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1.
Physiology (Bethesda) ; 39(5): 0, 2024 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-38713090

RESUMO

Oxidative phosphorylation is regulated by mitochondrial calcium (Ca2+) in health and disease. In physiological states, Ca2+ enters via the mitochondrial Ca2+ uniporter and rapidly enhances NADH and ATP production. However, maintaining Ca2+ homeostasis is critical: insufficient Ca2+ impairs stress adaptation, and Ca2+ overload can trigger cell death. In this review, we delve into recent insights further defining the relationship between mitochondrial Ca2+ dynamics and oxidative phosphorylation. Our focus is on how such regulation affects cardiac function in health and disease, including heart failure, ischemia-reperfusion, arrhythmias, catecholaminergic polymorphic ventricular tachycardia, mitochondrial cardiomyopathies, Barth syndrome, and Friedreich's ataxia. Several themes emerge from recent data. First, mitochondrial Ca2+ regulation is critical for fuel substrate selection, metabolite import, and matching of ATP supply to demand. Second, mitochondrial Ca2+ regulates both the production and response to reactive oxygen species (ROS), and the balance between its pro- and antioxidant effects is key to how it contributes to physiological and pathological states. Third, Ca2+ exerts localized effects on the electron transport chain (ETC), not through traditional allosteric mechanisms but rather indirectly. These effects hinge on specific transporters, such as the uniporter or the Na+/Ca2+ exchanger, and may not be noticeable acutely, contributing differently to phenotypes depending on whether Ca2+ transporters are acutely or chronically modified. Perturbations in these novel relationships during disease states may either serve as compensatory mechanisms or exacerbate impairments in oxidative phosphorylation. Consequently, targeting mitochondrial Ca2+ holds promise as a therapeutic strategy for a variety of cardiac diseases characterized by contractile failure or arrhythmias.


Assuntos
Cálcio , Mitocôndrias Cardíacas , Humanos , Animais , Cálcio/metabolismo , Mitocôndrias Cardíacas/metabolismo , Fosforilação Oxidativa , Espécies Reativas de Oxigênio/metabolismo , Miocárdio/metabolismo , Cardiopatias/metabolismo
2.
BMC Cancer ; 24(1): 323, 2024 Mar 08.
Artigo em Inglês | MEDLINE | ID: mdl-38459456

RESUMO

BACKGROUND: Increased mitochondrial activities contributing to cancer cell proliferation, invasion, and metastasis have been reported in different cancers; however, studies on the therapeutic targeting of mitochondria in regulating cell proliferation and invasiveness are limited. Because mitochondria are believed to have evolved through bacterial invasion in mammalian cells, antibiotics could provide an alternative approach to target mitochondria, especially in cancers with increased mitochondrial activities. In this study, we investigated the therapeutic potential of bacteriostatic antibiotics in regulating the growth potential of colorectal cancer (CRC) cells, which differ in their metastatic potential and mitochondrial functions. METHODS: A combination of viability, cell migration, and spheroid formation assays was used to measure the effect on metastatic potential. The effect on mitochondrial mechanisms was investigated by measuring mitochondrial DNA copy number by qPCR, biogenesis (by qPCR and immunoblotting), and functions by measuring reactive oxygen species, membrane potential, and ATP using standard methods. In addition, the effect on assembly and activities of respiratory chain (RC) complexes was determined using blue native gel electrophoresis and in-gel assays, respectively). Changes in metastatic and cell death signaling were measured by immunoblotting with specific marker proteins and compared between CRC cells. RESULTS: Both tigecycline and tetracycline effectively reduced the viability, migration, and spheroid-forming capacity of highly metastatic CRC cells. This increased sensitivity was attributed to reduced mtDNA content, mitochondrial biogenesis, ATP content, membrane potential, and increased oxidative stress. Specifically, complex I assembly and activity were significantly inhibited by these antibiotics in high-metastatic cells. Significant down-regulation in the expression of mitochondrial-mediated survival pathways, such as phospho-AKT, cMYC, phospho-SRC, and phospho-FAK, and upregulation in cell death (apoptosis and autophagy) were observed, which contributed to the enhanced sensitivity of highly metastatic CRC cells toward these antibiotics. In addition, the combined treatment of the CRC chemotherapeutic agent oxaliplatin with tigecycline/tetracycline at physiological concentrations effectively sensitized these cells at early time points. CONCLUSION: Altogether, our study reports that bacterial antibiotics, such as tigecycline and tetracycline, target mitochondrial functions specifically mitochondrial complex I architecture and activity and would be useful in combination with cancer chemotherapeutics for high metastatic conditions.


Assuntos
Neoplasias do Colo , Neoplasias Colorretais , Animais , Humanos , Tigeciclina/metabolismo , Tigeciclina/farmacologia , Reposicionamento de Medicamentos , Linhagem Celular Tumoral , Mitocôndrias/metabolismo , Antibacterianos/farmacologia , Neoplasias do Colo/metabolismo , Proliferação de Células , Apoptose , Trifosfato de Adenosina/metabolismo , Neoplasias Colorretais/tratamento farmacológico , Neoplasias Colorretais/genética , Neoplasias Colorretais/metabolismo , Mamíferos/metabolismo
3.
Soft Matter ; 20(8): 1824-1833, 2024 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-38305724

RESUMO

High-spin donor-acceptor conjugated polymers are extensively studied for their potential applications in magnetic and spintronic devices. Inter-chain charge transfer among these high-spin polymers mainly depends on the nature of the local structure of the thin film and π-stacking between the polymer chains. However, the microscopic structural details of high-spin polymeric materials are rarely studied with an atomistic force field, and the molecular-level local structure in the liquid phase remains ambiguous. Here, we have examined the effects of oligomer chain length, side chain, and processing temperature on the organization of the high-spin cyclopentadithiophene-benzobisthiadiazole donor-acceptor conjugated polymer in chloroform solvent. We find that the oligomers display ordered aggregates whose structure depends on their chain length, with an average π-stacking distance of 3.38 ± 0.03 Å (at T = 298 K) in good agreement with the experiment. Also, the oligomers with longer alkyl side chains show better solvation and a shorter π-stacking distance. Furthermore, the clusters grow faster at higher temperature with more ordered aggregation between the oligomer chains.

4.
J Chem Phys ; 160(22)2024 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-38856066

RESUMO

In the liquid phase of heterogeneous catalysis, solvent plays an important role and governs the kinetics and thermodynamics of a reaction. Although it is often difficult to quantify the role of the solvent, it becomes particularly challenging when a zeolite is used as the catalyst. This difficulty arises from the complex nature of the liquid/zeolite interface and the different solvation environments around catalytically active sites. Here, we use ab initio molecular dynamics simulations to probe the local solvation structure and dynamics of methanol and water over MWW zeolite nanosheets with varying Brønsted acidity. We find that the zeolite framework and the number and location of the acid sites in the zeolite influence the structure and dynamics of the solvent. In particular, methanol is more likely to be in the vicinity of the aluminum (Al3+) at the T4 site than at T1 due to easy accessibility. The methanol oxygen binds strongly to the Al at the T4 site, weakening the Al-O for the bridging acid site, which results in the formation of the silanol group, significantly reducing the acidity of the site. The behavior of methanol is in direct contrast to that of water, where protons can easily propagate from the zeolite to the solvent molecules regardless of the acid site location. Our work provides molecular-level insights into how solvent interacts with zeolite surfaces, leading to an improved understanding of the catalytic site in the MWW zeolite nanosheet.

5.
Phys Chem Chem Phys ; 24(38): 23699-23711, 2022 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-36148814

RESUMO

High-spin ground-state organic materials with unique spin topology can significantly impact molecular magnetism, spintronics, and quantum computing devices. However, strategies to control the spin topology and alignment of the unpaired spins in different molecular orbitals are not well understood. Here, we report modulating spin distribution along the molecular backbone in high-spin ground-state donor-acceptor (D-A) conjugated polymers. Density functional theory calculations indicate that substitution of different heteroatoms (such as C, Si, N, and Se) alters the aromatic character in the thiadiazole unit of the benzobisthiadiazole (BBT) acceptor and modulates the oligomer length to result in high-spin triplet ground-state, orbital and spin topology. The C, Si, and Se atom substituted polymers show a localized spin density at the two opposite ends of the polymers. However, a delocalized spin distribution is observed in the N substituted polymer. We find that the hybridization (sp3vs. sp2) of the substituent atom plays an important role in controlling the electronic structure of these materials. This study shows that atomistic engineering is an efficient technique to tune the spin topologies and electronic configurations in the high-spin ground-state donor-acceptor conjugated polymers, compelling synthetic targets for room-temperature magnetic materials.

6.
Hum Mol Genet ; 28(3): 422-433, 2019 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-30304398

RESUMO

Leber's hereditary optic neuropathy (LHON) is a classical mitochondrial disease caused by mutations in the mitochondrial DNA encoding complex I subunits. Oxidative stress associated with complex I defect has been implicated in developing LHON phenotype such as retinal ganglion cell (RGC) death and loss of vision. However, the mechanism of LHON pathogenesis is still not very clear and thus no effective therapies are available to date. Using cybrid models for LHON, we show that autophagy is significantly compromised in cells carrying LHON-specific mtDNA mutations, which results in reduced clearance of dysfunctional mitochondria contributing to cell death. We further show that pharmacological activation of autophagy selectively clears the damaged mitochondria and thus repairs mitochondrial defects and improves overall cell survival in LHON cell models. Our results suggest that compromised autophagy is the missing link from oxidative stress to LHON pathogenesis. Activation of mitophagy ameliorates mitochondrial defects and exerts a protective role by improving cell survival in cells carrying LHON mutations that could be utilized as a potential therapeutic target for LHON treatment.


Assuntos
Mitofagia/fisiologia , Atrofia Óptica Hereditária de Leber/genética , Atrofia Óptica Hereditária de Leber/fisiopatologia , Apoptose/genética , Morte Celular/efeitos dos fármacos , Linhagem Celular , Sobrevivência Celular/efeitos dos fármacos , DNA Mitocondrial/genética , Humanos , Mitocôndrias/fisiologia , Mutação , Estresse Oxidativo/fisiologia
7.
Sensors (Basel) ; 20(2)2020 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-31936425

RESUMO

Soil volumetric water content ( V W C ) is a vital parameter to understand several ecohydrological and environmental processes. Its cost-effective measurement can potentially drive various technological tools to promote data-driven sustainable agriculture through supplemental irrigation solutions, the lack of which has contributed to severe agricultural distress, particularly for smallholder farmers. The cost of commercially available V W C sensors varies over four orders of magnitude. A laboratory study characterizing and testing sensors from this wide range of cost categories, which is a prerequisite to explore their applicability for irrigation management, has not been conducted. Within this context, two low-cost capacitive sensors-SMEC300 and SM100-manufactured by Spectrum Technologies Inc. (Aurora, IL, USA), and two very low-cost resistive sensors-the Soil Hygrometer Detection Module Soil Moisture Sensor (YL100) by Electronicfans and the Generic Soil Moisture Sensor Module (YL69) by KitsGuru-were tested for performance in laboratory conditions. Each sensor was calibrated in different repacked soils, and tested to evaluate accuracy, precision and sensitivity to variations in temperature and salinity. The capacitive sensors were additionally tested for their performance in liquids of known dielectric constants, and a comparative analysis of the calibration equations developed in-house and provided by the manufacturer was carried out. The value for money of the sensors is reflected in their precision performance, i.e., the precision performance largely follows sensor costs. The other aspects of sensor performance do not necessarily follow sensor costs. The low-cost capacitive sensors were more accurate than manufacturer specifications, and could match the performance of the secondary standard sensor, after soil specific calibration. SMEC300 is accurate ( M A E , R M S E , and R A E of 2.12%, 2.88% and 0.28 respectively), precise, and performed well considering its price as well as multi-purpose sensing capabilities. The less-expensive SM100 sensor had a better accuracy ( M A E , R M S E , and R A E of 1.67%, 2.36% and 0.21 respectively) but poorer precision than the SMEC300. However, it was established as a robust, field ready, low-cost sensor due to its more consistent performance in soils (particularly the field soil) and superior performance in fluids. Both the capacitive sensors responded reasonably to variations in temperature and salinity conditions. Though the resistive sensors were less accurate and precise compared to the capacitive sensors, they performed well considering their cost category. The YL100 was more accurate ( M A E , R M S E , and R A E of 3.51%, 5.21% and 0.37 respectively) than YL69 ( M A E , R M S E , and R A E of 4.13%, 5.54%, and 0.41, respectively). However, YL69 outperformed YL100 in terms of precision, and response to temperature and salinity variations, to emerge as a more robust resistive sensor. These very low-cost sensors may be used in combination with more accurate sensors to better characterize the spatiotemporal variability of field scale soil moisture. The laboratory characterization conducted in this study is a prerequisite to estimate the effect of low- and very low-cost sensor measurements on the efficiency of soil moisture based irrigation scheduling systems.

8.
Molecules ; 25(13)2020 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-32645899

RESUMO

Herbal medicines are widely used worldwide and much appreciated because of their fewer side effects and the ability to fight diseases at the root cause. Active 'phyto' ingredients require a scientific approach and a mechanism to distribute components at the target site for better therapeutic results. Nanotechnology, on the other hand, has created new hope for cancer treatment but is still far from being proven in clinical settings. This article combines a unique approach to synthesis with the use of Pleurotus sajor-caju, followed by microwave irritation of silver and gold nanoparticles that ensures the capping of the active phyto ingredient and further enhances the effects of nanomedicine to fight colon cancer, thus opening a new era of what we call herbonanoceutics. The article also compares the characteristics and properties of silver (Au) and gold (Ag) nanoparticles synthesized by an in house developed novel microwave-assisted rapid green synthesis method. The as-prepared Ag NPs and Au NPs were compared using ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). Our comparative study revealed that both assemblies display face-centred cubic structures (FCCs) and are nanocrystalline in nature. The advantage of the approach was that the sizes of gold and silver were identical in range with a similar distribution pattern. This has helped us to study the activity against colon cancer cell line (HCT-116) without incoherence since size plays a key role in the application. More specifically, morphological changes, cell viability, the production of reactive oxygen species (ROS) and the fragmentation of DNA have been further reported to assess better the results obtained with the two metals. Our results suggest that the newly adopted synthesis method may ensure the dual benefits from phyto ingredients which further enhances the effectiveness of advanced nanomedicine.


Assuntos
Neoplasias do Colo/tratamento farmacológico , Ouro , Lentinula/química , Nanopartículas Metálicas , Prata , Neoplasias do Colo/metabolismo , Neoplasias do Colo/patologia , Ouro/química , Ouro/farmacologia , Células HCT116 , Humanos , Nanopartículas Metálicas/química , Nanopartículas Metálicas/uso terapêutico , Micro-Ondas , Prata/química , Prata/farmacologia
9.
J Chem Phys ; 151(11): 114708, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31542019

RESUMO

Lignin as a potential renewable source of biofuels, chemicals, and other value-added products has gained much attention. However, the complexity of lignin structure poses a significant challenge for developing efficient valorization techniques. As most processes involve solvothermal conditions to minimize energy cost, lignin depolymerization is governed by reaction conditions (temperature and pressure) and solvents. In this work, binding of ß-O-4 linkage consisting lignin dimers on MWW two-dimensional (2D) zeolite is investigated using periodic density functional theory. Furthermore, the effect of different terminated surfaces (H:OH% = 100:0; 50:50; 0:100%), different temperatures (323, 353, 373 K), and different solvents (water and methanol) on the binding modes is quantified. Our work shows that in the gas phase the binding strength increases 10-15 kcal/mol upon increasing the number of hydroxyl groups on the surface. Also, the phenolic dimer binds more strongly than the nonphenolic dimer, and the binding strength of model compounds increases in the presence of the solvent. Analysis of structural changes in the presence of the solvent reveals that the aromatic rings are parallel to the zeolite surface and primary interaction with zeolite is through the hydroxyl groups near the ß-O-4 linkage. Furthermore, while the solvation energy decreases with increasing temperature, the opposite trend is observed for the binding energy with the surface.

10.
Bioprocess Biosyst Eng ; 42(5): 763-776, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30710227

RESUMO

Microbial cell disruption using pressurized gases (e.g., CO2) is a promising approach to improve the lipid recovery from wet oleaginous microorganisms by eliminating the energy-intensive drying required for conventional methods. In this study, we perform cell disruption of Rhodotorula glutinis using pressurized CH4, N2, and Ar where we find the efficacy of these gases on cell viability is minimal. Since CO2 is found to be the only viable gas for microbial cell disruption among these four gases, we use a combination of Box-Behnken design and response surface methodology (RSM) to find the optimal cell disruption by tuning different parameters such as pressure (P), temperature (T), exposure time (t), and agitation (a). From RSM, we find 6 log reduction of viable cells at optimized conditions, which corresponds to more than 99% cell death at P = 4000 kPa, T = 296.5 K, t = 360 min, and a = 325 rpm. Furthermore, from the scanning electron microscope (SEM), we find a complete morphological change in the cell structure when treated with pressurized CO2 compared to the untreated cells. Finally, we find that up to 85% of total lipid can be recovered using optimized pressurized CO2 from wet biomass compared to the untreated wet cells where up to 73% lipid can be recovered.


Assuntos
Basidiomycota/química , Biocombustíveis , Biomassa , Dióxido de Carbono/química , Lipídeos , Basidiomycota/metabolismo , Lipídeos/química , Lipídeos/isolamento & purificação , Pressão
11.
J Comput Chem ; 39(8): 397-406, 2018 Mar 30.
Artigo em Inglês | MEDLINE | ID: mdl-29164642

RESUMO

Vapor liquid equilibria (VLE) and condensed phase properties of carbon dioxide and sulfur dioxide are calculated using first principles Monte Carlo (FPMC) simulations to assess the performance of several density functionals, notably PBE-D3, BLYP-D3, PBE0-D3, M062X-D3, and rVV10. GGA functionals were used to compute complete vapor liquid coexistence curves (VLCCs) to estimate critical properties, while the hybrid and nonlocal van der Waals functionals were used only for computing density at a single state point due to the high computational cost. Our results show that the BLYP-D3 functional performs well in predicting VLE properties for both molecules when compared with other functionals. In the liquid phase, pair correlation functions reveal that there is not a significant difference in the location of the peak for the first solvation shell while the peak heights are different for different functionals. Overall, the BLYP-D3 functional is a good choice for modeling VLE of acidic gases with significant environmental implications such as CO2 and SO2 . © 2017 Wiley Periodicals, Inc.

12.
Yeast ; 35(3): 261-271, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29065217

RESUMO

Mitogen-activated protein kinases (MAPKs) play vital roles in multiple cellular processes and represent prominently pursued targets for development of therapeutic regimes. The MAPK Spc1 (p38 homologue) is known to be very important for both mitotic promotion and delay in Schizosaccharomyces pombe. However, the mechanism responsible for mitotic inhibition has remained elusive. Cdc25 (Cdc2 activator) and Wee1 (Cdc2 inhibtor) are important determinants of mitotic timing in all eukaryotes. Our results show that Spc1 can sense the perturbations in the balance of Cdc25 and Wee1 activities in S. pombe and that its function as a mitotic inhibitor is very important for controlling the same. An Spc1-Srk1-Rad24-dependent pathway for mitotic inhibition has been reported earlier.Here we report the presence of an alternative mechanism wherein Spc1 targets the 14-3-3 protein, Rad24, independently of Srk1, leading to relocalization of Cdc25 and mitotic inhibition. Our observations suggest that this pathway can serve as a backup mechanism for Cdc2 inactivation in the absence of Wee1.


Assuntos
Proteínas Fúngicas/metabolismo , Regulação Enzimológica da Expressão Gênica/fisiologia , Quinases de Proteína Quinase Ativadas por Mitógeno/metabolismo , Schizosaccharomyces/metabolismo , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Clonagem Molecular , Proteínas Fúngicas/genética , Regulação Fúngica da Expressão Gênica/fisiologia , Peptídeos e Proteínas de Sinalização Intracelular/genética , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Quinases de Proteína Quinase Ativadas por Mitógeno/genética , Proteínas Quinases Ativadas por Mitógeno/genética , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Fosfoproteínas Fosfatases/genética , Fosfoproteínas Fosfatases/metabolismo , Proteínas Tirosina Quinases/genética , Proteínas Tirosina Quinases/metabolismo , Schizosaccharomyces/genética , Proteínas de Schizosaccharomyces pombe/genética , Proteínas de Schizosaccharomyces pombe/metabolismo
13.
Phys Chem Chem Phys ; 20(23): 15753-15763, 2018 Jun 13.
Artigo em Inglês | MEDLINE | ID: mdl-29868654

RESUMO

Actinyl ions (AnO2n+), the form in which actinides are commonly found in aqueous solution, are important species in the nuclear fuel cycle. These ions can form stable complexes with ionic ligands such as OH-, NO3-, Cl-, and even other actinyl ions in the aqueous phase. Knowledge of the relative stabilities of these complexes is important for the efficient design of separation processes used in recycling. These complexes also play a major role in the formation of actinide nanoclusters. A quantitative treatment of the stability of these actinyl ion complexes is therefore warranted. In the present work, molecular dynamics (MD) simulations have been performed to calculate the potential of mean force (PMF) between two actinyl ions (UO22+ and NpO2+) and various ligands (F-, Cl-, OH-, NO3-, SO42-, CO32-, Na+, and H2O) in explicitly-modeled aqueous solution. Equilibrium constants were calculated from the PMFs, and are consistent with experimental trends. Dication actinyls show stronger affinity for anions compared to monocation actinyls, whereas the opposite is true for cation-cation interactions between actinyls. Finally, the dynamics of actinyl-ligand contact ion pair (CIP) dissociation were characterized by calculating rate constants from transition state theory. The transmission coefficient, a dynamical correction factor used to correct for reaction barrier recrossing, was calculated for each actinyl-ligand CIP dissociation event.

14.
Phys Chem Chem Phys ; 20(26): 17859-17870, 2018 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-29923565

RESUMO

Iodine binding to thiophene rings in dyes for dye-sensitized solar cells (DSCs) has been hypothesized to be performance degrading in a number of literature cases. Binding of iodine to dyes near the semiconductor surface can promote undesirable electron transfers and lower the overall efficiency of devices. Six thiophene or furan containing dye analogs were synthesized to analyze iodine binding to the dyes via Raman spectroscopy, UV-Vis studies, device performance metrics and density functional theory (DFT) based computations. Evidence suggests I2 binds thiophene-based dyes stronger than furan-based dyes. This leads to higher DSC device currents and voltages from furan analogues, and longer electron lifetimes in DSC devices using furan based dyes. Raman spectrum of the TiO2 surface-bound dyes reveals additional and more instense peaks for thiophene dyes in the presence of I2 relative to no I2. Additionally, broader and shifted UV-Vis peaks are observed for thiophene dyes in the presence of I2 on TiO2 films suggesting significant interaction between the dye molecules and I2. These observations are also supported by DFT and TD-DFT calculations which indicate the absence of a key geometric energy minimum in the dye-I2 ground state for furan dyes which are readily observed for the thiophene based analogues.

15.
J Chem Phys ; 148(22): 224501, 2018 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-29907054

RESUMO

Predicting vapor liquid equilibria (VLE) of molecules governed by weak van der Waals (vdW) interactions using the first principles approach is a significant challenge. Due to the poor scaling of the post Hartree-Fock wave function theory with system size/basis functions, the Kohn-Sham density functional theory (DFT) is preferred for systems with a large number of molecules. However, traditional DFT cannot adequately account for medium to long range correlations which are necessary for modeling vdW interactions. Recent developments in DFT such as dispersion corrected models and nonlocal van der Waals functionals have attempted to address this weakness with a varying degree of success. In this work, we predict the VLE of argon and assess the performance of several density functionals and the second order Møller-Plesset perturbation theory (MP2) by determining critical and structural properties via first principles Monte Carlo simulations. PBE-D3, BLYP-D3, and rVV10 functionals were used to compute vapor liquid coexistence curves, while PBE0-D3, M06-2X-D3, and MP2 were used for computing liquid density at a single state point. The performance of the PBE-D3 functional for VLE is superior to other functionals (BLYP-D3 and rVV10). At T = 85 K and P = 1 bar, MP2 performs well for the density and structural features of the first solvation shell in the liquid phase.

17.
J Comput Chem ; 38(19): 1727-1739, 2017 07 15.
Artigo em Inglês | MEDLINE | ID: mdl-28436594

RESUMO

Cassandra is an open source atomistic Monte Carlo software package that is effective in simulating the thermodynamic properties of fluids and solids. The different features and algorithms used in Cassandra are described, along with implementation details and theoretical underpinnings to various methods used. Benchmark and example calculations are shown, and information on how users can obtain the package and contribute to it are provided. © 2017 Wiley Periodicals, Inc.

18.
Phys Chem Chem Phys ; 16(17): 8060-9, 2014 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-24653997

RESUMO

The dynamics of actinyl ions (AnO2(n+)) in aqueous solutions is important not only for the design of advanced separation processes but also for understanding the fate of actinides in the environment. The hazardous nature of actinides makes it difficult to measure transport and thermodynamic properties experimentally, so predictive simulations are an attractive method for studying these systems. Here, we report the results of atomistic-level molecular dynamics simulations of actinyl ions (of U, Np, Pu, and Am) in their mono- and dication states in aqueous solution. Quantum mechanically derived force field parameters are used to compute self-diffusion coefficients of the actinyl ions, water exchange mechanisms, and residence times of water molecules in the first solvation shell of the actinyl ions. We find that monocation actinyl ions diffuse slightly faster than their dication counterparts. Our simulations suggest that there are two distinct water exchange mechanisms for mono and dications. An associative interchange pathway is observed for water exchange involving dication actinyls, while in monocation actinyls the exchange occurs via a dissociative mechanism. The residence time of water molecules in the first solvation shell depends on the water exchange mechanism. In the case of dications, a stiffer actinyl bond angle results in a longer residence time, while for monocations, a shorter water coordination distance leads to a longer residence time. The simulations predict much faster water exchange for UO2(2+) than what is observed experimentally with NMR, but other properties are consistent with experiments.

19.
Nat Nanotechnol ; 2024 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-38448520

RESUMO

Free radicals, generally formed through the cleavage of covalent electron-pair bonds, play an important role in diverse fields ranging from synthetic chemistry to spintronics and nonlinear optics. However, the characterization and regulation of the radical state at a single-molecule level face formidable challenges. Here we present the detection and sophisticated tuning of the open-shell character of individual diradicals with a donor-acceptor structure via a sensitive single-molecule electrical approach. The radical is sandwiched between nanogapped graphene electrodes via covalent amide bonds to construct stable graphene-molecule-graphene single-molecule junctions. We measure the electrical conductance as a function of temperature and track the evolution of the closed-shell and open-shell electronic structures in real time, the open-shell triplet state being stabilized with increasing temperature. Furthermore, we tune the spin states by external stimuli, such as electrical and magnetic fields, and extract thermodynamic and kinetic parameters of the transition between closed-shell and open-shell states. Our findings provide insights into the evolution of single-molecule radicals under external stimuli, which may proof instrumental for the development of functional quantum spin-based molecular devices.

20.
Phys Chem Chem Phys ; 15(38): 15954-63, 2013 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-23958801

RESUMO

Intra- and intermolecular force field parameters for the interaction of actinyl ions (AnO2(n+), where, An = U, Np, Pu, Am and n = 1, 2) with water have been developed using quantum mechanical calculations. Water was modeled with the extended simple point charge potential (SPC/E). The resulting force field consists of a simple form in which intermolecular interactions are modeled with pairwise Lennard-Jones functions plus partial charge terms. Intramolecular bond stretching and angle bending are treated with harmonic functions. The new potentials were used to carry out extensive molecular dynamics simulations for each hydrated ion. Computed bond lengths, bond angles and coordination numbers agree well with known values and previous simulations. Hydration free energies, computed from molecular dynamics simulations as well as from quantum simulations with a solvation model, were in reasonable agreement with estimated experimental values.

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