How Aromatic Fluorination Exchanges the Interaction Role of Pyridine with Carbonyl Compounds: The Formaldehyde Adduct

The rotational spectrum of the weakly bound complex pentafluoropyridine⋅⋅⋅formaldehyde has been investigated using Fourier transform microwave spectroscopy. From the analysis of the rotational parameters of the parent species and of the 13 C and 15 N isotopologues, the structural arrangement of the adduct has been unambiguously established. The full ring fluorination of pyridine has a dramatic effect on its binding properties: It alters the electron density distribution at the π-cloud of pyridine creating a π-hole and changing its electron donor-acceptor capabilities. In the complex, formaldehyde lies above the aromatic ring with one of the oxygen lone pairs, as conventionally envisaged, pointing toward its centre. This lone pair⋅⋅⋅π-hole interaction, reinforced by a weak C-H⋅⋅⋅N interaction, indicates an exchange of the electron-acceptor roles of both molecules when compared to the pyridine⋅⋅⋅formaldehyde adduct. Tunnelling doublets due to the internal rotation of formaldehyde have also been observed and analysed leading to a discussion on the competition between lone pair⋅⋅⋅π-hole and π⋅⋅⋅π stacking interactions.

Explanation of the Formation of Complexes between Representatives of Oxazolidinones and HDAS-β-CD Using Molecular Modeling as a Complementary Technique to cEKC and NMR

Molecular modeling (MM) results for tedizolid and radezolid with heptakis-(2,3-diacetyl-6-sulfo)-β-cyclodextrin (HDAS-β-CD) are presented and compared with the results previously obtained for linezolid and sutezolid. The mechanism of interaction of chiral oxazolidinone ligands belonging to a new class of antibacterial agents, such as linezolid, tedizolid, radezolid, and sutezolid, with HDAS-β-CD based on capillary electrokinetic chromatography (cEKC), nuclear magnetic resonance (NMR) spectroscopy, and MM methods was described. Principles of chiral separation of oxazolidinone analogues using charged single isomer derivatives of cyclodextrin by the cEKC method were presented, including the selection of the optimal chiral selector and separation conditions, complex stoichiometry, and binding constants, which provided a comprehensive basis for MM studies. In turn, NMR provided, where possible, direct information on the geometry of the inclusion complexes and also provided the necessary structural information to validate the MM calculations. Consequently, MM contributed to the understanding of the structure of diastereomeric complexes, the thermodynamics of complexation, and the visualization of their structures. The most probable mean geometries of the studied supramolecular complexes and their dynamics (geometry changes over time) were determined by molecular dynamics methods. Oxazolidinone ligands have been shown to complex mainly the inner part of cyclodextrin, while the external binding is less privileged, which is consistent with the conclusions of the NMR studies. Enthalpy values of binding of complexes were calculated using long-term molecular dynamics in explicit water as well as using molecular mechanics, the Poisson-Boltzmann or generalized Born, and surface area continuum solvation (MM/PBSA and MM/GBSA) methods. Computational methods predicted the effect of changes in pH and composition of the solution on the strength and complexation process, and it adapted the conditions selected as optimal during the cEKC study. By changing the dielectric constant in the MM/PBSA and MM/GBSA calculations, the effect of changing the solution to methanol/acetonitrile was investigated. A fairly successful attempt was made to predict the chiral separation of the oxazolidinones using the modified cyclodextrin by computational methods.

ESI-MS studies of the non-covalent interactions between biologically important metal ions and N-sulfonylcytosine derivatives

The aim of this report is to present the electrospray ionization mass spectrometry results of the non-covalent interaction of two biologically active ligands, N-1-(p-toluenesulfonyl)cytosine, 1-TsC, 1 and N-1-methanesulfonylcytosine, 1-MsC, 2 and their Cu(II) complexes Cu(1-TsC-N3)₂ Cl₂ , 3 and Cu(1-MsC-N3)₂ Cl₂ and 4 with biologically important cations: Na⁺ , K⁺ , Ca²⁺ , Mg²⁺ and Zn²⁺ . The formation of various complex metal ions was observed. The alkali metals Na⁺ and K⁺ formed clusters because of electrostatic interactions. Ca²⁺ and Mg²⁺ salts produced the tris ligand and mixed ligand complexes. The interaction of Zn²⁺ with 1-4 produced monometal and dimetal Zn²⁺ complexes as a result of the affinity of Zn²⁺ ions toward both O and N atoms. Copyright © 2016 John Wiley & Sons, Ltd.

Halogen Bonding in Sulphonamide Co-Crystals: X···π Preferred over X···O/N?

Sulphonamides have been one of the major pharmaceutical compound classes since their introduction in the 1930s. Co-crystallisation of sulphonamides with halogen bonding (XB) might lead to a new class of pharmaceutical-relevant co-crystals. We present the synthesis and structural analysis of seven new co-crystals of simple sulphonamides N-methylbenzenesulphonamide (NMBSA), N-phenylmethanesulphonamide (NPMSA), and N-phenylbenzenesulphonamide (BSA), as well as of an anti-diabetic agent Chlorpropamide (CPA), with the model XB-donors 1,4-diiodotetrafluorobenzene (14DITFB), 1,4-dibromotetrafluorobenzene (14DBTFB), and 1,2-diiodotetrafluorobenzene (12DITFB). In the reported co-crystals, X···O/N bonds do not represent the most common intermolecular interaction. Against our rational design expectations and the results of our statistical CSD analysis, the normally less often present X···π interaction dominates the crystal packing. Furthermore, the general interaction pattern in model sulphonamides and the CPA multicomponent crystals differ, mainly due to strong hydrogen bonds blocking possible interaction sites.

Zn(II) Heteroleptic Halide Complexes with 2-Halopyridines: Features of Halogen Bonding in Solid State

Reactions between Zn(II) dihalides and 2-halogen-substituted pyridines 2-XPy result in a series of heteroleptic molecular complexes [(2-XPy)₂ZnY₂] (Y = Cl, X = Cl (1), Br (2), I (3); Y = Br, X = Cl (4), Br (5), I (6), Y = I, X = Cl (7), Br (8), and I (9)). Moreover, 1-7 are isostructural (triclinic), while 8 and 9 are monoclinic. In all cases, halogen bonding plays an important role in formation of crystal packing. Moreover, 1-9 demonstrate luminescence in asolid state; for the best emitting complexes, quantum yield (QY) exceeds 21%.

Theoretically Revealing the Response of Intermolecular Vibration Energy Transfer and Decomposition Process of the DNTF System to Electric Fields Using Two-Dimensional Infrared Spectra

The external electric field (E-field), which is an important stimulus, can change the decomposition mechanism and sensitivity of energetic materials. As a result, understanding the response of energetic materials to external E-fields is critical for their safe use. Motivated by recent experiments and theories, the two-dimensional infrared (2D IR) spectra of 3,4-bis (3-nitrofurazan-4-yl) furoxan (DNTF), which has a high energy, a low melting point, and comprehensive properties, were theoretically investigated. Cross-peaks were observed in 2D IR spectra under different E-fields, which demonstrated an intermolecular vibration energy transfer; the furazan ring vibration was found to play an important role in the analysis of vibration energy distribution and was extended over several DNTF molecules. Measurements of the non-covalent interactions, with the support of the 2D IR spectra, indicated that there were obvious non-covalent interactions among different DNTF molecules, which resulted from the conjugation of the furoxan ring and the furazan ring; the direction of the E-field also had a significant influence on the strength of the weak interactions. Furthermore, the calculation of the Laplacian bond order, which characterized the C-NO₂ bonds as trigger bonds, predicted that the E-fields could change the thermal decomposition process of DNTF while the positive E-field facilitates the breakdown of the C-NO₂ in DNTFⅣ molecules. Our work provides new insights into the relationship between the E-field and the intermolecular vibration energy transfer and decomposition mechanism of the DNTF system.

Interactions between paramyosin and actin greatly improve their thermostability and gel properties

BACKGROUND

Myofibrillar proteins, the main contributors to the quality of meat products, are the main structural protein component of muscle and have functional properties such as the formation of a 3D protein gel network and water binding. The susceptibility of meat-derived proteins to heat-induced aggregation is the functional constraint that hinders their applications in industry, and so establishing an effective but simple method to improve their thermostability of the proteins is of great importance.

RESULTS

In the present study, we describe an easy approach to perform high colloidal thermostability of both paramyosin and actin by mixing them at low ionic strength. The improvement in thermal stability was found to be derived from intermolecular interactions between these two different proteins through non-covalent binding with each other. Consequently, such interactions protected each of them from thermal-induced degradation compared to individual components. Notably, this binary native protein mixture rather than single paramyosin or actin component has the ability to form protein hydrogels with a shear-thinning and reversible sol-gel transformation behavior, which is markedly different from most of reported heat-induced, denatured protein hydrogels.

CONCLUSION

The present study not only presents a facile and effective strategy for improvement of the thermal stability and gel properties of a binary paramyosin and actin mixture, but also enhances our understanding of how mutual interactions of protein components affect their physicochemical and functional properties. © 2023 Society of Chemical Industry.

Crystals at a Carrefour on the Way through the Phase Space: A Middle Path

Multiple supramolecular functionalities of cyclic α-alkoxy tellurium-trihalides (including Te---O, Te---X (X = Br, I) and Te---π(C=C) supramolecular synthons) afford rich crystal packing possibilities, which consequently results in polymorphism or Z’ > 1 crystal structures. Example of three crystal forms of cyclohexyl-ethoxy-tellurium-trihalides, one of which combines the packing of two others, affords a unique model to observe the supramolecular synthon evolution at the early stages of crystallization, when crystals on the way find themself at a carrefour between the evolutionally close routes, but fail to choose between two energetically close packing patterns, so taking the “middle path”, which incorporates both of them (and results in two crystallographically independent molecules). In general, this allows a better understanding of the existing structures, and an instrument to search for the new polymorphic forms.

A Molecular Torsion Balance Study: A Nearby Anionic Group Exerts Little Influence on Hydrophobic Interactions between Nonpolar Surfaces

Polar groups have a solvent ordering effect on water and therefore may affect hydrophobic binding energies for nearby lipophilic surfaces. This would mean that determinations of excess surface free energy association energies require consideration of nearby polar functional groups. This paper reports results of a study to measure this possible effect. It was concluded from the models used here that an anionic polar group nearby a hydrophobic surface has little or no effect on the magnitude of hydrophobic association.

Crystal Structure Determination of 4-[(Di-p-tolyl-amino)-benzylidene]-(5-pyridin-4-yl-[1,3,4]thiadiazol-2-yl)-imine along with Selected Properties of Imine in Neutral and Protonated Form with Camforosulphonic Acid: Theoretical and Experimental Studies

The crystal structure was determined for the first time for 4-[(di-p-tolyl-amino)benzylidene]-(5-pyridin-4-yl-[1,3,4]thiadiazol-2-yl)-imine (trans-PPL9) by X-ray diffraction. The imine crystallized in the monoclinic P21/n space group with a = 18.9567(7) Å, b = 6.18597(17) Å, c = 22.5897(7) Å, and β = 114.009(4)°. Intermolecular interactions in the PPL9 crystal were only weak C-H⋯N hydrogen bonds investigated using the Hirshfeld surface. The electronic and geometric structure of the imine were investigated by the density functional theory and the time-dependent density-functional theory. The properties of the imine in neutral and protonated form with camforosulphonic acid (CSA) were investigated using cyclic voltammetry, UV-vis and 1H NMR spectroscopy. Theoretical and experimental studies showed that for the 1:1 molar ratio the protonation occured on nitrogen in pyridine in the PPL9 structure, as an effect of Brönsted acid-base interactions. Thermographic camera was used to defined defects in constructed simple devices with ITO/PPL9 (or PPL9:CSA)/Ag/ITO architecture. In conclusion, a thermally stable imine was synthesized in crystalline form and by CSA doping, a modification of absorption spectra together with reduction of overheating process was observed, suggesting its potential application in optoelectronics.

The Electrophilicities of XCF3 and XCl (X=H, Cl, Br, I) and the Propensity of These Molecules To Form Hydrogen and Halogen Bonds with Lewis Bases: An Ab Initio Study

Equilibrium dissociation energies, De , of four series of halogen- and hydrogen-bonded complexes B⋅⋅⋅XCF3 (X=H, Cl, Br and I) are calculated ab initio at the CCSD(T)(F12c)/cc-pVDZ-F12 level. The Lewis bases B involved are N2 , CO, PH3 , C2 H2 , C2 H4 , H2 S, HCN, H2 O and NH3 . Plots of De versus NB , where the NB are the nucleophilicities assigned to the Lewis bases previously, are good straight lines through the origin, as are those for the corresponding set of complexes B⋅⋅⋅XCl. The gradients of the De versus NB plots define the electrophilicities EXCF3 and EXCl of the various Lewis acids. The determined values are: EXCF3 =2.58(22), 1.40(9), 2.15(2) and 3.04(9) for X=H, Cl, Br and I, respectively, and EXCl =4.48(22), 2.31(9), 4.37(27) and 6.06(37) for the same order of X. Thus, it is found that, for a given X, the ratio EXCl / EXCF3 is 2 within the assessed errors, and therefore appears to be independent of the atom X and of the type of non-covalent interaction (hydrogen bond or different varieties of halogen bond) in which it is involved. Consideration of the molecular electrostatic surface potentials shows that De and the maximum positive electrostatic potential σmax (the most electrophilic region of XCF3 and XCl, which lies on the symmetry axes of these molecules, near to the atom X) are strongly correlated.

Modeling of the Response of Hydrogen Bond Properties on an External Electric Field: Geometry, NMR Chemical Shift, Spin-Spin Scalar Coupling

The response of the geometric and NMR properties of molecular systems to an external electric field has been studied theoretically in a wide field range. It has been shown that this adduct under field approach can be used to model the geometric and spectral changes experienced by molecular systems in polar media if the system in question has one and only one bond, the polarizability of which significantly exceeds the polarizability of other bonds. If this requirement is met, then it becomes possible to model even extreme cases, for example, proton dissociation in hydrogen halides. This requirement is fulfilled for many complexes with one hydrogen bond. For such complexes, this approach can be used to facilitate a detailed analysis of spectral changes associated with geometric changes in the hydrogen bond. For example, in hydrogen-bonded complexes of isocyanide C≡¹⁵N-¹H⋯X, ¹J(¹⁵N¹H) depends exclusively on the N-H distance, while δ(¹⁵N) is also slightly influenced by the nature of X.

Weak, Broken, but Working-Intramolecular Hydrogen Bond in 2,2'-bipyridine

From an academic and practical point of view, it is desirable to be able to assess the possibility of the proton exchange of a given molecular system just by knowing the positions of the proton acceptor and the proton donor. This study addresses the difference between intramolecular hydrogen bonds in 2,2'-bipyridinium and 1,10-phenanthrolinium. Solid-state ¹⁵N NMR and model calculations show that these hydrogen bonds are weak; their energies are 25 kJ/mol and 15 kJ/mol, respectively. Neither these hydrogen bonds nor N-H stretches can be responsible for the fast reversible proton transfer observed for 2,2'-bipyridinium in a polar solvent down to 115 K. This process must have been caused by an external force, which was a fluctuating electric field present in the solution. However, these hydrogen bonds are the grain that tips the scales precisely because they are an integral part of a large system of interactions, including both intramolecular interactions and environmental influence.

A Dispersion Corrected DFT Investigation of the Inclusion Complexation of Dexamethasone with β-Cyclodextrin and Molecular Docking Study of Its Potential Activity against COVID-19

The encapsulation mode of dexamethasone (Dex) into the cavity of β-cyclodextrin (β-CD), as well as its potential as an inhibitor of the COVID-19 main protease, were investigated using density functional theory with the recent dispersion corrections D4 and molecular docking calculations. Independent gradient model and natural bond orbital approaches allowed for the characterization of the host–guest interactions in the studied systems. Structural and energetic computation results revealed that hydrogen bonds and van der Waals interactions played significant roles in the stabilization of the formed Dex@β-CD complex. The complexation energy significantly decreased from −179.50 kJ/mol in the gas phase to −74.14 kJ/mol in the aqueous phase. A molecular docking study was performed to investigate the inhibitory activity of dexamethasone against the COVID-19 target protein (PDB ID: 6LU7). The dexamethasone showed potential therapeutic activity as a SARS CoV-2 main protease inhibitor due to its strong binding to the active sites of the protein target, with predicted free energy of binding values of −29.97 and −32.19 kJ/mol as calculated from AutoDock4 and AutoDock Vina, respectively. This study was intended to explore the potential use of the Dex@β-CD complex in drug delivery to enhance dexamethasone dissolution, thus improving its bioavailability and reducing its side effects.

One Dimensional Enhanced Anhydrous Proton Conduction in Well Defined Molecular Columns Induced by Non-Covalent Interactions

1D anhydrous proton conduction is enhanced significantly in ionic channels created by self-assembly of functionalized organic phosphonic acid and aromatic heterocyclic 1,2,4-triazole molecules. This study reveals high proton conduction in one dimension through a well-defined supramolecular architecture in which two different molecules undergo host-guest synergy and self-assemble to provide two-fold advantages: 1) formation of the ionic channels and 2) higher proton conduction in the absence of water. A clear correlation is found between the phenomena of ionic channels and anhydrous conductivity in the absolute dry state and we demonstrate that the one-dimensional conductivity can be as high as that recorded for 3D channels in, for instance, Nafion.

Large Stabilization Effects by Intramolecular Beryllium Bonds in Ortho-Benzene Derivatives

Intramolecular interactions are shown to be key for favoring a given structure in systems with a variety of conformers. In ortho-substituted benzene derivatives including a beryllium moiety, beryllium bonds provide very large stabilizations with respect to non-bound conformers and enthalpy differences above one hundred kJ·mol⁻¹ are found in the most favorable cases, especially if the newly formed rings are five or six-membered heterocycles. These values are in general significantly larger than hydrogen bonds in 1,2-dihidroxybenzene. Conformers stabilized by a beryllium bond exhibit the typical features of this non-covalent interaction, such as the presence of a bond critical point according to the topology of the electron density, positive Laplacian values, significant geometrical distortions and strong interaction energies between the donor and acceptor quantified by using the Natural Bond Orbital approach. An isodesmic reaction scheme is used as a tool to measure the strength of the beryllium bond in these systems in terms of isodesmic energies (analogous to binding energies), interaction energies and deformation energies. This approach shows that a huge amount of energy is spent on deforming the donor–acceptor pairs to form the new rings.

Porphyrin Supramolecular Arrays Formed by Weakly Interacting Meso-Functional Groups on Au(111)

The formation of a binary porphyrinic self-assembled system between meso-tetrakis(4-carboxyphenyl) porphyrin (TCPP) and meso-tetrakis(4-dimethyl amino) porphyrin (TDAP) was easily designed through non-covalent interactions in solution and adsorbed on a gold substrate. It was found that non-covalent interactions and geometrical conformations between porphyrins allow their self-assembly into a well-defined arrangement, which was confirmed by UV-Vis spectroscopy, electrochemistry, atomic force microscopy and density functional theory (DFT) studies.

Site-Selective Acylation of Pyranosides with Immobilized Oligopeptide Catalysts in Flow

We report the site-selective acetylation of partially protected monosaccharides using immobilized oligopeptide catalysts, which are readily accessible via solid-phase peptide synthesis. The catalysts are able to invert the intrinsic selectivity, which was determined using N-methylimidazole, for a variety of pyranosides. We demonstrate that the catalysts are stable for multiple reaction cycles and can be easily reused after separation from the reaction solution. The catalysts can also be used in flow without loss of reactivity and selectivity.

Selenium(IV) Polybromide Complexes: Structural Diversity Driven by Halogen and Chalcogen Bonding

Reactions between bromoselenate(IV)-containing solutions, dibromine and salts of pyridinium-family organic cations resulted in structurally diverse, bromine-rich polybromine-bromoselenates(IV): (4-MePyH)₅[Se₂Br₉][SeBr₆](Br₃)₂ (1), (2-MePyH)₂{[SeBr₆](Br₂)} (2), (PyH)₂{[SeBr₅]Br(Br₂)₂} (3), (1-MePy)₂{[SeBr₆](Br₂)} (4). The compounds feature halogen and (in the case of 3) chalcogen bonding in solid state, resulting in formation of supramolecular architectures of different dimensionality. DFT calculations allowed estimation of the energies of non-covalent interactions in 1–4; additionally, characterization by Raman spectroscopy was performed.

Self-Assembly of Short Amphiphilic Peptides and Their Biomedical Applications

A series of functional biomaterials with different sizes and morphologies can be constructed through self-assembly, among which amphiphilic peptide-based materials have received intense attention. One main possible reason is that the short amphiphilic peptides can facilitate the formation of versatile materials and promote their further applications in different fields. Another reason is that the simple structure of amphiphilic peptides can help establish the structure-function relationship. This review highlights the recent advances in the self-assembly of two typical peptide species, surfactant-like peptides (SLPs) and peptides amphiphiles (PAs). These peptides can self-assemble into diverse nanostructures. The formation of these different nanostructures resulted from the delicate balance of varied non-covalent interactions. This review embraced each non-covalent interaction and then listed the typical routes for regulating these non-covalent interactions, then realized the morphologies modulation of the self-assemblies. Finally, their applications in some biomedical fields, such as the stabilization of membrane proteins, templating for nanofabrication and biomineralization, acting as the antibacterial and antitumor agents, hemostasis, and synthesis of melanin have been summarized. Further advances in the self-assembly of SLPs and PAs may focus on the design of functional materials with targeted properties and exploring their improved properties.

Elucidation of Charge Contribution in Iridium-Chelated Hydrogen-Bonding Systems

We present two iridium complexes 1H⁺ and 2H⁺ that contain cationic ligands to extend the knowledge of charge-assisted hydrogen bonding (CAHB), which counts among the strongest non-covalent bonding interactions. Upon protonation, both complexes were converted into new hydrogen-bonding arrays with various selectivity for respective H-bonding partners. This study compares the association strengths of four hydrogen-bonding co-systems, emphasizing the roles of CAHB in supramolecular systems. We determined that the cationic charge in these systems contributed up to 2.7 kJ mol⁻¹ in the H-bonding complexation processes.

p-Sulfonato-Calix[4]arene Micelles Stabilize a Povidone Iodine Solution: Supramolecular Interactions, Iodine Retention, and Bactericidal Activity

Povidone iodine (PVPI) is an antiseptic widely used against a broad spectrum of pathogens. However, undesired side-effects are still associated with PVPI treatment due to the irritant effect of iodine. Reducing the concentration of a PVPI formulation could provide safer and more friendly formulations, for routine use and applications in very delicate organs such as the eye. However, managing the storage of a low-concentration solution of PVPI is challenging due to the high iodine volatility. In this study, we demonstrated that an amphiphilic p-sulfonato-calix[4]arene derivative forming micelles (SC4OC6) improves the stability of a 0.1% PVPI aqueous buffered solution. UV-vis and NMR spectra as well as dynamic and electrophoretic light scattering measurements showed that SC4OC6 establishes non-covalent supramolecular interactions with PVPI, resulting in the formation of nanoaggregates with a negatively charged surface. Isothermal titration calorimetry provided the aggregation parameters and evidenced that the formation of the supramolecular assembly is an enthalpically favored process. The interaction of SC4OC6 with PVPI enhances the iodine retention and stability of the solution without affecting the rapid and effective bactericidal activity of PVPI, as demonstrated by a time-killing assay with Staphylococcus epidermidis.

The Origin of Stereoselectivity in the Hydrogenation of Oximes Catalyzed by Iridium Complexes: A DFT Mechanistic Study

Herein the reaction mechanism and the origin of stereoselectivity of asymmetric hydrogenation of oximes to hydroxylamines catalyzed by the cyclometalated iridium (III) complexes with chiral substituted single cyclopentadienyl ligands (Ir catalysts A1 and B1) under acidic condition were unveiled using DFT calculations. The catalytic cycle for this reaction consists of the dihydrogen activation step and the hydride transfer step. The calculated results indicate that the hydride transfer step is the chirality-determining step and the involvement of methanesulfonate anion (MsO^-) in this reaction is of importance in the asymmetric hydrogenation of oximes catalyzed by A1 and B1. The calculated energy barriers for the hydride transfer steps without an MsO^- anion are higher than those with an MsO^- anion. The differences in Gibbs free energies between TSA5-1fR/TSA5-1fS and TSB5-1fR/TSB5-1fS are 13.8/13.2 (ΔΔG^‡ = 0.6 kcal/mol) and 7.5/5.6 (ΔΔG^‡ = 1.9 kcal/mol) kcal/mol for the hydride transfer step of substrate protonated oximes with E configuration (E-2a-H⁺) with MsO^- anion to chiral hydroxylamines product R-3a/S-3a catalyzed by A1 and B1, respectively. According to the Curtin-Hammet principle, the major products are hydroxylamines S-3a for the reaction catalyzed by A1 and B1, which agrees well with the experimental results. This is due to the non-covalent interactions among the protonated substrate, MsO^- anion and catalytic species. The hydrogen bond could not only stabilize the catalytic species, but also change the preference of stereoselectivity of this reaction.

Increasing Complexity in Adamantyl Thioethers Characterized by Rotational Spectroscopy

We report on the synthesis and characterization using high-resolution rotational spectroscopy of three bulky thioethers that feature an adamantyl group connected to a sulfur atom. Detailed experimental and theoretical structures are provided and compared with the 1,1'-diadamantyl ether. In addition, we expand on previous findings concerning microsolvation of adamantyl derivatives by investigating the cluster formation between these thioethers and a water molecule. The investigation of such clusters provides valuable insights into the sulfur-centered hydrogen bonding in thioethers with increasing size and steric repulsion.