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In this study, we examined the photophysical properties of an azacrown–iridium(III) complex while focusing on its interactions with calcium ions (Ca2+). We explored the dynamic processes within the complex combining time-dependent density functional theory (TDDFT) calculations and time-resolved spectroscopies. In the presence of Ca2+, the complex exhibits significant shifts in absorption and emission profiles, from 494 nm to 375 nm, aligning with theoretical predictions. Notably, we observed the ultrafast photo-ejection of Ca2+ within 70 femtoseconds, followed by its recapture in 250 nanoseconds, revealing a 10-million-fold timescale difference between the two phenomena. These behaviors confirm the established photophysical properties of polypyridyl iridium(III) complexes and their intrinsic sensitivity to their surrounding environment. Our comprehensive kinetic analysis highlights the azacrown moiety's competitive binding and photo-release capabilities, suggesting its potential for practical sensing applications. The versatile properties of these iridium(III) complexes offer promising prospects for their application as stimuli-responsive materials and in advanced optoelectronic devices, targeted imaging, and biomedical ion sensors and delivery systems. [ABSTRACT FROM AUTHOR]

The rate constants for the reaction of hydroperoxyl (or perhydroxyl) radical HOO˙ with fifteen phenols and ascorbyl palmitate were measured in acetonitrile at 37 °C by evaluating the effect that the antioxidants had on the rate of autoxidation of γ-terpinene. The HOO˙ radical represents an important reactive species that can be formed by protonation of superoxide anions (O2˙−) or by fragmentation of alkylperoxyl radicals (ROO˙) formed during the autoxidation of pro-aromatic derivatives like γ-terpinene. The phenols investigated in this study include natural compounds like phenolic acids (protocatechuic, caffeic and dihydrocaffeic acids), flavonoids (3-hydroxyflavone, pinobanksin, galangin, catechin, luteolin, quercetin, 6-methoxyluteolin), 4-methylcatechol and antioxidant additives ascorbyl palmitate and the a-tocopherol analogue 2,2,5,7,8-pentamethyl-6-chromanol. The rate constants for the reaction of HOO˙ with the above compounds (kinh) spanned from 1 × 103 M−1 s−1 for the unsubstituted phenol, to 7 × 104 and 9 × 104 M−1 s−1 for 4-methylcatechol and ascorbyl palmitate, respectively. As in a typical Evans–Polanyi plot, the log(kinh) was found to be inversely proportional to the bond dissociation enthalpy of the reactive OH. The comparison of the results with the data reported in the literature shows an unusual kinetic solvent effect that enlightens the unique behavior of HOO˙ and provides a rationale for the superior radical trapping ability of catechols and ascorbyl palmitate. [ABSTRACT FROM AUTHOR]

Free radical-caused oxidative stress can be reduced by various antioxidants. A new and promising type of antioxidant are monosubstituted Meldrum's acids. Herein the first dendritic architecture with 1,3-dioxane-4,6-dione units as surface groups is presented. The compounds were synthesized through the alkylation of phenol, the Knoevenagel condensation and sequential reduction. The antiradical activity (AA) against 1,1-diphenyl-2-picryl hydrazyl (DPPH) for all compounds is 80–90%, and the IC50 varies from 10–35 μM. These data are comparable with vitamin C, t-butylhydroquinone (TBHQ) or vitamin E. The AA against galvinoxyl (GO) increased with the number of surface groups. The AA was comparable with butylated hydroxytoluene (BHT) for compounds with at least two moieties of 1,3-dioxane-4,6-dione. The structure with a flexible glycerol core is highlighted among all the derivatives. Although the AA against DPPH for the glycerol derivative is comparable with those with aromatic cores it is more effective against GO (AA = 95%, IC50 = 60 μM): the AA is greater than for vitamin C and BHT. Thus, a flexible structure seems to be a promising core for elaborating powerful antioxidants with Meldrum's acid surface groups. [ABSTRACT FROM AUTHOR]

Various morphologies of a nano CuAl2O4 fiber microsphere were produced through diverse synthesis situations. The findings showed that the morphology, anatomy, and quantity of the fibers in the CuAl2O4 product are vigorously correlated with the various mechanical pressures, calcination, and hydrothermal processing time. Subsequent research has also shown that the best type of sample offers a variety of catalytic functions for carbocarboxylation of styrenes deploying CO2 and amines by reducing the efficiency of dandelion-like CuAl2O4 fiber anatomy. The reaction is catalyzed by the photoredox catalyst and is adaptable with various amines and styrenes. This approach provides extremely functionalized γ-amino acids in satisfactory efficiencies with extreme regioselectivity. The reported synthesis is the first example of visible light induced synthesis of a γ-amino acid from CO2 and includes several advantages like environmentally benign reaction conditions, a minimum amount of catalyst due to fiber structure, cost effectiveness, operational simplicity, short reaction times, excellent yields, and high atom economy, making it a genuinely green protocol. [ABSTRACT FROM AUTHOR]

There has been growing interest towards clay minerals such as halloysite nanotubes (HNTs) due to their biocompatibility, availability and potential applications in the field of catalysis. Halloysite nanotubes can be modified on both the surfaces to tune their properties explicitly for their innumerable applications in the field of catalysis. The outer surface of halloysite nanotubes is fit for functionalization to develop halloysite catalysts, which creates a valuable provision for endorsing catalytic applications with tunable properties. Furthermore, the occurrence of an empty lumen unlocks new perspectives for the creation of nanostructures with synergistic catalytic effects. This class of compounds displayed promising catalytic performances, and up to now, halloysite-based catalysts have been useful for promoting several chemical transformations. Taking into account the excellent catalytic performance of these nanotubes as catalysts or catalyst supports, the main focus of this review article is to unveil the research on halloysite nanotubes for the preparation of solid acids and their applications in acid catalytic processes. [ABSTRACT FROM AUTHOR]

The synthesis of pure fine chemicals for industrial purposes is one of the most attractive challenges of chemical research. The use of catalytic pathways mediated by palladium nanoparticles (PdNPs) for C–C bond formation is a useful way to obtain these kinds of compounds. To achieve this objective, the PdNPs can be efficiently loaded on a functionalized natural nanostructured support such as halloysite nanotubes (HNTs). Hybrid materials based on thiol functionalized halloysite nanotubes and highly cross-linked imidazolium salts were successfully developed and used for the stabilization of PdNPs. The HNT/Pd hybrids were thoroughly characterized from a physico-chemical point of view and tested as a catalyst in the Suzuki and Heck C–C coupling reactions under microwave irradiation to obtain innovative materials for fine chemicals synthesis. Catalytic tests highlighted the fact that the HNT/Pd hybrids show high performance and full recyclability (up to ten cycles) in both reactions. Regarding the Suzuki reaction, under the best experimental conditions, the remarkable values of a turnover number of 194 000 and a turnover frequency of 3 880 000 h−1 were achieved without metal contamination in the final products. [ABSTRACT FROM AUTHOR]

Fast electron-transfer reactions of newly synthesized (carbazole)n dendrimers (n = 1, 3 and 7), which are connected with C60 with a short linkage, have been investigated in polar benzonitrile. The (carbazole)n–C60 dendrimers were characterized by spectroscopic, computational and electrochemical methods. The geometric and electronic structures of the C60–(carbazole)n dendrimers were examined by using the ab initio B3LYP/6-311G method. The distribution of the highest occupied frontier molecular orbital (HOMO) was found on the carbazole (Cz) entities, whereas the lowest unoccupied molecular orbital (LUMO) was located on the fullerene entity, suggesting the formation of the charge-separated (CS) states (C60Ṗ−–(carbazole)nṖ+). The redox measurements revealed that the charge separation from carbazole to the singlet-excited state of C60 is thermodynamically feasible in polar benzonitrile. The femtosecond transient absorption measurements in the visible-NIR region revealed fast charge separation (∼1011 s−1) from the carbazole to the singlet-excited state of C60 producing the charge-separated states (C60Ṗ−–(carbazole)nṖ+) with lifetimes of 1.25–1.30 ns. The complementary nanosecond transient absorption measurements in the microsecond region revealed that the charge-separated states decayed to populate the triplet states of C60, as well as the ground states. The higher charge separation/charge recombination ratios (∼800) suggested the potential of compounds 1–3 to be light harvesting systems. [ABSTRACT FROM AUTHOR]