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Buckley A, Warren J, Hussain R, Smith R. Synchrotron radiation circular dichroism spectroscopy reveals that gold and silver nanoparticles modify the secondary structure of a lung surfactant protein B analogue. NANOSCALE 2023; 15:4591-4603. [PMID: 36763129 DOI: 10.1039/d2nr06107d] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Inhaled nanoparticles (NPs) depositing in the alveolar region of the lung interact initially with a surfactant layer and in vitro studies have demonstrated that NPs can adversely affect the biophysical function of model pulmonary surfactants (PS), of which surfactant protein B (SP-B) is a key component. Other studies have demonstrated the potential for NPs to modify the structure and function of proteins. It was therefore hypothesised that NPs may affect the biophysical function of PS by modifying the structure of SP-B. Synchrotron radiation circular dichroism (SRCD) spectroscopy was used to explore the effect of various concentrations of gold nanoparticles (AuNPs) (5, 10, 20 nm), silver nanoparticles (AgNPs) (10 nm) and silver citrate on the secondary structure of surfactant protein B analogue, SP-B1-25, in a TFE/PB dispersion. For Au and Ag NPs the SRCD spectra indicated a concentration dependent reduction in the α-helical structure of SP-B1-25 (5 nm AuNP ≈ 10 nm AgNP ≫ 10 nm AuNP > 20 nm AuNP). For AuNPs the effect was greater for the 5 nm size, which was not fully explained by consideration of surface area. The impact of the 10 nm AgNPs was greater than that of the 10 nm AuNPs and the effect of AgNPs was greater than that of silver citrate at equivalent Ag mass concentrations. For 10 nm AuNPs, SRCD spectra for dispersions in, the more physiologically relevant, DPPC showed a similar concentration dependent pattern. The results demonstrate the potential for inhaled NPs to modify SP-B1-25 structure and thus potentially adversely impact the physiological function of the lung, however, further studies are necessary to confirm this.
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Affiliation(s)
- Alison Buckley
- Toxicology Department, UK Health Security Agency, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0RQ, UK.
| | - James Warren
- Toxicology Department, UK Health Security Agency, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0RQ, UK.
| | - Rohanah Hussain
- Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, UK
| | - Rachel Smith
- Toxicology Department, UK Health Security Agency, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0RQ, UK.
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2
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Thalhammer A, Bröker NK. Biophysical Approaches for the Characterization of Protein-Metabolite Interactions. Methods Mol Biol 2023; 2554:199-229. [PMID: 36178628 DOI: 10.1007/978-1-0716-2624-5_13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
With an estimate of hundred thousands of protein molecules per cell and the number of metabolites several orders of magnitude higher, protein-metabolite interactions are omnipresent. In vitro analyses are one of the main pillars on the way to establish a solid understanding of how these interactions contribute to maintaining cellular homeostasis. A repertoire of biophysical techniques is available by which protein-metabolite interactions can be quantitatively characterized in terms of affinity, specificity, and kinetics in a broad variety of solution environments. Several of those provide information on local or global conformational changes of the protein partner in response to ligand binding. This review chapter gives an overview of the state-of-the-art biophysical toolbox for the study of protein-metabolite interactions. It briefly introduces basic principles, highlights recent examples from the literature, and pinpoints promising future directions.
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Affiliation(s)
- Anja Thalhammer
- Physical Biochemistry, University of Potsdam, Potsdam, Germany.
| | - Nina K Bröker
- Physical Biochemistry, University of Potsdam, Potsdam, Germany
- Health and Medical University Potsdam, Potsdam, Germany
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Del Giudice R, Lindvall M, Nilsson O, Monti DM, Lagerstedt JO. The Apparent Organ-Specificity of Amyloidogenic ApoA-I Variants Is Linked to Tissue-Specific Extracellular Matrix Components. Int J Mol Sci 2022; 24:318. [PMID: 36613763 PMCID: PMC9820410 DOI: 10.3390/ijms24010318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 12/15/2022] [Accepted: 12/22/2022] [Indexed: 12/28/2022] Open
Abstract
Apolipoprotein A-I (ApoA-I) amyloidosis is a rare protein misfolding disease where fibrils of the N-terminal domain of the protein accumulate in several organs, leading to their failure. Although ApoA-I amyloidosis is systemic, the different amyloidogenic variants show a preferential tissue accumulation that appears to correlate with the location of the mutation in the protein sequence and with the local extracellular microenvironment. However, the factors leading to cell/tissues damage, as well as the mechanisms behind the observed organ specificity are mostly unknown. Therefore, we investigated the impact of ApoA-I variants on cell physiology and the mechanisms driving the observed tissue specificity. We focused on four ApoA-I amyloidogenic variants and analyzed their cytotoxicity as well as their ability to alter redox homeostasis in cell lines from different tissues (liver, kidney, heart, skin). Moreover, variant-specific interactions with extracellular matrix (ECM) components were measured by synchrotron radiation circular dichroism and enzyme-linked immunosorbent assay. Data indicated that ApoA-I variants exerted a cytotoxic effect in a time and cell-type-specific manner that seems to be due to protein accumulation in lysosomes. Interestingly, the ApoA-I variants exhibited specific preferential binding to the ECM components, reflecting their tissue accumulation pattern in vivo. While the binding did not to appear to affect protein conformations in solution, extended incubation of the amyloidogenic variants in the presence of different ECM components resulted in different aggregation propensity and aggregation patterns.
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Affiliation(s)
- Rita Del Giudice
- Department of Experimental Medical Science, Lund University, 221 84 Lund, Sweden
| | - Mikaela Lindvall
- Department of Experimental Medical Science, Lund University, 221 84 Lund, Sweden
| | - Oktawia Nilsson
- Department of Experimental Medical Science, Lund University, 221 84 Lund, Sweden
| | - Daria Maria Monti
- Department of Chemical Sciences, University of Napoli Federico II, Complesso Universitario Monte Sant’Angelo, 80126 Napoli, Italy
- Istituto Nazionale di Biostrutture e Biosistemi (INBB), 00136 Rome, Italy
| | - Jens O. Lagerstedt
- Department of Experimental Medical Science, Lund University, 221 84 Lund, Sweden
- Islet Cell Exocytosis, Lund University Diabetes Centre, Department of Clinical Sciences Malmö, Lund University, 20506 Malmö, Sweden
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Kwan TOC, Kolek SA, Danson AE, Reis RI, Camacho IS, Shaw Stewart PD, Moraes I. Measuring Protein Aggregation and Stability Using High-Throughput Biophysical Approaches. Front Mol Biosci 2022; 9:890862. [PMID: 35651816 PMCID: PMC9149252 DOI: 10.3389/fmolb.2022.890862] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2022] [Accepted: 04/25/2022] [Indexed: 11/29/2022] Open
Abstract
Structure-function relationships of biological macromolecules, in particular proteins, provide crucial insights for fundamental biochemistry, medical research and early drug discovery. However, production of recombinant proteins, either for structure determination, functional studies, or to be used as biopharmaceutical products, is often hampered by their instability and propensity to aggregate in solution in vitro. Protein samples of poor quality are often associated with reduced reproducibility as well as high research and production expenses. Several biophysical methods are available for measuring protein aggregation and stability. Yet, discovering and developing means to improve protein behaviour and structure-function integrity remains a demanding task. Here, we discuss workflows that are made possible by adapting established biophysical methods to high-throughput screening approaches. Rapid identification and optimisation of conditions that promote protein stability and reduce aggregation will support researchers and industry to maximise sample quality, stability and reproducibility, thereby reducing research and development time and costs.
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Affiliation(s)
| | | | - Amy E. Danson
- National Physical Laboratory, Teddington, United Kingdom
| | - Rosana I. Reis
- National Physical Laboratory, Teddington, United Kingdom
| | | | - Patrick D. Shaw Stewart
- Douglas Instruments Ltd., Hungerford, United Kingdom
- *Correspondence: Patrick D. Shaw Stewart, ; Isabel Moraes,
| | - Isabel Moraes
- National Physical Laboratory, Teddington, United Kingdom
- *Correspondence: Patrick D. Shaw Stewart, ; Isabel Moraes,
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Ruzza P, Honisch C, Hussain R, Siligardi G. Free Radical Generation in Far-UV Synchrotron Radiation Circular Dichroism Assays-Protein and Buffer Composition Contribution. Int J Mol Sci 2021; 22:11325. [PMID: 34768758 PMCID: PMC8583428 DOI: 10.3390/ijms222111325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Revised: 10/14/2021] [Accepted: 10/15/2021] [Indexed: 11/29/2022] Open
Abstract
A useful tool to analyze the ligands and/or environmental contribution to protein stability is represented by the Synchrotron Radiation Circular Dichroism UV-denaturation assay that consists in the acquisition of several consecutive repeated far-UV SRCD spectra. Recently we demonstrated that the prevailing mechanism of this denaturation involves the generation of free radicals and reactive oxygen species (ROS). In this work, we analyzed the effect of buffering agents commonly used in spectroscopic measurements, including MOPS (3-(N-morpholino) propanesulfonic acid), HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid), TRIS-HCl (tris-hydroxymethil aminomethane hydrochloride), and phosphate, on the efficiency of protein denaturation caused by exposure to UV radiation. Fluorescence experiments confirmed the presence of ROS and were used to determine the rate of ROS generation. Our results indicate that the efficiency of the denaturation process is strongly influenced by the buffer composition with MOPS and HEPES acting also as scavengers and that the presence of proteins itself influenced the ROS formation rate.
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Affiliation(s)
- Paolo Ruzza
- Institute of Biomolecular Chemistry of CNR, Padua Unit, via Marzolo, 1, 35131 Padova, Italy;
| | - Claudia Honisch
- Institute of Biomolecular Chemistry of CNR, Padua Unit, via Marzolo, 1, 35131 Padova, Italy;
- Department of Chemical Sciences, University of Padua, via Marzolo, 1, 35131 Padova, Italy
| | - Rohanah Hussain
- Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK;
| | - Giuliano Siligardi
- Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK;
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Hussain R, Jávorfi T, Siligardi G. CD Imaging at High Spatial Resolution at Diamond B23 Beamline: Evolution and Applications. Front Chem 2021; 9:616928. [PMID: 33898387 PMCID: PMC8060634 DOI: 10.3389/fchem.2021.616928] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Accepted: 02/16/2021] [Indexed: 12/04/2022] Open
Abstract
Circular Dichroism imaging in the 190–650 nm spectral region pionered at Diamond Light Source B23 beamline, has been made possible by the highly collimated microbeam generated at the beamline and has been used to study the homogeneity of the supramolecular structures of thin films of chiral materials deposited on fused quartz substrates. This facility has been expanded with the installation of a Mueller Matrix Polarimeter, MMP, coupled to the beamlight, of which a preliminary data will be discussed. In the solid state, the measurement of CD related to the supramolecular structure is hampered by the presence of circular birefringence, linear dichroism, and linear birefringence that can only be evaluated using the MMP technique. The ability to characterize the chiroptical property of thin chiral films prepared under a variety of conditions and protocols such as drop cast, spin coating, spray at different temperatures and concentrations will enable the determination of the critical parameters for reproducible, uniform and homogeneous specimen preparation, which is the sine qua non for any commercial application. This is of particular importance for optoelectronic materials, but it can also be extended to a broad variety of materials with applications from biosensors to biological tissues.
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Affiliation(s)
- Rohanah Hussain
- Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot, United Kingdom
| | - Tamás Jávorfi
- Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot, United Kingdom
| | - Giuliano Siligardi
- Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot, United Kingdom
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7
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Diamond B23 CD Imaging of Thin Films of Chiral Materials or Achiral Polymers Coated with Chiral Molecules. Symmetry (Basel) 2020. [DOI: 10.3390/sym12111847] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The novel vertical sample chamber, developed at the B23 beamline for synchrotron radiation circular dichroism (SRCD), has enabled the Diamond User community to conduct different types of experiments from high throughput CD of protein and DNA folding using 96-well multiplates to CD imaging at high spatial resolution. Here, we present the application of CD imaging to large areas of achiral polymer PVA films doped with D-dopa to assess the chiral homogeneity of the film preparation with potential antimicrobial property. Synopsis: CDi application of Diamond B23 SRCD beamline.
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Evans LS, Hussain R, Siligardi G, Williamson PT. Magnetically aligned membrane mimetics enabling comparable chiroptical and magnetic resonance spectroscopy studies. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183343. [DOI: 10.1016/j.bbamem.2020.183343] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Revised: 04/30/2020] [Accepted: 05/04/2020] [Indexed: 10/24/2022]
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Townsend DJ, Mala B, Hughes E, Hussain R, Siligardi G, Fullwood NJ, Middleton DA. Circular Dichroism Spectroscopy Identifies the β-Adrenoceptor Agonist Salbutamol As a Direct Inhibitor of Tau Filament Formation in Vitro. ACS Chem Neurosci 2020; 11:2104-2116. [PMID: 32520518 DOI: 10.1021/acschemneuro.0c00154] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Potential drug treatments for Alzheimer's disease (AD) may be found by identifying compounds that block the assembly of the microtubule-associated protein tau into neurofibrillar tangles associated with neuron destabilization and cell death. Here, a small library of structurally diverse compounds was screened in vitro for the ability to inhibit tau aggregation, using high-throughput synchrotron radiation circular dichroism as a novel tool to monitor the structural changes in the protein as it assembles into filaments. The catecholamine epinephrine was found to be the most effective tau aggregation inhibitor of all 88 screened compounds. Subsequently, we tested chemically similar phenolamine drugs from the β-adrenergic receptor agonist class, using conventional circular dichroism spectroscopy, thioflavin T fluorescence, and transmission electron microscopy. Two compounds, salbutamol and dobutamine, used widely in the treatment of respiratory and cardiovascular disease, impede the aggregation of tau in vitro. Dobutamine reduces both the rate and yield of tau filament formation over 24 h; however, it has little effect on the structural transition of tau into β-sheet structures over 24 h. Salbutamol also reduces the yield and rate of filament formation and additionally inhibits tau's structural change into β-sheet-rich aggregates. Salbutamol has a good safety profile and a half-life that facilitates permeation through the blood-brain barrier and could represent an expediated approach to developing AD therapeutics. These results provide the motivation for the in vivo evaluation of pre-existing β-adrenergic receptor agonists as a potential therapy for AD through the reduction of tau deposition.
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Affiliation(s)
- David J Townsend
- Department of Chemistry, Lancaster University, Lancaster LA1 4YB, United Kingdom
| | - Barbora Mala
- Department of Chemistry, Lancaster University, Lancaster LA1 4YB, United Kingdom
| | - Eleri Hughes
- Department of Chemistry, Lancaster University, Lancaster LA1 4YB, United Kingdom
| | - Rohanah Hussain
- Diamond House, Harwell Science & Innovation Campus, Diamond Light Source Ltd., Didcot OX11 ODE, United Kingdom
| | - Giuliano Siligardi
- Diamond House, Harwell Science & Innovation Campus, Diamond Light Source Ltd., Didcot OX11 ODE, United Kingdom
| | - Nigel J. Fullwood
- Biomedical and Life Sciences, Lancaster University, Lancaster LA1 4YG, United Kingdom
| | - David A. Middleton
- Department of Chemistry, Lancaster University, Lancaster LA1 4YB, United Kingdom
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Enzyme-Ligand Interaction Monitored by Synchrotron Radiation Circular Dichroism. Methods Mol Biol 2019. [PMID: 31773649 DOI: 10.1007/978-1-0716-0163-1_6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
CD spectroscopy is the essential tool to quickly ascertain in the far-UV region the global conformational changes, the secondary structure content, and protein folding and in the near-UV region the local tertiary structure changes probed by the local environment of the aromatic side chains, prosthetic groups (hemes, flavones, carotenoids), the dihedral angle of disulfide bonds, and the ligand chromophore moieties, the latter occurring as a result of protein-ligand binding interaction. Qualitative and quantitative investigations into ligand-binding interactions in both the far- and near-UV regions using CD spectroscopy provide unique and direct information whether induced conformational changes upon ligand binding occur and of what nature that are unattainable with other techniques such as fluorescence, ITC, SPR, and AUC.This chapter provides an overview of how to perform circular dichroism (CD) experiments, detailing methods, hints and tips for successful CD measurements. Descriptions of different experimental designs are discussed using CD to investigate ligand-binding interactions. This includes standard qualitative CD measurements conducted in both single-measurement mode and high-throughput 96-well plate mode, CD titrations, and UV protein denaturation assays with and without ligand.The highly collimated micro-beam available at B23 beamline for synchrotron radiation circular dichroism (SRCD) at Diamond Light Source (DLS) offers many advantages to benchtop instruments. The synchrotron light source is ten times brighter than a standard xenon arc light source of benchtop instruments. The small diameter of the synchrotron beam can be up to 160 times smaller than that of benchtop light beams; this has enabled the use of small aperture cuvette cells and flat capillary tubes reducing substantially the amount of volume sample to be investigated. Methods, hints and tips, and golden rules to measure good quality, artifact-free SRCD and CD data will be described in this chapter in particular for the study of protein-ligand interactions and protein photostability.
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The role of circular dichroism spectroscopy in the era of integrative structural biology. Curr Opin Struct Biol 2019; 58:191-196. [DOI: 10.1016/j.sbi.2019.04.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Revised: 03/28/2019] [Accepted: 04/01/2019] [Indexed: 12/25/2022]
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12
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Siligardi G, Hughes CS, Hussain R. Characterisation of sensor kinase by CD spectroscopy: golden rules and tips. Biochem Soc Trans 2018; 46:1627-1642. [PMID: 30514767 PMCID: PMC6299240 DOI: 10.1042/bst20180222] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Revised: 09/19/2018] [Accepted: 09/21/2018] [Indexed: 01/22/2023]
Abstract
This is a review that describes the golden rules and tips on how to characterise the molecular interactions of membrane sensor kinase proteins with ligands using mainly circular dichroism (CD) spectroscopy. CD spectroscopy is essential for this task as any conformational change observed in the far-UV (secondary structures (α-helix, β-strands, poly-proline of type II, β-turns, irregular and folding) and near-UV regions [local environment of the aromatic side-chains of amino acid residues (Phe, Tyr and Trp) and ligands (drugs) and prosthetic groups (porphyrins, cofactors and coenzymes (FMN, FAD, NAD))] upon ligand addition to the protein can be used to determine qualitatively and quantitatively ligand-binding interactions. Advantages of using CD versus other techniques will be discussed. The difference CD spectra of the protein-ligand mixtures calculated subtracting the spectra of the ligand at various molar ratios can be used to determine the type of conformational changes induced by the ligand in terms of the estimated content of the various elements of protein secondary structure. The highly collimated microbeam and high photon flux of Diamond Light Source B23 beamline for synchrotron radiation circular dichroism (SRCD) enable the use of minimal amount of membrane proteins (7.5 µg for a 0.5 mg/ml solution) for high-throughput screening. Several examples of CD titrations of membrane proteins with a variety of ligands are described herein including the protocol tips that would guide the choice of the appropriate parameters to conduct these titrations by CD/SRCD in the best possible way.
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Affiliation(s)
- Giuliano Siligardi
- Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, Oxfordshire, U.K
| | - Charlotte S Hughes
- Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, Oxfordshire, U.K
| | - Rohanah Hussain
- Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, Oxfordshire, U.K.
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Kumagai PS, Araujo APU, Lopes JLS. Going deep into protein secondary structure with synchrotron radiation circular dichroism spectroscopy. Biophys Rev 2017; 9:517-527. [PMID: 28825203 DOI: 10.1007/s12551-017-0314-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Accepted: 08/03/2017] [Indexed: 10/25/2022] Open
Abstract
Circular dichroism (CD) spectroscopy is a fast, powerful, well-established, and widely used analytical technique in the biophysical and structural biology community to study protein secondary structure and to track changes in protein conformation in different environments. The use of the intense light of a synchrotron beam as the light source for collecting CD measurements has emerged as an enhanced method, known as synchrotron radiation circular dichroism (SRCD) spectroscopy, that has several advantages over the conventional CD method, including a significant spectral range extension for data collection, deeper access to the lower limit (cut-off) of conventional CD spectroscopy, an improved signal-to-noise ratio to increase accuracy in the measurements, and the possibility to collect measurements in highly absorbing solutions. In this review, we discuss different applications of the SRCD technique by researchers from Latin America. In this context, we specifically look at the use of this method for examining the secondary structure and conformational behavior of proteins belonging to the four main classes of the hierarchical protein domain classification CATH (Class, Architecture, Topology, Homology) database, focusing on the advantages and improvements associated with SRCD spectroscopy in terms of characterizing proteins composed of different structural elements.
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Affiliation(s)
- Patricia S Kumagai
- Instituto de Física de São Carlos, Universidade de São Paulo, São Paulo, SP, Brazil
| | - Ana P U Araujo
- Instituto de Física de São Carlos, Universidade de São Paulo, São Paulo, SP, Brazil
| | - Jose L S Lopes
- Departamento Física Aplicada, Instituto de Física,, Universidade de São Paulo, Rua do Matão 1371, Cidade Universitária, São Paulo, SP, 05508-090, Brazil.
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