Publications

Newly developed porous polymer monolithic capillary columns modified with gold nanoparticles coated with exchangeable functionalities allow easy switching of separation modes by a simple ligand exchange process. These columns are prepared from a poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith through reaction of its epoxide moieties with cysteamine to afford a monolith rich in surface thiol groups. Gold nanoparticles prepared via in situ reduction of chloroauric acid within the column become attached to the surface of the pores of the monolith. Alternatively, a solution of colloidal gold nanoparticles can be pumped through the thiol modified column to achieve their attachment. While the first approach is faster, it affords a lower coverage of nanoparticles than the second method, while both methods preserve the excellent hydrodynamic properties that are typical of the monolithic columns. Functionalization of the surface of the bound gold nanoparticles is then carried out using low molecular weight thiol-containing surface ligands. The dynamic nature of the bond between gold and these surface ligands enables the replacement of one surface ligand by another through a simple solution exchange process. This novel approach expands the application range of monoliths as a single column can now be used in different separations modes. Applications of the columns with exchangeable chemistries are demonstrated with the capillary electrochromatographic separation of peptides and the nano-high-pressure liquid chromatography (HPLC) separation of proteins in both reversed phase and ion exchange modes.

Materials capable of degradation upon exposure to light hold promise in a diverse range of applications including biomedical devices and smart coatings. Despite the rapid access to macromolecules with diverse compositions and architectures enabled by ring-opening metathesis polymerization (ROMP), a general strategy to introduce facile photodegradability into these polymers is lacking. Here, we report copolymers synthesized via ROMP that can be degraded by cleaving the backbone in both solution and solid states under irradiation with a 52 W, 390 nm Kessil LED to generate heterotelechelic low-molecular-weight fragments. To the best of our knowledge, this work represents the first instance of the incorporation of acylsilanes into a polymer backbone. Mechanistic investigation of the degradation process supports the intermediacy of an α-siloxy carbene, formed via a 1,2-photo Brook rearrangement, which undergoes insertion into water followed by cleavage of the resulting hemiacetal.

We present new spectroscopic observations of the LINER (and now Seyfert 1) nucleus of NGC 1097, and discuss the evolution of its broad, double-peaked Balmer lines. When originally discovered in 1991, the red peak of the double-peaked H-alpha line was stronger than the blue, while by 1994 the H-alpha profile had become almost symmetric and the integrated line flux had decreased to half its original value. Our new spectrum, taken in 1996, shows that the broad, double-peaked lines have returned to almost their original strengths, the profiles of H-beta and H-alpha are identical to within errors, and the broad-line emitting region is unreddened. However, the profile of the Balmer lines is now such that the blue peak is stronger than the red, opposite to the asymmetry observed in 1991. Various models are considered for the observed behavior, all assuming that the emission lines originate in an accretion disk. We present a refined version of the precessing, planar, elliptical accretion ring model proposed by Storchi-Bergmann et al. and Eracleous et al. This model provides an acceptable fit to the line profiles. We also consider the possibility that the line profile evolution results from a precessing warp in the disk, induced by irradiation from the center, and show that the range of radii and precession time scales expected in this model are consistent with the observations. The sudden appearance of the "disk-like" broad line profiles in NGC 1097 could have resulted from the formation of a new accretion disk due to, for example, the tidal disruption of a star, or the illumination of a pre-existing disk by a transient ionizing source at the center of the disk.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Significance A defining characteristic of living organisms is dynamic alignment of cellular responses to stress through activation of signal transduction pathways essential for fine-tuning of interorgannellar communication. Uncovering these communication signals is one of the prime challenges of biology. We have identified a chloroplast-produced retrograde signal, methylerythritol cyclodiphosphate (MEcPP), as a trigger of unfolded protein response (UPR) required for restoration of protein-folding homeostasis in the endoplasmic reticulum (ER). Increased levels of MEcPP via genetic manipulation or exogenous application potentiate expression of a sub-set of UPR genes, and alter plant’s resistance to the ER stress inducing agent. These findings provide a link between a plastidial retrograde signal and transcriptional reprogramming of ER genes critical for readjustment of protein-folding capacity in stressed cells.

A small array of various polythiophene derivative OTF' gas sensors with robust operation in air is demonstrated. Air stability is shown not to preclude gas sensor response, and good sensitivity to a range of gas analytes is observed down to 10 ppm. The active materials are all deposited from solution, making these sensors compatible with low-cost gas sensor arrays. Finally, the effect of varying the functional groups and size of a gas analyte on the response it induces in the sensor array is investigated.