Sunlight a catalyst for vitamin C oxidation?

[InFiNitY1]

hi
can someone please help me with this question "does sunlight affect oxidation of vitamin C" I have seen this as a common science fair topic and I have also done an experiment myself and have found that it does speed up vitamin C oxidation, But I don't know why! can someone please help me.

thanks

 

[matt grime]

I'm not sure that you should use the word catalyst. Just because something affects (speeds up) a reaction does not make it a catalyst in the chemical sense of the word. There are other considerations too, aren't there, such as they don't alter equilibrium positions, and are not themselves consumed in the process?

In anyccase, photon absorption can excite electrons and do something involving the words 'free' and 'radical'. I admit I am dredging my memory banks here, but I fancied stepping out of the safe confines of the mathematics forum; I hope I haven't done too much damage.

Do we not have a chemistry forum here? Hopefully someone there can help properly.

 

[Astronuc]

Matt is correct.

Vitamin C is damaged by oxidants or radicals, which are produced by sunlight in cells. Sunlight is not a catalyst since the light energy is absorbed.

We have Biology and Chemistry forums, but perhaps Biology is the appropriate venue for this question.

 

[Hootenanny]

Just to add to the information given, radicals are formed from the homolytic fission of a covalent bond, which in a single bond means that each atom receives a single electon. This electron is unpaired, which is the defining characteristic of a radical and means that it is very reactive and will go on to produce a radical chain reaction, to which there are three stages. Initiation is when the radical is intially formed (usally due to photodissociation but can also be formed when heated).

$$Cl_{2} + hv \rightarrow 2Cl\cdot$$

(the dots represent free electrons and hv is a photon)

Propagation occurs as radicals can induce homolytic fission is non radical molecules. An example of popagation;

$$Cl\cdot + H_{2} \rightarrow HCl + H\cdot$$

Termination occurs when two radicals react with each other thus;

$$H\cdot + Cl\cdot \rightarrow HCl$$

Radical chain reactions can be explosive as they are extreamly exothermic and progress rapidly. I have put down as much as I can remember and I apologise for any errors. As Astronuc says chemistry or biology forums should be your next step. If you would like more information on the mechanics of radical formation I would suggest the chemisty forums. However, if you would like biology specific information I would choose biology.

Regards,
~Hoot

 

[Astronuc]

I see that a thread by the same name got bumped to this forum.

The radicals that Hootenany mentioned, Cl^-, are strong oxidants, and HCl reaction is pretty potent.

However in the cell, its primarily reactive oxygen species (ROS).

ROS are oxygen-containing molecules that have higher reactivity than ground state molecular oxygen. These species include not only the oxygen radicals, such as superoxide, hydroxyl, and peroxyl, but also nonradical molecules like singlet oxygen and hydrogen peroxide. Radicals are molecules with unpaired electrons.

ROS are generated during aerobic metabolism. Increased levels of these species are produced during various forms of oxidative stress. The net intracellular concentration of ROS is the result of the production of ROS and the ability of substances to remove them.

from http://www.uihealthcare.com/news/currents/vol2issue3/8freeradical.html

 

[Gokul43201]

Another way to (partially) answer this question is to say that the reaction possesses at least one activated mechanism, with activation energy of the order of the energy of a solar photon (probably in the UV range).