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1.
J Chem Phys ; 161(4)2024 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-39056384

RESUMO

Molecular dynamics simulations have been employed to explore the hydrogen-bonding structure and dynamics in supercritical octanol-1 at a near-critical temperature and up to high densities and pressures. A substantial breakdown of the hydrogen-bonding network when going from ambient-liquid to supercritical conditions is revealed. The fraction of the non-hydrogen bonded molecules significantly increases in supercritical octanol-1, and a substantial decrease in the intermittent hydrogen-bond lifetime is observed. This behavior is also reflected on the maximum local density augmentation, which is comparable to the values obtained for non-polar and non-hydrogen bonded fluids. The existence of a structural transition from an inhomogeneous fluid phase to a soft-liquid one at densities higher than 2.0 ρc is also revealed. At higher densities, a significant change in the reorientational relaxation process is observed, reflected on the significant increase in the ratio of the Legendre reorientational times τ1R/τ2R. The latter becomes much higher than the value predicted by the Debye model of diffusive reorientation and the corresponding ratio for ambient liquid octanol-1. The non-polar tail of octanol-1 under supercritical conditions reorients more slowly in comparison with the polar tail. Interestingly, the opposite behavior is observed for the ambient liquid, further verifying the strong effect of the breakdown of the hydrogen bonding network on the properties of supercritical octanol-1. In accordance with the above-mentioned findings, the static dielectric constant of supercritical octanol-1 is very low even at high densities and pressures, comparable to the values obtained for non-polar and non-hydrogen bonded fluids.

2.
J Chem Phys ; 160(18)2024 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-38716849

RESUMO

Potential applications of previously synthesized pillared graphene oxide frameworks with phenyldiboronic acid linkers in the field of the adsorption and separation of polar protic and aprotic liquid solvents have been systematically explored using grand canonical Monte Carlo simulations. Particular attention was initially paid to the adsorption of pure liquid water, methanol, and dimethyl sulfoxide. The results obtained a significant increase in the isosteric heat of adsorption at low uptake in the case of dimethyl sulfoxide, which is about 17.9 and 26.8 kJ/mol higher than the values corresponding to methanol and water adsorption. These findings indicated that from a thermodynamic point of view, these pillared graphene oxide frameworks could be used in the separation of dimethyl sulfoxide-water liquid mixtures. Systematic grand canonical Monte Carlo simulations were then subsequently performed for dimethyl sulfoxide-water mixtures, with a low dimethyl sulfoxide concentration. The calculated values of the separation selectivity indicate that these materials could have potential applications in the separation of these mixed liquid solvents. Molecular dynamics simulations performed for a representative adsorbed mixture have revealed a substantial slowing down of the dynamics under confinement, particularly in the case of the hydrogen bonds formed between water and dimethyl sulfoxide.

3.
J Phys Chem Lett ; 13(33): 7636-7644, 2022 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-35952379

RESUMO

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 (1.03Tc). The crossing of the Frenkel line at about 1.17 GPa is characterized by a crossover in the rotational and translational entropy ratio Srot/Strans, 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 Srot/Strans. 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.

4.
ACS Omega ; 7(8): 6691-6699, 2022 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-35252664

RESUMO

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.

5.
J Phys Chem B ; 125(36): 10260-10272, 2021 Sep 16.
Artigo em Inglês | MEDLINE | ID: mdl-34491748

RESUMO

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 = 1.03Tc 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 3.4ρc 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 5.178ρc 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 0.8ρc, where the local density augmentation is also maximized. Another structural transition has been observed at 0.2ρc, 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.

6.
J Chem Phys ; 152(23): 234501, 2020 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-32571039

RESUMO

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.

7.
J Chem Phys ; 150(12): 124506, 2019 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-30927901

RESUMO

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.

8.
Curr Urol ; 12(1): 13-19, 2018 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30374275

RESUMO

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.

9.
Med Oncol ; 35(7): 97, 2018 May 25.
Artigo em Inglês | MEDLINE | ID: mdl-29802604

RESUMO

The goal of the study is to examine the possible use of HA (hyaluronic acid) and HAase (hyaluronidase) as novel urine biomarkers for the early diagnosis for prostate cancer (Pca). After a prostatic massage, the urine of 118 high-risk patients for Pca was collected, and the patients were submitted to ultrasound-guided transrectal biopsy. HA and HAase were detected and analyzed with Enzyme-Linked Immunosorbent Assay, and a statistical analysis of the urine levels of the two biomarkers according to the histology results was performed. HAase and HA were independently associated with Pca, and both HAase and HA showed significant predictive ability for prostate cancer. With an optimal cut-off point of 183.71 HAase had 70% sensitivity maintaining at the same time a 55.2% specificity, while the optimal cut-off point for HA was 50.13 with 65% sensitivity and 53.9% specificity. Patients with HAase more than 183.71 ng/ml had 3.67 times greater likelihood for prostate cancer and Patients with HA more than 50.13 ng/ml had 2.31 times greater likelihood for prostate cancer. The need of novel biomarkers that will improve the efficacy of PSA is urgent. HAase and HA showed significant predictive ability for prostate cancer and were independently associated with Pca, and greater levels were associated with greater odds for prostate cancer. To Our Knowledge, this is the first study referring to the detection of HAase and HA as potential urine biomarkers for the early diagnosis of Pca.


Assuntos
Biomarcadores Tumorais/urina , Detecção Precoce de Câncer/métodos , Ácido Hialurônico/urina , Hialuronoglucosaminidase/urina , Neoplasias da Próstata/diagnóstico , Idoso , Área Sob a Curva , Diagnóstico Diferencial , Grécia , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Neoplasias da Próstata/urina , Sensibilidade e Especificidade
10.
J Phys Chem Lett ; 9(11): 3014-3020, 2018 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-29763318

RESUMO

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.

11.
Arch Ital Urol Androl ; 89(1): 83-84, 2017 Mar 31.
Artigo em Inglês | MEDLINE | ID: mdl-28403603

RESUMO

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.


Assuntos
Linfócitos B/metabolismo , Leucemia Linfocítica Crônica de Células B/patologia , Próstata/patologia , Retenção Urinária/etiologia , Inibidores de 5-alfa Redutase/administração & dosagem , Humanos , Sintomas do Trato Urinário Inferior/etiologia , Masculino , Pessoa de Meia-Idade , Próstata/cirurgia , Hiperplasia Prostática/complicações , Hiperplasia Prostática/tratamento farmacológico , Ressecção Transuretral da Próstata/métodos
12.
J Chem Phys ; 145(15): 154505, 2016 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-27782484

RESUMO

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.

13.
J Phys Chem Lett ; 7(18): 3554-9, 2016 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-27560477

RESUMO

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.

14.
Case Rep Urol ; 2015: 492183, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26060594

RESUMO

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.

15.
J Phys Chem B ; 119(29): 8926-38, 2015 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-25313871

RESUMO

The local hydrogen-bonding structure and dynamics of liquid water have been investigated using the Car-Parrinello molecular dynamics simulation technique. The radial distribution functions and coordination numbers around water molecules have been found to be strongly dependent on the number of hydrogen bonds formed by each molecule, revealing also the existence of local structural heterogeneities in the structure of the liquid. The results obtained have also revealed the strong effect of the local hydrogen-bonding network on the local tetrahedral structure and entropy. The investigation of the dynamics of the local hydrogen-bonding network in liquid water has shown that this network is very labile, and the hydrogen bonds break and reform very rapidly. Nevertheless, it has been found that the hydrogen-bonding states associated with the formation of four hydrogen bonds by a water molecule exhibit the largest survival probability and corresponding lifetime. The reorientational motions of water molecules have also been found to be strongly dependent on their initial hydrogen-bonding state. Finally, the dependence of the librational and vibrational modes of water molecules on the local hydrogen-bonding network has been carefully examined, revealing a significant effect upon the libration and bond-stretching peak frequencies. The calculated low frequency peaks come in agreement with previously reported interpretations of the experimental low-frequency Raman spectrum of liquid water.


Assuntos
Água/química , Entropia , Hidrogênio/química , Ligação de Hidrogênio , Simulação de Dinâmica Molecular , Oxigênio/química , Análise Espectral Raman
16.
Phys Chem Chem Phys ; 16(8): 3675-85, 2014 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-24419252

RESUMO

Hydrogen bond (H-bond) dynamics have been investigated for "hot" 1-ethyl-3-methylimidazolium chloride and "cold" 1-butyl-3-methylimidazolium chloride ionic liquids (IL). While the average number of H-bonds remains constant for a ≈100 °C temperature change we show that the underlying dynamics of the H-bonding changes dramatically. H-bond dynamics are investigated based on distance and angle criteria, and on the H-bond state (zero, single or bifurcated H-bonds). Temperature effects on the cation ring reorientational dynamics are also examined. Angle deformations are found to be more important than bond stretching in determining the lifetime of individual H-bonds, and decay occurs on two time scales related to the magnitude of the deviation from linearity. Rapid angular oscillation of the anion breaks the H-bond (for the first time) and minimal temperature effects indicate that H-bonds are readily reformed even near the melting point. Intermittent H-bonds repeatedly break and reform over a longer timescale, and exhibit very strong temperature effects. In the hot IL H-bonding with ring and alkyl chain H-atoms occurs, ring reorientational dynamics is anisotropic and the corresponding lifetimes are similar to the intermittent H-bond lifetimes. In the cold IL ring H-atoms dominate the H-bonding and intermittent H-bonds last for ≈5 ns, ring reorientation occurs on a much slower timescale. The hot IL favours single H-bonds, but the individual ions often change, while the cold IL favours bifurcated H-bonds with the same co-located ions.

17.
Phys Chem Chem Phys ; 16(3): 876-9, 2014 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-24284834

RESUMO

The separation of an equimolar CO2-N2 mixture in a 3D porous carbon nanotube network has been investigated. An enhanced CO2 adsorption selectivity has been observed. The diffusion coefficients of the adsorbed molecules have been related to their residence dynamics in the vicinity of the carbon atoms of the nanopore.

18.
J Phys Chem B ; 116(16): 4921-33, 2012 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-22506654

RESUMO

A detailed investigation of hydrogen bonding in the pure ionic liquids [C4C1im]Cl and [C2C1im]Cl has been carried out using primarily molecular dynamics techniques. Analyses of the individual atom-atom pair radial distribution functions, and in particular those for C···Cl(-), have revealed that hydrogen bonding to the first methylene or methyl units of the substituent groups is important. Multiple geometric criteria for defining a hydrogen bond have been applied, and in particular the choice of the cutoff angle has been carefully examined. The interpretation of hydrogen bonding within these ionic liquids is highly angle dependent, and justification is provided for why it may be appropriate to employ a wider angle criteria than the 30° used for water or alcohol systems. The different types of hydrogen bond formed are characterized, and "top" conformations where the Cl anion resides above (or below) the imidazolium ring are investigated. The number of hydrogen bonds undertaken by each hydrogen atom (and the chloride anion) is quantified, and the propensity to form zero, one, or two hydrogen bonds is established. The effects of an increase in temperature on the static hydrogen bonding are also briefly examined.

19.
J Phys Chem B ; 115(42): 12098-107, 2011 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-21913703

RESUMO

Molecular dynamics simulation techniques have been employed to investigate the solvation structure and dynamics in dilute mixtures of cis- and trans-1,2-dichloroethene in supercritical carbon dioxide. The calculations were performed for state points along a near-critical isotherm (1.02 T(c)) over a wide range of densities, using new developed optimized potential models for both isomers. The similarities and differences in the solvation structures around each isomer have been presented and discussed. The local density augmentation and enhancement factors of CO(2) around the isomers have been found significantly larger than the corresponding values for pure supercritical CO(2). The dynamic local density reorganization has been investigated and related to previously proposed relaxation mechanisms. The density dependence of the calculated self-diffusion coefficients has revealed the existence of a plateau in the region of 0.7-1.1 ρ(c), where the local density augmentation exhibits the maximum value. The reorientational dynamics of the C═C bond vector have been also studied, exhibiting significant differences between the two isomers in the case of the second-order Legendre time correlation functions.

20.
J Phys Chem B ; 114(51): 17120-7, 2010 Dec 30.
Artigo em Inglês | MEDLINE | ID: mdl-21138307

RESUMO

The local intermolecular structure and dynamics of a recently proposed alternative refrigerant 2,3,3,3-tetrafluoro-1-propene has been investigated using classical molecular dynamics and ab initio quantum chemical techniques. The potential for hydrogen bonding is investigated, and evidence is found for weak interactions that do not differ substantially between the two types of fluorine atom acceptor. The dynamics of the weak hydrogen bonding are examined via residence and reorientational dynamics. Spectral densities are computed from atomic velocity autocorrelation functions and discussed in concert with the ab initio infrared vibrational spectrum of the (gas-phase) monomer and dimers; particular attention is paid to the presence of low-wavenumber librational motions. The net result of this study is a more detailed picture of the local structural ordering and dynamics within this weakly hydrogen-bonding liquid.

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