Front Cover: Understanding Local-Field Correction Factors in the Framework of the Onsager−Böttcher Model (ChemPhysChem 3/2019)

The determination of the appropriate local-field factor for quantifying the response of a molecule to an external electric field is of major importance in optical spectroscopy. Although numerous studies have dealt with the evolution of the optical properties of emitters as a function of their environment, the choice of the model used to quantify local fields is still ambiguous, and sometimes even arbitrary. In this paper, we review the Onsager–Böttcher model, which introduces the polarizability of the probe molecule as the determinant parameter for the local field factor, and we establish a simple conceptual framework encompassing all commonly used models. Finally, a discussion of published experimental research illustrates the potential of the measurement of local electric fields in dense dielectric media, as well as the subtleties involved in their interpretation.     

Front Cover: Can Nanoplastics Alter Cell Membranes? (ChemPhysChem 1/2020)

Whilst the formation of plastic nanoparticles (nanoplastics) from plastic wastes has been unequivocally evidenced, little is known about the effects of these materials on living organisms at the subcellular or molecular levels. In the present contribution we show through molecular dynamics simulations that polyethylene nanoparticles dissolve in the hydrophobic core of lipid bilayers into a network of disentangled, single polymeric chains. The thereby induced structural and dynamic changes in the bilayer alter vital functions of the cell membrane, which if lacking a mechanism to decompose the polymer chains may result in the death of the cell.     

Front Cover: Non-conventional Behavior of a 2,1-Benzazaphosphole: Heterodiene or Hidden Phosphinidene? (Chem. Eur. J. 52/2021)

The titled 2,1-benzazaphosphole ( 1 ) (i. e. ArP, where Ar=2-(DippN=CH)C₆H₄, Dipp=2,6-iPr₂C₆H₃) showed a spectacular reactivity behaving both as a reactive heterodiene in hetero-Diels-Alder (DA) reactions or as a hidden phosphinidene in the coordination toward selected transition metals (TMs). Thus, 1 reacts with electron-deficient alkynes RC≡CR (R=CO₂Me, C₅F₄N) giving 1-phospha-1,4-dihydro-iminonaphthalenes 2 and 3 , that undergo hydrogen migration producing 1-phosphanaphthalenes 4 and 5 . Compound 1 is also able to activate the C=C double bond in selected N-alkyl/aryl-maleimides RN(C(O)CH)₂ (R=Me, tBu, Ph) resulting in the addition products 7–9 with bridged bicyclic [2.2.1] structures. The binding of the maleimides to 1 is semi-reversible upon heating. By contrast, when 1 was treated with selected TM complexes, it serves as a 4e donor bridging two TMs thus producing complexes [μ-ArP(AuCl)₂] ( 10 ), [(μ-ArP)₄Ag₄][X]₄ (X=BF₄ ( 11 ), OTf ( 12 )) and [μ-ArP(Co₂(CO)₆)] ( 13 ). The structure and electron distribution of the starting material 1 as well as of other compounds were also studied from the theoretical point of view.     

Quantum Chemical Study of Potential Energy Surface in the Formation of Atmospheric Sulfuric Acid?

A new potential energy surface (PES) for the atmospheric formation of sulfuric acid from OH+SO₂ is investigated using density functional theory and high-level ab initio molecular orbital theory. A pathway focused on the new PES assumes the reaction to take place between the radical complex SO₃·HO₂ and H₂O. The unusual stability of SO₃·HO₂ is the principal basis of the new pathway, which has the same final outcome as the current reaction mechanism in the literature but it avoids the production and complete release of SO₃. The entire reaction pathway is composed of three consecutive elementary steps:(1) HOSO₂+O₂→SO₃·HO₂, (2) SO₃·HO₂+H₂O→SO₃·H₂O·HO₂, (3) SO₃·H₂O·HO₂→H₂SO₄+HO₂. All three steps have small energy barriers, under 10 kcal/mol, and are exothermic, and the new pathway is therefore favorable both kinetically and thermodynamically. As a key step of the reactions, step (3), HO₂ serves as a bridge molecule for low-barrier hydrogen transfer in the hydrolysis of SO₃. Two significant atmospheric implications are expected from the present study. First, SO₃ is not released from the oxidation of SO₂ by OH radical in the atmosphere. Second, the conversion of SO₂ into sulfuric acid is weakly dependent on the humidity of air.     

Front Cover: Can Cyanuric Acid and 2,4,6-Triaminopyrimidine Containing Ribonucleosides be Components of Prebiotic RNA? Insights from QM Calculations and MD Simulations (ChemPhysChem 11/2019)

As a step toward assessing their fitness as pre-RNA nucleobases, we employ DFT and MD simulations to analyze the noncovalent interactions of cyanuric acid (CA) and 2,4,6-triaminopyrimidine (TAP), and the structural properties of the associated ribonucleosides (rNs) and oligonucleotides. Our calculations reveal that the TAP : CA pair has a comparable hydrogen-bond strength to the canonical A : U pair. This strengthens the candidature of CA and TAP as prebiotic nucleobases. Further, the stacking between two canonical nucleobases is stronger than those between TAP or CA and a canonical base, as well as those between two TAP and/or CA, which indicates that enhanced stacking may have served as a driving force for the evolution from prebiotic to canonical nucleobases. Similarities in the DFT-derived anti/syn rotational barriers and MD-derived (anti) glycosidic conformation of the CA and TAP rNs and canonical rNs further substantiate their candidature as pre-RNA components. Greater deglycosylation barriers (as obtained by DFT calculations) for TAP rNs compared to canonical rNs suggest TAP rNs indicate higher resistance to environmental factors, while lower barriers indicate that CA rNs were likely more suitable for less-challenging locations. Finally, the tight packing in narrow CA:TAP-containing helices suggests that the prebiotic polymers were shielded from water, which would aid their evolution into self-replicating systems. Our calculations thus support proposals that CA and TAP can act as nucleobases of pre-RNA.     

Cover Feature: Mechanism of Oxidative Activation of Fluorinated Aromatic Compounds by N-Bridged Diiron-Phthalocyanine: What Determines the Reactivity? (Chem. Eur. J. 63/2019)

The biodegradation of compounds with C−F bonds is challenging due to the fact that these bonds are stronger than the C−H bond in methane. In this work, results on the unprecedented reactivity of a biomimetic model complex that contains an N-bridged diiron-phthalocyanine are presented; this model complex is shown to react with perfluorinated arenes under addition of H₂O₂ effectively. To get mechanistic insight into this unusual reactivity, detailed density functional theory calculations on the mechanism of C₆F₆ activation by an iron(IV)-oxo active species of the N-bridged diiron phthalocyanine system were performed. Our studies show that the reaction proceeds through a rate-determining electrophilic C−O addition reaction followed by a 1,2-fluoride shift to give the ketone product, which can further rearrange to the phenol. A thermochemical analysis shows that the weakest C−F bond is the aliphatic C−F bond in the ketone intermediate. The oxidative defluorination of perfluoroaromatics is demonstrated to proceed through a completely different mechanism compared to that of aromatic C−H hydroxylation by iron(IV)-oxo intermediates such as cytochrome P450 Compound I.     

Self-optimizing Diffusion Quantum Monte Carlo Calculation: the Potential Energy Curve of C_2

11NTRODUCTIONDiffusionquantumMonteCarlo(DMC)isoneofthesimplestofthevariousMonteCarlotechniquesavailabletosolvetheSchrodingerequation,forarecentre-viewofDMC(seeRef[1i).Foravarietyofsmallatomsandmolecules,DMChasbeenshowntobecapableofprovidinganestimateoftheground-state(nonrelativistic)energywithanaccuracycomparabletogoodqualityClcalculations,evenwhenarelativelysimpletrialwavefunctionisemployed.However,todate,thereareseveralobstaclesinaDMCcalculation:(1)BeforetheDMCcomputation,thepar…     

Cover Feature: Are the Accompanying Cations of Doping Anions Influential in Conducting Organic Polymers? The Case of the Popular PEDOT (Chem. Eur. J. 63/2019)

Conducting organic polymers (COPs) are made of a conjugated polymer backbone supporting a certain degree of oxidation. These positive charges are compensated by the doping anions that are introduced into the polymer synthesis along with their accompanying cations. In this work, the influence of these cations on the stoichiometry and physicochemical properties of the resulting COPs have been investigated, something that has previously been overlooked, but, as here proven, is highly relevant. As the doping anion, metallacarborane [Co(C₂B₉H₁₁)₂]⁻ was chosen, which acts as a thistle. This anion binds to the accompanying cation with a distinct strength. If the binding strength is weak, the doping anion is more prone to compensate the positive charge of the polymer, and the opposite is also true. Thus, the ability of the doping anion to compensate the positive charges of the polymer can be tuned, and this determines the stoichiometry of the polymer. As the polymer, PEDOT was studied, whereas Cs⁺, Na⁺, K⁺, Li⁺, and H⁺ as cations. Notably, with the [Co(C₂B₉H₁₁)₂]⁻ anions, these cations are grouped into two sets, Cs⁺ and H⁺ in one and Na⁺, K⁺, and Li⁺ in the second, according to the stoichiometry of the COPs: 2:1 EDOT/[Co(C₂B₉H₁₁)₂]⁻ for Cs⁺ and H⁺, and 3:1 EDOT/[Co(C₂B₉H₁₁)₂]⁻ for Na⁺, K⁺, and Li⁺. The distinct stoichiometries are manifested in the physicochemical properties of the COPs, namely in the electrochemical response, electronic conductivity, ionic conductivity, and capacitance.     

Cover Picture: Gold Nanoparticles Decorated with Sialic Acid Terminated Bi‐antennary N‐Glycans for the Detection of Influenza Virus at Nanomolar Concentrations (ChemistryOpen 6/2015)

Gold nanoparticles decorated with full‐length sialic acid terminated complex bi‐antennary N‐glycans, synthesized with glycans isolated from egg yolk, were used as a sensor for the detection of both recombinant hemagglutinin (HA) and whole influenza A virus particles of the H1N1 subtype. Nanoparticle aggregation was induced by interaction between the sialic acid termini of the glycans attached to gold and the multivalent sialic acid binding sites of HA. Both dynamic light scattering (DLS) and UV/Vis spectroscopy demonstrated the efficiency of the sensor, which could detect viral HA at nanomolar concentrations and revealed a linear relationship between the extent of nanoparticle aggregation and the concentration of HA. UV/Vis studies also showed that these nanoparticles can selectively detect an influenza A virus strain that preferentially binds sialic acid terminated glycans with α(2→6) linkages over a strain that prefers glycans with terminal α(2→3)‐linked sialic acids.     

Quantum Chemical Insight of the Dimetallic Sulfide Endohedral Fullerene Sc2S@C70: Does It Possess the Conventional D5h Cage?

Like C₆₀, C₇₀ is one of the most representative fullerenes in fullerene science. Even though there are 8149 C₇₀ isomers, only two of them have been found before: the conventional D_5h and an isolated pentagon rule (IPR)‐violating C_2v(7854). Through the use of quantum chemical methods, we report a new unconventional C₇₀ isomer, C₂(7892), which survives in the form of dimetallic sulfide endohedral fullerene Sc₂S@C₇₀. Compared with the IPR‐obeying C₇₀ and the C_2v(7854) fullerene with three pairs of pentagon adjacencies, the C₂(7892) cage violates the isolated pentagon rule and has two pairs of pentagon adjacencies. In Sc₂S@C₂(7892)‐C₇₀, two scandium atoms coordinate with two pentalene motifs, respectively, presenting two equivalent Sc? S bonds. The strong coordination interaction, along with the electron transfer from the Sc₂S cluster to the fullerene cage, results in the stabilization of the non‐IPR endohedral fullerene. The electronic structure of Sc₂S@C₇₀ can be formally described as [Sc₂S]⁴⁺@[C₇₀]^4?; however, a substantial overlap between the metallic orbitals and cage orbitals has also been found. Electrochemical properties and electronic absorption, infrared, and ¹³C NMR spectra of Sc₂S@C₇₀ have been calculated theoretically.     

Cover Feature: Effects of Microhydration on the Mechanisms of Hydrolysis and Cl− Substitution in Reactions of N2O5 and Seawater (ChemPhysChem 5/2023)

The reaction of N₂O₅ at atmospheric interfaces has recently received considerable attention due to its importance in atmospheric chemistry. N₂O₅ reacts preferentially with Cl⁻ to form ClNO₂/NO₃⁻ (Cl⁻ substitution), but can also react with H₂O to form 2HNO₃ (hydrolysis). In this paper, we explore these competing reactions in a theoretical study of the clusters N₂O₅/Cl⁻/nH₂O (n=2–5), resulting in the identification of three reaction motifs. First, we uncovered an S_N2-type Cl⁻ substitution reaction of N₂O₅ that occurs very quickly due to low barriers to reaction. Second, we found a low-lying pathway to hydrolysis via a ClNO₂ intermediate (two-step hydrolysis). Finally, we found a direct hydrolysis pathway where H₂O attacks N₂O₅ (one-step hydrolysis). We find that Cl⁻ substitution is the fastest reaction in every cluster. Between one-step and two-step hydrolysis, we find that one-step hydrolysis barriers are lower, making two-step hydrolysis (via ClNO₂ intermediate) likely only when concentrations of Cl⁻ are high.     

Quantum Entanglement of Parallel-Coupled Double Quantum Dots: a Theoretical Study Using the Hierarchical Equations of Motion Approach?

Quantum dots comprise a type of quantum impurity system. The entanglement and coherence of quantum states are significantly influenced by the strong electron-electron interactions among impurities and their dissipative coupling with the surrounding environment. Competition between many-body effects and transfer couplings plays an important role in determining the entanglement among localized impurity spins. In this work, we employ the hierarchical-equations-of-motion approach to explore the entanglement of a strongly correlated double quantum dots system. The relation between the total system entropy and those of subsystems is also investigated.