RESUMEN
Post-synthetic modification (PSM) of the interpenetrated diamondoid metal-organic framework (Me2 NH2 )[In(BDC-NH2 )2 ] (BDC-NH2 =aminobenzenedicarboxylate) SHF-61 proceeds quantitatively in a single-crystal-to-single-crystal manner to yield the acetamide derivative (Me2 NH2 )[In(BDC-NHC(O)Me)2 ] SHF-62. Continuous breathing behaviour during activation/desolvation is retained upon PSM, but pore closing now leads to ring-flipping to avert steric clash of amide methyl groups of the modified ligands. This triggers a reduction in the amplitude of the breathing deformation in the two dimensions associated with pore diameter, but a large increase in the third dimension associated with pore length. The MOF is thereby converted from predominantly 2D breathing (in SHF-61) to a distinctly 3D breathing motion (in SHF-62) indicating a decoupling of the pore-width and pore-length breathing motions. These breathing motions have been mapped by a series of single-crystal diffraction studies.
RESUMEN
Invited for this month's cover is the group of David Lidzey at the University of Sheffield. The image shows a futuristic view of large-scale perovskite solar cell (PSC) manufacture. This includes a high-volume roll-to-roll printing facility and cold-storage of PSC precursor solutions in large industrial fridges. The Full Paper itself is available at 10.1002/cssc.202100332.
RESUMEN
The development of stable perovskite precursor solutions is critical if solution-processable perovskite solar cells (PSCs) are to be practically manufacturable. Ideally, such precursors should combine high solution stability without using chemical additives that might compromise PSC performance. Here, it was shown that the shelf-life of high-performing perovskite precursors could be greatly improved by storing solutions at low-temperature without the need to alter chemical composition. Devices fabricated from solutions stored for 31â days at 4 °C achieved a champion power conversion efficiency (PCE) of 18.6 % (97 % of original PCE). The choice of precursor solvent also impacted solution shelf-life, with DMSO-based solutions having enhanced solution stability compared to those including DMF. The compositions of aged precursors were explored using NMR spectroscopy, and films made from these solutions were analysed using X-ray diffraction. It was concluded that the improvement in precursor solution stability is directly linked to the suppression of an addition-elimination reaction and the preservation of higher amounts of methylammonium within solution.
RESUMEN
HYPOTHESIS: Diblock copolymer nanoparticles prepared in non-polar solvents that are sterically stabilized but possess ionic functionality from the inclusion of cationic comonomers in the stabilizer shell are known to exhibit complex electrokinetic behavior (Chem. Sci. 9 (2018) 922-934). For example, core-shell nanoparticles with cationic comonomers located solely within the shell layer have lower magnitude electrophoretic mobilities than nanoparticles containing the same cationic comonomers located within the core, whereas nanoparticles prepared using a minor fraction of steric stabilizer chains containing cationic comonomer repeat units have comparable electrophoretic mobilities to nanoparticles prepared with this cationic comonomer solely located within the core. We hypothesize that these observations can be explained in terms of the strength of the Coulombic interaction between counterions and the nanoparticle interface. EXPERIMENTS: The highly-fluorinated anionic counterion associated with these cationic nanoparticles is studied by 19F nuclear magnetic resonance (NMR) spectroscopy in n-dodecane. This revealed only one type of 19F environment for a soluble macromolecular cation (the oil-soluble steric stabilizer chains used to prepare the nanoparticles), whereas two distinct environments were observed for the sterically-stabilized cationic nanoparticles. Both 19F diffusion NMR and 19F-13C heteronuclear single quantum correlation (HSQC) measurements support the existence of two environments for this counterion. FINDINGS: The existence of two distinct 19F environments for the highly-fluorinated anion associated with the sterically-stabilized nanoparticles demonstrates the presence of spectroscopically distinguishable populations of ion pairs and of fully dissociated free anions. 19F NMR spectra recorded for sterically-stabilized nanoparticles with a fully ionic shell (all stabilizer chains containing the cationic comonomer) and those with a partly ionic shell (10% of stabilizer chains containing the cationic comonomer) reveal a higher proportion of dissociated anions in the partly ionic case. This suggests a stronger Coulombic interaction between counterions and the cationic interface when the shell is fully ionic, which accounts for the observed reduction in the magnitude of the electrophoretic mobility.
RESUMEN
Sterically-stabilized diblock copolymer nanoparticles (a.k.a. micelles) are prepared directly in non-polar media via polymerization-induced self-assembly (PISA). More specifically, a poly(lauryl methacrylate) chain transfer agent is chain-extended via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of methyl methacrylate (MMA) to form sterically-stabilized spheres at 20% w/w solids in n-dodecane at 90 °C. Both fully hydrogenous (PLMA39-PMMA55 and PLMA39-PMMA94) and core-deuterated (PLMA39-d8PMMA57 and PLMA39-d8PMMA96) spherical nanoparticles with mean core diameters of approximately 20 nm were prepared using this protocol. After diluting each dispersion in turn to 1.0% w/w with n-dodecane, small-angle X-ray scattering studies confirmed essentially no change in spherical nanoparticle diameter after thermal annealing at 150 °C. Time-resolved small angle neutron scattering was used to examine whether copolymer chain exchange occurs between such nanoparticles at elevated temperatures. Copolymer chain exchange for a binary mixture of PLMA39-PMMA55 and PLMA39-d8PMMA57 nanoparticles produced hybrid (mixed) cores containing both PMMA55 and d8PMMA57 blocks within 3 min at 150 °C. In contrast, a binary mixture of PLMA39-PMMA94 and PLMA39-d8PMMA96 nanoparticles required 8 min at this temperature before no further reduction in neutron scattering intensity could be observed. These observations suggest that the rate of copolymer chain exchange depends on the degree of polymerization of the core-forming block. Relatively slow copolymer chain exchange was also observed at 80 °C, which is below the Tg of the core-forming PMMA block as determined by DSC studies. These observations confirm rapid exchange of individual copolymer chains between sterically-stabilized nanoparticles at elevated temperature. The implications of these findings are briefly discussed in the context of PISA, which is a powerful technique for the synthesis of sterically-stabilized nanoparticles.
RESUMEN
We report the synthesis of highly transparent poly(stearyl methacrylate)-poly(2,2,2-trifluoroethyl methacrylate) (PSMA-PTFEMA) diblock copolymer nanoparticles via polymerization-induced self-assembly (PISA) in nonpolar media at 70 °C. This was achieved by chain-extending a PSMA precursor block via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of TFEMA in n-tetradecane. This n-alkane has the same refractive index as the PTFEMA core-forming block at 70 °C, which ensures high light transmittance when targeting 33 nm spherical nanoparticles. Such isorefractivity enables visible absorption spectra to be recorded with minimal light scattering even at 30% w/w solids. However, in situ monitoring of the trithiocarbonate RAFT end-groups during PISA requires selection of a weak n â π* band at 446 nm. Conversion of TFEMA into PTFEMA causes a contraction in the reaction solution volume, leading to an initial increase in absorbance that enables the kinetics of polymerization to be monitored via dilatometry. At â¼98% TFEMA conversion, this 446 nm band remains constant for 2 h at 70 °C, indicating surprisingly high RAFT chain-end fidelity (and hence pseudoliving character) under monomer-starved conditions. In situ 19F NMR spectroscopy studies provide evidence for (i) the onset of micellar nucleation, (ii) solvation of the nanoparticle cores by TFEMA monomer, and (iii) surface plasticization of the nanoparticle cores by n-tetradecane at 70 °C. Finally, the kinetics of RAFT chain-end removal can be conveniently monitored by in situ visible absorption spectroscopy: addition of excess initiator at 70 °C causes complete discoloration of the dispersion, with small-angle X-ray scattering studies confirming no change in nanoparticle morphology under these conditions.
RESUMEN
A novel series of HDAC inhibitors demonstrating class I subtype selectivity and good oral bioavailability is described. The compounds are potent enzyme inhibitors (IC50 values less than 100 nM), and improved activity in cell proliferation assays was achieved by modulation of polar surface area (PSA) through the introduction of novel linking groups. Employing oral pharmacokinetic studies in mice, comparing drug levels in spleen to plasma, we selected compounds that were tested for efficacy in human tumor xenograft studies based on their potential to distribute into tumor. One compound, 21r (CHR-3996), showed good oral activity in these models, including dose-related activity in a LoVo xenograft. In addition 21r showed good activity in combination with other anticancer agents in in vitro studies. On the basis of these results, 21r was nominated for clinical development.