Impact of Whey Protein Corona Formation around TiO2 Nanoparticles on Their Physiochemical Properties and Gastrointestinal Fate.

Previously, we found that whey proteins form biomolecular coronas around titanium dioxide (TiO2) nanoparticles. Here, the gastrointestinal fate of whey protein-coated TiO2 nanoparticles and their interactions with gut microbiota were investigated. The antioxidant activity of protein-coated nanoparticles was enhanced after simulated digestion. The structure of the whey proteins was changed after they adsorbed to the surfaces of the TiO2 nanoparticles, which reduced their hydrolysis under simulated gastrointestinal conditions. The presence of protein coronas also regulated the impact of the TiO2 nanoparticles on colonic fermentation, including promoting the production of short-chain fatty acids. Bare TiO2 nanoparticles significantly increased the proportion of harmful bacteria and decreased the proportion of beneficial bacteria, but the presence of protein coronas alleviated this effect. In particular, the proportion of beneficial bacteria, such as Bacteroides and Bifidobacterium, was enhanced for the coated nanoparticles. Our results suggest that the formation of a whey protein corona around TiO2 nanoparticles may have beneficial effects on their behavior within the colon. This study provides valuable new insights into the potential impact of protein coronas on the gastrointestinal fate of inorganic nanoparticles.

Enhancing polyol/sugar cascade oxidation to formic acid with defect rich MnO2 catalysts.

Oxidation of renewable polyol/sugar into formic acid using molecular O2 over heterogeneous catalysts is still challenging due to the insufficient activation of both O2 and organic substrates on coordination-saturated metal oxides. In this study, we develop a defective MnO2 catalyst through a coordination number reduction strategy to enhance the aerobic oxidation of various polyols/sugars to formic acid. Compared to common MnO2, the tri-coordinated Mn in the defective MnO2 catalyst displays the electronic reconstruction of surface oxygen charge state and rich surface oxygen vacancies. These oxygen vacancies create more Mnδ+ Lewis acid site together with nearby oxygen as Lewis base sites. This combined structure behaves much like Frustrated Lewis pairs, serving to facilitate the activation of O2, as well as C-C and C-H bonds. As a result, the defective MnO2 catalyst shows high catalytic activity (turnover frequency: 113.5 h-1) and formic acid yield (>80%) comparable to noble metal catalysts for glycerol oxidation. The catalytic system is further extended to the oxidation of other polyols/sugars to formic acid with excellent catalytic performance.

Impact of pH on the Formation and Properties of Whey Protein Coronas around TiO2 Nanoparticles.

In aqueous media, titanium dioxide (TiO2) nanoparticles can interact with proteins in their environment and form a protein corona. The pH of the aqueous media affects the structure and properties of the protein corona, and currently there is a lack of understanding of the effects of pH on the characteristics of protein coronas. In this study, we examined the impact of pH (2-11) on the structural and physicochemical properties of whey protein coronas formed around TiO2 nanoparticles. The pH of the solution influenced the structure of whey protein molecules, especially around their isoelectric point. Thermogravimetric and quartz crystal microbalance analyses showed that the adsorption capacity of the whey proteins was the largest at their isoelectric points and the lowest under highly acidic or alkaline conditions. The majority of the proteins were tightly bound to the nanoparticle surfaces, forming a hard corona. The influence of solution pH on protein corona properties was mainly attributed to its impact on the electrostatic forces in the system, which impacted the protein conformation and interactions. This study provides useful insights into the influence of pH on the formation and properties of protein coronas around inorganic nanoparticles, which may be important for understanding the gastrointestinal and environmental fates.

A review of recent strategies to improve the physical stability of phycocyanin.

There is an increasing demand for more healthy and sustainable diets, which led to an interest in replacing synthetic colors with natural plant-based ones. Phycocyanin, which is commonly extracted from Spirulina platensis, has been explored as a natural blue pigment for application in the food industry. It is also used as a nutraceutical in food, cosmetic, and pharmaceutical products because of its potentially beneficial biological properties, such as radical scavenging, immune modulating, and lipid peroxidase activities. The biggest challenges to the widespread application of phycocyanin for this purpose are its high sensitivity to chemical degradation when exposed to heat, light, acids, high pressure, heavy metal cations, and denaturants. Consequently, it is of considerable importance to improve its chemical stability, which requires a thorough knowledge of the relationship between the structure, environment, and chemical reactivity of phycocyanin. To increase the application of this natural pigment and nutraceutical within foods and other products, the structure, biological activities, and factors affecting its stability are reviewed, as well as strategies that have been developed to improve its stability. The information contained in this article is intended to stimulate further studies on the development of effective strategies to improve phycocyanin stability and performance.

Impact of Heat Treatment on the Structure and Properties of the Plant Protein Corona Formed around TiO2 Nanoparticles.

Titanium dioxide (TiO2) nanoparticles are utilized within the food industry as an additive to alter food brightness and whiteness. Amphiphilic food ingredients, like proteins, can adsorb on to the surfaces of TiO2 nanoparticles and form protein coronas that could alter their gastrointestinal fate. At present, our understanding of the factors influencing the formation and properties of protein coronas was limited. In this study, we explored the influence of thermal treatments of proteins on the physicochemical properties of protein coronas formed on TiO2 nanoparticles. Four plant proteins (glutenin, soy protein isolate, gliadin, and zein) were heat-treated at different temperatures for 30 min. Heat treatment (100 °C) disrupted the structure of the original proteins and changed the structure properties of the protein and formed coronas. Quartz crystal microbalance with dissipation results showed that for the heat-sensitive proteins, such as glutenin, a high temperature treatment (100 °C) weakened the binding affinity between the protein and the nanoparticle surfaces. In contrast, for more heat-resistant proteins, such as gliadin, a high-temperature treatment had much less effect. In summary, this study showed that the structural properties of plant proteins affected by heat were an important factor affecting the formation of protein coronas on food nanoparticles.

Investigation on Adsorption and Separation Behavior of Propane/Propene Mixtures in Zeolites.

Propane/propene separation is among the most energy-intensive separation processes in the petrochemical industry. Separation based on adsorption on a nanoporous material (e.g., zeolites) has spawned new ideas for this process. Therefore, we conducted grand canonical ensemble Monte Carlo simulations to investigate the adsorption and separation of propane and propene in one-dimensional (ATS, MOR, and AWO), two-dimensional (MWW, FER, and BOG) and three-dimensional (MFI, BEA, FAU) zeolites. The computation of pure components indicates that the adsorption capacity is affected by the zeolite pore diameter, dimensionality, and isosteric heat. For a given diameter, three dimensional zeolites exhibit better adsorption properties than two or one-dimensional zeolites. Zeolites with diameters ranging from 4.8 Å to 5.4 Å show high propane and propene affinity. In binary mixture simulations, the separation capacity of propane and propene increases with elevated pressure and decreased temperature. Among these zeolites, AWO exhibits the best separation performance due to its eight-ring window channel, which is consistent with experimental results. Thus, our results provide better understanding on propane and propene adsorption and separation in different zeolites, as well as insight into how production conditions could be upgraded.

Adsorption and separation of n/iso-pentane on zeolites: A GCMC study.

Separation of branched chain hydrocarbons and straight chain hydrocarbons is very important in the isomerization process. Grand canonical ensemble Monte Carlo simulations were used to investigate the adsorption and separation of iso-pentane and n-pentane in four types of zeolites: MWW, BOG, MFI, and LTA. The computation of the pure components indicates that the adsorption capacity is affected by physical properties of zeolite, like pore size and structures, and isosteric heat. In BOG, MFI and LTA, the amount of adsorption of n-pentane is higher than iso-pentane, while the phenomenon is contrary in MWW. For a given zeolite, a stronger adsorption heat corresponds to a higher loading. In the binary mixture simulations, the separation capacity of n-and iso-pentane increases with the elevated pressure and the increasing iso-pentane composition. The adsorption mechanism and competition process have been examined. Preferential adsorption contributions prevail at low pressure, however, the size effect becomes important with the increasing pressure, and the relatively smaller n-pentane gradually competes successfully in binary adsorption. Among these zeolites, MFI has the best separation performance due to its high shape selectivity. This work helps to better understand the adsorption and separation performance of n- and iso-pentane in different zeolites and explain the relationship between zeolite structures and adsorption performance.

Multifunctional two-stage riser fluid catalytic cracking process.

This paper described the discovering process of some shortcomings of the conventional fluid catalytic cracking (FCC) process and the proposed two-stage riser (TSR) FCC process for decreasing dry gas and coke yields and increasing light oil yield, which has been successfully applied in 12 industrial units. Furthermore, the multifunctional two-stage riser (MFT) FCC process proposed on the basis of the TSR FCC process was described, which were carried out by the optimization of reaction conditions for fresh feedstock and cycle oil catalytic cracking, respectively, by the coupling of cycle oil cracking and light FCC naphtha upgrading processes in the second-stage riser, and the specially designed reactor for further reducing the olefin content of gasoline. The pilot test showed that it can further improve the product quality, increase the diesel yield, and enhance the conversion of heavy oil.

Short peptide-directed synthesis of one-dimensional platinum nanostructures with controllable morphologies.

Although one dimensional (1D) Pt nanostructures with well-defined sizes and shapes have fascinating physiochemical properties, their preparation remains a great challenge. Here we report an easy and novel synthesis of 1D Pt nanostructures with controllable morphologies, through the combination of designer self-assembling I3K and phage-displayed P7A peptides. The nanofibrils formed via I3K self-assembly acted as template. Pt precursors ((PtCl4)(2-) and (PtCl6)(2-)) were immobilized by electrostatic interaction on the positively charged template surface and subsequent reduction led to the formation of 1D Pt nanostructures. P7A was applied to tune the continuity of the Pt nanostructures. Here, the electrostatic repulsion between the deprotonated C-terminal carboxyl groups of P7A molecules was demonstrated to play a key role. We finally showed that continuous and ordered 1D Pt morphology had a significantly improved electrochemical performance for the hydrogen and methanol electro-oxidation in comparison with either 1D discrete Pt nanoparticle assemblies or isolated Pt nanoparticles.

Theoretical analysis of the conversion mechanism of acetylene to ethylidyne on Pt(111).

The conversion of acetylene to ethylidyne on Pt(111) has been comprehensively investigated using self-consistent periodic density functional theory. Geometries and energies for all of the intermediates involved as well as the conversion mechanism were analyzed. On Pt(111), the carbon atoms in the majority of stable C(2)H(x) (x = 1-4) intermediates prefer saturated sp(3) configurations with the missing H atoms substituted by the adjacent metal atoms. The most favorable conversion pathway for acetylene to ethylidyne is via a three-step reaction mechanism, acetylene → vinyl → vinylidene → ethylidyne. The first step, acetylene → vinyl, depends on the availability of surface H atoms: without preadsorbed H the reaction occurs via the initial disproportionation of acetylene, which resulted in adsorbed vinyl; with an abundance of preadsorbed H, acetylene could transform to vinyl via both the disproportionation and hydrogenation reactions. Conversions through initial dehydrogenation of acetylene and isomerizations of acetylene and vinyl are unfavorable due to high energy barriers along the relevant pathways. The conversion rate involving vinylidene as an intermediate is at least 100 times larger than that involving ethylidene.

Initial hydrogenations of pyridine on MoP(001): a density functional study.

The initial hydrogenations of pyridine on MoP(001) with various hydrogen species are studied using self-consistent periodic density functional theory (DFT). The possible surface hydrogen species are examined by studying interaction of H(2) and H(2)S with the surface, and the results suggest that the rational hydrogen source for pyridine hydrogenations should be surface hydrogen atoms, followed by adsorbed H(2)S and SH. On MoP(001), pyridine has two types of adsorption modes, i.e., side-on and end-on; and the most stable η(5)(N,C(α),C(ß),C(ß),C(α)) configuration of the side-on mode facilitates the hydrogenation of pyridine. The optimal hydrogenation path of pyridine with surface hydrogen atoms in the Langmuir-Hinshelwood mechanism is the formation of 3-monohydropyridine, followed by producing 3,5-dihydropyridine, in which the two-step hydrogenations take place on the C(ß) atoms. When adsorbed H(2)S is considered as the source of hydrogen, slightly higher hydrogenation barriers are always involved, while the energy barriers for hydrogenations involving adsorbed SH are much lower. However, the hydrogenation of pyridine should be suppressed by the adsorption of H(2)S, and the promotion effect of adsorbed SH is limited.

Theoretical investigation of the reaction of Mn+ with ethylene oxide.

The potential energy surfaces of Mn(+) reaction with ethylene oxide in both the septet and quintet states are investigated at the B3LYP/DZVP level of theory. The reaction paths leading to the products of MnO(+), MnO, MnCH(2)(+), MnCH(3), and MnH(+) are described in detail. Two types of encounter complexes of Mn(+) with ethylene oxide are formed because of attachments of the metal at different sites of ethylene oxide, i.e., the O atom and the CC bond. Mn(+) would insert into a C-O bond or the C-C bond of ethylene oxide to form two different intermediates prior to forming various products. MnO(+)/MnO and MnH(+) are formed in the C-O activation mechanism, while both C-O and C-C activations account for the MnCH(2)(+)/MnCH(3) formation. Products MnO(+), MnCH(2)(+), and MnH(+) could be formed adiabatically on the quintet surface, while formation of MnO and MnCH(3) is endothermic on the PESs with both spins. In agreement with the experimental observations, the excited state a(5)D is calculated to be more reactive than the ground state a(7)S. This theoretical work sheds new light on the experimental observations and provides fundamental understanding of the reaction mechanism of ethylene oxide with transition metal cations.

Decomposition of methanthiol on Pt(111): a density functional investigation.

Decomposition of methanthiol on Pt(111) is systematically investigated using self-consistent periodic density functional theory (DFT), and the decomposition network has been mapped out. The most stable adsorption of the involved species tends to form the sp(3) hybridized configuration of both C and S atoms, in which C is almost tetrahedral and S has the tendency to bond to three atoms. Spontaneous dissociation rather than desorption is preferred for adsorbed methanthiol. Based on the harmonic transition state theory calculations, the decomposition rate constants of the thiolmethoxy and thioformaldehyde intermediates are found to be much lower than those for their formation, leading to long lifetimes of the intermediates for observation. Under the ultrahigh vacuum (UHV) condition, the most possible decomposition pathway for methanthiol on Pt(111) is found as CH(3)SH --> CH(3)S --> CH(2)S --> CHS --> CH + S --> C + S, in which the C-S bond cleavage mainly occurs at the CHS species. However, the decomposition pathway is CH(3)SH --> CH(3)S --> CH(3) + S under the hydrogenation condition; the C-S bond scission mainly occurs at CH(3)S. The Brønsted-Evans-Polanyi relation holds for each of the S-H, C-H, and C-S bond scission reactions.

Dehydrogenation of methanol on Pd(100): comparison with the results of Pd(111).

Dehydrogenation of methanol on Pd(100) is systematically investigated using self-consistent periodic density functional theory. The theoretical results are compared with those of the same reaction on Pd(111) published very recently [J. Phys. Chem. C, 2009, 113, 4188-4197]. Switching from (111) to (100), adsorptions are strengthened for most species except for CHO, CO and H at hollow sites. Moreover, Pd(100) affords relatively low energy barriers and higher rate constants for most elementary dehydrogenation steps as well as smaller desorption rates for the saturated adsorbates (methanol and formaldehyde), suggesting that the more open Pd surface indeed possesses the higher activity and selectivity for the complete dehydrogenation of methanol. At lower temperatures (e.g., 250 K), Pd(100) affords the same dehydrogenation path as Pd(111) for methanol, which is unchanged on the latter surface at both lower and higher temperatures; whereas at the typical steam re-forming (MSR) temperature (500 K), the path on Pd(100), i.e., CH(3)OH --> CH(3)O and/or CH(2)OH --> CH(2)O --> CHO --> CO, is different from the situation of Pd(111). In both cases, the initial bond scission process constitutes the rate-determining step.

Molecular self-assembly and applications of designer peptide amphiphiles.

Short synthetic peptide amphiphiles have recently been explored as effective nanobiomaterials in applications ranging from controlled gene and drug release, skin care, nanofabrication, biomineralization, membrane protein stabilization to 3D cell culture and tissue engineering. This range of applications is heavily linked to their unique nanostructures, remarkable simplicity and biocompatibility. Some peptide amphiphiles also possess antimicrobial activities whilst remaining benign to mammalian cells. These attractive features are inherently related to their selective affinity to different membrane interfaces, high capacity for interfacial adsorption, nanostructuring and spontaneous formation of nano-assemblies. Apart from sizes, the primary sequences of short peptides are very diverse as they can be either biomimetic or de novo designed. Thus, their self-assembling mechanistic processes and the nanostructures also vary enormously. This critical review highlights recent advances in studying peptide amphiphiles, focusing on the formation of different nanostructures and their applications in diverse fields. Many interesting features learned from peptide self-organisation and hierarchical templating will serve as useful guidance for functional materials design and nanobiotechnology (123 references).

Influence of ovalbumin on CaCO3 precipitation during in vitro biomineralization.

As a major constituent of egg white matrix, ovalbumin has long been perceived to be implicated in the formation of avian eggshells, in particular, the mammillary layer. However, very little is known about the detailed mechanism by which this protein mediates shell calcification. By the combined studies of AFM, SEM, and TEM, we have investigated the influence of ovalbumin on CaCO(3) precipitation under in vitro mineralization conditions. We observed that the influence was multifold. This protein modified the morphology of calcite crystals through a distinct anisotropic process with respect to the four crystal step edges. AFM characterization revealed that the modification was initiated at the obtuse-obtuse step corner and propagated predominantly along the obtuse steps. Furthermore, the protein favored the existence of unstable phases such as amorphous calcium carbonate and crystalline vaterite. In contrast, lysozyme, another protein also present in the system, played a very different role in modifying calcite morphology. The mechanistic understanding gained from this study is clearly also of practical significance in developing advanced inorganic CaCO(3) materials with the aid of morphological manipulation of crystalline structures via different protein mediation.

Theoretical investigation of the oxidation of propane by FeO(+).

We report herein a comprehensive theoretical study of the oxidation of propane by FeO(+) on both the sextet and quartet potential energy surfaces (PESs) using density functional theory. The geometries and energies of all the stationary points involved are located. Interaction of FeO(+) with propane could account for four types of encounters (i.e., alpha,beta,gamma-, 2alpha,beta-, 3alpha-eta(3), and 2alpha,2gamma-eta(4)) complexes. Various mechanisms leading to the loss of CH(3), H(2)O, C(3)H(7)OH (H(2)O + C(3)H(6)), and C(3)H(6) are analyzed in terms of the topology of the PES. The reaction of FeO(+) with propane involves initial C-H activation, while initial C-C activation is indeed unlikely to be important. The loss of CH(3) takes place adiabatically on the sextet PES via the simple C(alpha)-to-O H shift from eta(4)-OFe(+)(C(3)H(8)) followed by CH(3) shift. The C(3)H(7)OH elimination proceeds via direct C(alpha)-to-O H shift followed by C-O coupling, while the loss of H(2)O, C(3)H(6), and (H(2)O + C(3)H(6)) proceeds via the alpha,beta-H and beta,alpha-H abstraction mechanisms from all the eta(3) complexes. The most favorable channel is the alpha,beta-H abstraction mechanism for the H(2)O loss because it not only is energetically and dynamically favorable but also has a high crossing probability between the sextet and quartet PESs. The computational results are in concert with the available experimental information and add new insight into the details of the individual elementary steps.

Decomposition of ethanol on Pd(111): a density functional theory study.

Ethanol decomposition over Pd(111) has been systematically investigated using self-consistent periodic density functional theory, and the decomposition network has been mapped out. The most stable adsorption of the involved species tends to follow the gas-phase bond order rules, wherein C is tetravalent and O is divalent with the missing H atoms replaced by metal atoms. Desorption is preferable for adsorbed ethanol, methane, and CO, while for the other species decomposition is preferred. For intermediates going along the decomposition pathways, energy barriers for the C-C, C(alpha)-H, and O-H scissions are decreased, while it is increased for the C-O path or changes less for the C(beta)-H path. For each of the C-C, C-O, and C-H paths, the Bronsted-Evans-Polanyi relation holds roughly. The most likely decomposition path is CH(3)CH(2)OH --> CH(3)CHOH --> CH(3)CHO --> CH(3)CO --> CH(2)CO --> CHCO --> CH + CO --> CO + H + CH(4) + C.

Role of ovalbumin in the stabilization of metastable vaterite in calcium carbonate biomineralization.

The role of proteins in biomineralization has been examined in this work by studying the effect of ovalbumin on the stabilization of metastable CaCO(3) phases. In the absence of ovalbumin, the mixing of Na(2)CO(3) with CaCl(2) in an aqueous solution led to the formation of metastable phases that swiftly transformed into stable calcite crystals within 4 h under the experimental conditions. However, ovalbumin was found to favor the formation and stabilization of spherical vaterites, and the effect was concentration dependent. In the presence of 2 g/L ovalbumin, for example, vaterite microspheres with diameters ranging from 0.9 to 3.0 mum, composed of much smaller nanosized particles, were produced and stabilized even after 24 h following the initial mixing. In addition, the influence of ovalbumin on the CaCO(3) mineralization process from the very beginning was carefully examined. Both amorphous calcium carbonate (ACC) and vaterite were favored with ovalbumin present, but the ACC phase formed predominantly at the initial stage of mixing followed by the vaterite formation. Vaterite could then be embedded further in the mineralization process and become stabilized many hours afterward. The stabilizing effect of ovalbumin could arise from the strong binding between carboxylate groups of ovalbumin and the calcium ions on the CaCO(3) surface, preventing the metastable CaCO(3) from transformation via dissolution-recrystallization processes. The strong ovalbumin adsorption on vaterite microspheres was revealed from transmission electron microscopy imaging and thermogravimetric analysis, thereby providing useful evidence to support the proposed stabilizing mechanism.

Theoretical survey of the potential energy surface of Ti+ + methanol reaction.

The gas-phase reaction of Ti(+) ((4)F and (2)F) with methanol is investigated using density functional theory. Geometries and energies of the reactants, intermediates, and products involved are calculated. The approach of Ti(+) toward methanol could form either a "classical" O- or a "nonclassical" eta(3)-methyl H-attached complex. The reaction products observed in the experiment (Guo, Kerns, Castleman J. Phys. Chem. 1992, 96, 4879) are produced via the classical association rather than the nonclassical complex. All possible pathways starting with C-O, C-H, and O-H activation are searched. Methane and methyl loss products (TiO(+) and TiOH(+)) are produced via the C-O activation; the O-H activation accounts for the H(2) and H elimination (producing TiOCH(2)(+) and TiOCH(3)(+)); and the C-H activation is unlikely to be important. Through the bond insertion (H shift) reductive elimination mechanism, the products of a closed-shell molecule (H(2) or methane) elimination could take place on both the quartet and doublet PESs owing to a spin inversion occurring in the course of initial bond insertion, whereas only the quartet products are produced adiabatically via the simple bond insertion-reductive elimination mechanism for the loss of a radical-type species (H or CH(3)). The computational results are in concert with the available experimental information and add new insight into the details of the individual elementary steps.