Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 36.147
Filtrar
1.
J Chem Phys ; 151(8): 085102, 2019 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-31470725

RESUMO

In recent years, there has been a growing interest to quantify the energy landscape that governs ribosome dynamics. However, in order to quantitatively integrate theoretical predictions and experimental measurements, it is essential that one has a detailed understanding of the associated diffusive properties. Here, all-atom explicit-solvent simulations (50 µs of aggregate sampling) predict that the diffusion coefficient of a tRNA molecule will depend on its position within the ribosome. Specifically, during aa-tRNA accommodation (i.e., the process by which tRNA enters the ribosome), the apparent diffusion coefficient decreases by approximately an order of magnitude. By comparing these to values obtained with an energetically "smooth" model, we show that the observed nonuniform behavior likely arises from electrostatic and solvation interactions between the tRNA and ribosome. These calculations also reveal the hierarchical character of ribosomal energetics, where steric interactions induce a large-scale free-energy barrier, and short-scale roughness determines the rate of diffusive movement across the landscape.


Assuntos
Difusão , RNA de Transferência/metabolismo , Ribossomos/química , Ribossomos/metabolismo , Entropia , Simulação de Dinâmica Molecular , RNA de Transferência/química
2.
J Agric Food Chem ; 67(37): 10481-10488, 2019 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-31433940

RESUMO

Here, we report two methods that chemically modify alginate to achieve neutral-basic pH sensitivity of the resultant hydrogel. The first method involves direct amide bond formation between alginate and 4-(2-aminoethyl)benzoic acid. The second method that arose out of the desire to achieve better control of the degradation rate of the alginate hydrogel involves reductive amination of oxidized alginate. The products of both methods result in a hydrogel vehicle for targeted delivery of encapsulated payload under physiological conditions in the gastrointestinal tract. Two-dimensional diffusion-ordered spectroscopy and internal and coaxial external nuclear magnetic resonance standards were used to establish chemical bonding and percent incorporation of the modifying groups into the alginate polymer. The hydrogel made with alginate modified by each method was found to be completely stable under acidic pH conditions while disintegrating within minutes to hours in neutral-basic pH conditions. We found that, while alginate oxidation did not affect the ß-d-mannuronate/α-l-guluronate ratio of alginate, the rate of disintegration of the hydrogel made with oxidized alginate was dependent upon the degree of oxidation.


Assuntos
Alginatos/química , Portadores de Fármacos/química , Sistemas de Liberação de Medicamentos/instrumentação , Administração Oral , Difusão , Hidrogéis/química , Concentração de Íons de Hidrogênio , Oxirredução , Polímeros/química
3.
Soft Matter ; 15(33): 6660-6676, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31389467

RESUMO

The dynamic behavior of monoclonal antibodies (mAbs) at high concentration provides insight into protein microstructure and protein-protein interactions (PPI) that influence solution viscosity and protein stability. At high concentration, interpretation of the collective-diffusion coefficient Dc, as determined by dynamic light scattering (DLS), is highly challenging given the complex hydrodynamics and PPI at close spacings. In contrast, self-diffusion of a tracer particle by Brownian motion is simpler to understand. Herein, we develop fluorescence correlation spectroscopy (FCS) for the measurement of the long-time self-diffusion of mAb2 over a wide range of concentrations and viscosities in multiple co-solute formulations with varying PPI. The normalized self-diffusion coefficient D0/Ds (equal to the microscopic relative viscosity ηeff/η0) was found to be smaller than η/η0. Smaller ratios of the microscopic to macroscopic viscosity (ηeff/η) are attributed to a combination of weaker PPI and less self-association. The interaction parameters extracted from fits of D0/Ds with a length scale dependent viscosity model agree with previous measurements of PPI by SLS and SAXS. Trends in the degree of self-association, estimated from ηeff/η with a microviscosity model, are consistent with oligomer sizes measured by SLS. Finally, measurements of collective diffusion and osmotic compressibility were combined with FCS data to demonstrate that the changes in self-diffusion between formulations are due primarily to changes in the protein-protein friction in these systems, and not to protein-solvent friction. Thus, FCS is a robust and accessible technique for measuring mAb self-diffusion, and, by extension, microviscosity, PPI and self-association that govern mAb solution dynamics.


Assuntos
Anticorpos Monoclonais/química , Fenômenos Biofísicos , Difusão , Fluorescência , Corantes Fluorescentes/química , Microscopia de Fluorescência , Modelos Químicos , Multimerização Proteica , Estabilidade Proteica , Soluções , Viscosidade
4.
Phys Chem Chem Phys ; 21(35): 18811-18815, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31468044

RESUMO

Recent experiments have reported that diffusion of enzymes can be enhanced in the presence of their substrates. Using a fluctuating dumbbell model of enzymes, it has been argued that such an enhancement can be rationalized by the reduction of the enzyme size and by the suppression of the hydrodynamically coupled conformational fluctuations, induced by binding a substrate or an inhibitor to the enzyme [Nano Lett. 2017, 17, 4415]. Herein, we critically examine these expectations via extensive Brownian dynamics simulations of a similar model. The numerical results show that neither of the two mechanisms can cause an enhancement comparable to that reported experimentally, unless very large, physically counter-intuitive, enzyme deformations are invoked.


Assuntos
Enzimas/química , Enzimas/metabolismo , Simulação de Dinâmica Molecular , Difusão , Modelos Químicos
5.
J Agric Food Chem ; 67(33): 9399-9410, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31304753

RESUMO

This study investigated the feasibility of using hyperspectral imaging (HSI) to characterize the diffusion of acid and water within food structures during gastric digestion. Two different sweet potatoes (steamed and fried) and egg white gel (pH5 and pH9 EWGs) structures were exposed to in vitro gastric digestion before scanning by HSI. Afterward, the moisture or acid present in the digested sample was analyzed for calibration purposes. Calibration models were subsequently built using partial least-squares (PLS). The PLS models indicated that the full-wavelength spectral range (550-1700 nm) had a good ability to predict the spatial distribution of acid (Rcal2 > 0.82) and moisture (Rcal2 > 0.88). The spatiotemporal distributions of moisture and acid were mapped across the digested food, and they were shown to depend on the food composition and structure. The kinetic data revealed that the acid and moisture uptakes are governed by Fickian diffusion or by both diffusion and erosion-controlled mechanisms.


Assuntos
Ácidos/química , Clara de Ovo/química , Suco Gástrico/química , Ipomoea batatas/química , Ácidos/metabolismo , Animais , Galinhas , Difusão , Digestão , Suco Gástrico/metabolismo , Ipomoea batatas/metabolismo , Cinética , Água/análise
6.
J Chem Phys ; 151(2): 025102, 2019 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-31301703

RESUMO

Understanding the effect of a solid support on the dynamical properties of a supported lipid bilayer (SLB) is a prerequisite for the applications of SLB as a model biomembrane. Here, we applied two-dimensional fluorescence lifetime correlation spectroscopy to examine the effect of solution pH on the diffusion of lipids in the proximal/distal leaflets of a zwitterionic SLB. Leaflet-specific diffusion analyses at various pH revealed that the diffusion of lipids in the proximal leaflet facing a glass surface becomes slower by decreasing pH with the transition pH of ∼7.4. We attributed it to the reduction of the surface charge density of a glass support. Furthermore, the data clearly showed that the lipid diffusion in the distal leaflet facing a bulk solution is insensitive to the change in the diffusion property of the proximal leaflet. This reflects a weak interleaflet coupling between the proximal and distal leaflets of the SLB.


Assuntos
Difusão , Vidro/química , Bicamadas Lipídicas/química , Lipídeos/química , Concentração de Íons de Hidrogênio , Oxirredução , Espectrometria de Fluorescência , Propriedades de Superfície
7.
J Chem Phys ; 151(2): 024107, 2019 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-31301717

RESUMO

It is intuitive that the diffusivity of an isolated particle differs from those in a monodisperse suspension, in which hydrodynamic interactions between the particles are operative. Batchelor [J. Fluid Mech. 74, 1-29 (1976) and J. Fluid Mech. 131, 155-175 (1983)] calculated how hydrodynamic interactions influenced the diffusivity of a dilute suspension of spherical particles, and Russel et al. [Colloidal Dispersions (Cambridge University Press, 1991)] and Brady [J. Fluid Mech. 272, 109-134 (1994)] treated nondilute (higher particle volume fraction) suspensions. Although most particles lack perfect sphericity, little is known about the effects of hydrodynamic interactions on the diffusivity of spheroidal particles, which are the simplest shapes that can be used to model anisotropic particles. Here, we calculate the effects of hydrodynamic interactions on the translational and rotational diffusivities of spheroidal particles of arbitrary aspect ratio in dilute monodisperse suspensions. We find that the translational and rotational diffusivities of prolate spheroids are more sensitive to eccentricity than for oblate spheroids. The origin of the hydrodynamic anisotropy is that found in the stresslet field for the induced-dipole interaction. However, in the dilute limit, the effects of anisotropy are at the level of a few percent. These effects have influence on a vast range of settings, from partially frozen colloidal suspensions to the dynamics of cytoplasm.


Assuntos
Difusão , Hidrodinâmica , Coloides/química , Tamanho da Partícula , Propriedades de Superfície , Suspensões/química
8.
Phys Chem Chem Phys ; 21(30): 16686-16693, 2019 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31317978

RESUMO

Understanding the properties of cell membranes is important in the fields of fundamental and applied biology. While the characterization of simplified biological membrane mimics comprising liquid phase lipids has been routinely performed due to the ease of fabrication, the characterization of more realistic membrane mimics comprising multi-phase lipids remains challenging due to more complicated fabrication requirements. Herein, we report a convenient approach to fabricate and characterize multi-phase supported lipid bilayers (SLBs). We employed the solvent-assisted lipid bilayer (SALB) formation method to fabricate mixed lipid bilayers comprising liquid phase 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and gel phase 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipids at room temperature. The fabrication procedure was performed inside a newly designed microfluidic chamber, which facilitated the subsequent characterization of the SLBs without exposure to air. The SLBs were then characterized via fluorescence microscopy, fluorescence recovery after photobleaching (FRAP), atomic force microscopy (AFM) and AFM-based force-distance measurements. Interestingly, results from these characterization techniques revealed that regardless of the gel phase composition, the SALB formation method consistently yielded uniform SLBs at room temperature, even though the transition temperature of DPPC is considerably higher. Furthermore, the composition ratio of DOPC and DPPC in the precursor solution is well reproduced in the fabricated SLBs. We also identified from diffusivity measurements that a high ratio of gel phase lipid revitalizes lipid-lipid interactions, which led to reduced molecular fluidity and the suppression of thermal undulation within the SLBs. Taken together, our results highlight the robustness of the SALB formation method that allows the fabrication of complex lipid bilayers with a high degree of precision, which is suitable for functional studies of biological membranes.


Assuntos
Bicamadas Lipídicas/química , Fenômenos Mecânicos , Difusão
9.
J Chem Theory Comput ; 15(8): 4673-4686, 2019 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-31265271

RESUMO

The time step of atomistic molecular dynamics (MD) simulations is determined by the fastest motions in the system and is typically limited to 2 fs. An increasingly popular approach is to increase the mass of the hydrogen atoms to ∼3 amu and decrease the mass of the parent atom by an equivalent amount. This approach, known as hydrogen-mass repartitioning (HMR), permits time steps up to 4 fs with reasonable simulation stability. While HMR has been applied in many published studies to date, it has not been extensively tested for membrane-containing systems. Here, we compare the results of simulations of a variety of membranes and membrane-protein systems run using a 2 fs time step and a 4 fs time step with HMR. For pure membrane systems, we find almost no difference in structural properties, such as area-per-lipid, electron density profiles, and order parameters, although there are differences in kinetic properties such as the diffusion constant. Conductance through a porin in an applied field, partitioning of a small peptide, hydrogen-bond dynamics, and membrane mixing show very little dependence on HMR and the time step. We also tested a 9 Å cutoff as compared to the standard CHARMM cutoff of 12 Å, finding significant deviations in many properties tested. We conclude that HMR is a valid approach for membrane systems, but a 9 Å cutoff is not.


Assuntos
Membrana Celular/química , Hidrogênio/química , Bicamadas Lipídicas/química , Proteínas de Membrana/química , Simulação de Dinâmica Molecular , Difusão , Glicoforina/química , Humanos , Movimento (Física) , Peptídeos/química , Fosfatidilcolinas/química , Multimerização Proteica , Receptores Acoplados a Proteínas-G/química , Termodinâmica
10.
J Environ Radioact ; 208-209: 106019, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31336260

RESUMO

This paper presents radon diffusion coefficient values and radon resistance values determined for 650 widely-used waterproofing materials divided into 29 groups according to their chemical composition. The reliability of two different approaches for determining the radon resistance is discussed, and differences between the two approaches are identified. A comparison between the radon resistances of waterproofing materials and the requirements prescribed by various building standards indicates that some requirements are unnecessarily strict. It is shown that the most effective approach for setting the requirements is to prescribe several minimum radon resistance values in dependence on the parameters of the building and the subsoil.


Assuntos
Poluentes Radioativos do Ar/análise , Materiais de Construção , Monitoramento de Radiação , Radônio/análise , Poluentes Radioativos do Ar/normas , Difusão , Radônio/normas
11.
Environ Sci Pollut Res Int ; 26(23): 23542-23554, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31203540

RESUMO

Coal fly ash, as a solid waste produced from coal-fired power plants, was recycled for synthesis of zeolite A and geopolymer which were used for stabilization/solidification of Cs+ and Sr2+ from aqueous solutions. Specifically, the sorption data was successfully fitted by kinetic and thermodynamic models. The microstructure changes of zeolite A after loading Cs+ and Sr2+ were explored using XRD, FTIR, Raman, TG-DTA, and N2 adsorption/desorption isotherm. The solidification of the spent zeolites using geopolymer was conducted and evaluated. It was found that pseudo-second sorption mechanism was predominant and, according to the Boyd equation, film diffusion seemed to govern the sorption process. The maximum sorption capacities on Cs+ and Sr2+ based on Langmuir model were 2.12 and 1.93 mmol/g, respectively. During ion exchange with Cs+ and Sr2+, Cs+ was inclined to go through the window to occupy the position of eight-member ring, while the Sr2+ was more likely to replace the Na+ in the six-member ring, thereby easily leading to the different changes of zeolite structure. In addition, geopolymer could be a promising matrix for the treatment of radioactive waste because the leaching fraction greatly decreased after solidification by geopolymer. Therefore, the recycling of coal fly ash for radioactive waste disposal could achieve the concept of disposal waste with waste and recycling, which could greatly contribute to the sustainable development of society.


Assuntos
Césio/química , Cinza de Carvão/química , Eliminação de Resíduos/métodos , Estrôncio/química , Adsorção , Carvão Mineral , Difusão , Troca Iônica , Cinética , Centrais Elétricas , Resíduos Radioativos , Reciclagem , Termodinâmica , Zeolitas/química
12.
Phys Chem Chem Phys ; 21(25): 13746-13757, 2019 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-31209450

RESUMO

The phase behaviour as a function of temperature is explored for pure phospholipid (DPPC) and hybrid lipid-polymer (DPPC/Pluronic L64) bilayers with the aid of atomistic MD simulations. The range of the fixed-temperature simulations includes temperatures below and above the known melting temperature (Tm) for DPPC membranes. For the pure lipid bilayer, the main phase transition is discontinuous, as verified by the abrupt changes observed in the membrane structure, elasticity and the lipid diffusivity near the critical temperature Tm, which lies in the region 298.15-303.15 K. A pre-transition step is detected at 298.15 K which has been identified as the ripple phase (Pß'), where ordered and disordered lipids coexist, causing thickness fluctuations. In the ordered gel phase, the positional ordering as assessed by the lipid radial distribution functions is long-range and some degree of hexagonal packing is measured. The hybrid bilayers on the other hand, transform from a more ordered to a disordered phase in a continuous manner, without finite jumps in their properties. No signs of the ripple phase are identified and the ordered phase exhibits very limited hexagonal packing and some positional ordering that decays fast. The effect of the inserted polymers in the two phases is reversed; at low temperatures, they render the membrane thinner, less cohesive and less ordered compared to the pure one, with the lipids assuming faster diffusion rates, whereas at high temperatures, the polymer interaction with the lipids acts reducing their diffusivity, but also increasing the lipid tail ordering and the membrane stiffness. The ability of the amphiphilic L64 copolymers to change the nature of the main phase transition of lipid membranes and their properties both in the ordered and the disordered phase is of vital importance for the prediction of both the efficacy of hybrid lipid/polymer nanoparticles as drug delivery vehicles as well as their potential adverse implications during interactions with healthy cell membranes.


Assuntos
Bicamadas Lipídicas/química , Modelos Moleculares , Fosfolipídeos/química , Poloxâmero/química , Cristalização , Difusão , Cinética , Membranas Artificiais , Modelos Químicos , Transição de Fase , Termodinâmica , Temperatura de Transição
13.
J Chem Phys ; 150(23): 235101, 2019 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-31228916

RESUMO

We investigate by molecular dynamics simulations the mobility of the water located at the DNA minor and major grooves. We employ the TIP3P water model, and our system is analyzed for a range of temperatures 190-300 K. For high temperatures, the water at the grooves shows an Arrhenius behavior similar to that observed in the bulk water. At lower temperatures, a departure from the bulk behavior is observed. This slowing down in the dynamics is compared with the dynamics of the hydrogen of the DNA at the grooves and with the autocorrelation functions of the water hydrogen bonds. Our results indicate that the hydrogen bonds of the water at the minor grooves are highly correlated, which suggests that this is the mechanism for the slow dynamics at this high confinement.


Assuntos
Temperatura Baixa , DNA/química , Modelos Moleculares , Água/química , Difusão , Ligações de Hidrogênio , Simulação de Dinâmica Molecular
14.
Nat Methods ; 16(7): 611-614, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-31235884

RESUMO

The study of the aggregation of soluble proteins into highly ordered, insoluble amyloid fibrils is fundamental for the understanding of neurodegenerative disorders. Here, we present a method for the observation of single amyloid fibrils that allows the investigation of fibril growth, secondary nucleation or fibril breakup that is typically hidden in the average ensemble. Our approach of thermophoretic trapping and rotational diffusion measurements is demonstrated for single Aß40, Aß42 and pyroglutamyl-modified amyloid-ß variant (pGlu3-Aß3-40) amyloid fibrils.


Assuntos
Amiloide/química , Agregados Proteicos , Difusão , Dobramento de Proteína
16.
AAPS PharmSciTech ; 20(6): 229, 2019 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-31227930

RESUMO

Atropine sulfate (AS) fast-disintegrating sublingual tablets (FDSTs) were tested for AS sublingual permeation's feasibility as a potential alternative dosage form to treat organophosphates (OP) toxicity. More than 12,000 OP pesticide toxicity cases were reported in the USA from 2011 to 2014. AS is the recommended antidote for OP toxicity; however, it is only available as an ATROPEN® auto-injector, an IM injection, for self-administration, which is associated with several drawbacks and limitations. Six AS FDST batches were formulated and characterized. Two tablet sizes, group A weighing 150 mg and group B weighing 50 mg, were formulated with three different AS doses: 2 mg (A1 and B1), 4 mg (A2 and B2), and 8 mg (A3 and B3). AS in vitro diffusion and sublingual permeation were investigated in Franz cells using a cellulose membrane and an excised porcine sublingual membrane. The effect of AS load and tablet size on sublingual permeation was also evaluated. All batches passed quality control tests. AS FDSTs' size and AS load had a significant effect on tablet disintegration time and drug dissolution, which significantly impacted AS concentration gradient across the diffusional membrane. Group B FDSTs (smaller tablets) resulted in a significantly higher initial permeation (JAUC0-15) compared to group A FDSTs. Also, the cumulative AS (JAUC0-90) and AS influx (J) increased linearly with increasing AS dose. These AS FDSTs have the potential to be explored in vivo to determine the required bioequivalent sublingual AS dose as an alternative dosage form for the treatment of OP toxicity.


Assuntos
Atropina/administração & dosagem , Atropina/uso terapêutico , Intoxicação por Organofosfatos/tratamento farmacológico , Comprimidos/administração & dosagem , Administração Sublingual , Animais , Difusão , Permeabilidade , Suínos
17.
Chemosphere ; 232: 18-25, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31152899

RESUMO

In-situ sampling of 2-chlorophenol (CP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP) in industrial wastewater was carried out by the diffusive gradients in thin films (DGT) device based on mesoporous carbon (MC). The diffusion coefficients of CP ((1.33 ±â€¯0.05) × 10-6 cm2 s-1), DCP((1.35 ±â€¯0.04) × 10-6 cm2 s-1) and TCP((1.09 ±â€¯0.07) × 10-6 cm2 s-1)) in nylon membrane at 25 °C were independent of pH 3-9 and ionic strength as pNaCl from 0.155 to 3, and were less than their values in water, demonstrating that the nylon membrane with good tolerance and constant diffusion coefficients was suitable as the DGT diffusion layer for controlling the diffusion of CPs. MC-DGT accurately measured the concentrations of CP, DCP and TCP in synthetic solution (CDGT/CSOLN = 0.956-1.04) over the deployment of 120 h. The experimental data also agreed well with the theoretical data calculated on the DGT equation. The performance of MC-DGT for sampling CPs was independent of pH (3-8) and ionic strength as pNaCl (1.3-3) due to the change of the interaction between MC and CPs under relatively high pH and ionic strength. Deployments in laboratory and field trials demonstrated that the MC-DGT was a reliable simple, robust and accurate tool for the in-situ sampling of CP, DCP and TCP in the industrial wastewater.


Assuntos
Clorofenóis/análise , Monitoramento Ambiental , Poluentes Químicos da Água/análise , Carbono/química , Difusão , Nylons , Concentração Osmolar , Eliminação de Resíduos Líquidos , Águas Residuárias/análise , Águas Residuárias/química
18.
Environ Sci Pollut Res Int ; 26(23): 23416-23428, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31197675

RESUMO

The application of biosorption operation has gained attention in the removal and retrieval of toxic metal ions from water bodies. Wastewater from industrial activity generally presents great complexity due to the coadsorption of cations to the inactive biomass binding sites. In this work, the competitive biosorption of Cu(II) and Ag(I) ions was studied in batch systems. A kinetic study applying a non-acidified and acidified waste of Sargassum filipendula in equimolar and non-equimolar metal samples was carried out and the acidified biosorbent was selected due to higher removal rates and selectivity of silver ions. The assays were performed with 2 g L-1 of biosorbent concentration at 25 °C for 12 h and pH was controlled at around 5.0. Copper presented higher affinity for the biosorbent and a fast biosorption kinetic profile, while silver equilibrium times exhibited dependence on the copper concentration. External diffusion is the rate-limiting step in Cu(II) ion removal and it might also limit the kinetic rates of Ag(I) ions with intraparticle diffusion, depending on the initial concentration of metal cations. The ion-exchange mechanism is evidenced and complexation and electrostatic attraction mechanisms might be suggested, explained by simultaneous chemisorption and physisorption processes during the operation. Calcium and sodium were released in considerable amounts by the ion-exchange mechanism. Characterization analyses confirmed the role of several functional groups in the competitive biosorption accompanied by a homogenous covering of both metal ions on the surface of the particles. Particle porosity analyses revealed that the material is macroporous and an appreciable amount of macropores are filled with metal cations after biosorption.


Assuntos
Cobre/metabolismo , Alga Marinha/metabolismo , Prata/metabolismo , Poluentes Químicos da Água/metabolismo , Adsorção , Biomassa , Cobre/análise , Difusão , Concentração de Íons de Hidrogênio , Troca Iônica , Íons/análise , Cinética , Prata/análise , Águas Residuárias/análise , Poluentes Químicos da Água/análise
19.
Environ Sci Pollut Res Int ; 26(23): 24143-24161, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31228066

RESUMO

This batch and column kinetics study of arsenic removal utilized copper-impregnated natural mineral tufa (T-Cu(A-C)) under three ranges of particle size. Non-competitive kinetic data fitted by the Weber-Morris model and the single resistance mass transfer model, i.e., mass transfer coefficient kfa and diffusion coefficient (Deff) determination, defined intra-particle diffusion as the dominating rate controlling step. Kinetic activation parameters, derived from pseudo-second-order rate constants, showed low dependence on adsorbent geometry/morphology and porosity, while the diffusivity of the pores was significant to removal efficacy. The results of competitive arsenic adsorption in a multi-component system of phosphate, chromate, or silicate showed effective arsenic removal using T-Cu adsorbents. The high adsorption rate-pseudo-second-order constants in the range 0.509-0.789 g mg-1 min-1 for As(V) and 0.304-0.532 g mg1 min1 for As(III)-justified further application T-Cu(A-C) in a flow system. The fixed-bed column adsorption data was fitted using empirical Bohart-Adams, Yoon-Nelson, Thomas, and dose-response models to indicate capacities and breakthrough time dependence on arsenic influent concentration and the flow rate. Pore surface diffusion modeling (PSDM), following bed-column testing, further determined adsorbent capacities and mass transport under applied hydraulic loading rates.


Assuntos
Arsênico/isolamento & purificação , Cobre/química , Minerais/química , Purificação da Água/métodos , Adsorção , Arsênico/química , Cromatos/química , Difusão , Cinética , Fosfatos/química , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/instrumentação
20.
Soft Matter ; 15(27): 5400-5411, 2019 Jul 10.
Artigo em Inglês | MEDLINE | ID: mdl-31172158

RESUMO

Two colonies of Bacillus subtilis of identical strains growing adjacent to each other on an agar plate exhibit two distinct types of interactions: they either merge as they grow or demarcation occurs leading to formation of a line of demarcation at the colony fronts. The nature of this interaction depends on the agar concentration in the growth medium and the initial separation between the colonies. When the agar concentration was 0.67% or lower, the two sibling colonies were found to always merge. At 1% or higher concentrations, the colonies formed a demarcation line only when their initial separation was 20 mm or higher. Interactions of a colony with solid structures and liquid drops have indicated that biochemical factors rather than the presence of physical obstacles are responsible for the demarcation line formation. A reaction diffusion model has been formulated to predict if two sibling colonies will form a demarcation line under given agar concentration and initial separation. The model prediction agrees well with experimental findings and generates a dimensionless phase diagram containing merging and demarcation regimes. The phase diagram is in terms of a dimensionless initial separation, d[combining macron], and a dimensionless diffusion coefficient, D[combining macron], of the colonies. The phase boundary between the two interaction regimes can be described by a power law relation between d[combining macron] and D[combining macron].


Assuntos
Ágar/química , Bacillus subtilis/fisiologia , Bacillus subtilis/classificação , Técnicas Bacteriológicas , Meios de Cultura , Difusão , Modelos Biológicos , Movimento
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA