Marcelo Herbst | Universidade Federal Rural do Rio de Janeiro (original) (raw)
Papers by Marcelo Herbst
Journal of Molecular Structure, 2005
The crystal structure, electrochemical behaviour and spectroscopic properties (FT-IR, UV–vis and ... more The crystal structure, electrochemical behaviour and spectroscopic properties (FT-IR, UV–vis and EPR) of the mononuclear complex [Cu(HPClNOL)(CH3CN)](ClO4)21, are reported. The new tetradentate ligand, HPClNOL, 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol, reacts with 1equiv. of [Cu(OH2)6](ClO4)2, in methanol, to give 1, which crystallizes as blue monoclinic crystals, space group P21/c with a=14.906(3)Å, b=11.371(2)Å, c=14.113(3)Å, β=103.86(3)°, V=2322.4(8)Å3 and Z=4. In 1, the copper center is pentacoordinated, showing a distorted square pyramidal geometry. The electronic spectrum indicates that, in acetonitrile, the copper atom becomes hexacoordinated (λmax(ε) 621nm (87dm3mol−1cm−1). Frozen solution EPR spectra of 1 in pure acetonitrile (A‖=190G, g‖=2.24) and of 1 in acetonitrile/tetrabutylammonium perchlorate solution (A‖=185G, g‖=2.25) indicates a hexacoordinated environment for the copper(II) center. Complex 1 shows a quasi-reversible redox process at 70mV vs NHE, which is attributed to Cu(II)/Cu(I) redox couple.
Transition Metal Chemistry, 2005
We have investigated the reactions between 2,3,5,6-tetrakis(α-pyridyl)pyrazine (TPP) and CrCl3 · ... more We have investigated the reactions between 2,3,5,6-tetrakis(α-pyridyl)pyrazine (TPP) and CrCl3 · 6H2O in 1:2 and 2.6:1 (CrIII:TPP) stoichiometric ratios. The resulting products, [Cr(TPP)Cl3] (1) and [(CrCl3)2-μ-TPP] (2), respectively, have been characterized by elemental and thermogravimetric analyses, molar conductivities, vibrational and electronic spectroscopy, and powder e.p.r. spectroscopy at room temperature. In both (1) and (2), TPP behaves as a tridentate ligand. Whereas (1) is a monometallic species with three uncoordinated nitrogen atoms, (2) is bimetallic with TPP as a bridging ligand.
Journal of Materials Science, 2008
A purification method based on HCl treatment under reflux was employed for purification of carbon... more A purification method based on HCl treatment under reflux was employed for purification of carbon nanotube (CNT) samples, obtained by the electric discharge method utilizing Zr(Co 0.5 Ni 0.5 ) 2 , Ce 3 (Co 0.5 Ni 0.5 ) 2 and Ce(Co 0.5 Ni 0.5 ) 5 as catalysts. Raman Spectroscopy provided information on the SWCNT presence in the untreated samples. Scanning Electron Microscopy (SEM) showed CNT with different diameters and lengths. Different acid treatment conditions were employed and the best results were achieved for HCl 3 mol/L aqueous solution during 24 h reflux. Transmission Electron Microscopy (TEM) images, associated with EDS, revealed the catalyst removal from the original sample and the presence of other carbon structures near the CNT formation. CNT acid functionalization for Pt nanoparticles dispersion was successful, resulting in a homogeneously dispersed system, as seen in TEM images. Temperature Programmed Oxidation (TPO) analysis of the raw and purified samples indicated that after purification there are three different carbon species present on the purified material, each one showing a different behavior towards O 2 oxidation.
Catalysis Today, 2008
A comparative study was made in which two hydrotalcites were loaded with vanadium employing diffe... more A comparative study was made in which two hydrotalcites were loaded with vanadium employing different procedures: (1) aqueous phase impregnation, with vanadyl sulfate solution in pH 6.5 or 9.5; (2) solid phase mixing, with vanadyl sulfate or vanadium pentoxide physically mixed up. TPR investigation revealed that vanadium-loaded hydrotalcites obtained by aqueous phase impregnation in two distinct pH, resulted in different reduction profiles. The vanadium-loaded hydrotalcites were characterized by FTIR, XRD and TGA-DTA analysis. In situ dispersive XAS (DXAS) spectra obtained during thermal treatment in air showed that, for the physical mixture of solids, vanadium is oxidized above 350 8C. For the samples prepared by aqueous phase impregnation, the effect of alkaline pH was to produce polymeric vanadium species deposited onto the HT in comparison with the isolated vanadium species in acidic conditions. The influence of both, the hydrotalcite interlayer anion type and the vanadium loading procedure, on the reducibility of vanadium species is also discussed. #
Catalysis Letters, 2004
The effects of the SAR (14 and 38) and of the methodology of introduction of nickel (wetness impr... more The effects of the SAR (14 and 38) and of the methodology of introduction of nickel (wetness impregnation and ion exchange) on catalyst activation were investigated in Ni/USY model catalysts submitted to two activation treatments: reduction (A) and reduction/calcination/reduction, successively (B). the catalysts prepared by wetness impregnation, a marked increase in the catalytic activity after treatment B was observed. On the basis of the catalyst efficiency toward ethane hydrogenolysis, the lower SAR catalyst presents a threefold higher activity. On the contrary, the catalysts prepared by ion exchange, as well as a model catalyst prepared by wetness impregnation over a USY exhaustively exchanged with nickel ions, do not present measurable increasing of the catalytic activity under the same activation conditions. Monitoring the catalyst activation by EXAFS indicates the formation of nickel clusters in the impregnated catalysts after activation treatment B, which should be responsible for the high catalytic activity. However, TEM images reveal a bimodal particle size distribution, with large (ca. 20 nm) and small nickel particles. Temperature-programmed reduction performed under the same conditions of catalyst activation suggests that only the small nickel particles are activated under the experimental conditions adopted in this work.
Polyhedron, 2008
A deamination process was observed after copper(II) complexation reaction with guanidinoacetic (G... more A deamination process was observed after copper(II) complexation reaction with guanidinoacetic (Gaa) and glutamic acids (Glu), forming the binuclear copper(II) complex K 2 Cu 2 C 16 H 23 N 7 O 12 · 1/2H 2 O (1), which was characterized by elemental analysis (CHN), ...
Applied Catalysis A-general, 2007
... Complex 2 exhibited the best results, reaching as high as 68.9% of total yield in 24 h with H... more ... Complex 2 exhibited the best results, reaching as high as 68.9% of total yield in 24 h with H 2O 2 . In general, H 2 O 2 showed better results than tert-butyl hydroperoxide as terminal oxidant. ... 2.3. Synthesis of {[Cu(BMPA)Cl 2 ][Cu(BMPA)(H 2 O)Cl][Cu(BMPA)Cl][CuCl 4 ]} (2). ...
Inorganic Chemistry Communications, 2005
The green crystalline, homoleptic vanadium(IV) alkoxide [V 2 (l-OPr i ) 2 (OPr i ) 6 ] (I) has be... more The green crystalline, homoleptic vanadium(IV) alkoxide [V 2 (l-OPr i ) 2 (OPr i ) 6 ] (I) has been reproducibly prepared in more than 60% yield; its identity was confirmed by chemical and physical methods including single-crystal X-ray diffractometry. Complex I is thermochromic in solution, changing reversibly from royal blue to gold yellow when cooled from 300 to 210 K. The assignment of this thermochromic behaviour to a mononuclear (S ¼ 1 2 ) M binuclear (S = 1) solution equilibrium is discussed. Complex I is a potential precursor of industrially-relevant vanadium-(IV), -(V) and mixed-valence vanadium oxides.
Inorganic Chemistry Communications, 2004
A novel trianionic disubstituted guanidine, ( 1 N-carboxymethylguanidino)hydroxyacetic acid-C 5 H... more A novel trianionic disubstituted guanidine, ( 1 N-carboxymethylguanidino)hydroxyacetic acid-C 5 H 6 N 3 O 5 ), oag 3À , has been formed through a desamidination process occurred during copper(II) complexation with guanidinoacetic acid, C 3 H 7 N 3 O 2 (Gaa), which produced [Cu 2 (oag)(Gaa)(H 2 O)]NO 3 AE 2H 2 O (1). A proposal mechanism of formation of 1 is presented based on the low temperature electron paramagnetic resonance and previous potentiometric studies, which have indicated the presence of CuH 2 Gaa as the precursor species.
Applied Catalysis A-general, 2007
Piperonal is an important intermediate in the synthesis of drugs like L-DOPA. Vanadyl-Y-zeolites ... more Piperonal is an important intermediate in the synthesis of drugs like L-DOPA. Vanadyl-Y-zeolites have been tested as potential catalysts for this process. The use of encapsulated vanadyl compounds in Y-zeolite pores led to excellent rates of isosafrol oxidation under microwave irradiation. Native Y-zeolite better allowed the diffusion of the oxidant agent (hydrogen peroxide) through the catalyst pores compared to the VO-exchanged catalysts. This led to piperonal, which was also obtained due to the presence of V 5+ supported on one of the catalysts. These factors aided the extension of the oxidation process of isosafrol. On the other hand, vanadyl-zeolites, containing V 4+ species, promoted the reaction to intermediate (epoxide) with high selectivity under microwave radiation. Finally the impregnation of VO(Salen) on Y-zeolite showed better selectivity for epoxide formation than did the incorporated VO(Salen)-zeolite. Catalyst's surface area and availability of the vanadyl group were the main factors which allowed this superior performance. #
Janeiro (IQ/UFRJ), buscou-se identificar obstáculos epistemológicos entre pós-graduandos em bioqu... more Janeiro (IQ/UFRJ), buscou-se identificar obstáculos epistemológicos entre pós-graduandos em bioquímica e áreas correlatas. Um questionário com perguntas e excertos de artigos científicos de revistas de alto fator de impacto foi respondido, anonimamente, por pós-graduandos de diferentes cursos da UFRJ e de outras universidades, que nunca cursaram disciplina relacionada à epistemologia. Foi possível identificar concepções vitalistas (animismo) tanto nas respostas às perguntas como na aceitação ou não identificação deste obstáculo nos excertos. O obstáculo pragmático e unitário foi identificado através de uma concepção teleológica dos processos evolutivos, em afirmações como a existência de objetivos/finalidades na adaptação dos organismos. Verificou-se a presença de figuras de linguagem, metáforas e analogias (obstáculo verbal) na explicação da evolução e do sistema imune, também encontradas nos excertos dos artigos. Foram também identificados obstáculos associados à observação primeira e generalização prematura. A partir deste diagnóstico verificou-se a necessidade de enfatizar o caráter objetivo, material, não teleológico da bioquímica, em disciplinas oferecidas desde a graduação. © Cien. Cogn. 2012; Vol. 17 (2): 076-097.
Journal of Molecular Structure, 2005
The crystal structure, electrochemical behaviour and spectroscopic properties (FT-IR, UV–vis and ... more The crystal structure, electrochemical behaviour and spectroscopic properties (FT-IR, UV–vis and EPR) of the mononuclear complex [Cu(HPClNOL)(CH3CN)](ClO4)21, are reported. The new tetradentate ligand, HPClNOL, 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol, reacts with 1equiv. of [Cu(OH2)6](ClO4)2, in methanol, to give 1, which crystallizes as blue monoclinic crystals, space group P21/c with a=14.906(3)Å, b=11.371(2)Å, c=14.113(3)Å, β=103.86(3)°, V=2322.4(8)Å3 and Z=4. In 1, the copper center is pentacoordinated, showing a distorted square pyramidal geometry. The electronic spectrum indicates that, in acetonitrile, the copper atom becomes hexacoordinated (λmax(ε) 621nm (87dm3mol−1cm−1). Frozen solution EPR spectra of 1 in pure acetonitrile (A‖=190G, g‖=2.24) and of 1 in acetonitrile/tetrabutylammonium perchlorate solution (A‖=185G, g‖=2.25) indicates a hexacoordinated environment for the copper(II) center. Complex 1 shows a quasi-reversible redox process at 70mV vs NHE, which is attributed to Cu(II)/Cu(I) redox couple.
Transition Metal Chemistry, 2005
We have investigated the reactions between 2,3,5,6-tetrakis(α-pyridyl)pyrazine (TPP) and CrCl3 · ... more We have investigated the reactions between 2,3,5,6-tetrakis(α-pyridyl)pyrazine (TPP) and CrCl3 · 6H2O in 1:2 and 2.6:1 (CrIII:TPP) stoichiometric ratios. The resulting products, [Cr(TPP)Cl3] (1) and [(CrCl3)2-μ-TPP] (2), respectively, have been characterized by elemental and thermogravimetric analyses, molar conductivities, vibrational and electronic spectroscopy, and powder e.p.r. spectroscopy at room temperature. In both (1) and (2), TPP behaves as a tridentate ligand. Whereas (1) is a monometallic species with three uncoordinated nitrogen atoms, (2) is bimetallic with TPP as a bridging ligand.
Journal of Materials Science, 2008
A purification method based on HCl treatment under reflux was employed for purification of carbon... more A purification method based on HCl treatment under reflux was employed for purification of carbon nanotube (CNT) samples, obtained by the electric discharge method utilizing Zr(Co 0.5 Ni 0.5 ) 2 , Ce 3 (Co 0.5 Ni 0.5 ) 2 and Ce(Co 0.5 Ni 0.5 ) 5 as catalysts. Raman Spectroscopy provided information on the SWCNT presence in the untreated samples. Scanning Electron Microscopy (SEM) showed CNT with different diameters and lengths. Different acid treatment conditions were employed and the best results were achieved for HCl 3 mol/L aqueous solution during 24 h reflux. Transmission Electron Microscopy (TEM) images, associated with EDS, revealed the catalyst removal from the original sample and the presence of other carbon structures near the CNT formation. CNT acid functionalization for Pt nanoparticles dispersion was successful, resulting in a homogeneously dispersed system, as seen in TEM images. Temperature Programmed Oxidation (TPO) analysis of the raw and purified samples indicated that after purification there are three different carbon species present on the purified material, each one showing a different behavior towards O 2 oxidation.
Catalysis Today, 2008
A comparative study was made in which two hydrotalcites were loaded with vanadium employing diffe... more A comparative study was made in which two hydrotalcites were loaded with vanadium employing different procedures: (1) aqueous phase impregnation, with vanadyl sulfate solution in pH 6.5 or 9.5; (2) solid phase mixing, with vanadyl sulfate or vanadium pentoxide physically mixed up. TPR investigation revealed that vanadium-loaded hydrotalcites obtained by aqueous phase impregnation in two distinct pH, resulted in different reduction profiles. The vanadium-loaded hydrotalcites were characterized by FTIR, XRD and TGA-DTA analysis. In situ dispersive XAS (DXAS) spectra obtained during thermal treatment in air showed that, for the physical mixture of solids, vanadium is oxidized above 350 8C. For the samples prepared by aqueous phase impregnation, the effect of alkaline pH was to produce polymeric vanadium species deposited onto the HT in comparison with the isolated vanadium species in acidic conditions. The influence of both, the hydrotalcite interlayer anion type and the vanadium loading procedure, on the reducibility of vanadium species is also discussed. #
Catalysis Letters, 2004
The effects of the SAR (14 and 38) and of the methodology of introduction of nickel (wetness impr... more The effects of the SAR (14 and 38) and of the methodology of introduction of nickel (wetness impregnation and ion exchange) on catalyst activation were investigated in Ni/USY model catalysts submitted to two activation treatments: reduction (A) and reduction/calcination/reduction, successively (B). the catalysts prepared by wetness impregnation, a marked increase in the catalytic activity after treatment B was observed. On the basis of the catalyst efficiency toward ethane hydrogenolysis, the lower SAR catalyst presents a threefold higher activity. On the contrary, the catalysts prepared by ion exchange, as well as a model catalyst prepared by wetness impregnation over a USY exhaustively exchanged with nickel ions, do not present measurable increasing of the catalytic activity under the same activation conditions. Monitoring the catalyst activation by EXAFS indicates the formation of nickel clusters in the impregnated catalysts after activation treatment B, which should be responsible for the high catalytic activity. However, TEM images reveal a bimodal particle size distribution, with large (ca. 20 nm) and small nickel particles. Temperature-programmed reduction performed under the same conditions of catalyst activation suggests that only the small nickel particles are activated under the experimental conditions adopted in this work.
Polyhedron, 2008
A deamination process was observed after copper(II) complexation reaction with guanidinoacetic (G... more A deamination process was observed after copper(II) complexation reaction with guanidinoacetic (Gaa) and glutamic acids (Glu), forming the binuclear copper(II) complex K 2 Cu 2 C 16 H 23 N 7 O 12 · 1/2H 2 O (1), which was characterized by elemental analysis (CHN), ...
Applied Catalysis A-general, 2007
... Complex 2 exhibited the best results, reaching as high as 68.9% of total yield in 24 h with H... more ... Complex 2 exhibited the best results, reaching as high as 68.9% of total yield in 24 h with H 2O 2 . In general, H 2 O 2 showed better results than tert-butyl hydroperoxide as terminal oxidant. ... 2.3. Synthesis of {[Cu(BMPA)Cl 2 ][Cu(BMPA)(H 2 O)Cl][Cu(BMPA)Cl][CuCl 4 ]} (2). ...
Inorganic Chemistry Communications, 2005
The green crystalline, homoleptic vanadium(IV) alkoxide [V 2 (l-OPr i ) 2 (OPr i ) 6 ] (I) has be... more The green crystalline, homoleptic vanadium(IV) alkoxide [V 2 (l-OPr i ) 2 (OPr i ) 6 ] (I) has been reproducibly prepared in more than 60% yield; its identity was confirmed by chemical and physical methods including single-crystal X-ray diffractometry. Complex I is thermochromic in solution, changing reversibly from royal blue to gold yellow when cooled from 300 to 210 K. The assignment of this thermochromic behaviour to a mononuclear (S ¼ 1 2 ) M binuclear (S = 1) solution equilibrium is discussed. Complex I is a potential precursor of industrially-relevant vanadium-(IV), -(V) and mixed-valence vanadium oxides.
Inorganic Chemistry Communications, 2004
A novel trianionic disubstituted guanidine, ( 1 N-carboxymethylguanidino)hydroxyacetic acid-C 5 H... more A novel trianionic disubstituted guanidine, ( 1 N-carboxymethylguanidino)hydroxyacetic acid-C 5 H 6 N 3 O 5 ), oag 3À , has been formed through a desamidination process occurred during copper(II) complexation with guanidinoacetic acid, C 3 H 7 N 3 O 2 (Gaa), which produced [Cu 2 (oag)(Gaa)(H 2 O)]NO 3 AE 2H 2 O (1). A proposal mechanism of formation of 1 is presented based on the low temperature electron paramagnetic resonance and previous potentiometric studies, which have indicated the presence of CuH 2 Gaa as the precursor species.
Applied Catalysis A-general, 2007
Piperonal is an important intermediate in the synthesis of drugs like L-DOPA. Vanadyl-Y-zeolites ... more Piperonal is an important intermediate in the synthesis of drugs like L-DOPA. Vanadyl-Y-zeolites have been tested as potential catalysts for this process. The use of encapsulated vanadyl compounds in Y-zeolite pores led to excellent rates of isosafrol oxidation under microwave irradiation. Native Y-zeolite better allowed the diffusion of the oxidant agent (hydrogen peroxide) through the catalyst pores compared to the VO-exchanged catalysts. This led to piperonal, which was also obtained due to the presence of V 5+ supported on one of the catalysts. These factors aided the extension of the oxidation process of isosafrol. On the other hand, vanadyl-zeolites, containing V 4+ species, promoted the reaction to intermediate (epoxide) with high selectivity under microwave radiation. Finally the impregnation of VO(Salen) on Y-zeolite showed better selectivity for epoxide formation than did the incorporated VO(Salen)-zeolite. Catalyst's surface area and availability of the vanadyl group were the main factors which allowed this superior performance. #
Janeiro (IQ/UFRJ), buscou-se identificar obstáculos epistemológicos entre pós-graduandos em bioqu... more Janeiro (IQ/UFRJ), buscou-se identificar obstáculos epistemológicos entre pós-graduandos em bioquímica e áreas correlatas. Um questionário com perguntas e excertos de artigos científicos de revistas de alto fator de impacto foi respondido, anonimamente, por pós-graduandos de diferentes cursos da UFRJ e de outras universidades, que nunca cursaram disciplina relacionada à epistemologia. Foi possível identificar concepções vitalistas (animismo) tanto nas respostas às perguntas como na aceitação ou não identificação deste obstáculo nos excertos. O obstáculo pragmático e unitário foi identificado através de uma concepção teleológica dos processos evolutivos, em afirmações como a existência de objetivos/finalidades na adaptação dos organismos. Verificou-se a presença de figuras de linguagem, metáforas e analogias (obstáculo verbal) na explicação da evolução e do sistema imune, também encontradas nos excertos dos artigos. Foram também identificados obstáculos associados à observação primeira e generalização prematura. A partir deste diagnóstico verificou-se a necessidade de enfatizar o caráter objetivo, material, não teleológico da bioquímica, em disciplinas oferecidas desde a graduação. © Cien. Cogn. 2012; Vol. 17 (2): 076-097.