Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
LECTURE 20. THE D-BLOCK ELEMENTS. VII-VIII B GROUPS PhD. Halina Falfushynska MANGANESE Manganese is obtained mainly from the mineral pyrolusite, MnO2. Ferromanganese alloys are wear resistant and shock resistant and are used for railroad tracks, bulldozers, and road scrapers. Manganese(IV) oxide is the starting point for making most other manganese compounds. Potassium permanganate, KMnO4, is an important oxidizing agent that is used in both analytical and organic chemistry laboratories, and in water treatment. THE IRON TRIAD: FE, CO, AND NI Iron is the fourth most abundant element in Earth’s crust. Cobalt and nickel are not nearly as common. All three elements form 2+ and 3+ ions. The most common ions of Co and of Ni are the 2+. The most common ion of Fe is the 3+ due to the half-filled dsubshell: FERROMAGNETISM The iron triad exhibits ferromagnetism which is a much stronger magnetic effect than paramagnetism. A ferromagnetic solid consists of regions called domains in which atoms have their magnetic moments aligned. • When placed in a magnetic field, all the domains are aligned and the solid becomes magnetized. Examples of variable oxidation states in the transition metals Iron Iron has two common oxidation states (+2 and +3) in, for example, Fe2+ and Fe3+. It also has a less common +6 oxidation state in the ferrate(VI) ion, FeO42-. Manganese Manganese has a very wide range of oxidation states in its compounds. For example: +2 in Mn2+ +3 in Mn2O3 +4 in MnO2 +6 in MnO42+7 in MnO4- Thinking about a typical transition metal (iron) Here are the changes in the electronic structure of iron to make the 2+ or the 3+ ion. Fe [Ar] 3d64s2 Fe2+ [Ar] 3d6 Fe3+ [Ar] 3d5 The 4s orbital and the 3d orbitals have very similar energies. There isn't a huge jump in the amount of energy you need to remove the third electron compared with the first and second. The figures for the first three ionisation energies (in kJ mol-1) for iron compared with those of calcium are: metal 1st IE 2nd IE 3rd IE Ca 590 1150 4940 Fe 762 1560 2960 There is an increase in ionisation energy as you take more electrons off an atom because you have the same number of protons attracting fewer electrons. Manganese Mn (Manganum) trace element - cofactor of enzymes: superoxide dismutase pyruvate carboxylase KMnO4 Potassium permanganate (INN: Kalii permanganas) - in water dissolves to give deep purple solutions - strong oxidizing agent - dilute solutions can act as desinfectant Iron Fe (Ferrum) important microelement human body: 4–5 g Fe a) functional form - heme iron proteins hemoglobin 70 % myoglobin 5% some enzymes - non-heme iron proteins b) tranport form (transferrin) c) storage of iron (ferritin, hemosiderin)-20 % Fe in food 10-30 mg/day absorption: only 710% ~ 1 mg/day HEME iron proteins Hemoglobin - O2 transport in blood - in red blood cells - tetramer = 4 subunits (each subunit: one heme + one globin) HbA HbF ("adult") ("fetal") a2b2 a2g2 Myoglobin - "O2 storage" in muscle cell Cytochromes - electron transport (oxidized) - their function is based on: heme Fe2+ (reduced) Fe3+ Non-heme iron proteins FeII or FeIII bound to protein SH iron–sulphur proteins (FeS proteins) Transferrin - blood plasma protein ( b1 globulin ) - transport of Fe - 1 molecule of transferrin can carry 2 iron ions in form of Fe3+ Ferritin - intracellular iron storage protein (liver, bone marrow) - 1 ferritin complex can store about 4500 Fe3+ - ferritin without iron = apoferritin Hemosiderin - "damaged (Fe-overloaded) ferritin" - Fe from it is less available OVERVIEW OF IRON METABOLISM FOOD tissues CYTOCHROMES Fe-S proteins liver FERRITIN HEMOSIDERIN blood plasma TRANSFERRIN bone marrow FERRITIN muscles MYOGLOBIN spleen FERRITIN red blood cells HEMOGLOBIN BLEEDING (Fe losses) Iron metabolism = unique - reutilization ! (closed system) NO regulated excretion system for Fe ! Fe absorption must be "regulated" Loss of Fe through loss of blood (females - mestrual bleeding) Iron deficiency - microcytic anemia "iron deficiency anemia" Iron overload - hemochromatosis = accumulation of iron in the body (depositions as hemosiderin) organ dysfunction (liver, heart, ...) IRON ABSORPTION FOOD Fe3+ STOMACH HCl pH 1-2 ascorbic acid gastroferrin - iron binding protein reduction Fe2+ Fe3+ apoferritin ferritin (Fe3+) INTESTINAL MUCOSA CELL Fe2+ BLOOD transferrin (Fe3+)