Ethyl methyl 1,4‐dihydro‐4‐(3‐nitrophenyl)‐2,6‐bis(1‐piperidylmethyl)­pyridine‐3,5‐dicarboxylate

In the title compound, C₂₈H₃₈N₄O₆, the 4‐aryl substituent occupies a pseudo‐axial position approximately orthogonal to the plane of the di­hydro­pyridine ring [88.1 (3)°]. The di­hydro­pyridine ring adopts a flattened boat conformation. The H atom on the pyridine N atom is involved in a bifurcated intramolecular hydrogen bond, the acceptors being the N atoms of the two piperidyl­methyl groups [N?N 2.629 (4) and 2.695 (4) Å].     

A Fractional Factorial Design Applied to the Optimization of Microwave- and Ultrasound-Assisted Acid Leaching Methods for Heavy Metals Determination in Sludges by Flame Atomic Absorption Spectrometry

Abstract

The sampling performance of C₁₈ cartridges coated with DNPH has been studied for twenty four C₁-C₉ carbonyls in experiments involving sampling of parts per billion levels of carbonyls in urban air. indoor air and laboratory experiments. The cartridge background carbonyl content in thirty six batches of cartridges averaged 85, 137 and 155 nanogram/cartridge for formaldehyde, acetaldehyde and acetone, respectively, and was below analytical detection for all other carbonyls. Carbonyl-DNPH derivative recovery from the cartridge was complete in the first elution with 2 mL acetonitrile, and this for twenty four carbonyls at concentrations of 0.02–73 μg carbonyl/cartridge. Studies carried out using two cartridges in series showed no breakthrough, for the sixteen carbonyls tested, at concentrations of 0.10–49 μg carbonyl/cartridge and volumes of air sampled = 6–370 L. Average relative standard deviations (RSD) for replicate analyses were 0.20–13.2% for twenty one carbonyls. Average RSD for co-located samples were 0.9–16.2% for eighteen carbonyls. Comparison of RSD for replicates and RSD for co-located samples for thirteen carbonyls indicated that the overall method precision was limited by sampling precision rather than by analytical precision.     

A capillary electrophoresis procedure for the screening of oligosaccharidoses and related diseases

The most widely used method for the biochemical screening of oligosaccharidoses is the analysis of the urinary oligosaccharide pattern by thin-layer chromatography on silica gel plates. However, this method is not always sensitive enough, and it is extremely time-consuming and laborious. In this work, the analysis of the urine oligosaccharide pattern was standardized for the first time by using capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection (Beckman P/ACE MDQ) with a 488-nm argon ion laser module. All of the analyses were conducted using the Carbohydrate Labeling and Analysis Kit (Beckman-Coulter), which derivatizes samples with 8-aminopyrene-1,3,6-trisulfonate. Urine samples from 40 control subjects (age range, 1 week to 16 years) and from ten patients diagnosed with eight different lysosomal diseases (six of them included in the Educational Oligosaccharide Kit from ERNDIM EQA schemes) were analyzed. Two oligosaccharide excretion patterns were established in our control population according to age (younger or older than 1 year of age). Abnormal peaks with slower migration times than the tetrasaccharide position were observed for fucosidosis, α-mannosidosis, GM1 gangliosidosis, GM2 gangliosidosis variant 0, Pompe disease, and glycogen storage disease type 3. In conclusion, the first CE-LIF method to screen for oligosaccharidoses and related diseases, which also present oligosacchariduria, has been standardized. In all of the cases, the urine oligosaccharide analysis was strongly informative and showed abnormal patterns that were not present in any of the urine samples from the control subjects. Only urine from patients with aspartylglucosaminuria and Schindler disease displayed normal results.

Structural study of highly halogenated dihydropyridine derivatives as potential calcium channel modulators

Two dihydropyridines endowed with fluorine atoms ( 3 ) and fluorine and chlorine atoms ( 4 ) have been synthesized and structurally characterized by experimental X‐ray analyses and theoretical calculations at the semiempirical (AMI) and ab initio (HF/6–31G*) levels. The results show that these compounds meet the required criteria to act as potential calcium channel modulators.     

Salt effects in reactions between ions of opposite charge

Summary The kinetics of reactions between ions of opposite charge have been studied in concentrated salt solutions of supporting electrolytes. An increase in rate constant is observed at the higher concentrations of supporting electrolytes. The results are discussed in connection with kinetic salt effects on reactions between similary charged ions. It is concluded that the positive salt effects observed in all cases can be explained either as a consequence of nonequilibrium solvation in the transition state or as a result of solvent reorganisation in the activation process.     

Amperometric cholesterol biosensors based on the electropolymerization of pyrrole and the electrocatalytic effect of Prussian-Blue layers helped with self-assembled monolayers

Three cholesterol biosensor configurations based on the formation of a layer of Prussian-Blue (PB) on a Pt electrode for the electrocatalytic detection of the H₂O₂ generated during the enzymatic reaction of cholesterol with cholesterol oxidase (ChOx) were constructed. The enzyme was entrapped within a polypyrrole (PPy) layer electropolymerized onto the PB film. The influence of the formation of self-assembled monolayers (SAMs) on the Pt surface on the adherence and stability of the PB layer and the formation of an outer layer of nafion (Nf) as a means of improving selectivity were both studied. A comparative study was made of the analytical properties of the biosensors corresponding to the three configurations named: Pt/PB/PPy-ChOx, Pt/SAM/PB/PPy-ChOx and Pt/SAM/PB/PPy-ChOx/Nf. The sensitivity (from 600 to 8500 nA mM⁻¹ cm⁻²) and selectivity of the developed biosensors permitted the determination of the cholesterol content in reference and synthetic serum samples. The detection limit for the Pt/SAM/PB/PPy-ChOx/Nf biosensor was 8 μM. Formation of the SAM on the electrode surface and covering with a Nf film considerably improved the stability and lifetime of the biosensor based on the catalytic effect of the PB layer (as the PB layer was retained longer on the electrode), and the Nf layer protects the enzyme from the external flowing solutions. Lifetime is up to 25 days of use. The formation of the SAM also has an effect on the charge transfer and the formation of the PB layer.     

Synthesis, crystal structure and molecular modeling (AM1) of two 5-arylidene derivatives of Meldrum's acid

The synthesis and structural characterization of two 5-Arylidene derivatives of Meldrum's acid (2,2-dimethyl-1,3-dioxane-4,6-dione) are described: 5-(4-Nitrobenciliden)-2,2-dimethyl-1,3-dioxane-4,6-dione (3a), and 5-(4-Methoxybenciliden)-2,2-dimethyl-1,3-dioxane-4,6-dione (3b). The structure of 3a was refined to R₁ = 0.0421 for 2148 reflections (with I > 2 (I)). Crystal data for 3a: C₁₃H₁₁NO₆, orthorhombic, space group Pbca, a = 16.008(3), b = 6.137(1), c = 25.281(5) Å, V = 2483.6(8) ų, Z = 8. The structure of 3b was refined to R₁ = 0.0496 for 4681 reflections (with I > 2(I)). Crystal data for 3b: C₁₄H₁₄O₅, triclinic, space group P1, a = 9.131(2), b = 9.922(2), c = 14.490(3)Å, = 85.076(6), = 84.80(3), = 89.37(2)°,V = 1302.4(5) ų, Z = 4. The results of crystallographic and molecular modeling (AM1) were compared. The molecules in the crystal are held together, in both compounds, by van der Waals forces and C—H···O hydrogen bond interactions.