Mechanism of CO2 in promoting the hydrogenation of levulinic acid to γ-valerolactone catalyzed by RuCl3 in aqueous solution.

A Ru-containing complex shows good catalytic performance toward the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) with the assistance of organic base ligands (OBLs) and CO2. Herein, we report the competitive mechanisms for the hydrogenation of LA to GVL, 4-oxopentanal (OT), and 2-methyltetrahydro-2,5-furandiol (MFD) with HCOOH or H2 as the H source catalyzed by RuCl3 in aqueous solution at the M06/def2-TZVP, 6-311++G(d,p) theoretical level. Kinetically, the hydrodehydration of LA to GVL is predominant, with OT and MFD as side products. With HCOOH as the H source, initially, the OBL (triethylamine, pyridine, or triphenylphosphine) is responsible for capturing H+ from HCOOH, leading to HCOO- and [HL]+. Next, the Ru3+ site is in charge of sieving H- from HCOO-, yielding [RuH]2+ hydride and CO2. Alternatively, with H2 as the H source, the OBL stimulates the heterolysis of H-H bond with the aid of Ru3+ active species, producing [RuH]2+ and [HL]+. Toward the [RuH]2+ formation, H2 as the H source exhibits higher activity than HCOOH as the H source in the presence of an OBL. Thereafter, H- in [RuH]2+ gets transferred to the unsaturated C site of ketone carbonyl in LA. Afterwards, the Ru3+ active species is capable of cleaving the C-OH bond in 4-hydroxyvaleric acid, yielding [RuOH]2+ hydroxide and GVL. Subsequently, CO2 promotes Ru-OH bond cleavage in [RuOH]2+, forming HCO3- and regenerating the Ru3+-active species owing to its Lewis acidity. Lastly, between the resultant HCO3- and [HL]+, a neutralization reaction occurs, generating H2O, CO2, and OBLs. Thus, the present study provides insights into the promotive roles of additives such as CO2 and OBLs in Ru-catalyzed hydrogenation.

Theoretical comparison of fructose with methylglucoside for the production of formate and levulinate catalyzed by Brønsted acids in a methanol solution.

For the conversion of fructose/methylglucoside (MG) into both methyl formate (MF) and methyl levulinate (MLev), the C-source of formate [HCOO]- remains unclear at the molecular level. Herein, reaction mechanisms catalyzed by [CH3OH2]+ in a methanol solution were theoretically investigated at the PBE0/6-311++G(d,p) level. For the conversion of fructose into MF and MLev, the formate [HCOO]- comes from the C1-atom of fructose, in which the rate-determining step lies in the reaction of 5-hydroxymethylfurfural (HMF) with CH3OH to yield MF and MLev. The reaction of fructose with CH3OH kinetically tends to generate HMF intermediates rather than yield (MF + MLev). When MG is dissolved in a methanol solution, its O2, O3, and O4 atoms are closer to the first layer of the solvent than O1, O5, and O6 atoms. For the dehydration of MG with methanol into MF and MLev, the formate [HCOO]- stems from the dominant C1- and secondary C3-atoms of MG. Kinetically, MG is ready to yield (MF + MLev), whereas fructose can induce the reaction to remain at the HMF intermediate, inhibiting the further conversion of HMF with CH3OH into MF and MLev. If MG isomerizes into fructose, the reaction will be more preferable for yielding HMF rather than (MF + MLev).

Metagenomic next-generation sequencing for detection of pathogens in children with hematological diseases complicated with infection.

OBJECTIVE: Infection is one of the most common causes of death in children with hematological diseases. Here, we aim to investigate the value of metagenomic next-generation sequencing (mNGS) in the detection of causative pathogens in children with hematological diseases. METHODS: In this retrospective study, specimens from children with hematological diseases, who were admitted to Sun Yat-Sen University between June 2019 and September 2021, were collected for culture and mNGS. RESULTS: A total of 67 pediatric patients were enrolled, and 96 specimens were collected. The positive rate of mNGS was significantly higher than that of culture (57.2% vs 12.5%, P < 0.01). The concordance (90.9%, 10/11) between the positive results of the two methods was high. mNGS detected more cases with Pneumocystis jeroveci, Aspergillus flavus, viruses, and some rare pathogens than culture. Mixed infections were detected by mNGS in 16 cases. Clinical anti-infective treatment was adjusted according to the results of mNGS, the conditions of most patients improved. CONCLUSION: Compared to culture, mNGS shows great advantages in diagnosing bacterial, fungal, viral, and mixed infections in children with hematologic diseases, positively impacting clinical care. mNGS can be used as a complement to culture for pathogen detection.

Coordination of sorbitol to Ga(OTf)3 in the liquid phase: an experimental and theoretical study.

In a solution of sorbitol (SBT) and Ga(OTf)3 compounds, the coordination of sorbitol (SBT) to [Ga(OTf)n]3-n (n = 0-3) has been investigated, using both ESI-MS spectra and density functional theory (DFT) calculations at the M06/6-311++g(d,p), aug-cc-pvtz level using a polarized continuum model (PCM-SMD). In sorbitol solution, the most stable conformer of sorbitol includes three intramolecular H-bonds, i.e., O2H⋯O4, O4H⋯O6, and O5H⋯O3. Through ESI-MS spectra, in a tetrahydrofuran solution of both SBT and Ga(OTf)3 compounds, five main species are observed, i.e., [Ga(SBT)]3+, [Ga(OTf)]2+, [Ga(SBT)2]3+, [Ga(OTf)(SBT)]2+, and [Ga(OTf)(SBT)2]2+. Through DFT calculations, in a solution of sorbitol (SBT) and Ga(OTf)3 compounds, the Ga3+ cation tends to form five six-coordination complexes, i.e., [Ga(η2O,O-OTf)3], [Ga(η3O2-O4-SBT)2]3+, [(η2O,O-OTf)Ga(η4O2-O5-SBT)]2+, [(η1O-OTf)(η2O2,O4-SBT)Ga(η3O3-O5-SBT)]2+, and [(η1O-OTf)(η2O,O-OTf)Ga(η3O3-O5-SBT)]+, which are in good agreement with the experimental observation of the ESI-MS spectra. For both [Ga(OTf)n]3-n (n = 1-3) and [Ga(SBT)m]3+ (m = 1, 2) complexes, the negative charge transfer from ligands to the Ga3+-center plays an important role in their stability, because of the strong polarization of the Ga3+ cation. For [Ga(OTf)n(SBT)m]3-n (n = 1, 2; m = 1, 2) complexes, the negative charge transfer from ligands to the Ga3+-center plays an essential role in their stability, accompanied by an electrostatic interaction between the Ga3+-center and ligands and/or spatial inclusion of ligands toward the Ga3+-center.

Cooperative Catalysis Mechanism of Brønsted and Lewis Acids from Al(OTf)3 with Methanol for ß-Cellobiose-to-Fructose Conversion: An Experimental and Theoretical Study.

Al-containing catalysts, e.g., Al(OTf)3, show good catalytic performance toward the conversion of cellulose to fructose in methanol solution. Here, we report the catalytic isomerization and alcoholysis mechanisms for the conversion of cellobiose to fructose at the PBE0/6-311++G(d,p), aug-cc-pVTZ theoretical level, combining the relevant experimental verifications of electrospray ionization mass spectrometry (ESI-MS), high-performance liquid chromatography (HPLC), and the attenuated total reflection-infrared (ATR-IR) spectra. From the alcoholysis of Al(OTf)3 in methanol solution, the catalytically active species involves both the [CH3OH2]+ Brønsted acid and the [Al(CH3O)(OTf)(CH3OH)4]+ Lewis acid. There are two reaction pathways, i.e., one through glucose (glycosidic bond cleavage followed by isomerization, w-G) and another through cellobiulose (isomerization followed by glycosidic bond cleavage, w-L). The Lewis acid ([Al(CH3O)(OTf)(CH3OH)4]+) is responsible for the aldose-ketose tautomerization, while the Brønsted acid ([CH3OH2]+) is in charge of ring-opening, ring-closure, and glycosidic bond cleavage. For both w-G and w-L, the rate-determining steps are related to the intramolecular [1,2]-H shift between C1-C2 for the aldose-ketose tautomerization catalyzed by the [Al(CH3O)(OTf)(CH3OH)4]+ species. The Lewis acid ([Al(CH3O)(OTf)(CH3OH)4]+) exhibits higher catalytic activity toward the aldose-ketose tautomerization of glycosyl-chain-glucose to glycosyl-chain-fructose than that of chain-glucose to chain-fructose. Besides, the Brønsted acid ([CH3OH2]+) shows higher catalytic activity toward the glycosidic bond cleavage of cellobiulose than that of cellobiose. Kinetically, the w-L pathway is predominant, whereas the w-G pathway is minor. The theoretically proposed mechanism has been experimentally testified. These insights may advance on the novel design of the catalytic system toward the conversion of cellulose to fructose.

high-throughput droplet vitrification of stallion sperm using permeating cryoprotective agents.

Stallion sperm is typically cryopreserved using low cooling rates and low concentrations of cryoprotective agents (CPAs). The inevitable water-to-ice phase transition during cryopreservation is damaging and can be prevented using vitrification. Vitrification requires high cooling rates and high CPA concentrations. In this study, the feasibility of stallion sperm vitrification was investigated. A dual-syringe pump system was used to mix sperm equilibrated in a solution with a low concentration of CPAs, with a solution containing a high CPA concentration, and to generate droplets of a defined size (i.e., ~20 µL) that were subsequently cooled by depositing on an aluminum alloy block placed in liquid nitrogen. Mathematical modeling was performed to compute the heat transfer and rate of cooling. The minimum CPA concentration needed for vitrification was determined for various CPAs (glycerol, ethylene glycol, propylene glycol, dimethyl sulfoxide) and combinations thereof, while effects of droplet size and carrier solution were also identified. Sperm vitrification was eventually done using a glycerol/propylene glycol (1/1) mixture at a final concentration of 45% in buffered saline supplemented with 3% albumin and polyvinylpyrrolidon, while warming was done in standard diluent supplemented with 100 mM sucrose. The sperm concentration was found to greatly affect sperm membrane integrity after vitrification-and-warming, i.e., was found to be 21 ± 12% for 10 × 106 sperm mL-1 and 54 ± 8% for 1 × 106 sperm mL-1. However, an almost complete loss of sperm motility was observed. In conclusion, successful sperm vitrification requires establishing the narrow balance between droplet size, sperm concentration, CPA type and concentration, and exposure time.

Mechanistic study of cellobiose conversion to 5-hydroxymethylfurfural catalyzed by a Brønsted acid with counteranions in an aqueous solution.

The fundamental understanding of the cooperativity of a Brønsted acid together with its anion for cellulose conversion in an aqueous solution is limited at present, in which cellobiose has usually been regarded as a bridge that connects monosaccharides and cellulose. The mechanism of ß-cellobiose conversion to 5-hydroxymethylfurfural (HMF) catalyzed by a Brønsted acid (H3O+) accompanied by counteranions in an aqueous solution has been studied using quantum chemical calculations at the M06-2X/6-311++G(d,p) level under a polarized continuum model (PCM-SMD). For the formation of the first HMF from cellobiose, there are three reaction pathways, i.e., through cellobiulose and glycosyl-HMF (C/H), through cellobiulose and fructose (C/F/H), and through glucose (C/G/H). For these three reaction pathways, the rate-determining steps are associated with the intramolecular [1,2]-H shift in the aldose-ketose tautomerization. C/H is the thermodynamically predominant pathway, while C/G/H is the kinetically dominant pathway. From cellobiose, the origin of the first HMF results kinetically from a small proportion of both C/H and C/F/H and from a large proportion of C/G/H. For the role of the counteranion in the catalytic activity of H3O+, the halide anions (Cl- and Br-) act as promoters, whereas both NO3- anions and carboxylate-containing anions behave as inhibitors. The roles of these anions in ß-cellobiose conversion to HMF can be correlated with their electrostatic potential and atomic number, which may cause a decrease in the relative enthalpy energy and the value of entropy on interacting with the cation moiety. These insights may advance the novel design of sustainable conversion systems for cellulose conversion into HMF.

Efficacy and safety of MAO-B inhibitor versus donepezil in Chinese elderly stroke patients with Alzheimer disease: A potential therapeutic option.

This pilot study designed to evaluate the efficacy and safety of MAO-B inhibitor in comparison with Donepezil (DNP) in elderly Chinese patients with Alzheimer disease (AD). In the present clinical trial, Chinese elderly patients aged ≥65 years with a confirmed diagnosis of AD were enrolled. The patients received MAO-B inhibitor (Selegiline 5 mg) or DNP 10 mg daily (reference) for 6 months. The efficacy and safety data were collected from 120 patients (60 patients in each group) every 3 weeks until 6 months. The primary endpoints were to assess the change in cognitive score from baseline in both the treatment group. The result of the present study showed that the patients treated with MAO-B inhibitor and DNP have similar efficacy and safety profile Considering the clinical benefit, mean (SD) improvement in sign and symptoms was numerically greater in DNP-treated patients as compared to MAO-B inhibitor at endpoint visit (SIB: 12.3 (3.7) vs 11.3 (4.2); AD severity: 14.2 (3.5); CIBIS+/CIBIC: 10.2 (2.7) vs 9.4 (3.2); ADCS-ADL: 14.3 (4.2) vs 13.2 (3.4); MMSE: 14.3 (3.7) vs 12.2 (3.2), P>0.05 respectively for each comparison). However, a statistical difference in terms of clinical benefit was similar between both the treatment groups (p>0.05). Overall, both the study drugs were found comparable in relieving the symptoms of AD (severity score after end of treatment: 14.2 vs 13.4 respectively; p >0.05). This indicates that MAO-B inhibitor is a potential target for the treatment of AD in China. The results of the present study may help to design a large clinical trial to evaluate the efficacy and safety of MAO-B inhibitor in comparison with DNP in AD patients.

Molecular mechanism comparison of decarbonylation with deoxygenation and hydrogenation of 5-hydroxymethylfurfural catalyzed by palladium acetate.

The selective removal of oxygen from 5-hydroxymethylfurfural (HMF) is challenging for the effective utilization of biomass. The catalytic mechanisms of palladium acetate toward the conversion of HMF to furfuryl alcohol (FFA), 5-methylfurfural (5-MF) and 2,5-dihydroxymethyl furan (DHMF) have been theoretically investigated. The decarbonylation of HMF to FFA includes (i) migratory extrusion, (ii) metal-acetate-co-assisted deprotonation, (iii) decarbonylation, (iv) metal-assisted deprotonation, and (v) migratory extrusion and catalyst regeneration. Both hydrogenation and deoxidation of HMF with HCOOH as the H-source involve (i) migratory extrusion, (ii) oxidative addition, (iii) reductive elimination, (iv) metal-assisted deprotonation, and (v) migratory extrusion and catalyst regeneration. The C-H bond cleavage is the crucial reaction step, in which the metal-acetate-co-assisted deprotonation is kinetically more preferable than the oxidative addition. Both FFA and DHMF are kinetically superior to 5-MF. In terms of selectivity, increasing the temperature is beneficial to decarbonylation and decreasing the temperature is advantageous to hydrogenation. The present finding provides molecular-level insight into the functions of both the metal-center and coordinated-ligand in the Pd(OAc)2 catalyst, which may drive the novel design of catalytic systems toward both decarbonylation and hydrogenation reactions.

Regular patterns of the effects of hydrogen-containing additives on the formation of CdSe monomer.

It is unclear at the molecular level why HY (HY = RSH, or ROH, or RNH2) with HPPh2 additives kinetically affects the reaction pathway to the formation of different monomers (Ph2P-SeCd-Y or Ph2P-SeCdSe-Y) in the systhesis of semiconductor nanocrystals. In the present work, it was found that in a [Cd(OA)2 + Se[double bond, length as m-dash]P(C8H17)3 + HPPh2 + HY] mixture, HY behaves as a mediator for the formation of the initial kind of monomer, besides as a hydrogen/proton donor in the release of oleic acid and as an accelerant in the Se-P bond cleavage, which follows the mechanism of hydrogen-shift/nucleophilic-attack. The capability of the HY additive to provide a H-source decreases in the order SePPh2H > RSH > HPPh2 > ROH > RNH2, while the performance of HY to accelerate Se-P bond cleavage decreases in the order HPPh2 > RSH > RNH2 > ROH. The capacity of HY to promote the formation of the Ph2P-SeCd-Y monomer decreases in the order RSH > HPPh2 > ROH > RNH2, while the effect of HY to drive the formation of the Ph2P-SeCdSe-Y monomer decreases in the order HPPh2 > RSH > RNH2 > ROH. The activation strain energy plays a key role in both the Se-P and H-Y bond cleavage, which correlates negatively to the size of the coordinated atom radius. When only HPPh2 is present without other HY species (HY = RNH2, or RSH, or ROH), Ph2P-SeCdSe-PPh2 is preferentially formed. Alternatively, when both HY (HY = RNH2, or RSH, or ROH) and HPPh2 are present, Ph2P-SeCd-Y is favorably formed. For the formation of Ph2P-SeCd-Y (Y = -PPh2, -SR, -OR, and -NHR), SePPh2H embodies the catalytic performance, while HPPh2 serves as the catalyst for the formation of Ph2P-SeCdSe-Y (Y = -NHR or -OR). Our study brings a molecular-level insight into the relationship between the CdSe monomer and the phosphorous-containing side-product, which may advance the rational design and synthesis of quantum dots.

Insights into the Mechanistic Role of Diphenylphosphine Selenide, Diphenylphosphine, and Primary Amines in the Formation of CdSe Monomers.

The formation mechanism of CdSe monomers from the reaction of cadmium oleate (Cd(OA)2) and SePPh2H in the presence of HPPh2 and RNH2 was studied systematically at the M06//B3LYP/6-31++G(d,p),SDD level in 1-octadecene solution. Herein, SePPh2H, HPPh2, and RNH2 act as hydrogen/proton donors with a decreased capacity, leading to the release of oleic acid (RCOOH). The longer the radius of the coordinated atom is, the larger the size of the cyclic transition state is, which lowers the activation strain and the Gibbs free energy of activation for the release of RCOOH. From the resulting RCOOCdSe-PPh2, for the formation of Ph2P-CdSe-PPh2 (G), SePPh2H acts as a catalyst, in which the turnover frequency determining transition state (TDTS) is characteristic of the Se-P bond cleavage. For the formation of RHN-CdSe-PPh2 (H), SePPh2H also serves as a catalyst, in which the TDTS is representative of the N-H bond cleavage. For the formation of Ph2PSe-CdSe-NHR (I), HPPh2 behaves as a catalyst, in which the TDTS is typical of the Se-P and N-H bond cleavage. The rate constants increase as kI < kH < kG, which is in good agreement with our previous experimental observations reported. The present study brings insight into the use of additives such as HPPh2 and RNH2 to synthesize colloidal quantum dots.

Theoretical Study on the Catalytic Reduction Mechanism of NO by CO on Tetrahedral Rh4 Subnanocluster.

The catalytic mechanism of 2NO + 2CO → N2 + 2CO2 on Rh4 cluster has been systematically investigated on the ground and first excited states at the B3LYP/6-311+G(2d),SDD level. For the overall reaction of 2NO + 2CO → N2 + 2CO2, the main reaction pathways take place on the facet site rather than the edge site of the Rh4 cluster. The turnover frequency (TOF) determining transition states are characteristic of the second N-O bond cleavage with rate constant k4 = 1.403 × 10(11) exp (-181 203/RT) and the N-N bond formation for the intermediate N2O formation with rate constant k2 = 3.762 × 10(12) exp (-207 817/RT). The TOF-determining intermediates of (3)N(b)Rh4NO and (3)N(b)Rh4O(b)(NO) are associated with the nitrogen-atom molecular complex, which is in agreement with the experimental observation of surface nitrogen. On the facet site of Rh4 cluster, the formation of CO2 stems solely from the recombination of CO and O atom, while N2 originates partly from the recombination of two N atoms and partly from the decomposition of N2O. For the N-O bond cleavage or the synchronous N-O bond cleavage and C-O bond formation, the neutral Rh4 cluster exhibits better catalytic performance than the cationic Rh4(+) cluster. Alternatively, for N-N bond formation, the cationic Rh4(+) cluster possesses better catalytic performance than the neutral Rh4 cluster.

Mechanistic study of the role of primary amines in precursor conversions to semiconductor nanocrystals at low temperature.

Primary alkyl amines (RNH2) have been empirically used to engineer various colloidal semiconductor nanocrystals (NCs). Here, we present a general mechanism in which the amine acts as a hydrogen/proton donor in the precursor conversion to nanocrystals at low temperature, which was assisted by the presence of a secondary phosphine. Our findings introduce the strategy of using a secondary phosphine together with a primary amine as new routes to prepare high-quality NCs at low reaction temperatures but with high particle yields and reproducibility and thus, potentially, low production costs.

microRNA-29b-3p/sirtuin-1/peroxisome proliferator-activated receptor γ suppress osteogenic differentiation.

Osteoporosis is described as an age-associated impairment of bone formation. microRNA (miR)-29b-3p was thought to be linked to osteoblast differentiation; however, the underlying molecular pathways are yet unknown. The study's goal was to look into the involvement of miR-29b-3p in osteoporosis and the pathophysiological mechanisms. A murine model of estrogen deficiency-induced bone loss was established to simulate postmenopausal osteoporosis. Reverse transcription-quantitative PCR (RT-qPCR) was performed to assess the level of miR-29b-3p of bone tissue. Additionally, miR-29b-3p/sirtuin-1 (SIRT1)/peroxisome proliferator-activated receptor γ (PPARγ) axis in the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) was examined. Osteogenesis-related markers, including alkaline phosphatase (ALP), osteocalcin (OCN), and runt-related transcription factor 2 (RUNX2), were assessed at protein and molecular levels. ALP staining and Alizarin Red staining were used to detect ALP activity and calcium deposition. The ovariectomy group was shown to express miR-29b-3p at higher levels in vitro, and miR-29b-3p mimics suppressed osteogenic differentiation and protein/mRNA expression levels of osteogenesis-related markers in vivo. SIRT1 was identified as a target of miR-29b-3p using luciferase reporter assays. Overexpression of SIRT1 reduced the inhibition of osteogenic differentiation by miR-29b-3p. Rosiglitazone, an activator of PPARγ signaling, was able to reverse the downregulation of the osteogenic differentiation of BMSCs and the protein expression of PPARγ caused by miR-29b-3p inhibitors. The results revealed that osteogenesis was suppressed by miR-29b-3p, which blocks the SIRT1/PPARγ axis. These results suggested that postmenopausal osteoporosis could be treated by targeting miR-29b-3p SIRT1/PPARγ.

The positive feedback loop of MAD2L1/TYK2/STAT3 induces progression in B-cell acute lymphoblastic leukaemia.

PURPOSE: Mitotic arrest deficient 2 like 1 (MAD2L1) has been extensively studied in several malignancies; however, its role in B-cell acute lymphoblastic leukaemia (B-ALL) remains unclear. METHODS: The expression of MAD2L1 was evaluated by real-time quantitative polymerase chain reaction. The biological functions of MAD2L1 in B-ALL were explored through Cell Counting Kit-8 (CCK-8), 5-Ethynyl-2'-deoxyuridine assay (EDU), transwell assay, flow cytometry and xenograft models. The Western blotting and co-immunoprecipitation were utilized to evaluate the interplay between MAD2L1 and the TYK2/STAT3 pathway. The luciferase reporter and chromatin immunoprecipitation (ChIP) assay were employed to identify interactions between STAT3 and MAD2L1. RESULTS: We demonstrated that MAD2L1 was markedly upregulated in B-ALL, and its expression level not only correlated with the relapse and remission of the condition but also with a poor prognosis. MAD2L1 promoted the proliferation, migration and invasion of B-ALL cells in vitro and in vivo, whereas MAD2L1 knockdown had the opposite effects. Mechanistically, MAD2L1 induces the progression of B-ALL by activating the TYK2/STAT3 signaling pathway to phosphorylate. Interestingly, STAT3 induces the expression of MAD2L1 by binding directly to its promoter region, resulting in a positive-feedback loop of MAD2L1/TYK2/STAT3. CONCLUSION: This study uncovered a reciprocal loop of MAD2L1/TYK2/STAT3, which contributed to the development of B-ALL. Therefore, MAD2L1 can be considered a potential diagnostic biomarker as well as a novel therapeutic target for B-ALL.

Hydroxylation mechanism of methane and its derivatives over designed methane monooxygenase model with peroxo dizinc core.

The peroxo dizinc Zn(2)O(2) complex Q coordinated by imidazole and carboxylate groups for each Zn center has been designed to model the hydroxylase component of methane monooxygenase (MMO) enzyme, on the basis of the experimentally available structure information of enzyme with divalent zinc ion and the MMO with Fe(2)O(2) core. The reaction mechanism for the hydroxylation of methane and its derivatives catalyzed by Q has been investigated at the B3LYP*/cc-pVTZ, Lanl2tz level in protein solution environment. These hydroxylation reactions proceed via a radical-rebound mechanism, with the rate-determining step of the C-H bond cleavage. This radical-rebound reaction mechanism is analogous to the experimentally available MMOs with diamond Fe(2)O(2) core accompanied by a coordinate number of six for the hydroxylation of methane. The rate constants for the hydroxylation of substrates catalyzed by Q increase along CH(4) < CH(3)F < CH(3)CN ≈ CH(3)NO(2) < CH(3)CH(3). Both the activation strain ΔE(≠)(strain) and the stabilizing interaction ΔE(≠)(int) jointly affect the activation energy ΔE(≠). For the C-H cleavage of substrate CH(3)X, with the decrease of steric shielding for the substituted CH(3)X (X = F > H > CH(3) > NO(2) > CN) attacking the O center in Q, the activation strain ΔE(≠)(strain) decreases, whereas the stabilizing interaction ΔE(≠)(int) increases. It is predicted that the MMO with peroxo dizinc Zn(2)O(2) core should be a promising catalyst for the hydroxylation of methane and its derivatives.

Activation of propane C-H and C-C bonds by gas-phase Pt atom: a theoretical study.

The reaction mechanism of the gas-phase Pt atom with C(3)H(8) has been systematically investigated on the singlet and triplet potential energy surfaces at CCSD(T)//BPW91/6-311++G(d, p), Lanl2dz level. Pt atom prefers the attack of primary over secondary C-H bonds in propane. For the Pt + C(3)H(8) reaction, the major and minor reaction channels lead to PtC(3)H(6) + H(2) and PtCH(2) + C(2)H(6), respectively, whereas the possibility to form products PtC(2)H(4) + CH(4) is so small that it can be neglected. The minimal energy reaction pathway for the formation of PtC(3)H(6) + H(2), involving one spin inversion, prefers to start at the triplet state and afterward proceed along the singlet state. The optimal C-C bond cleavages are assigned to C-H bond activation as the first step, followed by cleavage of a C-C bond. The C-H insertion intermediates are kinetically favored over the C-C insertion intermediates. From C-C to C-H oxidative insertion, the lowering of activation barrier is mainly caused by the more stabilizing transition state interaction ΔE(≠) (int), which is the actual interaction energy between the deformed reactants in the transition state.

Mechanism of Preferential Hydrogenation of Hydroxymethyl Group to Aldehyde Group in 5-Hydroxymethylfurfural over W2 C-Based Catalyst.

A W4 C2 cluster was used to model a W2 C catalyst with the armchair model of activated carbon support, noted as W4 C2 /AC. Over W4 C2 /AC, the mechanism for the hydrogenation of both -H2 OH and -CHO groups in 5-hydroxymethylfurfural (HMF) was theoretically studied in tetrahydrofuran at GGA-PBE/DNP level. 5-Methylfurfural was the major product from only hydrodehydration of the -CH2 OH group, whereas 2,5-dihydroxymethylfuran was the minor product from the hydrogenation of both -CH2 OH and -CHO groups. The rate-determining steps were concerned with the -C(H)2 -H bond formation for the hydrodehydration of -CH2 OH group, and the -(OH)(H)-H bond formation for the hydrogenation of -CHO group. Kinetically, W-sites promoted the hydrodehydration of -CH2 OH group and inhibited the hydrogenation of -CHO group. This stemmed from the strong Lewis acidity of W-sites, which easily accepted the lone-pair electrons of the oxygen atom in the -C(OH)(H)- group, making -C(OH)(H)-H bond formation hard, and hampering the hydrogenation of the -CHO group.

One-step synthesis of ultrabright amphiphilic carbon dots for rapid and precise tracking lipid droplets dynamics in biosystems.

Fluorescent probes enabling precisely labeling lipid droplets (LDs) in complex systems are highly desirable in life science for studying LDs-related physiological processes and metabolic diseases. However, most of the current LDs fluorophores fail to achieve rapid wash-free LDs labeling, especially in vivo labeling due to their strong hydrophobicity and poor water solubility. We report here one-step synthesis of highly efficient carbon dots (CDs) that feature robust solvatochromic emission, high quantum yield (QY) up to 76.35% in oil, good water solubility and lipophilicity, thus allowing to stain LDs in a bright and selective manner. Detailed characterizations reveal the presence of a well-defined molecule, 2-dimethylamino-5-fluorobenzimidazole in a large amount in CDs. Its D-π-A structure and dimethylamino-induced spatial torsion configuration and extended π-electron conjugation account for solvatochromic emission with high QY. Notably, the CDs can image LDs with many advanced merits (high brightness, ultrafast staining within 10 s, wash-free, excellent LDs specificity, good biocompatibility) and have been successfully applied to monitor cellular LDs dynamics. Moreover, the CDs for the first time allow in situ labeling of LDs and epidermal cell membranes simultaneously in live zebrafish. This work expands the diversity for optical properties and applications of CDs, facilitating the design of new LDs-targeting CDs.

Amniotic membrane for covering high myopic macular hole associated with retinal detachment following failed primary surgery.

AIM: To evaluate the therapeutic effect of amniotic membrane (AM) for covering high myopic macular hole associated with retinal detachment following failed primary surgery. METHODS: Seventeen eyes of 17 patients whose axial length was more than 29 mm suffered from macular hole (MH) or MH associated with retinal detachment (RD), and had previously surgery of pars plana vitrectomy (PPV) with internal limiting membrane (ILM) peeling and silicone oil (SO) tamponade. Half a year after the surgery, optical coherence tomography (OCT) showed that MH did not heal in all 17 eyes and RD was still maintained in 13 eyes of these 17 eyes. We performed SO removal combined with AM covering on macular area and C3F8 tamponade, and phacoemulsification combined with intraocular lens implantation simultaneously cataract eyes. We followed up these patients for one year. RESULTS: In all 17 eyes, SO was removed successfully, MHs were healed and RDs were reattached. One eye (5.89%, 1/17) had AM shifted half a month after surgery and underwent a second surgery to adjust the position of the AM and supplement C3F8. After surgery, the visual acuity (VA) improved in 15 eyes (88.24%, 15/17), no change in two eyes (11.76%, 2/17). No serious complications occurred in all eyes. CONCLUSION: AM covering is helpful to rescue the previous failure surgery of high myopic MH.