Andrzej Wojtczak

Publications (4)4.11 Total impact

• Article: The studies of tautomerism in 6-mercaptopurine derivatives by 1H–13C, 1H–15N NMR and 13C, 15N CPMAS-experimental and quantum chemical approach

  Leszek Pazderski, Iwona Łakomska, Andrzej Wojtczak, Edward Szłyk, Jerzy Sitkowski, Lech Kozerski, Bohdan Kamieński, Wiktor Koźmiński, Jaromír Tousek, Radek Marek
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  ABSTRACT: Tautomerism in 6-mercaptopurine (6mpH), 2,6-dimercaptopurine (2,6dmp) and 6-mercaptopurine-9-riboside (6mp-9rb) was studied in the solution with 2D NMR methods-1H–13C HMBC and 1H–15N HMQC. The 15N NMR signals were assigned and the distribution of mobile protons proposed on the basis of δ13C, δ15N chemical shifts and JHC, JHN coupling constants, determined with HECADE. These heterocycles appear in DMSO-d6 as the thionic species with predominance of the following tautomers: N(1)H, N(7)H for 6mpH; N(1)H, N(3)H, N(7)H for 2,6dmp; N(1)H for 6mp-9rb. Quantum-chemical NMR calculations by GIAO method(RHF/6-31G**//B3LYP/6-31G**) allowed to evaluate the ratios of N(7)H, N(9): N(7), N(9)H tautomeric forms as ca. 3:1 for 6mpH and nearly 10:0 for 2,6dmp. The 13C and 15N CPMAS spectra were measured for solid 6mpH·H2O, anhydrous 6mpH, 2,6dmp and 6-mercaptopurinium chloride (6mpH2Cl), confirming the thionic character of all compounds. The 15N chemical shifts in the solid phase were calculated (B3LYP/6–31G**) for 6mpH·H2O and 6mpH2Cl, basing on the re-determined single crystal X-ray data (optimised with RHF/3-21G**).
  Journal of Molecular Structure. 785:205-215.
• Article: X-ray structure and multinuclear NMR studies of platinum(II) complexes with 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one

  Iwona Łakomska, Andrzej Wojtczak, Jerzy Sitkowski, Lech Kozerski, Edward Szłyk
  Polyhedron 26(4):803-810. · 2.06 Impact Factor
• Article: The crystal and molecular structure of potassium aquapentachloroiridate(III) and the 1H, 13C, 15N NMR coordination shifts in iridium(III) chloride complexes with 2,2′-bipyridine or 1,10-phenanthroline

  Leszek Pazderski, Jaromír Toušek, Andrzej Wojtczak, Jerzy Sitkowski, Lech Kozerski, Edward Szłyk
  Polyhedron 27(14):3067-3078. · 2.06 Impact Factor
• Article: The crystal and molecular structures of catena[bis(μ2-chloro)-(μ2-pyridazine-N,N′)]cadmium(II) and catena[bis(μ2-chloro)-(μ2-pyridazine-N,N′)]mercury(II) and the solid-phase 13C, 15N NMR studies of Zn(II), Cd(II), Hg(II) chloride complexes with pyridazine

  Leszek Pazderski, Edward Szlyk, Andrzej Wojtczak, Lech Kozerski, Jerzy Sitkowski, Bohdan Kamieński
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  ABSTRACT: The zinc triad metal chloride complexes with pyridazine of [M(pyridazine)Cl2]n type, M=Zn(II) (1), Cd(II) (2), Hg(II) (3), were synthesized. The crystal and molecular structures of 2 and 3 were studied by single crystal X-ray diffraction. They are isostructural polymers of formulae catena[bis(μ2-chloro)-(μ2-pyridazine-N,N′)]cadmium(II) and catena[bis(μ2-chloro)-(μ2-pyridazine-N,N′)]mercury(II). They crystallize in the orthorhombic Imma space group (2: a=7.056(1), b=7.447(1), c=13.113(1) Å; 3: a=7.129(1), b=7.398(1), c=13.073(2) Å). The central atoms have the geometry of square bipyramid and are bridged by axial pyridazines and equatorial chlorides. The Cd–N and Hg–N bonds are 2.371(3) and 2.407(5) Å, the Cd–Cl and Hg–Cl being 2.6279(7) and 2.6626(12) Å, respectively. The X-ray powder diffractograms suggest 1 has a similar structure, being different from the monomeric species Zn(pyridazine)2Cl2 (4), already described by several authors as the sole product of ZnCl2+pyridazine reaction. The 15N CPMAS-NMR measurements of 1–3 reveal significant shielding (65–90 ppm) of nitrogen nuclei upon the formation of coordination bondings, the observed low-frequency shifts decreasing with the atomic mass of the metal.
  Journal of Molecular Structure. 697:143-149.