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Chemistry (including Biochemistry)/Stœchiométrie (Reaction yields never 100%?)


Pourquoi le % de rendement est rarement 100%?
Pourquoi est-il désirable de maximiser le rendement d'une réaction chimique dans l'industrie de synthèse de produits chimiques?

Hope you understand French, answer in English is fine, thanks Michelle

No hablo Francaís, pero hablo un poquito Español y tengo Google. ¡Vamos!

I'll answer in English and I'll pass the English through Google to French. With luck Google will not confuse you more!

Reactions are rarely 100% complete, it is true. This happens because:

1) Some reactions are reversible. This means there will always be some small percent of the reactants hanging around unless you set up a second reaction to steal the products away. (see Equilibrium)

2) Carbon chemistry happens in three dimensions. This means that some reactions (especially synthesis ones) can stick your two parts together in multiple different orientations. The products in this case can have radically different properties because of this 3D difference. (See chirality) Sometimes the 'wrong' or 'left-handed' molecules must then be purified away somehow from the 'right-handed' ones. This added step is a pain and reduces the percent yield.

3) Physics. Put simply, the laws of thermodynamics tell you that while matter and energy cannot be created or destroyed, some energy is typically lost as heat that is not recoverable. So again, even spontaneous reactions leave bits behind unless more energy is put into the system to make sure it 'finishes'. (See Thermodynamics)

4) Viscosity. Sometimes the products of a reaction may prevent the reactants from encountering each other completely. Stirring can help with this.

Good luck! Please ask again if this is confusing.

Je vais répondre en anglais et je vais passer l' anglais par Google en français. Avec de la chance, Google ne sera pas vous embrouiller plus!!

Les réactions sont rarement 100 % complet , il est vrai . Cela arrive parce que :

1) Certaines réactions sont réversibles. Cela signifie qu'il y aura toujours une petite pour cent des réactifs traîner sauf si vous définissez une seconde réaction de voler les produits loin . ( voir Equilibrium )

2) La chimie du carbone se produit dans les trois dimensions. Cela signifie que certaines réactions (en particulier les synthèse ) peuvent se coller vos deux parties ensemble dans plusieurs orientations différentes. Les produits dans ce cas peuvent avoir des propriétés radicalement différentes en raison de cette différence 3D. ( Voir chiralité ) Parfois, le «mauvais» ou molécules « gauchers » doivent ensuite être purifiés loin en quelque sorte de ceux « droitiers ». Cette étape supplémentaire est une douleur et réduit le rendement en pour cent .

3 ) Physique. En d'autres termes, les lois de la thermodynamique vous dire que tandis que la matière et l'énergie ne peuvent pas être créés ou détruits, de l'énergie est généralement perdue sous forme de chaleur qui n'est pas récupérable. Encore une fois, même des réactions spontanées laissent derrière morceaux moins plus d'énergie est mis dans le système pour s'assurer qu'il « finitions ». ( Voir la thermodynamique )

4) Viscosité. Parfois, les produits d'une réaction peuvent empêcher les réactifs de la rencontre avec l'autre complètement. L'agitation peut aider.

Bonne chance! S'il vous plaît demander si c'est un peu confus.  

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Trista Robichaud, PhD


No homework questions, especially ones copied and pasted from textbooks. I will answer questions about principles or give hints, but I do not do other's homework. I'm comfortable answering basic biochemistry, chemistry, and biology questions up to and including an undergraduate level of understanding. This includes molecular biology, protein purification, and genetics. My training/inclination is primarily in structural biology, or how the shapes of things affect their function. Other interests include protein design, protein engineering, enzyme kinetics, and metabolic diseases such as cancer, atherosclerosis, and diabetes. My chemistry weaknesses are that I do not know organic or inorganic synthesis well, nor am I familiar with advanced inorganic reactions. I will attempt quantum mechanics and thermodynamics questions, but primarily as they relate to biological systems. Furthermore, I cannot tell you if a skin photograph is cancerous, or otherwise diagnose any disease. I can tell you how we currently understand the basic science behind a disease state, but I cannot recommend treatment in any way. Please direct such questions to your medical professional.


I hold a PhD in Biomedical Science from the University of Massachusetts Medical School in Worcester. I specialize in Biochemistry, with a focus on protein chemistry. My thesis work involved the structure and functions of the human glucose transporter 1. (hGLUT1) Currently I am a postdoc working in peptide (mini-protein) design and enzymology at the University of Texas Health Science Center in San Antonio, Texas. I am in Bjorn Steffensen's lab (PhD, DDS), studying gelatinase A and oral carcinoma.

2001 American Association for the Advancement of Science
2007 American Chemical Society
2007 Protein Society
2011 UTHSCSA Women’s Faculty Association

Levine KB, Robichaud TK, Hamill S, Sultzman LA, Carruthers A. Properties of the human erythrocyte glucose transport protein are determined by cellular context. Biochemistry 44(15):5606-16, 2005. (PMID 15823019)
Robichaud TK, Appleyard AN, Herbert RB, Henderson PJ, Carruthers A “Determinants of ligand binding affinity and cooperativity at the GLUT1 endofacial site” Biochemistry 50(15):3137-48, 2011. (PMID 21384913)
Xu X, Mikhailova M, Chen Z, Pal S, Robichaud TK, Lafer EM, Baber S, Steffensen B. “Peptide from the C-terminal domain of tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) inhibits membrane activation of matrix metalloproteinase-2 (MMP-2)” Matrix Biol. 2011 Sep;30(7-8):404-12. (PMID: 21839835)
Robichaud TK, Steffensen B, Fields GB. Exosite interactions impact matrix metalloproteinase collagen specificities. J Biol Chem. 2011 Oct 28;286(43):37535-42 (PMID: 21896477)

Poster Abstracts:
Robichaud TK, Carruthers. A "Mutagenesis of the Human type 1 glucose transporter exit site: A functional study." ACS 234th Meeting, Boston MA. Division of Biological Chemistry, 2007
Robichaud TK, Bhowmick M, Tokmina-Roszyk D, Fields GB “Synthesis and Analysis of MT1-MMP Peptide Inhibitors” Biological Chemistry Division of the Protein Society Meeting, San Diego CA 2010
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Catalytic Domain Exosites Contribute to Determining Matrix Metalloproteinase Triple Helical Collagen Specificities” Dental Science Symposium. UTHSCSA 2011
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon Research Conference on Matrix Metalloproteinase Biology, Bristol RI 2011

Oakland University, Auburn Hills MI BS, Biochemistry 1998
University of Massachusetts Medical School, Worcester MA PhD, Biochemistry & Molecular Pharmacology 2001-2008
University of Texas Health Science Center, San Antonio TX Postdoc, Biochemistry 2009-Present

Awards and Honors
1998 Honors College Graduate, Oakland University
2009 Institutional National Research Service Award, Pathobiology of Occlusive Vascular Disease T32 HL07446
2011 1st Place, Best Postdoctoral Poster, Dental Science Symposium, UTHSCSA, April 2011

Past/Present Clients
Invited Seminars:
Robichaud TK, Fields GB. “Synthesis and Analysis of MTI-MMP Triple Helical Peptide Inhibitors” Pathology Research Conference, University of Texas Health Science Center San Antonio Pathology Department (June 18th, 2010)
Robichaud TK & Hill, B “How To Give A Great Scientific Talk” Invited Lecture, Pathobiology of Occlusive Vascular Disease Seminars, UTHSCSA (Nov 11th 2010), Cardiology Seminar Series, Texas Research Park (Feb 21st, 2011)
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon-Keenan Research Seminar “Everything You Wanted to Know About Matrix Metalloproteinases But Were Afraid to Ask” Bristol, RI (Aug 6th, 2011)

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