The aim of this study was to compare selected ankle and knee kinematic and kinetic parameters before and a
fter a prolonged exhaustive treadmill run between two groups of non-rearfoot footstrike ...pattern (NRFP) runners with different training volumes. Twenty-eight habitual NRFP runners were assigned to two groups based on their weekly training volume (Highly-trained (HT)/Moderately-trained (MT)). Participants underwent the VO2max test, and the exhaustive treadmill ran with biomechanical analysis at the beginning and the end. The two-way RMANOVA was used to assess differences between the groups and the phase of the run. A paired t-test was used for post-hoc analysis in case of significant interaction effect. Kinetic results showed significant group effect for ankle plantarflexion moment and hip external rotation moment (end-phase: both greater in MT group). Kinematic results showed significant group×phase interaction for ankle dorsiflexion angle (end-phase: greater in MT group) at initial contact (IC), peak knee flexion angle (end-phase: greater in MT group), and peak ankle eversion angle during the stance phase (end-phase: greater in HT group). Additionally, a group effect was found for knee flexion angle at IC (end-phase: greater in HT group). This study suggests that HT healthy NRFP runners may have less potential for increased biomechanical risk of AT overload during an exhaustive run.
Nitric oxide (NO) is a signaling molecule employed to regulate essential physiological processes. Thus, there is great interest in understanding the interaction of NO with heme, which is found at the ...active site of many proteins that recognize NO, as well as those involved in its creation and elimination. We summarize what we have learned from investigations of the structure, vibrational properties, and conformational dynamics of NO complexes with ferrous porphyrins, as well as computational investigations in support of these experimental studies. Multitemperature crystallographic data reveal variations in the orientational disorder of the nitrosyl ligand. In some cases, equilibria among NO orientations can be analyzed using the van't Hoff relationship and the free energy and enthalpy of the solid-state transitions evaluated experimentally. Density functional theory (DFT) calculations predict that intrinsic barriers to torsional rotation are smaller than thermal energies at physiological temperatures, and the coincidence of observed NO orientations with minima in molecular mechanics potentials indicates that nonbonded interactions with other chemical groups control the conformational freedom of the bound NO. In favorable cases, reduced disorder at low temperatures exposes subtle structural features including off-axis tilting of the Fe−NO bond and anisotropy of the equatorial Fe−N bonds. We also present the results of nuclear resonance vibrational spectroscopy measurements on oriented single crystals of Fe(TPP)(NO) and Fe(TPP)(1-MeIm)(NO). These describe the anisotropic vibrational motion of iron in five- and six-coordinate heme−NO complexes and reveal vibrations of all Fe−ligand bonds as well as low-frequency molecular distortions associated with the doming of the heme upon ligand binding. A quantitative comparison with predicted frequencies, amplitudes, and directions facilitates identification of the vibrational modes but also suggests that commonly used DFT functionals are not fully successful at capturing the trans interaction between the axial NO and imidazole ligands. This supports previous conclusions that heme−NO complexes exhibit an unusual degree of variability with respect to the computational method, and we speculate that this variability hints at a genuine electronic instability that a protein can exploit to tune its reactivity. We anticipate that ongoing characterization of heme−NO complexes will deepen our understanding of their structure, dynamics, and reactivity.
The isolation of two polymorphic forms of nitrosyl(1-methylimidazole)(tetra-p-fluorophenylporphinato)iron(II) provides a unique opportunity to explore the interplay of structure and vibrational ...dynamics in six-coordinate {FeNO}7 nitrosyliron porphyrinates. The two species display differing vibrational spectroscopic properties both in νNO (IR) and the iron vibrational modes obtained through the use of nuclear resonance vibrational spectroscopy. Structural characterization of the two complexes has yielded extremely high-quality structures that further confirm that coordination of NO leads to ligand tilting and asymmetry in the equatorial Fe−Np bond distances. The two polymorphic structures (monoclinic and triclinic crystal systems) differ in the relative orientations of the two axial ligands and small but significant differences in coordination group bond distances. Although DFT calculations suggest that the NO/imidazole orientations should be indistinguishable, real experimental (structural and vibrational) differences between the two are found. The observed variation in the axial and equatorial Fe−N bonds is strongly correlated to the dynamics of the Fe−NO unit and other motions of iron. Other structural differences appear to have little effect on the vibrational properties of the two forms. The in-plane motions of iron in CO versus NO heme complexes illustrate distinct dynamic differences.
We use nuclear resonance vibrational spectroscopy and computational predictions based on density functional theory (DFT) to explore the vibrational dynamics of
57Fe in porphyrins that mimic the ...active sites of histidine-ligated heme proteins complexed with carbon monoxide. Nuclear resonance vibrational spectroscopy yields the complete vibrational spectrum of a Mössbauer isotope, and provides a valuable probe that is not only selective for protein active sites but quantifies the mean-squared amplitude and direction of the motion of the probe nucleus, in addition to vibrational frequencies. Quantitative comparison of the experimental results with DFT calculations provides a detailed, rigorous test of the vibrational predictions, which in turn provide a reliable description of the observed vibrational features. In addition to the well-studied stretching vibration of the Fe-CO bond, vibrations involving the Fe-imidazole bond, and the Fe-N
pyr bonds to the pyrrole nitrogens of the porphyrin contribute prominently to the observed experimental signal. All of these frequencies show structural sensitivity to the corresponding bond lengths, but previous studies have failed to identify the latter vibrations, presumably because the coupling to the electronic excitation is too small in resonance Raman measurements. We also observe the FeCO bending vibrations, which are not Raman active for these unhindered model compounds. The observed Fe amplitude is strongly inconsistent with three-body oscillator descriptions of the FeCO fragment, but agrees quantitatively with DFT predictions. Over the past decade, quantum chemical calculations have suggested revised estimates of the importance of steric distortion of the bound CO in preventing poisoning of heme proteins by carbon monoxide. Quantitative agreement with the predicted frequency, amplitude, and direction of Fe motion for the FeCO bending vibrations provides direct experimental support for the quantum chemical description of the energetics of the FeCO unit.
The synthesis and molecular structures of three iron(II) porphyrinates with only CO as the axial ligand(s) are reported. Two five-coordinate Fe(OEP)(CO) derivatives have Fe−C = 1.7077(13) and ...1.7140(10) Å, much shorter than those of six-coordinate Fe(OEP)(Im)(CO), although νC - O is 1944−1948 cm-1. The six-coordinate species Fe(OEP)(CO)2 has also been studied. The competition for π-back-bonding of two CO ligands leads to Fe−C distance of 1.8558(10) Å and νC - O being increased to 2021 cm-1. The Mössbauer spectrum has a quadrupole splitting constant of 0 mm/s at 4.2 K, indicating high electronic symmetry.
The vibrational spectrum of a six-coordinate nitrosyl iron porphyrinate, monoclinic Fe(TpFPP)(1-MeIm)(NO) (TpFPP=tetra-para-fluorophenylporphyrin; 1-MeIm=1-methylimidazole), has been studied by ...oriented single-crystal nuclear resonance vibrational spectroscopy (NRVS). The crystal was oriented to give spectra perpendicular to the porphyrin plane and two in-plane spectra perpendicular or parallel to the projection of the FeNO plane. These enable assignment of the FeNO bending and stretching modes. The measurements reveal that the two in-plane spectra have substantial differences that result from the strongly bonded axial NO ligand. The direction of the in-plane iron motion is found to be largely parallel and perpendicular to the projection of the bent FeNO on the porphyrin plane. The out-of-plane Fe-N-O stretching and bending modes are strongly mixed with each other, as well as with porphyrin ligand modes. The stretch is mixed with v50 as was also observed for dioxygen complexes. The frequency of the assigned stretching mode of eight Fe-X-O (X=N, C, and O) complexes is correlated with the Fe-XO bond lengths. The nature of highest frequency band at ≈560 cm(-1) has also been examined in two additional new derivatives. Previously assigned as the Fe-NO stretch (by resonance Raman), it is better described as the bend, as the motion of the central nitrogen atom of the FeNO group is very large. There is significant mixing of this mode. The results emphasize the importance of mode mixing; the extent of mixing must be related to the peripheral phenyl substituents.
We use nuclear resonance vibrational spectroscopy (NRVS) to identify the Fe−NO stretching frequency in the NO adduct of myoglobin (MbNO) and in the related six-coordinate porphyrin ...Fe(TPP)(1-MeIm)(NO). Frequency shifts observed in MbNO Raman spectra upon isotopic substitution of Fe or the nitrosyl nitrogen confirm and extend the NRVS results. In contrast with previous assignments, the Fe−NO frequency of these six-coordinate complexes lies 70−100 cm-1 lower than in the analogous five-coordinate nitrosyl complexes, indicating a significant weakening of the Fe−NO bond in the presence of a trans imidazole ligand. This result supports proposed mechanisms for NO activation of heme proteins and underscores the value of NRVS as a direct probe of metal reactivity in complex biomolecules.
Heme-carbonyl complexes are widely exploited for the insight they provide into the structural basis of function in heme-based proteins, by revealing the nature of their bonded and nonbonded ...interactions with the protein. This report presents two novel results which clearly establish a FeCO vibrational signature for crystallographically verified pentacoordination. First, anisotropy in the NRVS density of states for νFe–C and δFeCO in oriented single crystals of Fe(OEP)(CO) clearly reveals that the Fe–C stretch occurs at higher frequency than the FeCO bend and considerably higher than any previously reported heme carbonyl. Second, DFT calculations on a series of heme carbonyls reveal that the frequency crossover occurs near the weak trans O atom donor, furan. As νFe–C occurs at lower frequencies than δFeCO in all heme protein carbonyls reported to date, the results reported herein suggest that they are all hexacoordinate.
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