Wikipedia:Reference desk/Archives/Science/2020 March 29

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March 29

UV light and the coronavirus

There are medical devices that use UV light to "kill" viruses. I have two novelty 75 watt Blacklight incandescent bulbs of the type that are sold in Halloween superstores. I was thinking of rigging up a lightbox lined with aluminum foil and putting things like car keys, credit cards, work gloves, facemasks and the like into it. I would ventilate the box because these bulbs run hot. My son who is a geek says these bulbs emit UVA and what I need is UVC LEDs. He seems to be saying politely that this project is a waste of time, and I concede that he is probably right. Can I get a second opinion? At least I can make Velvet Elvis paintings glow. Cullen³²⁸ Let's discuss it

I'm not going to make any claims about what wavelengths of ultraviolet light kill this virus, but in general party blacklights are UVA whereas germicidal lamps are UVC. But if you have enough Velvet Elvis paintings whose glow can be seen from afar, nobody will get within 6 miles feet of you and you won't get infected. DMacks (talk) 04:35, 29 March 2020 (UTC)

UVC LED's are nowhere near powerful enough to sterilize stuff. Germicidal UV lamps are fluorescent and you have to wear safety goggles and stuff when using them. As for actually sterilizing stuff like masks, that is edging towards medical advice and all I can say is better check some good scientific or medical references about UV sterilization. This is about UV germicidal irradiation (UVGI) but I haven't read it. There is also starting to be a literature about sterilizing facemasks using an oven,[1] steam from boiiling water etc. General recommendations I've seen for credit cards, mobile phones etc. are to wipe them down with spray cleaner. 2601:648:8202:96B0:E0CB:579B:1F5:84ED (talk) 09:34, 29 March 2020 (UTC)

There are UVC LEDs intended for sterilization now. But yes, most germicidal lamps have historically used a fluorescent design. DNA has a specific UV absorption band ~260 nm (in the UVC), which is what makes germicidal UV so effective. At the same intensity, UVA absorption is less than 1/1000th of the effect of UVC. Dragons flight (talk) 11:20, 29 March 2020 (UTC)

• UVC LEDs have been a thing for a while now.[2] They could become an important means of improving water sterilisation for small-scale, low-power, such as solar-powered units. There are still questions out there on their longevity, and such applications should really have built-in testing for light output. But they're certainly viable as UVC sources, and as replacements for fluorescents. They avoid the mercury too. Andy Dingley (talk) 20:32, 29 March 2020 (UTC)

Novelty blacklights usually are coated with phosphor to produce a purple light while also allowing some UV to escape. Fluorescent lamps used for sterilization have a clear tube with no phosphor, to allow UV to escape unimpeded. Remember, most humans can't see UV; if you can see a lamp giving off light, that tells you at least some of what it's giving off is visible light. Side topic: all "white" fluorescents are mercury lamps, which are the same kind used in blacklights and germicidal lamps. Fluorescence is a quantum mechanical phenomenon; electrons become excited and emit photons to become un-excited. The wavelengths of the emitted photons are very specific and depend on the electronic properties of the material. Mercury is used because it has a low vapor pressure (it can be a gas at room temperature) and fluoresces in UV. The resulting UV photons can be absorbed by phosphor molecules, which themselves become excited and re-emit photons at longer wavelengths; for "white" lamps, a mixture of phosphors is chosen that produces visible light. Also note that UV is good at promoting lots of photochemical reactions. A lot of plastics will degrade when exposed to UV light. Plastic items intended for outdoor use have UV stabilizers added to inhibit this, if needed (not all plastics react to UV). --47.146.63.87 (talk) 01:56, 30 March 2020 (UTC)

UVC vs UVA lamps

Just to expand on "Novelty blacklights usually are coated with phosphor to produce a purple light while also allowing some UV to escape. Fluorescent lamps used for sterilization have a clear tube with no phosphor, to allow UV to escape unimpeded.". the phosphor actually puts out quite a bit of blue along with UVA and looks bluish white. These bulbs are often used in bug zappers. The ones used to make your dogs playing poker velvet painting fluoresce also have colored glass that mostly filters out everything except UVA and a bit of deep violet. The UVC tubes are made of quartz, because glass blocks most UVC.

At a trendy hip-hop fashion event in Hong Kong, attendees experienced sunburn and eye problems after the lighting contractor used UVC bulbs instead of UVA.[3][4] --Guy Macon (talk) 04:26, 30 March 2020 (UTC)

Commodity glass is also quartz, although it often has impurities and additives. Germicidal lamps usually use fused quartz which as you note transmits UV better. --47.146.63.87 (talk) 06:21, 31 March 2020 (UTC)

Whether you use leds or fluorescent tubes be very careful about eye exposure and somewhat careful of skin exposure. 2601:648:8202:96B0:E0CB:579B:1F5:84ED (talk) 08:23, 30 March 2020 (UTC)

Are there protein vitamins?

I've told two different opinions about vitamins: one opinion (biological science student) says that there are vitamins made of proteins. Second opinion (a PhD from Bristol university) says it can't be because if they were they’d be broken down into amino-acid units during digestion by proteases rather than absorbed. Now, according to the article here (vitamin) there is one vitamin (U) which is protein metabolize. So as far as I understand the student is wrong. Am I correct? 93.126.116.89 (talk) 20:07, 29 March 2020 (UTC)

S-Methylmethionine is a single amino acid, not a protein. There is a cited statemnt in that article "S-Methylmethionine is sometimes referred to as vitamin U,[3] but it is not considered a true vitamin." DMacks (talk) 20:19, 29 March 2020 (UTC)

The article says it is a protein metabolite, not a protein metabolize. A metabolite is a molecule that results from breaking up larger molecules, in this case proteins. So a protein gets broken up into amino acids, one of which is methionine. This then gets modified (by methylation, that is, a methyl group is added to the molecule) and becomes S-methylmethionine, aka vitamin U. The PhD was right in this case.  --Lambiam 21:33, 29 March 2020 (UTC)

You'll note that "vitamin U" is listed as a reclassified vitamin: something that some people considered at one time to be a vitamin, but is not generally considered one at present. The modern definition of "vitamin" is an essential micronutrient that isn't a mineral. SMM is not a vitamin, as it's not essential; the body produces it from other chemicals, and this production appears adequate for its needs. It is correct that proteins and peptides are generally digested if consumed orally. This is why we can't administer insulin, a peptide hormone, orally. There is some interesting research suggesting some peptides are resistant to digestion and might be a viable route for drug administration, but that's a different topic. Some amino acids are essential nutrients, but they're not considered vitamins because they're macronutrients. Generally you ingest them in proteins, which are digested into their component amino acids. --47.146.63.87 (talk) 01:37, 30 March 2020 (UTC)