Monthly Archives: January 2024

Chemoselective direct amidation of fatty acids with furfurylamine without coupling reagents in reversed micellar microenvironment

Posted on by
Chemoselective direct amidation of fatty acids with furfurylamine without coupling reagents in reversed micellar microenvironment

A convenient chemoselective and direct amidation method to access to fatty acids-based furfurylamides as versatile building blocks in Diels-Alder reactions.


Abstract

Furan heterocyclic compounds derived from renewable sources are popular versatile candidates for the production of multifunctional macromolecular materials. These compounds are also used as hydrophobilization monomers for reversible polyadducts or as versatile building blocks in Diels-Alder reactions. In the present study, an efficient approach to chemoselective acylation of furfurylamine with a series of non-preactivated monocarboxylic or dicarboxylic long-chain fatty acids and some of their functionalized derivatives has been achieved via catalytic direct amidation in reversed micellar medium. A convenient and environmentally friendly method has been developed for furfurylamides via a dehydrative coupling reaction. For this purpose, a new cationic Brønsted-type sulfonic acid catalyst containing a hexadecyl alkyl chain was synthesized and fully characterized. The present catalytic reaction produced the respective N-furfurylamides materials in good to excellent yields. This study also confirms that the direct amidation of carboxylic acids with selected amine compounds can be successfully catalyzed by Brønsted acids. Its simplicity and high atom economy are the main advantages of this method.

Circularly Polarized Luminescence Switching of Chiral Perylene Diimide‐Doped Nematic Liquid Crystal Using DC Electric Field

Posted on by
Circularly Polarized Luminescence Switching of Chiral Perylene Diimide-Doped Nematic Liquid Crystal Using DC Electric Field

Chiral luminescent nematic liquid crystals emit strong CPL signals and act as a reversible CPL switch regulated by turning the applied DC electric field on and off.


Abstract

To obtain chiral luminescent nematic liquid crystals (N*-LCs), two sets of chiral perylene luminescent materials (R,R)/(S,S)-N,N′-bis(1-cyclohexylethyl)perylene-3,4,9,10-tetracarboxylic diimide [(R,R)/(S,S)-CPDI] and (R,R)/(S,S)-N,N′-bis(1-phenylethyl)perylene-3,4,9,10-tetracarboxylic diimide [(R,R)/(S,S)-BPP] were prepared and doped into a nematic liquid crystal (N-LC), 5CB. The obtained liquid crystals N*-LC-CPDI and N*-LC-BPP emitted stronger circularly polarized luminescence (CPL) signals than the CPDI- and BPP-containing chiral poly(methyl methacrylate) (PMMA) luminescent films owing to higher helical twist power. When a direct current (DC) electric field was applied to N*-LC, a reversible CPL response was obtained due to the field-induced phase transition from the chiral nematic phase to the nematic phase. This demonstrated the successful construction of an ′′on-off-on′′ CPL system based on a DC electric field and was attributed to the change in the liquid crystalline organization from a uniformly lying helical structure to a planar one. This work can provide an effective strategy for the development of functional CPL devices in which the CPL can be regulated by applying a DC electric field to the N*-LC.

A Cationic Catechol Derivative Binds Anions in Competitive Aqueous Media

Posted on by
A Cationic Catechol Derivative Binds Anions in Competitive Aqueous Media

A simple acyclic molecule binds sulfate strongly (K a>104 M−1) in a competitive 4 : 1 d6-acetone:D2O mixture. The molecule also reacts readily with BF4 − and BPh4 − to give zwitterions containing an anion tetrahedral boronate centre. These zwitterions were characterised crystallographically.


Abstract

A simple dihydroxy isoquinolinium molecule (3+ ) was prepared by a modification of a literature procedure. Interestingly, during optimisation of the synthesis a small amount of the natural product pseudopalmatine was isolated, and characterised for the first time by X-ray crystallography. Compound 3+ contains a catechol motif and positive charge on the same scaffold and was found to be a potent anion receptor, binding sulfate strongly in 8 : 2 d6-acetone:D2O and 7 : 3 d6-acetone:D2O (K a>104 and 2,100 M−1, respectively). Unsurprisingly, chloride binding was much weaker, even in the less polar solvent mixture 9 : 1 d6-acetone:D2O. The sulfate binding is remarkably strong for such a simple molecule, however anion binding studies were complicated by the tendency of the molecule to react with BPh4 − or BF4 − species during anion metathesis reactions. This gave two unusual zwitterions containing tetrahedral boronate centres, which were both characterised by X-ray crystallography.

Slowing Hot Electron Cooling in CdSe Quantum Dots Using Electron‐Rich Exciton‐Delocalizing Ligands

Posted on by
Slowing Hot Electron Cooling in CdSe Quantum Dots Using Electron-Rich Exciton-Delocalizing Ligands

Ordinarily, hot electrons cool within a few hundred femtoseconds in CdSe. However, chemical treatment of CdSe with the electron-rich MeOPTC generates hole-ligand interfacial states which disrupt the hot electrons’ cooling process, preventing a fraction of them from cooling efficiently.


Abstract

Understanding hot carrier dynamics in semiconductor nanocrystals is an important research focus due to their applications in photonics and photovoltaic devices. In this report, we investigated the effects of surface-bound exciton-delocalizing ligands (EDLs) on the lifetimes of hot electrons in CdSe quantum dots (QDs). After treatment of CdSe with two different phenylithiocarbamates (PTCs), a class of EDLs, the depletion times of the band-edge exciton bleach were roughly equivalent as observed through ultrafast transient absorption spectroscopy. However, following the initial ultrafast depletion, the PTC-treated samples continued to deplete while the untreated CdSe began recovering. Inspection of other transient features – such as the 3rd exciton and hot biexciton – reveal a general trend in which the PTC-treated samples relax more slowly at short times (<10 ps) when compared with the untreated CdSe. At longer delay times, in the range of nanoseconds, the CdSe+CF3OPTC loses nearly 80 % of its excited state populations, while the CdSe+MeOPTC loses only 20–40 %. We discuss the role that exciton delocalization plays in determining these observed rates as well as how they compare to previous studies. Kinetic differences between the two ligands are attributed to their electron donating/withdrawing abilities and coupling to the CdSe QD. Coherent vibrational wavepacket analysis supports this line of reasoning, showing increased coupling between the exciton and the longitudinal optical (LO) phonon due to increased Coulombic field strength around the hole and electron-donating MeOPTC. These results indicate that electron-rich PTCs are especially good candidates for use in QD devices that would make use of hot carriers.

Photocatalytic metal‐free oxidation of alcohols with molecular oxygen in supercritical CO2 medium

Posted on by
Photocatalytic metal-free oxidation of alcohols with molecular oxygen in supercritical CO2 medium

2-Fluoroanthraquinone has been identified as a non-toxic and accessible organic photocatalyst for green oxidation of alcohols to carbonyls in supercritical (sc) CO2. Tuning of scCO2 medium near the critical point allowed attaining high conversions (90–99 %). Molecular oxygen and air were used as safe and atom efficient oxidants. A plausible Hydrogen Atom Transfer (HAT) mechanism of the catalytic photooxidation process has been proposed.


Abstract

Near-UV-light-induced oxidative conversion of cyclic and linear alcohols into corresponding carbonyl compounds was achieved in the supercritical CO2 medium under the action of molecular oxygen in the presence of 2-fluoroanthraquinone (1 mol %), a simple and available metal-free photocatalyst. A thorough examination of the impact of various process parameters on the reaction outcome allowed to identify a narrow density area at ~0.3 g/cm3 in the vicinity of the medium critical point and optimal reaction conditions (~45 °C, ~8.4 MPa) where up to 99 % conversions and 65–93 % yields of the oxidation products could be attained. Furthermore, it has been shown that compressed atmospheric air, a far cheaper and safer oxidizer than pure oxygen, can be applied to the reaction. Based on the experimental data, a plausible mechanism of the photocatalytic process has been proposed comprising photocatalyst excitation with near-UV light followed by the hydrogen atom transfer (HAT) as the key stages.

A RaPID Response to SARS‐CoV‐2

Posted on by
A RaPID Response to SARS-CoV-2


Abstract

Genetically encoded peptide libraries are at the forefront of de novo drug discovery. The RaPID (Random Nonstandard Peptides Integrated Discovery) platform stands out due to the unique combination of flexible in vitro translation (FIT) and mRNA display. This enables the incorporation of non-canonical amino acids, improving chemical diversity and allowing macrocyclisation of the peptide library. The resulting constrained peptides are valued for their strong binding affinity and stability, especially in the context of protein-protein interactions. In response to SARS-CoV-2, the causative agent of the COVID-19 pandemic, the RaPID system proved valuable in identifying high-affinity ligands of viral proteins. Among many peptide ligands of SARS-CoV-2 spike and main protease (Mpro), several macrocycles stand out for their exceptional binding affinities. Structural data showcases distinct binding modes in complex with the receptor-binding domain (RBD) of the spike glycoprotein or the catalytic active site of Mpro. However, translating these in vitro findings into clinical applications remains challenging, especially due to insufficient cell permeability.

[3 + 2] Cycloaddition of nitrile oxides to dichloropropenes and 1,3‐dichlorobut‐2‐ene: A regioselectivity issue

Posted on by
[3 + 2] Cycloaddition of nitrile oxides to dichloropropenes and 1,3-dichlorobut-2-ene: A regioselectivity issue

[3 + 2] Cycloaddition of nitrile oxides to chloroalkenes—common organochlorine wastes: experimental and DFT study.


Abstract

The reaction of nitrile oxides with 2,3-dichloroprop-1-ene, 1,3-dichloroprop-1-ene, and 1,3-dichlorobut-2-ene leads to 5-(chloromethyl)isoxazoles, 4-(chloromethyl)isoxazoles, or to mixtures of both regioisomers. The direction of cycloaddition and reactivity of substrate is determined by the steric hindrance at the terminal carbon atom of the alkene double bond. It has been found that the isomeric products of cycloaddition of nitrile oxides to 1,3-dichloropropene have significantly different dehydrochlorination capabilities. The experimental data on the regioselectivity of cycloaddition and the relative reactivity of substrates are in agreement with the results of quantum chemical calculations.

Recent Advances in C—F Bond Formation from Carbon‐Centered Radicals

Posted on by
Recent Advances in C—F Bond Formation from Carbon-Centered Radicals


Comprehensive Summary

Construction of C—F bonds is a direct and efficient method for introducing fluorine into pharmaceuticals, agrochemicals, and materials. Strategies such as nucleophilic, electrophilic, radical, and transition-metal catalyzed fluorination have been developed to meet the demand of diverse C—F bond formation. Among them, radical fluorination has been witnessed with substantial advancement in a recent decade. Herein, we reviewed methods for formation of C—F bonds with carbon-centered radicals as key intermediates, especially in recent five years. We introduce in the paper with different fluorinating reagents, strategies for radical generation, and application in late-stage functionalization and synthesis of PET tracers. We also indicate the current limitations and propose the direction of the field for the future development.

Key Scientists

Radical fluorination was recognized as an old and uncontrolled reaction that may date back to the time when element fluorine was first mixed with organic compounds by Henri Moissan in 1891. The development of the field was slow in combination with discovery of new fluorinating reagents. Substantial changes took place in 2012, when the first example of carbon radical fluorination with robust and mild fluorinating reagents, such as NFSI and Selectfluor, was reported by the Sammis group. In the same year, Groves, Lectka, Li, and Boger led the pioneering works on aliphatic C—H fluorination, decarboxylative fluorination, and fluorofunctionalization of alkenes in a radical manner. Photoredox catalysis was introduced to radical fluorination in 2013 by the Chen group, which opens up a new avenue for diverse fluorinative transformations. Most of the previous works focus on radical fluorination to form C(sp3)–F bonds. In 2018, the challenging non-directed aromatic C—H fluorination was solved by Ritter and coworkers. Direct arene fluorination with fluoride ion was later disclosed by the Nicewicz group in 2019. There are many other scientists that have also made tremendous contribution to the development of radical fluorination, with too limited space to list them all. We only list those with first discoveries that may point to the new direction of radical fluorination.