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1.
Food Chem ; 312: 126032, 2020 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-31874408

RESUMO

The concentrated liquid egg white (LEW) by dewatering process displays the remarkable advantages. However, the concentration process was hindered by the high viscosity and heat sensitivity of LEW. Forward osmosis (FO) as an emerging membrane technology to concentrate LEW was evaluated for the first time in this study. The effects of process conditions on FO flux, fouling control, and product quality were investigated. The LEW can be concentrated up to about 2.1 folds by a single FO process. Flux decline (up to 80%) occurred during the process which was attributed to membrane fouling and dilution of draw solution. However, the membrane fouling could be mitigated by higher cross-flow velocity and the flux could be recovered up to 100% by osmotic backwash. There was no significant leakage of draw solutes and loss of protein in LEW during FO process. The concentration of LEW resulted in a promoted products quality.


Assuntos
Proteínas do Ovo/química , Clara de Ovo/química , Animais , Fenômenos Químicos , Galinhas , Osmose , Soluções/química , Temperatura Ambiente , Viscosidade
2.
Nucleic Acids Res ; 48(3): 1406-1422, 2020 02 20.
Artigo em Inglês | MEDLINE | ID: mdl-31863586

RESUMO

Recent advances in gene editing have been enabled by programmable nucleases such as transcription activator-like effector nucleases (TALENs) and CRISPR-Cas9. However, several open questions remain regarding the molecular machinery in these systems, including fundamental search and binding behavior as well as role of off-target binding and specificity. In order to achieve efficient and specific cleavage at target sites, a high degree of target site discrimination must be demonstrated for gene editing applications. In this work, we studied the binding affinity and specificity for a series of TALE proteins under a variety of solution conditions using in vitro fluorescence methods and molecular dynamics (MD) simulations. Remarkably, we identified that TALEs demonstrate high sequence specificity only upon addition of small amounts of certain divalent cations (Mg2+, Ca2+). However, under purely monovalent salt conditions (K+, Na+), TALEs bind to specific and non-specific DNA with nearly equal affinity. Divalent cations preferentially bind to DNA over monovalent cations, which attenuates non-specific interactions between TALEs and DNA and further stabilizes specific interactions. Overall, these results uncover new mechanistic insights into the binding action of TALEs and further provide potential avenues for engineering and application of TALE- or TALEN-based systems for genome editing and regulation.


Assuntos
Cálcio/química , Cátions Bivalentes/química , DNA/química , Magnésio/química , Nucleases dos Efetores Semelhantes a Ativadores de Transcrição/química , Sistemas CRISPR-Cas/genética , Proteínas de Ligação a DNA/química , Edição de Genes , Potássio/química , Ligação Proteica , Sódio/química , Soluções/química , Nucleases dos Efetores Semelhantes a Ativadores de Transcrição/metabolismo
3.
Biophys Chem ; 257: 106280, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-31877450

RESUMO

High pressure acts as a mild and non-destructive activation mode for chemical reactions. However, in the context of organo-/biocatalysis, high pressure activation, has not been investigated systematically, although there are significant benefits such as rate acceleration, increased selectivity and the possibility of suppressing side product formation. The influence of hydrostatic pressure in solution on the catalytic performance of enzymes and small molecule organocatalysts such as amino acids, peptides, amines, cinchona alkaloids and thioureas is evaluated in this review, taking reactivity and selectivity as a probe to identify pressure effects on biomolecules.


Assuntos
Aminoácidos/química , Alcaloides de Cinchona/química , Peptídeos/química , Pressão , Catálise , Reação de Cicloadição , Enzimas/química , Enzimas/metabolismo , Soluções/química , Tioureia/análogos & derivados
4.
Chemosphere ; 238: 124646, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31473523

RESUMO

Humic substances (HS) in the aqueous solutions can be considered as colloidal particles formed by amphiphilic units. HS form micelles-like structures at concentrations close to 5 g/L. However colloidal behavior of HS at concentrations below 100 mg/L is unknown. Using radiotracer assay we have shown that in this concentration range HS form rare adsorption layers at the liquid/liquid interface and penetrate into the organic phase with the distribution ratio close to 10-3. We found that pH and HS molecular weight strongly influence on the distribution ratio but do not significantly change the adsorption. Furthermore, colloidal properties of HS are strongly depending on its origin: the highest surface activity was shown for HS separated from peat and the least was observed for HS separated from soils. We anticipate our assay to be a helpful tool for detailed analysis and modeling HS and humic-like materials colloidal behavior in the environment.


Assuntos
Substâncias Húmicas/análise , Soluções/química , Adsorção , Coloides , Concentração de Íons de Hidrogênio , Micelas , Peso Molecular , Solo , Trítio/análise
5.
Food Chem ; 309: 125659, 2020 Mar 30.
Artigo em Inglês | MEDLINE | ID: mdl-31734005

RESUMO

This research aimed to compare the efficiency of five washing solutions (0.9% NaCl, 0.1% NaHCO3, DI water, 0.001% KMnO4, and 0.1% acetic acid) for removing carbaryl residues from cucumber and chili. The vegetables were soaked in 10 mg/L of carbaryl solution for 30 min and then washed for 30 min in one of the five washing solutions and the results compared. Each experiment was performed in triplicate and the amounts of carbaryl residues remaining were determined using high-performance liquid chromatography (HPLC). The results showed that 0.001% KMnO4 was the most effective at removing carbaryl from both vegetables. Washing with 0.001% KMnO4 reduced carbaryl residues to 64% and 28%, respectively, of the original concentrations. Washing with DI water was the least effective method of removing carbaryl residues. Hopefully, the results will encourage further research, into reducing carbaryl contamination by washing with chemical solutions, which will enable producers to reduce pesticide residues.


Assuntos
Carbaril/análise , Cromatografia Líquida de Alta Pressão , Cucumis sativus/química , Resíduos de Praguicidas/análise , Soluções/química , Ácido Acético/química , Carbaril/isolamento & purificação , Cucumis sativus/metabolismo , Contaminação de Alimentos/análise , Resíduos de Praguicidas/isolamento & purificação , Bicarbonato de Sódio/química , Cloreto de Sódio/química , Água/química
6.
Biophys Chem ; 254: 106265, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31669866

RESUMO

The impact of the differently hydrated non-electrolytes (protein structure destabilizers) on the fibrillation of hen egg white lysozyme (HEWL) was investigated. Two isomeric urea derivatives i.e. butylurea (BU) and N,N,N',N'-tetramethylurea (TMU) were chosen as a tested compounds. The obtained results show that butylurea exerts greater impact on HEWL and its fibrillation than tetramethylurea. Both substances decrease the time of induction of the fibrillation (lag time) but only BU increases the efficiency of amyloidogenesis. For the systems with equivalent reduction of the HEWL stability (250mM BU and 500mM TMU) the not-equivalent increase of the protein fibrillation was recorded (higher for BU). This fact suggests that specific interactions with protein, possibly water mediated, are responsible for the action of the tested substances.


Assuntos
Amiloide/química , Muramidase/química , Água/química , Animais , Galinhas , Dicroísmo Circular , Microscopia de Força Atômica , Muramidase/metabolismo , Estabilidade Proteica , Soluções/química , Ureia/química
7.
Pediatrics ; 144(6)2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31767714

RESUMO

Aluminum has no known biological function; however, it is a contaminant present in most foods and medications. Aluminum is excreted by the renal system, and patients with renal diseases should avoid aluminum-containing medications. Studies demonstrating long-term toxicity from the aluminum content in parenteral nutrition components led the US Food and Drug Administration to implement rules for these solutions. Large-volume ingredients were required to reduce the aluminum concentration, and small-volume components were required to be labeled with the aluminum concentration. Despite these rules, the total aluminum concentration from some components continues to be above the recommended final concentration. The concerns about toxicity from the aluminum present in infant formulas and antiperspirants have not been substantiated but require more research. Aluminum is one of the most effective adjuvants used in vaccines, and a large number of studies have documented minimal adverse effects from this use. Long-term, high-concentration exposure to aluminum has been linked in meta-analyses with the development of Alzheimer disease.


Assuntos
Alumínio/efeitos adversos , Soluções/química , Adjuvantes Farmacêuticos/química , Alumínio/análise , Alumínio/farmacocinética , Doença de Alzheimer , Antiperspirantes/química , Criança , Soluções para Diálise/química , Contaminação de Medicamentos/legislação & jurisprudência , Rotulagem de Medicamentos/legislação & jurisprudência , Regulamentação Governamental , Humanos , Lactente , Fórmulas Infantis/química , Recém-Nascido , Recém-Nascido Prematuro , Rim/metabolismo , Nefropatias/metabolismo , Nutrição Parenteral , Soluções/normas , Estados Unidos , United States Food and Drug Administration , Vacinas/química
8.
Molecules ; 24(20)2019 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-31614514

RESUMO

We apply the formally exact quantum power functional framework (J. Chem. Phys. 2015, 143, 174108) to a one-dimensional Hooke's helium model atom. The physical dynamics are described on the one-body level beyond the density-based adiabatic approximation. We show that gradients of both the microscopic velocity and acceleration field are required to correctly describe the effects due to interparticle interactions. We validate the proposed analytical forms of the superadiabatic force and transport contributions by comparison to one-body data from exact numerical solution of the Schrödinger equation. Superadiabatic contributions beyond the adiabatic approximation are important in the dynamics and they include effective dissipation.


Assuntos
Hélio/química , Teoria Quântica , Soluções/química , Aceleração , Simulação por Computador
9.
Molecules ; 24(20)2019 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-31614645

RESUMO

The effects of hydrogen bonds on the molecular structure of water-tetrahydrofuran (H2O-THF), water-dimethyl sulfoxide (H2O-DMSO), and water-tetrahydrofuran-dimethyl sulfoxide (H2O-THF-DMSO) in binary aqueous solutions and ternary aqueous solutions were studied using Raman spectroscopy. The results indicate that in the binary aqueous solution, the addition of THF and DMSO will generate hydrogen bonds with water molecules, resulting in changes in the peak positions of S=O bonds and C-O bonds. Compared with the binary aqueous solutions, the hydrogen bonds between DMSO and THF, and the hydrogen bonds between DMSO and H2O in the ternary aqueous solutions are competitive, and the hydrogen bond competition is susceptible to water content. In addition, the formation of hydrogen bonds will destroy the fully hydrogen-bonded water and make it change to the partially hydrogen-bonded water. By fitting the spectra into the three Gaussian components assigned to water molecules with different hydrogen bonding (HB) environments, these spectral features are interpreted by a mechanism that H2O in different solution systems has equal types of water molecules with similar HB degrees-fully hydrogen-bonded H2O (FHW) and partially hydrogen-bonded H2O (PHW). The ratio of the intensity transition from FHW to PHW is determined based on Gaussian fitting. Therefore, the variation of hydrogen bond competition can be supplemented by the intensity ratio of PHW/FHW ((IC2 + IC3)/IC1). This study provides an experimental basis for enriching the hydrogen bonding theory of multivariate aqueous solution systems.


Assuntos
Dimetil Sulfóxido/química , Furanos/química , Ligações de Hidrogênio , Água/química , Estrutura Molecular , Soluções/química , Espectroscopia de Infravermelho com Transformada de Fourier , Análise Espectral Raman
10.
Molecules ; 24(20)2019 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-31614943

RESUMO

The adsorption of methyl orange (MO) from aqueous solutions onto a KOH-activated polypyrrole-based adsorbent (PACK) was investigated using batch and fixed-bed column techniques. The structural, thermal, and morphological properties of the PACK, analyzed by various methods, support its applicability as an adsorbent. An adsorption kinetic study revealed a preferably pseudo-second-order (R2 = 0.9996) and rate-limiting step controlled by both film and intra-particle diffusions. The thermodynamic adsorption tests resulted in negative ΔG°, ΔH°, and ΔS° values, which decreased as the temperature and concentration increased, indicating the spontaneous and exothermic adsorption over 25-45 °C. The adsorption isotherms fit the experimental data in the order of Langmuir ≈ Freundlich > Temkin, with evidence of adsorption operating well via the monolayer physical adsorption process, and maximum monolayer adsorption ranging from 520.8 to 497.5 mg/g. The breakthrough curve of the fixed-bed column experiment was modeled using the Thomas, Yoon-Nelson, and Hill models, resulting in an equilibrium capacity of 57.21 mg/g. A 73% MO recovery was achieved, indicating the possibility of column regeneration. Compared to other adsorbents reported, PACK had comparable or even superior capacity toward MO. For cost-effectiveness, similar nitrogen-containing polymeric wastes could be exploited to obtain such excellent materials for various applications.


Assuntos
Compostos Azo/química , Purificação da Água , Água/química , Adsorção , Grafite/química , Cinética , Polímeros/química , Pirróis/química , Soluções/química , Temperatura Ambiente , Termodinâmica
11.
Nat Commun ; 10(1): 4718, 2019 10 17.
Artigo em Inglês | MEDLINE | ID: mdl-31624254

RESUMO

Almost all commercial proteins are purified using ammonium sulfate precipitation. Protein-polymer conjugates are synthesized from pure starting materials, and the struggle to separate conjugates from polymer, native protein, and from isomers has vexed scientists for decades. We have discovered that covalent polymer attachment has a transformational effect on protein solubility in salt solutions. Here, protein-polymer conjugates with a variety of polymers, grafting densities, and polymer lengths are generated using atom transfer radical polymerization. Charged polymers increase conjugate solubility in ammonium sulfate and completely prevent precipitation even at 100% saturation. Atomistic molecular dynamic simulations show the impact is driven by an anti-polyelectrolyte effect from zwitterionic polymers. Uncharged polymers exhibit polymer length-dependent decreased solubility. The differences in salting-out are then used to simply purify mixtures of conjugates and native proteins into single species. Increasing protein solubility in salt solutions through polymer conjugation could lead to many new applications of protein-polymer conjugates.


Assuntos
Polimerização , Polímeros/química , Proteínas/química , Solubilidade , Eletroforese em Gel de Poliacrilamida , Polímeros/metabolismo , Conformação Proteica , Proteínas/metabolismo , Sais , Soluções/química
12.
J Food Sci ; 84(11): 3129-3139, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31599976

RESUMO

Although aluminum lakes are widely used in food industry for dyeing demands, there is still a dearth in the understanding of the colorant lake formation mechanism. In this study, indigo carmine (IC) lake (IC-aluminum hydroxide complex), a frequently used blue lake in the food industry, was investigated in terms of kinetics, isotherms, properties of colloidal particles, infrared (IR) spectra, and titration curves. Pseudo-second-order model presented the strongest correlation with the kinetic data at all pH levels (R2  ≥ 0.994). In pH range from 4 to 7, the colloidal particles of aluminum hydroxide were positively charged with zeta potential around 44 mV; a further pH increase induced to a decreased zeta potential, which reached negative levels at pH 10 and beyond. Diameter maximized at pH 10 (22.47 µm) and declined when the pH was reduced. Isotherm analysis showed that the adsorption followed monolayer adsorption patterns, as described by the Langmuir isotherm model. IR spectra indicated sulfonic acid groups participated in a chemical reaction during adsorption, and the titration assay further confirmed the formation of coordination bonds between sulfonic acid groups and aluminum atoms. This study profiled the reaction responsible for the formation of the blue lake and elucidated its reaction mechanism. Furthermore, the outcome could assist in improving the production efficiency of the lake through achieving higher reaction rate and adsorption capacity. PRACTICAL APPLICATION: The study elucidated the mechanism of indigo carmine (IC)-aluminum hydroxide lake formation, including profile of the adsorption process and molecular interaction between the blue dye and the hydroxide. The outcome of this study would help to improve the production efficiency of IC-aluminum hydroxide lakes, and to decrease the content of aluminum required in the lake by optimizing the production parameters to enhance the adsorption capacity of aluminum hydroxide, which would facilitate the alleviation of the potential health hazards caused by excessive intake of aluminum through foods.


Assuntos
Hidróxido de Alumínio/química , Corantes de Alimentos/química , Indústria Alimentícia/métodos , Índigo Carmim/química , Adsorção , Coloides/química , Concentração de Íons de Hidrogênio , Cinética , Soluções/química , Espectrofotometria Infravermelho
13.
Nucleic Acids Res ; 47(19): 10282-10295, 2019 11 04.
Artigo em Inglês | MEDLINE | ID: mdl-31511899

RESUMO

We perform molecular dynamics simulations, based on recent crystallographic data, on the 8-17 DNAzyme at four states along the reaction pathway to determine the dynamical ensemble for the active state and transition state mimic in solution. A striking finding is the diverse roles played by Na+ and Pb2+ ions in the electrostatically strained active site that impact all four fundamental catalytic strategies, and share commonality with some features recently inferred for naturally occurring hammerhead and pistol ribozymes. The active site Pb2+ ion helps to stabilize in-line nucleophilic attack, provides direct electrostatic transition state stabilization, and facilitates leaving group departure. A conserved guanine residue is positioned to act as the general base, and is assisted by a bridging Na+ ion that tunes the pKa and facilitates in-line fitness. The present work provides insight into how DNA molecules are able to solve the RNA-cleavage problem, and establishes functional relationships between the mechanism of these engineered DNA enzymes with their naturally evolved RNA counterparts. This adds valuable information to our growing body of knowledge on general mechanisms of phosphoryl transfer reactions catalyzed by RNA, proteins and DNA.


Assuntos
Biocatálise , DNA Catalítico/química , RNA Catalítico/genética , Soluções/química , Sequência de Bases , Domínio Catalítico/genética , DNA/química , DNA/genética , DNA Catalítico/genética , Cinética , Chumbo/química , Simulação de Dinâmica Molecular , Conformação de Ácido Nucleico , Clivagem do RNA/genética , Sódio/química
14.
Biophys Chem ; 254: 106260, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31522071

RESUMO

Molecular simulations based on classical force fields are a powerful method for shedding light on the complex behavior of biomolecules in solution. When cosolutes are present in addition to water and biomolecules, subtle balances of weak intermolecular forces have to be accounted for. This imposes high demands on the quality of the underlying force fields, and therefore force field development for small cosolutes is still an active field. Here, we present the development of a new urea force field from studies of urea solutions at ambient and elevated hydrostatic pressures based on a combination of experimental and theoretical approaches. Experimental densities and solvation shell properties from ab initio molecular dynamics simulations at ambient conditions served as the target properties for the force field optimization. Since urea is present in many marine life forms, elevated hydrostatic pressure was rigorously addressed: densities at high pressure were measured by vibrating tube densitometry up to 500 bar and by X-ray absorption up to 5 kbar. Densities were determined by the perturbed-chain statistical associating fluid theory equation of state. Solvation properties were determined by embedded cluster integral equation theory and ab initio molecular dynamics. Our new force field is able to capture the properties of urea solutions at high pressures without further high-pressure adaption, unlike trimethylamine-N-oxide, for which a high-pressure adaption is necessary.


Assuntos
Simulação de Dinâmica Molecular , Ureia/química , Pressão , Soluções/química , Termodinâmica , Água/química
15.
Artigo em Inglês | MEDLINE | ID: mdl-31546761

RESUMO

A lab-scale study on the application of supported liquid membranes (SLM) has been conducted for recovery and selective removal of Malachite Green dye from wastewater. Naturally occurring non-toxic vegetable oils have been used as membrane liquids. Polyvinylidene fluoride (PVDF) films have been used as supports for the liquid membrane. Various parameters affecting the dye permeation such as initial dye concentration, pH, stripping acid concentration, oil viscosity and membrane stability have been investigated. The highest flux value (1.65 × 10-5 mg/cm2/sec) was obtained with a sunflower oil supported membrane at pH 11 in the feed and 0.25 M HCl in the stripping solution. The membrane showed good stability under optimum conditions and maximum transport was achieved in 8 h of permeation time.


Assuntos
Recuperação e Remediação Ambiental/métodos , Membranas Artificiais , Corantes de Rosanilina/química , Soluções/química , Águas Residuárias/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Concentração de Íons de Hidrogênio
16.
J Nutr Sci Vitaminol (Tokyo) ; 65(4): 285-302, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31474678

RESUMO

Recently a new assay method that can quantify the singlet oxygen absorption capacity (SOAC) of antioxidants (AOs) and food extracts was proposed. Singlet oxygen (1O2) quenching rates (kQ) and the relative SOAC values were measured for many carotenoids and phenolic AOs in ethanol/chloroform/D2O (50 : 50 : 1, v/v/v) solution at 35ºC using UV-vis spectrophotometry. It has been clarified that the SOAC method is useful to evaluate the 1O2-quenching activity of lipophilic and hydrophilic AOs having 5 orders of magnitude different rate constants (kQ). Measurements of the kQ and SOAC values were also performed for 39 kinds of food extracts. The results indicate that the SOAC method is useful to evaluate the 1O2-quenching activity of food extracts having two orders of magnitude different kQ values. Further, the kQ values for the reaction of 1O2 with 8 carotenoids and 8 vitamin E homologues were measured in an aqueous Triton X-100 (5.0 wt %) micellar solution (pH 7.4). Results obtained demonstrate that the kQ values of AOs in homogeneous and heterogeneous solutions vary notably depending on (i) polarity (dielectric constant (ε)) of the reaction field between AOs and 1O2, (ii) local concentration of AOs, and (iii) mobility of AOs in solution. Measurements of kQ and SOAC values in a micellar solution may be useful for evaluating the 1O2-quenching activity of AOs in biological systems. Furthermore, measurements of the SOAC values were performed for 32 kinds of food extracts using a microplate reader. The SOAC assay method was validated by inter-laboratory validation study due to 14 laboratories.


Assuntos
Antioxidantes/química , Análise de Alimentos/métodos , Alimentos , Oxigênio Singlete/química , Carotenoides/química , Fenômenos Químicos , Micelas , Fenóis/química , Reprodutibilidade dos Testes , Soluções/química , Espectrofotometria/métodos , Vitamina E/química
17.
J Pharm Biomed Anal ; 175: 112788, 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31382116

RESUMO

During the HPLC related substances testing of pregabalin API, an unknown peak was observed at a level exceeding the identification threshold. Preliminary investigation revealed that this impurity is not a process impurity but rather an artifactual solution degradant or "ghost peak" during the HPLC analysis. By using a strategy that combines LC-PDA/UV-MSn with mechanism-based stress studies, the unknown peak was rapidly identified as a covalent adduct formed between pregabalin and acetonitrile (the latter is a component of the HPLC sample diluent), which is structurally an ethylamidine derivative of pregabalin. It appeared that the formation of this solution degradant was catalyzed by alkaline impurities during the sample preparation. This plausible mechanism was verified by a mechanism-based forced degradation study, in which a base was added into the sample diluent and consequently, the pregabalin-acetonitrile adduct was produced extremely efficiently at a level of ˜92%. Subsequently, the structure of the solution degradant was confirmed as an ethylamidine derivative of pregabalin through characterization by 1D and 2D NMR; the formation of the ethylamidine moiety is apparently via a nucleophilic attack on the cyano group of acetonitrile by the amino group of pregabalin. Due to the extensive presence of primary and secondary amine moieties in drug substances, this kind of artifactual solution degradation would likely occur during the sample preparations of these amine drugs in their HPLC analyses. In a GMP environment, such an event would trigger undesirable out-of-specification (OOS) investigations. The results of this study should help resolve such OOS investigations or prevent their happening from the very beginning. Furthermore, the somewhat surprising finding of the rather facile reaction that produces the ethylamidine moiety using simple alkylnitrile reagents, such as acetonitrile, may be of practical value in the synthesis of alkylamidines.


Assuntos
Acetonitrilos/química , Pregabalina/química , Soluções/química , Aminas/química , Catálise , Química Farmacêutica/métodos , Cromatografia Líquida de Alta Pressão/métodos , Contaminação de Medicamentos , Excipientes/química , Espectroscopia de Ressonância Magnética/métodos
18.
Molecules ; 24(16)2019 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-31412646

RESUMO

Organosilanes (e.g., R'-SiOR3) provide hydrophobic functionality in thin-film coatings, porous gels, and particles. Compared with tetraalkoxysilanes (SiOR4), organosilanes exhibit distinct reaction kinetics and assembly mechanisms arising from steric and electronic properties of the R' group on the silicon atom. Here, the hydrolysis and condensation pathways of n-propyltrimethoxy silane (nPM) and a tri-fluorinated analog of nPM, 3,3,3-trifluoropropyl trimethoxy silane (3F), were investigated under aqueous conditions at pH 1.7, 2.0, 3.0, and 4.0. Prior to hydrolysis, 3F and nPM are insoluble in water and form a lens at the bottom (3F) or top (nPM) of the solutions. This phase separation was employed to follow reaction kinetics using a Turbiscan instrument to monitor hydrolysis through solubilization of the neat silane lens while simultaneously tracking condensation-induced turbidity throughout the bulk solution. Dynamic light scattering confirmed the silane condensation and particle aggregation processes reported by the turbidity scanning. Employing macroscopic phase separation of the starting reactants from the solvent further allows for control over the reaction kinetics, as the interfacial area can be readily controlled by reaction vessel geometry, namely by controlling the surface area to volume. In-situ turbidity scanning and dynamic light scattering revealed distinct reaction kinetics for nPM and 3F, attributable to the electron withdrawing and donating nature of the fluoro- and organo-side chains of 3F and nPM, respectively.


Assuntos
Difusão Dinâmica da Luz , Géis/química , Transição de Fase , Silanos/química , Soluções/química , Fenômenos Químicos , Difusão Dinâmica da Luz/métodos , Concentração de Íons de Hidrogênio , Hidrólise , Interações Hidrofóbicas e Hidrofílicas , Cinética , Nanopartículas/química
19.
Eur J Pharm Biopharm ; 143: 91-97, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31446043

RESUMO

Particle size reduction to sub-micrometer dimensions in stirred media mills is an increasingly common formulation strategy used for improving the bioavailability of poorly aqueous soluble active pharmaceutical ingredients (APIs). Due to their hydrophobic character, the API particles need to be stabilised by a surfactant in order to form a stable nano-suspension. This work is concerned with the understanding of an undesired phenomenon often encountered during the development and scale-up of wet nano-milling processes for hydrophobic APIs - the formation of foams. We investigate the microstructure, rheology and stability of these foams, and find them to be Pickering foams stabilised by solid particles at the gas-liquid interface rather than by a surfactant. By exploring the effect of surfactant concentration on the on-set of foaming in conjunction with the milling kinetics, we find a relationship between the specific surface area of the nano-suspension, the quantity of surfactant present in the formulation and the occurrence of foaming. We propose a mechanistic explanation of foam formation, and find that in order to prevent foaming, a large surfactant excess of approx. 100x above the critical micelle concentration has to be present in the solution in order to ensure a sufficiently rapid coverage of freshly exposed hydrophobic surfaces formed during the wet nano-milling process.


Assuntos
Nanopartículas/química , Disponibilidade Biológica , Interações Hidrofóbicas e Hidrofílicas , Tamanho da Partícula , Soluções/química , Tensoativos/química , Suspensões/química , Tecnologia Farmacêutica/métodos
20.
Chemistry ; 25(61): 13885-13889, 2019 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-31469925

RESUMO

Precipitation reactions under flow in confined media are relevant to the control of pathological biomineralization, processes affecting aquifers, and challenges in the petroleum industry. Here we show that for a simple geometry, such conditions create macroscopic structures including helices, tubes, lamellae, slugs, and disordered patterns. All structures emerge when salt solution is slowly injected into thin capillaries filled with hydroxide solution. For the helices, the pitch is proportional to the pump rate revealing a constant period of 0.63 s. Different morphologies of the insoluble metal hydroxide can co-exist causing random transitions along the capillary. On average, 15 % of the final system contains residual hydroxide solution. While mechanically stable for flow speeds above 25 mm min-1 , structures collapse and sediment for slower injection speeds. Some of the observed features share similarities with precipitate tubes in chemical gardens and the dynamics of liquid-liquid pipe flow.


Assuntos
Precipitação Química , Hidróxido de Sódio/química , Soluções/química , Sulfato de Zinco/química
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