Ivana Matanović | University of New Mexico (original) (raw)
Papers by Ivana Matanović
While Fe-N-C materials are a promising alternative to platinum for catalyzing oxygen reduction in... more While Fe-N-C materials are a promising alternative to platinum for catalyzing oxygen reduction in acidic polymer fuel cells, limited understanding of their operando degradation restricts rational approaches towards improved durability. Here we show that Fe-N-C catalysts initially comprising two distinct FeNx sites (S1 and S2) degrade via the transformation of S1 into iron oxides while the structure and number of S2 were unmodified. Structure-activity correlations drawn from end-of-test 57Fe Mössbauer spectroscopy reveal that both sites initially contribute to the ORR activity but only S2 significantly contributes after 50 h of operation. From in situ 57Fe Mössbauer spectroscopy in inert gas coupled to calculations of the Mössbauer signature of FeNx moieties in different electronic states, we identify S1 to be a high-spin FeN4C12 moiety and S2 a low- or intermediate spin FeN4C10 moiety. These insights lay the ground for rational approaches towards Fe-N-C cathodes with improved durabi...
ChemElectroChem, 2019
The integration of different catalytic modalities to control precursors, intermediates, and produ... more The integration of different catalytic modalities to control precursors, intermediates, and products requires a method for understanding these complex systems. A modular analytical platform is presented here that allows for catalytic conversion reactions and the delivery of catalytically transformed analytes to subsequent surface enhanced Raman scattering (SERS) detection zones. The paper‐based platforms are compatible for studying biochemical conversion reactions and electrochemical transformations. The full oxidation of glycerol to carbon dioxide follows a cascade reaction of 9 steps, chosen to illustrate the use of a molecular, biological, and metallic catalyst. Designated catalytic reaction zones and SERS detection zones integrated into the pores of paper at specific locations allows all of the reactions to take place within the pores of the analytical platform. Multiple chemical reactions were performed in sequence and the SERS spectra of the resulting intermediates and product...
ChemElectroChem, 2018
Benefits of utilizing cascade reactions for chemical synthesis include minimizing waste and decre... more Benefits of utilizing cascade reactions for chemical synthesis include minimizing waste and decreasing experimentation times. However, these complex systems lack an efficient screening platform for evaluating their progression. A paper-based microfluidic platform was developed to monitor cascade systems without the need for off-line product verification. Two types of paper-based platforms were fabricated to facilitate this study: electrochemical and spectro-electrochemical. Electrochemical platforms were integrated with stencil-printed electrodes and used to perform electrochemical alcohol oxidation reactions with two derivatives of the organocatalyst TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidinyl-N-oxyl). The catalyst 4amino-TEMPO (TEMPO-NH 2) was used as a model catalyst that was studied not immobilized and immobilized (pyrene-amido-TEMPO) on electrochemical platforms. These platforms were designed to provide quasi-stationary flow allowing constant electrochemical data collection as catalytic reactions proceeded. TEMPO-NH 2 and pyrene-amido-TEMPO were evaluated for the partial oxidation of glycerol and its intermediates. In comparison to TEMPO-NH 2 , the pyrene-amido-TEMPO catalyst produced higher current outputs. Spectro-electrochemical platforms were integrated with stencil-printed electrodes, and a surface enhanced Raman spectroscopy (SERS) detection zone. The spectro-electrochemical platforms allowed for catalytic conversions at the electrodes and subsequent delivery of catalytically transformed analytes to a SERS detection zone for product analysis. This platform was demonstrated for pyrene-amido-TEMPO and was shown to convert glycerol to mesoxalic acid. The experimental procedures for making components of the spectro-electrochemical device were described and include: preparation of the paper-based platform, construction of stencil-printed electrodes, and fabrication of SERS detection zones. These platforms provide an approach to analyzing multistep cascade chemical reactions.
Electrochimica Acta, 2017
The oxygen reduction reaction (ORR) is one of the major factors that is limiting the overall perf... more The oxygen reduction reaction (ORR) is one of the major factors that is limiting the overall performance output of microbial fuel cells (MFC). In this study, Platinum Group Metal-free (PGM-free) ORR catalysts based on Fe, Co, Ni, Mn and the same precursor (Aminoantipyrine, AAPyr) were synthesized using identical sacrificial support method (SSM). The catalysts were investigated for their electrochemical performance, and then integrated into an air-breathing cathode to be tested in "clean" environment and in a working microbial fuel cell (MFC). Their performances were also compared to activated carbon (AC) based cathode under similar conditions. Results showed that the addition of Mn, Fe, Co and Ni to AAPyr increased the performances compared to AC. Fe-AAPyr showed the highest open circuit potential (OCP) that was 0.307 AE 0.001 V (vs. Ag/AgCl) and the highest electrocatalytic activity at pH 7.5. On the contrary, AC had an OCP of 0.203 AE 0.002 V (vs. Ag/AgCl) and had the lowest electrochemical activity. In MFC, Fe-AAPyr also had the highest output of 251 AE 2.3 mWcm À2 , followed by Co-AAPyr with 196 AE 1.5 mWcm À2 , Ni-AAPyr with 171 AE 3.6 mWcm À2 , Mn-AAPyr with 160 AE 2.8 mWcm À2 and AC 129 AE 4.2 mWcm À2. The best performing catalyst (Fe-AAPyr) was then tested in MFC with increasing solution conductivity from 12.4 mScm À1 to 63.1 mScm À1. A maximum power density of 482 AE 5 mWcm À2 was obtained with increasing solution conductivity, which is one of the highest values reported in the field.
The Journal of Physical Chemistry B, 2016
An example of biocathode based on bilirubin oxidase (BOx) was used to demonstrate how density fun... more An example of biocathode based on bilirubin oxidase (BOx) was used to demonstrate how density functional theory can be combined with docking simulations in order to study the interface interactions between the enzyme and specifically designed electrode surface. The electrode surface was modified through the adsorption of bilirubin, the natural substrate for BOx, and the prepared electrode was electrochemically characterized using potentiostatic measurements. The experimentally determined current densities showed that the presence of bilirubin led to significant improvement of the cathode operation. On the basis of the computationally calculated binding energies of bilirubin to the graphene support and BOx and the analysis of the positioning of bilirubin relative to the support and T1 Cu atom of the enzyme, we hypothesize that the bilirubin serves as a geometric and electronic extension of the support. The computational results further confirm that the modification of the electrode surface with bilirubin provides an optimal orientation of BOx toward the support but also show that bilirubin facilitates the interfacial electron transfer by decreasing the distance between the electrode surface and the T1 Cu atom.
Journal of the American Chemical Society, 2015
Stable nitroxyl radical-containing compounds, such as 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO... more Stable nitroxyl radical-containing compounds, such as 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and its derivatives, are capable of electrocatalytically oxidizing a wide range of alcohols under mild and environmentally friendly conditions. Herein, we examine the structure-function relationships that determine the catalytic activity of a diverse range of water-soluble nitroxyl radical compounds. A strong correlation is described between the difference in the electrochemical oxidation potentials of a compound and its electrocatalytic activity. Additionally, we construct a simple computational model that is able to accurately predict the electrochemical potential and catalytic activity of a wide range of nitroxyl radical derivatives.
The Journal of Physical Chemistry C, 2011
We have carried out an extensive computational study using periodic density functional theory of ... more We have carried out an extensive computational study using periodic density functional theory of the structure, reactivity, and stability of three different PtÀNi alloys, Pt 3 Ni, PtNi, and PtNi 3 , with the aim of determining the effect of the subsurface layer composition on the catalytic activity of the platinum surface. The segregation effect was taken into account by modeling slabs with a platinum surface monolayer supported on a second layer containing 50%, 100%, and 75% of nickel, respectively, with a bulk layer below. Calculated equilibrium adsorption potentials for the oxygen reduction reaction (ORR) intermediates and construction of free energy diagrams for the ORR dissociative mechanism are used to gauge the catalytic activity. The critical question of the stability of these materials in an aqueous environment is also assessed in terms of the relative shifts in electrochemical dissolution energies and by the identification of the most stable state of the surface as a function of pH and potential as illustrated in Pourbaix diagrams. The (111) surface of all three models of PtÀNi alloys is found to exhibit improved oxygen reduction activity compared with that of pure Pt(111). The ORR overpotential was calculated to decrease in the order Pt (0.55 V) > Pt 3 Ni (0.24 V) > PtNi 3 (0.19 V) > PtNi (0.15 V). We can therefore conclude that the catalytic activity for ORR will increase as Pt < Pt 3 Ni < PtNi 3 < PtNi and find that the largest improvement occurs for a PtNi alloy with 100% nickel in the second layer. We also predict that PtNi is the least susceptible to corrosion at similar pH and cell potentials based on the calculated shifts of the electrochemical dissolution potentials for the PtÀNi alloys relative to platinum with values of À0.27 V for PtNi 3 , þ0.13 V for Pt 3 Ni, and þ0.30 V for PtNi.
The Journal of Physical Chemistry A, 2009
We consider the effect of isotopic labeling on the electric charge distribution and dynamics of t... more We consider the effect of isotopic labeling on the electric charge distribution and dynamics of the formic acid dimer. Our investigation is based on accurate ab initio calculations of vibrationally induced dipole moments and multidimensional quantum calculations of vibrational ground-state splittings. It is found that non-negligible dipole moments of µ) 0.032 D and µ) 0.021 D arise in HCOOH-DOOCD and HCOOH-DOOCH, respectively, suggesting the feasibility of microwave studies. Within the reaction surface Hamiltonian approach a ratio of splittings of 1:0.2:0.045 is predicted for HCOOH-HOOCH:HCOOH-DOOCH:HCOOD-DOOCH.
Journal of The Electrochemical Society, 2013
The Journal of Chemical Physics, 2007
There has been some controversy concerning the assignment of measured tunneling splittings for th... more There has been some controversy concerning the assignment of measured tunneling splittings for the formic acid dimer in the vibrational ground state and the asymmetric CO-stretching excited state. The discussion is intimately related to the question whether the fundamental excitation of the CO-vibration promotes or hinders tunneling. Here we will address this issue on the basis of a five-dimensional reaction space Hamiltonian which includes three large amplitude coordinates as well as two harmonic modes whose linear superposition reproduces the asymmetric CO-vibrational mode. Within density functional theory using the B3LYP functional together with a 6-311++G(3df,3pd) basis set we obtain a ground state tunneling splitting which is about 2.4 larger than the one for the CO-stretching excited state.
The Journal of Physical Chemistry Letters, 2017
Carbon, 2014
Surface roughness, porosity and contact angles of different carbon paper materials (TORAY paper w... more Surface roughness, porosity and contact angles of different carbon paper materials (TORAY paper with PTFE from 0% to 60% of and SGL paper with 0% and 20% of PTFE) suitable as electrodes in microbial fuel cells were investigated. The changes of contact angle between dry and clean anode surfaces and the ones after exposure to wastewater were measured using different liquids (pure water and sodium acetate solutions). The results showed that bacterial attachment to the carbon papers caused a significant decrease in the contact angle, shifting the surface property from highly hydrophobic to slightly hydrophobic or even hydrophilic. The quantity of biofilm attached on the anode surface decreased with the increase in PTFE content. Positive correlation between dry biomass content and the amount of pores at the small scale (5-10 lm) was observed. The start up time of MFCs was shortened by using the carbon anodes without PTFE or with low PTFE content (<20 wt%), probably due to the easier biofilm attachment on the surface. On the contrary, the carbon anodes with high PTFE contents had longer start up time. After several cycles of MFC operation, the performances became similar (20-30 mV of differences) regardless of the carbon anode used.
![Research paper thumbnail of ChemInform Abstract: Bergman Cyclization of Acyclic Amino Acid Derived Enediynes Leads to the Formation of 2,3-Dihydrobenzo[f]isoindoles](https://attachments.academia-assets.com/44102822/thumbnails/1.jpg)
](ChemInform, 2010
Enediyne-peptide conjugates are recently recognized as useful tools in targeting various proteins... more Enediyne-peptide conjugates are recently recognized as useful tools in targeting various proteins, while the mechanism underlying the observed activity remains somewhat unclear. Addressing these issues, we have prepared acyclic amino acid derived enediynes and disclosed a novel thermally induced cyclization-elimination pathway. Initial formation of 1,4-benzene diradical and H-atom abstraction from an external donor is followed by S N 2 substitution leading to 2,3-dihydrobenzo-[f]isoindoles. The proposed mechanism is supported by experimental and computational data. Additionally, we showed that amino acid side chains, although placed three bonds away from acetylene terminuses, have an appreciable influence on the reactivity of studied enediynes. These results demonstrate that amino acid or peptide parts of enediyne-peptide conjugates cannot be considered as recognition elements exclusively but may also participate in various reactions through amine functionality.
The Journal of Chemical Physics, 2008
A set of mass-weighted internal coordinates was derived and applied to the double proton transfer... more A set of mass-weighted internal coordinates was derived and applied to the double proton transfer reaction in the formic acid dimer (FAD). The coordinate set was obtained starting from the Hirschfelder &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;mobile&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; by an optimization procedure consisting of a sequence of kinematic rotations. In FAD, the optimization procedure leads to three coordinates that do change significantly along the reaction path. These coordinates span the reaction space, whereas the remaining modes are treated in a harmonic approximation. The effect that the dimer dissociative motion has on the ground and excited vibrational states dynamics was explored. In the frequency region corresponding to the symmetric OH-stretch vibration four doublets have been identified with splittings of 2.76, 0.07, 0.60, and 4.03 cm(-1).
Chemistry - A European Journal, 2010
A range of N-protected aziridines [N-Tosyl (N-Ts), N-2-trimethylsilylethanesulfonamide (N-SES), N... more A range of N-protected aziridines [N-Tosyl (N-Ts), N-2-trimethylsilylethanesulfonamide (N-SES), N-tert-butoxycarbonylamido (N-Boc), and N-o-nitrobenzenesulfonamide (oNs)] were prepared in moderate to good yield and with high enantiomeric excess of both isomers starting from N-protected imines, using a sulfonium salt derived from Eliel&amp;amp;amp;amp;amp;amp;amp;#39;s oxathiane. The diastereoselectivities of the reactions are influenced by the imine N-protecting group, the imine substituent, and the sulfide structure. An unusual cis selectivity was observed in the formation of N-tosyl-2-phenyl-3-tert-butylaziridine and N-o-trimethylsilylethanesulfonamide-2-phenyl-3-tert-butylaziridine, which was explained by using computational models. The analysis suggests that betaine formation in the case of N-tosyl-tert-butylaldimine aziridination using oxathiane benzyl sulfonium ylide 1&amp;amp;amp;amp;amp;amp;amp;#39; is reversible and that the selectivity is determined at the rotation step, which is unusual for semistabilized ylide aziridination. We have shown herein that the steric bulk of an imine substituent, in combination with a sterically demanding sulfonium ylide, can also affect the reversibility of the reaction. This is the first example of this sort involving aziridinations using semistabilized ylides.
The Journal of Physical Chemistry A, 2005
The intramolecular hydrogen bond in the enol-acethylacetone (ACAC) is investigated by performing ... more The intramolecular hydrogen bond in the enol-acethylacetone (ACAC) is investigated by performing reduced-dimensional quantum calculations. To analyze the shared proton vibrations, two sets of coordinates were employed: normal mode coordinates describing the motion in the vicinity of the most stable configuration, and internal coordinates accounting for the double minimum proton motion. It is proved that the extreme broadness of the OH-stretch band in ACAC is a consequence of the coexistence of two enol-ACAC structures: the global minimum and the transition state for rotation of the distal methyl group. Further, a ground-state tunneling splitting of 116 cm(-1) is found, and it is shown that the inclusion of the kinematic coupling is mandatory when treating large-amplitude proton motion. In the OH-stretch direction a splitting of 853 cm(-1) was predicted.
International Journal of Quantum Chemistry, 2006
The spectroscopic proprieties of two energetically close conformers of acetylacetone have been in... more The spectroscopic proprieties of two energetically close conformers of acetylacetone have been investigated using density functional methods. The calculated anharmonic frequencies are in very satisfactory agreement with experimental data. The low height of the conversion barrier explains why the signature of both conformers can be found in the vibrational spectrum.
Journal of the American Chemical Society, 2015
In this study, the influence of two quinones (1,2-and 1,4-benzoquinone) on the operation and mech... more In this study, the influence of two quinones (1,2-and 1,4-benzoquinone) on the operation and mechanism of electron transfer in PQQ-dependent glucose dehydrogenase (PQQ−sGDH) anodes has been determined. Benzoquinones were experimentally explored as mediators present in the electrolyte. The electrochemical performance of the PQQ− sGDH anodes with and without the mediators was examined and for the first time molecular docking simulations were used to gain a fundamental understanding to explain the role of the mediator molecules in the design and operation of the enzymatic electrodes. It was proposed that the higher performance of the PQQ−sGDH anodes in the presence of 1,2-and 1,4benzoquinones introduced in the solution is due to the shorter distance between these molecules and PQQ in the enzymatic molecule. It was also hypothesized that when 1,4benzoquinone is adsorbed on a carbon support, it would play the dual role of a mediator and an orienting agent. At the same time, when 1,2-benzoquinone and ubiquinone are adsorbed on the electrode surface, the enzyme would transfer the electrons directly to the support, and these molecules would primarily play the role of an orienting agent.
Phys. Chem. Chem. Phys., 2015
We report a novel non-platinum group metal (non-PGM) catalyst derived from Mn and amino- antipyri... more We report a novel non-platinum group metal (non-PGM) catalyst derived from Mn and amino- antipyrine (MnAAPyr) that shows electrochemical activity towards the oxidation of oxalic acid comparable to Pt with an onset potential for oxalate oxidation measured to be 0.714 ± 0.002 V vs. SHE at pH = 4. The material has been synthesized using a templating Sacrificial Support Method with manganese nitrate and 4-aminoantipyrine as precursors. This catalyst is a nano-structured material in which Mn is atomically dispersed on a nitrogen-doped graphene matrix. XPS studies reveal high abundance of pyridinic, Mn-Nx, and pyrrolic nitrogen pointing towards the conclusion that pyridinic nitrogen atoms coordinated to manganese constitute the active centers. Thus, the main features of the MnAAPyr catalyst are it exhibits similarity to the active sites of naturally occurring enzymes that are capable of efficient and selective oxidation of oxalic acid. Density functional theory in plane wave formalism with Perdew, Burke and Ernzerhof functional was further used to study the stability and activity of different one-metal active centers that could exist in the catalyst. The results show that the stability of the Mn-Nx sites changes in the following order: MnN4 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; MnN3C &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; MnN2C2 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; MnN3. Based on the overpotentials of 0.64 V and 0.71 V vs. SHE, calculated using the free energy diagrams for the oxalate oxidation mechanism, we could conclude that the MnN3C and MnN2C2 sites are most probable Mn-Nx sites responsible for the reported catalytic activity of the new catalyst.
While Fe-N-C materials are a promising alternative to platinum for catalyzing oxygen reduction in... more While Fe-N-C materials are a promising alternative to platinum for catalyzing oxygen reduction in acidic polymer fuel cells, limited understanding of their operando degradation restricts rational approaches towards improved durability. Here we show that Fe-N-C catalysts initially comprising two distinct FeNx sites (S1 and S2) degrade via the transformation of S1 into iron oxides while the structure and number of S2 were unmodified. Structure-activity correlations drawn from end-of-test 57Fe Mössbauer spectroscopy reveal that both sites initially contribute to the ORR activity but only S2 significantly contributes after 50 h of operation. From in situ 57Fe Mössbauer spectroscopy in inert gas coupled to calculations of the Mössbauer signature of FeNx moieties in different electronic states, we identify S1 to be a high-spin FeN4C12 moiety and S2 a low- or intermediate spin FeN4C10 moiety. These insights lay the ground for rational approaches towards Fe-N-C cathodes with improved durabi...
ChemElectroChem, 2019
The integration of different catalytic modalities to control precursors, intermediates, and produ... more The integration of different catalytic modalities to control precursors, intermediates, and products requires a method for understanding these complex systems. A modular analytical platform is presented here that allows for catalytic conversion reactions and the delivery of catalytically transformed analytes to subsequent surface enhanced Raman scattering (SERS) detection zones. The paper‐based platforms are compatible for studying biochemical conversion reactions and electrochemical transformations. The full oxidation of glycerol to carbon dioxide follows a cascade reaction of 9 steps, chosen to illustrate the use of a molecular, biological, and metallic catalyst. Designated catalytic reaction zones and SERS detection zones integrated into the pores of paper at specific locations allows all of the reactions to take place within the pores of the analytical platform. Multiple chemical reactions were performed in sequence and the SERS spectra of the resulting intermediates and product...
ChemElectroChem, 2018
Benefits of utilizing cascade reactions for chemical synthesis include minimizing waste and decre... more Benefits of utilizing cascade reactions for chemical synthesis include minimizing waste and decreasing experimentation times. However, these complex systems lack an efficient screening platform for evaluating their progression. A paper-based microfluidic platform was developed to monitor cascade systems without the need for off-line product verification. Two types of paper-based platforms were fabricated to facilitate this study: electrochemical and spectro-electrochemical. Electrochemical platforms were integrated with stencil-printed electrodes and used to perform electrochemical alcohol oxidation reactions with two derivatives of the organocatalyst TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidinyl-N-oxyl). The catalyst 4amino-TEMPO (TEMPO-NH 2) was used as a model catalyst that was studied not immobilized and immobilized (pyrene-amido-TEMPO) on electrochemical platforms. These platforms were designed to provide quasi-stationary flow allowing constant electrochemical data collection as catalytic reactions proceeded. TEMPO-NH 2 and pyrene-amido-TEMPO were evaluated for the partial oxidation of glycerol and its intermediates. In comparison to TEMPO-NH 2 , the pyrene-amido-TEMPO catalyst produced higher current outputs. Spectro-electrochemical platforms were integrated with stencil-printed electrodes, and a surface enhanced Raman spectroscopy (SERS) detection zone. The spectro-electrochemical platforms allowed for catalytic conversions at the electrodes and subsequent delivery of catalytically transformed analytes to a SERS detection zone for product analysis. This platform was demonstrated for pyrene-amido-TEMPO and was shown to convert glycerol to mesoxalic acid. The experimental procedures for making components of the spectro-electrochemical device were described and include: preparation of the paper-based platform, construction of stencil-printed electrodes, and fabrication of SERS detection zones. These platforms provide an approach to analyzing multistep cascade chemical reactions.
Electrochimica Acta, 2017
The oxygen reduction reaction (ORR) is one of the major factors that is limiting the overall perf... more The oxygen reduction reaction (ORR) is one of the major factors that is limiting the overall performance output of microbial fuel cells (MFC). In this study, Platinum Group Metal-free (PGM-free) ORR catalysts based on Fe, Co, Ni, Mn and the same precursor (Aminoantipyrine, AAPyr) were synthesized using identical sacrificial support method (SSM). The catalysts were investigated for their electrochemical performance, and then integrated into an air-breathing cathode to be tested in "clean" environment and in a working microbial fuel cell (MFC). Their performances were also compared to activated carbon (AC) based cathode under similar conditions. Results showed that the addition of Mn, Fe, Co and Ni to AAPyr increased the performances compared to AC. Fe-AAPyr showed the highest open circuit potential (OCP) that was 0.307 AE 0.001 V (vs. Ag/AgCl) and the highest electrocatalytic activity at pH 7.5. On the contrary, AC had an OCP of 0.203 AE 0.002 V (vs. Ag/AgCl) and had the lowest electrochemical activity. In MFC, Fe-AAPyr also had the highest output of 251 AE 2.3 mWcm À2 , followed by Co-AAPyr with 196 AE 1.5 mWcm À2 , Ni-AAPyr with 171 AE 3.6 mWcm À2 , Mn-AAPyr with 160 AE 2.8 mWcm À2 and AC 129 AE 4.2 mWcm À2. The best performing catalyst (Fe-AAPyr) was then tested in MFC with increasing solution conductivity from 12.4 mScm À1 to 63.1 mScm À1. A maximum power density of 482 AE 5 mWcm À2 was obtained with increasing solution conductivity, which is one of the highest values reported in the field.
The Journal of Physical Chemistry B, 2016
An example of biocathode based on bilirubin oxidase (BOx) was used to demonstrate how density fun... more An example of biocathode based on bilirubin oxidase (BOx) was used to demonstrate how density functional theory can be combined with docking simulations in order to study the interface interactions between the enzyme and specifically designed electrode surface. The electrode surface was modified through the adsorption of bilirubin, the natural substrate for BOx, and the prepared electrode was electrochemically characterized using potentiostatic measurements. The experimentally determined current densities showed that the presence of bilirubin led to significant improvement of the cathode operation. On the basis of the computationally calculated binding energies of bilirubin to the graphene support and BOx and the analysis of the positioning of bilirubin relative to the support and T1 Cu atom of the enzyme, we hypothesize that the bilirubin serves as a geometric and electronic extension of the support. The computational results further confirm that the modification of the electrode surface with bilirubin provides an optimal orientation of BOx toward the support but also show that bilirubin facilitates the interfacial electron transfer by decreasing the distance between the electrode surface and the T1 Cu atom.
Journal of the American Chemical Society, 2015
Stable nitroxyl radical-containing compounds, such as 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO... more Stable nitroxyl radical-containing compounds, such as 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and its derivatives, are capable of electrocatalytically oxidizing a wide range of alcohols under mild and environmentally friendly conditions. Herein, we examine the structure-function relationships that determine the catalytic activity of a diverse range of water-soluble nitroxyl radical compounds. A strong correlation is described between the difference in the electrochemical oxidation potentials of a compound and its electrocatalytic activity. Additionally, we construct a simple computational model that is able to accurately predict the electrochemical potential and catalytic activity of a wide range of nitroxyl radical derivatives.
The Journal of Physical Chemistry C, 2011
We have carried out an extensive computational study using periodic density functional theory of ... more We have carried out an extensive computational study using periodic density functional theory of the structure, reactivity, and stability of three different PtÀNi alloys, Pt 3 Ni, PtNi, and PtNi 3 , with the aim of determining the effect of the subsurface layer composition on the catalytic activity of the platinum surface. The segregation effect was taken into account by modeling slabs with a platinum surface monolayer supported on a second layer containing 50%, 100%, and 75% of nickel, respectively, with a bulk layer below. Calculated equilibrium adsorption potentials for the oxygen reduction reaction (ORR) intermediates and construction of free energy diagrams for the ORR dissociative mechanism are used to gauge the catalytic activity. The critical question of the stability of these materials in an aqueous environment is also assessed in terms of the relative shifts in electrochemical dissolution energies and by the identification of the most stable state of the surface as a function of pH and potential as illustrated in Pourbaix diagrams. The (111) surface of all three models of PtÀNi alloys is found to exhibit improved oxygen reduction activity compared with that of pure Pt(111). The ORR overpotential was calculated to decrease in the order Pt (0.55 V) > Pt 3 Ni (0.24 V) > PtNi 3 (0.19 V) > PtNi (0.15 V). We can therefore conclude that the catalytic activity for ORR will increase as Pt < Pt 3 Ni < PtNi 3 < PtNi and find that the largest improvement occurs for a PtNi alloy with 100% nickel in the second layer. We also predict that PtNi is the least susceptible to corrosion at similar pH and cell potentials based on the calculated shifts of the electrochemical dissolution potentials for the PtÀNi alloys relative to platinum with values of À0.27 V for PtNi 3 , þ0.13 V for Pt 3 Ni, and þ0.30 V for PtNi.
The Journal of Physical Chemistry A, 2009
We consider the effect of isotopic labeling on the electric charge distribution and dynamics of t... more We consider the effect of isotopic labeling on the electric charge distribution and dynamics of the formic acid dimer. Our investigation is based on accurate ab initio calculations of vibrationally induced dipole moments and multidimensional quantum calculations of vibrational ground-state splittings. It is found that non-negligible dipole moments of µ) 0.032 D and µ) 0.021 D arise in HCOOH-DOOCD and HCOOH-DOOCH, respectively, suggesting the feasibility of microwave studies. Within the reaction surface Hamiltonian approach a ratio of splittings of 1:0.2:0.045 is predicted for HCOOH-HOOCH:HCOOH-DOOCH:HCOOD-DOOCH.
Journal of The Electrochemical Society, 2013
The Journal of Chemical Physics, 2007
There has been some controversy concerning the assignment of measured tunneling splittings for th... more There has been some controversy concerning the assignment of measured tunneling splittings for the formic acid dimer in the vibrational ground state and the asymmetric CO-stretching excited state. The discussion is intimately related to the question whether the fundamental excitation of the CO-vibration promotes or hinders tunneling. Here we will address this issue on the basis of a five-dimensional reaction space Hamiltonian which includes three large amplitude coordinates as well as two harmonic modes whose linear superposition reproduces the asymmetric CO-vibrational mode. Within density functional theory using the B3LYP functional together with a 6-311++G(3df,3pd) basis set we obtain a ground state tunneling splitting which is about 2.4 larger than the one for the CO-stretching excited state.
The Journal of Physical Chemistry Letters, 2017
Carbon, 2014
Surface roughness, porosity and contact angles of different carbon paper materials (TORAY paper w... more Surface roughness, porosity and contact angles of different carbon paper materials (TORAY paper with PTFE from 0% to 60% of and SGL paper with 0% and 20% of PTFE) suitable as electrodes in microbial fuel cells were investigated. The changes of contact angle between dry and clean anode surfaces and the ones after exposure to wastewater were measured using different liquids (pure water and sodium acetate solutions). The results showed that bacterial attachment to the carbon papers caused a significant decrease in the contact angle, shifting the surface property from highly hydrophobic to slightly hydrophobic or even hydrophilic. The quantity of biofilm attached on the anode surface decreased with the increase in PTFE content. Positive correlation between dry biomass content and the amount of pores at the small scale (5-10 lm) was observed. The start up time of MFCs was shortened by using the carbon anodes without PTFE or with low PTFE content (<20 wt%), probably due to the easier biofilm attachment on the surface. On the contrary, the carbon anodes with high PTFE contents had longer start up time. After several cycles of MFC operation, the performances became similar (20-30 mV of differences) regardless of the carbon anode used.
ChemInform, 2010
Enediyne-peptide conjugates are recently recognized as useful tools in targeting various proteins... more Enediyne-peptide conjugates are recently recognized as useful tools in targeting various proteins, while the mechanism underlying the observed activity remains somewhat unclear. Addressing these issues, we have prepared acyclic amino acid derived enediynes and disclosed a novel thermally induced cyclization-elimination pathway. Initial formation of 1,4-benzene diradical and H-atom abstraction from an external donor is followed by S N 2 substitution leading to 2,3-dihydrobenzo-[f]isoindoles. The proposed mechanism is supported by experimental and computational data. Additionally, we showed that amino acid side chains, although placed three bonds away from acetylene terminuses, have an appreciable influence on the reactivity of studied enediynes. These results demonstrate that amino acid or peptide parts of enediyne-peptide conjugates cannot be considered as recognition elements exclusively but may also participate in various reactions through amine functionality.
The Journal of Chemical Physics, 2008
A set of mass-weighted internal coordinates was derived and applied to the double proton transfer... more A set of mass-weighted internal coordinates was derived and applied to the double proton transfer reaction in the formic acid dimer (FAD). The coordinate set was obtained starting from the Hirschfelder &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;mobile&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; by an optimization procedure consisting of a sequence of kinematic rotations. In FAD, the optimization procedure leads to three coordinates that do change significantly along the reaction path. These coordinates span the reaction space, whereas the remaining modes are treated in a harmonic approximation. The effect that the dimer dissociative motion has on the ground and excited vibrational states dynamics was explored. In the frequency region corresponding to the symmetric OH-stretch vibration four doublets have been identified with splittings of 2.76, 0.07, 0.60, and 4.03 cm(-1).
Chemistry - A European Journal, 2010
A range of N-protected aziridines [N-Tosyl (N-Ts), N-2-trimethylsilylethanesulfonamide (N-SES), N... more A range of N-protected aziridines [N-Tosyl (N-Ts), N-2-trimethylsilylethanesulfonamide (N-SES), N-tert-butoxycarbonylamido (N-Boc), and N-o-nitrobenzenesulfonamide (oNs)] were prepared in moderate to good yield and with high enantiomeric excess of both isomers starting from N-protected imines, using a sulfonium salt derived from Eliel&amp;amp;amp;amp;amp;amp;amp;#39;s oxathiane. The diastereoselectivities of the reactions are influenced by the imine N-protecting group, the imine substituent, and the sulfide structure. An unusual cis selectivity was observed in the formation of N-tosyl-2-phenyl-3-tert-butylaziridine and N-o-trimethylsilylethanesulfonamide-2-phenyl-3-tert-butylaziridine, which was explained by using computational models. The analysis suggests that betaine formation in the case of N-tosyl-tert-butylaldimine aziridination using oxathiane benzyl sulfonium ylide 1&amp;amp;amp;amp;amp;amp;amp;#39; is reversible and that the selectivity is determined at the rotation step, which is unusual for semistabilized ylide aziridination. We have shown herein that the steric bulk of an imine substituent, in combination with a sterically demanding sulfonium ylide, can also affect the reversibility of the reaction. This is the first example of this sort involving aziridinations using semistabilized ylides.
The Journal of Physical Chemistry A, 2005
The intramolecular hydrogen bond in the enol-acethylacetone (ACAC) is investigated by performing ... more The intramolecular hydrogen bond in the enol-acethylacetone (ACAC) is investigated by performing reduced-dimensional quantum calculations. To analyze the shared proton vibrations, two sets of coordinates were employed: normal mode coordinates describing the motion in the vicinity of the most stable configuration, and internal coordinates accounting for the double minimum proton motion. It is proved that the extreme broadness of the OH-stretch band in ACAC is a consequence of the coexistence of two enol-ACAC structures: the global minimum and the transition state for rotation of the distal methyl group. Further, a ground-state tunneling splitting of 116 cm(-1) is found, and it is shown that the inclusion of the kinematic coupling is mandatory when treating large-amplitude proton motion. In the OH-stretch direction a splitting of 853 cm(-1) was predicted.
International Journal of Quantum Chemistry, 2006
The spectroscopic proprieties of two energetically close conformers of acetylacetone have been in... more The spectroscopic proprieties of two energetically close conformers of acetylacetone have been investigated using density functional methods. The calculated anharmonic frequencies are in very satisfactory agreement with experimental data. The low height of the conversion barrier explains why the signature of both conformers can be found in the vibrational spectrum.
Journal of the American Chemical Society, 2015
In this study, the influence of two quinones (1,2-and 1,4-benzoquinone) on the operation and mech... more In this study, the influence of two quinones (1,2-and 1,4-benzoquinone) on the operation and mechanism of electron transfer in PQQ-dependent glucose dehydrogenase (PQQ−sGDH) anodes has been determined. Benzoquinones were experimentally explored as mediators present in the electrolyte. The electrochemical performance of the PQQ− sGDH anodes with and without the mediators was examined and for the first time molecular docking simulations were used to gain a fundamental understanding to explain the role of the mediator molecules in the design and operation of the enzymatic electrodes. It was proposed that the higher performance of the PQQ−sGDH anodes in the presence of 1,2-and 1,4benzoquinones introduced in the solution is due to the shorter distance between these molecules and PQQ in the enzymatic molecule. It was also hypothesized that when 1,4benzoquinone is adsorbed on a carbon support, it would play the dual role of a mediator and an orienting agent. At the same time, when 1,2-benzoquinone and ubiquinone are adsorbed on the electrode surface, the enzyme would transfer the electrons directly to the support, and these molecules would primarily play the role of an orienting agent.
Phys. Chem. Chem. Phys., 2015
We report a novel non-platinum group metal (non-PGM) catalyst derived from Mn and amino- antipyri... more We report a novel non-platinum group metal (non-PGM) catalyst derived from Mn and amino- antipyrine (MnAAPyr) that shows electrochemical activity towards the oxidation of oxalic acid comparable to Pt with an onset potential for oxalate oxidation measured to be 0.714 ± 0.002 V vs. SHE at pH = 4. The material has been synthesized using a templating Sacrificial Support Method with manganese nitrate and 4-aminoantipyrine as precursors. This catalyst is a nano-structured material in which Mn is atomically dispersed on a nitrogen-doped graphene matrix. XPS studies reveal high abundance of pyridinic, Mn-Nx, and pyrrolic nitrogen pointing towards the conclusion that pyridinic nitrogen atoms coordinated to manganese constitute the active centers. Thus, the main features of the MnAAPyr catalyst are it exhibits similarity to the active sites of naturally occurring enzymes that are capable of efficient and selective oxidation of oxalic acid. Density functional theory in plane wave formalism with Perdew, Burke and Ernzerhof functional was further used to study the stability and activity of different one-metal active centers that could exist in the catalyst. The results show that the stability of the Mn-Nx sites changes in the following order: MnN4 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; MnN3C &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; MnN2C2 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; MnN3. Based on the overpotentials of 0.64 V and 0.71 V vs. SHE, calculated using the free energy diagrams for the oxalate oxidation mechanism, we could conclude that the MnN3C and MnN2C2 sites are most probable Mn-Nx sites responsible for the reported catalytic activity of the new catalyst.