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A 12‐step total synthesis of the natural product dysiherbol A, a strongly anti‐inflammatory and anti‐tumor avarane meroterpene isolated from the marine sponge Dysidea sp., was elaborated. As key steps, the synthesis features an enantioselective Cu‐catalyzed 1,4‐addition/enolate‐trapping opening move, an Au‐catalyzed double cyclization to build up the tetracyclic core‐carbon skeleton, and a late installation of the C5‐bridgehead methyl group via proton‐induced cyclopropane opening associated with spontaneous cyclic ether formation. The obtained pentacyclic compound (corresponding to an anhydride of the originally suggested structure for dysiherbol A) showed identical spectroscopic data as the natural product, but an opposite molecular rotation. CD‐spectroscopic measurements finally confirmed that both the constitution and the absolute configuration of the originally proposed structure of (+)‐dysiherbol A need to be revised., In a key step of the first enantioselective total synthesis of the anti‐inflammatory marine meroterpene dysiherbol A, the tetra‐carbocyclic core skeleton is set‐up in a unique gold‐catalyzed double cyclization, and the ether bridge of the pentacyclic target structure is spontaneously formed under cyclopropane opening upon deprotection of a late intermediate.

Molecular dynamics simulations are performed to explore if isotopic chirality can induce unidirectional rotary motion in molecular motors operated through double-bond photoisomerizations. Using a high-quantum yield motor featuring a chemically asymmetric carbon atom as reference, it is found that isotopically chiral counterparts of this motor sustain such motion almost equally well. Overall, the study reveals a previously unexplored role for isotopic chirality in the design of rotary molecular motors B.D. acknowledges financial support from the Olle Engkvist Foundation (Grants 184-568 and 204-0183) and the Swedish Research Council (Grant 2019-03664), and grants of computing time at the National Supercomputer Centre (NSC) in Linköping

Controllable molecular release from delivery vehicles is essential to successfully reduce drug toxicity and improve therapeutic efficacy. Light-powered hydrophobic molecular motors were therefore incorporated in liposomes to use molecular rotation to facilitate on-demand release. The extent of the release was precisely controlled by irradiation times, providing a simple yet sophisticated responsive molecular nanocarrier. This journal is

The goal of the studies presented in this dissertation is to continuously expand the capability of a scanning tunneling microscope (STM) by improving its chemical sensitivity and temporal resolution. It has been demonstrated that the combination of STM with other techniques gains insight into the physical and chemical properties of single molecules. Single molecule rotational spectroscopy and microscopy is demonstrated using STM inelastic tunneling spectroscopy (IETS). We conduct real-space measurements of rotational transitions of gaseous hydrogen molecules physisorbed on surfaces at 10 K. The j=0 to j=2 rotational transition for para-H2 and HD were observed by STM-IETS. It is also found that the rotational energy is very sensitive to its local environment, we could precisely investigate how the environmental coupling modifies the structure, including the bond length, of a single molecule with sub-Ångström resolution. Due to this high sensitivity, the spatial variation in the potential energy surface can be quantified by the rotational and vibrational energies of the trapped H2. The ability of the tip to drag along a hydrogen molecule as it scans over another adsorbed molecule combined with the sensitivity of the hydrogen rotational excitation recorded by IETS to its immediate environment lead to the implementation of rotational spectromicroscopy, which helps us reveal the intermolecular interaction and charge transfer between H2 and a large molecule. Furthermore, we demonstrate that the H2 in the STM junction can be dissociated by the mechanical motion of the STM tip. Hydrogen rotational spectroscopy and microscopy provides novels approach toward visualizing and quantifying the local potential energy surface as well as the potential landscape of chemical reactions.Joint Ångström-femtosecond resolution is achieved by the combination of an STM with a femtosecond laser. We demonstrate the bond-selected, photo-assisted activation of a single C-H bond in an azulene molecule adsorbed on a Ag(110) surface. When the junction is illuminated by femtosecond laser, the electrons in the tip can be photo-excited into higher energy states and dissociate the molecule through a photo-assisted tunneling process. The photon-electron coupling at the junction enables the investigation of coherence molecular transformation with joint fs-Å resolution. We also show the band bending and laser induced band flattening at a molecule-semiconductor interface. More importantly, we observe the photo-induced, reversible conformational change between two structures for a single pyrrolidine molecule on a Cu(001) surface. The conductance changes of the STM junction associated with the structural transitions exhibits oscillates in time with periods corresponding to specific molecular vibrations. The vibrational frequencies and decay time are observed in real-space and real-time. Our laser-STM technique enables the investigation of inhomogeneous environmental effect on the molecular dynamics. We have found that the intermolecular interaction between two pyrrolidine molecules can increase the vibrational period while shortening its decay time. We anticipate that this novel technique would lead to a broad impact in physics and chemistry through direct visualization of coherently driven reactions resolved in space and time.

We report velocity controls of a directional molecular motion by a femtosecond intense laser pulse. A laser-induced, direction-controlled rotational wave packet in N2 molecules was subjected to a l...

The racemization process of various 1,1′-binaphthyl derivatives is studied by quantum calculations. The preferred racemization pathway passes through a transition state belonging to the Ci symmetry group. The energy barrier for this process is independent of solvation, the electron-withdrawing/releasing power of substituents, or their ability to engage in H-bonds within the molecule. The primary factor is instead the substituent size. The barrier is thus reduced when the −OH groups of 1,1′-bi-2-naphthol are replaced by H. There is a drop in the barrier also when the substituents are moved from the 2,2′ positions to 6,6′, where they will not come close to one another in the transition state. Upon removal of the peripheral aromatic rings of the binaphthyl system, the biphenyl system undergoes a facile racemization. It is concluded that the optimal means of improving optical stability of 1,1′-binaphthyl systems is the substitution of large bulky groups in the 2,2′ positions.

This work proposes the data augmentation by molecular rotation, with consideration that the protein-ligand binding events are rotation-variant. As a proof-of-concept, known active (i. e., 1-labeled) ligands to human β-secretase 1 (BACE-1) are rotated for the generation of 0-labeled data, and the rotation-dependent prediction accuracy of 3D graph convolutional network (3DGCN) is investigated after data augmentation. The data augmentation makes the orientation-recognizing ability of 3DGCN improved significantly in the classification task for BACE-1/ligand binding. Furthermore, the data-augmented 3DGCN has a capability for predicting active ligands from a candidate dataset, via improved performance of orientation recognition, which would be applied to virtual drug screening and discovery.

Measurements of the decay of electric fields, formed spontaneously within vapour-deposited films ofcis-methyl formate, provide the first direct assessment of the energy barrier to secondary relaxation in a molecular glass. At temperatures far below the glass transition temperature, the mechanism of relaxation is shown to be through hindered molecular rotation. Magnetically-polarised neutron scattering experiments exclude diffusion, which is demonstrated to take place only close to the glass transition temperature.

A dominating F···π*aromatic interaction is found to govern the benzaldehyde···tetrafluoromethane complex, as revealed by this rotational spectroscopic investigation. Secondary F···π*-C=O- and C σ*CF4···πaromatic interactions also contribute to the stability of the observed isomer. Narrow splittings have been observed in the rotational spectrum originating from a 3-fold internal rotation of CF4 above the aromatic moiety, and a corresponding V3 barrier was determined to be 1.572(14) kJ mol-1. This is the first rotational spectroscopic evidence in the literature implying that the aromatic π* antibonding orbital can be activated not only by electron-withdrawing substituents but also by complexation partners containing atoms with high electronegativity, like CF4. The results emphasize the partner molecules' role to modulate the π electron structure and show a change in the orbital character (π or π*) when participating in the formation of noncovalent interactions.

The authors report the ultrafast molecular rotation of dicationic acetylene dimers during Coulomb explosion using time-resolved pump-probe experiments and ab-initio molecular dynamics simulations.

Unidirectional molecular rotation based on alternating photochemical and thermal isomerizations of overcrowded alkenes is well established, but rotary cycles based purely on photochemical isomerizations are rare. Herein we report three new second-generation molecular motors featuring a phosphorus center in the lower half, which engenders a unique element of axial chirality. These motors exhibit unusual behavior, in that all four diastereomeric states can interconvert solely photochemically. Kinetic analysis and modeling reveal that the behavior of the new motors is consistent with all-photochemical unidirectional rotation. Furthermore, X-ray crystal structures of all four diastereomeric states of two of these new motors were obtained, which constitute the first achievements of crystallographic characterization of the full 360° rotational cycle of overcrowded-alkene-based molecular motors. Finally, the axial phosphorus stereoelement in the phosphine motor can be thermally inverted, and this epimerization enables a “shortcut” of the traditional rotational cycle of these compounds.

A highly sensitive fluorescent probe CBH based on solvatochromism and molecular rotation was designed and developed for imaging of hERG channels by employing a novel targeting group 4-benzylaniline. More importantly, CBH has the potential for the quantitative analysis of the hERG channels expressed in tumor cells.

Four donor–acceptor salicylaldimines with benzoheterocyclic substituents at nitrogen imine were prepared and characterised by means of optical spectroscopy. Their luminescent properties were compared with two isoelectronic carbocyclic analogues. In contrast to the typical salicylaldimines, our reported benzoheterocyclic compounds exhibit solely local emissive behaviour in all media whereas for the carbocyclic analogues we expectedly observe dominant ESIPT emission in the majority of instances. Low temperature (5 K - liquid helium) fluorescence measurements revealed the effect of the restriction of the molecular rotation which was manifested by significant increment of the fluorescence intensity. The comprehensive experimental and ab initio study reveal effect of solvent polarity, viscosity and temperature on the complex photophysics of heterocyclic and carbocyclic substituted salicylaldimines with several degrees of freedom for molecular transformations. This work adds considerable insight in emission lifetime data which greatly facilitates understanding of the fluorescence mechanism of the molecules with environmentally dependent restrictions.

The elucidation of conformations and relative potential energies (rPEs) of small molecules has a long history across a diverse range of fields. Periodically, it is helpful to revisit what conformations have been investigated and to provide a consistent theoretical framework for which clear comparisons can be made. In this paper, we compute the minima, first- and second-order saddle points, and torsion-coupled surfaces for methanol, ethanol, propan-2-ol, and propanol using consistent high-level MP2 and CCSD(T) methods. While for certain molecules more rigorous methods were employed, the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pV5Z theory level was used throughout to provide relative energies of all minima and first-order saddle points. The rPE surfaces were uniformly computed at the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVTZ level. To the best of our knowledge, this represents the most extensive study for alcohols of this kind, revealing some new aspects. Especially for propanol, we report several new conformations that were previously not investigated. Moreover, two metrics are included in our analysis that quantify how the selected surfaces are similar to one another and hence improve our understanding of the relationship between these alcohols.

Here a structural design aimed at the control of phosphorescence emission as the result of changes in molecular rotation in a crystalline material is presented. The proposed strategy includes the use of aurophilic interactions, both as a crystal engineering tool and as a sensitive emission probe, and the use of a dumbbell-shaped architecture intended to create a low packing density region that permits the rotation of a central phenylene.

It was found that for H-shape dimers, the parity of the number of atoms in the spacer linking the mesogenic cores has important influence on the mesogenic properties only for the molecules with weak mesogenic core anisotropy. In the case of stronger core anisotropy, the parallel arrangement of mesogenic units is induced regardless of the spacer parity. As a result, phase transition temperatures and layer spacing are only weakly affected by spacer parity. By studying the properties of six new homologue series it was found that for H-shape dimers the orthogonal smectic (SmA) is strongly disfavoured: most compounds form a tilted smectic (SmC) phase, which is related to hindrances in molecular rotation for molecules with large breath to length ratio. For dimers with very long spacer, and thus decoupled mesogenic units, the smectic phase is replaced by a nematic phase, and for stiff polycatenar molecules with very short spacers the cubic phase can appear.

This review article presents the generation and control of polarization-shaped femtosecond laser pulses. Some applications of these pulses to coherent control are described, including multiphoton photoionization, forced molecular rotation, optical control of lattice vibrations, nano-optics, and wavelength conversion. Theoretical expectations for enantiomeric purification and magnetization are also discussed.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná Neste trabalho são descritos o planejamento, a síntese, a caracterização e alguns estudos das propriedades ópticas, térmicas e da organização supramolecular de derivados não simétricos do núcleo tris-[1,2,4]-triazolo-[1,3,5]-triazina. Seis compostos não simétricos foram obtidos pela reação do cloreto cianúrico com três diferentes tetrazóis estrategicamente utilizados, os quais foram preparados a partir de compostos comercias seguindo reações clássicas de alquilação e adição 1,3-dipolar. Todos os compostos finais tiveram sua formação confirmada por HRMS. Entretanto, as misturas formadas nas reações se mostraram de difícil separação e apenas dois compostos foram isolados com elevada pureza. Os compostos isolados, TTT331 e TTT311, com estrutura molecular não simétrica, tiveram suas estruturas confirmadas por RMN de 1H, 13C. Apenas o TTT331 apresentou propriedades líquido-cristalinas, e teve suas propriedades térmicas e mesomórficas investigadas por MOLP, DSC e SAXS, este último realizado no Laboratório Nacional de Luz Síncrotron. O composto analisado apresentou mesofase do tipo Colh em ampla faixa de temperatura (220,7 °C, de -21,7 °C a 199,0 °C), confirmando uma mesofase de grande estabilidade térmica quando comparada a outros derivados simétricos do mesmo núcleo tristriazolotriazina. Desta forma foi possível fazer um estudo sistemático comparando a estrutura molecular e suas propriedades, mostrando que a formação de mesofase depende do número de cadeias periféricas, para derivados não simétricos do núcleo estudado. Além disso, a perda de simetria dificulta a organização molecular necessária para o processo de cristalização aumentando a estabilidade térmica da mesofase, como observado para o composto não simétrico TTT331. In this work are described, the design, synthesis, characterization and some studies of the optical, thermal properties and supramolecular organization of the first asymmetric derivatives of tris-[1,2,4]-triazolo-[1,3,5]-triazine nucleus. Six asymmetric compounds were obtained by reaction of the cyanuric chloride with three strategically used different tetrazoles, which were prepared from commercial compounds following classical reactions of alkylation and 1,3-dipolar addition. All the final compounds had their formation confirmed by HRMS. However, the mixtures formed in the reactions were difficult to separate and only two compounds were isolated with high purity. The isolated compounds, TTT331 and TTT311, with asymmetric molecular structure, had their structures confirmed by 1H, 13C NMR. Only TTT331 had shown liquid-crystalline properties and had its thermal and mesomorphic properties investigated by MOLP, DSC and SAXS, the latter carried out at the National Synchrotron Light Laboratory. The analyzed compound presented Colh type mesophase over a wide temperature range (220.7 ° C, -21.7 ° C to 199.0 ° C), confirming a mesofase of great thermal stability when compared to other symmetric derivatives of the same tristriazolotriazine nucleus. In this way it was possible to make a systematic study comparing the molecular structure and its properties, showing that mesophase formation depends on the number of peripheral chains, for asymmetric derivatives of the nucleus studied. In addition, the loss of symmetry hinders the molecular organization necessary for the crystallization process by increasing the thermal stability of the mesophase, as observed for the asymmetric compound TTT331.

Aggregation-induced emission (AIE) is a phenomenon where non-luminescent compounds in solution become strongly luminescent in aggregate and solid phase. It provides a fertile ground for luminescent applications that has rapidly developed in the last 15 years. In this review, we focus on the contributions of theory and computations to understanding the molecular mechanism behind it. Starting from initial models, such as restriction of intramolecular rotations (RIR), and the calculation of non-radiative rates with Fermi's golden rule (FGR), we center on studies of the global excited-state potential energy surfaces that have provided the basis for the restricted access to a conical intersection (RACI) model. In this model, which has been shown to apply for a diverse group of AIEgens, the lack of fluorescence in solution comes from radiationless decay at a CI in solution that is hindered in the aggregate state. We also highlight how intermolecular interactions modulate the photophysics in the aggregate phase, in terms of fluorescence quantum yield and emission color LB thanks financial support from the Spanish Ministerio de Economía y Competitividad (CTQ2015-69363-P)

An asymmetric mechanism for correlated motion occurring in noninteracting pairs of adjacent orthogonal 1,4-bis(carboxyethynyl)bicyclo[1.1.1]pentane (BCP) rotators 1 in the solid state is unraveled and shown to play an important role in understanding the dynamics in the crystalline rotor, Bu4N+[1–]·H2O. Single crystal X-ray diffraction and calculation of rotor–rotor interaction energies combined with variable-temperature, variable-field 1H spin–lattice relaxation experiments led to the identification and microscopic rationalization of two distinct relaxation processes., Work in Bellaterra and Tarragona was supported by the Spanish Ministerio de Economía y Competitividad (projects FIS2015-64886-C5-4-P and CTQ2017-87269-P) and Generalitat de Catalunya (2014GR301 and 2014GR199). E.C. acknowledges the support of the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under grant SEV-2015-0496. J.K. and J.M. gratefully acknowledge financial support from the European Research Council under the European Community’s Framework Programme (FP7/2007-2013) ERC grant agreement no. 227756 and the Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic (RVO: 61388963). This material is based upon work supported by the National Science Foundation under grant no. CHE-1566435. Work at Orsay was supported by the CNRS. Work at Angers was supported by the CNRS and the Région des Pays de la Loire grant MOVAMOL. Joint work at Angers, Orsay, and Prague was supported by the Ministère de l’Europe et des Affaires Etrangères under the grant PHC Barrande no. 864563J.

The temperature dependence of the UV absorption spectra of biphenyl in solution is herein reported. The UV spectral shapes vary with an increase in temperature, where a decrease in intensity (hypochromism) and blue shifts are observed. The predicted UV spectra in the Time Dependent-Density Functional Theory (TD-DFT) framework within the B97D3 functional indicate a lowering of the biphenyl conjugation band and a blue shift of the spectra upon increasing the biphenyl twist dihedral angle.

Organic luminogens with aggregation-induced emission (AIE) properties have unusual emission behaviour in that their non- or weakly-emissive solutions can be tuned to emit strongly in the solution aggregated and solid states. As restricted molecular rotation of luminogens is the main mechanism leading to AIE activity, hydrogen bond (H bond) interactions are therefore used in organic and polymeric luminogens to impose efficient rotational restriction and to intensify the emission intensity of the AIE-active luminogens. Luminogenic polymers containing H-bonding groups and luminogenic blends consisting of H-bond donors and acceptors are therefore described in this review to evaluate the relationship between H bond interactions, rotational restriction and AIE-related emission intensity.

Because restricted molecular rotation is the main mechanism responsible for aggregation-induced emission (AIE), a Jeffamine-included polyrotaxane (JCD) was therefore used in this study as a rigid template to impose effective rotational restriction on the AIE-active luminogen of 1,2-bis(2,4-dihydroxybenzylidene)hydrazine (CN4OH). Besides rigidifying the flexible Jeffamine chain, the β-cyclodextrin (β-CD) rings of JCD also provided hydroxyl (OH) groups to hydrogen bond to the OHs of CN4OH, furnishing emissive CN4OH/JCD(x/y) (x/y: molar ratio between CN4OH and JCD) blends with emission efficiency higher than the pure CN4OH itself. Dependent on the composition of the blends, CN4OHs in the blends are arrayed differently to experience varied levels of rotational restriction and thus emit with an intensity correlated with the molecular arrangement of the CN4OHs in the blends. The relationship between molecular arrangement, restricted molecular rotation and AIE-oriented emission behavior is the focus of this study.

Because restricted intramolecular rotation (RIR) is the main mechanism responsible for the aggregation-induced or -enhanced emission (AIE or AEE), we thus used a rigid polyrotaxane to impose effective RIR for an ionic, water-soluble and AEE-active luminogen of sodium 4,4′,4′′,4′′′-(thiophene-2,3,4,5-tetrayl)tetrabenzenesulfonate (TPS). Jeffamine-included β-cyclodextrin (JA-included β-CD) with cationic ammonium terminals was used as a rigid component to complex with the sulfonate anions of TPS, resulting in an iTP–CD-JA complex, which was used for characterization. Comparison was also made with a complex of iTP–JA prepared from the complexation of TPS with flexible JA chains. Without the incorporation of rigid β-CD rings, the emission efficiency of the iTP–JA complex was inferior to that of the iTP–CD-JA complex. The role of a rigid template in imposing effective RIR on an AEE-active luminogen was thus demonstrated in this study.

The differences in the rotational temperatures between neutral molecules and molecular ions are examined for low-pressure microwave discharge nitrogen plasma and oxygen plasma. For N2 plasma, the rotational temperatures of the second positive system (2PS) and first negative system (1NS) are measured, whereas for O2 plasma, those of the atmospheric absorption band (A-band) and 1NS are measured for neutrals and ions, respectively. The experimentally measured spectra are compared with the theoretically calculated ones to determine the vibrational and rotational temperatures as best fitting parameters. It is found that the ions have a higher rotational temperature than neutrals for the N2 plasma, while both have almost the same temperature for the O2 plasma, for which a discussion is made on the basis of atomic and molecular processes. The difference in the rotational temperature between the neutrals and the ions is also discussed from the viewpoint of the atomic and molecular processes in the plasmas.

Restriction on molecular rotation of fluorophores reduces non-radiative decay channels and promotes strong fluorescence due to aggregation-enhanced emission (AEE) behavior. To evaluate the important role of restricted molecular rotation on AEE behavior, tetraphenylthiophene (TP) derivatives with two pyridine (Py) or two triphenylamine (TPA) terminals were synthesized and characterized to be AEE-active fluorophores. Because of the efficient hindered molecular rotation of the larger TPA terminals, TP-2TPA emitted with higher emission efficiency than TP-2Py with smaller Py terminals. In addition, Py and TPA terminals can serve as hydrogen-bond (H-bond) accepting groups to bind with H-bond donating hydroxyl groups in poly(vinyl phenol) (PVPh) and poly(vinyl alcohol) (PVA) to further reinforce rotational restriction on the TP-2Py and TP-2PTA fluorophores. TP-2Py and TP-2PTA were therefore blended with PVPh and PVA and the emissive properties of the resultant blends were characterized and compared with the unblended TP-2Py and TP-2PTA to emphasize the role of H-bond on restricted molecular rotation.

The phase transition mechanism of AZADO radical has been examined in terms of the molecular rotation. Drastic changes in optical, magnetic and dielectric properties associated with the phase transition can be explained by molecular rotation and an associated order–disorder transition.

4-Methylanilinium derivatives were used to introduce spaces for molecular rotation in crystals. The [Ni(dmit)2]− (dmit2– = 2-thioxo-1,3-dithiole-4,5-dithiolate) salts with supramolecular cations of dibenzo[18]crown-6 (DB[18]crown-6) and 4-methylanilinium derivatives, (4-methylanilinium+)(DB[18]crown-6)[Ni(dmit)2]− (1), (2-fluoro-4-methylanilinium+)(DB[18]crown-6)[Ni(dmit)2]− (2), and (3-fluoro-4-methylanilinium+)(DB[18]crown-6)[Ni(dmit)2]− (3) were synthesized. The potential energy curves for the molecular rotations of the cations in the crystals had double minimum shapes with maxima of 100, 210, and 230 kJ mol–1 for crystals 1, 2, and 3, respectively. Introduction of a methyl substituent at the p-position was effective in reducing the potential energy maxima. For crystals 2 and 3, large dielectric responses originating from the flip-flop motions of the cationic molecules were observed upon applying an AC voltage. The temperature-dependent magnetic susceptibilities of complexes 1, 2, and 3 followed the Cu...

Solid-state NMR (SS-NMR) of proteins requires that those molecules be immobilized, usually by crystallization, freezing, or lyophilization. However, self-crowding can also slow molecular rotation sufficiently to prevent the nuclear interactions from averaging. To achieve self-crowding, researchers can use a centrifugal field to create a concentration gradient or use regular ultracentrifugation to produce highly concentrated, gel-like solutions. Thus sedimented solute NMR (SedNMR) provides a simple method to prepare biological samples for SS-NMR experiments with minimal perturbation. This method may also give researchers a way to investigate species that are not otherwise accessible by NMR. We induce the sedimentation in one of two ways: (1) by the extreme centrifugal force exerted during magic angle spinning (MAS-induced sedimentation or in situ) or (2) by an ultracentrifuge (UC-induced sedimentation or ex situ). Sedimentation is particularly useful in situations where it is difficult to obtain protein crystals. Furthermore, because the proteins remain in a largely hydrated state, the sedimented samples may provide SS-NMR spectra that have better resolution than the spectra from frozen solutions or lyophilized powders. If sedimentation is induced in situ, the same protein sample can be used for both solution and SS-NMR studies. Finally, we show that in situ SedNMR can be used to detect the NMR signals of large molecular adducts that have binding constants that are too weak to allow for the selective isolation and crystallization of the complexed species. We can selectively induce sedimentation for the heaviest molecular species. Because the complexed molecules are subtracted from the bulk solution, the reaction proceeds further toward the formation of complexes.

Four kinds of liquid crystalline polymers (LCPs) with phenyl benzoate side groups were synthesized and their photoinduced reorientation behavior was investigated using linearly polarized (LP) UV light based on the axis-selective photo-Fries rearrangement and thermally induced self-organization of the mesogenic side groups of the materials. Due to different effect of the axis-selectively photoreacted side groups, reorientation direction and its performance depended on the chemical structure of the side groups. Both alignment ability and the molecular rotation of the photoreacted side groups played an important role in the reorientation behavior.

As a stacked form of ultrathin polymer films, multilayer nanostructures are of great interest in various applications. Coarse-grained molecular dynamics simulations were carried out to understand the behaviors of interfacial diffusion and bonding of multilayer polymer films. We found two obvious stages for the interfacial diffusion of polymers in the multilayer film, and it is 3 times faster in the first stage than in the second one due to the evolution of molecular conformations. The polymers near the interfaces have an in-plane mobility much higher than the out-of-plane one. The strength of interfacial bonding has been characterized by the fast tensile stress-strain curve along the normal direction. It shows multiple yielding points for the multilayer polymer films, which is distinct from the tensile behavior of the bulk. The ultimate tensile stress (UTS) and corresponding separating strain, surprisingly, do not necessarily increase with diffusion time. Because of the dramatic molecular rotation and extension during the first stage of interfacial diffusion, the interlayer interpenetration is nonuniformly distributed in the plane of the interface. Such a nonuniform distribution may be one of the reasons for the decrease of the UTS and separating strain.

Despite the fact that 2-(2′-hydroxyphenyl)benzimidazole (HPBI) exists as the cis and trans enol in neutral form, it was reported to exist only in the trans form upon deprotonation in an aqueous medium. It was also shown that the dianion formed in the ground state can be re-protonated to form the trans-anion in the excited state. In the present study, the cis-anion and dianion could be obtained upon proper stabilization in suitable environments. Switching between the cis and trans-anion was demonstrated to be possible by changing the environment. Theoretical calculations were performed to substantiate the existence of the cis-anion and dianion. In contrast to a literature report, it was shown that the ‘OH’ group deprotonates before the ‘NH’ group to form a monoanion not only in protic solvents but also in aprotic solvents.

For the computation of rovibrational levels and their spectroscopic intensities, the Eckart conditions are essential to achieve the optimal separation between rotation and vibration. Dymarsky and Kudin [J. Chem. Phys. 122, 124103 (2005)] proposed a procedure for a simplified calculation of the Eckart rotation matrix. In the present work, we have adapted their approach to obtain a kinetic energy operator in curvilinear coordinates using a numerical but exact procedure without resorting to finite differences. Furthermore, we have modified this approach for the study of molecular systems with several minima, for which several Eckart reference geometries are required. The HONO molecular system has been used to show the efficiency of our implementation. Using the Eckart conditions with multi-reference geometries allows for a calculation of the rotational levels as well as frequencies and intensities of the infrared spectra of both HONO isomers with a single calculation.

A new definition of atomic charge, Mean Gradient Charge (MGC) is proposed on the basis of ‘induced atomic gradient’. Conceptually the connection between electric response to external point charge and Coulomb’s law made exact, providing a unique way of extracting atomic charges from quantum mechanical calculations without any numerical ambiguities. Furthermore MGC is relatively invariant with respect to molecular rotation, choices of basis set and even correlation treatments. Preliminary test calculations show that MGC values are in between Mulliken and NPA charges.

The orientational order parameter, rotational ground-state energy, and lattice distortion parameter (the deviation of the c/a ratio from the ideal hcp value 1.633) in hcp lattice of phase I of p-H2 and o-D2 are calculated using a semi-empirical approach. It is shown that the lattice distortion in these J-even species is small compared with that found in n-H2, and n-D2. The difference presumably is caused by the J-odd species.

The molecular rotation parameters of cholesteric liquid crystals (LCs) are calculated based on their phase transition temperatures using a semi-empirical molecular orbital method. A molecular rotation model is employed to evaluate the correlation between the LC phase transition and their molecular structure. The cholesteric-isotropic phase transition temperature and critical rotational velocity are regularly reduced with increasing molecular length. A novel explanation for the molecular interaction effect on phase transition is proposed. For low-temperature phases, the molecular interaction is strong and plays a key role in the phase transition. In contrast, for high-temperature phases, the molecular rotation effect becomes the important factor for the phase transition.