RSC Mechanochemistry最新文献

Widespread usage of single-use plastics such as polyethylene terephthalate (PET) has heavily contributed to a global plastic pollution crisis, necessitating the improvement and development of recycling methods. We previously established a chemo-microbial degradation process for post-consumer PET plastic, consisting of PET depolymerization to form bis(2-hydroxyethyl) terephthalate (BHET) followed by the complete degradation of BHET by a bacterial consortium found to synergistically degrade PET and BHET. The BHET produced during PET depolymerization consists of two polymorphic forms, the α and δ forms. This work investigates the effect of BHET polymorphism on microbial degradation to further optimize the chemo-microbial process. Reversible interconversion methods for BHET polymorphs were effectively developed using mechanochemistry, achieving pure α and δ forms by modulating milling conditions. When inoculated with the bacterial consortium, the α form was degraded faster than the δ form, indicating solid polymorphism is a significant factor for the biodegradation level. This work paves the way to optimize the chemo-microbial process for an increased degradation rate of post-consumer PET and furthers the effort for sustainable plastic recycling methods.

A solvent-free mechanochemical synthesis of two fluorinated perovskites, KCuF₃ and KNiF₃, including the optimization of milling time at constant rotational speed, was studied as a practical and green alternative to the classical solvothermal synthesis. The presence of KCuF₃ and KNiF₃ in the desired crystalline phase as the main product was observed after 6 h of milling. At higher milling times K₂CuF₄ and K₂NiF₄ were detected as additional crystalline phases for the Cu- and Ni- based perovskites, respectively. The fluorinated perovskites were characterized by using X-Ray Powder Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM), confirming the selective formation of the fluorinated perovskites. The mechanochemical route was also compared to a new mild solvothermal method. An evaluation of the environmental impact and the energy efficiency was performed; moreover, the effectiveness of the mechanochemical process was compared to that of the solvothermal method. The promising results obtained from this innovative method opened the door to the use of solvent-free mechanochemical syntheses as a suitable approach in the field of crystal engineering also.

A cyanation reaction was performed inside a ball mill system utilizing catalytically active milling balls, while avoiding the use of solvents and ligands. Additionally, replacing the highly toxic cyanide source with potassium hexacyanoferrate(II) leads to a safer reaction environment. Yields of up to 90% were achieved in as little as 4 hours at room temperature. The oxidative addition and transmetalation step could be observed via X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (PXRD) analysis, respectively, giving a first indication of the mechanism of this mechanochemical reaction.

Mechanochemistry is a promising approach for chemical recycling of commodity plastics, and in some cases depolymerization to the monomer(s) has been reported. However, while poly(olefin)s comprise the largest share of global commodity plastics, mechanochemical depolymerization of these polymers in standard laboratory-scale ball mill reactors suffers from slow rates. In this work, the observed reactivities of poly(styrene), poly(ethylene) and poly(propylene) are rationalized on the basis of thermodynamic limitations of their depolymerization by depropagation of free radical intermediates. In addition, subsequent phase partitioning equilibria for the removal of monomers from the reactor via a purge gas stream are discussed for these polymers. For poly(styrene), a typical vibratory ball mill supplies just enough energy for its depolymerization to be driven by either thermal hotspots or adiabatic compression of the impact site, but the same energy supply is far from sufficient for poly(propylene) and poly(ethylene). Meanwhile, removal of styrene from the reactor is thermodynamically hindered by its lower volatility, but this is not an issue for either propylene or ethylene. The implications of these thermodynamic limitations for mechanochemical reactor design and potential for mechanocatalytic processes are highlighted.

Secondary α-helix and β-sheet structures are key scaffolds around which the rest of the residues condense during protein folding. Despite their key role in numerous processes to maintain life, little is known about their properties under force. Their stability under mechanical stress, as constantly experienced in the turbulent environment of cells, is however essential. Here, we designed and synthesized two pH-responsive polypeptides, poly(L-glutamic acid) and poly(L-lysine), for single-molecule mechanochemistry experiments using AFM to probe the mechanical unfolding of α-helix and β-sheet secondary motifs. The force experiments, supported by simulations, reveal a superior mechanical stability of the poly(L-lysine) α-helix, which we attribute to hydrophobic interactions of the alkyl side chains. Most importantly, our results show that these interactions play a key role in inhibiting the formation of a metastable β-sheet-like structure when the polypeptide is subjected to mechanical deformations, which might have important implications in the mechanism behind polyQ diseases.

Beta blockers are a class of ubiquitous cardiovascular drugs that have collectively received little attention from a crystal engineering standpoint. Here, we describe the use of mechanochemistry in the salification of five beta blockers (propranolol, metoprolol, acebutolol, atenolol, and labetalol) with nicotinic and isonicotinic acid. Firstly, liquid assisted grinding (LAG) was used to neutralize the commercial beta blocker salts, enabling the efficient gram-scale formation of the free bases, which are essential for cocrystallization. Thereafter, 1 : 1 mechanochemical cocrystallizations were successful in all but one case and nine salts were characterized, eight of which are novel. Furthermore, the racemic free base crystal structure of acebutolol is reported for the first time, as well as the first multicomponent crystal of labetalol that is not a simple salt. Salification was enabled by the large pK_a differences between the components, which facilitated the protonation of the basic amine on the beta blockers' alkanolamine skeleton. Thereafter, charge-assisted hydrogen bonding promoted cocrystallization. We envisage salification to be applicable to any beta blocker, considering the current study encompasses approximately one quarter of this drug class. Lastly, the role of different liquid additives in the LAG process was assessed, and the solvent identity was found to play a substantial role in the mechanochemical outcome, although it did not strictly correlate with polarity. This study demonstrates that LAG screening with a wide selection of solvents provides a path to achieve full conversion to products, explore the crystal landscape of multicomponent crystals, and assist in identifying additional phases and/or late stage polymorphs in solid form development.

Here, we report the reaction of calcium-based heavy Grignard reagents, which are easily generated by a mechanochemical method, with unactivated alkyl fluorides in the absence of transition metal catalysts to produce the corresponding arylated products in moderate to good yields. This is the first example of the nucleophilic substitution of an inert C(sp³)–F bond by an organocalcium species. Preliminary mechanistic studies based on theoretical calculations indicate that tetrameric aryl calcium species facilitate the unprecedented C(sp³)–F bond arylation.

Complex molybdates are traditionally prepared via solid-state synthesis and aqueous chemistry methods, which generally require long reaction times and large solvent volumes or high sintering temperatures. However, these techniques often result in undesired secondary species, incomplete reactions, and relatively low yields. Mechanochemistry has proven effective for the synthesis of complex molybdates. This work expands on the development of the mechanochemical synthesis of various heptamolybdates (i.e., sodium, rubidium, and cesium), and trimolybdates (i.e., sodium, rubidium, cesium, strontium, and barium). The obtained materials were characterized via powder X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, thermo-gravimetric analysis, and scanning electron microscopy to assess the purity, morphology, and quality of the sample. High purity samples of the various trimolybdates and heptamolybdates were obtained in less than three hours of reaction time, with minimal energy input and by-products. Mechanochemistry provides a fast, more sustainable, and simple procedure for the synthesis of a wide variety of both trimolybdates and heptamolybdates including the monohydrate form of sodium trimolybdate instead of the trihydrate variant commonly obtained from aqueous reactions.

An efficient diazotization of phenolic compounds with aryltriazenes is herein demonstrated by employing ball milling under catalyst-, promoter- and solvent-free conditions. The present protocol offers several advantages including mild conditions, good selectivity and high yields, simple operation and practical gram-scale synthesis. Overall, this novel strategy significantly improves the reaction efficiency, simplifies purification procedures of the diazotization reaction and provides potential for the industrial preparation of azo dyes.

Ball milling stands as a versatile and widely used technique that involves the mechanical grinding of solid materials via ball mills. Conventionally employed for synthesizing nanomaterials and complex compounds, this method has now been harnessed directly for catalysis due to its capability for surface charge separation. Herein, in the present study, we have explored the potential of ball milling to activate material with low piezoelectric coefficient for catalysis by demonstrating the ball-milling-induced mechano-catalytic activity of SrTiO₃ (STO) nanoparticles for the degradation of toxic methylene blue (MB) dye. With the assistance of ball milling, STO nanoparticles (of 0.3 g dosage) were found capable of degrading 70% of 10 ppm MB dye at 400 rpm speed with 10 Zr balls in just 1 hour. A series of parametric studies were performed to analyze the effect of various process conditions, like catalyst dosage, initial concentration of dye, ball milling speed, and number of milling balls. Further, scavenging tests were carried out to detect the responsible reactive species for dye degradation. Moreover, the present ball milling process was compared with the trivial ultrasonication method where STO showed just 12% degradation in 1 hour. The results manifest the superiority of ball milling catalysis which not only offers precise control over reaction parameters but also encompasses scalability, simplicity, and better potential to conduct catalysis under environmentally benign conditions.