Immobilized Enzymes — Intraparticle Mass Transfer Effects: In which immobilization formats can internal diffusion resistance limit the observed reaction rate?

Introduction:
When enzymes are immobilized within or onto solid matrices, substrates and products must diffuse to and from the active sites. This introduces intraparticle mass transfer resistance that can depress the apparent activity compared with free enzymes. Identifying formats where diffusion matters is key for reactor design and performance troubleshooting.

Given Data / Assumptions:

• Particles, gels, or porous carriers provide internal pathways for diffusion.
• Substrates are small molecules; enzymes are immobilized within/onto a solid phase.
• External film resistance can be minimized by agitation, but internal effects may remain.

Concept / Approach:

Any immobilization that places enzyme sites behind a diffusion barrier can be intraparticle-limited. Encapsulated or copolymerized enzymes reside inside gel networks. Crosslinked enzyme aggregates create dense matrices with tortuous paths. Porous adsorbents require diffusion into pores to reach bound enzyme. The result is an effectiveness factor less than 1, especially at high intrinsic activity or thick diffusion layers.

Step-by-Step Solution:

Verification / Alternative check:

Weisz–Prater or Thiele-modulus analyses routinely diagnose diffusion limitations for immobilized systems, confirming that geometry and porosity drive the magnitude of intraparticle effects.

Why Other Options Are Wrong:

E: Contradicted by extensive literature; internal diffusion is a hallmark issue in immobilized catalysis.

Common Pitfalls:

Assuming vigorous stirring removes internal resistance; agitation mainly addresses external film resistance, not diffusion inside particles.

Final Answer:

All of the above