Iodine(V) reagents in organic synthesis. Part 3. New routes to heterocyclic compounds via o-iodoxybenzoic acid-mediated cyclizations: generality, scope, and mechanism

The discovery and development of the o-iodoxybenzoic acid (IBX) reaction with certain unsaturated N-aryl amides (anilides) to form heterocycles are described. The application of the method to the synthesis of delta-lactams, cyclic urethanes, hydroxy amines, and amino sugars among other important building blocks and intermediates is detailed. In addition to the generality and scope of this cyclization reaction, this article describes a number of mechanistic investigations suggesting a single electron transfer from the anilide functionality to IBX and implicating a radical-based mechanism for the reaction.     

Post-column reaction detection of biotin in human plasma ultrafiltrate based on laser-induced fluorescence energy transfer in the far-red spectral region

High performance liquid chromatography followed by post-column reaction detection in the far-red spectral region provides added sensitivity and selectivity. A homogeneous fluorescence energy transfer assay in the competitive mode based on the binding of biotin and streptavidin was developed as an on-line post-column reaction detection system. The labels used for energy transfer were R-Phycoerythrin conjugated to biotin and Cyanine 5 labeled with streptavidin. The energy transfer peak was measured at 670 nm and excitation was achieved using the 488 nm line of an argon ion laser. The biotin concentration in plasma ultrafiltrate ranged from 0.024 to 6.12 ng/mL (n = 6). The precision of the two controls, 0.24 and 2. 44 ng/mL, was found to be 18.70% and 9.92% relative standard deviation respectively. Accuracy was 10.47% and 1.95% difference from spiked, respectively (n = 6). The limit of detection was 21.70 pg/mL (8.90 x 10(-11)M) calculated based on a factor of 2x the standard deviation of the blank (n = 6). The correlation coefficient for the calibration curve was found to be 0.9995. Recovery from plasma ultrafiltrate at 2.44 ng/mL was 103.40% (n = 6). Detection selectivity was indicated by the absence of background fluorescence in six different plasma samples collected from six individual donors. Endogenous levels were detected in two of the six pools of plasma ultrafiltrates.     

Biomimetic dyes as affinity chromatography tools in enzyme purification

Affinity adsorbents based on immobilized triazine dyes offer important advantages circumventing many of the problems associated with biological ligands. The main drawback of dyes is their moderate selectivity for proteins. Rational attempts to tackle this problem are realized through the biomimetic dye concept according to which new dyes, the biomimetic dyes, are designed to mimic natural ligands. Biomimetic dyes are expected to exhibit increased affinity and purifying ability for the targeted proteins. Biocomputing offers a powerful approach to biomimetic ligand design. The successful exploitation of contemporary computational techniques in molecular design requires the knowledge of the three-dimensional structure of the target protein, or at least, the amino acid sequence of the target protein and the three-dimensional structure of a highly homologous protein. From such information one can then design, on a graphics workstation, the model of the protein and also a number of suitable synthetic ligands which mimic natural biological ligands of the protein. There are several examples of enzyme purifications (trypsin, urokinase, kallikrein, alkaline phosphatase, malate dehydrogenase, formate dehydrogenase, oxaloacetate decarboxylase and lactate dehydrogenase) where synthetic biomimetic dyes have been used successfully as affinity chromatography tools.     

Determination of low levels of an antioxidant in polyolefins by large-volume injection temperature-programmed packed capillary liquid chromatography

Sub-ambient column temperatures, promoting strong interactions between the analyte and the stationary phase material, were utilized to focus large volumes of the polyolefin antioxidant Irganox 1076 [benzenepropanoic acid, 3.5-bis(1,1-dimethylethyl)-4-hydroxy-, octadecyl ester] on the column inlet, using pure acetonitrile as sample solvent and mobile phase. Injection volumes up to 100 microl were successfully employed on a 50 cm x 320 microm I.D. capillary column packed with 5 microm Kromasil 100 ODS particles. Irganox 1076 was eluted after completed injection by temperature programming, using a temperature program from 7 to 90 degrees C, in 3 degrees C min(-1). UV detection, using a low-dispersion "U"-shaped flowcell, was performed at 280 nm. The method was applied for the determination of Irganox 1076 that was extracted from low-density polyethylene (0.6 ppm, w/w). Both Soxhlet and microwave-aided solvent extractions were performed, using chloroform and acetonitrile as solvents, respectively. The microwave-aided extraction with acetonitrile was found to give approximately the same yield as the standard Soxhlet reference method. Consequently, small volumes of acetonitrile could be used both as extraction solvent, sample solvent and mobile phase, simplifying the analysis process. The mass limit of detection of the method was found to be 3.3 ng, corresponding to a concentration limit of detection of 33 ng ml(-1), utilizing an injection volume of 100 microl. The within and between day precision of retention times displayed relative standard deviations below 1.2%.     

Itinerant electron ferromagnetism in Sr2+-, Ca2+-, and Ba2+-doped rare-earth orthocobaltites (Ln3+1−xM2+xCoO3)

Electronic and magnetic properties of Ln_1?xSr_xCoO₃ (Ln = Pr, Nd, Sm, Eu, and Gd) systems show that above a critical value of x, the d electrons become itinerant while the materials become ferromagnetic at low temperatures. The ferromagnetic component increases with increase in x and decrease in temperature. The Curie temperature increases with x and decreases with decrease in the size of the rare-earth ion. Incorporation of Ba²⁺ in LaCoO₃ favors itinerant electron ferromagnetism relative to Sr²⁺ while Ca²⁺ is less favorable than Sr²⁺.     

The nonlinear shear gradient effect on the shear viscosity of a ternary system near a plait point

We have studied the shear viscosity of a ternary liquid mixture (water-ethanol-chloroform) near a plait point by the capillary method and found an apparently strong levelling-off as we approach the critical point. This levelling-off cannot be explained simply in terms of a strong cusp. It is found that the nonlinear shear gradient effect suggested by Oxtoby can be used to explain this behavior.     

Effect of temperature on the basicity of certain aliphatic-aromatic amino alcohols

Conclusions Ionization constants were obtained of 14 amino alcohols and one tertiary amine in 50% ethanol in the range of 10–25° and thermodynamic characteristics of the ionization process of the investigated ammonium ions were calculated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 669–671, March, 1976.The authors express their gratitude to S. V. Bogatkov for participation in discussion of the obtained results.     

Calculations of electric dipole hyperpolarizability of polyatomic molecules

Coupled Hartree-Fock perturbation theory is employed to compute electric dipole hyperpolarizabilities of water, ammonia and methane with three different GTO basis sets. The results were extremely sensitive to the form of zero-order HF wave-functions. In some cases large discrepancies between computed and experimental values suggest that the latter ones must be reviewed. A comparison with other computations is also made.     

Exchange of deuterium with OH groups of HY zeolites

The exchange reaction of D₂ with OH groups of HY zeolites was followed both in the solid and gas phase by IR and MS. The rates of D₂–OH and D₂–H₂ exchange increase considerably with dehydroxylation of the sample. The active centers are probably vacancies formed by removal of oxygen from the lattice, they catalyze the dissociation of D₂. Dehydroxylation of the sample is accompanied by the formation of 3 740 cm^–1 hydroxyls, whose exchange with D₂ is slower than that with other OH groups and which affect the kinetics in the gas phase.

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D₂ OH HY - O₂–OH O₂–H₂ . , , , O₂. OH, 3740 ^–1, , OH .

     

Chromatographic analysis of hydrocarbons in marine sediments and seawater.

The low concentration of hydrocarbons anticipated in pollution baseline studies necessitates the development of analytical techniques sensitive at the sub-microgram per kilogram concentration level. The method of analysis developed in this laboratory involves dynamic headspace sampling for volatile hydrocarbon components of the sample, followed by coupled-column liquid chromatography for the non-volatile components. These techniques require minimal sample handling, reducing the risk of sample component loss and/or sample contamination. Volatile sample components are separated from the matrix in a closed system and concentrated on a TENAX-GC packed pre-column, free from large amounts of solvent and ready for GC/GC-MS analysis. Non-volatile compounds, such as the benzpyrenes, may be extracted from large volumes of water and concentrated on a Bondapak C18 packed pre-column for coupled-column liquid chromatographic separation and analysis. Results of the application of these techniques to the analysis of samples from sites of known low level hydrocarbon contamination are presented and discussed.