Preparation of thiocyanates and isothiocyanates from alcohols, thiols, trimethylsilyl-, and tetrahydropyranyl ethers using triphenylphosphine/2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)/n-Bu4NSCN system

A combination of triphenylphosphine (PPh₃) and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) provides a safe and easily available mixed reagent system for the conversion of 1° and 2° alcohols, thiols, trimethylsilyl-, and tetrahydropyranyl ethers to their corresponding thiocyanates and the 3° ones to isothiocyanates in good to high yields.     

Determination of Flavonoid Markers in Honey with SPE and LC using Experimental Design

Determination of flavonoid markers quercetin, hesperetin, and chrysin, found in north Iranian citrus honey samples, was carried out by solid phase extraction (SPE) and isocratic liquid chromatographic separation using central composite design. Optimum conditions for SPE were achieved using 10 mL methanol/water (13:87, v/v, pH = 7) as the washing solvent and 4 mL methanol for elution. Good clean-up and high recovery >90% were observed for all analytes. The use of water/ACN/THF/AcOH (54:36:5:5, v/v) was found to serve as the optimum mobile phase composition and allowed for the separation of analytes from endogenous compounds present in honey. SPE parameters, such as maximum loading capacity and breakthrough volume, were also determined for each analyte. Limit of detection, linear range, recovery, repeatability of retention times, and peak heights were 3.11 × 10⁻⁸–4.44 × 10⁻⁸ g g⁻¹, 0.50–50.0 μg mL⁻¹ (R ² > 0.99), 90.7–96.9%, 3.0–3.6%, and 1.0–2.6%, respectively. Precision of the overall analytical procedure, estimated by five replicate measurements for quercetin, hesperetin and chrysin in citrus honey, as well as the relative standard deviations were 4.3%, 3.8%, and 5.5%, respectively.

     

Justification of a Malyshev-Type Formula in the Nonnormal Case

Let A be a complex matrix of order n, n ≥ 3 . We associate with A the 3n $$Q(\gamma ) = \left( {\begin{array}{*{20}c} A & {_{\gamma 1} I_n } & {_{\gamma 3} I_n } \\ 0 & A & {_{\gamma 2} I_n } \\ 0 & 0 & A \\ \end{array} } \right),$$ where γ₁, γ₂, γ₃ are scalar parameters and γ = (γ₁, γ₂, γ₃). Let σ_i, 1 ≤ i ≤ 3n, be the singular values of Q(γ), in decreasing order. Under certain assumptions on A, the authors have proved earlier that the 2-norm distance from A to the set $\mathcal{M}$ of matrices with a zero eigenvalue of multiplicity at least 3 is equal to max $$\begin{array}{*{20}c} {\max } \\ {\gamma 1,\gamma 2,\gamma 3 \in \mathbb{C}} \\ \end{array} \;^\sigma 3n - 2(Q(\gamma )).$$ Now, the justification of this formula for the distance is given for an arbitrary matrix A.     

Synthesis, characterization and application of β-cyclodextrin-silica nanocomposite as potential microvessel in nucleophilic substitution reaction of phenacyl halides

In the present study, β-cyclodextrin-silica hybrid is synthesized as a novel, efficient and eco-friendly microvessel and solid–liquid phase-transfer catalyst. This molecular host system was applied for nucleophilic substitution reaction of phenacyl halides in water. No evidence was observed for the formation of by-product for example isothiocyanate or alcohol. Also the products were obtained in pure form without further purification. The structure and morphology of the obtained system were investigated by infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis and differential thermal analysis techniques. The surface porosity of the synthesized catalyst was evaluated from the nitrogen adsorption isotherm. All the results provided evidence for incorporation of β-cyclodextrin inside silica pores.     

On the inverse eigenvalue problem for nonnegative matrices of order two to five

In this paper, for a given set of numbers with special conditions, we construct a nonnegative matrix such that the given set is its spectrum.     

铜催化硫代硫酸钠与卤代芳烃偶联的无硫醇路径合成二芳基硫化物

报道了一个在聚乙二醇中由卤代芳烃合成不同二芳基硫化物的高效方法.在Cu催化剂作用下,无味、易得、稳定的Na2S2O3· 5H2O盐是有效的硫源.     

Nitration of aromatic compounds under neutral conditions using the Ph2PCl/I2/AgNO3 reagent system

Aromatic compounds were nitrated efficiently under essentially neutral conditions by employing Ph₂PCl in the presence of I₂ and AgNO₃. This method minimizes waste products compared to traditional methods and gives the corresponding mononitro derivatives in good to excellent yields in dichloromethane at room temperature.     

Methods for Examining the Fatigue and Fracture Behavior of Hard Tissues

An understanding of the fatigue and fracture behavior of hard tissues (e.g., bone and tissues of the human tooth) is critical to the maintenance of physical and oral health. Recent studies suggest that there are a number of mechanisms contributing to crack extension and crack arrest in these materials, and that they appear to be a function of moisture and age of the tissue. An understanding of these processes can provide new ideas that are relevant to the design of multi-functional engineering materials. As a result, we have adopted the use of microscopic Digital Image Correlation (DIC) to examine the mechanisms of crack growth resistance and near-tip displacement distribution for cracks in human dentin that are subjected to opening mode loads. We have also developed a special compact tension (CT) specimen that permits evaluation of crack extension within small portions of tissue under both quasi-static and fatigue loads. The specimen embodies a selected portion of hard tissue within a resin composite restorative and enables an examination of diseased tissue, or portion with specific physiology, that would otherwise be impossible to evaluate. In this paper we describe application of these experimental methods and present some recent results concerning fatigue crack growth and stable crack extension in dentin and across the dentin-enamel-junction (DEJ) of human teeth.

Regioselective Synthesis of 2-Substituted [1,2,4]Triazolo[5,1-b][1,3]thiazin-7-ones by Heteropolyacids

2-Substituted [1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones 3 were synthesized via regioselective cyclization of 4H-[1,2,4]triazol-3-ylsulfanyl-acrylic acids 2 in the presence of catalytic amounts of heteropolyacids at room temperature in very good yields and rates.