Fingerprints of the Crossing of the Frenkel and Melting Line on the Properties of High-Pressure Supercritical Water

Using molecular dynamics simulations in combination with the two-phase thermodynamic model, we reveal novel characteristic fingerprints of the crossing of the Frenkel and melting line on the properties of high-pressure water at a near-critical temperature (1.03T_c). The crossing of the Frenkel line at about 1.17 GPa is characterized by a crossover in the rotational and translational entropy ratio S^rot/S^trans, indicating a change in the coupling between translational and rotational motions which is also reflected in the shape of the rotational density of states. The observed isosbestic points in the translational and rotational density of states are also blue-shifted at density and pressure conditions higher than the ones corresponding to the Frenkel line. The first-order phase transition from a rigid liquid to a face-centered cubic plastic crystal phase at about 8.5 GPa is reflected in the discontinuous changes in the translational and rotational entropy, particularly in the significant increase of the ratio S^rot/S^trans. A noticeable discontinuous increase of the dielectric constant has also been revealed when crossing this melting line, which is attributed to the different arrangement of the water molecules in the plastic crystal phase. The reorientational dynamics in the plastic crystal phase is faster in comparison with the "rigid" liquid-like phase, but it remains unchanged upon a further pressure increase in the range of 8.5-11 GPa.

CF4 Capture and Separation of CF4-SF6 and CF4-N2 Fluid Mixtures Using Selected Carbon Nanoporous Materials and Metal-Organic Frameworks: A Computational Study

The adsorption of pure fluid carbon tetrafluoride and the separation of CF₄-SF₆ and CF₄-N₂ fluid mixtures using representative nanoporous materials have been investigated by employing Monte Carlo and molecular dynamics simulation techniques. The selected materials under study were the three-dimensional carbon nanotube networks, pillared graphene using carbon nanotube pillars, and the SIFSIX-2-Cu metal-organic framework. The selection of these materials was based on their previously reported efficiency to separate fluid SF₆-N₂ mixtures. The pressure dependence of the thermodynamic and kinetic separation selectivity for the CF₄-SF₆ and CF₄-N₂ fluid mixtures has therefore been investigated, to provide deeper insights into the molecular scale phenomena taking place in the investigated nanoporous materials. The results obtained have revealed that under near-ambient pressure conditions, the carbon-based nanoporous materials exhibit a higher gravimetric fluid uptake and thermodynamic separation selectivity. The SIFSIX-2-Cu material exhibits a slightly higher kinetic selectivity at ambient and high pressures.

On the Different Faces of the Supercritical Phase of Water at a Near-Critical Temperature: Pressure-Induced Structural Transitions Ranging from a Gaslike Fluid to a Plastic Crystal Polymorph

The present study reports a systematic analysis of a wide variety of structural, thermodynamic, and dynamic properties of supercritical water along the near-critical isotherm of T = 1.03T_c and up to extreme pressures, using molecular dynamics and Monte Carlo simulations. The methodology employed provides solid evidence about the existence of a structural transition from a liquidlike fluid to a compressed, tightly packed liquid, in the density and pressure region around 3.4ρ_c and 1.17 GPa, introducing an alternative approach to locate the crossing of the Frenkel line. Around 8.5 GPa another transition to a face-centered-cubic plastic crystal polymorph with density 5.178ρ_c is also observed, further confirmed by Gibbs free energy calculations using the two-phase thermodynamic model. The isobaric heat capacity maximum, closely related to the crossing of the Widom line, has also been observed around 0.8ρ_c, where the local density augmentation is also maximized. Another structural transition has been observed at 0.2ρ_c, related to the transformation of the fluid to a dilute gas at lower densities. These findings indicate that a near-critical isotherm can be divided into different domains where supercritical water exhibits distinct behavior, ranging from a gaslike one to a plastic crystal one.

Solvation structure and dynamics of the dimethylammonium cation diluted in liquid water: A molecular dynamics approach

Classical molecular dynamics simulation techniques were employed to investigate the local solvation structure and related dynamics of the dimethylammonium cation diluted in liquid water at ambient conditions. The translational and orientational order around the dimethylammonium cation was investigated in terms of the corresponding radial and angular distribution functions. The results obtained revealed that the first solvation shell of the dimethylammonium consists mainly of two and, less frequently, three water molecules. The two nearest water neighbors form hydrogen bonds with the ammonium hydrogen atoms of the cation, whereas the third neighbor interacts with the methyl hydrogen atoms as well. The distribution of the trigonal order parameter exhibits a bimodal behavior, signifying the existence of local orientational heterogeneities in the solvation shell of the dimethylammonium cation. The calculated continuous and intermittent residence and hydrogen bond lifetimes for the cation-water pairs have also been found to be longer in comparison with the water-water ones. The very similar self-diffusion coefficients of the dimethylammonium cation and the water molecules in the bulk dilute solution indicate that the translational motions of the cation are mainly controlled by the translational mobility of the surrounding water molecules.

The effect of polymorphism on the structural, dynamic and dielectric properties of plastic crystal water: A molecular dynamics simulation perspective

We have employed molecular dynamics simulations based on the TIP4P/2005 water model to investigate the local structural, dynamical, and dielectric properties of the two recently reported body-centered-cubic and face-centered-cubic plastic crystal phases of water. Our results reveal significant differences in the local orientational structure and rotational dynamics of water molecules for the two polymorphs. The probability distributions of trigonal and tetrahedral order parameters exhibit a multi-modal structure, implying the existence of significant local orientational heterogeneities, particularly in the face-centered-cubic phase. The calculated hydrogen bond statistics and dynamics provide further indications of the existence of a strongly heterogeneous and rapidly interconverting local orientational structural network in both polymorphs. We have observed a hindered molecular rotation, much more pronounced in the body-centered-cubic phase, which is reflected by the decay of the fourth-order Legendre reorientational correlation functions and angular Van Hove functions. Molecular rotation, however, is additionally hindered in the high-pressure liquid compared to the plastic crystal phase. The results obtained also reveal significant differences in the dielectric properties of the polymorphs due to the different dipolar orientational correlation characterizing each phase.

Detecting Novel Urine Biomarkers for the Early Diagnosis of Prostate Cancer: Platelet Derived Growth Factor-BB as a Possible New Target

Introduction

Although the prostate specific antigen revolutionized the diagnosis of prostate cancer (PCa), it has its limitations. We prospectively examined the potential use of the platelet-derived growth factor-BB (PDGF-BB) as a urine biomarker for the early diagnosis of PCa.

Materials and Methods

The urine samples of 118 patients were collected after a prostatic massage and all the patients subsequently underwent ultrasound-guided transrectal biopsy. PDGF-BB was detected in the urine by enzyme-linked immunosorbent assay.

Results

Patients with PCa had greater levels of prostate specific antigen and PDGF-BB. Receiver operating characteristic curve analysis showed that the optimal cut-of of PDGF-BB for the prediction of PCa was 1,504.9 with a sensitivity of 60% and a specificity of 51.3%. For a 100 unit increase in PDGF-BB, the likelihood for PCa increased about 4%.

Conclusion

PDGF-BB showed a significant predictive ability for PCa. Detection of PDGF-BB in urine with Elisa was easy and improved our diagnostic accuracy in the diagnosis of PCa.

Peculiar Molecular Shape and Size Dependence of the Dynamics of Fluids Confined in a Small-Pore Metal-Organic Framework

Force-field-based molecular dynamics simulations were deployed to systematically explore the dynamics of confined molecules of different shapes and sizes, that is, linear (CO₂ and N₂) and spherical (CH₄) fluids, in a model small pore system, that is, the metal-organic framework SIFSIX-2-Cu-i. These computations unveil an unprecedented molecular symmetry dependence of the translational and rotational dynamics of fluids confined in channel-like nanoporous materials. In particular, this peculiar behavior is reflected by the extremely slow decay of the Legendre reorientational correlation functions of even-parity order for the linear fluids, which is associated with jump-like orientation flips, while the spherical fluid shows a very fast decay taking place on a subpicosecond time scale. Such a fundamental understanding is relevant to diverse disciplines such as in chemistry, physics, biology, and materials science, where diatomic or polyatomic molecules of different shapes/sizes diffuse through nanopores.

B-lymphocytic infiltration of the prostate to a patient with chronic lymphocytic leukemia. A case report

Involvement of the prostate gland, as an early extra-nodal manifestation of a hematologic disease, or as a secondary infiltration is rare. Even rarer is the acute urinary retention due to infiltration by lymphocytes and simultaneously enlarged prostate. We present a case of a 61 years old male patient with a history of chronic lymphocytic leukemia, who was under oncological follow-up with no active treatment and had typical lower urinary tract symptoms due to benign prostatic hyperplasia and was receiving 5-alpha reductase inhibitor. After an acute urinary retention episode which was managed with a suprapubic catheter due to urethral catheter insertion failure, the patient was submitted to a transurethral prostatectomy. Histological examination revealed lymphocytic infiltration of the prostatic parenchyma by mostly small B cells. B-lymphocytic infiltration of the prostate gland, causes symptoms similar to benign prostatic hyperplasia. Acute urinary retention due to B-lymphocytic infiltration of the prostate is rare and the diagnosis is always histological and an oncological re-evaluation is necessary. The prognosis of these patients is related to the generalized disease rather than to the prostatic involvement.

Structure and dynamics of liquid CS2: Going from ambient to elevated pressure conditions

Molecular dynamics simulation studies were performed to investigate the structural and dynamic properties of liquid carbon disulfide (CS₂) from ambient to elevated pressure conditions. The results obtained have revealed structural changes at high pressures, which are related to the more dense packing of the molecules inside the first solvation shell. The calculated neutron and X-ray structure factors have been compared with available experimental diffraction data, also revealing the pressure effects on the short-range structure of the liquid. The pressure effects on the translational, reorientational, and residence dynamics are very strong, revealing a significant slowing down when going from ambient pressure to 1.2 GPa. The translational dynamics of the linear CS₂ molecules have been found to be more anisotropic at elevated pressures, where cage effects and librational motions are reflected on the shape of the calculated time correlation functions and their corresponding spectral densities.

The Anion Effect on Li(+) Ion Coordination Structure in Ethylene Carbonate Solutions

Rechargeable lithium ion batteries are an attractive alternative power source for a wide variety of applications. To optimize their performances, a complete description of the solvation properties of the ion in the electrolyte is crucial. A comprehensive understanding at the nanoscale of the solvation structure of lithium ions in nonaqueous carbonate electrolytes is, however, still unclear. We have measured by femtosecond vibrational spectroscopy the orientational correlation time of the CO stretching mode of Li(+)-bound and Li(+)-unbound ethylene carbonate molecules, in LiBF4, LiPF6, and LiClO4 ethylene carbonate solutions with different concentrations. Surprisingly, we have found that the coordination number of ethylene carbonate in the first solvation shell of Li(+) is only two, in all solutions with concentrations higher than 0.5 M. Density functional theory calculations indicate that the presence of anions in the first coordination shell modifies the generally accepted tetrahedral structure of the complex, allowing only two EC molecules to coordinate to Li(+) directly. Our results demonstrate for the first time, to the best of our knowledge, the anion influence on the overall structure of the first solvation shell of the Li(+) ion. The formation of such a cation/solvent/anion complex provides a rational explanation for the ionic conductivity drop of lithium/carbonate electrolyte solutions at high concentrations.

Synchronous Bilateral Testicular Tumors with Different Histopathology

A 40-year-old male presented to our outpatient department with the chief complaint of a painless mass on his right testis with gradual size increase over the past two months. Physical examination and ultrasound revealed a firm and nontender mass both on the right and on the left testis. The only elevated biomarker was b-hcG (24,7 mIU/mL) and computer tomography (CT) did not reveal any pathology. Bilateral high orchiectomies were performed, without previous frozen storage of the sperm. Histology proved typical seminoma of the left testis and embryonal carcinoma of the right testis. He received two cycles of adjuvant combination chemotherapy with bleomycin, etoposide, and cisplatin. Six months after the operation no residual tumor or recurrence was observed.

Hydrogen bond, electron donor-acceptor dimer, and residence dynamics in supercritical CO(2)-ethanol mixtures and the effect of hydrogen bonding on single reorientational and translational dynamics: A molecular dynamics simulation study

The hydrogen bonding and dynamics in a supercritical mixture of carbon dioxide with ethanol as a cosolvent (X(ethanol) approximately 0.1) were investigated using molecular dynamics simulation techniques. The results obtained reveal that the hydrogen bonds formed between ethanol molecules are significantly more in comparison with those between ethanol-CO(2) molecules and also exhibit much larger lifetimes. Furthermore, the residence dynamics in the solvation shells of ethanol and CO(2) have been calculated, revealing much larger residence times for ethanol molecules in the ethanol solvation shell. These results support strongly the ethanol aggregation effects and the slow local environment reorganization inside the ethanol solvation shell, reported in a previous publication of the authors [Skarmoutsos et al., J. Chem. Phys. 126, 224503 (2007)]. The formation of electron donor-acceptor dimers between the ethanol and CO(2) molecules has been also investigated and the calculated lifetimes of these complexes have been found to be similar to those corresponding to ethanol-CO(2) hydrogen bonds, exhibiting a slightly higher intermittent lifetime. However, the average number of these dimers is larger than the number of ethanol-CO(2) hydrogen bonds in the system. Finally, the effect of the hydrogen bonds formed between the individual ethanol molecules on their reorientational and translational dynamics has been carefully explored showing that the characteristic hydrogen bonding microstructure obtained exhibits sufficiently strong influence upon the behavior of them.

Investigation of the local composition enhancement and related dynamics in supercritical CO2-cosolvent mixtures via computer simulation: The case of ethanol in CO2

The supercritical mixture ethanol-carbon dioxide (EtOH-CO2) with mole fraction of ethanol X(EtOH) congruent with 0.1 was investigated at 348 K, by employing the molecular dynamics simulation technique in the canonical ensemble. The local intermolecular structure of the fluid was studied in terms of the calculated appropriate pair radial distribution functions. The estimated average local coordination numbers and mole fractions around the species in the mixture reveal the existence of local composition enhancement of ethanol around the ethanol molecules. This finding indicates the nonideal mixing behavior of the mixture due to the existence of aggregation between the ethanol molecules. Furthermore, the local environment redistribution dynamics have been explored by analyzing the time correlation functions (TCFs) of the total local coordination number (solvent, cosolvent) around the cosolvent molecules in appropriate parts. The analysis of these total TCFs in the auto-(solvent-solvent, cosolvent-cosolvent) and cross-(solvent-cosolvent, cosolvent-solvent) TCFs has shown that the time dependent redistribution process of the first solvation shell of ethanol is mainly determined by the redistribution of the CO2 solvent molecules. These results might be explained on the basis of the CO2-CO2 and EtOH-CO2 intermolecular forces, which are sufficiently weaker in comparison to the EtOH-EtOH hydrogen bonding interactions, creating in this way a significantly faster redistribution of the CO2 molecules in comparison with EtOH. Finally, the self-diffusion coefficients and the single reorientational dynamics of both the cosolvent and solvent species in the mixture have been predicted and discussed in relationship with the local environment around the species, which in the case of the EtOH molecules seem to be strongly affected.

Local density augmentation and dynamic properties of hydrogen-and non-hydrogen-bonded supercritical fluids: A molecular dynamics study

The local density inhomogeneities in neat supercritical fluids were investigated via canonical molecular dynamics simulations. The selected systems under investigation were the polar and hydrogen-bonded fluid methanol as well as the quadrupolar non-hydrogen-bonded carbon dioxide one. Effective local densities, local density augmentation, and enhancement factors were calculated at state points along an isotherm close to the critical temperature of each system (T(r)=1.03). The results obtained reveal strong influence of the polarity and hydrogen bonding upon the intensity of the local density augmentation. It is found that this effect is sufficiently larger in the case of the polar and associated methanol in comparison to those predicted for carbon dioxide. For both fluids the local density augmentation values are maximized in the bulk density region near 0.7rho(c), a result that is in agreement with experiment. In addition, the local density dynamics of each fluid were investigated in terms of the appropriate time correlation functions. The behavior of these functions reveals that the bulk density dependence of the local density reorganization times is very sensitive to the specific intermolecular interactions and to the size of the local region. Also, the estimated local density reorganization time as a function of bulk density of each fluid was further analyzed and successfully related to two different time-scale relaxation mechanisms. Finally, the results obtained indicate a possible relationship between the single-molecule reorientational dynamics and the local density reorganization ones.

Local Density Inhomogeneities and Dynamics in Supercritical Water: A Molecular Dynamics Simulation Approach

Molecular dynamics atomistic simulations in the canonical ensemble (NVT-MD) have been used to investigate the "Local Density Inhomogeneities and their Dynamics" in pure supercritical water. The simulations were carried out along a near-critical isotherm (Tr = T/Tc = 1.03) and for a wide range of densities below and above the critical one (0.2 rho(c) - 2.0 rho(c)). The results obtained reveal the existence of significant local density augmentation effects, which are found to be sufficiently larger in comparison to those reported for nonassociated fluids. The time evolution of the local density distribution around each molecule was studied in terms of the appropriate time correlation functions C(Delta)rhol(t). It is found that the shape of these functions changes significantly by increasing the density of the fluid. Finally, the local density reorganization times for the first and second coordination shell derived from these correlations exhibit a decreasing behavior by increasing the density of the system, signifying the density effect upon the dynamics of the local environment around each molecule.