Engineering topics
Publications and source records attributed to Johnson, Darren W..
Host-mediated liquid–liquid extraction is a convenient method for the separation of inorganic salts.
Cyclophanes are a fundamentally interesting class of compounds that host a wide range of unique and emergent properties. Furthermore, synthesis of complex and/or functionalized cyclophanes can often suffer from harsh reaction conditions, long reaction times, and sometimes low yields using stepwise methods. We have previously reported an efficient, high-yielding, metalloid-directed self-assembly method to prepare disulfide, thioether, and hydrocarbon cyclophanes and cages that feature mercaptomethyl-arenes as starting materials. Herein, we report the synthesis of 21 new disulfide and thioether assemblies that expand this high yielding self-assembly method to a wide breadth of macrocycles and cages with diverse structures. Remarkably, the high-yielding, efficient syntheses still proceed under dynamic covalent control using electron-deficient, heteroaryl, cycloalkyl, spiro, and even short alkenyl/alkynyl substrates.
Inclusion of a second nitrogen atom in the aromatic core of phosphorus-nitrogen (PN) heterocycles results in unexpected tautomerization to a nonaromatic form. This tautomerization, initially observed in the solid state through X-ray crystallography, is also explained by computational analysis. We prepared an electron deficient analogue (2 e) with a fluorine on the pyridine ring and showed that the weakly basic pyridine resisted tautomerization, providing key insights to why the transformation occurs. To study the difference in solution vs. solid-state heterocycles, alkylated analogues that lock in the quinoidal tautomer were synthesized and their different 1 H NMR and UV/Vis spectra studied. Ultimately, we determined that all heterocycles are the aromatic tautomer in solution and all but 2 e switch to the quinoidal tautomer in the solid state. Better understanding of this transformation and under what circumstances it occurs suggest future use in a switchable on/off hydrogen-bond-directed receptor that can be tuned for complementary hydrogen bonding.
Abstract not provided
Disclosed herein is a material comprising a functionalized solid support surface, wherein the functionalization comprises a thioalkylene linker bound to the support surface and the thioalkylene linker is coupled to a moiety derived from a ligand, wherein the ligand includes a terminal alkenyl and at least one first functional group configured to bind to at least one predetermined target species.
Thin films formed by the condensation of metal oxo–hydroxo clusters offer a promising approach to ultrahigh-resolution patterning including next-generation photolithography using extreme ultraviolet (EUV) radiation and electron-beam lithography. In this work, we elucidate the thermal and radiative mechanisms that drive the chemical transformations in these materials and therefore control the patterning performance. Beginning from aqueous hafnium clusters, peroxide and sulfate additions serve to modify the clusters and, upon spin coating to form a thin film, provide the chemical contrast necessary to create resist. The coordination and functionality of peroxide and sulfate in hafnium-based metal oxo–hydroxo clusters were monitored at various stages of the patterning process which provided insight into the chemical and structural evolution of the material. Peroxide serves as the radiation sensitive species while sulfate enhances solubility and controls the concentration of hydroxide in the films. In conclusion, peroxide and hydroxide species decompose via radiative and thermal energy, respectively, to form hafnium oxide; controlling these processes is central to the function of the resist.