Biomedical subjects

M Descamps

Publications and source records attributed to M Descamps.

At least 19 recordsLinked to original sources

PubMed2006

Analysis of sugar bioprotective mechanisms on the thermal denaturation of lysozyme from Raman scattering and differential scanning calorimetry investigations.

Sugar-induced thermostabilization of lysozyme was analyzed by Raman scattering and modulated differential scanning calorimetry investigations, for three disaccharides (maltose, sucrose, and trehalose) characterized by the same chemical formula (C(12)H(22)O(11)). This study shows that trehalose is the most effective in stabilizing the folded secondary structure of the protein. The influence of sugars on the mechanism of thermal denaturation was carefully investigated by Raman scattering experiments carried out both in the low-frequency range and in the amide I band region. It was determined that the thermal stability of the hydrogen-bond network of water, highly dependent on the presence of sugars, contributes to the stabilization of the native tertiary structure and inhibits the first stage of denaturation, that is, the transformation of the tertiary structure into a highly flexible state with intact secondary structure. It was found that trehalose exhibits exceptional capabilities to distort the tetra-bonded hydrogen-bond network of water and to strengthen intermolecular O-H interactions responsible for the stability of the tertiary structure. Trehalose was also observed to be the best stabilizer of the folded secondary structure, in the transient tertiary structure, leading to a high-temperature shift of the unfolding process (the second stage of denaturation). This was interpreted from the consideration that the transient tertiary structure is less flexible and inhibits the solvent accessibility around the hydrophobic groups of lysozyme.

Amides↗

PubMed2006

Metastability release of the form alpha of trehalose by isothermal solid state vitrification.

Kinetic investigations of the polymorphic form alpha of anhydrous trehalose have been performed below its apparent melting temperature (Tm) by differential scanning calorimetry (DSC) and X-ray diffraction. The results reveal a spontaneous isothermal vitrification process which indicates that the phase alpha is in a very unusual superheating situation. This behavior has been attributed to the fact that the effective melting temperature (Tm(eff)) of the phase alpha is likely to be located far below the glass transition temperature (Tg) of this compound. The high viscosity of the liquid trehalose between Tm(eff) and Tg is thus invoked to explain the long lifetime of the phase alpha in this temperature range.

Letter↗

PubMed2006

Molecular mobility in glass forming fananserine: a dielectric, NMR, and TMDSC investigation.

PURPOSE: This study was conducted to characterize the molecular mobility of supercooled fananserine and derive from this analysis the non-Arrhenius and nonexponential properties of the primary alpha-relaxation. METHODS: The use of three investigation techniques of the molecular mobility, namely, dielectric relaxation, modulated differential scanning calorimetry, and proton nuclear magnetic resonance, allowed us to describe the dynamic properties of supercooled fananserine on a wide range of frequencies and temperatures, ranging from the melting temperature T(m) = 372 K down to the glass transition temperature T(g) = 292 K. RESULTS: We emphasized the capacity of these three techniques to give a coherent set of information. We used the coupling-model theory to interpret the dielectric results. It allowed us to identify two relaxation processes (alpha and beta), corresponding to different molecular motions. The temperature evolution of the alpha-relaxation indicates that fananserine is a fragile glass former, as reflected by the steepness index value, m = 77. The temperature T(o) where the relaxation times diverge was also determined. CONCLUSIONS: The description of the dielectric relaxation data in terms of the Kohlrausch-Williams-Watt relaxation function has shown the existence of an additional low-amplitude relaxation process assigned to the so-called Johari-Goldstein process. Mainly concerned by the primary alpha-process directly involved in the glass formation, we derived from this analysis the characteristic features of this process and showed that supercooled fananserine is characterized by a strongly non-Arrhenius and nonexponential behavior.

Air Pressure↗

PubMed2006

Dynamics of the amorphous and crystalline alpha-, gamma-phases of indomethacin.

Crystallization processes in indomethacin can be observed below Tg leading to different forms depending on the thermal treatment: a rapid and deep quench below Tg leads to the metastable alpha-phase and a slow cooling close to Tg gives rise to the stable gamma-phase. To understand this atypical behavior, we have studied the molecular mobility of the amorphous and crystalline forms of indomethacin by dielectric relaxation and 1H NMR spectroscopy. Two relaxations were detected in the glassy state obtained from the deeply quenched liquid. One, also present in the gamma-phase, was attributed to local rotations. The other one, of very low amplitude, was attributed to the Johari-Goldstein relaxation. The results allowed to discuss the relationship between these two relaxation processes and the crystallization properties of amorphous indomethacin.

Crystallization↗

PubMed2006

Evidence of a two-stage thermal denaturation process in lysozyme: a Raman scattering and differential scanning calorimetry investigation.

Raman spectroscopy (in the low-frequency range and the amide I band region) and modulated differential scanning calorimetry investigations have been used to analyze temperature-induced structural changes in lysozyme dissolved in 1H2O and 2H2O in the thermal denaturation process. Low-frequency Raman data reveal a change in tertiary structure without concomitant unfolding of the secondary structure. Calorimetric data show that this structural change is responsible for the configurational entropy change associated with the strong-to-fragile liquid transition and correspond to about 1/3 of the native-denaturated transition enthalpy. This is the first stage of the thermal denaturation which is a precursor of the secondary structure change and is determined to be strongly dependent on the stability of the hydrogen-bond network in water. Low-frequency Raman spectroscopy provides information on the flexibility of the tertiary structure (in the native state and the transient folding state) in relation to the fragility of the mixture. The unfolding of the secondary structure appears as a consequence of the change in the tertiary structure and independent of the solvent. Protein conformational stability is directly dependent on the stability of the native tertiary structure. The structural transformation of tertiary structure can be detected through the enhanced 1H/2H exchange inhibited in native proteins. Taking into account similar features reported in the literature observed for different proteins it can be considered that the two-stage transformation observed in lysozyme dissolved in water is a general mechanism for the thermal denaturation of proteins.

Amides↗

PubMed2005

Onset of slow dynamics in difluorotetrachloroethane glassy crystal.

Complementary neutron spin-echo and x-ray experiments and molecular-dynamics simulations have been performed on difluorotetrachloroethane (CFCl2-CFCl2) glassy crystal. Static, single-molecule reorientational dynamics and collective dynamics properties are investigated. Our results confirm the strong analogy between molecular liquids and plastic crystals. The orientational disorder is characterized at different temperatures and a change in the nature of rotational dynamics is observed. A careful check of the rotational diffusion model is performed using self-angular correlation functions Cl with high l values and compared to results obtained on molecular liquids composed of A-B dumbbells. Below the crossover temperature at which slow dynamics emerge, we show that some scaling predictions of the mode coupling theory hold and that alpha-relaxation times and nonergodicity parameters are controlled by the nontrivial static correlations.

Journal Article↗

PubMed2005

Analogy of the slow dynamics between the supercooled liquid and supercooled plastic crystal states of difluorotetrachloroethane.

Slow dynamics of difluorotetrachloroethane in both supercooled plastic crystal and supercooled liquid states have been investigated with molecular dynamics simulations. The temperature and wave-vector dependence of collective dynamics in both states are probed using coherent dynamical scattering functions S (Q,t). Our results confirm the strong analogy between molecular liquids and plastic crystals for which alpha-relaxation times and nonergodicity parameters are controlled by the nontrivial static correlations S (Q), as predicted by the mode coupling theory.

Journal Article↗

PubMed2005

How homogeneous are the trehalose, maltose, and sucrose water solutions? An insight from molecular dynamics simulations.

The structural properties resulting from the reciprocal influence between water and three well-known homologous disaccharides, namely, trehalose, maltose, and sucrose, in aqueous solutions have been investigated in the 4-66 wt % concentration range by means of molecular dynamics computer simulations. Hydration numbers clearly show that trehalose binds to a larger number of water molecules than do maltose or sucrose, thus affecting the water structure to a deeper extent. Two-dimensional radial distribution functions of trehalose solutions definitely reveal that water is preferentially localized at the hydration sites found in the trehalose dihydrate crystal, this tendency being enhanced when increasing trehalose concentration. Over a rather wide concentration range (4-49 wt %), the fluctuations of the radius of gyration and of the glycosidic dihedral angles of trehalose indicate a higher flexibility with respect to maltose and sucrose. At sugar concentrations between 33 and 66 wt %, the mean sugar cluster size and the number of sugar-sugar hydrogen bonds formed within sugar clusters reveal that trehalose is able to form larger clusters than sucrose but smaller than maltose. These features suggest that trehalose-water mixtures would be more homogeneous than the two others, thus reducing both desiccation stresses and ice formation.

Biophysics↗

PubMed2005

Composition of bone and apatitic biomaterials as revealed by intravital Raman microspectroscopy.

Microcharacterization of biominerals allows a better understanding of the pathophysiological events that occur in calcified tissues and synthetic biomaterials. Different methods have been extensively used to conduct such investigations. A new model for the intravital study of the composition and structure of membranous bone by Raman microspectroscopy is described. Titanium bone chambers equipped with a fused-silica optical window were implanted transcutaneously in the calvaria of New Zealand rabbits. The implanted optical windows were well tolerated, and spectral acquisitions were performed without any additional invasive procedure. Bone and implanted apatitic biomaterials were analyzed at different times after surgery. All Raman bands were unambiguously identified in the bone and biomaterial spectra. The main PO4 and CO3 Raman bands in bone spectra were consistent with those found in the carbonated apatite spectrum. The major collagen bands were always observed around 1200-1300 (amide III) and 1600-1700 (amide I) delta cm(-1) and, 1400-1470 and 2800-3100 delta cm(-1) (bending and stretching modes of CH groups, respectively). The phenylalanine (Phe) band was identified in all spectra at 1003 delta cm(-1) and overlapped that of the weak HPO4(2-) ion. The CH bands frequently overlapped the lipid bands. However a distinct protein and lipid bands were detected at 2950 and 2852 delta cm(-1), respectively. In bone areas close to blood vessels, the Raman signature of hemoglobin was detected with a characteristic band at 754 delta cm(-1). The changes observed in bone varied as a function of time and location. The composition and structure of all of the biomaterials studied--including those that were resorbable--seemed to remain stable over time and location. We report for the first time the complete intravital study of Raman spectra of bone and calcium phosphate biomaterials over a period of 8 months. This new approach does not require specimen preparation and allows simultaneous observation of mineral and organic bone constituents over time, which therefore should provide insightful information about their relationship.

Animals↗

PubMed2005

Nuclear magnetic resonance and dielectric investigations of molecular motions in a glassy crystal: the mixed compound (CN-adm)0.75(Cl-adm)0.25.

The dynamic properties of plastic crystalline mixed adamantane's derivatives namely cyanoadamantane (75%) and chloroadamantane (25%) were investigated by dielectric and nuclear magnetic resonance (NMR) spectroscopy, covering a spectral range of 12 decades in the temperature range 110-420 K. Phase transformations were studied and dynamical parameters of the plastic (I), glassy (Ig), and ordered (III) phases were determined and compared with those of pure compounds. The dynamics of the supercooled plastic phase is characterized by an alpha-process exhibiting an Arrhenius behavior which classified the mixed compound as a strong glass former. In the plastic phase, NMR relaxation times were interpreted by using a Frenkel model, which takes into account structural equilibrium positions. This model explains adequately the experimental results by considering two molecular motions. In both the glassy state and plastic phase the motional parameters agree with those of 1-cyanoadamantane. On the contrary, in the ordered phase, the motional parameters related to the uniaxial rotation of chloroadamantane molecules indicate an accelerated motion.

Journal Article↗

PubMed2004

Relaxation modes in glass forming meta-toluidine.

The dynamics in supercooled meta-toluidine was studied using dielectric relaxation, modulated differential scanning calorimetry, proton spin-lattice relaxation times, and viscosity measurements. The combination of these different techniques has clearly shown a large decoupling of the relaxation modes whose origin is attributed to the formation of clusters via the NH2 bonding. This decoupling starts at a temperature also corresponding to a change of the dynamical behavior from a high temperature Arrhenius evolution to a Vogel-Fulcher-Tamman low temperature evolution.

Journal Article↗

PubMed2004

Solid state NMR and DSC methods for quantifying the amorphous content in solid dosage forms: an application to ball-milling of trehalose.

The purpose of this study was to determine quantitatively the amorphous fraction in crystalline-amorphous powder mixtures of trehalose, in order to assess the ability of the (13)C NMR technique for quantitative amorphous characterization. The NMR method is described in detail and its accuracy is compared to that of the DSC technique. Amorphous trehalose was prepared by mechanical milling. Samples with different amorphous fractions were prepared by physical mixing of purely amorphous and purely crystalline powders. The results reveal a close correlation between the imposed compositions of the physical mixtures and those determined by NMR and DSC, indicating that both are useful and accurate methods for compositional characterization of powders. The NMR method is then used to determine the evolution of the amorphous fraction in a trehalose powder, during a milling procedure which ultimately leads to a fully amorphous state.

Calorimetry, Differential Scanning↗

PubMed2004

Orientated growth of crystalline anhydrous maltitol (4-O-alpha-D-glucopyranosyl-D-glucitol).

In the industrial crystallisation process of maltitol (C(12)H(24)O(11)), the presence of maltotriitol (C(18)H(34)O(16)) in the maltose syrup is responsible for a change of the crystal morphology. Two different crystal forms of maltitol were obtained: a prismatic one and a 'bipyramidal' one. IR and X-ray diffraction experiments (single crystal and powder) were performed to identify both crystal parameters. It is concluded that a structural polymorphism has to be ruled out. Close coincidences in some of the crystal cell parameters of maltitol and maltotriitol allow to assume the process through which maltotriitol affects the morphology of maltitol crystals.

Carbohydrate Conformation↗

PubMed2002

In vitro studies of human and rat osteoclast activity on hydroxyapatite, beta-tricalcium phosphate, calcium carbonate.

Investigations on the ceramic degradation caused by osteoclasts are designed to assess osteoclast-ceramic interactions and to determine which ceramics are more suitable for use as bone substitute. This study investigated the resorptive activity of osteoclasts on ceramics presenting different solubility rates. Osteoclasts isolated from new-born rat and from human giant cell tumour were cultured on different bioceramics: hydroxyapatite (HA), beta-tricalcium phosphate (TCP) and calcium carbonate (calcite). Cytoskeletal was revealed by actin labelling and ceramic surfaces were observed by scanning electron microscopy (SEM). On all materials, the distribution of actin in typical ring was revealed. SEM examinations showed a clear difference in the shape and the depth of resorption lacunae on different ceramics. On pure HA, a superficial attack, clearly visible but very little extended. Numerous resorption lacunae, deep and well-delimited were observed on pure beta-TCP, but attacks less punctually were detected too. On pure calcite, an attack with form of spikes, very widespread but superficial was revealed. Degradation measurements revealed a significant increase of P release from the phosphocalcic ceramics and of Ca from all ceramics in the presence of osteoclasts. The both cell models found these characteristics, the rat osteoclasts were also an excellent model to study the ceramic resorption.

Adsorption↗

PubMed2001

Is there something of mode coupling theory in orientationally disordered crystals?

Molecular dynamics simulations have been performed on the orientationally disordered crystal chloroadamantane. We stress that universal behavior, relatively well described by the mode coupling theory, is shared by systems whose dynamics are almost completely controlled by translations or rotations. This investigation also shows the existence of a second remarkable dynamical crossover at the temperature Tx>Tc, consistent with a previous NMR and molecular dynamics study [F. Affouard et al., Europhys. Lett. 53, 611 (2001)]. This allows us to support clearly the existence of a "landscape-influenced" regime as recently proposed [S. Sastry et al., Nature 393, 554 (1998)].

Journal Article↗

PubMed2001

Porous HA ceramic for bone replacement: role of the pores and interconnections - experimental study in the rabbit.

Hydroxyapatite (HA) porous ceramics are increasingly used in biomedical applications. Their physical characteristics, such as porous volume, require perfect control of the pore shape, as well as the number and the size of their interconnections. The aim of our study was to evaluate a new HA ceramic using polymethylmethacrylate microbeads (PMMA) as the porous agent. Four interconnection sizes (30, 60, 100 and 130 microm) with a 175-260 microm pore size and three pore sizes (175-260, 260-350 and 350-435 microm) for a 130 microm interconnection size were tested. Various HA implants were appraised by microscopic evaluation in a 4.6 x 10 mm rabbit femur cancellous bone defect 12 weeks after implantation. The best osteoconduction result was obtained in the center of the ceramic by means of a 130 microm interconnection size and a 175-260 microm mean pore size. Bone formation obtained within the pores was double that obtained in our previous study where naphtalen microbeads were used as the porous agents.

Journal Article↗

PubMed2001

Psychophysiological reactivity in female sexual abuse survivors.

This study examined psychophysiological reactivity in 37 female childhood sexual abuse (CSA) survivors. After assessment of posttraumatic stress disorder (PTSD), psychiatric comorbidity, and trauma history, we conducted a psychophysiological assessment of forehead muscle tension, electrodermal activity, and heart rate during a mental arithmetic task and4 script-driven imagery tasks (neutral, consensual sex, pleasant, and trauma). PTSD symptom severity correlated positively with psychophysiologic changes and negative emotions during the trauma imagery task. During mental arithmetic, PTSD symptom severity correlated negatively with autonomic changes and positively with negative emotions. These results extend earlier PTSD research showing trauma-specific increased psychophysiological reactivity related to CSA in women with PTSD. They further suggest a negative association between PTSD severity and autonomic reactions to mental arithmetic.

Adolescent↗

PubMed2001

Molecular mobility and fragility in indomethacin: a thermally stimulated depolarization current study.

PURPOSE: To show that thermally stimulated depolarization currents (TSDC), which is a dielectric experimental technique relatively unknown in the pharmaceutical scientists community, is a powerful technique to study molecular mobility in pharmaceutical solids, below their glass transition temperature (Tg). Indomethacin (Tg = 42 degrees C) is used as a model compound. METHODS: TSDC is used to isolate the individual modes of motion present in indomethacin, in the temperature range between -165 degrees C and +60 degrees C. From the experimental output of the TSDC experiments, the kinetic parameters associated with the different relaxational modes of motion were obtained, which allowed a detailed characterization of the distribution of relaxation times of the complex relaxations observed in indomethacin. RESULTS: Two different relaxational processes were detected and characterized: the glass transition relaxation, or alpha-process, and a sub-Tg relaxation, or secondary process. The lower temperature secondary process presents a very low intensity, a very low activation energy, and a very low degree of cooperativity. The fragility index (Angell's scale) of indomethacin obtained from TSDC data is m = 64, which can be compared with other values reported in the literature and obtained from other experimental techniques. CONCLUSIONS: TSDC data indicate that indomethacin is a relatively strong glass former (fragility similar to glycerol but lower than sorbitol, trehalose, and sucrose). The high-resolution power of the TSDC technique is illustrated by the fact that it detected and characterized the secondary relaxation in indomethacin, which was not possible by other techniques.

Calorimetry↗