The bonding character of AlSO isomers in quartet excited states: Ab initio and density functional theory studies

The geometries and the bonding properties have been predicted for four isomers of AlSO species in the quartet state at density functional theory and coupled cluster [CCSD(T)] all‐electron correlation levels with a large 6‐311+G(3df) basis set. Results have indicated that for the AlSO species in quartet state the lowest state is ⁴A″ state which corresponds to a cyclic structure; the other three isomers (cyclic, bent, and linear) are higher than the lowest state by 26.9 kcal/mol (cyclic ⁴A′), 19.4 kcal/mol (⁴A″), and 28.3 kcal/mol (linear AlSO ⁴Σ), respectively. The calculated dissociation energies for the lowest quartet state species (AlSO: ⁴A″) are 27.3 kcal/mol for the radical mechanism [M(²P)+SO(³Σ^?)] and 154.7 kcal/mol for the mechanism [M(²P)+S(³P)+O(³P)]. Inspection of the bonding character indicates that the cyclic AlSO species in the lowest quartet state (⁴A″) should be classified as thiodioxide (similar to disulfide or dioxide), and the cyclic ⁴A′ state should be classified as thiosuperoxide. The bent Al? SO(⁴A″) species has some thiosuperoxide character, while the linear Al? SO(⁴Σ) structure should be classified as a molecular complex with a weak interaction bonding. However, this thiosuperoxide is not as ionic as LiO₂ and LiSO and is also less ionic than the cyclic AlO₂. In addition, the combinations of Al with SO species exhibit the amphoteric character of Al. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002     

Bimetallic Rod-Packing Metal–Organic Framework Combining Two Charged Forms of 2-Hydroxyterephthalic Acid

Although many rod-packing metal-organic frameworks are known, few are based on ordered heterometallic rod building unit. We show here the synthesis of CPM-76 based on an unprecedented Zn-Mg bimetallic rod with crystallographically distinguishable metal sites. The configuration of the rod offers two types of coordination site with trigonal bipyramidal and octahedral sites selectively occupied by Zn and Mg, respectively. Also unusual is the inter-connection mode between the rods, which is based on dual-charged forms (−3 and −2) of the 2-hydroxyterephthalic acid (H₃OBDC) ligand. Interestingly, each metal site in CPM-76 binds one solvent molecule, leading to a high density of solvent binding sites.     

Solar-Driven Nitrogen Fixation Catalyzed by Stable Radical-Containing MOFs: Improved Efficiency Induced by a Structural Transformation

Herein we present a new viologen-based radical-containing metal–organic framework (RMOF) Gd-IHEP-7, which upon heating in air undergoes a single-crystal-to-single-crystal transformation to generate Gd-IHEP-8. Both RMOFs exhibit excellent air and water stability as a result of favorable radical-radical interactions, and their long-lifetime radicals result in wide spectral absorption in the range 200–2500 nm. Gd-IHEP-7 and Gd-IHEP-8 show excellent activity toward solar-driven nitrogen fixation, with ammonia production rates of 128 and 220 μmol h⁻¹ g⁻¹, respectively. Experiments and theoretical calculations indicate that both RMOFs have similar nitrogen fixation pathways. The enhanced catalytic efficiency of Gd-IHEP-8 versus Gd-IHEP-7 is attributed to intermediates stabilized by enhanced hydrogen bonding.     

Dynamic Features of Transition States for β-Scission Reactions of Alkenes over Acid Zeolites Revealed by AIMD Simulations

Zeolite-catalyzed alkene cracking is key to optimize the size of hydrocarbons. The nature and stability of intermediates and transition states (TS) are, however, still debated. We combine transition path sampling and blue moon ensemble density functional theory simulations to unravel the behavior of C₇ alkenes in CHA zeolite. Free energy profiles are determined, linking π-complexes, alkoxides and carbenium ions, for B₁ (secondary to tertiary) and B₂ (tertiary to secondary) β-scissions. B₁ is found to be easier than B₂. The TS for B₁ occurs at the breaking of the C−C bond, while for B₂ it is the proton transfer from propenium to the zeolite. We highlight the dynamic behaviors of the various intermediates along both pathways, which reduce activation energies with respect to those previously evaluated by static approaches. We finally revisit the ranking of isomerization and cracking rate constants, which are crucial for future kinetic studies.     

Direct Syntheses of Diphenylmethanol Derivatives from Substituted Benzenes and CHCl3 through Friedel-Crafts Alkylation and Post-Synthetic Hydrolysis or Alcoholysis Catalyzed by Alumina

The present study reports an innovative finding that alumina containing water or primary alcohol catalyzes the hydrolysis or alcoholysis, respectively, of the product formed through AlCl₃-mediated Friedel-Crafts alkylation of methyl-substituted benzenes and CHCl₃. The former and later reactions mainly provided hydroxy- and alkoxy-substituted diarylmethanes, respectively, while the reference reactions without alumina provided bisarylchloromethane. This method enables the selective syntheses of diphenylmethanol derivatives with very simple procedures, without expensive reagents and apparatuses. Furthermore, the alumina used in the reaction could be recycled by washing with water and subsequent drying. From the viewpoint of material recycling, this function is very important for the development of sustainable chemical reactions.     

X‐ray Radiation‐Controlled NO‐Release for On‐Demand Depth‐Independent Hypoxic Radiosensitization

Multifunctional stimuli‐responsive nanotheranostic systems are highly desirable for realizing simultaneous biomedical imaging and on‐demand therapy with minimized adverse effects. Herein, we present the construction of an intelligent X‐ray‐controlled NO‐releasing upconversion nanotheranostic system (termed as PEG‐USMSs‐SNO) by engineering UCNPs with S‐nitrosothiol (R‐SNO)‐grafted mesoporous silica. The PEG‐USMSs‐SNO is designed to respond sensitively to X‐ray radiation for breaking down the S N bond of SNO to release NO, which leads to X‐ray dose‐controlled NO release for on‐demand hypoxic radiosensitization besides upconversion luminescent imaging through UCNPs in vitro and in vivo. Thanks to the high live‐body permeability of X‐ray, our developed PEG‐USMSs‐SNO may provide a new technique for achieving depth‐independent controlled NO release and positioned radiotherapy enhancement against deep‐seated solid tumors.     

Bond strengths evaluation of laser ceramic bracket debonding

Ceramic brackets often used for an orthodontic treatment can lead to problems such as enamel tear outs because of their low fracture resistance and high bond strengths. Therefore the aim of our study was to investigate the positive laser radiation effect on bracket debonding. Moreover, the influence of the enamel shape surface under the bracket and laser radiation power on the debonding strength was investigated. The source of the radiation was the longitudinally diode-pumped Tm:YAP laser operating at 1997 nm. To eliminate the tooth surface roughness the flat enamel surface was prepared artificially and the bracket was bonded on it. The debonding was accomplished by Tm:YAP laser radiation with different the power value while recording the temperature rise in the pulp. To simulate the debonding process in vivo the actual bond strength was measured by the digital force gauge. The results were analyzed by scanning electron microscope.     

Separation and characterization of clindamycin phosphate and related impurities in injection by liquid chromatography/electrospray ionization mass spectrometry

A simple high‐performance liquid chromatography/electrospray ionization tandem mass spectrometric (HPLC/ESI‐MS/MS) method has been developed for the rapid identification of clindamycin phosphate and its degradation products or related impurities in clindamycin phosphate injection. Detection was performed by quadrupole time‐of‐flight mass spectrometry (Q‐TOFMS) via an ESI source in positive mode. Clindamycin phosphate and its related substances lincomycin, 7‐epilincomycin‐2‐phosphate, lincomycin‐2‐phosphate, clindamycin B, clindamycin B‐2‐phosphate, and clindamycin were identified simultaneously by HPLC/ESI‐MS/MS results. Based on the MS/MS spectra of their quasi‐molecular ions, the fragmentation pathways of clindamycin phosphate and its related substances were compared and proposed, which are specific and useful for the identification of the lincosamide antibiotics and related impurities. The method was rapid, sensitive and specific and can be used to identify clindamycin phosphate and its related impurities in clindamycin phosphate injection without control compounds. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation of PMMA Foam by Supercritical CO_2 with Ethanol

Supercritical (SC) CO2 can plasticize many amorphous polymers, which reduce the glass transition temperature of the polymers significantly. Recently, it was used as blowing agent to foam amorphous materials such as poly(methyl methacrylate) (PMMA)1,2, polystyrene (PS)3, polycarbonate (PC)4 and poly(ethylene terephthalate) (PET)4. In this foaming process, a polymer is saturated with SC CO2, and followed by rapid depressurization to atmospheric pressure. The microcellular foams can be ob…