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The indole ring of tryptophan can form NH/π hydrogen bonds, acting both as a hydrogen donor at the NH group in the pyrrole subring and as a hydrogen acceptor at the benzene subring. In the structural core of the trimeric stable protein Pholiota squarrosalectin (PhoSL), three indoles are symmetrically arranged and form NH/π hydrogen bonds among each other. Here, we conducted quantum chemical calculations on this indole triad by using various methods and basis sets. The analyses revealed cooperativity in triad formation, with the many-body effect contributing approximately −2 kcal mol–1, which significantly stabilizes this protein. Symmetry-adapted perturbation theory ascribed this effect to the induced polarization. The electrostatic potential and atomic charges indeed revealed a charge redistribution through the NH/π hydrogen bond, which was favorable for triad formation.

Here, we systematically investigated the effects of the thiophene-fused isomer and the end-cap substitution on high-layered crystallinity, film formability, and field-effect transistor characteristics in π-extended and alkylated organic semiconductors (OSCs). We developed four kinds of unsymmetric rod-like OSCs based on syn-/anti-isomers of benzothieno[6,5-b]-/benzothieno[5,6-b]-benzothieno[3,2-b]thiophene (BTBTT) with phenyl/alkyl substitutions with different alkyl chain lengths: synCnand antiCn(n= 6, 10). The layered molecular packing motifs of the compounds are distinct from the thiophene orientation of isomeric π-cores but are unaffected by the alkyl chain length. The synCnforms a bilayer-typelayered herringbone (b-LHB) packing composed of head-to-headarrangement of unidirectionally aligned molecular layers showing high-layered crystallinity and high carrier mobility over 10 cm2V–1s–1. By contrast, the antiCnforms an antiparallel alkyl-interdigitatedherringbone (aai-HB) structure in which the respective π-core layer is composed of alternating antiparallel alignment of π-cores and the alkyl chains are interdigitated with each other between the adjacent π-core layers. The latter shows relatively poor crystalline-film formability and moderate carrier mobility. Dispersion-corrected density functional theory calculations of intermolecular interaction energy reveal that the overall shape of the rigid π-core components is crucial for achieving unidirectionally aligned and closely packed 2D π-core layers and that the flexible end-cap substituents strengthen and balance the layered crystallinity. The findings will be crucial for designing and developing the highly layered crystalline and high-performance OSCs.

The parameters of the polarizable force field used for molecular dynamics simulations of Li diffusion in high-concentration lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]) sulfone (sulfolane, dimethylsulfone, ethylmethylsulfone, and ethyl-i-propylsulfone) solutions were refined. The densities of the solutions obtained by molecular dynamics simulations reproduced well the experimental values. The calculated concentration, temperature, and solvent dependencies of self-diffusion coefficients of ions and solvents in the mixtures well reproduce the experimentally observed dependencies. Ab initiocalculations show that the intermolecular interactions between Li ions and four sulfones are not largely different. Conformational analyses show that sulfolane can change the conformation more easily owing to lower barrier height for pseudorotation compared to the rotational barrier heights of diethylsulfone and ethylmethylsulfone. Molecular dynamics simulations indicate that the easy conformation change of solvent affects the rotational relaxation of the solvent and the diffusion of Li ion in the mixture. The easy conformation change of sulfolane is one of the causes of faster diffusion of Li ion in the mixture of Li[TFSA] and sulfolane compared to the mixtures of smaller dimethylsulfone and ethylmethylsulfone.

Here, we report the use of molecular dynamics simulations with a polarizable force field to investigate Li-ion dynamics in sulfolane (SL)-based electrolytes. In SL-based highly concentrated electrolytes (HCEs) (e.g., SL/Li = 2:1), Li displays faster translational motion than other components, which should be related to the structural and dynamical properties of SL. In HCEs, a transient conduction network that penetrated the simulation system was always observed. Rapid (<1 ns) Li-ion hopping between adjacent coordination sites was observed throughout the network. Additionally, SLs rotated in the same timeframe without disrupting the conduction network. This rotation is believed to promote the hopping diffusion in the network. This was followed by a rotational relaxation of the SL dipole axis around the non-polar cyclohydrocarbon segment of SL (∼3.3 ns), which involves a reorganization of the network structure and an enhancement of the translational motion of the coordinating Li ions. The observed lifetime of Li–SL coordination was longer (>11 ns). Hence, it was concluded that the faster Li translational motion was obtained due to the faster rotational relaxation time of SL rather than the lifetime of Li–SL binding. The faster rotation of SL is related to its amphiphilic molecular structure with compact non-polar segments. Transport properties, such as the Onsager transport coefficients, ionic conductivity, and transference number under anion-blocking conditions, were also analyzed to characterize the features of the SL-based electrolyte.

Two-dimensional (2D) structures of Cu(II)-coordinated curcumin derivatives were revealed by scanning tunneling microscopy at the solid/liquid interface. The Cu(II)-coordination resulted in the formation of dimerized structure, which was different from the pristine curcumin derivatives. The appearance and disappearance of 2D structure modulation due to odd-even effect were dependent on the number of alkyl chain substituents. In addition, the appearance of the odd-even was found to be maintained before and after the Cu(II) coordination.Scanning tunneling microscopy observations revealed the two-dimensional (2D) structures of Cu(II)-coordinated curcumin derivatives at a solid/liquid interface. A dimerized structure was formed due to Cu(II) coordination, and the 2D structures of metallated curcumin derivatives were different from the pristine ones. Appearance of odd-even effect was dependent on the alkyl chain substituents, and was maintained before and after the Cu(II) coordination.

The Li+conduction mechanism in highly concentrated ethylene carbonate (EC) solution of lithium bis(fluorosulfonyl)amide (LiFSA) was studied based on the measurements of thermal properties, density, viscosity, ionic conductivity, self-diffusion coefficients, Raman spectra, and proton nuclear magnetic resonance relaxation time. The compositions of EC and LiFSA were varied from dilute to concentrated states ([EC]/[LiFSA] = 9.2–0.80). For compositions of [EC]/[LiFSA] ≤ 1.5, the free solvents decrease, and contact ion pairs and aggregates become dominant, causing a significant change in the transport properties. Faster diffusion of Li+compared with solvent (Li+hopping conduction) was observed when the molar composition of [EC]/[LiFSA] ≤ 1.0 as in the case of sulfolane.

Electrochemical separation methods utilizing quinones as CO2capture agents have gained considerable interest owing to their low-energy requirements for near-isothermal CO2separation. However, the low solubility of quinones in nonaqueous solvents limits their total CO2carrying capacity in the system. In this study, we synthesized an ionically modified anthraquinone, 1-butyl-3-((2′-anthraquinoyl)methyl)imidazolium bis(trifluoromethanesulfonyl)amide ([BAQMIM][TFSA]), which exhibited a 360-fold increase in solubility compared to pristine anthraquinone in dimethyl sulfoxide. The synthesized ionic quinone derivative can also serve as a supporting electrolyte, offering both high ionic conductivity (12.2 mS cm–1) and quinone concentration (200 mM). Constant-potential electrolysis demonstrated a high CO2carrying capacity in a highly concentrated [BAQMIM][TFSA] solution. The predominantly reversible CO2capture and subsequent release processes were successfully monitored through in situspectroscopic analysis and density functional theory calculations. These findings provide a promising approach toward large-scale volumetric CO2separation through the functionalization of quinones.

Lithium–sulfur (Li–S) batteries can theoretically deliver high energy densities exceeding 2500 Wh kg–1. However, high sulfur loading and lean electrolyte conditions are two major requirements to enhance the actual energy density of the Li–S batteries. Herein, the use of carbon-dispersed highly concentrated electrolyte (HCE) gels with sparingly solvating characteristics as sulfur hosts in Li–S batteries is proposed as a unique approach to construct continuous electron-transport and ion-conduction paths in sulfur cathodes as well as achieve high energy density under lean-electrolyte conditions. The sol–gel behavior of carbon-dispersed sulfolane-based HCEs was investigated using phase diagrams. The sol-to-gel transition was mainly dependent on the amount of the carbonaceous material and the Li salt content. The gelation was caused by the carbonaceous-material-induced formation of an integrated network. Density functional theory (DFT) calculations revealed that the strong cation−π interactions between Li+and the induced dipole of graphitic carbon were responsible for facilitating the dispersion of the carbonaceous material into the HCEs, thereby permitting gel formation at high Li-salt concentrations. The as-prepared carbon-dispersed sulfolane-based composite gels were employed as efficient sulfur hosts in Li–S batteries. The use of gel-type sulfur hosts eliminates the requirement for excess electrolytes and thus facilitates the practical realization of Li–S batteries under lean-electrolyte conditions. A Li–S pouch cell that achieved a high cell-energy density (up to 253 Wh kg–1) at a high sulfur loading (4.1 mg cm–2) and low electrolyte/sulfur ratio (4.2 μL mg–1) was developed. Furthermore, a Li–S polymer battery was fabricated by combining the composite gel cathode and a polymer gel electrolyte.

Neutron diffraction measurements on 34S/natS isotopically substituted (natS: natural abundance) 6.9 mol% *S8solutions in CS2(natural abundance for both S and C atoms) have successfully been carried out in order to examine the possibility of the 34S/natS isotopic difference method neutron diffraction for liquid samples and to obtain novel structural insights into both intramolecular structure and the solvation structure of S8molecule in concentrated CS2solutions. Intramolecular structural parameters within the S8molecule as well as the intermolecular parameters concerning the nearest neighbor *S⋯CS2interaction have been determined through the least squares fitting analysis of the observed difference interference function, ΔS(Q), which has been derived from the numerical difference between scattering cross sections observed for *S8with 34S-enriched and natural S solutions in natural CS2. MD simulations were performed with newly developed force field parameters for sulfur atoms in S8molecule. The results derived by the simulations adequately agree with the neutron experiments.Neutron diffraction with 34S/natS isotopic substitution was firstly applied for 6.9 mol% S8-CS2solutions. Structural parameters within the S8molecule and those for intermolecular nearest neighbor *S…CS2interaction have been determined from the observed difference interference function, ΔS(Q). The results agree well with those from MD simulations with newly developed force field parameters for sulfur atoms in S8.

Graphical abstract:

We developed a nitroxyl-catalyzed bromoesterification of alkenes with bromo reagents, which includes a six-membered ring bromolactonization of alkenyl carboxylic acids catalyzed by AZADO as the nitroxyl radical catalyst, and an intermolecular bromoesterification of alkenes with carboxylic acids using NMO as the N-oxide catalyst. We also accomplished a remote diastereoselective bromohydroxylation via an AZADO-catalyzed six-membered ring bromolactonization and a subsequent ring cleavage reaction with alkylamines to furnish ε-bromo-δ-hydroxy amides with high diastereoselectivity.

The phase behavior, Na+coordination structures, and transport and electrochemical properties of binary mixtures of NaN(SO2F)2(NaFSA) and sulfolane (SL) solvent were investigated. The NaFSA and SL form stable solvates at molar ratios [NaFSA]/[SL] = 1/3 and 1/0.5, and there is a crystallinity gap in the range 1/1.6 ≤ [NaFSA]/[SL] ≤ 1/0.8. In the crystals of both NaFSA–(SL)3and NaFSA–(SL)0.5, the solvent-bridged Na+–SL–Na+and anion-bridged Na+–FSA–Na+structures are formed. In the crystallinity gap, the mixtures remain liquid at room temperature and can be regarded as molten SL solvates of NaFSA. The Raman spectra of the molten solvates suggest that the solvent- and anion-bridged structures are partially maintained even in the liquid. However, Na+ions exchange the ligands (solvent and anion) dynamically in the liquids. This significantly affects the Na+ion transport in the liquids under an anion-blocking condition. The Na+ion transference numbers (tNa+) of molten solvates were estimated using symmetric Na/Na cells, and a molten solvate of [NaFSA]/[SL] = 1/1 exhibited a high tNa+of 0.8. Charge and discharge tests of a Na/Na0.44MnO2battery were performed with the molten solvate as the electrolyte. The rate capability of the battery was found to be significantly affected by tNa+in the electrolyte.

Controlling chiral crystallization, which remains one of the biggest challenges in crystal engineering, brings enormous advantages in material sciences, especially chiral industries. This work demonstrates that chiral crystallization is controllable by designing structures of 2-fold helices, which affect the manner of interhelical interactions. Here we show an example of chiral crystallization by using achiral primary ammonium carboxylates having simple chemical structures: naphthyl and tert-butyl groups. Their crystal structures were precisely investigated by focusing on hydrogen-bonded 2-fold helices along with theoretical calculations. Consequently, a key role of interhelical CH/π contacts in chiral crystallization was found to be not attracting but arranging chiral 2-fold helices. More importantly, a clear difference was found in densities of 2-fold helices and their stacking between chiral and achiral crystals.

To elucidate the properties of binary system of room temperature ionic liquids (RTILs), we measured and compared the temperature dependence of densities, viscosities, and refractive indices of seven binary RTILs as well as neat RTILs. The observed densities, viscosities, and refractive indices of the binary systems showed intermediate properties between those of two starting RTILs. The values observed for the binary RTILs were only deviated from the values estimated based on the data of neat RTILs (±0.5%), and this deviation depended on both the combination of RTILs and the structures of the cation/anion. These results indicate that the properties of RTILs can be easily tuned by mixing RTILs depending on their applications.

We demonstrate that Li+hopping conduction, which cannot be explained by conventional models i.e., Onsager’s theory and Stokes’ law, emerges in highly concentrated liquid electrolytes composed of LiBF4and sulfolane (SL). Self-diffusion coefficients of Li+(DLi), BF4–(DBF4), and SL (DSL) were measured with pulsed-field gradient NMR. In the concentrated electrolytes with molar ratios of SL/LiBF4≤ 3, the ratios DSL/DLiand DBF4/DLibecome lower than 1, suggesting faster diffusion of Li+than SL and BF4–, and thus the evolution of Li+hopping conduction. X-ray crystallographic analysis of the LiBF4/SL (1:1) solvate revealed that the two oxygen atoms of the sulfone group are involved in the bridging coordination of two different Li+ions. In addition, the BF4–anion also participates in the bridging coordination of Li+. The Raman spectra of the highly concentrated LiBF4–SL solution suggested that Li+ions are bridged by SL and BF4–even in the liquid state. Moreover, detailed investigation along with molecular dynamics simulations suggests that Li+exchanges ligands (SL and BF4–) dynamically in the highly concentrated electrolytes, and Li+hops from one coordination site to another. The spatial proximity of coordination sites, along with the possible domain structure, is assumed to enable Li+hopping conduction. Finally, we demonstrate that Li+hopping suppresses concentration polarization in Li batteries, leading to increased limiting current density and improved rate capability compared to the conventional concentration electrolyte. Identification and rationalization of Li+ion hopping in concentrated SL electrolytes is expected to trigger a new paradigm of understanding for such unconventional electrolyte systems.

The physicochemical and electrochemical properties of an equimolar complex of pentaglyme (G5) and sodium bis(fluorosulfonyl)amide (NaFSA), [Na(G5)][FSA], mixed with a hydrofluoroether (HFE) were investigated. Ab initiocalculations and Raman spectroscopy showed that the coordination structure of [Na(G5)][FSA] was similar to that of [Na(G5)][TFSA] (TFSA: bis(trifluoromethanesulfonyl)amide). The ligand G5 remained coordinated to Na+and was not liberated from the cationic [Na(G5)]+complex even in the presence of HFE. The charge transport property was greater in [Na(G5)][FSA]/HFE than in [Na(G5)][TFSA]/HFE. A prominent difference was found in the Na metal deposition/dissolution behavior. Highly reversible Na deposition/dissolution with a Coulombic efficiency (95%) could be achieved in [Na(G5)][FSA]/HFE; however, the reversibility in [Na(G5)][TFSA]/HFE was very low. X-ray photoelectron spectroscopy (XPS) of the deposited Na metal in each electrolyte revealed that a thin and compact layer of electrolyte decomposition products was formed on the Na deposits in [Na(G5)][FSA]/HFE. The FSA-derived thin layer can effectively inhibit the further decomposition of the electrolyte. By contrast, a thick electrolyte decomposition product found for [Na(G5)][TFSA]/HFE suggested continuous decomposition of the electrolyte during Na deposition-dissolution. Highly stable charge and discharge of a hard carbon (HC) electrode was accomplished in [Na(G5)][FSA]/HFE, with high Coulombic efficiency over 99.9% and negligible capacity decrease over 300 cycles. Electrochemical impedance measurements of a symmetrical cell for Na, HC, and Na0.44MnO2electrodes with the above electrolytes verified that a stable electrode | electrolyte interface was formed on the HC and Na0.44MnO2electrodes in [Na(G5)][FSA]/HFE.

The physicochemical properties and electrochemical behavior of 1-butyl-3-methylimidazolium aryltrifluoroborate ([C4mim][ArBF3]) with various substituents, e.g., methoxy, fluoro, trifluoromethyl, and cyano groups, introduced on the phenyl moiety on the anion are examined. Several position isomers of the [ArBF3]−anion are also prepared to provide further insight into the effect of the position. The equivalent conductivity and the electrochemical stability for some [C4mim][ArBF3] room-temperature ionic liquids (RTILs) is qualitatively discussed from the results of quantum chemical calculations of the cation–anion interaction and the HOMO energy level of the anion. Interestingly, [C4mim][ArBF3] RTILs with an electron-withdrawing group on the phenyl moiety electrochemically form an ion-selective membrane on a Pt electrode, and only neutral and cationic species can pass through the membrane.

To investigate physicochemical relationships between ionic radii, valence number and cationic metal species in electrolyte solutions, propylene carbonate with Li[N(SO2CF3)2], Na[N(SO2CF3)2], Mg[N(SO2CF3)2]2 and Ca[N(SO2CF3)2]2 were prepared. The temperature dependence of density, viscosity, ionic conductivity (AC impedance method) and self-diffusion coefficient (pulsed-gradient spin-echo nuclear magnetic resonance) was measured. The effects of cationic radii and cation valence number on the fluidity and transport properites (conductivity and self-diffusion coefficient) were analyzed.

Localized high-concentration electrolytes (LHCEs), which are mixtures of highly concentrated electrolytes (HCEs) and non-coordinating diluents, have attracted significant interest as promising liquid electrolytes for next-generation Li secondary batteries, owing to their various beneficial properties both in the bulk and at the electrode/electrolyte interface. We previously reported that the large Li+-ion transference number in sulfolane (SL)-based HCEs, attributed to the unique exchange/hopping-like Li+-ion conduction, decreased upon dilution with the non-coordinating hydrofluoroether (HFE) despite the retention of the local Li+-ion coordination structure. Therefore, in this study, we investigated the effects of HFE dilution on the Li+transference number and the solution structure of SL-based LHCEs via the analysis of dynamic ion correlations and molecular dynamics simulations. The addition of HFE caused nano-segregation in the SL-based LHCEs to afford polar and nonpolar domains and fragmentation of the polar ion-conducting pathway into smaller clusters with increasing HFE content. Analysis of the dynamic ion correlations revealed that the anti-correlated Li+–Li+motions were more pronounced upon HFE addition, suggesting that the Li+exchange/hopping conduction is obstructed by the non-ion-conducting HFE-rich domains. Thus, the HFE addition affects the entire solution structure and ion transport without significantly affecting the local Li+-ion coordination structure. Further studies on ion transport in LHCEs would help obtain a design principle for liquid electrolytes with high ionic conductivity and large Li+-ion transference numbers.

Single-ion conducting liquid electrolytes are key to achieving rapid charge/discharge in Li secondary batteries. The Li+transference (or transport) numbers are the defining properties of such electrolytes and have been discussed in the framework of concentrated solution theories. However, the connection between macroscopic transference and microscopic ion dynamics remains unclear. Molecular dynamics simulations were performed to obtain direct information regarding the microscopic behaviors in highly concentrated electrolytes, and the relationships between these behaviors and the transference number were determined under anion-blocking conditions. Various solvents with different donor numbers (DNs) were used along with a Li salt of the weakly Lewis basic bis(fluorosulfonyl)amide anion for electrolyte preparation. Favorable ordered Li+structuring and a continuous Li+conduction pathway were observed for the fluoroethylene carbonate-based electrolyte due to its low DN. The properties were less pronounced at higher DNs, e.g., for the dimethyl sulfoxide-based electrolyte. The τLi–solventlife/τdipolerelaxratio was introduced as a factor for ion dynamics, and the two mechanisms of ion transport were considered an exchange mechanism (τLi–solventlife/τdipolerelax< 1) and a vehicle mechanism (translational motion of solvated Li+) (τLi–solventlife/τdipolerelax≥ 1). Vehicle-type transport was dominant with high DNs, while exchangeable transport was preferable at lower DNs. These findings should aid the further selection of solvents and Li salts to prepare single-ion conducting electrolytes.

Physicochemical properties and battery performance of [Na(glyme)][TFSA] complexes (TFSA: bis(trifluoromethanesulfonyl)amide) dissolved in a hydrofluoroether (HFE) were investigated. Glyme (tetraglyme (G4) or pentaglyme (G5)) coordinates to Na+to form a 1:1 complex [Na(G4 or G5)]+cation. Raman spectroscopy revealed that the complex structure of [Na(glyme)]+is maintained in the HFE solution, and free (uncoordinated) glymes are not liberated on adding HFE. HFE molecules are scarcely involved in the first solvation shell of Na+because of their low electron-pair-donating ability. Raman spectra of the [TFSA]−anion suggests that the attractive interaction between the complex [Na(glyme)]+cation and [TFSA]−anion is enhanced on adding HFE. The population of contact ion-pair (CIP) and/or aggregate (AGG) is smaller for the G5 system than for the G4 one, and the [Na(G5)][TFSA]/HFE has higher ionic conductivity. The self-diffusion coefficients of the [Na(glyme)]+complex and [TFSA]−were measured by pulsed field gradient (PFG) NMR, and the dissociativity of [Na(glyme)][TFSA] was assessed. The dissociativity of the G5 system is greater than that of the G4 one, and the dissociativity can be correlated with the attractive interaction between [Na(glyme)]+and [TFSA]−, as evaluated by ab initio calculations. The dissociativity of the complexes gave significant effects on the battery performance.

An equimolar mixture of lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]) and either triglyme (G3) or tetraglyme (G4) yielded stable molten complexes: [Li(G3)][TFSA] and [Li(G4)][TFSA]. These are known as solvate ionic liquids (SILs). Glyme-based SILs have thermal and electrochemical properties favorable for use as lithium-conducting electrolytes in lithium batteries. However, their intrinsically high viscosities and low ionic conductivities prevent practical application. Therefore, we diluted SILs with molecular solvents in order to enhance their ionic conductivities. To determine the stabilities of the complex cations in diluted SILs, their conductivity and viscosity, the self-diffusion coefficients, and Raman spectra were measured. [Li(G3)]+and [Li(G4)]+were stable in nonpolar solvents, that is, toluene, diethyl carbonate, and a hydrofluoroether (HFE); however, ligand exchange took place between glyme and solvent when polar solvents, that is, water and propylene carbonate, were used. In acetonitrile (AN) mixed solvent complex cations [Li(G3)(AN)]+and [Li(G4)(AN)]+were formed. [Li(G4)][TFSA] was more conductive than [Li(G3)][TFSA] when diluted with nonpolar solvents due to the greater ionic dissociativity in [Li(G4)][TFSA] mixtures. In view of the stability of the Li–glyme complex cations, the enhanced ionic conductivities, and the intrinsic electrochemical stabilities of the diluting solvents, [Li(G4)][TFSA] diluted by toluene or HFE, can be a candidate for an alternative battery electrolyte.

Phase behavior of binary mixtures of tetraglyme (G4) and Mg[TFSA]2(TFSA: bis(trifluoromethanesulfonyl)amide) was investigated. In a 1:1 molar ratio, G4 and Mg[TFSA]2formed a stable complex with a melting point of 137 °C. X-ray crystallography of a single crystal of the complex grown from a G4-Mg[TFSA]2binary mixture revealed that the G4 molecule wraps around Mg2+to form a complex [Mg(G4)]2+cation, and the two [TFSA]−anions also participate in the Mg2+coordination in the crystal. The thermal stability of [Mg(G4)][TFSA]2was examined by thermogravimetry, and it was found that the complex is stable up to 250 °C. Above 250 °C, desolvation of the Mg2+ion takes place and G4 evaporates. On the other hand, the weight loss starts at around 140 °C in solutions containing excess G4 (n> 1 in Mg[TFSA]2:G4 = 1:n) due to the evaporation of free (uncoordinated) G4. The suppression of G4 volatility in the [Mg(G4)][TFSA]2complex is attributed to strong electrostatic and induction interactions between divalent Mg2+and G4. In addition, complexation of G4 with Mg2+is effective in enhancing the oxidative stability of G4. Linear sweep voltammetry revealed that the oxidative decomposition of [Mg(G4)][TFSA]2occurs at electrode potentials >5 V vs Li/Li+, while the oxidation of uncoordinated G4 occurs at around 4.0 V. This oxidative stability enhancement occurs because the HOMO energy level of G4 is reduced by complexation with Mg2+, which is supported by the ab initiocalculations.

Various lengths of alkyl chains were introduced to the basic skeleton of isobutenyl ether compounds via ester bond (D1-OCn), and the 2D structures were investigated by using scanning tunneling microscopy at a solid/liquid interface. In the D1-OCn, two naphthalene units with ester-linked alkyl chains were connected with the isobutenyl group. The D1-OCnpossessing C18–21 alkyl chains displayed alternate changes in the 2D structures, in which the alkyl chains were oriented in the same direction to form an interdigitation, whereas those with C15–17 chains showed the same dumbbell-shaped structures, suggesting that there is a specific alkyl chain length range exhibiting the odd–even effect. After the thermal reaction of tandem Claisen rearrangement (TCR), ether functions in the D1-OCnwere converted to hydroxy groups accompanied by a new C–C bond formation (D2-OCn). Then, odd–even effect in the D1-OCnwas completely cancelled to show only linear alignment in which the alkyl chains turned to the opposite direction, regardless of the alkyl chain length in the rearranged compounds (D2-OCn). This result indicates that various 2D structures of the isobutenyl compounds with ester groups can be transformed to the same linear alignment by the TCR. However, odd–even effect and structural transformation due to the Claisen rearrangement were unavailable for the “half” molecule containing a single naphthalene unit with an alkyl chain and an allyl moiety. Therefore, it can be concluded that dual alkyl chains connected to the naphthalene units are necessary for the isobutenyl ether compounds to reveal the odd–even effect and structural transformation by the TCR.

Aromatic trifluoroborate ([Ar-BF3][?]) is a useful anion structure for molten salt and ionic liquid (IL) designing because we can attach various sorts of substituents on the aromatic ring with ease. A number of alkali metal salts having [Ar-BF3][?] were synthesized and their physical properties were measured. The salts showed lower melting point than simple inorganic salt, e.g., KCl and LiCl. When phenyltrifluoroborate ([PhBF3][?]) and 1-ethyl-3-methylimidazolium ([C2mim]+) or 1-butyl-3-methylimidazolium ([C4mim]+) were combined, the resulting salts became a liquid state at room temperature. These ILs exhibited favorable viscosity and ionic conductivity comparable to a typical IL species, [C4mim][BF4].

We demonstrate the spontaneous formation of spherical complex M12L24, which is composed of 12 palladium ions and 24 bidentate ligands, by molecular dynamics simulations. In contrast to our previous study on the smaller M6L8cage, we found that the larger M12L24self-assembly process involves noticeable kinetic trapping at lower nuclearity complexes, e.g., M6L12, M8L16, and M9L18. We also found that the kinetic trapping behaviors sensitively depend on the bend angle of ligands and the metal–ligand binding strength. Our results show that these kinetic effects, that have generally been neglected, are important factor in self-assembly structure determination of larger complexes as M12L24in this study.

Raman spectra of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide [C2mIm+][FSA–] ionic liquid solutions dissolving LiFSA salt of various concentrations were measured at 298 K. FSA–((FSO2)2N–) is an analogue anion of bis(trifluoromethanesulfonyl)amide ((CF3SO2)2N–; TFSA–). We found that a solvation number of the Li+ion in [C2mIm+][FSA–] is 3, though it has been well established that Li+ion is solvated by two TFSA–anions in the corresponding ionic liquids below the Li+ion mole fraction of xLi+< 0.2. To yield further insight into larger solvation numbers, Raman spectra were measured at higher temperatures up to 364 K. The Li+ion solvation number in [C2mIm+][FSA–] evidently decreased when the temperature was elevated. Temperature dependence of the Li+ion solvation number was analyzed assuming an equilibrium between [Li(FSA)2]−and [Li(FSA)3]2–, and the enthalpy ΔH° and the temperature multiplied entropy TΔS° for one FSA–liberation toward a bulk ionic liquid were successfully evaluated to be 35(2) kJ mol–1and 29(2) kJ mol–1, respectively. The ΔH° and ΔS° suggest that the Li+ion is coordinated by one of bidentate and two of monodentate FSA–at 298 K, and that the more weakly solvated monodentate FSA–is liberated at higher temperatures. The high-energy X-ray diffraction (HEXRD) experiments of these systems were carried out and were analyzed with the aid of molecular dynamics (MD) simulations. In radial distribution functions evaluated with HEXRD, a peak at about 1.94 Å appeared and was attributable to the Li+–O(FSA–) correlations. The longer Li+–O(FSA–) distance than that for the Li+–O(TFSA–) of 1.86 Å strongly supports the larger solvation number of the Li+ions in the FSA–based ionic liquids. MD simulations at least qualitatively reproduced the Raman and HEXRD experiments.

The geometries and interaction energies of complexes of pyridine with C6F5X, C6H5X (X=I, Br, Cl, F and H) and RFI (RF=CF3, C2F5and C3F7) have been studied by ab initio molecular orbital calculations. The CCSD(T) interaction energies (Eint) for the C6F5X–pyridine (X=I, Br, Cl, F and H) complexes at the basis set limit were estimated to be −5.59, −4.06, −2.78, −0.19 and −4.37 kcal mol−1, respectively, whereas the Eintvalues for the C6H5X–pyridine (X=I, Br, Cl and H) complexes were estimated to be −3.27, −2.17, −1.23 and −1.78 kcal mol−1, respectively. Electrostatic interactions are the cause of the halogen dependence of the interaction energies and the enhancement of the attraction by the fluorine atoms in C6F5X. The values of Eintestimated for the RFI–pyridine (RF=CF3, C2F5and C3F7) complexes (−5.14, −5.38 and −5.44 kcal mol−1, respectively) are close to that for the C6F5I–pyridine complex. Electrostatic interactions are the major source of the attraction in the strong halogen bond although induction and dispersion interactions also contribute to the attraction. Short‐range (charge‐transfer) interactions do not contribute significantly to the attraction. The magnitude of the directionality of the halogen bond correlates with the magnitude of the attraction. Electrostatic interactions are mainly responsible for the directionality of the halogen bond. The directionality of halogen bonds involving iodine and bromine is high, whereas that of chlorine is low and that of fluorine is negligible. The directionality of the halogen bonds in the C6F5I– and C2F5I–pyridine complexes is higher than that in the hydrogen bonds in the water dimer and water–formaldehyde complex. The calculations suggest that the CI and CBr halogen bonds play an important role in controlling the structures of molecular assemblies, that the CCl bonds play a less important role and that CF bonds have a negligible impact.

The physicochemical (e.g., density, viscosity, ionic conductivity, and self-diffusion coefficient) and electrochemical (e.g., electrochemical window and electric double-layer capacitor performance) properties of two new types of room-temperature ionic liquids, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (EMIm-FAP) and 1-ethyl-3-methylimidazolium tetracyanoborate (EMIm-TCB), were investigated and compared. EMIm-FAP showed a wider electrochemical window with a carbon working electrode compared with EMIm-TCB, in spite of lower viscosity, larger self-diffusion coefficients and higher ionic conductivity. Also, the electric double-layer capacitor using EMIm-FAP shows better cycle reversibility and higher charge/discharge voltage operation (over 3 V) than that using EMIm-TCB.

Physicochemical properties such as density, viscosity, ionic conductivity, and self-diffusion coefficient of two types of room-temperatureionic liquids composed of cations with N-P bonds were investigated. One is an ionic liquid composed of cations with N-P-O bond, namely, tri(N,N-dimethylamino)-n-butoxyphosphonium bis(trifluoromethanesulfonyl)amide (TABP-TFSA) and has a relatively low viscosity (38 mPa s at 30degC) due to the high internal mobility of the cation, despite its large ion size. TABP-TFSA showed a characteristic electrochemical oxidation behavior, such as a wide electrochemical potential window of stability without gas evolution. Formation of passivation film on a Pt electrode was suggested from the results of potential sweep experiments. The lithium secondary battery ([LiCoO2|Li] cell) using TABP-TFSA as the electrolyte achieved stable charge-discharge operations in over 500 cycles. For another ionic liquid with N-P bond, namely, TAEP-TFSA (TAEP+ = tri(N-methyl-N-(n-butylamino))ethylphosphonium), less battery cycle stability and low rate performances were observed, despite the higher ionic dissociation than TABP-TFSA, probably because of the high viscosity and low electrochemical oxidative stability. It is shown that the introduction of oxygen in the cation like N-P-O produces better performances compared with the cation having N-P structure.

The rate property of Li/LiCoO2 cell using ionic liquids (ILs) containing fluorosulfonyl(trifluoromethylsulfonyl) amide (FTA[?]) anion and N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium (DEME+) was investigated. comparing with corresponding amide ionic liquids composed of such bis(trifluoromethyl)sulfonylamide (TFSA[?]) and bis(fluoromethylsulfonyl)amide (FSA[?]). As a result, the cell using DEME[FTA] was also exhibit good rate performance as in the case of DEME[FSA]. This result suggests that an existence of FSO2 group in anionic species might be a key factor to improve the battery performance containing neat ILs.

ew room temperature ionic liquids (RTILs) containing phosphoniaspiro[4.4]nonan (PS4,4+) could be obtained by selecting an amide anion with structural asymmetry such as fluorosulfonyl (trifluoromethylsulfonyl) amide (FTA-). PS44+ could not form RTILs with another amide anion such as FSA- ([(FSO2)2N]-, and TFSA- ([(CF3SO2)2N]-), which indicated that the structural asymmetry in an anion effectively decreasing the melting point of symmetric phosphonium such as PS4,4+.

The stabilization energies (Eform) for the formation of the perfluoroalkyltrifluoroborate complexes with Li+ and 1-ethyl-3- methylimidazolium cation (emim+) were calculated at the MP2/6- 311G** level. The order of the Eform calculated for the Li+ complexes is Li[BF4] >> Li[BF3CF3] > Li[BF3C2F5] ~ Li[BF3C3F7] ~ Li[BF3C4F9]. The Eform calculated for the emim+ complexes have the same order, while they are substantially smaller than those for the Li+ complexes. The calculations suggest that the weaker interactions of the BF3CF3- with emim+ compared with the BF4- are the cause of the lower viscosity of the [emim][BF3CF3] ionic liquid compared with the [emim][BF4] ionic liquid. The trend of the experimentally observed perfluoroalkyl chain length dependence of the self-diffusion coefficients of ions is well reproduced by molecular dynamics simulations. The correlation of the rotational relaxation of the emim+ and the self-diffusion coefficients of the cation and anion suggests that the translational motion of ions in the ionic liquids is associated with the rotational motion of the emim+.

What's it got in its pockets?Symmetry carry‐over crystallization of hexadehydrotribenzo[12]annulene derivatives was provided by specific complexation between the annulene and the chloroform molecule through mainly dispersion forces (see picture). In the complex, a hydrogen atom of the chloroform fits into the annulene's “pocket” surrounded by π electrons.

We studied transport properties, i.e., viscosity (e), conductivity (s), and cation and anion self-diffusion coefficients (Dcation, Danion), for C2mim-ILs, N122.1O2-ILs, and N1224-ILs, where C2mim+ is 1-ethyl-3-methylimidazolium, N122.1O2+ is N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium, and N1224+ is N-butyl-N,N-diethyl-N-methylammonium, composed of perfluorosulfonylamide anions. Ten perfluorosulfonylamide anions, i.e., C0C0 (FSA, FSI), C0C1 (FTA), C1C1 (TFSA, TFSI), C1C2, C2C2 (BETA, BETI), C1C4, C4C4, CTFSA, C3FSA, and TSAC, were used in this work. Walden product and "ionicity" quantity were determined from the transport property data. It became apparent that there was high correlation between the Walden product and the "ionicity" quantity for the ILs. The results of the Walden product and the "ionicity" quantity indicated that by comparison with the N122.1O2-ILs and the N1224-ILs the ion dissociation of the C2mim-ILs was large and hardly changed with the amide anion structures.

We report a theoretical study of molecular wires which are designed to detect a single nucleic acid base thymine, through electrical conductance change. Three model sensors with ethynylphenyl backbones having suitable detection units and capable of forming hydrogen bonds with thymine are proposed. A combination of density functional theory and nonequilibrium Green's function formalism were used for the theoretical studies. The results show that subtle changes in electronic properties of the sensors due to hydrogen bond formation with the target may give rise to measurable changes in conductance. We also report experimental conductance studies for one model sensor, which agrees qualitatively with the theoretical results.

The self-assembled monolayer of bipyridine derivative 1, which has two alkyl chains on each end, at the HOPG/1-phenyloctane interface was studied by in situ scanning tunneling microscopy (STM). The detailed mechanism of a spontaneous change in the monolayer packing pattern by Pd coordination was studied. Uncomplexed 1existed in a bent form in the monolayer, and the alkyl chains were interdigitated, whereas Pd-complexed 1was in a straight form and the alkyl chains were not interdigitated. An intermediate state of 1was successfully observed during metal coordination. The structure was the bent form with noninterdigitated alkyl chains. Equilibrium intermolecular distances reported from ab initio calculations indicate that the molecular width of the central aromatic part of uncomplexed 1(7.5 Å) is substantially smaller than that of the peripheral alkyl chain part (9.2 Å). The bent form was suitable for covering up the surface to maximize the packing density. However, the molecular width of the aromatic unit of Pd-complexed 1(9.1 Å) was almost identical to that of the alkyl chain unit (9.2 Å). Therefore, Pd-complexed 1took the straight form in the monolayer. The observation of surface coverage by STM suggests that the bent form increases the packing density by as much as 16% compared with that of the straight form. These results indicate that the control of molecular width can be used to design molecular templates for nanostructure formation.

Molecular interactions between π systems having different π‐electron character (benzene, hexafluorobenzene, and borazine), and a Lewis acid/base (borane and ammonia) were theoretically studied. An attractive interaction between benzene, the electron‐rich π system, and borane was observed. On the other hand, repulsive interactions between benzene and ammonia was observed when the lone pair of nitrogen points toward the benzene ring. In contrast, an attractive interaction between hexafluorobenzene, an electron‐deficient π system, and ammonia was observed. Unexpectedly, a weak attractive interaction between hexafluorobenzene and borane was also observed. Borazine shows an interaction both to borane and ammonia. The attraction between the nitrogen atom of borazine and borane was larger than that between the boron atom of borazine and ammonia.

The intermolecular interaction energy curves of CH3OCH3CH2F2, CF3OCH3CH2F2, CF3OCF3CH2F2, CH3OCH3CHF3, CF3OCH3CHF3, and CF3OCF3CHF3complexes were calculated by the MP2 level ab initiomolecular orbital method using the 6‐311G** basis set augmented with diffuse polarization functions. We investigate the fluorine substitution effects of both methane and dimethyl ether on intermolecular interactions. In addition, orientation dependence of intermolecular interaction energies is also studied with utilizing eight types of orientations. Our analyses demonstrate that partial fluorinations of methane make electrostatic interaction dominant, and consequently enhance attractive interaction at several specific orientations. On the contrary, fluorine substitutions of dimethyl ether substantially decrease the electrostatic interaction between ether and CH2F2or CHF3; thus, there is no such characteristic interaction between the CH of fluorinated methane and ether oxygen of CF3OCF3as conventional hydrogen bonding, due to reduced polarity of fluorinated ether. The combination of different pairs of the electrostatic interaction is therefore responsible for the intermolecular interaction differences among the complexes investigated herein and also their orientations. © 2003 Wiley Periodicals, Inc. J Comput Chem 25: 447–459, 2004

The intermolecular interaction energies between a water molecule and four models of pendant chains for perfluorinated ionomers, such as CF3OCF2CF2SO3H, CF3OCF2CF2SO3−, CF3CF2CF2COOH, CF3CF2CF2COO−, were analyzed by using a molecular orbital calculation. In order to investigate a variety of configurations, five hundred random configurations that water and monomer contact at their van der Waals surfaces were generated for each system. We employed an empirical correction method for dispersion energy defined by the equation Edisp  −fdRC6R−6, so as to reduce the computational costs. The C6coefficients of this equation were optimized to reproduce the energies obtained at the MP2aug-cc-pVDZ level of calculations, and then overall intermolecular interaction energies Eint  EHF  Edisp were evaluated as a summation of Edispand intermolecular interaction energy at the HFaug-cc-pVDZ level EHF. From these analyses, we obtained the following conclusions. 1 The ether oxygen in the pendant chain cannot bind with water strongly due to fluorination. 2 De-protonations of sulfonic and carboxylic acids extend the region where water molecules sufficiently bind with pendant chains, and this effect would cause rich water absorption when these pendant chains form membranes. Therefore, the degree of proton disassociation would be one of the key factors for the water sorption ratio and membrane morphology. 3 The binding energy of the optimized configuration for CF3CF2CF2COO−  H2O is about 2.5 kcal mol−1larger than that for the CF3OCF2CF2SO3−  H2O system because of the larger electron negativities of the oxygen atoms on deprotonated carboxylic acid compared with those on the sulfonic acid.

The 1H NMR chemical shifts and X-ray crystal structures of various salicylideneaniline derivatives containing an isobutenylene (2-methylenepropane-1,3-diyl) chain were analyzed in detail. In solution, these compounds were present to some extent as syn–synconformers with respect to the isobutenylene chain; the actual syn–synpopulation depended on the molecular structure, especially on the size of the macrocycle. Small substituents on the phenyl ring hardly affected the stability of the syn–synform at all, whereas replacement of the phenyl group with a naphthalene moiety considerably destabilized the syn–synform relative to the syn–skew form. The conformation–chemical shift relationship was validly maintained irrespective of the substituent, provided the conformational preference was correctly taken into account.

This article describes an ab initioinvestigation on the potential surfaces for one of the simplest hydrogen atom abstraction reactions, that is, HO + H2O ↔ H2O + OH. In accord with the findings in the previously reported theoretical investigations, two types of the hydrogen‐bonding complexes [HOHOH] and [H2OHO] were located on the potential energy surface. The water molecule acts as a hydrogen donor in the [HOHOH] complex, while the OH radical acts as a hydrogen donor in the [H2OHO] complex. The energy evaluations at the MP2(FC) basis set limit, as well as those through the CBS‐APNO procedure, have provided estimates for enthalpies of association for these complexes at 298 K as −2.1 ≈ −2.3 and −4.1 ≈ −4.3 kcal/mol, respectively. The IRC calculations have suggested that the [H2OHO] complex should be located along the reaction coordinate for the hydrogen abstraction. Our best estimate for the classical barrier height for the hydrogen abstraction is 7.8 kcal/mol, which was obtained from the CBS‐APNO energy evaluations. After fitting the CBS‐APNO potential energy curve to a symmetrical Eckart function, the rate constants were calculated by using the transition state theory including the tunneling correction. Our estimates for the Arrhenius parameters in the temperature region from 300 to 420 K show quite reasonable agreement with the experimentally derived values. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1538–1548, 2003

This article describes an ab initio investigation on the potential surfaces for one of the simplest hydrogen atom abstraction reactions, that is, HO + H2O ↔ H2O + OH. In accord with the findings in the previously reported theoretical investigations, two types of the hydrogen-bonding complexes [HOH&bond;OH] and [H2O&bond;HO] were located on the potential energy surface. The water molecule acts as a hydrogen donor in the [HOH&bond;OH] complex, while the OH radical acts as a hydrogen donor in the [H2O&bond;HO] complex. The energy evaluations at the MP2(FC) basis set limit, as well as those through the CBS-APNO procedure, have provided estimates for enthalpies of association for these complexes at 298 K as −2.1 ≈ −2.3 and −4.1 ≈ −4.3 kcal/mol, respectively. The IRC calculations have suggested that the [H2O&bond;HO] complex should be located along the reaction coordinate for the hydrogen abstraction. Our best estimate for the classical barrier height for the hydrogen abstraction is 7.8 kcal/mol, which was obtained from the CBS-APNO energy evaluations. After fitting the CBS-APNO potential energy curve to a symmetrical Eckart function, the rate constants were calculated by using the transition state theory including the tunneling correction. Our estimates for the Arrhenius parameters in the temperature region from 300 to 420 K show quite reasonable agreement with the experimentally derived values. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1538–1548, 2003

The intermolecular interaction energies of the CH3OCH3CH4, CF3OCH3CH4, and CF3OCF3CH4systems were calculated by ab initiomolecular orbital method with the electron correlation correction at the second order Møller–Plesset perturbation (MP2) method. The interaction energies of 10 orientations of complexes were calculated for each system. The largest interaction energies calculated for the three systems are −1.06, −0.70, and −0.80 kcal/mol, respectively. The inclusion of electron correlation increases the attraction significantly. It gains the attraction −1.47, −1.19, and −1.27 kcal/mol, respectively. The dispersion interaction is found to be the major source of the attraction in these systems. In the CH3OCH3CH4system, the electrostatic interaction (−0.34 kcal/mol) increases the attraction substantially, while the electrostatic energies in the other systems are not large. Fluorine substitution of the ether decreases the electrostatic interaction, and therefore, decreases the attraction. In addition the orientation dependence of the interaction energy is decreased by the substitution. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 1472–1479, 2002

The intermolecular interaction energies of the CX₃OCHO dimers, CX₃OCHO–n(H₂O), and CX₃OCHO–n(HO₂) (X = H,F; n = 1,2) complexes are studied by using molecular orbital calculations at the (U)MP2/aug(df,pd)-6-311G**//(U)B3LYP/6-311G** level. We first confirmed the reliability of this level of calculation by utilizing examples of two complexes, CH₃OCHO–HO₂ (syn) and CF₃OCHO–HO₂ (syn). The calculated intermolecular interaction energies for the formate dimers (−3.75 to −5.19 kcal mol−1) and CX₃OCHO–H₂O (−2.39 to −4.90 kcal mol−1) are relatively small. On the other hand, the CX₃OCHO–HO₂ complexes have larger interaction energies (−4.78 to −9.69 kcal mol−1). The complexes, CX₃OCHO–2(H₂O) and CX₃OCHO–2(HO₂), have the largest intermolecular interaction energies (−12.42 to −13.89 kcal mol−1 and −14.47 to −18.39 kcal mol−1, respectively). Except for the formate dimer of syn–syn type, the interaction energies for the complexes with CF₃OCHO are always smaller than the corresponding complexes with CH₃OCHO. Finally, we estimated the concentrations of the complexes in the low and high water concentration conditions. In conclusion, it has been observed that the complexes studied in this work are not likely to form in the atmosphere.

Novel bis(benzoxazole) derivatives were easily synthesized from isobutenyl bis(amide−ether)s by tandem Claisen rearrangement and subsequent intramolecular cyclization of the amide−phenol intermediates. The yields of the bis(benzoxazole)s depended on whether the reaction was carried out with or without solvent, as well as on the substituents on the aryl group and the carbonyl group. The solvent effect was dramatic. No significant difference in the overall reaction rate constant with variation of the substituents on the carbonyl group was observed, but the nature of the aryl group on the ether had a large effect on the tandem Claisen rearrangement. The corresponding amide−phenol derivatives were confirmed as intermediates in this rearrangement. The fluorescence quantum yields of the obtained bis(benzoxazole)s were high, but the yields were lower than those of the corresponding monobenzoxazoles. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

A new variety of salicylideneaniline derivatives were prepared from a substituted aniline and a bis(hydroxybenzaldehyde) which has been synthesized through a tandem Claisen rearrangement reaction. X-ray crystal structures were obtained for many of the products. With respect to the conformation of their isobutenylene chain, the crystal structures can be classified into three groups: i.e., skew–skew (I), syn–skew (II), and syn–syn(III) conformers. The 1H NMR spectra were significantly different among these compounds, especially for the isobutenylene moiety. The set of the chemical shifts, (δ(Ha), δ(Hb)), of exo-methylene (Ha) and benzylic methylene (Hb) is a good index for classifying the NMR spectra, and these values also reflect the conformation of the isobutenylene chain found in the crystal state. Namely, each conformer of I, II, and III corresponds to the (δ(Ha), δ(Hb)) values (ppm) around (5.10, 3.43), (4.86, 3.43), and (4.74, 3.56), respectively. This result is verified by the complexation study of a 15-crown-5 derivative with alkali metal ions. The chemical shift change caused by the complexation is successfully explained by the conformation changes among I, II, and III.

The gas phase cation-π complexation of oligo[(dimethylsilylene)phenylene]s with alkali metal cations was observed by electrospray mass spectrometry for the first time. The cation-π complexes were derived not only from cyclic oligomers but also from acyclic derivatives in spite of the large conformational flexibility. The substituent effect of silyl groups on cation-π interaction was investigated by ab initio calculations of the model compounds. The calculation showed that not the silyl (SiH₃) group but the trimethylsilyl (SiMe₃) group substantially increased the attraction between the cation and the π system, especially due to the large gain in induction energy. Theoretical calculations for trimethylsilylbenzene and a model compound of silamacrocycles suggested that significant conformational changes occurred due to the complexation. The observed Cs⁺ selectivity of the silamacrocycle in the electrospray mass spectrometry was explained by the calculated binding energies of the cation-π complexes, if the solvation of the cations was considered. The results from mass spectrometry can be understood in terms of competition between cation-π complexation and solvation by species in the solvent matrix.

AbstractInvestigation of the origin of a dimeric pair structure of the title compound molecules in a crystal was extensively conducted. Molecular dynamics calculations suggested that conventional van der Waals and electrostatic estimations did not accurately reproduce the temperature dependence of the interatomic distance of the dimeric pair, as observed in X-ray structure analyses. A dimeric pair formation of the monomer in a solution was also observed by spectroscopic studies. X-ray structure analysis of a photodimer crystal revealed that the packing motif of the monomer crystal is quite similar to the dimer crystal. It is speculated that, on crystallisation from a solution, the monomer molecule form a dimeric structure near the crystal surface and make a stack similar to the dimer crystal.

Ab initioand semi-empirical calculations were carried out on keto/enol tautomers of 6-methyl-7,8-dihydropterin, a model compound for the natural substrate of dihydrofolate reductase. The most likely conformer of pterin ring (inner enol 3) during the hydride transfer from NADPH was computationally chracterized.