A paper in Angewandte Chemie suggests that models predict that climate change will lead to an accelerated recovery of the ozone layer. However, reliable predictions are complicated by the ozone-depleting effect of N₂O. If emissions of this greenhouse gas remain at current levels, by 2050 they could account for 30% of the ozone-destroying effects of chlorofluorocarbons at their peak.1

It is concluded that "the regulation of N₂O levels in the atmosphere is not only important for the protection of Earth's climate (Kyoto Protocol) but also for the future evolution of the stratospheric ozone layer (Montreal Protocol). A reduction of N₂O emissions would decrease the anthropogenic greenhouse effect and it would have a positive impact on the recovery of the ozone layer."

• 1. Depletion of the Ozone Layer in the 21st Century,
  Dameris, Martin
  , Angewandte Chemie International Edition, Volume 9999, Number 9999, p.NA, (2009)
  

Depletion of the Ozone Layer in the 21st Century, Dameris, Martin , Angewandte Chemie International Edition, Volume 9999, Number 9999, p.NA, (2009)

Trace amounts of manganese is essential to human health. Now, a team of scientists from the University of Delaware, Scripps Institution of Oceanography, the University of Hawaii, and Oregon Health and Science University has found that a dissolved form of manganese, Mn(III), is important in waterways such as the Black Sea and Chesapeake Bay. It can keep toxic hydrogen sulfide (sulphide) zones in check.1

The research is based on research conducted in 2003 that explored the chemistry of the Black Sea. Nearly 90% of the mile-deep system is a no-oxygen "dead zone," containing large amounts of naturally produced hydrogen sulfide (sulphide), which is lethal to most marine life. Only specialized microbes can survive in this underwater region.

Above this "dead zone" in the Black Sea lies another aquatic layer, the "suboxic zone,". This has both minimal amounts of oxygen and minimal amounts of hydrogen sulfide. This layer may be up to 40 metres (130 feet) deep in the Black Sea, but only 4 metres (13 feet) deep in the Chesapeake Bay.

The research team found that a chemical form of dissolved manganese, Mn(III), can maintain the existence of the suboxic zone by reacting as a reductant with oxygen and as an oxidant with hydrogen sulfide, preventing deadly hydrogen sulfide from reaching the surface layer of water, which is where most fish, algae and microscopic plants live. The scientists used an electrochemical analyzer to locate and map the chemistry of the suboxic zone in real time under changing salinity, temperature and depth.

The finding is surprising, George Luther (Delaware) said, because dissolved manganese as Mn(III) was assumed not to form in the environment and thus was largely ignored by scientists. The research team conclude that "Manganese in natural oxygen-poor waters can persist in a +3 oxidation state, a state previously seen only in the lab, necessitating a major revision of the current understanding of manganese aqueous geochemistry".

"Now we've learned that this form of dissolved manganese [Mn(III)] can constitute almost all the dissolved manganese in suboxic water columns and can react with hydrogen sulfide and other compounds that only solid manganese(IV) phases were thought to be doing," Luther noted. "It is also more reactive than the solid phases."

"Our research shows that the impact of dissolved manganese(III) is significant in any aquatic environment, including lakes, plus sediments on the seafloor and soils on land," Luther said. "And for the public who live near the water, dissolved manganese(III) actually helps prevent naturally occurring hydrogen sulfide from getting to the surface, so it prevents both fish kills and the foul odours from this compound's telltale 'rotten egg' smell."

• 1. Soluble Mn (III) in suboxic zones,
  Trouwborst, R., Clement B., Tebo B., and Glazer B.
  , science, Jan, (2006)
  

OzoneOzone measurements made by the European Space Agency Envisat satellite reveal the ozone loss of 40 million tons by 2 October in 2006 and that this exceeds the record ozone loss of about 39 million tons for the whole of 2000. The size of this year's ozone hole is 28 million square km.

The Ozone layer is a protective layer found about 25 kilometres above us mostly in the stratospheric stratum of the atmosphere that acts as a sunlight filter shielding life on Earth from harmful ultraviolet rays. Over the last few years the effective thickness of the ozone layer declined, increasing the risk of skin cancers, cataracts and harm to marine life. The thinning of the ozone layer is caused by the presence of pollutants in the atmosphere originating from, for instance, chlorofluorocarbons (CFCs), which have still not vanished from the air although banned under the 1987 Montreal Protocol.

"Such significant ozone loss requires very low temperatures in the stratosphere combined with sunlight. This year’s extreme loss of ozone can be explained by the temperatures above Antarctica reaching the lowest recorded in the area since 1979," European Space Agency Atmospheric Engineer Claus Zehner said.

Background Information

Ozone (O₃) is another allotrope of oxygen. It is bent with a O-O-O angle of about 123° It is formed from electrical discharges or ultraviolet light acting on O₂. It is an important component of the atmosphere (in total amounting to the equivalent of a layer about 3 mm thick at ordinary pressures and temperatures) which is vital in preventing harmful ultraviolet rays of the sun from reaching the earth's surface. Aerosols in the atmosphere have a detrimental effect on the ozone layer. Large holes in the ozone layer are forming over the polar regions and these are increasing in size annually. Paradoxically, ozone is toxic! Undiluted ozone is bluish in colour. Liquid ozone is bluish-black, and solid ozone is violet-black.

For chemical robots

IUPAC Name: ozone
Canonical SMILES: [O-][O+]=O
InChI: InChI=1/O3/c1-3-2

Ozone. Credit Mark Winter

Researchers from the Massachusetts General Hospital in Boston (USA) have announced that hydrogen sulfide (sulphide) gas, H₂S, can induce a state of suspended animation in mice while maintaining normal blood pressure. It is hoped that this result eventually will help in the treatment critically-ill patients. This result was presented at the American Physiological Society conference, "Comparative Physiology 2006: Integrating Diversity," in Virginia Beach, Virginai, USA, October 2006.

Hydrogen sulfide (sulphide) gas, sometimes called sewer gas, produces a noxious odour often described as a rotten egg smell. This highly toxic gas occurs naturally in swamps, some springs, and volcanoes.

The researchers administered 80 parts per million of H₂S gas to their and found that their:

• heart rate fell from 500 beats per minute to 200 beats per minute
• respiration rate decreased from 120 breaths to 25 breaths per minute
• core body temperature fell from 38° C to 30° C
• activity level fell dramatically, moving only when the researchers touched them or shook their chambers

After the mice returned to breathing normal air they quickly returned to normal. Normally, as oxygen consumption goes down and heart rate decreases, blood pressure decreases also. Since the heart rate of the mice fell by more than 50%, the researchers expected blood pressure to fall, but it didn't.

"These findings demonstrate that mice that breathe 80 parts per million of hydrogen sulfide become hypothermic and decrease their respiration rate, heart rate and cardiac output without affecting stroke volume or mean arterial pressure," the authors said. This line of research could have a variety of helpful applications, including sustaining the function of organs of critically ill people, Ichinose said. It may also be possible to use the finding for patients undergoing surgery. This would be an advance, because anesthesia usually causes blood pressure to drop.

Researchers at the Carnegie Institution of Washington (Washington DC, USA) have managed to make a remarkable alloy of hydrogen and oxygen from water! They used X-rays to dissociate water at high pressure to form a solid mixture, that is, an alloy, of molecular oxygen (O₂) and molecular hydrogen (H₂).

The researchers placed some water under an extremely high pressure, about 170,000 atmospheres (17 Gigapascals), using a diamond anvil and then beamed high-energy X-rays at the water. Nearly all the water molecules split and reformed as a solid alloy of O₂ and H₂. The X-rays are key to cleaving the O—H bonds in water. Without it, the water remains as a high-pressure form of ice known as ice VII. Ice VII is one of at least 15 kinds of ice that exist under various high pressure and variable temperature conditions.

Russell Hemley of the Carnegie Institution of Washington said "we managed to hit on just the right level of X-ray energy input. Any higher, and the radiation tends to pass right through the sample. Any lower, and the radiation is largely absorbed by the diamonds in our pressure apparatus."

The researchers subjected the alloy to a range of pressures and temperatures, and also bombardment with X-ray and laser radiation. Provided the alloy is kept at about 10,000 times atmospheric pressure at sea level (1 Gigapascal), it withstands the treatment. Although clearly a crystalline solid, more experiments are needed to determine the alloy's precise crystal structure.

"The new radiation chemistry at high pressure was surprising," said Wendy Mao of the Los Alamos National Laboratory in the USA. "The new alloy containing the incompatible oxygen and hydrogen molecules will be a highly energetic material." An explosive alloy!

For the last few days there have been many reports of damage to car oxygen sensors in England's south east. This seems to have been cause by faulty fuel supplied by some supermarker chains, including Tesco and Morrison's. Initial reports suggested the fuel was up to standard but one wonders if this is a consequence of not applying the correct tests. Expecially now that reports are emerging (for instance from The BBC) that indeed there is a contamination arising from silcon, probably from silcone contaminants. Silicones are used in diesel but damage high-tech petrol engines.

The silicones were probably introduced inadvertantly at storage rather than at the refinery stage.

This is going to get expensive for someone as it sounds as though thousands of cars have been affected.

Only carbon from the Group 14 elements forms stable double bonds with oxygen under normal conditions. When frozen, carbon dioxide is known as "dry-ice". A non-molecular single-bonded crystalline form of carbon dioxide (phase V) exists at high pressure according to Italian and French researchers.1

Amorphous forms of silica (a-SiO₂) and germania (a-GeO₂) are known at ambient conditions but only recently has an amorphous, silica-like form of carbon dioxide, a-CO₂. This is labelled a-carbonia and made by compression of CO₂ at room temperature at pressures between 40 and 48 GPa (that's a staggering 400-500 thousand atmospheres).

During this compression, infrared spectra at temperatures up to 680 K show the progressive formation of C–O single bonds and the simultaneous disappearance of all infrared bands associated with molecular CO₂. Raman and synchrotron X-ray diffraction measurements confirm the amorphous character of the CO₂. Vibrational and diffraction data for a-SiO₂ and a-GeO₂ are closely related and calculations also suggest shows that a-CO₂ is structurally homologous to a-silica (a-SiO₂) and a-germania (a-GeO₂).

This research helps to understanding the nature of the interiors of gas-giant planets where carbon dioxide may be squeezed at very high pressures. Maybe it could be used to make very hard glass because it is expected to be very stiff rather like diamond. The researchers ponder whether "small amounts of these new glasses could be of interest for technology applications like hard and resistant coatings for micro-electronics, for example."

• 1. Amorphous silica-like carbon dioxide,
  Santoro, Mario, Gorelli Federico A., Bini Roberto, Ruocco Giancarlo, Scandolo Sandro, and Crichton Wilson A.
  , Nature, 6/2006, Volume 441, Issue 7095, p.857 - 860, (2006)
  

Polonium metal structureIt is suggested that poisoning by polonium-210 may have caused the death of Alexander Litvinenko, said to be a former Russian spy, in November 2006. Following his death at the end of November 2006, traces of polonium were found at several places he had visited before becoming ill. Before his death it was thought that thallium, or even radiothallium, might have been the cause of his illness. At the time of writing it is not clear who killed him, but not surprisingly the Russians deny it. Polonium-210 decays through the emission of α-particles and these emissions are noramlly easy to stop, but they are very dangerous if the polonium is inside the body.

Polonium is radioactive and present only in extremely low abundances in the environment. It is quite metallic in nature despite its location beneath oxygen in the periodic table. It is made in very small quantities through a nuclear reaction of bismuth. Neutron irradiation of ²⁰⁹bismuth (atomic number 83) gives ²¹⁰polonium (atomic number 84).

²⁰⁹Bi + ¹n → ²¹⁰Po + e^-

Polonium-210, ²¹⁰Po, transmutes into the lead isotope ²⁰⁶Pb by the emission of an α-particle. The half life for this process is just over 138 days meaning that after 138 days one-half of the original ²¹⁰Po has disappeared and after 2 times 138 days ³/₄ has gone.

²¹⁰₈₄Po → ²⁰⁶₈₂Pb + ⁴₂He

The short half life of polonium-210 and the heat generated with the above radioactive decay means that polonium metal generates considerable heat (141 W), meaning that the metal and its compounds self-heat. This is a useful property and polonium can be used as a small heat source (if expensive!). It can be used in space satellites for this purpose and is especially desirable as there are no moving parts. It was also used in the lunar rovers to keep internal parts warm during the frigid lunar nights.

Polonium metal is unique in that it is the only element whose structure (known as the α-form) is a simple cubic array of atoms in which each atom is surrounded by six other polonium atoms. On gentle warming to 36°C, this converts into a second form known as the β-form.

Polonium dioxidePolonium dissolves in acids to form pink hydrated Po(II), presumably as[Po(OH₂)₆]²⁺. This seems to oxidize to yellow Po(IV) species perhaps as a consequence of oxidizing agents produced through the α-particle induced decay of water. The polonium(II) oxide PoO is known but this oxidizes easily to the Po(IV) oxide PoO₂.

Polonium dichlorideThe Po(II) halides PoX₂ (X = Cl, Br, I) are known (the chloride and bromide are particularly well characterised) while all the Po(IV) halides PoX₄ (X = F, Cl, Br, I) are known.

There are few crystallographically characterised polonium compounds largely because not many researchers work with polonium and the difficulties associated with characterising such radioactive compounds. The 14-electron polonium(IV) anion [PoI₆]^2– is strictly octahedral meaning the lone pair is sterochemically inactive.