In chemistry, hydrophobicity (from the combining form of water in Greek hydrosÂ and for fear phobos) is the physical property of a molecule that is repelled from water. Hydrophobic molecules tend to be non-polar and thus have a greater affinity for other neutral molecules and non-polar solvents. Hydrophobic molecules in water often cluster together forming tiny bubble-like structures known as micelles.
The opposite of hydrophobic is hydrophilic.Â A hydrophilic substance, from the Greek hydros for water and philia love, is a molecule or other molecular entity that is attracted to, and tends to be dissolved by, water. A hydrophilic molecule is one that has a tendency to interact with or be dissolved by water and other polar substances including solvents; the interactions are more thermodynamically favourable.
Water always was a slippery character. Now, scientists at Pacific Northwest National Laboratory have made an incredible thin layer of water, just a single molecule thick, that sits on a slab of platinum metal and refuses to freeze. Strictly speaking, the monolayer held at just 60 Kelvin becomes hydrophobic and will not allow ice crystallites to form on its surface.
What’s that you say, “hydrophobic water”?
Denial doesn’t get any more profound than that, even if we are talking about molecules.
According to Physics News Update: “Weaker bonding results in a “classic” hydrophobic state, in which the water merely balls up immediately.” So, it’s a balls up, is it? That explains a lot.
Diethylstilbestrol (DES) is a synthetic nonsteroidal estrogen that was first synthesized in 1938. Human exposure to DES has allegedly occurred through diverse sources, such as dietary ingestion from supplemented cattle feed and medical treatment for certain conditions, including breast and prostate cancers.
From 1940 to 1970, DES was actually given to pregnant women in the belief that it would reduce the risk of pregnancy complications and losses. In 1971, DES was shown to cause a rare vaginal tumour in girls and young women who had been exposed to this drug in utero and the US FDA subsequently withdrew DES from use in pregnant women.
Dan Lednicer offered us a guest editorial some time ago that mentioned the ill-fated drug diethyl stilbestrol (DES) and the toxicity of this and other compounds. Here’s the 3D chemical structure of DES for recent visitors to Sciencebase who were looking for it!
Diethylstilbestrol is an orally active non-steroidal estrogen first made in 1938 and originally approved for use in gonorrheal vaginitis, atrophic vaginitis, for menopausal symptoms, and in postpartum lactation suppression to prevent breast engorgement.
However, in 1971 it was found to be a teratogen – causing birth defects – when given to pregnant women and later a carcinogen. It is currently used only in veterinary practice at very low (hypocarcinogenic) doses for treating female canine incontinence.
According to my good friend chemist Martyn Poliakoff, the principles of green chemistry should be as easy as A,B,C. Or, more precisely, PRODUCTIVELY. Poliakoff, who is Prof of Chemistry at Nottingham University and famed for his pioneering work with supercritical fluids (SCFs), PRODUCTIVELY spells out –
Prevent wastes Renewable materials Omit derivitization steps Degradable chemical products Use safe synthetic methods Catalytic reagents Temperature, pressure ambient In-process monitoring Very few auxiliary substances E-factor, maximize feed in product Low toxicity of chemical products Yes, it is safe!
Reminds me of a creative writing exercise from school, but if it gets the message across to other chemists it can’t be a bad thing.
As the weather turns colder, you can count on one thing: Organisations with a health expert to hand will publish a press release offering tips on how to avoid catching a cold or flu in the coming months. I spotted the first of the season on Physorg.com today announcing the anti-disease advice of Pamela Aaltonen at Purdue Uni’s School of Nursing. There’ll be an epidemic of them by the end of October, mark my words.
In a guest sciencebase editorial, Dean L Sinclair suggests that neutrons may not exist in the nucleus and goes on to explain how nuclear structure might be explained by an altogether different model that sidesteps problematic forces that have to be invoked by the proton-neutron model of the atomic nucleus. Tell us what you think…
The British government is to ban schools from offering sugary and fatty snacks, such as potato chips and candy (sorry I mean crisps and chocolate), to students through vending machines and to improve the lunchtime menu, partly thanks to public pressure and media campaigning over the last year. The BBC interviewed several studens who said it was unfair and that should be given the same choices as adults. One student said he’d just head to the local shops to buy his snacks, implying that the initiative would have little effect on student health…
But, at least he’s going to have to walk or cycle to the shop to get his snack fix rather than grabbing it on site from a vending machine. It’s only a generation since children were not allowed to eat anything in school never mind choosing between apples or chocolate.
Lots of visitors to the sciencebase.com site search for “4-aminobutanoic acid” using the site’s Google search box. 4-aminobutanoic acid, or GABA, is (of course) the main inhibitor of neurotransmission in the central nervous system. According to Wikipedia, GABA is affected by drugs such as alcohol, benzodiazepines and barbiturates, thujone, zolpidem, and several others. You can see its chemical structure here. Click through this blog entry to read my recent chemistry news story for Reactive Reports on the subject of the GABA-A receptor and its role in catamenial epilepsy, a form of epilepsy that affects women during menstruation.
Here’s one to really get the animal rights activists up in arms (as if they aren’t already). The BBC reports that scientists have been able to “introduce most of a human chromosome into mice – and create the most successful recreation of Down’s syndrome so far.” I’m not sure whether the activists will find this better or worse than the ear grown on a mouse’s back in 1999 by Joseph Vacanti. Regardless, a mouse model of the disease will inevitably lead to controversy, but more importantly, it will lead to a better understanding of the syndrome itself.
Those free iPods ads are everywhere on the net and in your email inbox, but are they for real? They sure don’t look it at first glance. Almost everything about them screams “scam!!!” But only almost. What at first appears to be a “something for nothing” pyramid marketing scheme is nothing of the sort as Wired magazine, CNN, Good Housekeeping, MSNBC, New York Times, and others have reported over the last few months.
In fact, what it boils down to is simply signing up, partaking of a special offer such as freebie DVD rentals or making your first bid on ebay (you don’t even have to win the auction!), or, perish the thought, signing up for an AOL trial, and then persuading a few friends to do the same. You can always cancel the agreement after any minimum period.
Of course, if you’ve got a website, any visitor can become an instant friend if you can both get a free iPod out of that visit. The organizing company Gratis Internet has sent out tens of thousands of ipods and other pricey gadgets already. In return they get a bung from the likes of ebay and AOL who might gain a new customer out of the deal. They don’t sell your name on to mailing list companies so it really is a win-win situation.
Quite a lot of visitors to Sciencebase hit the site asking questions of the search engines, but a recent spate of similar questions would suggest lots of students doing a science assignment: What does boron smell like? What does carbon smell like? What is molecules plasma? (sic) Picture of zinc element etc etc.
As the question about boron seems to come up the most frequently and has garnered the most comments on this post, I thought I would get a definitive answer from boron expert John Kennedy Professor of Inorganic Chemistry at the University of Leeds, UK. This is what he has to say and it pretty much confirms my own suspicions about boron, although I am still curious as to why this question comes up so often and wonder whether there are volatile compounds formed when boron comes into contact with your skin in the same way that metallic BO arises.
“Elemental boron is a ceramic, and completely involatile,” Kennedy told me, “So it should have no smell associated with it, just like porcelain.” He points out that very fine boron dust might stimulate the nostrils in the same way that any dust would and could feasibly have a particular nuance of flavour. “As I recall when I did handle some course boron powder,” adds Kennedy, “there was no smell, just like sand.”
So there you have it, volatility is the key. If something is involatile, then it cannot reach the smell (olfactory) receptors in your nose to stimulate them. If it is finely powdered, particles could conceivably reach your nose, but would stimulate it in a similar way to any other fine dust. Some time ago, we discussed on Sciencebase.com an odd theory that the nose acts as a sophisticated natural spectrometer rather than a straightforward detector. This theory suggests that different compounds smell differently because they vibrate with different frequencies, a property observed by vibrational spectroscopy.