Vladimír Karpenko

Heat denaturation of human orosomucoid in water/methanol mixtures

Heat denaturation of orosomucoid in solutions of methanol concentrations ranging from 0 to 70% (v/v) has been studied by using circular dichroism, intrinsic protein fluorescence and thermal difference absorption spectroscopy. Regardless of its high saccharide content (40%), the highly cooperative denaturation transition of orosomucoid is fully reversible in neutral water solution. A two-state model has been successfully applied; the numerical analysis results in thermodynamical parameter values that are in close agreement with previously reported experimental data from calorimetric measurements. However, in solutions containing even minute concentrations of methanol (5%) the heat denaturation is irreversible. After cooling of the denatured protein the refolded molecules exhibit a higher alpha-helical content than the native one. Possibilities of methanol interaction with native and denatured protein molecule are discussed.

Thermal stability of the human blood serum acid α1-glycoprotein in acidic media

Abstract Thermal stability of human α 1 -acid glycoprotein and its desialyzed form were studied in the pH range of 1.5–5.2, i.e. about its p I . Circular dichroism, fluorescence and UV-absorption were used to determine the conformational changes and their reversibility in the temperature range 25–80 °C. These changes were tested in a three step process—heating, cooling and a second heating. Principal component analysis was applied for analyzing the spectral sets obtained in these experiments. Fully reversible behavior of Trp residues, as characterized by fluorescence spectroscopy, was observed during the heating process at all pH values. Nevertheless, three different types of the protein motion (reversible, irreversible and rearrangement of the protein core) were determined by UV-absorption spectroscopy. Thus, an environment of Tyr and Phe is modified or reversibly rearranged during the heating process in acid media. These types of α 1 -acid glycoprotein behavior were not significantly affected by desialyzation.

Not All That Glitters is Gold: Gold Imitations in History

Abstract When gold became considered as a precious metal for decorative purposes and later for coinage, attempts at producing imitations soon began to appear. There were two motives behind this activity: to make a metal that could pass as gold, and to quite openly imitate this precious metal for people who could not afford true gold. Imitation gold was produced by metallurgists, and later also by alchemists. This paper is about gold imitations that did not contain any precious metal. Gold-like alloys of silver are thus excluded. An attempt is further undertaken to classify into separate groups the various gold imitations that have appeared in different cultures throughout time, with an emphasis on brass as a typical imitation of gold.

Two thousand years of numerical magic squares

A magic square is any square-shaped array of numbers or letters exhibiting certain properties: in numerical squares it is the constant sum of numbers in each row, column, or diagonal. This is the constant of a square, while the number of cells in a row gives its order. Any set of numbers can be used if the condition of a constant summation is met. In natural magic squares only natural numbers from 1 to 2 are used. The same set of natural numbers written sequentially into a square grid leads to a natural square which is not magic. Numerical magic squares attracted attention in the distant past. They have been used in charms, talismans, and in other objects destined to magical use. More rarely, these squares appeared in philosophical or alchemical speculations as expressions of certain ideas, or even as an instruction to experiments. Now studied as problems in number theory, numerical magic squares once had deeper significance, far from purely mathematical questions.

Systems of metals in alchemy

Abstract Two distinct ways of ordering of the seven ancient metals, denoted as System I and II in this paper, can be found in alchemical sources. In System I metals are arranged with gold in the central position: lead, tin, iron, gold, copper, mercury, silver. This arrangement bears resemblance with Ptolemaic system of planets which could have contributed to the origin of this System. Symmetrical positions of the pairs lead-silver and iron-copper with respect to the central, gold-Sun were supported by practical observations. More widespread System II arranges metals from the least to the most precious ones. In this system gold is always the last member of the series. The ordering of base metals in System II has only one typical feature: in most cases iron precedes copper. Therefore attention was paid to redox deposition of copper from cupric solutions on metallic iron. This reaction was important support of claims that transmutation of metals is possible. Further redox depositions mentioned in alchemical and chemical works are also discussed with special attention paid to the influence of impurities on resulting process. One reaction described in alchemical manuscript was repeated in laboratory to show the possible approach chosen by alchemist.