Synthesis of dihydropyrimidinones via multicomponent reaction route over acid functionalized Metal-Organic framework catalysts

Multi component reactions over heterogeneous solid acid catalysts are extremely important owing to easy separation, amenable recycling, and prospective scaling up of the process. Here, we are reporting the synthesis of biologically important dihydropyrimidinones over postsynthetic modified Cr-based metal-organic framework materials as heterogeneous catalysts containing the bifunctional Lewis and Brønsted acid sites. Cr-based metal-organic frameworks contained coordinatively unsaturated metal sites as inherent Lewis acid sites, whereas postsynthetic modifications introduced the Brønsted acid sites in the framework. A direct one pot synthesis route was employed to produce the pristine MOF in pure aqueous medium without using any additives. The bulk structure, morphology, surface and bonding properties of the synthesized materials were thoroughly characterized with powder XRD, FTIR, XPS, FE-SEM, TGA, and N₂ sorption isotherms. A qualitative evolution of acid strength was carried out over the functionalized MOFs. Among the post synthetic functionalized materials, carboxylic acid functionalized framework exhibited a very high yield of dihydropyrimidinones under solvent less moderate reaction conditions. The catalyst also demonstrated a robust recyclability and wide substrate scope. Comparative study showed a very high catalytic activity of the postsynthetic modified MOFs in comparison to the reported literature. The reaction condition was optimized by varying parameters like solvent, temperature, reaction duration and catalyst loadings. The mechanistic studies indicated the involvement of both the Lewis and Brønsted sites acid sites of the catalysts in the multicomponent reaction.

An efficient Nozaki-Hiyama allenylation promoted by the acid derived MIL-101 MOF

A concise synthesis of the sulfonic acid-containing MIL-101 MOF catalyst was reported using commercially available materials. A series of characterization of as-synthesized MIL-101-SO3H including SEM, XRD, FTIR, BET and TGA was also demonstrated. Using MIL-101-SO3H as a catalyst, an efficient Nozaki-Hiyama allenylation reaction was achieved to generate various polyfunctionalized α-allenic alcohols in high yield and good selectivity. Taking advantage of the high acidity of the MIL-101-SO3H MOF structure, such transformations were also achieved under mild reaction conditions and short reaction times. Based on our observed evidence during this study, a mechanism was proposed involving a substrate activation/γ-nucleophilic addition reaction sequence. In addition, the MIL-101-SO3H catalyst can be recycled ten times during the Nozaki-Hiyama allenylation reaction without compromising the yield and selectivity.

Comparative research on three types of MIL-101(Cr)-SO3H for esterification of cyclohexene with formic acid

MIL-101(Cr)-SO₃H was prepared by a one-pot synthesis method using CrO₃ or Cr(NO₃)₃^·9H₂O as a Cr source and 2-sulfoterephthalic acid monosodium salt as a ligand with three different mineralizers, HCl, HF and NaAC, respectively. Among the prepared catalysts, MIL-101(Cr)-SO₃H, which uses HCl as a mineralizer, has a high specific surface area and the strongest acidity compared with the other two mineralizers. When these catalysts were used to catalyze the esterification of cyclohexene with formic acid, MIL-101(Cr)-SO₃H prepared using HCl as a mineralizer possessed the highest catalytic activity in the esterification, because the conversion rate of cyclohexene is 63.97%, whereas MIL-101(Cr)-SO₃H prepared using NaAC and HF as a mineralizer shows cyclohexene conversion rates of 38.40% and 32.46%, while their selectivity to cyclohexyl formate is about 97.50%. MIL-101(Cr)-SO₃H with HCl as a mineralizer can be reused three times in succession without any loss of catalytic activity.

MIL-101(Cr)-SO₃H was prepared with three different mineralizers, namely HCl, HF and NaAC, respectively. And catalytic performance and stability of three samples catalyzing the esterification of cyclohexene with formic acid were compared.

Recent Development of pH-Responsive Polymers for Cancer Nanomedicine

Cancer remains a leading cause of death worldwide with more than 10 million new cases every year. Tumor-targeted nanomedicines have shown substantial improvements of the therapeutic index of anticancer agents, addressing the deficiencies of conventional chemotherapy, and have had a tremendous growth over past several decades. Due to the pathophysiological characteristics that almost all tumor tissues have lower pH in comparison to normal healthy tissues, among various tumor-targeted nanomaterials, pH-responsive polymeric materials have been one of the most prevalent approaches for cancer diagnosis and treatment. In this review, we summarized the types of pH-responsive polymers, describing their chemical structures and pH-response mechanisms; we illustrated the structure-property relationships of pH-responsive polymers and introduced the approaches to regulating their pH-responsive behaviors; we also highlighted the most representative applications of pH-responsive polymers in cancer imaging and therapy. This review article aims to provide general guidelines for the rational design of more effective pH-responsive nanomaterials for cancer diagnosis and treatment.

A Perspective on Reversibility in Controlled Polymerization Systems: Recent Progress and New Opportunities

The field of controlled polymerization is growing and evolving at unprecedented rates, facilitating polymer scientists to engineer the structure and property of polymer materials for a variety of applications. However, the lack of degradability, particularly in vinyl polymers, is a general concern not only for environmental sustainability, but also for biomedical applications. In recent years, there has been a significant effort to develop reversible polymerization approaches in those well-established controlled polymerization systems. Reversible polymerization typically involves two steps, including (i) forward polymerization, which converts small monomers into macromolecule; and (ii) depolymerization, which is capable of regenerating original monomers. Furthermore, recycled monomers can be repolymerized into new polymers. In this perspective, we highlight recent developments of reversible polymerization in those controlled polymerization systems and offer insight into the promise and utility of reversible polymerization systems. More importantly, the current challenges and future directions to solve those problems are discussed. We hope this perspective can serve as an "initiator" to promote continuing innovations in this fairly new area.