Mariusz Pilch - Academia.edu (original) (raw)
Papers by Mariusz Pilch
Journal of The Royal Society Interface
In carotenoids, by analogy to polyenes, the symmetry of the π-electron system is often invoked to... more In carotenoids, by analogy to polyenes, the symmetry of the π-electron system is often invoked to explain their peculiar electronic features, in particular the inactivity of the S 0 → S 1 transition in one-photon excitation. In this review, we verify whether the molecular symmetry of carotenoids and symmetry of their π-electron system are supported in experimental and computational studies. We focus on spectroscopic techniques which are sensitive to the electron density distribution, including the X-ray crystallography, electronic absorption, two-photon techniques, circular dichroism, nuclear magnetic resonance, Stark and vibrational spectroscopies, and on this basis we seek for the origin of inactivity of the S 1 state. We come across no experimental and computational evidence for the symmetry effects and the existence of symmetry restrictions on the electronic states of carotenoids. They do not possess an inversion centre and the C 2h symmetry approximation of carotenoid structure...
Tetrapyrrole pigments of photosynthetic antennae and reaction centers of higher plants: Structures, biophysics, functions, biochemistry, mechanisms of regulation, applications
Advances in Botanical Research
Side Methyl Groups Control the Conformation and Contribute to Symmetry Breaking of Isoprenoid Chromophores
Angewandte Chemie International Edition
The Journal of Physical Chemistry Letters, 2016
I n the introductory section of our article, we state that "the electronic transition from the S ... more I n the introductory section of our article, we state that "the electronic transition from the S 0 state to the S 1 state is never directly observed in Crts", which is incorrect. In fact, the observation of this forbidden transition in deoxyperidinin in organic solvents has been very recently reported by Greco et al. 1 prior to our publication.
The Journal of Physical Chemistry Letters, 2016
Chirality, Jan 5, 2002
The absorption and circular dichroism (CD) spectra of (-)-2,2'-dimethyl-4,5-(1-naphthyl)-1,3-... more The absorption and circular dichroism (CD) spectra of (-)-2,2'-dimethyl-4,5-(1-naphthyl)-1,3-dioxolane (DND) were studied in the energy region 30,000 cm(-1) to 50,000 cm(-1). The DND ketal is treated as a naphthalene dimer and its spectra are interpreted in terms of a vibronic dimer model which includes the (1)L(a) and (1)B(b) states of the naphthalene chromophore. To fix the most stable conformation of DND molecule, the MNDO/AM1, RHF/6-31G, and SVWN5, BPW91 methods are employed with 6-31G and 6-31G(d',p') basis sets. All the methods are shown to yield the DND geometry that is entirely consistent with the CD and absorption spectra studied.
Circular dichroism study of the ligh-harvesting PCP complexes within the vibronic multistate dimer theory
Acta Physica Polonica a, 1991
Inorganic Chemistry, 2014
High pressure in combination with optical spectroscopy was used to gain insights into the interac... more High pressure in combination with optical spectroscopy was used to gain insights into the interactions between Mg 2+ , Zn 2+ , and Ni 2+ ions and macrocyclic ligands of porphyrinoid type. In parallel, the central metal ion−macrocycle bonding was investigated using theoretical approaches. The symmetry properties of the orbitals participating in this bonding were analyzed, and pigment geometries and pressure/ligation effects were computed within DFT. Bacteriopheophytin a was applied as both a model chelator and a highly specific spectroscopic probe. The analysis of solvent and pressure effects on the spectral properties of the model Mg 2+ , Zn 2+ , and Ni 2+ complexes with bacteriopheophytin a shows that various chemical bonds are formed in the central pocket, depending on the valence configuration of the central metal ion. In addition, the character of this bonding depends on symmetry of the macrocyclic system. Since in most cases it is not coordinative bonding, these results challenge the conventional view of metal ion bonding in such complexes. In (labile) complexes with the main group metals, the metal ion−macrocycle interaction is mostly electrostatic. Significantly, water molecules are not preferred as a second axial ligand in such complexes, mainly due to the entropic constraints. The metal ions with a closed d shell may form (stable) complexes with the macrocycle via classical coordination bonds, engaging their p and s orbitals. Transition metals, due to the unfilled d shell, do form much more stable complexes, because of strong bonding via both coordination and covalent interactions. These conclusions are confirmed by DFT computations and theoretical considerations, which altogether provide the basis to propose a consistent and general mechanism of how the central metal ion and its interactions with the core nitrogens govern the physicochemical properties of metalloporphyrinoids.
The Journal of Physical Chemistry B, 2009
Modular photosynthetic LH1 complex is applied as a model system to investigate the thermodynamics... more Modular photosynthetic LH1 complex is applied as a model system to investigate the thermodynamics of a self-assembling membrane protein and the effects of cosolvents and cofactor (carotenoid) on the process. Native chromophores of LH1, bacteriochlorophyll, and carotenoid are excellent intrinsic spectroscopic reporter molecules. Their presence allows us to follow the association of transmembrane helices of LH1, without the use of any external markers, by electronic absorption/emission and circular dichroism. Furthermore, the assembly correctness can be monitored by the intracomplex energy transfer. Both the cosolvent and carotenoid markedly affect ∆H°and ∆S°associated with the complex formation in detergent, but the driving force of the process remains almost constant due to an efficient enthalpy-entropy compensation in the system. In the absence of cosolvent and cofactor, the energy of interactions between transmembrane helices in LH1 equals -580 kJ/mol. ∆H°drastically increases upon the addition of acetone (-1160 kJ/mol) and carotenoid (-1900 kJ/mol), whereas ∆S°lowers from +1.5 kJ/mol · K to -0.4 kJ/mol · K and to -2.6 kJ/mol · K, respectively. The stabilization of the ensemble by cofactor seems to be due to the π-π stacking of aromatic residues of LH1 polypeptides with the carotenoid π-electron system. The cosolvent, lowering the medium permittivity and thus enhancing helix-helix interactions, has an ordering effect on the system (∆S°< 0). This effect of cosolvent on ∆H°and ∆S°of association of transmembrane helices is relevant for crystallization of membrane proteins, as it explains in thermodynamic terms the action of amphiphiles used for crystallization of membrane proteins in the micellar phase.
Circular dichroism (CD) study of peridinin[ndash ]chlorophyll a protein (PCP) complexes from marine dinoflagellate algae The tetramer approach
Journal of the Chemical Society, Faraday Transactions, 1998
ABSTRACT The absorption and circular dichroism spectra of PCP (peridinin-chlorophyll a protein) l... more ABSTRACT The absorption and circular dichroism spectra of PCP (peridinin-chlorophyll a protein) light-harvesting complexes from . and are studied in terms of vibronic coupling theory. Analysis based on a tetramer model allows the determination of the relative positions of peridinin molecules in the PCP complexes studied. The tetrameric arrangementof four peridinins around the chlorophyll a is suggested to favour the efficient transfer of energy from the peridinin to thechlorophyll. The simple arguments presented suggest that the energy transfer from peridin to chlorophyll might occur from the[capital Psi] states of the peridinin tetramer to the B, and B states of the chlorophyll a.
Vibronic theory of magnetic vibrational circular dichroism in systems with fourfold symmetry: Theoretical analysis for copper tetraphenylporphyrin
The Journal of Chemical Physics, 1992
ABSTRACT A vibronic theory which includes multimode and multistate effects is developed to study ... more ABSTRACT A vibronic theory which includes multimode and multistate effects is developed to study magnetic vibrational circular dichroism (MVCD) and absorption spectra for molecular systems with fourfold symmetry. The MVCD and absorption spectra of the e fundamental transition and its combinations with infrared inactive modes are discussed in some detail to demonstrate the importance of electric and magnetic anharmonicity arising from vibronic coupling. The theory is applied to experimental MVCD spectra for the CuTPP molecule.
Chirality, 2002
The absorption and circular dichroism (CD) spectra of (-)-2,2¢-dimethyl-4,5-(1-naphthyl)-1,3-diox... more The absorption and circular dichroism (CD) spectra of (-)-2,2¢-dimethyl-4,5-(1-naphthyl)-1,3-dioxolane (DND) were studied in the energy region 30,000 cm )1 to 50,000 cm )1 . The DND ketal is treated as a naphthalene dimer and its spectra are interpreted in terms of a vibronic dimer model which includes the 1 L a and 1 B b states of the naphthalene chromophore. To fix the most stable conformation of DND molecule, the MNDO/AM1, RHF/6-31G, and SVWN5, BPW91 methods are employed with 6-31G and 6-31G(d',p') basis sets. All the methods are shown to yield the DND geometry that is entirely consistent with the CD and absorption spectra studied.
Theoretical analysis of magnetic vibrational circular dichroism for 1,3,5-trihalobenzene derivatives
Chemical Physics Letters, 1992
Abstract The theoretical of magnetic vibrational circular dichroism (MVCD) A terms is reported fo... more Abstract The theoretical of magnetic vibrational circular dichroism (MVCD) A terms is reported for the degenerate ν 9 and ν 10 vibrations of sym-C 6 H 3 X 3 (X= D, Cl, Br) molecules. An attempt to determine the A 1/D 0 ratios for A′ 1→ E′(ν 9) and A′ 1→ E′ ...
Chemical Physics Letters, 2002
The electronic structure of the low-energy states of 1,4,5,8-naphthalenetetracarboxy diimide (1) ... more The electronic structure of the low-energy states of 1,4,5,8-naphthalenetetracarboxy diimide (1) is investigated in terms of CASSCF method. At this level of approximation the Franck-Condon (FC) parameters were evaluated for the 13 totally symmetric modes of (1) molecule in its dipole-allowed low-energy 1 1 B 2u and 1 1 B 3u electronic states. These parameters are then employed to simulate the vibrational structures of absorption and fluorescence spectra of N ; N 0dibutyl (2) and N; N 0 -bis-hydroxypropyl (3) derivatives of naphthyl diimides measured in the region corresponding to the low-energy 1 1 A g ! 1 1 B 2u and 1 1 A g ! 1 1 B 3u overlapping transitions. Ó
Chemical Physics, 1993
Theoretical analysis of the vibrational magnetic moments for the four T,, fundamental vibrational... more Theoretical analysis of the vibrational magnetic moments for the four T,, fundamental vibrational states of the Cso fitllerene molecule is reported. An attempt to determine these moments is made in terms of a theory which includes both mechanical and vibronic contributions. At this level the theory leads to magnetic moments which are consistent in sign and relative magnitude with those measured for vs= 1183 cm-' and Y,= 1430 cm-' vibrations of Cso using magnetic vibrational circular dichroism. Predictions for the lower energy vibrations at v, = 528 cm-' and us= 577 cm-' are also provided. The moments of these latter transitions appear to arise almost totally from the mechanical (ground state) terms in the theory while those of higher energy modes have both vibronic and mechanical contributions. For the v, vibration the absolute magnitude of the combined vibronic and nuclear contributions was found to be larger than found in MVCD experiment. This may be due to the severe approximations implicit in the SCFPPP-CI method used.
The circular dichroism (CD) and absorption studies of 1,4,5,8-naphthalene tetracarboxydiimide dimer in terms of vibronic coupling theory
Chemical Physics, 2003
The vibronic dimer model is formulated in order to study the absorption and circular dichroism (C... more The vibronic dimer model is formulated in order to study the absorption and circular dichroism (CD) spectra of (1R, 2R)-1, 2-bis-(N′-cyclohexyl-1′, 4′, 5′, 8′-naphthalenetetracarboxydiimido) cyclohexane (NTD) molecule treated as a dimer with the ...
![Research paper thumbnail of Excited-State Double Proton Transfer in 1 H -Pyrazolo[3,4- b ]quinoline Dimers](https://attachments.academia-assets.com/44754581/thumbnails/1.jpg)
](J Phys Chem a, 2009
Pyrazoloquinolines are highly fluorescent, both in liquid solutions and in the solid state, which... more Pyrazoloquinolines are highly fluorescent, both in liquid solutions and in the solid state, which makes them good candidates for various optical devices. The aim of the current work is to understand the photochemical behavior of pyrazolo[3,4-b]quinoline (PQ), which is quite complicated since in n-alkane solvents PQ tends to form strong complexes with protic solvent constituents (often present as minor impurities), as well as dimers. Both types of H-bond complexes were studied systematically by temperature-dependent conventional absorption and fluorescence spectroscopy; the effect of protic solvent constituents was mimicked by varying the ethanol concentration in n-octane in the range from 0.0 to 0.8%. At room temperature the PQ:ethanol association constant was estimated at 80 M -1 and the dimerization constant at 2 × 10 3 M -1 . Dimer formation is enhanced upon lowering the temperature in pure n-alkane down to 220 K, and the fluorescence is strongly reduced since the dimer is nonfluorescent. Surprisingly, when irradiating a frozen sample for several minutes at very low temperatures (<40 K), a narrow-banded Shpol'skii-type fluorescence spectrum gradually appears. To explain this unusual photochemical behavior, PQ and its deuterated analogue were studied using lowtemperature absorption and fluorescence spectroscopy over the 300-5 K temperature range. In the case of normal (protonated) PQ, very fast excited-state intermolecular double proton transfer is responsible for the efficient quenching of PQ dimer fluorescence. Deuteration significantly slows down this proton transfer process, and in that case under cryogenic conditions a fluorescent dimer is observed. Photoirradiation under cryogenic conditions leads to molecular rearrangement of the dimers and the appearance of monomer spectra. For both H-PQ and D-PQ, these processes were found to be reversible. A simplified reaction scheme, in which the excited tautomeric dimer plays a crucial role, is presented to explain the observations.
Geometry computations of xH-pyrazolo[3,4-b]quinolines (x=1,2,9) in the ground state in tautomerism phenomenon
Journal of Molecular Structure: THEOCHEM, 2004
Pyrazoloquinoline is the basic structural unit whose derivatives are used in producing light-emit... more Pyrazoloquinoline is the basic structural unit whose derivatives are used in producing light-emitting diodes. The presented computations of ground state energies and equilibrium geometry in these states for three probable pyrazolo[3,4-b] quinolines (PQ) structures and PQ anion have been carried out using density functional theory. The changes in the geometry and energy of the ground states in computations both taking
The journal of physical chemistry. B, Jan 24, 2009
Modular photosynthetic LH1 complex is applied as a model system to investigate the thermodynamics... more Modular photosynthetic LH1 complex is applied as a model system to investigate the thermodynamics of a self-assembling membrane protein and the effects of cosolvents and cofactor (carotenoid) on the process. Native chromophores of LH1, bacteriochlorophyll, and carotenoid are excellent intrinsic spectroscopic reporter molecules. Their presence allows us to follow the association of transmembrane helices of LH1, without the use of any external markers, by electronic absorption/emission and circular dichroism. Furthermore, the assembly correctness can be monitored by the intracomplex energy transfer. Both the cosolvent and carotenoid markedly affect DeltaH degrees and DeltaS degrees associated with the complex formation in detergent, but the driving force of the process remains almost constant due to an efficient enthalpy-entropy compensation in the system. In the absence of cosolvent and cofactor, the energy of interactions between transmembrane helices in LH1 equals -580 kJ/mol. Delt...
Journal of The Royal Society Interface
In carotenoids, by analogy to polyenes, the symmetry of the π-electron system is often invoked to... more In carotenoids, by analogy to polyenes, the symmetry of the π-electron system is often invoked to explain their peculiar electronic features, in particular the inactivity of the S 0 → S 1 transition in one-photon excitation. In this review, we verify whether the molecular symmetry of carotenoids and symmetry of their π-electron system are supported in experimental and computational studies. We focus on spectroscopic techniques which are sensitive to the electron density distribution, including the X-ray crystallography, electronic absorption, two-photon techniques, circular dichroism, nuclear magnetic resonance, Stark and vibrational spectroscopies, and on this basis we seek for the origin of inactivity of the S 1 state. We come across no experimental and computational evidence for the symmetry effects and the existence of symmetry restrictions on the electronic states of carotenoids. They do not possess an inversion centre and the C 2h symmetry approximation of carotenoid structure...
Tetrapyrrole pigments of photosynthetic antennae and reaction centers of higher plants: Structures, biophysics, functions, biochemistry, mechanisms of regulation, applications
Advances in Botanical Research
Side Methyl Groups Control the Conformation and Contribute to Symmetry Breaking of Isoprenoid Chromophores
Angewandte Chemie International Edition
The Journal of Physical Chemistry Letters, 2016
I n the introductory section of our article, we state that "the electronic transition from the S ... more I n the introductory section of our article, we state that "the electronic transition from the S 0 state to the S 1 state is never directly observed in Crts", which is incorrect. In fact, the observation of this forbidden transition in deoxyperidinin in organic solvents has been very recently reported by Greco et al. 1 prior to our publication.
The Journal of Physical Chemistry Letters, 2016
Chirality, Jan 5, 2002
The absorption and circular dichroism (CD) spectra of (-)-2,2'-dimethyl-4,5-(1-naphthyl)-1,3-... more The absorption and circular dichroism (CD) spectra of (-)-2,2'-dimethyl-4,5-(1-naphthyl)-1,3-dioxolane (DND) were studied in the energy region 30,000 cm(-1) to 50,000 cm(-1). The DND ketal is treated as a naphthalene dimer and its spectra are interpreted in terms of a vibronic dimer model which includes the (1)L(a) and (1)B(b) states of the naphthalene chromophore. To fix the most stable conformation of DND molecule, the MNDO/AM1, RHF/6-31G, and SVWN5, BPW91 methods are employed with 6-31G and 6-31G(d',p') basis sets. All the methods are shown to yield the DND geometry that is entirely consistent with the CD and absorption spectra studied.
Circular dichroism study of the ligh-harvesting PCP complexes within the vibronic multistate dimer theory
Acta Physica Polonica a, 1991
Inorganic Chemistry, 2014
High pressure in combination with optical spectroscopy was used to gain insights into the interac... more High pressure in combination with optical spectroscopy was used to gain insights into the interactions between Mg 2+ , Zn 2+ , and Ni 2+ ions and macrocyclic ligands of porphyrinoid type. In parallel, the central metal ion−macrocycle bonding was investigated using theoretical approaches. The symmetry properties of the orbitals participating in this bonding were analyzed, and pigment geometries and pressure/ligation effects were computed within DFT. Bacteriopheophytin a was applied as both a model chelator and a highly specific spectroscopic probe. The analysis of solvent and pressure effects on the spectral properties of the model Mg 2+ , Zn 2+ , and Ni 2+ complexes with bacteriopheophytin a shows that various chemical bonds are formed in the central pocket, depending on the valence configuration of the central metal ion. In addition, the character of this bonding depends on symmetry of the macrocyclic system. Since in most cases it is not coordinative bonding, these results challenge the conventional view of metal ion bonding in such complexes. In (labile) complexes with the main group metals, the metal ion−macrocycle interaction is mostly electrostatic. Significantly, water molecules are not preferred as a second axial ligand in such complexes, mainly due to the entropic constraints. The metal ions with a closed d shell may form (stable) complexes with the macrocycle via classical coordination bonds, engaging their p and s orbitals. Transition metals, due to the unfilled d shell, do form much more stable complexes, because of strong bonding via both coordination and covalent interactions. These conclusions are confirmed by DFT computations and theoretical considerations, which altogether provide the basis to propose a consistent and general mechanism of how the central metal ion and its interactions with the core nitrogens govern the physicochemical properties of metalloporphyrinoids.
The Journal of Physical Chemistry B, 2009
Modular photosynthetic LH1 complex is applied as a model system to investigate the thermodynamics... more Modular photosynthetic LH1 complex is applied as a model system to investigate the thermodynamics of a self-assembling membrane protein and the effects of cosolvents and cofactor (carotenoid) on the process. Native chromophores of LH1, bacteriochlorophyll, and carotenoid are excellent intrinsic spectroscopic reporter molecules. Their presence allows us to follow the association of transmembrane helices of LH1, without the use of any external markers, by electronic absorption/emission and circular dichroism. Furthermore, the assembly correctness can be monitored by the intracomplex energy transfer. Both the cosolvent and carotenoid markedly affect ∆H°and ∆S°associated with the complex formation in detergent, but the driving force of the process remains almost constant due to an efficient enthalpy-entropy compensation in the system. In the absence of cosolvent and cofactor, the energy of interactions between transmembrane helices in LH1 equals -580 kJ/mol. ∆H°drastically increases upon the addition of acetone (-1160 kJ/mol) and carotenoid (-1900 kJ/mol), whereas ∆S°lowers from +1.5 kJ/mol · K to -0.4 kJ/mol · K and to -2.6 kJ/mol · K, respectively. The stabilization of the ensemble by cofactor seems to be due to the π-π stacking of aromatic residues of LH1 polypeptides with the carotenoid π-electron system. The cosolvent, lowering the medium permittivity and thus enhancing helix-helix interactions, has an ordering effect on the system (∆S°< 0). This effect of cosolvent on ∆H°and ∆S°of association of transmembrane helices is relevant for crystallization of membrane proteins, as it explains in thermodynamic terms the action of amphiphiles used for crystallization of membrane proteins in the micellar phase.
Circular dichroism (CD) study of peridinin[ndash ]chlorophyll a protein (PCP) complexes from marine dinoflagellate algae The tetramer approach
Journal of the Chemical Society, Faraday Transactions, 1998
ABSTRACT The absorption and circular dichroism spectra of PCP (peridinin-chlorophyll a protein) l... more ABSTRACT The absorption and circular dichroism spectra of PCP (peridinin-chlorophyll a protein) light-harvesting complexes from . and are studied in terms of vibronic coupling theory. Analysis based on a tetramer model allows the determination of the relative positions of peridinin molecules in the PCP complexes studied. The tetrameric arrangementof four peridinins around the chlorophyll a is suggested to favour the efficient transfer of energy from the peridinin to thechlorophyll. The simple arguments presented suggest that the energy transfer from peridin to chlorophyll might occur from the[capital Psi] states of the peridinin tetramer to the B, and B states of the chlorophyll a.
Vibronic theory of magnetic vibrational circular dichroism in systems with fourfold symmetry: Theoretical analysis for copper tetraphenylporphyrin
The Journal of Chemical Physics, 1992
ABSTRACT A vibronic theory which includes multimode and multistate effects is developed to study ... more ABSTRACT A vibronic theory which includes multimode and multistate effects is developed to study magnetic vibrational circular dichroism (MVCD) and absorption spectra for molecular systems with fourfold symmetry. The MVCD and absorption spectra of the e fundamental transition and its combinations with infrared inactive modes are discussed in some detail to demonstrate the importance of electric and magnetic anharmonicity arising from vibronic coupling. The theory is applied to experimental MVCD spectra for the CuTPP molecule.
Chirality, 2002
The absorption and circular dichroism (CD) spectra of (-)-2,2¢-dimethyl-4,5-(1-naphthyl)-1,3-diox... more The absorption and circular dichroism (CD) spectra of (-)-2,2¢-dimethyl-4,5-(1-naphthyl)-1,3-dioxolane (DND) were studied in the energy region 30,000 cm )1 to 50,000 cm )1 . The DND ketal is treated as a naphthalene dimer and its spectra are interpreted in terms of a vibronic dimer model which includes the 1 L a and 1 B b states of the naphthalene chromophore. To fix the most stable conformation of DND molecule, the MNDO/AM1, RHF/6-31G, and SVWN5, BPW91 methods are employed with 6-31G and 6-31G(d',p') basis sets. All the methods are shown to yield the DND geometry that is entirely consistent with the CD and absorption spectra studied.
Theoretical analysis of magnetic vibrational circular dichroism for 1,3,5-trihalobenzene derivatives
Chemical Physics Letters, 1992
Abstract The theoretical of magnetic vibrational circular dichroism (MVCD) A terms is reported fo... more Abstract The theoretical of magnetic vibrational circular dichroism (MVCD) A terms is reported for the degenerate ν 9 and ν 10 vibrations of sym-C 6 H 3 X 3 (X= D, Cl, Br) molecules. An attempt to determine the A 1/D 0 ratios for A′ 1→ E′(ν 9) and A′ 1→ E′ ...
Chemical Physics Letters, 2002
The electronic structure of the low-energy states of 1,4,5,8-naphthalenetetracarboxy diimide (1) ... more The electronic structure of the low-energy states of 1,4,5,8-naphthalenetetracarboxy diimide (1) is investigated in terms of CASSCF method. At this level of approximation the Franck-Condon (FC) parameters were evaluated for the 13 totally symmetric modes of (1) molecule in its dipole-allowed low-energy 1 1 B 2u and 1 1 B 3u electronic states. These parameters are then employed to simulate the vibrational structures of absorption and fluorescence spectra of N ; N 0dibutyl (2) and N; N 0 -bis-hydroxypropyl (3) derivatives of naphthyl diimides measured in the region corresponding to the low-energy 1 1 A g ! 1 1 B 2u and 1 1 A g ! 1 1 B 3u overlapping transitions. Ó
Chemical Physics, 1993
Theoretical analysis of the vibrational magnetic moments for the four T,, fundamental vibrational... more Theoretical analysis of the vibrational magnetic moments for the four T,, fundamental vibrational states of the Cso fitllerene molecule is reported. An attempt to determine these moments is made in terms of a theory which includes both mechanical and vibronic contributions. At this level the theory leads to magnetic moments which are consistent in sign and relative magnitude with those measured for vs= 1183 cm-' and Y,= 1430 cm-' vibrations of Cso using magnetic vibrational circular dichroism. Predictions for the lower energy vibrations at v, = 528 cm-' and us= 577 cm-' are also provided. The moments of these latter transitions appear to arise almost totally from the mechanical (ground state) terms in the theory while those of higher energy modes have both vibronic and mechanical contributions. For the v, vibration the absolute magnitude of the combined vibronic and nuclear contributions was found to be larger than found in MVCD experiment. This may be due to the severe approximations implicit in the SCFPPP-CI method used.
The circular dichroism (CD) and absorption studies of 1,4,5,8-naphthalene tetracarboxydiimide dimer in terms of vibronic coupling theory
Chemical Physics, 2003
The vibronic dimer model is formulated in order to study the absorption and circular dichroism (C... more The vibronic dimer model is formulated in order to study the absorption and circular dichroism (CD) spectra of (1R, 2R)-1, 2-bis-(N′-cyclohexyl-1′, 4′, 5′, 8′-naphthalenetetracarboxydiimido) cyclohexane (NTD) molecule treated as a dimer with the ...
J Phys Chem a, 2009
Pyrazoloquinolines are highly fluorescent, both in liquid solutions and in the solid state, which... more Pyrazoloquinolines are highly fluorescent, both in liquid solutions and in the solid state, which makes them good candidates for various optical devices. The aim of the current work is to understand the photochemical behavior of pyrazolo[3,4-b]quinoline (PQ), which is quite complicated since in n-alkane solvents PQ tends to form strong complexes with protic solvent constituents (often present as minor impurities), as well as dimers. Both types of H-bond complexes were studied systematically by temperature-dependent conventional absorption and fluorescence spectroscopy; the effect of protic solvent constituents was mimicked by varying the ethanol concentration in n-octane in the range from 0.0 to 0.8%. At room temperature the PQ:ethanol association constant was estimated at 80 M -1 and the dimerization constant at 2 × 10 3 M -1 . Dimer formation is enhanced upon lowering the temperature in pure n-alkane down to 220 K, and the fluorescence is strongly reduced since the dimer is nonfluorescent. Surprisingly, when irradiating a frozen sample for several minutes at very low temperatures (<40 K), a narrow-banded Shpol'skii-type fluorescence spectrum gradually appears. To explain this unusual photochemical behavior, PQ and its deuterated analogue were studied using lowtemperature absorption and fluorescence spectroscopy over the 300-5 K temperature range. In the case of normal (protonated) PQ, very fast excited-state intermolecular double proton transfer is responsible for the efficient quenching of PQ dimer fluorescence. Deuteration significantly slows down this proton transfer process, and in that case under cryogenic conditions a fluorescent dimer is observed. Photoirradiation under cryogenic conditions leads to molecular rearrangement of the dimers and the appearance of monomer spectra. For both H-PQ and D-PQ, these processes were found to be reversible. A simplified reaction scheme, in which the excited tautomeric dimer plays a crucial role, is presented to explain the observations.
Geometry computations of xH-pyrazolo[3,4-b]quinolines (x=1,2,9) in the ground state in tautomerism phenomenon
Journal of Molecular Structure: THEOCHEM, 2004
Pyrazoloquinoline is the basic structural unit whose derivatives are used in producing light-emit... more Pyrazoloquinoline is the basic structural unit whose derivatives are used in producing light-emitting diodes. The presented computations of ground state energies and equilibrium geometry in these states for three probable pyrazolo[3,4-b] quinolines (PQ) structures and PQ anion have been carried out using density functional theory. The changes in the geometry and energy of the ground states in computations both taking
The journal of physical chemistry. B, Jan 24, 2009
Modular photosynthetic LH1 complex is applied as a model system to investigate the thermodynamics... more Modular photosynthetic LH1 complex is applied as a model system to investigate the thermodynamics of a self-assembling membrane protein and the effects of cosolvents and cofactor (carotenoid) on the process. Native chromophores of LH1, bacteriochlorophyll, and carotenoid are excellent intrinsic spectroscopic reporter molecules. Their presence allows us to follow the association of transmembrane helices of LH1, without the use of any external markers, by electronic absorption/emission and circular dichroism. Furthermore, the assembly correctness can be monitored by the intracomplex energy transfer. Both the cosolvent and carotenoid markedly affect DeltaH degrees and DeltaS degrees associated with the complex formation in detergent, but the driving force of the process remains almost constant due to an efficient enthalpy-entropy compensation in the system. In the absence of cosolvent and cofactor, the energy of interactions between transmembrane helices in LH1 equals -580 kJ/mol. Delt...