When I treat Humic acid with ligninase enzymes, its absorbance at 280 increases. Most references say that absorbance should decrease. What may be the reason?
Thanks for suggestions. I take into account the contribution due to addition of enzyme. My thinking is that if humic acid polymer is degraded into aromatic subunits, absorbance can increase or remain constant. However if aromatic rings are further degraded (ring opening) then the absorbance (254 or 280 nm) will decrease. Does it make sense?? Ewa can you attach your reference which explains these possibilities (decreased or increased absorbance) as a result of Humic acid degradation. Thanks a lot.
I think that the absobance at 254 nm is dependent upon the number of peptide links in the polypeptide
chain and must decrease at depolymerization, while the absorbances at 280 nm are the result of
the number of aromatic aminoacids present, but could be influenced also by molecules or ions interacting
with the specified free aminoacids enhancing their absorbances.
My opinion is only a supposition, not more.
Oswald Hörer
You are right Oswald as far as Proteins are concerned but what about HUMIC ACID Molecule? If I degrade humic acid molecule and assuming the concentration does not change, why the absorbance/decrease and or increase with time? As Ewa pointed out the increase or decrease in absorbance is due to change in Extinction coefficient. But the question remains WHY the Extinction coefficient increase/and or decrease when HUMIC acid is degraded?
I agrre with Ewa. There are a lot of works about Absorbance at 254 and 280 I studied aquatic humic substances and calculated the MW with this extinction coefficients.
Hi Martha. I would really like if you could share a reference of the work where you have illustrated that calculations of MW (distributions?) of humic substances from measurements of absorbance at 254 and 280 nm. Thank you
Peuravuori, J. y K. Pihlaja. 1997. Molecular size distribution and spectroscopic properties of aquatic humic substances. Analytica Chimica Acta. 337: 133-149.
Scapini, M. C.; V. Conzonno, V. Balzaretti y A. Fernandez Cirelli A. 2008. Propiedades ópticas del ácido fúlvico del río Chubut. en Estudio de las fracciones orgánicas en suelos de la Argentina. (Ed.)Juan Alberto Galantini Compiladores: Liliana Suñer, María Rosa Landriscini y Julio Osvaldo Iglesias. Asociación Argentina de la Ciencia del Suelo. 231-243
Primeras Jornadas Interdisciplinarias "Ciclo del Agua en Agroecosistemas” Setiembre de 2010. Centro de Estudios Transdisciplinarios del Agua, Facultad de Ciencias Veterinarias-UBA. Buenos Aires
..Martha Bargiela y Alicia Fabrizio de Iorio. Caracterización de la materia orgánica disuelta en aguas superficiales de la zona periurbana y rural de la Cuenca Matnza Riachuelo. Ponencia Oral.
Bargiela 2009. Influencia de la relación entre metales pesados y las sustancias húmicas de ríos de llanura sobre la movilidad de estos elementos.Tesis de Maestria en Ciencias del suelo EPG Dr Alberto Soriano, Facultad de Agronomía, Universidad de Buenos Aires.
Hi Luis: Here there are two works (specially Peuravuori and Pihlaja), that study this relationship, The last one is my thesis and a work related.
Dear Martha,
Is it possible to attach the 1st paper in the list published in Analytica Chimica Acta 337. We do not have this in our Library. Your comments are very useful. Sohail
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