Sandra Cerqueira Barros

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

AbstractSol / gel derived poly(oxyethylene)/siloxane hybrids doped with lithium triflate, LiCF 3 SO ,have been investigated. The hosthybrid matrix of these materials, named di-ureasil and represented by U(600), is composed by a siliceous framework to whichpolyether chains containing 8.5 oxyethylene repeat units are covalently bonded through urea linkages. Xerogel samplesU(600) n LiCF 3 SO 3 with n (where n is the molar ratio of oxyethylene moieties per Li ion) between and 0.1 have beenexamined. X-ray diffraction and differential scanning calorimetry have provided conclusiveevidence that the xerogels analyzed areentirely amorphous. The salt-rich material with n / 1 exhibits the highest conductivity over the whole range of temperature analyzed(e.g. 4.3 6 / 10 and 2.0 / 10 4 V 1 cm , respectively, at 25 and 94 8C). # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Di-ureasils; Li ; X-ray diffraction; Differential scanning calorimetry; Ionic conductivity 1. IntroductionHighly conducting, thin, solvent-free electrolyte filmsmay be produced by dissolving salts in high molecularweight polymers carrying adequate coordinating species,such as ether oxygen atoms or amine nitrogen atoms [1

Sol–gel-derived POE/siliceous hybrids doped with Na+ ions: morphology and ionic conductivity

Abstract Hybrid materials produced by the versatile sol–gel process with a wide sodium triflate, NaCF 3 SO 3 , concentration range have been studied. The host matrix of these xerogels, designated as di-ureasil and represented by U(600), is composed by a siliceous network bonded through covalent bonds to short polyether chains by means of bridging urea groups. The results obtained reveal that at high salt concentration, this system forms crystalline phases. The most conducting ormolyte exhibits a conductivity of 3.6×10 −7 Ω −1 cm −1 at room temperature.

Characterization of potential elastase inhibitor-peptides regulated by a molecular switch for wound dressings applications

Elastase plays an important role in wound healing process, degrading damaged tissue and allowing complete tissue recovery. The levels of human neutrophil elastase (HNE) are usually controlled by endogenous inhibitors. However, in the presence of high levels of elastase, like the ones present in chronic wounds, the inhibitors cannot overcome this overproduction and the enzyme starts to degrade the surrounding healthy tissue. In this work we report the development of a molecular switch to control the elastase activity in the exudate of non-healing chronic wounds. A peptide library was generated and screened in a microarray format for protein kinase-mediated phosphorylation. Two peptides were identified as casein kinase Iδ (CKI) substrates: KRCCPDTCGIKCL and its analogous peptide KRMMPDTMGIKML, with cysteine residues replaced by methionine residues. These peptides were studied in solution, both in the phosphorylated and non-phosphorylated forms as potential inhibitors for elastase. The obtained results show that the reversible process of phosphorylation/dephosphorylation results in differential inhibitory activity of the peptides. Thus the reversible process of phosphorylation/dephosphorylation can be used as a kind of molecular switch to control elastase activity. Degradation studies reveal that both the inhibitor-peptides and CKI are degraded by elastase. These results envisage the safe utilisation of these inhibitor-peptides together with CKI in the formulation of wound dressings.

An investigation of the morphological, electrical and optoelectronic properties of short chain Di-ureasils doped with Er3+ ions

Hybrid organic/inorganic xerogels containing Er3+ ions have been prepared by the solgel process. The hybrid framework of these compounds, designated as di-ureasils and represented by U(600), is composed of a siliceous backbone to which polyether chains containing 8.5 oxyethylene repeat units are linked through urea (-NHC(=O)NH-) bridges. The trivalent cations have been incorporated in the matrix as erbium triflate, Er(CF3SO3)3. Compositions with n (where n is the molar ratio of (OCH2CH2) repeat units per Er+ ion) between ∞ and 3 have been studied. The morphology of the materials was characterized by means of X-ray Diffraction and Differential Scanning Calorimetry. Complex Impedance spectroscopy was used to evaluate the levels of conductivity exhibited by the xerogels as a function of temperature. The results obtained clearly demonstrate the amorphous character of the samples analysed. At about 100 °C the most conducting sample is U(600)5Er(CF3SO3)3 (approximately 2×10−5 Scm−1), whereas the U(600)60Er(CF3SO3)3 compound displays the highest conductivity at room temperature (1×10−7 Scm−1). We have shown that concentration effects on the quenching of the 1.53 μm emission intensity (excited at 488 nm) are negligible. We have also shown that the Er3+ ions are active at room temperature.

Short-chain di-ureasil ormolytes doped with potassium triflate: Phase diagram and conductivity behavior

Di-urea cross-linked poly(oxyethylene)/siloxane hybrids, synthesized by the sol-gel process and containing a wide concentration range of potassium triflate, KCF3SO3, have been analyzed by x-ray diffraction and differential scanning calorimetry. The pseudo-phase diagram proposed has been taken into account in the interpretation of the complex impedance measurements. The xerogels prepared are obtained as transparent, thin monoliths. At room temperature the highest conductivity found was 2 × 10−6 Ω−1 cm−1.

Influence of secretory leukocyte protease inhibitor‐based peptides on elastase activity and their incorporation in hyaluronic acid hydrogels for chronic wound therapy

Chronic nonhealing skin wounds, such as leg ulcers and pressure sores, represent a major clinical problem and a financial burden for the health care systems. Chronic wounds are characterized by prolonged inflammatory phase that results in high levels of elastase, reactive oxygen species (ROS), and diminished growth factor activity. Under normal physiological conditions, elastase is a powerful host defence and its activity is regulated by endogenous inhibitors. The unrestrained elastase activity in chronic wounds may be tuned by exogenous active materials that inhibit elastase. Secretory leucocyte protease inhibitor, SLPI, is a potent endogenous inhibitor of elastase. Peptide fragments, KRCCPDTCGIKCL (Pep4) and KRMMPDTMGIKML (Pep4M), selected from SLPI primary structure were studied as potential elastase inhibitors. Kinetic studies performed for human neutrophil elastase (HNE) and porcine pancreatic elastase (PPE) in presence of these peptides revealed that both behave as uncompetitive and noncompetitive inhibitors of HNE and PPE, respectively. The influence of ROS and albumin on Pep4 and Pep4M inhibitory activity toward elastase reveals that this mixture increases the inhibitory activity of both peptides. These peptides were incorporated in hyaluronic acid hydrogels to evaluate the possibility of being used as active compounds in a drug delivery system. Assessment of HNE and PPE activity in the presence of these hydrogels formulations revealed a considerable decrease in enzyme activity. Although, only moderated elastase inhibition was observed, these peptides represent potential candidates for chronic wound applications, as there is no need for complete elastase inhibition in the normal wound healing process.

Short chain U(600) di-urea cross-linked poly(oxyethylene)/siloxane ormolytes doped with lanthanum triflate salt

Abstract Promising La 3+ -doped electrolytes based on a hybrid poly(oxyethylene)/siliceous host matrix, U(600), have been produced. The organic and inorganic components of the hybrid structure are covalently bonded through urea linkages. The low molecular weight of the polyether segments of U(600) is thought to be responsible for the total amorphous character and high conductivity at room temperature (1.1×10 −4 S cm −1 ) of these ormolytes.

Preparation and Characterization of a Novel Polymer Electrolyte Based on Lithium Hexafluoroarsenate

Shell Chemicals Limited Fundacao Calouste Gulbenkian – FCG Fundacao para a Ciencia e Tecnologia - FCT

Erratum to: Thermal–mechanical behaviour of chitosan–cellulose derivative thermoreversible hydrogel films

The authors are thankful to the Chemistry and Physic Centres at Minho University (Pest-C/QUI/UI0686/2013 and PEST-C/FIS/UI607/2013), CNPq, FAPESP and CAPES for the financial support of this research. Sandra Cerqueira Barros and Carlos M. Costa acknowledge the Portuguese Foundation for Science and Technology for the Post-Doc and PhD grants provided (SFRH/BPD/85399/2012 and SFRH/BD/68499/2010) and M. M. Silva acknowledges to CNPq, for the mobility grant provided by this institution. The authors of this paper are grateful to the Company Devan-Micropolis, S.A., for the material support, namely the natural polymers chitosan (CH) and (hydroxypropyl)methyl cellulose (HPMC) employed in this study. JLGR acknowledges the support of Ministerio de Economia y Competitividad, MINECO, through the MAT2013-46467-C4-1-R project. CIBER-BBN is an initiative funded by the VI National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions and financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund.