Chemistry Flashcards
(29 cards)
Most abundant elements employed in mammalian biochemistry ?
C, N, O, H, S, P
But, augmented by a range of other elements – many of which are metals; I, Se,Cl, Na, K, Ca, Mg, Co, Cu, Ni, Zn, Fe, Mo, V
Many of the metals employed in mammalian biochemistry are associated with a protein . how many?
1/3 are metalloproteins
• Ionization energy equation?
A(g) > A+(g) + e-(g)
ionization energy increases or decreases across period?(left to right)
increase
ionization energy increase or decrease down a group?
decrease
Electron Affinity equation?
A(g) + e-(g) > A-(g)
elements towards….. of the period table have highest electron affinities?
top right
Electronegativity DEFINITION?
the ability of an atom within a compound to attract electrons towards itself.
Atoms of elements at the top left of the periodic table are the most electronegative. true or false
FALSE. TOP RIGHT
WHAT IS POLARIZABILITY?
underpins the idea of ‘Hard and Soft Lewis Acids and Bases’
-It is the ease with which an atom or ion can be distorted by an electric field.
• The hardest atoms and ions are those with high ionization energies – typically small atoms and ions near fluorine.
• The softest atoms and ions are those with low ionization energy and low electron affinity.
> Soft acids and bases are MORE/LESS polarizable and form bonds with more ‘COVALENT/IONIC character’.
Hard acids and bases are MORE/LESS polarizable and form bonds with more ‘COVALENT/IONIC character’.
MORE
COVALENT
LESS
IONIC
The biological roles performed by metals?
Structural
Catalytic
Redox
Other
The factors that influence the BIOLOGICAL role of the metal ?
- Valency.
- Ionic radius.
- Polarizability.
- Hydration energy (ease with which water molecules can be removed from the metal ion). • Radius of the hydrated ion.
explain lewis acid-base theory
• Broad definition of acids and bases that covered reactions that did NOT involve proton transfer.
• The theory allowed metal-ligand interactions to be described – ligand is the Lewis base and metal the Lewis acid.
Lewis Acids and Bases
• Lewis Acid – substance that accepts an electron pair
• Lewis Base – substance that donates an electron pair
• The theory states that ‘Hard Acids prefer Hard Bases’ while ‘Soft Acids prefer Soft Bases’
The most common coordination geometries found in biological systems are …………
…………..4 and 6 ( and 5).
• But as we’ll see, many metals are not fixed to only one coordination geometry.
coordination geometry number 4. name 2 geometries it can form
square planar
tetrahedral
coordination geometry number 6. name 1 geometry it can form
octahedral
a ligand can be monodentate or polydentate. explain both terms
- Monodentate – only one point of attachment to the metal.
- Polydentate – more than one point of attachment to the metal.
• Both types of ligand feature in biology, but the polydentate ligands are critical features of a range of important biological molecules.
- In a biological sense, these are a special case of polydentate ligands…
- A macrocyclic molecule is a ……………………?
a cyclic molecule (with at least 9 atoms), containing at least 3 donor atoms (Lewis base) – typically N, O, S or P.
are macrocyclic LIGANDS generally MORE OR LESS thermodynamically and kinetically stable than non-cyclic ligands.?
MORE T+K STABLE
Why are MACROCYCLIC LIGANDS more stable THAN NON-CYCLIC LIGANDS?
THE CHELATE EFFECT
• Simply stated, complexes with polydentate ligands will be more stable than complexes with similar monodentate ligands.
• Favourable entropic factor accompanying the release of nonchelating ligands from the metal ion.
• It is generally the case that stability increases with the number of donor atoms in the ring.
WHAT IS CHELATE?
a compound containing a ligand (typically organic) bonded to a central metal atom at two or more points.
BIOLOGICAL EXAMPLE OF MYCROCYCLIC LIGAND?
Porphyrin units (haem unit) of haemoglobin: N groups to iron metal in centre
WHAT IS CHELATE EFFECT?
the enhanced affinity of chelating ligands for a metal ion compared to the affinity of a collection of similar nonchelating (monodentate) ligands for the same metal
