The molecular dynamics of guests as well as the conformational dynamics of both hosts and guests further addresses nature of the recognition between host and guest. Finally, we were surprised to discover that water can bind reversibly to the trimer carceplexes, which will have ramifications to any inner phase reactions conducted inside the cage.
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