Inorganic Ions

3 Key excerpts on "Inorganic Ions"

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  eBook - ePub

  Introduction to Modern Inorganic Chemistry, 6th edition

  • R.A. Mackay, W. Henderson(Authors)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Table 20.1 shows the elements in the Periodic Table which are utilized by biological systems. Many, such as potassium, phosphorus and sulfur, are ubiquitous whilst elements such as selenium, molybdenum, copper and many others are essential to life in trace amounts. The role of many of these elements is well understood though for others educated speculation is necessary. In the first section we describe several aspects of biological inorganic chemistry, using the Periodic Table as a framework for this discussion. The use of model complexes, to mimic biological systems, is a very important experimental method and we refer to this at several points in the discussion.

  20.1.2 The s elements in biochemistry

  The ions Na+ , K+ , Mg2+ and Ca2+ are of great importance in biochemistry. Potassium is an essential plant nutrient and the major production of potassium compounds is for use in fertilizers, in animals Na+ and K+ ions are mobile throughout the body and participate in many cell functions, such as nerve impulse transmissions, which depend on the ratio of Na+ to K+ and the concentration gradient across the cell membrane. The ions are thought to traverse the cell membrane by means of channels whose surface contains donor groups in an array similar to the multidentate donors of Fig. 10.5 . The 6-oxygen donors (like the crown ether, Fig. 10.5a ) have a cavity size which matches the size of K+ better than Na+ while a similar 5-oxygen donor favours Na+ over K+ so the channels through the cell membrane may select for K+ or Na+ under different cell conditions. This allows the build-up of concentration gradients between the inside and outside of the cell. It also results in the creation of charge differences since the total number of cations in the cell changes and anions transfer less readily or not at all. Thus, a nerve cell starts with a higher concentration of K+ inside the cell than outside and this concentration gradient is maintained by a corresponding negative membrane potential of -70 mV. On stimulation the membrane becomes more permeable to Na+ ions which flow from the higher external concentration into the lower internal one faster than the K+ can now move out, causing a brief period when the cell loses its large internal negative charge. Thus charge may be transferred down a line of cells as each stimulates the next. The concentrations of Na+ and K+ are restored by chemical action via the hydrolysis of adenosine triphosphate (ATP) by the Na+ /K+ ATP-ase

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  eBook - PDF

  Inorganic Biochemistry

  Volume 3

  • H A O Hill(Author)
  • 2007(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  Other major areas of descriptive conflict come in the indiscriminate use of the terms ‘trace metals’ and ‘heavy metals’. Many of the elements involved are present in appreciable quantities, have relatively low atomic weights, and may not even be metals. The distribution of a range of elements has been discussed. Another point is of concern to us, that of the implied assumption that each element has characteristic properties in living systems. While this may be true of the lighter elements that readily form ions, it is important to appreciate that, for the bulk of the elements in Nature, the biological properties depend largely on the molecular environment of fie element and hence its co-ordination chemistry. The two extremes of behaviour may be seen in the elements which are most widely used as inorganic drugs. Lithium and magnesium are absorbed as simple ions, and the form in which they are administered has very little effecton the final pharmacological action; the ions or their complexes with naturally occurring biological ligands are the active species. By contrast, gold and platinum 1 N. J. Birch and P. J. Sadler, in ‘Inorganic Biochemistry’ (Specialist Periodical Reports) ed. H. A. 0. Hill, The Chemical Society, London, 1979, Vol. 1, Ch. 9. a N. J. Birch and P. J. Sadler, in ‘Inorganic Biochemistry’ (Specialist Periodical Reports), ed. H. A. 0. Hill, The Royal Society of Chemistry, London, 1981, Vol. 2, Ch. 8. 8 J. R. Arthur, I. Bremner, and G. K. Chesters, in ‘Inorganic Biochemistry’ (Specialist Periodical Reports) ed. H. A. 0. Hill, The Royal Society of Chemistry, London, 1981, Vol. 2, Ch. 7. * J. R. Arthur, I. Bremner, and G. K. Chesters, in this volume, Ch. 8. 372 Inorganic Elements in Biology and Medicine 373 compounds have a variety of actions, and these depend on the configuration of the particular compound; the whole compound, and not just the metal, is absorbed, and may be the active species.

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  eBook - ePub

  Practical Approaches to Biological Inorganic Chemistry

  • Robert R. Crichton, Ricardo O. Louro(Authors)
  • 2012(Publication Date)
  • Elsevier

    (Publisher)

  Chapter 1 An Overview of the Roles of Metals in Biological Systems

  Robert R. Crichton, Batiment Lavoisier, Université Catholique de Louvain, Louvain-la-Neuve, Belgium

  Chapter Outline

  Introduction: Which Metals Ions and Why? Some Physicochemical Considerations on Alkali Metals

  Na+ and K+ – Functional Ionic Gradients

  Mg2+ – Phosphate Metabolism

  Ca2+ and Cell Signalling

  Zinc – Lewis Acid and Gene Regulator Iron and Copper – Dealing with Oxygen Ni and Co – Evolutionary Relics Mn – Water Splitting and Oxygen Generation Mo and V – Nitrogen Fixation

  Introduction: Which Metals Ions and Why?

  In the companion book to this one, ‘Biological Inorganic Chemistry 2nd edition’ (Crichton, 2011 ), we explain in greater detail why life as we know it would not be possible with just the elements found in organic chemistry – namely carbon, oxygen, hydrogen, nitrogen, phosphorus and sulfur. We also need components of inorganic chemistry as well, and in the course of evolution nature has selected a number of metal ions to construct living organisms. Some of them, like sodium and potassium, calcium and magnesium, are present at quite large concentrations, constituting the so-called ‘bulk elements’, whereas others, like cobalt, copper, iron and zinc, are known as ‘trace elements’, with dietary requirements that are much lower than the bulk elements.

  Just six elements – oxygen, carbon, hydrogen, nitrogen, calcium and phosphorus – make up almost 98.5% of the elemental composition of the human body by weight. And just 11 elements account for 99.9% of the human body (the five others are potassium, sulfur, sodium, magnesium and chlorine). However, between 22 and 30 elements are required by some, if not all, living organisms, and of these are quite a number are metals. In addition to the four metal ions mentioned above, we know that cobalt, copper, iron, manganese, molybdenum, nickel, vanadium and zinc are essential for humans, while tungsten replaces molybdenum in some bacteria. The essential nature of chromium for humans remains enigmatic.

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