Kinetic Carbon Isotope Effects in the Decarbonylation of Lactic Acid of Natural Isotopic Composition and of [1-14C] Lactic Acid

Studies of carbon-13 and carbon-14 kinetic isotope effects (K. I. E.) in the decarbonylation of lactic acid (L. A.) in sulphuric acid and in phosphoric acids media have been summarized and compared with earlier studies of ¹⁴C and ¹³C K. I. E. in the decarbonylation of formic and oxalic acids in concentrated sulphuric acid. Supplementary data concerning the decarbonylation of L. A. in sulphuric acid diluted with water and in pyrophosphoric acid are presented and discussed. The observed temperature dependences of ¹³C and ¹⁴C K. I. E. in concentrated H₂SO₄ and in concentrated phosphoric acids media have been rationalized by invoking a change of the mechanism of decarbonylation of L. A. in concentrated sulphuric and phosphoric acids with temperature. Preliminary calculational results concerning ¹³C and ^1??C K. I. E. in decarbonylation processes are also presented. In H₂SO₄ diluted with water and in H₃PO₄ diluted with water the temperature dependence of ¹³C and ¹⁴C K. I. E. is normal and well reproduced by one frequency approximation. In concentrated sulphuric acid and in concentrated phosphoric acids besides the C—OH bond rupture the rupture of a C—C bond had to be considered also to reproduce the observed ¹³C K. I. E. in selected temperature regions.     

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Studies on the workability of precise seeders by means of labelling methods has been possible due to the solution of the following problems: labelling of seeds, radiation collimation of labelled seeds being sown, elaboration of measuring and registering systems as well as processing systems of a measuring signal. The developed method allows for precise, quick and fully objective evaluation of the studied seeders to be done under natural conditions.     

Application of Autoradiography to the Investigation of New Doping Techniques of Semiconductor Materials

The development of technology of new semiconductor devices requires fundamental studies of a number of phenomena taking place in semiconductors during the doping process or accompanying the doping process.

These studies are concerned with the following problems:

1. Diffusion of gold in silicon and the effect of diffusion layers (particularly phosphorus layers) and epitaxial silicon layers on the distribution of gold in thin silicon plates.

2. Distribution of admixtures in silicon introduced with the aid of the ion implantation technique. Our studies concerned with the second of the above mentioned problems comprised an autoradiographic examination of the homogeneity of the beam of phosphorus ions implanted in silicon, and a study of some apparatus factors and of the purity of the basic material on the implantation.     

Laser prototyping of printed circuit boards

This paper describes the application of laser micromachining to rapid prototyping of printed circuit boards (PCB) using nano-second lasers: the solid-state Nd:YAG (532/1064 nm) laser and the Yb:glass fiber laser (1060 nm). Our investigations included tests for various mask types (synthetic lacquer, light-sensitive emulsion and tin). The purpose of these tests was to determine some of the basic parameters such as the resolution of PCB prototyping, speed of processing and quality of PCB mapping with commonly available laser systems. Optimization of process parameters and the proposed conversion algorithm have allowed us to produce circuit boards with a resolution similar to that of the Laser Direct Imaging (LDI) technology.     

Spontaneous generation of chirality and chiroptical spectra of N-nitroso-2,4-diaryl-3-azabicyclo[3.3.1]nonanes

The crystal structures of several bicyclic N-nitrosamines indicate that they crystallize in the chiral (Sohncke) space group P2₁2₁2₁ as conglomerates. This allows the resolution of these compounds by manual picking of the enantiomorphous crystals. The optical activity of the single crystals was confirmed by their CD spectra taken in KBr disks. The absolute configurations of the title nitrosamines were assigned by crystallographic measurements and by a comparison of their CD spectra with those of a reference compound resolved by classical methods. The observed Cotton effect signs, corresponding to the n–π¹ transition, were correlated with the helicity of the inherently chiral nitrosamine chromophore.     

A ruthenium(II) hydride carbonyl complex with 4-phenylpyrimidine as co-ligand

The reaction of [RuHCl(CO)(PPh₃)₃] with 4-phenylpyrimidine gave a new ruthenium(II) complex, namely [RuHCl(CO)(PPh₃)₂(pyrim-4-Ph)]. The complex has been studied by IR and UV?Cvis spectroscopy and by X-ray crystallography. The molecular orbitals of the complex have been calculated by density functional theory. The spin-allowed singlet?Csinglet electronic transitions of the complex have been calculated by time-dependent DFT, and the UV?Cvis spectrum of the compound has been discussed on this basis. The emission properties of the complex were also studied.     

One Way Traffic: Base-to-Backbone Hole Transfer in Nucleoside Phosphorodithioate

The directionality of the hole-transfer processes between DNA backbone and base was investigated by using phosphorodithioate [P(S⁻)=S] components. ESR spectroscopy in homogeneous frozen aqueous solutions and pulse radiolysis in aqueous solution at ambient temperature confirmed initial formation of G^.+-P(S⁻)=S. The ionization potential of G-P(S⁻)=S was calculated to be slightly lower than that of guanine in 5′-dGMP. Subsequent thermally activated hole transfer from G^.+ to P(S⁻)=S led to dithiyl radical (P-2S^.) formation on the μs timescale. In parallel, ESR spectroscopy, pulse radiolysis, and density functional theory (DFT) calculations confirmed P-2S^. formation in an abasic phosphorodithioate model compound. ESR investigations at low temperatures and higher G-P(S⁻)=S concentrations showed a bimolecular conversion of P-2S^. to the σ²-σ*¹-bonded dimer anion radical [-P-2S 2S-P-]⁻ [ΔG (150 K, DFT)=−7.2 kcal mol⁻¹]. However, [-P-2S 2S-P-]⁻ formation was not observed by pulse radiolysis [ΔG° (298 K, DFT)=−1.4 kcal mol⁻¹]. Neither P-2S^. nor [-P-2S 2S-P-]⁻ oxidized guanine base; only base-to-backbone hole transfer occurs in phosphorodithioate.