FRONTIER-ORBITAL RING CURRENTS AND THE ANNULENE ANALOGY

Perimeter and ring currents induced in planar monocycles and polycycles by perpendicular magnetic fields are commonly taken as diagnostic of aromaticity and antiaromaticity in these systems. Diatropic π currents are associated with aromaticity, paratropic with its opposite. The ipsocentric method is an accurate and economical way of calculating ab initio current-density maps. In π systems it provides a natural interpretation of ring currents in terms of nonredundant orbital contributions, governed by simple symmetry rules for π–π* virtual excitations and dominated by the frontier electrons. Thus, in planar [4n + 2] monocycles, the product of π HOMO and π* LUMO symmetries includes that of the in-plane translations and leads to a 4-electron diatropic current. In planar [4n] monocycles, this product includes the symmetry of the in-plane rotation and leads to a 2-electron paratropic current. Perturbation arguments based on the monocycle explain the opposite senses of the π ring currents in naphthalene (diatropic) and pentalene (paratropic) as consequences of their different frontier-orbital symmetry products. In a generalization to heterocycles, ring current maps for benzotriazole (BtH), its conjugate base (Bt^?) and the cation (Bt⁺) are calculated at an ab initio level. The diatropic current of the two 10π systems and the paratropic current of the 8π system are rationalized in terms of the perturbed-annulene orbital model, giving an explanation of the applicability of simple electron counting in these cases: where the frontier-orbital structure remains close to that of the [4n+ 2]/[4n] annulene, so does the current-density map.     

Nucleus-Independent Chemical Shift Criterion for Aromaticity in Some of the Corannulene Derivatives as Carbon Nanostructure: Effect of Substituent Groups on Aromaticity

Substitution of the peripheral H atoms in the corannulene molecule as a carbon nanostructure by OH, CH₃, NH₂, and NO₂ groups was done and the obtained structures were optimized employing MP2/6-31G(d) level of theory. Calculations of the nucleus-independent chemical shift (NICS) were performed to analyze the aromaticity of the corannulene rings and its derivatives upon substitution at B3LYP/6-311+G(d) level of theory. Comparison of NICS(1)_zz for concave and convex sides of corannulene derivatives indicated that substitution of H atoms in the corannulene molecule with OH, CH₃, NO₂, and NH₂ groups leads to decreasing of the aromaticity character of corannulene. We discussed about two efficient factors on the aromaticity and antiaromaticity of polycyclic aromatic compounds: electron donating or withdrawing and resonance effects. We showed that NICS values in all structures are strongly dependent on the type, number, and position of the substituted groups.     

Double bond migration of eugenol to isoeugenol over as-synthesized hydrotalcites and their modified forms

Double bond migration of eugenol to isoeugenol was carried out over as-synthesized hydrotalcites and their modified forms. The catalysts of general formula M(II)M(III)-xHT with carbonate as interlayer anion were synthesized by a co-precipitation method where M(II)=Mg, Ni, Co, Zn, Cu and M(III)=Al, Cr, Fe, La, V with varying M(II)/M(III) atomic compositions (here represented as ‘x’). The synthesized catalysts were tested for the reaction. Among various binary hydrotalcites investigated, Mg and Ni offered maximum activity, wherein MgAl-4HT showed nearly 73% conversion and NiAl-4HT showed 75% conversion with 15:85 cis:trans ratio at 200 °C with a substrate:catalyst mass ratio of 2:1. The other binary systems showed poor activity (less than 5%) under similar reaction conditions. The preservation of HT-like lattice is presumed to be crucial for this reaction, as evidenced from “in situ” powder X-ray diffraction (PXRD) and thermogravimetric (TG) analysis measurements. Variation in the trivalent metal ions indicated a maximum activity for Al, followed by Fe and Cr, in accordance with the crystallinity. A co-operative phenomenon was noted when both Mg and Ni were present together in a ternary MgNiAl-HT, however the activity varied with Mg/Ni atomic composition. Solvent variation studies indicated that more polar solvents favored the reaction. Significant promotional influence in the activity was noted with alkali and ruthenium impregnation on MgAl-4HT, wherein maximum activity was showed by catalysts modified with Cs (among the alkali metal ions studied) and higher content of ruthenium. Comparison of the activity with conventional bases such as KOH and KOBu^t revealed a superior performance of HT-based catalysts, although conventional bases had been used under stoichiometrically excess conditions (around 9% conversion for KOH with 1:10 and 5% conversion for KOBu^t with 1:3 substrate:catalyst mole ratio). The good performances of these catalysts encouraged further studies. A reaction mechanism involving the hydroxyl group of HT-like lattice is proposed for this isomerization reaction.     

Ab Initio Prediction of Boron Compounds Arising from Borozene: Structural and Electronic Properties

Structure and electronic properties of two unusual boron clusters obtained by fusion of borozene rings have been studied by means of first principles calculations based on the generalized-gradient approximation of the density functional theory. Moreover, a semiempirical tight-binding model has been appropriately calibrated for transport calculations on these clusters. Results show that the pure boron clusters are topologically planar and characterized by (3c–2e) bonds, which can explain, together with the aromaticity (estimated by means of NICS), the remarkable cohesive energy values obtained. Such feature makes these systems competitive with the most stable boron clusters to date. The energy gap values indicate that these clusters possess a semiconducting character, while when the larger system is considered, zero-values of the density of states are found exclusively within the HOMO–LUMO gap. Electron transport calculations within the Landauer formalism confirm these indications, showing semiconductor-like low bias differential conductance for these structures. Differences and similarities with carbon clusters are highlighted in the discussion.     

Theoretical Modeling of the Nucleation and Growth of Aluminium Films Thermally Evaporated onto Poly(ethylene terephthalate) Substrate

The interface between aluminium and poly(ethylene terephthalate) (PET) has been studied using the density functional theory (DFT) formalism within the local density approximation (LDA). An examination of the charge transfers during Al bonding with the polymer functional groups provides a better understanding of the nucleation of the metallic film. Indeed, when reacting with the doubly-bonded oxygen atom of the ester function, the metal particle induces strong modifications in the highest occupied molecular orbitals (HOMOs) as well as in the lowest unoccupied molecular orbitals (LUMOs) of the PET. The shape of the HOMO, HOMO-3 and HOMO-4 of the Al/PET complex confirms the evolution of the phenyl structure to a quinoid structure. We emphasise the extent to which the reactivity of the PET can be modified after Al interaction with the ester function. After losing their aromaticity, the phenyl rings of the polymer are no longer available for subsequent interactions. Hence, we propose that the Al film will then grow following a compact cubic stacking on top of Al atoms already fixed on the ester functions.     

Theoretical Modeling of the Nucleation and Growth of Aluminium Films Thermally Evaporated onto Poly(ethylene terephthalate) Substrate

The interface between aluminium and poly(ethylene terephthalate) (PET) has been studied using the density functional theory (DFT) formalism within the local density approximation (LDA). An examination of the charge transfers during Al bonding with the polymer functional groups provides a better understanding of the nucleation of the metallic film. Indeed, when reacting with the doubly-bonded oxygen atom of the ester function, the metal particle induces strong modifications in the highest occupied molecular orbitals (HOMOs) as well as in the lowest unoccupied molecular orbitals (LUMOs) of the PET. The shape of the HOMO, HOMO-3 and HOMO-4 of the Al/PET complex confirms the evolution of the phenyl structure to a quinoid structure. We emphasise the extent to which the reactivity of the PET can be modified after Al interaction with the ester function. After losing their aromaticity, the phenyl rings of the polymer are no longer available for subsequent interactions. Hence, we propose that the Al film will then grow following a compact cubic stacking on top of Al atoms already fixed on the ester functions.     

Isomeric Structures of Furoxan-Fused [2,2]paracyclophane—A DFT Study

The present study theoretically deals with furoxan-fused [2,2]paracyclophane systems and some structures possibly involved in their isomerization processes. These intermediate structures are certain di- and tetra-nitroso derivatives and systems having dioxadiazatidine ring(s). Computationally, B3LYP/6–31G(d,p) level of density functional theory has been employed. Certain properties of the systems, such as geometries, energies, and aromaticity of the benzenoid rings, are harvested and discussed.     

Influence of Particle Size and Mixing Technology on Combustion of HMX/Al Compositions

In this work, two widely used components of high‐energy condensed systems – HMX and aluminium – were studied. Morphology, thermal behaviour, chemical purity and combustion parameters of HMX as a monopropellant and Al/HMX as a binary system were investigated using particles of different sizes. It was shown that in spite of the differences in composition and particle size, combustion velocities are almost identical for micrometer‐sized HMX (m‐HMX) and ultrafine HMX (u‐HMX) monopropellants under pressure from 2 to 10 MPa. Replacement of the micrometer‐sized aluminium with ultrafine one in the system with m‐HMX leads to a burning rate increase by a factor of 2.5 and the combustion completeness raise by a factor of 4. Two mixing techniques to prepare binary Al/HMX compositions were applied: conventional and ‘wet’ technique with ultrasonic processing in liquid. Applying wet mixing results in a burning rate increase of 18% compared to the conventional mixing for systems with ultrafine metal. The influence of the component's particle size and the composition microstructure on the burning rate of energetic systems is discussed and analysed.     

Hydrothermal Solidification of Kaolinite–Quartz–Lime Mixtures

The strength development of hydrothermally solidified kaolinite–quartz–lime systems with kaolinite as the aluminum source was studied. The starting materials were mixed so that the Ca/(Si + Al) atomic ratio was in the range 0.23 to 0.25, and the Al/(Si + Al) ratio was between 0 to 0.50. Specimens were formed by uniaxial pressing and hydrothermal treatment under saturated steam pressure at 200°C for 2 to 20 h. For quartz-rich systems with Al/(Si + Al) = 0 and 0.05, strength development by the formation of calcium silicate hydrates, such as C–S–H and tobermorite (Ca₅(Si₆O₁₈H₂)·(4H₂O), was observed. On the other hand, in the case of kaolinite-rich systems with Al/(Si + Al) = 0.24 to 0.50, strength development by the formation of hydrogarnet (Ca₃Al₂(SiO₄)(OH)₈) was recognized, resulting in flexural strengths between 15 to 20 MPa. It is proposed that strength development is related to the formation of mesopores (∼0.04 μm) that accompanied formation of the hydrogarnet.     

Pile electrique a anode d'aluminium—I electrolyte acide

An acid electrolyte (pH ) 3) for an aluminium primary battery has been studied. It contains: Al(CIO₄)₃. 1 M: AlCl₃. $\text{1}\text{30}$ M; (NH₄)₂CrO₄, $\text{1}\text{50}$ M. The performance of three binary aluminium alloys AlZn 2%; AlZn 5%; AlGa 0·3% are compared. Capacity of Al primary battery made with Al 2% is twice that of a conventional Leclanché cell on continuous discharge test. Unfortunately CrO⁼₄ disappears in presence of MnO₂ which is prejudicial to the good conservation of the aluminium cell.     

C_(24)团簇异构体的量子化学计算

采用密度泛函B3LYP方法在6-31G~*水平上对设计的3种新型笼状C_(24)异构体进行了计算,从能量分析发现这3种异构体均为稳定的笼状团簇,其中部分碳原子呈现局部共轭,共轭程度不大.除C_(24)-38具有芳香性外,其他结构均是反芳香性的.根据计算所得结合能可知,其热力学稳定性顺序为:C_(24)-56＞C_(24)-46＞C_(24)-38＞C_(24)-68.C_(24)团簇HOMO-LUMO能隙△ε＞5 eV,是绝缘体,而较大的△ε,电子难以激发,有利于体系的稳定.     

Phase development in metal-dropped silicon oxycarbides under water vapor and argon hybrid atmosphere

In this study, metal-modified silicon oxycarbides ceramics (SiOC/M, M = Fe, Al, and Zr) were fabricated, and the thermal stability of the SiOC/M (M = Fe, Al, and Zr) ceramics was investigated under the water-vapor- argon hybrid atmosphere. The phase and microstructural analysis showed that the thermal stability was in the order of SiOC/Zr ＞ SiOC/Al > SiOC/Fe. The SiOC/Zr and SiOC/Al ceramics possessed better thermal stability than SiOC/Fe ceramics, because they formed metallic oxides (ZrO₂, mullite, or sillimanite). Additionally, the water-vapor-argon hybrid atmosphere increases the defects within the carbon clusters of SiOC/M ceramics and refines the lateral size of the nanocrystalline carbon. Understanding thermal stability and microstructural evolutions of metal-dropped polymer derived ceramics provided a new method for achieving high-temperature ceramics for application in an extreme environment.     

Evaluation of adsorption and coagulation characteristics of humic acids preceded by alternative advanced oxidation techniques

Humic substances mainly humic acids constitute the major fraction of natural organic matter in water supplies. Humics express diverse actions primarily related to the formation of potentially harmful disinfection by products (DBPs). Therefore, the removal of DBP precursors through numerous treatment techniques gains high importance. Besides the conventional treatment processes, the applications of advanced oxidation techniques are considered as effective tools for the elimination of humic acids (HAs) from natural waters. In the present study, both the adsorption and coagulation characteristics of humic acid samples are evaluated subsequent to pretreatment by photocatalytic oxidation and ozonation. The changes in preoxidized humic acid solutions are assessed in relation to the alterations induced in the UV-vis and fluorescence spectroscopic properties. The removal efficiency of color in terms of Color₄₃₆ and aromaticity with respect to UV₂₅₄ are presented relevant to each treatment step. Major key parameters such as the selection of coagulant types (alum and ferric chloride), coagulant aids (ionic and non-ionic polyelectrolyte) and optimum coagulant dose were comparatively discussed. The adsorption characteristics of powdered activated carbon (PAC) and granular activated carbon (GAC) were investigated.     

The induced magnetic field

Aromaticity is indispensable for explaining a variety of chemical behaviors, including reactivity, structural features, relative energetic stabilities, and spectroscopic properties. When interpreted as the spatial delocalization of π-electrons, it represents the driving force for the stabilization of many planar molecular structures. A delocalized electron system is sensitive to an external magnetic field; it responds with an induced magnetic field having a particularly long range. The shape of the induced magnetic field reflects the size and strength of the system of delocalized electrons and can have a large influence on neighboring molecules. In 2004, we proposed using the induced magnetic field as a means of estimating the degree of electron delocalization and aromaticity in planar as well as in nonplanar molecules. We have since tested the method on aromatic, antiaromatic, and nonaromatic compounds, and a refinement now allows the individual treatment of core-, σ-, and π-electrons. In this Account, we describe the use of the induced magnetic field as an analytical probe for electron delocalization and its application to a large series of uncommon molecules. The compounds include borazine; all-metal aromatic systems Al(4)(n-); molecular stars Si(5)Li(n)(6-n); electronically stabilized planar tetracoordinate carbon; planar hypercoordinate atoms inside boron wheels; and planar boron wheels with fluxional internal boron cluster moieties. In all cases, we have observed that planar structures show a high degree of electron delocalization in the π-electrons and, in some examples, also in the σ-framework. Quantitatively, the induced magnetic field has contributions from the entire electronic system of a molecule, but at long range the contributions arising from the delocalized electronic π-system dominate. The induced magnetic field can only indirectly be confirmed by experiment, for example, through intermolecular contributions to NMR chemical shifts. We show that calculating the induced field is a useful method for understanding any planar organic or inorganic system, as it corresponds to the intuitive Pople model for explaining the anomalous proton chemical shifts in aromatic molecules. Indeed, aromatic, antiaromatic, and nonaromatic molecules show differing responses to an external field; that is, they reduce, augment, or do not affect the external field at long range. The induced field can be dissected into different orbital contributions, in the same way that the nucleus-independent chemical shift or the shielding function can be separated into component contributions. The result is a versatile tool that is particularly useful in the analysis of planar, densely packed systems with strong orbital contributions directly atop individual atoms.     

New opportunities to understand heterogeneous catalysis processes on nanoscale bimetallic particles through synchrotron radiation and theoretical studies

New advances in theoretical background and recent experimental results concerning nanoscale bimetallic clusters are presented. From theoretical point of view, we will show how both the relaxation of the intermetallic distances and the chemical local ordering can be predicted from the electronic structure. Here, we compare these predictions at thermodynamical equilibrium to a review of recent results obtained using XAS for bimetallic systems Pt–M where M is a 4d transition metal. Even though the distribution of the two species inside the cluster can be affected by preparation parameters, such as, the nature of the precursor, it appears that these theoretical calculations are a valuable starting point for the study of such entities.     

Multivalent,Stabilized Mannose-6-Phosphates for the Targeted Delivery of Toll-Like Receptor Ligands and Peptide Antigens

Mannose-6-phosphate (M6P) is recognized by the mannose-6-phosphate receptor and plays an important role in the transport of cargo to the endosomes, making it an attractive tool to improve endosomal trafficking of vaccines. We describe herein the assembly of peptide antigen conjugates carrying clusters of mannose-6-C-phosphonates (M6Po). The M6Po's are stable M6P mimics that are resistant to cleavage of the phosphate group by endogenous phosphatases. Two different strategies for the incorporation of the M6Po clusters in the conjugate have been developed: the first relies on a “post-assembly” click approach employing an M6Po bearing an alkyne functionality; the second hinges on an M6Po C-glycoside amino acid building block that can be used in solid-phase peptide synthesis. The generated conjugates were further equipped with a TLR7 ligand to stimulate dendritic cell (DC) maturation. While antigen presentation is hindered by the presence of the M6Po clusters, the incorporation of the M6Po clusters leads to increased activation of DCs, thus demonstrating their potential in improving vaccine adjuvanticity by intraendosomally active TLR ligands.     

Application of EXAFS in Catalysis. Structure of Bimetallic Cluster Catalysts

In recent years the utility of extended x-ray absorption fine structure (EXAFS) as a probe for the study of catalysts has been clearly demonstrated [1–13]. Measurements of EXAFS are particularly valuable for very highly dispersed catalysts. Supported metal systems, in which small metal clusters or crystallites are commonly dispersed on a refractory oxide such as alumina or silica, are good examples of such catalysts. The rätio of surface atoms to total atoms in the metal clusters is generally high and may even approach unity in some cases. With such catalysts it is difficult or impossible to obtain structural information by conventional x-ray diffraction methods [14].     

Theoretical studies of IM-12 zeolite for acidic catalysts

We theoretically investigate the properties of the IM-12 to address a catalyst for acidic conversion reaction of larger organic molecules. The acidic characteristics of the IM-12 are investigated by density functional theory (DFT) considering both the local density and generalized gradient approximations, LDA and GGA, respectively. Based on quantum mechanical (QM) calculation results, we find that the zeolite with Al element prefers the tetrahedral (T) sites, T4 and T6, when replacing Si in IM-12 framework. Isomorphously substituted IM-12 on the T4 and T6 sites by B, Al, and Ga is studied, respectively. Both of the sites give the Brönsted acidity order: B–IM-12 < Ga–IM-12 < Al–IM-12, which is the same as other zeolites. The calculated NH₃ adsorption energies are compared with the calculated and experimental results of H–[Al]MOR [M. Elanany, D.P. Vercauteren, M. Koyama, M. Kubo, P. Selvam, E. Broclawik, A. Miyamoto, J. Mol. Catal. A 243 (2006) 1; C. Lee, D.J. Parrillo, R.J. Gorte, W.E. Farneth, J. Am. Chem. Soc. 118 (1996) 3262]. Molecular dynamics (MD) results show that IM-12 zeolite allows the large molecules such as diisopropylbenzene (DIPB) and triisopropylbenzene (TIPB) to diffuse faster than those in MOR zeolite and IM-12 may have significant selectivity for TIPB over DIPB. We conclude that the IM-12 with Al impurity would be a good candidate for large organic molecule acidic conversion reaction.