From covalent bonding to coalescence of metallic nanorods

Growth of metallic nanorods by physical vapor deposition is a common practice, and the origin of their dimensions is a characteristic length scale that depends on the three-dimensional Ehrlich-Schwoebel (3D ES) barrier. For most metals, the 3D ES barrier is large so the characteristic length scale is on the order of 200 nm. Using density functional theory-based ab initio calculations, this paper reports that the 3D ES barrier of Al is small, making it infeasible to grow Al nanorods. By analyzing electron density distributions, this paper shows that the small barrier is the result of covalent bonding in Al. Beyond the infeasibility of growing Al nanorods by physical vapor deposition, the results of this paper suggest a new mechanism of controlling the 3D ES barrier and thereby nanorod growth. The modification of local degree of covalent bonding, for example, via the introduction of surfactants, can increase the 3D ES barrier and promote nanorod growth, or decrease the 3D ES barrier and promote thin film growth

Targeting cholesterol-rich microdomains to circumvent tamoxifen-resistant breast cancer

Adjuvant treatment with tamoxifen substantially improves survival of women with estrogen-receptor positive (ER+) tumors. Tamoxifen resistance (TAMR) limits clinical benefit. RRR alpha tocopherol ether-linked acetic acid analogue (alpha-TEA) is a small bioactive lipid with potent anticancer activity. We evaluated the ability of alpha-TEA in the presence of tamoxifen to circumvent TAMR in human breast cancer cell lines. Methods: Two genotypically matched sets of TAM-sensitive (TAMS) and TAM-resistant (TAMR) human breast cancer cell lines were assessed for signal-transduction events with Western blotting, apoptosis induction with Annexin V-FITC/PI assays, and characterization of cholesterol-rich microdomains with fluorescence staining. Critical involvement of selected mediators was determined by using RNA interference and chemical inhibitors. Results: Growth-factor receptors (total and phosphorylated forms of HER-1 and HER-2), their downstream prosurvival mediators pAkt, pmTOR, and pERK1/2, phosphorylated form of estrogen receptor-alpha (pER-alpha at Ser-167 and Ser-118, and cholesterol-rich lipid microdomains were highly amplified in TAMR cell lines and enhanced by treatment with TAM. alpha-TEA disrupted cholesterol-rich microdomains, acted cooperatively with TAM to reduce prosurvival mediators, and induced DR5-mediated mitochondria-dependent apoptosis via an endoplasmic reticulum stress-triggered pro-death pJNK/CHOP/DR5 amplification loop. Furthermore, methyl-beta-cyclodextrin (M beta CD), a chemical disruptor of cholesterol rich microdomains, acted cooperatively with TAM to reduce prosurvival mediators and to induce apoptosis. Conclusions: Data for the first time document that targeting cholesterol-rich lipid microdomains is a potential strategy to circumvent TAMR, and the combination of alpha-TEA + TAM can circumvent TAMR by suppression of prosurvival signaling via disruption of cholesterol-rich lipid microdomains and activation of apoptotic pathways via induction of endoplasmic reticulum stress.Clayton Foundation for ResearchCenter for Molecular and Cellular Toxicology at the University of TexasNIEHS/NIH T32 ES07247Nutritional Science

Approaches in biotechnological applications of natural polymers

Natural polymers, such as gums and mucilage, are biocompatible, cheap, easily available and non-toxic materials of native origin. These polymers are increasingly preferred over synthetic materials for industrial applications due to their intrinsic properties, as well as they are considered alternative sources of raw materials since they present characteristics of sustainability, biodegradability and biosafety. As definition, gums and mucilages are polysaccharides or complex carbohydrates consisting of one or more monosaccharides or their derivatives linked in bewildering variety of linkages and structures. Natural gums are considered polysaccharides naturally occurring in varieties of plant seeds and exudates, tree or shrub exudates, seaweed extracts, fungi, bacteria, and animal sources. Water-soluble gums, also known as hydrocolloids, are considered exudates and are pathological products; therefore, they do not form a part of cell wall. On the other hand, mucilages are part of cell and physiological products. It is important to highlight that gums represent the largest amounts of polymer materials derived from plants. Gums have enormously large and broad applications in both food and non-food industries, being commonly used as thickening, binding, emulsifying, suspending, stabilizing agents and matrices for drug release in pharmaceutical and cosmetic industries. In the food industry, their gelling properties and the ability to mold edible films and coatings are extensively studied. The use of gums depends on the intrinsic properties that they provide, often at costs below those of synthetic polymers. For upgrading the value of gums, they are being processed into various forms, including the most recent nanomaterials, for various biotechnological applications. Thus, the main natural polymers including galactomannans, cellulose, chitin, agar, carrageenan, alginate, cashew gum, pectin and starch, in addition to the current researches about them are reviewed in this article.. }To the Conselho Nacional de Desenvolvimento Cientfíico e Tecnológico (CNPq) for fellowships (LCBBC and MGCC) and the Coordenação de Aperfeiçoamento de Pessoal de Nvíel Superior (CAPES) (PBSA). This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit, the Project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462) and COMPETE 2020 (POCI-01-0145-FEDER-006684) (JAT)

Thermopower and nature of the hole-doped states in LaMnO3 and related systems showing giant magnetoresistance

We have measured the thermopower (S) of hole-doped LaMnO3 systems in order to see its dependence on the Mn4+ content as well as to investigate other crucial factors that determine S. We have carried out hole doping (creation of Mn4+ by two distinct means, namely, by the substitution of La by divalent cations such as Ca and Sr and by self-doping without aliovalent substitution). The thermopower is sensitive not only to the hole concentration but also to the process employed for hole doping, which we explain as arising from the differences in the nature of the hole-doped states. We also point out a general trend in the dependence of S on hole concentration at high temperatures (T> T-c), similar to that found in the normal-state thermopower of the cuprates

Electrical transport, magnetism, and magnetoresistance in ferromagnetic oxides with mixed exchange interactions: A study of the La0.7Ca0.3Mn1−xCoxO3La_{0.7}Ca_{0.3}Mn_{1-x}Co_xO_3 system

In this paper we report the results of an extensive investigation of the $La_{0.7}Ca_{0.3}Mn_{1-x}Co_xO_3$ system. Substitution of Mn by Co dilutes the double-exchange (DE) mechanism and changes the long range ferromagnetic order of $La_{0.7}Ca_{0.3}MnO_3$ to a cluster glass-type ferromagnetic (FM) order similar to that observed in $La_{0.7}Ca_{0.3}CoO_3$. This happens even for the lowest Co substitution of x50.05 and persists over the entire composition range studied (0.05\leqx\leq0.5). The Co substitution also destroys the metallic state and the resistivity increases by orders of magnitude even with a very small extent of Co substitution. The charge localization due to Co substitution is likely to have its origin in polaronic lattice distortion. The Co substitution also suppresses the colossal magnetoresistance (CMR) of the pure manganate (x = 0) over the entire temperature and composition range and it becomes very small for $x\geq0.2$. We conclude that the DE interaction and the resulting metallic state is very ‘‘fragile’’ and hence even a small amount of Co substitution can destroy the FM order, the metallic state, and the CMR

Synthesis, structural relationships and magnetic properties of new amine-templated manganese(II) phosphate-oxalate framework materials

Three novel three-dimensional framework materials in the manganese(II)-phosphate-oxalate system have been prepared hydrothermally using organic amines as structure-directing agents. [H3NC6H10NH3][Mn-2(HPO4)(2)(C2O4)(H2O)(2)] 1 and [H3N(CH2)(2)NH3][Mn-2(HPO4)(2)(C2O4)(H2O)(2)] 2 have related, but not isomorphous, structures based on layers of vertex-sharing MnO6 and PO4 polyhedra linked by bridging oxalate groups. [H3N(CH2)(2)NH3][Mn-4(HPO4)(2)(C2O4)(3)(H2O)(2)]. 2H(2)O 3 has a very different structure composed of edge-sharing dimeric MnO6 units linked into chains by PO4 groups, and into a 3-D framework by oxalate units. 3 can be topotactically dehydrated, with loss of both extra-framework and co-ordinated water, to produce a new phase 4. The magnetic susceptibilities of phases 1, 3 and 4 all show Curie-Weiss behaviour above about 50 K, and a maximum in the susceptibility curve in the vicinity of 7-12 K, indicating significant antiferromagnetic exchange. Structural relationships to other phosphate-oxalate frameworks are discussed.</p

Synthesis, structural relationships and magnetic properties of new amine-templated manganese(II) phosphate-oxalate framework materials

Three novel three-dimensional framework materials in the manganese(II)-phosphate-oxalate system have been prepared hydrothermally using organic amines as structure-directing agents. [H3NC6H10NH3][Mn-2(HPO4)(2)(C2O4)(H2O)(2)] 1 and [H3N(CH2)(2)NH3][Mn-2(HPO4)(2)(C2O4)(H2O)(2)] 2 have related, but not isomorphous, structures based on layers of vertex-sharing MnO6 and PO4 polyhedra linked by bridging oxalate groups. [H3N(CH2)(2)NH3][Mn-4(HPO4)(2)(C2O4)(3)(H2O)(2)]. 2H(2)O 3 has a very different structure composed of edge-sharing dimeric MnO6 units linked into chains by PO4 groups, and into a 3-D framework by oxalate units. 3 can be topotactically dehydrated, with loss of both extra-framework and co-ordinated water, to produce a new phase 4. The magnetic susceptibilities of phases 1, 3 and 4 all show Curie-Weiss behaviour above about 50 K, and a maximum in the susceptibility curve in the vicinity of 7-12 K, indicating significant antiferromagnetic exchange. Structural relationships to other phosphate-oxalate frameworks are discussed.</p