Electron-donating Research Articles

Advancements in organic fluorescent materials: unveiling the potential of peripheral group modification in dithienyl-diketopyrrolopyrrole derivatives for one- and two-photon bioimaging.

The quest for novel organic fluorescent materials capable of two-photon absorption (2PA) has intensified in recent years due to their promising applications in biological imaging. Two-photon fluorescence microscopy (2PFM) offers high spatial-temporal resolution, reduced photodamage, and deeper tissue penetration compared to conventional techniques. However, the development of bright two-photon molecular markers remains a challenge, necessitating compounds with high fluorescence quantum yield and 2PA cross-section (σ2PA). Strategies such as increasing π-conjugation have shown promise but are hindered by synthesis complexities and limited biocompatibility. Alternatively, incorporating electron-donating (ED) or electron-withdrawing (EW) peripheral groups in a main structure has emerged as a viable approach, leading to significant enhancements in σ2PA. This study highlights the advantages and challenges of these strategies, emphasizing the importance of exploring new organic compounds and evaluating the efficacy of peripheral groups for advanced two-photon bioimaging applications.

Isochroman-3,4-dione and Tandem Aerobic Oxidation of 4-Bromoisochroman-3-one in the Highly Regio- and Diastereoselective Diels-Alder Reaction for the Construction of Bridged Polycyclic Lactones.

Herein we report two processes facilitated by diisopropylethylamine (DIPEA) for the synthesis of novel bridged polycyclic molecule analogues to natural products. The use of 4-bromoisochroman-3-one initiated an autoxidation reaction, followed by a Diels-Alder cycloaddition in the presence of electron-deficient dienophiles. Mechanistic studies revealed isochromane-3,4-dione as a key intermediate, which undergoes in situ dienolization/dearomatization followed by a [4 + 2] cycloaddition. Subsequently, the synthesis and direct application of isochromane-3,4-diones in the Diels-Alder reaction enabled the development of an alternative method with an enhanced efficiency and improved atom economy. In addition to chalcones, other enones and common electron-poor alkenes, bearing ester, nitro and cyano electron-withdrawing groups (including both terminal, cis acyclic and cyclic alkenes), were successfully reacted. The mechanism was also investigated, and a subsequent reductive ring opening was successfully carried out.

Theoretical Mechanism of Rh-Containing Species Catalyzing the Hydrogenolysis of Lignin Model Compounds Using -CαO-H and -Cα-H Groups as Superior H-Sources.

The hydrogenolysis of lignin model compounds (MCs) into high-value chemicals has received increasing attention, but their catalytic reaction mechanisms are not yet very clear. Here, we report the reaction mechanisms of the hydrogenolysis of MC into 4-acetylanisole (AAL) and guaiacol (GAL) catalyzed by LRuCl3 (L = 4'-(4-methoxyphenyl)-2,2':6',2″-terpyridine) with MC, H2, and 1-phenylethan-1-ol (PEO) as the H-sources in aqueous solution with the Bro̷nsted base (NaOH), at the M06/def2-TZVP, 6-311++G (d,p) theoretical level, namely, RS-Self, RS-H2, and RS-PEO, respectively. After dissociation in NaOH aqueous solution, the LRuCl3 compound can form a stable complex LRh (OH)3 as the initial catalytically active species. Their rate-determining steps are related to the cleavage of the -CαO-H bond in both RS-Self-and RS-PEO, whereas it is associated with the heterolysis of the H-H bond in RS-H2. From NaOH aqueous solution, the OH- ligand of LRh(OH)3 promotes the cleavage of the -CαO-H bond with MC and PEO as H-sources, whereas it advances the heterolysis of the H-H bond with H2 as the H-source, owing to its strong Bro̷nsted basicity. Furthermore, the Rh center of LRh(OH)3 mediates the cleavage of the -Cα-H bond, because of its Lewis acidity. The reaction activity lowers as RS-Self > RS-PEO ≫ RS-H2, which is positively dependent on the protonation degree of the departing H atom. Compounds containing both -CαO-H and -Cα-H groups can act as effective donors for H-sources. In the meantime, the stronger the electron-withdrawing groups they contain, the more pronounced the protonation of the -CαO-H group and the higher the reaction activity in providing H-sources. The present results provide insights into utilizing lignin's own functional groups as a hydrogen source for high-value conversion.

Real-time in situ monitoring as a tool for comparison of electrochemical advanced oxidation processes for the decolourisation of azo and indigoid dyes.

The widespread use of synthetic dyes has led to the release of substantial amounts of dye-contaminated wastewater, posing significant environmental and health concerns. This study focuses on the use of anodic and electrochemically activated persulfate oxidation for the degradation of organic contaminants. Specifically, the structural variations of nine dyes in the indigoid and azo families, and their impact on the efficiency of electrochemical oxidation were analysed. An in situ continuous monitoring apparatus with a UV-visible detector was employed to collect data in real-time. The electrochemically activated persulfate system demonstrated higher efficiency compared to the anodic oxidation approach. In both systems the efficiency of decolourisation was highly dependent on the structure of the pollutant. Electron-withdrawing substituents in direct conjugation with the chromophore, bulky auxochromes, and extended aromatic systems significantly decreased the decolourisation efficiency. Conversely, changing the location of electron-withdrawing groups and adding electron-donating substituents increased the decolourisation efficiency, even overcoming the detrimental effects of bulky groups and extended conjugation. This type of systematic structural comparison study is essential for highlighting the interconnected nature of pollutant structure and degradation speed so that efficient electrochemical oxidation systems can be designed for the treatment of genuine wastewater effluent containing more than one pollutant.

Emission-Tunable B←N Lewis Pair-Functionalized Naphthalenes.

Herein, we simultaneously synthesized three different double B←N Lewis pair-functionalized naphthalenes including the asymmetric BNNY and BNNO and the mirror-symmetric BNNR, via a one-pot method. The annulation modes of the B←N Lewis pairs and the substituents on the boron atoms efficiently tune the molecular frontier orbitals and emission colors. α-Position fusion leads to a significant enhancement of the HOMO energy level and a decrease in the HOMO-LUMO gap, while the electron-withdrawing groups attached to the boron atom make the LUMO energy level more stable. In particular, the LUMO energy level of BNNO is as low as -3.12 eV. BNNY, BNNO, and BNNR emit cyan, green, and red fluorescence at 509, 534, and 620 nm, respectively, with fluorescence quantum yields of 24%, 49%, and 30%, respectively.

Synthesis and Functionalization of Sulfoximine-Bicyclo[1.1.0]butanes: Functionalizable, Tuneable and Cysteine-Selective Chiral Warheads.

Electrophilic covalent warheads with appropriate reactivity and selectivity are crucial to the investigation of protein function and the discovery of therapeutics. Here we report the synthesis of sulfoximine bicyclo[1.1.0] butanes (BCBs) as novel thiol reactive chiral warheads, achieved in one-pot from methylsulfoximines. Unusually the warhead can then be derivatized, keeping the BCB intact, over 3 vectors: i) sulfoximine N-modification instills a broad range of strain-release reactivity; ii) sp2-cross-coupling reactions on aryl-BCB-sulfoximines allows direct diversification, and iii) functionalization of the BCB motif itself is achieved by metalation and trapping with electrophiles. The BCB sulfoximines are shown to react selectively with cysteine including in a protein model (CDK2) under biocompatible conditions. Preliminary data indicate suitability for chemoproteomic applications, and enantioselective cysteine-labelling. The reactivity of sulfoximine BCBs with electron withdrawing groups on nitrogen is comparable to acrylamides with low to moderate reactivity.

Unveiling the influence of open metal sites in quasi ZIF-67 for eco-friendly catalysis of solvent-free aldehyde cyanosilylation

Quasi metal–organic frameworks (Q-MOFs) containing a high density of open metal centers are considered as an effective method of expanding the effectiveness of defective MOF-based catalysts. To achieve this, quasi ZIF-67 (Q-ZIF-67), having large scale structural defects in the framework, is produced through partial deligandation of ZIF-67 under controlled thermal treatment at 310 °C in air. This generates many unsaturated cobalt centers as Lewis acid sites, and results in the coexistence of micro and meso-pores within the Q-ZIF-67 network. Subsequently Q-ZIF-67 was employed in the catalytic cyanosilylation of benzaldehyde with trimethylsilyl cyanide, resulting in the corresponding cyanohydrin within 30 min under solvent free-conditions in air at 40 °C and room temperature with TOF values of 1.62, 1.53 min−1, respectively. The related cyanohydrin product was identified via 1H NMR. Importantly, Q-ZIF-67 displayed a highly efficient heterogeneous Lewis acid catalyst for the cyanosilylation of benzaldehyde compared to the pristine ZIF-67 and related cobalt oxide. Furthermore, investigating the impact of the electron-donating and electron-withdrawing para-substitutions on benzaldehyde revealed that electron-withdrawing groups are suitable for nucleophilic reactions. It was also observed that there was no significant decrease in catalytic activity after five catalytic runs. Thus, the Q-ZIF-67 has considerable potential as environmentally friendly catalyst for wide range of practical application in aldehyde cyanosilylation reactions.

Organogermanium(IV) complexes with O,N,O’-tridentate Schiff bases: synthesis, electrochemical transformations, photophysical properties, and anti/prooxidant activity

A series of novel diorganogermanium(IV) complexes of the type [R2Ge(Ln)] (where R is Et, Ph) with O,N,O’-tridentate redox-active Schiff bases has been synthesized. Compounds 1–7 were characterized by 1H, 13C{1H} NMR, IR spectroscopy, and elemental analysis. The molecular structures of complexes 1, 3, and 7 in crystal state have been established using single-crystal X-ray analysis. The complexes are pentacoordinate mononuclear compounds of germanium(IV). The bond lengths in tridentate ligands correspond to their diamagnetic dianionic forms. The electrochemical properties of complexes 1–7 were studied by cyclic voltammetry. A feature of the electrochemical behavior of target complexes is the ability to form relatively stable reduced/oxidized species as a result of the one-electron transfer. The stability of electrogenerated forms is influenced by both the organic groups at the germanium(IV) atom and the substituents in the Schiff bases. The energy gap (ΔEel) between the boundary redox orbitals obtained from electrochemical data for the complexes varies from 2.43 to 2.60 eV, while the optical ΔE was observed in the narrow range (2.46 – 2.50 eV). Luminescent activity was detected for some complexes in the solution. The maximal values ​​of the relative quantum yield were determined for complexes containing an electron-withdrawing nitro group in the redox-active ligand. In the reaction with ABTS radical cation, compound 1 only possessed the radical scavenging activity while the other compounds are characterized by weak neutralizing properties. The dual anti/prooxidant action was observed for compounds 1–7 in the process of rat liver (Wistar) homogenate lipid peroxidation.

Molecular dynamics study on effects of the synergistic effect of anions and cations on the dissolution of cellulose in ionic liquids

This work systematically explores the interaction between cellulose and various ionic liquids (ILs) formed by the pairing of glycine cations with diverse anions. Results show that the interaction of anions with cellulose decreases in the order of [CH3COO]− > [Im]− > [SCN]− > Cl− > [PF6]−, differing from imidazole-based ionic liquids. The synergistic effect of anions and cations is crucial for cellulose dissolution. Moreover, the electronegativity of anions can enhance their interaction with cellulose. Short alkyl chains (n = 1, 3, 5) reduce hydrogen bonding due to steric hindrance, while longer chains (n = 9) promote diffusion and hydrogen bond formation. The introduction of electron-withdrawing groups to anions weakens their interaction with cellulose, while marginally strengthening the association between cations and cellulose. Overall, a delicate balance among anion-cation-cellulose interactions is essential for effective cellulose dissolution. The obtained results are anticipated to be of significant importance in the rational design of innovative amino acid-based ionic liquids, aiming to achieve efficient cellulose dissolution.

Amplified Light-Induced pKa Modulation with Diarylethene Photoswitches.

The reversible modulation of acidity using molecular photoswitches enables the remote control of a variety of (bio)chemical processes with light. Herein we investigated the structural features that allow amplifying photoinduced pKa variation in phenol-diarylethene conjugates, which toggle between low- and high-acidity states by switching the conjugation between the ionizable moiety and electron-withdrawing groups upon photoisomerization. By tuning the structure of these conjugates, high pKa modulation amplitudes were accomplished that surpass those previously reported.

Insights on exploring the therapeutic potential and structural modification of Tetrandrine.

Tetrandrine (Tet), a bisbenzylisoquinoline alkaloid from Stephania tetrandra, is noted for its diverse pharmacological effects but faces limitations in clinical use due to toxicity, poor solubility, and low bioavailability. Researchers are working to address these issues by developing Tet derivatives with greater therapeutic potential through structural modification. Generally, key modifications include: 1) introducing an aromatic heterocycle or a hydrophobic alkyne unit at the C-5 position can enhance its antitumor activity; 2) adding an amide, sulfonamide, or electron-withdrawing group at the C-14 position can enhance its antitumor activity; 3) changing its structure to a quaternary ammonium salt can alter its solubility and greatly boost its antibacterial activity; 4) structural modification of the C-12-methoxybenzyl motif can enhance its metabolic stability and thus change the activity of the analogs; 5) Tet structural simplification may result in the identification of anticancer lead compounds with novel mechanisms of action. This review systematically summarizes these modification strategies and evaluates the biological activities of Tet derivatives, aiming to guide further optimization and facilitate the discovery of lead analogs with improved efficacy. The future direction and possibility of Tet structural optimization are also considered.

μ-nitrido diiron phthalocyanines: Electron-withdrawing vs electron-donating substituent effect on oxidation reaction catalysis

μ-nitrido diiron phthalocyanines: Electron-withdrawing vs electron-donating substituent effect on oxidation reaction catalysis

N-Boron-pyrrole: A negative charge stabilizing group

We show that the N-boron-pyrrole (B-pyrrole) group stabilizes the negatively charged compounds, despite not being an electron withdrawing group (EWG). Density functional theory (DFT) calculations revealed that this distinctive property of the B-pyrrole group arises from enhanced π-electron delocalization within the pyrrole ring. The effect of B-pyrrole group on the Brønsted and Lewis acidity of various compound classes was examined and compared with common EWGs including F, Cl, Br, CN, NO2. Substitution of pyrrole into the boracyclohexadiene derivatives enhances their acidity by about 1–6 kcal mol−1 while the acidity enhancement due to pyrrole substitution into boric acid was about 17 kcal mol−1. Interestingly, B(Pyrrole)3 exhibited a fluoride affinity comparable to BF3 (∼78 kcal mol−1) and approximately 15 kcal mol−1 higher than that of BH3.

SAR Study on Thiolato-Bridged Triosmium Carbonyl Clusters: Higher Reactivity Does Not Equal Higher Antiproliferative Activity.

A structure-activity relationship study on triosmium clusters of the general formula Os3(μ-H)(μ-SC6H4X)(CO)10 (2-X, where X = o-, m- or p-NH2; o-, m- or p- OH; p-H, -Br, -NO2, -COOH or -CH2COOH) show that their antiproliferative activity is through the cluster core, and the nature and position of the phenyl ring substituent X shows a significant impact on the activity. Clusters with an electron-withdrawing group are more reactive but are thus quickly consumed through reaction with serum, while those with an electron-donating group persists sufficiently to enter the cells and result in higher antiproliferative activity. Interestingly, m-substituted clusters and those with lipophilicity >6.0 also exhibit higher antiproliferative activity. In contrast, o-substituted clusters capable of intramolecular hydrogen bonding have lower cytotoxicity. The cluster 2-m-OH, with higher antiproliferative activity and lower reactivity with serum, is a potential lead compound for further mode of action studies.

Stenhouse Salts: Visible Light Photoswitches for Protic Environments.

Designing photoswitches that have large structural changes, are visible-light responsive, and are compatible with water is a major challenge for moving toward applications in biological systems. Despite the potential for Stenhouse salts to be a water-compatible counterpart to the popular DASA photoswitches, there has not yet been any major investigation into their properties as a photoswitch. Here, we report a series of aniline-based Stenhouse salt (AnSten) photoswitches with electron donating and withdrawing groups. AnSten photoswitches reversibly switch from a visible light absorbing isomer to a visible light transparent isomer upon irradiation with green light. The dark equilibrium and switching kinetics are dependent on the electronics of the aniline. These molecules switch reversibly in common protic solvents including water and hydrogels. Stenhouse salts show significant potential as a visible light active, water compatible, negative photochromic, T-type photoswitch with a large structural change.

Microwave-assisted Reduction of Ketones Using Decaborane in Aqueous Solution

The reduction of ketones to secondary alcohols is an essential reaction in organic chemistry, and various reagents are utilized for this purpose. Herein, we have reported the reduction of ketone using decaborane in conventional as well as microwave-assisted methods in aqueous solution. Different types of aromatic ketones containing distinct functional groups were analyzed. We observed that ketones having an electron-withdrawing group showed a faster reaction rate with higher yield as compared to the ketones with electron-donating groups. Additionally, a comparison between microwave- assisted and conventional synthesis was done by evaluating the total reaction time and percentage yield. The results indicate that microwave-assisted syntheses lead to higher yields within very short reaction times.

Synthesis of Pyranocoumarin through MCRs: Modulation of this Approach as a Function of Substituent Effect Forms the Furocoumarin and 4-Hydroxy-3-styryl Coumarin as a Function of Solvent Effect.

The synthesis of pyranocoumarin is reported from 4-hydroxycoumarin, styrene oxide, and DMSO in the presence of p-TSA·H2O at 110 °C using a three-component reaction. Interestingly, a CH2 moiety from DMSO gets inserted in this reaction to form the pyranocoumarin ring. The plausible mechanism for this interesting reaction was proposed and validated using quantum chemical methods. Interestingly, when the reactions were performed with 7-methoxy-4-hydroxycoumarin and styrene oxides, having an electron-withdrawing group, the reaction followed a two-component pathway, and furocoumarins were obtained in good yields. Switching the solvent from DMSO to CH3CN for the same reactants results in the exclusive formation of the novel monomeric product 4-hydroxy-3-styryl-2H-chromen-2-one (5) instead of the expected furocoumarins. Interestingly, one of the novel monomeric products, 4-hydroxy-3-styryl-2H-chromen-2-one, directly undergoes unexpected cyclization to provide a more interesting and complex tricyclic product. The salient features of the present strategy are its easy handling, commercial availability of starting material, metal-free synthesis, inexpensive catalysts, environmentally benign, and high atom economy.

The Dual-Role of Benzothiadiazole Fluorophores for Enabling Electrofluorochromic and Electrochromic Devices.

Three unsymmetric fluorophores differing in their flanking electron acceptor (-NO2, -CN, -CHO) were investigated for their electrofluorochromism and electrochromism. The emission yield of the -NO2 substituted fluorophore in the solid state was ca. 9-fold less than its -CN and -CHO counterparts. Visible color changes of the fluorophores were observed with an applied potential. The intensity of the near-infrared absorption at ca. 1500 nm formed upon electrochemical oxidation was contingent on the electron-withdrawing group: 2-fold more intense with the -CN substitution than its -H counterpart. The coloration efficiency was upwards of 655 cm2 C-1 and the bleaching kinetics (tb; 22 s) of the NIR band decreased according to -NO2 > -CN > - CHO ≈ -H. The electrochemically generated states could be reversibly formed during 120 min of switching the applied potential. The contrast ratio of the radical cation and the NIR absorption was near unity and 60-82%, respectively. The photoemission intensity of the fluorophores could also be modulated with applied potentials. The collective electrochemically mediated color switching and emission intensity modulation along with their solid-state emission demonstrate that benzothiadiazole fluorophores can play a dual role in chromic devices both as the color switching and photoemission intensity modulating material.

Stabilized Ag nanoparticles loaded smart poly(chitosan-N-isopropylacrylamide-methacrylic acid) hybrid microgels for catalytic reduction of nitroarenes

Nitroarenes (NAs) are one of the most toxic pollutants in the water which cannot easily be eliminated. This challenge can be resolved with conversion of NAs into less toxic aryl amines (AAs) rapidly in the presence of a suitable catalyst. Therefore, poly(chitosan-N-isopropylacrylamide-methacrylic acid) P(ChS-NIPAM-MAA) P(ChNM) microgels were synthesized by microwave irradiations which were then fabricated with silver (Ag) nanoparticles (NPs) by in-situ reduction method and characterized with TEM, XRD, DLS, FTIR, and SEM techniques. The Ag-P(ChNM) hybrid microgels showed pH and temperature responsive behavior along with long time stability. The catalytic efficiency of Ag-P(ChNM) was evaluated for the reduction of 4-nitroaniline (4NiA) under different conditions such as concentration of NaBH4, temperature, content of Ag-P(ChNM), and 4NiA concentration. The Ag-P(ChNM) successfully converted different NAs into their corresponding AAs catalytically with high yields. The highest yield was obtained for 4-nitrophenol (4NiP) (99%) and the lowest for 2,4-dinitrophenylhydrazine (2,4DNiPH) (71%). Electron-withdrawing group containing derivatives of NAs rapidly reduced into AAs than electron-donating substituents. They exhibited excellent catalytic efficiency, stability, recyclability, and maintained their catalytic efficiency over multiple cycles.

Structural optimization of pyridine quinoxaline cobalt (II) catalysts for MMA polymerization based on systematical SCSC transformation study

The Schiff base condensation reaction was adopted to synthesize a series of pyridine-based quinoxaline ligands (L1, L2, L3, L4) using 2-acetylpyridine and 1,2-phenylenediamine aromatic amines with different substituents of –OCH3, –F, -Cl, -Br. Then, four symmetrical dinuclear metal complexes (1–4) were obtained by coordination reaction of the synthesized ligands with CoCl2·6H2O, and six unexpectedly systematic and novel solvent-involved asymmetric mononuclear metal complexes (1A-4A, 3B, 4B) were obtained during single crystals cultivating by solvent diffusion method. The microscopic composition of the complexes were proved by a series of characterizations such as elemental analysis, IR and UV–vis. At the same time, by improving the single crystal culture technology, full crystal sample of compounds was obtained and X-ray single crystal diffraction showed a rare single crystal to single crystal structure transition (SCSC) phenomenon in this study. Furthermore, the catalytic properties of the complexes for MMA polymerization was explored, it was found that the catalytic activity of complexes 1–4 containing different types of substituents on pyridyl quinoxaline ligand was in the order of 1 < 2 <3 < 4, indicating that the complex with an electron-withdrawing substituent showed the higher activity than that of electron-donating substituent. Complexes 1A-4A, 3B and 4B showed higher catalytic activity in MMA polymerization than 1–4, which confirmed that the catalytic activity of mononuclear complexes were generally higher than that of binuclear complexes.