SCIENCE/TECHNOLOGY contrast, HMGl does not bind to B-form DNA or to DNA modified with the cisplatin isomer trans-DDP or other inactive platinum analogs. A variety of observations suggest that the degree to which cisplatin bends and unwinds the DNA helix is an important determinant for HMGl binding, Lippard says. For example, HMGl does not bind to cisplatin-DNA adducts that are 1,3-intrastrand cross-links. This cross link bends the DNA helix to a degree similar to the 1,2-intrastrand cross-links, but unwinds it by 23°. Lippard stresses that the "biological role of HMGl binding to cisplatin ad ducts in vivo is currently unknown." The observation that the protein recog nizes cisplatin-modified DNA is consis tent with hypotheses proposed by the MIT chemists to account for cisplatin's cytotoxicity. For instance, binding of
HMGl to cisplatin-modified DNA may prevent recognition of the damaged nucleic acid by the cellular repair ma chinery, thereby inhibiting replication and leading to cell death. Alternatively, Lippard notes, if HMGl is required for active transcription in rapidly dividing tumor cells, then tying up the protein in complexes with cisplatin-DNA ad ducts might "lead to internal cellular disarray and, eventually, cell death." The MIT chemists currently are working to determine whether binding of HMGl to cisplatin-modified DNA is, in fact, directly involved in mediating cisplatin cytotoxicity. One basic ques tion they are probing is whether HMGl binds to cisplatin-DNA adducts in vivo. They are also investigating the functions of HMGl, SSRP1, other DNA-binding proteins. Rudy Baum
Electrochromic system may have many uses
[Fe(CN)6]3, containing ferrous iron and called Everitt's salt. And viologen ex ists as an oxidized bipyridinium dication that is also colorless. When current is passed between the electrodes through the electrolyte, the
iron salt is oxidized to the blue form, Fe4[Fe(CN)6]3, and the viologen is re duced to a violet diquinoid compound. The reinforcing effect of two electrochro mic substances heightens the contrast between colored and colorless states. The demonstration device shown in San Francisco was a 4- by 4-inch sand wich between two glass plates. Each glass plate was coated on the inside with a transparent, electrically conduct ing layer of stannic oxide. On the Prussian blue side, the stannic oxide layer on the glass plate was coated with polypyrrole by electropolymerization from an aqueous solution of pyr role. Then the polypyrrole chains were "electroplated" with Prussian blue from an aqueous solution of ferric sulfate and potassium ferrocyanide. On the viologen side, the stannic oxide layer was functionalized with a trimethoxysilylpropyl derivative, to which viologen adhered in a layer. The two plates were then sand wiched together around an aqueous polymeric gel containing potassium sul fate—a gel electrolyte—and sealed with a gasket to exclude air. Young and Leventis explain that the flexibility of the polypyrrole resin con-
Complementary counterelectrodes intensify colors A fast-responding, high-contrast, dura ble, low-power electrochromic system has been developed by chemists at Mo lecular Displays, Waltham, Mass. It was demonstrated in San Francisco to the Division of Polymer Chemistry. Electrochromic materials change col or and light transmittancy on applica tion of electric current. Because of this property, they may find applications in architectural windows; automotive windshields, sun roofs, and rearview mirrors; and flat-panel displays. Young C. Chung, technical director for Molecular Displays, and Nicholas Leventis, vice president for R&D, ex plain that the characteristics of their system are derived from use of two complementary electrochromic sub stances as electrodes in a redox panthat are separated by an electrolyte. One electrode consists of Prussian blue embedded in polypyrrole, a resin that can be doped to electrical conduc tivity. The other electrode consists of viologen (1,1 '-diethyl-^'-bipyridinium). In the colorless state, the Prussian blue exists in its reduced form, K4Fe420
APRIL 20,1992 C&EN
Glass Transparent conductive coating - Prussian blue in polypyrrole
Viologen -
- Gel electrolyte
-Gasket
0.8-0.9 Volt
HsCo—V V - ^
V—C2H5 + 2e-
H5C2—Ν
\=(
N— C2H5
Viologen K4Fe4[Fe(CN)e]3 Everitt's salt [Fe (II)]
4e" + 4K + + Fe4[Fe(CN)e]3 Prussian blue [Fe (III)]
ψιψιψνηηψ:
According to Farcasiu, the organic "shorting out" the content from the tires and treads is com two plates. This effect raises pletely converted to heptane-soluble liq the possibility that uids when processed under these condi the device may find tions. Gas formation is less than 1%. use as a battery. When shredded tires and coals were coThough current den processed, conversions to methylenesities are low, the chloride-soluble materials were 51% and Two electrochrotnic substances in the same device enhance effect are cheap 56%, respectively, in the typical case. materials The researchers found carbon black and the redox reac tributes to long-term stability by accom tions are readily reversible for recharg to be a good catalyst for hydrocracking reactions. Thus, they expected the modating volume changes in iron com ing. pounds during electrochemical cycling. Another possible variation is electro- carbon black in recycled tires to exhibit And providing reciprocal redox process catalysis. Oxidations or reductions a similar catalytic activity during co es at each electrode avoids decomposi might be carried out at a Prussian blue processing. To check this hypothesis, tion of the gel electrolyte between them. electrode with current passed through runs were made with and without The Molecular Displays investigators the cell to keep the iron compound in carbon black. Coprocessing without carbon black exhibited a significant re also say that the two redox reactions re the reduced or oxidized form. duce power consumption by providing The response time of the device duction of the liquid yield and an in twice the electrochromic effect per cou shown in San Francisco was two to five crease in gas formation. This suggests lomb. And the colored form of the de seconds. Young and Leventis say this is that the aromatic fragments from the vice retains its color when the external because of its relatively large size. With coal or rubber are alkylated with ali circuit is broken. So no passage of cur smaller arrays, they have achieved phatic fragments formed during the depolymerization, Farcasiu says. Fur rent is needed to maintain the colored switching times of milliseconds. state. The device can be decolorized by Stephen Stinson ther verification is under way involv ing the use of model compounds. Heavy residual oils, however, have probably received more attention for co processing with coal. Results on that as rubber also has intrinsic solvent prop pect of coprocessing were reported at erties in the liquefaction, and the the meeting by a group from UOP Inc., carbon black acts as a catalyst in the headed by senior research associate John process. The crude oil produced may G. Gatsis. The project is being sponsored S A N FRANCISCO be refined for use as motor fuels or by the Department of Energy. The overall aim of evaluating the tech may be a source of aromatic oils for the Most coal conversion interest in the production of new tires. Unreacted coal nical feasibility of using residual oils and past has focused on indirect coal lique and carbon black can be burned for establishing a coprocessing database have been met, Gatsis says. In addition, faction and the use of synthesis gas. their fuel values. Nonetheless, direct liquefaction has re Farcasiu's group at PETC has investi he explains, the group has demonstrated ceived some attention and funding, gated coprocessing Illinois No. 6 coal, the concept of a single-stage catalytic with a growing realization of the value tire tread materials, styrene-butadiene process in a bench-scale continuous sys derived from coprocessing other feed rubber, ds-polybutadiene rubber, ele tem using a UOP vanadium-based cata stocks with the coal. mental sulfur, carbon black, and aromat lyst. The design for a conceptual plant Two such feedstocks for coprocess ic oils. The liquefaction experiments with a 100,000-barrel-per-day capacity ing with coal were subjects for presen used shredded tire materials and other has been completed. Work is now aimed tation to the Division of Fuel Chemis reactants in a shaker autoclave. Reaction at optimizing the single-stage, slurrytry—scrap tires and heavy residual oil. temperature was 425 °C, autoclave time catalyzed coprocessing scheme. Eco Use of scrap tires is appealing because was 60 minutes, and hydrogen pressure nomic improvement now depends on catalyst development, he adds. it offers a virtually free feedstock with in the autoclave was 1000 psig. Gatsis says a newer molybdenumvaluable properties and, simultaneously, After liquefaction, the products were helps solve a major disposal problem. separated by methylene chloride extrac based catalyst has been developed and Malvina Farcasiu, a process research tion followed by filtration. The residue, evaluated on a bench scale. Conse er at the Department of Energy's Pitts after methylene chloride removal, was quent plant modifications have been burgh Energy Technology Center extracted with heptane, the solid residue made for operation at a much higher (PETC) who is investigating this use of filtered out, and the heptane evaporated. level of severity—which, he notes, scrap tires, says an incentive is the po The heptane-soluble fraction is defined should provide a significant improve tential for disposing of about 200 mil in the experiments as "oils" and the hep ment in process economics. A crucial matter in the operation of lion tires annually. tane-insoluble portion as "asphaltenes." Coprocessing of tires with coal pro The insoluble solid residue includes un the process is its ability to make longduces liquid synthetic crude oil, taking reacted coal, mineral matter from the term runs. Gatsis says this seems to advantage of the high hydrogen con coal, and carbon black and zinc oxide have been resolved by a demonstration of good operability at 3000 psig, a 5:1 tent in the tires. The depolymerized from the tires.
Coprocessing is possible coal liquefaction route
APRIL 20,1992 C&EN 21
