Low-angle X-ray Diffraction Patterns Research Articles

Synthesis of spherical amine-functionalized silica molecular sieve and application as selective adsorbents for aromatic hydrocarbons analysis

In this work, spherical amine-functionalized mesoporous silica (Sp-Amino-Si) molecular sieve was fabricated by an acid hydrothermal method using 3-aminopropyltriethoxysilane as a modifier and toluene as the solvent. The results of scanning electron microscopy, Barrett-Joyner-Halenda pore size distribution, Fourier transform-infrared spectroscopy, and low-angle X-ray diffraction patterns revealed that the Sp-Amino-Si was monodispersed microspheres with uniform and controllable pore sizes sharing two-dimensional hexagonal P6mm symmetry and a large number of amino groups. The Sp-Amino-Si molecular sieve was verified to be suitable for the selective separation of aromatic hydrocarbons (AMHs) containing two fused benzene rings among other compounds from environmental water matrix. Under the optimized conditions, the Sp-Amino-Si exhibited much higher adsorption efficiency for AMHs (above 88.19%), comparing to the original SBA-15 (below 44.52%). The maximum adsorption capacities for naphthalene, methyl naphthalene, 2-methyl naphthalene, and acenaphthene were 477.1, 1006.5, 893.3, and 1253.2 µg·g−1, respectively. The high selectivity of Sp-Amino-Si for the four AMHs attributed to the size sieving and p-π interactions between the lone pair electrons of amine groups and the π-electrons in AMHs molecules. The Sp-Amino-Si based solid-phase extraction coupled with high performance liquid chromatography detection method was constructed for the analysis of the four AMHs, and the recoveries of spiked AMHs ranged from 89.67% to 112.74% with a relative standard deviation lower than 5.75%. This study provides some inspiration and a reliable method for AMHs separation, removal, and analysis.

Spontaneous chiral self-assembly of CdSe@CdS nanorods

Spontaneous chiral self-assembly of CdSe@CdS nanorods

Photoluminescence study of SBA-15@ZnO/Au nanocomposite for potential use in Staphylococcus aureus detection

Staphylococcus aureus is most common causes of hospital-acquired infections and food-associated disease. In the last years, sensing platform based on fluorescence- nanomaterials and nanocomposites have been attracted a great attention for detection of bacteria and macromolecules. In this study, a new modified mesoporous silica SBA-15 with ZnO and Au nanoparticles (SBA-15@ZnO/Au) was prepared to enhance the photoluminescence emission of SBA-15 matrix and investigate the potential use as a nano probe for detection of S. aureus bacteria. Au nanoparticles were added to the SBA-15 after loading ZnO nanoparticles and the SBA-15@ZnO/Au nanocomposite was successfully fabricated. The Structural, morphological, physicochemical and optical properties of the prepared samples have been studied. The low-angle X-ray diffraction (XRD) pattern showed highly ordered two-dimensional hexagonal lattice of SBA-15 and the wide-angle XRD pattern proved the formation of ZnO and Au nanoparticles. The results of the Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis showed that the prepared nanocomposite have a regular two dimensional hexagonal structure with cylindrical channels even after loading ZnO and Au nanoparticles. According to Nitrogen adsorption–desorption isotherm measurement, the pore diameter and the specific surface area of SBA-15@ZnO/Au nanocomposite have been obtained 3.15 nm and 604.19 m2/g. Photoluminescence (PL) spectra of bare SBA-15@ZnO/Au nanocomposite showed three peaks at central wavelength of 410, 500 and 750 nm arising from electron transfer process and radiative decay of collective plasmonic states. After addition of S. aureus bacteria, the nano probe-target complex was formed and the PL re-emission at 640 nm and quenching of PL emissions at 750 and 410 nm was observed. Furthermore, the new nanocomposite was demonstrated to have the proper sensitivity toward bacteria concentrations. The results can open promising prospect for this nanocomposite as a nano probe for detection of S. aureus in the UV–Visible region of electromagnetic spectrum.

Modeling of gyroidal mesoporous CMK-8 and CMK-9 carbon nanostructures and their X-Ray diffraction patterns

1. Abstract Powder X-ray diffraction (XRD) patterns of ordered mesoporous CMK-8 and CMK-9 carbon materials are simulated by geometric modeling. The materials are amorphous at the atomic length scale but exhibit highly symmetric gyroidal structures at the nanometer scale, corresponding to regular, continuous nanopore systems with cubic symmetry. Their structures lead to characteristic low-angle XRD signatures. We introduce a model based on geometrical considerations to simulate CMK-8 and CMK-9 structures with variable volume fraction of carbon (vs. pore volume, i.e., variable 'pore wall thickness'). In addition, we also simulate carbon materials with variable amounts of guest species (e.g., sulfur) residing in their pores. The corresponding XRD patterns are calculated. The carbon volume fraction turns out to have a significant impact on the relative diffraction peak intensities, especially in case of CMK-9 carbon that features a bimodal porosity. Likewise, the presence of guest species in the pores may also strongly affect the relative peak intensities. Our study suggests that careful evaluation of experimental low-angle XRD patterns of (real) CMK-8 or CMK-9 materials offers an opportunity to obtain detailed information about the nanostructural properties in addition to the mere identification of the pore systems geometry.

Efficacy-shaping nanomedicine by loading Calcium Peroxide into Tumor Microenvironment-responsive Nanoparticles for the Antitumor Therapy of Prostate Cancer.

Rationale: Prostate cancer has become one of the most threatening malignant tumors in men, leading to an imperative need to develop effective and safe therapies. Because of the unique metabolism of tumor cells, the tumor microenvironment (TME) exhibits distinctive properties compared with normal tissues, among which the pH difference has been utilized as an ideal antitumor strategy. Herein, we introduce a reactive oxygen species (ROS)-controlled-release nanosystem with TME-responsiveness by applying hollow mesoporous silica nanoparticles (HMSNs) as carriers loaded with calcium peroxide (CaO2) and coated with polyacrylic acid (PAA) to construct the functional material CaO2@HMSNs-PAA. The differences in pH values and exogenous ROS scavenging abilities between the tumor tissue and normal tissues and the dual pH-responsiveness from CaO2 and PAA lay a scientific foundation for the application of CaO2@HMSNs-PAA in the tumor-selective therapy for prostate cancer.Methods: The morphology and the structure of the nanosystem were characterized by the transmission electron microscope, scanning electron microscope, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, zeta potential, dynamic light scattering measurement, low-angle X-ray diffraction patterns and nitrogen adsorption/desorption isotherm. The CaO2 loading capacity and release profiles in different buffer solutions were determined by inductively coupled plasma-mass spectrometry. The in vitro intracellular uptake of CaO2@HMSNs-PAA was explored on the PC-3 prostate cancer cell line via confocal laser scanning microscopy. The CCK-8 cell proliferation assay was conducted to evaluate the cytotoxicity of CaO2@HMSNs-PAA against PC-3 cells. ROS produced by CaO2@HMSNs-PAA was observed by a fluorescence microscope. The flow cytometry was utilized to analyze the apoptosis of PC-3 cells induced by CaO2@HMSNs-PAA. The Western blot analysis was performed to detect expressions of critical mitochondria-mediated apoptosis markers in PC-3 cells after incubation with CaO2@HMSNs-PAA. The in vivo biosafety and antitumor efficacy were evaluated out on BALB/c mice and BALB/c nude mice subcutaneously transplanted with PC-3 cells, respectively.Results: Comprehensive characterizations indicated the successful synthesis of CaO2@HMSNs-PAA with significant TME-responsiveness. The experimental results demonstrated that the well-developed nanocarrier could efficiently deliver CaO2 to the tumor site and release ROS in response to the decreased pH value of TME, exerting ideal antitumor effects both in vitro and in vivo by activating the mitochondria-mediated apoptosis pathway. Simultaneously, this nanoplatform caused no detectable damage to normal tissues.Conclusions: After loading into the above nanocomposite, the free CaO2 without a significant antitumor effect can exert excellent antitumor efficacy by responsively releasing ROS under the acidic TME to induce the mitochondria-mediated apoptosis via remarkable oxidative stress and simultaneously minimize damages to normal tissues. The current study presents a new concept of “efficacy-shaping nanomedicine” for the tumor-selective treatment of prostate cancer.

The Interacting Head Motif Structure Does Not Explain the X-Ray Diffraction Patterns in Relaxed Vertebrate (Bony Fish) Skeletal Muscle and Insect (Lethocerus) Flight Muscle.

Unlike electron microscopy, which can achieve very high resolution but to date can only be used to study static structures, time-resolved X-ray diffraction from contracting muscles can, in principle, be used to follow the molecular movements involved in force generation on a millisecond timescale, albeit at moderate resolution. However, previous X-ray diffraction studies of resting muscles have come up with structures for the head arrangements in resting myosin filaments that are different from the apparently ubiquitous interacting head motif (IHM) structures found by single particle analysis of electron micrographs of isolated myosin filaments from a variety of muscle types. This head organization is supposed to represent the super-relaxed state of the myosin filaments where adenosine triphosphate (ATP) usage is minimized. Here we have tested whether the interacting head motif structures will satisfactorily explain the observed low-angle X-ray diffraction patterns from resting vertebrate (bony fish) and invertebrate (insect flight) muscles. We find that the interacting head motif does not, in fact, explain what is observed. Previous X-ray models fit the observations much better. We conclude that the X-ray diffraction evidence has been well interpreted in the past and that there is more than one ordered myosin head state in resting muscle. There is, therefore, no reason to question some of the previous X-ray diffraction results on myosin filaments; time-resolved X-ray diffraction should be a reliable way to follow crossbridge action in active muscle and may be one of the few ways to visualise the molecular changes in myosin heads on a millisecond timescale as force is actually produced.

Monitoring the myosin crossbridge cycle in contracting muscle: steps towards \u2018Muscle\u2014the Movie\u2019

Some vertebrate muscles (e.g. those in bony fish) have a simple lattice A-band which is so well ordered that low-angle X-ray diffraction patterns are sampled in a simple way amenable to crystallographic techniques. Time-resolved X-ray diffraction through the contractile cycle should provide a movie of the molecular movements involved in muscle contraction. Generation of ‘Muscle—The Movie’ was suggested in the 1990s and since then efforts have been made to work out how to achieve it. Here we discuss how a movie can be generated, we discuss the problems and opportunities, and present some new observations. Low angle X-ray diffraction patterns from bony fish muscles show myosin layer lines that are well sampled on row-lines expected from the simple hexagonal A-band lattice. The 1st, 2nd and 3rd myosin layer lines at d-spacings of around 42.9 nm, 21.5 nm and 14.3 nm respectively, get weaker in patterns from active muscle, but there is a well-sampled intensity remnant along the layer lines. We show here that the pattern from the tetanus plateau is not a residual resting pattern from fibres that have not been fully activated, but is a different well-sampled pattern showing the presence of a second, myosin-centred, arrangement of crossbridges within the active crossbridge population. We also show that the meridional M3 peak from active muscle has two components of different radial widths consistent with (i) active myosin-centred (probably weak-binding) heads giving a narrow peak and (ii) heads on actin in strong states giving a broad peak.

Beyond Conventional Reaction Mechanism of Ordered Mesoporous Nickel Oxide for Lithium Ion Batteries

In a recent days, as cutting-edge devices, such as cell phone, electric vehicle (EV) and energy storage system (ESS) become more sophisticated, the battery performance is required to be higher. As a result, metal oxides having a capacity several times larger than that of carbon have attracted attention as a candidate for a next-generation secondary battery. Although metal oxides show higher capacity than one of conventional theory, which is insertion, alloy and conversion reaction, but it has not been clearly determined. Nickel oxide (NiO) is very attractive anode material due to its chemically stable, cheap, environmentally benign, easy to synthesize properties, and high theoretical capacity (718 mAh/g). However, commercialization of NiO is hampered by its poor cycle performance and rate capability due to inherently severe volume changes during cycling. One of strategies to overcome these limitations is to synthesize nanostructured NiO with various morphology, such as nanofibers, nanowalls, hollow spheres, hierarchical structures, and especially porous structure. In this study ordered mesoporous NiO is synthesized by using KIT-6 as a hard template for the sake of higher performance. Low-angle X-ray diffraction (XRD) patterns of highly ordered mesoporous NiO is quite different from KIT-6 silica template. A new (110) peak appears before 2θ=1°, which indicates the meso-structure transformation from cubic to tetragonal or the lower space group after the silica template etching process. In wide angle XRD pattern, synthesized highly ordered mesoporous NiO is matched with cubic NiO (JCPDS 47-1049). N2 adsorption-desorption isotherms show that the obtained replicas possess high specific surface areas (92 m2/g), and large pore volumes (0.24 cm3/g). The SEM images prove their mesoporous structures, indicating that nanoreplication was uniformly performed without formation of other metal oxide phase. Its theoretical capacity is calculated through conversion reaction, in which NiO reacts with Li ion and is converted to metallic Ni nanoparticles and Li2O, but the conventional reaction mechanism cannot elucidate its high reversible capacity (~1000 mAh/g). So synchrotron radiation analyses are used to research detail mechanism study. Conventional reaction mechanisms in anode, such as insertion, conversion, and alloy, have respective consistency as shown in operando SAXS. Operando SAXS spectra of mesoporous NiO shows different behavior during 1st discharge compared to one of other anode materials, which follow conversion reaction. There are no significant changes of SAXS until ~1 mol of Li ion is reacted. Thereafter, the pore net volume changes increase and peak intensity decrease gradually indicating the loss of mesostructure upon the conversion reaction to form Ni and Li2O. These observation is similar to in situ XRD, which shows constant peak intensity until ~1 mol of Li ion is reacted and decrease because of phase transition from ordered mesoporous structure to amorphous phase, result of conversion reaction. In these results, retained peak intensity might be attributed to electrolyte participation reaction, not associated with the NiO lattice. For further study, ex situ XAS analysis is used to study the local atomic structure of cycled NiO in detail. Ni K-edge XANES spectra show negligible changes in initial stage of 1st discharge. These changes are also clearly observed in Ni K-edge EXAFS spectra, which show pristine and discharged to 200 mAh/g samples are similar and peak intensity of discharged to 400 mAh/g sample is lower. It indicates that electrolyte participation reaction (oligomer layer formation) takes place first, and then the conversion reaction occurs. In the middle stage of 1st discharge, it goes to metallic Ni, product of conversion reaction. The amplitudes of Ni-O and Ni-Ni peaks in mesoporous NiO decrease significantly and the amplitudes of Ni-Ni peak in metallic Ni increase with the increase of depth of the discharge due to displacement of reacting species during conversion reaction. There are no significant changes due to SEI layer formation in final stage of 1st discharge. Note that little changes of Ni K-edge XANES spectra are observed until charged to 600 mAh/g sample, and it goes to NiO-like phase till fully charged state in the 1st charge. It indicates that reversible conversion reaction takes only some part of entire reversible capacity, and the reversible oligomer formation / decomposition attributes to the remained reversible capacity. A similar consistency is shown on 2nd discharge. The XPS and HRTEM experiments were carried out for research of the electrolyte participation reaction. More details will be discussed in the meeting.

Vesicle formation by cholesterol based hydrazone tethered amphiphiles: Stimuli responsive dissipation of self-assembly

Stimuli are one of the key parameters to achieve a control over the association/dissociation of molecular tectons in self‐assemblies. In this present article, we synthesized cholesterol based pH-sensitive hydrazone-tailored low molecular mass amphiphiles (CBH-1-3). The hydrazone residue was modified by varying the carbonyl moieties from aldehyde (benzaldehyde (CBH-1), p-dimethylaminobenzaldehyde (CBH-2)) to ketone (benzophenone (CBH-3)). Microscopic and spectroscopic characterizations were carried out to investigate the pattern of self-aggregation and its morphology. Among these amphiphiles, CBH-1 and CBH-2 were found to form vesicular aggregates through H-type aggregation in 1:3 v/v, DMSO-water having dimension of around 50–120 nm in the case of CBH-1 and ∼150–250 nm for CBH-2. Moreover, low angle X-ray diffraction (XRD) pattern of the self-aggregates confirmed the formation of bilayer vesicles through highly ordered lamellar like structure for the hydrazone-tailored amphiphiles. These vesicles are stable at pH 7.0 and above, however get disassembled at acidic pH (pH < 5.0). This dissipation of the vesicular self-aggregates because of the cleavage of the hydrazone bond under acidic environment was investigated by UV–visible, FTIR and mass spectrometric studies. Moreover, absence of any spherical aggregate in the transmission electron microscopic (TEM) images of the acid treated vesicles confirmed its disintegration in acidic medium. Furthermore, dye encapsulation and its pH-responsive release from the CBH-1 vesicles were tested using doxorubicin as drug.

Reduced-Dimensional α-CsPbX3 Perovskites for Efficient and Stable Photovoltaics

Summary Inorganic CsPbX3 perovskites have gained great attention owing to their excellent thermal stability and carrier transport properties. However, the power conversion efficiency (PCE) of solution-processed CsPbX3 perovskite solar cells is still far inferior to that of their hybrid analogues. Insufficient film thickness and undesirable phase transition are the two major obstacles limiting their device performance. Here, we show that by adopting a new precursor pair, cesium acetate (CsAc) and hydrogen lead trihalide (HPbX3), we were able to overcome the notorious solubility limitation for Cs precursors to fabricate high-quality CsPbX3 perovskite films with large film thickness (∼500 nm). We further introduced a judicious amount of phenylethylammonium iodide (PEAI) into the system to induce reduced-dimensional perovskite formation. Unprecedentedly, the resulting quasi-2D perovskites significantly suppressed undesirable phase transition and thus reduced the film's trap density. Following this approach, we reported a state-of-the-art PCE to date, 12.4%, for reduced-dimensional α-CsPbI3 perovskite photovoltaics with greatly improved performance longevity.

Structure and magnetic properties of Tb-Co/Ti and Tb-Co/Al2O3 multilayers

The influence of the nanoscale thicknesses of the ferrimagnetic Tb-Co layers on the structure and magnetic properties of magnetron sputtered Tb-Co/Ti and Tb-Co/Al2O3 magnetic multilayers were comparatively studied. Low angle X-ray diffraction patterns testified to the existence of a well defined layered structure in all the cases under consideration. For all samples, the magnetization was positioned in the plane of the films in the entire investigated temperature interval from 5 to 350 K. The temperature dependence of magnetization of the multilayered structures is the function of the Tb-Co layer thickness. The material of the spacers was shown to significantly influence the magnetic properties of the multilayers.

Selective pore filling of mesoporous CMK-5 carbon studied by XRD: Comparison between theoretical simulations and experimental results

It is possible to infiltrate a guest species selectively in one pore system of bimodal mesoporous CMK-5 carbon by an optimized nanocasting procedure. The selective filling has a drastic impact on the low-angle X-ray diffraction pattern of this novel class of materials. The structures of CMK-5, CMK-5 composite materials (sulfur and SnO2 as guest species), and CMK-3 carbon were simulated to investigate the influence of the pore filling with different guest species on the diffraction pattern and compared with experimental results. Additionally, the impact of structural defects is taken into account. The nature of the guest species strongly influences the relative intensity of the diffraction peaks. It turns out that the diffraction patterns of sulfur-carbon composite materials are nearly identical as those of CMK-3 carbon, which is attributed to a similar electron density of carbon and sulfur. Thus, sulfur is an ideal guest species to investigate the selective pore filling in CMK-5 carbon.

Natural clay attapulgite as the raw material for synthesis of Al/Ti/Mg-containing mesoporous silicates with cubic, 3D hexagonal, and lamellar mesostructures

A series of Al/Ti/Mg-containing ordered mesostructured silicates were synthesized using the natural attapulgite clay as the raw material, which was first pretreated by 4 M hydrochloric acid without other special treatment such as grinding. By varying the pH value in the synthetic gel, different mesophases with cubic, 3D hexagonal, and lamellar mesostructures were obtained. Their mesostructures were confirmed by low-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their morphology and textural properties were analyzed by scanning electron microscopy (SEM) and N2 adsorption. It was found that the hetero-atoms including Al, Ti, and Mg in the clay could be effectively transformed into these ordered mesostructured silicate frameworks in sufficient content, as revealed by inductively coupled plasma (ICP) emission spectroscopy and fourier transform infrared (FT-IR) spectrum. NH3-TPD showed the accessibility of Al species as Bronsted and Lewis acid sites in the mesostructured framework located on the pore surface. All above suggests the potential of attapulgite as a low-cost precursor for the industrial scale production of high quality heteroatom-doped mesophases for various applications. Low-angle powder X-ray diffraction patterns of mesostructured silicates with cubic, 3D hexagonal, and lamellar mesophases, synthesized by using natural clay attapulgite as raw material: uncalcined (left) and calcined (right).

Computer simulations of the structure and properties of organic pillared MFI zeolite catalyst

Multifunctional porous hybrid materials have recently received a lot of attentions because they combine the advantages of incorporating both inorganic oxides and organic species into the structure to solve the limitation of sole component material. This paper reports a type of model of organic pillared MFI zeolite catalyst, in which the full-atom mimetic model is constructed by using molecular modeling technique. Dreiding force field is used to calculate the interactions between sorbate–sorbate and sorbate–sorbent in the organic pillared MFI zeolite. The optimized model is characterized by calculating low-angle and high-angle X-ray diffraction patterns. Besides, the adsorption behavior of benzene and toluene is also investigated through the mimetic model. Simulated adsorption isotherms of benzene and toluene are agreement with the experimental data at low pressure. Density distributions of benzene and toluene show that toluene adsorbs preferentially in the region of interlayer space of lamellar MFI zeolite while benzene tends to adsorb in the area of micropores at low pressure. With increasing pressure, the guest molecules gradually fill in the area of micropores and mesopores of the organic pillared MFI zeolite. Moreover, the developed strategy in the present work can be applied to build other model for organic pillared zeolite catalyst by arranging different zeolite frameworks or organic species.

Investigation of carbon dioxide adsorption by nitrogen-doped carbons synthesized from cubic MCM-48 mesoporous silica

Copyright © Korean Carbon Society http://carbonlett.org Carbon dioxide (CO2) is a component of the flue gas of power plants and automobile emissions. This gas is recognized as a primary greenhouse gas and is a presumed agent of climate change [1,2]. The drawbacks of the traditional MEA liquid method that is used for CO2 capture include the requirement for heavy equipment, and the toxic, flammable, corrosive, and volatile nature of the process [3]. Therefore, CO2 capture by means of adsorption in porous materials has received increasing attention because this method has proven to be superior than the conventional technologies in terms of the advantages associated with it. Compared to traditional processes, the convenient reversibility of adsorption on porous solid materials based on physisorption for the capture and release of CO2 makes this technique a greener and more cost-efficient method. To date, a variety of solid-based materials have been intensively studied for gas adsorption, especially CO2 capture, such as metal organic frameworks, covalent organic frameworks, zeolites, activated carbons, functionalized graphene, carbon molecular sieves, chemically modified mesoporous materials, etc [4-13]. Furthermore, the low concentration of CO2 in flue gas (ca. 15%) requires selective separation from the large volume of other component gases, mainly N2 [14]. Ideally, solid sorbents designed for CO2 capture should offer reduced energy consumption for regeneration, greater capture capacity, stability, selectivity, ease of handling, reduced environmental impact, etc. Currently, there is significant interest in the development of solid carbon adsorbents that are capable of selectively adsorbing CO2, because of their large surface area, porosity, abundance, cost efficiency, low density, fast adsorption kinetics, and high chemical and thermal stability [15-18]. Furthermore, these materials offer some advantages in terms of ease of handing, pore structure, and surface characteristics, as well as low-regeneration energy [19]. Therefore, carbon materials are currently considered attractive candidate sorbents for CO2 capture in the development of alternate clean and sustainable energy technologies. Based on these strengths, increasing efforts have recently been devoted to the synthesis of element-doped porous carbons that combine the high porosity and unique properties of doped carbon frameworks. The MCM-48 templated carbons have a high porosity without activation usually required to develop an accessible porous structure. Nitrogen doping has earned particular distinction because of the enhanced surface polarity, electrical conductivity, and electron-donor tendency conferred to the mesoporous carbons by nitrogen incorporation, which enables their application in CO2 capture, electric double-layer capacitors, fuel cells, catalysis, etc [20,21]. In the present study, we describe an alternate approach for the production of nitrogen-containing carbon materials with a cubic structure that facilitates CO2 diffusion and capture. Fig. 1a presents the low angle X-ray diffraction (XRD) pattern of MCM-48.The pattern exhibits several well-resolved peaks in the low-angle range of 2θ = 2°–6°, which can be indexed as the (211), (220), (420), and (332) diffraction peaks; this pattern corresponds to the cubic Ia3d space group [2,22]. In Fig. 1b high-angle XRD patterns, the synthesized carbon materials show two apparent peaks at around 2θ = 25° and 44°, which correspond to the (002) and (101) diffractions of the graphite structure, involving the hexagonal graphitic site and rhombohedral graphitic site, respectively [23]. Low-angle XRD patterns of the carbons synthesized with various amounts of pyrrole were acquired, as shown in Fig. DOI: http://dx.doi.org/ DOI:10.5714/CL.2016.18.062

Direct decomposition of methane over SBA-15 supported Ni, Co and Fe based bimetallic catalysts

Thermocatalytic decomposition of methane is an alternative route for the production of COx-free hydrogen and carbon nanomaterials. In this work, a set of novel Ni, Co and Fe based bimetallic catalysts supported over mesoporous SBA-15 was synthesized by a facile wet impregnation route, characterized for their structural, textural and reduction properties and were successfully used for the methane decomposition. The fine dispersion of metal oxide particles on the surface of SBA-15, without affecting its mesoporous texture was clearly shown in the low angle X-ray diffraction patterns and the transmission electron microscopy (TEM) images. The nitrogen sorption analysis showed the reduced specific surface area and pore volume of SBA-15, after metal loading due to the partial filling of hexagonal mesopores by metal species. The results of methane decomposition experiments indicated that all of the bimetallic catalysts were highly active and stable for the reaction at 700°C even after 300min of time on stream (TOS). However, a maximum hydrogen yield of ∼56% was observed for the NiCo/SBA-15 catalyst within 30min of TOS. A high catalytic stability was shown by the CoFe/SBA-15 catalyst with 51% of hydrogen yield during the course of reaction. The catalytic stability of the bimetallic catalysts was attributed to the formation of bimetallic alloys. Moreover, the deposited carbons were found to be in the form of a new set of hollow multi-walled nanotubes with open tips, indicating a base growth mechanism, which confirm the selectivity of SBA-15 supported bimetallic catalysts for the formation of open tip carbon nanotubes. The Raman spectroscopic and thermogravimetric analysis of the deposited carbon nanotubes over the bimetallic catalysts indicated their higher graphitization degree and oxidation stability.

Why Muscle is an Efficient Shock Absorber

Skeletal muscles power body movement by converting free energy of ATP hydrolysis into mechanical work. During the landing phase of running or jumping some activated skeletal muscles are subjected to stretch. Upon stretch they absorb body energy quickly and effectively thus protecting joints and bones from impact damage. This is achieved because during lengthening, skeletal muscle bears higher force and has higher instantaneous stiffness than during isometric contraction, and yet consumes very little ATP. We wish to understand how the actomyosin molecules change their structure and interaction to implement these physiologically useful mechanical and thermodynamical properties. We monitored changes in the low angle x-ray diffraction pattern of rabbit skeletal muscle fibers during ramp stretch compared to those during isometric contraction at physiological temperature using synchrotron radiation. The intensities of the off-meridional layer lines and fine interference structure of the meridional M3 myosin x-ray reflection were resolved. Mechanical and structural data show that upon stretch the fraction of actin-bound myosin heads is higher than during isometric contraction. On the other hand, the intensities of the actin layer lines are lower than during isometric contraction. Taken together, these results suggest that during stretch, a significant fraction of actin-bound heads is bound non-stereo-specifically, i.e. they are disordered azimuthally although stiff axially. As the strong or stereo-specific myosin binding to actin is necessary for actin activation of the myosin ATPase, this finding explains the low metabolic cost of energy absorption by muscle during the landing phase of locomotion.

HOP Skip and Jump; but How?

Apart from fast, efficient and coordinated contraction of several skeletal muscles, running and jumping require effective absorption of the kinetic energy of the body during the landing phase, to absorb impact forces and prevent injury. This is done not only by joints, bones and tendons, but also by activated muscles which resist stretch. During lengthening, skeletal muscle bears higher force and has higher instantaneous stiffness than during isometric contraction, and yet consumes very little ATP. These properties allow muscle to absorb the energy of a fall or landing by stretching. Our work shows how the actomyosin molecules change their structure and interaction to implement these physiologically useful mechanical and thermodynamical properties. The low angle x-ray diffraction pattern of rabbit skeletal muscle fibers was monitored during isometric contraction and compared to that during ramp stretch. The experiments were carried out at physiological temperature, using low-angle X-ray synchrotron radiation at ID2, ESRF, Grenoble. The intensities of the off-meridional layer lines and fine interference structure of the meridional M3 myosin X-ray reflection were resolved. Mechanical and structural data show that upon stretch the fraction of actin-bound myosin heads is higher than during isometric contraction. This finding accounts for the higher stiffness and greater energy absorbing capacity of stretched muscle compared to isometric. However the intensities of the actin layer lines are lower than during isometric contraction. These results suggest that during stretch, a significant fraction of actin-bound heads is bound weakly or non-stereo-specifically. That is, the actin-bound myosin heads are disordered azimuthally but are stiff axially. As the strong or stereo-specific myosin binding to actin is necessary for actin activation of the myosin ATPase, this finding explains the low metabolic cost of energy absorption by muscle during the landing phase of locomotion.

Catalytic Performance of Al-MCM-48 Molecular Sieves for Isopropylation of Phenol with Isopropyl Acetate

Al-MCM-48 molecular sieves (Si/Al molar ratios = 25, 50, 75, and 100) were synthesized hydrothermally using cetyltrimethylammonium bromide as the structure directing template. The orderly arrangement of mesopores was evident from the low angle X-ray diffraction patterns and transmission electron microscopy images. The catalytic performance of the materials was evaluated in the vapor phase isopropylation of phenol with isopropyl acetate. Phenol conversion decreased with the increase in the Si/Al ratio of the catalysts. The major reaction product was 4-isopropyl phenol with 78% selectivity. The delocalization of phenolic oxygen electron pair over the aromatic ring promoted para-selective alkylation. Such delocalization could be aided by the hydrophilic surface of the molecular sieves. Although an ester was used as the alkylating agent, phenyl isopropyl ether was not formed in the reaction.

The Low Angle X-Ray Diffraction Pattern from Skinned Fibers of Rabbit Psoas Muscle: Effect of Changes in [Ca++] and [Orthophosphate

Bundles of 3-5 fibers were activated isometrically at different pCa by a temperature jump from 1°C to 12°C using a mechanical apparatus (Linari et al., Biophys. J. 92:2476, 2007) modified to collect the X-ray diffraction pattern. The M3 meridional reflection from the axial repeat of the myosin heads was sampled by X-ray interference between half-sarcomeres. In relaxed fibers at 12°C, the M3 reflection had a major peak at 14.56 nm and a minor peak at 14.37 nm. The ratio of peak intensities (RM3) was 0.43±0.06 and the spacing (SM3) was 14.49±0.01 nm. In relaxed fibers the intensity of the main peak reduced with increasing temperature, so that at 36°C (the physiological temperature) the 14.37 nm peak was dominant, with small satellite peaks on either side, as in resting intact fibers from frog muscle. During activation at 12°C at saturating [Ca++], pCa 4.5, the intensity of the M3 reflection (IM3) increased to 1.9±0.4 times the relaxed value with major and minor peaks at 14.68 nm and 14.46 nm; RM3 was 0.62±0.03 and SM3 was 14.59±0.01 nm. Activation at pCa 5.5 or at pCa 4.5 with addition of 10 mM orthophosphate (Pi) had similar effects: force was reduced to 0.34±0.10 the control value and IM3 to 0.56±0.03; RM3 was 0.46±0.07 and SM3 was 14.55±0.02 nm. These results give structural support to the conclusion from mechanical experiments (Linari et al., 2007) that both decreasing [Ca++] and increasing [Pi] reduce isometric force by a decrease in the number of force generating myosin heads with no change in force per head.Supported by FIRB-Futuro in Ricerca and Ente Cassa di Risparmio di Firenze (Italy), MRC (UK).