Enhancing β3 -peptide bundle stability by design

We reported recently that certain β(3) -peptides self-assemble in aqueous solution into discrete bundles of unique structure and defined stoichiometry. The first β-peptide bundle reported was the octameric Zwit-1F, whose fold is characterized by a well-packed, leucine-rich core and a salt-bridge-rich surface. Close inspection of the Zwit-1F structure revealed four nonideal interhelical salt-bridge interactions whose heavy atom-heavy atom distances were longer than found in natural proteins of known structure. Here we demonstrate that the thermodynamic stability of a β-peptide bundle can be enhanced by optimizing the length of these four interhelical salt bridges. Combined with previous work on the role of internal packing residues, these results provide another critical step in the "bottom-up" formation of β-peptide assemblies with defined sizes, reproducible structures, and sophisticated function.     

Structural Characterization of α,β-Unsaturated Aldehydes by GC/MS is Dependent upon Ionization Method

alpha,beta-unsaturated aldehydes are toxic products of lipid peroxidation. Detection and characterization of these aldehydes is important in many human disease states as well as in the food industry. Our study shows that electron ionization-mass spectrometry (EI-MS) and positive-ion chemical ionization-mass spectrometry (PICI-MS), but not electron capture negative ionization-mass spectrometry (ECNI-MS), can be used to detect the C4-hydroxylation state of alpha,beta-unsaturated aldehydes derivatized with pentafluorobenzyl hydroxylamine alone. EI-MS and PICI-MS spectra of 4-hydroxy-2-alkenals contained a fragment with m/z 252, whereas spectra of 2-alkenals contained a fragment with m/z 250. These fragments are consistent with fragmentation between C3 and C4 with transfer of two hydrogens from C4 and the C4 hydroxyl group in the case of 4-hydroxy-2-alkenals. In addition, EI-MS and PICI-MS were able to distinguish 4-hydroxy-2-alkenals and 2-alkenals from 4-keto-2-alkenals and 4-hydroxyalkanals. On the other hand, ECNI-MS provided complex spectra regarding C4-hydroxylation state. Furthermore, the syn- and anti-configurations of PFB-oximes had different resultant spectra using ECNI-MS, but not with EI-MS or PICI-MS. These data indicate that EI-MS and PICI-MS are more amenable for structural analysis of alpha,beta-unsaturated aldehydes than ECNI-MS.     

Formation of α/β-Si3N4 nanoparticles by carbothermal reduction and nitridation of geopolymers

Silicon nitride (Si₃N₄) particles with various α/β-Si₃N₄ ratios were fabricated from geopolymer (GP)-carbon compositions (M₂O·Al₂O₃·4.5SiO₂·12H₂O+18C), where M is an alkali ion (Na⁺, K⁺ and Cs⁺). They were made by carbothermal reduction and nitridation at 1400°, 1500°, and 1600°C for 2 hours under flowing nitrogen. Characterization of carbothermally reacted GP-carbon compositions was based on XRD, SEM-EDS, HRTEM, and selected area electron diffraction analyses. Depending on the alkaline composition of GP, the carbon content and the reaction temperature, a compositionally variable α/β-Si₃N₄ or SiAlON was achieved. Crystallization of the GPs gradually increased by heat treatment over 1400°C with corresponding weight loss. It was found that NaGP, KGP, and CsGP crystallized into a major phase of α-Si₃N₄, β-Si₃N₄, and SiAlON, respectively. Prolonged heating at 1600°C led to an increase in the α/β-Si₃N₄ ratio in NaGP due to the formation of aluminum nitride, while it led to a decrease in α/β-Si₃N₄ ratio in KGP. In the case of CsGP, SiAlON replaced the pollucite which mainly formed at lower temperatures. Transmission electron microscopy revealed that the needle-like particles were of ~0.5 µm in size and consisting of α/β-Si₃N₄ mixtures.     

Structural and electrochemical characterization of α-MoO3 nanorod-based electrochemical energy storage devices

Orthorhombic molybdenum trioxide (α-MoO₃) nanorods have been synthesized on a large scale by a hydrothermal method for electrochemical energy storage supercapacitor devices. The electrochemical properties of nanorods synthesized at different temperatures were investigated using cyclic voltammetry. The effects of synthesis temperature, scan rate and different scan cycles on the cyclic voltammograms were systematically studied. Nanorods synthesized at 180 °C for 6 h show the best electrochemical properties compared to those synthesized at other temperatures.     

High temperature bending creep behavior of a multi-cation doped α/β-SiAlON composite

SiAlON ceramics with high hardness and high toughness can be made through designing α/β-SiAlON composites. An important advantage of α-SiAlON phase is that the amount of intergranular phase is reduced by the transient liquid phase being absorbed into the matrix of α-SiAlON phase during sintering. But, the thermal stability of the α-SiAlON phase is an important concern for α/β-SiAlON composites especially at high temperatures. The use of different types of single or multiple cations during fabrication directly affects resultant microstructures and mechanical behavior of α/β-SiAlON composites. In this study, the creep behavior of a multi-cation (Y, Sm and Ca) doped α/β-SiAlON composite, in which aluminum-containing nitrogen melilite solid solution phase was designed as intergranular phase, was investigated by four-point bending creep tests under stresses from 50 to 150 MPa and at temperatures from 1300 °C to 1400 °C in air. The stress exponent was determined to be 1.6 ± 0.13 at 1400 °C and the creep activation energy was calculated to be 692 ± 37 kJ/mol⁻¹. Grain boundary sliding coupled with diffusion was identified as the rate-controlling creep mechanism for the α/β-SiAlON composite.     

Protein engineering of α/β-hydrolase fold enzymes

The superfamily of α/β-hydrolase fold enzymes is one of the largest known protein families, including a broad range of synthetically useful enzymes such as lipases, esterases, amidases, hydroxynitrile lyases, epoxide hydrolases and dehalogenases. This minireview covers methods developed for efficient protein engineering of these enzymes. Special emphasis is placed on the alteration of enzyme properties such as substrate range, thermostability and enantioselectivity for their application in biocatalysis. In addition, concepts for the investigation of the evolutionary relationship between the different members of this protein superfamily are covered, together with successful examples.     

Wear properties of α- and α/β-SiAlON ceramics obtained by gas pressure sintering and spark plasma sintering

In this study, α- and α/β-SiAlON materials, doped with Y₂O₃ and Nd₂O₃, were sintered using two different sintering processes: spark plasma sintering (SPS) and gas pressure sintering (GPS). The wear and mechanical properties of the samples were compared related to the composition, additives and sintering processes. The results show that the hardness was not affected by the processing type whereas the toughness values were lower for spark plasma sintered materials than gas pressure sintered materials. This can be explained by the changed microstructure of the two different types of material. Additionally, α/β-SiAlON materials, sintered using gas pressure sintering, showed a lower wear than the spark plasma sintered materials. The results of the wear test were compared with β-Si₃N₄ materials and it was observed that α/β-SiAlON, sintered by GPS, has better wear properties than the tested β-Si₃N₄ materials.     

Hydrolysis of Oligosaccharides by a Thermostable α-Galactosidase from Termitomyces eurrhizus

The genus of Termitomyces purchased from the market has been identified as Termitomyces eurrhizus using the Internal Transcribed Spacer (ITS) method. An α-galactosidase from T. eurrhizus (TEG), a monomeric protein with a molecular mass of 72 kDa, was purified 146 fold by employing ion exchange chromatography and gel filtration. The optimum pH and temperature was 5.0 and 60 °C, respectively. TEG was stable over pH 2–6, and also exhibited good thermostablility, retaining 100% of the original activity after incubation at 60 °C for 2 h. Inhibition of the enzyme activity by N-bromosuccinimide (NBS) constituted evidence for an essential role of tryptophan in the catalytic action of the isolated enzyme. Besides 4-nitro-phenyl α-d-galactophyranoside (pNPGal), natural substrates could also be effectively hydrolyzed by TEG. Results of thin-layer chromatography (TLC) revealed complete enzymatic hydrolysis of raffinose and stachyose to galactose at 50 °C within 6 h. These properties of TEG advocate its utilization for elevating the nutritional value of soymilk.     

Preparation of micrometer-sized α-Al2O3 platelets by thermal decomposition of AACH

Micrometer-sized α-Al₂O₃ platelets with hexagonal shape were prepared by thermal decomposition of ammonium aluminum carbonate hydroxide (AACH) using AlF₃ as an additive. The precursor and the calcined product were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and differential scanning calorimetry. The α-Al₂O₃ platelets with the size of 2-3 μm were obtained by calcining AACH at 1200 °C with 5 wt.% AlF₃. The morphology modification is attributed to the various growth rates along different crystal orientations due to the adsorption and uneven distribution of AlF₃. A step growth mode is responsible for the formation of the platelets.     

Structural characterization of a biosurfactant produced by Bacillus subtilis at 45°C

Structural and biochemical characterization of a biosurfactant produced by Bacillus subtilis under thermophilic conditions was performed. Preliminary structural determination of CHCl₃/CH₃OH (65∶15) extracts by thin-layer chromatographic reagents showed it to be identical to surfactin. Also, the infrared, ¹H nuclear magnetic resonance, and mass spectroscopy analysis confirmed it to be identical to surfactin. Biochemically, the surfactant was a lipopeptide-containing lipid (17.05%) and protein (13.2%). The surfactant yielded a minimal aqueous surface-tension value of 28 dyne/cm and an interfacial tension value at 0.1% concentration of 0.2 dyne/cm against diesel oil. The critical micelle concentration of the surfactant was 35 mg/L. The biosurfactant exhibited an emulsification value (E ₂₄) of 90 against diesel oil and a sand-pack oil recovery of 62%. It has potential application in microbial-enhanced oil recovery in thermophilic, alkaline, acidic, and halophilic environments.     

Synthesis of ultrafine α-Al2O3 powder by two-step hydrolysis

The ultrafine α-Al₂O₃ powder has been successfully synthesized via two-step hydrolysis of aluminum isopropoxide. The effects of synthesis parameters on the α-Al₂O₃ were investigated. The experimental results indicated that the concentration of aluminum isopropoxide, water bath temperature, the molar ratio of aluminum isopropoxide to isopropanol and aluminum isopropoxide to deionized water greatly affect the amount of nuclei and the microstructure of α-Al₂O₃. Additionally, the water bath temperature affects the rate of nucleation and growth of crystals. Transmission electron microscopy (TEM) images display that the well-dispersed α-Al₂O₃ powder with particle size about 100 nm was obtained via the method after calcination at 1200 °C for 1 h. The coalescence of crystal particles led to the formation of vermicular α-Al₂O₃ particles. The X-ray diffraction (XRD) and Fourier transform infrared spectra (FTIR) analysis demonstrated the possible phase transition process of α-Al₂O₃. The scanning electron microscopy (SEM) images of samples calcined at various temperatures showed the microstructure transformation. Brunauer-Emmett-Teller (BET) surface area and mean pore size of the samples varied with the calcination temperature. The addition of cetylrimethylammonium bromide (CTAB) has impacts on the phase transformation of α-Al₂O₃.     

Agglomeration of α-Al2O3 powders prepared by gel combustion

Ultrafine α-Al₂O₃ powders were prepared by a gel combustion method and the agglomeration characteristic of the resultant powders was studied. A variety of fine crystallite α-Al₂O₃ powders with different agglomeration structures could be obtained by altering the citrate-to-nitrate ratio γ and calcining the precursors at 1050 °C for 2 h. All the powders were of nearly equivalent crystallite size (60–80 nm) except for the P1 powder (113 nm) from the gel with γ = 0.033. The primary crystallites of the obtained α-Al₂O₃ powders were formed into large secondary particles with different degree of agglomeration. Except for the powder P1, the mean particle sizes from specific surface area and particle size distribution measurement increase with increasing citrate-to-nitrate ratio in the fuel-lean condition and decrease in the fuel-rich condition. Densities of alumina ceramics from powders P4 and P5 sintered at different temperatures were relatively low due to the wide particle size distribution.     

Multimodal interventional molecular imaging of tumor margins and distant metastases by targeting αvβ3 integrin

α(v)β(3) integrin is involved in (tumor-induced) angiogenesis and is a promising candidate for the specific visualization of both primary tumors and of their distant metastases. Combination of radioactive and fluorescent imaging labels in a single multimodal, or rather hybrid, RGD-based imaging agent enables integration of pre-, intra-, and postoperative angiogenesis imaging. A hybrid imaging agent targeting the α(v)β(3) integrin--(111)In-MSAP-RGD (MSAP = multifunctional single-attachment-point reagent), which contains a targeting moiety, a pentetic acid (DTPA) chelate, and a cyanine dye--was evaluated for its potential value in combined lesion detection and interventional molecular imaging in a 4T1 mouse breast cancer model. SPECT/CT and fluorescence imaging were used to visualize the tumor in vivo. Tracer distribution was evaluated ex vivo down to the microscopic level. The properties of (111)In-MSAP-RGD were compared with those of (111)In-DTPA-RGD. Biodistribution studies revealed a prolonged retention and increased tumor accumulation of (111)In-MSAP-RGD relative to (111)In-DTPA-RGD. With (111)In-MSAP-RGD, identical features could be visualized preoperatively (SPECT/CT) and intraoperatively (fluorescence imaging). As well as the primary tumor, (111)In-MSAP-RGD also enabled detection and accurate excision of distant metastases in the head and neck region of the mice. Therefore, the hybrid RGD derivative (111)In-MSAP-RGD shows potential in preoperative planning and fluorescence-based surgical intervention.     

Preparation of α-Fe2O3 submicro-flowers by a hydrothermal approach and their electrochemical performance in lithium-ion batteries

Uniform α-Fe₂O₃ submicron-sized flowers have been synthesized by a simple hydrothermal process conducted at 160 °C for 24 h. The crystalline structure and morphology of the as-synthesized powder have been characterized by using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and field emission scanning electron microscopy (FE-SEM). The results revealed that the highly crystalline α-Fe₂O₃ submicro-flowers were composed of nanospheres with an average size of 20-30 nm. The electrochemical performance as anode material for lithium-ion batteries was further evaluated by cyclic voltammetry (CV) and by electrochemical impedance and charge-discharge measurements. It was demonstrated that the material could provide an initial reversible capacity of 959.6 mAh/g at a current density of 20 mA/g over the voltage range from 0.01 to 3.0 V. The capacity retention upon the 50th cycle was 44.4 and 35.9% at 60 and 100 mA/g, respectively. The superior electrochemical performance may be resulted from the high surface area and the small and uniform grain size.     

Morphology control of α-Al2O3 platelets by molten salt synthesis

It is of great importance to control the morphology of α-Al₂O₃ plate-like powders since α-Al₂O₃ platelets with different shapes are needed in various applications. This paper was focused on how to control the morphology of α-Al₂O₃ platelets by molten salt synthesis. Results show that the morphology of α-Al₂O₃ platelets is affected by the heating temperature, heating time, the molten salts species, the weight ratio of salt to powders, additives and the addition of nano-sized seeds. Especially, it is very effective to control the morphology of α-Al₂O₃ platelets by adjusting the addition of additives such as Na₃PO₄·12H₂O and TiOSO₄. α-Al₂O₃ flakes with irregular shape are obtained by the addition of Na₃PO₄·12H₂O, while thick α-Al₂O₃ particles with hexagonal shape are obtained by the addition of TiOSO₄. The combination addition of Na₃PO₄·12H₂O and TiOSO₄ makes it possible to obtain thin α-Al₂O₃ platelets with discal shape. A small amount of nano-sized seeds addition also has a strong effect on the size of α-Al₂O₃ platelets. However, if the seeds are added too much, the overlapping and abnormal crystal growth of α-Al₂O₃ platelets occur, and the size distribution becomes nonuniform. The effect mechanism of additives and seeds on the morphology of α-Al₂O₃ platelets was also discussed in this paper.     

Low-temperature synthesis of α-Al2O3 powder aided by ball milling and a trace amount of sodium chloride

It is crucial to synthesize α-Al₂O₃, which is a multifunctional material, at high temperatures due to the nature of the material. However, this high-temperature preparation process is not energy efficient, which goes against the global aim of carbon neutrality. In this study, we explored the effect of adding 1 wt.% (NaCl) as an additive and a suitable amount of Al(OH)₃ in a ball mill to form a precursor. The impact of NaCl and ball milling duration on the phase transition from Al(OH)₃ to α-Al₂O₃ at low temperatures was investigated. After the conversion from Al(OH)₃ to γ-Al₂O₃, the NaCl particles on the surface of γ-Al₂O₃ act as diffusion channels, helping to accelerate the substance diffusion during the transition from γ-Al₂O₃ to α-Al₂O₃, resulting in a lower formation temperature of α-Al₂O₃, which is 700°C. Additionally, the presence of NaCl results in α-Al₂O₃ particles growing into hexagonal plates. The α-Al₂O₃ plates produced from calcining the mixture of Al(OH)₃ and NaCl at 700°C have an average diameter of 3 µm, an average diameter/thickness ratio of 10 and a specific surface area of 12.0085 m²/g. These results indicate that low-temperature synthesis of α-Al₂O₃ powder is possible by using NaCl as an additive instead of molten salt in the ball milling process.     

Efficient α/β-Bi2O3 composite for the sequential photodegradation of two-dyes mixture

A mixture of α/β-Bi₂O₃ and α-Bi₂O₃ powders were obtained by a simple solid state reaction–annealing route at 550 °C. The structure, optical properties and surface area of the commercial α and β-Bi₂O₃ and the synthesized α-phase and α/β-composite were well characterized by X-ray diffraction, diffuse reflectance spectra and N₂ physisorption. The annealed sample at 550 °C showed 20% of β-phase, forming a heterojunction of α/β-Bi₂O₃ whereas annealing at elevated temperature (650 °C) lead to the α-phase. Optical properties showed that the presence of the β-phase is mainly responsible for narrowing the energy band gap. The photocatalytic activity of the commercial α and β-Bi₂O₃ and the synthesized α-phase and α/β-composite were investigated in degradation of single dyes, Indigo Carmine (IC) and Rhodamine-B (RhB) under both UV and visible light-induced photocatalysis. For the best photocatalyst, the photodegradation in a two-dye mixture solution was systematically studied considering the type of dye, the adsorption capacity of the samples and the behavior of dye photodegradation. The photocatalytic performance of α/β-Bi₂O₃ was comparatively much higher than the commercial α and β-Bi₂O₃, indicating that better performance of efficient charge separation and transfer across α/β-Bi₂O₃ composite was obtained. Possible mechanism of the single dye and two-dye mixture degradation was given by using α/β-Bi₂O₃ composite.     

Enhanced performance of a macroporous ceramic support for nanofiltration by using α-Al2O3 with narrow size distribution

Enhanced performance of a macroporous disk alumina support was fabricated through colloidal filtration route, by using α-Al₂O₃ powder with an average particle size of 1.1 μm. The support, sintered at 1250 °C, showed relative high permeances towards water (101 L h⁻¹ m⁻² bar⁻¹) and nitrogen (∼2×10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹), with an average surface roughness of ∼175 nm and a high mechanical strength of 61.1 MPa. Titania supported γ-Al₂O₃ mesoporous layers were deposited onto this promising disk α-Al₂O₃ support through dip-coating. The disk membrane A1100/TiO₂/γ-Al₂O₃, with pore size of ca. 4.4 nm, showed a pure water flux as high as 4.5 L m⁻² h⁻¹ bar⁻¹, which is four times higher than that of γ-Al₂O₃ membrane reported in literature. This mesoporous membrane showed relative high retention rate (∼80%) towards di-valent cations like Ca²⁺, Mg²⁺, but not for the mono-valent cation (Na⁺).