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Single coating of zinc ferrite renders magnetic nanomotors therapeutic and stable against agglomeration
No full textMagnetic nanomotors with integrated theranostic capabilities can revolutionize biomedicine of the future. Typically, these nanomotors contain ferromagnetic materials, such that small magnetic fields can be used to maneuver and localize them in fluidic or gel-like environments. Motors with large permanent magnetic moments tend to agglomerate, which limits the scalability of this otherwise promising technology. Here, we demonstrate the application of a microwave-synthesized ferrite layer to reduce the agglomeration of helical ferromagnetic nanomotors by an order of magnitude, which allows them to be stored in a colloidal suspension for longer than six months and subsequently be manoeuvred with undiminished performance. The ferrite layer also rendered the nanomotors suitable as magnetic hyperthermia agents, as demonstrated by their cytotoxic effects on cancer cells. The two functionalities were inter-related since higher hyperthermia efficiency required a denser suspension, both of which were achieved in a single microwave-synthesized ferrite coating
Strengthening mechanisms in Fe-Al based ferritic low-density steels
No full textLow-density steels with different aluminium contents have been investigated with an aim to examine the occurrence of different strengthening mechanisms leading to its higher strength. A composition corresponding to 6.8 wt% aluminium has been studied to understand the underlying strengthening mechanisms. Different factors contributing to the strengthening mechanisms have been separately analyzed. Microstructural features have been analyzed using Mossbauer spectroscopy, small angle X-ray scattering (SAXS), X-ray line profile analysis and transmission electron microscopy (TEM). The enhanced yield strength of the low-density steel containing 6.8 wt % Al was attributed to the strengthening effects arising from the ferrite grain size, dislocations incorporated during processing, ordered phase formation and the presence of Al atoms in the solid solution. Each of these operating mechanisms was modelled by using its constitutive equation for example, grain size strengthening by classical Hall-fetch equation and the strengthening from dislocations by Taylor's equation. In addition, the formation of nano-sized ordered phase was evaluated by TEM, Mossbauer spectroscopy, SAXS and hence order strengthening was modelled by using the size and volume fraction (as determined by TEM and SAXS). Strengthening due to lattice frictional stress required for dislocation motion was also incorporated into the model
DNA structural basis for fragility at peak III of BCL2 major breakpoint region associated with t(14;18) translocation
No full textMaintaining genome integrity is crucial for normal cellular functions. DNA double-strand breaks (DSBs), when unrepaired, can potentiate chromosomal translocations. t(14;18) translocation involving BCL2 gene on chromosome 18 and IgH loci at chromosome 14, could lead to follicular lymphoma. Molecular basis for fragility of translocation breakpoint regions is an active area of investigation. Previously, formation of non-B DNA structures like G-quadruplex, triplex, B/A transition were investigated at peak I of BCL2 major breakpoint region (MBR); however, it is less understood at peak III. In vitro gel shift assays show faster mobility for MBR peak III sequences, unlike controls. CD studies of peak III sequences reveal a spectral pattern different from B-DNA. Although complementary C-rich stretches exhibit single-strandedness, corresponding guanine-rich sequences do not show DMS protection, ruling out G-quadruplex and triplex DNA. Extrachromosomal assay indicates that peak III halts transcription, unlike its mutated version. Taken together, multiple lines of evidence suggest formation of potential cruciform DNA structure at MBR peak III, which was also supported by in silico studies. Thus, our study reveals formation of non-B DNA structure which could be a basis for fragility at BCL2 breakpoint regions, eventually leading to chromosomal translocations
Multi-scale surface topography to minimize adherence and viability of nosocomial drug-resistant bacteria
No full textToward minimizing bacterial colonization of surfaces, we present a one-step etching technique that renders aluminumalloys withmicro-and nano-scale roughness. Such amulti-scale surface topography exhibited enhanced antibacterial effect against awide range of pathogens. Multi-scale topography of commercially grade pure aluminumkilled 97% of Escherichia coli and 28% of Staphylococcus aureus cells in comparison to 7% and 3%, respectively, on the smooth surfaces. Multi-scale topography on Al 5052 surfacewas shown to kill 94% of adhered E. coli cells. Themicroscale features on the etched Al 1200 alloy were not found to be significantly bactericidal, but shown to decrease the adherence of S. aureus cells by one-third. The fabricationmethod is easily scalable for industrial applications. Analysis of roughness parameters determined by atomic forcemicroscopy revealed a set of significant parameters that can yield a highly bactericidal surface; thereby providing the design to make any surface bactericidal irrespective of the method of fabrication. The multi-scale roughness of Al 5052 alloy was also highly bactericidal to nosocomial isolates of E. coli, K. pneumoniae and P. aeruginosa. We envisage the potential application of engineered surfaces with multi-scale topography to minimize the spread of nosocomial infections. (C) 2017 The Author(s). Published by Elsevier Ltd
Cu6S6 Clusters as a Building Block for the Stabilization of Coordination Polymers with NiAs, NaCl, and Related Structures: Synthesis, Structure, and Catalytic Studies
No full textFour new three-dimensional heterometallic coordination polymers (CPs), {Zn-3(Hen)(OH)}{Cu-6(6-mna)(6)}<bold></bold>(H2O)(6)] (I), {Zn-2(OH)(en)}{Cu-6(6-mna)(6)}(0.5)<bold></bold>(H2O)(2)<bold>EtO H</bold>] (II), {Zn-3(dap)(3)(H2O)}{Cu-6(6-mna)(6)}<bold></bold>(H2O)(4)] (III), and {Zn-2(4,4-bpy)(0.5)(OH)(H2O)}{Cu-6(6-mna)(6)}(0.5)<bold></bold>(H 2O)] (IV) (en = ethylenediamine, 6-H(2)mna = 6-mercaptonicotinic acid, dap = 1,2-diaminopropane, 4,4-bpy = 4,4-bipyridine), have been synthesized and their structures determined by single-crystal X-ray crystallography. The compounds consist of Cu6S6 octahedral clusters linked through the carboxylates to different zinc-oxo clusters. Thus, the compounds contain Cu-I- and Zn-II-based clusters, which are not commonly observed in coordination polymer structures. Compound I stabilizes in a NiAs-related structure, compounds II and IV in a NaCl-related structure, and compound III is a new type of network structure. All the compounds were active catalysts in the heterogeneous nitroaldol reaction
Interplay of Structural and Bonding Characters in Thermal Conductivity and Born-Effective Charge of Transition Metal Dichalcogenides
No full textThermal transport in a material is governed by anharmonicity of crystal potential, which depends on the type of interatomic interaction. Using first-principles calculations, we report that lattice thermal conductivity (kappa(latt)) and its anisotropy (kappa(x,y) - kappa(z)) of transition metal dichalcogenides (TMDs) increase by orders of magnitude with the change of constituent metal atom from Zr/Hf to Mo/W. This unprecedented difference in kappa(latt) is substantiated by lower phonon group velocity, and 4 times larger anharmonicity of Zr/Hf based TMDs compared to Mo/W based TMDs. The sign and the absolute value of the Born effective charges, which emerges from the ionicity of the bonds, are found to be different for these two classes of materials. This leads to a significant difference in their interlayer van der Waals (vdW) interaction strengths, which are shown to be inversely related to the anisotropy in kappa(latt)
What Gives an Insulin Hexamer Its Unique Shape and Stability? Role of Ten Confined Water Molecules
No full textSelf-assembly of proteins often gives rise to interesting quasi-stable structures that serve important biological purposes. Insulin hexamer is such an assembly. While monomer is the biologically active form of insulin, hexamer serves as the storehouse of the hormone. The hexamer also prevents the formation of higher order aggregates. While several studies explored the role of bivalent metal ions like Zn2+, Ca2+, etc., in the stabilization of the hexameric form, the role of water molecules has been ignored. We combine molecular dynamics simulations, quantum calculations, and X-ray analyses to discover that a team of approximately 10 water molecules confined inside a barrel-shaped nanocavity at the center of insulin hexamer is one of the major causes that account for the unusual stability of the biomolecular assembly. These cavity water molecules exhibit interesting, dynamical features like intermittent escape and reentrance. We find that these water molecules are dynamically slower than the bulk and weave an intricate hydrogen bond network among themselves and with neighboring protein residues to generate a robust backbone at the center of the hexamer that holds the association strongly from inside and maintains the barrel shape
Characterization of Staphylococcus epidermidis Polynucleotide phosphorylase and its interactions with ribonucleases RNase J1 and RNase J2
No full textPolynucleotide phosphorylase catalyzes both 3'-5' exoribonuclease and polyadenylation reactions. The crystal structure of Staphylococcus epidermidis PNPase revealed a bound phosphate in the PH2 domain of each protomer coordinated by three adjacent serine residues. Mutational analysis suggests that phosphate coordination by these serine residues is essential to maintain the catalytic center in an active conformation. We note that PNPase forms a complex with RNase J1 and RNase J2 without substantially altering either exo-ribonuclease or polyadenylation activity of this enzyme. This decoupling of catalytic activity from protein-protein interactions suggests that association of these endo-or exo-ribonucleases with PNPase could be more relevant for cellular localization or concerted targeting of structured RNA for recycling. (C) 2017 Elsevier Inc. All rights reserved
Environment and dispersal influence changes in species composition at different scales in woody plants of the Western Ghats, India
No full textQuestionWhat are the relative roles of environmental and spatial factors in influencing variation in species composition of tropical woody plants at different spatial scales? LocationTropical evergreen forests, Western Ghats, South India. MethodsUsing a plot-based species inventory spanning the entire latitudinal extent (1,200km) of the Western Ghats' wet evergreen forests, we collected primary data on spatial variation in species composition of woody plants. Each plot was characterized by a set of environmental descriptors consisting of topographic, edaphic and climatic variables, while eigenvector-based spatial variables and plot coordinates were used as spatial descriptors. We used ordination-based as well as distance-based variation partitioning techniques to partition the variation in species composition into components uniquely and jointly explained by environmental and spatial factors. ResultsThe compositional similarity of woody plants largely showed a linear decline with log-geographic distance. However, this relationship was spatially structured. After controlling for the differences in environment, compositional similarity was found to be strongly associated with geographic distance only at the smallest spatial scale. Variation partitioning analysis revealed that environmental variables explained a much larger proportion of variation in species composition overall compared to spatial variables. Among environmental variables, climatic variables emerged as the most important predictors of variation in species composition at regional and landscape scales. ConclusionsStrong association between compositional similarity and geographic distance at local scales indicates the influence of dispersal limitation, while niche differentiation seems to be a more important driver of variation in species composition at larger spatial scales. Overall, our results provide evidence for scale-dependent shifts in the relative importance of factors that are responsible for variation in species composition
Thermodynamics and Kinetics of Single-Chain Monellin Folding with Structural Insights into Specific Collapse in the Denatured State Ensemble
No full textProteins, which behave as random coils in high denaturant concentrations undergo collapse transition similar to polymers on denaturant dilution. We study collapse in the denatured ensemble of single-chain monellin (MNEI) using a coarse-grained protein model and molecular dynamics simulations. The model is validated by quantitatively comparing the computed guanidinium chloride and pH-dependent thermodynamic properties of MNEI folding with the experiments. The computed properties such as the fraction of the protein in the folded state and radius of gyration (R-g) as function of GuHCI] are in good agreement with the experiments. The folded state of MNEI is destabilized with an increase in pH due to the deprotonation of the residues Glu24 and Cys42. On decreasing GuHCI], the protein in the unfolded ensemble showed specific compaction. The R-g of the protein decreased steadily with GuHCI] dilution due to increase in the number of native contacts in all the secondary structural elements present in the protein. MNEI folding kinetics is complex with multiple folding pathways and transiently stable intermediates are populated in these pathways. In strong stabilizing conditions, the protein in the unfolded ensemble showed transition to a more compact unfolded state where Rg decreased by approximate to 17% due to the formation of specific native contacts in the protein. The intermediate populated in the dominant MNEI folding pathway satisfies the structural features of the dry molten globule inferred from experiments. (C) 2017 Elsevier Ltd. All rights reserved