A singular thermodynamically consistent temperature at the origin of the anomalous behavior of liquid water

The density maximum of water dominates the thermodynamics of the system under ambient conditions, is strongly P-dependent, and disappears at a crossover pressure P[subscript cross] ~ 1.8 kbar. We study this variable across a wide area of the T–P phase diagram. We consider old and new data of both the isothermal compressibility K[subscript T](T, P) and the coefficient of thermal expansion αP(T, P). We observe that KT(T) shows a minimum at T* ~ 315±5 K for all the studied pressures. We find the behavior of αP to also be surprising: all the αP(T) curves measured at different P cross at T*. The experimental data show a “singular and universal expansivity point” at T* ~ 315 K and αP(T*) ≃ 0.44 10[superscript −3] K[superscript −1]. Unlike other water singularities, we find this temperature to be thermodynamically consistent in the relationship connecting the two response functions.Fulvio Frisone FondazioneNational Science Foundation (U.S.) (NSF Chemistry Division (grant CHE 0911389))National Science Foundation (U.S.) (NSF Chemistry Division CHE 1213217))Italy. Ministero dell'istruzione, dell'università e della ricerca (MIUR-PRIN2008

Molecular degradation of ancient documents revealed by 1H^1H HR-MAS NMR spectroscopy

For centuries mankind has stored its knowledge on paper, a remarkable biomaterial made of natural cellulose fibers. However, spontaneous cellulose degradation phenomena weaken and discolorate paper over time. The detailed knowledge of products arising from cellulose degradation is essential in understanding deterioration pathways and in improving durability of cultural heritage. In this study, for the first time, products of cellulose degradation were individually detected in solid paper samples by means of an extremely powerful proton HR-MAS NMR set-up, in combination to a wise use of both ancient and, as reference, artificially aged paper samples. Carboxylic acids, in addition to more complex dicarboxylic and hydroxy-carboxylic acids, were found in all samples studied. Since these products can catalyze further degradation, their knowledge is fundamental to improve conservation strategies of historical documents. Furthermore, the identification of compounds used in ancient production techniques, also suggests for artifacts dating, authentication and provenance

Water and lysozyme: Some results from the bending and stretching vibrational modes

The dynamic or glass transition in biomolecules is important to their functioning. Also essential is the transition between the protein native state and the unfolding process. To better understand these transitions, we use Fourier transform infrared spectroscopy to study the vibrational bending and stretching modes of hydrated lysozymes across a wide temperature range. We find that these transitions are triggered by the strong hydrogen bond coupling between the protein and hydration water. More precisely, we demonstrate that in both cases the water properties dominate the evolution of the system. We find that two characteristic temperatures are relevant: in the supercooled regime of confined water, the fragile-to-strong dynamic transition occurs at T[subscript L], and in the stable liquid phase, T* ≈ 315 ± 5 K characterizes the behavior of both isothermal compressibility K[subscript T] (T,P) and the coefficient of thermal expansion a[subscript P] (T,P)

On the ergodicity of supercooled molecular glass-forming liquids at the dynamical arrest: the o-terphenyl case

The dynamics of supercooled ortho-terphenyl has been studied using photon-correlation spectroscopy (PCS) in the depolarized scattering geometry. The obtained relaxation curves are analyzed according to the mode-coupling theory (MCT) for supercooled liquids. The main results are: i) the observation of the secondary Johari-Goldstein relaxation (β) that has its onset just at the dynamical crossover temperature T[subscript B] (T[subscript M] > T[subscript B] > T[subscript g]); ii) the confirmation, of the suggestion of a recent statistical mechanical study, that such a molecular system remains ergodic also below the calorimetric glass-transition temperature T[subscript g]. Our experimental data give evidence that the time scales of the primary (α) and this secondary relaxations are correlated. Finally a comparison with recent PCS experiments in a colloidal system confirms the primary role of the dynamical crossover in the physics of the dynamical arrest.United States. Dept. of Energy. Office of Basic Energy Sciences (Contract DE-FG02-90ER45429

Synthesis and Characterization of a Colloidal Novel Folic Acid–β-cyclodextrin Conjugate for Targeted Drug Delivery

A novel folic acid–b-cyclodextrin (b-CD) conjugate was synthesized and preliminarily characterized by 1H NMR, ESI-MS, and MALDI-MS. 1H NMR shows the presence of a- and c-conjugates which are generated by b-CD linkage in turn with both carboxylic functions of folic acid. Moreover ROESY evidences supramolecular interactions between the benzene ring of the folic acid and the b-CD cavity. DOSY suggests that ethylenediamine derived b-CD–folic acid forms a colloidal dispersion difficult to purify from free folic acid. An analysis of self-diffusion coefficient (Ds) of the three species (a-, c-conjugates, and free folic acid) and relaxation times (T1 and T2) is reported to tentatively explain the colloidal behaviour of the new species in an aqueous solution

Energy landscape in protein folding and unfolding

We use (1)H NMR to probe the energy landscape in the protein folding and unfolding process. Using the scheme [Formula: see text] reversible unfolded (intermediate) [Formula: see text] irreversible unfolded (denatured) state, we study the thermal denaturation of hydrated lysozyme that occurs when the temperature is increased. Using thermal cycles in the range [Formula: see text] K and following different trajectories along the protein energy surface, we observe that the hydrophilic (the amide NH) and hydrophobic (methyl CH(3) and methine CH) peptide groups evolve and exhibit different behaviors. We also discuss the role of water and hydrogen bonding in the protein configurational stability

The dynamic crossover in water does not require bulk water

Many of the anomalous properties of water may be explained by invoking a second critical point that terminates the coexistence line between the low- and high-density amorphous states in the liquid. Direct experimental evidence of this point, and the associated polyamorphic liquid–liquid transition, is elusive as it is necessary for liquid water to be cooled below its homogeneous-nucleation temperature. To avoid crystallization, water in the eutectic LiCl solution has been studied but then it is generally considered that “bulk” water cannot be present. However, recent computational and experimental studies observe cooperative hydration in which case it is possible that sufficient hydrogen-bonded water is present for the essential characteristics of water to be preserved. For femtosecond optical Kerr-effect and nuclear magnetic resonance measurements, we observe in each case a fractional Stokes–Einstein relation with evidence of the dynamic crossover appearing near 220 K and 250 K respectively. Spectra obtained in the glass state also confirm the complex nature of the hydrogen-bonding modes reported for neat room-temperature water and support predictions of anomalous diffusion due to “worm-hole” structure

Quantifying probabilities of eruption at a well-monitored active volcano: an application to Mount Etna (Sicily, Italy).

At active volcanoes, distinct eruptions are preceded by complex and different precursory patterns; in addition, there are precursory signals which do not necessarily lead to an eruption. The main purpose of this paper is to present an unprecedented application of the recently developed code named BET_EF (Bayesian Event Tree_Eruption Forecasting) to the quantitative estimate of the eruptive hazard at Mt. Etna volcano. We tested the model for the case history of the July-August 2001 flank eruption. Anomalies in geophysical, geochemical and volcanological monitoring parameters were observed more than a month in advance of the effective onset of the eruption. As a consequence, eruption probabilities larger than 90% were estimated. An important feature of the application of BET_EF to Mt. Etna was the probabilistic estimate of opening vent locations. The methodology allowed a clear identification of assumptions and monitoring parameter thresholds and provided rational means for their revision if new data or information are incoming

From Critical Point to Critical Point: The Two-States Model Describes Liquid Water Self-Diffusion from 623 to 126 K

Liquid’s behaviour, when close to critical points, is of extreme importance both for fundamental research and industrial applications. A detailed knowledge of the structural–dynamical correlations in their proximity is still today a target to reach. Liquid water anomalies are ascribed to the presence of a second liquid–liquid critical point, which seems to be located in the very deep supercooled regime, even below 200 K and at pressure around 2 kbar. In this work, the thermal behaviour of the self-diffusion coefficient for liquid water is analyzed, in terms of a two-states model, for the first time in a very wide thermal region (126 K < T < 623 K), including those of the two critical points. Further, the corresponding configurational entropy and isobaric-specific heat have been evaluated within the same interval. The two liquid states correspond to high and low-density water local structures that play a primary role on water dynamical behavior over 500 K