Organocatalytic Ring-Opening Polymerization of ε-Caprolactone Using bis(N-(N′-butylimidazolium)alkane Dicationic Ionic Liquids as the Metal-Free Catalysts: Polymer Synthesis, Kinetics and DFT Mechanistic Study

In this work, we successfully synthesized high thermal sTable 1,n-bis(N-(N′-butylimidazolium)alkane bishexafluorophosphates (1,n-bis[Bim][PF6], n = 4, 6, 8, and 10) catalysts in 55–70% yields from imidazole which were applied as non-toxic DILs catalysts with 1-butanol as initiator for the bulk ROP of ε-caprolactone (CL) in the varied ratio of CL/nBuOH/1,4-bis[Bim][PF6] from 200/1.0/0.25–4.0 to 700/1.0/0.25–4.0 by mol%. The result found that the optimal ratio of CL/nBuOH/1,4-bis[Bim][PF6] 400/1.0/0.5 mol% at 120 °C for 72 h led to the polymerization conversions higher than 95%, with the molecular weight (Mw) of PCL 20,130 g mol−1 (Đ~1.80). The polymerization rate of CL increased with the decreasing linker chain length of ionic liquids. Moreover, the mechanistic study was investigated by DFT using B3LYP (6–31G(d,p)) as basis set. The most plausible mechanism included the stepwise and coordination insertion in which the alkoxide insertion step is the rate-determining step.

Porphyrin Photoabsorption and Fluorescence Variation with Adsorptive Loading on Gold Nanoparticles

Here, we report the photophysical structure–property relationship of porphyrins adsorbed on gold nanoparticles. The number of porphyrin–alkanethiolate adsorbates per particle was adjusted by a post-synthetic thiol/thiolate exchange reaction on 1-dodecanethiolate–protected gold nanoparticles. Even with a low loading level of adsorbates (<10% of all thiolate sites on gold nanoparticles), the shoulder absorption at the Soret band was intensified, indicating the formation of aggregates of porphyrin adsorbates on the nanoparticles. Steady-state fluorescence quantum yields could be adjusted by the bulkiness of substituents at the meso-positions of the porphyrin or the methylene linker chain length, regardless of the porphyrin loading level and the nanoparticle diameter.

Bis-dihydroisoxazolines: Synthesis, Structural Elucidation, Antimicrobial Evaluation, and DNA Photocleavage Assay

Aim and Objective: Isoxazole is an active core found in many drugs. The aim of this work was to synthesize bis-isoxazoline compounds and to analyze the effect of linker chain length on biological activities. Material and Methods: A simple, convenient, and efficient method for the conversion of bischalcones to new bis(4,5-dihydroisoxazole) derivatives was developed by using hydroxylamine hydrochloride under basic medium. Synthesized moieties were also evaluated for their antimicrobial potencies and DNA photocleavage assay. Results and Discussion: The synthesized compounds were more active than their chalcone precursors and the long-chain linkers (4e&4f) were more potent in antimicrobial, as well as in DNA photocleavage activity. Conclusion: It was found that many of the tested bischalcones and bis-isoxazolines exhibited moderate to significant antimicrobial activity against various strains. Furthermore, the present study also provides significant information and interesting outcomes regarding cyclization, increasing the length of linker chains, and their effects on the DNA photocleavage and antimicrobial activities.

Tacrine, Trolox and Tryptoline as Lead Compounds for the Design and Synthesis of Multi-target Agents for Alzheimer’s Disease Therapy

The versatile biological activities of tacrine, trolox and β-carboline derivatives make them promising lead structures for the development of multifunctional Alzheimer’s disease (AD) agents. Based on the topology of the active site of cholinesterases and other target proteins involved in the pathogenesis of AD, we have designed and synthesized tacrine-trolox and tacrine-tryptoline hybrids with various linker chain lengths. The hybrids containing the trolox moiety (8a-8d) showed moderate to high TcAChE inhibition (IC50: 17.37 - 2200 nM), eqBuChE inhibition (IC50: 3.16 – 128.82 nM) and free radical scavenging activities (IC50: 11.48 – 49.23 µM). The hybrids with longer linker chain lengths in general showed better ChE inhibitory activity. As expected, free radical scavenging activities were not significantly affected by varying linker chain lengths. The hybrid compound containing the tryptoline moiety linked with a 7 carbon spacer to tacrine (14) displayed the best AChE and BuChE inhibitory activity (IC50 = 17.37 and 3.16 nM). Docking experiments exhibited that compounds 8d and 14 were able to bind to both the CAS and PAS of TcAChE and eqBuChE, suggesting that they will be able to inhibit ChE induced Aβ aggregation. Novel multi-target agents that exhibit good ChE inhibition (8d and 14) and anti-oxidant (8d) activity were identified as suitable candidates for further investigation.