proton transfer reaction
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2022 ◽  
Author(s):  
Reman Kumar Singh ◽  
Rakesh Pant ◽  
G Naresh Patwari

The ability of phenol to transfer the proton to surrounding ammonia molecules in a phenol-(ammonia)n cluster will depend on the relative orientation of the ammonia molecules and a critical field of about 285 MV cm-1 is essential along the O–H bond for the transfer process. Ab-initio MD simulations reveal that for a spontaneous proton transfer process, the phenol molecule must be embedded in a cluster consisting of at least eight ammonia molecules, even though several local minima with proton transferred can be observed for clusters consisting of 5-7 ammonia molecules. Further, phenol solvated in large clusters of ammonia, the proton transfer is spontaneous with the proton transfer event being instantaneous (about 20-120 fs). These simulations indicate that the rate-determining step for the proton transfer process is the reorganization of the solvent around the OH group and the proton transfer process in phenol-(ammonia)n clusters. The fluctuations in the solvent occur until a particular set of configurations projects the field in excess of critical electric field along the O–H bond which drives the proton transfer process with a respone time of about 70 fs. Further, the proton transfer process follows a curvilinear path which includes the O–H bond elongation and out-of-plane movement of the proton and can be referred to as a “Bend-to-Break” process.


2021 ◽  
Author(s):  
Wenjie Wang ◽  
Bin Yuan ◽  
Yuwen Peng ◽  
Hang Su ◽  
Yafang Cheng ◽  
...  

Abstract. Volatile organic compounds (VOCs) regulate atmospheric oxidation capacity, and the reactions of VOCs are key in understanding ozone formation and its mitigation strategies. When evaluating its impact, most previous studies did not fully consider the role of oxygenated VOCs due to limitations of measurement technology. By using a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) combined with gas chromatography mass spectrometer (GC-MS) technology, we are able to quantify a large number of oxygenated VOCs in a representative urban environment in southern China. Based on the new dataset, we find that non – formaldehyde (HCHO) OVOCs can contribute large fractions (22–44 %) of total ROX radical production, comparable or larger than the contributions from nitrous acid and formaldehyde. We demonstrate that constraints using OVOCs observations are essential in modeling radical and ozone production, as modelled OVOCs can be substantially lower than measurements, potentially due to primary emissions and/or missing secondary sources. Our results show that models without OVOC constraints using ambient measurements will underestimate P(ROX) and ozone production rate, and may also affect the determination of sensitivity regime in ozone formation. Therefore, a thorough quantification of photodegradable OVOCs species is in urgent need to understand accurately the ozone chemistry and to develop effective control strategies.


2021 ◽  
Vol 42 ◽  
pp. 101207
Author(s):  
Aikaterini Liangou ◽  
Antonios Tasoglou ◽  
Heinz J. Huber ◽  
Christopher Wistrom ◽  
Kevin Brody ◽  
...  

Author(s):  
Zhining Zhang ◽  
Hanyang Man ◽  
Fengkui Duan ◽  
Zhaofeng lv ◽  
Songxin Zheng ◽  
...  

Abstract A second wave of coronavirus disease 2019 (COVID-19) infections have emerged in summer Beijing, 2020, which provided an opportunity to explore the response of air pollution to reduced human activity. Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) coupled with Positive Matrix Factorization (PMF) source apportionment were applied to evaluate the pollution pattern and capture the detailed dynamic emission characteristics of volatile organic compounds (VOCs) during the representative period with the occurrence of O3 pollution episodes and the Beijing resurgence of COVID-19. The level of anthropogenic VOC was lower than the same period of previous years due to the pandemic and emission reduction measures. More than two-thirds of the observation period were identified as high-O3 days and VOCs exhibited higher mixing ratios and faster consumption rates in the daytime under high-O3 days. The identified VOC emission sources and the corresponding contributions during the whole observation period included: vehicle + fuel (12.41 ± 9.43%), industrial process (9.40 ± 8.65%), solvent usage (19.58 ± 13.46%), biogenic (6.03 ± 5.40%), background + long-lived (5.62 ± 11.37%), and two groups of oxygenated VOC (OVOC) factors (primary emission and secondary formation, 26.14 ± 15.20% and 20.84 ± 14.0%, respectively). Refined dynamic source apportionment results show that the “stay at home” tendency led to decreased emission (- 34.47 ± 1.90 %) and weakened morning peak of vehicle + fuel during the Beijing resurgence. However, growing emission of primary OVOCs (+ 51.10 ± 8.28%) with similar diurnal variation was observed in the new outbreak and afterwards, which might be related to the enhanced usage of pandemic products. The present study illustrated that more stringent VOC reduction measures towards pandemic products should be carried out to achieve the balanced emission abatement of NOx and VOC when adhering to regular epidemic prevention and control measures.


2021 ◽  
Author(s):  
Haiyan Li ◽  
Thomas Golin Almeida ◽  
Yuanyuan Luo ◽  
Jian Zhao ◽  
Brett B. Palm ◽  
...  

Abstract. Proton-transfer-reaction (PTR) is a commonly applied ionization technique for mass spectrometers, where hydronium ions (H3O+) transfer a proton to analytes with higher proton affinities than the water molecule. This method has most commonly been used to quantify volatile hydrocarbons, but later generation PTR-instruments have been designed for better throughput of less volatile species, allowing detection of more functionalized molecules as well. For example, the recently developed Vocus PTR time-of-flight mass spectrometer (PTR-TOF) has been shown to agree well with an iodide adduct based chemical ionization mass spectrometer (CIMS) for products with 3-5 O-atoms from oxidation of monoterpenes (C10H16). However, while several different types of CIMS instruments (including those using iodide) detect abundant signals also at “dimeric” species, believed to be primarily ROOR peroxides, no such signals have been observed in the Vocus PTR, even though these compounds fulfil the condition of having higher proton affinity than water. More traditional PTR instruments have been limited to volatile molecules as the inlets have not been designed for transmission of easily condensable species. Some newer instruments, like the Vocus PTR, have overcome this limitation, but are still not able to detect the full range of functionalized products, suggesting that other limitations need to be considered. One such limitation, well-documented in PTR literature, is the tendency of protonation to lead to fragmentation of some analytes. In this work, we evaluate the potential for PTR to detect dimers and the most oxygenated compounds, as these have been shown to be crucial for forming atmospheric aerosol particles. We studied the detection of dimers using a Vocus PTR-TOF in laboratory experiments as well as through quantum chemical calculations. Only noisy signals of potential dimers were observed during experiments on the ozonolysis of the monoterpene α-pinene, while a few small signals of dimeric compounds were detected during the ozonolysis of cyclohexene. During the latter experiments, we also tested varying the pressures and electric fields in the ionization region of the Vocus PTR-TOF, finding that only small improvements were possible in the relative dimer contributions. Calculations for model ROOR and ROOH systems showed that most of these peroxides should fragment partially following protonation. With inclusion of additional energy from the ion-molecule collisions driven by the electric fields in the ionization source, computational results suggest substantial or nearly complete fragmentation of dimers. Our study thus suggests that while the improved versions of PTR-based mass spectrometers are very powerful tools for measuring hydrocarbons and their moderately oxidized products, other types of CIMS are likely more suitable for the detection of ROOR and ROOH species.


Author(s):  
Benjamin Bayer ◽  
Andreas Maccani ◽  
Johanna Jahn ◽  
Mark Duerkop ◽  
Ewald Kapeller ◽  
...  

Abstract Objectives The applicability of proton-transfer-reaction mass spectrometry (PTR-MS) as a versatile online monitoring tool to increase consistency and robustness for recombinant adeno-associated virus (rAAV) producing HEK 293 bioprocesses was evaluated. We present a structured workflow to extract process relevant information from PTR-MS data. Results Reproducibility of volatile organic compound (VOC) measurements was demonstrated with spiking experiments and the process data sets used for applicability evaluation consisted of HEK 293 cell culture triplicates with and without transfection. The developed data workflow enabled the identification of six VOCs, of which two were used to develop a soft sensor providing better real-time estimates than the conventional capacitance sensor. Acetaldehyde, another VOC, provides online process information about glucose depletion that can directly be used for process control purposes. Conclusions The potential of PTR-MS for HEK 293 cell culture monitoring has been shown. VOC data derived information can be used to develop soft sensors and to directly set up new process control strategies.


2021 ◽  
Author(s):  
Rakesh Pant ◽  
Reman Kumar Singh ◽  
G Naresh Patwari

The ability of phenol to transfer the proton to surrounding ammonia molecules in a phenol-(ammonia)n cluster will depend on the relative orientation of the ammonia molecules and a critical field of about 285 MV cm-1 is essential along the O–H bond for the transfer process. Ab-initio MD simulations reveal that for a spontaneous proton transfer process, the phenol molecule must be embedded in a cluster consisting of at least eight ammonia molecules, even though several local minima with proton transferred can be observed for clusters consisting of 5-7 ammonia molecules. Further, phenol solvated in large clusters of ammonia, the proton transfer is spontaneous with the proton transfer event being instantaneous (about 20-120 fs). These simulations indicate that the rate-determining step for the proton transfer process is the organization of the solvent around the OH group and the proton transfer process in phenol-(ammonia)n clusters follows a curvilinear path which includes the O–H bond elongation and out-of-plane movement of the proton and can be referred to as a “Bend-to-Break” process.


2021 ◽  
Author(s):  
Yuanyuan Luo ◽  
Olga Garmash ◽  
Haiyan Li ◽  
Frans Graeffe ◽  
Arnaud P. Praplan ◽  
...  

Abstract. Diterpenes (C20H32) are biogenically emitted volatile compounds that only recently have been observed in ambient air. They are expected to be highly reactive, and their oxidation is likely to form condensable vapors. However, until now, no studies have investigated gas-phase diterpene oxidation. In this paper, we explored the ozonolysis of a diterpene, ent-kaurene, in a simulation chamber. Using state-of-the-art mass spectrometry, we characterized diterpene oxidation products for the first time, and we identified several products with varying oxidation levels, including highly oxygenated organic molecules (HOM) monomers and dimers. The most abundant monomers measured using a nitrate chemical ionization mass spectrometer were C19H28O8 and C20H30O5, and dimers were C38H60O6 and C39H62O6. The exact molar yield of HOM from kaurene ozonolysis was hard to quantify due to uncertainties in both the kaurene and HOM concentrations, but our best estimate was a few percent, which is similar to values reported earlier for many monoterpenes. We also monitored the decrease of the gas-phase oxidation products in response to an increased condensation sink in the chamber to deduce their affinity to condense. The oxygen content was a critical parameter affecting the volatility of products, with 4–5 O-atoms needed for the main monomeric species to condense. Finally, we report on the observed fragmentation and clustering patterns of kaurene in a Vocus proton transfer reaction time-of-flight mass spectrometer. Our findings highlight similarities and differences between diterpenes and smaller terpenes during their atmospheric oxidation, but more studies on different diterpenes are needed for a broader view of their role in atmospheric chemistry.


2021 ◽  
Author(s):  
Kun Zhang ◽  
Zhiqiang Liu ◽  
Xiaojuan Zhang ◽  
Qing Li ◽  
Andrew Jensen ◽  
...  

Abstract. The outbreak of COVID-19 promoted strict restrictions to human activities in China, which led to dramatic decrease in most air pollutant concentrations (e.g., PM2.5, PM10, NOx, SO2, and CO). However, abnormal increase of ozone (O3) concentrations was found during the lockdown period in most urban areas of China. In this study, we conducted a field measurement targeting ozone and its key precursors by utilizing a novel proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) in Changzhou, which is representative for the Yangtze River Delta (YRD) city cluster of China. We further applied the integrated methodology including machine learning, observation-based model (OBM), and sensitivity analysis to get insights into the reasons causing the abnormal increase of ozone. Major findings include: (1) By deweathered calculation, we found changes in precursor emissions contributed 5.1 ppbv to the observed O3 during the Full-lockdown period, while meteorological conditions only contributed 0.5 ppbv to the O3 changes. (2) By using an OBM model, we found that although significant reduction of O3 precursors was observed during Full-lockdown period, the photochemical formation of O3 was stronger than that during the Pre-lockdown period. (3) The NOx / VOCs ratio dropped dramatically from 1.84 during Pre-lockdown to 0.79 in Full-lockdown period, which switched O3 formation from VOCs-limited regime to the conjunction of NOx- and VOC-limited regime. Additionally, the decrease in NOx / VOCs ratio during Full-lockdown period was supposed to increase the MeanO3 by 2.4 ppbv. Results of this study investigate insights into the relationship between O3 and its precursors in urban area, demonstrating reasons causing the abnormal increase of O3 in most urban areas of China during the COVID-19 lock-down period. This study also underlines the necessity of controlling anthropogenic OVOCs, alkenes, and aromatics in the sustained campaign of reducing O3 pollution in China.


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