Fluorine is very pale yellow, chlorine is yellow-green, and bromine is red-brown. Iodine crystals are shiny purple - but easily turn into a dark purple vapour when they are warmed up. When we can see a trend in the properties of some of the elements in a group, it is possible to predict the properties of other elements in that group. Astatine is below iodine in Group 7. The colour of these elements gets darker as you go down the group.
Iodine is purple, and astatine is black. Early-stage clinical trials have shown some promise for astatine-based therapies. Duke University chemist Michael R. Zalutsky showed that At attached to antibodies doubled the life expectancy of brain-cancer patients when administered after the patients had large tumors surgically removed J. Meanwhile, at the University of Washington, D. Scott Wilbur has led efforts to test astatine-based therapies on blood-borne cancers like leukemia and multiple myeloma.
They have experimented with tagging antibodies, antibody fragments, and small molecules with aromatic boron cages that hold the At atoms J. Imaging Radiat. In addition to being more stable, Wilbur says the reaction between At and the boron cage is faster and more predictable than attaching At to antibodies. For all these astatine therapies, a technician would need to assemble the drug from the isotope and its cancer-targeting carrier shortly before treating a patient.
Duke scientists have also had chemistry trouble with their astatine-antibody complexes. The researchers have since developed an alternate procedure that emphasizes avoiding reductants and chemicals that can become reductants when irradiated—like chlorine radicals from chlorinated solvents—which interfere with At binding to antibodies Cancer Biother. With this new methodology in hand, they are now looking into trials involving molecules that can deliver higher radiation dosages.
These troubles with chemistry go back to one of the fundamental difficulties of astatine: it acts like both a halogen and a metal. In water, depending on the conditions, astatine can be a cation like a metal or an anion like a halogen, says Nicolas Galland of the University of Nantes.
Astatine also has its own unique behaviors. But Galland says astatine makes theoretical work tricky too. Its innermost electrons move so fast that computer models must take into account relativistic effects, which complicate calculations.
But finding efficient chemistry to deliver At to tumors is only half the battle for chemists. First they have to make and purify the isotopes. The energy of the particles and the temperatures have to be controlled to get the right astatine isotope and prevent the target from overheating and vaporizing the astatine.
Next, scientists have to separate At from the target and other decay products. University of Washington researchers initially experimented with the same technique, but switched to a wet chemistry method because of problems when purifying large amounts and because they worried that radioactive material could escape the lab if filters and other safety measures failed. The wet chemistry method starts with dissolving the bismuth target in acid, then isolating At using a liquid-liquid extraction or chromatography.
The dark horse for At production methods is through radon Radon also has a half-life twice as long as At. Time is a constant worry for astatine researchers. Ethan Balkin, formerly of the University of Washington and now the program manager at the US Department of Energy DOE for isotope research and development, remembers that at his fastest he could purify a sample of At in 1 h and 20 min.
The other thing astatine researchers are short on is funding. The DOE isotope program exists to fund research on astatine production and processing. Currently, only Duke and the University of Washington produce enough At to supply researchers and doctors in their regions the DOE does sell At and other isotopes through the National Isotope Development Center.
This story was updated on Aug. Contact the reporter. Physical properties of the halogens Group 7 contains non-metal elements placed in a vertical column on the right of the periodic table. Group 7 is on the right-hand side of the periodic table, next to group 0 The halogens show trends in their physical and chemical properties. Physical properties The halogens exist as simple molecules. This is because, going down group 7: the molecules become larger the intermolecular forces become stronger more energy is needed to overcome these forces Example The graph shows the melting and boiling points of the first four group 7 elements.
Chlorine, Cl 2. Pale green.
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