NO says yes to MOF: Infrared spectroscopy, pores for thought

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  • Published: Jan 8, 2015
  • Author: David Bradley
  • Channels: Infrared Spectroscopy
thumbnail image: NO says yes to MOF: Infrared spectroscopy, pores for thought

A framework for treatment

Representation of the assembly of the rigid, porous, 3-periodic MIL-100(Fe) (top), MIL-127(Fe) (bottom), and MOFs from the inorganic trinuclear iron cluster and tricarboxylate or tetracarboxylate ligands. (From APL Mater, Fig 1)

Infrared spectroscopy and other techniques have been used by researchers in France to show how the biologically important gas molecule nitric oxide, NO, can be trapped within porous materials known as metal-organic frameworks (MOFs). The work opens up the new possibility of controlled delivery of this gas, which acts as a neurotransmitter as well as having other stimulatory roles in human biology, to targeted sites.

The researchers at the Université de Versailles' Institut Lavoisier in France and their colleagues suggest that encapsulating NO in this way might be useful for novel treatments for dangerous infections and heart conditions.

Select gas

NO is one of a select group of gas molecules, along with carbon monoxide, active oxygen species, hydrogen sulfide and others that are crucial to biological signalling pathways, NO is found in bacteria, plant, animal and fungi cells. In mammals, NO is a powerful vasodilator, increasing blood flow and lowering vascular pressure. As such, it can be used to treat respiratory failure in premature infants as well as being the key ingredient to the sexual arousal response - acting as a vasoactive neurotransmitter - a point raised after the advent of alkyl and amyl nitrite drugs of abuse (poppers) and sildenafil citrate, or Viagra. NO also has strong antibacterial potency because it acts as a destructive free radical and is generated naturally to kill invading pathogens.

As a small molecule drug itself, NO is not tenable because it is a gas and so cannot be readily delivered to the target site. However, separate efforts to develop high-density gas storage materials for carbon dioxide sequestration and safe hydrogen fuel storage have been investigated widely. The biocompatibility of some of these porous materials of the metal-organic-framework type show promise as they can trap gas molecules in a stable environment and can be triggered to release their payload only under certain conditions, at a target site. The French team has now shown that MOFs can store and slowly deliver NO over a long period of time.

Elegant efficiency

"This is an elegant and efficient method to store and deliver large amounts of NO for antibacterial purposes," explains Christian Serre. "Or it can release controlled amounts of nitric oxide at the very low biological level for a prolonged period of time, in order to use it as a way to inhibit platelet aggregation [as an anti-thrombosis drug]."

Serre and colleagues have previously reported the use of porous hybrid solids, including MOFs for controlled delivery of NO gas but have now demonstrated great efficacy with derivatives of iron polycarboxylates as the framework. Serre and colleagues have now collaborated with Russell Morris's team at the University of St Andrews in Scotland and researchers from Université de Basse-Normandie in France. They analysed the NO adsorption and release properties of several porous biodegradable and biocompatible iron carboxylate MOFs using infrared spectroscopy analysis, adsorption and desorption isotherms and water-triggered release tests. They found that the NO binds to the acidic metal sites in the MOF and that partial reduction of the Fe(III) to Fe(II) improves the affinity of the MOF for the gas, a parameter that could be adjusted according to release rate needs for a given treatment.

Related Links

APL Mater, 2015, online: "Porous, rigid metal(III)-carboxylate MOFs for the delivery of nitric oxide"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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