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Multivalent Cations (multivalent + cation)

Distribution by Scientific Domains
Polymers and Materials Science50%

Selected Abstracts

Role of laccase in the biology and virulence of Cryptococcus neoformans

FEMS YEAST RESEARCH, Issue 1 2004
Xudong Zhu
Abstract Laccase is an important virulence factor for the human pathogen, Cryptococcus neoformans. In this review, we examine the structural, biological and genetic features of the enzyme and its role in the pathogenesis of cryptococcosis. Laccase is expressed in C. neoformans as a cell wall enzyme that possesses a broad spectrum of activity oxidizing both polyphenolic compounds and iron. Two paralogs, CNLAC1 and CNLAC2, are present in the fungus, of which the first one expresses the dominant enzyme activity under glucose starvation conditions. Regulation of the enzyme is in response to various environmental signals including nutrient starvation, the presence of multivalent cations and temperature stress, and is mediated through multiple signal transduction pathways. Study of the function and regulation of this important virulence factor has led to further understanding of mechanisms of fungal pathogenesis and the regulation of stress response in the host cell environment. [source]

B,Z DNA Transition Triggered by a Cationic Comb-Type Copolymer

ADVANCED FUNCTIONAL MATERIALS, Issue 22 2009
Naohiko Shimada
Abstract The conformational transition from right-handed B,DNA to left-handed Z,DNA,the B,Z transition,has received increased attention recently because of its potential roles in biological systems and its applicability to bionanotechnology. Though the B,Z transition of poly(dG,dC),·,poly(dG,dC) is inducible under high salt concentration conditions (over 4,M NaCl) or by addition of multivalent cations, such as hexaamminecobalt(III), no cationic polymer were known to induce the transition. In this study, it is shown by circular dichroism and UV spectroscopy that the cationic comb-type copolymer, poly(L -lysine)- graft -dextran, but not poly(L -lysine) homopolymer or a basic peptide, induces the B,Z transition of poly(dG,dC),·,poly(dG,dC). At a cationic amino group concentration of 10,4,M the copolymer stabilizes Z,DNA. The transition pathway from the B to the Z form is different to that observed previously. We speculate that the cationic backbone of the copolymer, which reduces electrostatic repulsion among DNA phosphate groups, and the hydrophilic dextran chains, which reduce activity of water, cooperate to induce the B,Z transition. The copolymer specifically modified the micro-environment around DNA molecules to induce Z,DNA formation through stable and spontaneous inter-polyelectrolyte complex formation. [source]

Shaped Films of Ionotropic Hydrogels Fabricated Using Templates of Patterned Paper

ADVANCED MATERIALS, Issue 4 2009
Paul J. Bracher
Patterned paper wet with multivalent cations can template the production of films of ionotropic hydrogels in topologically complex shapes such as Möbius strips and interlocking rings (see figure). The films have lateral dimensions as low as 2mm, and range in thickness from 0.2 to 1.3mm. The films are magnetically responsive when cross-linked by Ho3+ or Gd3+. [source]

Soil organic matter beyond molecular structure Part I: Macromolecular and supramolecular characteristics

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2006
Gabriele E. Schaumann
Abstract This contribution reviews and discusses structural aspects of soil organic matter (SOM) and humic substances (HS) with special respect to the macromolecular and the supramolecular view. It can be concluded that (1) dissolved humic acids behave as supramolecular associations of relatively small molecules with an enormous flexibility of reaction of environmental conditions, (2) multivalent cations may increase the apparent molecular weight by the formation of coordinative crosslinks in dissolved and undissolved natural organic matter (NOM), (3) sorption nonlinearity in solid humic acids and SOM may be due to polymer properties of NOM, (4) sorbates affect sorbent characteristics of SOM, and (5) hysteresis and conditioning effects in SOM can up to now best be explained with the polymer analogy. A distinct polydispersivity of SOM over a wide range of molecular masses is to be assumed. The supramolecular and the macromolecular models were derived from humic acids with different composition and on the basis of different sample states. Although the supramolecular model has not explicitely been shown for unfractionated DOM, the combination of all discussed studies suggests supramolecular as well as macromolecular characteristics of NOM. Neither macromolecules nor small molecules can be fully excluded in solid and dissolved SOM. Microregions with different properties provide different types of sorption sites. SOM is suggested to be regarded as amorphous material. This point of view is not restricted to high molecular masses and may supplement our understanding of SOM by the model of physical aging. [source]