Role of Gas-Phase Halogen Bonding in Ambient Chemical Ionization Mass Spectrometry Utilizing Iodine

Abstract

Ambient ionization processes are becoming more widely used for the measurement of atmospherically relevant particles and gases. We report here ambient ionization mass spectra utilizing a commercial tincture of iodine and a piezoelectric discharge gun (PDG) to generate the ionizing reagents. Analytes include Cl 2 , Br 2 , HNO 3 , the C 1 −C 9 series of saturated monocarboxylic acids, benzoic acid, 2,2-dimethylpropanoic acid, 9-decenoic acid, and trichloroacetic acid. While Cl 2 and Br 2 form the [M + I] − iodide adducts, HNO 3 and the organic acids show unexpected peaks corresponding to [2M − 2H + I] −. For HNO 3 , the new ion formed is interpreted as the [NO 3 − •••IONO 2 ] complex, where IONO 2 is likely formed upon reaction of HOI with gaseous NO 3 −. Similarly, for the organic acids, the [2M − 2H + I] − peaks are interpreted as [RC(O)O − •••IOC(O)R] complexes formed by association of RC(O)O − with acyl hypoiodites [RC(O)OI]. It is proposed that the association of (1) Cl 2 and Br 2 with I − , (2) IONO 2 with NO 3 − ions, and (3) RC(O)OI with carboxylate ions occurs via non-covalent halogen bonding. The results suggest the possibility that halogen bonding may play a role in chemical transformations in the atmosphere, particularly in particles where concentrations of iodinated species may be significant.

Insights into the Chemistry of Iodine New Particle Formation: The Role of Iodine Oxides and the Source of Iodic Acid

“…These masses can be identified as the ion clusters IONO 2 ·NO 3 – , OIONO 2 ·NO 3 – , and O 2 IONO 2 ·NO 3 – . We have seen that the m / z = 251 signal appears simply by adding I 2 to the ion–molecule reaction zone, in line with the CIMS observations of Ganske et al 34 However, this signal also tracks the iodate core ion signals ( Figure S5 ), which means that part of it is associated with the neutral chemistry in the I x O y flow tube. In fact, iodine nitrate, IONO 2 , is a product of reaction R3 , OIONO 2 is a product of reaction R7 , and O 2 IONO 2 is a product of an analogous reaction of I 2 O 5 and NO 3 – .…”

“… 34 The peak at m / z = 251 increases by 2 orders of magnitude, and we identify it now as the halogen-bonded complex IONO 2 ·NO 3 – observed in previous CIMS work when I 2 and NO 3 – are present in sampled air. 34 Other minor masses observed are m / z = 205 (IO·NO 3 ), m / z = 221 (OIO·NO 3 – ), m / z = 222 (HNO 3 ·IO 2 – ), m / z = 254 (I 2 – ), m / z = 267 (OIONO 2 ·NO 3 – ), m / z = 314 (IONO 2 ·HNO 3 ·NO 3 – ), m / z = 316 (I 2 ·NO 3 – ), m / z = 440 ((IONO 2 ) 2 ·NO 3 – or IONO 2 ·(HNO 3 ) 3 ·NO 3 – ), and m / z = 443 (I 2 O 4 ·HNO 3 ·NO 3 – ). The oxidation of I 2 is not photochemical but caused by surface chemistry following I 2 deposition on the wall downstream of the ionization region (note that the gas-phase reaction NO 3 – + I 2 → IONO 2 + I – is endothermic using evaluated enthalpies of formation 43 , 44 ).…”

“… 33 This is not too surprising, considering that halogen bonding has been found to play an important role in the iodine CIMS when used for detecting HNO 3 . 34 Here, we have revisited our previous calculations 22 and extended them to reactions R6.2 , R3.2 , R3.3 , and R7 using the larger aug-cc-pVQZ basis set (see Methods). We have confirmed at this level of theory that no barriers exist in the PESs of reactions R3.1 and R7 ( Figures S9 and S10 , respectively).…”

HIOx–IONO2 Dynamics at the Air–Water Interface: Revealing the Existence of a Halogen Bond at the Atmospheric Aerosol Surface

“…The role of halogen bonding in drug design, material discovery, and catalysis is well appreciated. − Some studies have explored the role of halogen bonding in gas phase atmospheric chemistry, e.g., in the formation of hydrated HOX clusters (X = Cl, Br), iodine oxide clusters and hydrated iodine oxide clusters, and others . It has been recently proposed that halogen bonding may play a role in chemical transformations in particles .…”

“…The role of halogen bonding in drug design, material discovery, and catalysis is well appreciated. − Some studies have explored the role of halogen bonding in gas phase atmospheric chemistry, e.g., in the formation of hydrated HOX clusters (X = Cl, Br), iodine oxide clusters and hydrated iodine oxide clusters, and others . It has been recently proposed that halogen bonding may play a role in chemical transformations in particles . Our work is the first inspecting in detail these unusual interactions in the context of atmospheric aerosol surface chemistry.…”