Talk:Fluorescein

From Wikipedia, the free encyclopedia

Chemicals WikiProject
Chemistry Portal
Fluorescein is within the scope of WikiProject Chemicals, which aims to improve Wikipedia's coverage of chemicals. To participate, help improve this article or visit the project page for details on the project.
Chemistry WikiProject This article is also supported by WikiProject Chemistry.

Article Grading: The article has not been rated for quality and/or importance yet. Please rate the article and then leave comments here to explain the ratings and/or to identify the strengths and weaknesses of the article..
WikiProject Medicine This article is within the scope of WikiProject Medicine. Please visit the project page for details or ask questions at the doctor's mess.
Start This page has been rated as start-Class on the quality assessment scale
Mid This article has been rated as mid-importance on the importance assessment scale

Contents

[edit] Fluorescein colour

In slit lamp, based on an article from the NIH MedlinePlus medical encyclopedia, it is stated that flourescein is orange-coloured, but in this article it is used to colour a river green? Which is it? Dewet 15:34, 16 May 2005 (UTC)

It's both. :) Pure fluorescein is a red-orange crystalline substance. In water or ethanol solution, it's green or yellow-green depending on the solvent and pH. --TenOfAllTrades (talk/contrib) 16:07, 16 May 2005 (UTC)
Actually even in solution fluorscein is orange (just have a look at the picture included in the article). The greenish look it has, is it's fluorescent light emission. Chris
Ah, many thanks, then. I'll leave it as is. Dewet 16:59, 16 May 2005 (UTC)
At lower concentrations (uM), a fluorescein solution has a green yellowish color. As the dye concentration increases (mM), the solution appears orange. KingHanneman (talk) 04:57, 1 February 2008 (UTC)

I'm pretty sure the wavelengths here are wrong. I think the absorption wavelength is 488 nm and emission 520nm. I haven't changed it as someone might change it back straight away :-) Dwayne Dibly 00:26, 21 December 2005 (UTC)

Close Dwayne. I have some results of my own: abs = 491nm and emission = 514nm. It's probably better to find a literature value though. Tomid 16:38, 18 July 2006 (UTC)
It's solvent dependent. Both the excitation and emission peaks shift a little based on solvent and pH. 490/520 nm are pretty accepted general areas, though. chihowa 01:44, 14 March 2007 (UTC)

[edit] what causes fluorescence?

In the articles that I've looked at, they talk about how Fluorochromes, based on their chemical makeup, are able to absorb short wavelengths of light and emit long wavelenths of light, which then are visible. Why is this so? What is different about the structure of, for example, isothiocyanate, that it does emit light at longer wavelengths? Why do other compounds not do this? For example, why do some organisms, such as Cyanobacteria, fluoresce while others do not?

For answers to general reference questions, might I suggest placing a note at Wikipedia:Reference desk? More editors are likely to see your question there, and it's a more appropriate forum—the article Talk pages (like this one) are better suited for discussion that directly relates to the content of each article. With regard to your question, I'd also recommend starting with our article on fluorescence, and start following links from there. It's a pretty big topic. TenOfAllTrades(talk) 19:33, 9 August 2005 (UTC)
Fluorescence of this dye is primarily due the fluorone segment, which is highly conjugated and increases the probability that relaxation from the excited state occurs through fluorescence. The isothiocyanate group on fluorescein is typically used for covalent attachment to polymers and in biology. As for the isothiocyanate group by itself, if it doesn't fluoresce, then it would primarily undergo non-radiative relaxation pathway(s) from the excited state. I think less than 10% of molecules fluoresce; even less fluoresce well (ie have a high quantum yield). KingHanneman (talk) 05:10, 1 February 2008 (UTC)

[edit] SMILES

Okay, I added the SMILES string, but it's pretty large and makes the chembox look ugly. I'm not very good at formating in Wikipedia so hopefully someone with more skill will be able to clean it up and make it look nice. :) Mrestko 21:23, 4 July 2006 (UTC)


[edit] different abs and em peak positions

there are two different sets of adsorption and emission peak wavelengths mention in the article. Are the values under "chemical properties" related to FITC and not fluorescein? Benkeboy 10:39, 6 September 2006 (UTC)

[edit] Toxicity?

Apparently all the folks involved in using fluorescein dyes know that it has a low toxicity; presumably it wouldn't be poured into a river or injected into the bloodstream for eye photography if it were toxic. However, does it not bear comment in the article that such a dramatically colored chemical is harmless? Yes, it obviously is a relevant issue that should be explicated. I, for one, am curious about its toxicity thresholds. -PLK —The preceding unsigned comment was added by 71.59.70.21 (talk) 21:41, 17 March 2007 (UTC).

I was also missing information about that, good point. 141.84.139.181

Fluorescein may have low toxicity but that does not make it harmless. In some people, exposure triggers anaphylaxis. --Una Smith 03:09, 18 August 2007 (UTC)

[edit] 2',7' Fluorescein Derivatives

I don't know if this is useful or not, but in the work I'm doing now with fluorescein, I've read that the pKa of the dye can be controlled by the substituents in the 2' and 7' positions. For example, an electron withdrawing group decreases the pKa. The pKa for dichlorofluorescein is 5, and the pKa for difluorofluorescein (aka Oregon Green 488) is 4.7. Likewise, an electron donating group increases the pKa. An ethyl group increases the pKa 0.2-0.3 pH units, and a hexyl group increases the pKa to 8.4. Also, in water, the absorption and emission maxima shift a bit (~10 nm). KingHanneman (talk) 05:19, 1 February 2008 (UTC)