Vraag 1 – Sideroforen en ijzerbinding bij endobacteriën (4
punten)
Bij deze vraag wordt een chemische structuur van een siderofoor
weergegeven.
a. Duid in de structuur aan waar het ijzeratoom gebonden is.
To 6 O-donor atoms in octahedral geometry
b. Bepaal het oxidatiegetal van het gebonden ijzeratoom. +III
c. Geef aan welke andere metaalionen, naast ijzer, zich aan deze siderofoor kunnen
binden. Relatively strong to Ga3+ and weakly to Al3+ and all divalent cations (M2+)
d. Leg uit welk functioneel voordeel de binding van ijzer aan de siderofoor biedt bij
het binnendringen van een bacteriecel.
Free Fe³⁺ is almost insoluble at physiological pH and would precipitate as Fe(OH)₃.
When bound to a siderophore, Fe³⁺ becomes highly soluble and safely chelated,
preventing harmful ROS formation.
. .
Fe2++H2O2 Fe3+ +OH + OH- Fe3+ + H2O2 Fe2+ + HOO + H+
Only iron-loaded siderophores are recognized by bacterial receptors. Free
siderophores are hydrophilic and membrane-impermeable, but binding Fe³⁺ triggers a
conformational shift that makes them hydrophobic, enabling membrane passage or
receptor-mediated uptake.Once inside, bacteria reduce Fe³⁺ → Fe²⁺ or enzymatically
break down the siderophore. This provides usable iron while avoiding toxicity.
e. Beschrijf het mechanisme waarmee het ijzer in de cel wordt vrijgezet uit de
siderofoorcomplexen.
Inside the cell, iron is released from siderophore complexes primarily through
reduction of Fe³⁺ to Fe²⁺ by intracellular reductases. Because Fe²⁺ has a much
lower binding affinity for the siderophore than Fe³⁺, the reduction weakens the metal–
ligand interaction and causes the iron to dissociate. For siderophores with
hydrolysable backbones (such as enterobactin), enzymatic cleavage of the ligand
can further facilitate or complete iron release. Thus, iron liberation occurs through a
combination of Fe³⁺ reduction and, in some cases, enzymatic degradation of the
siderophore scaffold.
Vraag 2 – Eigenschappen en productie van ⁹⁹ᵐTc voor SPECT (2 punten)
a. Leg uit waarom het isotoop technetium-99m (⁹⁹ᵐTc) bijzonder geschikt is voor
toepassing in single photon emission computed tomography (SPECT).
Technetium-99m, the metastable nuclear isomer of ⁹⁹Tc, is a decay product whose
nucleus remains in a long-lived excited state, giving it properties that make it
exceptionally well suited for medical imaging.
It emits gamma rays at 140 keV, an energy easily detected by standard gamma
cameras and comparable to conventional X-rays, ensuring high-quality diagnostic
images.
Its physical half-life of roughly 6 hours allows rapid data collection while keeping the
patient’s radiation exposure low, with more than 90% of the isotope decaying within
24 hours. The biological half-life of about one day ensures that the compound is
,cleared efficiently from the body, further reducing dose. Around 88% of its decays
involve clean gamma emission without harmful particles, preventing unnecessary
tissue damage. After decay, it forms ⁹⁹Tc and eventually stable ⁹⁹Ru, leaving negligible
residual radioactivity.
In addition to these safety and imaging advantages, ⁹⁹ᵐTc can be conveniently
produced on-site: it is generated from ⁹⁹Mo via β⁻ decay with a yield above 87%,
enabling hospitals to use portable generators rather than relying on direct reactor
transport.
b. Beschrijf hoe ⁹⁹ᵐTc in een klinische setting wordt geproduceerd en beschikbaar
gesteld voor diagnostisch gebruik.
• 99Mo extracted from neutron irradiated targets is used as a source of 99mTc
• 99Mo undergoes spontaneous β-decay to excited states of 99Tc (>87% of decays
lead to 99mTc)
• 99Mo is present as water-soluble molybdate (MoO₄²⁻) adsorbed onto acid
alumina (Al₂O₃)
• As 99Mo decays, it forms pertechnetate ( 99mTcO₄⁻), which binds less strongly to the
alumina due to its lower charge and higher oxidation state (+7 for Tc vs. +6 for
Mo). This difference allows 99mTcO₄⁻ to be selectively eluted using physiological
saline (in column chromatography).
• The resulting solution is sodium pertechnetate (Na99mTcO4), which is sterile,
pyrogen-free, and ready for radiopharmaceutical labeling.
To prepare a technetium-99m (99mTc) coordination complex for medical imaging,
several criteria must be met to ensure clinical efficiency, safety, and specificity. The
process typically follows a simplified “kit method,” which involves one-pot synthesis
with a short reaction time, performed directly in physiological media without requiring
extreme conditions or extensive purification. This allows for rapid and practical
preparation in hospital settings. The resulting complex must be target-specific,
thermodynamically stable, and kinetically inert to ligand substitution in vivo, ensuring
reliable imaging and minimal interference from biological processes. In practice,
sterile and pyrogen-free sodium pertechnetate (Na99mTcO4) is injected into a vial
containing the ligand mixture, followed by brief shaking—often referred to as the
“shoot and shake” method. This streamlined approach enables fast and reproducible
labeling of radiopharmaceuticals for diagnostic use.
Vraag 3 – Rol van Zn²⁺ in hydrolysereacties (1 punt)
Leg uit waarom het Zn²⁺-ion bijzonder geschikt is om hydrolysereacties te katalyseren.
1. High charge density → strong Lewis acid: Zn²⁺ has a +2 charge and a small
ionic radius (~0.65 Å). This gives it a highly concentrated positive charge,
making it an excellent Lewis acid.
It strongly polarizes ligands (especially H₂O and carbonyl groups).
2. Zn²⁺ acts as a strong Lewis acid: it activates the substrate upon
coordination and simultaneously lowers the pKa of bound water, generating
a Zn–OH⁻ nucleophile for hydrolysis.
When water binds to Zn²⁺:
+¿ ¿
−¿ +H ¿
2 +¿−OH 2 ⟶ Zn 2+ ¿−OH ¿
¿
Zn
, Zn²⁺ stabilizes the deprotonated form, so the pKa drops dramatically. At
physiological pH, this produces Zn–OH⁻ nucleophile that would otherwise be
unavailable. A powerful, localized OH⁻ is generated directly in the active
site → ideal for hydrolysis.
3. Activation of the substrate: Zn²⁺ can bind the substrate (e.g., carbonyl oxygen,
phosphate oxygen):
Polarizes the bond to be cleaved
Stabilizes the negative charge in the transition state
Aligns the substrate for nucleophilic attack
Lower activation energy for hydrolysis.
4. Redox-inert (d¹⁰ configuration)
Zn²⁺ has a fully filled d¹⁰ shell.
It does not participate in redox chemistry.
Avoids unwanted electron transfer reactions — crucial in hydrolytic enzymes.
5. Borderline hardness → versatile ligand binding: Zn²⁺ can bind: O-donors (Asp,
Glu, H₂O), N-donors (His) and S-donors (Cys) Flexible coordination environment →
stable yet adaptable active sites.
Vraag 5 – Mössbauer-spectrum van een [2Fe–2S]⁺ Rieske-eiwit (3 punten)
a. Beschrijf het typische voorkomen van het Mössbauer-spectrum van een [2Fe–2S]⁺
Rieske-cluster. Waarom zie je twee doubletten?
A reduced [2Fe–2S]⁺ Rieske cluster shows two distinct
quadrupole doublets in its Mössbauer spectrum. This is
because the electron is valence-localized—not delocalized—
between the two iron atoms. One iron remains in the Fe(III)
oxidation state, while the other is reduced to Fe(II).
The Fe(III) site typically shows an isomer shift δ ≈ 0.30
mm/s.
The Fe(II) site shows δ ≈ 0.72 mm/s.
These differences arise due to their distinct
oxidation states and ligand environments: one
iron is coordinated by thiolate (cysteine), the
other by nitrogen atoms (histidine). This
asymmetry leads to different electron densities
and electric field gradients, resulting in two
separate doublets.
b. Bepaal de oxidatietoestanden van de ijzeratomen en verklaar deze op basis van
hun elektronconfiguratie.
In the reduced [2Fe–2S]⁺ cluster:
One iron is Fe(III) → oxidation state +3 → electron configuration: [Ar] 3d⁵
One iron is Fe(II) → oxidation state +2 → electron configuration: [Ar] 3d⁶
Both ions are in high-spin states due to weak ligand fields from sulfur and nitrogen
donors:
Fe(III): 5 unpaired electrons → S =
5/2
Fe(II): 4 unpaired electrons → S = 2
punten)
Bij deze vraag wordt een chemische structuur van een siderofoor
weergegeven.
a. Duid in de structuur aan waar het ijzeratoom gebonden is.
To 6 O-donor atoms in octahedral geometry
b. Bepaal het oxidatiegetal van het gebonden ijzeratoom. +III
c. Geef aan welke andere metaalionen, naast ijzer, zich aan deze siderofoor kunnen
binden. Relatively strong to Ga3+ and weakly to Al3+ and all divalent cations (M2+)
d. Leg uit welk functioneel voordeel de binding van ijzer aan de siderofoor biedt bij
het binnendringen van een bacteriecel.
Free Fe³⁺ is almost insoluble at physiological pH and would precipitate as Fe(OH)₃.
When bound to a siderophore, Fe³⁺ becomes highly soluble and safely chelated,
preventing harmful ROS formation.
. .
Fe2++H2O2 Fe3+ +OH + OH- Fe3+ + H2O2 Fe2+ + HOO + H+
Only iron-loaded siderophores are recognized by bacterial receptors. Free
siderophores are hydrophilic and membrane-impermeable, but binding Fe³⁺ triggers a
conformational shift that makes them hydrophobic, enabling membrane passage or
receptor-mediated uptake.Once inside, bacteria reduce Fe³⁺ → Fe²⁺ or enzymatically
break down the siderophore. This provides usable iron while avoiding toxicity.
e. Beschrijf het mechanisme waarmee het ijzer in de cel wordt vrijgezet uit de
siderofoorcomplexen.
Inside the cell, iron is released from siderophore complexes primarily through
reduction of Fe³⁺ to Fe²⁺ by intracellular reductases. Because Fe²⁺ has a much
lower binding affinity for the siderophore than Fe³⁺, the reduction weakens the metal–
ligand interaction and causes the iron to dissociate. For siderophores with
hydrolysable backbones (such as enterobactin), enzymatic cleavage of the ligand
can further facilitate or complete iron release. Thus, iron liberation occurs through a
combination of Fe³⁺ reduction and, in some cases, enzymatic degradation of the
siderophore scaffold.
Vraag 2 – Eigenschappen en productie van ⁹⁹ᵐTc voor SPECT (2 punten)
a. Leg uit waarom het isotoop technetium-99m (⁹⁹ᵐTc) bijzonder geschikt is voor
toepassing in single photon emission computed tomography (SPECT).
Technetium-99m, the metastable nuclear isomer of ⁹⁹Tc, is a decay product whose
nucleus remains in a long-lived excited state, giving it properties that make it
exceptionally well suited for medical imaging.
It emits gamma rays at 140 keV, an energy easily detected by standard gamma
cameras and comparable to conventional X-rays, ensuring high-quality diagnostic
images.
Its physical half-life of roughly 6 hours allows rapid data collection while keeping the
patient’s radiation exposure low, with more than 90% of the isotope decaying within
24 hours. The biological half-life of about one day ensures that the compound is
,cleared efficiently from the body, further reducing dose. Around 88% of its decays
involve clean gamma emission without harmful particles, preventing unnecessary
tissue damage. After decay, it forms ⁹⁹Tc and eventually stable ⁹⁹Ru, leaving negligible
residual radioactivity.
In addition to these safety and imaging advantages, ⁹⁹ᵐTc can be conveniently
produced on-site: it is generated from ⁹⁹Mo via β⁻ decay with a yield above 87%,
enabling hospitals to use portable generators rather than relying on direct reactor
transport.
b. Beschrijf hoe ⁹⁹ᵐTc in een klinische setting wordt geproduceerd en beschikbaar
gesteld voor diagnostisch gebruik.
• 99Mo extracted from neutron irradiated targets is used as a source of 99mTc
• 99Mo undergoes spontaneous β-decay to excited states of 99Tc (>87% of decays
lead to 99mTc)
• 99Mo is present as water-soluble molybdate (MoO₄²⁻) adsorbed onto acid
alumina (Al₂O₃)
• As 99Mo decays, it forms pertechnetate ( 99mTcO₄⁻), which binds less strongly to the
alumina due to its lower charge and higher oxidation state (+7 for Tc vs. +6 for
Mo). This difference allows 99mTcO₄⁻ to be selectively eluted using physiological
saline (in column chromatography).
• The resulting solution is sodium pertechnetate (Na99mTcO4), which is sterile,
pyrogen-free, and ready for radiopharmaceutical labeling.
To prepare a technetium-99m (99mTc) coordination complex for medical imaging,
several criteria must be met to ensure clinical efficiency, safety, and specificity. The
process typically follows a simplified “kit method,” which involves one-pot synthesis
with a short reaction time, performed directly in physiological media without requiring
extreme conditions or extensive purification. This allows for rapid and practical
preparation in hospital settings. The resulting complex must be target-specific,
thermodynamically stable, and kinetically inert to ligand substitution in vivo, ensuring
reliable imaging and minimal interference from biological processes. In practice,
sterile and pyrogen-free sodium pertechnetate (Na99mTcO4) is injected into a vial
containing the ligand mixture, followed by brief shaking—often referred to as the
“shoot and shake” method. This streamlined approach enables fast and reproducible
labeling of radiopharmaceuticals for diagnostic use.
Vraag 3 – Rol van Zn²⁺ in hydrolysereacties (1 punt)
Leg uit waarom het Zn²⁺-ion bijzonder geschikt is om hydrolysereacties te katalyseren.
1. High charge density → strong Lewis acid: Zn²⁺ has a +2 charge and a small
ionic radius (~0.65 Å). This gives it a highly concentrated positive charge,
making it an excellent Lewis acid.
It strongly polarizes ligands (especially H₂O and carbonyl groups).
2. Zn²⁺ acts as a strong Lewis acid: it activates the substrate upon
coordination and simultaneously lowers the pKa of bound water, generating
a Zn–OH⁻ nucleophile for hydrolysis.
When water binds to Zn²⁺:
+¿ ¿
−¿ +H ¿
2 +¿−OH 2 ⟶ Zn 2+ ¿−OH ¿
¿
Zn
, Zn²⁺ stabilizes the deprotonated form, so the pKa drops dramatically. At
physiological pH, this produces Zn–OH⁻ nucleophile that would otherwise be
unavailable. A powerful, localized OH⁻ is generated directly in the active
site → ideal for hydrolysis.
3. Activation of the substrate: Zn²⁺ can bind the substrate (e.g., carbonyl oxygen,
phosphate oxygen):
Polarizes the bond to be cleaved
Stabilizes the negative charge in the transition state
Aligns the substrate for nucleophilic attack
Lower activation energy for hydrolysis.
4. Redox-inert (d¹⁰ configuration)
Zn²⁺ has a fully filled d¹⁰ shell.
It does not participate in redox chemistry.
Avoids unwanted electron transfer reactions — crucial in hydrolytic enzymes.
5. Borderline hardness → versatile ligand binding: Zn²⁺ can bind: O-donors (Asp,
Glu, H₂O), N-donors (His) and S-donors (Cys) Flexible coordination environment →
stable yet adaptable active sites.
Vraag 5 – Mössbauer-spectrum van een [2Fe–2S]⁺ Rieske-eiwit (3 punten)
a. Beschrijf het typische voorkomen van het Mössbauer-spectrum van een [2Fe–2S]⁺
Rieske-cluster. Waarom zie je twee doubletten?
A reduced [2Fe–2S]⁺ Rieske cluster shows two distinct
quadrupole doublets in its Mössbauer spectrum. This is
because the electron is valence-localized—not delocalized—
between the two iron atoms. One iron remains in the Fe(III)
oxidation state, while the other is reduced to Fe(II).
The Fe(III) site typically shows an isomer shift δ ≈ 0.30
mm/s.
The Fe(II) site shows δ ≈ 0.72 mm/s.
These differences arise due to their distinct
oxidation states and ligand environments: one
iron is coordinated by thiolate (cysteine), the
other by nitrogen atoms (histidine). This
asymmetry leads to different electron densities
and electric field gradients, resulting in two
separate doublets.
b. Bepaal de oxidatietoestanden van de ijzeratomen en verklaar deze op basis van
hun elektronconfiguratie.
In the reduced [2Fe–2S]⁺ cluster:
One iron is Fe(III) → oxidation state +3 → electron configuration: [Ar] 3d⁵
One iron is Fe(II) → oxidation state +2 → electron configuration: [Ar] 3d⁶
Both ions are in high-spin states due to weak ligand fields from sulfur and nitrogen
donors:
Fe(III): 5 unpaired electrons → S =
5/2
Fe(II): 4 unpaired electrons → S = 2
