Dihedral Angle Research Articles

Accuracy compensation method for 2D curve reconstruction of torsional FBG shape sensor of scraper conveyor

The straightness perception of scraper conveyor is a technology that helps to achieve intelligent operation of coal mine working faces. However, there is a problem of accuracy degradation caused by sensor torsion based on fiber Bragg grating (FBG) shape sensing technology. This paper proposes an accuracy compensation method based on torsion angle, and verifies the effectiveness of accuracy compensation through simulation and experimental research. Experimental tests have shown that when the torsion angle of the sensing substrate is 10° and 20°, the end accuracy of the reconstructed curve after accuracy compensation is increased by 2.77% and 1.93% compared to before compensation, respectively. This study indicates that compensation based on the torsion angle can significantly improve the accuracy of two-dimensional (2D) curve reconstruction, and it has broad engineering application prospects in fields such as straightness perception of scraper conveyors and monitoring of underwater pipelines.

Regulation of Dihedral Angle on Molecular Engineering for Enhancing Triboelectric Performance

AbstractThe performance of triboelectric polymers relies on their molecular structure. Therefore, investigating how to construct high‐performance molecular structures of triboelectric polymers becomes imperative, yet the relationship between microscopic structural parameters and triboelectric performance remains unclear. In this study, the relationship is studied between dihedral angles of adjacent conjugated planes and triboelectric performance. Various polyimide monomers are synthesized to manipulate the conjugated dihedral angles within the molecular chains. Introducing larger dihedral angles in polyimides (PIs) reduces the conjugation between molecular chains, suppressing the formation of charge transfer complexes (CTCs), and widening the energy gap between molecular orbitals. With the increase in dihedral angles, the output performance improved by 100%. The surface charge density of 335 µC·m−2 is achieved through the synergistic effect of the high charge retention capability of the PI film and the high triboelectric properties of the corona‐polarized fluorinated ethylene propylene (FEP). A large dihedral angle can form numerous deep traps and effectively prevent charge escaping while ensuring stable output. This study provides a feasible strategy for investigating the construction of high triboelectric performance molecular structures, enriching the understanding of how molecular structures influence the triboelectric properties of polymer materials and promote high‐performance fluorine‐free and environmentally friendly polymers.

Torque expression of superelastic NiTi V-Slot and conventional stainless steel orthodontic bracket-archwire combinations - a Finite Element Analysis

BackgroundTo investigate the torque expression of conventional stainless steel (SS) brackets in combination with rectangular SS archwires and nickel-titanium (NiTi) V-slot brackets in combination with V-shaped NiTi archwires using finite element analysis (FEA). MethodsCAD models were created for a conventional bracket and rectangular archwires with dimensions of 0.018”x0.025” and 0.019”x0.025”, and for a V-slot bracket and V-shaped archwires with heights of 0.55mm, 0.60 mm and 0.70 mm. FEA was performed using Ansys 2022R2 software to assess the forces and moments during simulated torsion of the archwires in the brackets between 0° and 25° with varying interbracket distances and free path lengths. ResultsThe V-slot bracket-archwire combination exhibited force transmission and moment generation within 1° of torsion. The transmissible force increased with the torsion angle, but showed an upper limit of about 13- 14 Nmm. The SS bracket-archwire combination showed negligible forces and moments for simulated torsion between 0° and 15°. At torsions of 25°, moments of 12 Nmm and 14 Nmm occurred for the 0.018”x0.025” and 0.019”x0.025” archwire dimensions, respectively. ConclusionsThe V-slot bracket-archwire combination is effective in expressing torque and preventing both over- and under-activation. Conventional bracket-archwire combinations showed torsional losses due to play between 10-15°, depending on the dimensions of the respective archwire, and no upper torsional moment limit.

Effect and optimization of geometric parameters and arrangement on film cooling performance of fan-shaped holes based on generalized regression neural network

Inadequate design of film cooling holes can significantly reduce film cooling effectiveness of turbine blades, compromising high temperature resistance. By comparing experimental data, the most suitable turbulence model is selected to calculate film cooling effectiveness on the leading edge of turbine blades. A high-precision nonlinear mapping relationship between the geometric parameters and arrangement of fan-shaped holes, and film cooling effectiveness is established by using machine learning which is trained by 1200 cases. The genetic algorithm is employed to search for optimal parameters. Sensitivity and correlation analyses are conducted to assess the influence degree of the geometric parameters and arrangement on film cooling effectiveness and these mechanisms are analyzed in depth. Findings reveal that the injection angle exerts the most significant effect on film cooling effectiveness, with significant effects observed for the forward expansion angle and the angle with respect to stagnation line. Interactions among parameters play a crucial role in influencing film cooling effectiveness and cannot be disregarded. In the design space, the optimal configuration comprises the injection angle of 30°, the forward expansion angle of 10°, the streamwise torsion angle of 10°, the pitch of holes of 12 mm and the angle with respect to stagnation line of 30°.

Influence of Solvent Polarity on the Conformer Ratio of Bicalutamide in Saturated Solutions: Insights from NOESY NMR Analysis and Quantum-Chemical Calculations

The study presents a thorough and detailed analysis of bicalutamide’s structural and conformational properties. Quantum chemical calculations were employed to explore the conformational properties of the molecule, identifying significant energy differences between conformers. Analysis revealed that hydrogen bonds stabilise the conformers, with notable variations in torsion angles. Conformers were classified into ‘closed’ and ‘open’ types based on the relative orientation of the cyclic fragments. NOE spectroscopy in different solvents (CDCl3 and DMSO-d6) was used to study the conformational preferences of the molecule. NOESY experiments provided the predominance of ‘closed’ conformers in non-polar solvents and a significant presence of ‘open’ conformers in polar solvents. The proportions of open conformers were 22.7 ± 3.7% in CDCl3 and 59.8 ± 6.2% in DMSO-d6, while closed conformers accounted for 77.3 ± 3.7% and 40.2 ± 6.2%, respectively. This comprehensive study underscores the solvent environment’s impact on its structural behaviour. The findings significantly contribute to a deeper understanding of conformational dynamics, stimulating further exploration in drug development.

Experimental and theoretical study of the photochemical properties and acidchromism of nonconventional 2,4,6-triarylpyridine-based materials

2,4,6-Triarylpyridines (TAPs) represent a versatile class of N-heterocycles with broad applications in many fields. This study presents an investigation on photochemical properties and acidchromism behavior of novel 2,6-bis(4-(dodecyloxy)phenyl)-4-(4-substituted-phenyl)pyridine-based derivatives (1a-1g). Photochemical study in dichloromethane (DCM) and acetone (ACT) solutions showed a small solvent effect for the TAP derivatives, except for the carbazole derivative 1a, which was characterized as the most emissive material in all conditions, but especially in DCM solution for blue emission (λEM = 406 nm, ϕf = 0.36). The presence of electron-donating groups at the 4-phenyl moiety contributes to more intense and redshifted emissions in both DCM and ACT solutions, as well as in the solid state. In aqueous ACT, while TAPs bearing EDGs such as 1a presented more intense emissions depending on the water fraction, an opposite effect was verified for fluorinated derivative 1f. The acidchromism of selected TAPs 1a and 1f (fluorinated derivative) in aqueous aacetone was characterized by the decreasing of the emission intensity at 436 nm and 388 nm, respectively, in the presence of aqueous HCl for both TAPs, however, the protonated 1f showed strong emission in higher wavelength (λEM = 476 nm) in acidic medium. A 1H NMR study allowed a better understanding of the structural features associated to the acidchromism. The photochemical and acidchromism results obtained for the TAP derivatives are strongly supported by computational results, and particularly noteworthy is the favoring of the resonance effect as consequence of the decreasing in the torsion angle between the 4-alkoxyaryl substituents and the pyridine core after protonation of 1f. The emissive properties and acidchromism capacity of 1a and 1f allowed the potential application of TAP-adsorbed paper strips as disposable sensors for qualitative detection of gaseous HCl.

Temperature dependence of the near infrared absorption spectrum of single-wall carbon nanotubes dispersed by sodium dodecyl sulfate in aqueous solution: experiments and molecular dynamics study.

Single-wall carbon nanotubes (SWCNT) dispersed in water with the help of sodium dodecyl sulfate (SDS) surfactants exhibit a temperature dependent near infrared (NIR) exciton spectrum. Due to their biocompatibility and NIR spectrum falling within the transparent window for biological tissue, SWCNTs hold potential for sensing temperature inside cells. Here, we seek to elucidate the mechanism responsible for this temperature dependence, focusing on changes in the water coverage of the SWCNT as the surfactant structure changes with temperature. We compare optical absorption spectra in the UV-Vis-IR range and fully atomistic molecular dynamics (MD) simulations. The observed temperature dependence of the spectra for various SWCNTs may be attributed to changes in the dielectric environment and its impact on excitons. MD simulations reveal that the adsorbed SDS molecules effectively shield the SWCNT, with ~ 70% of water molecules removed from the first two adlayers; this coverage shows a modest temperature dependence. Although we are not able to directly demonstrate how this influences the NIR spectrum, this represents a potential pathway given the strong influence of the water environment on the excitons in SWCNTs. Optical absorption measurements were carried out in the UV-Vis-NIR range using a Varian Cary 5000 spectrophotometer in a temperature-controlled environment. PeakFit™ v. 4.06 was used as peak-fitting program in the spectral range 900-1400nm (890-1380meV) as a function of the temperature. Fully atomistic molecular dynamics simulations were conducted using the NAMD2 package. The CHARMM force field comprising two-body bond stretching, three-body angle deformation, four-body dihedral angle deformation, and nonbonded interactions (electrostatic and Lennard-Jones 6-16 potentials) was employed.

A Rare-Earth-Based Borate Optical Crystal with Enlarged Dihedral Angles of Distinct [BO3] Groups Exhibiting a Wide UV Transparent Range.

Borates, as advanced optical materials, have garnered wide interest due to their diverse structural configurations and great potential for applications in the ultraviolet (UV) regions. Herein, we synthesized a new rare-earth borate crystal, namely, K2NaYB2O6, which is classified as one of the ABReB2O6 compounds, where A and B represent alkali metal and Re denotes rare-earth metal. K2NaYB2O6 adopts in the monoclinic space group P21/c (No. 14), showcasing a three-dimensional (3D) framework composed of a planar triangular configuration of [BO3] units and distortive [YO7] polyhedra. Notably, both dihedral angles between distinct [BO3] units reach 79.6°, which represents an unprecedented structural feature in monoclinic ABReB2O6-type crystals. Moreover, the compound has a short UV absorption edge at around 204 nm, corresponding to a wide band gap of approximately 5.67 eV. Additionally, it possesses a moderate birefringence of 0.028 at 1064 nm. Further analysis utilizing theoretical calculations suggests that the optical behaviors of K2NaYB2O6 are mainly governed by its basic structural unit [BO3] triangles and distorted [YO7] polyhedra. These findings enrich the structure chemistry of rare-earth borates and offer valuable insights for the design of optical crystals in the UV wavelength range.

Mechanical characteristics of biomimetic twisted honeycomb structures fabricated by powder bed fusion

Honeycomb structures have been widely used in aerospace and automotive applications due to their high efficiency, high strength and high specific stiffness. However, most of the reported publications have focused on the surface shape variations of honeycomb structures, and there is a lack of studies on the variations of honeycomb structures with respect to the internal cell walls (Z-direction). To address these issues, this study proposes to combine the torsional design of honeycomb and Bouligand structures to fabricate twisted honeycomb structures (THS) with cell wall (z-direction) variations using powder bed fusion technology. The THS (30°) exhibits excellent specific energy absorption (SEA) performance, and the SEA of THS (0°), THS (60°), and THS (90°) are reduced by 8.5%, 19.7%, and 37.3%, respectively, compared with that of THS (30°) structure, and the THS (30°) has better repeatability. The effects of structural parameters on the energy absorption performance were analyzed. At THS (30°), changing the number of unit cells, wall length and wall thickness has a large effect on the compression performance. The results show that the specific energy absorption performance of THS reaches a maximum value of 74.6 kJ/kg for the number unit cells n = 3, wall length l = 5 mm and wall thickness t = 1 mm. (Honeycomb structures are widely used in aerospace and automotive applications because of their high efficiency, high strength, and high specific stiffness. However, most of reported publications focus on surface shape variations of honeycomb structures and the lack of honeycomb structures with variations in the internal cell wall (Z direction). Facing these problems, this investigation has proposed to create twisted honeycomb structures (THS) with internal cell wall (Z-direction) variations by combining the torsional design of honeycomb and Bouligand structures using powder bed fusion. In this study, the effects of different torsion angles on the quasi-static mechanical response and deformation patterns of the honeycomb structures have been evaluatedviaconducting axial compression tests. Numerical simulations are performed using the ABAQUS software and compared with experimental results to verify the accuracy of the simulations. In addition, the effects of the construction parameters on the energy absorption performance have been analyzed. Experimental results show that the THS with a torsion angle of 30° exhibit the best mechanical properties with good repeatability. The specific energy absorption performance of THS reaches a maximum of 74.6 kJ/kg for structural parameters of the number of unit cells n = 3, wall length l = 5 mm, and wall thickness t = 1 mm)

Computed Tomographic Measurement Method for Morphoanatomical Comparison of Femur, Tibia, and Patella in Cats with and without Medial Patellar Luxation.

The aims of this study are to describe a computed tomographic (CT) measurement method of feline femoral, tibial, and patellar conformation, and to compare these measurements between a cat population diagnosed with medial patellar luxation (MPL) and cats without MPL. Eleven measurements were performed by two observers, including anatomical lateral distal femoral angle (aLDFA), femoral trochlear width (FTW) and femoral trochlear depth (FTD), anteversion angle of the femoral neck, patellar length, patellar width, patellar height, patellar volume, mechanical medial proximal tibial angle, tibial torsion angle, and tibial tuberosity displacement. Mean and standard deviation differences between the groups were statistically assessed. Intraobserver and interobserver interclass correlation coefficients (ICCs) were calculated. The aLDFA was significantly higher in the MPL II compared with the control and MPL III. The FTW was significantly larger in the MPL III than in the control or the MPL II group. The FTD in the control group was significantly larger than in the MPL II and III groups. The TTA of the control group was significantly smaller than the MPL II and III. The intraobserver ICC was high at 64%, and the interobserver ICC was high at 36% of the measurements. This study identified shallower FTD and increased TTA in cats diagnosed with MPL. The TTA difference was less than 5 degrees and FTD was less than 1 mm. The findings provide information on feline pelvic limb morphology. However, the differences between the two populations are small.

Orthogonal magnetic orbitals in high spin Cu-VO units: structure, magnetism and EPR study of anisotropic heterometallic complexes.

Molecular-based magnetic materials are expected to serve as building blocks for quantum bits. To realize high-dimensional Hilbert space and addressability, we constructed anisotropic multi-level systems based on CuII and VIV with orthogonal magnetic orbitals. The crystal structures and intramolecular magnetic couplings of four CuIIVOII complexes [{CuVO(appen)2}2], [{CuVO(fhma)2EDA}2], [{CuVO(hfca)2EDA}2] and [CuVO(hfca)2DPEDA]n are characterized. Due to the orthogonal magnetic orbitals of CuII and VIV, the Cu-V pairs in the four complexes have strong ferromagnetic couplings, and the coupling strength is linearly related to the dihedral angle between the two equatorial planes of the two coordination polyhedra. Because of the triplet ground state, the system can be described by an effective Hamiltonian model consisting of two S = 1 spins coupled together. The anisotropy parameters of [{CuVO(hfca)2EDA}2] and [CuVO(hfca)2DPEDA]n were obtained by the simulation of X-band continuous wave electron paramagnetic resonance (cw-EPR) spectra, confirming that both complexes have zero-field splitting addressable on the relative energy scale. The results indicate that constructing multi-centre complexes based on orthogonal magnetic orbitals is a promising strategy for designing multidimensional quantum bits.

An unusual CAr^CNHC- and bidentate NAr^CNHC-cyclometalated Re(I)-NHC complexes with quinoline-functionalized ligands: Syntheses, structures, and blue-luminescent properties

An unusual CAr^CNHC-cyclometalated rhenium(I) tetracarbonyl complexes fac- (CAr^CNHC)Re(CO)4 (13) (the first report) and six NAr^CNHC-cyclometalated rhenium(I) tricarbonyl iodide/chloride complexes with quinoline-functionalized N-heterocyclic carbenes (NHC), fac-Re(CO)3(LNHC)I / fac-Re(CO)3(LNHC)Cl (LNHC = 1-(quinolin-8-yl)-3-methyl-1H-imidazol-2-ylidene (4, 10); 1-(quinolin-8-yl)-4-methyl-1H-1,2,4-triazoline-5-ylidene (5, 11); 1-(quinolin-8-yl)-3-benzyl-1H-imidazol-2-ylidene (6, 12) have been synthesized under controllable reaction conditions and characterized by their 1H NMR, 13C NMR, ESI–MS, IR spectra, and single-crystal X-ray diffraction analysis. X-ray crystallography revealed that the Re(I)-NHC complex 13 is a rare five-member bidentate CAr^CNHC-cyclometalated structure containing the coplanar system of quinoline and imidazole ring with a dihedral angle of 7.6°. The density functional theory (DFT) calculations also indicated that the blue shift of 50 nm for the MLCT absorption band of 13 is in good agreement with the coplanar five-member cyclometalated structure and the Re(I)-NHC complex 10 is a thermodynamic product. Seven Re(I)-NHC complexes exhibit photoluminescence emission in the blue region (410–470 nm) with relatively short decay lifetime on the nanosecond time scale, and high quantum yields of the Re(I)-NHC complexes 5 (Φ = 0.558) and 6 (Φ = 0.629) based-triazole were calculated by using [Ru(bpy)3](PF6)2 in degassed acetonitrile solution (Φstd = 0.062) as standard, due to the coordination of quinoline rings, NHC ligands to Re(I) center.

Pressure-Induced Enhancement of Room-Temperature Phosphorescence in Heavy Halogen-Containing Imide and Polyimide.

To investigate the correlation between the aggregated state and photoluminescence (PL) mechanism of dual fluorescent (FL) and phosphorescent (PH) polyimides (PIs), the photophysical processes of FL-type BP-PI, PH-type DBrBP-PI, and their corresponding imide model compounds (BP-MC and DBrBP-MC) dispersed in poly(methyl methacrylate) (PMMA) films were analyzed at elevated pressures up to 8 GPa using a diamond anvil cell. Dibromo-substituted DBrBP-MC demonstrated a shorter wavelength absorption than BP-MC owing to the larger dihedral angle in the biphenyl moiety. Both MCs exhibited red-shifts in their absorption spectra with increasing pressure, indicating planarization occurred at the biphenyl moieties associated with the compression of the free volume in PMMA. The PL intensity of BP-MC increased with increasing pressure, while its quantum yield (ΦPL) decreased sharply due to the enhanced energy transfer via the Förster mechanism. In contrast, the PH quantum yield (ΦPH) of DBrBP-MC monotonically increased at lower pressures, while it showed excitation wavelength-dependent behaviors at higher pressures: ΦPH remained unchanged under excitation at 340 nm but gradually increased under excitation at 365 nm. This fact suggests that, at higher pressures, 365 nm excitation promoted intersystem crossing (ISC) from excited singlet states at higher energy levels. Using this phenomenon, a significant pressure-induced PH enhancement (PIPE) was observed for DBrBP-PI up to 0.9 GPa upon excitation at 365 nm, which is a rare phenomenon for organic polymers. This study indicates that even in colorless and optically transparent amorphous polymers, an enhancement of PH due to restricted molecular motion and intensified ISC outweighs the deactivation due to intermolecular energy transfer under certain pressures, leading to an increase in ΦPH.

The controllable of BODIPY dimers without installing blocking groups as both fluorescence and singlet oxygen generators

AbstractWe compared a range of BODIPY dimer derivatives without installing blocking groups by optimizing geometry structures and analyzing energies, frontier molecular orbitals, Chole&Cele map, electron density difference, spin‐orbit coupling (SOC) matrix and decay rate constants from excited states. The dihedral angles of the β‐β‐linked BODIPY dimer and the α‐α‐linked BODIPY dimer tend to flatten in the T1 state, which is detrimental to the occurrence of the intersystem crossing (ISC). Conversely, the dihedral angle of the meso‐β‐linked BODIPY dimer, the meso‐meso‐linked BODIPY dimer and α‐γ‐linked BODIPY dimer is within the range of 125°–143° in the T1 state, facilitating ISC and the generation of singlet oxygen. Notably, the transition from S1 to S0 involving lowest unoccupied molecular orbital to highest occupied molecular orbital with long‐wavelength emission and moderate oscillator strength underpins the remarkable long emission peaks observed experimentally for α‐γ‐linked BODIPY dimer. Moreover, the apparent SOC matrix enhances the ISC process, resulting in a respectable efficiency in generating singlet oxygen for this dimer. In meso‐β‐linked BODIPY, meso‐meso‐linked BODIPY, and α‐γ‐linked BODIPY, the S1→T1 process is characterized by a significant charge transfer, specifically transitioning from the 1CT state to the 3LE state, indicative of a spin‐orbit charge transfer ISC (SOCT‐ISC) mechanism. The ability to regulate the photosensitivity of BODIPY dimers by adjusting the dihedral angle between the two units in the T1 state unveils new avenues for designing high‐performance photosensitizers for both therapeutic and imaging applications.

Biphenyl tetracarboxylic acid-based metal-organic frameworks: a case of topology-dependent thermal expansion.

The large inherent flexibility and highly modular nature of metal-organic frameworks (MOFs) make them ideal candidates for the study of negative thermal expansion (NTE). Among diverse organic ligands, the biphenyl unit, which can unrestrictedly rotate along its C-C single bond, can largely enhance the structural flexibility. Herein, we explored the thermal expansion behaviors of four indium biphenyl tetracarboxylates (BPTCs). Owing to the different dihedral angles of BPTC ligands and coordination mode of In3+, they show distinct topologies: InOF-1 (nti), InOF-2 (unc), InOF-12 (pts) and InOF-13 (nou). Intriguingly, it is found that the thermal expansion is highly dependent on the specific topology. The MOFs featuring mononuclear nodes show normal positive thermal expansion (PTE), and the magnitudes of coefficients follow the trend of InOF-2 < InOF-12 < InOF-13, inversely related to averaged molecular volumes. In contrast, the InOF-1, composed of a 1D chain of corner-shared InO6 octahedrons, shows pronounced NTE. Detailed high-resolution synchrotron powder X-ray diffraction and lattice dynamic analyses shed light on the fact that NTE in the InOF-1 is a synergy effect of the spring-like distortion of the inorganic 1D helical chain and twisting of the BPTC ligands. The present work shows how the topological arrangement of building blocks governs the thermal expansion behaviors.

A new method for assessing tibial torsion using computerized tomography in a pediatric population.

Tibial torsion disorders may lead to abnormal gait, frequently leading to a consultation with a pediatric orthopedic surgeon. The present study evaluated an alternative method for assessing tibial torsion on computerized tomography (CT) images that considers the tibial distal axis to be equivalent to the geometric axis of the tibiotalar joint. One hundred CT scans were reviewed retrospectively, and four measurements were taken: proximal transtibial angle (PTTA), posterior margin tibial plateau angle (PMTPA), intermalleolar angle (IMA), and talar angle (TA). The tibial torsion angle was then calculated using these different angles. The patient cohort comprised 38 girls and 62 boys, with a mean age of 12 ± 4.4 years. Median PTTA and PMTPA were -8.4° ± 14.7° and -8.8° ± 14.2°, respectively, with no statistically significant difference. Mean IMA and TA were 23° ± 16.2° and 17.2° ± 16.9°, respectively, with a statistically significant difference. Mean total measurement time per patient was 6'44", with means of 2'24" for PTTA, 36" for PMTPA, 2'14" for IMA, and 1'12" for TA. Tibial torsion values may differ significantly depending on the axis chosen to define tibial orientation. At the level of the proximal tibia, the choice of PTTA or PMTPA had little influence on the calculation of the tibial torsion angle. There was a significant difference of 5.8° when measuring the distal tibia. Measuring the PMTPA and TA is probably more suited for use in clinical practice because their tracing is simple and faster.

Microwave Spectroscopy of Chiral Astrochemical Candidate Vinyloxirane: The Missing Gauche Conformer.

The recent detection of a chiral molecule, propylene oxide, in the interstellar medium provides impetus for investigation of related analogues as candidates for discovery of a second chiral species. Vinyloxirane (VO) shares many of the characteristics of propylene oxide that favored its remote detection such as modest size, appreciable dipole moment and modest adsorption to water ice. The microwave spectrum of vinyloxirane at room temperature has been studied in the 18 - 26 GHz region. Rotational transitions of the previously undetected gauche-1 conformer have been assigned and fitted. The quantum number range of anti conformer transitions has been greatly expanded, providing improved molecular constants. Vibrational satellite transitions were assigned and fitted for the lowest frequency ν27 torsion mode, for 2ν27, and for the ν26 C=CC bend of anti VO, along with ν27 satellites of gauche-1. The rovibrational analyses were assisted by anharmonic vibrational calculations at B3LYP-D3/aug-cc-PVTZ, B2PLYPD3/cc-pVTZ, and DSDPBEP86/cc-pVTZ levels. Experimental peak intensities provide a population ratio Ngauche-1/Nanti of 0.36 ± 0.06, corresponding to a Gibbs free energy difference of 2.5 ± 0.4 kJ mol-1 in favor of the anti conformer, in agreement with the density functional theory results. In the gauche-1 conformer, the torsional angle between vinyl group and oxirane ring, τC=CCM, is optimized at -35° to favor an intramolecular CvinylH11...O interaction. The gauche-2 conformer with τC=CCM of + 74° suffers from CvinylH11...HCcyclopropyl repulsion so that it is calculated to be 8-9 kJ mol-1 higher than gauche-1. Reinterpretation of earlier Raman spectra suggests that the gauche-2 conformer had not been observed as reported.

Quamtum Mechanical Study on Structural and Electronic Properties of Tert-Butyl Based Bridged Dithiophene Oxide Derivatives

Computational modeling is vital to designing and creating organic semiconductors used in solar cells, organic field-effect transistors, and other areas. This work studied the structural and electronic features of a group of substituted tert-butyl bridged dithiophene oxide derivatives using Density Functional Theory (DFT) calculations. Geometry improvements were carried out using the B3LYP hybrid functional and the 6-31G(d,p) basis set in Gaussian 09. Molecular shapes, bond lengths, bond angles, and dihedral angles were studied to find out how substitution patterns change the packing and conformation of molecules. Energy levels, distribution, and makeup of frontier molecular orbitals were found. This calculation also included finding other electronic qualities, such as electronic charges, dipole moments, and polarizabilities. Findings show that tert-butyl substitution makes the molecular backbone stiffer and limits its ability to twist compared to similar molecules that have not been replaced. The chemical geometry stays mostly the same when electron-withdrawing or electron-donating substituents are added to the tert- butyl groups. Nevertheless, the strength and location of substituents have a significant impact on frontier orbital energies. The HOMO-LUMO gap grew significantly when the nitro or cyano groups firmly pulled electrons away from derivatives. For successful charge transport, electron density plots show that the HOMO and LUMO are mainly located on the thiophene and substituent moieties, respectively. Molecular dipole moments are also strongly affected by the electronic features of substituents. This research shows how to change the optoelectronic properties of tert-butyl-based dithiophene oxide derivatives and how their structure-property relationships can be improved. The results help makes new organic semiconductors that work better in various electronic and optoelectronic uses.

Exploring Conformational Landscapes Along Anharmonic Low-Frequency Vibrations.

We aim to automatize the identification of collective variables to simplify and speed up enhanced sampling simulations of conformational dynamics in biomolecules. We focus on anharmonic low-frequency vibrations that exhibit fluctuations on time scales faster than conformational transitions but describe a path of least resistance toward structural change. A key challenge is that harmonic approximations are ill-suited to characterize these vibrations, which are observed at far-infrared frequencies and are easily excited by thermal collisions at room temperature. Here, we approached this problem with a frequency-selective anharmonic (FRESEAN) mode analysis that does not rely on harmonic approximations and successfully isolates anharmonic low-frequency vibrations from short molecular dynamics simulation trajectories. We applied FRESEAN mode analysis to simulations of alanine dipeptide, a common test system for enhanced sampling simulation protocols, and compared the performance of isolated low-frequency vibrations to conventional user-defined collective variables (here backbone dihedral angles) in enhanced sampling simulations. The comparison shows that enhanced sampling along anharmonic low-frequency vibrations not only reproduces known conformational dynamics but can even further improve the sampling of slow transitions compared to user-defined collective variables. Notably, free energy surfaces spanned by low-frequency anharmonic vibrational modes exhibit lower barriers associated with conformational transitions relative to representations in backbone dihedral space. We thus conclude that anharmonic low-frequency vibrations provide a promising path for highly effective and fully automated enhanced sampling simulations of conformational dynamics in biomolecules.

Trigonometric Bundling Disulfide Unit Starship Synergizes More Effectively to Promote Cellular Uptake.

A small molecule disulfide unit technology platform based on dynamic thiol exchange chemistry at the cell membrane has the potential for drug delivery. However, the alteration of the CSSC dihedral angle of the disulfide unit caused by diverse substituents directly affects the effectiveness of this technology platform as well as its own chemical stability. The highly stable open-loop relaxed type disulfide unit plays a limited role in drug delivery due to its low dihedral angle. Here, we have built a novel disulfide unit starship based on the 3,4,5-trihydroxyphenyl skeleton through trigonometric bundling. The intracellular delivery results showed that the trigonometric bundling of the disulfide unit starship effectively promoted cellular uptake without any toxicity, which is far more than 100 times more active than that of equipment with a single disulfide unit in particular. Then, the significant reduction in cell uptake capacity (73-93%) using thiol erasers proves that the trigonometric bundling of the disulfide starship is an endocytosis-independent internalization mechanism via a dynamic covalent disulfide exchange mediated by thiols on the cell surface. Furthermore, analysis of the molecular dynamics simulations demonstrated that trigonometric bundling of the disulfide starship can significantly change the membrane curvature while pushing lipid molecules in multiple directions, resulting in a significant distortion in the membrane structure and excellent membrane permeation performance. In conclusion, the starship system we built fully compensates for the inefficiency deficiencies induced by poor dihedral angles.