Number 189, August 9, 1994 by Phillip F. Schewe and Ben Stein
A GEOMAGNETIC LIMIT ON PHOTON MASS can be obtained through satellite
measurements of the Earth's magnetic field. In this way a Purdue-Goddard-Johns
Hopkins- Hughes team of scientists has used data recorded by the Charge
Composition Explorer spacecraft to derive a limit of 8 x 10**-16 eV/c**2
for the mass of photons. Besides constraining the possibility of a nonzero-mass
photon, the data were also used to set limits on the range and strength
of hypothetical fields that would coexist with conventional electromagnetic
fields. (E. Fischbach et al., Physical Review Letters, 25 July 1994.)
THAT METAL ATOMS CAN SIT INSIDE BUCKYBALLS has now been proved by an
IBM Almaden-Caltech-Virginia Polytechnic collaboration. Using transmission
electron microscopy, the physicists showed that the lattice spacing for
a pure crystals of C-84 molecules was the same (11.2 angstroms) as that
for a crystal of Sc2@C84 molecules, the first such pure metallofullerene
crystal to be prepared. They assert that the Sc2@C84 molecules are truly
endohedral; that is, the metal atoms reside within and not alongside the
fullerenes. (R. Beyers et al., Nature, 21 July.)
LIGHT EMISSION FROM SINGLE MOLECULES is being studied in a number of
labs, including AT&T Bell Labs (see Update 186), where individual luminescence
centers in quantum wells can be identified, and IBM Almaden, where W.E.
Moerner looks at the spectroscopy of single isolated impurity molecules
in solids. Unlike the study of single neutral atoms, ions, or electrons
in electromagnetic traps, the observations of single molecules constrained
on every side by a lattice provides information about the nanoenvironment
of the molecule. Moerner uses a small sample (only hundreds of cubic microns
in volume), a small impurity concentration (down to 10**-9), and a careful
tuning of a micron-sized laser beam, which causes the impurity molecule
to fluoresce. The spectroscopy of this fluorescence will change slightly
because of changes in the host lattice. One such change is "spectral
diffusion," the shift of the molecule's resonance frequency owing
to a the presence of a particular phonon (lattice vibration) mode. The
ability to control the optical properties of single molecules may lead
to extremely high density optical information storage devices and may facilitate
the development of a single-molecule light source for microscopy. (Science,
1 July 1994.)
THE P53 MOLECULE , a protein whose damaged form is associated with half
of all human cancers, has been imaged using x-ray crystallography by Nikola
Pavletich and his colleagues at the Memorial Sloan-Kettering Cancer Center
in New York. In its normal state, p53 actually prevents the spread of cancer,
by halting the division of cells with mistakes in their DNA. But when p53
gets damaged, it can no longer prevent the spread of cancer, and mutated
forms of p53 have been found in at least 51 types of human tumors. Pavletich
studied the part of p53 responsible for halting cell growth, the part that
binds to DNA. Shown at the recent American Crystallographic Association
meeting in Atlanta, the new image has 2.2 angstroms resolution and shows
exactly where the defects occur on the protein's binding sites. This could
enable the development of drugs to repair the damaged sites. However, this
task may be complex: researchers believe a different drug may be needed
to repair each of the defects on the protein. (Science, 15 July 1994)
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