Structure-reactivity Relationships Research Articles

Integrating Polyoxometalates and Silver Clusters into Atomically Precise Molecular Heterojunction.

The Ag cluster-POM assemblies have been shown to possess interesting and potentially useful properties. However, there is no precedent example of atomically precise Ag cluster-POM assemblies showing heterojunction effects in photocatalysis. Herein, the synthesis and total structure determination of the periodically distributed molecular heterojunction [Ag12(SCy)6(CH3CN)12(PW12O40)]n (Ag12-PW12) are reported. The assembly of Ag/W clusters into 3D network can endow the resulting binary structure with an aesthetic topology and unique physicochemical properties. More remarkably, the incorporation of Ag12 cluster with PW12 can efficiently facilitate the separation of photogenerated electrons and holes, thus significantly promoting the catalytic efficiency in selective oxidation of sulfides. The Ag12-PW12 heterojunction can be recovered and reused five times with no drastic change in the catalytic performance. This research is expected to assist in the rational design of cluster-based heterojunction catalysts. The increase of catalytic activity of the Ag12-PW12 assembly in comparison with the unassembled Ag12 and PW12 clusters is attributed to the synergistic effect of Ag12 and PW12 clusters, offering the splendid opportunity for deciphering structure-reactivity relationship of heterostructure-coupled photosystem.

Experimentally validating sabatier plot by molecular level microenvironment customization for oxygen electroreduction

Microenvironmental modifications on metal sites are crucial to tune oxygen reduction catalytic behavior and decrypt intrinsic mechanism, whereas the stochastic properties of traditional pyrolyzed single-atom catalysts induce vague recognition on structure-reactivity relations. Herein, we report a theoretical descriptor relying on binding energies of oxygen adsorbates and directly associating the derived Sabatier volcano plot with calculated overpotential to forecast catalytic efficiency of cobalt porphyrin. This Sabatier volcano plot instructs that electron-withdrawing substituents mitigate the over-strong *OH intermediate adsorption by virtue of the decreased proportion of electrons in bonding orbital. To experimentally validate this speculation, we implement a secondary sphere microenvironment customization strategy on cobalt porphyrin-based polymer nanocomposite analogs. Systematic X-ray spectroscopic and in situ electrochemical characterizations capture the pronounced accessible active site density and the fast interfacial/outward charge migration kinetics contributions for the optimal carboxyl group-substituted catalyst. This work offers ample strategies for designing single-atom catalysts with well-managed microenvironment under the guidance of Sabatier volcano map.

Well-defined tricobalt tetraoxide's critical morphology effect on the structure-reactivity relationship.

This review focuses on exploring the intricate relationship between the catalyst particle size and shape on a nanoscale level and how it affects the performance of reactions. Drawing from decades of research, valuable insights have been gained. Intentionally shaping catalyst particles makes exposing a more significant percentage of reactive facets possible, enabling the control of overactive sites. In this study, the effectiveness of Co3O4 nanoparticles (NPs) with nanometric size as a catalyst is examined, with a particular emphasis on the coordination patterns between oxygen and cobalt atoms on the surface of these NPs. Investigating the correlation between the structure and reactivity of the exposed NPs reveals that the form of Co3O4 with nanometric size can be modified to tune its catalytic capabilities finely. Morphology-dependent nanocatalysis is often attributed to the advantageous exposure of reactive crystal facets accumulating numerous active sites. However, experimental evidences highlight the importance of considering the reorganization of NPs throughout their actions and the potential synergistic effects between nearby reactive and less-active aspects. Despite the significant role played by the atomic structure of Co3O4 NPs with nanometric size, limited attention has been given to this aspect due to challenges in high-resolution characterizations. To bridge this gap, this review strongly advocates for a comprehensive understanding of the relationship between the structure and reactivity through real-time observation of individual NPs during the operation. Proposed techniques enable the assessment of dimensions, configuration, and interfacial arrangement, along with the monitoring of structural alterations caused by fluctuating temperature and gaseous conditions. Integrating this live data with spectroscopic methods commonly employed in studying inactive catalysts holds the potential for an enhanced understanding of the fundamental active sites and the dynamic behavior exhibited in catalytic settings.

Reactivity of diethyl benzylidenemalonates with secondary cyclic amine dimers in acetonitrile: Structure-reactivity relationships and mechanism

We report on a kinetic study for the nucleophilic addition reactions of diethyl 4-X-substituted benzylidenemalonates 1a-c (X = N(CH3)2, OCH3 and CH3) with N-nucleophiles, such as morpholine 2a, piperidine 2b and pyrrolidine 2c by UV–vis spectroscopy in acetonitrile solution at 20 °C. The Hammett plots demonstrate much better linear correlations with σp+ constants than with σp constants. These results are best interpreted in terms of ground state stabilization through resonance interactions between the electron-donating substituent and the CO2Et group. The effect of amine basicity on the reaction rate was examined quantitatively, leading to linear correlations with high βnuc values in the 0.82–0.93 range. The origin of the abnormally high βnuc values was interpreted in terms of dimer mechanism. Finally, with the help of our new proposed linear free energy relationship log k1K (20 °C) = sN (E + N) + log K, the stability of the dimer amines (K) have been evaluated from the measured apparent second-order rate constant (k1K) and the previously reported E, N and sN parameters of the employed electrophiles 1a-c and nucleophiles 2a-c. Additionally, a complementary theoretical study utilizing Density Functional Theory (DFT) with the B3LYP/6-311g(d,p) method was conducted in acetonitrile. An attempt is made to establish the correlation between equilibrium constant and stabilization energy the studied systems.

Synthetic Mn3Ce2O5-Cluster Mimicking the Oxygen-Evolving Center in Photosynthesis.

The photosynthetic oxygen-evolving center (OEC) is a unique Mn4CaO5-cluster that catalyzes water splitting into electrons, protons, and dioxygen. Precisely structural and functional mimicking of the OEC is a long-standing challenge and pressingly needed for understanding the structure-function relationship and catalytic mechanism of O-O bond formation. Herein we report two simple and robust artificial Mn3Ce2O5-complexes that display a remarkable structural similarity to the OEC in regarding of the ten-atom core (five metal ions and five oxygen bridges) and the alkyl carboxylate peripheral ligands. This Mn3Ce2O5-cluster can catalyze the water-splitting reaction on the surface of ITO electrode. These results clearly show that cerium can structurally and functionally replace both calcium and manganese in the cluster. Mass spectroscopic measurements demonstrate that the oxide bridges in the cluster are exchangeable and can be rapidly replaced by the isotopic oxygen of H218O in acetonitrile solution, which supports that the oxide bridge(s) may serve as the active site for the formation of O-O bond during the water-splitting reaction. These results would contribute to our understanding of the structure-reactivity relationship of both natural and artificial clusters and shed new light on the development of efficient water-splitting catalysts in artificial photosynthesis.

Deconstruction of Polymers through Olefin Metathesis.

The consumption of synthetic polymers has ballooned; so has the amount of post-consumer waste generated. The current polymer economy, however, is largely linear with most of the post-consumer waste being either landfilled or incinerated. The lack of recycling, together with the sizable carbon footprint of the polymer industry, has led to major negative environmental impacts. Over the past few years, chemical recycling technologies have gained significant traction as a possible technological route to tackle these challenges. In this regard, olefin metathesis, with its versatility and ease of operation, has emerged as an attractive tool. Here, we discuss the developments in olefin-metathesis-based chemical recycling technologies, including the development of new materials and the application of olefin metathesis to the recycling of commercial materials. We delve into structure-reactivity relationships in the context of polymerization-depolymerization behavior, how experimental conditions influence deconstruction outcomes, and the reaction pathways underlying these approaches. We also look at the current hurdles in adopting these technologies and relevant future directions for the field.

Reactivity-based detection of nitrite ion: Rapid colorimetric and fluorometric response down to nM level

Recent developments in our lab provided significant insight into the structure–reactivity relationship between electronic properties and the detection of nitrite ions. By fine-tuning electron-withdrawing and electron-donating power, the sulfonamide group on aniline moiety was found to be the fastest nitrite probe among the first generation of probe molecules. Based on our understanding of the detection mechanism, our attention was moved to additional modification by installing stronger electron-donating groups on the azo-coupling partner. Accordingly, the bis methoxy group version of the probe molecule was prepared. It showed clean conversion from the probe to the benzo[c]cinnoline product and excellent linear response to very low levels of nitrite ions. Proton NMR and high-resolution mass spectrometer captured the reaction between the probe molecule and nitrite ions. As the reaction with nitrite ion triggers diazonium intermediate formation followed by intramolecular cyclization, both absorption and emission property changes were monitored as the signal readout to assay nitrite ion. In this report, our design principle of a probe molecule and its performance in colorimetric and fluorimetric responses will be discussed. In addition, the low detection limit achieved by leveraging chromatographic separation and assaying by the mass detector will be discussed.

N-Butyltin(IV) trichloride initiator for the solvent-free ring-opening polymerization of ε-caprolactone: evaluation of the structure-reactivity relationship of tin(IV) derivatives

n-Butyltin(IV) trichloride initiator for the solvent-free ring-opening polymerization of ε-caprolactone: evaluation of the structure-reactivity relationship of tin(IV) derivatives

Highlighting the “structure–reactivity” relationship and the impact on the kinetics for the autoxidation reaction of hydrocarbons

The interactions between heteroatomic species and the hydrocarbons present in Jet A-1 make the determination of degradation mechanisms difficult to elucidate and predict. This study aims to investigate the reaction mechanisms and kinetics of hydrocarbon molecules constituting jet fuel, excluding molecules with polar species. Five model hydrocarbons were selected (n-dodecane and its isomeric mixture, n-butylcyclohexane, 1,2,4-trimethylbenzene and 1-methylnaphthalene) and individually subjected to oxidation using the PetroOXY apparatus, focusing on the onset of autoxidation (ΔP/Pmax = 2 to 10 %). For the first time, an experimental protocol has been developed for the monitoring of gas and liquid phase reagent consumption and the identification and quantification of oxidation products formed in these phases. The results showed that oxygen consumption was always higher than that of the initial hydrocarbons, suggesting competitive reactions, with alkanes consuming more oxygen than aromatic molecules, as confirmed by induction periods (IP), demonstrating the different reactivity depending on the structure of the oxidized hydrocarbon molecule. A relationship between initial hydrocarbon structure and the type and number of carbon atoms in oxidation products was also demonstrated. A gel, probably a precursor deposit, was obtained after oxidation of the molecules, indicating a potential precipitation of polar species due to the difference in polarity with the hydrocarbon molecules. In addition, the overall kinetic and hydroperoxide dissociation constants of the reaction could be calculated from tests carried out at different temperatures (140, 150 and 160 °C). The Arrhenius parameter values were higher for alkanes than for aromatics, confirming the structure–reactivity relationship of hydrocarbons. A strong correlation between the Arrhenius parameters and the nature of the oxidized molecules was also demonstrated. This experimental study will be useful for the calibration of future kinetic models according to the chemical structure of the oxidized hydrocarbons and for the assessment of thermal stability behavior of 100 % Synthetic Alternative Fuels (SAF).

Kinetic Resolution of Cyclic Tertiary Alcohols with Lipase A from Candida Antarctica

AbstractEnzyme‐catalyzed acylative kinetic resolution (KR) and dynamic kinetic resolution (DKR) of racemic primary and secondary alcohols have been widely reported to produce esters with high enantiomeric purity. In contrast, similar KRs of tertiary alcohols have been reported for only a limited range of substrates and require prolonged reaction times of several days. To gain deeper insight into the substrate scope and increase the process efficiency, we examined the reaction conditions using commercially available immobilized lipase A from Candida antarctica and found that the addition of the heterogeneous, inorganic base sodium carbonate significantly increased the reaction rate while maintaining high enantioselectivity. The use of vinyl hexanoate as the acyl donor provided esters that were stable during chromatography purification. The optimized reaction conditions were then successfully applied to a range of cyclic tertiary alcohols containing tetralin, dihydroindene, chromane, and thiochromane skeletons having, in part, a substituent on the aromatic ring. In this study on the structure–reactivity relationship of enzymatic KR‐type reactions, we achieved >30 % conversion for various tertiary alcohols in 24 h at 25 °C, producing optically active esters with 88–99 % ee.

Monodispersed and Organic Amine Modified La(OH)3 Nanocrystals for Superior Advanced Phosphate Removal.

Advanced phosphate removal is critical for alleviating the serious and widespread aquatic eutrophication, strongly depending on the development of superior adsorption materials to overcome low chemical affinity and sluggish mass transfer at low phosphate concentrations. Herein, the first synthesis of monodispersed and organic amine modifiedlanthanum hydroxide nanocrystals (OA-La(OH)3) for advanced phosphate removal by modulating inner Helmholtz plane (IHP), is reported. These OA-La(OH)3 nanocrystals with positively charged surfaces and abundant exposed La sites exhibitspecific affinity toward phosphate, delivering a maximum adsorption capacity of 168mg Pg⁻1 and a wide pH adaptability from 3.0 to 11.0, as well as a robust anti-interference performance, far surpassing those of documented phosphate removal materials. The superior phosphate removal performance of OA-La(OH)3 is attributed to its protonated organic amine in IHP, which enhances the electrostatic attraction around the adsorbent-solution interface. Impressively, OA-La(OH)3 can treat ≈5 000 and ≈3 200 bed volumes of simulated and real phosphate-containing wastewater to below extremely strict standard (0.1mgL⁻1) in a fixed-bed adsorption mode, exhibiting great potential for advanced phosphate removal. This study offers a facile modification strategy to improve phosphate removal performance of nanoscale adsorbents, and sheds light on the structure-reactivity relationship of La-based materials.

Non-Tertiary Alkyl Substituents Enhance High-Temperature Radical Trapping by Phenothiazine and Phenoxazine Antioxidants.

Radical-trapping antioxidants (RTAs) are an indispensable class of additive used to preserve hydrocarbon materials from oxidative degradation. Materials that are regularly subjected to elevated temperatures where autoxidation is self-initiated (i.e., >120 °C) require high concentrations of RTA for protection. Not only is this costly, but it can negatively impact material performance. Herein we show that inhibition of the autoxidation of a model hydrocarbon (n-hexadecane) by phenothiazine (PTZ) at ≥160 °C can be greatly enhanced by the incorporation of either 1° or 2° alkyl substituents in the 3- and/or 7-positions of the scaffold. Structure-reactivity studies, product analyses and computations suggest that this results from hydrogen atom transfer (HAT) from the benzylic carbon of these alkyl substituents in the PTZ-derived aminyl radical intermediate. The resultant iminoquinone methide can then undergo further radical-trapping reactions, depending on the nature of the alkyl substituent. Similar structure-reactivity relationships are observed for the phenoxazine (PNX) scaffold. These results not only have significant implications for the design and development of new high-temperature RTA technology, but also for understanding aminic RTA activity at elevated temperatures. Specifically, they suggest that a stoichiometric model better accounts for the RTA activity of aromatic amines in saturated hydrocarbons than the widely accepted catalytic model.

Enhanced Fe(OH)2-driven reductive Dechlorination via shortened Fe-O bonds and colloidal medium

Fe2+ is usually adsorbed to the surface of iron-bearing clay, and iron (hydr)oxide in groundwater. However, the reductive activity of Fe(OH)2, a prevalent intermediate during the transformation of Fe2+, remains unclear. In this study, high-purity Fe(OH)2 was synthesized and tested for its activity in the degradation of carbon tetrachloride (CT). XRD data confirm that the synthesized material is a pure Fe(OH)2 crystal, exhibiting sharp peaks of (001) and (100) facets. Zeta potential analysis confirms that the off-white Fe(OH)2 is a colloidal suspension with a positive charge of ∼+35-50 mV. FTIR spectra reveal the formation of a coordination compound Fe2+ with OH−/OD−, derived from NaOH/OD. SEM and HRTEM results demonstrate that the Fe(OH)2 crystal has a regular octahedral structure with a size of ∼30-70 nm and average lattice spacings of 2.58 Å. Mössbauer spectrum verifies that the Fe2+ in Fe(OH)2/Fe(OD)2 is hexacoordinated with six Fe-O bonds. XAFS data demonstrate that the Fe-O bonds become shorter as the OH−:Fe(II) ratios increase. DFT results indicate that the (100) crystal face of Fe(OH)2 more readily transfers electrons to CT. In addition to being adsorbed to iron compounds, structural Fe2+ compounds such as Fe(OH)2 could also accelerate the electron transfer from Fe2+ to CT through shortened Fe-O bonds. The rate constant of CT reduction by Fe(OH)2 is as high as 0.794 min−1 when the OH−:Fe(II) ratio is 2.5 in water. This study aims to enhance our understanding of the structure-reactivity relationship of Fe2+ compounds in groundwater, particularly in relation to electron transfer mechanisms.

Anthraquinone fused sulfolenoporphyrins: Regulation of reactivity and property through annulations

The sulfolenoporphyrin-based Diels-Alder reaction is an efficient strategy in the construction of aromatic ring-fused porphyrins. However, the structure-reactivity relationship is still less explored. Here, we have synthesized the mono-, bis- and tri-anthraquinone fused sulfolenoporphyrins and explore the effect of anthraquinone fusion on their further Diels-Alder reactions. As a result, more anthraquinone fusions lead to higher reactivity but lower annulation yield. Theoretical calculation discloses that anthraquinone fusion has the HOMO of the dienes (i.e., the intermediates after extrusion of SO2 from sulfolenoporphyrins) raised owing to the [Formula: see text]-extension, affording high reactivity. However, as the number of ring fusions increases, the LUMO energy levels of dienes are reduced, which seems to benefit the side reaction (i.e., the dimer/oligomerization owing to the Diels-Alder reaction among porphyrin dienes), leading to the rapid consumption of dienes and low yields. Besides, the influence of the peripheral anthraquinone units on molecular stacking, absorption as well as aromaticity was investigated experimentally and computationally. In brief, this work has investigated the structure-reactivity relationship of sulfolenoporphyrins in the Dies-Alder reaction, which will help construct [Formula: see text]-extended porphyrin rationally.

Mechanistic and Kinetic Insights into Cellular Uptake of Biomimetic Dinitrosyl Iron Complexes and Intracellular Delivery of NO for Activation of Cytoprotective HO-1.

Dinitrosyl iron unit (DNIU), [Fe(NO)2], is a natural metallocofactor for biological storage, delivery, and metabolism of nitric oxide (NO). In the attempt to gain a biomimetic insight into the natural DNIU under biological system, in this study, synthetic dinitrosyl iron complexes (DNICs) [(NO)2Fe(μ-SCH2CH2COOH)2Fe(NO)2] (DNIC-COOH) and [(NO)2Fe(μ-SCH2CH2COOCH3)2Fe(NO)2] (DNIC-COOMe) were employed to investigate the structure-reactivity relationship of mechanism and kinetics for cellular uptake of DNICs, intracellular delivery of NO, and activation of cytoprotective heme oxygenase (HO)-1. After rapid cellular uptake of dinuclear DNIC-COOMe through a thiol-mediated pathway (tmax = 0.5 h), intracellular assembly of mononuclear DNIC [(NO)2Fe(SR)(SCys)]n-/[(NO)2Fe(SR)(SCys-protein)]n- occurred, followed by O2-induced release of free NO (tmax = 1-2 h) or direct transfer of NO to soluble guanylate cyclase, which triggered the downstream HO-1. In contrast, steady kinetics for cellular uptake of DNIC-COOH via endocytosis (tmax = 2-8 h) and for intracellular release of NO (tmax = 4-6 h) reflected on the elevated activation of cytoprotective HO-1 (∼50-150-fold change at t = 3-10 h) and on the improved survival of DNIC-COOH-primed mesenchymal stem cell (MSC)/human corneal endothelial cell (HCEC) under stressed conditions. Consequently, this study unravels the bridging thiolate ligands in dinuclear DNIC-COOH/DNIC-COOMe as a switch to control the mechanism, kinetics, and efficacy for cellular uptake of DNICs, intracellular delivery of NO, and activation of cytoprotective HO-1, which poses an implication on enhanced survival of postengrafted MSC for advancing the MSC-based regenerative medicine.

Structure–reactivity relationships in the ionic-liquid-catalyzed oxidation of cumene: Cation effects

Cumene oxidation is a key step in the industrial synthesis of phenol via cumyl hydroperoxide (CHP) formation. Ionic liquids (ILs) are attractive as green, metal-free alternatives catalysts for this reaction, but few studies have explored their potential. The study of the relationship between the structure and catalytic performance of ILs is crucial for the development of ionic liquids with excellent performance. In this study, we aimed to establish a theoretical protocol to evaluate the catalytic activity of ILs for cumene oxidation, as well as the structure–activity relationship, using density functional theory calculations. The calculations showed that the catalytic activity of the studied ILs decreased as follows: 1-n-butyl-3-methylimidazolium bromide > 1-butyl-1-methylpyrrolidinium bromide > N-n-butylpyridinium bromide > triethylammonium bromide > 1-n-butyl-2-methylpyrrolinium bromide. Moreover, the polarity, solubility, and maximum electrostatic potential of the ILs were linearly correlated with their catalytic activity. The theoretical predictions were verified by experiment. Additionally, DFT calculation and EPR analysis demonstrated that the catalytic activity of ionic liquids originates from the formation of hydrogen-abstracting radicals. Furthermore, using 1-butyl-1-methylpyrrolidinium bromide as a representative catalyst, we optimized the reaction conditions, a cumene conversion of 24.2 % and a CHP selectivity of > 90 % were obtained. Compared with the aqueous NaOH as a stabilizing agent, the reaction time is reduced by 8 h. This study provides new insights for designing efficient, low-cost, and environmentally friendly catalysts for cumene oxidation.

Efficient catalytic conversion of cellulose into 5-hydroxymethylfurfural by modified cerium zirconium phosphates in a biphasic system

Numerous metal phosphates have shown activity in the conversion of cellulose into 5-hydroxymethylfurfural (HMF). However, challenges persist due to low HMF yields and unclear structure-reactivity relationships. Herein, a series of zirconium-cerium phosphate-based catalysts were prepared by the co-precipitation method. These catalysts were sulfonated and loaded with tungsten to introduce Brønsted acidity. The effects of catalyst types and operating conditions on the production of HMF from cellulose using a biphasic system of tetrahydrofuran (THF) and water were systematically investigated in an autoclave reactor. The structure-reactivity relationship of these catalysts was subsequently elucidated using various catalyst characterization techniques. For an understanding of the reaction mechanism, in-situ attenuated total reflectance infrared spectroscopy (ATR-FTIR) was employed to monitor the reaction process. Experimental results revealed that the optimal HMF yield of 41.5% could be obtained using the 2W/CeZr2P + AC–SO3H–2 catalyst at 180 °C with a reaction time of 4 h. Compared to monometallic phosphate pairs of zirconium and cerium, this represents an enhancement in HMF yield by approximately 8%–20%. The enhancement could be attributed to the adequate acid amount and the balanced Brønsted/Lewis acid site ratio of this catalyst. These findings provide valuable guidance for future design and optimization of bimetallic phosphate catalysts.

Non-enzymatic degradation of aliphatic Brassicaceae isothiocyanates during aqueous heat treatment

Glucosinolate-derived isothiocyanates are valuable for human health as they exert health promoting effects. As thermal food processing could affect their levels in a structure dependent way, the stability and reactivity of 12 Brassicaceae isothiocyanates during aqueous heating at 100 °C and pH 5–8 were investigated. The formation of their corresponding amines and N,N′-dialk(en)yl thioureas was quantified. Further, the potential to form odor active compounds was investigated by HRGC–MS-olfactometry. A strong structure-reactivity relationship was found and shorter side chains and electron withdrawing groups increase the reactivity of isothiocyanates. 3-(Methylsulfonyl)-propyl isothiocyanate was least stable. The main products are the corresponding amines (up to 69% recovery) and formation of N,N′-dialk(en)yl thioureas is only relevant at neutral to basic pH values. Apart from allyl isothiocyanate also 3-(methylthio)propyl isothiocyanate is precursor to many sulfur-containing odor active compounds. Thus, the isothiocyanate-structure affects their levels but also contributes to the flavor of boiled Brassicaceae vegetables.

Hexafluoroisopropanol as a Bioconjugation Medium of Ultrafast, Tryptophan-Selective Catalysis.

The past decade has seen a remarkable growth in the number of bioconjugation techniques in chemistry, biology, material science, and biomedical fields. A core design element in bioconjugation technology is a chemical reaction that can form a covalent bond between the protein of interest and the labeling reagent. Achieving chemoselective protein bioconjugation in aqueous media is challenging, especially for generally less reactive amino acid residues, such as tryptophan. We present here the development of tryptophan-selective bioconjugation methods through ultrafast Lewis acid-catalyzed reactions in hexafluoroisopropanol (HFIP). Structure-reactivity relationship studies have revealed a combination of thiophene and ethanol moieties to give a suitable labeling reagent for this bioconjugation process, which enables modification of peptides and proteins in an extremely rapid reaction unencumbered by noticeable side reactions. The capability of the labeling method also facilitated radiofluorination application as well as antibody functionalization. Enhancement of an α-helix by HFIP leads to its compatibility with a certain protein, and this report also demonstrates a further stabilization strategy achieved by the addition of an ionic liquid to the HFIP medium. The nonaqueous bioconjugation approaches allow access to numerous chemical reactions that are unavailable in traditional aqueous processes and will further advance the chemistry of proteins.

Tracking Dynamic Chemical Reactivity Networks with High-Resolution Mass Spectrometry: A Case of Microplastic-Derived Dissolved Organic Carbon.

Chemical degradation testing often involves monitoring the loss of a chemical or the evolution of a single diagnostic product through time. Here, we demonstrate a novel approach to tracing complex degradation networks using mass-spectrometry-based methods and open cheminformatics tools. Ester- and ether-based thermoplastic polyurethane (TPU_Ester and TPU_Ether) microplastics (350 μm) and microplastics-derived dissolved organic carbon (MP-DOC) were photoweathered in a simulated marine environment and subsequently analyzed by liquid chromatography coupled to high-resolution mass spectrometry. We formula-annotated 1342 and 2344 unique features in the MP-DOC of TPU_Ester and TPU_Ether, respectively. From these, we extracted 199 and 568 plausible parent-transformation product pairs via matching of features (a) with complementary increasing and decreasing trends (Spearman's correlation coefficient between normalized intensity and time), (b) spectral similarities of at least three accurate mass MS2 fragments, and (c) at least 3 ppm agreement between the theoretical and measured change in m/z between the parent-transformation product formula. Molecular network analysis revealed that both chain scission and cross-linking reactions occur dynamically rather than degradation proceeding in a monotonic progression to smaller or more oxygenated structures. Network nodes with the highest degree of centrality were tentatively identified using in silico fragmentation and can be prioritized for toxicity screening or other physicochemical properties of interest. This work has important implications for chemical transformation tracking in complex mixtures and may someday enable improved elucidation of environmental transformation rules (i.e., structure-reactivity relationships) and fate modeling.