Selectivity from quantum states to chemical products
An unclonable quantum cipher, a protein pore separating microcystins and a copper-zinc pair selecting an ethanol pathway show how selectivity is built across scales.
Science··Morning
A bit that cannot reach two receivers
Prabhanjan Ananth of UC Santa Barbara and Amit Sahai of UCLA defined a one-time private-key unclonable quantum encryption construction for one-bit messages. The preprint, posted to arXiv on 23 July and not peer reviewed, uses the principle that an unknown quantum state cannot be copied exactly. A secret key scrambles the hidden zero or one across a sequence of quantum states; the receiver measures those states together with the same key to recover the message. If an interceptor tries to divide the data between two accomplices, measurement disturbs the information. Even if the key is released later, the two receivers do not retain a joint advantage in recovering the message. The authors' security result has the attacker's advantage shrinking exponentially as more quantum states are used. This is a mathematical construction with a security proof, and the report contains no hardware implementation.[1]
Molecules distinguished in one pore
At EPFL in Lausanne, the groups of Matteo Dal Peraro and Tamar Kohn built a different form of selectivity around the pore that the protein aerolysin forms spontaneously in a membrane. Individual microcystin molecules passing through the pore under voltage interrupt the electric current briefly. Each microcystin variant leaves a characteristic trace in that interruption, allowing the sensor to distinguish seven variants. The MC-LR result from a Lake Lugano sample was close to the result from liquid chromatography-mass spectrometry on the same material. Adding a salt gradient brought detection below the World Health Organization guideline value. Tamar Kohn nevertheless identifies analysis without filtering the samples as an obstacle still to be solved. Selectivity therefore does not come from pore size alone; it depends on reading the electrical trace left during passage and remains tied to how the sample is prepared.[2]
Neighbouring atoms redirect the product pathway
A team at Sungkyunkwan University changed product selection in the electrical reduction of carbon dioxide by placing copper and zinc atoms side by side on a carbon support. In the reported division of labour, zinc prepares reaction intermediates while copper eases formation of the carbon-carbon bond required for ethanol. Ethanol becomes the selected product in a membrane-electrode assembly, but the authors say current density, energy efficiency, product concentration and long-term operation still need improvement. The result remains at laboratory scale and reports no industrial performance. Across the three developments, selectivity is built at different boundaries: the quantum cipher prevents intact information from being distributed to two receivers, the protein pore distinguishes molecules through electrical traces, and neighbouring metals steer carbon towards a particular product pathway. The common thread is the design of a physical arrangement that suppresses an unwanted copy, a confusable molecule or a competing product.[3], [1], [2]
