Regular arrays of C60-based molecular rotors mounted on the surface of tris(o-phenylenedioxy)cyclotriphosphazene nanocrystals.

Dielectric spectroscopy has been used to determine the barriers of rotation of surface-mounted fullerenes (2.3 ± 0.1 and 4.3 ± 0.1 kcal mol-1). In order to achieve this, a C60 derivative equipped with an anchoring group designed to form a surface inclusion with the hexagonal form of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) has been synthesized. Solid-state NMR analysis revealed that approximately 50% of the surface-mounted molecules have a chemical environment different from the others suggesting two distinct insertion modes. These observations correlate with results of DFT calculations.

Regular Arrays of Rod-Shaped Molecular Photoswitches: Synthesis, Preparation, Characterization, and Selective Photoswitching within Mono- and Bilayer Systems.

We assembled photoresponsive mono- and bilayer systems with well-defined properties from rod-shaped molecules equipped with different photoswitches. Using properly chosen chromophores (diarylethene-based switch and unidirectional light-driven molecular motor), we then selectively targeted layers made of the same types of photoswitches using appropriate monochromatic light. UV-vis analysis confirmed smooth and unrestricted photoisomerization. To achieve this, we synthesized a new class of triptycene-based molecular pedestals adept at forming sturdy Langmuir-Blodgett films on a water-air interface. The films were smoothly transferred to gold and quartz surfaces. Repeated deposition afforded bilayer systems: one layer containing diarylethene-based photoswitches and the other a unidirectional light-driven molecular motor. Structural analysis of both mono- and bilayer systems revealed the molecules to be tilted with carboxylic functions pointing to the surface. At least two different polymorphs differing in monolayer thickness and tilt angle (~40° and ~60°) were identified on the gold surface.

Effect of age and speed on the step-to-step transition strategies in children.

The development and acquisition of mature walking in children is multifactorial, depending among others on foot interaction with the ground, body dynamics and the knowledge of the 'rules' stemming from the gravity field. Indeed, each step the velocity of the centre of mass must be redirected upwards. This redirection may be initiated by the trailing leg, propulsing forward and upward the body before foot contact, or later by the loading limb after the contact with the ground. While it has been suggested that mature walking develops slowly from first independent steps to about 7 years of age, it is still unknown how children acquire the appropriate loading and propulsion forces during the step-to-step transition. To answer that question, twenty-four children (from 3 to 12 years old) and twelve young adults (from 20 to 27 years old) walked on force platforms at different walking speed. The ground reaction forces under each foot were recorded and the vertical velocity of the centre of mass of the body was computed. With decreasing age and increasing velocity (or Froude number), the occurrence of unanticipated transition is higher, related to a different ratio between the vertical support of the front and back leg. The different transition strategy observed in children indicates that body weight transfer from one limb to the other is not fully mature at 12 years old.

Chlorinated Cubane-1,4-dicarboxylic Acids.

Herein, we report radical chlorination of cubane-1,4-dicarboxylic acid leading preferentially to one monochlorinated cubane dicarboxylate (ca. 70%) that is accompanied by four dichlorinated derivatives (ca. 20% in total). The exact positions of the chlorine atoms have been confirmed by X-ray diffraction of the corresponding single crystals. The acidity constants of all dicarboxylic acids in water were determined by capillary electrophoresis (3.17 ± 0.04 and 4.09 ± 0.05 for monochlorinated and ca. 2.71 ± 0.05 and 3.75 ± 0.05 for dichlorinated cubanes). All chlorinated derivatives as well as the parent diacid showed high thermal stability (decomposition above 250 °C) as documented by differential scanning calorimetry. The probable reaction pathways leading to individual isomers were proposed, and the energies of individual transition states and intermediates were obtained using density functional theory calculations (B3LYP-D3BJ/6-311+G(d,p)). The relative strain energies for all newly prepared derivatives as well as for hypothetical hexahalogenated (fluorinated, chlorinated, brominated, and iodinated) derivatives of cubane-1,4-dicarboxylic acids were predicted using wavefunction theory methods. The hexafluorinated derivative was identified as the most strained compound (57.5 kcal/mol), and the relative strain decreased as the size of halogen atoms increased (23.7 for hexachloro, 16.7 for hexabromo, and 4.0 kcal/mol for the hexaiodo derivative).

The stability of covalent dative bond significantly increases with increasing solvent polarity.

It is generally expected that a solvent has only marginal effect on the stability of a covalent bond. In this work, we present a combined computational and experimental study showing a surprising stabilization of the covalent/dative bond in Me3NBH3 complex with increasing solvent polarity. The results show that for a given complex, its stability correlates with the strength of the bond. Notably, the trends in calculated changes of binding (free) energies, observed with increasing solvent polarity, match the differences in the solvation energies (ΔEsolv) of the complex and isolated fragments. Furthermore, the studies performed on the set of the dative complexes, with different atoms involved in the bond, show a linear correlation between the changes of binding free energies and ΔEsolv. The observed data indicate that the ionic part of the combined ionic-covalent character of the bond is responsible for the stabilizing effects of solvents.

Quantum spin-liquid states in an organic magnetic layer and molecular rotor hybrid.

The exotic properties of quantum spin liquids (QSLs) have continually been of interest since Anderson's 1973 ground-breaking idea. Geometrical frustration, quantum fluctuations, and low dimensionality are the most often evoked material's characteristics that favor the long-range fluctuating spin state without freezing into an ordered magnet or a spin glass at low temperatures. Among the few known QSL candidates, organic crystals have the advantage of having rich chemistry capable of finely tuning their microscopic parameters. Here, we demonstrate the emergence of a QSL state in [EDT-TTF-CONH2]2 +[[Formula: see text]] (EDT-BCO), where the EDT molecules with spin-1/2 on a triangular lattice form layers which are separated by a sublattice of BCO molecular rotors. By several magnetic measurements, we show that the subtle random potential of frozen BCO Brownian rotors suppresses magnetic order down to the lowest temperatures. Our study identifies the relevance of disorder in the stabilization of QSLs.

CB11H10- and Related Carborenes.

Starting with HOOC-CB11Me11- or CB11Me12- as the starting material, collision-induced dissociation has produced a series of methylated analogs of didehydro-closo-carbadodecaborane anions by sequential losses of up to 5 equiv of ethylene. These reactive intermediates are carborane analogues of doubly pyramidalized alkenes and, more distantly, arynes. Density functional theory calculations have been used to develop a proposal for the mechanism of the unusual formation of ethylene from the carborane methyl substituents.

Regular Two-Dimensional Arrays of Surface-Mounted Molecular Switches: Switching Monitored by UV-vis and NMR Spectroscopy.

Using solid-state 15N NMR spectroscopy, the cis/trans isomerization in a two-dimensional (2-D) array of surface-mounted azobenzene-based switches was detected for the first time. In order to achieve this, a new class of rod-shaped molecular switches, suitable for formation of 2-D regular arrays on large facets of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) nanocrystals, was synthesized. A mechanochemical approach was used to prepare corresponding host-guest surface inclusions in a TPP matrix. Comparison of thermal steps in solution and supramolecular surface inclusions revealed that switching of individual molecules is not compromised by the close proximity of neighbors.

A robust machine learning enabled decomposition of shear ground reaction forces during the double contact phase of walking.

BACKGROUND: Dynamic analyses of walking rely on the 3D ground reaction forces (GRF) under each foot, while only the resultant force of both limbs may be recorded on a single-belt instrumented treadmill or when both feet touch the same force platform. RESEARCH QUESTION: This study aims to develop a robust decomposition of the shear GRF to complete the most accurate decomposition of the vertical GRF [8]. METHODS: A retrospective study of 374 healthy adults records (age: 22.8 ±â€¯2.6 years, speed: 1.34 ±â€¯0.28 m/s) and of 434 patient records (age: 21.3 ±â€¯17.8 years, speed: 0.64 ±â€¯0.19 m/s) were used in a machine learning process to develop a robust predictive model to decompose the fore-aft GRF. The lateral GRF was decomposed by resolving the equilibrium of transverse moments around the center of pressure. RESULTS: A predictive linear model of the fore-aft GRF under the back foot every 5% of the double contact phase was obtained from 2 predictors: the total fore-aft GRF and the vertical GRF under the back foot. Each predictor uses a time series of 31 samples before and during the double contact. The model performs accurately in healthy (median[IQR] error of 3.0[2.2-4.1]%) and in clinical gaits (7.7[4.7-13.4]%). The error in lateral GRF decomposition is of 5.7[3.9-10.2]% in healthy gaits and of 12.0[7.2-19.2]% in patients under the back foot and about half of that under the front foot. SIGNIFICANCE: The decomposition of shear GRFs achieved in this study supports the mechanics of walking. It provides outstanding accuracy in healthy gait and also applies to neurologic and orthopedic disorders. Together with the vertical GRF decomposition [8], this approach for the shear components paves the way for robust single limb GRF determination on a single-belt instrumented treadmill or when both feet touch the same force platform in normal and clinical gait analysis.

Bulk Inclusions of Double Pyridazine Molecular Rotors in Hexagonal Tris( o-phenylene)cyclotriphosphazene.

A new generation of double pyridazine molecular rotors differing in intramolecular dipole-dipole spacing was synthesized. All rotor molecules formed bulk inclusions in a tris( o-phenylenedioxy)cyclotriphosphazene (TPP) host. Results of dielectric spectroscopy were fitted to a pair of nine-state models that accounted for interactions of neighboring dipoles at either an aligned or opposed possible orientation of the local threefold dipole rotation potentials within a channel of the TPP host. The results indicate dipole-dipole interaction strengths at the 100 to 200 K scale that lead dipoles to preferentially populate a subset of low-energy configurations. They also reveal that pyridazines with ethynyl substituents in 3- and 6-positions have slightly higher rotational barriers (3.2-3.5 kcal/mol) than those carrying one ethynyl and one tert-butyl group (1.9-3.0 kcal/mol). Upon cooling, these barriers reduce the rate of thermal transitions between the potential wells so much that the inclusions cannot achieve ordered dipolar ground states.

Effect of age and speed on the step-to-step transition phase during walking.

Gait is a powerful measurement tool to evaluate the functional decline throughout ageing. Falls in elderly adults happen mainly during the redirection of the center of mass of the body (CoM) in the transition between steps. In young adults, this step-to-step transition begins before the double contact phase (DC) with a simultaneous forward and upward acceleration of the CoM. We hypothesize that, compared to young adults, elderly adults would exhibit unbalanced contribution of the back leg and the front leg during the transition. We calculated the mean vertical push-off done by the back leg (FBACK) and the mean impact force on the front leg (FFRONT) during the transition. Eight young (mean ±â€¯SD; age: 24 ±â€¯2 y) and 19 elderly (age: 74 ±â€¯6 y) healthy adults walked on a force-measuring treadmill at five selected speeds ranging from 0.56 to 1.67 m·s-1. Results show that, at mid and high speeds, elderly adults exhibit a smaller FBACK compared to young adults, possibly linked to the decreased plantar flexion of the back foot. As a consequence, FFRONT is significantly increased and the transition begins lately in the step, at the beginning of DC. Also, elderly adults show an inability to accelerate the CoM upward and forward simultaneously. Our findings show a different adaptation of the step-to-step transition with speed in elderly adults and identify two potential indicators of gait impairment with age: the FFRONT/FBACK contribution and the synchronization between the upward and forward acceleration of the CoM during the transition.

Static Modulation Wave of Arrays of Halogen Interactions Transduced to a Hierarchy of Nanoscale Change Stimuli of Crystalline Rotors Dynamics.

Here we present a study where what can be seen as a static modulation wave encompassing four successive arrays of interacting iodine atoms in crystalline 1,4-Bis((4'-(iodoethynyl)phenyl) ethynyl)bicyclo[2,2,2]octane rotors changes the structure from one-half molecule to three-and-a-half molecules in the asymmetric unit below a phase transition at 105 K. The remarkable finding is that the total 1H spin-lattice relaxation rate, T1-1, of unprecedented complexity to date in molecular rotors, is the weighted sum of the relaxation rates of the four contributing rotors relaxation rates, each with distinguishable exchange frequencies reflecting Arrhenius parameters with different activation barriers ( Ea) and attempt frequencies (τo-1). This allows us to show in tandem with rotor-environment interaction energy calculations how the dynamics of molecular rotors are able to decode structural information from their surroundings with remarkable nanoscale precision.

Surface Inclusion of Unidirectional Molecular Motors in Hexagonal Tris(o-phenylene)cyclotriphosphazene.

A new unidirectional light-driven molecular motor suitable for host-guest surface inclusion complexes with tris(o-phenylene)cyclotriphosphazene (TPP) was synthesized. The motor molecules formed regular two-dimensional trigonal arrays covering the large facets of disc-shaped TPP nanocrystals. Photochemical and thermal isomerization studies demonstrated that the light-driven rotation of the anchored motors is similar to that observed in solution and is not compromised neither by either the surface confinement or the density of surface coverage (50 vs 100%).

C60 Recognition from Extended Tetrathiafulvalene Bis-acetylide Platinum(II) Complexes.

The favorable spatial organization imposed by the square planar 4,4'-di(tert-butyl)-2,2'-bipyridine (dbbpy) platinum(II) complex associated with the electronic and shape complementarity of π-extended tetrathiafulvalene derivatives (exTTF) toward fullerenes is usefully exploited to construct molecular tweezers, which display good affinities for C60.

Determination of the vertical ground reaction forces acting upon individual limbs during healthy and clinical gait.

In gait lab, the quantification of the ground reaction forces (GRFs) acting upon individual limbs is required for dynamic analysis. However, using a single force plate, only the resultant GRF acting on both limbs is available. The aims of this study are (a) to develop an algorithm allowing a reliable detection of the front foot contact (FC) and the back foot off (FO) time events when walking on a single plate, (b) to reconstruct the vertical GRFs acting upon each limb during the double contact phase (DC) and (c) to evaluate this reconstruction on healthy and clinical gait trials. For the purpose of the study, 811 force measurements during DC were analyzed based on walking trials from 27 healthy subjects and 88 patients. FC and FO are reliably detected using a novel method based on the distance covered by the centre of pressure. The algorithm for the force reconstruction is a revised version of the approach of Davis and Cavanagh [24]. In order to assess the robustness of the algorithm, we compare the resulting GRFs with the real forces measured with individual force plates. The median of the relative error on force reconstruction is 1.8% for the healthy gait and 2.5% for the clinical gait. The reconstructed and the real GRFs during DC are strongly correlated for both healthy and clinical gait data (R(2)=0.998 and 0.991, respectively).

Impact of ankle osteoarthritis on the energetics and mechanics of gait: the case of hemophilic arthropathy.

BACKGROUND: Osteoarthritis may affect joints in any part of the body, including the ankle. The purpose of this study was to assess the impact of ankle osteoarthritis on the energetics and mechanics of gait, while taking into account the effect of slower speed generally adopted by patients with osteoarthritis. METHODS: Using a motion analysis system, synchronous kinematic, kinetics, spatiotemporal, mechanics and metabolic gait parameters were measured in 10 patients diagnosed with ankle osteoarthritis consecutive to hemophilia. The subjects walked at a self-selected speed and their performance was compared to speed-matched normal values obtained in healthy control subjects. FINDINGS: Speed-normalization using a Z-score transformation showed a significant increase in metabolic cost (Z=1.78; P=0.006) and decrease in mechanical work (Z=-0.97; P=0.009). As a consequence, muscular efficiency also decreased (Z=-0.97; P=0.001). These changes were associated with a surprising efficacy of the pendular mechanism, i.e., an improved recovery index (Z=0.97; P=0.004). INTERPRETATION: Our findings suggest that patients with ankle osteoarthritis adopt a walking strategy which improves recovery through the pendular mechanism. This may be a compensatory mechanism in order to economize energy which would counterbalance the energy waste due to low muscle efficiency. These modifications are proportional to the impaired ankle function. Our data provides a quantitative baseline to better understand the dynamics of ankle osteoarthritis and determine the individual role that lower limb joints play in the multiple chronic joint affections.

Execution time, kinetics, and kinematics of the mae-geri kick: comparison of national and international standard karate athletes.

Little is known of the performance characteristics of the shotokan karate mae-geri kick. The aim of this study was to compare the execution time, the lower limb kinetics and kinematics, and their respective repeatability in the mae-geri kick of karate athletes of two different standards. Seventeen adult black belt karate competitors (9 national and 8 international athletes) performed six kicks with their dominant lower limb on a striking surface, combining maximum force impact and velocity. Execution time of movement and lower limb kinematics were recorded with a high-speed camera. Maximum force at impact and the forces exerted on the ground were measured using three force plates. The duration of the kick was significantly shorter for international than for national standard athletes. However, no significant difference in the maximum impact force of the kick was observed between the two groups. In addition, significant kinematic differences were observed between the groups, with two angles of motion and one velocity peak occurring sooner in the kick movement for the international athletes, specifically for the knee joint. International athletes also performed the kick with a significantly higher repeatability for duration and kinematics, specifically during the pre-loading phase that precedes the attack phase. We conclude that the duration of the kick and repeatability of lower limb kinematics could be useful in selecting top-level karate athletes and monitoring their training status.

Effect of speed on the energy cost of walking in unilateral traumatic lower limb amputees.

In this work, the effect of walking speed on the energy expenditure in traumatic lower-limb amputees was studied. The oxygen consumption was measured in 10 transfemoral amputees, 9 transtibial amputees and 13 control subjects, while they stood and walked at different speeds from 0.3 m s(-1) to near their maximum sustainable speed. Standing energy expenditure rate was the same in lower-limb amputees and in control subjects (approximately 1.85 W kg(-1)). On the contrary, during walking, the net energy expenditure rate was 30-60% greater in transfemoral amputees and 0-15% greater in transtibial amputees than in control subjects. The maximal sustainable speed was about 1.2 m s(-1) in transfemoral amputees and 1.6 m s(-1) in transtibial amputees, whereas it was above 2 m s(-1) in control subjects. Among these three groups, the cost of transport versus speed presented a U-shaped curve; the minimum cost increased with the level of amputation, and the speed at which this minimum occurred decreased.

Energetics of load carrying in Nepalese porters.

Nepalese porters routinely carry head-supported loads equal to 100 to 200% of their body weight (Mb) for many days up and down steep mountain footpaths at high altitudes. Previous studies have shown that African women carry head-supported loads of up to 60% of their Mb far more economically than army recruits carrying equivalent loads in backpacks. Here we show that Nepalese porters carry heavier loads even more economically than African women. Female Nepalese porters, for example, carry on average loads that are 10% of their Mb heavier than the maximum loads carried by the African women, yet do so at a 25% smaller metabolic cost.