Field of the invention

The present invention relates to methods for capturing and storing anaesthetics. More particularly, the present invention relates to methods for capturing and storing anaesthetics using metal organic frameworks.

Background of the invention

Nitrous oxide (N ₂ 0) and volatile fluorinated ethers including isoflurane (I) and sevoflurane (II) are widely used as inhalation anaesthetics. When administered to a patient, only a small proportion of inhaled anaesthetics are metabolised by the body leading to substantial release of these compounds upon exhalation into enclosed spaces such as operating theatres or ultimately the external environment. Both short term and long term exposure to the compounds can adversely affect the health of those who work in the immediate environment in which inhalation anaesthetics are in use. In addition to having a local detrimental impact on health, the release of these gases/vapours poses a significant environmental problem because, in general, they are extremely potent greenhouse gases.

If

Although not in routine use, xenon (Xe) has been viewed as the closest substance to an ideal anaesthetic. It is non-flammable, non-explosive, has low toxicity, allows rapid induction/emergence and is environmentally benign. However, its widespread use is unsustainable because the production of xenon requires considerable energy.

There are examples of materials developed for capturing gases, e.g. see White et ai, "A new structural family of gas-sorbing coordination polymers derived from phenolic carboxylic acids", Chem. Eur. J., 2015, 21 , 18057-18061 . However, the efficient capture of a gas requires preferential capturing of the gas by the capturing material. The preferential capturing of a gas will depend on many variables, such as, the affinity of the gas and the material for each other, and the affinity of the gas molecules for each other. The affinity of a gas may also change depending on the temperature and the pressure. Hence, a capturing material developed for a specific gas will not necessarily work well for other gases due to the difference in physisorption properties of gases.

It was estimated that 313.4 million major surgical procedures were performed in 2012 throughout the world. Hence, it is desired to have materials and processes that are able to capture and recycle anaesthetics. Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art. Summary of the invention

The present inventors have found that the metal organic frameworks of the present invention can sorb unexpectedly high amounts of an anaesthetic compound under treatment conditions in an operating theatre. Further, these metal organic frameworks have such high affinity for anaesthetic compounds that they preferentially sorb the anaesthetic compounds at rapid rates from a nearby liquid comprising the anaesthetic compound in question. Furthermore, these metal organic frameworks display highly selective sorption of the anaesthetic compounds.

In a first aspect, the present invention provides a method of capturing an anaesthetic compound, the method comprising: - contacting the anaesthetic compound with a metal organic framework wherein the anaesthetic compound sorbs to the metal organic framework thereby capturing the anaesthetic compound; wherein the metal organic framework comprises tetrahedrally co-ordinated metal centres and bridging ligands selected from 4-hydroxy-benzoic acid (hba), hydroxyl-4- biphenylcarboxylic acid (hbpc) and 2-methyl-4-hydroxybenzoic acid (2-mehba).

In a second aspect, the present invention provides a method of storing an anaesthetic compound, the method comprising:

- contacting the anaesthetic compound with a metal organic framework wherein the anaesthetic compound sorbs to the metal organic framework thereby storing the anaesthetic compound; wherein the metal organic framework comprises tetrahedrally co-ordinated metal centres and bridging ligands selected from 4-hydroxy-benzoic acid (hba), hydroxyl-4- biphenylcarboxylic acid (hbpc) and 2-methyl-4-hydroxybenzoic acid (2-mehba).

In a third aspect, the present invention provides a method of delivering an anaesthetic compound, the method comprising:

- capturing or storing an anaesthetic compound (according to the first and second aspects of the invention),

- releasing the sorbed anaesthetic compound from the metal organic framework by exposing the metal organic framework to a lower partial pressure of the anaesthetic compound than the partial pressure at which the anaesthetic compound was sorbed to the metal organic framework thereby delivering the anaesthetic compound. As used herein, except where the context requires otherwise, the term

"comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.

Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings. Brief description of the drawings

Figure 1. Structure of ML networks showing a) a helical chain of Zn ²⁺ centres and hba ^2" as bridging ligands, b) a space-filling representation of the Zn(hba) framework showing the square channels and c) a space filling representation of the topologically equivalent Zn(hbpc) framework.

Figure 2. Absorption isotherm at 298 K for xenon (Xe) measured on Zn(hba), Zn(hbpc) and Zn(2-mehba).

Figure 3. Absorption isotherm at 298 K for nitrous oxide (N ₂ 0) measured on Zn(hba), Zn(hbpc) and Zn(2-mehba). Figure 4. Absorption isotherm at 298 K for isoflurane measured on Zn(hba).

Figure 5. Absorption isotherm at 298 K for isoflurane measured on Zn(hbpc).

Figure 6. Absorption isotherm at 298 K for isoflurane measured on Zn(2-mehba).

Figure 7. Uptake of isoflurane over time by Zn(hba) and Zn(hbpc).

Figure 8. Uptake of isoflurane over time by Zn(hba), carbon fibre material Kuractive and activated charcoal.

Figure 9. Uptake of isoflurane over time by metal organic framework material UI066.

Figure 10. Uptake from atmosphere over time by metal organic framework material UI066. Detailed description of the embodiments

As discussed above, the present invention relates to a method of capturing an anaesthetic compound, the method comprising:

- contacting the anaesthetic compound with a metal organic framework wherein the anaesthetic compound sorbs to the metal organic framework thereby capturing the anaesthetic compound; wherein the metal organic framework comprises tetrahedrally co-ordinated metal centres and bridging ligands selected from 4-hydroxy-benzoic acid (hba), hydroxyl-4- biphenylcarboxylic acid (hbpc) and 2-methyl-4-hydroxybenzoic acid (2-mehba).

Capturing is defined as sorbing from the external environment a molecule or an atom and may include but is not limited to absorption and adsorption.

The present invention also relates to a method of storing an anaesthetic compound, the method comprising:

- contacting the anaesthetic compound with a metal organic framework wherein the anaesthetic compound sorbs to the metal organic framework thereby storing the anaesthetic compound; wherein the metal organic framework comprises tetrahedrally co-ordinated metal centres and bridging ligands selected from 4-hydroxy-benzoic acid (hba), hydroxyl-4- biphenylcarboxylic acid (hbpc) and 2-methyl-4-hydroxybenzoic acid (2-mehba).

Storing is defined as maintaining the level of captured molecules or atoms within the metal organic framework.

The metal organic frameworks of the present invention are 3D coordination polymers of composition ML, where M is the metal centre and L is the bridging ligand. In the present invention the metal centres may be selected from Zn ²⁺ and Co ²⁺ .

In preferred embodiments, the metal centres are Zn ²⁺ . In the present invention, the metal centre M is tetrahedrally co-ordinated by the bridging ligands. The metal organic frameworks comprise tetrahedrally co-ordinated metal centres linked by bridging ligands to crystallographically equivalent metal centres within a helical chain that extends in a direction parallel to the c-axis. An example of such a chain for the metal organic framework Zn(hba) is given in Figure 1 a. In the present invention, the bridging ligands may be selected from the dianion of 4- hydroxybenzoic acid (hba), the dianion of hydroxy-4-biphenylcarboxylic acid (hbpc) and the dianion of 2-methyl-4-hydroxybenzoic acid (2-mehba). In the present invention the extended Zn(hba) structure has channel dimensions of about 6 x 6 A (van der Waals surface to van der Waals surface). An example of the extended Zn(hba) metal organic framework is given in Figure 1 b.

In the present invention the extended Zn(hbpc) structure has channel dimensions of about 10 x 10 A. An example of the extended Zn(hbpc) metal organic framework is given in Figure 1 c.

In preferred embodiments, the bridging ligands are hbpc.

In preferred embodiments, the metal centres are Zn ²⁺ and the bridging ligands are hbpc. In one embodiment, the anaesthetic compound is selected from nitrous oxide

(N ₂ 0), xenon (Xe), desflurane, enflurane, halothane, isoflurane, methoxyflurane and sevoflurane.

Nitrous oxide, also known as laughing gas, is a chemical compound, an oxide of nitrogen with the formula N ₂ 0. Nitrous oxide is inert at room temperature and has few reactions. Nitrous oxide, even at 80% concentration, does not quite produce surgical level anaesthesia in most persons at standard atmospheric pressure, so it must be used as an adjunct anaesthetic, along with other agents. The pharmacological mechanism of action of nitrous oxide in medicine is not fully known. However, it has been shown to directly modulate a broad range of ligand-gated ion channels, and this likely plays a major role in many of its effects.

Xenon is a chemical element with symbol Xe. It is a colorless, dense, odorless noble gas found in the Earth's atmosphere in trace amounts. Xenon is generally unreactive due to its electronic configuration and only weakly interactive with other materials. As an anaesthetic, xenon is odourless and xenon is a usable anaesthetic at 80% concentration and normal atmospheric pressure.

Desflurane, enflurane, halothane, isoflurane, methoxyflurane and sevoflurane (structures shown below) are volatile anaesthetic agents, which share the property of being liquid at room temperature, but evaporating easily for administration by inhalation. desflurane

enflurane

lothane

isoflurane

methoxyflurane 3C _^ -O^ ^F sevoflurane

As liquids, the volatile anaesthetic agents are not freely miscible with water, and as gases they dissolve in oils better than in water. In sorption interaction, these anaesthetic agents may interact with the surface in various ways. Firstly, all adsorptives will form dispersion interactions with the adsorbent surface. Secondly, these anaesthetic agents have a dipole moment due to the presence of halogen substituents, so they can form dipole-dipole interactions with polar groups on the surface. However, owing to the high molecular symmetry, the molecular dipole moments of these compounds are only moderate, in spite of the large electronegativity differences between the carbon and the halogen atoms. Not much is known about the adsorption behaviour of the electronegative halogen atoms. In adsorption processes dominated by dispersion interactions, the polarizability of the outer atoms in the molecular chains may play a role. Hence, the sorbing properties of desflurane, enflurane, halothane, isoflurane, methoxyflurane and sevoflurane are difficult to predict.

Preferably, the anaesthetic compound is selected from isoflurane, N ₂ 0 and Xe.

In preferred embodiments, the anaesthetic compound is isoflurane. Figure 2 shows xenon isotherms (298 K) measured on Zn(hba), Zn(hbpc) and

Zn(2-mehba). The isotherms rise steeply at low pressures and at 1 bar the xenon adsorbed by Zn(hba) and Zn(2-mehba) is 343 and 200 mg/g respectively. The isotherms plateau at pressures greater than 1 bar with a xenon uptake by Zn(hba) of 440 mg/g at 9 bar and by Zn(2-mehba) of 348 mg/g at 4 bar. Considering xenon is known to only weakly interact with other materials, both Zn(hba) and Zn(2-mehba) have good efficacy in capturing xenon. The Zn(hbpc) is surprisingly effective in absorbing Xe with significantly more xenon being captured compared to Zn(hba) and Zn(2-mehba). The isotherm has a sigmoidal path. At pressures below 2.5 bar the xenon Zn(hbpc) isotherm rises gradually, between 2.5 and 3 bar the isotherm takes a sharp upward turn and as the pressure is raised above 3 bar the isotherm begins to plateau. An overall xenon uptake of 1020 mg/g is observed at a pressure close to 10 bar.

Figure 3 shows nitrous oxide (N ₂ 0) isotherms (298 K) measured on Zn(hba), Zn(hbpc) and Zn(2-mehba). Isotherms measured at 298 K for the adsorption of N ₂ 0 by Zn(hba), and Zn(2-mehba) resemble type I isotherms whilst the isotherm for Zn(hbpc) has a point of inflection (Figure 3). At a pressure of 1 bar Zn(hba), Zn(hbpc) and Zn(2- mehba) adsorb 109, 65 and 58 mg/g of the gas respectively (mass of adsorbed gas per gram of framework material). At this pressure the N ₂ 0 adsorption capacity is significantly higher than that observed for the materials MOF-5 and MOF-177 (D. Saha, Z. Bao, F. Jia, S. Deng, Environ./ Sci. & Tech., 2010, 44, 1820-1826). The N ₂ 0 isotherms for Zn(hbpc) show a sigmoidal profile. The Zn(hbpc) is surprisingly effective in absorbing N ₂ 0.

Figure 4 shows the isotherm for the uptake of isoflurane by Zn(hba) at low pressures. Figure 5 and Figure 6 show the isotherms for the adsoption of isoflurane for Zn(hbpc) and Zn(2-mehbba). The isotherms of all three metal organic framework show steep uptake of the vapor at very low pressure and approach saturation by 5 mbar, corresponding to a relative vapor pressure (P/Po) of 0.0127.

A summary of the anesthetic uptake of the metal organic framework at saturation (or at the maximum pressure measured) at 298 K (milligrams of guest per gram of metal organic framework). As can be seen, Zn(hba) has better capturing and storing properties for the gases in question compared to Zn(2-mehba). This difference may be due to the less spacious channels of Zn(2-mehba) where the methyl groups line the surfaces of the channels. Zn(hbpc) has even better capturing and storing properties than Zn(hba). All three metal organic framework materials show good capturing and storing properties of nitrous oxide, xenon and isoflurane despite the gases weakly interactive properties. Zn(hbpc) is surprisingly effective in capturing and storing the gases with double the amount or more of the gas being sorbed by the metal organic framework. It is unclear what contributes to this effect.

Table 1 .

N ₂ 0 Xe Isoflurane

Zn(hba) 230 (15 bar) 440 (9 bar) 417 (0.3 bar)

Zn(hbpc) 510 (15 bar) 1020 (10 bar) 775 (0.1 bar)

Zn(2-mehba) 140 (15 bar) 348 (4 bar) 187 (0.1 bar)

In one embodiment, more than 100 mg Xe per gram metal organic framework is sorbed to the metal organic framework at a pressure of 1 bar and at a temperature of 298 K.

In one embodiment, more than 100 mg N ₂ 0 per gram metal organic framework is sorbed to the metal organic framework at a pressure of 6 bar and at a temperature of 298 K.

In one embodiment, more than 100 mg isoflurane per gram metal organic framework is sorbed to the metal organic framework at a pressure of 0.1 bar and at a temperature of 298 K. In preferred embodiments, the metal centres are Zn ²⁺ and the bridging ligands are hpbc, and more than 500 mg of the anaesthetic compound per gram metal organic framework is sorbed to the metal organic framework at a temperature of 298 K.

In the present invention the anaesthetic compound may be part of a mixture of compounds. The mixture of compounds may be a fluid. Examples of such a fluid include but are not limited to the exhaled breath of a patient, the ambient air in an operating theatre or other space where anaesthetic compounds may be used or released.

In the present invention, the anaesthetic compound may be in the liquid form. The anaesthetic compound may also be in the gaseous form. In one embodiment, the anaesthetic compound is part of a fluid.

In one embodiment, the fluid is exhaled breath of a patient.

In one embodiment, the fluid is ambient air in an operating theatre.

The present invention also relates to a method of delivering an anaesthetic compound, the method comprising: - capturing or storing an anaesthetic compound (as described above),

- releasing the sorbed anaesthetic compound from the metal organic framework by exposing the metal organic framework to a lower partial pressure of the anaesthetic compound than the partial pressure at which the anaesthetic compound was sorbed to the metal organic framework thereby delivering the anaesthetic compound. In one embodiment, the method further comprises heating the metal organic framework.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention. Embodiments of the invention will now be discussed in more detail with reference to the examples which is provided for exemplification only and which should not be considered limiting on the scope of the invention in any way.

Examples Example 1

Synthesis of Zn(hba) n-Amyl alcohol (20 ml_) was added to a methanolic solution (15 ml_) containing 4- hydroxy benzoic acid (0.0622 g, 0.451 mmol) and Zn(OAc) ₂ 2H ₂ 0 (0.100 g, 0.459 mmol). The reaction mixture was heated in an open flask at 1 10 °C. With continued heating the more volatile methanol was selectively lost from the reaction mixture. The removal of nearly all of the MeOH allowed the separation of colourless needle-like crystals. The crystals were collected and subsequently dried in an oven at 250 °C for 5 hours. Yield 39.7 mg. Elemental analysis calc'd (%) for Zn(hba)- 1 .2H ₂ 0: C 38.3, H 2.7, N 0.0; found (%): C 37.9, H 2.7, N 0.0. X-ray crvstallographic investigation of Zn(hba)

The crvstallographic data for Zn(hba) data were collected on the MX1 beamline at the Australian Synchrotron, which was operating at 17.4 keV (λ= 0.7109 A). The data collection was run using Bluelce control software. The Zn(hba) framework yielded a diffraction pattern with very broad, streaky reflections consistent with intergrown crystals that were close to being aligned. The structure solution yielded the position of Zn centres and the bridging ligands, however refinement of the structure revealed the Zn centres were disordered. In addition the ligand exhibited orientational disorder.

Mr = 201.47, tetragonal, P4122, a = 9.1425(13), c = 12.663(3) A, V = 1058.4(4) A3, Z = 4, 0max = 27.86°, Australian SynchrotronKa = 0.71073 A, T = 470 K, (SynchrotronKa) = 2.283 mm-1 , 17129 reflections measured, 1259 unique which were used in all calculations, 58 parameters. The structure was solved by direct methods and refined using a full-matrix least squares procedure (SHELXL-2014),[S4] wR2 = 0.3426 (all data) and R1 = 0.1 196 (/>2o).

Example 2 Synthesis of Zn(hbpc) n-Amyl alcohol (20 ml_) was added to a methanolic solution (15 ml_) containing 4'-hydroxy-4-biphenyl carboxylic acid (0.0496 g, 0.232 mmol) and Zn(OAc) ₂ 2H ₂ 0 (0.0515 g, 0.235 mmol). The reaction mixture was heated in an open flask at a temperature of 100 °C. Upon the removal of MeOH from the reaction mixture colourless needle-like crystals separated from hot the n-amyl alcohol solution. The crystals were collected and dried in a 200 °C oven for five hours. Yield 25.1 mg. Elemental analysis calc'd (%) for Zn(hbpc)- 1 .67H ₂ 0: C 50.7, H 3.7, N 0.0; found (%): C 50.7, H 3.6, N 0.0.

X-ray crystallographic investigation of Zn(hba) The crystallographic data for Zn(hbpc) was collected at 130 K on a SuperNova

Oxford Diffractometer using Cu Ka (1.54184 A) source. Numerical absorption corrections were carried out using a multifaceted crystal model, and the ABSPACK routine within the CrysAlis software package.

Mr = 277.56, tetragonal, P4122, a = 13.456(1 ), c = 12.512(1 ) A, V = 2265(4) A3, Z = 4, 0max = 69.989°, ^(CuKa) = 1 .479 mm-1 , 5706 reflections measured, 2141 unique which were used in all calculations, 97 parameters. The structure was solved by direct methods and refined using a full-matrix least squares procedure (SHELXL- 2014/7),[S4] wR2 = 0.3292 (all data) and R1 = 0.1 168 (/>2σ). Within the crystal, large intraframework regions are occupied by highly disordered solvent molecules that could not be sensibly modelled. As a result the SQUEEZE routine from the crystallographic program PLATON [S5] was employed to produce a modified data set in which the contribution of the disordered solvent was removed.

Example 3

Synthesis of Zn(2-mehba) Crystals of Zn(2-mehba) were prepared by adding n-amyl alcohol (10 ml_) to a methanolic mixture (5 ml_) containing 4-hydroxy-2-methylbenzoic acid (0.160 g, 1 .05 mmol) and zinc acetate dihydrate (0.230 g, 1 .05 mmol). Upon heating the mixture in an open flask at 100 °C, the more volatile methanol was selectively lost from the reaction. The removal of nearly all of methanol allowed the separation of colourless crystals. The crystals were removed from the mother liquor and dried over air. Yield: 0.124 g. Elemental analysis calc'd for Zn(2-mehba).3H ₂ O: C 43.45, H 2.72, N 0.0; found C 43.42, H 2.77, N 0.0.

X-ray crvstallographic investigation of Zn(2-mehba) Single crystal X-ray data on Zn(2-mehba) were collected at 130 K on a

SuperNova Oxford Diffractometer using a CuKa (1 .54184 A) X-ray source. Crystals of Zn(2-Mehba) yield a diffraction pattern with extremely broad reflection bands, which were consistent with intergrown crystals that were close to being aligned. Similar broad and streaky reflections crystals are a characteristic of crystals of the parent compound, Zn(hba). Despite the difficulties associated with the broad diffraction peaks, it was possible to obtain data suitable to define the tetragonal unit cell parameters: a, b = 9.1 10 A and c = 12.551 A. This cell that is very similar to the unit cell parameters of Zn(hba) a, b = 9.0759(9) A and c = 12.1289(10) A.

Example 4 Inhalation anaesthetic uptake studies

The following general procedures relate to gas/vapor adsorption studies undertaken on samples of Zn(hba), Zn(hbpc) and Zn(2-mehba).

Nitrous oxide and xenon adsorption data were measured using a Sieverts- type BELsorp-HP automatic gas adsorption apparatus (BEL Japan Inc.). Helium, xenon 99.999 % and N ₂ O 99.9 % purity used for adsorption studies were purchased from BOC or Coregas. The inhalation anesthetic, Isothesia (100 % isoflurane), used for experiments was purchased from Henry Schein. Non-ideal gas behaviour at high pressures of each gas at each measurement and reference temperature was corrected for. Source data were obtained from the NIST fluid properties website. Prior to gas adsorption measurements a freshly prepared a batch of Zn(hba) solvate was heated at 250 °C whilst under dynamic vacuum, batches of Zn(hbpc) and Zn(2-Mehba) were heated at 200 °C under dynamic vacuum. For isotherm measurements, sample compartment temperatures were controlled by a Julabo F25-ME chiller/heater that recirculated fluid at ± 0.1 °C through a capped, jacketed stainless steel flask housed within a polystyrene box. A calibrated external Pt 100 temperature probe monitored the flask temperature. Prior to gas adsorption measurements, samples were held at the measurement temperature for a minimum of 1 hour to allow full thermal equilibrium to be attained before data collection.

Isoflurane vapor adsorption measurements up to 300 mbar were performed using an IGA-002 Intelligent Gravimetric Analyser supplied by Hiden Analytical Ltd. For measurements that relate to Zn(hba), 65.5 mg of pre-evacuated sample were initially heated to 130 °C under vacuum (~10 ^~5 mbar) for five hours and then heated to 250 °C for 23 hours. The sample was then cooled to the analysis temperature of 25 °C under vacuum and the dry mass of 64.18 was recorded. For Zn(hbpc), a fresh sample of Zn(hbpc). solvate of weight 44.31 mg was heated up to 165 °C to give a dry mass of 30.88 mg. For all isotherms, the temperature of the sample was maintained at 25 ±0.1 °C and the sample chamber was pressurised to a set pressure of the adsorbate and allowed to equilibrate for a minimum of 30 min before moving to the next pressure point.

Example 5 Sorption of anaesthetic from ambient air

The equipment consisted of an analytical balance (Denver instruments, accurate to 0.1 mg) on which the metal organic framework or the control absorbent (~50 mg) was placed in a petri dish on the pan of the balance. A bell jar was placed over the sample and the increase in mass was monitored in the presence of ambient air or an anaesthetic compound. When measuring the sorption of an anaesthetic compound, the anaesthetic compound was placed into an anaesthetic cell, which is an open cup attached to the bottom of a glass stopper and the bell jar was capped with the glass stopper with the attached anaesthetic cell. The anaesthetic compound vaporises out of the open cup into the atmosphere of the bell jar. As the metal organic framework sorbed the anaesthetic compound from of the atmosphere, the weight displayed on the balance increased. In the case of Zn(hba) and Zn(hbpc) there was no mass increase over a 20 minute period on when the metal organic frameworks were exposed to the atmosphere. When the metal organic frameworks were placed on the balance pan and enclosed by the bell jar with liquid isoflurane loaded in the anaesthetic cell, the mass indicated by the balance increased with 41 % for Zn(hba) and 73% for Zn(hbpc) (see Figure 7). By comparison the carbon fibre material Kuractive showed an uptake of 50% whilst activated charcoal showed an uptake of 40% (see Figure 8). Upon re-exposure to the atmosphere the activated charcoal and the carbon fibre material Kuractive lost mass fairly quickly whereas the metal organic frameworks Zn(hbpc) and Zn(hba) had much better retention of the isoflurane. Even after two hours the mass of Zn(hba) had only dropped by a small amount.

The metal organic framework material Ui066 (a zirconium based material) was shown to increase its mass by 98 % (see Figure 9), but in this case it was noted that the sample increased its mass by 14% upon exposure to the atmosphere (see Figure 10) whereas Zn(hbpc) and Zn(hba) show no increase when exposed to the atmosphere. Zn(hba) and Zn(hbpc) selectively sorbed isoflurane from the atmosphere and retained it when re-exposed to the atmosphere.