2-hydroxy-1-naphthaldehyde-derived Schiff bases: synthesis, characterization, and structure

Four Schiff base molecules were synthesized from the condensation of 2-hydroxy-1-naphthaldehyde with various amines having additional ligating centers, and the resulting products were characterized by analytical and spectral methods, and also by single crystal X-ray diffraction. 2-(-Naphthalideneamino)-2-methyl-1-propanol, 1, is orthorhombic, P2₁2₁2₁, a = 9.918(1), b = 12.629(1), c = 10.416(1) Å. 2-(-Naphthalideneamino)-2-hydroxymethyl-1-propanol, 2, is monoclinic, P2₁/c, a = 14.522(3), b = 9.723(2), c = 9.534(9) Å, = 107.75(4)°. 2-(-Naphthalideneamino)-2-hydroxymethyl-1,3-propanediol, 3, is monoclinic, P2₁/c, a = 20.981(9), b = 5.943(3), c = 10.549(5) Å, = 91.23(3)°. 2-(-Naphthalideneamino)-pyridine, 4, is monoclinic, P2₁/c, a = 5.804(4), b = 17.363(2), c = 24.032(11) Å, = 92.03(5)°. The molecular structures of these were found to be in extended conformation where the aromatic moiety is coplanar with that of the imine bond and the imine bond exhibited trans-geometry. The naphthyl moiety in each of these molecules is stabilized in quinoid form in the solid state. Interesting lattice structures were noticed owing to intermolecular interactions.     

Quality Control of Krill Oil by Nuclear Magnetic Resonance (NMR) Spectroscopy: Composition and Detection of Foreign Species

Krill oil is currently among the most highly promoted products in the dietary supplement market, which, due to its high price, can be potentially adulterated with fish species and artificial oil. For a holistic control of krill oil quality, ¹H, ¹³C, and ³¹P nuclear magnetic resonance (NMR) spectroscopies were used. The fatty acid and phospholipid composition as well as secondary ingredients, such as homarine, amino acids, and chitin, were examined. The following phospholipid species were detected: phosphatidylcholine (75–85?mol %), phosphatidylethanolamine (4–7?mol%) and their lyso derivatives 1-lysophosphatidylcholine (1–2?mol%)–2-lysophosphatidylcholine (10–16?mol%) and lysophosphatidylethanolamine (1?mol%). In the -2 position of phospholipids, the content of eicosapentaenoic acid (mean 68.23%; relative standard deviation 2.23%) was twice as high as the content of docosahexaenoic acid (mean 31.77%; relative standard deviation 4.79%). ¹³C NMR spectroscopy was used to distinguish between krill and fish oil-based dietary supplements. The adulteration of krill oil can be detected by fatty acid distribution in the sn-2 triacylglycerol position. The sensitivity of the method is about 10% (w/w) of fish content in blends, which is enough to detect deliberate adulteration. The same methodology can be used to recognize synthetically modified krill oil. The method was successfully applied to 30 commercially available krill and fish oil supplements.     

Study of the protonation of 1-methylimidazo (4,5-B)pyrazines by1H and13C NMR methods

Conclusions A study of the¹H and¹³C NMR spectra of the neutral molecules, monocations, and dications of 1-methyl- and 1,5,6-trlmethylimidazo(4,5-b)pyrazLnes has shown that the first protonation of these compounds occurs at the 3-N atom of the imidazole fragment and the second at the 4-N atom of the pyrazine ring.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1060–1068, May, 1977.     

Synthesis of derivatives of pyrazine-2,3-dicarboxylic acids and pyrazine-2,3-dicarbonamides from 2,3-dichloroquinoxaline

The synthesis of dimethyl 2,3-dichloropyrazine-5,6-dicarboxylate from dichloroquinoxaline has been effected. The nucleophilic substitution reactions of the compound obtained have been studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1548–1551, November, 1973.     

Synthesis, 1 H, 13 C, 15 N, and 113 Cd NMR, ESI-TOF MS, Semiempirical MO (PM3), ab initio/HF and Cation/Anion Binding Studies of N-deoxycholyl-l-tryptophan

The synthesis, structural characterization, and cation/anion binding properties ofa new bile acid-amino acid conjugate, N-deoxycholyl-l-tryptophan, aredescribed. The structures of the ligand and its cadmium adduct at different pHconditions and various cadmium perchlorate concentrations were determined bymodern multinuclear magnetic resonance spectroscopic as well as ESI-TOF MStechniques. Also semiempirical PM3 and ab initio/HF molecular modellingstudies were performed. Based on ¹H,¹H NOESY measurementsN-deoxycholyl-l-tryptophan in alkaline conditions was found to appearin a bent conformation which was clearly different from the conformations in neutraland acidic solutions. According to molecular modelling in its minimum energy structurethe tryptophan backbone of the ligand was folded close to the deoxycholic acid skeletonand the structure was stabilized by an intramolecular hydrogen bond. The multinuclearmagnetic resonance experiments indicated that Cd²⁺-cation was bound with theligand in neutral and alkaline conditions while in acidic conditions protons block thebinding site. ESI-TOF MS revealed clearly a competition between sodium and cadmiumions, the ligand having a stronger affinity for sodium. Cadmium binding occurred onlywhen excess of cadmium was used. Further, ESI-TOF MS spectra showed that variouschlorine oxyanions originated from perchlorate anion formed together with cationsdifferent adducts with the ligand.     

Luminescence of Europium(III) Chelates with 4-(Arylethynyl)pyridines as Ligands

Some Spectral properties and luminescence intensities of Eu^III chelates with 4-(arylethynyl)pyridine-2,6-dicarboxylic acids 1 – 15 and 2,2′,2″,2′″-{[4-(arylethynyl)pyrridine-2,6-diyl]bis(methylenenitrilo)} tetrakis(acetic acids) 16 – 26 were measured both in H₂O and EtOH solutions for the purpose of developing suitable labels to be used in time-resolved luminescence-based bioaffinity assays (Tables 1 and 2). The substitution at the Ar group has a significant effect upon the observed luminescence intensities, excitation wavelengths, and decay constants of the complexes, Moreover, the changes in the environment cause great variation in those properties of certain Eu^III chelates.     

Some NN′-substituted 1,2,3,4-tetrahydroquinox alines and the Hofmann degradation of the quaternary base from NN′-dimethyltetrahydroquinoxaline

Some N- and NN-substituted 1, 2, 3, 4-tetrahydroquinoxalines ate synthesized. The quaternary base of NN-dimethyl-1, 2, 3, 4-tetrahydroquinoxaline, obtained from the corresponding methiodide, undergoes the Hofmann degradation reaction. The degradation product, NNN-trimethyl-o-phenylenediamine, is apparently formed via the intermediate NN-dimethyl-N-methyl-N-vinyl-o-phenylenediamine.We wish to express our sincere thanks to Prof. O. Yu. Magidson for the interest he has shown in this work.     

Determination of nitrosamines in preserved sausages by solid-phase extraction-micellar electrokinetic chromatography

A new methodology for extraction, pre-concentration and analysis of nitrosamines in meat derived products was developed. The samples (canned sausages) were distilled in vacuum steam and the nitrosamines were pre-concentrated by solid-phase extraction with active carbon. Then, micellar electrokinetic chromatography was used for the separation and determination of the different nitrosamines contained in a real sample and gas chromatography with mass spectrometry detection was used as the confirmation technique. The method allowed the determination of nitrosamine compounds at trace levels with relative standard deviation ranging from 4.0 to 22%.     

Synthesis and properties of 4-substituted 1,5-naphthyridines and their N-oxides

4-Substituted 1,5-naphthyridines and their N-oxides were synthesized, and their structures and properties were studied. The IR and UV spectra of 4-hydroxy- and 4-methoxy-1,5-naphthyridines and their 1-oxides and 1-ethyl-4-oxo-1,4-dihydro-1,5-naphthyridine were examined. It is shown that 4-hydroxy-1,5-naphthyridine and its 1-oxide exist in the crystalline state in the lactam form. A quantitative estimate of the position of the tautomeric equilibrium of 4-hydroxy-1,5-naphthyridine as a function of the polarity of the solvent is given, and the tautomeric equilibrium constants and the percentages of the lactim form are calculated. The basicity constants of 4-chloro-, 4-methoxy-, 4-hydrazino-, 4-methylthio-, 4-acetamido-, and 4-amino-1,5-naphthyridines were measured. A comparison of the calculated and experimental pK_a data provides evidence in favor of the fact that the compounds are protonated at the N₁ atom. A correlation of the basicity constants with the substituent constants is examined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 792–799, June, 1981.