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Polycyclic aromatic hydrocarbons (PAHs) continue to attract increasing interest with respect to their applications as luminescent materials. The ordered structure of the metal-organic complex facilitates the selective integration of PAHs that can be tuned to function cooperatively. Here, a unique highly twisted anthracene-based organoplatinum metallacycle was prepared via coordination-driven selfassembly. Single-crystal X-ray diffraction analysis revealed that the metallacycle was twisted through the cooperation of strong π···π stacking interactions and steric hindrance between two anthracenebased ligands. Notably, the intramolecular twist and aggregation behavior introduced restrictions to the conformational change of anthracenes, which resulted in increased emission intensity of the metallacycle in solution. The emission behaviors and suprastructures based on the highly twisted metallacycle can be modulated by the introduction of different solvents. This study demonstrates that this metallacycle with highly twisted structure is a promising candidate for sensing and bioimaging applications. [ABSTRACT FROM AUTHOR]

Transcription of highly expressed genes has been shown to occur in stochastic bursts. But the origin of such ubiquitous phenomenon has not been understood. Here, we present the mechanism in bacteria. We developed a high-throughput, in vitro, single-molecule assay to follow transcription on individual DNA templates in real time. We showed that positive supercoiling buildup on a DNA segment by transcription slows down transcription elongation and eventually stops transcription initiation. Transcription can be resumed upon gyrase binding to the DNA segment. Furthermore, using single-cell mRNA counting fluorescence in situ hybridization (FISH), we found that duty cycles of transcriptional bursting depend on the intracellular gyrase concentration. Together, these findings prove that transcriptional bursting of highly expressed genes in bacteria is primarily caused by reversible gyrase dissociation from and rebinding to a DNA segment, changing the supercoiling level of the segment. • A high-throughput single-molecule assay follows in vitro transcription in real time • Positive supercoiling buildup inhibits transcription initiation and elongation • Transcriptional bursting is dependent on the intracellular gyrase level • Gyrase dissociation from and rebinding to a DNA loop cause transcriptional bursts Transcriptional bursting in bacteria is inhibited by positive supercoiling of DNA, and the extent of bursting is consequently regulated by the levels of intracellular gyrase, an enzyme that releases positive supercoiling. [ABSTRACT FROM AUTHOR]

Three alkyl-polypeptide hybrid amphiphiles were synthesized by the ring-opening polymerization (ROP) of γ-(2-methoxyethoxy)esteryl-L-glutamate N-carboxyanhydride (L-EG[sub 1]G1u NCA) using alkylamine, i.e. C[sub 6]H[sub 13]NH[sub 2], C[sub 14]H[sub 29]NH[sub 2], and C[sub 16]H[sub 33]NH[sub 2], as initiators. As-prepared alkyl-poly-L-EG[sub 1]Glu hybrids were found to form clear organogels in several organic solvents at low concentration. FTIR and circular dichroism characterizations suggested that poly-L-EG[sub 1]Glu formed a predominantly β-sheet conformation, which accounted for the gelation. Transmission electron and atomic force microscopy characterizations revealed that these copolymers formed nanoribbon structures in THF. [ABSTRACT FROM AUTHOR]

A new type of hetero-grafted molecular bottlebrush with polypeptide as backbone was synthesized using graft-onto strategy. Poly(γ-propargyl-L-glutamate) (PPLG) as backbone was firstly synthesized via ring-opening polymerization (ROP) of γ-propargyl-L-glutamate (PLG) N-carboxyanhydride (NCA). Next, polystyrene-N3 (PS-N3) and monomethoxy poly(ethylene glycol)-N3 (mPEG-N3) as side chains were grafted onto the PPLG backbone using copper-catalyzed click reaction, which afforded good grafting density and efficiency. Two polypeptide bottlebrushes with PS-to-mPEG molar ratio at 70/30 and 30/70 were prepared. The self-assembly behaviors of these two polypeptide bottlebrushes were investigated using the cosolvent method, and their supramolecular structures were characterized using light scattering (LS) and electron microscopy. [ABSTRACT FROM AUTHOR]

Amphiphilic rod–coil dendritic–linearblock copolymersPEG(Gm)-b-PMPCS (where mis the number of dendron generation, and m= 1, 2, 3) composed of a semirigid Percec-type dendron with hydrophilicpoly(ethylene glycol) (PEG) tails and a rod-like mesogen-jacketedliquid crystalline polymer, poly{2,5-bis[(4′-methoxy-phenyl)oxycarbonyl]styrene}(PMPCS), were successfully prepared. The self-assembled structuresundergo a transition from vesicles through large compound vesicles(LCVs) to short cylindrical micelles with increasing dendron generation.PEG(G2)-b-PMPCS forms stable LCVs withporous surfaces of a narrow size distribution in a mixed solvent oftetrahydrofuran and water. The formation mechanism of the supramolecularstructure with nano- and microsized scales is studied through changingthe rate of water addition. It is composed of two steps: morphologicaltransformation and vesicles fusion or differentiation. Vesicles areprecursors for LCVs regardless of what the initial morphology is.However, the final LCV structures are different. Slow addition ofwater produces spherical LCVs, while those formed during fast wateraddition are irregular (like deformed spherical) LCVs. [ABSTRACT FROM AUTHOR]

Ribozymes synthesize proteins in a highly regulated local environment to minimize side reactions caused by various competing species. In contrast, it is challenging to prepare synthetic polypeptides from the polymerization of N-carboxyanhydrides (NCAs) in the presence of water and impurities, which induce monomer degradations and chain terminations, respectively. Inspired by natural protein synthesis, we herein report the preparation of welldefined polypeptides in the presence of competing species, by using a water/dichloromethane biphasic system with macroinitiators anchored at the interface. The impurities are extracted into the aqueous phase in situ, and the localized macroinitiators allow for NCA polymerization at a rate which outpaces water-induced side reactions. Our polymerization strategy streamlines the process from amino acids toward high molecular weight polypeptides with low dispersity by circumventing the tedious NCA purification and the demands for air-free conditions, enabling low-cost, largescale production of polypeptides that has potential to change the paradigm of polypeptide-based biomaterials. [ABSTRACT FROM AUTHOR]

Hybrid hydrogels based on electrostatic co-assembly of polyoxometalates and ABA triblock copolymers were readily prepared and exhibit excellent luminescence and self-healing performance. [ABSTRACT FROM AUTHOR]

We demonstrate that a tripeptide hydrogelator, Nap-FFG, can selectively self-assemble at the surface of platelets, thus inhibiting ADP-, collagen-, thrombin- and arachidonic acid (AA)-induced human platelet aggregations with the IC50 values of 0.035 (41), 0.14 (162), 0.062 (68), and 0.13 mg/mL (148 μM), respectively. Other tripeptide hydrogelators with chemical structures of Nap-FFX (X = A, K, S, or E) could not or possessed less potencies to inhibit platelet aggregations. We observed higher amounts of Nap-FFG at the platelet surface by the techniques of LC-MS and confocal microscopy. We also observed self-assembled nanofibers around the platelet incubated with the Nap-FFG by cryo-TEM. The ζ potential of Nap-FFG treated platelets was a little bit more negative than that of untreated ones. The amount of Nap-FFG at the surface of NIH 3T3 cells was much less than that of platelets. These observations suggested that Nap-FFG could selectively self-assemble through unknown ligand-receptor interactions and form thin layers of hydrogels at the surface of platelets, thus preventing the aggregation of them. This study not only broadened the application and opened up a new door for biomedical applications of molecular hydrogels but also might provide a novel strategy to counteract infection diseases through selective surface-induced hydrogelations at pathogens, such as bacteria and virus. [ABSTRACT FROM AUTHOR]