Mihai Medeleanu | Politehnica University of Timisoara (original) (raw)
Papers by Mihai Medeleanu
The di-O-isopropylidene derivatives of aldohexoses, in their furanose form, are easily recognized... more The di-O-isopropylidene derivatives of aldohexoses, in their furanose form, are easily recognized during positive mode electron ionization mass spectrometry analysis because they all exhibit a strong intensity peak at m/z 101, which is usually the base peak. The literature data indicate that this peak appears due to the 2,2-dimethyl-1,3-dioxolan-4-ylium ion, which is formed through the detachment of the exocyclic dioxolane acetal. In the molecular ion, the radical character seems to be localized at the conjunction between the exocyclic dioxolane acetal and the furanose hemiacetal, the carbon-carbon bond between the two rings thus gaining a long bond character. We have used semi-empirical calculations to prove that such long bonds represent a rational explanation for the genesis of the m/z 101 cation in diastereomeric hexofuranose diacetals and their alkyl derivatives. The theoretical results seem to confirm the conclusions resulted from the analysis of mass spectra acquired for a se...
A conformational analysis of the (3S,5R,6R)-6-acetylamidopenicillanic acid was performed using AM... more A conformational analysis of the (3S,5R,6R)-6-acetylamidopenicillanic acid was performed using AM1, omega, and PM3 conformers. Their geometries were optimized at the ab initio HF/STO-3G level. The AM1 semiempirical MO method yields only eight conformers, the PM3 and Omega methods give 47 conformers, while the ab initio HF/STO-3G method leads to 28 conformers. For comparing the geometry of these conformers three geometrical properties were considered: the pseudo-chirality at N atom of the exocyclic amidic group, the anti/syn conformation of the O and H atoms from the exocyclic amidic group, and the three puckering classes of the thiazolidinic ring. The HF/STO-3G geometries do not differ significantly from the experimental ones or from those obtained by other authors who used basis sets of higher performance. However, unlike the high performant basis sets which tend to equalize the S1..C9 and S1..C10 distances, the HF/STO-3G basis set is able to distinguish between these bond lengths,...
Iranian journal of mathematical chemistry, 2011
Hyperdiamonds are covalently bonded fullerenes in crystalline forms, more or less related to diam... more Hyperdiamonds are covalently bonded fullerenes in crystalline forms, more or less related to diamond, and having a significant amount of sp3 carbon atoms. Design of several hypothetical crystal networks was performed by using our original software programs CVNET and NANO-STUDIO. The topology of the networks is described in terms of the net parameters and several counting polynomials, calculated by NANO-STUDIO, OMEGA and PI software programs.
Indian journal of chemistry. Sect. A: Inorganic, physical, theoretical & analytical, 1998
The distance matrix of an alkane has a unique positive eigenvalue 1\., which has recently been ap... more The distance matrix of an alkane has a unique positive eigenvalue 1\., which has recently been applied as a topological index and used for ordering alkane isomers with respect to their branching and for calculating their boiling points. We have now determined the main structural features ofthe alkane molecule, on which I\. depends. These are the number of vertices of the molecular graph (n) and the sum of the squares of the distances between all pairs of vertices (S). A good linear correlation between I\. and (nSJln is shown to exist. Lower and upper bounds of I\. are deduced, both depending solely on n and S. Because S = 2 WW W, there exists a connection between A, the Wiener index (W) and the hyperWiener index (WW).
The heteroanalogues of benzene where one or many CH units are replaced with isovalent atoms repre... more The heteroanalogues of benzene where one or many CH units are replaced with isovalent atoms represent interesting research areas in experimental and theoretical chemistry [1]. Some of these compounds have been synthesized [2], and important data regarding their stability and aromatic character were obtained. Starting from the study of the six-membered homocycles (λ-X)6 (X = CH, N, P, As, Sb, Bi) and sixmembered alternant heterocycles (λ3-Xλ-Y)3 (X, Y = CH, N, P, As, Sb, Bi) stability, estimated from their individual computed heat of formation [3], the aromatic character of these compounds was evaluated. The methyne groups from the benzene skeleton were replaced with dicoordinated trivalent heteroatoms, so the first condition of aromaticity the Hückel’s ruleis fulfilled. The complexity of the concept of aromaticity and the lack of universal definition led to the emerging of different criteria for its quantification. There are often used geometric criteria [4,5] (the bond lengths and ...
A new method of screening between two mannose isomeric derivatives, based on mass spectra (EI-GC-... more A new method of screening between two mannose isomeric derivatives, based on mass spectra (EI-GC-MS) analysis and their correlation with heats of formation estimated from semi-empirical calculations, is presented. The heats of formation for some main fragments, selected from the analyzed compounds mass spectra, were calculated with HyperChem and MOPAC software using semi-empirical methods (AM1, MINDO3, MNDO, RM1, PM3 and PM7) in trying to explain the difference between peak intensities obtained experimentally. These glycoderivatives can find multiple applications as biocompatible and biodegradable surfactant precursors in fields like pharmacy, medicine and biotechnologies. Rezumat In această lucrare este prezentată o metodă de discriminare intre doi derivaţi izomeri ai manozei, pe baza analizei spectrelor de masă (EI-GC-MS) si a corelării acestora cu călduri de formare estimate din calcule semiempirice. Căldurile de formare pentru câţiva ioni de fragmentare semnificativi, selectaţi ...
Revista de Chimie, 2019
Degradation and breakage of Aluminium Clad Steel Reinforced (ACSR) conductors leads to power outa... more Degradation and breakage of Aluminium Clad Steel Reinforced (ACSR) conductors leads to power outages that have catastrophic impact from an economic, social and national security point of view. Frictions, vibrations, corrosion, as well as other chemical compounds from the environment, can be the main source of the damages. Environment provides much of the time less restrictive conditions than those designed in the standards. In this respect, issues of optimization and development of current diagnostics and forecasting techniques personalized on geographic areas arise.
Studia Universitatis Babeș Bolyai Chemia, 2010
Revista De Chimie Bucharest Original Edition, 2013
The aromatic character of the heterobenzenes of type 1,2,4-(λ-CH-λ-X)3 and 1,3,5-(λ-CH-λ-X)3, whe... more The aromatic character of the heterobenzenes of type 1,2,4-(λ-CH-λ-X)3 and 1,3,5-(λ-CH-λ-X)3, where X is an element from group 15: N, P, As, Sb or Bi, has been investigated. Ab initio and DFT methods have been used in order to compute properties like bond orders based indices, anisotropy of the magnetic susceptibility, electron density and Laplacian of the electron density at the ring critical points of the heterocycles, natural charges for each C and X atoms of the heterobenzenes.
The paper presents the application of Laplacian matrix and its modifications in the characterizat... more The paper presents the application of Laplacian matrix and its modifications in the characterization of the chemical graphs associated to chemical structures. The eigenvalues of these matrices and some derived topological descriptors were computed. The alkane series C 3 to C 9 was used as the benchmark set in the ordering/discriminating analysis as well as in the QSPR with the normal boiling points.
Digest Journal of Nanomaterials and Biostructures
Carbon Materials: Chemistry and Physics, 2013
Hyperdiamonds are covalently bonded carbon phases, more or less related to the diamond network, h... more Hyperdiamonds are covalently bonded carbon phases, more or less related to the diamond network, having a significant amount of sp3 carbon atoms and similar physical properties. Many of them have yet a hypothetical existence but a well-theorized description. Among these, the diamond D5 was studied in detail, as topology, at TOPO GROUP CLUJ, Romania. The theoretical instrument used was the Omega polynomial, also developed in Cluj. It was computed in several 3D network domains and analytical formulas have been derived, not only for D5 but also for the well-known diamond D6 and other known networks.
International Journal of Molecular Sciences, 2006
Molecular modeling and MTD methods are useful tools to assess both qualitative (SAR) and quantita... more Molecular modeling and MTD methods are useful tools to assess both qualitative (SAR) and quantitative (QSAR) chemical structure-biological activity relationships. The 1-[(2-hydroxiethoxi)-methyl]-6-(phenylthio)thymine congeners (HEPT ligands) show in vitro anti-viral activity against the type-1 human immunodeficiency virus (HIV-1), which is the etiologic agent of AIDS. This work shows an extensive QSAR study performed upon a large series of 79 HEPT ligands using the MTD and HyperChem molecular modeling methods. The studied HEPT ligands are HIV reverse-transcriptase inhibitors. Their geometries were optimized and conformational analysis was carried out to build the hypermolecule, which allowed applying the MTD method. The hypermolecule was used for space mapping of the receptor's interaction site. The obtained results show that there are three 3D molecular zones important for the anti-HIV biological activity of the HEPT ligands under study.
Journal of Chemical Information and Modeling, 1998
Eigenvectors corresponding to the lowest eigenvalue of adjacency and distance matrices are used t... more Eigenvectors corresponding to the lowest eigenvalue of adjacency and distance matrices are used to generate new real-number local vertex invariants (LOVIs), by applying a Schultz-type algorithm. The intramolecular ordering of vertices was tested. From these LOVIs, several new topological indices have been defined and tested on the basis of intermolecular ordering of isomeric alkanes. Correlation with properties such as the normal boiling temperature and octane numbers have also been studied.
Journal of Chemical Information and Modeling, 1991
Eigenvectors obtained from the adjacency or distance matrix of graphs, corresponding to the large... more Eigenvectors obtained from the adjacency or distance matrix of graphs, corresponding to the largest negative eigenvalue, are useful real number vertex invariants for intramolecular ordering of vertices. From them or from eigenvalues, several new topological indices have been tested on the basis of intermolecular ordering of isomeric alkanes and of correlating ability with properties such as the boiling temperature.
tmj.ro
10 topological indicators of molecular similarity derived from cluster analysis, and based on bin... more 10 topological indicators of molecular similarity derived from cluster analysis, and based on binary distance measures were examined. The correlation coefficients (r) between these similarity measures and the biological activity (A) of a series of 22 alkyl alcohols that competitively inhibit the microsomal p-hydroxylation of aniline (A is pI 50 , that is, the logarithm of reciprocal concentration that causes 50% inhibition) are in the range of 0.032-0.907. We also propose a topological similarity/ dissimilarity measure (TSDM) developed on the basis of original Minimal Topological Difference (MTD) method, named MSD. Thus, the bioactive molecules are treated as hydrogen depleted graphs and the geometrical congruencies of the molecule with the highest activity vs. compared molecules are performed seeking the maximal superposition. The TSDM was obtained by normalization of MSD values. The range of variation is [0,1]. A value of TSDM close to 1 implies a high topological similarity. The degree of dissimilarity is maximum if TSDM=0. The results obtained by QSAR analysis of the same series of alcohols with TSDM values were: the correlation coefficient r=0.944 and the cross-validation coefficient was r 2 CV =0.736. This supports the hypothesis that the binding of alcohols to the enzymatic site of cytochrome P-450 takes place in a two-stage mechanism, the so-called "zipper" mechanism.
revistadechimie.ro
The aromaticity of the heterobenzenes containing 15-group elements is investigated using the magn... more The aromaticity of the heterobenzenes containing 15-group elements is investigated using the magnetic criterion (nucleus independent chemical shifts - NICS) and reactivity based descriptors (HOMO-LUMO gap) at B3LYP/6-31G(d) level, respectively B3LYP/LanL2DZ level. The ...
revistadechimie.ro
The conformational minima of 2-formylazoles (2-formyl-imidazole, respectively 2-formyl-thiazole) ... more The conformational minima of 2-formylazoles (2-formyl-imidazole, respectively 2-formyl-thiazole) have been computed using ab initio methods at HF/6-31G(d) level. The transition state structures for the addition of the hydroxyl ion at imidazole-2-carboxaldehyde, ...
The di-O-isopropylidene derivatives of aldohexoses, in their furanose form, are easily recognized... more The di-O-isopropylidene derivatives of aldohexoses, in their furanose form, are easily recognized during positive mode electron ionization mass spectrometry analysis because they all exhibit a strong intensity peak at m/z 101, which is usually the base peak. The literature data indicate that this peak appears due to the 2,2-dimethyl-1,3-dioxolan-4-ylium ion, which is formed through the detachment of the exocyclic dioxolane acetal. In the molecular ion, the radical character seems to be localized at the conjunction between the exocyclic dioxolane acetal and the furanose hemiacetal, the carbon-carbon bond between the two rings thus gaining a long bond character. We have used semi-empirical calculations to prove that such long bonds represent a rational explanation for the genesis of the m/z 101 cation in diastereomeric hexofuranose diacetals and their alkyl derivatives. The theoretical results seem to confirm the conclusions resulted from the analysis of mass spectra acquired for a se...
A conformational analysis of the (3S,5R,6R)-6-acetylamidopenicillanic acid was performed using AM... more A conformational analysis of the (3S,5R,6R)-6-acetylamidopenicillanic acid was performed using AM1, omega, and PM3 conformers. Their geometries were optimized at the ab initio HF/STO-3G level. The AM1 semiempirical MO method yields only eight conformers, the PM3 and Omega methods give 47 conformers, while the ab initio HF/STO-3G method leads to 28 conformers. For comparing the geometry of these conformers three geometrical properties were considered: the pseudo-chirality at N atom of the exocyclic amidic group, the anti/syn conformation of the O and H atoms from the exocyclic amidic group, and the three puckering classes of the thiazolidinic ring. The HF/STO-3G geometries do not differ significantly from the experimental ones or from those obtained by other authors who used basis sets of higher performance. However, unlike the high performant basis sets which tend to equalize the S1..C9 and S1..C10 distances, the HF/STO-3G basis set is able to distinguish between these bond lengths,...
Iranian journal of mathematical chemistry, 2011
Hyperdiamonds are covalently bonded fullerenes in crystalline forms, more or less related to diam... more Hyperdiamonds are covalently bonded fullerenes in crystalline forms, more or less related to diamond, and having a significant amount of sp3 carbon atoms. Design of several hypothetical crystal networks was performed by using our original software programs CVNET and NANO-STUDIO. The topology of the networks is described in terms of the net parameters and several counting polynomials, calculated by NANO-STUDIO, OMEGA and PI software programs.
Indian journal of chemistry. Sect. A: Inorganic, physical, theoretical & analytical, 1998
The distance matrix of an alkane has a unique positive eigenvalue 1\., which has recently been ap... more The distance matrix of an alkane has a unique positive eigenvalue 1\., which has recently been applied as a topological index and used for ordering alkane isomers with respect to their branching and for calculating their boiling points. We have now determined the main structural features ofthe alkane molecule, on which I\. depends. These are the number of vertices of the molecular graph (n) and the sum of the squares of the distances between all pairs of vertices (S). A good linear correlation between I\. and (nSJln is shown to exist. Lower and upper bounds of I\. are deduced, both depending solely on n and S. Because S = 2 WW W, there exists a connection between A, the Wiener index (W) and the hyperWiener index (WW).
The heteroanalogues of benzene where one or many CH units are replaced with isovalent atoms repre... more The heteroanalogues of benzene where one or many CH units are replaced with isovalent atoms represent interesting research areas in experimental and theoretical chemistry [1]. Some of these compounds have been synthesized [2], and important data regarding their stability and aromatic character were obtained. Starting from the study of the six-membered homocycles (λ-X)6 (X = CH, N, P, As, Sb, Bi) and sixmembered alternant heterocycles (λ3-Xλ-Y)3 (X, Y = CH, N, P, As, Sb, Bi) stability, estimated from their individual computed heat of formation [3], the aromatic character of these compounds was evaluated. The methyne groups from the benzene skeleton were replaced with dicoordinated trivalent heteroatoms, so the first condition of aromaticity the Hückel’s ruleis fulfilled. The complexity of the concept of aromaticity and the lack of universal definition led to the emerging of different criteria for its quantification. There are often used geometric criteria [4,5] (the bond lengths and ...
A new method of screening between two mannose isomeric derivatives, based on mass spectra (EI-GC-... more A new method of screening between two mannose isomeric derivatives, based on mass spectra (EI-GC-MS) analysis and their correlation with heats of formation estimated from semi-empirical calculations, is presented. The heats of formation for some main fragments, selected from the analyzed compounds mass spectra, were calculated with HyperChem and MOPAC software using semi-empirical methods (AM1, MINDO3, MNDO, RM1, PM3 and PM7) in trying to explain the difference between peak intensities obtained experimentally. These glycoderivatives can find multiple applications as biocompatible and biodegradable surfactant precursors in fields like pharmacy, medicine and biotechnologies. Rezumat In această lucrare este prezentată o metodă de discriminare intre doi derivaţi izomeri ai manozei, pe baza analizei spectrelor de masă (EI-GC-MS) si a corelării acestora cu călduri de formare estimate din calcule semiempirice. Căldurile de formare pentru câţiva ioni de fragmentare semnificativi, selectaţi ...
Revista de Chimie, 2019
Degradation and breakage of Aluminium Clad Steel Reinforced (ACSR) conductors leads to power outa... more Degradation and breakage of Aluminium Clad Steel Reinforced (ACSR) conductors leads to power outages that have catastrophic impact from an economic, social and national security point of view. Frictions, vibrations, corrosion, as well as other chemical compounds from the environment, can be the main source of the damages. Environment provides much of the time less restrictive conditions than those designed in the standards. In this respect, issues of optimization and development of current diagnostics and forecasting techniques personalized on geographic areas arise.
Studia Universitatis Babeș Bolyai Chemia, 2010
Revista De Chimie Bucharest Original Edition, 2013
The aromatic character of the heterobenzenes of type 1,2,4-(λ-CH-λ-X)3 and 1,3,5-(λ-CH-λ-X)3, whe... more The aromatic character of the heterobenzenes of type 1,2,4-(λ-CH-λ-X)3 and 1,3,5-(λ-CH-λ-X)3, where X is an element from group 15: N, P, As, Sb or Bi, has been investigated. Ab initio and DFT methods have been used in order to compute properties like bond orders based indices, anisotropy of the magnetic susceptibility, electron density and Laplacian of the electron density at the ring critical points of the heterocycles, natural charges for each C and X atoms of the heterobenzenes.
The paper presents the application of Laplacian matrix and its modifications in the characterizat... more The paper presents the application of Laplacian matrix and its modifications in the characterization of the chemical graphs associated to chemical structures. The eigenvalues of these matrices and some derived topological descriptors were computed. The alkane series C 3 to C 9 was used as the benchmark set in the ordering/discriminating analysis as well as in the QSPR with the normal boiling points.
Digest Journal of Nanomaterials and Biostructures
Carbon Materials: Chemistry and Physics, 2013
Hyperdiamonds are covalently bonded carbon phases, more or less related to the diamond network, h... more Hyperdiamonds are covalently bonded carbon phases, more or less related to the diamond network, having a significant amount of sp3 carbon atoms and similar physical properties. Many of them have yet a hypothetical existence but a well-theorized description. Among these, the diamond D5 was studied in detail, as topology, at TOPO GROUP CLUJ, Romania. The theoretical instrument used was the Omega polynomial, also developed in Cluj. It was computed in several 3D network domains and analytical formulas have been derived, not only for D5 but also for the well-known diamond D6 and other known networks.
International Journal of Molecular Sciences, 2006
Molecular modeling and MTD methods are useful tools to assess both qualitative (SAR) and quantita... more Molecular modeling and MTD methods are useful tools to assess both qualitative (SAR) and quantitative (QSAR) chemical structure-biological activity relationships. The 1-[(2-hydroxiethoxi)-methyl]-6-(phenylthio)thymine congeners (HEPT ligands) show in vitro anti-viral activity against the type-1 human immunodeficiency virus (HIV-1), which is the etiologic agent of AIDS. This work shows an extensive QSAR study performed upon a large series of 79 HEPT ligands using the MTD and HyperChem molecular modeling methods. The studied HEPT ligands are HIV reverse-transcriptase inhibitors. Their geometries were optimized and conformational analysis was carried out to build the hypermolecule, which allowed applying the MTD method. The hypermolecule was used for space mapping of the receptor's interaction site. The obtained results show that there are three 3D molecular zones important for the anti-HIV biological activity of the HEPT ligands under study.
Journal of Chemical Information and Modeling, 1998
Eigenvectors corresponding to the lowest eigenvalue of adjacency and distance matrices are used t... more Eigenvectors corresponding to the lowest eigenvalue of adjacency and distance matrices are used to generate new real-number local vertex invariants (LOVIs), by applying a Schultz-type algorithm. The intramolecular ordering of vertices was tested. From these LOVIs, several new topological indices have been defined and tested on the basis of intermolecular ordering of isomeric alkanes. Correlation with properties such as the normal boiling temperature and octane numbers have also been studied.
Journal of Chemical Information and Modeling, 1991
Eigenvectors obtained from the adjacency or distance matrix of graphs, corresponding to the large... more Eigenvectors obtained from the adjacency or distance matrix of graphs, corresponding to the largest negative eigenvalue, are useful real number vertex invariants for intramolecular ordering of vertices. From them or from eigenvalues, several new topological indices have been tested on the basis of intermolecular ordering of isomeric alkanes and of correlating ability with properties such as the boiling temperature.
tmj.ro
10 topological indicators of molecular similarity derived from cluster analysis, and based on bin... more 10 topological indicators of molecular similarity derived from cluster analysis, and based on binary distance measures were examined. The correlation coefficients (r) between these similarity measures and the biological activity (A) of a series of 22 alkyl alcohols that competitively inhibit the microsomal p-hydroxylation of aniline (A is pI 50 , that is, the logarithm of reciprocal concentration that causes 50% inhibition) are in the range of 0.032-0.907. We also propose a topological similarity/ dissimilarity measure (TSDM) developed on the basis of original Minimal Topological Difference (MTD) method, named MSD. Thus, the bioactive molecules are treated as hydrogen depleted graphs and the geometrical congruencies of the molecule with the highest activity vs. compared molecules are performed seeking the maximal superposition. The TSDM was obtained by normalization of MSD values. The range of variation is [0,1]. A value of TSDM close to 1 implies a high topological similarity. The degree of dissimilarity is maximum if TSDM=0. The results obtained by QSAR analysis of the same series of alcohols with TSDM values were: the correlation coefficient r=0.944 and the cross-validation coefficient was r 2 CV =0.736. This supports the hypothesis that the binding of alcohols to the enzymatic site of cytochrome P-450 takes place in a two-stage mechanism, the so-called "zipper" mechanism.
revistadechimie.ro
The aromaticity of the heterobenzenes containing 15-group elements is investigated using the magn... more The aromaticity of the heterobenzenes containing 15-group elements is investigated using the magnetic criterion (nucleus independent chemical shifts - NICS) and reactivity based descriptors (HOMO-LUMO gap) at B3LYP/6-31G(d) level, respectively B3LYP/LanL2DZ level. The ...
revistadechimie.ro
The conformational minima of 2-formylazoles (2-formyl-imidazole, respectively 2-formyl-thiazole) ... more The conformational minima of 2-formylazoles (2-formyl-imidazole, respectively 2-formyl-thiazole) have been computed using ab initio methods at HF/6-31G(d) level. The transition state structures for the addition of the hydroxyl ion at imidazole-2-carboxaldehyde, ...