8

NEWS

March 2023 ESRFnews

C H A N T A L A R G O U D S T E F C A N D É/E S R F

Pressure destroys ionic bonds

Scientists from China and the US

have used the ESRF to demonstrate

that extreme pressure can destroy

ionic bonds. The study, which

involved state-of-the-art computer

modelling, saw the transition of

so-called superionic silver iodide

(AgI) into elemental silver and iodine.

The use of mechanical force to

prompt a chemical transition is well

known for organic materials, but less

so for inorganic compounds. Jianfu

Li at Yantai University in China and

colleagues simulated the behaviour of

AgI at high pressures using a “particle

swarm optimisation algorithm”,

before using a diamond anvil cell to

compress AgI powder to pressures

over 40 GPa at the ESRFs ID15B

Xray diffraction beamline

As predicted the AgI first formed

a superionic solid in which the

iodine component flows like a liquid

through the solid silver and then

decomposed into elemental silver

and iodine JACS Au doi101021

jacsau2c00550 Each bond has

its own chemical limit says group

member Qingyang Hu at the Centre

for High Pressure Science and

Technology Advanced Research in

Beijing. “In this superionic solid,

we have reached the chemical limit

of AgI by applying pressure … the

decomposition and the collapse

of ionicity.” He added that similar

transitions should occur in other ionic

solids such as silver chloride and silver

bromide, but at even higher pressures.

New ‘prodrug’ self-activates

Users of ESRF structural-biology

beamlines have discovered a type of

“produg” that activates itself, rather

than relying on enzymes or human

intervention. Led by the Institute

for Advanced Biosciences (IAB) and

the Institute of Structural Biology in

Grenoble, the research team believes

that the novel activation mechanism

could improve solubility, permeability

and metabolic stability.

A prodrug is a type of drug that

is biologically inactive until it is

metabolised into its therapeutically

active form, usually through

conversion by enzymes in the body or

human intervention. It is of interest

to medicine because it offers the

potential for the targeted delivery of a

drug to a specific area of the body.

The new prodrugs are in a class of

boron compounds called benzoxa-

boroles, including an antibiotic that

has recently completed phase II clinical

trials to cure tuberculosis. Instead

of binding directly to their target – a

key protein for protein synthesis,

leucyl-tRNA synthetase (LeuRS) –

they react first with adenosine-based

biomolecules in the body, such as ATP,

to become active. The researchers

combined X-ray crystallography at

the ESRF with nuclear magnetic

resonance spectroscopy to reveal how

the prodrugs do this at physiological

concentrations (J. Am. Chem. Soc.

145 800).

“No-one knew how this molecule

was forming the active drug with

adenosine-based biomolecules,” says

Andrés Palencia at the IAB. “We’ve

just proven this antibiotic is a prodrug,

and to our knowledge, the first one

that self-activates with adenosines.”

CO

2

electrolysis studied

Scientists led by the Denmark

Technical University and the ESRF

have worked out why devices used

to convert carbon dioxide (CO

2

) into

useful chemicals become unstable

during use. The results should help

researchers to build better performing

devices, which could one day form part

of a circular carbon economy.

In CO

2

electrolysis, CO

2

and water

can be turned into chemicals such as

ethanol, ethylene or synthetic fuels

using electricity alone. The process

requires a membrane electrode

assembly, comprising a membrane,

catalytic layers and gas diffusion

electrodes (GDEs). In existing

laboratory devices, these electrodes

can become flooded, form salt deposits

and suffer performance losses, but

no-one has been sure why.

Asger Moss at the Technical

University of Denmark in Kongens

Lyngby and colleagues were assisted

by Jakub Drnec (below) and others

at the ESRF to monitor water and

bicarbonate formation in an operational

GDE, using X-ray diffraction at the ID31

beamline. Meanwhile, they used in-line

gas chromatography to link the changes

taking place in the device to the formed

products. “You can only do this kind of

experiment at a high-energy beamline

such as ours,” says Drnec.

The team found that when certain

salts form in the cathode GDE, they

cause water to collect and flood it, which

in turn promotes the chemical reaction

producing hydrogen. This causes the

total cell potential to drop and alters

ion transport through the membrane,

in an imbalanced, oscillatory manner.

“I believe these findings will help us

to build efficient and environmentally

friendly technologies for a CO

2

circular

economy, a much needed step for a

sustainable future,” says Drnec.

The prodrug

studied by Andrés

Palencia (centre)

and colleagues

works without

enzyme or human

intervention.

Phase diagram of silver iodide AgI At relatively low pressures

AgI exists in various solid phases IV II I before melting at

sufficiently high temperature At pressures above about 05 Gpa

AgI has an ionic structure like rock salt III or above about

10 GPa a superionic structure V Based on the new study the

background colour depicts the gradual transition of these ionic

structures blue to elemental silver and iodine green

J I A N F U L I / Y A N T A I U N I V E R S I T Y I N C H I N A