Probing the Lewis acidity and catalytic activity of the metal-organic framework [Cu3(btc)2] (BTC=benzene-1,3,5-tricarboxylate)

An optimized procedure was designed for the preparation of the microporous metal-organic framework (MOF) [Cu3(btc)2] (BTC=benzene-1,3,5-tricarboxylate). The crystalline material was characterized by X-ray diffraction, optical microscopy, SEM, X-ray photoelectron spectroscopy, N2 sorption, thermogravimetry, and IR spectroscopy of adsorbed CO. CO adsorbs on a small number of Cu2O impurities, and particularly on the free CuII coordination sites in the framework. [Cu3(btc)2] is a highly selective Lewis acid catalyst for the isomerization of terpene derivatives, such as the rearrangement of alpha-pinene oxide to campholenic aldehyde and the cyclization of citronellal to isopulegol. By using the ethylene ketal of 2-bromopropiophenone as a test substrate, it was demonstrated that the active sites in [Cu3(btc)2] are hard Lewis acids. Catalyst stability, re-usability, and heterogeneity are critically assessed.     

The application of liquid chromatography-electrospray ionization mass spectrometry and collision-induced dissociation in the structural characterization of acylated flavonol O-glycosides from the seeds of Carrichtera annua

The flavonoid fraction from the seeds of Carrichtera annua was studied using high-performance liquid chromatography simultaneously coupled to a photodiode array detector (LC/UV-DAD) and a mass spectrometer equipped with an electrospray source (LC/ESI-MS). Collision-induced dissociation (CID) mass spectral data obtained off-line by nanospray (nano-ESI) analysis provided a wealth of complementary structural information, which was consistent with structures established by NMR or led to the proposal of base structures of the flavonol O-glycosides present in the Carrichtera annua seed extract. The flavonoid fraction was found to contain 12 structurally related flavonol O-glycosides. Eleven flavonoids, of which several were new compounds, were acylated with one or more benzoyl, feruloyl or sinapoyl groups. These acyl groups gave rise to characteristic product ions in the [M + H](+) and [M + Na](+) CID spectra as well as to radicalar acid-related product ions at high-energy collisional activation. In addition to the characterization of the acyl substituents, the mass spectral data allowed the identification of the aglycone, the determination of the base structure and the differentiation of several positional isomers.     

Ein Sylowsatz für endlichep-Untergruppen von GL (n, ℤ)

Ohne Zusammenfassung     

Determination of ruthenium originating from the investigational anti-cancer drug NAMI-A in human plasma ultrafiltrate, plasma, and urine by inductively coupled plasma mass spectrometry

We present a highly sensitive, rapid method for the determination of ruthenium originating from the investigational anti-cancer drug NAMI-A in human plasma ultrafiltrate, plasma, and urine. The method is based on the quantification of ruthenium by inductively coupled plasma mass spectrometry and allows quantification of 30 ng L(-1) ruthenium in plasma ultrafiltrate and urine, and 75 ng L(-1) ruthenium in human plasma, in 150 microL of matrix. The sample pretreatment procedure is straightforward and only involves dilution with appropriate diluents. The performance of the method, in terms of accuracy and precision, fulfilled the most recent FDA guidelines for bioanalytical method validation. Validated ranges of quantification were 30.0 to 1 x 10(4) ng L(-1) for ruthenium in plasma ultrafiltrate and urine and 75.0 to 1 x 10(4) ng L(-1) for ruthenium in plasma. The applicability of the method and its superiority to atomic-absorption spectrometry were demonstrated in two patients who were treated with intravenous NAMI-A in a phase I trial. The assay is now successfully used to support pharmacokinetic studies in cancer patients treated with NAMI-A.     

Zinc Silicates: Very Efficient Heterogeneous Catalysts for the Addition of Primary Alcohols to Alkynes and Allenes

There is an astonishing parallel between the mechanism generally accepted for the addition of water to CO₂ catalyzed by the enzyme carbonic anhydrase and the mechanism calculated for the addition of methanol to allene catalyzed by the naturally occurring zinc silicate hemimorphite. The latter reaction was investigated in detail following the observation that hemimorphite as well as an amorphous zinc silicate prepared in situ are excellent heterogeneous catalysts for the addition of primary alcohols to alkynes and allenes [Eq. (1)].     

Comparison of high- and low-energy collision-induced dissociation tandem mass spectrometry in the analysis of glycoalkaloids and their aglycons

Four aglycons (tomatidine, demissidine, solanidine, and solasodine) and three glycoalkaloids (α-tomatine, α-chaconine, and α-solanine) have been analyzed by positive ion liquid secondary ion high-energy and low-energy collision-induced dissociation (CID) tandem mass Spectrometry, performed on a four-sector (EBEB) and a hybrid (EBQQ) instrument, respectively. Both high- and low-energy collision-induced dissociation mass spectra of [M+H]⁺ ions of these compounds provided structural information that aided the characterization of the different aglycons and of the carbohydrate sequence and linkage sites in the glycoalkaloids. Low-energy CID favors charge-driven fragmentation of the aglycon rings, whilst high-energy CID spectra are more complex and contain additional ions that appear to result from charge-remote fragmentations, multiple cleavages, or complex charge-driven rearrangements. With respect to the structural characterization of the carbohydrate part, low-energy CID fragmentations of sugar residues in the glycoalkaloids generate Y _n ⁺ ions and some low intensity Z _n ⁺ ions; the high-energy spectra also exhibit strong ^1,5X _n ⁺ ions, formed by multiple cleavage of the sugar ring, and significant Z _n ⁺ ions.     

Charge-remote and charge-proximate fragmentation processes in alkali-cationized fatty acid esters upon high-energy collisional activation. A new mechanistic proposal

The effect of the metal ion on the high-energy collision-induced dissociation (CID) of alkali metal-cationized n-butyl and methyl ester derivatives of palmitic and oleic acid was examined. The results show that the alkali metal ion has a pronounced effect and does not act as a mere ‘spectator’ ion with respect to the fragmentation process. While C–H cleavage is a dominant process for [M+Li]⁺ as well as [M+Na]⁺ precursor ions, C–C cleavage is also significant for the [M+Na]⁺ ions. Homolytic mechanisms involving the formation of a transient biradical cation are proposed which enable us to rationalize in a straightforward manner all product ions formed by both charge-remote and charge-proximate fragmentations. The mechanistic proposal is discussed in view of available knowledge on electron impact, CID and related processes. In order to predict how the alkali metal ion could affect the reactivity of the postulated biradical state formed following electronic excitation of the alkali metal-cationized molecules, quantum chemical calculations were performed on methyl and n-butyl acetate as model substances. The decreased spin density at the carbonyl oxygen atom in the biradical state may provide an explanation for the greater tendency towards C–C cleavage reactions of the sodium-cationized fatty acid esters relative to the corresponding lithium complexes. © 1988 John Wiley & Sons, Ltd.     

Non-ergodic effect of LiCl on the anionic polymerization of styrene in ether-solvents. Specific solvation of Li+ ions in THF solution and prevention of this effect by LiCl

In this work conductance measurements were performed on polystyryllithium PStLi in tetrahydrofuran (THF) in the concentration range of 10⁻³ mol dm⁻³ at various temperatures between −60°C and 20°C. The comparison with the other alkali salts shows that in these solutions Li⁺ gives specific interactions with partial electronic charge transfer from the solvent molecules, presumably of the formula LiS₄⁺. A quantitative treatment shows that at 25°C the extrapolated stabilization factor K_S is larger than 50000 but rapidly drops for the heavier alkali ions: 3000 for Na⁺, 200 for K⁺ and negligible for C_s⁺. Surprisingly, such a stabilization is not observed for LiCl, although the ionic radii of the anions are quite comparable. The conductances κ at given concentration C of the electrolyte are 100 times smaller. Furthermore the curves of κ² versus C exhibit in this case an important curvature whereas they are practically linear for PStLi. The absence of specific solvation for LiCl seems thus to be accompanied by the formation of triple ions. Due to the symmetry of the electrolyte the formation of both triple anions ClLiCl⁻ and cations LiClLi⁺ has to be considered. Moreover, the concentrations of these ions is then always much smaller than that of the neutral dimer LiClLiCl, even if the extent of dimerization of LiCl remains small. The triple ions therefore appear as related to the dissociation of the dimer. This means that through the intermediate formation of the neutral dimer the couples triple ion - counterfoil perpetually exchange an LiCl entity in the course of time: Li⁺ + ClLiCl⁻⇋ LiClLiCl ⇋ LiClLi⁺ + Cl⁻. Only in the dimer the central LiCl is in possession of the (negative) energy of the insertion bond. In the solution this bond can be attributed neither to ClLiCl⁻ nor to LiClLi⁺. These entities have to be considered as transient ones during the life-time of which the energy of the insertion bond is transferred to the medium or vice-versa and which possess the energy of the insertion bond only during half of their life-time. The energy of such entities is thus not unambiguously defined in the ensemble at a given time and the ergodic principle does not hold. Such transient species cannot be specifically solvated by the solvent molecules because this would prevent the necessary passage through the dimer form. It is therefore the dimerization of LiCl which opposes itself to the formation of LiS₄⁺ in the THF solutions. Quantitatively the problem can be treated by a thermodynamics based not on ensemble fractions but on time fractions. One considers that a given LiCl can only give solvated ions during a fraction ξ_C° of the time and that during the remaining fraction it participates in a dissociation process which passes through the formation of non-ergodic triple ions and neutral dimers. (1-ξ_C°)/ξ_C° is equal to K^aC^3/2/[(1 + K_S)K^do]^½ where K^a is the non-ergodic equilibrium constant governing the formation of dimers and higher aggregates and K^do the dissociation constant of LiCl in non-solvated ions. This non-ergodic treatment also allows to describe quantitatively the strange conductometric behaviour of ternary solutions of LiCl and PStLi in THF. The addition of amounts of LiCl in a mole ratio of 7/1 to a given solution of PStLi increases unexpectedly in a very spectacular way the conductivity and provokes the appearance of a non-linear term in the κ² versus concentration function. In fact this behaviour is due to the replacement of a LiCl entity in the dimers by a PStLi molecule, yielding mixed dimers LiClLiStP. The displaced LiCl molecules are again susceptible of ergodic dissociation and specific solvation of the Li⁺ ions which originate from this dissociation. Thus for the LiCl entities the time fraction ξ_C increases. Moreover, at higher concentrations the dissociation of the mixed dimers leads to an important formation of non-ergodic triple anions: Li⁺ + ClLiStP⁻ ⇋ LiClLiStP ⇋ LiClLi⁺ + StP⁻ where the entity LiCl constantly jumps in the course of time from an StP⁻ to an Li⁺ and vice-versa.