Enantioseparation/Recognition based on nano techniques/materials

Enantiomers show different behaviors in interaction with the chiral environment. Due to their identical chemical structure and their wide application in various industries, such as agriculture, medicine, pesticide, food, and so forth, their separation is of great importance. Today, the term "nano" is frequently encountered in all fields. Technology and measuring devices are moving towards miniaturization, and the usage of nanomaterials in all sectors is expanding substantially. Given that scientists have recently attempted to apply miniaturized techniques known as nano-liquid chromatography/capillary-liquid chromatography, which were originally accomplished in 1988, as well as the widespread usage of nanomaterials for chiral resolution (back in 1989), this comprehensive study was developed. Searching the terms "nano" and "enantiomer separation" on scientific websites such as Scopus, Google Scholar, and Web of Science yields articles that either use miniaturized instruments or apply nanomaterials as chiral selectors with a variety of chemical and electrochemical detection techniques, which are discussed in this article.

Synthesis of New Quinoline-Conjugated Calixarene as a Fluorescent Sensor for Selective Determination of Cu2+ Ion

A novel quinoline-functionalized calix [4] arene derivative (Quin-Calix) has been successfully synthesized at partial cone conformation and duly characterized by using FTIR, ¹H-NMR, ¹³C-NMR, ESI-MS and elemental analysis techniques. Moreover, the cation-binding property of the calix [4] arene derivative (Quin-Calix) has been investigated towards Cu²⁺, Ba²⁺, Cd²⁺, Co²⁺, Ni²⁺, Zn²⁺ and Fe³⁺ ions, and the recognition event monitored by UV-Vis absorption and fluorescence studies. The results indicated that Quin-Calix displays a remarkable affinity and selectivity only for Cu²⁺ ion. The binding constant and stoichiometry of the complex formed between Quin-Calix and Cu²⁺ ion have been also calculated from the fluorescence data. In addition, Stern-Vohmer equation has been used to elucidate the mechanism of quenching.

Calix[4]arene tetracarboxylic acid-treated lipase immobilized onto metal-organic framework: Biocatalyst for ester hydrolysis and kinetic resolution

Metal organic frameworks (MOFs) are hybrid organic inorganic materials with unique properties such as well-defined pore structure, extremely high surface area, excellent chemical-thermal stability. MOFs-based constructs have been extensively engineered and used for applications, such as enzyme immobilization for bio-catalysis. To obtained a zeolitic imidazole framework-8 (ZIF-8) for enzyme immobilization, Candida rugosa lipase (CRL) was pretreated with calix [4]arene tetracarboxylic acid (Calix) and reacted with Zn and imidazole by co-precipitation method. The prepared biocomposite was characterized by SEM, EDX, FT-IR, and XRD. The prepared CRL@Calix-ZIF-8 with high encapsulation efficiency showed improved resistance to alkali and thermal conditions. The CRL@Calix-ZIF-8 with the biocatalytic activity was 2-folds higher than that of the CRL@ZIF-8 (without Calix). The free lipase lost its catalytic activity completely at 60 °C after 100 min, while the CRL@Calix-ZIF-8 and CRL@ZIF-8 retained about 84% and 73%. It was found that CRL@Calix-ZIF-8 and CRL@ZIF-8 still retained ~83 and 67% of catalytic activity after its 6th use, respectively. The kinetic resolution of the immobilized lipases was examined for enantioselective hydrolysis of racemic naproxen methyl ester. CRL@Calix-ZIF-8 showed enantioselectivity against the racemic naproxen methyl ester, with E = 183 and 131 compared to the CRL@ZIF-8.

Synthesis and evaluation of the antitumor activity of Calix[4]arene l-proline derivatives

The unique conformational properties, functionality, low toxicity, and low cost make calixarene-based compounds a valuable candidate against cancer. The aim of the present study is the synthesis of the upper rim and lower rim-functionalized l-proline-based calix[4]arene derivatives and evaluation of their cytotoxic potential for human cancerous cells as well as to determine the death mechanism. Synthesized calix[4]arene (3, 8a, 8b 13a, and 13b) derivatives were characterized by different spectroscopic techniques such as ¹HNMR, ¹³CNMR, and FTIR. In vitro effects of compounds 3, 8a, 8b, 13a and 13b were tested on human cancerous cells (HEPG2, PC-3, A-549, and DLD-1) as well as human healthy epithelium cell (PNT1A). Results show that compounds 3, 8a, 8b and 13b have cytotoxic potential on human colorectal carcinoma cells (DLD-1) with IC₅₀ values of 43 µM, 45.2 µM, 64.57 µM, and 29.35 µM respectively. Apoptosis ratios of cell death were investigated with flow cytometer using 7-AAD and Annexin-V as markers. Cytotoxic potential of 8a was found to be higher due to increased apoptosis, when compared with healthy cells the apoptotic cell death was significantly (p < 0.0001) increased up to 1.7-fold and 2.4-fold in DLD-1 and A549 cells, respectively. In conclusion, these l-proline derived calix[4]arenes with their selective cytotoxic potential on human cancerous cells may be a potential candidate for the treatment of human CRC and lung cancer.

Enantiomeric Recognition and Separation by Chiral Nanoparticles

Chiral molecules are stereoselective with regard to specific biological functions. Enantiomers differ considerably in their physiological reactions with the human body. Safeguarding the quality and safety of drugs requires an efficient analytical platform by which to selectively probe chiral compounds to ensure the extraction of single enantiomers. Asymmetric synthesis is a mature approach to the production of single enantiomers; however, it is poorly suited to mass production and allows for only specific enantioselective reactions. Furthermore, it is too expensive and time-consuming for the evaluation of therapeutic drugs in the early stages of development. These limitations have prompted the development of surface-modified nanoparticles using amino acids, chiral organic ligands, or functional groups as chiral selectors applicable to a racemic mixture of chiral molecules. The fact that these combinations can be optimized in terms of sensitivity, specificity, and enantioselectivity makes them ideal for enantiomeric recognition and separation. In chiral resolution, molecules bond selectively to particle surfaces according to homochiral interactions, whereupon an enantiopure compound is extracted from the solution through a simple filtration process. In this review article, we discuss the fabrication of chiral nanoparticles and look at the ways their distinctive surface properties have been adopted in enantiomeric recognition and separation.

Synthesis of environmentally friendly, efficient and highly recyclable Lewis acid-type calix[4]arene catalysts containing flexible or bulky groups for the Mannich reaction

Two new calix[4]arene-based Lewis acid-type catalysts containing flexible and bulky groups (2 and 3) were successfully synthesized.

Kinetic resolution of (RS)-1-chloro-3-(4-(2-methoxyethyl)phenoxy)propan-2-ol: a metoprolol intermediate and its validation through homology model of Pseudomonas fluorescens lipase

Kinetic resolution of (±)-1-chloro-3-(4-(2-methoxyethyl)phenoxy)propan-2-ol: a metoprolol intermediate and its validation through homology model of Pseudomonas fluorescens lipase.

Calix-Based Nanoparticles: A Review

Calixarenes are considered as third generation supramolecules with hollow cavity-like architecture whereas nanoparticles are small entities with dimensions in the nanoscale. Many exciting achievements are seen when the calix system merges with nanoparticles which produces many fascinating facets in all fields of contemporary chemistry. The properties of nanoparticles which are tuned by calixarenes find applications in sensing, catalysis, molecular recognition, etc. Here, we have reviewed the chemistry of calix-based nanoparticles, and emphasis is laid on the modified, reducing, templated and stabilizing roles of calixarenes. This review covers the research being carried out in the domain of calix protected metal nanoparticles during last 18 years under the canopy of important 109 references. This article contains 58 figures which include 81 easy to understand structures. Calix-protected nanoparticles have enthralled researchers in the field of nanoscience with a tremendous growth in its applications, which heralds much promise to become in future a separate area of research.

Recent Advances in Lipase-Mediated Preparation of Pharmaceuticals and Their Intermediates

Biocatalysis offers an alternative approach to conventional chemical processes for the production of single-isomer chiral drugs. Lipases are one of the most used enzymes in the synthesis of enantiomerically pure intermediates. The use of this type of enzyme is mainly due to the characteristics of their regio-, chemo- and enantioselectivity in the resolution process of racemates, without the use of cofactors. Moreover, this class of enzymes has generally excellent stability in the presence of organic solvents, facilitating the solubility of the organic substrate to be modified. Further improvements and new applications have been achieved in the syntheses of biologically active compounds catalyzed by lipases. This review critically reports and discusses examples from recent literature (2007 to mid-2015), concerning the synthesis of enantiomerically pure active pharmaceutical ingredients (APIs) and their intermediates in which the key step involves the action of a lipase.

Calixarene assembly with enhanced photocurrents using P(SNS-NH2)/CdS nanoparticle structure modified Au electrode systems

Two novel calix[n]arene-adorned gold electrodes producing high photocurrent intensities were successfully constructed.

Enantioselectivity and catalysis improvements of Pseudomonas cepacia lipase with Tyr and Asp modification

A concise strategy to improve the p-nitrophenyl palmitate catalytic activity and enantioselectivity towards secondary alcohols of PcL is described.