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The identification of thermodynamic descriptors of catalytic performance is essential for the rational design of heterogeneous catalysts. Here, we investigate how spillover energy, a descriptor quantifying whether intermediates are more stable at the dopant or host metal sites, can be used to design single-atom alloys (SAAs) for formic acid dehydrogenation. Using theoretical calculations, we identify NiCu as a SAA with favorable spillover energy and demonstrate that formate intermediates produced after the initial O-H activation are more stable at Ni sites where rate-determining C-H activation occurs. Surface science experiments demonstrated that NiCu(111) SAAs are more reactive than Cu(111) while they still follow the formate reaction pathway. However, reactor studies of silica-supported NiCu SAA nanoparticles showed only a modest improvement over Cu resulting from surface coverage effects. Overall, this study demonstrates the potential of engineering SAAs using spillover energy as a design parameter and highlights the importance of adsorbate-adsorbate interactions under steady-state operation.

We observe that the T g confinement effect of polymer films can saturate with polymer-substrate interaction. Thickness dependences of the glass transition temperature, T g ( h 0 ), of random copolymer films of 4- tert -butylstyrene (TBS) and 4-acetoxystyrene (AS) supported by silica (SiOx) were measured for different TBS concentrations, X TBS . For 0 ≤ X TBS ≤ 0.47, T g ( h 0 ) displays identical enhancements, independent of X TBS . For X TBS > ∼0.66; however, T g ( h 0 ) decreases steadily with X TBS . The X TBS > 0.66 result is in keeping with expectations that TBS interacts less strongly with SiOx than AS does, and weaker polymer-substrate interaction renders greater dominance of the air surface over substrate surface on T g , and thereby T g reduction. We propose that saturation in T g ( h 0 ) found for X TBS ≤ 0.47 is caused by the maximization in polymer-substrate-specific bond formation. Further experiments and a calculation support this proposition.

Ras, a small GTPase found primarily on the inner leaflet of the plasma membrane, is an important signaling node and an attractive target for anticancer therapies. Lateral organization of Ras on cellular membranes has long been a subject of intense research; in particular, whether it forms dimers on membranes as part of its regulatory function has been a point of great interest. Here we report Ras dimer formation on membranes by Type II photosensitization reactions, in which molecular oxygen mediates the radicalization of proteins under typical fluorescence experimental conditions. The presence of Ras dimers on membranes was detected by diffusion-based fluorescence techniques including fluorescence correlation spectroscopy and single particle tracking, and molecular weights of the stable covalently coupled species were confirmed by gel electrophoresis. Fluorescence spectroscopy implicates interprotein dityrosine as one of the dimerization motifs. The specific surface tyrosine distribution on Ras renders the protein especially sensitive to this reaction, and point mutations affecting surface tyrosines are observed to alter dimerization potential. The photosensitization reactions are reflective of physiological oxidative stress induced by reactive oxygen species, suggesting such processes may occur naturally and influence signaling pathways in cells.

A total synthesis of daptomycin, the first natural product antibiotic launched in a generation, was achieved. This convergent synthesis relies on an efficient macrocyclization via a serine ligation to assemble the 31-membered cyclic depsipeptide. The difficult esterification by the nonproteinogenic amino acid kynurenine was accomplished via the esterification of a threonine residue by a suitably protected Trp ester, followed by ozonolysis. This synthesis provides a foundation and framework to prepare varied analogues of daptomycin to establish its structure-activity profile.

A serine/threonine-based chemoselective ligation method is described. It uses an O-salicylaldehyde ester at the C-terminus, reacting with N-terminal serine or threonine to realize peptide ligations. The utility of the O-salicylaldehyde ester enables the rapid coupling reaction and the production of an N,O-benzylidene acetal intermediate, which is readily converted into natural peptidic linkages (Xaa-Ser/Thr) at the ligation site.

Four steroidal nitrosoureas with structures which may permit specific binding to estrogen receptor were synthesized. Inhibitory activity was observed against the growth of the DMBA-induced transplantable rat mammary tumor 13762.