In situ disorder-order transformation in synthetic gallosilicate zeolites with the NAT topology

Here, we report that synthetic gallosilicate molecular sieves with the NAT topology and Si/Ga ratios close to but slightly higher than 1.50 undergo an in situ transformation under their crystallization conditions. The materials have been studied ex situ by using powder X-ray diffraction, elemental and thermal analyses, and multinuclear MAS NMR. The transformation is characterized by a change in the distribution of Si and Ga of the NAT framework, from a quite (but not completely) disordered phase to a very highly (but not completely) ordered one, accompanied by a change from tetragonal to orthorhombic symmetry. During most of the solution-mediated transformation, no noticeable signs of fresh precipitation, phase segregation, or changes in the chemical composition are detected. Intermediate materials show variations in the degree of Si-Ga ordering and orthorhombic distortion and are not physical mixtures of the disordered and ordered phases. Ab initio calculations strongly suggest a preferential siting of Si in the tetrahedral sites involved in a smaller number of 4-rings in the NAT topology (i.e., the low multiplicity site). The cost of violations of Loewenstein's rule has also been calculated. For this topology and chemical composition the preferential siting and Loewenstein's rule drive together the system to the ordered configuration. A Monte Carlo sampling procedure affords a reasonable model for the initial, mainly disordered state, which fits well within the experimental disorder-order series.     

Synthesis of tetrahydroimidazo[1,5-b]-β-carboline derivatives with complex basic substituents

Novel tetrahydroimidazo[1,5-b]-β-carbolines derivatives 6 bearing complex basic chains as substituents on the imidic nitrogen have been prepared in a one-pot reaction. This simple experimental procedure overcomes the direct handle of isocyanates which can be favorably generated “in situ” from carbonyldiimidazole (CDI) and different amines. The stereochemistry of the novel compounds was determined by nmr experiments.     

Validated, non-destructive and environmentally friendly determination of cocaine in euro bank notes

A non-destructive, fast and environmentally friendly procedure has been developed for cocaine determination in euro bank notes. Cocaine was extracted with 15 ml methanol by vortex agitation during 5 min. The extract was evaporated and reconstituted in 0.5 ml methanol. GC-MS-MS analysis was performed using as precursor ion m/z 182.2, with an excitation energy voltage of 1.60 eV, being the product ions measured m/z 150.2 and 82.0. A limit of detection of 0.15 ng per note and a repeatability of 6%, established from the relative standard deviation, of a 1 ng ml(-1) level, were achieved. Recoveries of 101+/-2 and 98+/-3% were obtained for samples spiked with 100 and 10 microg respectively. Results show that all the euro bank notes measured (16 samples) were contaminated with cocaine in the range between 1.25 and 889 microg. Two different contamination levels, high level (150-889 microg) and low one (1.25-77 microg) were found and it could be related with the direct or indirect contact with the drug.     

Synthesis of (-)-Vulcanolide by enantioselective protonation

Two efficient enantioselective syntheses of the more active (S,S)-enantiomer of the powerful musk odorant Vulcanolide are described. In both syntheses, the key step is an enantioselective protonation of a ketone enolate. A third enantioselective protonation, of a thiol ester enolate, was applied for the determination of the absolute configuration of Vulcanolide by comparison with a known compound.     

Determination of rotational barriers of carbon?carbon bonds in 2-arylpiperidines

Carbon-carbon sp³-sp² rotational barriers of 3,3-dimethyl-2-(3,4,5-trimethoxyphenyl)-4-piperidones and their ethylene ketals have been evaluated using nmr techniques. The conformation of 1 hydrochloride has been studied by NOE determinations. Values found for the hydrochlorides of the title compounds are discussed in terms of equilibria with free bases and nitrogen inversion.     

Simultaneous-fluorimetric methods for the determination of ammonia and urea by use of flow injection configurations with dual injection valves

Summary Two fluorimetric methods are proposed for the simultaneous determination of ammonia and urea based on the reaction of the former with o-phthalaldehyde/2-mercaptoethanol and on the use of a dual injection system in which the valves are coupled in series or in parallel. An enzymatic reactor converts urea into ammonia which is determined by the same reaction. These configurations provide very similar results with a linear determination range between 0.5 and 10.0 g ml^–1 and a sampling frequency of 60 h^–1. The proposed methods are very tolerant to foreign species commonly found in water, as shown by applying them to samples of different origins.     

Potentiometric, luminescence and NMR study of the interaction of Eu with glyceryl phosphates

Complexation of europium(III) with glyceryl-1- and -2-phosphates has been studied by metal ion luminescence, ¹H and ¹³C NMR spectroscopy and potentiometry. From the luminescence and NMR studies, the formation of a 1:1 inner-sphere complex, in which the glyceryl phosphate is directly bound to the metal, is confirmed. Similar apparent binding constants at pH 2 were obtained by the three methods. Values obtained by NMR at pH 2 are 53 M⁻¹ and 12 M⁻¹ for glyceryl-1- and -2-phosphate, respectively. By comparison with literature data on related systems it is suggested that the ligands bind through the phosphate group. To obtain structural information from the NMR data, complexation has also been studied with the lanthanide ions Dy(III), Er(III) and Gd(III) using both chemical shift and relaxation data. From this, metal-proton distance ratios have been calculated. Comparison of ¹H and ¹³C NMR spectral data in the presence of paramagnetic lanthanides suggests conformational equilibria in the solutions. From the potentiometric studies, global formation constants have been determined, and speciation diagrams obtained over the pH range 1.5pH7.0 for ligand/metal ratios of 1 and 30. Implications of these results on lanthanide induced fusion of phospholipid membranes are discussed.     

Asymmetric multicomponent reactions (AMCRs): the new frontier

Asymmetric multicomponent reactions involve the preparation of chiral compounds by the reaction of three or more reagents added simultaneously. This kind of addition and reaction has some advantages over classic divergent reaction strategies, such as lower costs, time, and energy, as well as environmentally friendlier aspects. All these advantages, together with the high level of stereoselectivity attained in some of these reactions, will force chemists in industry as in academia to adopt this new strategy of synthesis, or at least to consider it as a viable option. The positive aspects as well as the drawbacks of this strategy are discussed in this Review.     

Preparation and characterization of individual peptide-wrapped single-walled carbon nanotubes

Two challenges for effectively exploiting the remarkable properties of single-walled carbon nanotubes (SWNTs) are the isolation of intact individual nanotubes from the raw material and the assembly of these isolated SWNTs into useful structures. In this study, we present atomic force microscopy (AFM) evidence that we can isolate individual peptide-wrapped SWNTs, possibly connected end-to-end into long fibrillar structures, using an amphiphilic alpha-helical peptide, termed nano-1. Transmission electron microscopy (TEM) and well-resolved absorption spectral features further corroborate nano-1's ability to debundle SWNTs in aqueous solution. Peptide-assisted assembly of SWNT structures, specifically in the form of Y-, X-, and intraloop junctions, was observed in the AFM and TEM images.     

Synthesis of cationic carbonyl complexes of manganese(I) with bidentate ligands

Summary Bidentate ligands can readily replace acetone in thefac-[Mn(CO)₃(chel)(OCMe₂)]⁺ complexes or the perchlorate group fromfac-[Mn(CO)₃(chel)(OClO₃)] yieldingfac-[Mn(CO)₃(chel)(L-L)]⁺ or [{fac-Mn(CO)₃(chel)}₂(L-L)]²⁺ [chel = 1,10-phenanthroline (phen), 2,2-bipyridine (bipy), 1,2-bis(diphenylphosphine)ethane (dpe); L-L = bis(diphenylphosphine)methane (dpm), dpe, 1,4-bis(diphenylphosphine)butane (dpb), succinonitrile (suc), and glutaronitrile (glu)]. Some of these mononuclear complexes are precursors for binuclear complexes which are linked by bridging phosphines or nitriles.