Problems in data retrieval systems for analytical spectroscopy

Some of the existing retrieval systems for analytical purposes based on different spectrometric data are described and compared with systems under development. Requirements concerning input data, coding of fragments or complete chemical structures, preprocessing of input data, and evaluation of the retrieved results are discussed, and some examples are given. Some trends for future developments in this field are outlined.     

Computerized search system based on digitized infrared spectra

During previous work with the chemical information systems [1] we became aware of the shortcomings of the classical IR spectral data banks, consisting of the positions of the characteristic peaks only. Due to this fact and also because better IR data files with digitized spectra are rare and expensive, hardware and software for the digitization of the IR spectra had to be developed in our laboratory. It was employed for the generation of digitized IR spectral data files which were used with success in the analysis of polymers [2]. The existing search system [1] was further developed and upgraded. In the present version, the user can constantly update not only the spectral files, but also the inverted files of peak positions, needed during the search. The system was tested in routine industrial analysis and can be compared favourably with the existing commercialized IR search systems.

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Suchsystem für digitalisierte IR-Spektren mit Hilfe des Computers

     

Room temperature fluorination of aromatic molecules with cesium fluoroxysulphate

Room -temperature fluorination of benzene with cesium fluoroxysulphate in the presence of boron trifluoride as catalyst resulted in the formation of fluorobenzene, while reaction with naphthalene gave 1-fluoro and 2-fluoronaphthalene in the ratio 5:1, the overall yield being between 38 and 42%. The fluorination of phenanthrene and pyrene should be carried out at higher dilution and needs no catalyst. Phenanthrene gave 9-fluorophenanthrene and 9, 9-difluoro-10-keto-9, 10-dihydrophenanthrene in the ratio 1:6 in a yield of about 70%, while pyrene gave 1-fluoro and 4-fluoropyrene in the ratio 7.5:1.     

Acylation of the 4,5- and 5,6-double bond isomers of 3-steroidal thiazolidines: The chemical stability of spiro-3-steroidal 4,5- and 5,6-double bond isomers

It has been shown that the 5,6-double bond steroidal thiazolidines can be N-acylated if there is no substituent in the 4'-position on the thiazolidine ring; substituents in the 4'-position of the thiazolidine sterically hinder acylation. On the other hand, the 4,5-double bond steroidal thiazolidine isomers decomposed on attempted acylation. The lability of these 4,5-double bond isomers was attributed to the contribution of a hyperconjugative resonance form to the structure of the 4,5-double bond isomers.     

Validation of analytical methods used for determination of nitrate in soil

The standard method (ISO/DIS 14255) and the quick test were used for determination of nitrate in soil. We validated both methods using parameters such as accuracy, reproducibility within 1 day and between days, limit of detection and limit of quantification. The accuracy of the results was determined using the analysis of samples from the international interlaboratory scheme WEPAL. The accuracy of the standard method was good, while for the quick test the results were not accurate. The standard method showed a solid reproducibility of measurement results (in 1 day, relative standard deviation, RSD=0.2%; between days, RSD=0.8%). The quick test gave poorer results (in 1 day, RSD=6%; between days, RSD=7%). We tried to established the compatibility of both methods on real soil samples and we were satisfied to obtain the correlation coefficient 0.98 using the regression straight line. The analyses with the quick field instrument are much simpler and cheaper than the standard laboratory analyses and can be used for advising on nitrogen fertilisation.     

Highly compact 2D graphical representation of DNA sequences

Most 2D graphical representations of primary DNA sequences, while offering visual geometrical patterns for depicting sequences, do require considerable space if enough details of such representations are to be visible. In this contribution, we consider a highly compact graphical representation of DNA, which allows visual inspection and numerical characterization of DNA sequences having a large number of nucleic acid bases. The approach is illustrated on the DNA sequences of the first exon of human beta-globin. The same graphical approach not only allows one to depict differences in composition within a single DNA, but makes possible graphical representation of protein sequences, which have hitherto evaded similar 2D visual representations.     

Free radical bromination by the H2O2-HBr system on water

An aqueous solution of hydrogen peroxide and hydrogen bromide illuminated by a 40 W incandescent light bulb serves as a source of bromine radicals. Various substituted toluenes (H, Me, tBu, Br, COOEt, COPh, NO₂) were brominated at the benzyl position. This haloperoxidase-like system for benzylic bromination does not require the presence of metal ions or an organic solvent for efficient conversion of methyl-arenes to benzyl bromides.     

XYZ,a program for modeling,validation, prediction and graphic display of data

A program for modeling, validation, prediction and graphic display of data is reported. The package is useful for dealing with responses that area function of a reduced number of variables. Implementation of user-defined models is easy and several very general equations can be selected. The structure of the program is shown and the use of the different modules is explained. Two typical, applications based on distinct mathematical models are shown.