Mesoporous bioactive glass and glass-ceramics: Influence of the local structure on in vitro bioactivity

Mesoporous quaternary bioactive glasses and glass-ceramic with alkali-alkaline-earth oxide were successfully synthesized by using non-ionic block copolymer P123 and evaporation induced self assembly (EISA) process followed by acid treatment assisted sal-gel method. As prepared samples has been characterized for the structural, morphological and textural properties with the various analytical techniques. Glass dissolution/ion release rate in simulated body fluid (SBF) was monitored by inductively coupled plasma (ICP) emission spectroscopy, whereas the formation of apatite phase and its crystallization at the glass and glass-ceramic surface was examined by structural, textural and microscopic probes. The influence of alkaline-earth oxide content on the glass structure followed by textural property has become more evident. The pristine glass samples exhibit a wormhole-like mesoporous structure, whereas the glass-ceramic composition is found to be in three different phases, namely crystalline hydroxyapatite, wollastonite and a residual glassy phase as observed in Cerabone (R) A/W. The existence of calcium orthophosphate phase is closely associated with the pore walls comprising nanometric-sized ``inclusions''. The observed high surface area in conjunction with the structural features provides the possible explanation for experimentally observed enhanced bioactivity through the easy access of ions to the fluid. On the other hand, presence of multiple phases in glass-ceramic sample inhibits or delays the kinetics of apatite formation. (C) 2013 Elsevier Inc. All rights reserved.

Boron doped defective graphene as a potential anode material for Li-ion batteries

Graphene with large surface area and robust structure has been proposed as a high storage capacity anode material for Li ion batteries. While the inertness of pristine graphene leads to better Li kinetics, poor adsorption leads to Li clustering, significantly affecting the performance of the battery. Here, we show the role of defects and doping in achieving enhanced adsorption without compromising on the high diffusivity of Li. Using first principles density functional theory (DFT) calculations, we carry out a comprehensive study of diffusion kinetics of Li over the plane of the defective structures and calculate the change in the number of Li atoms in the vicinity of defects, with respect to pristine graphene. Our results show that the Li-C interaction, storage capacity and the energy barriers depend sensitively on the type of defects. The un-doped and boron doped mono-vacancy, doped di-vacancy up to two boron, one nitrogen doped di-vacancy, and Stone-Wales defects show low energy barriers that are comparable to pristine graphene. Furthermore, boron doping at mono-vacancy enhances the adsorption of Li. In particular, the two boron doped mono-vacancy graphene shows both a low energy barrier of 0.31 eV and better adsorption, and hence can be considered as a potential candidate for anode material.

A 3.8-V earth-abundant sodium battery electrode

Rechargeable lithium batteries have ushered the wireless revolution over last two decades and are now matured to enable green automobiles. However, the growing concern on scarcity and large-scale applications of lithium resources have steered effort to realize sustainable sodium-ion batteries, Na and Fe being abundant and low-cost charge carrier and redox centre, respectively. However, their performance is limited owing to low operating voltage and sluggish kinetics. Here we report a hitherto-unknown material with entirely new composition and structure with the first alluaudite-type sulphate framework, Na2Fe2(SO4)(3), registering the highest-ever Fe3+/ Fe2+ redox potential at 3.8V (versus Na, and hence 4.1V versus Li) along with fast rate kinetics. Rare-metal-free Na-ion rechargeable battery system compatible with the present Li-ion battery is now in realistic scope without sacrificing high energy density and high power, and paves way for discovery of new earth-abundant sustainable cathodes for large-scale batteries.

t-Na-2(VO)P2O7: A 3.8 V Pyrophosphate Insertion Material for Sodium-Ion Batteries

Pyrophosphate oxyanionic framework compounds offer a great platform to investigate new battery materials. In our continuing effort to explore pyrophosphate cathodes for sodium-ion batteries, we report, for the first time, the synthesis and use of tetragonal Na-2(VO)P2O7 as a potential sodium-ion insertion material. This material can be easily prepared by using a conventional solid-state route at a relatively low temperature of 400 degrees C. Stabilizing as a tetragonal structure with an open framework, the material offers pathways for Na+ diffusion. The as-synthesized material, with no further cathode optimization, yields a reversible capacity (Q) approaching 80 mAh g(-1) (Q(Theoretical) = 93.4 mAh g(-1)) involving a one electron V5+/V4+ redox potential located at 3.8 V (vs. Na/Na+). Furthermore, the material exhibits decent rate kinetics and reversibility. Combining green synthesis and moderate electrochemical properties, t-Na-2(VO)P2O7 is reported as a new addition to the growing family of pyrophosphate cathodes for sodium-ion batteries.

Hydrogen bonding, halogen bonding and lithium bonding: an atoms in molecules and natural bond orbital perspective towards conservation of total bond order, inter- and intra-molecular bonding

One hundred complexes have been investigated exhibiting D-X center dot center dot center dot A interactions, where X = H, Cl or Li and DX is the `X bond' donor and A is the acceptor. The optimized structures of all these complexes have been used to propose a generalized `Legon-Millen rule' for the angular geometry in all these interactions. A detailed Atoms in Molecules (AIM) theoretical analysis confirms an important conclusion, known in the literature: there is a strong correlation between the electron density at the X center dot center dot center dot A bond critical point (BCP) and the interaction energy for all these interactions. In addition, we show that extrapolation of the fitted line leads to the ionic bond for Li-bonding (electrostatic) while for hydrogen and chlorine bonding, it leads to the covalent bond. Further, we observe a strong correlation between the change in electron density at the D-X BCP and that at the X center dot center dot center dot A BCP, suggesting conservation of the bond order. The correlation found between penetration and electron density at BCP can be very useful for crystal structure analysis, which relies on arbitrary van der Waals radii for estimating penetration. Various criteria proposed for shared-and closed-shell interactions based on electron density topology have been tested for H/Cl/Li bonded complexes. Finally, using the natural bond orbital (NBO) analysis it is shown that the D-X bond weakens upon X bond formation, whether it is ionic (DLi) or covalent (DH/DCl) and the respective indices such as ionicity or covalent bond order decrease. Clearly, one can think of conservation of bond order that includes ionic and covalent contributions to both D-X and X center dot center dot center dot A bonds, for not only X = H/Cl/Li investigated here but also any atom involved in intermolecular bonding.

Oxygen-participated electrochemistry of new lithium-rich layered oxides Li3MRuO5 M = Mn, Fe)

We describe the synthesis, crystal structure and lithium deinsertion-insertion electrochemistry of two new lithium-rich layered oxides, Li3MRuO5 (M = Mn, Fe), related to rock salt based Li2MnO3 and LiCoO2. The Li3MnRuO5 oxide adopts a structure related to Li2MnO3 (C2/m) where Li and (Li0.2Mn0.4Ru0.4) layers alternate along the c-axis, while the Li3FeRuO5 oxide adopts a near-perfect LiCoO2 (R (3) over barm) structure where Li and (Li0.2Fe0.4Ru0.4) layers are stacked alternately. Magnetic measurements indicate for Li3MnRuO5 the presence of Mn3+ and low spin configuration for Ru4+ where the itinerant electrons occupy a pi*-band. The onset of a net maximum in the chi vs. T plot at 9.5 K and the negative value of the Weiss constant (theta) of -31.4 K indicate the presence of antiferromagnetic superexchange interactions according to different pathways. Lithium electrochemistry shows a similar behaviour for both oxides and related to the typical behaviour of Li-rich layered oxides where participation of oxide ions in the electrochemical processes is usually found. A long first charge process with capacities of 240 mA h g(-1) (2.3 Li per f.u.) and 144 mA h g(-1) (1.38 Li per f.u.) is observed for Li3MnRuO5 and Li3FeRuO5, respectively. An initial sloping region (OCV to ca. 4.1 V) is followed by a long plateau (ca. 4.3 V). Further discharge-charge cycling points to partial reversibility (ca. 160 mA h g(-1) and 45 mA h g(-1) for Mn and Fe, respectively). Nevertheless, just after a few cycles, cell failure is observed. X-ray photoelectron spectroscopy (XPS) characterisation of both pristine and electrochemically oxidized Li3MRuO5 reveals that in the Li3MnRuO5 oxide, Mn3+ and Ru4+ are partially oxidized to Mn4+ and Ru5+ in the sloping region at low voltage, while in the long plateau, O2- is also oxidized. Oxygen release likely occurs which may be the cause for failure of cells upon cycling. Interestingly, some other Li-rich layered oxides have been reported to cycle acceptably even with the participation of the O2- ligand in the reversible redox processes. In the Li3FeRuO5 oxide, the oxidation process appears to affect only Ru (4+ to 5+ in the sloping region) and O2- (plateau) while Fe seems to retain its 3+ state.

Effect of solvent; enhancing the wettability and engineering the porous structure of a calcium phosphate/agarose composite for drug delivery

Tissue engineering deals with the regeneration of tissues for bone repair, wound healing, drug delivery, etc., and a highly porous 3D artificial scaffold is required to accommodate the cells and direct their growth. We prepared 3D porous calcium phosphate ((hydroxyapatite/beta-tricalcium phosphate)/agarose, (HAp/beta-TCP)/agarose) composite scaffolds by sol-gel technique with water (WBS) and ethanol (EBS) as solvents. The crystalline phases of HAp and beta-TCP in the scaffolds were confirmed by X-ray diffraction (XRD) analysis. The EBS had reduced crystallinity and crystallite size compared to WBS. WBS and EBS revealed interconnected pores of 1 mu m and 100 nm, respectively. The swelling ratio was higher for EBS in water and phosphate buffered saline (PBS). An in vitro drug loading/release experiment was carried out on the scaffolds using gentamicin sulphate (GS) and amoxicillin (AMX). We observed initial burst release followed by sustained release from WBS and EBS. In addition, GS showed more extended release than AMX from both the scaffolds. GS and AMX loaded scaffolds showed greater efficacy against Pseudomonas than Bacillus species. WBS exhibited enhanced mechanical properties, wettability, drug loading and haemocompatibility compared to EBS. In vitro cell studies showed that over the scaffolds, MC3T3 cells attached and proliferated and there was a significant increase in live MC3T3 cells. Both scaffolds supported MC3T3 proliferation and mineralization in the absence of osteogenic differentiation supplements in media which proves the scaffolds are osteoconducive. Microporous scaffolds (WBS) could assist the bone in-growth, whereas the presence of nanopores (EBS) could enhance the degradation process. Hence, WBS and EBS could be used as scaffolds for tissue engineering and drug delivery. This is a cost effective technique to produce scaffolds of degradable 3D ceramic-polymer composites.

One-step synthesis of a cyclic 2,17-dioxo3,3](4,4 `)biphenylophane and first preparation of a microporous polymer network from a macrocyclic precursor by cyclotrimerization

One-step synthesis of a cyclic 2,17-dioxo3,3](4,4') biphenylophane (MC) was achieved in high yield; its structure was verified by single crystal X-ray analysis. As a first example, a microporous polymer network was formed from macrocycle MC via acid-catalysed cyclotrimerization yielding a BET surface area of ca. 570 m(2) g(-1).

Improved capacity and stability of integrated Li and Mn rich layered-spinel Li1.17Ni0.25Mn1.08O3 cathodes for Li-ion batteries

A Li-rich layered-spinel material with a target composition Li1.17Ni0.25Mn1.08O3 (xLiLi1/3Mn2/3]O-2.(1 - x) LiNi0.5Mn1.5O4, (x = 0.5)) was synthesized by a self-combustion reaction (SCR), characterized by XRD, SEM, TEM, Raman spectroscopy and was studied as a cathode material for Li-ion batteries. The Rietveld refinement results indicated the presence of monoclinic (LiLi1/3Mn2/3]O-2) (52%), spinel (LiNi0.5Mn1.5O4) (39%) and rhombohedral LiNiO2 (9%). The electrochemical performance of this Li-rich integrated cathode material was tested at 30 degrees C and compared to that of high voltage LiNi0.5Mn1.5O4 spinel cathodes. Interestingly, the layered-spinel integrated cathode material exhibits a high specific capacity of about 200 mA h g(-1) at C/10 rate as compared to 180 mA h g(-1) for LiNi0.5Mn1.5O4 in the potential range of 2.4-4.9 V vs. Li anodes in half cells. The layered-spinel integrated cathodes exhibited 92% capacity retention as compared to 82% for LiNi0.5Mn1.5O4 spinel after 80 cycles at 30 degrees C. Also, the integrated cathode material can exhibit 105 mA h g(-1) at 2 C rate as compared to 78 mA h g(-1) for LiNi0.5Mn1.5O4. Thus, the presence of the monoclinic phase in the composite structure helps to stabilize the spinel structure when high specific capacity is required and the electrodes have to work within a wide potential window. Consequently, the Li1.17Ni0.25Mn1.08O3 composite material described herein can be considered as a promising cathode material for Li ion batteries.

Synthesis, and crystal and electronic structure of sodium metal phosphate for use as a hybrid capacitor in non-aqueous electrolyte

Energy storage devices based on sodium have been considered as an alternative to traditional lithium based systems because of the natural abundance, cost effectiveness and low environmental impact of sodium. Their synthesis, and crystal and electronic properties have been discussed, because of the importance of electronic conductivity in supercapacitors for high rate applications. The density of states of a mixed sodium transition metal phosphate (maricite, NaMn1/3Co1/3Ni1/3PO4) has been determined with the ab initio generalized gradient approximation (GGA)+Hubbard term (U) method. The computed results for the mixed maricite are compared with the band gap of the parent NaFePO4 and the electrochemical experimental results are in good agreement. A mixed sodium transition metal phosphate served as an active electrode material for a hybrid supercapacitor. The hybrid device (maricite versus carbon) in a nonaqueous electrolyte shows redox peaks in the cyclic voltammograms and asymmetric profiles in the charge-discharge curves while exhibiting a specific capacitance of 40 F g(-1) and these processes are found to be quasi-reversible. After long term cycling, the device exhibits excellent capacity retention (95%) and coulombic efficiency (92%). The presence of carbon and the nanocomposite morphology, identified through X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) studies, ensures the high rate capability while offering possibilities to develop new cathode materials for sodium hybrid devices.

Designing Novel Sulphate-based Ceramic Materials as Insertion Host Compounds for Secondary Batteries

Rechargeable batteries have propelled the wireless revolution and automobiles market over the past 25 years. Developing better batteries with improved energy density demands unveiling of new cathode ceramic materials with suitable diffusion channels and open framework structure. In this pursuit of achieving higher energy density, one approach is to realize enhanced redox voltage of insertion of ceramic compounds. This can be accomplished by incorporating highly electronegative anions in the cathode ceramics. Building on this idea, recently various sulphate- based compounds have been reported as high voltage cathode materials. The current article highlights the use of sulphate (SO4) based cathodes to realize the highest ever Fe3+/Fe2+ redox potentials in Li-ion batteries (LiFeSO4F fluorosulphate: 3.9V vs Li/Li+) and Na-ion batteries (Na2Fe2(SO4)(3) polysulphate: 3.8V vs Na/Na+). These sulphate-based cathode ceramic compounds pave way for newer avenues to design better batteries for future applications.

Flower-like porous cobalt(II) monoxide nanostructures as anode material for Li-ion batteries

In the present study, a microwave-assisted, solution-based route has been employed to obtain porous CoO nano structures. Detailed characterization reveals that the flower-like nanostructures comprise petal-like sheets, each of which is made of an ordered, porous arrangement of crystallites of CoO measuring about 6 nm. TEM analysis shows that each ``petal'' is an oriented aggregate of CoO nanocrystals, such aggregation promoted by the hydroxyl moieties derived from the solution. The structure provides a large specific area as well as the porosity desirable in electrodes in Li-ion batteries. Electrochemical measurements carried out on electrodes made of nanostructured CoO show excellent Li ion-storing capability. A specific capacitance of 779 mAh g(-1) has been measured at a specific current of 100 mA g(-1). Measurements show also excellent cyclability and coulombic efficiency. Impedance spectroscopy provides evidence for charge transfer occurring in the porous networks. (C) 2015 Elsevier B.V. All rights reserved.

Na2M2(SO4)(3) (M = Fe, Mn, Co and Ni): towards high-voltage sodium battery applications

Sodium-ion-based batteries have evolved as excellent alternatives to their lithium-ion-based counterparts due to the abundance, uniform geographical distribution and low price of Na resources. In the pursuit of sodium chemistry, recently the alluaudite framework Na2M2(SO4)(3) has been unveiled as a high-voltage sodium insertion system. In this context, the framework of density functional theory has been applied to systematically investigate the crystal structure evolution, density of states and charge transfer with sodium ions insertion, and the corresponding average redox potential, for Na2M2(SO4)(3) (M = Fe, Mn, Co and Ni). It is shown that full removal of sodium atoms from the Fe-based device is not a favorable process due to the 8% volume shrinkage. The imaginary frequencies obtained in the phonon dispersion also reflect this instability and the possible phase transition. This high volume change has not been observed in the cases of the Co- and Ni-based compounds. This is because the redox reaction assumes a different mechanism for each of the compounds investigated. For the polyanion with Fe, the removal of sodium ions induces a charge reorganization at the Fe centers. For the Mn case, the redox process induces a charge reorganization of the Mn centers with a small participation of the oxygen atoms. The Co and Ni compounds present a distinct trend with the redox reaction occurring with a strong participation of the oxygen sublattice, resulting in a very small volume change upon desodiation. Moreover, the average deintercalation potential for each of the compounds has been computed. The implications of our findings have been discussed both from the scientific perspective and in terms of technological aspects.

X-Ray Studies On The Bilayer Structure Of Trypsin-Treated Rat-Brain Myelin

Trypsin-treated rat brain myelin was subjected to biochemical and X-ray studies. Untreated myelin gave rise to a pattern of three rings with a fundamental repeat period of 155 Angstrom consisting of two bilayers per repeat period, whereas myelin treated with trypsin showed a fundamental repeat period of 75 Angstrom with one bilayer per repeat period. The integrated raw intensity of the h=4 reflection with respect to the h=2 reflection is 0.38 for untreated myelin. The corresponding value reduced to 0.23, 0.18, 0.17 for myelin treated with 5, 10, 40 units of trypsin per mg of myelin, respectively, for 30 min at 30 degrees C. The decrease in relative raw intensity of the higher-order reflection relative to the lower-order reflection is suggestive of a disordering of the phosphate groups upon trypsin treatment or an increased mosaicity of the membrane or a combination of both these effects, However, trypsin treatment does not lead to a complete breakdown of the membrane, The integrated intensity of the h=1 reflection, though weak, is above the measurable threshold for untreated myelin, whereas the corresponding intensity is below the measurable threshold for trypsin-treated myelin, indicating a possible asymmetric to symmetric transition of the myelin bilayer structure about its centre after trypsin treatment.

X-ray Structure of Gelonin at 1.8 Ã… Resolution

Gelonin is a single chain ribosome inactivating protein (RIP) with potential application in the treatment of cancer and AIDS. Diffraction quality crystals grown using PEG3350, belong to the space group P2(1), with it a = 49.4 Angstrom b = 44.9 Angstrom, c = 137.4 Angstrom and beta = 98.4 degrees, and contain two molecules in the asymmetric unit. Diffraction data collected to 1.8 Angstrom resolution has a R(m) value of 7.3%. Structure of gelonin has been solved by the molecular replacement method, using ricin A chain as the search model. Crystallographic refinement using X-PLOR resulted in a model for which the r.m.s deviations from ideal bond lengths and bond angles are 0.012 Angstrom and 2.7 degrees, respectively The final R-factor is 18.4% for 39,806 reflections for which I > 1.0 sigma(I).The C-alpha atoms of the two molecules in the asymmetric unit superpose to within 0.38 Angstrom for 247 atom pairs. The overall fold of gelonin is similar to that of other RIPs such as ricin A chain and alpha-momorcharin, the r.m.s.d. for C-alpha superpositions being 1.3 and 1.4 Angstrom, respectively The-catalytic residues (Glu166, Arg169 and Tyr113) in the active site form a hydrogen bond scheme similar to that observed in other RIPs. The conformation of Tyr74 in the active site, however, is significantly different from that in alpha-momorcharin. Three well defined water molecules are located in the active site cavity and one of them, X319, superposes to within 0.2 Angstrom of a corresponding water molecule in the structure of alpha-momorcharin. Any of the three could be the substrate water molecule in the hydrolysis reaction catalysed by gelonin.Difference electron density for a N-linked sugar moiety has been observed near only one of the two potential glycosylation sites in the sequence. The amino acid at position 239 has been established as Lys by calculation of omit electron density maps.The two cysteine residues in the sequence, Cys44 and Cys50, form a disulphide bond, and are therefore not available for disulphide conjugation with antibodies. Based on the structure, the region of the molecule that is involved in intradimer interactions is suggested to be suitable for introducing a Cys residue for purposes of conjugation with an antibody to produce useful immunotoxins.