Theoretical Investigation of Water Exchange on the Nanometer-Sized Polyoxocation AlO₄Al₁₂(OH)₂₄(H₂O)₁₂⁷⁺ (Keggin-Al₁₃) in Aqueous Solution

Theoretical Investigation of Water Exchange on the Nanometer-Sized Polyoxocation AlO4Al12(OH)24(H2O)127+ (Keggin-Al13) in Aqueous Solutio

Synthesis of (<i>Z</i>)‑1-Thio- and (<i>Z</i>)‑2-Thio-1-alkenyl Boronates via Copper-Catalyzed Regiodivergent Hydroboration of Thioacetylenes: An Experimental and Theoretical Study

A Cu-catalyzed divergent hydroboration of thioacetylenes has been achieved, providing (<i>Z</i>)-1-thio- or (<i>Z</i>)-2-thio-1-alkenyl boronates in moderate to high yields with excellent regio- and stereoselectivity, by using pinacolborane or bis­(pinacolato)­diboron as the hydroborating reagents, respectively. DFT calculations indicate that the sulfur atom plays a key role in determining the regioselectivity through polarizing the C–C triple bonds and participating in the HOMO orbitals. Moreover, the SR group can serve as a good leaving group, resulting in the concise synthesis of six regio- and stereoisomers of trisubstituted alkenes <b>5</b> via the iterative cross-coupling of C–B and C–S bonds. Clearly, it will be valuable for assembling stereochemically diverse trisubstituted olefins in organic synthesis

Intermolecular Oxidative Radical Addition to Aromatic Aldehydes: Direct Access to 1,4- and 1,5-Diketones via Silver-Catalyzed Ring-Opening Acylation of Cyclopropanols and Cyclobutanols

A novel silver-catalyzed ring-opening acylation of cyclopropanols and cyclobutanols is described. The reaction proceeds under mild and neutral conditions and provides a facile access to nonsymmetric 1,4- and 1,5-diketones in promising yields with broad substrate scope. Mechanistic studies including DFT calculations suggest the involvement of an uncommon water-assisted 1,2-HAT process, which is strongly exothermic and thus promotes addition of carbon radicals to aldehydes. In contrast to traditional reductive radical addition protocols, this work represents the first example of the intermolecular oxidative radical addition to aldehydes, thus offering a novel strategy for the direct synthesis of acyclic ketones from readily accessible aldehydes

Intermolecular Oxidative Radical Addition to Aromatic Aldehydes: Direct Access to 1,4- and 1,5-Diketones via Silver-Catalyzed Ring-Opening Acylation of Cyclopropanols and Cyclobutanols

A novel silver-catalyzed ring-opening acylation of cyclopropanols and cyclobutanols is described. The reaction proceeds under mild and neutral conditions and provides a facile access to nonsymmetric 1,4- and 1,5-diketones in promising yields with broad substrate scope. Mechanistic studies including DFT calculations suggest the involvement of an uncommon water-assisted 1,2-HAT process, which is strongly exothermic and thus promotes addition of carbon radicals to aldehydes. In contrast to traditional reductive radical addition protocols, this work represents the first example of the intermolecular oxidative radical addition to aldehydes, thus offering a novel strategy for the direct synthesis of acyclic ketones from readily accessible aldehydes

Density Functional Theory Study on Aqueous Aluminum−Fluoride Complexes: Exploration of the Intrinsic Relationship between Water-Exchange Rate Constants and Structural Parameters for Monomer Aluminum Complexes

Density functional theory (DFT) calculation is carried out to investigate the structures, 19F and 27Al NMR chemical shifts of aqueous Al−F complexes and their water-exchange reactions. The following investigations are performed in this paper: (1) the microscopic properties of typical aqueous Al−F complexes are obtained at the level of B3LYP/6-311+G**. AlOH2 bond lengths increase with F− replacing inner-sphere H2O progressively, indicating labilizing effect of F− ligand. The Al−OH2 distance trans to fluoride is longer than other AlOH2 distance, accounting for trans effect of F− ligand. 19F and 27Al NMR chemical shifts are calculated using GIAO method at the HF/6-311+G** level relative to F(H2O)6− and Al(H2O)63+ references, respectively. The results are consistent with available experimental values; (2) the dissociative (D) activated mechanism is observed by modeling water-exchange reaction for [Al(H2O)6-iFi](3−i)+ (i = 1−4). The activation energy barriers are found to decrease with increasing F− substitution, which is in line with experimental rate constants (kex). The log kex of AlF3(H2O)30 and AlF4(H2O)2− are predicted by three ways. The results indicate that the correlation between log kex and AlO bond length as well as the given transmission coefficient allows experimental rate constants to be predicted, whereas the correlation between log kex and activation free energy is poor; (3) the environmental significance of this work is elucidated by the extension toward three fields, that is, polyaluminum system, monomer Al-organic system and other metal ions system with high charge-to-radius ratio

Density Functional Investigation of the Water Exchange Reaction on the Gibbsite Surface

The water exchange reactions on the gibbsite surface have been investigated by density functional calculations (B3LYP/6-31G(d) level) combining the supermolecular model and PCM model in this paper, and the water exchange rate constants on the gibbsite surface have also been predicted. In the proposed reaction pathways, the clusters Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are used as the models of gibbsite surface and protonated gibbsite surface respectively to examine the effect of protonation of gibbsite surface on the water exchange rate constants. The activation energy barriers ΔEs≠(aq) for Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are 28.6 and 27.2 kJ mol−1, respectively. The reaction energies ΔEs(aq) for Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are 2.9 and 14.4 kJ·mol−1, respectively, indicating that hexacoordinate aluminum in the gibbsite surface is more stable. The log kTST for Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are 6.5 and 7.5 respectively, and the log kex calculated by the given transmission coefficient for Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are 2.4 and 3.4 respectively, indicating that the protonation of gibbsite surface promotes the water exchange reaction of gibbsite surface and accelerates the dissolution rate of gibbsite. The relationship between the calculated free energy and experimental rate constants was explored, and according to this relationship, the log kex for Al6(OH)18(H2O)60 and Al6(OH)12(H2O)126+ are 2.5 and 3.1 respectively, close to the corresponding values calculated by the given transmission coefficient. The water exchange rate constant of gibbsite surface is close to those of K−MAl12(M = Al, Ga, and Ge) polyoxocations, but deviates from that of Al(H2O)63+, implying that the same reactions with similar structure have similar water exchange rate constants

Si-Doped Carbon Quantum Dots: A Facile and General Preparation Strategy, Bioimaging Application, and Multifunctional Sensor

Heteroatom doping of carbon quantum dots not only enables great improvement of fluorescence efficiency and tunability of fluorescence emission, but also provides active sites in carbon dots to broaden their application in sensor. Silicon as a biocompatible element offers a promising direction for doping of carbon quantum dots. Si-doped carbon quantum dots (SiCQDs) were synthesized through a facile and effective approach. The as-prepared Si-doped carbon quantum dots possess visible fluorescence with high quantum yield up to 19.2%, owing to fluorescence enhancement effect of introduced silicon atoms into carbon dots. The toxicity test on human Hela cells showed that SiCQDs have lower cellular toxicity than common CQDs, and bioimaging experiments clearly demonstrated their excellent biolabelling ability and outstanding performance in resistance to photobleaching. Strong fluorescence quenching effect of Fe­(III) on SiCQDs can be used for its selective detection among general metal ions. Specific electron transfer between SiCQDs and hydrogen peroxide enables SiCQDs as a sensitive fluorescence sensing platform for hydrogen peroxide. The subsequent fluorescence recovery induced by removal of hydrogen peroxide from SiCQDs due to formation of the stable adducts between hydrogen peroxide and melamine was taken advantage of to construct effective sensor for melamine

Photophysical Tuning of Organic Ionic Crystals from Ultralong Afterglow to Highly Efficient Phosphorescence by Variation of Halides

Manipulation of photophysical properties of pure organic materials via simple alteration is attractive but extremely challenging because of the lack of valid design strategies for achieving ultralong afterglow or efficient room-temperature phosphorescence. Herein, we report a first photophysical manipulation of organic ionic crystals from ultralong afterglow to highly efficient phosphorescence by variation of halides in the crystals. Crystal structural analysis reveals ultralong organic afterglow of tetraphenylphosphonium chloride is promoted by strong intermolecular electronic coupling in the crystal, and theoretical analysis demonstrates that the tremendous boost of the phosphorescence of tetraphenylphosphonium iodide is caused by the coupling effects of significant heavy atom effect from iodine atoms and a small energy difference between the first singlet and triplet states. This work contributes to regulating long-lived emissive behaviors of pure organic ionic crystals in a controlled way and will promote the development of optical switches controlled by external stimuli

Functionalized Carbon Quantum Dots with Dopamine for Tyrosinase Activity Monitoring and Inhibitor Screening: In Vitro and Intracellular Investigation

Sensitive assay of tyrosinase (TYR) activity is in urgent demand for both fundamental research and practical application, but the exploration of functional materials with good biocompatibility for its activity evaluation at the intracellular level is still challenging until now. In this work, we develop a convenient and real-time assay with high sensitivity for TYR activity/level monitoring and its inhibitor screening based on biocompatible dopamine functionalized carbon quantum dots (Dopa-CQDs). Dopamine with redox property was functionalized on the surface of carbon quantum dots to construct a Dopa-CQDs conjugate with strong bluish green fluorescence. When the dopamine moiety in Dopa-CQDs conjugate was oxidized to a dopaquinone derivative under specific catalysis of TYR, an intraparticle photoinduced electron transfer (PET) process between CQDs and dopaquinone moiety took place, and then the fluorescence of the conjugate could be quenched simultaneously. Quantitative evaluation of TYR activity was established in terms of the relationship between fluorescence quenching efficiency and TYR activity. The assay covered a broad linear range of up to 800 U/L with a low detection limit of 7.0 U/L. Arbutin, a typical inhibitor of TYR, was chosen as an example to assess its function of inhibitor screening, and positive results were observed that fluorescence quenching extent of the probe was reduced in the presence of arbutin. It is also demonstrated that Dopa-CQD conjugate possesses excellent biocompatibility, and can sensitively monitor intracellular tyrosinase level in melanoma cells and intracellular pH changes in living cells, which provides great potential in application of TYR/pH-associated disease monitoring and medical diagnostics

Photophysical Tuning of Organic Ionic Crystals from Ultralong Afterglow to Highly Efficient Phosphorescence by Variation of Halides

Manipulation of photophysical properties of pure organic materials via simple alteration is attractive but extremely challenging because of the lack of valid design strategies for achieving ultralong afterglow or efficient room-temperature phosphorescence. Herein, we report a first photophysical manipulation of organic ionic crystals from ultralong afterglow to highly efficient phosphorescence by variation of halides in the crystals. Crystal structural analysis reveals ultralong organic afterglow of tetraphenylphosphonium chloride is promoted by strong intermolecular electronic coupling in the crystal, and theoretical analysis demonstrates that the tremendous boost of the phosphorescence of tetraphenylphosphonium iodide is caused by the coupling effects of significant heavy atom effect from iodine atoms and a small energy difference between the first singlet and triplet states. This work contributes to regulating long-lived emissive behaviors of pure organic ionic crystals in a controlled way and will promote the development of optical switches controlled by external stimuli