Different types of enzymes such as lipases, several phosphatases, dehydrogenases, oxidases, amylases and others are well suited for the reactions in SC-CO2. The stability and the activity of enzymes exposed to carbon dioxide under high pressure depend on enzyme species, water content in the solution and on the pressure and temperature of the reaction system. The three-dimensional structure of enzymes may be significantly altered under extreme conditions, causing their denaturation and consequent loss of activity. If the conditions are less adverse, the protein structure may be largely retained. Minor structural changes may induce an alternative active protein state with altered enzyme activity, specificity and stability.
Natural
and abundant plant triterpenoids are attractive starting
materials for the synthesis of conformationally rigid and chiral building
blocks for functional soft materials. Here, we report the rational
design of three oleanolic acid–triazole–spermine conjugates,
containing either one or two spermine units in the target molecules,
using the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction.
The resulting amphiphile-like molecules 2 and 3, bearing just one spermine unit in the respective molecules, self-assemble
into highly entangled fibrous networks leading to gelation at a concentration
as low as 0.5% in alcoholic solvents. Using step-strain rheological
measurements, we show rapid self-recovery (up to 96% of the initial
storage modulus) and sol ⇔ gel transition under several cycles.
Interestingly, rheological flow curves reveal the thixotropic behavior
of the gels. To the best of our knowledge, this kind of behavior was
not shown in the literature before, neither for a triterpenoid nor
for its derivatives. Conjugate 4, having a bolaamphiphile-like
structure, was found to be a nongelator. Our results indicate that
the position and number of spermine units alter the gelation properties,
gel strength, and their self-assembly behavior. Preliminary cytotoxicity
studies of the target compounds 2–4 in four human cancer cell lines suggest that the position and number
of spermine units affect the biological activity. Our results also
encourage exploring other triterpenoids and their derivatives as sustainable,
renewable, and biologically active building blocks for multifunctional
soft organic nanomaterials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.