Oxidation of mandelic acid derivatives catalysed by Bi(0)/O2 systems: mechanistic considerations

Mandelic acid and some aryl substituted derivatives were oxidised under molecular oxygen and a catalytic amount of Bi(0). The corresponding aldehydes and/or the carboxylic acids were obtained selectively depending on the nature of the substituent. Aldehydes and α-keto acids were oxidised under the same Bi(0)/O₂ system and α-keto acids were proposed as intermediates in the formation of benzoic acid derivatives.     

Synthese von „Dithio-Oxolinsäure“

5-Amino-benzo-1,3-dithiol, available by reduction of 5-amino-benzo-1,3-dithiol-2-thion, was elaborated into dithio-oxolinic Acid (6 a).

     

Ligand creation via linking—a rapid and convenient method for construction of novel supported PyOX-ligands

A novel supported amino alcohol linker was synthesized and utilized for attachment of picolinic acid derivatives onto different supports. When the resin bound molecule was further activated, the PyOX-moiety could be constructed reliably in enantiopure form. Furthermore, an efficient Pd-catalyzed modification of a picolinic acid derivative is presented.     

Anion-pi interactions in cyanuric acids: a combined crystallographic and computational study

Several structures of pi complexes of isocyanuric acid and of several thio derivatives with anions have been computed by using high level ab initio calculations. The nature of the complexes has been studied by means of the method of molecular interaction potential with polarization (MIPp) and Bader's theory of atoms-in-molecules. These molecules form favorable complexes with anions and can be used as binding units for building receptors for the molecular recognition of anions. In several cases, the anion-pi interaction has been demonstrated experimentally by means of X-ray crystallography.     

Post-column oxidative derivatization for the liquid chromatographic determination of phenothiazines

A first post-column chemical derivatization method for the liquid chromatographic determination of phenothiazines is presented. Peroxyacetic acid is introduced as a derivatizing agent for phenothiazines, yielding the colored radical cations or fluorescent sulfoxides, depending on reaction conditions. Both reaction products were successfully employed for the detection of the phenothiazines after their liquid chromatographic separation. The fluorescence spectroscopic detection of the sulfoxides proved to be the more robust and sensitive method. Limits of detection ranged from 4 nM for triflupromazine and trimeprazine to 300 nM for phenothiazine for the fluorescence spectroscopic detection of the sulfoxide and from 0.3 μM for phenothiazine and triflupromazine to 2 μM for trifluperazine for the UV–Vis spectroscopic detection of the radical cation. The calibration functions for the fluorimetric sulfoxide determination ranged from two to more than three decades, starting at the limit of quantification.     

Photochemical degradation of hyaluronic acid by singlet oxygen

Changes of the rheological properties of hyaluronic acid (sodium-magnesium salt) solutions after exposure to UV radiation indicate a vigorous decrease in their viscosity, but its still strong shear rate dependence. Whereas the presence of the singlet oxygen sensitizer (anthracene-1-sulphonic acid) brings about a loss of shear dependence; the studied solutions show newtonian behavior.     

Salts of α-cyanoacrylic acid with sterically hindered tertiary amines

Syntheses are reported for representatives of a new class of derivatives of -cyanoacrylic acid, namely, its salts with brucine, tert-butyldimethylamine, and diisopropylmethylamine.A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 212–214, January, 1992.     

Fractionation and purification of antioxidant peptides from Chinese sturgeon (Acipenser sinensis) protein hydrolysates prepared using papain and alcalase 2.4L

Protein hydrolysates have the potential to be natural and safer sources of bioactive peptides. In this study, two proteases were used to hydrolyze Chinese sturgeon (Acipenser sinensis) protein, and the hydrolysates were then purified to yield antioxidant peptides. The degree of hydrolysis of 23.56 % and 18.14 % was obtained using papain and alcalase 2.4L, respectivly, and hydrolysates had 96.80 % and 87.24 % total amino acid content, respectivly. The papain hydrolysate (PH) and alcalase 2.4L hydrolysate (AH) showed good antioxidant activity against DPPH^? (IC₅₀ of 3.64 and 3.15 mg/mL) and ABTS^?+ (IC₅₀ of 1.92 and 1.58 mg/mL), respectively. The low-molecular-weight (<1000 Da) fraction of both hydrolysates demonstrated the highest antiradical activity (IC₅₀ of 2.59 and 2.31 mg/mL, DPPH) and (IC₅₀ of 1.54 and 1.36 mg/mL, ABTS), respectively. Nine peptides were separated from both hydrolysates using reverse phase high performance liquid chromatography (RP-HPLC). The IC₅₀ for ABTS^?+ scavenging activity of peptide P5 with valine, glycine and asparagine (MW of 282.13 Da) from PH, and peptide P3 with histidine, glycine and alanine (MW of 302.74 Da) from AH was 0.89 and 0.72 mg/mL, respectively. The fractions and purified peptides obtained from Chinese sturgeon hydrolysates could be utilized as natural antioxidant substitutes in pharmaceuticals and food products.     

A quick method for the simultaneous determination of ascorbic acid and sorbic acid in fruit juices by capillary zone electrophoresis

A method of quickly determining ascorbic acid and sorbic acid by capillary zone electrophoresis with ultraviolet detection was developed. The choice of background electrolyte, wavelength, injection time and applied voltage were discussed. Ascorbic acid and sorbic acid were well separated in 80 mmol L⁻¹ boric acid-5 mmol L⁻¹borax (pH = 8.0) in 5 min at the detecting wavelength of 270 nm. Under the optimum condition, the method has linear ranges of 2.54-352.00 mg L⁻¹ for ascorbic acid and 1.08-336.39 mg L⁻¹ for sorbic acid with the detection limit of 1.70 mg L⁻¹ for ascorbic acid and 0.54 mg L⁻¹ for sorbic acid, respectively. Other organic acids in fruit juices have no effect on the detection. This method is very feasible and simple and can be used to detect ascorbic acid and sorbic acid in fruit juices.     

Transference numbers for ultra concentrated solutions of aqueous hydrochloric acid at 25°C

Transference numbers of HCl(aq) solutions at 25°C, from 0.01 to 13.6 mol-kg^–1(m) have been obtained by measuring the emf of cells with transference using hydrogen gas/platinum electrodes. Good agreement is obtained at concentrations up to 1 m with all previous data, and our results strongly corroborate those of King and Spiro over the 2–8m concentration range. The transference numbers of the hydronium ion fit the empirical equation, _H ^HCl = 0.821 + 0.0457m ^1/2 – 2.476×10^–2m – 1.90×10^–4 m ² – 1.45×10^–5 m ³ the maximum deviation in T _H ^HCl being 0.003.