[putsona]

i need help in my research about, "henna as a sunblock" and the major role will be played by lawsone molecule.when henna colour is fading,i read that it is an oxidation process.what happen when henna exposed to sunlight which protects the skin from UVB and UVA?will lawsone molecule undergo photodegradation process?because lawsone molecule has benzene ring, and it is fond of being changed into another molecule which causes the henna colour to be lighter.the lawsone molecule is also called chromophore, right?after it absorbs UV light will lawsone molecule turns into another molecule?because the colour is fading from day to day.

tq so much if there's anyone can help me solve this.

[Borek]

Search forums for lawsone, some aspects of its chemistry were recently discussed.

[putsona]

yes i know and i have read.but the topic that they are discussing are not answering my questions.theyare discussing bout the process of lawsone molecule binds to the hair and skin.my question was-what happened when lawsone molecules hit by sunlight.

[ARGOS++]

Dear Putsona,

You are right!, - I told not very much and not very clear about the Quality of the Pigment.
Anthraquinone (you remember?) are usually known as the highest qualitative “Organic Dyes” we know, but not all times of nicest Shade.
Therein stability is an important attribute too, but by far not the only!

So also the Henna Pigment is very stabile. As a minimal sign for this fact is, that the hair remains coloured for more then several months.
The fading in case of coloured skin is not only mainly caused, that “only” the top layer of the skin will be finally coloured, and this layer is very easy and very fast exfoliated by the skin itself.

With Light of the “right” wavelength the molecule reach its excited state and transfers the energy finally into heat, when it “falls” back to the ground state again.
So the Pigment Absorption is in concurrence to all other absorbing processes inside the cell, and that results in some sun protection.

But this is not the same as a “sun block crème”, because they work like a filter in front of the skin with a high content of the acting ingredients.

I hope this may bee of some help to you!

Good Luck!
                    ARGOS⁺⁺

[putsona]

dear argos,
thank you soooo much !!! 
thanx for your help.now i understand bout the effect of the right wavelength been absorbed bcoz my experiment shows the expected results in which it acts as a sunblock.i have tested that it absorb wavelength at 400nm-500nm the most. this wavelength is UVB and UVA

however, does the absorption of sunlight by this lawsone molecule causes the henna colour to fade from day to day?

[ARGOS++]

Dear Putsona,

(I’m happy, that my answer was of some help.)

In your last post we have a little bit to correct:
The range 400nm – 500nm is not UVA and not UVB, it is the lower part of the “Visible Spectrum”.
For UVA and UVB you may read under:

“Ultraviolet” (Wiki)

Of course, also the final Henna Pigment shows you a respectable Absorption in the range 200nm – 400nm which helps to “protect” against UVA and UVB, but the blocked “Leucoform” could do a better job, as long as you are able to keep it blocked (Otherwise you get coloured.)!

The Henna Pigment should stay quite stabile for “normal” Sun Light, but with Light of “sufficient” short wavelength you are able to crack nearly any bond/substance.
(Remember the Henna-Hair usually keeps coloured for a lot of months.)


Good Luck!

                    ARGOS⁺⁺

[putsona]

i would like to know more about the molecule anthraquinone.
wat is the new molecule produced after being hit by UV ray ( 200-400nm)
since it is a quinone molecule,i do not know where to search it's new chemical compound after undergo photodegradation.

[ARGOS++]

Dear Putsona;

Anthraquinone will not undergo any photodegradation with sunlight or light with a wavelength above 200nm (UVA or UVB). As I told you Anthraquinone-Dyes are Dyes of the highest Quality we know and reach a value of 8 (where 8 is the best) in its tests in the Fadeometer.
The value of 8 means, that after expose a sample to a “Light Equivalent” of 1.0 Million Sunlight-Hours not any visible degradation (photo or oxidative) is measurable!

For Photodegradiation of this kind of Dyes light of significant higher energy (= shorter wavelength) then 200 nm is required. What the product will be I can’t tell you and I believe nobody has really tried to identify it yet.
So if any degradation can be found, it will be of mechanical or chemical nature.

To get an Idea about Energy, Wavelength, and “Bond-Breaking” you may study the Diagram:  "FAQ: Why Einstein meets Beer-Lambert?”

There is no good literature/info about Fadeometer, but you may at least read:   "Fadeometer”

If you need other information about Anthraquinone, please tell me.
I hope this will again be of some help to you.

Good Luck!
                    ARGOS⁺⁺

[putsona]

yup.i need more information about anthraquinone.will it be affected by ph changes, or temperauture?or none since it is a dye of high quality?

[ARGOS++]

Dear Putsona;

Your Imagination/Perception is coming quite near the “Truth”!
(Who ever know where/what the real “Truth” is!)

Application Quality goes nearly hand in hand with chem. & phys. Quality!

There are a lot of Indications for the different Anthraquinones:

•   A.)  Very drastic methods are required to destroy it oxidative!
•   B.)  Quite drastic methods are required to reduce it to its “Leucoform”, and in such case already oxygen from air is sufficient to re-oxidize it reversible. This process is used during the “Dyeing Process”, because only the Salt of the “Leucoform” is water soluble and shows now the required affinity to the fibre.
•   C.)  Also very drastic methods are required for realising Substitution on the “final” Anthraquinone Body. In most case more then one step is required and the first is mostly a strong Sulfonation or Halogenation with its later exchange. That’s why most Derivatives are normally “made” before the final “Quinone Ring” is build.
•   D.)  Also a Bp. of  380°C of the simple Anthraquinone without decomposition is a good demonstration for its temperature stability(see on:  "Anthraquinone”)
•   E.)  Anthraquinone itself and most of its derivates are nearly not influenced (depending of other functional groups) by pH. Also an indication for this may be that this kind of Dyes is very “Sweat stable/resistant” (Not only in Shade!).
•   F.)  The “benzoic Quinone Ring” has similar or even higher Stabilisation energy as only the aromatic analogon has.
•   G.) A simple Derivate is used to produce commercially “Hydrogen Peroxide”,  ─   an impressible Demonstration too (see on:  "Hydrogen Peroxide”)
•   H.)  Most Anthraquinones are “only” soluble in concentrated  H₂SO₄, mostly without  decomposition. 
•   I.)  Etc., etc. 

Of course, you can always find one or another exception, but as the golden Rule of Chemistry tells:

“Exceptions always only validate the demonstrated Rule!”

I hope I have been of help to you.

Good Luck!
                    ARGOS⁺⁺