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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). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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(η 2O,O -OTf)3], [Ga(η 3O2–O4 -SBT)2]3+, [(η 2O,O -OTf)Ga(η 4O2–O5 -SBT)]2+, [(η 1O -OTf)(η 2O2,O4 -SBT)Ga(η 3O3–O5 -SBT)]2+, and [(η 1O -OTf)(η 2O,O -OTf)Ga(η 3O3–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. [ABSTRACT FROM AUTHOR]

A W4C2 cluster was used to model a W2C catalyst with the armchair model of activated carbon support, noted as W4C2/AC. Over W4C2/AC, the mechanism for the hydrogenation of both −H2OH 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 −CH2OH group, whereas 2,5‐dihydroxymethylfuran was the minor product from the hydrogenation of both −CH2OH and −CHO groups. The rate‐determining steps were concerned with the −C(H)2−H bond formation for the hydrodehydration of −CH2OH group, and the −(OH)(H)−H bond formation for the hydrogenation of −CHO group. Kinetically, W‐sites promoted the hydrodehydration of −CH2OH 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. [ABSTRACT FROM AUTHOR]

Cellobiose is usually preferred as model compound of cellulose to explore its conversion mechanism, in which the first challenge is to acquire the molecular solvation mechanism. The interactions of β-cellobiose with the hydrated Na+ cation and Cl− anion in aqueous solution have been theoretically investigated, using quantum chemical calculations at LC-ωPBE/6-311++G(d,p), aug-cc-pVTZ level under a polarized continuum model (PCM-SMD), together with molecular dynamics stimulation. In aqueous solution, the most stable form of β-cellobiose is syn-ϕ/syn-φ (CB2), including the exocylcic hydroxyl groups and three intramolecular H-bonds. The favorite solvation structure of NaCl is concerned with [Na(H2O)3]+···Cl− ion pair. The Cl− anion interacts with β-cellobiose, favorably affording [ η H 6 , H 2 ′ 2 - CB 2) Cl ] - and [ η H 3 ′ , H 4 ′ 2 - CB 2) Cl ] - with a bridge of OH···Cl···HO interaction. Alternatively, the [Na(H2O)3]+ cation interacts with β-cellobiose, preferably yielding [ η O 3 , O 5 ′ , O 6 ′ 3 - CB 2) Na ] + . Additionally, the [Na(H2O)3]+···Cl− ion-pair interacts cooperatively with β-cellobiose, preferentially producing [ η O 3 , O 5 ′ , O 6 ′ , H 6 , H 2 ′ 3 - CB 2) Na H 2 O 1 ] Cl . For CB2, the reactive sites for the nucleophilic and electrophilic reactions locate at the O5 atom on the reducing end and the H6′ atom on the non-reducing end, respectively. Alternatively, for [ η O 3 , O 5 ′ , O 6 ′ , H 6 , H 2 ′ 3 - CB 2) Na H 2 O 1 ] Cl , the O5 and H6′ atoms should no longer be characteristic of nucleophilicity and electrophilicity. Moreover, [Na(H2O)3]+···Cl− ion-pair can break some intramolecular H-bonds of CB2, which may promote the solvation of β-cellobiose in aqueous solution. It also shields the glycosidic bond by steric effect, which make CB2 not readily hydrated at the glycosidic bond. These functions would alter the reaction pathway in the further degradation of β-cellobiose. This study may advance on the novel design for sustainable conversion system of cellulose into high-added value chemicals. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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=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. [ABSTRACT FROM AUTHOR]

The activation mechanism of CH catalyzed by the homonuclear bimetallic Pt cluster has been detailedly explored on the singlet and triplet potential energy surfaces at BPW91/aug-cc-pvtz, Lanl2tz level. The C-H bond cleavage channel (dehydrogenation and the release of propylene) is kinetically predominant, whereas the C-C bond cleavage channel (demethanation and the release of ethane) should be ruled out. Furthermore, the release of propylene channel is kinetically favorable, while the dehydrogenation channel is thermodynamically preferable. Besides, both the C-H cleavage intermediate (PtHCHb) and the C-C cleavage intermediates (CHHPtCHCH and CHPtPtHCH) are thermodynamically preferred. The C-H cleavage intermediate (PtHCHb) is kinetically favored, while the C-C cleavage intermediates (CHHPtCHCH and CHPtPtHCH) are kinetically hindered. The homonuclear bimetallic Pt cluster toward propane exhibits higher reactivity than the Pt atom, which is in good agreement with the experimental observation. [ABSTRACT FROM AUTHOR]

The reaction mechanism of Pt cluster with CH has been theoretically investigated on the singlet and triplet potential energy surfaces at BPW91/aug-cc-pvtz, Lanl2tz level. The deethylenation channel (PtH + CH) is kinetically favorable with the rate constant (in dm mol s) of $$k = 1.8 \times 10^{6} \exp (-18,277/RT)$$ , while the dehydrogenation channel (PtCH + H) is thermodynamically preferable. The twofold dehydrogenation of ethane to acetylene by Pt cluster is both thermodynamically and kinetically almost equivalent to the single dehydrogenation to ethylene. In addition, both the C-H cleavage intermediate (H)PtCH and the C-C cleavage intermediate CHHPtPtCH are thermodynamically favored in the Pt + CH reaction. Furthermore, (H)PtCH is kinetically preferred, while CHHPtPtCH is kinetically hindered. According to analysis of activation strain model, the stabilizing interaction $$\Updelta E^{ \ne }_{\text{int}}$$ prefers the C-H bond cleavage, while the activation strain $$\Updelta E^{ \ne }_{\text{strain}}$$ favors the C-C bond cleavage. From C-C to C-H bond cleavage, the lowering of activation barrier is mainly caused by the transition states interaction $$\Updelta E^{ \ne }_{\text{int}}$$ becoming more stabilizing. Compared with mononuclear Pt atom, Pt cluster exhibits a more promising catalyst, because the synchronous effect of the atoms of Pt cluster makes two C-H bonds of CH break simultaneously and then kinetically releases CH readily from CH. This result is in good agreement with the experimental observation. Moreover, Pt cluster exhibits more efficient twofold dehydrogenation from ethane. [ABSTRACT FROM AUTHOR]

The gas-phase reaction mechanism of NO and CO catalyzed by Rh atom has been systematically investigated on the ground and first excited states at CCSD(T)//B3LYP/6-311+G(2d), SDD level. This reaction is mainly divided into two reaction stages, NO deoxygenation to generate NO and then the deoxygenation of NO with CO to form N and CO. The crucial reaction step deals with the NO deoxygenation to generate NO catalyzed by Rh atom, in which the self-deoxygenation of NO reaction pathway is kinetically more preferable than that in the presence of CO. The minimal energy reaction pathway includes the rate-determining step about N-N bond formation. Once the NO deoxygenation with CO catalyzed by rhodium atom takes place, the reaction results in the intermediate RhN. Then, the reaction of RhN with CO is kinetically more favorable than that with NO, while both of them are thermodynamically preferable. These results can qualitatively explain the experimental finding of NO, NCO, and CN species in the NO + CO reaction. For the NO deoxygenation with CO catalyzed by rhodium atom, the reaction goes facilely forward, which involves the rate-determining step concerning CO formation. CO plays a dominating role in the RhO reduction to regenerate Rh atom. The complexes, OCRhNO, RhON, RhNNO, ORhN, RhCO, RhNCO, and ORhCN, are thermodynamically preferred. Rh atom possesses stronger capability for the NO deoxygenation than Rh cation. [ABSTRACT FROM AUTHOR]

Objective: To assess the effect of puerarin, a natural flavonoid found in Chinese Pueraria Lobata (Wild.) Ohwi, on promotion of new bone formation. Methods: Osteoblasts isolated from calvarial of newborn rats were cultured in vitro in the presence of puerarin at various concentrations. The viability of osteoblasts and alkaline phosphotase activity and mineral node formation were determined. In addition, osteoblasts seeded in the β-tricaclium phosphate scalfolds as bone substitute were implanted in rat dorsal muscles. Half -of the recipient rats received intramuscular injection of puerarin at 10 mg/(kg·d) for 7 days. Osteogenesis was analyzed by examining the histology after 4 weeks of implantation. Results: The viability of osteoblasts treated with puerarin at either 40 or 80 μmol/L was significantly higher than that of the control ( P<0.05 and P<0.01, respectively). Alkaline phosphatase and mineral modules were significantly increased in osteoblasts cultured with puerarin at 40 or 80 mol/L when compared with that of the untreated cells. The puerarin-treated rats had a higher rate of bone formation in the osteoblast implants than the control rats (6.35% vs. 1.32%, respectively, P<0.05). Conclusion: Puerarin was able to affect osteoblast proliferation and differentiation, and promote the new bone formation in osteoblast implants. [ABSTRACT FROM AUTHOR]

The gas-phase reaction mechanism between palladium monoxide and methane has been theoretically investigated on the singlet and triplet state potential energy surfaces (PESs) at the CCSD(T)/AVTZ//B3LYP/6-311+G(2d, 2p), SDD level. The major reaction channel leads to the products PdCH2 + H2O, whereas the minor channel results in the products Pd + CH3OH, CH2OPd + H2, and PdOH + CH3. The minimum energy reaction pathway for the formation of main products (PdCH2 + H2O), involving one spin inversion, prefers to start at the triplet state PES and afterward proceed along the singlet state PES, where both CH3PdOH and CH3Pd(O)H are the critical intermediates. Furthermore, the rate-determining step is RS-CH3PdOH → RS-2-TS1cb → RS-CH2Pd(H)OH with the rate constant of k = 1.48 × 1012 exp(−93,930/ RT). For the first CH bond cleavage, both the activation strain Δ E≠strain and the stabilizing interaction Δ E≠int affect the activation energy Δ E≠, with Δ E≠int in favor of the direct oxidative insertion. On the other hand, in the PdCH2 + H2O reaction, the main products are Pd + CH3OH, and CH3PdOH is the energetically preferred intermediate. In the CH2OPd + H2 reaction, the main products are Pd + CH3OH with the energetically preferred intermediate H2PdOCH2. In the Pd + CH3OH reaction, the main products are CH2OPd + H2, and H2PdOCH2 is the energetically predominant intermediate. The intermediates, PdCH2, H2PdCO, and t-HPdCHO are energetically preferred in the PdC + H2, PdCO + H2, and H2Pd + CO reactions, respectively. Besides, PdO toward methane activation exhibits higher reaction efficiency than the atom Pd and its first-row congener NiO. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011 [ABSTRACT FROM AUTHOR]

The gas-phase reaction mechanism between rhodium monoxide cation and methane has been investigated on the singlet and triplet state potential energy surfaces at the CCSD(T)/6-311+G(2d,2p), SDD//B3LYP/6-311+G(2d,2p), SDD level. Over the 300-1100 K temperature range, the branching ratios of Rh + CHOH and RhCH + HO are 83.8-52.6% and 16.2-47.4%, respectively, whereas the branching ratio of CHORh + H is so small to be negligible. For the main products (Rh + CHOH and RhCH + HO) formation, the minimum energy reaction pathway involves singlet-triplet spin inversion, and both b-RhCHOH and HORhCH are the energetically preferred intermediates. Alternatively, in the CHORh + H reaction, both b-RhCHOH and HRhOCH are the energetically favorable intermediates, and the main products are Rh + CHOH. In the RhCH + HO reaction, the main products are Rh + CHOH with the energetically predominant intermediate b-RhCHOH. In the reaction of Rh + CHOH, both b-RhCHOH and HRhOCH are the energetically preferable intermediates, and the main products are CHORh + H. Besides, toward methane activation, the cation RhO exhibits higher reaction efficiency than the cation Rh, the neutral RhO, and its first-row congener CoO, and it exhibits lower methanol branching ratio and higher water branching ratio than RhO and CoO. [ABSTRACT FROM AUTHOR]

Objective: To investigate the effects and possible mechanism of Panax Notoginseng saponins (PNS) on oxidative stress-induced damage and apoptosis in bone marrow stromal cells (BMSCs). Methods: BMSCs were isolated and cultured from 2-month-old New Zealand rabbits by the density gradient centrifugation combined with adherent method. The third passage cells were used for subsequent experiments. Oxidative stress was induced in cultured BMSCs by HO (0.1 mmol/L). BMSCs were pretreated with 25-200 μg/mL PNS for 4 h before HO treatment. Proliferation of BMSCs was observed using MTT assay. Alkaline phosphatase (ALP) activity, as an index of early osteoblastic differentiation, was determined with an ALP assay kit. Flow cytometry was used to observe the apoptosis of BMSCs by staining with annexinV-FITC/propidium iodide. Oxidative stress level was examined by reactive oxygen species (ROS) assay. The protein expressions of Bax, Bcl-2 and Caspase-3 in BMSCs were analyzed by Western blotting. Results: PNS had different concentration-dependent effects on proliferation and osteoblast differentiation of BMSCs induced by HO. A PNS concentration of 100 μg/mL was determined as the optimal effective concentration. PNS markedly attenuated HO-induced apoptosis rate from 41.91% to 14.67% ( P<0.01). PNS significantly decreased ROS level induced by HO ( P<0.01). Furthermore, pretreatment with PNS significantly reversed HO-induced inhibition of Bcl-2 expression and augmentation of Bax and Caspase-3 expression ( P<0.01). Conclusion: PNS had a protective effect on oxidative stress-induced damage and apoptosis in cultured rabbit BMSCs through scavenging ROS and regulating the Bcl-2/Bax pathway. [ABSTRACT FROM AUTHOR]