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1.
Artigo em Inglês | MEDLINE | ID: mdl-32283617

RESUMO

As the demand for potable water increases, direct potable reuse of wastewater is an attractive alternative method to produce potable water. However, implementation of such a process will require the removal of emerging contaminants which could accumulate in the drinking water supply. Here, the removal of atrazine, a commonly used herbicide, has been investigated. Using real and synthetic wastewater, as well as sludge from two wastewater treatment facilities in the United States in Norman, Oklahoma and Fayetteville, Arkansas, atrazine removal has been investigated. Our results indicate that about 20% of the atrazine is removed by adsorption onto the particulate matter present. Significant biodegradation of atrazine was only observed under aerobic conditions for sludge from Norman, Oklahoma. Next-generation sequencing of the activated sludge revealed the abundance of Noncardiac with known atrazine degradation pathways in the Norman aerobic sludge, which is believed to be responsible for atrazine biodegradation in our study. The detection of these bacteria could also be used to determine the likelihood of biodegradation of atrazine for a given wastewater treatment facility.

2.
Membranes (Basel) ; 9(12)2019 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-31817680

RESUMO

Membrane-based processes are attractive for treating oily wastewaters. However, membrane fouling due to the deposition of oil droplets on the membrane surface compromises performance. Here, real-time observation of the deposition of oil droplets by direct confocal microscopy was conducted. Experiments were conducted in dead-end and crossflow modes. Base NF 270 nanofiltration membranes as well as membranes modified by grafting poly(N-isopropylacrylamide) chains from the membrane surface using atom transfer radical polymerization were investigated. By using feed streams containing low and high NaCl concentrations, the grafted polymer chains could be induced to switch conformation from a hydrated to a dehydrated state, as the lower critical solution temperature for the grafted polymer chains moved above and below the room temperature, respectively. For the modified membrane, it was shown that switching conformation of the grafted polymer chains led to the partial release of adsorbed oil. The results also indicate that, unlike particles such as polystyrene beads, adsorption of oil droplets can lead to coalescence of the adsorbed oil droplets on the membrane surface. The results provide further evidence of the importance of membrane properties, feed solution characteristics, and operating mode and conditions on membrane fouling.

3.
Biotechnol Bioeng ; 116(10): 2621-2631, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31184371

RESUMO

A combined pore blockage and cake filtration model was applied to the virus filtration of an Fc-fusion protein using the three commercially available filters, F-1, F-2, and F-3 in a range of buffer conditions including sodium-phosphate and tris-acetate buffers with and without 200 mM NaCl at pH 7.5. The fouling behaviors of the three filters for the feed solutions spiked with minute virus of mice were described well by this combined model for all the solution conditions. This suggests that fouling of the virus filters is dominated by the pore blockage mechanism during the initial stage of the filtration and transformed to the cake filtration mechanism during the later stage of the filtration. Both flux and transmembrane resistance can be described well by this model. The pore blockage rate and the rate of increase of protein layer resistance over blocked pores are found to be affected by membrane properties as well as the solution conditions resulting from the modulation of interactions between virus, protein, and membrane by the solution conditions.

4.
J Phys Chem B ; 123(23): 4986-4995, 2019 06 13.
Artigo em Inglês | MEDLINE | ID: mdl-31124684

RESUMO

Poly( N-vinylcaprolactam) (PVCL) is a thermo-responsive polymer, which exhibits a lower critical solution temperature (LCST) in an aqueous solution. The LCST of this hydrophilic-to-hydrophobic transition is found to be strongly dependent on the salt-type and salt-concentration as well as on the molecular weight and concentration of the polymer. Here, atomistic molecular dynamics simulations have been successfully conducted for the first time to investigate the LCST transition of a 100 degree of polymerization PVCL chain in water, 1 M NaCl, 3.5 M NaCl, and 0.5 M CaCl2 solutions. Our results show that steric hindrance resulting from the bulky 7-member ring on the PVCL chain plays a critical role in the conformational transition. Moreover, the degrees of hydration and dehydration below or above the transition temperature are highly dependent on the specific solution condition and temperature. Water molecules are found to be trapped inside the collapsed polymer chains leading to the varying degrees of hydration and dehydration of the polymer chain in different solutions. Calculated water diffusion coefficients for both trapped and free water molecules agree very well with experimental measurements.

5.
Artigo em Inglês | MEDLINE | ID: mdl-30988273

RESUMO

Direct potable reuse of wastewater is attractive as the demand for potable water increases. However, the presence of organic micropollutants in industrial and domestic wastewater is a major health and environmental concern. Conventional wastewater treatment processes are not designed to remove these compounds. Further many of these emerging pollutants are not regulated. Membrane bioreactor based biological wastewater treatment has recently become a preferred method for treating municipal and other industrial wastewaters. Here the removal of five selected micropollutants representing different classes of emerging micropollutants has been investigated using a membrane bioreactor. Acetaminophen, amoxicillin, atrazine, estrone, and triclosan were spiked into wastewaters obtained from a local wastewater treatment facility prior to introduction to the membrane bioreactor containing both anoxic and aerobic tanks. Removal of these compounds by adsorption and biological degradation was determined for both the anoxic and aerobic processes. The removal as a function of operating time was investigated. The results obtained here suggest that removal may be related to the chemical structure of the micropollutants.


Assuntos
Reatores Biológicos , Membranas Artificiais , Águas Residuárias/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Poluentes Químicos da Água/análise
6.
Macromol Rapid Commun ; 40(2): e1800333, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30027594

RESUMO

This article presents the synthesis of poly(methacrylic acid)-b-poly(methyl methacrylate) diblock copolymer via polymerization-induced self-assembly in the presence of iron-oxide nanoparticles. Detailed phase diagrams with and without inorganic nanoparticles were constructed. Scanning transmission electron microscopy and energy dispersive X-ray photometry studies confirme the decoration of the polymeric nanoparticles with the iron-oxide nanoparticles. These hybrid nanoparticles were used to prepare porous thin film membranes by spin coating. Finally, the magneto-responsive properties of the membranes were assessed using water filtration tests in the presence and absence of a magnetic field.


Assuntos
Técnicas de Química Sintética/métodos , Nanopartículas de Magnetita/química , Nanopartículas/química , Polímeros/química , Ácidos Polimetacrílicos/química , Polimetil Metacrilato/química , Materiais Revestidos Biocompatíveis/química , Campos Magnéticos , Nanopartículas de Magnetita/ultraestrutura , Membranas Artificiais , Microscopia Eletrônica de Transmissão e Varredura , Nanopartículas/ultraestrutura , Polimerização , Polímeros/síntese química , Porosidade
7.
Polymers (Basel) ; 10(7)2018 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-30960703

RESUMO

Purification of biologically-derived therapeutics is a major cost contributor to the production of this rapidly growing class of pharmaceuticals. Monoclonal antibodies comprise a large percentage of these products, therefore new antibody purification tools are needed. Small peptides, as opposed to traditional antibody affinity ligands such as Protein A, may have advantages in stability and production costs. Multiple heptapeptides that demonstrate Fc binding behavior that have been identified from a combinatorial peptide library using M13 phage display are presented herein. Seven unique peptide sequences of diverse hydrophobicity and charge were identified. All seven peptides showed strong binding to the four major human IgG isotypes, human IgM, as well as binding to canine, rat, and mouse IgG. These seven peptides were also shown to bind human IgG4 from DMEM cell culture media with 5% FCS and 5 g/L ovalbumin present. These peptides may be useful as surface ligands for antibody detection and purification purposes. Molecular docking and classical molecular dynamics (MD) simulations were conducted to elucidate the mechanisms and energetics for the binding of these peptides to the Fc region. The binding site was found to be located between the two glycan chains inside the Fc fragment. Both hydrogen bonding and hydrophobic interactions were found to be crucial for the binding interactions. Excellent agreement for the binding strength was obtained between experimental results and simulations.

8.
J Biomed Mater Res B Appl Biomater ; 105(8): 2455-2464, 2017 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-27652573

RESUMO

Biphasic materials, comprised of an ordered arrangement of two different material phases within a material, have the potential for a wide variety of applications including filtration, protective clothing and tissue engineering. This study reports for the first time, a process for engineering biphasic Janus-type polymeric nanofiber (BJPNF) networks via the centrifugal jet spinning technique. BJPNF alignment and fiber diameter was dependent on fabrication rotational speed as well as solution composition. The biphasic character of these BJPNFs, which was controlled via the rotational speed of fabrication, was confirmed at the individual nanofiber scale using energy dispersive X-ray spectroscopy, and at the bulk, macro-scale using attenuated total reflectance-Fourier transform infrared spectroscopy. Biphasic character was also demonstrated at the functional level via differing affinities on either side of the BJPNF for cell attachment. Our work thus presents a method for fabricating BJPNF scaffold networks where there might be a need for different properties on either side of a material. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2455-2464, 2017.


Assuntos
Nanofibras/química , Tecidos Suporte/química , Anisotropia , Humanos
9.
J Comput Chem ; 37(10): 877-85, 2016 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-26519612

RESUMO

Combined quantum mechanical calculations and classical molecular dynamics simulations were conducted to investigate the hydration properties of carboxybetaine zwitterion brushes with varying separation distances between the quaternary ammonium cation and carboxylic anion. The brushes consist of zwitterion trimers and are investigated to mimic interacting zwitterion chains grafted on a substrate as well as polymers with interacting zwitterion side chains. Our results show that the values of both positive and negative charges, their separation distances as well as chain interactions appear to play a critical role in the hydration properties of the zwitterions. The overall hydration property of these zwitterions is dictated by the competition between the strong hydration of the charged groups and the dehydration of the hydrocarbon chains. The strongest hydration occurs when the -CH2- unit in the hydrocarbon chain reaches 6-8 for these trimers. Further increase in the hydrocarbon chain length to 10-14 leads to significant and sudden dehydration of the trimers. The water structure and the water residence time surrounding the zwitterions also demonstrate substantial alteration at this length scale. This hydrophilic-to-hydrophobic transition is induced by the hydrophobic interactions of the trimer chains. Our hydration results could explain the observed trend of the superiority of the methylated carbohydrates and poly(ethylene glycol) as antifouling materials compared to corresponding hydroxyl-terminated compounds.


Assuntos
Betaína/química , Água/química , Betaína/análogos & derivados , Carboidratos/química , Interações Hidrofóbicas e Hidrofílicas , Simulação de Dinâmica Molecular , Polietilenoglicóis/química , Teoria Quântica
10.
Langmuir ; 30(35): 10651-60, 2014 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-25127078

RESUMO

A bisphosphonate derived ligand was successfully synthesized and grafted from the surface of regenerated cellulose membrane using atom transfer radical polymerization (ATRP) for protein separations. This ligand has a remarkable affinity for arginine (Arg) residues on protein surface. Hydrophilic residues N-(2-hydroxypropyl) methacrylamide (HPMA) was copolymerized to enhance the flexibility of the copolymer ligand and further improve specific protein adsorption. The polymerization of bisphosphonate derivatives was successful for the first time using ATRP. Static and dynamic binding capacities were determined for binding and elution of Arg rich lysozyme. The interaction mechanism between the copolymer ligand and lysozyme was elucidated using classical molecular dynamics (MD) simulations.


Assuntos
Proteínas/química , Arginina/química , Interações Hidrofóbicas e Hidrofílicas , Metacrilatos/química , Polimerização
11.
Carbohydr Res ; 388: 50-60, 2014 Mar 31.
Artigo em Inglês | MEDLINE | ID: mdl-24631668

RESUMO

The mechanisms and free energy surfaces (FES) for the initial critical steps during proton-catalyzed glucose condensation and dehydration reactions were elucidated in dimethyl sulfoxide (DMSO) using Car-Parrinello molecular dynamics (CPMD) coupled with metadynamics (MTD) simulations. Glucose condensation reaction is initiated by protonation of C1--OH whereas dehydration reaction is initiated by protonation of C2--OH. The mechanisms in DMSO are similar to those in aqueous solution. The DMSO molecules closest to the C1--OH or C2--OH on glucose are directly involved in the reactions and act as proton acceptors during the process. However, the energy barriers are strongly solvent dependent. Moreover, polarization from the long-range electrostatic interaction affects the mechanisms and energetics of glucose reactions. Experimental measurements conducted in various DMSO/Water mixtures also show that energy barriers are solvent dependent in agreement with our theoretical results.


Assuntos
Dimetil Sulfóxido/química , Glucose/química , Prótons , Água/química , Desidratação , Simulação de Dinâmica Molecular , Solventes , Eletricidade Estática , Termodinâmica
12.
J Phys Chem B ; 117(39): 11460-5, 2013 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-23992399

RESUMO

Car-Parrinello-based molecular dynamics coupled with metadynamics simulations were used to determine the mechanism and associated free energy surface for opening the ring structure of cyclic glucopyranose in acidic aqueous solutions. The ring-opening process is initiated by the protonation of the ring oxygen atom and the breakage of the C1-O5 bond. The barrier for this process is about 25 kcal/mol, in good agreement with experimental measurements. Moreover, the glucose cyclic conformation is found to be more stable than the open chain form. The barrier for proton-catalyzed ring-opening in aqueous solution appears to be largely solvent induced due to the high affinity of water molecules for protons.


Assuntos
Ácidos/química , Glucose/química , Água/química , Aldeídos/química , Carbono/química , Hidrogênio/química , Modelos Químicos , Conformação Molecular , Simulação de Dinâmica Molecular , Oxigênio/química , Soluções/química , Solventes/química , Termodinâmica
13.
J Phys Chem B ; 117(17): 5090-101, 2013 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-23590832

RESUMO

Classical molecular dynamics (MD) simulations were conducted for PNIPAM in 1 M monovalent alkali chloride salt solutions as well as in 0.5 M divalent Mg(2+) and Ca(2+) chloride salt solutions. It was found that the strength for the direct alkali ion-amide O binding is strongly correlated with the size of the ionic radius. The smallest Li(+) ion binds strongest to amide O, and the largest Cs(+) ion has the weakest interaction with the amide bond. For the divalent Mg(2+) and Ca(2+) ions, their interactions with the amide bond are weak and appear to be mediated by the water molecules, particularly in the case of Mg(2+), resulting from their strong hydration. The direct binding between the cations and amide O requires partial desovlation of the ions that is energetically unfavorable for Mg(2+) and also to a great extent for Ca(2+). The higher cation charge makes the electrostatic interaction more favorable but the dehydration process less favorable. This competition between electrostatic interaction and the dehydration process largely dictates whether the direct binding between the cation and amide O is energetically preferred or not. For monovalent alkali ions, it is energetically preferred to bind directly with the amide O. Moreover, Li(+) ion is also found to associate strongly with the hydrophobic residues on PNIPAM.


Assuntos
Acrilamidas/química , Polímeros/química , Resinas Acrílicas , Cloreto de Cálcio/química , Cátions/química , Ligação de Hidrogênio , Cloreto de Magnésio/química , Simulação de Dinâmica Molecular , Água/química
14.
J Phys Chem B ; 116(35): 10898-904, 2012 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-22897167

RESUMO

Car-Parrinello molecular dynamics simulations (CPMD) coupled with metadynamics (MTD) simulations were conducted to investigate glucose isomerization to fructose in acidic aqueous solution. Glucose to fructose isomerization is initiated by protonation of the C2-OH and the formation of a furanose aldehyde intermediate. Fructose is produced via a hydride transfer from C2 to C1 on the furanose aldehyde followed by the rehydration of the C2 carbocation. Hydride 1,2 shift to form a C2 carbocation is an energetically favorable process but the barrier is relatively high at around 35 kcal/mol. The final step during glucose to fructose isomerization involves the rehydration of the C2 carbocation with an estimated barrier of 25 kcal/mol from our CPMD-MTD simulations.


Assuntos
Frutose/química , Glucose/química , Simulação de Dinâmica Molecular , Isomerismo , Água/química
15.
J Phys Chem A ; 115(42): 11740-8, 2011 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-21916465

RESUMO

Car-Parrinello based ab initio molecular dynamics (CPMD) coupled with metadynamics (MTD) simulations were carried out to investigate the mechanism and energetics for acid-catalyzed ß-d-glucose conversion to 5-hydroxymethylfurfurl (HMF) in water. HMF is a critical intermediate for biomass conversion to biofuels. It was found that protonation of the C2-OH on glucose, the breakage of the C2-O2 bond, and the formation of the C2-O5 bond is the critical rate-limiting step for the direct glucose conversion to HMF without converting to fructose first, contrary to the wide-spread assumption in literature that fructose is the main intermediate for glucose conversion to HMF. The calculated reaction barrier of 30-35 kcal/mol appears to be solvent-induced and is in excellent agreement with experimental observations.


Assuntos
Biocombustíveis , Química Orgânica , Furaldeído/análogos & derivados , Furanos/química , Glucose/química , Prótons , Ácidos/química , Catálise , Furaldeído/síntese química , Simulação de Dinâmica Molecular , Solventes , Termodinâmica , Água/química
16.
Carbohydr Res ; 346(13): 1985-90, 2011 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-21704309

RESUMO

Quantum mechanical calculations were carried out to determine the mechanisms for the superiority of the imidazolium acetate-based ionic liquids to the corresponding chloride-based ionic liquids. Our results indicate that the imidazolium cation can react with the acetate anion to generate a carbene, a highly reactive intermediate. The carbene produced then reacts with cellulose to facilitate its dissolution in the ionic liquid solvents in addition to the stronger hydrogen bonds formed between the acetate anion and the hydroxyl groups on cellulose. The mechanisms for the imidazolium cation and acetate anion reactions involve the initial ion pairing of the cation and anion via hydrogen bonding and electrostatic interactions. The hydrogen bond formed between the C2-H on the imidazolium cation and COO(-) of the anion facilitates the transfer of the H(+) to the anion to form a carbene intermediate.


Assuntos
Ácido Acético/química , Ânions/química , Celulose/química , Imidazóis/química , Líquidos Iônicos/química , Modelos Moleculares
17.
Langmuir ; 27(9): 5574-81, 2011 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-21462955

RESUMO

Presented here is a radically novel approach to reduce concentration polarization and, potentially, also fouling by colloids present in aqueous feeds: magnetically responsive micromixing membranes. Hydrophilic polymer chains, poly(2-hydroxyethyl methacrylate) (PHEMA), were grafted via controlled surface-initiated atom transfer radical polymerization (SI-ATRP) on the surface of polyamide composite nanofiltration (NF) membranes and then end-capped with superparamagnetic iron oxide magnetite (Fe(3)O(4)) nanoparticles. The results of all functionalization steps, that is, bromide ATRP initiator immobilization, SI-ATRP, conversion of PHEMA end groups from bromide to amine, and carboxyl-functional Fe(3)O(4) nanoparticle immobilization via peptide coupling, have been confirmed by X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). These nanoparticles experience a magnetic force as well as a torque under an oscillating external magnetic field. It has been shown, using particle image velocimetry (PIV), that the resulting movement of the polymer brushes at certain magnetic field frequencies induces mixing directly above the membrane surface. Furthermore, it was demonstrated that with such membranes the NF performance could significantly be improved (increase of flux and salt rejection) by an oscillating magnetic field, which can be explained by a reduced concentration polarization in the boundary layer. However, the proof-of-concept presented here for the active alteration of macroscopic flow via surface-anchored micromixers based on polymer-nanoparticle conjugates has much broader implications.

18.
J Phys Chem A ; 114(49): 12936-44, 2010 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-21086968

RESUMO

Ab initio molecular dynamics and metadynamics simulations were used to determine the free energy surfaces (FES) for the acid catalyzed ß-D-glucose condensation reaction. Protonation of C1-OH on the ß-D-glucose, breakage of the C1-O1 bond, and the formation of C1 carbocation is the rate-limiting step. The effects of solvent on the reaction were investigated by determining the FES both in the absence and presence of solvent water. It was found that water played a critical role in these reactions. The reaction barrier for the proton-catalyzed glucose condensation reaction is solvent induced because of proton's high affinity for water. During these simulations, ß-D-glucose conversion to α-d-glucose process via the C1 carbocation was also observed. The associated free energy change and activation barrier for this reaction were determined.


Assuntos
Glucose/química , Simulação de Dinâmica Molecular , Configuração de Carboidratos , Termodinâmica
19.
J Phys Chem B ; 114(49): 16594-604, 2010 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-21090725

RESUMO

Classical molecular dynamics simulations were performed to investigate the effects of salt on the lower critical solution temperature (LCST) of Poly (N-isopropylacrylamide) (PNIPAM). PNIPAM is often studied as a protein proxy due to the presence of a peptide bond in its monomer unit. PNIPAM is a temperature sensitive polymer which exhibits hydrophobic-hydrophilic phase transition at its LCST. The presence of salt in the solution will shift its LCST, typically to a lower temperature. This LCST shift follows the so-called Hofmeister series. Molecular dynamics (MD) simulations of PNIPAM in 1 M of NaCl, NaBr, NaI, and KCl were carried out to elucidate the effects of different salt on LCST and protein stability. Our results suggest that direct interactions between the salt cations and the polymer play a critical role in the shift of LCST and subsequently on protein stability. Further, cations have a much stronger affinity with the polymer, whereas anions bind weakly with the polymer. Moreover, the cation-polymer binding affinity is inversely correlated with the cation-anion contact pair association constant in solution.

20.
Carbohydr Res ; 345(13): 1945-51, 2010 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-20667524

RESUMO

Previously, theoretical multiple sugar (beta-d-xylose and beta-d-glucose) reaction pathways were discovered that depended on the initial protonation site on the sugar molecules using Car-Parrinello-based molecular dynamics (CPMD) simulations [Qian, X. H.; Nimlos, M. R.; Davis, M.; Johnson, D. K.; Himmel, M. E. Carbohydr. Res.2005, 340, 2319-2327]. In addition, simulation results showed that water molecules could participate in the sugar reactions, thus altering the reaction pathways. In the present study, the temperature and water density effects on the sugar degradation pathways were investigated with CPMD. We found that changes in both temperature and water density could profoundly affect the mechanisms and pathways. We attributed these effects to both the strength of hydrogen bonding and proton affinity of water.


Assuntos
Glucose/química , Xilose/química , Configuração de Carboidratos , Ligação de Hidrogênio , Hidróxidos/química , Modelos Moleculares , Prótons , Temperatura , Água/química
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