Aromatic compounds in molecular phase of Baltic amber-synchronous luminescence analysis

Synchronous luminescence analysis was performed in order to identify aromatic compounds in solvent extracts of Baltic amber. The investigated extracts were obtained, for comparisons, as products of extraction by various techniques and solvents. Methylene chloride and ethanol were applied independently for extraction at the ambient temperature (conservative extraction), as well as at the temperature of solvent boiling (extraction in Soxhlet apparatus). Ethanol, as the solvent, was also used for extraction in an ultrasonic bath and for the decoction process. The extraction, by techniques mentioned, of the analysed amber has resulted in products generally containing the same groups of aromatics: mainly naphthalenes, phenanthrenes and anthracenes. Among phenanthrenes, in all samples the retene was also identified, being one of the characteristic links of the diagenetic chain of chemical transformations of vegetal precursors. The identification of a series of individual compounds made, using the synchronous luminescence technique, was verified by the record of conventional emission and excitation spectra. Presented identified compounds were also confirmed by the results of GC-MS analysis. The luminescence analysis was also performed comparatively for fossil resin from Galicia, Spain (Cretaceous) older than Baltic amber (Tertiary, Eocene). The obtained preliminary results of synchronous luminescence analysis suggest the possibility of diversification in this manner of fossil resins of various ages by characterisation of aromatisation degree and alkyl substitution of aromatic rings. It is since well known that aromatisation progress is an indicator of a natural process of maturation of fossil organic matter. However, a greater number of samples should be taken to further testify to the investigations.     

Electronic spectra and structure of 2-bromopicolines, their N-oxides, and 2-bromo-4-nitropicoline N-oxides

The UV spectra of 2-bromopicolines, their N-oxides, and 2-bromo-4-nitropicoline N-oxides are presented and the influence of substituents onλ _max andε _max of spectral bands are discussed. The electronic spectra were calculated using the modified INDO method. Transition energies, intensities, and assignments were compared with UV spectra. The degree of intramolecular CT in 2-bromopicoline N-oxides is greater than those in 2-bromopicolines and smaller than those in 2-bromo-4-nitropicoline N-oxides. The differences of the HOMO-LUMO energies indicate that the susceptibilities in the photochemical reaction lie in the order: 2-bromo-4-nitropicoline N-oxides>2-bromopicoline N-oxides>2-bromopicolines. Department of Organic Chemistry, University of Economics, PL-53 342 Wroclaw, Poland. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 197–207, February, 1998.     

Synthesis of nitro derivatives of 2-alkylamino-4-nitropicolines and their N-oxides

2-Alkylamino-4-nitro-3- or-5-methylpyridines, 2-alkylnitramino-4-nitro-3- or-5-methylpyridines, and their N-oxides were synthesized in good yields. Some properties of the products are reported.Department of Organic Chemistry, University of Economics, PL-53-342 Wroclaw, Poland. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 652–656, May, 1998.     

Synthesis of dihalopicoline N-oxides and their 4-nitro derivatives

Three aminohalo-substituted - and -picolines, six dihalo-substituted - and -picolines, six dihalo-substituted - and -picoline N-oxides and six respective dihalo-4-nitropicoline N-oxides were synthesized in excellent yields. Some properties of the products were reported.Academy of Economics, Department of Organic Chemistry, PL 53-423, Wroclaw. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1366–1371, October, 1996. Original article submitted November 15, 1995.     

Simultaneous Determination of 4‐Chlorophenol and Oxalic Acid Using an Expanded Graphite‐Epoxy Composite Electrode

An expanded graphite‐epoxy composite electrode (EG‐Epoxy) was employed for the simultaneous determination of 4‐chlorophenol (4‐CP) and oxalic acid (OA) by using cyclic voltammetry (CV), chronoamperometry (CA), and differential pulse voltammetry (DPV). The results indicated that OA could be determined in the presence of the same concentrations of 4‐CP within the concentration range of 0.1 mM to 0.5 mM with a relative standard deviation (RSD) smaller than 5%. Electrode fouling occurred during CA for 4‐CP concentrations larger than 0.5 mM. The DPV method was used for the simultaneous determination of 4‐CP and OA before and after electrochemical oxidation by chronopotentiometry under galvanostatic conditions (j=0.04 mA cm^?2, t=2 h) of a tap water sample spiked with 0.19 mM 4‐CP and 0.1 M Na₂SO₄.     

The13C NMR, UV and IR spectra of 2-fluoropyridine methyl derivatives

¹³C NMR, UV, and IR spectra of methyl derivatives of 2-fluoropyridine have been recorded. The influence of the substituents on the spectral characteristics of the compounds has been discussed. The electronic spectra have been calculated by a modified INDO method. Transition energies, intensities, and assignments are compared with UV spectra.Department of Organic Chemistry, Academy of Economics, Pl-53 342 Wroclaw, Poland Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 763–773, June, 1999.     

Multinuclear 1H, 13C and 15N NMR study of some substituted 2-amino-4-nitropyridines and their N-oxides

1H, 13C and 15N NMR chemical shift assignments based on pulsed field gradient selected PFG 1H,X (X = 15C and 15N) HMQC and HMBC experiments are reported for three 4-nitropyridine N-oxides and four 4-nitropyridines. It was found that an ortho effect of a methyl group inhibits the deshielding effect of the 4-nitro group and that this effect and the so-called back donation is influenced by electronegativity and position of substituents in the multisubstituted pyridine N-oxides. The shielding effect of N-oxide group is most pronounced in the 15N NMR chemical shifts of the studied compounds. This effect is further modified by methylamino, methylnitramino, 5- or 3-methyl and 4-nitro groups. Among them the 4-nitro group exerts the highest influence on the shielding effect of the N-oxide functionality. Experimental 1H, 13C and 15N NMR chemical shifts and GIAO/DFT theoretical calculations are consistent with each other and supported by the reactivity on nucleophilic substitution, the UV spectral and the dipole moment data.     

Electronic spectra and crystal structure of dinuclear Cu(II) ‘paddle wheel’ acetate complex containing axially coordinated 3-methyl-4-nitropyridine-<Emphasis Type="Italic">N</Emphasis>-oxide

This article presents the electronic spectral characteristics enhanced with the structural, IR and magnetic data of the copper(II) acetate complex with 3-methyl-4-nitropyridine-N-oxide. The complex of the formula, [Cu₂(OAc)₄(3-mnpn)₂], belongs to the group of the ‘paddle wheel’ type species with a very short (2.58 Å) metal–metal distance. In the electronic spectra, new bands were found at 16,000 and 24,000 cm^?1, which have been tentatively assigned to the metal–metal interactions and solid state effects, respectively. The complex show fast kinetic exchange of the apical ligand, i.e. 3-methyl-4-nitropyridine-N-oxide.     

Retro-leapfrog and related retro map operations

Operations on maps are well-known theoretical tools for transforming a given polyhedral tessellation. Several theoretical investigations of fullerenes, such as their pi-electronic structure and stability, need information on the original map which was transformed into a larger molecular structure. In this respect, retro-operations, particularly those of the most used leapfrog, chamfering, and capra operations, appear particularly useful in searching the associate graphs of fullerenes. A series of analyzed cages proved to be leapfrog transforms of smaller cages. This information was useful in understanding their closed pi-electronic structure and related properties including the local aromaticity. An index based on the optimized geometries enabled the evaluation of aromaticity of their various substructures. Pictorial images of the pi-electron distribution as the main Kekulé valence structures have been performed by the aid of the JSCHEM software package.     

Non-enzymatic electrochemical detection of glycerol on boron-doped diamond electrode

A non-enzymatic direct electrochemical glycerol detection method at a commercial boron-doped diamond (BDD) electrode in 0.1 M NaOH supporting electrolyte was developed. All the used electrochemical techniques proved useful features for the oxidation and direct amperometric determination of glycerol at a BDD electrode in 0.1 M NaOH aqueous solution. It was found that the direct electrooxidation of glycerol on the BDD electrode requires both adsorbed glycerol and hydroxyls at the electrode surface. Also, the sp(2) carbon did not allow enhancement of the glycerol oxidation process. The electronalytical sensitivity for the determination of glycerol at the BDD electrode ranged from 0.040 to 0.226 μA mM(-1) as a function of the technique used. The highest electroanalytical sensitivity for the determination of glycerol at the BDD electrode was reached in batch system amperometric quantification under stirring conditions. Performed recovery studies indicated that it is possible to determine glycerol in real samples, and the proposed batch system analysis-based methodology can be a valuable tool for practical glycerol analysis.