Simple Bond Research Articles

Revealing the Reasons for Degeneration of Resonance-Assisted Hydrogen Bond on the Aromatic Platform: Calculations of Ortho-, Meta-, Para-Disubstituted Benzenes, and (Z)-(E)-Olefins

The energies of the O-H∙∙∙O=C intramolecular hydrogen bonds were compared quantitatively for the series of ortho-disubstituted benzenes and Z-isomers of olefins via a molecular tailoring approach. It was established that the hydrogen bond energy in the former series is significantly less than that in the latter one. The reason for lowering the hydrogen bond energy in the ortho-disubstituted benzenes compared to the Z-isomers of olefins is the decrease in the π-contribution to the total energy of the complex interaction, in which the hydrogen bond per se is enhanced by the resonance effect. By the example of the para- and meta-disubstituted benzenes, as well as E-isomers of olefins, it was explicitly shown that the aromatic ring is a much poorer conductor of the resonance effect compared to the double bond. The hydrogen bond in the ortho-disubstituted benzenes has a lower energy than a typical resonance-assisted hydrogen bond because the aromatic moiety cannot properly assist the hydrogen bond with a resonance effect. Thus, a hydrogen bond on an aromatic platform should fall into a special category, namely an aromaticity-assisted hydrogen bond, which is closer by nature to a simple hydrogen bond rather than to a resonance-assisted one.

Directed chemical dimerisation enhances the antibacterial activity of the antimicrobial peptide MSI-78(4–20)

Antimicrobial resistance (AMR) is on the rise, leading to 700 000 deaths worldwide in 2020. Antimicrobial peptides (AMPs) are antibiotic agents that are active against multi-drug resistant pathogens and also have a reduced risk of AMR development. Previous studies have shown that dimerisation of the proline-rich antibacterial peptide (PrAMP) Chex1–Arg20 can enhance its antimicrobial activity while also reducing its toxicity. To determine if dimerisation via a simple disulfide bond can similarly improve other classes of AMPs, the α-helical cationic peptide MSI-78(4–20) was used as a model. The monomer alone, an S-carboxamidomethyl-capped N-terminal Cys–MSI-78(4–20) analogue and the disulfide-linked dimer were successfully synthesised and their antimicrobial activity and toxicity were determined. It was shown that dimerisation enhanced antimicrobial activity against the Gram-positive opportunistic pathogen Staphylococcus aureus ATCC 29213, the Gram-negative bacteria Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 47615. The peptides showed no significant haemolytic activity with red blood cells and only induced 50% lactate dehydrogenase (LDH) release in mammalian cells at the highest tested concentration, 15 µM. The MSI-78(4–20) dimer was less cytotoxic than the monomer and S-alkyl monomer. Together, the data support the strategy of AMP chemically directed dimerisation as a means of producing potentially more therapeutically useful antimicrobial agents.

The effect of fluorine replacement on the physical properties of oxyfluorotellurite glasses TeO2-Li2O-ZnO-ZnF2

Oxyfluorotellurite glasses in the composition 65TeO2–15Li2O-(20-x)ZnO-xZnF2 (x = 0, 5, 10 mol%) were prepared by melting quenching technique and their physical, thermal and structural properties were investigated. The results showed that the density and the oxygen packing density values decrease with increasing x. By the differential scanning calorimetry, the crystallization kinetic for each sample was evaluated and showed that activation energy decreases with increasing x, which can be related to the exchange of simple Te-O bonds for Te-F bonds. The variation on the quantity of these bonds were confirmed by FTIR and Raman spectroscopy. The mass attenuation coefficient values were found to reduce exponentially with increasing the energy. The radiation protection efficiency of glasses with 10 mm was 100, 50, and 30% for X-ray (40 KeV), 60Co (2.5MeV), and 137Cs energy lines (284 KeV & 66 KeV), respectively.

Applications of Bond Energy‐Based Thermodynamic Analysis to the Feasibility of Unfunctionalized C−C Cross‐Coupling Reactions

AbstractCarbon‐Carbon bond forming reactions are ubiquitous in nature and important for chemical and drug synthesis. Modern methods mostly utilize activated reactants, and despite recent developments in organic synthesis, and theoretical understanding, these have had limited success with unactivated C−H bonds. Here we apply a simple yet powerful Bond Dissociation Energy (BDE)‐based Reaction Enthalpy (BDERE) analysis to model C−C cross‐coupling reactions. BDERE appears in classical textbooks (halogenation of alkanes) but has not been applied to cross‐coupling reactions. BDERE allows one to rationalize the ease of coupling reactions for both homolytic and heterolytic mechanisms for all six C−C bond hybridization types. It facilitates the identification of a simple but unexplored reaction for ethane synthesis. BDERE values give valuable insights into recent advancements in C−C cross‐couplings of fully unfunctionalized (UFCC) and semi‐functionalized (SFCC) reactants that utilize metal, photoredox, organo, and biocatalysis. BDERE analysis may enable others to investigate and design novel cross‐coupling reactions.

Kingship and Covenant: Reconsidering the Oath of David and Jonathan

Abstract Frank Moore Cross’s model of covenant as an early legal means of extending fictive kinship has dominated Anglo-American biblical scholarship for the last thirty years. His central case study is the covenant between David and Jonathan and the associated oath sworn by Jonathan in 1 Sam 20. In trying to distill a simple covenant concept, however, Cross collapses distinctions of genre and context, reducing the significance of secular covenant as a form of political bond to simply merging kinship groups. In this article, I reanalyze the oath in 1 Sam 20:12–17, contextualizing it with other material throughout 1 and 2 Samuel and comparing it to ancient Near Eastern treaty formulations to show its political significance in Israelite history. In contrast to Cross’s notion of imposing kinship obligations, the oath addresses questions of succession and dynasty, anticipating the political turmoil of David’s ascension to the throne. Deuteronomistic language and concern with Davidic succession shared between the oath and the divine promise in 2 Sam 7 point to a common vision of a united kingship. Far from the reiteration of a simple kinship bond, Jonathan’s oath of loyalty to their covenant becomes a keystone in the Deuteronomistic ideal of an eternal Davidic dynasty.

Co-MOFs as Emerging Pulse Modulators for Femtosecond Ultrafast Fiber Laser.

The metal organic framework (MOF) has attracted more and more attention due to its unique morphology, functional linkers, and orderly network structure. Zeolitio imidazolata frameworks (ZIFs), which are formed by bivalent transition metals (Zn, Co, etc.) and nitrogen-containing heterocyclic imidazole or purine organic ligands, are a very attractive subclass of MOFs. ZIF-67, obtained by the nucleation growth of dimethylimidazole and Co 2p, has been developed as a precursor for porous nanostructured cobalt-based metal oxides. During material preparation we add rGO because it can be used as a basic element to construct macroscopic three-dimensional carbon structural materials, which self-assemble into a 3D network structure with ZIF-67 through simple van der Waals forces or hydrogen bonds, and some samples contain specific functional groups that are added to the precursor. In this paper, we employ liquid-phase synthesis to generate rGO-ZIF-67 and calcine it at the temperature of 350 °C to obtain rGO-Co3O4. Then we fabricate rGO-Co3O4 and rGO-ZIF-67 modulators based on microfibers and test their nonlinear optical absorption in 1.5 μm range. The modulation depths of rGO-Co3O4 and rGO-ZIF-67 are measured as 10.41% and 6.61%, respectively. By using microfiber-based rGO-Co3O4 modulator, we have obtained a conventional soliton and a soliton molecule in Er3+-doped fiber lasers. The conventional soliton has a pulse width of 793.4 fs and a spectral width of 3.3 at 1558.9 nm, respectively. The obtained soliton molecule has a spectral modulation period of 1.65 nm and temporal separation of 4.94 ps at 1563.2 nm. By employing a microfiber-based rGO-ZIF-67 modulator, we obtain conventional solitons with a spectral width of 1.9 nm at the central wavelength of 1529.8 nm. Our research may expand the MOF-based materials for ultrafast photonics, blazing a new path for fiber laser, optical communications, and optoelectronics, etc.

Tightening the Screws: The Importance of Tight d Functions in Coupled-Cluster Calculations up to the CCSDT(Q) Level

It is well established that the basis set convergence of the correlation consistent (cc-pVnZ) basis sets depends on the presence of high-exponent "tight" d functions in the basis set for second-row atoms. The effect has been linked to low-lying 3d virtual orbitals approaching the valence shell. However, since most of this effect is captured at the self-consistent field level, the effect of tight d functions in high-level coupled-cluster calculations has not been extensively studied. Here, we construct an extensive data set of 45 second-row species to examine the effect of tight d functions in CCSD, CCSD(T), CCSDT, and CCSDT(Q) calculations in conjunction with basis sets of up to sextuple-ζ quality. The selected set of molecules covers the gamut from systems where the tight d functions play a relatively minor role (e.g., SiH, SH, SiF, PF3, HOCl, Cl2, and C2Cl2) to challenging systems containing a central second-row atom bonded to many oxygen or fluorine atoms (e.g., PF5, SF6, SO3, ClO3, and HClO4) and systems containing many second-row atoms (e.g., P4, S4, CCl4, and C2Cl6). In conjunction with the cc-pVDZ basis set, we find chemically significant contributions to the total atomization energies (TAEs) of up to ∼2 kcal/mol at the CCSD level, ∼1 kcal/mol at the (T) level, and contributions of up to ∼0.1 kcal/mol for the post-CCSD(T) components. The effects of the tight d functions are diminished with the size of the basis set; however, they are still chemically significant at the CCSD and (T) levels. For example, with the cc-pVTZ basis set, we obtain contributions to the TAEs of up to ∼1.5 and ∼0.3 kcal/mol at the CCSD and (T) levels, respectively, and with the cc-pVQZ basis set, we obtain contributions of up to ∼1.0 and ∼0.2 kcal/mol at the CCSD and (T) levels, respectively. We also find that a simple natural bond orbital population analysis of the 3d orbitals of the second-row atom provides a useful a priori indicator of the magnitude of the effect of tight d functions on post-CCSD(T) contribution to the TAEs in oxide and fluoride systems. These results are particularly important in the context of high-level composite ab initio methods capable of confident benchmark accuracy in thermochemical predictions.

In Situ Functionalization of Cellulose with Polyoxometalate for UV-Resistant Performance

ABSTRACT Polyoxometalate-based composite materials have recently attracted extensive attention due to their unique structural characteristics and physicochemical properties. In the present work, a flexible anti-UV blocker compatible with cotton fabric was prepared by simple covalent bond self-assembly of carboxyl group (−COOH) and phosphomolybdate. The resultant cotton fabrics were investigated and confirmed by FT-IR, PXRD and SEM-EDS, demonstrating the successful preparation of polyoxometalate-based composite fabric. The UV spectrum of as-designed composite fabric imparts excellent UV absorption capacity and the UPF value reaches 397.19, which is far superior to original cotton (7.09). Furthermore, the blocker was tested on the photosensitive material in direct UV irradiation, which proved its outstanding performance as a flexible, wearable, and visualized UV blocker. In addition, the experimental results confirmed that the prepared composite material exhibited an excellent and stable UV resistant performance (UPF: 100+) after 5 days UV aging irradiation and five times washing. The proposed fabrication strategy could promisingly endow polyoxometalate-based fiber materials with extensive applicability potential.

Atropisomerism in Drug Discovery: A Medicinal Chemistry Perspective Inspired by Atropisomeric Class I PI3K Inhibitors.

Atropisomerism is a type of axial chirality resulting from hindered rotation about a σ bond that gives rise to nonsuperimposable stereoisomers (termed "atropisomers"). The inversion of chirality of an atropisomeric axis is a time- and temperature-dependent dynamic process occurring by simple bond rotation. For this reason, the rotational energy barrier (ΔErot) and the interconversion rate between an atropisomeric pair of biologically active molecules are important parameters to consider in drug discovery.Many compounds with atropisomeric axes advance into development every year. The vast majority of them have low rotational energy barriers (ΔErot lower than 20 kcal/mol), meaning they are rapidly equilibrating conformers and considered achiral (class 1 atropisomers). Compounds in class 2 (ΔErot = 20 to 30 kcal/mol) can be challenging to develop given that the stereochemical integrity of the atropisomeric axes can be compromised over time. It has been recommended that small molecule drug candidates containing one or more atropisomeric axes with rotational energy barriers greater than 30 kcal/mol (class 3 atropisomers) should be developed as single atropisomers.In medicinal chemistry, a σ bond with restricted rotation is engineered into a bioactive molecule primarily to limit its number of accessible conformations, thereby minimizing entropic and/or enthalpic energy penalties associated with biological target binding. In addition to enhanced pharmacology, potential positive outcomes of introducing atropisomerism include improved physicochemical properties and superior pharmacokinetics/ADME profiles. The application of atropisomerism in medicinal chemistry has become increasingly enabled due to recent advances in synthesis, purification, and analysis, as described in this special issue and recent review articles.Herein, we discuss two case studies from our own work in which restricting rotation about axes of atropisomerism led to significant improvements in pharmacological, physicochemical, and ADME properties for different series of PI3K inhibitors. In the first instance, a restricted axis of rotation was designed to mitigate an acid-mediated hydrolytic degradation pathway observed in a series of PI3Kδ inhibitors. The conformational constraint disrupts conjugation between a quinazolinone and a pyridine, leading to improved chemical stability under acidic conditions. In the second case study, introduction of a restricted axis of rotation between two heteroaromatic systems in a series of PI3Kβ inhibitors generated pairs of atropisomeric compounds with significantly different biological activities. Advanced profiling also demonstrated clear substrate stereospecificity in regard to metabolism by aldehyde oxidase. Gratifyingly, the eutomer (more active atropisomer) shows significantly less susceptibility for oxidative metabolism relative to the distomer (less active atropisomer). The improvements in potency, selectivity, chemical stability, and metabolic stability discussed in this manuscript are all directly related to the concept of atropisomerism.

Dissociative multiple ionization of carbon dioxide dimers in intense femtosecond laser fields

Molecular dimers have attracted much attention in the study of molecular structure and dynamics due to their complex interactions involving both weak van der Waals and strong covalent bonds. We investigate the dissociative ionization of carbon dioxide dimers exposed to intense femtosecond laser fields. The angular distributions of ionic fragments of the breakup channels ${({\mathrm{CO}}_{2})}_{2}{}^{2+}\ensuremath{\rightarrow}{\mathrm{CO}}_{2}^{+}+{\mathrm{CO}}_{2}^{+}$ and ${({\mathrm{CO}}_{2})}_{2}{}^{3+}\ensuremath{\rightarrow}{\mathrm{CO}}_{2}{}^{2+}+{\mathrm{CO}}_{2}^{+}$ strongly depend on the laser intensity. Simulations based on time-dependent density-functional theory reproduce the experimental observations qualitatively and show that the angular distribution of fragments is determined by the angle-dependent orbital ionization probability and the relative contributions of different orbitals, both of which are intensity sensitive. By comparing the ionization of the dimer with ${\mathrm{CO}}_{2}$ monomer, we find that the weak van der Waals bond and molecular geometry in the dimer play considerable roles. This work extends significantly earlier studies of simple linear covalent bond molecules.

Coupled Electron Pair-Type Approximations for Tensor Product State Wave Functions.

Size extensivity, defined as the correct scaling of energy with system size, is a desirable property for any many-body method. Traditional configuration interaction (CI) methods are not size extensive, hence the error increases as the system gets larger. Coupled electron pair approximation (CEPA) methods can be constructed as simple extensions of a truncated CI that ensures size extensivity. One of the major issues with the CEPA and its variants is that singularities arise in the amplitude equations when the system starts to be strongly correlated. In this work, we extend the traditional Slater determinant based coupled electron pair approaches like CEPA-0, averaged coupled-pair functional, and average quadratic coupled-cluster to a new formulation based on tensor product states (TPS). We show that a TPS basis can often be chosen such that it removes the singularities that commonly destroy the accuracy of CEPA based methods. A suitable TPS representation can be formed by partitioning the system into separate disjoint clusters and forming the final wave function as the tensor product of the many body states of these clusters. We demonstrate the application of these methods on simple bond breaking systems such as CH4 and F2 where determinant based CEPA methods fail. We further apply the TPS-CEPA approach to stillbene isomerization and few planar π-conjugated systems. Overall, the results show that the TPS-CEPA method can remove the singularities and provide improved numerical results compared to common electronic structure methods.

A “local” stacking fault energy model for concentrated alloys

We propose a simple bond energy model that can accurately predict the average stacking fault energy (SFE) in concentrated solid-solution alloys. The SFE is approximated by the energy difference of relevant bulk phases for which bond energies are determined. These bond energies are then used to determine the SFE distribution across the compositional space within a given alloy system, without performing additional calculations or refit parameters, thereby avoiding the computational cost and other limitations of stacking fault supercell calculations. We demonstrate that the model can be applied to random solid solutions and alloys with short-range ordering.

Bifurcated Chalcogen Bonds Based on One σ-Hole

Chalcogen bonds are noncovalent interactions and are increasingly coming into focus for the design of complex structures in research areas such as crystal engineering, molecular recognition and catalysis. Conceptionally, chalcogen bonds can be considered as interaction between one σ-hole and one Lewis base center. Herein, we analyze the interaction between bidentate chelating ligands having two nucleophilic centers with one single σ-hole of a chalcogenazole (two-lone-pair/one-σ-hole interactions). Referring to this, we show by quantum chemical calculations and X-ray studies that three bond types are possible: in the first case, a chalcogen bond is formed between the σ-hole and only one of the Lewis base centers. In the second case, a strong bond is formed by one nucleophilic center; the second center provides only a small amount of additional stabilization. In the third case, two equivalent bonds to the σ-hole are formed by both Lewis base centers. According to the calculations, the bifurcated bonds are stronger than simple chalcogen bonds and lead to a more rigid molecular arrangement in the complex.

Does Cr(CO)3 Really behave as Catalyst in the Diels‐Alder Reaction of Styrene with Cyclopentadiene? A Molecular Electron Density Theory Study

AbstractThe role of the coordination of the Cr(CO)3 complex to the aromatic ring of styrene in the Diels‐Alder (DA) reaction towards cyclopentadiene (Cp) has been studied within the Molecular Electron Density Theory (MEDT) at the ωB97X−D/6‐311G(d,p) level. While Electron Localization Function (ELF) topological analysis of the reagents indicates that coordination of Cr(CO)3 to the aromatic ring of styrene does not cause any remarkable change in its electronic structure, it increases its global electrophilicity but does not efficiently activate the C−C double bond. Thus, the DA reaction of styrene with Cp, which has a high activation energy, 15.9 kcal ⋅ mol−1, is decreased by only 2.1 kcal ⋅ mol−1 with the formation of the corresponding Cr(CO)3 complex. This DA reaction is endo and anti stereoselective. Analysis of the geometrical parameters and the electron density distribution at the endo TSs confirms that coordination of the Cr(CO)3 complex to the aromatic ring of styrene does not produce any appreciable change at the corresponding TSs. These DA reactions, which have low polar character, take place through a one‐step mechanism via an asynchronous endo TS, in which the formation of the C4−C5 simple bond is more advanced than the C1−C6 one. The present MEDT study shows that the Cr(CO)3 complex has no effective catalytic activity in the non‐polar DA reactions of styrene with Cp.

Theoretical exploration of the reactivity of cellulose models under non-thermal plasma conditions-mechanistic and NBO studies.

Mechanistic details of cellulose depolymerization by non‐thermal (atmospheric) plasma (NTAP) remains under‐explored given the complexity of the medium. In this study, we have investigated the reaction mechanism of glycosidic‐bond degradation triggered by reaction with hydroxyl radicals, considered as the principal reactive species in NTAP medium. In the first step of reaction sequence, H‐abstraction reactions by HO‧. radical on different C—H sites of the pyranose ring were found to be non‐selective and markedly exergonic giving rise to a set of cellobiosyl carboradicals likely to undergo further reactions. We then showed that cellobiosyl carboradicals are protected against direct hydrolysis, no activation of the (1–4)‐ β‐glycosidic bond being characterized. Interestingly, a simple homolytic bond cleavage allowed to obtain desired monomer. Among the 18 possible fragmentations, involving C—C and C—O bond breaking from cellobiosyl carboradicals, 14 transition states were successfully identified, and only three reaction pathways proved kinetically and thermodynamically feasible. Natural bond orbital (NBO) analysis was performed to shed light on electronic structures of different compounds.

DeePN$^2$: A Deep Learning-Based Non-Newtonian Hydrodynamic Model

A long standing problem in the modeling of non-Newtonian hydrodynamics of polymeric flows is the availability of reliable and interpretable hydrodynamic models that faithfully encode the underlying micro-scale polymer dynamics. The main complication arises from the long polymer relaxation time, the complex molecular structure and heterogeneous interaction. DeePN$^2$, a deep learning-based non-Newtonian hydrodynamic model, has been proposed and has shown some success in systematically passing the micro-scale structural mechanics information to the macro-scale hydrodynamics for suspensions with simple polymer conformation and bond potential. The model retains a multi-scaled nature by mapping the polymer configurations into a set of symmetry-preserving macro-scale features. The extended constitutive laws for these macro-scale features can be directly learned from the kinetics of their micro-scale counterparts. In this paper, we develop DeePN$^2$ using more complex micro-structural models. We show that DeePN$^2$ can faithfully capture the broadly overlooked viscoelastic differences arising from the specific molecular structural mechanics without human intervention.

Demonstration of Coherent Interference between Acoustic Waves Using a Fiber Ring Resonator.

Optical fibers were previously demonstrated to propagate and detect acoustic modes that were converted from Lamb waves for structural health-monitoring applications; typically, a fiber Bragg grating sensor in the optical fiber is used to detect acoustic modes. Acoustic modes can transfer from one fiber to another through a simple adhesive bond coupler, preserving the waveform of the acoustic mode. This paper experimentally investigates the coherence of acoustic waves through the adhesive coupler, using a fiber ring resonator (FRR) configuration. This configuration was chosen because the wave coupled to the second fiber interferes with the original wave after it encircles the fiber ring. We performed this experiment using different geometries of optical fibers in the ring, including a standard single-mode optical fiber, a hollow silica capillary tube, and a large-diameter multi-mode fiber. The results demonstrate that the acoustic wave, when transferring through an adhesive coupler, interferes coherently even when the main and ring fibers are of different types. Finally, we demonstrate that the FRR can be applied for sensing applications by measuring the mode attenuations in the ring due to a changing external environment (water-level sensing) and measuring the optical-path length change in the ring (temperature sensing).

Simple rebar anchorage slip macromodel considering corrosion

Reinforcement slip in the footing of a reinforced concrete (RC) column can significantly influence the lateral displacement of the column, a critical structural response under lateral loads such as seismic loading. Many past researchers studied and developed models to capture the anchorage slip of rebar; however, there is still a need for a model that can reflect the actual bond-slip relationship (especially in the presence of corrosion) and yet is simple-to-use for structural analysis. In this study, a simple bar stress-slip macromodel is developed to predict reinforcement anchorage slip given a rebar stress. The proposed rebar anchorage slip model is derived by implementing a macromodel solution based on a simple bond stress distribution function that captures the bond stress distribution numerically obtained from a real bond-slip relationship. Available experimental bond stress-slip data collected from literature are used to optimize the model parameter in the proposed bond stress distribution function, which reflects the impact of the structural parameters on the rebar slippage such as concrete strength and corrosion level. The proposed rebar slip model is then incorporated into a fiber beam-column model for numerical analysis, and is further validated by comparing flexural behavior of several RC columns (with and without corrosion) based on the numerical model with the experimental data. The results demonstrate the importance of incorporating rebar slippage and corrosion effect on bond. Using this fiber beam-column model, seismic performance of an example RC bridge column is evaluated, and one can conclude the rebar slip plays a critical role in the seismic evaluation. As the proposed rebar slip macromodel provides simple formulation and it is explicitly expressed with a model parameter that can be updated easily to incorporate new information, it is practical for structural analysis applications.

Theoretical investigations on the unimolecular decomposition mechanisms of isopropyl acetate

In this work, a comprehensive theoretical study was performed on the pyrolysis mechanism of Isopropyl acetate (IPA) using density functional methods (M06–2X, ωB97XD) and ab initio complete basis set−quadratic Becke3 (CBS-QB3) methods under combustion conditions over temperature ranges 600−1700 K and pressure ranging from 0.001 to 100 atm. The enthalpies of formation (AE), bond dissociation energies (BDEs), ionization energies (IE), and electron affinities (EA) of IPA and its main dissociation were calculated at the CBS-QB3 method and compared with available experimental results. The IPA pyrolysis mechanism was extended to include fourteen channels, seven complex fission reactions, and seven simple bond fission reactions. Among the investigated reactions, the formation of acetic acid and propene can occur through two different pathways; six-membered ring transition state (TS1SMR) or four-membered ring transition state (TS1FMR), with TS1SMR being 17.40 kcal mol−1 more preferable. The effect of temperature and pressure change was investigated using the transition state theory (TST) in conjunction with Wigner (W) tunneling corrections and the Statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory, respectively. The branching ratios (BR) of all chemical reactions involved were estimated. The results indicate that acetic acid and propene dominate up to 1400 K, but at high temperatures, simple bond fission reactions lead IPA pyrolysis. The BR analysis results are excellent agreement with the obtained BDEs and previous literature on similar biodiesel esters.

Transition Bond Frameworks: Goals, Issues, and Guiding Principles

In the context of reaching our climate targets—for example, the 2°C target set at Paris—the role of transition finance, and therefore transition bonds, is going to be key. This article provides a discussion of the goals, issues, and guiding principles for transition bonds. It first argues that a comprehensive transition bonds framework needs to align with appropriate climate transitions, allow for flexibility in getting to climate goals, and minimize greenwashing. The article then offers a simple transition bond rating framework based on the stringencies of climate targets as well as transition pathways. In this process, the crucial roles of sector-based approaches, offsets, regulations, and data quality are also discussed. In addition, the article sets out a research agenda, including identifying potential transition pathways, developing methodologies for additionality of proposed interventions, and creating regulation to ensure transparency.