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1.
Phys Rev Lett ; 126(12): 128101, 2021 Mar 26.
Artículo en Inglés | MEDLINE | ID: mdl-33834804

RESUMEN

Protein conformational fluctuations are highly complex and exhibit long-term correlations. Here, molecular dynamics simulations of small proteins demonstrate that these conformational fluctuations directly affect the protein's instantaneous diffusivity D_{I}. We find that the radius of gyration R_{g} of the proteins exhibits 1/f fluctuations that are synchronous with the fluctuations of D_{I}. Our analysis demonstrates the validity of the local Stokes-Einstein-type relation D_{I}∝1/(R_{g}+R_{0}), where R_{0}∼0.3 nm is assumed to be a hydration layer around the protein. From the analysis of different protein types with both strong and weak conformational fluctuations, the validity of the Stokes-Einstein-type relation appears to be a general property.


Asunto(s)
Modelos Químicos , Proteínas/química , Agua/química , Difusión , Simulación de Dinámica Molecular , Oligopéptidos/química , Conformación Proteica , Soluciones
2.
Adv Exp Med Biol ; 1310: 1-30, 2021.
Artículo en Inglés | MEDLINE | ID: mdl-33834430

RESUMEN

Confocal laser scanning microscopy (CLSM) and related microscopic techniques allow a unique and versatile approach to image and analyze living cells due to their specificity and high sensitivity. Among confocal related techniques, fluorescence correlation methods, such as fluorescence correlation spectroscopy (FCS) and dual-color fluorescence cross-correlation spectroscopy (FCCS), are highly sensitive biophysical methods for analyzing the complex dynamic events of molecular diffusion and interaction change in live cells as well as in solution by exploiting the characteristics of fluorescence signals. Analytical and quantitative information from FCS and FCCS coupled with fluorescence images obtained from CLSM can now be applied in convergence science such as drug delivery and nanomedicine, as well as in basic cell biology. In this chapter, a brief introduction into the physical parameters that can be obtained from FCS and FCCS is first provided. Secondly, experimental examples of the methods for evaluating the parameters is presented. Finally, two potential FCS and FCCS applications for convergence science are introduced in more detail.


Asunto(s)
Microscopía Confocal , Color , Difusión , Espectrometría de Fluorescencia , Coloración y Etiquetado
3.
Int J Mol Sci ; 22(6)2021 Mar 12.
Artículo en Inglés | MEDLINE | ID: mdl-33809376

RESUMEN

The diffusion process of water molecules within a polyetherimide (PEI) glassy matrix has been analyzed by combining the experimental analysis of water sorption kinetics performed by FTIR spectroscopy with theoretical information gathered from Molecular Dynamics simulations and with the expression of water chemical potential provided by a non-equilibrium lattice fluid model able to describe the thermodynamics of glassy polymers. This approach allowed us to construct a convincing description of the diffusion mechanism of water in PEI providing molecular details of the process related to the effects of the cross- and self-hydrogen bonding established in the system on the dynamics of water mass transport.


Asunto(s)
Transporte Biológico/genética , Polímeros/química , Termodinámica , Agua/química , Difusión , Enlace de Hidrógeno , Cinética , Simulación de Dinámica Molecular , Polímeros/metabolismo
4.
Int J Nanomedicine ; 16: 2585-2595, 2021.
Artículo en Inglés | MEDLINE | ID: mdl-33833513

RESUMEN

Background: In cancer nanomedicine, drugs are transported by nanocarriers through a biological system to produce a therapeutic effect. The efficacy of the treatment is affected by the ability of the nanocarriers to overcome biological transport barriers to reach their target. In this work, we focus on the process of nanocarrier penetration through tumour tissue after extravasation. Visualising the dynamics of nanocarriers in tissue is difficult in vivo, and in vitro assays often do not capture the spatial and physical constraints relevant to model tissue penetration. Methods: We propose a new simple, low-cost method to observe the transport dynamics of nanoparticles through a tissue-mimetic microfluidic chip. After loading a chip with triplicate conditions of gel type and loading with microparticles, microscopic analysis allows for tracking of fluorescent nanoparticles as they move through hydrogels (Matrigel and Collagen I) with and without cell-sized microparticles. A bespoke image-processing codebase written in MATLAB allows for statistical analysis of this tracking, and time-dependent dynamics can be determined. Results: To demonstrate the method, we show size-dependence of transport mechanics can be observed, with diffusion of fluorescein dye throughout the channel in 8 h, while 20 nm carboxylate FluoSphere diffusion was hindered through both Collagen I and Matrigel™. Statistical measurements of the results are generated through the software package and show the significance of both size and presence of microparticles on penetration depth. Conclusion: This provides an easy-to-understand output for the end user to measure nanoparticle tissue penetration, enabling the first steps towards future automated experimentation of transport dynamics for rational nanocarrier design.


Asunto(s)
Geles/química , Microfluídica/métodos , Nanopartículas/administración & dosificación , Nanopartículas/metabolismo , Andamios del Tejido/química , Colágeno/química , Colágeno/metabolismo , Difusión , Humanos , Nanomedicina/métodos , Nanopartículas/química
5.
Sensors (Basel) ; 21(6)2021 Mar 21.
Artículo en Inglés | MEDLINE | ID: mdl-33801002

RESUMEN

Machine learning (ML)-based algorithms are playing an important role in cancer diagnosis and are increasingly being used to aid clinical decision-making. However, these commonly operate as 'black boxes' and it is unclear how decisions are derived. Recently, techniques have been applied to help us understand how specific ML models work and explain the rational for outputs. This study aims to determine why a given type of cancer has a certain phenotypic characteristic. Cancer results in cellular dysregulation and a thorough consideration of cancer regulators is required. This would increase our understanding of the nature of the disease and help discover more effective diagnostic, prognostic, and treatment methods for a variety of cancer types and stages. Our study proposes a novel explainable analysis of potential biomarkers denoting tumorigenesis in non-small cell lung cancer. A number of these biomarkers are known to appear following various treatment pathways. An enhanced analysis is enabled through a novel mathematical formulation for the regulators of mRNA, the regulators of ncRNA, and the coupled mRNA-ncRNA regulators. Temporal gene expression profiles are approximated in a two-dimensional spatial domain for the transition states before converging to the stationary state, using a system comprised of coupled-reaction partial differential equations. Simulation experiments demonstrate that the proposed mathematical gene-expression profile represents a best fit for the population abundance of these oncogenes. In future, our proposed solution can lead to the development of alternative interpretable approaches, through the application of ML models to discover unknown dynamics in gene regulatory systems.


Asunto(s)
Carcinoma de Pulmón de Células no Pequeñas , Neoplasias Pulmonares , Algoritmos , Difusión , Perfilación de la Expresión Génica , Humanos , Neoplasias Pulmonares/diagnóstico , Neoplasias Pulmonares/genética
6.
Int J Mol Sci ; 22(5)2021 Mar 06.
Artículo en Inglés | MEDLINE | ID: mdl-33800824

RESUMEN

A new copper complex, trans-diaqua-trans-bis [1-hydroxy-1,2-di (methoxycarbonyl) ethenato] copper (abbreviation Cu(II) complex), was synthesized and its plant growth regulation properties were investigated. The results show a sharp dependence of growth regulation activity of the Cu(II) complex on the type of culture and its concentration. New plant growth regulator accelerated the development of the corn root system (the increase in both length and weight) but showed a smaller effect on the development of the wheat and barley root systems. Stimulation of corn growth decreased with increasing Cu(II) complex concentration from 0.0001% to 0.01% (inhibition at high concentrations-0.01%). The development of corn stems was also accelerated but to a lesser extent. Chitosan-coated calcium alginate microcapsules suitable for delivery of Cu(II) complex to plants were prepared and characterized. Analysis of the FTIR spectrum showed that complex molecular interactions between functional groups of microcapsule constituents include mainly electrostatic interactions and hydrogen bonds. Microcapsules surface exhibits a soft granular surface structure with substructures consisting of abundant smaller particles with reduced surface roughness. Release profile analysis showed Fickian diffusion is the rate-controlling mechanism of Cu(II) complex releasing. The obtained results give new insights into the complexity of the interaction between the Cu(II) complex and microcapsule formulation constituents, which can be of great help in accelerating product development for the application in agriculture.


Asunto(s)
Alginatos/administración & dosificación , Quitosano/administración & dosificación , Portadores de Fármacos/administración & dosificación , Composición de Medicamentos/métodos , Reguladores del Crecimiento de las Plantas/síntesis química , Rastreo Diferencial de Calorimetría , Cápsulas , Difusión , Portadores de Fármacos/química , Germinación/efectos de los fármacos , Enlace de Hidrógeno , Microscopía Electrónica de Rastreo , Raíces de Plantas/efectos de los fármacos , Raíces de Plantas/crecimiento & desarrollo , Tallos de la Planta/efectos de los fármacos , Tallos de la Planta/crecimiento & desarrollo , Poaceae/efectos de los fármacos , Poaceae/crecimiento & desarrollo , Espectrometría por Rayos X , Espectroscopía Infrarroja por Transformada de Fourier , Electricidad Estática , Propiedades de Superficie
7.
Anticancer Res ; 41(3): 1163-1170, 2021 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-33788707

RESUMEN

BACKGROUND/AIM: Magnetic resonance imaging is used for staging purposes in cervical cancer (CC). Diffusion-weighted imaging and the apparent diffusion coefficient (ADC) are associated with tumor microstructure. The present analysis sought to compare pre-treatment ADC values to predict treatment outcome of radiochemotherapy for CC based upon a large patient sample. MATERIALS AND METHODS: MEDLINE library and SCOPUS databases were assessed for suitable articles up to May 2020. The primary endpoint was the mean ADC value of CC according to the treatment response to radiochemotherapy. In total, 16 studies were included in the analysis. RESULTS: For the response group, 416 patients were included in the analysis (72.5%) and for the no-response group 158 patients were included (27.5%). The mean ADC value of patients with CC with treatment response was 0.87×10-3 mm2/s (95% confidence interval=0.81-0.94×10-3 mm2/s), and for the patients with no response was 0.92×10-3 mm2/s (95% confidence interval=0.85-0.98×10-3 mm2/s). CONCLUSION: Pre-treatment ADC values alone cannot be used to reliably predict treatment response to radiochemotherapy in CC.


Asunto(s)
Quimioradioterapia , Imagen de Difusión por Resonancia Magnética/métodos , Neoplasias del Cuello Uterino/terapia , Difusión , Femenino , Humanos , Neoplasias del Cuello Uterino/diagnóstico por imagen
8.
Food Chem ; 351: 129316, 2021 Jul 30.
Artículo en Inglés | MEDLINE | ID: mdl-33647701

RESUMEN

This study aimed to understand how the microstructure of gelled foods impacts the diffusion of a volatile antimicrobial compound and its efficacy at different depths from the surface. Carvacrol-loaded polylactic acid film was used to inhibit the growth of Pseudomonas fluorescens in WPI-carrageenan gels during storage at 4 °C. The diffusion of antimicrobials was increased in gels having larger average pore size. The antimicrobial efficacy of the antimicrobial packaging was dependent on the diffusion of carvacrol within the gels. The final concentration of carvacrol in the top layer was more than 4 fold higher than that in the middle layer and more than 13-fold higher than that in the bottom layer, resulting in a more effective inhibition in the top layer than those in the middle and bottom layers. Our study demonstrates the importance of considering the diffusion of antimicrobials in solid/semi-solid foods in the antimicrobial packaging design.


Asunto(s)
Antiinfecciosos/química , Cimenos/química , Conservación de Alimentos/métodos , Carragenina/química , Difusión , Geles , Porosidad
9.
Nat Commun ; 12(1): 1748, 2021 03 19.
Artículo en Inglés | MEDLINE | ID: mdl-33741958

RESUMEN

Super-resolution microscopy and single molecule fluorescence spectroscopy require mutually exclusive experimental strategies optimizing either temporal or spatial resolution. To achieve both, we implement a GPU-supported, camera-based measurement strategy that highly resolves spatial structures (~100 nm), temporal dynamics (~2 ms), and molecular brightness from the exact same data set. Simultaneous super-resolution of spatial and temporal details leads to an improved precision in estimating the diffusion coefficient of the actin binding polypeptide Lifeact and corrects structural artefacts. Multi-parametric analysis of epidermal growth factor receptor (EGFR) and Lifeact suggests that the domain partitioning of EGFR is primarily determined by EGFR-membrane interactions, possibly sub-resolution clustering and inter-EGFR interactions but is largely independent of EGFR-actin interactions. These results demonstrate that pixel-wise cross-correlation of parameters obtained from different techniques on the same data set enables robust physicochemical parameter estimation and provides biological knowledge that cannot be obtained from sequential measurements.


Asunto(s)
Microscopía Fluorescente/métodos , Imagen Individual de Molécula/métodos , Actinas/metabolismo , Animales , Células CHO , Membrana Celular , Cricetulus , Difusión , Receptores ErbB/metabolismo , Fluorescencia , Humanos , Espectrometría de Fluorescencia/métodos
10.
J Vis Exp ; (169)2021 03 05.
Artículo en Inglés | MEDLINE | ID: mdl-33749684

RESUMEN

Analyzing the diffusional dynamics of nanoparticles on cell membrane plays a significant role in better understanding the cellular uptake process and provides a theoretical basis for the rational design of nano-medicine delivery. Single particle tracking (SPT) analysis could probe the position and orientation of individual nanoparticles on cell membrane, and reveal their translational and rotational states. Here, we show how to use traditional dark-field microscopy to monitor the dynamics of gold nanorods (AuNRs) on live cell membrane. We also show how to extract the location and orientation of AuNRs using ImageJ and MATLAB, and how to characterize the diffusive states of AuNRs. Statistical analysis of hundreds of particles show that single AuNRs perform Brownian motion on the surface of U87 MG cell membrane. However, individual long trajectory analysis shows that AuNRs have two distinctly different types of motion states on the membrane, namely long-range transport and limited-area confinement. Our SPT methods can be potentially used to study the surface or intracellular particle diffusion in different biological cells and can become a powerful tool for investigations of complex cellular mechanisms.


Asunto(s)
Membrana Celular/química , Oro/química , Microscopía/métodos , Nanopartículas/química , Nanotubos/química , Línea Celular Tumoral , Cetrimonio/química , Análisis de Datos , Difusión , Humanos , Imagen Individual de Molécula , Factores de Tiempo
11.
Nat Commun ; 12(1): 1913, 2021 03 26.
Artículo en Inglés | MEDLINE | ID: mdl-33772014

RESUMEN

Diffusion is a major molecular transport mechanism in biological systems. Quantifying direction-dependent (i.e., anisotropic) diffusion is vitally important to depicting how the three-dimensional (3D) tissue structure and composition affect the biochemical environment, and thus define tissue functions. However, a tool for noninvasively measuring the 3D anisotropic extracellular diffusion of biorelevant molecules is not yet available. Here, we present light-sheet imaging-based Fourier transform fluorescence recovery after photobleaching (LiFT-FRAP), which noninvasively determines 3D diffusion tensors of various biomolecules with diffusivities up to 51 µm2 s-1, reaching the physiological diffusivity range in most biological systems. Using cornea as an example, LiFT-FRAP reveals fundamental limitations of current invasive two-dimensional diffusion measurements, which have drawn controversial conclusions on extracellular diffusion in healthy and clinically treated tissues. Moreover, LiFT-FRAP demonstrates that tissue structural or compositional changes caused by diseases or scaffold fabrication yield direction-dependent diffusion changes. These results demonstrate LiFT-FRAP as a powerful platform technology for studying disease mechanisms, advancing clinical outcomes, and improving tissue engineering.


Asunto(s)
Córnea/metabolismo , Espacio Extracelular/metabolismo , Recuperación de Fluorescencia tras Fotoblanqueo/métodos , Microscopía de Fluorescencia por Excitación Multifotónica/métodos , Tendones/metabolismo , Animales , Anisotropía , Colágeno/química , Colágeno/metabolismo , Difusión , Análisis de Fourier , Microscopía Confocal/métodos , Microscopía Electrónica de Rastreo/métodos , Ratas Sprague-Dawley , Reproducibilidad de los Resultados , Porcinos , Ingeniería de Tejidos/métodos , Andamios del Tejido/química
12.
Environ Monit Assess ; 193(4): 238, 2021 Mar 30.
Artículo en Inglés | MEDLINE | ID: mdl-33783638

RESUMEN

In the practical application of air protection, diverse dispersion models are used to calculate the concentration of contaminants in the air. They usually involve a universal character, which typically makes them sufficient for use in almost all conditions, with the exception of those clearly deviating from the average. This is especially relevant to industrial objects of large areas, introducing a great amount of heat and mechanical energy into the air. For such cases, the standard models can be extended in order to adapt them to the unusual local diffusion conditions. Next, to be applied in practice, they must have undergone validation to document the correctness of its operation. The article describes the process of validation of the air quality assessment model containing extended procedures to incorporate special factors affecting atmospheric dispersion in a coke industry. The set of statistical indicators, obtained on the basis of SF6 field experiment, evaluate its performance. The short comparison with some popular models of general-purpose character and an assessment of the suitability of individual indicators for validation purposes are also presented.


Asunto(s)
Contaminantes Atmosféricos , Contaminación del Aire , Coque , Contaminantes Atmosféricos/análisis , Contaminación del Aire/análisis , Difusión , Monitoreo del Ambiente , Modelos Teóricos
13.
Sci Total Environ ; 764: 142903, 2021 Apr 10.
Artículo en Inglés | MEDLINE | ID: mdl-33757256

RESUMEN

In this study, we report on the applicability of passive sampling with Carbopack X adsorbent tubes followed by thermal desorption gas-chromatography-mass spectrometry (TD-GC-MS) to monitor the concentrations of emerging organic contaminants (EOCs) and solvents in ten indoor environments in a conventional and a vocational training school. However, if passive sampling is to be used as a reliable sampling technique, a specific diffusive uptake rate is required for each target compound. Accordingly, the aim of the present study was twofold. The first was to determine the experimental diffusive uptake rates of the target EOCs and solvents in one of the sampling sites of the vocational training school using Carbopack X adsorbent tubes and active sampling as the reference technique. The results showed experimental diffusive uptake rates between 0.46 mL min-1 and 0.94 mL min-1 with RSD % below 5% for the 28 target compounds. The second was to apply the uptake rates obtained experimentally to determine EOCs and solvents in schools. The monitoring results showed that solvents were ubiquitous throughout the conventional school with a concentrations range between 51.93 µg m-3 and 164.6 µg m-3, while EOCs were detected to a lesser extent. Moreover, the concentrations of EOCs in the vocational training school were much higher than those in the conventional school with concentrations of up to 562.9 µg m-3 for solvents and 344.3 µg m-3 for acrylate polymer monomers. After actively sampling for seven days in each school, we concluded that the concentrations of EOCs and solvents found are mostly linked to cleaning products (conventional school) and the activities carried out in the classroom (vocational training school).


Asunto(s)
Contaminantes Atmosféricos , Monitoreo del Ambiente , Contaminantes Atmosféricos/análisis , Difusión , Cromatografía de Gases y Espectrometría de Masas , Instituciones Académicas , Solventes
14.
Int J Mol Sci ; 22(4)2021 Feb 14.
Artículo en Inglés | MEDLINE | ID: mdl-33672949

RESUMEN

Two different types of ordered mesoporous nanoparticles, namely MCM-41 and MCM-48, with similar pore sizes but different pore connectivity, were loaded with aprepitant via a passive diffusion method. The percentage of the loaded active agent, along with the encapsulation efficiency, was evaluated using High-performance Liquid Chromatography (HPLC) analysis complemented by Thermogravimetric Analysis (TGA). The determination of the pore properties of the mesoporous particles before and after the drug loading revealed the presence of confined aprepitant in the pore structure of the particles, while Powder X-ray Diffractometry(pXRD), Differential Scanning Calorimetry (DSC), and FTIR experiments indicated that the drug is in an amorphous state. The release profiles of the drug from the two different mesoporous materials were studied in various release media and revealed an aprepitant release up to 45% when sink conditions are applied. The cytocompatibility of the silica nanoparticles was assessed in Caco-2 cell monolayers, in the presence and absence of the active agent, suggesting that they can be used as carriers of aprepitant without presenting any toxicity in vitro.


Asunto(s)
Aprepitant/administración & dosificación , Sistemas de Liberación de Medicamentos/métodos , Nanopartículas/química , Dióxido de Silicio/química , Administración Oral , Antieméticos/administración & dosificación , Antieméticos/farmacocinética , Aprepitant/farmacocinética , Células CACO-2 , Rastreo Diferencial de Calorimetría , Cromatografía Líquida de Alta Presión , Difusión , Liberación de Fármacos , Humanos , Microscopía Electrónica de Rastreo , Nanopartículas/ultraestructura , Tamaño de la Partícula , Porosidad , Solubilidad , Espectroscopía Infrarroja por Transformada de Fourier
15.
Int J Nanomedicine ; 16: 2237-2246, 2021.
Artículo en Inglés | MEDLINE | ID: mdl-33762823

RESUMEN

Background: Translation of nanomedical developments into clinical application is receiving an increasing interest. However, its use for oral squamous cell carcinoma (OSCC) diagnosis remains limited. We present an advanced nanophotonic method for oral cancer detection, based on diffusion reflection (DR) measurements of gold-nanorods bio-conjugated to anti-epidermal growth factor receptor (C-GNRs) specifically attached to OSCC cells. Objective: To investigate in a rat model of oral carcinogenesis the targeting potential of C-GNRs to OSCC by using the DR optical method. Materials and Methods: OSCC was induced by the carcinogen 4-nitroquinoline-N-oxide (4NQO). C-GNRs were introduced locally and systemically and DR measurements were recorded from the surface of the rat tongue following illumination with red laser beam. Rats were divided into experimental and control groups. The results were compared with the histologic diagnosis. Results: A total of 75 Wistar-derived rats were enrolled in the study. Local application did not reveal any statistical results. DR measurements following intravenous injection of C-GNRs revealed a significant increase in light absorption in rats with OSCC compare with rats without cancer (p<0.02, sensitivity 100%, specificity 89%). In addition, absorption of light increased significantly in cases of severe dysplasia and cancer (high risk) compared to rats without cancer and rats with mild dysplasia (low risk) (86% sensitivity and 89% specificity, AUC=0.79). Conclusion: Combining nanotechnology and nanophotonics for in vivo diagnosis of OSCC serves as additional tier in the translation of advanced nanomedical developments into clinical applications. The presented method shows a promising potential of nanophotonics for oral cancer identification, and provides support for the use of C-GNRs as a selective drug delivery.


Asunto(s)
Carcinoma de Células Escamosas/diagnóstico , Detección Precoz del Cáncer , Receptores ErbB/antagonistas & inhibidores , Oro/química , Neoplasias de la Boca/diagnóstico , Nanotubos/química , Animales , Carcinoma de Células Escamosas/patología , Difusión , Receptores ErbB/metabolismo , Masculino , Neoplasias de la Boca/tratamiento farmacológico , Ratas Wistar
16.
Int J Mol Sci ; 22(4)2021 Feb 16.
Artículo en Inglés | MEDLINE | ID: mdl-33669232

RESUMEN

Tracer diffusion coefficients obtained from the Taylor dispersion technique at 25.0 °C were measured to study the influence of sodium, ammonium and magnesium salts at 0.01 and 0.1 mol dm-3 on the transport behavior of sodium hyaluronate (NaHy, 0.1%). The selection of these salts was based on their position in Hofmeister series, which describe the specific influence of different ions (cations and anions) on some physicochemical properties of a system that can be interpreted as a salting-in or salting-out effect. In our case, in general, an increase in the ionic strength (i.e., concentrations at 0.01 mol dm-3) led to a significant decrease in the limiting diffusion coefficient of the NaHy 0.1%, indicating, in those circumstances, the presence of salting-in effects. However, the opposite effect (salting-out) was verified with the increase in concentration of some salts, mainly for NH4SCN at 0.1 mol dm-3. In this particular salt, the cation is weakly hydrated and, consequently, its presence does not favor interactions between NaHy and water molecules, promoting, in those circumstances, less resistance to the movement of NaHy and thus to the increase of its diffusion (19%). These data, complemented by viscosity measurements, permit us to have a better understanding about the effect of these salts on the transport behaviour of NaHy.


Asunto(s)
Aniones/química , Cationes/química , Ácido Hialurónico/química , Agua/química , Sulfato de Amonio/química , Transporte Biológico , Difusión , Cloruro de Litio/química , Sulfato de Magnesio/química , Concentración Osmolar , Sales (Química)/química , Cloruro de Sodio/química , Soluciones , Sulfatos/química , Temperatura , Tiocianatos/química , Viscosidad
17.
Environ Sci Technol ; 55(8): 4772-4782, 2021 04 20.
Artículo en Inglés | MEDLINE | ID: mdl-33729766

RESUMEN

Determining whether aqueous diffusion and dispersion lead to significant isotope fractionation is important for interpreting the isotope ratios of organic contaminants in groundwater. We performed diffusion experiments with modified Stokes diaphragm cells and transverse-dispersion experiments in quasi-two-dimensional flow-through sediment tank systems to explore isotope fractionation for benzene, toluene, ethylbenzene, 2,6-dichlorobenzamide, and metolachlor at natural isotopic abundance. We observed very small to negligible diffusion- and transverse-dispersion-induced isotope enrichment factors (ε < -0.4 ‰), with changes in carbon and nitrogen isotope values within ±0.5‰ and ±1‰, respectively. Isotope effects of diffusion did not show a clear correlation with isotopologue mass with calculated power-law exponents ß close to zero (0.007 < ß < 0.1). In comparison to ions, noble gases, and labeled compounds, three aspects stand out. (i) If a mass dependence is derived from collision theory, then isotopologue masses of polyatomic molecules would be affected by isotopes of multiple elements resulting in very small expected effects. (ii) However, collisions do not necessarily lead to translational movement but can excite molecular vibrations or rotations minimizing the mass dependence. (iii) Solute-solvent interactions like H-bonds can further minimize the effect of collisions. Modeling scenarios showed that an inadequate model choice, or erroneous choice of ß, can greatly overestimate the isotope fractionation by diffusion and, consequently, transverse dispersion. In contrast, available data for chlorinated solvent and gasoline contaminants at natural isotopic abundance suggest that in field scenarios, a potential additional uncertainty from aqueous diffusion or dispersion would add to current instrumental uncertainties on carbon or nitrogen isotope values (±1‰) with an additional ±1‰ at most.


Asunto(s)
Agua Subterránea , Biodegradación Ambiental , Isótopos de Carbono/análisis , Fraccionamiento Químico , Difusión , Tolueno , Agua
18.
Adv Colloid Interface Sci ; 290: 102400, 2021 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-33713994

RESUMEN

We review concepts involved in describing the chemodynamic features of nanoparticles and apply the framework to gain physicochemical insights into interactions between SARS-CoV-2 virions and airborne particulate matter (PM). Our analysis is highly pertinent given that the World Health Organisation acknowledges that SARS-CoV-2 may be transmitted by respiratory droplets, and the US Center for Disease Control and Prevention recognises that airborne transmission of SARS-CoV-2 can occur. In our theoretical treatment, the virion is assimilated to a core-shell nanoparticle, and contributions of various interaction energies to the virion-PM association (electrostatic, hydrophobic, London-van der Waals, etc.) are generically included. We review the limited available literature on the physicochemical features of the SARS-CoV-2 virion and identify knowledge gaps. Despite the lack of quantitative data, our conceptual framework qualitatively predicts that virion-PM entities are largely able to maintain equilibrium on the timescale of their diffusion towards the host cell surface. Comparison of the relevant mass transport coefficients reveals that virion biointernalization demand by alveolar host cells may be greater than the diffusive supply. Under such conditions both the free and PM-sorbed virions may contribute to the transmitted dose. This result points to the potential for PM to serve as a shuttle for delivery of virions to host cell targets. Thus, our critical review reveals that the chemodynamics of virion-PM interactions may play a crucial role in the transmission of COVID-19, and provides a sound basis for explaining reported correlations between episodes of air pollution and outbreaks of COVID-19.


Asunto(s)
/transmisión , Células Epiteliales/virología , Material Particulado/química , Virión/química , Aerosoles , Fenómenos Biomecánicos , Difusión , Humanos , Interacciones Hidrofóbicas e Hidrofílicas , Modelos Químicos , Nanopartículas/química , Alveolos Pulmonares/virología , /patogenicidad , Electricidad Estática , Virión/metabolismo , Virión/patogenicidad , Internalización del Virus , Agua/química
19.
J Chromatogr A ; 1642: 462033, 2021 Apr 12.
Artículo en Inglés | MEDLINE | ID: mdl-33714774

RESUMEN

Multiple-open-tubular columns enabling transverse diffusion (MOTTD) are made of straight, parallel, and cylindrical flow channels separated by a mesoporous stationary phase. In Part 1, a model of band broadening along MOTTD columns accounting for longitudinal diffusion, the trans-channel velocity bias, and mass transfer resistance in the stationary phase was proposed and validated. In this Part 2, the model is completed by considering the impact of short-range inter-channel velocity biases on the MOTTD plate number. These velocity biases are caused by the wide distribution of the channel diameters. Different ratios, ρ, of the average inner diameter, 2, of the flow channels to their closest center-to-center distance d (d= 5 µm, ρ= 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9) with a relative standard deviation (RSD) increasing from 0 to 50% are considered. The zone retention factor k1 was increased from 1 to 25. The complete model of band broadening is validated after adjustment to dispersion data obtained by 1) the lattice-Boltzmann method for modeling fluid flow, 2) a random-walk particle-tracking (RWPT) technique to address advective-diffusive transport, and 3) by considering two distinct populations of flow channels (inner radii rc,1=(1-RSD) and rc,2=(1+RSD)) arranged at the nodes of a hexagonal compact array. The completed model of band broadening in MOTTD columns reveals that the RSD of the channel diameters has only a moderate impact on the optimum plate number of MOTTD columns: the relative increase of the minimum plate height do not exceed 30% even for the largest RSDs. However, when the mass transfer of the analyte is governed by its slow rate of transverse diffusion across the MOTTD column, the plate height can be increased by up to 100% at high average velocities. Regarding the best trade-off between analysis speed and column performance at a fixed pressure drop of 400 bar, irrespective of the zone retention factor and RSD of the distribution of the channel diameters, the fastest analyses are recommended for MOTTD columns having a small structural parameter ρ. In contrast, for the longest analysis times, the largest values of ρ are required to maximize the performance of MOTTD columns.


Asunto(s)
Cromatografía/instrumentación , Simulación por Computador , Difusión , Cinética
20.
Nat Commun ; 12(1): 1478, 2021 03 05.
Artículo en Inglés | MEDLINE | ID: mdl-33674570

RESUMEN

The recently introduced minimal photon fluxes (MINFLUX) concept pushed the resolution of fluorescence microscopy to molecular dimensions. Initial demonstrations relied on custom made, specialized microscopes, raising the question of the method's general availability. Here, we show that MINFLUX implemented with a standard microscope stand can attain 1-3 nm resolution in three dimensions, rendering fluorescence microscopy with molecule-scale resolution widely applicable. Advances, such as synchronized electro-optical and galvanometric beam steering and a stabilization that locks the sample position to sub-nanometer precision with respect to the stand, ensure nanometer-precise and accurate real-time localization of individually activated fluorophores. In our MINFLUX imaging of cell- and neurobiological samples, ~800 detected photons suffice to attain a localization precision of 2.2 nm, whereas ~2500 photons yield precisions <1 nm (standard deviation). We further demonstrate 3D imaging with localization precision of ~2.4 nm in the focal plane and ~1.9 nm along the optic axis. Localizing with a precision of <20 nm within ~100 µs, we establish this spatio-temporal resolution in single fluorophore tracking and apply it to the diffusion of single labeled lipids in lipid-bilayer model membranes.


Asunto(s)
Imagenología Tridimensional/instrumentación , Imagenología Tridimensional/métodos , Microscopía Fluorescente/instrumentación , Microscopía Fluorescente/métodos , Difusión , Diseño de Equipo , Fluorescencia , Colorantes Fluorescentes , Procesamiento de Imagen Asistido por Computador , Fotones
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