Decomposition of Triethylamine Over Acid Catalysts

The effect of hydrochloric acid, boric acid, and silica content in alumina on its catalytic activity towards the decomposition of triethylamine was investigated at 310°, 320°, and 330°. The study was carried out in a flow system and the reaction product was analyzed chromotographically. Ethylene formation is a zero order reaction independent of the partial pressure of triethylamine. Treating γ-alumina with hydrochloric acid increases its catalytic activity towards ethylene formation whereas silica-alumina is less active than γ-alumina. Boric acid-treated alumina has the same activity of γ-alumina. Formation of ethylene from preadsorbed triethylamine was studied. The similarity between reactions of aliphatic alcohols and amines over acid catalysts is concluded.     

Ion-Pair LC Method for Simultaneous Determination of Aliskiren Hemifumarate,Amlodipine Besylate and Hydrochlorothiazide in Pharmaceuticals

A rapid and precise LC method was developed for the simultaneous determination of aliskiren hemifumarate (ALS), amlodipine besylate (AML) and hydrochlorothiazide (HCZ) using acetonitrile:25 mM octane sulfonic acid sodium salt monohydrate in water (60:40 v/v) as the mobile phase. The flow rate was maintained at 1.2 mL min^?1 on a stationary phase composed of Supelco, Discovery^® HS (C18) column (25 cm × 4.6 mm, 5 μm). Isocratic elution was applied throughout the analysis. Detection was carried out at λ _max (232 nm) at ambient temperature. The method was validated according to ICH guidelines. Linearity, accuracy and precision were satisfactory over the concentration ranges of 32–320, 2–44 and 4–64 μg mL^?1 for ALS, AML and HCZ, respectively. LOD and LOQ were estimated and found to be 0.855 and 2.951 μg mL^?1, respectively, for ALS, 0.061 and 0.202 μg mL^?1, respectively, for AML as well as 0.052 and 0.174 μg mL^?1, respectively, for HCZ. The method was successfully applied for the determination of the three drugs in their co-formulated tablets. The results were compared statistically with reference methods and no significant difference was found. The developed method is specific and accurate for the quality control and routine analysis of the cited drugs in pharmaceutical preparations.     

A new coumarin laser dye 3-(benzothiazol-2-yl)-7-hydroxycoumarin

The electronic absorption, and emission spectra as well as fluorescence quantum yield of 3-(benzothiazol-2-yl)-7-hydroxycoumarin (BTHC) were measured in different solvents and are affected by solvent polarity (Δf). The deprotonation of BTHC by triethylamine is a reversible process. BTHC is relatively photostable, the quantum yield of photodecomposition (φ_c) was found to be 2×10⁻⁴ and 2.7×10⁻⁴ in EtOH and DMF, respectively. The fluorescence lifetimes of BTHC were measured in the absence and in the presence of molecular oxygen and were found to be 2.82 and 2.78 ns, respectively. BTHC acts as good laser dye upon pumping with nitrogen laser (λ_ex=337.1 nm) in ethanol and gives laser emission with maxima at 508 and 522 nm.     

Quantum chemical studies on structures and spectra of 2,5-distyrylpyrazine (DSP) laser dye

Semiempirical (MNDO and PM3) molecular orbital calculations have been undertaken to study the structures of the ground and excited states of 2,5-distrylpyrazine dye to assess its activity as a laser dye. In the ground and first excited singlet states, the trans-trans structure of C_2h symmetry is the most stable structure in the gas phase and in DMSO, which agrees with the experimental findings. Upon excitation, the flexibility of the molecule decreases, leading to a subsequent decrease in the radiationless deactivation pathway and this increases the fluorescence efficiency of DSP. The absorption, excitation, and emission spectra have been calculated at the MNDO level using the PM3 optimized geometries in DMSO. At this level the agreement between theory and experiment is quite good. An estimated absorption band at 377 nm (expt 380 nm) is assigned to the S₀→S₁ transition. The excited state absorption band at 457 nm (expt 460 nm) is assigned to the S₁→S₁₂ transition. The emission band at 458 nm (expt 460 nm) is assigned to the S′₁→S′₀ transition. The overlap between the emission and the excited-state absorption spectra is presumably the main reason behind the reduced laser activity of the investigated dye. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 585–592, 1998     

Spectral properties of (5-phenyl-1,3,4-oxadiazol-2-yl)-7-hydroxycoumarin (POHC)

The electronic absorption, emission and excitation spectra of POHC were measured in different solvents and are affected by solvent polarity. The fluorescence quantum yield of POHC decreases with increasing Richardt and Dimorth solvent parameter (E(T)) value of the solvent. In dilute solutions POHC is almost totally present in its protonated nitrogen tautomer form. The deprotonation is a reversible process. A shoulder in the absorption spectra at approximately 473 nm indicates the presence of a portion of the tautomer (s) that disappears on lowering the temperature. Molecular oxygen acts as a quencher with quenching rate constant of 1.8 x 10(10) M(-1) s(-1) in DMF. Energy transfer from POHC to rhodamine 6G in ethanol was also studied. POHC is relatively photostable in ethanol (phic approximately 1.7 x 10(-4)). Quantum chemical calculations were carried out and correlated to experimental observations.     

Development of a liquid phase radioimmunoassay for the measurement of serum ferritin levels for the detection of Covid-19 in patients

Journal of Radioanalytical and Nuclear Chemistry - The aim of this study was the development and analytically validation of a radioimmunoassay system for the measurement of the serum ferritin...     

Polarography of metal-gallic complexes

The polarographic behavior of metal ions in perchlorate media containing gallic acid is described. Tungsten(VI) forms a complex with gallic acid which yields a single wave in these media, useful in the polarographic determination of tungsten. Evidence for complexation of chromium(III), copper(II), iron(III), molybdenum(VI), uranium(VI), vanadium(V), tungsten(VI), praseodymium(III), samarium(III), neodymium(III) and gadolinium(III) is obtained and the behavior of these metal ions is summarized.     

Spectral Behavior and Photophysical Parameters of Dihydrophenanthro[9,10-e][1,2,4]Triazine Derivative Dyes in Sol–Gel and Methyl Methacrylate Polymer Matrices

Journal of Fluorescence - This paper deals with the optical and photophysical properties of dihydrophenanthro[9,10-e][1,2,4]triazine fluorescent dyes doped in Silicate based sol–gel and...     

On <Emphasis Type="Italic">τ</Emphasis>-adic representations of integers

Elliptic curve cryptosystems (ECCs) have become increasingly popular due to their efficiency and the small size of the keys they use. Particularly, the anomalous curves introduced by Koblitz allow a complex representation of the keys, denoted τNAF, that make the computations over these curves more efficient. In this article, we propose an efficient method for randomizing a τNAF to produce different equivalent representations of the same key to the same complex base τ. We prove that the average Hamming density of the resulting representations is 0.5. We identify the pattern of the τNAFs yielding the maximum number of representations and the formula governing this number. We also present deterministic methods to compute the average and the exact number of possible representations of a τNAF.