CHEMISTRY GLOSSARY

nuclear magnetic resonance    →   nuklearna magnetska rezonancija

Nuclear magnetic resonance (NMR) is a type of radio-frequency spectroscopy based on the magnetic field generated by the spinning of electrically charged atomic nuclei. This nuclear magnetic field is caused to interact with a very large (1 T - 5 T) magnetic field of the instrument magnet. NMR techniques have been applied to studies of electron densities and chemical bonding and have become a fundamental research tool for structure determinations in organic chemistry.

nucleic acid    →   nukleinska kiselina

Nucleic acids are a complex, high-molecular-weight biochemical macromolecules composed of nucleotide chains that convey genetic information. The most common nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Each nucleic acid chain is composed of subunits called nucleotides, each containing a sugar, a phosphate group, and nitrogenous base. DNA was first discovered in 1869 by the Swiss biochemist Friedrich Miescher (1844-1895).

Both DNA and RNA contain the two major purine bases adenine (A) and guanine (G) and one of the major pyrimidines, cytosine (C). Of the other two pyrimidines, thymine (T) is found in DNA and uracil (U) is found in RNA. There are two major pentoses in nucleic acids:2'-deoxy-D-ribose in DNA and D-ribose in RNA.

Nucleotides are linked together in both DNA and RNA in a polymeric fashion via covalent bonds. These bonds exist through phosphate-group bridges in which the 5' hydroxyl group of one nucleotide unit is joined to the 3' hydroxyl group of the next nucleotide. RNA is usually a single-stranded molecule, whereas DNA is usually double-stranded.

nucleotide    →   nukleotid

Nucleotides are the components that made up nucleic acids. They have three major components: the first component is a nitrogenous base, which is derivative of one of two parent compounds, pyrimidine or purine; the second is a pentose, or five carbon sugar group; the third is a unit of phosphate. Each group of three nucleotides in a gene is known as a codon. Whenever the phosphate group is not present, a nucleotide becomes a nucleoside.

octet rule    →   pravilo okteta

Octet rule states that the chemical properties of the elements repeat on a regular basis with increasing atomic mass, and that the chemical properties of each eight element are similar. Since the inert gases, with the exception of helium have eight electrons in their outer shells, this stable electronic configuration is called the octet rule. In chemical reactions atoms of elements tend to react in such a way as to achieve the electronic configuration of the inert gas nearest to them in the periodic table. There are a number of exceptions to the octet rule.

organic    →   organski

1. Organic refers to any chemical compound based on carbon (C) with the exception of some of the simple compounds of carbon, such as carbon dioxide, which are frequently classified as inorganic compounds. Additional elements that are commonly found in organic compounds are hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P) and sulfur (S).

2. Organic or organically-grown foods are grown or raised without synthetic fertilizers, pesticides, growth stimulators, or antibiotics and other drugs. Pests are controlled by cultivation techniques and the use of pesticides derived from natural sources and the use of natural fertilizers. In addition, organically grown foods must also be stored without the use of chemicals such as artificial additives and preservatives, and without food irradiation.

pH    →   pH

pH is a convenient measure of the acid-base character of a solution, usually defined by

where c(H⁺) is the concentration of hydrogen ions in moles per litre. The more precise definition is in terms of activity rather than concentration.

A solution of pH 0 to 7 is acid, pH of 7 is neutral, pH over 7 to 14 is alkaline.

plastic    →   plastika

Plastic is a material that can be shaped by the application of heat or pressure. Most are based on synthetic polymers although some are the product of natural substances (such as cellulose derivatives, but excluding the rubbers.). They are usually light and permanent solids, being also heat and electric isolators. If the materials soften again when reheated, they are said to be thermoplastic. If, after fashioning, they resist further applications of heat, they are said to be thermoset.

polarography    →   polarografija

Polarography is a volumetric technique which is based on a diffusion controlled analyte travel to the surface of dropping mercury electrode (DME). The surface of the working electrode (dropping mercury electrode) is constantly renewed under dropping conditions and, thus, the conditions under which reaction takes place are readily reproducible. Depolarisation potential enables identification of ions present in the solution, and by measuring the diffusion current their concentration is calculated. Polarography was discovered in 1922 by the Czech chemist Jaroslav Heyrovský (1890-1967).

potentiometric titration    →   potenciometrijska titracija

Potentiometric titration is a volumetric method in which the potential between two electrodes is measured (referent and indicator electrode) as a function of the added reagent volume. Types of potentiometric titrations for the determination of analytes in photoprocessing solutions include acid-base, redox, precipitation, and complexometric.

Potentiometric titrations are preferred to manual titrations, since they are more accurate and precise. They are also more easily adapted to automation, where automated titration systems can process larger volumes of samples with minimal analyst involvement.

A titration curve has a characteristic sigmoid curve. The part of the curve that has the maximum change marks the equivalence point of the titration. The first derivative, ΔE/ΔV, is the slope of the curve, and the endpoint occurs at the volume, V', where ΔE/ΔV has the maximum value.

redox titration    →   redoks-titracija

Redox titration (oxidation-reduction titration) is a titration based on a redox reaction. For example, iron in water can be determined by converting dissolved iron to Fe²⁺ and titrating the solution with potassium permanganate (KMnO₄), a powerful oxidising agent.