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PM3 CONFORMATIONAL ANALYSIS OF THE (3S,5S,6S)-6 ACETYLAMIDOPENICILLANIC ACID. … Taking into account the syn-anti arrangement, the average charges are: q O8 (syn) = -0.243±0.008 q O8 (anti) = -0.241±0.012 q O12 (syn) = -0.370±0.006 q O12 (anti) = -0.372±0.013 q O13 (syn) = -0.293±0.006 q O13 (anti) = -0.291±0.010 q O17 (syn) = -0.346±0.013 q O17 (anti) = -0.335±0.026 and taking the three puckering classes into account the following average values are obtained: q O8 (a) = -0.249±0.009; q O8 (b) = -0.240±0.011 q O8 (c) = -0.240±0.009 q O12 (a) = -0.371±0.015 q O12 (b) = -0.372±0.011 q O12 (c) = -0.369±0.006 q O13 (a) = -0.298±0.005 q O13 (b) = -0.290±0.011 q O13 (c) = -0.291±0.005 q O17 (a) = -0.336±0.029 q O17 (b) = -0.341±0.021 q O17 (c) = -0.342±0.015 Statistically, it results that the oxygen net charges do not differ significantly from the average values for all conformers. If the puckering classes and the syn-anti or R-S criteria are taken into account, there is also no regular pattern. Based on these results we can affirm that the net charges do not fluctuate following certain regular patterns. The only exception is the N14 atom whose net charge depends on the conformation. This means that the conformational changes generated by the rotation of the free groups and by the different puckering classes do not influence significantly the charges, except for the N14 atom. The effect of this relatively constant distribution on the net charges determines an isosurface of the electrostatic potential relatively similar for all conformers. This is illustrated by the isosurface of the electrostatic potential presented in Fig. 4 for the conformers of the minimum energy (01pm3) and maximum energy (105pm3), respectively. The iso-surfaces of the electrostatic potential depend in a small degree on the spatial arrangement mode of the exocyclic groups attached to the N14 amidic atom. 01pm3 105pm3 Figure 4. Iso-surface of the electrostatic potential computed with PM3 for the contour value of 0.04, for conformers 01pm3,and 105pm3. 125
DANIELA IVAN, MIRCEA MRACEC In case the atoms O8 and O17 are closer, an extended negative potential occurs (the case of conformer 105pm3). Function of distance between the O12 or O13 atoms and the N4 atom, the isosurface of the negative electrostatic potential changes its shape (the case of conformer 01pm3). CONCLUSIONS A conformational analysis performed by the PM3 method on the 105 conformational isomers of (3S,5S,6S)-6-acetylamidopenicillanic acid led to the conclusions: - for all the conformers, the pseudochirality of the atom N14 does not influence significantly the HOMO and LUMO energies. On the contrarily, the energy of these levels is influenced by the syn-anti arrangement of the exocyclic amidic group as well as by the puckering of the thiazolidinic ring. - the analysis of orbital contribution to the HOMO and LUMO levels, suggested the S1 atom has the dominant contribution, while the geometry factors - pseudochirality of the N14 atom, the syn-anti arrangement and the puckering of the thiazolidinic cycle do not influence significantly this contribution. - the dipole moment is influenced strongly by the syn-anti arrangement. The puckering slightly influences the dipole moment, while the pseudochirality does not influence it at all. - from the vibration analysis one can draw the conclusion that both the backbone vibrations as well as the vibrations of the functional groups do not depend by the syn-anti arrangement or by the pseudochirality at the N14 atom, but depend significantly on the puckering. ZPVE does not depend significantly on the geometry of the conformer. Analysing the average values of the net atomic charges one can conclude that the charge densities on the N4 atom are not dependent on conformation, they being almost constant. For the N14 atom the net density is dependent on the conformation and this was proved by the high dispersion of the values. There is a certain pattern with respect of the puckering, but such pattern was not observed for pseudochirality or the syn-anti arrangement. The constant charge distribution leads to an isosurface of the electrostatic potential relatively similar for all conformers. METHODS Gas phase equilibrium geometry of conformers was obtained by semiempirical PM3 calculations with an SCF convergence of 10 -5 , and an RMS gradient of 10 -2 kcal/Å·mol [2,3]. Conformational search was performed by varying the C2-C3-C11-C12, C5-C6-N14-C15 and C6-N14-C15-C16 dihedrals in the range 0 ±180° with steps of 15°. Energy crit erion was set to 30 kcal/mol 126
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CHEMIA 3/2011
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CORINA COSTESCU, LAURA CORPAŞ, NIC
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Studia Universitatis Babes-Bolyai C
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MONICA BAIA, MONICA SCARISOREANU, I
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STUDIA UBB CHEMIA, LVI, 3, 2011 (p.
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PREPARATION, CHARACTERIZATION AND S
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SPECTROSCOPIC EVIDENCE OF COLLAGEN
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CORNEL-VIOREL POP, TRAIAN ŞTEFAN,
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VITALY ERUKHIMOVITCH, IGOR MUKMANOV
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DUMITRU GEORGESCU, ZSOLT PAP, MONIC
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MAHDIEH AZARI, ALI IRANMANESH DEFIN
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MAHDIEH AZARI, ALI IRANMANESH V ( G
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MAHDIEH AZARI, ALI IRANMANESH Now,
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MAHDIEH AZARI, ALI IRANMANESH Let T
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MAHDIEH AZARI, ALI IRANMANESH Let G
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MAHDIEH AZARI, ALI IRANMANESH ACKNO
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CRISTINA GRUIAN, HEINZ-JÜRGEN STEI
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HASTI ATEFI, MAHMOOD GHORANNEVISS,
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HASTI ATEFI, MAHMOOD GHORANNEVISS,
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LUCIANA UDRESCU, BOGDAN MARTA, MIHA
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ALI MADANSHEKAF, MARJAN MORADI wher
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ALI MADANSHEKAF, MARJAN MORADI and
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ALI MADANSHEKAF, MARJAN MORADI Agai
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ALI MADANSHEKAF, MARJAN MORADI 9. M
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ROZALIA VERES, CONSTANTIN CIUCE, VI
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EVALUATION OF FREE RADICAL CONCENTR
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EVALUATION OF FREE RADICAL CONCENTR
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ECCENTRIC CONNECTIVITY INDEX OF TOR
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ECCENTRIC CONNECTIVITY INDEX OF TOR
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DORINA GIRBOVAN, MARIUS AUREL BODEA
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YONG WANG, TAMARIA G. DEWDNEY, ZHIG
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ALEXANDRU LUPAN, CSONGOR MATYAS, AU
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EMILIA VANEA, SIMONA CAVALU, FLORIN
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ANDRA TĂMAŞ, MARTIN VINCZE The ma
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ANDRA TĂMAŞ, MARTIN VINCZE 2%B +
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ANDRA TĂMAŞ, MARTIN VINCZE increa
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EFFECT OF CATALYST LAYER THICKNESS
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SPECTRAL INVESTIGATIONS AND DFT STU
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TOPOLOGICAL SYMMETRY OF TWO FAMILIE
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TOPOLOGICAL SYMMETRY OF TWO FAMILIE
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NEW 1-AZABICYCLO[3.2.2]NONANE DERIV
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