Design, Synthesis, In Vitro Antifungal Activity and Mechanism Study of the Novel 4-Substituted Mandelic Acid Derivatives

Plant diseases caused by phytopathogenic fungi are a serious threat in the process of crop production and cause large economic losses to global agriculture. To obtain high-antifungal-activity compounds with novel action mechanisms, a series of 4-substituted mandelic acid derivatives containing a 1,3,4-oxadiazole moiety were designed and synthesized. In vitro bioassay results revealed that some compounds exhibited excellent activity against the tested fungi. Among them, the EC₅₀ values of E₁₃ against Gibberella saubinetii (G. saubinetii), E₆ against Verticillium dahlia (V. dahlia), and E₁₈ against Sclerotinia sclerotiorum (S. sclerotiorum) were 20.4, 12.7, and 8.0 mg/L, respectively, which were highly superior to that of the commercialized fungicide mandipropamid. The morphological studies of G. saubinetii with a fluorescence microscope (FM) and scanning electron microscope (SEM) indicated that E₁₃ broke the surface of the hyphae and destroyed cell membrane integrity with increased concentration, thereby inhibiting fungal reproduction. Further cytoplasmic content leakage determination results showed a dramatic increase of the nucleic acid and protein concentrations in mycelia with E₁₃ treatment, which also indicated that the title compound E₁₃ could destroy cell membrane integrity and affect the growth of fungi. These results provide important information for further study of the mechanism of action of mandelic acid derivatives and their structural derivatization.

Synthesis of a molecularly imprinted polymer using MOF-74(Ni) as matrix for selective recognition of lysozyme

A molecularly imprinted polymer and metal organic framework were combined to prepare protein imprinted material. MOF-74(Ni) was used as a matrix to prepare surface-imprinted material with lysozyme as a template and polydopamine as an imprinting polymer. MOF-74(Ni) not only provides a large surface area (150.0 m²/g) to modify the polymer layer with more recognition sites (Wt (Ni) = 42.24%), but also facilitates the immobilization of lysozyme by using the chelation between Ni²⁺ of the MOF-74(Ni) and protein. The thin polydopamine layer (10 nm) of the molecularly imprinted material (named MOF@PDA-MIP) enables surface imprinting. Benefiting from the thin polymer layer, MOF@PDA-MIP reached adsorption equilibrium within 10 min. The maximum adsorption capacity reaches 313.5 mg/g with the highest imprinting factor (IF) of 7.8. The specific recognition sites can distinguish target lysozyme from other proteins such as egg albumin (OVA), bovine serum albumin (BSA) and ribonuclease A (RNase A). The material was successfully applied to separation of lysozyme from egg white. Graphical abstract.

Synthesis of molecularly imprinted polymer modified magnetic particles for chiral separation of tryptophan enantiomers in aqueous medium

Molecularly imprinted polymers coated magnetic particles (Fe₃O₄@MIPs) were prepared and used as adsorbents in solid phase extraction for efficient enantioseparation of racemic tryptophan (Trp) in aqueous medium. The amino-modified magnetic particles (Fe₃O₄-NH₂) were first synthesized by one-pot hydrothermal method. Then the template molecules (L-Trp) were assembled on the surface of Fe₃O₄-NH₂. Finally, Fe₃O₄@MIPs were prepared via a sol-gel method using L-Trp@Fe₃O₄-NH₂ complex as matrix, 3-aminopropyltriethoxylsilane and n-octyltriethoxysilane as functional monomers. The as-prepared Fe₃O₄@MIPs were spherical with an average diameter about 149 ± 6.0 nm. The thickness of MIPs layer was approximately 3.5 ± 2.3 nm. The adsorption isotherms data of Fe₃O₄@MIPs toward L-Trp and D-Trp were well described by the Langmuir model. The maximum adsorption capacities of Fe₃O₄@MIPs for L-Trp and D-Trp were calculated to be 17.2 ± 0.34 mg/g and 7.2 ± 0.19 mg/g, respectively. The material exhibited good selectivity toward L-Trp with imprinting factor of 5.6. Excitingly, the enantiomeric excess (ee) of Trp in supernatant after adsorption of racemic Trp by Fe₃O₄@MIPs was as high as 100%. The result suggests that the imprinted caves in Fe₃O₄@MIPs are highly matched with L-Trp molecule in space structure and spatial arrangement of active functional groups. The work also demonstrates that sol-gel technology has great potential in preparation of MIPs for chiral separation.

Polydopamine-based molecularly imprinted thin films for electro-chemical sensing of nitro-explosives in aqueous solutions

A sensitive electrochemical sensor was developed for the detection of nitro-explosives in aqueous solutions based on thin molecularly imprinted polydopamine films. Dopamine was identified in silico, based on DFT (density functional theory) calculations with the ωB97X-D/6-31G* basis set, as the best functional monomer and electropolymerized via cyclic voltammetry (CV) in the presence of carboxylic acid-based structural analogues ('dummy' templates) for two model nitro-explosives: TNT (2,4,6-trinitrotoluene) and RDX (Research Department eXplosive, 1,3,5-trinitroperhydro-1,3,5-triazine). This approach afforded a homogenous coverage of gold electrodes with imprinted films of tunable thickness. The electropolymerized molecularly imprinted polydopamine films allowed for a 10⁵-fold sensitivity improvement over a bare gold electrode based on tracking the redox peaks of the targets by CV. This improved sensitivity is ascribed to the ability of the MIP to concentrate its target in proximity to the transduction element. The MIP films showed reproducible binding in phosphate buffer (10 mM, pH 7.4), with a dynamic range from 0.1 nM to 10 nM for both TNT and RDX and an increased selectivity over closely related structural analogues.