Dear Seda, 

according to the answers of previous answerers, you can see the effect of a too vague formulated question!!

On other part you answer  (giving the following info) :

Stanislav, I am looking for a protein and nanoparticle interaction which has a absorbance at 550 nm and 900 nm respectively.

Protein and nanoparticle are too vague.

Please read this paper:

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

http://www.jnanobiotechnology.com/content/11/1/26

Interaction of nanoparticles with proteins: relation to bio-reactivity of the nanoparticle

Shruti R Saptarshi1, Albert Duschl2 and Andreas L Lopata1*

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

If you don 't give more precise infos prior a thesis or paper in preparation, please read the excellent book of David Freifelder:

Physical biochemistry/ Application to biochemistry and molecular biology  

W.H. freeman and Company San Francisco

Edition 1976.

In this book, you 'll find valuable infos about the factors affecting the absorption properties of a chromophore  of proteins and biological substances (page 383,384....).

P.e  the absorption spectrum of tyrosine at pH 6 and 13 shows an increase of lambda (max) and epsilon when the phenolic OH is dissociated.

If you want to interpretate the absorption spectra of biological macromolecules e.g. proteins and nanoparticles, you must know and apply the rules of a good spectroscopist:

- Use of a good UV-Vis spectrometer (single or dual beam or diode arrays).

- quartz cuvettes and cutoff of your solutions.

- Detection and identification of substances by measurement of the complete spectrum. you must have a  spectrum of your protein (pure) and compare the absorbance at different pH . 

Search infos about the pH titration of proteins and changes in the configuration of them.

- You must test if the spectrum of your protein is sensitive to changes in the polarity of the solvent too.

Good luck

JRG

In my experience, it strongly depends on the particular molecule and its pKa etc... Are you interested in certain molecule?

pH can have an effect on the UV spectra, though usually by affecting the substance you are trying to analyse.

UV-Vis spectroscopy is based upon measuring the electronic transitions within the UV-Vis range. Generally, Molecules containing π-electrons or non-bonding electrons (n-electrons) can absorb the energy in the form of ultraviolet or visible light to excite these electrons to higher anti-bonding molecular orbitals. For organics, this is stuff with a high degree of conjugation such as aromatic compounds. Include also ligands from metal ion solutions.

So when pH changes, particularly in the case of metal ion solutions, the ligands are directly affected which can result in a shift in the UV-Vis absorption.

By following the Le-chatlier Principal and equilibrium. 

Nature of the solvent, temperature conditions and interfering molecule in your particular compound also influence the absorption.

Thank you very much

Stanislav, I am looking for a protein and nanoparticle interaction which has a absorbance at 550 nm and 900 nm respectively.

Dear Seda,

Please see the next paper.

https://www.researchgate.net/publication/8064232_pH-dependent_quenching_of_the_fluorescence_of_tryptophan_residues_in_class_A_beta-lactamase_from_E._coli_%28TEM-1%29

I hope it will give you some direction especially you are working with protein molecule.

Also, if you have protein sequence send it to [email protected] and will return you some information about predicted pH-dependent stability of you protein.

Kind regards

Article pH-Dependent Quenching of the Fluorescence of Tryptophan Res...

Hello Dimitar,

Thank you very much . I am sending the e mail.

I am agree with Dr Abirami

In general it follows the Le-chatlier Principal and equilibrium.

Nature of the solvent, temperature conditions and interfering molecule in your particular compound also influence the absorption.

Hi Seda,

          UV Vis spectrum will depend upon the molecule you are trying to characterize. If the molecule has functional groups which have exchangeable protons like hydroxy, amines, or carboxylates, then the pH would have an affect on the spectrum of the molecule. Read about the chemical deviations section on this link. It explains your issue well. 

http://pharmaxchange.info/press/2012/05/ultraviolet-visible-uv-vis-spectroscopy-%E2%80%93-limitations-and-deviations-of-beer-lambert-law/

it depend on the effect of the protonated/deprotonated group on the conjugated system which absorbs

UV spectra can create considerable impact on the pH of the sample solution. A shift in the equilibrium between the different chemical forms of an analyte is a primary mechanism for this. For Instance, pH indicators used in acid/base titrations alter color at a particular pH because the chemical form of the indicator-compound endures a change at this point.

If pH is recognized to be a factor, a remedy is to prepare the sample in an appropriate buffer solution so as to keep up the pH at a stable value. Although, the buffer needs to be transparent over the wavelength range of the measurements.

In addition, effect of the solvent, concentration of the sample, and the temperature of the sample should be considered as well.

http://pubs.acs.org/doi/abs/10.1021/j100068a039

As we measure the electronic transitions between the atoms, hence pH changes could effects on those transitions such as protonation or deprotonation and that finally change shift the position (peak) of absorption.

Yes, there will a chance of spectral differences when pH of the measuring solution changes, that is bathochromic shift.

This is true in case of the molecule nature like functional groups such as ionisable groups.

By this change in pH of the solution , we do measure pKa by spectrophotometric methods

having below 2 and above 9 pKa values otherwise by titration methods

Best regards

Dear Seda, 

according to the answers of previous answerers, you can see the effect of a too vague formulated question!!

On other part you answer  (giving the following info) :

Stanislav, I am looking for a protein and nanoparticle interaction which has a absorbance at 550 nm and 900 nm respectively.

Protein and nanoparticle are too vague.

Please read this paper:

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

http://www.jnanobiotechnology.com/content/11/1/26

Interaction of nanoparticles with proteins: relation to bio-reactivity of the nanoparticle

Shruti R Saptarshi1, Albert Duschl2 and Andreas L Lopata1*

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

If you don 't give more precise infos prior a thesis or paper in preparation, please read the excellent book of David Freifelder:

Physical biochemistry/ Application to biochemistry and molecular biology  

W.H. freeman and Company San Francisco

Edition 1976.

In this book, you 'll find valuable infos about the factors affecting the absorption properties of a chromophore  of proteins and biological substances (page 383,384....).

P.e  the absorption spectrum of tyrosine at pH 6 and 13 shows an increase of lambda (max) and epsilon when the phenolic OH is dissociated.

If you want to interpretate the absorption spectra of biological macromolecules e.g. proteins and nanoparticles, you must know and apply the rules of a good spectroscopist:

- Use of a good UV-Vis spectrometer (single or dual beam or diode arrays).

- quartz cuvettes and cutoff of your solutions.

- Detection and identification of substances by measurement of the complete spectrum. you must have a  spectrum of your protein (pure) and compare the absorbance at different pH . 

Search infos about the pH titration of proteins and changes in the configuration of them.

- You must test if the spectrum of your protein is sensitive to changes in the polarity of the solvent too.

Good luck

JRG

What about phosphorus, is pH change of the sample to be analysed by UV/Vis can affect the concentration of P measured?