Wikipedia:Reference desk/Archives/Science/2010 October 11

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October 11

Ascorbic acid (or other antioxidants) as a redox catalyst

What are some good examples of ascorbic acid encouraging redox reactions? Can it be used to encourage the production of nitrite, nitrate or nitric oxide from ammonia in the presence of an oxidant like bleach or chlorate? John Riemann Soong (talk) 05:53, 11 October 2010 (UTC)

From my experience, mixing ascorbic acid with bleach and a catalyst makes heat, possibly a redox reaction itself. --Chemicalinterest (talk) 11:01, 11 October 2010 (UTC)

From your personal experience, ascorbic acid is a slow direct reducing agent in acidic conditions, right, encouraging other pathways instead? I'm particularly thinking of using Vitamin C in a catalytic cycle. John Riemann Soong (talk) 19:25, 11 October 2010 (UTC)

How do I grow a really long beard?

I've seen guys with thick, smooth beards that are like a foot long - yet my beard, although thick and face-covering seems to stop growing at about an inch and a half long, even if I just leave it alone (it just goes frizzy then, and looks as though I have moss on my face). Is there a trick to encouraging it to grow longer that these guys know about and I don't, or is it just a matter of my genetics? I'm white, fair-haired, northern-European if that makes a difference. —Preceding unsigned comment added by 95.148.109.95 (talk) 07:33, 11 October 2010 (UTC)

Wikipedia has an article on the Beard that cites an anecdote that suggests increased beard growth is increased by sexual activity. Facial hair will continue to get coarser, darker and thicker for 2–4 years after puberty, sometimes taking 10 years to develop fully. This is mostly a matter of genetics. According to the article, Hair transplantation can be applied to beards. There are many suppliers of false beards if you want to trick people. Cuddlyable3 (talk) 08:25, 11 October 2010 (UTC)

It's likely to be genetic. Like with head hair where some people's grows long and straight, others becomes curly or wavy, facial hair can vary as it gets longer. Seems yours may not be inclined to grow long and straight. Some other considerations - as it gets longer you won't notice it getting long as quickly as the relative change in length is less; most people who grow those really luxuriant beards have extremely thick facial hair; any hair has a certain 'cycle length' (how long it grows before falling out and starting to regrow) and like with pubic hair and underarm hair (and in reality, although not usually recognised as such, facial hair and underarm hair are really just types of pubic hair) facial hair may have have a genetically limited length, falling out after a certain period period of time and therefore length - it's worth noting that some people have genetic abnormalities that mean they will grow extremely long pubic/underarm hair if left to grow to its natural length but most peoples' is pretty short. If you want your beard to look less 'moss-like' you may need to trim and undertake a bit of maintenance as it grows, and if you're really keen, as it gets longer you could try using a hair straightener, shampooing and conditioning, that type of thing that people do to maintain their head hair. --jjron (talk) 13:37, 11 October 2010 (UTC)

Probably the best way to make it long if it is inclined to curl is to plat it like Jack Sparrow -- Q Chris (talk) 14:27, 11 October 2010 (UTC)

So I have pubes on my face? —Preceding unsigned comment added by 81.147.58.110 (talk) 17:45, 11 October 2010 (UTC)

Well, looking at your face, are you really surprised? lmao - you set yourself up royally for that joke... --Ludwigs2 21:44, 11 October 2010 (UTC)

Small text. Small joke. Cuddlyable3 (talk) 09:21, 12 October 2010 (UTC)

And serious response, effectively yes. Read again Cuddlyable3's link to Puberty#Body_and_facial_hair. Essentially, the growth of body and facial hair is in response to the same hormones responsible for pubic hair, and all are 'indicators' of puberty. So basically all are a type of pubic hair - thereafter it's up to you what you want to call them... --jjron (talk) 12:56, 13 October 2010 (UTC)

Glamorous superstars and rich useless celebutantes often have hair extensions glued to their hair to get great looking long hair. Musicians with really long beards might similarly have extensions. More realistic than a long fake beard hung from the ears with rubber bands. Edison (talk) 16:37, 13 October 2010 (UTC)

B12

IS B12 A VASCO-CONSTRICTER —Preceding unsigned comment added by Kj650 (talk • contribs) 08:12, 11 October 2010 (UTC)

Are you referring to Vitamin B12? If so, it's not a vasoconstrictor. You can view its effects at our article. Regards, --—Cyclonenim | Chat  12:49, 11 October 2010 (UTC)

Folding my own proteins @home

What if I'm interested in how a particular protein folds - is there a program that I can use to on my computers to solve the folding of that particular protein? Or can that only be done in a reasonable time-frame (months) with hundreds of computers? Is other experimentation needed as well, or can folding be predicted perfectly in silico? ----Seans Potato Business 11:05, 11 October 2010 (UTC)

If I understand correctly, it takes that huge amount of computational power just to correctly fold a single protein (it varies, of course. Some proteins are easier than others). And there's no guarantee that the result will be precisely right; see CASP, a competition between research groups to get as close as possible to the real thing. It sounds like you might be interested in FoldIt, a protein-folding game, built on the theory that people can use their peculiar insight to find solutions that computers might take longer to get. Paul (Stansifer) 12:48, 11 October 2010 (UTC)

The short answer – for now – is no; there's no practical way to reliably predict the tertiary structure of a folded protein using the amount of computing power the average graduate student might have access to. See de novo protein structure prediction, protein folding problem, Folding@home. TenOfAllTrades(talk) 15:20, 11 October 2010 (UTC)

It also depends how you intend to validate your results. You can write or run homebrew molecular dynamics simulations, or check out our list of major software for MD, but if you want or need accurate results, the simulation complexity rapidly grows beyond the compute-capability of a single programmer or computer. Nimur (talk) 23:42, 12 October 2010 (UTC)

Holes of insects in old wood

In the summer we stored a 14 cm diameter and 2 m long log of, 30 year old, rotten wood next to the house in southern bavaria. We now cut it to pieces to get it transportable for deposition. We found long holes of the diameter of a finger inside the log. In this holes leafs leaves of a redcurrant were stored looking like dolma (first image in the article). In the following empty space there was a small white larva. Several of these chambers where located on after the other. My question would be is this a wide spread way to feed the maggots with leafs leaves? I know the behaviour to store the maggots and the food together in burrow. I saw sphecidae bring caterpillars of butterflies to small burrows in the sand to feed the larva. Dead insects might be a better food for which this kind of storage is necessary, but leafs leaves are everywhere. Has anybody a good suggestion who was lifing living in the log?--Stone (talk) 12:43, 11 October 2010 (UTC)

Leaf has an irregular plural - leaves. Your English is very good. "Lifing" - I think you mean living. 92.15.11.165 (talk) 19:06, 11 October 2010 (UTC)

It might be a Carpenter Bee Richard Avery (talk) 14:52, 11 October 2010 (UTC)

Also possibly something in the Megachilidae family, which are known as leaf-cutter bees. Most of these (and carpenter) bees are solitary, though they will aggregate at good nest sites (like your log). A few things to look for: Are there any pollen balls in the leaves or holes? The leaves may NOT be a food source for the larvae. Instead, they may just be functioning as protection/ hole plugs / climate control. Also, are all the larvae the same? If they are different, it could be the visible larvae that ARE the food source for some smaller (possibly internal) larvae. Parisitism is very common among the hymenoptera. --SemanticMantis (talk) 15:29, 11 October 2010 (UTC)

Here [1] is a picture of a leaf-cutter bee house, designed to attract them for their pollinating services in orchards. --SemanticMantis (talk) 15:33, 11 October 2010 (UTC)

Thanks!! The leaf-cutter bee house seems the best fit for what I saw. I did not open the green leaf things and that would have been the storage of pollen for the larva. The hymenoptera guess is less likely, because the larva where very small and all the same.--Stone (talk) 17:37, 11 October 2010 (UTC)

Two images like [2] and [3] look very like what I saw. --Stone (talk) 18:09, 11 October 2010 (UTC)

Passing on sex genes

I've heard that each of a person's pair of chromosomes are mixed up before being passed on. For example, I won't give my kid either my 5th chromosome from my mom or my 5th chromosomes from my dad, I give my kid a hybrid of the two. My question is, when I have a son, does my Y-chromosome get mixed up with any genes from my X-chromosome, or are Xs and Ys so different that they can't be mixed? If they don't mix, does that mean that I have the same Y-chromosome as everyone in my family all the way up the male line of my family (ignoring mutations)? Also, if the Xs and Ys don't mix, do X-chromosome being passed on from mothers mix, or does the 23rd chromosome never mix? Thank you! —Preceding unsigned comment added by 174.91.12.159 (talk) 16:39, 11 October 2010 (UTC)

Chromosomes are not necessarily "mixed up" during meiosis, however chromosomal crossovers do occur. These crossovers are limited almost entirely to homologous chromosomes, however, and the X chromosome and Y chromosome are not considered highly homologous and do not typically cross over. However, in those rare occurrences, chromosomally XX males or XY females can be the result of aberrant crossovers. — Scientizzle 16:47, 11 October 2010 (UTC)

X chromosomes can certainly pair and undergo crossover in females, leading to slightly "mixed up" X chromosomes. In addition, there is actually a significant amount of crossing over in the pseudoautosomal region of the X and Y chromosomes. See this article for details. That being said, the parts of the Y chromosome that do not cross over are inherited in a strictly patrilineal fashion. --- Medical geneticist (talk) 17:13, 11 October 2010 (UTC)

plasma phase carbanions

If I pass methane gas through a gas-phase ioniser (I've never seen one -- maybe it has a strong electric field?), at high temperatures, maybe in the form of a reducing flame, can I generate carbanions? These won't be very stable, but the idea is for them to quickly react with a surface before they can be reprotonated. John Riemann Soong (talk) 19:34, 11 October 2010 (UTC)

No. Well, never say never, but not in any useful or controllable way. Physchim62 (talk) 19:42, 11 October 2010 (UTC)

The idea is really to reduce an oxidised surface, that is destroy it, so some other desired reaction can take place. So it's supposed to be rather chaotic. Metal oxides usually don't burn, but I wonder if they can be removed with an ionised reducing flame. John Riemann Soong (talk) 19:45, 11 October 2010 (UTC)

Not really, no. How are you going to get your reduced metal surface from the flame (which needs oxygen) to a place with no oxygen so you can do you reaction? See Raney nickel for one practical way of making an oxide-free metal surface. Physchim62 (talk) 20:00, 11 October 2010 (UTC)

Quickly transfer the surface? Metal carbides are often metastable in oxygen. John Riemann Soong (talk) 20:09, 11 October 2010 (UTC)

Not if you want them to be reducing agents they're not! Honestly, there are methods to prepare clean surfaces of various metals: you will find entire books about them in your university library if you're actually interested in that problem. Physchim62 (talk) 21:56, 11 October 2010 (UTC)

Well once I remove the flame, won't the carbide layer remain? I mean aluminum carbide is stable in a dry atmosphere, and I imagine aluminum carbide will be exposed to moist air for only a very short time while you transfer the surfaces. John Riemann Soong (talk) 22:24, 11 October 2010 (UTC)

Yes, but is aluminium carbide reducing? I don't know myself, but metal carbides are always less reducing than the parent metals. If all you want to do is create a clean carbide surface than that can be done: you wouldn't use a flame, but rather electrically heat the metal under a stream of methane. That way, you can let it cool down under methane or some other inert atmosphere before testing the surface. Physchim62 (talk) 22:31, 11 October 2010 (UTC)

The methane is the reducing agent, not the surface! I just thought they'd be more potent reducing agents if they were deprotonated in plasma. John Riemann Soong (talk) 22:43, 11 October 2010 (UTC)

where can I get tris(pentafluorophenyl)boron?

I have a moderate budget but this Lewis acid seems interesting. Once you use it to catalyse a reaction can it be easily recycled? John Riemann Soong (talk) 20:15, 11 October 2010 (UTC)

You can get at at TCI, Aldrich, or Acros. On a small scale, it should be readily recoverable by chromatography. —Preceding unsigned comment added by 148.177.1.211 (talk) 20:23, 11 October 2010 (UTC)

OK this catalyst seems ridiculously expensive. The reason why I need it is because I want to use silanes as selective reducing agents and apparently this was cited in a few papers. Are there any cheaper or simpler Lewis acid catalysts for silane reductions? John Riemann Soong (talk) 20:22, 11 October 2010 (UTC)

Read your papers, track down their precedent for this catalyst to see what others have tried. Check what articles cite your papers to see if any note other possibilities. You really need to learn how to do research in a library rather than just asking everyone else if you want to become a scientist rather than just a lab tech. Even google gives me various other options for silane reducing agent catalysts, I didn't even need to go to google scholar or any of the specialized chemistry search systems. "selective reducing agents" is almost hopelessly vague--pretty hard to recommend a good "selective" agent unless you say what particular selectivity you have in mind! But since this is Wikipedia, and wikipedia has an article about just about everything, silane has a comment about uses as a reducing agent, cited to a review of various methods/catalysts/etc. DMacks (talk) 20:29, 11 October 2010 (UTC)

This is carboxylic acid --> methyl, revisited. I've tried a few alternative catalysts, like the simpler triphenylborane, but apparently the existing literature only cites reduction of alcohols. I just don't want to buy a reagent only to find it doesn't work. John Riemann Soong (talk) 20:33, 11 October 2010 (UTC)

Btw, the alternative catalysts that come up in google are really expensive organometallic catalysts which are even more expensive than tris-(pentafluorenyl)boron. I work in a cellular biology lab, not an organic chemistry lab! John Riemann Soong (talk) 20:36, 11 October 2010 (UTC)

Looking at my own (Alfa) company's page, I estimate by the catalogue number that it's been around for 10 years or so, with such a high price of £90/g, I would also guess that is due to a) Low volume of sales & b) Difficulty of manufacture. My only suggestion is to ask the suppliers if they would be willing to do a smaller (& cheaper) pack as a special so you can test it - I've no idea if they will or not - it's not my department - and it will depend on if they hold bulk stock or just pre-packs.  Ronhjones  ^(Talk) 20:53, 11 October 2010 (UTC)

It's quite difficult and dangerous to manufacture: the chemistry to make it is simple, but there is a known explosive hazard in the preparation procedure (not in the product itself), so people are obviously rather wary of conducting the prep without time-consuming (and hence expensive) precautions. Physchim62 (talk) 21:17, 11 October 2010 (UTC)

And Grignards are more of a headache than the explosion-inducing fluorinated-organolithium reagent? John Riemann Soong (talk) 21:21, 11 October 2010 (UTC)

I assume you can't make the Grignard and, even if you could, it would have similar hazards. I can remember hearing a talk by Gerhardt Erker (who developed the stuff) as a young postdoc: in the pub afterwards we asked him "so how do you make it?", and he told us. We said "that sounds simple", and he laughed and replied "Ah, I don't know how it does it, but it just knows it can squeeze out lithium fluoride from somewhere." The lattice energy of magnesium fluoride is only slightly less than that of lithium fluoride, so you wouldn't get any safety advantage. Physchim62 (talk) 21:38, 11 October 2010 (UTC)

I can see a mechanism right away. The electropositive lithium atoms easily coordinate around a fluoride ion as a leaving group, and the ring is highly nucleophilic so fluoride becomes an unusually good leaving group. It produces an analogue of benzyne, which rapidly decomposes of course, especially in the presence of nucleophilic carbons! You can get a polymerisation reaction which rapidly spins out of control. However, in C6F5-Mg-Br, the MgBr+ cationic analogue would seem to have a harder time coordinating to F-. The group also likes to form dimers, apparently. Thus F- doesn't leave as well. John Riemann Soong (talk) 22:07, 11 October 2010 (UTC)

I think this is the original prep of (C₆F₅)₃B: doi:10.1016/S0022-328X(00)80518-5. Searching for reactions that use (C₆F₅)Li, it appears there are various scramlings/exchanges possible, with loss of F other than ortho to Li. DMacks (talk) 21:42, 12 October 2010 (UTC)

Phosphodiesterase vs. phosphoesterase?

I've been working through the night, so please forgive me if the answer turns out to be obvious. I recently ran across the GeneCard for a gene called metallophosphoesterase domain containing 2. Now, I know what a phosphodiesterase is, but I've never heard of a phosphoesterase (or a metallophosphoesterase, for that matter). What's the difference between a phospho-diesterase and a phospho-esterase? Thanks! – ClockworkSoul 20:15, 11 October 2010 (UTC)

I've looked only briefly, and I'm drawing some inferences from context that may be wrong. But a PubMed search for metallophosphoesterase yields 12 records, most of which appear to use it in the generic sense of a protein superfamily. Following your GeneCard to EBI gets [4], in which the metallophosphoesterase becomes a "metallo-dependent phosphatase".

Now going back to first principles, a phosphoester is (P=O)-O-R. A phosphodiester is R1-O-(P=O)-O-R2 (these are incomplete). A "phosophomonoesterase" would release a free phosphate and whatever it was bound to, and is called a phosphatase in polite society. So I think the only time you need to use the term "phosphoesterase" or "metallophosphoesterase" is when you deliberately want to leave it ambiguous whether the ester bond cleavage releases a free phosphate + O-R or a bound phosphate + O-R. This might be due to describing a whole superfamily of related enzymes, or if an enzyme's activity is as yet uncharacterized, or if it does both things to some degree. Wnt (talk) 21:04, 11 October 2010 (UTC)

relativity question

This may be a FAQ, but as an object approaches the speed of light its mass increases and its size decreases. Can this cause it to reach the density to become a black hole? Bubba73 ^{You talkin' to me?} 20:21, 11 October 2010 (UTC)

No it can't, because it its rest frame it still has its proper mass and size. A heuristic (but oversimplified and not mathematically rigorous) way of looking at it from the frame where it moves fast might be that there is not time for a black hole to form before the moving object is already elsewhere. –Henning Makholm (talk) 20:38, 11 October 2010 (UTC)

Hmmm... suppose you have a massive neutron star just under the Tolman–Oppenheimer–Volkoff limit with a strong magnetic field. You turn on your super-sized magnetic stirrer and make it spin faster. Now by doing so you've added energy and mass to the system, so it should collapse into a black hole, right...?

(On the other hand, I see that the event horizon for a rotating black hole is still spherical, even though the ergosphere is oblate... maybe the star would oblate just the right amount to offset the added energy?) Wnt (talk) 21:13, 11 October 2010 (UTC)

Oh, I'm not saying that kinetic energy can't contribute to a black-hole collapse. It obviously can, since rest mass is not fundamentally different from other energy. What I'm saying is that "lots of mass, concentrated in a small volume of space for an arbitrarily brief moment of time" is not a sufficient condition to form a black hole. Gravity does not just react to mass/energy; it's influenced by momentum and momentum transport too, so it is not surprising that spacetime around a fast object with lots of momentum acts differently than that around a stationary spinning disc with (momentarily) the same energy density but no net momentum. –Henning Makholm (talk) 21:41, 11 October 2010 (UTC)

See (also) If you go too fast, do you become a black hole? from the Usenet Physics FAQ. -- BenRG (talk) 07:22, 13 October 2010 (UTC)

Pigeons on my TV aerial?

Would one or two pigeons sitting on my TV aerial affect its reception? I sometimes get a bad (analogue) TV signal for a couple of minutes or so, and then it returns to normal. The TV signal is rather weak where I live. 92.15.11.165 (talk) 21:22, 11 October 2010 (UTC)

Yes. Or, more probably, your signal is faded by a flock of birds flying between you and the transmitter. Bird echo is a common problem at UHF - as mentioned in this textbook on weather RADARs. (Pigeons are just about the correct size to muss up the signal for a 10 cm wave; two pigeons in a row constitute a half-wave antenna at 700 MHz - and they aren't conducting the signal into your coaxial cable - so that's RF energy you've lost!) There are also other ways a bird can dissipate or attenuate RF energy, including dielectric heating. Whether a particular bout of bad-reception is due to birds, weather, or some other radio-phenomenon requires more careful study, but bird interference is both possible and common. Nimur (talk) 21:40, 11 October 2010 (UTC)

Egg in Vinegar

I'm doing the experiment where you leave an egg in vinegar for a while and the shell disintegrates. Now, I know why that happens, but my question is "when the egg grows, does only water go across the membrane, or does the vinegar move also?" On one hand, I think that the vinegar particles can't move across the membrane, but on the other hand, the egg white denatured a little, and the only reason for that I can think of is a change in pH. --Simeon24601 (talk) 23:47, 11 October 2010 (UTC)

Yes. That is how pickling works, via absorbption of the pickling liquid. → ROUX ₪ 23:51, 11 October 2010 (UTC)

Why do you think the "vinegar particles can't move across the membrane"? I don't really know for sure, but I would assume they do move. Ariel. (talk) 04:59, 12 October 2010 (UTC)

I would assume they wouldn't or would move much less than the water molecules since they were much bigger and had a harder time passing through the semipermeable membrane. --Chemicalinterest (talk) 11:29, 12 October 2010 (UTC)

What is a "vinegar particle"? Vinegar is made of lots of different molecules, and the smallest molecules will pass through faster (water is certainly one of the smallest, and it is present in large quantity). --Lgriot (talk) 14:25, 12 October 2010 (UTC)

Presumably Ariel meant the ethanoic acid. CS Miller (talk) 15:24, 12 October 2010 (UTC)