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van Der Voort M Rella CW van Der Meer LF Akimov AV Dijkhuis JI 《Physical review letters》2000,84(6):1236-1239
We present results of the first vibrational photon-echo, transient-grating, and temperature dependent transient-bleaching experiments on a-Si:H. Using these techniques, and the infrared light of a free electron laser, the vibrational population decay and phase relaxation of the Si-H stretching mode were investigated. Careful analysis of the data indicates that the vibrational energy relaxes directly into Si-H bending modes and Si phonons, with a distribution of rates determined by the amorphous host. Conversely, the pure dephasing appears to be single exponential, and can be modeled by dephasing via two-phonon interactions. 相似文献
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Danielle Goveia Fabiana Aparecida Lobo Peter Burba Leonardo Fernandes Fraceto Newton Luiz Dias Filho André Henrique Rosa 《Analytical and bioanalytical chemistry》2010,397(2):851-860
This paper deals with the development and optimization of an analytical procedure using ultrafiltration and a flow-injection system, and its application in in-situ experiments to characterize the lability and availability of metal species in humic-rich hydrocolloids. The on-line system consists of a tangential flow ultrafiltration device equipped with a 3-kDa filtration membrane. The concentration of free ions in the filtrate was determined by atomic-absorption spectrometry, assuming that metals not complexed by aquatic humic substances (AHS) were separated from the complexed species (M–AHS) retained by the membrane. For optimization, exchange experiments using Cu(II) solutions and AHS solutions doped with the metal ions Ni(II), Mn(II), Fe(III), Cd(II), and Zn(II) were carried out to characterize the stability of the metal–AHS complexes. The new procedure was then applied in-situ at a tributary of the Ribeira do Iguape river (Iguape, São Paulo State, Brazil) and evaluated using the ions Fe(III) and Mn(II), which are considered to be essential constituents of aquatic systems. From the exchange between metal–natural organic matter (M–NOM) and the Cu(II) ions it was concluded that Cu(II) concentrations >485 μg L?1 were necessary to obtain maximum exchange of the complexes Mn–NOM and Fe–NOM, corresponding to 100% Mn and 8% Fe. Moreover, the new analytical procedure is simple and opens up new perspectives for understanding the complexation, transport, stability, and lability of metal species in humic-rich aquatic environments. 相似文献
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Carolina Morales Moraes Renata de Lima André Henrique Rosa Eneida de Paula Leonardo Fernandes Fraceto 《Macromolecular Symposia》2009,281(1):106-112
Summary: Local anesthetic agents cause temporary blockade of nerve impulses productiong insensitivity to painful stimuli in the area supplied by that nerve. Bupivacaine (BVC) is an amide-type local anesthetic widely used in surgery and obstetrics for sustained peripheral and central nerve blockade. In this study, we prepared and characterized nanosphere formulations containing BVC. To achieve these goals, BVC loaded poly(DL-lactide-co-glycolide) (PLGA) nanospheres (NS) were prepared by nanopreciptation and characterized with regard to size distribution, drug loading and cytotoxicity assays. The 23-1 factorial experimental design was used to study the influence of three different independent variables on nanoparticle drug loading. BVC was assayed by HPLC, the particle size and zeta potential were determined by dynamic light scattering. BVC was determined using a combined ultrafiltration-centrifugation technique. The results of optimized formulations showed a narrow size distribution with a polydispersivity of 0.05%, an average diameter of 236.7 ± 2.6 nm and the zeta potential −2.93 ± 1,10 mV. In toxicity studies with fibroblast 3T3 cells, BVC loaded-PLGA-NS increased cell viability, in comparison with the effect produced by free BVC. In this way, BVC-loaded PLGA-NS decreased BVC toxicity. The development of BVC formulations in carriers such as nanospheres could offer the possibility of controlling drug delivery in biological systems, prolonging the anesthetic effect and reducing toxicity. 相似文献
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Carolina Morales Moraes Priscila Abrami Daniele Riberio de Araujo Angélica F. A. Braga Michelle Georges Issa Humberto G. Ferraz Eneida de Paula Leonardo Fernandes Fraceto 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):313-316
An inclusion complex was prepared between the local anesthetic lidocaine (LDC) and hydroxypropyl-β-CD (HP-β-CD). The complex
was characterized by thermal analysis (differential scanning calorimetry, DSC), UV absorption and high-pressure liquid chromatography
(HPLC). DSC results were indicative of complexation, due to the loss of the characteristic endothermic peak of LDC (77 °C).
Phase-solubility diagrams allowed the determination of the association constant between LDC and HP-β-CD (35.7 ± 4.7 M−1). The rate of LDC release decreased after complexation and thermodynamic parameters from the HPLC studies (ΔG° = −2.65 kJ/mol)
revealed that a stable complex was formed. 相似文献
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Goveia D Rosa AH Bellin IC Lobo FA Fraceto LF Roveda JA Romão LP Dias Filho NL 《Analytical and bioanalytical chemistry》2008,390(4):1173-1180
This work involved the development and application of a new analytical procedure for in-situ characterization of the lability
of metal species in aquatic systems by using a system equipped with a diffusion membrane and cellulose organomodified with
p-aminobenzoic acid groups (DM-Cell-PAB). To this end, the DM-Cell-PAB system was prepared by adding cellulose organomodified
with p-aminobenzoic acid groups (Cell-PAB) to pre-purified cellulose bags. After the DM-Cell-PAB system was sealed, it was examined
in the laboratory. The in-situ application involved immersing the DM-Cell-PAB system in two different rivers, enabling us
to study the relative lability of metal species (Cu, Cd, Fe, Mn, and Ni) as a function of time and quantity of exchanger.
The procedure is simple and opens up a new perspective for understanding environmental phenomena relating to the complexation,
transport, stability, and lability of metal species in aquatic systems rich in organic matter. 相似文献
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Isaac Vaz Soares Eduardo Guimarães Vieira Newton Luiz Dias Filho Niléia Cristina da Silva Andréa de Castro Bastos Lucélia Julia A. Lima Leonardo Fernandes Fraceto André Henrique Rosa 《Journal of separation science》2013,36(4):817-825
In this work, a silica surface chemically modified with [3‐(2,2′‐dipyridylamine)propyl] groups, named [3‐(2,2′‐dipyridylamine)propyl]silica (Si‐Pr‐DPA) was prepared, characterized, and evaluated for its heavy metal adsorption characteristics from aqueous solution. To our knowledge, we are the first authors who have reported the present modification. The material was characterized using infrared spectroscopy, SEM, and NMR 29Si and 13C solid state. Batch and column experiments were conducted to investigate for heavy metal removal from dilute aqueous solution by sorption onto Si‐Pr‐DPA. From a number of studies the affinity of various metal ions for the Si‐Pr‐DPA sorbent was determined to follow the order Fe(III) > Cr(III) >> Cu(II) > Cd(II) > Pb(II) > Ni(II). Two standard reference materials were used for checking the accuracy and precision of the method. The proposed method was successfully applied to the analysis of environmental samples. This ligand material has great advantage for adsorption of transition‐metal ions from aqueous medium due to its high degree of organofunctionalization associated with the large adsorption capacity, reutilization possibility, and rapidity in reaching the equilibrium. 相似文献
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Danielle Goveia Fabiana A. Lobo Iramaia C. Bellin Leonardo F. Fraceto Amauri A. Menegário Peter Burba 《International journal of environmental analytical chemistry》2013,93(13):1296-1309
The present study deals with a new analytical procedure based on a cellulose diffusion membrane and immobilised tetraethylene-pentamine-hexaacetate chelator (DM-TEPHA) for an in situ differentiation of labile and inert metal species in aquatic systems. The DM-TEPHA system was prepared by placing TEPHA chelator in pre-purified cellulose bags and in situ applied immersing the system in two Brazilian rivers to study the relative lability of metal species (Cu, Pb, Fe, Mn and Ni) as a function of the time and the quantity of exchanger, respectively. The procedure is simple and enables a new perspective for understanding the complexation, transport, stability and lability of metal species in aquatic systems rich in organic matter. 相似文献
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