Thin layers of water on biomolecular and other nanostructured surfaces can be supercooled to temperatures not accessible with bulk water. Chen et al. [PNAS 103, 9012 (2006)] suggested that anomalies near 220 K observed by quasi-elastic neutron scattering can be explained by a hidden critical point of bulk water. Based on more sensitive measurements of water on perdeuterated phycocyanin, using the new neutron backscattering spectrometer SPHERES, and an improved data analysis, we present results that show no sign of such a fragile-to-strong transition. The inflection of the elastic intensity at 220 K has a dynamic origin that is compatible with a calorimetric glass transition at 170 K. The temperature dependence of the relaxation times is highly sensitive to data evaluation; it can be brought into perfect agreement with the results of other techniques, without any anomaly. In contrast to bulk water, protein hydration water can be supercooled down to a glass transition at T g ≃ 170 K. Near T g translational degrees of freedom arrest, which induces discontinuities in the specific heat and the thermal expansion coefficient of the hydration water [1][2][3][4]. Due to the dynamic nature of the glass transition, freezing of microscopic degrees of freedom can already be observed far above T g .The protein dynamic transition is an abrupt onset of atomic displacements on the microscopic length and time scale probed by quasielastic neutron scattering (QENS). First observed twenty years ago in hydrated myoglobin and lysozyme at T ∆ ≃ 240 K [5], it is now known to be a generic property of hydrated proteins, while it is absent in dehydrated systems. It is therefore related to the dynamics of the hydration shell.In QENS, mean squared dispacements δx 2 are deduced from the elastic scattering intensity S(q, 0). Due to the finite spectrometer resolution (fwhm 2∆ω), one actually measures S(q, |ω| ∆ω). Full spectral measurements show that the anomalous decrease of the central peak is compensated by increasing inelastic wings [5,6]. These effects have been interpreted as precursors of the glass transition. Since QENS probes structural relaxation at ∆ω −1 ≃ 100 ps, while the calorimetric T g refers to a time scale of 100 s, it is natural that T ∆ is located far above T g : the protein dynamic transition is the microscopic manifestation of the glass transition in the hydration shell. The time-scale dependence of T ∆ also explains its variation with viscosity [7][8][9]. * Electronic address: wdoster@ph.tum.de Recently, these views have been challenged by the suggestion that there might be a time-scale independent transition. Support came mainly from QENS experiments on the backscattering spectrometer HFBS at NIST. In hydrated lysozyme, DNA and RNA, a kink was found not only in S(q, |ω| ∆ω), but also in the α relaxation time τ deduced from full spectra S(q, ω) [10][11][12][13]. This change of τ (T ) from high-T super-Arrhenius to low-T Arrhenius behavior at T L ≃ 220 K has been interpreted as a fragile-to-strong-transition (FST) from the...

The aim of this study was to develop and to evaluate the biological properties of bacterial cellulose-hydroxyapatite (BC-HA) nanocomposite membranes for bone regeneration. Nanocomposites were prepared from bacterial cellulose membranes sequentially incubated in solutions of CaCl2 followed by Na2HPO4. BC-HA membranes were evaluated in noncritical bone defects in rat tibiae at 1, 4, and 16 weeks. Thermogravimetric analyses showed that the amount of the mineral phase was 40%–50% of the total weight. Spectroscopy, electronic microscopy/energy dispersive X-ray analyses, and X-ray diffraction showed formation of HA crystals on BC nanofibres. Low crystallinity HA crystals presented Ca/P a molar ratio of 1.5 (calcium-deficient HA), similar to physiological bone. Fourier transformed infrared spectroscopy analysis showed bands assigned to phosphate and carbonate ions. In vivo tests showed no inflammatory reaction after 1 week. After 4 weeks, defects were observed to be completely filled in by new bone tissue. The BC-HA membranes were effective for bone regeneration.

A nanocomposite based on bacterial cellulose (BC) and type I collagen (COL) was evaluated for in vitro bone regeneration. BC membranes were modified by glycine esterification followed by cross-linking of type I collagen employing 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide. Collagen incorporation was studied by spectroscopy analysis. X-Ray diffraction showed changes in the BC crystallinity after collagen incorporation. The elastic modulus and tensile strength for BC-COL decreased, while the strain at failure showed a slight increase, even after sterilization, as compared to pristine BC. Swelling tests and contact angle measurements were also performed. Cell culture experiments performed with osteogenic cells were obtained by enzymatic digestion of newborn rat calvarium revealed similar features of cell morphology for cultures grown on both membranes. Cell viability/proliferation was not different between BC and BC-COL membranes at day 10 and 14. The high total protein content and ALP activity at day 17 in cells cultured on BC-COL indicate that this composite allowed the development of the osteoblastic phenotype in vitro. Thus, BC-COL should be considered as alternative biomaterial for bone tissue engineering.

Among remarkable discoveries concerning propolis, such as antifungal, antiviral, and antioxidant activities, its anti-inflammatory, and mainly its antibacterial, properties deserve special attention when skin wound healing is concerned. Based on this and knowing the distinctive performance of bacterial (BC) membranes on wound healing, in this work it is proposed to demonstrate the potent antimicrobial activity and wound healing properties of a novel propolis containing biocellulose membrane. The obtained propolis/BC membrane was able to adsorb propolis not only on the surface, but also in its interstices demonstrated by scanning electron microscopy, X-ray diffraction, Fourier transform infrared (FT-IR) spectroscopy, and thermogravidimetric assays. Additionally, the polyphenolic compounds determination and the prominent antibacterial activity in the membrane are demonstrated to be dose dependent, supporting the possibility of obtaining propolis/BC membranes at the desired concentrations, taking into consideration its application and its skin residence time. Finally, it could be suggested that propolis/BC membrane may favor tissue repair in less time and more effectively in contaminated wounds.

Casein proteins belong to the class of natively disordered proteins. The existence of disordered biologically active proteins questions the assumption that a well-folded structure is required for function. A hypothesis generally put forward is that the unstructured nature of these proteins results from the functional need of a higher flexibility. This interplay between structure and dynamics was investigated in a series of time-of-flight neutron scattering experiments, performed on casein proteins, as well as on three well-folded proteins with distinct secondary structures, namely, myoglobin (alpha), lysozyme (alpha/beta) and concanavalin A (beta). To illustrate the subtraction of the solvent contribution from the scattering spectra, we used the dynamic susceptibility spectra emphasizing the high frequency part of the spectrum, where the solvent dominates. The quality of the procedure is checked by comparing the corrected spectra to those of the dry and hydrated protein with negligible solvent contamination. Results of spectra analysis reveal differences in motional amplitudes of well-folded proteins, where beta-sheet structures appear to be more rigid than a cluster of alpha-helices. The disordered caseins display the largest conformational displacements. Moreover their global diffusion rates deviate from the expected dependence, suggesting further large-scale conformational motions.