PHD
  1. Inorganic chemistry  1.1. Coordination chemistry  1.1.1. Ligand field theory  1.1.2. Crystal field theory  1.1.3. Molecular Orbital Theory for Coordination Compounds  1.1.4. Stability of Coordination Compounds  1.1.5. Electronic spectra of coordination compounds  1.1.6. Isomerism in Coordination Compounds  1.1.7. Kinetics and mechanism of coordination reactions  1.2. Organometallic Chemistry  1.2.1. Metal Carbonyls  1.2.2. Metal alkyl and aryl  1.2.3. Fischer and Schrock carbonaceans  1.2.4. Oxidative Addition and Reductive Elimination  1.2.5. Metal Hydrides  1.2.6. Catalysis by organometallic compounds  1.2.7. Metallocenes and Sandwich Complexes  1.2.8. CH activation  1.3. Solid state chemistry  1.3.1. Crystal structures and lattices  1.3.2. Band theory and electrical properties  1.3.3. Defects in the crystal  1.3.4. Synthesis of solid state materials  1.3.5. Magnetic and optical properties of solids  1.3.6. Superconductivity  1.3.7. Solid state ionics  1.4. Bio-inorganic chemistry  1.4.1. Metalloproteins and enzymes  1.4.2. Metal ion transport and storage  1.4.3. The role of metals in medicine  1.4.4. Bioinspired catalysis  1.4.5. Metal–DNA interactions  1.4.6. Metal Complexes in Medical Science  1.5. Lanthanides and Actinides  1.5.1. Electronic configuration and oxidation states in lanthanides and actinides  1.5.2. Spectral and Magnetic Properties in Lanthanides and Actinides  1.5.3. Separation and Extraction of Lanthanides and Actinides  1.5.4. Coordination chemistry of f-block elements  1.6. Main Group Chemistry  1.6.1. Chemistry of boron compounds  1.6.2. Chemistry of Silicon and Germanium Compounds  1.6.3. Chemistry of Phosphorus and Sulfur Compounds  1.6.4. Organosilicon chemistry  1.6.5. Noble Gas Chemistry
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition and substitution reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic Reactions  2.1.7. Photochemical reactions  2.2. Stereoscopic  2.2.1. Chirality and optical activity  2.2.2. Structural analysis  2.2.3. Stereoelectronic effects  2.2.4. Asymmetric synthesis  2.2.5. Dynamic Stereochemistry  2.3. Organometallic Chemistry in Organic Synthesis  2.3.1. Organolithium and organomagnesium reagents  2.3.2. Transition metal catalyzed coupling reactions  2.3.3. Palladium-catalyzed reactions  2.3.4. Olefin Metathesis  2.3.5. Gold and silver catalysis  2.4. Natural products chemistry  2.4.1. Alkaloids and terpenoids  2.4.2. Steroids and Flavonoids  2.4.3. Total synthesis of natural products  2.4.4. Biosynthesis of natural products  2.5. Supramolecular Chemistry  2.5.1. Host-Guest Chemistry  2.5.2. Self-assembly and molecular recognition  2.5.3. Supramolecular Catalysis  2.5.4. Molecular Machines
  3. Physical Chemistry  3.1. Thermodynamics  3.1.1. Laws of Thermodynamics  3.1.2. Chemical Potential and Equilibrium  3.1.3. Statistical thermodynamics  3.1.4. Non-equilibrium thermodynamics  3.2. Quantum Chemistry  3.2.1. Schrödinger equation and its applications  3.2.2. Molecular orbital theory  3.2.3. Density functional theory  3.2.4. Post-Hartree–Fock methods  3.3. Chemical kinetics  3.3.1. Reaction rate theory  3.3.2. Mechanism and rate laws  3.3.3. Catalysis and enzyme kinetics  3.3.4. Reaction dynamics  3.4. Spectroscopy and molecular structure  3.4.1. Infrared Spectroscopy  3.4.2. UV-visible spectroscopy  3.4.3. Nuclear Magnetic Resonance Spectroscopy  3.4.4. Mass Spectrometry  3.4.5. Raman Spectroscopy  3.5. Surface and Colloid Chemistry  3.5.1. Absorption and Catalysis  3.5.2. Surfactants and micelles  3.5.3. Colloidal Stability  3.5.4. Nanomaterials and Interfaces
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.1.4. Ion Chromatography  4.2. Electroanalytical techniques  4.2.1. Voltammetry and Polarography  4.2.2. Conductometry and potentiometry  4.2.3. Colometry  4.3. Spectroscopic Methods  4.3.1. Atomic absorption spectroscopy  4.3.2. Fluorescence Spectroscopy  4.3.3. X-ray diffraction  4.3.4. Electron paramagnetic resonance spectroscopy  4.4. Chemometrics  4.4.1. Data processing and statistical methods  4.4.2. Multidisciplinary analysis  4.4.3. Machine Learning in Analytical Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.2. Quantum chemistry methods  5.3. Computational drug design  5.4. Machine Learning in Chemistry  5.5. Ab initio molecular dynamics
  6. Biophysics and Medicinal Chemistry  6.1. Drug discovery and design  6.2. Enzyme kinetics and inhibition  6.3. Chemical biology approach  6.4. Protein-ligand interactions  6.5. Bioorthogonal chemistry
  7. Materials chemistry  7.1. Polymer chemistry  7.1.1. Polymerization mechanism  7.1.2. Functional Polymers  7.1.3. Biodegradable Polymer  7.1.4. Conducting and semiconducting polymers  7.2. Nano Chemistry  7.2.1. Nanoparticles and nanostructures  7.2.2. Carbon-based nanomaterials  7.2.3. Quantum dots  7.3. Energy and Environmental Chemistry  7.3.1. Battery and Fuel Cell Chemistry  7.3.2. Green chemistry and sustainable materials  7.3.3. Photocatalysis

PHD → Inorganic chemistry → Bio-inorganic chemistry ↓


Metal ion transport and storage


Metal ions play vital roles in biological systems, with functions ranging from structural support to catalytic activity in enzymes. The transport and storage of metal ions is essential for maintaining cellular homeostasis, facilitating metabolic processes, and ensuring that essential metal ions are available where they are needed, while preventing toxicity due to excess metal accumulation.

Observation of metal ion transport

Metal ion transport involves the movement of ions across cell membranes, which can occur via passive diffusion, facilitated transport, or active transport. Each metal ion may have specific transport mechanisms corresponding to its chemical properties and roles in biological systems.

  • Passive diffusion: This involves the movement of ions down a concentration gradient without the need for energy input. This method is generally restricted to small, uncharged molecules due to the hydrophobic nature of the lipid bilayer in the cell membrane.
  • Facilitated transport: uses transport proteins to control the movement of ions down a concentration gradient. These proteins provide specific pathways, or channels, through which ions can pass. For example, aquaporins facilitate water transport while avoiding the passage of ions.
  • Active transport: Moving ions against their concentration gradient requires energy, often in the form of ATP. Transport proteins such as pumps actively move ions across membranes. An example of this is the sodium-potassium pump (Na + /K + ATPase), which moves sodium and potassium ions across the cell membrane, maintaining cellular osmotic balance and membrane potential.

Mechanism of metal ion storage

Storage of metal ions is essential for protecting cells from metal toxicity and for regulating the availability of metal ions for cellular processes. Common storage methods include sequestration in organelles, binding to proteins, and incorporation into macromolecular structures.

  • Organelles: Some organelles, such as vacuoles and vesicles, can sequester metal ions. Vacuoles in plant cells often store metals such as iron and zinc, while lysosomes in animal cells may contain metals as part of their degradation and storage roles.
  • Protein binding: Metalloproteins such as ferritin and metallothioneins can bind metal ions. Ferritin stores iron by forming a hollow sphere in which the iron is oxidized and stored as ferric hydroxide. Metallothioneins are small, cysteine-rich proteins that are able to bind metal ions, especially zinc, cadmium, and copper.
  • Incorporation into macromolecules: Metals can be incorporated into larger complexes or structures; for example, some metals are central to enzyme function, and their presence is essential for enzymatic activity. The iron ions of hemoglobin are important for oxygen transport in the bloodstream.

Importance of metal ion transporters

Transporters are proteins or complexes that facilitate the movement of metal ions across cell membranes. Each transporter is often specific for a particular metal ion or group of metal ions. These transporters play several important roles:

  • Nutrient absorption: Transporters aid in the absorption of essential metal ions such as iron, zinc, and copper, which are required for various bodily functions.
  • Detoxification: By controlling the excretion of unnecessary or excess metal ions, transporters prevent potentially toxic effects. This role is important in maintaining cellular homeostasis.
  • Intracellular distribution: Transporters ensure the proper distribution of metal ions within cells, and facilitate their delivery to target sites such as metalloproteins and enzymes.

Examples of metal ion transporters

Several transporters facilitate the movement of major metal ions:

  • Ferroportin: The only known vertebrate iron exporter. It is involved in the transport of ferrous iron (Fe2+) and plays an essential role in iron homeostasis.
  • ZIP and ZnT transporters: These are important for zinc transport. The ZIP family is responsible for zinc absorption into cells, while the ZnT family mainly aids in zinc expulsion.
  • CTR1: Copper transporter 1 (CTR1) is essential for copper absorption and is integral to the supply of copper to copper-dependent enzymes.

Regulation of metal ion homeostasis

Biological systems use a sophisticated regulatory network to maintain metal ion homeostasis. This regulation is important for preventing deficiency or toxicity:

  • Regulatory proteins: Proteins such as hepcidin control iron levels by inhibiting the function of ferroportin, adjusting iron absorption and release from stores.
  • Gene expression: Transcription factors respond to metal ion concentrations, affecting the expression of metal transporter and storage proteins. For example, the iron-responsive element (IRE) and its binding protein (IRP) regulate iron metabolism by controlling the stability and translation of mRNAs involved in iron absorption and storage.
  • Inter-organ communication: Organs communicate to coordinate systemic metal ion levels. For example, the liver plays a central role in systemic iron regulation, balancing absorption, storage, and release.

Metal ion storage: ferritin as an example

Ferritin is an example of how cells effectively store metal ions. This protein can store up to 4500 iron ions, indicating its potential as a major iron reservoir:

Ferritin has a hollow cage like structure that contains iron:
    [ Ferritin cages ]
         ,
    fe—fe—fe—fe—fe—fe—fe

Ferritin is composed of 24 subunits that form a hollow sphere, allowing iron ions to be stored in a bioavailable and non-toxic form. It stores iron in the ferric state (Fe3+) within its core, using ferroxidase activity to oxidize ferrous iron (Fe2+).

Challenges and growth

Despite progress in understanding metal ion transport and storage, several challenges remain:

  • Disease connection: Impaired metal ion homeostasis is associated with diseases such as Alzheimer's, Parkinson's and Wilson's disease. Understanding the exact mechanisms of transport and storage may provide insight into these conditions.
  • Technological advances: Developments in imaging and spectroscopy are increasing our ability to study metal ions in biological systems, shedding light on previously obscure processes.

Conclusion

The transport and storage of metal ions is fundamental to supporting the myriad functions of life. Through carefully regulated mechanisms, cells ensure that metal ions are available for essential processes, while minimizing the risks posed by excess metals. Continued research in this area holds great promise for understanding the complexities of medicine, biotechnology, and biological systems.

Reference

For further reading on this topic, refer to the following scientific papers and reviews:

  • Andrews, NC (2000). Iron homeostasis: insights from genetics and animal models. Nature Reviews Genetics, 1(3), 208-217.
  • Cowan, J. (1997). Inorganic Biochemistry: An Introduction. New York: John Wiley & Sons.
  • Finney, L. A., & O'Halloran, T. V. (2003). Transition metal speciation in the cell: insights from the chemistry of metal ion receptors. Science, 300(5621), 931-936.

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