Studying Microstructure in Molecular Crystals With Nanoindentation: Intergrowth Polymorphism in Felodipine

Intergrowth polymorphism refers to the existence of distinct structural domains within a single crystal of a compound. The phenomenon is exhibited by form II of the active pharmaceutical ingredient felodipine, and the associated microstructure is a significant feature of the compound’s structural identity. Employing the technique of nanoindentation on form II reveals a bimodal mechanical response on specific single‐crystal faces, demonstrating distinct properties for two polymorphic forms within the same crystal.     

Variation of granule mass fraction with coordination number in wet granulation process

In granulation, fine particles combine to form a coarse granule in the form of a particle matrix partially or fully saturated with a binder liquid. The final product of granulation possesses a wide variety of granule size distributions with surface mean diameters which differ with operating conditions. The final granule size depends on the operating conditions, e.g. operating gas velocity, inlet air temperature, initial feed particle size, and viscosity of the binder. The objective of this paper is to find out the uniformity in the relation between the granule mass fraction in the final granule size distribution and the number of feed particles present in the granules. The total number of granules obtained depends on the experimental conditions but the granule mass fraction and the number of feed particles forming a single granule are independent of operating variables, feed material and method of granulation. The paper purports further to compare the uniform nature of mass fraction of the granules in final granule size distribution and the primary particles required to form that particular granule size irrespective of experimental conditions of granulation.     

Behavior of disordered boron carbide under stress

Gibbs free-energy calculations based on density functional theory have been used to determine the possible source of failure of boron carbide just above the Hugoniot elastic limit (HEL). A range of B4C polytypes is found to be stable at room pressure. The energetic barrier for shock amorphization of boron carbide is by far the lowest for the B12(CCC) polytype, requiring only 6 GPa approximately = P(HEL) for collapse under hydrostatic conditions. The results clearly demonstrate that the collapse of the B12(CCC) phase leads to segregation of B12 and amorphous carbon in the form of 2-3 nm bands along the (113) lattice direction, in excellent agreement with recent transmission electron microscopy results.     

In search for structure of active site in iron-based oxygen reduction electrocatalysts

Calculations to elucidate the structure of Fe-based electrocatalysts were performed. Lowest energy configurations for incorporation of nitrogen in bulk of graphene sheet as well as on edge were determined. Substitution of nitrogen in bulk graphene is endothermic, while on the edge it can be either exothermic, if hydrogen is present, or endothermic. Energies of various configurations for the incorporation of iron on the edge of the nitrided graphene sheet were also examined. In the absence of hydrogen, iron prefers to bond with nitrogen and a carbon atom. In the presence of hydrogen, however, iron was found to prefer bonding to two nitrogen atoms on the graphene edge.     

On the compositum of wildly ramified extensions

The ramification filtration on the compositum of two wildly ramified extensions is computed in various cases. Some positive results towards Abhyankar's inertia conjecture have been also proved.     

Elemental characterization of coal fly ash using k0-based IM-NAA and EDXRF towards its potential utilization and environmental concern

Journal of Radioanalytical and Nuclear Chemistry - India is a major producer of fly ash due to its coal-based thermal power plants. The elemental characterization of the fly ash facilitates its...     

Growth of first generation dendrons on SiO2: controlling chemisorption of transition metal coordination complexes

We have investigated the growth of first generation branched polyamidoamine dendrons on silicon dioxide as a way to tailor and control the subsequent chemisorption of transition metal coordination complexes. Beginning with straight-chain alkyl, amine-terminated self-assembled monolayers as anchors, we find that the efficiency of the dendritic branching step depends on the length of the anchor, it being nearly perfect on a 12-carbon chain anchor. The reaction of these layers, both the anchor layers and the first generation dendrons, with Ta[N(CH3)2]5 and Ti[N(CH3)2]4 have been examined in ultrahigh vacuum using X-ray photoelectron spectroscopy. We find that the saturation coverage increases with the density of terminal -NH2 groups; thus, the branching step has effectively amplified the chemisorptive capacity of the surface. Concerning the spatial extent of reaction we find that it depends on the thickness and structure of the organic layer. The thinnest layer cannot prevent penetration of the metal complex to the organic/SiO2 interface, where it can react with residual -OH, whereas, on the longer straight chain anchor, reaction occurs exclusively at the terminal -NH2 group. On the branched dendrons, the situation is more complex, and reaction occurs not only with the terminal -NH2 group but also likely with functional groups, such as -NH-(C=O)-, on the backbone of the branched dendron.     

Highly Efficient Non‐Palladium‐Catalyzed Controlled Synthesis and X‐ray Analysis of Functionalized 1,2‐Diaryl‐, 1,2,3‐Triaryl‐, and 1,2,3,4‐Tetraarylbenzenes

A general, two‐step, highly efficient synthesis of 1,2‐diaryl‐, 1,2,3‐triaryl‐, and 1,2,3,4‐tetraarylbenzenes from simple stitching of α‐oxo‐ketene‐S,S‐acetals and active methylene compounds via a lactone intermediate is described. This procedure offers easy access to highly functionalized arylated benzenes that contain sterically demanding groups in good to excellent yields. The novelty of the procedure lies in the construction of aromatic compounds with the desired conformational flexibility along the molecular axis in a transition‐metal‐free environment through easily accessible precursors. Crystal analysis of these arylated benzene scaffolds showed that the peripheral aryl rings are arranged in a propeller‐like fashion with respect to the central benzene ring. Examination of the crystal packing in the structure of a 1,2,3,4‐tetraarylbenzene revealed an N???π interaction between molecules related by a two‐fold screw axis running in the direction of the a axis. Interestingly, the repeating array of N???π interactions around the axis of this 1,2,3,4‐tetraarylbenzene forces the molecules into a helical pattern.     

Self-assembled monolayer of organic iodine on a Au surface for attachment of redox-active metal clusters

The attachment of a bifunctional iodo-organo-phosphinate compound to gold (Au) surfaces via chemisorption of the iodine atom is described and used to chelate a redox-active metal cluster via the phosphinate group. XPS, AFM, and electrochemical measurements show that (4-iodo-phenyl)phenyl phosphinic acid (IPPA) forms a tightly bound self-assembled monolayer (SAM) on Au surfaces. The surface coverage of an IPPA monolayer on Au was quantified by an electrochemical method and found to be 0.40 +/- 0.03 nmol/cm2, roughly corresponding to 0.4 monolayers. We show that the Au/IPPA SAM, but not the underivatized Au, adsorbs Mn4O4(Ph2PO2)6 from solution by a phosphinate exchange reaction to yield Au/IPPA/Mn4O4(Ph2PO2)5 SAM. The resulting SAM is firmly bound and not removed by sonication, as confirmed by manganese XPS (Mn 2p1/2) and by AFM. Electrochemistry confirms that Mn4O4(Ph2PO2)6 is anchored on the Au/IPPA surface and that redox chemistry can be mediated between the electrode and the surface-attached complex. Mn4O4(Ph2PO2)6 contains the reactive Mn4O46+ cubane core, a redox-active bioinspired catalyst.