Reaction Dynamics in Extreme Environments and Astrochemistry

Ralf I. Kaiser is Professor of Physical Chemistry at the Department of Chemistry and Director of the W.M. Keck Laboratory in Astrochemistry, Department of Chemistry, University of Hawaii at Manoa (USA). He is a current member of the ChemPhysChem Editorial Board.     

Laser-Assisted Synthesis of Non-Equilibrium Nanoalloys

Vincenzo Amendola is Professor of Physical Chemistry at Padova University, where he established and directs the Laser-Assisted Synthesis and Plasmonics (LASP) lab. He obtained a PhD in Materials Science and Engineering in 2008 and the Italian qualification as Full Professor in 2017, after research experience at Massachusetts Institute of Technology and Cambridge University. He is part of the Program Committee of the ANGEL conference series and he is a current member of the ChemPhysChem Editorial Advisory Board.     

Meet the Board of ChemistryOpen: Sheshanath V. Bhosale

Sheshanath V. Bhosale received his PhD from Freie University Berlin (Germany) in supramolecular chemistry under the supervision of Prof. J. H. Fuhrhop in 2004. He then pursued his postdoctoral studies with Prof. S. Matile at University of Geneva (Switzerland) under the auspices of a Roche Foundation Fellowship. This was followed by a stay at Monash University (Australia) for 5 years as an ARC-APD Fellow. He worked at RMIT University, Melbourne (Australia) for 6 years as ARC-Future Fellowship. Currently, Prof. Bhosale is working at the Department of Chemistry, Goa University (India) as a UGC-FRP Professor, His research interests lie in the design and synthesis of π-functional materials, especially small molecules, for sensing, biomaterials, and supramolecular chemistry applications. So far, Prof. Bhosale has produced 185 research articles and his work has been cited more than 4400 times, giving him an h-index of 32. He currently serves as an active Editorial Board member for ChemistryOpen.     

Meet the Board of ChemistryOpen: Thomas Wirth

Thomas Wirth is Professor of organic chemistry at Cardiff University. He received the Werner Prize from the New Swiss Chemical Society in 2000, the Wolfson Research Merit Award from the Royal Society, and the Bader Award from the Royal Society of Chemistry in 2016. He is an elected fellow of The Learned Society of Wales and currently serves as Chair of the Editorial Board for ChemistryOpen.     

Back Cover: Lewis Acid‐Catalyzed Intramolecular [3 + 2] Cross‐Cycloaddition of Donor‐ Acceptor Epoxides with Alkenes for Construction of Oxa‐[n.2.1] Skeletons (Chin. J. Chem. 7/2019)

The back cover picture shows the first LA‐catalyzed [3+2]IMCC of GDA‐epoxides with carbon‐carbon double bonds. This provides an efficient and general strategy for construction of bridged oxa‐[n.2.1] skeletons. A novel SN‐like mechanism through a carbon‐carbon bond cleavage of epoxide ring has been proposed. The colorful fireworks in the picture imply the generation of skeletal diversity from the epoxide‐diene, and express a dedication to the 100th Anniversary of Nankai University as well. More details are discussed in the article by Wang et al. on page 695–699.

     

On the Mechanical Properties of Popgraphene-Based Nanotubes: a Reactive Molecular Dynamics Study

Carbon-based tubular materials have sparked a great interest in future electronics and optoelectronics device applications. In this work, we computationally studied the mechanical properties of nanotubes generated from popgraphene (PopNTs). Popgraphene is a 2D carbon allotrope composed of 5-8-5 rings. We carried out fully atomistic reactive (ReaxFF) molecular dynamics for PopNTs of different chiralities ( and ) and/or diameters and at different temperatures (from 300 up to 1200 K). Results showed that the tubes are thermally stable (at least up to 1200 K). All tubes presented stress/strain curves with a quasi-linear behavior followed by an abrupt drop of stress values. Interestingly, armchair-like PopNTs ( ) can stand a higher strain load before fracturing when contrasted to the zigzag-like ones ( ). Moreover, it was obtained that Young's modulus (Y_Mod) (750–900 GPa) and ultimate strength (σ_US) (120–150 GPa) values are similar to the ones reported for conventional armchair and zigzag carbon nanotubes. Y_Mod values obtained for PopNTs are not significantly temperature-dependent. While the σ_US values for the showed a quasi-linear dependence with the temperature, the exhibited no clear trends.     

Reaction of Pertechnetate in Highly Alkaline Solution: Synthesis and Characterization of the Nitridotrioxotechnetate Ba[TcO3N]

The preparation of novel technetium oxides, their characterization and the general investigation of technetium chemistry are of significant importance, since fundamental research has so far mainly focused on the group homologues. Whereas the structure chemistry of technetium in strongly oxidizing media is dominated by the anion, our recent investigation yielded the new anion. Brown single crystals of Ba[TcO₃N] were obtained under hydrothermal conditions starting from Ba(OH)₂ ⋅ 8H₂O and NH₄[TcO₄] at 200 °C. crystallizes in the monoclinic crystal system with the space group P2₁/n (a=7.2159(4) Å, b=7.8536(5) Å, c=7.4931(4) Å and β=104.279(2)°). The crystal structure of consists of isolated tetrahedra, which are surrounded by Ba²⁺ cations. XANES measurements complement the oxidation state +VII for technetium and Raman spectroscopic experiments on Ba[TcO₃N] single crystals exhibit characteristic Tc−O and Tc−N vibrational modes.     

Mirror Symmetry Breaking and Network Formation in Achiral Polycatenars with Thioether Tail

Mirror symmetry breaking in systems composed of achiral molecules is of importance for the design of functional materials for technological applications as well as for the understanding of the mechanisms of spontaneous emergence of chirality. Herein, we report the design and molecular self-assembly of two series of rod-like achiral polycatenar molecules derived from a π-conjugated 5,5’-diphenyl-2,2’-bithiophene core with a fork-like triple alkoxylated end and a variable single alkylthio chain at the other end. In both series of liquid crystalline materials, differing in the chain length at the trialkoxylated end, helical self-assembly of the π-conjugated rods in networks occurs, leading to wide temperature ranges (>200 K) of bicontinuous cubic network phases, in some cases being stable even around ambient temperatures. The achiral bicontinuous cubic Ia d phase (gyroid) is replaced upon alkylthio chain elongation by a spontaneous mirror symmetry broken bicontinuous cubic phase (I23) and a chiral isotropic liquid phase (Iso₁^[*^]). Further chain elongation results in removing the I23 phase and the re-appearance of the Ia d phase with different pitch lengths. In the second series an additional tetragonal phase separates the two cubic phase types.     

Blended Conjugated Host and Unconjugated Dopant Polymers Towards N-type All-Polymer Conductors and High-ZT Thermoelectrics

N-Type thermoelectrics typically consist of small molecule dopant+polymer host. Only a few polymer dopant+polymer host systems have been reported, and these have lower thermoelectric parameters. N-type polymers with high crystallinity and order are generally used for high-conductivity ( ) organic conductors. Few n-type polymers with only short-range lamellar stacking for high-conductivity materials have been reported. Here, we describe an n-type short-range lamellar-stacked all-polymer thermoelectric system with highest of 78 S⁻¹, power factor (PF) of 163 μW m⁻¹ K⁻², and maximum Figure of merit (ZT) of 0.53 at room temperature with a dopant/host ratio of 75 wt%. The minor effect of polymer dopant on the molecular arrangement of conjugated polymer PDPIN at high ratios, high doping capability, high Seebeck coefficient (S) absolute values relative to , and atypical decreased thermal conductivity ( ) with increased doping ratio contribute to the promising performance.     

Substitutional carbon defects in silicon: A quantum mechanical characterization through the infrared and Raman spectra

The infrared (IR) and Raman spectra of eight substitutional carbon defects in silicon are computed at the quantum mechanical level by using a periodic supercell approach based on hybrid functionals, an all electron Gaussian type basis set and the CRYSTAL code. The single substitutional C _s case and its combination with a vacancy (C _sV and C _sSiV) are considered first. The progressive saturation of the four bonds of a Si atom with C is then examined. The last set of defects consists of a chain of adjacent carbon atoms C, with i = 1–3. The simple substitutional case, C _s, is the common first member of the three sets. All these defects show important, very characteristic features in their IR spectrum. One or two C related peaks dominate the spectra: at 596 cm⁻¹ for C _s (and C _sSiV, the second neighbor vacancy is not shifting the C _s peak), at 705 and 716 cm⁻¹ for C _sV, at 537 cm⁻¹ for C and C (with additional peaks at 522, 655 and 689 for the latter only), at 607 and 624 cm⁻¹, 601 and 643 cm⁻¹, and 629 cm⁻¹ for SiC, SiC, and SiC, respectively. Comparison with experiment allows to attribute many observed peaks to one of the C substitutional defects. Observed peaks above 720 cm⁻¹ must be attributed to interstitial C or more complicated defects.     

Cover Picture: A Stepwise Annulation for the Transformation of Cyclic Ketones to Fused 6 and 7‐Membered Cyclic Enimines and Enones (Chin. J. Chem. 4/2019)

The cover picture shows a typical building within the Campus of Xiamen University displaying Chen Jiageng (Tan Kah Kee)'s style. Just like many beautiful buildings designed and constructed by human, Nature “designs and constructs” a huge number of useful molecules with fascinating structures called natural products. Many natural products possess a fused six or seven‐membered carbocyclic unity. On page 315–322, the Huang's group disclosed a three‐step “[2+n]” annulation method for the construction of fused six and seven‐membered carbocyclic enimines and enones. The method starts from simple cyclic ketones and terminal olefinic amides, and relies on both the Suzuki coupling reaction and the olefin‐amide based Friedel‐Crafts type acylating reaction, a method developed by Huang and coworkers.

     

Azobenzene Isomerization-Induced Photomodulation of Electronic Properties of N-Heterocyclic Carbenes

Azobenzene-based protonated N-heterocyclic carbenes (NHCs), N,N’-bis(azobenzene)imidazolium chlorides (IAz-X⋅HCl; X=OMe, Br, H) were successfully synthesized and switching abilities of the attached azobenzene units along with the concomitant photoinduced generation of geometric isomers were studied. Upon irradiation with 365 nm UV light, a p-methoxy-azobenzene derivative get transformed from all-trans isomer to nearly all-cis isomer at the photostationary state. The extent of photomodulation of electronic properties in the NHC ring of the p-methoxy-azobenzene derivative is determined through the Tolman Electronic Parameter (TEP). Iridium complex, [(IAz-OMe)IrCl(CO)₂] was synthesized and infrared spectra were recorded in dichloromethane solution as film in NaCl crystals and by drop-casting in an ATR crystal. Comparison in averaged carbonyl stretching frequency between all-trans isomer ( ) and all-cis isomer ( ) indicates a significant decrement of Δ^tt–cc _av=2.7 cm⁻¹ (film) and 3.8 cm⁻¹ (ATR). Therefore, moderate to excellent enhancement of electron density (Δ^tt–cc TEP=2.3 cm⁻¹ [film] and 3.2 cm⁻¹ [ATR]) at the C-2 position of the NHC is achieved through trans→cis isomerization of the remotely placed azobenzene units. This fine phototuning of electron-donating ability at the catalytic center would pave the way to control NHC/NHC-metal catalyzed organic transformations through external stimuli.     

Front Cover: Critical Assessment of pH-Dependent Lipophilicity Profiles of Small Molecules: Which One Should We Use and In Which Cases? (ChemPhysChem 24/2023)

Lipophilicity is a physicochemical property with wide relevance in drug design, computational biology, food, environmental and medicinal chemistry. Lipophilicity is commonly expressed as the partition coefficient for neutral molecules, whereas for molecules with ionizable groups, the distribution coefficient (D) at a given pH is used. The logD_pH is usually predicted using a pH correction over the logP_N using the pK_a of ionizable molecules, while often ignoring the apparent ion pair partitioning . In this work, we studied the impact of on the prediction of both the experimental lipophilicity of small molecules and experimental lipophilicity-based applications and metrics such as lipophilic efficiency (LipE), distribution of spiked drugs in milk products, and pH-dependent partition of water contaminants in synthetic passive samples such as silicones. Our findings show that better predictions are obtained by considering the apparent ion pair partitioning. In this context, we developed machine learning algorithms to determine the cases that should be considered. The results indicate that small, rigid, and unsaturated molecules with logP_N close to zero, which present a significant proportion of ionic species in the aqueous phase, were better modeled using the apparent ion pair partitioning . Finally, our findings can serve as guidance to the scientific community working in early-stage drug design, food, and environmental chemistry.     

Proton Relaxometry of Long-Lived Spin Order

A study of long-lived spin order in chlorothiophene carboxylates at both high and low magnetic fields is presented. Careful sample preparation (removal of dissolved oxygen in solution, chelating of paramagnetic impurities, reduction of convection) allows one to obtain very long-lived singlet order of the two coupled protons in chlorothiophene derivatives, having lifetimes of about 130 s in D₂O and 240 s in deuterated methanol, which are much longer than the T₁-relaxation times (18 and 30 s, respectively, at a field =9.4 T). In protonated solvents the relaxation times become shorter, but the lifetime is still substantially longer than . In addition, long-lived coherences are shown to have lifetimes as long as 30 s. Thiophene derivatives can be used as molecular tags to study slow transport, slow dynamics and slow chemical processes, as has been shown in recent years.     

Extremal Wiener and Kirchhoff indices of globular caterpillars

The Wiener and Kirchhoff indices of a graph G are two of the most important topological indices in mathematical chemistry. A graph G is called to be a globular caterpillar if G is obtained from a complete graph K _s with vertex set {v₁,v₂,…, v _s} by attaching n _i pendent edges to each vertex v _i of K _s for some positive integers s and n₁,n₂,…,n _s, denoted by . Let be the set of globular caterpillars with n vertices (). In this article, we characterize the globular caterpillars with the minimal and maximal Wiener and Kirchhoff indices among , respectively.     

The Reaction of Sulfur Dioxide Radical Cation with Hydrogen and its Relevance in Solar Geoengineering Models

SO₂ has been proposed in solar geoengineering as a precursor of H₂SO₄ aerosol, a cooling agent active in the stratosphere to contrast climate change. Atmospheric ionization sources can ionize SO₂ into excited states of , which quickly reacts with trace gases in the stratosphere. In this work we explore the reaction of with excited by tunable synchrotron radiation, leading to ( ), where H contributes to O₃ depletion and OH formation. Density Functional Theory and Variational Transition State Theory have been used to investigate the dynamics of the title barrierless and exothermic reaction. The present results suggest that solar geoengineering models should test the reactivity of with major trace gases in the stratosphere, such as H₂ since this is a relevant channel for the OH formation during the nighttime when there is not OH production by sunlight. OH oxides SO₂, triggering the chemical reactions leading to H₂SO₄ aerosol.     

Cover: Journal of the Chinese Chemical Society 3/2023

Professor Sheng-Hsien Lin passed away on November 15, 2021 at home in Houston, Texas, under the warm care of his family (he was 84 years old). He was a pioneering theoretical chemist who applied quantum theory to understand many of the central problems in photochemistry, photophysics, and nonlinear spectroscopy at the molecular level. With the contributions from those who have worked and learnt from Prof. Lin, we are honored to present this special issue of The Journal of Chinese Chemical Society to commemorate Prof. Lin's scientific contributions and his efforts to develop the theoretical chemistry community in Taiwan. The 8 reviews and 45 original research articles with authors from 8 different countries spanning a breadth of research topics speak loudly about the impact Prof. Lin made during his luminous academic career. It is our hope that we all will remember Prof. Lin as an outstanding scholar with a strong mind to focus to the exclusion of all else until a scientific problem is solved and an educator with a warmful smile.

     

A Multiconformational Transition State Theory Approach to OH Tropospheric Degradation of Fluorotelomer Aldehydes

Experimental work on the OH-initiated oxidation reactions of fluorotelomer aldehydes (FTALs) strongly suggests that the respective rate coefficients do not depend on the size of the C_xF_2x+1 fluoroalkyl chain. FTALs hence represent a challenging test to our multiconformer transition state theory (MC-TST) protocol based on constrained transition state randomization (CTSR), since the calculated rate coefficients should not show significant variations with increasing values of . In this work we apply the MC-TST/CTSR protocol to the cases and calculate both rate coefficients at 298.15 K with a value of cm³ molecule⁻¹ s⁻¹, practically coincident with the recommended experimental value of k_exp= cm³ molecule⁻¹ s⁻¹. We also show that the use of tunneling corrections based on improved semiclassical TST is critical in obtaining Arrhenius-Kooij curves with a correct behavior at lower temperatures.     

Nanoscale Structure in Short-Chain Ionic Liquids

The temperature (T) and cationic chain length (n) evolution of the nanoscale structure of the sub-layering-threshold members of a model family of room temperature ionic liquids (RTILs) is investigated by x-ray scattering. The measured curves are computer-resolved into individual Teubner-Strey-like lineshapes. The polar-apolar layering is found to start at . Opposite n-trends are found at for the spacings and correlation lengths associated with the diffraction patterns’ two main peaks, and assigned to a shift of balance between the two main interactions, Coulomb and van der Waals, and to increasing packing constraints due to the addition of methylenes. The spacings’ thermal expansion coefficients are found to deviate from the macroscopically-measured values, and to anomalously decrease with increasing temperature. Finally, the reduced temperature scale, , ( melting temperature), is demonstrated to render the observed trends significantly more systematic than those on a conventional T scale.     

The Apparently Unreactive Substrate Facilitates the Electron Transfer for Dioxygen Activation in Rieske Dioxygenases

Rieske dioxygenases belong to the non-heme iron family of oxygenases and catalyze important cis-dihydroxylation as well as O-/N-dealkylation and oxidative cyclization reactions for a wide range of substrates. The lack of substrate coordination at the non-heme ferrous iron center, however, makes it particularly challenging to delineate the role of the substrate for productive activation. Here, we studied the role of the substrate in the key elementary reaction leading to activation from a theoretical perspective by systematically considering (i) the 6-coordinate to 5-coordinate conversion of the non-heme Fe^II upon abstraction of a water ligand, (ii) binding of , and (iii) transfer of an electron from the Rieske cluster. We systematically evaluated the spin-state-dependent reaction energies and structural effects at the active site for all combinations of the three elementary processes in the presence and absence of substrate using naphthalene dioxygenase as a prototypical Rieske dioxygenase. We find that reaction energies for the generation of a coordination vacancy at the non-heme Fe center through thermoneutral H₂O reorientation and exothermic binding prior to Rieske cluster oxidation are largely insensitive to the presence of naphthalene and do not lead to formation of any of the known reactive Fe-oxygen species. By contrast, the role of the substrate becomes evident after Rieske cluster oxidation and exclusively for the 6-coordinate non-heme Fe sites in that the additional electron is found at the substrate instead of at the iron and oxygen atoms. Our results imply an allosteric control of the substrate on Rieske dioxygenase reactivity to happen prior to changes at the non-heme Fe in agreement with a strategy that avoids unproductive activation.