Metal-iodosylarene complexes have been recently viewed as a second oxidant alongside of the well-known high-valent metal-oxo species. Extensive efforts have been exerted to unveil the structure-function relationship of various metal-iodosylarene complexes. In the present manuscript, density functional theoretical calculations were employed to investigate such relationship of a specific manganese-iodosylbenzene complex [Mn III (TBDAP)(PhIO)(OH)] 2+ (1). Our results fit the experimental observations and revealed new mechanistic findings. 1 acts as a stepwise 1e+1e oxidant in sulfoxidation reactions. Surprisingly, C-H bond activation of 9,10-dihydroanthracene (DHA) by 1 proceeds via a novel ionic hydride transfer/proton transfer (HT/PT) mechanism. As a comparison to 1, the electrophilicity of an iodosylbenzene monomer PhIO was investigated. PhIO performs concerted 2e-oxidations both in sulfoxidation and C-H activation. Hydroxylation of DHA by PhIO was found to proceed via a novel ionic and concerted proton-transfer/hydroxylrebound mechanism involving 2e-oxidation to form a transient carbonium species.
Coinage metal clusters stabilized by organic ligands such as phosphine or organothiolate are well known to possess multi-twinned gold cores, and the face-centered-cubic (fcc) metal atom packing is unstable until the cluster size reaches a certain threshold. In this study, we searched for the smallest size gold nanocrystal protected by thiolate ligands by means of the crystal facet cleavage (CFC) method. Starting from the nanocrystal-like Au28(SR)20 cluster, after cleaving two different crystal facets and patching the ligand shells, we obtained five nanocrystal-like Au20(SR)16 isomers. These fcc-structured Au20 clusters were quite different from non-fcc Au20(SPh-tBu)16; the latter's total structure was determined by single X-ray diffraction. By employing dispersion correction density functional theory (DFT-D) calculations and considering ligand effects, we found that fcc-structured Au20(SR)16 isomers had comparable or even lower energies when compared with the non-fcc structure found in Au20(SPh-tBu)16. Furthermore, the calculation of optical absorption spectra based on predicted fcc isomers indicated that the cubic nanocrystal-like isomer structure is a good candidate to understand the structure of the Au20(SCH2CH2Ph)16 cluster.
We demonstrate here the synthesis of a novel class of metallo-supramolecular polymers with shackled structure, via the coordination of cyclic di(bis-terpyridine-triphenyl ether ester) ligands with ruthenium(II) ions. The constraint from the ring topology via the shackling of ligands provides novel properties to these metallo-supramolecular polymers, including the formation of dendritic crystals, red-shift of absorption bands in the UV-vis spectra from interchain charge-transfer transitions, and a typical flash-type memory behavior.
Four Ala‐Ala dipeptides with a perfluoroalkyl chain at the N‐terminal were synthesized. They were able to self‐assemble into helical nanofibers and/or twisted nanobelts in a mixture of DMSO/H2O. The handedness of nanofibers and nanobelts was controlled by the chirality of the alanine at the N‐terminal. The stacking handedness of the phenylene groups and the helicity of the perfluoroalkyl chain were studied using circular dichroism spectroscopy and vibrational circular dichroism, respectively. The chirality of the alanine at N‐terminal controlled the stacking handedness of the neighboring phenylene groups. Moreover, due to the low potential barrier between M‐ and P‐helices of the perfluorocarbon chain, the handedness of the organic self‐assemblies eventually controlled the helicity of the perfluorocarbon chain. X‐ray diffraction indicated that a lamellar structure was formed by the dimers of the dipeptides.
Bicycle saddle height configurations have been shown to affect knee joint biomechanics. Research suggests that an excessively low saddle height may lead to Patellofemoral Pain Syndrome, which is thought to be caused by the knee adduction moment during cycling. However, how saddle heights affect frontal plane knee biomechanics was not clear. We aimed to compare different saddle heights on frontal plane knee biomechanics during cycling. Twenty healthy young recreational cyclists (23.4 ± 0.5 years) performed 3 min of cycling at four different saddle heights (Medium [25°knee flexion angle], Preferred [a height chosen by cyclists], Low [Preferred + 15°], High [Preferred -15°] measured at the bottom-dead-center). Cycling workload and cadence were set at 60 w and 60 RPM, respectively, since our project was focused on rehabilitation. A motion analysis system and a custom instrumented pedal were used to collect three-dimensional kinematics d (200 Hz) and pedal reaction force (1000 Hz). Results showed that, compared with other saddle heights, Low saddle height produced greater adduction knee moments (11.9 ± 1.9 Nm, P < 0.05), a longer duration (0.15 ± 0.01 s, P < 0.05), larger knee flexion (58.5 ± 2.6°, P < 0.05) and larger abduction angles (−4.5 ± 0.8°, P < 0.05). We showed that Low saddle height resulted in increased knee adduction moments with longer duration. In contrast, High saddle height reduced both knee moments and time duration. The results suggest that increased saddle heights may provide a safe and efficient cycling strategy for healthy young recreational cyclists.
The purpose of this study was to investigate the effects of surface slope and body posture (i.e., seated and standing) on lower extremity joint kinetics during cycling. Fourteen participants cycled at 250 watts power in three cycling conditions: level seated, uphill seated and uphill standing at a 14% slope. A motion analysis system and custom instrumented pedal were used to collect the data of fifteen consecutive cycles of kinematics and pedal reaction force. One crank cycle was equally divided into four phases (90° for each phase). A two-factor repeated measures MANOVA was used to examine the effects of the slope and posture on the selected variables. Results showed that both slope and posture influenced joint moments and mechanical work in the hip, knee and ankle joints (p < 0.05). Specifically, the relative contribution of the knee joint to the total mechanical work increased when the body posture changed from a seated position to a standing position. In conclusion, both surface slope and body posture significantly influenced the lower extremity joint kinetics during cycling. Besides the hip joint, the knee joint also played the role as the power source during uphill standing cycling in the early downstroke phase. Therefore, adopting a standing posture for more power output during uphill cycling is recommended, but not for long periods, in view of the risk of knee injury.
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