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Benech-Arnold T, Navarro DA, Rodríguez C, Schmidt W, Fredericq S, Rojas AM, Stortz CA. Structure and rheology of the polysaccharides from Schizymenia dubyi: Isolation of an unusual glucurono-carrageenan. Carbohydr Polym 2024; 342:122324. [PMID: 39048213 DOI: 10.1016/j.carbpol.2024.122324] [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] [Received: 03/19/2024] [Revised: 05/12/2024] [Accepted: 05/24/2024] [Indexed: 07/27/2024]
Abstract
The system of polysaccharides from Schizymenia dubyi (Nemastomatales) was investigated. It contains a mixture of hybrid dl galactans (SH-S) and carrageenan-like polysaccharides, which were separated by means of precipitation with KCl at high concentrations. The structural features of the carrageenan-like fraction (SH-I) were investigated by methylation analysis, desulfation, uronic acid reduction, and NMR spectroscopy. It was concluded that the structure has the typical alternance α-(1 → 3), β-(1 → 4) of d-galactose units, with most of the 3-linked units sulfated in O-2 (and some in O-4), and most of the 4-linked units sulfated in O-3, and substituted in O-2 by single stubs of β-d-glucuronic acid (partly sulfated in each of the three available positions). This substituent has been only seldom found in red seaweed galactans. Rheological studies of 5 % and 10 % w/v SH, SH-S and SH-I aqueous systems, either without ions, or in KCl or CaCl2 solution gave thickening behaviors. Their random coil conformations justify the pseudoplastic behavior observed in the viscosity versus shear rate curves. As SH-S and SH-I are both contained in SH, an interpenetrating network could form in SH between the glucurono-carrageenan and the agaran, as inferred from the mechanical spectra recorded in water, especially with potassium ion.
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Affiliation(s)
- Tomás Benech-Arnold
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Centro de Investigaciones en Hidratos de Carbono (CIHIDECAR/CONICET), Departamento de Química Orgánica, Ciudad Universitaria, 1428 Buenos Aires, Argentina
| | - Diego A Navarro
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Centro de Investigaciones en Hidratos de Carbono (CIHIDECAR/CONICET), Departamento de Química Orgánica, Ciudad Universitaria, 1428 Buenos Aires, Argentina
| | - Cristian Rodríguez
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, UMYMFOR/CONICET, Departamento de Química Orgánica, Ciudad Universitaria, 1428 Buenos Aires, Argentina
| | - William Schmidt
- Biology Department, University of Louisiana at Lafayette, Lafayette 70504-3602, LA, United States
| | - Suzanne Fredericq
- Biology Department, University of Louisiana at Lafayette, Lafayette 70504-3602, LA, United States
| | - Ana M Rojas
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Tecnología de Alimentos y Procesos Químicos (ITAPROQ/CONICET-UBA), Departamento de Industrias, Ciudad Universitaria, 1428 Buenos Aires, Argentina
| | - Carlos A Stortz
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Centro de Investigaciones en Hidratos de Carbono (CIHIDECAR/CONICET), Departamento de Química Orgánica, Ciudad Universitaria, 1428 Buenos Aires, Argentina.
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Gao JN, Li Y, Liang J, Xiao L, Kuang HX, Xia YG. A Reverse Thinking Based on Partially Methylated Aldononitrile Acetates to Analyze Glycoside Linkages of Polysaccharides Using Liquid Chromatography-Multiple Reaction Monitoring Mass Spectrometry. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2024. [PMID: 39036888 DOI: 10.1021/acs.jafc.4c04160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/23/2024]
Abstract
Glycoside linkage analyses of medicine and food homologous plant polysaccharides have always been a key point and a difficulty of structural characterization. The gas chromatography-mass spectrometry (GC-MS) method is one of the commonly used traditional techniques to determine glycoside linkages via partially methylated alditol acetates and aldononitrile acetates (PMAAs and PMANs). Due to the simplicity of derivatization and the highly structural asymmetry of PMANs, reverse thinking is proposed using liquid chromatography-electrospray ionization-multiple reaction monitoring mass spectrometry (LC-ESI-MRM-MS) for the first time to directly determine the neutral and acidic glycosyl linkages of polysaccharides. The complete characterization of glycoside linkages deduced from PMANs was achieved using a combination of tR values, characteristic MRM ion pairs, diagnostic ESI+-MS/MS fragmentation ions (DFIs), and optimal collision energy (OCE). The DFI and OCE parameters were confirmed to be effective for the auxiliary discrimination of some isomers of the PMANs. The practicality of LC-ESI+-MRM-MS was further verified by analyzing the glycoside linkages of polysaccharides in five medicine and food homologous plants. This method can serve as an alternative to GC-MS for the simultaneous determination of neutral and acidic glycosyl linkages in polysaccharides.
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Affiliation(s)
- Jia-Ning Gao
- Key Laboratory of Basic and Application Research of Beiyao, Ministry of Education, Heilongjiang University of Chinese Medicine, 24 Heping Road, Harbin 150040, PR China
| | - Ye Li
- Key Laboratory of Basic and Application Research of Beiyao, Ministry of Education, Heilongjiang University of Chinese Medicine, 24 Heping Road, Harbin 150040, PR China
| | - Jun Liang
- Key Laboratory of Basic and Application Research of Beiyao, Ministry of Education, Heilongjiang University of Chinese Medicine, 24 Heping Road, Harbin 150040, PR China
| | - Li Xiao
- Key Laboratory of Basic and Application Research of Beiyao, Ministry of Education, Heilongjiang University of Chinese Medicine, 24 Heping Road, Harbin 150040, PR China
| | - Hai-Xue Kuang
- Key Laboratory of Basic and Application Research of Beiyao, Ministry of Education, Heilongjiang University of Chinese Medicine, 24 Heping Road, Harbin 150040, PR China
| | - Yong-Gang Xia
- Key Laboratory of Basic and Application Research of Beiyao, Ministry of Education, Heilongjiang University of Chinese Medicine, 24 Heping Road, Harbin 150040, PR China
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Sznaider F, Rojas AM, Stortz CA, Navarro DA. Chemical structure and rheological studies of arabinoglucuronoxylans from the Cercidium praecox exudate brea gum. Carbohydr Polym 2019; 228:115388. [PMID: 31635746 DOI: 10.1016/j.carbpol.2019.115388] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Revised: 09/11/2019] [Accepted: 09/25/2019] [Indexed: 12/28/2022]
Abstract
The structure of the arabinoglucuronoxylans from brea gum was elucidated through an chemical and NMR spectroscopical analysis. They are composed of xylose, arabinose, glucuronic acid and 4-O-methylglucuronic acid in a molar ratio 1:0.44:0.16:0.22. The structure consists of a central chain of (1→4)-β-d-xylopyranose of which ca.70% are susbstituted in C2 with single stubs of others sugars (β-d-Xylp, α-d-GlcpA and 4-O-Me-α-d-GlcpA), with disaccharides (α-l-Arap-(1→2)-4-O-Me-α-d-GlcpA-(1→, α-l-Arap-(1→2)-α-d-GlcpA-(1→, β-l-Araf-(1→3)-α-l-Araf-(1→ and α-l-Araf-(1→3)-α-l-Araf-(1→5), and possibly with trisaccharides of xylose. The determination of the location of the acetyl groups and their quantification in these arabinoglucuronoxylans has been achieved for the first time. Brea gum presents a higher thickening effect than gum arabic in 5% aqueous solution, demonstrating its potential usefulness for food and pharmaceutical applications.
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Affiliation(s)
- Frank Sznaider
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Centro de Investigaciones en Hidratos de Carbono (CIHIDECAR/CONICET), Departamento de Química Orgánica, Ciudad Universitaria, 1428 Buenos Aires, Argentina
| | - Ana M Rojas
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Tecnología de Alimentos y Procesos Químicos (ITAPROQ/CONICET), Departamento de Industrias, Ciudad Universitaria, 1428 Buenos Aires, Argentina
| | - Carlos A Stortz
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Centro de Investigaciones en Hidratos de Carbono (CIHIDECAR/CONICET), Departamento de Química Orgánica, Ciudad Universitaria, 1428 Buenos Aires, Argentina
| | - Diego A Navarro
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Centro de Investigaciones en Hidratos de Carbono (CIHIDECAR/CONICET), Departamento de Química Orgánica, Ciudad Universitaria, 1428 Buenos Aires, Argentina.
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Ponce NMA, Flores ML, Pujol CA, Becerra MB, Navarro DA, Córdoba O, Damonte EB, Stortz CA. Fucoidans from the phaeophyta Scytosiphon lomentaria: Chemical analysis and antiviral activity of the galactofucan component. Carbohydr Res 2019; 478:18-24. [PMID: 31048118 DOI: 10.1016/j.carres.2019.04.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Revised: 03/22/2019] [Accepted: 04/16/2019] [Indexed: 12/15/2022]
Abstract
The brown seaweed Scytosiphon lomentaria produces moderate amounts of fucoidans. By cetrimide fractionation, typical heavily sulfated galactofucans are obtained, with no major signs of chemical heterogeneity, together with fractions with higher proportions of xylose, mannose and uronic acids. Anyway, fucose is the most important monosaccharide in most of the subfractions of the subsequent extracts. The fucan moieties appear to be mostly as 3-linked α-l-fucopyranosyl units, with several patterns of sulfate and branching. Galactose is mostly 6-linked, whereas mannose appears to be 2-linked, and xylose appears mostly as terminal stubs. Small amounts of 2-O-acetylated fucose units appear. A high and selective antiviral activity against HSV-1 and HSV-2 was determined for the galactofucan fractions whereas the uronofucoidans were inactive.
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Affiliation(s)
- Nora M A Ponce
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Centro de Investigaciones en Hidratos de Carbono (CIHIDECAR), Departamento de Química Orgánica, Ciudad Universitaria, 1428, Buenos Aires, Argentina
| | - María L Flores
- Farmacognosia, GQBMRNP, AAI, Centro Regional de Investigación y Desarrollo Científico Tecnológico (CRIDECIT), Facultad de Ciencias Naturales y Ciencias de la Salud, Universidad Nacional de la Patagonia San Juan Bosco, Km 4, s/N°, 9000, Comodoro Rivadavia, Provincia de Chubut, Argentina
| | - Carlos A Pujol
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Química Biológica (IQUIBICEN), Departamento de Química Biológica, Laboratorio de Virología, Ciudad Universitaria, 1428, Buenos Aires, Argentina
| | - Mónica B Becerra
- Farmacognosia, GQBMRNP, AAI, Centro Regional de Investigación y Desarrollo Científico Tecnológico (CRIDECIT), Facultad de Ciencias Naturales y Ciencias de la Salud, Universidad Nacional de la Patagonia San Juan Bosco, Km 4, s/N°, 9000, Comodoro Rivadavia, Provincia de Chubut, Argentina; Química Biológica II, GQBMRNP, AAI, Centro Regional de Investigación y Desarrollo Científico Tecnológico (CRIDECIT), Facultad de Ciencias Naturales y Ciencias de la Salud, Universidad Nacional de la Patagonia San Juan Bosco, Km 4, s/N°, 9000, Comodoro Rivadavia, Provincia de Chubut, Argentina
| | - Diego A Navarro
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Centro de Investigaciones en Hidratos de Carbono (CIHIDECAR), Departamento de Química Orgánica, Ciudad Universitaria, 1428, Buenos Aires, Argentina
| | - Osvaldo Córdoba
- Química Biológica II, GQBMRNP, AAI, Centro Regional de Investigación y Desarrollo Científico Tecnológico (CRIDECIT), Facultad de Ciencias Naturales y Ciencias de la Salud, Universidad Nacional de la Patagonia San Juan Bosco, Km 4, s/N°, 9000, Comodoro Rivadavia, Provincia de Chubut, Argentina
| | - Elsa B Damonte
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Química Biológica (IQUIBICEN), Departamento de Química Biológica, Laboratorio de Virología, Ciudad Universitaria, 1428, Buenos Aires, Argentina
| | - Carlos A Stortz
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Consejo Nacional de Investigaciones Científicas y Técnicas, Centro de Investigaciones en Hidratos de Carbono (CIHIDECAR), Departamento de Química Orgánica, Ciudad Universitaria, 1428, Buenos Aires, Argentina.
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Cosenza VA, Navarro DA, Stortz CA. Minor polysaccharidic constituents from the red seaweed Hypnea musciformis. Appearance of a novel branched uronic acid. Carbohydr Polym 2017; 157:156-166. [DOI: 10.1016/j.carbpol.2016.09.071] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Revised: 09/22/2016] [Accepted: 09/22/2016] [Indexed: 10/21/2022]
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Chemical and rheological characterization of the carrageenans from Hypnea musciformis (Wulfen) Lamoroux. Carbohydr Polym 2014; 102:780-9. [DOI: 10.1016/j.carbpol.2013.10.090] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Revised: 09/24/2013] [Accepted: 10/29/2013] [Indexed: 11/23/2022]
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Structure of highly substituted agarans from the red seaweeds Laurencia obtusa and Laurencia filiformis. Carbohydr Polym 2014; 101:705-13. [DOI: 10.1016/j.carbpol.2013.09.089] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2013] [Revised: 09/24/2013] [Accepted: 09/24/2013] [Indexed: 11/24/2022]
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Abstract
Red algae (Rhodophyta) are known as the source of unique sulfated galactans, such as agar, agarose, and carrageenans. The wide practical uses of these polysaccharides are based on their ability to form strong gels in aqueous solutions. Gelling polysaccharides usually have molecules built up of repeating disaccharide units with a regular distribution of sulfate groups, but most of the red algal species contain more complex galactans devoid of gelling ability because of various deviations from the regular structure. Moreover, several red algae may contain sulfated mannans or neutral xylans instead of sulfated galactans as the main structural polysaccharides. This chapter is devoted to a description of the structural diversity of polysaccharides found in the red algae, with special emphasis on the methods of structural analysis of sulfated galactans. In addition to the structural information, some data on the possible use of red algal polysaccharides as biologically active polymers or as taxonomic markers are briefly discussed.
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Xylogalactans from Lithothamnion heterocladum, a crustose member of the Corallinales (Rhodophyta). Carbohydr Polym 2011. [DOI: 10.1016/j.carbpol.2010.12.048] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Navarro DA, Stortz CA. The system of xylogalactans from the red seaweed Jania rubens (Corallinales, Rhodophyta). Carbohydr Res 2008; 343:2613-22. [PMID: 18667196 DOI: 10.1016/j.carres.2008.06.015] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2008] [Revised: 06/09/2008] [Accepted: 06/11/2008] [Indexed: 10/22/2022]
Abstract
The main acidic polysaccharides from the red seaweed Jania rubens share the general characteristics of corallinans (agar-like xylogalactans). After fractionation by ion-exchange chromatography, ten fractions were separated and characterized by sugar composition, other components, methylation, ethylation, desulfation-methylation, and NMR analyses. The main group of fractions carry the agaran disaccharidic repeating unit [-->3)-beta-D-Gal-(1-->4)-alpha-L-Gal-(1-->] substituted mainly on O-6 of the beta-D-Gal unit by beta-xylosyl side stubs, and less with sulfate or methoxyl groups, and also on O-2 of the alpha-l-Gal unit with methoxyl or sulfate, or less on O-3 of the same unit with methoxyl groups. These features are somehow common to the four members of the order already studied. However, a sugar uncommon to the order appears in moderate proportions for all the fractions: it is 3,6-anhydro-l-galactose (partly sulfated or methoxylated on O-2) replacing the L-Gal unit. Besides, several other structural features never found in the order (and uncommon in any polysaccharide) appear in some minor fractions: the presence of side stubs of 2,3-di- and 3-O-methyl-D-galactose, and also part of the 3-O-methyl-L-galactose acting as side stubs. These results show that, although the main features of the corallinean xylogalactans are common to all the species studied, each one has minor characteristics of its own.
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Affiliation(s)
- Diego A Navarro
- Departamento de Química Orgánica, Universidad de Buenos Aires, Ciudad Universitaria, 1428 Buenos Aires, Argentina
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Matsuhiro B, Conte AF, Damonte EB, Kolender AA, Matulewicz MC, Mejías EG, Pujol CA, Zúñiga EA. Structural analysis and antiviral activity of a sulfated galactan from the red seaweed Schizymenia binderi (Gigartinales, Rhodophyta). Carbohydr Res 2006; 340:2392-402. [PMID: 16125685 DOI: 10.1016/j.carres.2005.08.004] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2005] [Revised: 08/10/2005] [Accepted: 08/11/2005] [Indexed: 11/19/2022]
Abstract
Aqueous extraction of gametophytic Schizymenia binderi afforded a polysaccharide composed of galactose and sulfate groups in a molar ratio of 1.0:0.89 together with uronic acids (6.8 wt%) and minor amounts of other neutral sugars. Alkali-treatment of the polysaccharide afforded a polysaccharide devoid of 3,6-anhydrogalactose. 13C NMR spectroscopy of the desulfated alkali-treated polysaccharide showed a backbone structure of alternating 3-linked beta-D-galactopyranosyl and 4-linked alpha-galactopyranosyl units that are predominantly of the D-configuration and partly of the L-configuration. Methylation, ethylation and NMR spectroscopic studies of the alkali-treated polysaccharide indicated that the sulfate groups are located mainly at positions O-2 of 3-linked beta-D-galactopyranosyl residue and at position O-3 of 4-linked-alpha-galactopyranosyl residues, the latter is partially glycosylated at position O-2. The sulfated galactan from S. binderi exhibited highly selective antiviral activity against Herpes simplex virus types 1 and 2, with selectivity indices (ratio cytotoxicity/antiviral activity) >1000 for all assayed virus strains. This compound was shown to interfere with the initial adsorption of viruses to cells.
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Affiliation(s)
- Betty Matsuhiro
- Departamento de Ciencias Químicas, Facultad de Química y Biología, Universidad de Santiago de Chile, Casilla 40, Santiago 33, Chile.
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Abstract
The water-soluble polysaccharides from Georgiella confluens, collected in Antarctica, were fractionated with cetrimide. The complexed material was subjected to fractional solubilization in solutions of increasing sodium chloride concentration. The initially extracted polysaccharide and the major fraction isolated, soluble in 0.5 M NaCl, were studied. These are sulfated xylogalactans naturally rich in methylated sugar residues, comprising of 3,6-anhydro-2-O-methyl-L-galactose, 2-O-methyl-L-galactose and 6-O-methyl-D-galactose. Structural analysis was carried out by methylation, ethylation, desulfation-ethylation, desulfation-methylation, Smith degradation, 13C NMR spectroscopy and determination of the absolute configuration of monosaccharides by gas chromatography of diastereomeric derivatives produced by reductive amination. The results indicated the presence of an agaran backbone with an unusual substitution pattern: sulfation mainly at the 3-position of the alpha-L-galactose units and the presence of xylose side chains at the 4-position of the beta-D-galactose residues.
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Affiliation(s)
- Adriana A Kolender
- Departamento de Química Orgánica, CIHIDECAR-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, 1428 Buenos Aires, Argentina
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Chapter 27 Mass spectrometry of oligosaccharides. ACTA ACUST UNITED AC 2002. [DOI: 10.1016/s0301-4770(02)80052-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/10/2023]
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Estevez JM, Ciancia M, Cerezo AS. The system of low-molecular-weight carrageenans and agaroids from the room-temperature-extracted fraction of Kappaphycus alvarezii. Carbohydr Res 2000; 325:287-99. [PMID: 10839122 DOI: 10.1016/s0008-6215(00)00006-9] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
The room-temperature-extracted fraction from the red seaweed Kappaphycus alvarezii consists mainly of low-molecular-weight carrageenans, with structural dispersion around a basic kappa-pattern. This dispersion results from: (a) low percentages of 3,6-anhydrogalactose and the presence of precursor units; (b) important quantities of 6-O-methyl beta-D-galactose (4-sulfate) residues; (c) significant amounts of iota-repeating structure, and (d) small amounts of non-sulfated and disulfated beta-D-galactose residues. Significant quantities of alpha-L-galactose units suggest the presence of agaroids, as it has been reported in several other carrageenophytes.
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Affiliation(s)
- J M Estevez
- Departamento de Química Orgánica (CIHIDECAR-CONICET), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria-Pabellón 2, Argentina
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