Insight into the mechanisms of the ethylbenzene disproportionation: transition state shape selectivity on zeolites

The direct experimental evidence shows that ethylbenzene disproportionation is a transition state shape selective reaction on zeolites: a bimolecular reaction mechanism via diphenylethane-mediated pathway on large-pore zeolites X and Y (ca. 0.74 nm) and a monomolecular reaction mechanism on medium-pore zeolites ZSM-5 (ca. 0.56 nm) via the ethoxy-mediated intermolecular ethyl group transfer. The lifetime of bulky diphenylethane species was prolonged by a fine-tune of FAU-zeolites, which makes this transition state detectable by 13C MAS NMR spectroscopy. Due to tunable catalytic properties and pore shapes, zeolites are promising catalysts toward emulating the efficiency and selectivity in desired reactions.     

Heliconols A-C: antimicrobial hemiketals from the freshwater aquatic fungus Helicodendron giganteum

[Structure: see text] Cultures of the freshwater aquatic fungus Helicodendron giganteum afforded three new compounds, heliconols A-C (1-3), that contain an unusual reduced furanocyclopentane unit. The structures of these metabolites were assigned by analysis of 1D and 2D NMR data. The absolute configuration of heliconol A (1) was assigned by single-crystal X-ray crystallographic analysis of its dibromobenzoate derivative. Heliconol A showed antifungal and antibacterial activities in disk diffusion assays.     

Insight into binding of alkanes to transition metals from NMR spectroscopy of isomeric pentane and isotopically labeled alkane complexes

Alkane complexes of the type Cp'Re(CO)2(alkane) (Cp' = cyclopentadienyl or (isopropyl)cyclopentadienyl; alkane = isotopomers of n-pentane and cyclopentane) have been characterized using NMR spectroscopy following photolysis of Cp'Re(CO)3 in the appropriate alkane at 163-193 K. In the case of n-pentane, three different complexes are observed corresponding to binding of the three different types of carbon in this alkane. ROESY NMR experiments indicate that these isomeric complexes are slowly interconverting intramolecularly at 173 K. The order of the energetically preferred site of coordination is methylene (C2) approximately central methylene (C3) > methyl (C1) but with a spread of <0.2 kcal mol-1. Isotopic perturbation of resonance (IPR) experiments, conducted on several isotopomers of (i-PrCp)Re(CO)2(1-pentane), showed a large shielding of the 1H NMR chemical shift of the proton in a bound CHD2 moiety (delta -3.62) and CH2D (delta -2.64) compared with that of a bound CH3 moiety (delta -1.99). Likewise, the value of 1JCH for the coordinated methyl group of isotopomers of (i-PrCp)Re(CO)2(1-pentane) reduces in the order CH3 > CH2D > CHD2. This suggests that the alkane coordinates in an eta2-C,H fashion with a rapid exchange of bound hydrogen or deuterium within a methyl or methylene group, and that binding of a hydrogen atom is preferred over a deuterium by an amount of 0.23 +/- 0.03 kcal mol-1.     

Towards two-dimensional electrophoresis mapping of the cerebrospinal fluid proteome from a single individual

We test the ability of state-of-the-art two-dimensional electrophoresis (2-DE) technology to enable the proteome mapping of ante mortem cerebrospinal fluid (CSF) from a single individual. Using the sensitive technologies of a fluorescent protein stain and fluorescence laser scanning of 2-DE gels, combined with matrix-assisted laser desorption/ionization-time of flight/time of flight-mass spectrometry (MALDI-TOF/TOF-MS) for protein identification, a highly detailed 2-DE map of the CSF proteome was created. The 2-DE map contains 600 identified spots representing 82 different proteins. Of the 82 proteins identified, 25 have not appeared in any previously published 2-DE map of CSF, and 11 have not been previously reported to exist in CSF. Most of the identifications originate from an ante mortem CSF sample collected from a single hydrocephalus patient. A supplemental map created from neurologically normal patients is also presented. A webpage with protein identification and scoring information from both maps is available at http://www.leelab.org/csfmap.     

Energetic Insight into the Formation of Solids from Aluminum Polyoxocations

The ε‐Keggin [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ ion (AlAl₁₂⁷⁺) is a metastable precursor in the formation of aluminum oxyhydroxide solids. It also serves as a useful model for the chemistry of aluminous mineral surfaces. Herein we calculate the enthalpies of formation for this aqueous ion and its heterometal‐substituted forms, GaAl₁₂⁷⁺ and GeAl₁₂⁸⁺, using solution calorimetry. Rather than measuring the enthalpies of the MAl₁₂^7/8+ ions directly from solution hydrolysis, we measured the metathesis reaction of the crystallized forms with barium chloride creating an aqueous aluminum solution monospecific in MAl₁₂^7/8+. Then, the contributions to the heat of formation from the crystallized forms were subtracted using referenced states. When comparing the aqueous AlAl₁₂⁷⁺ ion to solid aluminum (oxy)‐hydroxide phases, we found that this ion lies closer in energy to solid phases than to aqueous aluminum monomers, thus explaining its role as a precursor to amorphous aluminum hydroxide phases.     

Insight into the binding of divalent cations to Sepia eumelanin from IR absorption spectroscopy

IR absorption spectroscopy is used to examine the binding of the divalent cations Mg(II), Ca(II), Zn(II) and Cu(II) to melanin granules isolated from the ink sacs of Sepia officinalis. The functional groups of the melanin granules interacting with the bound metal ions are deduced by examining the effect of metal concentration on transition frequencies associated with the COOH, NH and OH moieties of the pigment. The coordinating groups vary with metal ion and with concentration. For the experimental conditions used (initial solution pH of 4, ionic strength of 100 mM and a melanin concentration of 1 mg mL(-1)) Mg(II), Ca(II) and Zn(II) bind to carboxylate groups and Cu(II) binds predominantly to phenolic (catechol) groups However, at a concentration of 10 mM Cu(II) also shows evidence of binding to carboxylate and amine groups, reflecting a secondary binding site that becomes populated as the catechol sites are depleted.     

Transition metal phthalocyanines: Insight into the electronic structure from soft x-ray spectroscopy

Transition metal phthalocyanines (MPc's) are an interesting class of material, and their magnetic and electronic properties are determined by the orbital occupation of the transition metal 3d orbitals incorporated in the molecules center. Thus, the ground state configuration of the transition metal center is very important for a complete understanding of these materials. We present experimental data taken using x-ray absorption and x-ray photoemission spectroscopy together with a theoretical interpretation of MPc series with M=Zn, Cu, Ni, Co, Fe, and Mn. The combination of these methods allows us to narrow down possible dominating ground state configurations and shed a brighter light on the electronic structure of these complexes.     

Insight into the development of electrolytes for aqueous zinc metal batteries from alkaline to neutral

Aqueous zinc metal batteries are considered as promising candidates for next-generation electrochemical energy storage devices, especially for large-scale energy storage, due to the advantages of high-safety,high energy density and low cost. As the bridge connecting cathode and anode, electrolyte provides a realistic operating environment. In alkaline and neutral aqueous zinc metal batteries, issues associated with electrolyte and anode are still intractable. In this review, we reveal the develo...     

Insight into the Behaviour of a Lithium Enolate in Solution

(2S,4S)-2-(tert-Butyl)-5-oxo-1,3-dioxolan-4-acetic acid ( 1 ) was dilithiated to the enolate 2 in toluene and THF with lithium diisopropylamide (LiN(i-Pr)₂) under various conditions. Deuteration experiments with 2 showed that two different stable forms of the enolate could be produced, depending on whether the deprotonation of 1 had been carried out in toluene or THF. The generated (i-Pr)₂NH was coordinated to the enolate and, hence, served as a strong lipophilic solvating agent. LiN(i-Pr)₂ could substitute the amine ligands of the two species to a different extent. THF was partially able to displace (i-Pr)₂NH that solvated the species produced in toluene, but the coordination of the amine to the one produced in THF was quantitive. Correlations with given explanations are made.     

Insight into the mechanism of three component condensation leading to aminomethylenebisphosphonates

Three-component reaction of a primary amine, diethyl phosphite and triethyl orthoformate followed by acid hydrolysis of the adduct provides N-substituted aminomethylenebisphosphonic acids in good yields. Being extremely versatile, it is commonly utilized for preparation of compounds possessing potential antiosteoporotic, antibacterial, anticancer, antiparasitic or herbicidal activity. However, the mechanism of the reaction remains unknown. p-Nitroaniline has been found an interesting tool to shed light on this matter. Its use allowed to separate and identify four intermediates, both non-phosphorus and phosphorus containing, and subsequently suggest the mechanism of the whole process. The acquired knowledge was helpful in explanation the route and the final product structure obtained for more complex reaction proceeding with the use of 4-aminopyridine. Additional alkylation of the pyridine nitrogen atom, leading to unexpected N-(1-alkylpyridinium-4-amino)methylenebisphosphonic acids was unambiguously proved.     

Insight into the solvent effect: a density functional theory study of cisplatin hydrolysis

The solvent effect on reactions in solutions is crucial for many systems. In this study, the reaction barrier with respect to the number of solvent molecules included in the system is systematically studied using density function theory calculations. Our results show that the barriers rapidly converge with respect to the number of solvent molecules. The solvent effect is investigated by calculating cisplatin hydrolysis in several types of solvents. The results are analyzed and a linear relationship between the reaction barrier and the interaction strength of solvent-reactants is found. Insight into the general solvent effect is obtained.     

Insight into the extraction and characterization of cellulose nanocrystals from date pits

This study aims to extract and characterize cellulose nanocrystals (CNCs) from date pits (DP), an agricultural solid waste. Two methods were used and optimized for the cellulose nanocrystals (CNCs) extraction, namely the mechanical stirrer method (CNCs₁) and the Soxhlet apparatus method (CNCs₂) in terms of chemical used, cost, and energy consumption. The results showed that scanning electron microscopy revealed the difference in the morphology as they exhibit rough surfaces with irregular morphologies due to the strong chemical treatments during the delignification and bleaching process. Moreover, transmission electron microscopy analysis for CNCs reveals the true modification that was made through sulfuric acid hydrolysis as it presents cellulose microfibrils with a packed structure. Fourier transform infrared proved that the CNCs were successfully extracted using the two methods since most of the lignin and hemicellulose components were removed. The crystallinity index of CNCs₁ and CNCs₂ was 69.99%, and 67.79%, respectively, and both presented a high yield of CNCs (≥10%). Ultimately, both techniques were successful at extracting CNCs. Based on their cost-effectiveness and time consumption, it was concluded that method 1 was less expensive than method 2 based on the breakdown of the cost of each step for CNCs production.     

The freezing transition of a hard sphere fluid subject to the Percus-Yevick approximation

A classical density functional theory is applied to the calculation of the fluid-solid transition for hard spheres, using the Percus-Yevick (PY) direct correlation function. Three algebraic conditions are established for the coexistence densities and the Lindemann parameter. The terms neglected in the present analysis are small and the present theory, in our eyes, is essentially an exact solution given the PY approximation. No fluid-solid transition is found for the bcc lattice, whereas for expanded fcc lattices, the agreement with previous density functional theory-based theories is good.     

Insight into the Reaction of a Dinuclear Phosphinidene Complex with Nitriles

The phosphinidene complex [Cp*P{W(CO)₅}₂] ( 1 ; Cp*=C₅Me₅) reacted with malononitrile to give the 1,2‐dihydro‐1,3,2‐diazaphosphinine derivative 2 . The reaction of 1 with 1,4‐benzodinitrile gave [1,4‐{{W(CO)₅}₂P‐N=C(Cp*)}₂(C₆H₄)] ( 3 ), the first example of a cumulene‐like aminophosphinidene complex. The reaction of 1 with aniline gave the aminophosphinidene complex [(Ph)N(H)P{W(CO)₅}₂] ( 4 ). To compare the reactivity of benzonitrile and aniline with 1 , the phosphinidene complex 1 was reacted with three different isomers of aminobenzonitrile (2‐, 3‐, and 4‐aminobenzonitrile). These reactions gave an insight into the reaction pathway of 1 with benzonitrile derivatives. Compounds 5 , 6 a , 6 b , and 7 , which are derivatives of 1,2‐dihydro‐1,3,2‐diazaphosphinine or benzo‐2H‐1,2‐azaphospholes, were, as well as all other products, characterized by mass spectrometry, NMR and IR spectroscopy, and X‐ray structure analysis.     

A Thermodynamic and Kinetic Insight into the Pathways Leading to a Highly Functionalized Ketenimine: A Computational Study

All steps of two mechanistic pathways for the synthesized ketenimine through a multicomponent reaction between cyclohexyl isocyanide 1 and acetylen ester 2 in the presence of CH‐acid 3 have been thermodynamically and kinetically evaluated. Intrinsic reaction coordinate calculations were performed for the optimized structures to verify the connectivity of all transition states with reactants and products. The kinetic data showed that the step 1 of the two proposed mechanisms was a rate‐determining step. Also, activation (ΔG^?, ΔH^?, ΔS^?) and thermodynamic (ΔG°, ΔH°, ΔS°) parameters confirmed that the second mechanism for generation product 4b was favored energetically. In addition, the single‐point ¹H and ¹³C NMR (GIAO) chemical shift calculations showed that the product obtained from the approval pathway was according to the experimental data.     

into the Role of Additives in Catalytic Synthesis of Insight Cyclohexylamine from Nitrobenzene

Cyclohexylamine is a versatile intermediate in various chemical industries,which can be expediently synthesized via hydrogenation of aniline or nitrobenzene.However,such processes always suffer from side reactions.Many reports have found that specific additives can suppress the formation of side products,but the mechanism is still not clear.In this work,results suggest that it is the hydroxide ion of alkali metal hydroxides,rather than the cations,which plays a key role in suppressing the side reactions on supported Ru-based catalysts.With the assistance of LiOH,the selectivity toward cy- clohexylamine increased from 85.4% to 100%.Side products,such as dicyciohexylamine,cyclohexanol and N-isopropyl cyclohexylamine,could no longer be detected.Theoretical calculations further disclosed that addition of alkali metal hydroxides inhibited the dissociation of enamine and decreased the adsorption energy of cyclohexylamine,which might be the reasons for a better selectivity.However,the addition of alkali metal hydroxides reduced the activity of nitrobenzene hydrogenation by unfolding the condensation reaction route.To recover or even further enhance the catalytic performance,a second metal component was introduced and the resultant RuNi/AC exhibited a significant improvement in activity compared with Ru/AC.     

Insight into acid-mediated asymmetric spirocyclization in the presence of a chiral diol

Asymmetric spirocyclization based on intramolecular conjugate addition using a combination of a Lewis acid and an optically active cyclohexane-1,2-diol has been studied in connection with 1) the effect of substituents on the cyclohexane-1,2-diol and 2) the effect of substituents on the substrate. This reaction was found to be both thermodynamically and kinetically controlled under restricted conditions.     

Prediction of a structural transition in the hard disk fluid

Starting from the second equilibrium equation in the BBGKY hierarchy under the Kirkwood superposition closure, we implement a new method for studying the asymptotic decay of correlations in the hard disk fluid in the high density regime. From our analysis and complementary numerical studies, we find that exponentially damped oscillations can occur only up to a packing fraction η(?)～0.718, a value that is in substantial agreement with the packing fraction, η～0.723, believed to characterize the transition from the ordered solid phase to a dense fluid phase, as inferred from Mak's Monte Carlo simulations [Phys. Rev. E 73, 065104 (2006)]. Next, we show that the same method of analysis predicts that the exponential damping of oscillations in the hard sphere fluid becomes impossible when λ=4nπσ(3)[1+H(1)]≥34.81, where H(1) is the contact value of the correlation function, n is the number density, and σ is the sphere diameter in exact agreement with the condition, λ≥34.8, which is first reported in a numerical study of the Kirkwood equation by Kirkwood et al. [J. Chem. Phys. 18, 1040 (1950)]. Finally, we show that our method confirms the absence of any structural transition in hard rods for the entire range of densities below close packing.     

Insight into detailed mechanism of the atmospheric reaction of imidogen with hydroxyl: a computational study

The details of reaction mechanism of imidogen (NH) and hydroxyl radicals are explored at the UMP2(FC)/cc–pVDZ and PMP4(FC,SDTQ)/cc–pVQZ//UMP2 + ZPE levels, theoretically. The initial association between NH and OH radicals leads to the formation of the intermediates, NH…OH, HN…HO, cis HNOH, and trans HNOH, through the barrierless and exothermic processes. By starting from the initial intermediates, all possible paths for the formation of H + HNO, H₂ + NO, H₂O + ⁴N, H₂N + ³O, and H + ³HON products are investigated on potential energy surface. The results reveal that H₂O + ⁴N is the main product involved in the mechanism of hydrogen atom abstraction of NH by OH radical through the intermediate NH…OH.