Single-chain polymer nanoparticles (SCNPs) are emerging as versatile catalytic platforms that provide excellent control over solubility. The confined nature of SCNPs can improve the rate of catalysis. While significant headway has been made in thermally-induced transition-metal catalysis with SCNPs, lightactivated SCNP catalysts have received little attention. We are developing triarylpyrylium tetrafluoroborate (TPT)-functionalized SCNPs as oxidative photocatalysts. Herein, we comprehensively study the impact of light source on both SCNP compaction and TPT absorbance through gel-permeation chromatography and UV/Vis spectroscopy. We observe that compaction is expedited using light sources that excite the photocatalyst (e.g., blue LEDs), which is attributed to the ability of TPT to dimerize sytrenics under similar photoredox conditions. The resultant metal-free SCNP photocatalysts enable the oxidation of benzyl alcohols in good yields. The SCNP is further investigated for the amidation of 4-bromobenzaldehyde, wherein it affords higher yields of the benzamide product compared to both small-molecule and unfolded polymer controls. We attribute the combined results to the colocalization of the TPT photoredox catalyst and pyrene electron relay within the SCNP, which likely aids in single-electron transfer processes. The scope of amidation reactions was also extended to other aryl aldehydes, wherein deactivated substrates afforded the highest yield of the desired amide.

Metrics & MoreArticle Recommendations * sı Supporting InformationH erein, we comment on the of spectroscopic data in "Arresting an Unusual Amide Tautomer Using Divalent Cations", J. Phys. Chem. B 2019, 123 (40), 8419−8424, by Bagchi and co-workers. 1 In their paper, the authors assign the appearance of a blue-shifted shoulder on the amide I vibration of N-methylacetamide (NMA), N,Ndimethylacetamide (DMA), and urea to the formation of a tautomer-like structure in the presence of divalent metal cations. In other words, the shoulder should originate from a CN + resonance that is stabilized by the presence of divalent metal cations. Moreover, Bagchi and co-workers argue that the CN + resonance is coincidently located at a position just to the blue of the amide I band upon the introduction of divalent metal cation salts. This assignment represents an alternative to the idea that the blue-shifted shoulder on the amide I band arises from the dehydration of the amide oxygen upon interaction with metal cations. 2,3 Bagchi's putative new assignment can be directly tested by studying 15 N-isotopelabeled NMA. Such experiments were performed in our laboratory and are described below.We synthesized NMA and 15 N-labeled NMA by reacting acetyl chloride with methylamine•HCl and 15 N-labeled methylamine•HCl, respectively (see Supporting Information for details). The resulting amide-containing molecules were introduced into D 2 O at a concentration of 100 mM (Figure 1A). In the absence of salt, there is a small isotope shift upon substitution with the 15 N-labeled molecule. This very modest red shift from 1620 to 1617 cm −1 in the case of 15 N-labeled NMA is expected because the amide I resonance is not purely CO in character. Upon adding 4 M CaCl 2 , a blue-shifted shoulder appears at 1645 cm −1 with NMA as well as with 15 Nlabeled NMA (Figure 1B). This is not what one would expect if the blue shoulder was from CN + . Indeed, if the CN + assignment was correct, then this mode should have been quite sensitive to the mass of the nitrogen atom. Moreover, one can look for an isotope shift upon the addition of acid to solution. As Bagchi and co-workers point out, one expects to observe the formation of a CN + resonance at low pH. As such, we added 1 M DCl to solution to directly examine this feature (Figure 1C). In the case of NMA, a new peak appears at 1680 cm −1 (Figure 1C, black curve). Next, the same experiment was performed with a solution containing 15 N-labeled NMA

Water-splitting dye-sensitized photoelectrochemical cells rely on molecular sensitizers to harvest light energy and drive the catalytic reactions necessary to generate hydrogen and oxygen from water. The desorption of sensitizer molecules from the semiconductor−aqueous electrolyte interface is a significant barrier to the practical implementation of these cells. To address this problem, we synthesized an oligomeric ruthenium dye ([RuP] n ) that has dramatically improved stability as a photosensitizer for TiO 2 electrodes over the pH range of interest (4−7.8) for DSPECs. Additionally, the efficiency of photoelectrochemical charge separation is known to depend on the rate of cross-surface hole diffusion between dye molecules. The oligomeric dye ([RuP] n ) shows an order of magnitude faster cross-surface hole diffusion than the commonly used monomeric [Ru(bpy) 2 (4,4-PO 3 H 2 ) 2 bpy] 2+ (RuP) sensitizer. The enhanced stability of the polymeric dye also enables the use of intensity-modulated photovoltage spectroscopy to measure the recombination rate of photogenerated electrons and holes as a function of electrolyte pH.Article pubs.acs.org/JPCC

Nuclear receptors function as ligand-regulated transcription factors whose ability to regulate diverse physiological processes is closely linked with conformational changes induced upon ligand binding. Understanding how conformational populations of nuclear receptors are shifted by various ligands could illuminate strategies for the design of synthetic modulators to regulate specific transcriptional programs. Here, we investigate ligand-induced conformational changes using a reconstructed, ancestral nuclear receptor. By making substitutions at a key position, we engineer receptor variants with altered ligand specificities. We combine cellular and biophysical experiments to characterize transcriptional activity, as well as elucidate mechanisms underlying altered transcription in receptor variants. We then use atomistic molecular dynamics (MD) simulations with enhanced sampling to generate ensembles of wildtype and engineered receptors in combination with multiple ligands, followed by conformational analysis and correlation of MD-based predictions with functional ligand profiles. We determine that conformational ensembles accurately describe ligand responses based on observed population shifts. These studies provide a platform which will allow structural characterization of physiologically-relevant conformational ensembles, as well as provide the ability to design and predict transcriptional responses in novel ligands.

Controlling the primary sequence of synthetic polymers remains a grand challenge in chemistry. A variety of methods that exert control over monomer sequence have been realized wherein differential reactivity, pre-organization, and stimuli-response have been key factors in programming sequence. Whereas much has been established in nonconjugated systems, π-extended frameworks remain systems wherein subtle structural changes influence bulk properties. The recent introduction of electronically biased ring-opening metathesis polymerization (ROMP) extends the repertoire of feasible approaches to prescribe donor–acceptor sequences in conjugated polymers, by enabling a system to achieve both low dispersity and controlled polymer sequences. Herein, we discuss recent advances in obtaining well-defined (i.e., low dispersity) polymers featuring donor–acceptor sequence control, and present our design of an electronically ambiguous (4-methoxy-1-(2-ethylhexyloxy) and benzothiadiazole-(donor–acceptor-)based [2.2]paracyclophanediene monomer that undergoes electronically dictated ROMP. The resultant donor–acceptor polymers were well-defined (Đ = 1.2, Mn > 20 k) and exhibited lower energy excitation and emission in comparison to ‘sequence-ill-defined’ polymers. Electronically driven ROMP expands on prior synthetic methods to attain sequence control, while providing a promising platform for further interrogation of polymer sequence and resultant properties.1 Introduction to Sequence Control2 Sequence Control in Polymers3 Multistep-Synthesis-Driven Sequence Control4 Catalyst-Dictated Sequence Control5 Electronically Governed Sequence Control6 Conclusions