Matrix Assisted Formation of Ferrihydrite Nanoparticles in a Siloxane/Poly(Oxyethylene) Nanohybrid

Matrix-assisted formation of ferrihydrite, an iron oxide hydroxide analogue of the protein ferritin-core, in a sol-gel derived organic-inorganic hybrid is reported. The hybrid network (named di-ureasil) is composed of poly(oxyethylene) chains of different average polymer molecular weights grafted to siloxane domains by means of urea cross-linkages and accommodates ferrihydrite nanoparticles. Magnetic measurements, Fourier transform infrared and nuclear magnetic resonance spectroscopy reveal that the controlled modification of the polymer molecular weight allows the fine-tuning of the ability of the hybrid matrix to assist and promote iron coordination at the organic-inorganic interface and subsequent nucleation and growth of the ferrihydrite nanoparticles whose core size (2-4 nm) is tuned by the amount of iron incorporated. The polymer chain length, its arrangement and crystallinity, are key factors on the anchoring and formation of the ferrihydrite particles.Comment: 7 pages, 6 figures. To be published in J. Mater. Che

Pengembangan Perangkat Pembelajaran Matematika dengan Model Pembelajaran Berbasis Masalah pada Materi Kubus dan Balok untuk Siswa Kelas VIII Smp/mts

The background of this study is the restrict of mathematics learning instruments as supporting learning referring to 2013 Curriculum. This study aimed to develop mathematics learning instruments with problem based learning's model on cubes and cuboids for 8th grade SMP/MTs. Learning instruments in this study are syllabus, lesson plans, and student worksheet. This study method used is 4D model by Thiagarajan, Dorothy S. Semmel, and Melvyn I. Semmel that consist of define, design, development, and disseminate, but the study was limited only to development step. Based on the data analysis, it can be conclude that mathematics learning instruments is very valid with mean score of syllabus is 4,53, mean score of lesson plans is 4,26, and mean score of student worksheet is 4,21. This student worksheet has also reached the practical qualification with mean percentage of student responses is 97,33 on a small test group

Sterol 3β-glucosyltransferase biocatalysts with a range of selectivities, including selectivity for testosterone

The main objectives of this work were to characterise a range of purified recombinant sterol 3β-glucosyltransferases and show that rational sampling of the diversity that exists within sterol 3β-glucosyltransferase sequence space can result in a range of enzyme selectivities. In our study the catalytically active domain of the Saccharomyces cerevisiae 3β-glucosyltransferase was used to mine putative sterol 3β-glucosyltransferases from the databases. Selected diverse sequences were expressed in and purified from Escherichia coli and shown to have different selectivities for the 3β-hydroxysteroids ergosterol and cholesterol. Surprisingly, three enzymes were also selective for testosterone, a 17β-hydroxysteroid. This study therefore reports for the first time sterol 3β-glucosyltransferases with selectivity for both 3β- and 17β-hydroxysteroids and is also the first report of recombinant 3β-glucosyltransferases with selectivity for steroids with a hydroxyl group at positions other than C-3. These enzymes could therefore find utility in the pharmaceutical industry for the green synthesis of a range of glycosylated compounds of medicinal interest

Mg2+-doped poly(ε-caprolactone)/siloxane biohybrids

Electrolytes based on a poly(ε-caprolactone) (PCL)/siloxane organic/inorganic host framework doped with magnesium triflate (Mg(CF3SO3)2) were synthesized by the sol-gel process. In the biohybrid matrix short PCL chains are covalently bonded via urethane linkages to the siliceous network. In this study the salt content of samples was identified using the conventional n notation, where n indicates the number of (C(=O)(CH2)5O) PCL repeat units per Mg2+ ion. Materials with compositions ranging from n=∞ to 2 were prepared. The only composition prepared that is not entirely amorphous is that with n = 1. Xerogels with n ≥ 7 are thermally stable up to up to at least 200 ºC. The most conducting ormolyte of the series is that with n = 26 (5.9x10-9 and 9.8x10-7 Scm-1 at 24 and 104 ºC, respectively).Fundação para a Ciência e Tecnologi

Chitosan membranes containing micro or nano-size bioactive glass particles : evolution of biomineralization followed by in-situ dynamic mechanical analysis

A newfamilyofbiodegradablepolymer/bioactiveglass(BG)compositematerialshas emergedbasedontheavailabilityofnano-sizedbioactiveparticles.Suchnovelbiocompo- sites canhaveenhancedperformance,intermsofmechanicalpropertiesandbioactivity, and theycanbedesignedtobeusedinboneregenerationapproaches. In thiswork,membranesofchitosan(CTS)andchitosanwithbioactiveglass(BG)both micron andnanosizedparticles(CTS/mBG,CTS/nBG,respectively)werepreparedby solvent casting.Microstructuralandmechanicalpropertieswereevaluatedinorderto compare theeffectsoftheincorporationofmicro(mBG) andnano(nBG)particlesinthe chitosan matrix. In vitro bioactivity testswereperformedtocharacterizetheapatitelayer that isformedonthesurfaceofthematerialafterbeingimmersedinsimulatedbodyfluid (SBF). Thebiomineralizationprocessonthebiomaterialswasalsofollowedusingnon- conventionaldynamicmechanicalanalysis(DMA),bothonlineandoffline.InsuchDMA experiments,thechangeinthestoragemodulus, E0, andthelossfactor,tan d, were measured asafunctionoftheimmersiontimeinSBF.TheresultsdemonstratedthatCTS/ nBG membranespossessenhancedmechanicalpropertiesandhigherbioactivityin comparisonwiththeCTS/mBG membranes.SuchresultssuggestthepotentialofnBGfor the developmentofbioactivecompositesforboneregenerationapplications.This work was financially supported by Foundation for Science and Technology (FCT) by the projects PTDC/QUI/69263/2006, PTDC/CTM-BPC/112774/2009 and, through the scholarship SFRH/BD/64601/2009 granted to Sofia G. Caridade. The authors acknowledge Dr D. Mohn and Prof. W. Stark (Em Zurich) for providing the nBG particles used

Evidence of random magnetic anisotropy in ferrihydrite nanoparticles based on analysis of statistical distributions

We show that the magnetic anisotropy energy of antiferromagnetic ferrihydrite depends on the square root of the nanoparticles volume, using a method based on the analysis of statistical distributions. The size distribution was obtained by transmission electron microscopy, and the anisotropy energy distributions were obtained from ac magnetic susceptibility and magnetic relaxation. The square root dependence corresponds to random local anisotropy, whose average is given by its variance, and can be understood in terms of the recently proposed single phase homogeneous structure of ferrihydrite.Comment: 6 pages, 2 figure

Progress on lanthanide-based organic–inorganic hybrid phosphors

Research on organic–inorganic hybrid materials containing trivalent lanthanide ions (Ln3+) is a very active field that has rapidly shifted in the last couple of years to the development of eco-friendly, versatile and multifunctional systems, stimulated by the challenging requirements of technological applications spanning domains as diverse as optics, environment, energy, and biomedicine. This tutorial review offers a general overview of the myriad of advanced Ln3+-based organic–inorganic hybrid materials recently synthesised, which may be viewed as a major innovation in areas of phosphors, lighting, integrated optics and optical telecommunications, solar cells, and biomedicin

Structural and magnetic studies in ferrihydrite nanoparticles formed within organic-inorganic hybrid matrices

6 pages, 6 figures, 1 table.We report detailed transmission electron microscopy, high resolution transmission electron microscopy (HRTEM), and scanning transmission electron microscopy/energy dispersive x-ray spectroscopy (STEM/EDS) studies on ferrihydrite nanoparticles in an organic-inorganic matrix. The Fourier transform of HRTEM images indicates the existence of six-line ferrihydrite. Combined STEM and EDS studies give further confirmation of the presence of iron in the observed particles and its absence in the matrix. The derived mean particle size and size distribution is 4.7±0.2 nm with a lognormal deviation of s=0.4±0.1. These values were used for analysis of magnetic measurements, yielding the determination of the anisotropy constant Keff=4×105 erg/cm3 and the power relation between the number of iron ions per particle and the number of uncompensated ones p≈1/3. This value indicates that the uncompensated spins are mainly randomly distributed at the surface. According to this model, a shell thickness of about one ferrihydrite unit cell is estimated.The financial support from FCT, POCTI/ CTM/46780/02, research grant MAT2004-03395-C02-01 from the Spanish CICYT, and Acción Integrada Luso- Española E-105/04 is gratefully recognized. One of the authors (N.J.O.S.) acknowledges a grant from FCT (Grant No. SFRH/BD/10383/2002). Another author (L.M.L.-M.) acknowledges support from Xunta de Galicia (Grant No. PGIDIT03TMT30101PR).Peer reviewe

Morphological and conductivity studies of di-ureasil xerogels containing lithium triflate

Sol–gel derived poly(oxyethylene)/siloxane hybrids doped with lithium triflate, LiCF3SO3, have been investigated. The host hybrid matrix of these materials, named di-ureasil and represented by U(600), is composed by a siliceous framework to which polyether chains containing 8.5 oxyethylene repeat units are covalently bonded through urea linkages. Xerogel samples U(600)nLiCF3SO3 with n (where n is the molar ratio of oxyethylene moieties per Li+ ion) between ∞ and 0.1 have been examined. X-ray diffraction and differential scanning calorimetry have provided conclusive evidence that the xerogels analyzed are entirely amorphous. The salt-rich material with n=1 exhibits the highest conductivity over the whole range of temperature analyzed (e.g. 4.3×10−6 and 2.0×10−4 Ω−1 cm−1, respectively, at 25 and 94 °C).Fundação para a Ciência e a Tecnologia (FCT

Structure and photoluminescent features of di-amide cross-linked alkylene-siloxane hybrids

Novel amide cross-linked alkylene/siloxane hybrid materials (di-amidosils) synthesized by the sol-gel process have been investigated. Two samples identified by the notation d-A(x) with x = 4 and 8 (where x is the number of methylene groups of the alkylene chain) have been produced as transparent, amorphous, rigid monoliths, thermally stable up to about 381 and 400 ºC, respectively. In the d-A(8) hybrid the siliceous framework is composed of [(SiO)3Si(CH2)-] and [(SiO)2(HO)Si(CH2)-] substructures. Structural unit distances of 4.1 and 4.2 Å and average interparticle distances of 12 and 17 Å have been determined for d-A(4) and d-A(8), respectively. In these compounds the alkyl chains are disordered and adopt gauche conformations. While a negligible proportion of the amide linkages remain non-bonded, the great majority of these groups belong to highly disordered strong hydrogen-bonded amide-amide associations. The hybrids introduced are room temperature white light emitters, presenting an emission large, broad band in the blue/purplish-blue spectral region. The origin of such band have been ascribed to the convolution of donor-acceptor pair (D-A) recombinations that occur in the NH groups of the urea linkages and in the siliceous nanodomains. The maximum quantum yield value of the d-A(8) di-amidosil is 5.4 %.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/P/CTM/46780/03; SFRH/BD/13559/03