82 Questions
What is the primary focus of this chapter in relation to metal ions?
Their roles in biology
What do metal ions in biology frequently bind to?
Donor ligands
What is a characteristic of 'hard' species in the hard-soft theory of acids and bases?
They are small and less easily polarized
What is the term for species that are large and fairly polarizable?
Soft
What do ligand atoms coordinate to in a biological medium?
Metal centers
What is the purpose of understanding the special properties of metal ions?
To understand the functions of metal centers
What is the general rule regarding hard acids and hard bases?
Hard acids bind preferentially to hard bases and soft acids to soft bases.
What type of metal ions tend to bind to cysteine sulfhydryl groups or methionine thioether linkages?
Soft metal ions like Pt(I1).
What is the primary function of metallothionein proteins?
To protect cells against the toxic effects of metal ions.
What is the term used to describe the coordination of two or more donor atoms from a single ligand to a central metal atom?
Chelation.
What is the purpose of adding EDTA to buffer solutions in biological research?
To reduce the concentration of free metal ions.
What type of metal ions are typically coordinated by carboxylate oxygen atoms?
Hard metal ions like Ca2+.
What is the name of the ligand used in medicine to chelate metal ions that might be present in toxic excess?
EDTA.
What is the term used to describe the stability of metal-chelate complexes resulting from the favorable entropic factor?
The chelate effect.
What is the name of the macrocyclic molecules that have four nearly coplanar pyrrole rings with their nitrogen donor atoms directed toward a central metal ion?
Porphyrins.
What is the biological function of metallothionein proteins?
To protect cells against the toxic effects of metal ions.
What is the effect of adding bulky R groups to Cu(R-sal) complexes?
It raises the redox potential.
What is the preferred coordination geometry of divalent copper(II) complexes?
Square-planar
What is the general order of binding preference for divalent first-row transition-metal ions?
Ca2+ < Mg2+ < Mn2+ < Fe2+ < Co2+ < Ni2+ < Cu2+ > Zn2+
What is the effect of the positive charge on most metal ions in biology on protic ligands bound in the coordination sphere?
It stabilizes the acid anion (conjugate base) of protic ligands.
What is the effect of soft ligands such as RS- or R2S on the Cu(I)/Cu(II) reduction potential?
It raises the potential.
What is the effect of coordinating multiple metal ions to a protic ligand on the pK, value?
It decreases the pK, value.
What is the role of noncoordinating residues in proteins?
They contribute to local hydrophilicity or hydrophobicity and stereochemistry.
What is the redox potential of the Cu(I)/Cu(II) couple affected by?
The ligand donor atom and stereochemistry at the metal center.
What determines the thermodynamic stability of a metal center in a biological environment?
Both the inherent preferences of the metal and the ability of the biopolymer to control the stereochemistry and ligands available for coordination.
What is the significance of the Irving-Williams series?
It is a series of metal ions in order of their tendency to bind to hard donors.
What is the preferred coordination geometry of copper(I), a closed-shell d10 ion?
Tetrahedral four-coordinate or trigonal three-coordinate.
What is the general term for the study of the principles governing the formation of complexes of metal ions with biological molecules?
Bioinorganic chemistry.
What is the effect of the protein environment on the redox potential of metal ions?
It can either raise or lower the potential.
What is an example of a metalloprotein that has a strong and specific metal-binding site?
Superoxide dismutase
What is the deprotonation of coordinated water to form a hydroxo ligand related to?
Metalloenzyme catalysis.
What is the function of the chelate effect in bioinorganic chemistry?
To provide a specific and strong metal-binding site.
What is the effect of divalent metal ions on the pK, values of protic ligands compared to trivalent metal ions?
Trivalent metal ions have a greater effect.
What is the effect of the local dielectric constant on the redox potential of metal ions?
It can either raise or lower the potential.
What is the structure of the [Fe(H2O)5OH]+ complex?
Octahedral with a hydroxo ligand.
What is the function of EDTA (ethylenediaminetetraacetic acid) in bioinorganic chemistry?
It is a metal chelating agent.
What is the phenomenon referred to as the alteration of energy levels of d-orbitals in a metal ion due to the surrounding ligands?
Ligand-field splitting
What determines the strength of the ligand field at a metal center?
The set of ligand donor atoms
What is the spectrochemical series used to determine?
The ability of ligands to split d-orbitals
What can be used to highlight a very localized region of a metalloprotein?
Measuring the magnetic and spectroscopic properties
What is the effect of metal ions on the reactivity of ligands?
Increase the acidity of coordinated ligands
What is the term used to describe the energy separation between the lower and upper sets of orbitals in octahedral complexes?
Δo
What is the shape of a coordination polyhedron with a coordination number of 5?
Square pyramidal
What is the term used to describe the alteration of d-orbital energies due to the surrounding ligands?
Ligand-field splitting
What is the purpose of ligand-field splitting diagrams?
To correlate physical properties with structure
What is the effect of the positively charged metal center on the acidity of coordinated water?
Decrease the pKa value
What is the primary reason for the kinetic inertness of metalloproteins?
The solvent inaccessibility to the metal coordination sphere due to steric shielding by the protein.
What is the general trend for ligand exchange rates among metal ions?
Faster for M2+ than for M3+ metal ions.
Which of the following metal ions is characterized by very inert ligand exchange rates?
Cr3+
What is the effect of multidentate chelating ligands on the metal-ligand exchange rates of first-row transition-metal ions?
They decrease the metal-ligand exchange rates.
What is the typical coordination number of metal ions that undergo associative ligand displacement reactions?
2-4
What is the characteristic of inner-sphere electron transfer reactions?
The presence of one or more bridging ligands directly bonded to the coordination spheres of the reactants.
Which of the following ligands is known to form a more inert M-L bond?
CO
What is the effect of denaturing a protein on the metal ions bound to it?
The metal ions can be released.
What is the characteristic of substitution reactions at metal centers bound to proteins or nucleic acids?
They are more complex due to interactions of the incoming ligand with other nearby groups.
What is the typical feature of metalloporphyrins?
They are kinetically inert.
What is the role of the chloride ion in the electron-transfer reaction between [CO(NH3)5CI]2+ and [Cr(H2O)5CI]2+?
It is transferred from the Co(III) to the Cr(I) center.
What is the characteristic of the electron-transfer reaction between metal centers within and between metalloprotein molecules?
It is a long-range process that can occur over distances up to 30 Å.
What is the prediction of the Marcus theory for outer-sphere electron-transfer reactions?
The rate of electron transfer has an optimal driving force.
What is the d-electron configuration of the Fe(III) ion?
d5
What is the coordination geometry typically exhibited by metal ions in bioinorganic chemistry?
A variety of coordination geometries, including tetrahedral and octrahedral, are observed.
What is the role of the precursor complex in outer-sphere electron-transfer reactions?
It is the initial step in the electron-transfer reaction.
What is the characteristic of the inner-sphere electron-transfer reaction?
It involves the formation of a bridged binuclear complex.
Why is the rate of electron transfer affected in the inverted region?
The driving force is too high.
What is the term used to describe the correlation between the equilibrium and rate constants for outer-sphere electron-transfer reactions?
Marcus theory
What is the purpose of understanding the special properties of metal ions in biology?
To understand the biological functions of metal ions
What is the term used to describe the approach of forming a desired replica molecule by reacting a metal with the simplest ligands containing the known or suspected biological donor atoms?
Spontaneous self-assembly
Why do the molecules formed between metal and ligands become major components of the mixture of compounds?
Because of the tactical skills of the synthetic inorganic chemist
What is the characteristic of metal-ligand bonds in most bioinorganic centers?
They are labile
What is the advantage of the spontaneous self-assembly approach in replicating metalloprotein core structures?
It is a simple and straightforward approach that mimics nature's strategy
What is the criticism of the spontaneous self-assembly approach by some scientists?
It is just a matter of dumb luck
What is the significance of the interaction between the geosphere and the biosphere in the development of bioinorganic chemistry?
It has led to the discovery of metal centers in biology
What facilitates nucleophilic attack on the carbonyl group in the hydrolysis of amino-acid esters at neutral pH?
Coordination to a positively charged metal ion
What is an example of a reaction that is facilitated by metal centers?
The hydrolysis of amino-acid esters
Why is the uncatalyzed reaction of amino-acid ester hydrolysis essentially unobservable at neutral pH?
Due to the slow rate of the reaction
What is the purpose of using model complexes in bioinorganic chemistry?
To replicate the physical and chemical properties of metal centers in biopolymers
What is the term for the phenomenon in which the metal serves to organize reactive units in condensation reactions?
The template effect
What is promoted by coordination of cupric ion to the leaving group in phosphate ester hydrolysis?
The hydrolysis of phosphate esters
Why is it challenging to obtain high-resolution structural information about the metal coordination sphere in metallobiopolymers?
Due to the complexity of the molecule
What is the term for a model complex designed to replicate the physical and chemical properties of the metal center in a biopolymer?
A replicative model
What is essential to know when studying model complexes?
The structure of the model complex
What has the model approach provided in the field of bioinorganic chemistry?
Insights into metallobiochemistry
This quiz covers the role of metal ions in biological systems, their special properties, and chemical reactions. It also explores the electronic structural features of metal ions and their measurement. Test your knowledge of inorganic coordination chemistry in a biological context.
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