Monthly Archives: January 2024

A Guide to Chemical Reactions Design in Carbon Nitride Photocatalysis

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A Guide to Chemical Reactions Design in Carbon Nitride Photocatalysis

This article provides general guidelines, which are used to design photocatalytic organic transformations using graphitic carbon nitrides. It includes discussion of the local chemical structure of carbon nitride excited state, its redox potentials and the redox potentials of the reagents, and the chemical reactivity of the open-shell intermediates.


Abstract

Graphitic carbon nitride semiconductors are inexpensive and reusable photocatalysts, which are actively studied in organic synthesis. Successful design of photocatalytic reactions is based on the next considerations. i) Thermodynamic feasibility of photoinduced processes, which involve transfer of electrons or electron-proton couples. ii) Redox activity of reagents. iii) Reactivity of the open-shell intermediates generated from the reagents. Herein, we summarize current understanding of how local chemical structure of graphitic carbon nitrides and their redox potentials are used to design photocatalytic reactions. This work intends to serve as a guideline for materials scientists, who are willing to apply their carbon nitride semiconductors in reactions involving organic substrates, and for organic chemists, who are interested to dive into heterogeneous carbon nitride photocatalysis.

Selective O‐Acylation of Enol Silyl Ethers with Acyl Fluorides Catalyzed by Fluoride Ions Derived from Potassium Fluoride and 18‐Crown‐6

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Selective O-Acylation of Enol Silyl Ethers with Acyl Fluorides Catalyzed by Fluoride Ions Derived from Potassium Fluoride and 18-Crown-6

Fluoride ions derived from potassium fluoride and 18-crown-6 efficiently catalyzed the selective O-acylation of a variety of enol silyl ethers with aromatic and aliphatic acyl fluorides to produce unique enol ester derivatives.


Abstract

The fluoride ion-catalyzed selective O-acylation of enol silyl ethers with acyl fluorides using KF and 18-Crown-6 is described herein. This catalytic system facilitated the practical and facile reaction of a variety of enol silyl ethers derived from aromatic/aliphatic ketones and aldehydes with acyl fluorides to afford useful and valuable enol esters.

Structural‐Functional Correlations between Unique N‐terminal Region and C‐terminal Conserved Motif in Short‐chain cis‐Prenyltransferase from Tomato

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Structural-Functional Correlations between Unique N-terminal Region and C-terminal Conserved Motif in Short-chain cis-Prenyltransferase from Tomato

This study demonstrates that the unique N-terminal region and the C-terminal conserved RXG motif of neryl diphosphate synthase function with cooperative structural transitions in the dimer. X-ray crystallography employing massive data collections and a hierarchical clustering analysis revealed a heterogeneity of the active site and polymorphs of substrate binding mode.


Abstract

Neryl diphosphate (C10) synthase (NDPS1), a homodimeric soluble cis-prenyltransferase from tomato, contains four disulfide bonds, including two inter-subunit S−S bonds in the N-terminal region. Mutagenesis studies demonstrated that the S−S bond formation affects not only the stability of the dimer but also the catalytic efficiency of NDPS1. Structural polymorphs in the crystal structures of NDPS1 complexed with its substrate and substrate analog were identified by employing massive data collections and hierarchical clustering analysis. Heterogeneity of the C-terminal region, including the conserved RXG motifs, was observed in addition to the polymorphs of the binding mode of the ligands. One of the RXG motifs covers the active site with an elongated random coil when the ligands are well-ordered. Conversely, the other RXG motif was located away from the active site with a helical structure. The heterogeneous C-terminal regions suggest alternating structural transitions of the RXG motifs that result in closed and open states of the active sites. Site-directed mutagenesis studies demonstrated that the conserved glycine residue cannot be replaced. We propose that the putative structural transitions of the order/disorder of N-terminal regions and the closed/open states of C-terminal regions may cooperate and be important for the catalytic mechanism of NDPS1.

Microwave‐assisted synthesis of benzo[4,5]imidazo[1,2‐a]pyrimidines and pyrano[4,3‐b]pyrans catalyzed by L‐glutamine functionalized magnetic nanoparticles in water:ethanol mixture

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Microwave-assisted synthesis of benzo[4,5]imidazo[1,2-a]pyrimidines and pyrano[4,3-b]pyrans catalyzed by L-glutamine functionalized magnetic nanoparticles in water:ethanol mixture

This work presents a one-pot synthesis of benzo[4,5]imidazo[1,2-a]pyrimidine and pyrano[4,3-b]pyran derivatives using the magnetic Fe3O4@SiO2@L-glutamine nanoparticles as an organo-nanocatalyst. This protocol offers great efficiency, cost-effectiveness and environmental friendliness, with microwave irradiation and multicomponent reactions yielding excellent product yields, shorter reaction times, wider substrate scope, and formation of new compounds.


Abstract

In this work, we report an effective, one-pot syntheses of benzo[4,5]imidazo[1,2-a]pyrimidine and pyrano[4,3-b]pyran derivatives using L-glutamine functionalized nanoparticles (Fe3O4@SiO2@L-glutamine NPs) under microwave irradiation. The organo-nanocatalyst underwent characterization through diverse techniques, including FT-IR, p-XRD, SEM, TEM, EDX, XPS, TGA, and VSM. Microwave irradiation and multicomponent reactions synergistically yield excellent product yields (≈80%–95%) in shorter reaction times (≈6–15 min) with a broader substrate scope. The organo-nanocatalyst displays notable catalytic efficacy, evidenced by high turnover numbers (TON) and turnover frequencies (TOF) across syntheses. This innovative protocol showcases exceptional efficiency, cost-effectiveness, and environmental friendliness, with advantages like minimal reaction conditions, easy catalytic recovery, recyclability, operational simplicity, and the use of eco-friendly solvents.

Charge‐Transfer Modulation of Emissivity in Polarized Diketopyrrolopyrroles

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Charge-Transfer Modulation of Emissivity in Polarized Diketopyrrolopyrroles

Modulation of strength and position of electron-donating substituent directly linked to a diketopyrrolopyrrole core offers an interesting approach towards fine-tuning their photophysics. Depending on the type of cyclic tertiary aromatic amine either Franck-Condon or charge-transfer excited states have the lowest energy. The N-carbazolyl substituent enables DPPs to have very strong fluorescence while other donors such as phenothiazine red-shift the emission at the expense of quantum yield.


Abstract

Strongly polarized donor-acceptor-donor′ diketopyrrolopyrroles, differing in the type of key donor moiety, were designed and synthesized to examine how this affects the non-radiative decay. Dyes possessing less electron-rich N-carbazolyl substituents are characterized by strong yellow emission from a locally excited (LE) state, whereas replacing this donor with more electron-rich N-phenothiazinyl substituent changes the relative position of charge-transfer (CT) and LE states, leading to weaker, reddish-orange fluorescence. As a result, there is solvent-dependent charge-transfer emission shifted to as far as 700 nm. The opening of the intersystem crossing channel to the triplet state possessing CT character is the most likely cause of the fluorescence quantum yield variation in some cases. These results reveal that the fate of molecules in their excited state can be fine-tuned by very small structural changes.

Green Emission of Erbium Doped SYW Phosphors for Optical Thermometry And Solid‐State Lighting

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Green Emission of Erbium Doped SYW Phosphors for Optical Thermometry And Solid-State Lighting

Graphical abstract showing the photoluminescence studies (emission spectra) of Er3+ doped SYW phosphors. The emission spectra recorded under the 380 nm excitation wavelength in the range 500–700 nm


Abstract

A series of Er3+ ions doped Sr9Y2W4O24 (SYW) phosphors have been synthesised using solid-state reaction technique. For optical thermometry and solid state lighting applications, the crystal structure, morphological, and luminescence features of the SYW : Er3+ phosphors were explored. X-ray diffraction (XRD) reveal that synthesized phosphors having single phase with a tetragonal crystal structure and I41/a space group. Scanning electron microscopy (SEM) was used to examine the morphological behaviour and presence of composition elements. The optical bandgap of the phosphor was evaluated using UV-Vis diffuse reflection spectra (DRS). The photoluminescence (PL) emission spectra were captured under 380 nm excitation, and the peak with the maximum intensity was identified at 563 nm ascribed to transition 4S3/2→4I15/2, that emits green color in visible region. The temperature dependent PL (TD-PL) spectra show that SYW phosphor is substantially more thermally stable, having thermal activation energy of about 0.247 eV. Additionally, the fluorescence intensity ratio (FIR) was used to study the optical sensing characteristics of the thermal quenching transitions (2H11/2, 4S3/2) with maximum relative sensitivity (SR) and an absolute sensitivity (SA) being 1.33 % K−1and 0.307 % K−1, respectively. All of the aforementioned findings demonstrate that SYW : Er3+ ions doped phosphors have potential for optical thermometry and other photonic devices.

Nanopore Direct RNA Sequencing for Modified Uridine Nucleotides Yields Signals Dependent on the Physical Properties of the Modified Base

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Nanopore Direct RNA Sequencing for Modified Uridine Nucleotides Yields Signals Dependent on the Physical Properties of the Modified Base


Abstract

Sequencing for RNA modifications with the nanopore direct RNA sequencing platform provides ionic current levels, helicase dwell times, and base call data that differentiate the modifications from the canonical form. Herein, model RNAs were synthesized with site-specific uridine (U) base modifications that enable the study of increasing an alkyl group size, halogen identity, or a change in base acidity to impact the nanopore data. The analysis concluded that increases in alkyl size trend with greater current blockage but a similar change in base-call error was not found. The addition of a halogen series to C5 of U revealed that the current levels recorded a trend with the water-octanol partition coefficient of the base, as well as the base call error. Studies with U modifications that are deprotonated (i. e., anionic) under the sequencing conditions gave broad current levels that influenced the base call error. Some modifications led to helicase dwell time changes. These insights provide design parameters for modification-specific chemical reagents that can shift nanopore signatures to minimize false positive reads, a known issue with this sequencing approach.

Pathogenicity Prediction of GABAA Receptor Missense Variants

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Pathogenicity Prediction of GABAA Receptor Missense Variants


Abstract

Variants in the genes encoding gamma-aminobutyric acid type A (GABAA) receptor subunits are associated with epilepsy. To date, over 1000 clinical variants have been identified in these genes. However, the majority of these variants lack functional studies and their clinical significance is uncertain although accumulating evidence indicates that proteostasis deficiency is the major disease-causing mechanism. Here, we apply two state-of-the-art modeling tools, namely AlphaMissense and Rhapsody to predict the pathogenicity of saturating missense variants in genes that encode the major subunits of GABAA receptors in the central nervous system, including GABRA1, GABRB2, GABRB3, and GABRG2. We demonstrate that the predicted pathogenicity correlates well between AlphaMissense and Rhapsody. In addition, AlphaMissense pathogenicity score correlates modestly with plasma membrane expression, peak current amplitude, and GABA potency of the variants that have available experimental data. Furthermore, almost all annotated pathogenic variants in the ClinVar database are successfully identified from the prediction, whereas uncertain variants from ClinVar partially due to the lack of experimental data are differentiated into different pathogenicity groups. The pathogenicity prediction of GABAA receptor missense variants provides a resource to the community as well as guidance for future experimental and clinical investigations.

Effect of Direct Alkyne Substitution on the Photophysical Properties of Two Novel Octasubstituted Zinc Phthalocyanines

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Effect of Direct Alkyne Substitution on the Photophysical Properties of Two Novel Octasubstituted Zinc Phthalocyanines

The synthesis and characterization of two new alkynyl-substituted phthalonitrile derivatives and their peripherally octasubstituted zinc phthalocyanine (ZnPc) compounds were reported. The aggregation behavior of phthalocyanines was investigated. Fluorescence quantum yields, lifetimes, and quench studies of phthalocyanines were examined. The photophysical parameters obtained for synthesized phthalocyanines were compared with each other and with the unsubstituted ZnPc used as a standard.


Abstract

The synthesis of two novel phthalonitrile derivatives (3–4) bearing ethynylcyclohex-1-ene and ethynylcyclohexane groups and two peripherally octa substituted zinc (II) phthalocyanines (5–6) were prepared. The synthesis of phthalonitrile derivatives was performed with Sonagashira coupling reaction by using palladium-catalyzed. The newly synthesized compounds were characterized by using FT-IR, NMR, mass, and UV-Vis absorption spectroscopy techniques. Aggregation studies of 5 and 6 were performed in various organic solvents and different concentrations in tetrahydrofuran (THF). The photophysical studies of the Pcs were performed in THF to determine the effect of the alkyne groups on the fluorescence of the Pc ring. Substances showing fluorescence properties can be used in practical applications such as to create an image in microscopy. Fluorescence quantum yield (ΦF) and fluorescence lifetime (τF) of 5–6 were calculated. The fluorescence quenching studies of 5–6 were performed by adding the different concentrations of 1,4-benzoquinone (BQ) to a constant concentration of the Pcs in THF and it was found that benzoquinone was an effective quencher. The values of the Stern-Volmer constant (Ksv) and quenching constant (kq) of zinc phthalocyanines (5–6) were examined. All obtained results were compared with each other and with unsubstituted zinc Pc compound used as a reference.