Amine-grafted on lanthanide metal-organic frameworks:Three solid base catalysts for Knoevenagel condensation reaction

A post-synthetic modification strategy has been used to prepare three solid base catalysts, including Er（btc）（ED）075（H2O）0.25 （2, btc = 1,3,5-benzenetricarboxylates, ED = 1,2-ethanediamine）, Er（btc）（PP）0.55（H20）0.45 （3, PP = piperazine）, and Er（btc）（DABCO）0.15（H2O）0.85 （4, DABCO = 1,4- diazabicyclo[2.2.2]octane）, by grafting three different diamines onto the coordinatively unsaturated Er（III） ions into the channels of the desolvated lanthanide metal-organic framework （Er（otc））. The resulting metal-organic frameworks were characterized by elemental analysis, thermogravimetric analysis, powder X-ray diffraction, and N2 adsorption. Based on its higher loading ratio of the diamine, as well as its greater stability and porosity, catalyst 2 exhibited higher catalytic activity and reusability than catalysts 3 and 4- for the Knoevenagel condensation reaction. The catalytic mechanism of 2 has also been investigated using size-selective catalysis tests.

Effects of freeze-thaw on soil erosion processes and sediment selectivity under simulated rainfall

The freeze-thaw （FT） processes affect an area of 46.3% in China. It is essential for soil and water conservation and ecological construction to elucidate the mechanisms of the FF processes and its associated soil erosion processes. In this research, we designed the control simulation experiments to promote the understanding of FT-water combined erosion processes. The results showed that the runoff of freeze-thaw slope （FTS） decreased by 8% compared to the control slope （CS）, and the total sediment yield of the FTS was 1.10 times that of the CS. The sediment yield rate from the FTS was significantly greater than that from the CS after 9 min of runoff （P〈0.01）. Both in FTS and CS treatments, the relationships between cumulative runoff and sediment yield can be fitted well with power functions （R2〉0.98, P〈0.01）. Significant differences in the mean weight diameter （MWD） values of particles were between the CS and the FTS treatments in the erosion were smaller than those under FTS for both washed and observed for washed particles and splashed particles process （P〈0.05）. The mean MWD values under CS splashed particles. The ratio of the absolute value of a regression coefficient between the CS and the FTS was 1.15, being roughly correspondent with the ratio of K between the two treatments. Therefore, the parameter a of the power function between cumulative runoff and sediment yield could be an acceptable indicator for expressing the soil erodibility. In conclusion, the FTS exhibited an increase in soil erosion compared to the CS.

Selective synthesis of heteroleptic Pd2A3B-cages:modulating size-preference of supramolecular hosts via endo-functionalization

The size complementarity between a host and a guest is a critical prerequisite for selective molecular recognition.Numerous artificial host systems have been designed to achieve size-selective recognition and chemical transformations.However,the inherent challenge lies in the fixed selectivity governed by a size-exclusion mechanism dictated by the host's structure.Modulating the selectivity necessitates structural modifications of hosts.Examples of host systems with modifiable sizeselectivity are rare.In this study,we present an approach to modulating guest-selectivity via endo-functionalization of supramolecular cavities.Heteroleptic Pd2A3B-cages are constructed with a Pd2A3precursor or directly from palladium ions and relevant ligands.Furthermore,the simultaneous and selective formation of multiple hetero-cages was achieved by simply mixing PdIIand the free ligands in a one-pot reaction.The fidelity of the assembly process relies on cooperative steric control at the periphery and within the cavity of the hetero-cages,respectively.The central steric group also functions as the endohedral moiety.Variations of the endohedral groups facilitate facile and modular derivatization of the microenvironment within the cages,enabling the fine-tuning of guest binding affinities as evidenced by titration experiments.This strategy offers a new solution for the development of customized host structures.