2 research outputs found
Do Molecular Gelators Cluster in Hansen Space?
Hansen
solubility parameters (HSP) aid in the a priori prediction
of which low molecular weight molecules have the potential to act
as low molecular weight organogelators (LMOGs) and can immobilize
certain liquids. The hydrogen-bonding HSP parameter individually has
some predictive capacity on whether a molecule will form a gel, solution,
or precipitate in a known liquid; in the case of benzene, gelators
with δ<sub>h</sub> > 5 MPa<sup>0.5</sup> form gels, while
molecules
with δ<sub>h</sub> < 10 MPa<sup>0.5</sup> gel ethanol. Small
molecules, which gel or remain in a solution state tend to cluster
in specific regions of Hansen space. Excellent confinement of solutions
was observed within a solubility sphere of benzene, ethanol, and acetonitrile.
On the basis of the LMOGs selected, both the magnitude and directionality
of the vector in Hansen space are important in predicting the gelation
capacity (i.e., a gelator tends to gel toluene Δδ<sub>p</sub> < −4 MPa<sup>0.5</sup> when combining the role
of Δ2δ<sub>d</sub> and Δδ<sub>p</sub> and
ignoring Δδ<sub>h</sub>)
Potential applications of luminescent molecular rotors in food science and engineering
<p>Fluorescent molecular rotors (MRs) are compounds whose emission is modulated by segmental mobility; photoexcitation generates a locally excited (LE), planar state that can relax either by radiative decay (emission of a photon) or by formation of a twisted intramolecular charge transfer (TICT) state that can relax nonradiatively due to internal rotation. If the local environment around the probe allows for rapid internal rotation in the excited state, fast non-radiative decay can either effectively quench the fluorescence or generate a second, red-shifted emission band. Conversely, any environmental restriction to twisting in the excited state due to free volume, crowding or viscosity, slows rotational relaxation and promotes fluorescence emission from the LE state. The environmental sensitivity of MRs has been exploited extensively in biological applications to sense microviscosity in biofluids, the stability and physical state of biomembranes, and conformational changes in macromolecules. The application of MRs in food research, however, has been only marginally explored. In this review, we summarize the main characteristics of fluorescent MRs, their current applications in biological research and their current and potential applications as sensors of physical properties in food science and engineering.</p