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1.
Phys Chem Chem Phys ; 21(37): 20727-20742, 2019 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-31509121

RESUMO

The left-handed polyproline II (PPII) type helical structures are thought to play a very important role in many essential biological processes, particularly in recognition mechanisms. However, reliable characterisation of PPII conformation in solution can be experimentally challenging. Computational simulation of these structures offers an attractive alternative, but the accuracy of the results is dependent on the accuracy of the force field employed. In this report, we present the results of simulation of the structural and dynamical properties of a proline-rich viral fusion peptide for which a solution NMR study reported a substantial stretch of PPII conformation in the central region. The suggested mode of action of the p15 fusion peptide depended on the exposure of the flanking N-terminal hydrophobic residues to solvent thereby facilitating their interaction with the target membrane. Our simulations with a set of four force field and water model combinations consisting of (AMBER ff99SB*-ILDNP + TIP3P), (OPLS-AA + SPC/E), (AMBER ff03ws + TIP4P/2005 water with scaled protein-water interactions) and (CHARMM36m + TIP3P) showed a general agreement with the NMR results for all the four force field and water model combinations. The central region encompassing positions 9-15 showed a large PPII propensity, reduced flexibility and lower conformational entropy. The PPII conformations were stable and satisfied the Burgi-Dunitz criteria without the participation of any significant water bridging interaction. However, comparison of the experimentally observed chemical shifts with the distribution of shifts predicted from the simulated ensembles showed a much better agreement for the CHARMM36m + TIP3P and AMBER ff03ws + TIP4P/2005 combinations. The models based on these two force fields also generated conformations which were in much better agreement with the NMR model than the much more compact structures predicted by the AMBER ff99SB*-ILDNP and OPLS-AA force fields and predicted a substantially larger solvent accessible surface area in accordance with the suggested mechanism of action of the peptide.


Assuntos
Modelos Moleculares , Prolina/química , Proteínas Recombinantes de Fusão/química , Simulação por Computador , Espectroscopia de Ressonância Magnética , Conformação Molecular , Água/química
2.
Chem Pharm Bull (Tokyo) ; 67(8): 786-794, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31366828

RESUMO

Teriflunomide (TEF, A771726) is the active metabolite of leflunomide (LEF), a disease-modifying anti-rheumatic drug. The main purpose of this study was to develop and evaluate water-in-oil (W/O) microemulsion formulation of TEF. The W/O microemulsion was optimized formula is the physical and chemical stability of lecithin, ethanol, isopropyl myristate (IPM) and water (20.65/20.78/41.52/17.05 w/w) by using the pseudo-ternary phase diagram and the average droplet size is about 40 nm. The permeability of TEF microemulsion is about 6 times higher than control group in vitro penetration test. The results of anti-inflammatory effect showed that compared with the control group, the external TEF microemulsion group could significantly inhibit swelling of paw in rats, and no significant difference compared with oral LEF group. The results of hepatotoxicity test show that there were normal content of alanine aminotransferase (ALT)/aspartate aminotransferase (AST) and no obvious inflammatory infiltration of TEF microemulsion group compared with LEF group. The plasma concentration curve showed that compared with LEF group, the peak concentration of TEF microemulsion group was decreased, the half-life (t1/2) was prolonged, and the relative bioavailability of TEF microemulsion was 75.35%. These results suggest that TEF W/O microemulsion can be used as a promising preparation to play an anti-inflammatory role while significantly reducing hepatotoxicity.


Assuntos
Antirreumáticos/farmacologia , Crotonatos/farmacologia , Sistemas de Liberação de Medicamentos , Edema/tratamento farmacológico , Toluidinas/farmacologia , Animais , Antirreumáticos/química , Crotonatos/química , Composição de Medicamentos , Edema/patologia , Emulsões/síntese química , Emulsões/química , Estrutura Molecular , Óleos/química , Medição da Dor , Ratos , Ratos Sprague-Dawley , Toluidinas/química , Água/química
3.
World J Microbiol Biotechnol ; 35(9): 137, 2019 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-31432268

RESUMO

The presence of very high concentrations of organic pollutants, phenols, tannins and heavy metals mainly chromium in wastewater discharged from leather industries, tags it as one of the most polluting industries. The phenolic syntans discharged from tanning units have an adverse effect on living organisms and cause serious environmental pollution, thereby making it very imperative to remove it. Among various treatment methods available for removal of phenols, biodegradation is environment friendly. The present study aims at the remediation of phenolic syntan used in the leather industry employing individual as well as co-culture of Bacillus cereus and Pseudomonas aeruginosa at varying syntan concentration in the medium. Parameters such as chemical oxygen demand (COD), total organic carbon (TOC), total phenol content (TPC) and Fourier Transform Infrared Spectroscopy (FTIR) indicating biodegradation were analyzed. Promising results were observed with P. aeruginosa, which exhibited a reduction in TPC by 62-72% in all the concentrations of syntan tested just within 12 h of inoculation, whereas about 67 and 83% reduction in COD and TOC respectively was observed for 2000 ppm concentration at the end of 5 days. B. cereus also demonstrated very good reduction in the above parameters however; percentage was less as compared to P. aeruginosa. In the case of co-culture, the TPC reduction was higher than B. cereus but lesser than P. aeruginosa. The percentage reduction in TOC and COD was highest for 500 ppm which eventually decreased for subsequent concentrations.


Assuntos
Bacillus cereus/metabolismo , Resíduos Industriais , Fenóis/metabolismo , Pseudomonas aeruginosa/metabolismo , Poluentes Químicos da Água/metabolismo , Bacillus cereus/crescimento & desenvolvimento , Análise da Demanda Biológica de Oxigênio , Biotransformação , Carbono/análise , Técnicas de Cocultura , Fenóis/análise , Pseudomonas aeruginosa/crescimento & desenvolvimento , Espectroscopia de Infravermelho com Transformada de Fourier , Água/química
4.
Acta Crystallogr C Struct Chem ; 75(Pt 8): 1091-1101, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31380792

RESUMO

A new set of differently hydrated barium and strontium squarates, namely poly[[triaqua(µ-1,2-dioxocyclobut-3-ene-1,2-diolato)barium] monohydrate], {[Ba(C4O4)(H2O)3]·H2O}n (1), poly[[diaqua(µ-1,2-dioxocyclobut-3-ene-1,2-diolato)strontium] monohydrate], {[Sr(C4O4)(H2O)2]·H2O}n (2), and poly[[triaqua(µ-1,2-dioxocyclobut-3-ene-1,2-diolato)barium/strontium(0.85/0.15)] monohydrate], {[Ba0.85Sr0.15(C4O4)(H2O)3]·H2O}n (3), is reported. The study of their crystal structures indicates that all the complexes crystallize in the triclinic space group P-1. Complexes 1 and 3 have a rare combination of squarate units coordinated through monodentate O atoms to two different metal atoms and through two bidentate O atoms to three different metal atoms. Furthermore, they have three coordinated water molecules to give a coordination number of nine. The squarate ligands in complex 2 exhibit two different coordination modes: (i) monodentate O atoms coordinated to four different Sr atoms and (ii) two monodentate O atoms coordinated to two different metal atoms with the other two O atoms bidentate to four different Sr atoms. All the compounds decompose to give the respective carbonates when heated to 800 °C, as evidenced by thermogravimetry/differential thermal analysis (TG-DTA), which are clusters of nanoparticles. Complexes 1 and 3 show additional endothermic peaks at 811 and 820 °C, respectively, indicating the phase transition of BaCO3 from an orthorhombic (α-Pmcn) to a trigonal phase (ß-R3m). All three complexes have significant DNA-binding constants, ranging from 2.45 × 104 to 9.41 × 104 M-1 against EB-CT (ethidium bromide-calf thymus) DNA and protein binding constants ranging from 1.1 × 105 to 8.6 × 105 with bovine serum albumin. The in vitro cytotoxicity of the complexes is indicated by the IC50 values, which range from 128.8 to 261.3 µg ml-1. Complex 3 shows better BSA binding, antioxidant activity against the DPPH radical and cytotoxicity than complexes 1 and 2.


Assuntos
Antineoplásicos/farmacologia , Complexos de Coordenação/farmacologia , Ciclobutanos/farmacologia , Depuradores de Radicais Livres/farmacologia , Substâncias Intercalantes/farmacologia , Animais , Antineoplásicos/síntese química , Antineoplásicos/química , Antineoplásicos/metabolismo , Bário/química , Bovinos , Complexos de Coordenação/síntese química , Complexos de Coordenação/química , Complexos de Coordenação/metabolismo , Cristalografia por Raios X , Ciclobutanos/síntese química , Ciclobutanos/química , Ciclobutanos/metabolismo , DNA/metabolismo , Depuradores de Radicais Livres/síntese química , Depuradores de Radicais Livres/química , Depuradores de Radicais Livres/metabolismo , Humanos , Ligações de Hidrogênio , Substâncias Intercalantes/síntese química , Substâncias Intercalantes/química , Substâncias Intercalantes/metabolismo , Ligantes , Células MCF-7 , Estrutura Molecular , Ligação Proteica , Soroalbumina Bovina/metabolismo , Estrôncio/química , Água/química
5.
Dokl Biochem Biophys ; 486(1): 206-208, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31367822

RESUMO

The aim of this work was to study the fine structure of bacterial films grown on the inner tube surface of a flow reactor. Using the scanning electron microscopy (SEM) approaches, the detailed biofilm relief was visualized. The action of electrochemically reduced water (ERW) on the biofilm ultrastructure generated by the plankton form of E. coli and/or lacto bacteria was investigated. The treatment with an ERW solution destroyed the biofilm organic polymer matrix and bacterial cells embedded in the matrix.


Assuntos
Biofilmes/efeitos dos fármacos , Água/química , Água/farmacologia , Biofilmes/crescimento & desenvolvimento , Eletroquímica , Escherichia coli/efeitos dos fármacos , Escherichia coli/fisiologia
6.
Phys Chem Chem Phys ; 21(35): 19226-19233, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31441492

RESUMO

As one of the main air pollutants, nitrogen oxides (NOx) have serious effects on human health and the environment. In our previous study, we found that Mn-MOF-74 shows excellent catalytic performance for the selective catalytic reduction (SCR) reaction with NH3 being the reductant (NH3-SCR) at low temperature. To obtain a further understanding of the NH3-SCR mechanism in Mn-MOF-74, in this paper, we investigated two important parts of the NH3-SCR process in Mn-MOF-74 using the density functional theory (DFT) method. On the one hand, the structural characteristics of two types of oxygen vacancies of Mn-MOF-74, namely carboxyl oxygen vacancies and hydroxyl oxygen vacancies, and their adsorption properties to reaction species were calculated. It was found that the oxygen vacancies not only activate the reaction species, but also promote the desorption of NO2 molecules from metal sites for the subsequent rapid SCR reactions. On the other hand, we studied the effect of H2O on the structural stability and catalytic performance of Mn-MOF-74. It was found that the interaction of Mn-O bonds was weakened by H2O. Therefore, the influence of H2O should be considered for the future design of MOF-based catalysts for the SCR process.


Assuntos
Teoria da Densidade Funcional , Estruturas Metalorgânicas/química , Oxigênio/química , Água/química , Poluentes Atmosféricos/química , Poluentes Atmosféricos/isolamento & purificação , Catálise , Óxidos de Nitrogênio/química , Óxidos de Nitrogênio/isolamento & purificação , Substâncias Redutoras/química
7.
Phys Chem Chem Phys ; 21(35): 19298-19310, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31451813

RESUMO

The ice/water interface recognition mechanism of antifreeze proteins (AFPs) is highly contentious. Conventionally, protein adsorption on a solid surface is primarily driven by the polar interactions between the hydrophilic residues of the protein and interfacial water of the solid surface. Ice surface recognition by a type III AFP is surprising in this context where the ice binding surface (IBS) is hydrophobic. The present study provides molecular insight into the unusual interface recognition phenomenon of a type III AFP (QAE isoform) from Macrozoarces americanus. Potential of mean force calculations show that the type III AFP adsorbs on the ice surface mediated through a layer of ordered water. Molecular dynamics simulations at lower than ambient temperature reveal that the flat hydrophobic IBS induces ordering of water. The excellent geometrical synergy between the hydration water structure around the IBS and water arrangements on the pyramidal surface favours adsorption on the pyramidal plane. Mutations that interrupt the hydration shell water ordering essentially lead to less efficient adsorption, which greatly reduces the anti-freezing activity of the AFP. Binding free energy calculations of the wild-type and several mutant AFPs reveal that the binding affinity is linearly correlated with the experimentally observed thermal hysteresis activity. Therefore, binding to a specific ice plane with considerable affinity is the dictating factor of the anti-freeze activity for a type III AFP. Mechanistic insights into the ice binding process of the wild-type and different mutant AFPs obtained from this study pave the way for rational design of type III variants with much improved activity, which possesses ample industrial applicability, particularly in cryo-preservation.


Assuntos
Proteínas Anticongelantes/química , Proteínas de Peixes/química , Gelo , Perciformes , Água/química , Animais , Proteínas Anticongelantes/genética , Temperatura Baixa , Proteínas de Peixes/genética , Proteínas de Peixes/metabolismo , Simulação de Dinâmica Molecular , Mutação , Ligação Proteica
8.
Phys Chem Chem Phys ; 21(35): 19469-19479, 2019 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-31461098

RESUMO

Using all-atom molecular dynamics simulations of aqueous solutions of the globular protein SNase, the dynamic behavior of water molecules and cosolvents (trimethylamine-N-oxide (TMAO) and urea) in the hydration shell of the protein was studied for different solvent compositions. TMAO is a potent protein-stabilizing osmolyte, whereas urea is known to destabilize proteins. For molecules that are initially located in successive narrow layers at a given distance from the protein, the mean displacements and the distribution of displacements for short time intervals are calculated. For molecules that are initially located in solvation shells of a given thickness around the protein, the characteristic residence times in these shells are determined to characterize the dynamic behavior of the solvent molecules as a function of the distance to the protein. A combined consideration of these characteristics allows to reveal additional features of the dynamics of the cosolvents. It is shown that TMAO molecules leave the nearest vicinity of the protein faster than urea molecules, despite the fact that the mobility of TMAO molecules, measured by their mean displacements, is lower than that of urea. Moreover, we show that the rate of release of TMAO molecules from the hydration shell is lower in ternary (TMAO + urea + H2O) solvent mixtures than in the binary ones. This is consistent with a recent observation that the fraction of TMAO near the protein decreases in the presence of urea. From the analysis of the decay of the number of particles initially located in the region of the first peak of the distribution function of solvent molecules around the protein, we estimated that about 20 water molecules and 6-7 urea molecules stay near the protein for more than 1000 ps.


Assuntos
Endodesoxirribonucleases/química , Endodesoxirribonucleases/metabolismo , Metilaminas/química , Simulação de Dinâmica Molecular , Ureia/química , Água/química , Estabilidade Proteica , Solventes/química
9.
Chem Biol Interact ; 311: 108788, 2019 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-31401088

RESUMO

Aqueous solutions of chlorpyrifos oxon are used to study the ability of chlorpyrifos oxon to catalyze protein crosslinking. Assays for protein crosslinking can avoid artifacts by using information on the stability of chlorpyrifos oxon in solution. We undertook to determine the half-life of chlorpyrifos oxon in aqueous solution because literature values do not exist. The rate of conversion of chlorpyrifos oxon to 3,5,6-trichloro-2-pyridinol was measured at 23 °C in 20 mM TrisCl pH 8 and pH 9 by recording loss of absorbance at 290 nm for chlorpyrifos oxon and increase in absorbance at 320 nm for 3,5,6-trichloro-2-pyridinol. The half-life of chlorpyrifos oxon was 20.9 days at pH 8 and 6.7 days at pH 9. Literature reports for the stability of other organophosphorus toxicants were summarized because our current studies suggest that other organophosphorus toxicants are also crosslinking agents.


Assuntos
Clorpirifos/análogos & derivados , Ésteres/química , Organofosfatos/química , Água/química , Butirilcolinesterase/química , Butirilcolinesterase/metabolismo , Clorpirifos/química , Clorpirifos/metabolismo , Meia-Vida , Humanos , Concentração de Íons de Hidrogênio , Hidrólise , Organofosfatos/metabolismo , Hidróxido de Sódio/química , Espectrofotometria
10.
Int J Nanomedicine ; 14: 4975-4989, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31371942

RESUMO

The porous surface of a polyetheretherketone (PK)-nanoporous lithium-doped magnesium silicate (NLS) blend (PKNLS) was fabricated on a PK surface by layer-by-layer pressuring, sintering, and salt-leaching. As controls, porous surfaces of a PK/lithium-doped magnesium silicate blend (PKLS) and PK were fabricated using the same method. The results revealed that porosity, water absorption, and protein absorption of the porous surface of PKNLS containing macropores and nanopores were obviously enhanced compared to PKLS and PK containing macropores without nanopores. In addition, PKNLS, with both macroporostiy and nanoporosity, displayed the highest ability of apatite mineralization in simulated body liquid, indicating excellent bioactivity. In vitro responses (including adhesion, proliferation, and differentiation) of MC3T3E1 cells to PKNLS were significantly enhanced compared to PKLS and PK. In vivo implantation results showed that new bone grew into the macroporous surface of PKNLS, and the amount of new bone for PKNLS was the highest. In short, PKNLS integration with PK significantly promoted cells/bone-tissue responses and exhibited excellent osteogenesis in vivo, which might have great potential for bone repair.


Assuntos
Osso e Ossos/fisiologia , Cetonas/farmacologia , Lítio/farmacologia , Silicatos de Magnésio/farmacologia , Nanoporos , Osteoblastos/citologia , Polietilenoglicóis/farmacologia , Adsorção , Fosfatase Alcalina/metabolismo , Animais , Apatitas/química , Osso e Ossos/efeitos dos fármacos , Diferenciação Celular/efeitos dos fármacos , Linhagem Celular , Proliferação de Células/efeitos dos fármacos , Imagem Tridimensional , Masculino , Camundongos , Nanoporos/ultraestrutura , Osteoblastos/efeitos dos fármacos , Osteoblastos/ultraestrutura , Osteogênese/efeitos dos fármacos , Porosidade , Coelhos , Água/química , Difração de Raios X
11.
J Agric Food Chem ; 67(35): 9926-9933, 2019 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-31398027

RESUMO

Vitamins and flavonoids are two kinds of essential trace bioactives which are prone to photodegradation during food processing and storage. In this study, a particle-stabilized water-in-water (W/W) emulsion system composed of soy protein isolate (SPI) and guar gum (GG) was applied in loading riboflavin. Based on the significant binding affinity differences of SPI (Ka = 1.11 × 105 L mol-1) and GG (Ka = 9.00 × 103 L mol-1) to riboflavin, this hydrophilic and light-sensitive bioactive compound was loaded in SPI-rich droplets. Confocal images indicated that a stable microstructure of SPI-rich droplets suspended in GG-rich continuous phase was successfully constructed by manipulating the proportion of the two polymeric components and using zein-based particles (ZPs) as stabilizers. These negatively charged particles modified by pectin with a hydrodynamic diameter of 533 ± 5.7 nm were able to adsorb at the SPI/GG interface and subsequently stabilized the SPI-in-GG emulsion. Fluorescence spectra of riboflavin suggested that the formation of such W/W emulsion could effectively delay the photodegradation of riboflavin during an 8 h ultraviolet irradiation, and its color was maintained to a maximum extent. Therefore, this structured W/W emulsion could be a desired architecture for delivering light-sensitive cargo.


Assuntos
Riboflavina/química , Água/química , Zeína/química , Composição de Medicamentos , Emulsões/química , Excipientes/química , Galactanos/química , Interações Hidrofóbicas e Hidrofílicas , Cinética , Mananas/química , Tamanho da Partícula , Fotólise , Gomas Vegetais/química
12.
Chem Commun (Camb) ; 55(66): 9797-9800, 2019 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-31360962

RESUMO

Molecular tubes with hydrogen bonding donors in their deep hydrophobic cavities are able to selectively bind organophosphorus compounds in water through hydrogen bonding and the hydrophobic effect. They can also be used as a fluorescent sensor for nerve agent simulants and as an inhibitor to reduce the toxicity of paraoxon to acetylcholinesterase.


Assuntos
Acetilcolinesterase/efeitos dos fármacos , Inibidores da Colinesterase/química , Inibidores da Colinesterase/toxicidade , Agentes Neurotóxicos/química , Agentes Neurotóxicos/toxicidade , Paraoxon/química , Paraoxon/toxicidade , Calorimetria , Corantes Fluorescentes/química , Ligações de Hidrogênio , Interações Hidrofóbicas e Hidrofílicas , Espectroscopia de Ressonância Magnética/métodos , Termodinâmica , Água/química
13.
J Chem Theory Comput ; 15(8): 4344-4350, 2019 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-31318548

RESUMO

Uracil DNA glycosylase catalyzes the N-glycosidic bond cleavage of uracil, thereby initiating the base excision repair mechanism for this DNA lesion. Here we employ hybrid quantum mechanics/molecular mechanics calculations to investigate the exact mechanism of the nucleophile attack and the role of the conserved His148 residue. Our calculations suggest that the C1'-N1 bond dissociation proceeds by a migration of the electrophilic sugar in the direction of the water nucleophile, resulting in a planar, oxocarbenium-like transition state. The subsequent nucleophile addition and proton transfer to a nearby base occur without a barrier. We assign the role of a proton acceptor to His148 and elucidate why mutations of this residue curtail the enzymatic activity but do not fully suppress it.


Assuntos
Histidina/química , Uracila-DNA Glicosidase/química , Ácido Aspártico/química , Ácido Aspártico/metabolismo , Histidina/metabolismo , Humanos , Modelos Moleculares , Prótons , Teoria Quântica , Termodinâmica , Uracila-DNA Glicosidase/metabolismo , Água/química
14.
Plant Foods Hum Nutr ; 74(3): 391-398, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31256321

RESUMO

A maize milling by-product was defatted by aqueous extraction and the residue was dehydrated, comminuted and sieved to obtain two powders differing in particle size and having a very high fibre content. The powders were then incorporated into the structure of short-dough biscuit, at two wheat flour substitution levels (10 and 20%), aiming at the development of a nutritionally improved product. Their impact on biscuit dough properties and the quality and sensory characteristics of the final products was evaluated. As it was revealed, powders' addition altered dough consistency and alveograph indices mainly due to interactions between wheat flour proteins and polysaccharides and enhanced the nutritional profile of the biscuits by inducing a 4- to 6-fold increase of their fibre content. Additionally, it influenced only to a limited extent the degree of some of the final product characteristics, e.g., protein and fat content, spread ratio, breaking strength, depending both on the level of incorporation and the particle size of the residue. On the whole, products' sensory quality was not negatively influenced, suggesting that it is possible to use both powders for the fortification with fibre of biscuits and possibly other bakery products.


Assuntos
Fibras na Dieta/análise , Alimentos Fortificados , Triticum/química , Zea mays/química , Pão/análise , Farinha/análise , Pós , Paladar , Água/química
15.
J Chem Phys ; 151(1): 015101, 2019 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-31272172

RESUMO

We use extended depolarized light scattering spectroscopy to study the dynamics of water in a lysozyme-trehalose aqueous solution over a broad time scale, from hundreds to fractions of picoseconds. We provide experimental evidence that the sugar, present in the ternary solution in quantity relevant for biopreservation, strongly modifies the solvation properties of the protein. By comparing aqueous solutions of lysozyme with and without trehalose, we show that the combined action of sugar and protein produces an exceptional dynamic slowdown of a fraction of water molecules around the protein, which become more than twice slower than in the absence of trehalose. We speculate that this ultraslow water may be caged between the sugar and protein surface, consistently with a water entrapment scenario. We also demonstrate that the dynamics of these water molecules gets slower and slower upon cooling. On the basis of these findings, we believe such ultraslow water close to the lysozyme is likely to be involved in the mechanism of bioprotection.


Assuntos
Luz , Muramidase/química , Espalhamento de Radiação , Análise Espectral/métodos , Trealose/química , Água/química
16.
Phys Chem Chem Phys ; 21(28): 15576-15583, 2019 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-31267115

RESUMO

In glass-forming substances, the addition of water tends to produce the effect of lowering the glass transition temperature, Tg. In a previous work by some of us (Ruiz et al., Sci. Rep., 2017, 7, 7470) we reported on a rare anti-plasticizing effect of water on the molecular dynamics of a simple molecular system, the pharmaceutically active prilocaine molecule, for which the addition of water leads to an increase of Tg. In the present work, we study pure and hydrated prilocaine confined in 0.5 nm and 1 nm pore size molecular sieves, and carry out a comparison with the bulk compounds in order to gain a better understanding of the microscopic mechanisms that result in this rare effect. We find that the Tg of the drug under nanometric confinement can be lower than the bulk value by as much as 17 K. Through the concurrent use of differential scanning calorimetry and broadband dielectric spectroscopy we are able to observe the antiplasticizing effect of water in prilocaine also under nanometric confinement, finding an increase of Tg of up to almost 6 K upon hydration. The extension of our analysis to nanoconfined systems provides a plausible explanation for the very uncommon antiplasticizing effect, based on the formation of water-prilocaine molecular complexes. Moreover, this study deepens the understanding of the behavior of drugs under confinement, which is of relevance not only from a fundamental point of view, but also for practical applications such as drug delivery.


Assuntos
Simulação de Dinâmica Molecular , Prilocaína/química , Água/química , Nanoestruturas
17.
J Agric Food Chem ; 67(33): 9325-9334, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31318196

RESUMO

In vitro dynamic aroma release over oil-in-water (o/w) and water-in-oil-in-water (w/o/w) emulsions stabilized with Tween 20 or octenyl succinic anhydride (OSA) starch as a hydrophilic emulsifier and polyglycerol polyricinoleate (PGPR) as a hydrophobic emulsifier was investigated. The equal-molecular-weight hydrophilic aroma diacetyl (2,3-butanedione) or relatively more-hydrophobic 3-pentanone was added to the emulsions prepared by high speed mixing, or membrane emulsification followed by thickened with xanthan gum removing droplet size distribution and creaming as variables affecting dynamic release. Results showed the differences of w/o/w emulsions in the dynamic release compared to o/w emulsions mainly depended on aroma hydrophobicity, emulsion type, emulsifier-aroma interactions, and creaming. Xanthan led to a reduced headspace replenishment. Interfacially adsorbed OSA starch and xanthan-OSA starch interaction influenced on diacetyl release over emulsions. OSA starch alone interacted with 3-pentanone. This study demonstrates the potential impact of emulsifying and thickening systems on aroma release systems and highlights that specific interactions may compromise product quality.


Assuntos
Emulsificantes/química , Odorantes/análise , Amido/química , Emulsões/química , Glicerol/análogos & derivados , Glicerol/química , Interações Hidrofóbicas e Hidrofílicas , Polissacarídeos Bacterianos/química , Polissorbatos/química , Ácidos Ricinoleicos/química , Anidridos Succínicos/química , Água/química
18.
J Phys Chem A ; 123(28): 5995-6002, 2019 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-31268326

RESUMO

High-resolution X-ray crystallography and two-dimensional NMR studies demonstrate that water-mediated conventional hydrogen-bonding interactions (N-H···N, O-H···N, etc.) bridging two or more amino acid residues contribute to the stability of proteins and protein-ligand complexes. In this work, we have investigated single water-mediated selenium hydrogen-bonding interactions (unconventional hydrogen-bonding) between amino acid residues in proteins through extensive protein data bank (PDB) analysis coupled with gas-phase spectroscopy and quantum chemical calculation of a model complex consisting of indole, dimethyl selenide, and water. Here, indole and dimethyl selenide represent the amino acid residues tryptophan and selenomethionine, respectively. The current investigation demonstrates that the most stable structure of the model complex observed in the IR spectroscopy mimics single water-mediated selenium hydrogen-bonded structural motifs present in the crystal structures of proteins. The present work establishes that water-mediated Se hydrogen-bonding interactions are ubiquitous in proteins and the number of these interactions observed in the PDB is more than that of direct Se hydrogen-bonds present there.


Assuntos
Proteínas/química , Selênio/química , Água/química , Biologia Computacional , Cristalografia por Raios X , Bases de Dados de Proteínas , Ligações de Hidrogênio , Indóis/química , Ligantes , Modelos Moleculares , Compostos Organosselênicos/química , Teoria Quântica , Selenometionina/química , Espectrofotometria Infravermelho , Triptofano/química
19.
J Chem Phys ; 151(3): 034504, 2019 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-31325935

RESUMO

Although by now the glass transition temperature of uncrystallized bulk water is generally accepted to manifest at temperature Tg near 136 K, not much known are the spectral dispersion of the structural α-relaxation and the temperature dependence of its relaxation time τα,bulk(T). Whether bulk water has the supposedly ubiquitous Johari-Goldstein (JG) ß-relaxation is a question that has not been answered. By studying the structural α-relaxation over a wide range of temperatures in several aqueous mixtures without crystallization and with glass transition temperatures Tg close to 136 K, we deduce the properties of the α-relaxation and the temperature dependence of τα,bulk(T) of bulk water. The frequency dispersion of the α-relaxation is narrow, indicating that it is weakly cooperative. A single Vogel-Fulcher-Tammann (VFT) temperature dependence can describe the data of τα,bulk(T) at low temperatures as well as at high temperatures from neutron scattering and GHz-THz dielectric relaxation, and hence, there is no fragile to strong transition. The Tg-scaled VFT temperature dependence of τα,bulk(T) has a small fragility index m less than 44, indicating that water is a "strong" glass-former. The existence of the JG ß-relaxation in bulk water is supported by its equivalent relaxation observed in water confined in spaces with lengths of nanometer scale and having Arrhenius T-dependence of its relaxation times τconf(T). The equivalence is justified by the drastic reduction of cooperativity of the α-relaxation in nanoconfinement and rendering it to become the JG ß-relaxation. Thus, the τconf(T) from experiments can be taken as τß,bulk(T), the JG ß-relaxation time of bulk water. The ratio τα,bulk(Tg)/τß,bulk(Tg) is smaller than most glass-formers, and it corresponds to the Kohlrausch α-correlation function, exp[-(t/τα,bulk)1-n], having (1-n) = 0.90. The dielectric data of many aqueous mixtures and hydrated biomolecules with Tg higher than that of water show the presence of a secondary ν-relaxation from the water component. The ν-relaxation is strongly connected to the α-relaxation in properties, and hence, it belongs to the special class of secondary relaxations in glass-forming systems. Typically, its relaxation time τν(T) is longer than τß,bulk(T), but τν(T) becomes about the same as τß,bulk(T) at sufficiently high water content. However, τν(T) does not become shorter than τß,bulk(T). Thus, τß,bulk(T) is the lower bound of τν(T) for all aqueous mixtures and hydrated biomolecules. Moreover, it is τß,bulk(T) but not τα(T) that is responsible for the dynamic transition of hydrated globular proteins.


Assuntos
Biopolímeros/química , Modelos Químicos , Água/química , Animais , Dissacarídeos/química , Glicogênio/química , Monossacarídeos/química , Mytilus/química , Polissacarídeos/química , Ribonuclease Pancreático/química , Termodinâmica
20.
J Agric Food Chem ; 67(29): 8197-8204, 2019 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-31287317

RESUMO

Potato pectin contains some proteinaceous components and exhibits emulsifying and emulsion stabilizing abilities. The objective of this study was to elucidate the effect of the pectin moiety of the pectin-protein conjugate present in pectic extracts from potato tubers on their interfacial properties. Potato pectin was extracted from highly purified cell wall materials to avoid the contamination of unconjugated proteins. The abilities of the potato pectin to adsorb to graphite surfaces and to resist surfactant-induced competitive displacement from the air-water interface were investigated using atomic force microscopy. The pectin moiety of the potato pectin was capable of adsorbing to graphite surfaces even after alkali treatment. Furthermore, the potato pectin exhibited enhanced resistance to surfactant-induced competitive displacement from the interface as a result of the formation of network structures of self-assembled pectin moieties at the interface. The present results suggest the importance of the pectin moiety with regard to the interfacial properties of potato pectin.


Assuntos
Pectinas/química , Extratos Vegetais/química , Proteínas de Plantas/química , Solanum tuberosum/química , Tensoativos/química , Ar/análise , Tubérculos/química , Água/química
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