Strong Lewis acids of air-stable metallocene bis(perfluorooctanesulfonate)s as high-efficiency catalysts for carbonyl-group transformation reactions

Strong Lewis acids of air-stable metallocene bis(perfluorooctanesulfonate)s [M(Cp)(2)][OSO(2)C(8)F(17)](2)?nH(2)O?THF (M = Zr (2?a?3?H(2)O?THF), M = Ti (2?b?2?H(2)O?THF)) were synthesized by the reaction of [M(Cp)(2)]Cl(2) (M = Zr (1?a), M = Ti (1?b)) with nBuLi and C(8)F(17)SO(3)H (2?equiv) or with C(8)F(17)SO(3)Ag (2?equiv). The hydrate numbers (n) of these complexes were variable, changing from 0 to 4 depending on conditions. In contrast to well-known metallocene triflates, these complexes suffered no change in open air for a year. thermogravimetry-differential scanning calorimetry (TG-DSC) analysis showed that 2?a and 2?b were thermally stable at 300 and 180?°C, respectively. These complexes exhibited unusually high solubility in polar organic solvents. Conductivity measurement showed that the complexes (2?a and 2?b) were ionic dissociation in CH(3)CN solution. X-ray analysis result confirmed 2?a?3?H(2)O?THF was a cationic organometallic Lewis acid. UV/Vis spectra showed a significant red shift due to the strong complex formation between 10-methylacridone and 2?a. Fluorescence spectra showed that the Lewis acidity of 2?a fell between those of Sc(3+) (λ(em)=474?nm) and Fe(3+) (λ(em)=478?nm). ESR spectra showed the Lewis acidity of 2?a (0.91?eV) was at the same level as that of Sc(3+) (1.00?eV) and Y(3+) (0.85?eV), while the Lewis acidity of 2?b (1.06?eV) was larger than that of Sc(3+) (1.00?eV) and Y(3+) (0.85?eV). They showed high catalytic ability in carbonyl-compound transformation reactions, such as the Mannich reaction, the Mukaiyama aldol reaction, allylation of aldehydes, the Friedel-Crafts acylation of alkyl aromatic ethers, and cyclotrimerization of ketones. Moreover, the complexes possessed good reusability. On account of their excellent catalytic efficiency, stability, and reusability, the complexes will find broad catalytic applications in organic synthesis.     

Application of on-line nano-liquid chromatography/mass spectrometry in metabolite identification studies

Metabolite identification is an important part of the drug discovery and development process. High sensitivity is necessary to identify metabolic products in vitro and in vivo. The most common method utilizes standard high-performance liquid chromatography (4.6 mm i.d. column and 1 mL/min flow rate) coupled to tandem mass spectrometry (HPLC/MS/MS). We have developed a method that utilizes a nano-LC system coupled to a high-resolution tandem mass spectrometer to identify metabolites from in vitro and in vivo samples. Using this approach, we were able to increase the sensitivity of analysis by approximately 1000-fold over HPLC/MS. In vitro samples were analyzed after simple acetonitrile precipitation, centrifugation, and dilution. The significant improvement in sensitivity enabled us to conduct experiments at very low substrate concentrations (0.01 μM), and very low incubation volumes (20 μL). In vivo samples were injected after simple dilution without any pre-purification. All the metabolites identified by conventional HPLC/MS/MS were also identified using the nano-LC method. This study demonstrates a very sensitive approach to identifying phase I and II metabolites with throughput and separation equivalent to the standard HPLC/MS/MS method.     

High-Tc ferromagnetic semiconductor-like behavior and unusual electrical properties in compounds with a 2×2×2 superstructure of the half-Heusler phase

Heusler phases, including the full- and half-Heusler families, represent an outstanding class of multifunctional materials on account of their great tunability in compositions, valence electron counts (VEC), and properties. Here we demonstrate a systematic design of a series of new compounds with a 2×2×2 superstructure of the half-Heusler unit cell in X-Y-Z (X=Fe, Ru, Co, Rh, Ir; Y=Zn, Mn; Z=Sn, Sb) systems. Their structures were solved by using both powder and single-crystal X-ray diffraction, and also directly observed by using high-angle annular dark-field imaging in a scanning transmission electron microscope (HAADF-STEM). The VEC values of these new compounds span a wide and continuous range comparable to those for the full- and half-Heusler families, thereby implying tunability in compositions and physical properties in the superstructure. In fact, we observed abnormal electrical properties and a ferromagnetic semiconductor-like behavior with a high and tunable Curie temperature in these superstructures.     

Isolable chiral aggregates of achiral π-conjugated carboxylic acids

The induced aggregation of achiral building blocks by a chiral species to form chiral aggregates with memorized chirality has been observed for a number of systems. However, chiral memory in isolated aggregates of achiral building blocks remains rare. One possible reason for this discrepancy could be that not much is understood in terms of designing these chiral aggregates. Herein, we report a strategy for creating such isolable chiral aggregates from achiral building blocks that retain chiral memory after the facile physical removal of the chiral templates. This strategy was used for the isolation of chiral homoaggregates of neutral achiral π-conjugated carboxylic acids in pure aqueous solution. Under what we have termed an "interaction-substitution" mechanism, we generated chiral homoaggregates of a variety of π-conjugated carboxylic acids by using carboxymethyl cellulose (CMC) as a mediator in acidic aqueous solutions. These aggregates were subsequently isolated from the CMC templates whilst retaining their memorized supramolecular chirality. Circular dichroism (CD) spectra of the aggregates formed in the acidic CMC solution exhibited bisignated exciton-coupled signals of various signs and intensities that were maintained in the isolated pure homoaggregates of the achiral π-conjugated carboxylic acids. The memory of the supramolecular chirality in the isolated aggregates was ascribed to the substitution of COOH/COOH hydrogen-bonding interaction between the carboxylic acid groups within the aggregates for the hydrogen-bonding interactions between the COOH groups of the building blocks and the chiral templates. We expect that this "interaction-substitution" procedure will open up a new route to isolable pure chiral aggregates from achiral species.     

Determination of the volatile composition in brown millet, milled millet and millet bran by gas chromatography/mass spectrometry

The volatile compounds from brown millet (BM), milled millet (MM) and millet bran (MB) were extracted using simultaneous distillation/extraction with a Likens-Nickerson apparatus. The extracts were analysed using gas chromatography coupled with mass spectrometry (GC-MS). A total of 65 volatile compounds were identified in all of the samples. Among these compounds, 51, 51 and 49 belonged to BM, MM and MB, respectively. Aldehydes and benzene derivatives were the most numerous among all of the compounds. Three compounds (hexanal, hexadecanoic acid and 2-methylnaphthalene) were dominant in the BM and MM materials. Eight compounds (hexanal, nonanal, (E)-2-nonenal, naphthalene, 2-methylnaphthalene, 1-methylnaphthalene, hexadecanoic acid and 2-pentylfuran) were dominant in the MB materials. Apart from the aromatic molecules, which were present in all fractions, compounds present only in BM, MM or MB were also identified.     

Thermodynamic study on the complexation of Am(III) and Eu(III) with tetradentate nitrogen ligands: a probe of complex species and reactions in aqueous solution

A thermodynamic investigation has been performed to study the complexation of trivalent metal (M) ions (M = Am(III), Eu(III)) with tetradentate ligands (L), 6,6'-bis(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2'-bipyridines (BTBPs), by using relativistic quantum mechanical calculations. The structures and stabilities of the inner-sphere BTBPs complexes were explored in the presence of various counterions such as NO(3)(-), Cl(-), and ClO(4)(-). According to our calculations, Am(III) and Eu(III) can chelate eight or nine water molecules at most, whereas more stable species like M(NO(3))(3)(H(2)O)(4) tend to be formed in the presence of nitrate ions. The inner sphere of the BTBPs complexes can accommodate four water molecules or three nitrate ions based on our calculations, forming species such as [ML(H(2)O)(4)](3+) and ML(NO(3))(3). Compared with Eu(III) complexes, the Am(III) counterparts have obviously lower binding energies in both the gas phase and solution. In addition, the solvent effect significantly decreases the binding energies of the BTBPs complexes. It has been found that the complexing reactions, in which products and reactants possess the same or close number of nitrate ions, are more favorable for formation of the BTBPs complexes. In short, the reactions of M(NO(3))(3)(H(2)O)(4) → ML(NO(3))(3) and [M(NO(3))(H(2)O)(7)](2+) → [ML(2)(NO(3))](2+) are probably the dominant ones in the Am(III)/Eu(III) separation process.     

Theoretical studies on the unimolecular decomposition of ethylene glycol

The unimolecular decomposition processes of ethylene glycol have been investigated with the QCISD(T) method with geometries optimized at the B3LYP/6-311++G(d,p) level. Among the decomposition channels identified, the H(2)O-elimination channels have the lowest barriers, and the C-C bond dissociation is the lowest-energy dissociation channel among the barrierless reactions (the direct bond cleavage reactions). The temperature and pressure dependent rate constant calculations show that the H(2)O-elimination reactions are predominant at low temperature, whereas at high temperature, the direct C-C bond dissociation reaction is dominant. At 1 atm, in the temperature range 500-2000 K, the calculated rate constant is expressed to be 7.63 × 10(47)T(-10.38) exp(-42262/T) for the channel CH(2)OHCH(2)OH → CH(2)CHOH + H(2)O, and 2.48 × 10(51)T(-11.58) exp(-43593/T) for the channel CH(2)OHCH(2)OH → CH(3)CHO + H(2)O, whereas for the direct bond dissociation reaction CH(2)OHCH(2)OH → CH(2)OH + CH(2)OH the rate constant expression is 1.04 × 10(71)T(-16.16) exp(-52414/T).     

Effects of micelle properties on the conformation of oligocholates and importance of rigidity of foldamers

The conformation of a cholate hexamer with a clicked tether in between two tricholate units and pyrene groups at the chain ends was studied by fluorescence spectroscopy. In contrast to the parent cholate hexamer that folded in all micelles investigated, the folding of the clicked hexamer was highly dependent on the type of surfactant used to solubilize the compound. The clicked oligocholate folded in the Brij 35 micelle, possibly due to the latter's small size and strong internal hydrophobicity. The oligocholate formed intermolecular aggregates in SDS solutions below the CMC of the surfactant. The aggregates were dissociated by the SDS micelles but the individual oligocholate stayed unfolded. In Triton X-100 and sodium cholate solutions, the aggregated, unfolded, and folded oligocholates coexisted and gradual unfolding occurred with an increasing concentration of the surfactant. The conformation of the clicked oligocholate was sensitive to the nonideal mixing of ionic/nonionic micelles and to the unconventional aggregation of sodium cholate.     

A solid molecular basket sorbent for CO2 capture from gas streams with low CO2 concentration under ambient conditions

In this paper, a solid molecular basket sorbent, 50 wt% PEI/SBA-15, was studied for CO(2) capture from gas streams with low CO(2) concentration under ambient conditions. The sorbent was able to effectively and selectively capture CO(2) from a gas stream containing 1% CO(2) at 75 °C, with a breakthrough and saturation capacity of 63.1 and 66.7 mg g(-1), respectively, and a selectivity of 14 for CO(2)/CO and 185 for CO(2)/Ar. The sorption performance of the sorbent was influenced greatly by the operating temperature. The CO(2)-TPD study showed that the sorbent could be regenerated under mild conditions (50-110 °C) and was stable in the cyclic operations for at least 20 cycles. Furthermore, the possibility for CO(2) capture from air using the PEI/SBA-15 sorbent was studied by FTIR and proved by TPD. A capacity of 22.5 mg g(-1) was attained at 75 °C via a TPD method using a simulated air with 400 ppmv CO(2) in N(2).