Simple benzene derivatives adsorption on defective single-walled carbon nanotubes: a first-principles van der Waals density functional study

We have investigated the interaction between open-ended zig-zag single-walled carbon nanotube (SWCNT) and a few benzene derivatives using the first-principles van der Waals density functional (vdW-DF) method, involving full geometry optimization. Such sp ²-like materials are typically investigated using conventional DFT methods, which significantly underestimate non-local dispersion forces (vdW interactions), therefore affecting interactions between respected molecules. Here, we considered the vdW forces for the interacting molecules that originate from the interacting π electrons of the two systems. The ?0.54 eV adsorption energy reveals that the interaction of benzene with the side wall of the SWCNT is typical of the strong physisorption and comparable with the experimental value for benzene adsorption onto the graphene sheet. It was found that aromatics are physisorbed on the sidewall of perfect SWCNTs, as well as at the edge site of the defective nanotube. Analysis of the electronic structures shows that no orbital hybridization between aromatics and nanotubes occurs in the adsorption process. The results are relevant in order to identify the potential applications of noncovalent functionalized systems.

IR and Raman spectroscopic studies on coulombic interaction between water-soluble porphyrins and nucleic acids

We have shown previously that the N-methylpyridyl group vibrations of water-soluble porphyrins, M(TMpy-P4), are shifted to lower frequencies (0.5-2.6 cm-1) as a result of coulombic interaction between the N(+)-CH3 group of M(TMpy-P4) and the PO2 group of a nucleic acid. We have now turned over our attention to the effect of this coulombic interaction on the PO2 group vibrations of nucleic acids. Using Fourier transform ir and Raman spectroscopy, we found that the va(PO2) at 1221 cm-1 is shifted 12 approximately 17 cm-1 to higher frequencies, whereas the vs(PO2) at 1087 cm-1 is shifted 18 approximately 26 cm-1 to lower frequencies, when DNA is mixed with M(TMpy-P4). These results indicate that the N(+)-CH3 group of M(TMpy-P4) interacts preferentially with one of the two oxygen atoms of the PO2 group of the DNA duplex.     

Resonance Raman spectroscopy of horseradish peroxidase derivatives and intermediates with excitation in the near ultraviolet

Resonance Raman enhancement of derivatives and intermediates of horseradish peroxidase in the near ultraviolet (N-band excitation) results in intensity and enhancement patterns that are different from those normally observed within the porphyrin Soret (B-band) and alpha-beta (Q-band) absorptions. In particular it allows the resolution of resonance Raman spectra of horseradish peroxidase compound I. The bands above 1300 cm-1 can be assigned to porphyrin vibrational modes that are characteristically shifted in frequency due to removal of an electron from the porphyrin ring. The resonance Raman frequency shifts follow normal mode compositions. Relative to resonance Raman spectra of compound II, the v4 frequency (primarily Ca-N) exhibits a 20 cm-1 downshift. The v2, v11, and v37 vibrational frequencies whose mode compositions are primarily porphyrin Cb-Cb, exhibit 10-20 cm-1 upshifts. The v3, v10, and v28 frequencies, whose mode compositions are primarily Ca-Cm, exhibit downshifts. The downshifts for v3 and v10 are small, 3-5 cm-1; however, the downshift for v28 is 14 cm-1. These frequency shifts are consistent with those of previously published resonance Raman studies of model compounds. In contrast to reports from other laboratories, the data presented here for horseradish peroxidase compound I can be attributed unambiguously to resonance Raman scattering from a porphyrin pi-cation radical.     

Colloidal stability of carbon nanotubes in an aqueous dispersion of phospholipid

Within the family of nanomaterials, carbon nanotubes (CNTs) have emerged as a new efficient scaffold for studying molecular interactions at interfaces. Poor dispersability of CNTs in any solvent presents a considerable drawback for the development of novel functional composite structures. Previous studies have demonstrated that the solubility of CNTs can be greatly enhanced by employing appropriate surfactants, some of them being biological molecules. In this work, we study the noncovalent wrapping of lipid chains onto the graphitic surface of single-walled material (SWCNTs) by electron microscopy and Raman spectroscopy. Stable and homogenous aqueous suspensions of SWCNTs in the presence of lipids have been prepared, whereas their electrophoretic mobility was confirmed by zeta-potential measurements. Raman measurements revealed that smaller diameter SWCNTs are preferentially dispersed by lipid molecules in the aqueous supernatant part of the prepared suspension.     

Interatomic potentials and solvation parameters from protein engineering data for buried residues

Van der Waals (vdW) interaction energies between different atom types, energies of hydrogen bonds (H-bonds), and atomic solvation parameters (ASPs) have been derived from the published thermodynamic stabilities of 106 mutants with available crystal structures by use of an originally designed model for the calculation of free-energy differences. The set of mutants included substitutions of uncharged, inflexible, water-inaccessible residues in alpha-helices and beta-sheets of T4, human, and hen lysozymes and HI ribonuclease. The determined energies of vdW interactions and H-bonds were smaller than in molecular mechanics and followed the "like dissolves like" rule, as expected in condensed media but not in vacuum. The depths of modified Lennard-Jones potentials were -0.34, -0.12, and -0.06 kcal/mole for similar atom types (polar-polar, aromatic-aromatic, and aliphatic-aliphatic interactions, respectively) and -0.10, -0.08, -0.06, -0.02, and nearly 0 kcal/mole for different types (sulfur-polar, sulfur-aromatic, sulfur-aliphatic, aliphatic-aromatic, and carbon-polar, respectively), whereas the depths of H-bond potentials were -1.5 to -1.8 kcal/mole. The obtained solvation parameters, that is, transfer energies from water to the protein interior, were 19, 7, -1, -21, and -66 cal/moleA(2) for aliphatic carbon, aromatic carbon, sulfur, nitrogen, and oxygen, respectively, which is close to the cyclohexane scale for aliphatic and aromatic groups but intermediate between octanol and cyclohexane for others. An analysis of additional replacements at the water-protein interface indicates that vdW interactions between protein atoms are reduced when they occur across water.     

Application of Raman spectroscopy to biological macromolecules.

The Raman spectra of biological macromolecules arise from molecular vibrations of either the backbone chains or the side chains. The frequencies of the Raman bands lie in a region between 200 cm-1 and 3000 cm-1. From certain frequencies of the vibrations of the backbone chains one can determine the conformation or secondary structure of a macromolecule. Thus for polypeptides and proteins the frequencies of the Amide I and Amide III vibrations allow one to determine the averge conformation of their backbone chain. In polynucleotides and nucleic acids, the frequency of the phosphate diester stretch of the phosphate furanose chain varies between 814 cm-1 for A conformation and 790 cm-1 for B conformation. Raman spectra of the bases in nucleic acids can be used to determine base stacking and hydrogen bonding interactions. Thus Raman spectroscopy is an important tool for determining the conformation structure of proteins and nucleic acids.     

Molecular dynamics analysis on tensile properties of carbon nanotubes with different cracks

Molecular dynamics simulation is employed for the axial tension of single-walled carbon nanotubes (SWCNTs) with different cracks. The cracks of SWCNTs in this study actually are the crack-like defects. AIREBO potential is used to simulate the interactions among carbon atoms. The effects of the crack length, temperature, strain rate and tube diameter on the mechanical properties of SWCNTs are studied. It is found that the failure stress and failure strain decrease with the increase of crack length. And the results show that the failure stress and failure strain are related to the applied strain rate and affected by temperature especially by lower temperature. It is also revealed that the failure stress increases with the increase in tube diameter. The deformation behaviours of SWCNTs are also obtained.     

Do electrostatic interactions destabilize protein–nucleic acid binding?

The negatively charged phosphates of nucleic acids are often paired with positively charged residues upon binding proteins. It was thus counter-intuitive when previous Poisson-Boltzmann (PB) calculations gave positive energies from electrostatic interactions, meaning that they destabilize protein-nucleic acid binding. Our own PB calculations on protein-protein binding have shown that the sign and the magnitude of the electrostatic component are sensitive to the specification of the dielectric boundary in PB calculations. A popular choice for the boundary between the solute low dielectric and the solvent high dielectric is the molecular surface; an alternative is the van der Waals (vdW) surface. In line with results for protein-protein binding, in this article, we found that PB calculations with the molecular surface gave positive electrostatic interaction energies for two protein-RNA complexes, but the signs are reversed when the vdW surface was used. Therefore, whether destabilizing or stabilizing effects are predicted depends on the choice of the dielectric boundary. The two calculation protocols, however, yielded similar salt effects on the binding affinity. Effects of charge mutations differentiated the two calculation protocols; PB calculations with the vdW surface had smaller deviations overall from experimental data.     

Detection, mapping, and quantification of single walled carbon nanotubes in histological specimens with photoacoustic microscopy

Aims

In the present study, the efficacy of multi-scale photoacoustic microscopy (PAM) was investigated to detect, map, and quantify trace amounts [nanograms (ng) to micrograms (µg)] of SWCNTs in a variety of histological tissue specimens consisting of cancer and benign tissue biopsies (histological specimens from implanted tissue engineering scaffolds).

Materials and Methods

Optical-resolution (OR) and acoustic-resolution (AR) - Photoacoustic microscopy (PAM) was employed to detect, map and quantify the SWCNTs in a variety of tissue histological specimens and compared with other optical techniques (bright-field optical microscopy, Raman microscopy, near infrared (NIR) fluorescence microscopy).

Results

Both optical-resolution and acoustic-resolution PAM, allow the detection and quantification of SWCNTs in histological specimens with scalable spatial resolution and depth penetration. The noise-equivalent detection sensitivity to SWCNTs in the specimens was calculated to be as low as ∼7 pg. Image processing analysis further allowed the mapping, distribution, and quantification of the SWCNTs in the histological sections.

Conclusions

The results demonstrate the potential of PAM as a promising imaging technique to detect, map, and quantify SWCNTs in histological specimens, and could complement the capabilities of current optical and electron microscopy techniques in the analysis of histological specimens containing SWCNTs.     

Resonance Raman spectra of carbon-13- and nitrogen-15-labeled riboflavin bound to egg-white flavoprotein.

The resonance Raman spectra of [2-13C]-, [4a-13C]-, [4-13C]-8 [10a-13C]-, [2,4,4a, 10a-13C]-, [5-15N]-, [1,3-15N]-, and [1,3,5-15N]riboflavin bound to egg-white proteins were observed for N(3)-H and N(3)-D forms with spontaneous Raman technique by using the 488.0-nm excitation line of an argon ion laser. The fluorescence of riboflavin was quenched by forming a complex with egg-white riboflavin binding protein. The in-plane displacements of the C(2), C(4a), N(1), N(3), and N(5) atoms during each Raman active vibration were calculated from the observed isotopic frequency shifts. The 1252-cm-1 mode of the N(3)-H form was found to involve large vibrational displacements of the C(2) and N(3) atoms and to be strongly coupled with the N(3)-H bending mode. This line can be used as an indicator for state of N(3)-H...protein interaction. The 1584-cm-1 mode, which is known to be resonance-enhanced upon excitation near the 370-nm absorption band, was accompanied by the displacement of the N(5) atom in particular. The 1355-cm-1 mode was most strongly resonance-enhanced by the 450-nm absorption band and involved the displacements of all carbon atoms of ring III. Both lines can be used as structure probes for elucidating the structure of electronically excited states of isoalloxazine.     

Resonance raman spectroscopy of iron (3)--ovotransferrin and iron (3)--human serum transferrin

We report the resonance Raman spectra in the frequency range 300–1800 cm^?1 of Fe (III)-ovotransferrin and Fe (III)-human serum transferrin in aqueous solution at about 10^?4M protein concentration. This is the first observation of resonance Raman scattering ascribable to amino acid ligand vibrational modes of a nonheme iron protein. The resonance Raman spectra of the transferrins are similar except that the resonance band near 1270 cm^?1 is shifted to a higher frequency for Fe(III)-human serum transferrin than that for Fe(III)-ovotransferrin. The resonance Raman bands observed near 1170, 1270, 1500 and 1600 cm^?1 may reflect resonance enhancement of p-hydroxy-phenyl frequencies of tyrosine residues and/or imidazolium frequencies of histidine residues.     

Resonance Raman spectra of riboflavin and its derivatives in the bound state with egg riboflavin binding proteins

The resonance Raman spectra of riboflavin (RF) and its derivatives, including 3-deuterated (3-D RF), 3-methyl (3-CH3 RF), 3-carboxymethyl (3-CH2COOH RF), and 7,8-dichlororiboflavins (7,8-Cl RF), in H2O and D2O were observed in the 700-1700 cm-1 region. The fluorescence problem of riboflavin was overcome by complex formation of riboflavin with riboflavin binding proteins. The observed frequencies of Raman lines of RF are in good agreement with those of glucose oxidase obtained by Spiro et al. by the resonance CARS method, although the present spectral range is extended to much lower frequency with a higher signal-to-noise ratio than that for glucose oxidase. The observed Raman lines were assigned to the individual ring modes of isoalloxazine on the basis of the Raman spectra of appropriate model compounds such as uracil, pyrazine, and o-xylene. The 1253 cm-1 line of RF was shifted to ca. 1300 cm-1 for 3-D RF, 3-CH3 RF, and 3-CH2COOH RF, and accordingly can be assigned to the CN stretching mode of Ring III. The 1632 cm-1 line of RF was shifted for 7,8-Cl RF and was assigned to a Ring I mode. No Raman line mainly due to C = O stretching mode was observed in the present resonance Raman spectra.     

Low-frequency dynamics and Raman scattering of crystals, of B-, A-, and Z-DNA, and fibers of C-DNA

Normal modes of vibration of DNA in the low-frequency region (10-300 cm-1 interval) have been identified from Raman spectra of crystals of B-DNA [d(CGCAAATTTGCG)], A-DNA [r(GCG)d(CGC) and d(CCCCGGGG)], and Z-DNA [d(CGCGCG) and d(CGCGTG)]. The lowest vibrational frequencies detected in the canonical DNA structures--at 18 +/- 2 cm-1 in the B-DNA crystal, near 24 +/- 2 cm-1 in A-DNA crystals, and near 30 +/- 2 cm-1 in Z-DNA crystals--are shown to correlate well with the degree of DNA hydration in the crystal structures, as well as with the level of hydration in calf thymus DNA fibers. These findings support the assignment [H. Urabe et al. (1985) J. Chem. Phys. 82, 531-535; C. Demarco et al. (1985) Biopolymers 24, 2035-2040] of the lowest frequency Raman band of each DNA to a helix mode, which is dependent primarily upon the degree of helix hydration, rather than upon the intrahelical conformation. The present results show also that B-, A-, C-, and Z-DNA structures can be distinguished from one another on the basis of their characteristic Raman intensity profiles in the region of 40-140 cm-1, even though all structures display two rather similar and complex bands centered within the intervals of 66-72 and 90-120 cm-1. The similarity of Raman frequencies for B-, A-, C-, and Z-DNA suggests that these modes originate from concerted motions of the bases (librations), which are not strongly dependent upon helix backbone geometry or handedness. Correlation of the Raman frequencies and intensities with the DNA base compositions suggests that the complex band near 90-120 cm-1 in all double-helix structures is due to in-plane librational motions of the bases, which involve stretching of the purine-pyrimidine hydrogen bonds. This would explain the centering of the band at higher frequencies in structures containing G.C pairs (greater than 100 cm-1) than in structures containing A.T pairs (less than 100 cm-1), consistent with the strengths of G.C and A.T hydrogen bonding.     

Unusual heme iron-lipid acyl chain coordination in Escherichia coli flavohemoglobin

Escherichia coli flavohemoglobin is endowed with the notable property of binding specifically unsaturated and/or cyclopropanated fatty acids both as free acids or incorporated into a phospholipid molecule. Unsaturated or cyclopropanated fatty acid binding to the ferric heme results in a spectral change observed in the visible absorption, resonance Raman, extended x-ray absorption fine spectroscopy (EXAFS), and x-ray absorption near edge spectroscopy (XANES) spectra. Resonance Raman spectra, measured on the flavohemoglobin heme domain, demonstrate that the lipid (linoleic acid or total lipid extracts)-induced spectral signals correspond to a transition from a five-coordinated (typical of the ligand-free protein) to a hexacoordinated, high spin heme iron. EXAFS and XANES measurements have been carried out both on the lipid-free and on the lipid-bound protein to assign the nature of ligand in the sixth coordination position of the ferric heme iron. EXAFS data analysis is consistent with the presence of a couple of atoms in the sixth coordination position at 2.7 A in the lipid-bound derivative (bonding interaction), whereas a contribution at 3.54 A (nonbonding interaction) can be singled out in the lipid-free protein. This last contribution is assigned to the CD1 carbon atoms of the distal LeuE11, in full agreement with crystallographic data on the lipid-free protein at 1.6 A resolution obtained in the present work. Thus, the contributions at 2.7 A distance from the heme iron are assigned to a couple of carbon atoms of the lipid acyl chain, possibly corresponding to the unsaturated carbons of the linoleic acid.     

Flavin and heme structures in lactate:cytochrome c oxidoreductase: a resonance Raman study

Resonance Raman spectra of Hansenula anomala L-lactate:cytochrome c oxidoreductase (or flavocytochrome b2), of its cytochrome b2 core, and of a bis(imidazole) iron-protoporphyrin complex were obtained at the Soret preresonance from the oxidized and reduced forms. Raman contributions from both the isoalloxazine ring of flavin mononucleotide (FMN) and the heme b2 were observed in the spectra of oxidized flavocytochrome b2. Raman diagrams showing frequency differences of selected FMN modes between aqueous and proteic environments were drawn for various flavoproteins. These diagrams were closely similar for flavocytochrome b2 and for flavodoxins. This showed that the FMN structure must be very similar in both types of proteins, despite their very different proteic pockets. However, the electron density at this macrocycle was found to be higher in flavocytochrome b2 than in these electron transferases. No significant difference was observed between the heme structures in flavocytochrome b2 and in cytochrome b2 core. The porphyrin center-N(pyrrole) distances in the oxidized and reduced heme b2 were estimated to be 1.990 and 2.022 A from frequencies of porphyrin skeletal modes, respectively. The frequency of the vinyl stretching mode of protoporphyrin was found to be very affected in resonance Raman spectra of flavocytochrome b2 and of cytochrome b2 core (1634-1636 cm-1) relative to those observed in the spectra of iron-protoporphyrin [bis(imidazole)] complexes (1620 cm-1). These specificities were interpreted as reflecting a near coplanarity of the vinyl groups of heme b2 with the pyrrole rings to which they are attached. The low-frequency regions of resonance Raman indicated that the iron atoms of the four hemes b2 are in the porphyrin plane whatever their oxidation state. The histidine-Fe-histidine symmetric stretching mode was located at 205 cm-1 in the spectra of flavocytochrome b2 and of cytochrome b2 core. It was insensitive to the iron oxidation state and indicated strong Fe-His bonds in both states.     

A theoretical study of red-shifting and blue-shifting hydrogen bonds occurring between imidazolidine derivatives and PEG/PVP polymers

A theoretical study is presented with the aim to investigate the molecular properties of intermolecular complexes formed by the monomeric units of polyvinylpyrrolidone (PVP) or polyethyleneglycol (PEG) polymers and a set of four imidazolidine (hydantoine) derivatives. The substitution of the carbonyl groups for thiocarbonyl in the hydantoin scaffold was taken into account when analyzing the effect of the hydrogen bonds on imidazolidine derivatives. B3LYP/6-31G(d,p) calculations and topological integrations derived from the quantum theory of atoms in molecules (QTAIM) were applied with the purpose of examining the N–H⋯O hydrogen bond strengths formed between the amide group of the hydantoine ring and the oxygen atoms of PVP and PEG polymers. The effects caused by the N–H⋯O interaction fit the typical evidence for hydrogen bonds, which includes a variation in the stretch frequencies of the N–H bonds. These frequencies were identified as being vibrational red-shifts because their values decreased. Although the values of such calculated interaction energies are between 12 and 33 kJ mol⁻¹, secondary intermolecular interactions were also identified. One of these secondary interactions is formed through the interaction of the benzyl hydrogen atoms with the oxygen atoms of the PVP and PEG structures. As such, we have analyzed the stretch frequencies on the C–H bonds of the benzyl groups, and blue-shifts were identified on these bonds. In this sense, the intermolecular systems formed by hydantoine derivatives and PVP/PEG monomers were characterized as a mix of red-shifting and blue-shifting hydrogen-bonded complexes.     

Effects of Hydroxylated Carbon Nanotubes on the Aggregation of Aβ16–22 Peptides: A Combined Simulation and Experimental Study

The pathogenesis of Alzheimer’s disease (AD) is associated with the aggregation of amyloid-β (Aβ) peptides into toxic aggregates with β-sheet character. In a previous computational study, we showed that pristine single-walled carbon nanotubes (SWCNTs) can inhibit the formation of β-sheet-rich oligomers in the central hydrophobic core fragment of Aβ (Aβ_16–22). However, the poor solubility of SWCNTs in water hinders their use in biomedical applications and nanomedicine. Here, we investigate the influence of hydroxylated SWCNT, a water-soluble SWCNT derivative, on the aggregation of Aβ_16–22 peptides using all-atom explicit-water replica exchange molecular dynamics simulations. Our results show that hydroxylated SWCNTs can significantly inhibit β-sheet formation and shift the conformations of Aβ_16–22 oligomers from ordered β-sheet-rich structures toward disordered coil aggregates. Detailed analyses of the SWCNT-Aβ interaction reveal that the inhibition of β-sheet formation by hydroxylated SWCNTs mainly results from strong electrostatic interactions between the hydroxyl groups of SWCNTs and the positively charged residue K16 of Aβ_16–22 and hydrophobic and aromatic stacking interactions between SWCNTs and F19 and F20. In addition, our atomic force microscopy and thioflavin T fluorescence experiments confirm the inhibitory effect of both pristine and hydroxylated SWCNTs on Aβ_16–22 fibrillization, in support of our previous and present replica exchange molecular dynamics simulation results. These results demonstrate that hydroxylated SWCNTs efficiently inhibit the aggregation of Aβ_16–22; in addition, they offer molecular insight into the inhibition mechanism, thus providing new clues for the design of therapeutic drugs against amyloidosis.     

Blood oxidative stress generation after intraperitoneal administration of functionalized single-walled carbon nanotubes in rats

Single-walled carbon nanotubes (SWCNTs) have been proposed for various medical applications. However, their safety for human administration has not been yet fully demonstrated. In vitro studies have pointed oxidative stress as a mechanism involved in their cytotoxic effects. In the present study we have evaluated the capacity of DNA functionalized SWCNTs to induce oxidative stress in blood after intraperitoneal (ip) administration in rats. The presence of SWCNTs in blood was confirmed by Raman spectroscopy 30 minutes after their ip administration. Oxidative stress parameters (malondialdehyde - MDA, protein carbonyls - PC, antioxidant capacity measured as hydrogen donating capacity - HD, sulfhydryl groups - SH, glutathione - GSH and nitrites - NO) were assessed in blood at 3, 6, 24, respectively, and 48 hours after ip injection. MDA, PC and NO exhibited a significant increase at 3-6 hours interval from exposure, followed by a recovery trend. The levels of HD reached a bottom level at 6 hours after administration, while SH strongly decreased at 3 hours interval and increased slightly up to 48 hours without attending the initial values. GSH level recorded an increasing tendency at the 3rd hour, an incomplete recovery process at 24 hours followed by a secondary significant increase following a 48-hour interval. Significant inverse correlations were obtained between the PC and SH levels and between the NO and HD values. In conclusion, the ip administration of DNA functionalized SWCNT in rats results in oxidative stress generation in plasma, with a transient pattern of evolution.     

Resonance Raman detection of bound dioxygen in cytochrome P-450cam

We have used resonance Raman spectroscopy and isotopic labeling techniques to unambiguously assign the dioxygen stretching frequency (vo-o) in the substrate-bound oxygenated complex of cytochrome P-450cam. The frequency found for Vo-o in the P-450cam system (1140 cm-1) is in remarkable agreement with recent studies of thiolate heme model compounds. The general features of the oxy-P-450cam Raman spectra are tabulated and comparisons are made with the oxy complexes of hemoglobin, myoglobin, and various model compounds. Most of the results are qualitatively explained by consideration of electron donation into the pi g (O2)/d pi (M) orbitals of the oxygenated complex (M = Fe or Co). It is also noted that the effect of the "extra" electron in the nitrogen base Co(II) oxy complexes, in some ways, parallels the effect of the lone pair electrons of thiolate in the oxy-P-450cam complex. This is evidenced by the enhanced resonance Raman activity of vo-o in both the Co(II) and P-450 systems as well as by the similarity of the vo-o frequencies.     

Comparison between kinematic and kinetic methods for computing the vertical displacement of the center of mass during human hopping at different frequencies

Kinematic and kinetic methods (sacral marker, reconstructed pelvis, segmental analysis, and force platform methods) have been used to calculate the vertical excursion of the center of mass (COM) during movement. In this study we compared the measurement of vertical COM displacement yielded by different methods during able-bodied subjects' hopping at different frequencies (varying between 1.2 and 3.2 Hz). ANOVA revealed a significant interaction between hopping frequency and method (p < 0.001), showing that increasing hopping frequency reduced the differences between methods. A post hoc analysis revealed a significant difference between all methods at the lowest hopping frequency and between the force platform and both the sacral marker and reconstructed pelvis methods at the intermediate hopping frequencies, with differences ranging from 16 to 67 millimeters (all p < 0.05). Results are discussed in view of each methods' limits. We conclude that the segmental analysis and force platform methods can be considered to provide the most accurate results for COM vertical excursion during human hopping in a large range of hopping frequency.