8 research outputs found
Three-electron two-centred bonds and the stabilisation of cationic sulfur radicals
Electronic communication in biological systems is fundamental to understanding protein signalling and electron hopping pathways. Frequently studied examples are cationic radical methionine and its functional derivatives. These systems are understood to be stabilised by a direct ‘three-electron two-centred’ bond. We demonstrate for methionine and a series of cationic radical methionine analogues that long-range multi-centred indirect stabilisation occurs, which cannot be attributed to three-electron two-centred interactions. A revised description of the radical stabilisation process is presented, which includes contributions from all atoms with accessible p-orbitals, independent of the distance to the sulfur radical
Helical frontier orbitals of conjugated linear molecules
Compounds containing allenes, cumulenes and oligoynes (polyalkynes) have attracted attention for both their conformation and reactivity. Whilst the textbook molecular orbital description explains the general electronic and molecular structure of the cumulenes, there are anomalies in both the crystal structures and cycloaddition products involving oligoynes and allenes; the understanding of these molecules is incomplete. Through a computational study we elucidate that the frontier orbitals of the allene and oligoyne families are extended helices. These orbitals are the linear analogue to the Möbius aromatic systems, which also display non-linear π interactions. The axial chirality found in allenes and oligoynes is intimately related to the topology of the frontier orbitals, and has implications for predictions of cycloaddition pathways, structure stability and spectroscopy
Environmental sensing and response genes in cnidaria : the chemical defensome in the sea anemone Nematostella vectensis
Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Cell Biology and Toxicology 24 (2008): 483-502, doi:10.1007/s10565-008-9107-5.The starlet sea anemone Nematostella vectensis has been recently established as a
new model system for the study of the evolution of developmental processes, as cnidaria
occupy a key evolutionary position at the base of the bilateria. Cnidaria play important
roles in estuarine and reef communities, but are exposed to many environmental stressors.
Here I describe the genetic components of a ‘chemical defensome’ in the genome of
N. vectensis, and review cnidarian molecular toxicology. Gene families that defend
against chemical stressors and the transcription factors that regulate these genes have
been termed a ‘chemical defensome,’ and include the cytochromes P450 and other
oxidases, various conjugating enyzymes, the ATP-dependent efflux transporters,
oxidative detoxification proteins, as well as various transcription factors. These genes
account for about 1% (266/27200) of the predicted genes in the sea anemone genome,
similar to the proportion observed in tunicates and humans, but lower than that observed
in sea urchins. While there are comparable numbers of stress-response genes, the stress
sensor genes appear to be reduced in N. vectensis relative to many model protostomes
and deuterostomes. Cnidarian toxicology is understudied, especially given the important
ecological roles of many cnidarian species. New genomic resources should stimulate the
study of chemical stress sensing and response mechanisms in cnidaria, and allow us to
further illuminate the evolution of chemical defense gene networks.WHOI Ocean Life Institute and NIH R01-ES01591
Enantiopure oxazolidinones as chiral acids in the asymmetric protonation of N-Boc pyrrole derived enolates.
The first use of geminally disubstituted oxazolidinones as chiral protonating agents is described: these new acids are able to directly protonate an enolate generated by the ammonia free partial reduction of an electron deficient pyrrole and give up to 68% ee in the pyrroline product
First Observation of Optical Activity in Hyper-Rayleigh Scattering
© 2019 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Chiral nano- or metamaterials and surfaces enable striking photonic properties, such as negative refractive index and superchiral light, driving promising applications in novel optical components, nanorobotics, and enhanced chiral molecular interactions with light. In characterizing chirality, although nonlinear chiroptical techniques are typically much more sensitive than their linear optical counterparts, separating true chirality from anisotropy is a major challenge. Here, we report the first observation of optical activity in second-harmonic hyper-Rayleigh scattering (HRS). We demonstrate the effect in a 3D isotropic suspension of Ag nanohelices in water. The effect is 5 orders of magnitude stronger than linear optical activity and is well pronounced above the multiphoton luminescence background. Because of its sensitivity, isotropic environment, and straightforward experimental geometry, HRS optical activity constitutes a fundamental experimental breakthrough in chiral photonics for media including nanomaterials, metamaterials, and chemical molecules.status: publishe