Valdemir Ludwig - Academia.edu (original) (raw)

Papers by Valdemir Ludwig

Journal of Physical Chemistry A, Apr 5, 2023

Journal of Molecular Liquids, Dec 1, 2020

Amino acids exhibit their most important properties in aqueous environment in physiological condi... more Amino acids exhibit their most important properties in aqueous environment in physiological conditions. These properties are related to their structural changes in water. Although several studies have been performed earlier for obtaining the structure of alanine in a solvent environment, an explicit consideration of the solvent molecular system is still in need. This work uses a Free Energy Gradient method to obtain the structures of alanine with an explicit consideration of the water environment. This is combined with a QM/MM method. Next, the electronic and vibrational properties of L-Alanine in water solution at different pH scales are obtained. The equilibrium structures of L-alanine are obtained in its neutral, anionic and cationic form. A systematic study of the solutesolvent hydrogen bonds was performed to predict the stability of neutral and charged L-alanine molecules. Quantum mechanical calculations were also performed to obtain the infrared spectrum, pH induced changes and to predict NMR parameters such as chemical shifts, magnetic shieldings and spin-spin coupling constants.

World Academy of Science, Engineering and Technology, International Journal of Physical and Mathematical Sciences, Jul 20, 2015

Physical Review E, Jun 1, 2004

Blucher Physics Proceedings, 2019

Glasses containing metallic nanoparticles are promising materials that should also possess the be... more Glasses containing metallic nanoparticles are promising materials that should also possess the best spectroscopic, chemical, mechanical and thermal characteristics for technological applications in optics and photonics. For this reason it was chosen to synthesize and characterize the pure silver doped borosilicate glasses and silver nitrate. The present work investigates the generation of silver nanoparticles on the surface and the mass of a borosilicate glass in which it was directed to the synthesis process in which it was consisted: in the stoichiometric calculations, in the determination of the melting temperature, in the choice of reagents with high degree of purity, in the manufacture of the samples, in the appropriate polishes and in the determination of heat treatments close to Tg of the glass in question. From this phase, the research followed the application of techniques of differential thermal analysis (ATD) and transmission electron microscopy (MET). Thus, from the results and analyzes obtained, it was possible to observe that the borosilicate glass samples of this work will obtain satisfactory experimental results, in which it was possible to prove its optical and structural properties similar to those recognized in literature, thus making it a promising material in area of vitreous materials applied to nanotechnology borosilicate glasses are obtained from the combination of silicon dioxide (SiO2) with boron oxide (B2O3) and the resulting samples were annealed at various temperatures. Due to the structural shape, these glasses have a high resistance to thermal shock, good chemical durability and excellent electrical resistivity compared to other glasses on the market today. Therefore, based on these important structural, physical and chemical characteristics and also in the variety of applications, this study was chosen for the synthesis and characterization of pure borosilicate glass and doped with silver nitrate. We verified the formation of silver nanoparticles, after the heat treatment, by transmission electron microscopy.

Journal of Molecular Liquids, 2021

Metal colloids or nanoclusters, embedded in glasses, have been found to introduce desired third-o... more Metal colloids or nanoclusters, embedded in glasses, have been found to introduce desired third-order optical non- linearities in the composites at wavelenghts very close to that of the characteristic surface-plasmon resonance of the metal clusters. Small spherical silver particles in a soda-lime silicate (SLS) glass were produced by means of the ion exchange method. Emphasis is given to the comparison among existing approaches to the understanding of the chemical interaction in these system. Soda lime silicate (SLS) glasses containing 0.020-0.015 wt % (AgNO 3), Nano 1 and Nano 2, respectively, were prepared in this experiment. A mixed batch was melted under an ambient atmosphere in alumina crucible at 1500 0 C-1400 0 C (depending of the composition) for 4 h. Glass samples were obtained by quenching the melt to room temperature. The resultant transparent glass was cut, polished on both sides, and subjected to experiments.The Figure 1 (a) and (b) shows the absorption spectra of the h...

Journal of Molecular Liquids, 2021

Radiation Measurements, 2007

ESR (electron spin resonance), XRD (X-ray diffraction) patterns and SEM (scanning electron micros... more ESR (electron spin resonance), XRD (X-ray diffraction) patterns and SEM (scanning electron microscopy) of irradiated calcium carbonate (CaCO 3) in eggshell was investigated. The ionizing radiation produces an electron centre CO 3− 3 , a hole centre CO − 3 , and the CO − 2 molecular ion also formed. The ESR centre with g // = 1.9977 and g ⊥ = 2.0021 was identified as the same found in hydroxyapatite. The work aims to standardize the samples preparation method and the conditions of measured for practical application by the specialist in emergency dosimetry. In this regard, practical consideration of sample preparation conditions and properties such as grain size, ESR spectra, and the temperature dependence of the signal were studied in detail. Dose response appears to be linear between 3 Gy and 1 kGy. No dose rate dependence was observed. The morphology of the calcined eggshell presented extensive morphological change on the calcinations process. Careful analyses of the ESR spectra are presently in progress in order to undertake and identify the radicals involved.

Radiation Measurements, 2007

ESR (electron spin resonance), XRD (X-ray diffraction) patterns and SEM (scanning electron micros... more ESR (electron spin resonance), XRD (X-ray diffraction) patterns and SEM (scanning electron microscopy) of irradiated calcium carbonate (CaCO 3) in eggshell was investigated. The ionizing radiation produces an electron centre CO 3− 3 , a hole centre CO − 3 , and the CO − 2 molecular ion also formed. The ESR centre with g // = 1.9977 and g ⊥ = 2.0021 was identified as the same found in hydroxyapatite. The work aims to standardize the samples preparation method and the conditions of measured for practical application by the specialist in emergency dosimetry. In this regard, practical consideration of sample preparation conditions and properties such as grain size, ESR spectra, and the temperature dependence of the signal were studied in detail. Dose response appears to be linear between 3 Gy and 1 kGy. No dose rate dependence was observed. The morphology of the calcined eggshell presented extensive morphological change on the calcinations process. Careful analyses of the ESR spectra are presently in progress in order to undertake and identify the radicals involved.

Chemical Physics Letters, 2010

The sequential Monte Carlo/CASPT2 approach was employed to investigate deactivation and emission ... more The sequential Monte Carlo/CASPT2 approach was employed to investigate deactivation and emission processes from the lowest-lying pp * and np * excited states of 9H-adenine in aqueous solution. It is found that conical intersections connecting the pp* and np* states with the ground state are also present in solution, whereas the barriers for the deactivation paths are significantly smaller on solvated conditions. The large destabilization of the np* state found in solution possibly prevents its involvement in the deactivation photophysics and explains the change from a bi-to a mono-exponential decay for the molecule in the gas phase and solution, respectively.

Chemical Physics Letters, 2010

The sequential Monte Carlo/CASPT2 approach was employed to investigate deactivation and emission ... more The sequential Monte Carlo/CASPT2 approach was employed to investigate deactivation and emission processes from the lowest-lying pp * and np * excited states of 9H-adenine in aqueous solution. It is found that conical intersections connecting the pp* and np* states with the ground state are also present in solution, whereas the barriers for the deactivation paths are significantly smaller on solvated conditions. The large destabilization of the np* state found in solution possibly prevents its involvement in the deactivation photophysics and explains the change from a bi-to a mono-exponential decay for the molecule in the gas phase and solution, respectively.

Chemical Physics Letters, 2008

The minimum energy path along the lowest-lying ππ∗ excited state of 2-aminopurine was calculated ... more The minimum energy path along the lowest-lying ππ∗ excited state of 2-aminopurine was calculated to elucidate the mechanisms of radiationless decay and emission in water. The sequential Monte Carlo quantum mechanics approach with a multiconfigurational and ...

Journal of Molecular Structure, 2002

Pure and Applied Chemistry, 2009

The accurate ab initio quantum chemical (QM) method multiconfigurational second-order perturbatio... more The accurate ab initio quantum chemical (QM) method multiconfigurational second-order perturbation (CASSPT2)/complete active space self-consistent field (CASSCF) has been used in conjunction with molecular mechanics (MM) procedures to compute molecular properties and photoinduced reactivity of DNA/RNA nucleobases (NABs) in isolation and within a realistic environment, in which the double helix strand, the aqueous media, and the external counterions are included. It is illustrated that the use of an MM model is helpful both to account for short- and long-range effects of the system surrounding the QM molecular core and to provide the proper structural constraints that allow more accurate QM geometry determinations.

ABSTRACT: Sequential Monte Carlo and quantum mechanical calculations of the electronic polarizati... more ABSTRACT: Sequential Monte Carlo and quantum mechanical calculations of the electronic polarization of the ground and first vertical excited states of 1H-benzotriazole in water are made. Using statistically uncorrelated configurations and CASSCF ab initio calculations the increase in the ground and excited state dipole moments of 1H-benzotriazole from gas phase to aqueous environment are obtained as 2.89 0.10 and 2.75 0.11 D, leading to total moments of 6.89 0.10 and 6.40 0.11 D, respectively. Structures are sampled using the statistical correlation interval obtained from the autocorrelation function of the energy and statistical convergence of the calculated dipole moments is shown. These water-polarized dipole moments of 1H-benzotriazole are used to obtain the solvatochromic shift of the first absorption transition. The resulting theoretical blue shift of 570 cm1 for the strong and characteristic 3 * transition is in good agreement with the inferred experimental value of 700 cm1. ...

Physical chemistry chemical physics : PCCP, 2007

The solvatochromic shifts of the n-pi(*) and pi-pi(*) states of uracil in water are analyzed usin... more The solvatochromic shifts of the n-pi(*) and pi-pi(*) states of uracil in water are analyzed using a combined and sequential Monte Carlo/quantum mechanics (MC/QM) approach. The role of the solute polarization and electronic delocalization into the solvent region are investigated. Electronic polarization of the solute is obtained using the HF/6-31G(d), the polarizable continuum model (PCM) and an iterative procedure using MP2/aug-cc-pVDZ in the MC/QM. The in-water dipole moment of uracil is obtained, respectively, as 5.12 D, 6.12 D and 7.01 +/- 0.05 D. This latter result, corresponding to an increase of 60% with respect to the gas phase value, is used in the classical potential of the MC simulation to obtain statistically uncorrelated configurations for subsequent QM calculations of the ultraviolet-visible absorption spectrum of uracil in water. QM calculations are performed at the time-dependent density-functional theory (TD-DFT) combined with the B3LYP and B3PW91 functionals, multi...

This work describes the spectroscopic characterization of a phosphate glass matrix doped with dif... more This work describes the spectroscopic characterization of a phosphate glass matrix doped with different Erbium concentrations. In order to increase the resistance of the glass, 3 mol % of silicon oxide were added to the phosphate matrix. A study of the optical absorption, luminescence and lifetime was conducted in order to characterize the infrared emission of Er3+ ions at 1540 nm, due to the radiative transition 4I13/2 → 4I15/2. Judd-Ofelt spectral analysis was carried out to determine the local structure and bonding in the vicinity of rare-earth ions. The experimental oscillator strengths calculated from the absorption spectra were used to evaluate the Judd-Ofelt intensity parameters Ωλ (λ = 2, 4 and 6). Changes in the glass density, refractive index and the values of Ω4 and Ω6 with different rare-earth concentrations are ascribed to changes in the glass network structure. Our results indicate that the present glass is a quite good matrix for Erbium ions, and the quantum efficienc...

Journal of Physical Chemistry A, Apr 5, 2023

Journal of Molecular Liquids, Dec 1, 2020

Amino acids exhibit their most important properties in aqueous environment in physiological condi... more Amino acids exhibit their most important properties in aqueous environment in physiological conditions. These properties are related to their structural changes in water. Although several studies have been performed earlier for obtaining the structure of alanine in a solvent environment, an explicit consideration of the solvent molecular system is still in need. This work uses a Free Energy Gradient method to obtain the structures of alanine with an explicit consideration of the water environment. This is combined with a QM/MM method. Next, the electronic and vibrational properties of L-Alanine in water solution at different pH scales are obtained. The equilibrium structures of L-alanine are obtained in its neutral, anionic and cationic form. A systematic study of the solutesolvent hydrogen bonds was performed to predict the stability of neutral and charged L-alanine molecules. Quantum mechanical calculations were also performed to obtain the infrared spectrum, pH induced changes and to predict NMR parameters such as chemical shifts, magnetic shieldings and spin-spin coupling constants.

World Academy of Science, Engineering and Technology, International Journal of Physical and Mathematical Sciences, Jul 20, 2015

Physical Review E, Jun 1, 2004

Blucher Physics Proceedings, 2019

Glasses containing metallic nanoparticles are promising materials that should also possess the be... more Glasses containing metallic nanoparticles are promising materials that should also possess the best spectroscopic, chemical, mechanical and thermal characteristics for technological applications in optics and photonics. For this reason it was chosen to synthesize and characterize the pure silver doped borosilicate glasses and silver nitrate. The present work investigates the generation of silver nanoparticles on the surface and the mass of a borosilicate glass in which it was directed to the synthesis process in which it was consisted: in the stoichiometric calculations, in the determination of the melting temperature, in the choice of reagents with high degree of purity, in the manufacture of the samples, in the appropriate polishes and in the determination of heat treatments close to Tg of the glass in question. From this phase, the research followed the application of techniques of differential thermal analysis (ATD) and transmission electron microscopy (MET). Thus, from the results and analyzes obtained, it was possible to observe that the borosilicate glass samples of this work will obtain satisfactory experimental results, in which it was possible to prove its optical and structural properties similar to those recognized in literature, thus making it a promising material in area of vitreous materials applied to nanotechnology borosilicate glasses are obtained from the combination of silicon dioxide (SiO2) with boron oxide (B2O3) and the resulting samples were annealed at various temperatures. Due to the structural shape, these glasses have a high resistance to thermal shock, good chemical durability and excellent electrical resistivity compared to other glasses on the market today. Therefore, based on these important structural, physical and chemical characteristics and also in the variety of applications, this study was chosen for the synthesis and characterization of pure borosilicate glass and doped with silver nitrate. We verified the formation of silver nanoparticles, after the heat treatment, by transmission electron microscopy.

Journal of Molecular Liquids, 2021

Metal colloids or nanoclusters, embedded in glasses, have been found to introduce desired third-o... more Metal colloids or nanoclusters, embedded in glasses, have been found to introduce desired third-order optical non- linearities in the composites at wavelenghts very close to that of the characteristic surface-plasmon resonance of the metal clusters. Small spherical silver particles in a soda-lime silicate (SLS) glass were produced by means of the ion exchange method. Emphasis is given to the comparison among existing approaches to the understanding of the chemical interaction in these system. Soda lime silicate (SLS) glasses containing 0.020-0.015 wt % (AgNO 3), Nano 1 and Nano 2, respectively, were prepared in this experiment. A mixed batch was melted under an ambient atmosphere in alumina crucible at 1500 0 C-1400 0 C (depending of the composition) for 4 h. Glass samples were obtained by quenching the melt to room temperature. The resultant transparent glass was cut, polished on both sides, and subjected to experiments.The Figure 1 (a) and (b) shows the absorption spectra of the h...

Journal of Molecular Liquids, 2021

Radiation Measurements, 2007

ESR (electron spin resonance), XRD (X-ray diffraction) patterns and SEM (scanning electron micros... more ESR (electron spin resonance), XRD (X-ray diffraction) patterns and SEM (scanning electron microscopy) of irradiated calcium carbonate (CaCO 3) in eggshell was investigated. The ionizing radiation produces an electron centre CO 3− 3 , a hole centre CO − 3 , and the CO − 2 molecular ion also formed. The ESR centre with g // = 1.9977 and g ⊥ = 2.0021 was identified as the same found in hydroxyapatite. The work aims to standardize the samples preparation method and the conditions of measured for practical application by the specialist in emergency dosimetry. In this regard, practical consideration of sample preparation conditions and properties such as grain size, ESR spectra, and the temperature dependence of the signal were studied in detail. Dose response appears to be linear between 3 Gy and 1 kGy. No dose rate dependence was observed. The morphology of the calcined eggshell presented extensive morphological change on the calcinations process. Careful analyses of the ESR spectra are presently in progress in order to undertake and identify the radicals involved.

Radiation Measurements, 2007

ESR (electron spin resonance), XRD (X-ray diffraction) patterns and SEM (scanning electron micros... more ESR (electron spin resonance), XRD (X-ray diffraction) patterns and SEM (scanning electron microscopy) of irradiated calcium carbonate (CaCO 3) in eggshell was investigated. The ionizing radiation produces an electron centre CO 3− 3 , a hole centre CO − 3 , and the CO − 2 molecular ion also formed. The ESR centre with g // = 1.9977 and g ⊥ = 2.0021 was identified as the same found in hydroxyapatite. The work aims to standardize the samples preparation method and the conditions of measured for practical application by the specialist in emergency dosimetry. In this regard, practical consideration of sample preparation conditions and properties such as grain size, ESR spectra, and the temperature dependence of the signal were studied in detail. Dose response appears to be linear between 3 Gy and 1 kGy. No dose rate dependence was observed. The morphology of the calcined eggshell presented extensive morphological change on the calcinations process. Careful analyses of the ESR spectra are presently in progress in order to undertake and identify the radicals involved.

Chemical Physics Letters, 2010

The sequential Monte Carlo/CASPT2 approach was employed to investigate deactivation and emission ... more The sequential Monte Carlo/CASPT2 approach was employed to investigate deactivation and emission processes from the lowest-lying pp * and np * excited states of 9H-adenine in aqueous solution. It is found that conical intersections connecting the pp* and np* states with the ground state are also present in solution, whereas the barriers for the deactivation paths are significantly smaller on solvated conditions. The large destabilization of the np* state found in solution possibly prevents its involvement in the deactivation photophysics and explains the change from a bi-to a mono-exponential decay for the molecule in the gas phase and solution, respectively.

Chemical Physics Letters, 2010

The sequential Monte Carlo/CASPT2 approach was employed to investigate deactivation and emission ... more The sequential Monte Carlo/CASPT2 approach was employed to investigate deactivation and emission processes from the lowest-lying pp * and np * excited states of 9H-adenine in aqueous solution. It is found that conical intersections connecting the pp* and np* states with the ground state are also present in solution, whereas the barriers for the deactivation paths are significantly smaller on solvated conditions. The large destabilization of the np* state found in solution possibly prevents its involvement in the deactivation photophysics and explains the change from a bi-to a mono-exponential decay for the molecule in the gas phase and solution, respectively.

Chemical Physics Letters, 2008

The minimum energy path along the lowest-lying ππ∗ excited state of 2-aminopurine was calculated ... more The minimum energy path along the lowest-lying ππ∗ excited state of 2-aminopurine was calculated to elucidate the mechanisms of radiationless decay and emission in water. The sequential Monte Carlo quantum mechanics approach with a multiconfigurational and ...

Journal of Molecular Structure, 2002

Pure and Applied Chemistry, 2009

The accurate ab initio quantum chemical (QM) method multiconfigurational second-order perturbatio... more The accurate ab initio quantum chemical (QM) method multiconfigurational second-order perturbation (CASSPT2)/complete active space self-consistent field (CASSCF) has been used in conjunction with molecular mechanics (MM) procedures to compute molecular properties and photoinduced reactivity of DNA/RNA nucleobases (NABs) in isolation and within a realistic environment, in which the double helix strand, the aqueous media, and the external counterions are included. It is illustrated that the use of an MM model is helpful both to account for short- and long-range effects of the system surrounding the QM molecular core and to provide the proper structural constraints that allow more accurate QM geometry determinations.

ABSTRACT: Sequential Monte Carlo and quantum mechanical calculations of the electronic polarizati... more ABSTRACT: Sequential Monte Carlo and quantum mechanical calculations of the electronic polarization of the ground and first vertical excited states of 1H-benzotriazole in water are made. Using statistically uncorrelated configurations and CASSCF ab initio calculations the increase in the ground and excited state dipole moments of 1H-benzotriazole from gas phase to aqueous environment are obtained as 2.89 0.10 and 2.75 0.11 D, leading to total moments of 6.89 0.10 and 6.40 0.11 D, respectively. Structures are sampled using the statistical correlation interval obtained from the autocorrelation function of the energy and statistical convergence of the calculated dipole moments is shown. These water-polarized dipole moments of 1H-benzotriazole are used to obtain the solvatochromic shift of the first absorption transition. The resulting theoretical blue shift of 570 cm1 for the strong and characteristic 3 * transition is in good agreement with the inferred experimental value of 700 cm1. ...

Physical chemistry chemical physics : PCCP, 2007

The solvatochromic shifts of the n-pi(*) and pi-pi(*) states of uracil in water are analyzed usin... more The solvatochromic shifts of the n-pi(*) and pi-pi(*) states of uracil in water are analyzed using a combined and sequential Monte Carlo/quantum mechanics (MC/QM) approach. The role of the solute polarization and electronic delocalization into the solvent region are investigated. Electronic polarization of the solute is obtained using the HF/6-31G(d), the polarizable continuum model (PCM) and an iterative procedure using MP2/aug-cc-pVDZ in the MC/QM. The in-water dipole moment of uracil is obtained, respectively, as 5.12 D, 6.12 D and 7.01 +/- 0.05 D. This latter result, corresponding to an increase of 60% with respect to the gas phase value, is used in the classical potential of the MC simulation to obtain statistically uncorrelated configurations for subsequent QM calculations of the ultraviolet-visible absorption spectrum of uracil in water. QM calculations are performed at the time-dependent density-functional theory (TD-DFT) combined with the B3LYP and B3PW91 functionals, multi...

This work describes the spectroscopic characterization of a phosphate glass matrix doped with dif... more This work describes the spectroscopic characterization of a phosphate glass matrix doped with different Erbium concentrations. In order to increase the resistance of the glass, 3 mol % of silicon oxide were added to the phosphate matrix. A study of the optical absorption, luminescence and lifetime was conducted in order to characterize the infrared emission of Er3+ ions at 1540 nm, due to the radiative transition 4I13/2 → 4I15/2. Judd-Ofelt spectral analysis was carried out to determine the local structure and bonding in the vicinity of rare-earth ions. The experimental oscillator strengths calculated from the absorption spectra were used to evaluate the Judd-Ofelt intensity parameters Ωλ (λ = 2, 4 and 6). Changes in the glass density, refractive index and the values of Ω4 and Ω6 with different rare-earth concentrations are ascribed to changes in the glass network structure. Our results indicate that the present glass is a quite good matrix for Erbium ions, and the quantum efficienc...