“Dibutylmagnesium”, a convenient reagent for the synthesis of useful organic magnesium reagents MgA2 including cyclopentadienyls,aryloxides, and amides. Preparation of Zr(C5H5)Cl3. X-ray structure of [Mg{μ-N(SiMe)3C6H4N}(SiMe3)-o(OEt2)]2

n-Heptane-soluble “di-butylmagnesium” (I) (a commercially available material, prepared by addition of LiBu^s to MgBuⁿCl, and subsequent addition of ca. 5% MgOct₂ⁿ) has been found to be a useful starting material for obtaining numerous organic magnesium compounds. This is illustrated by its reaction with a number of protic compounds HA to give in good yields Mg(C₅H₅)₂, Mg(C₅H₄Me)₂, or the new compounds MgA₂: IV (A = C₅H₄SiMe₃), V [A = C₅H₃(SiMe₃)₂], VII (A = OC₆H₂Bu₂^t-2,6-Me-4), and X [A₂ = N(SiMe₃)C₆H₄N(SiMe₃)-o(OEt₂)]. The value of such compounds MgA₂ as mild ligand transfer reagents is illustrated by the synthesis of Zr(C₅H₃X₂)Cl₃ (X = H or SiMe₃). Compound X was isolated from OEt₂ solution as the crystalline dimer

with two o-$\text{N}$(SiMe₃)C₆H₄$\text{N}$(SiMe₃) ligands bridging two magnesium atoms and a terminal OEt₂ ligand completing a distorted tetrahedral environment around each Mg. Some key parameters are: MgN_t 1.997(7), MgN_b 2.083(8), MgO 2.041(7) Å; OMgN_t 112.1(3), OMgN_b 119.7(3), and N_tMgN_b 118.5(3)°.     

Determination of cholesterol by flow injection analysis with immobilized cholesterol oxidase

The injected sample passes through a column of enzyme immobilized on controlled pore glass, at pH 7.0, and the hydrogen peroxide produced is detected amperometrically. As little as 0.2 μg of cholesterol can be detected. The method is applied to blood serum, wax-wool alcohol and an extract of butter.     

Determination of glucose in blood by flow injection analysis and an immobilized glucose oxidase column

A flow-injection system for glucose determination is described. Glucose oxidase is immobilized on controlled porosity glass (CPG) and used in a glass column (2.5 mm diameter × 2.5 cm). The hydrogen peroxide produced by the enzymatic reaction (? 1 × 10^?6 M) is detected by the current produced in a flow-through cell, with two platinum electrodes having a potential difference of 0.6 V. Glucose (0–20 mmol l^?1) can be determined in blood plasma either with a dialyser in the system or, better, by incorporating a column of copper(II) diethyldithiocarbamate on CPG before the enzyme column. The results compared well with those obtained by a conventional analyser system. The glucose oxidase column showed little change in activity over a 10-month period.     

Comparison of mass resolution criteria in mass spectrometry

For a single peak, mass spectral resolution can be expressed in terms of peak width or ratio of peak position to peak width. Alternatively, for two equally intense peaks of equal width, resolution can be defined as the minimum peak separation such that the height of the valley between the combined peaks is less than a specified ratio (1%, 10%, 50%, 100%) of the individual (or combined) peak maximum. All these definitions depend on peak shape. Conversion formulae between various mass resolution criteria are presented for each of eight spectral peak shapes: Gaussian, triangular, trapezoidal, Lorentzian (absorption-mode, magnitude-mode, and sine-apodized magnitude-mode), and sinc (absorption-mode and magnitude-mode). From these formulae, mass resolutions based upon different criteria are readily compared for the same or different line shapes.     

Synthesis and structural characterization of new polynuclear complexes of 1-hydroxymethyl-3,5-dimethylpyrazole with Ni(II) and Fe(II)

The complexation of the simple 1-hydroxymethyl-3,5-dimethylpyrazole (HL) ligand with Fe and Ni salts leads to interesting polynuclear complexes in good yield. X-ray diffraction reveals that the resulting complexes (μ₄-L)₄Ni₄Cl₄(H₂O)₄ and (μ₂-L)₄(μ₃-L)₂Fe₈Cl₁₆(μ₄-O)₆ adopt cubane-type and open-cubane-type structures in the solid state.     

A stripe-to-droplet transition driven by conformational transitions in a binary lipid-lipopolymer mixture at the air-water interface

We report the observation of an unusual stripe-droplet transition in precompressed Langmuir monolayers consisting of mixtures of poly(ethylene) glycol (PEG) amphiphiles and phospholipids. This highly reproducible and fully reversible transition occurs at approximately zero surface pressure during expansion (or compression) of the monolayer following initial compression into a two-dimensional solid phase. It is characterized by spontaneous emergence of an extended, disordered stripe-like morphology from an optically homogeneous phase during gradual expansion. These stripe patterns appear as a transient feature and continuously progress, involving gradual coarsening and ultimate transformation into a droplet morphology upon further expansion. Furthermore, varying relative concentrations of the two amphiphiles and utilizing amphiphiles with considerably longer ethylene glycol headgroups reveal that this pattern evolution occurs in narrow concentration regimes, values of which depend on ethylene oxide headgroup size. These morphological transitions are reminiscent of those seen during a passage through a critical point by variations in thermodynamic parameters (e.g., temperature or pressure) as well as those involving spinodal decomposition. While the precise mechanism cannot be ascertained using present experiments alone, our observations can be reconciled in terms of modulations in competing interactions prompted by the pancake-mushroom-brush conformational transitions of the ethylene glycol headgroup. This in turn suggests that the conformational degree of freedom represents an independent order parameter, or a switch, which can induce large-scale structural reorganization in amphiphilic monolayers. Because molecular conformational changes are pervasive in biological membranes, we speculate that such conformational transition-induced pattern evolution might provide a physical mechanism by which membrane processes are amplified.     

An efficient one-pot multicomponent approach to 5-amino-7-aryl-8-nitrothiazolo[3,2-a]pyridines

A series of thiazolo[3,2-a]pyridines have been prepared using a multicomponent reaction between aromatic aldehydes, 2-nitromethylenethiazolidine and nitriles containing an active methylene group (malononitrile, ethyl 2-cyanoacetate and 2-phenylsulfonylacetonitrile) in the presence of Et₃N under mild conditions with high yields. One of the compounds shows promising anticancer activity across a range of cancer cell lines.     

Addition of hydrazine to natural terpene-based isothiocyanates derivatives: density functional theory investigation

The hydrazine addition to isothiocyanoterpenes to produce thiosemicarbazides occurs with excellent yields. The reaction rate to conversion of the camphene-based (NCS1), R-(+)-limonene-based (NCS2), and (−)-α-bisabolol-based (NCS3) isothiocyanoterpene derivatives in the respective thiosemicarbazides was experimentally studied. It was observed that NCS3 reacts two times faster than NCS2 and 3.5 times faster than NCS1. A complete theoretical investigation of the transition states of these reactions was accomplished, showing that the difference in the reaction rates can be explained by the differences in the electrophilic character of the -NCS group and the relative stability of the proposed transition states.     

Synthesis and photochemistry of pH-sensitive GFP chromophore analogs

GFP chromophore analogs (7a-e, 8, and 10a,b) containing 2-thienyl-, 5-methyl-2-furyl-, 2-pyrryl, and 6-methyl-2-pyridyl-groups were synthesized and their fluorescence spectra recorded in the pH range 1-7. NMR studies showed that protonation of 8 (2-thienyl system) inhibited photoisomerization (Z-E) about the exocyclic double bond but that protonation of 7c (E + Z) (2-pyrryl system) gave only 7cE. Fluorescence studies revealed enhancement of fluorescence intensity of 7c and 7b,e (furyl system) below pH 2.5 and gave a similar result for 10a (pyridyl system) below pH 6. Quantum yields at pH 1 were low, probably due to excited state proton transfer (ESPT).     

A μ4‐oxide‐containing a dimeric variant of a sodium dialkyl(amido)zincate reagent

Post‐metallation derivatives of the sodium dialkyl(amido)zincate reagent (TMEDA)Na(μ‐TMP)Zn(^tBu)₂ (TMEDA is N,N,N′,N′‐tetramethylethylenediamine and TMP is 2,2,6,6‐tetramethylpiperidide) have been of structural interest due to the insight they give into aromatic metallation mechanisms. Here, the aromatic substrate is formally replaced with [ZnO]₂ to give tetra‐tert‐butyldi‐μ₄‐oxido‐bis(tetramethylethylenediamine‐κ²N,N′)bis(μ₂‐2,2,6,6‐tetramethylpiperidin‐1‐ido‐κ²N:N)disodiumtetrazinc hexane 0.59‐solvate, [Na₂Zn₄(C₄H₉)₄(C₉H₁₈N)₂O₂(C₆H₁₆N₂)₂]·0.59C₆H₁₄. The crystallographically centrosymmetric complex retains many of the structural features of its parent monomer but has an unusual dimeric structure, with a central planar Zn–O–Zn–O ring joined to two orthogonal near‐planar Zn–O–Na–N rings through the distorted tetrahedral geometries of the oxide ions.