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(CH3C5H4)2Vcl2 with Α-, Β-Andγ- Cyclodextrines: Synthesis, EPR Study and Microbiological Behavior Toward Escherichia Coli

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(CH3C5H4)2Vcl2 with Α-, Β-Andγ- Cyclodextrines: Synthesis, EPR Study and Microbiological Behavior Toward Escherichia Coli CEJC 3(1) 2005 72–81 Inclusion compounds of cystostatic active (C5H5)2VCl2 and (CH3C5H4)2VCl2 with α-, β-andγ- cyclodextrines: Synthesis, EPR study and microbiological behavior toward Escherichia coli. Jarom´ır Vinkl´arek∗, Jan Honz´ıˇcek, Jana Holubov´a Department of General and Inorganic Chemistry, University of Pardubice, n´am. Cs.ˇ legi´ı 565, 532 10 Pardubice, Czech Republic Received 21 July 2004; accepted 7 October 2004 Abstract: The inclusion of vanadocene dichloride (VDC) and 1,1’-dimethyl vanadocene dichloride (MeVDC) into cyclodextrines (α-CD, β-CD and γ-CD) was studied by EPR spectroscopy. It was found that VDC and MeVDC with β-CD and γ-CD form true inclusion compounds, but with α-CD, VDC and MeVDC gave only fine dispersion mixtures. The inclusion was validated by anisotropic EPR spectra of solid samples. In addition, the antimicrobial behavior (against E. coli) of each of the complexes was determined. It was established that not only did VDC and MeVDC cause elongation of E. coli, but also the new vanadocene inclusion complexes were effective in this regard. c Central European Science Journals. All rights reserved. Keywords: EPR spectroscopy, vanadocene complexes, cyclodextrine, inclusion compounds, Escherichia coli, bent metallocene 1 Introduction 5 Metallocene dihalide complexes, (η -Cp)2MX2 , of early transition metals are currently undergoing intensive studies due to their biological activity [1-4]. Titanocene dichloride (TDC) and vanadocene dichloride (VDC, 1) have been found to be the most active met- allocene complexes in many biological experiments [5]. Inclusion compounds of cyclodex- trines are known to form stable inclusion compounds with a variety of organometallics, in- cluding ferrocene and its derivatives [6-9], half-sandwich complexes of molybdenum[10,11] ∗ E-mail: [email protected] J. Vinkl´arek et al. / Central European Journal of Chemistry 3(1) 2005 72–81 73 and titanocene or molybdenocene dihalide complexes [12-14]. These inclusion compounds are being investigated for pharmaceutical uses owing to their ability to increase the aque- ous solubility of drugs, improve oral absorption, and enhance chemical stability with respect to oxidation by air, sensitivity to light etc [15]. For the validation of inclusion compounds it is necessary to choose an appropriate experimental method. The prepara- tion of a single-crystal, which is indispensable for X-ray structure analysis, is very difficult for these type of compounds and therefore another experimental method has to be cho- sen. In the case of inclusion compounds of titanocene dichloride with cyclodextrines, 1H-NMR spectroscopy has successfully been used for verification of inclusion compounds [12]. Unfortunately, use of this method for paramagnetic substances is very limited. The aim of this work is to find a method that could be used to verify paramagnetic compounds, such as vanadocene dichloride (VDC; 1) and its ring substituted derivative, 1,1’-dimethyl vanadocene dichloride (MeVDC; 2) as inclusion cyclodextrine compounds. The combination of vanadocene molecules with various dimensions and cyclodextrines with different cavity size’s gives either true inclusive complexes or only fine dispersion mixtures of starting compounds. In our previous work, we have studied paramagnetic bent metallocenes by means of electron paramagnetic resonance (EPR) and we have found that magnetic parameters are very sensitive to small changes in the surroundings of paramagnetic central metal d1 atom V (IV) [16,17]. In this paper, we intend to show how to distinguish true inclusion compounds from those that are just a fine dispersion of paramagnetic compound and cyclodextrine by means of EPR spectroscopy. The finding of elongation of Escherichia coli by Rosenberg at al. [18], was the first hint to the biological activity of the inorganic platinum complexes (cisplatin) and led to the detection of pronounced antitumor effectivity against animal and human tumors. Elongation is generally interpreted as evidence that the agents are effecting cell division and DNA replication [19]. 2 Results and discussion Solid samples of 3-8 were prepared by evaporation of aqueous solutions of vanadocenes 1 and 2 with appropriate cyclodextrines (α-CD, β-CD or γ-CD). These compounds were green, air stable paramagnetic powders that were soluble only in water and insoluble in the other common solvents. Isolated compounds 3-8 were characterized by the elemental analysis, IR and Raman spectroscopy and especially by the EPR spectroscopy. The results from infrared and Raman spectra measurements evidenced the keeping of vanadocene (methylvanadocene) fragment in compounds 3-8. Particularly, the pres- 5 ence of η -bonded C5H5 ring (in compounds 3-5) is validated by vibrations C5H5:C-H −1 −1 stretch (Raman: ∼ 3110 cm ), C5H5:C-C breath (Raman: ∼ 1135 cm )andC5H5:C-H −1 5 bend (IR: ∼ 833 cm ). The keeping of η -bonded CH3C5H4 ring (in compounds 6-8) −1 is validated by vibrations C5H4:C-H stretch (∼ 3110 cm ), CH3: C-H stretch (Raman: −1 −1 ∼ 2930 cm ), C5H4: C-H bend (IR: ∼ 833 cm ). The tilting of cyclopentadiene rings (Raman: ∼ 300 cm−1) validates the presence of both rings in the molecule [20].The vibra- 74 J. Vinkl´arek et al. / Central European Journal of Chemistry 3(1) 2005 72–81 tion spectra, however, does not give any information about inclusion. This information was obtained from anisotropic EPR spectra. The anisotropic spectra of vanadocene dichloride (1) is rhombic symmetric with a significant g-tensor and A-tensor anisotropy, that are characteristic for d1-metallocene dihalides (Tab. 1). The orientation of principal directions for magnetic tensors with respect to the molecular geometry according to related complexes was used [21]. The EPR parameters of compounds 1 and 2 are very similar (Tab. 1). Thus, the substitution by one methyl group on each of the Cp rings does not change the magnetic properties around the paramagnetic center of vanadium. The knowledge of the magnetic behavior of compounds 1 and 2 is important for discussion about the inclusion of vanadocene moiety into the cavity of cyclodextrine. Ax Ay Az gx gy gz α−CD-VDC (3) Single asymmetric peak β−CD-VDC (4) 73.6 115.9 18.0 1.982 1.971 2.011 γ−CD-VDC (5) 74.2 115.9 21.0 1.986 1.971 2.007 α−CD-MeVDC (6) Single asymmetric peak β−CD-MeVDC (7) 73.3 115.9 18.3 1.982 1.971 2.008 γ−CD-MeVDC (8) 76.1 115.6 21.0 1.988 1.971 2.011 Table 1 Hyperfine coupling tensors (104cm−1)andg-tensors for compounds 3-8. Overall, two different patterns of EPR spectra were obtained for compounds 3-8 (Fig. 1, 2). The compounds 3 (α-CD-VDC, Fig. 1 spectrum A) and 6 (α-CD-MeVDC, Fig. 2 spectrum A) gave similar anisotropic EPR spectra, in which the hyperfine inter- action with vanadium nucleus is not perceptible. The compounds 4 (β-CD-VDC, Fig. 1 spectrum B), 5(γ-CD-VDC, Fig. 1 spectrum C), 7(β-CD-MeVDC, Fig. 2 spec- trum B) and 8 (γ-CD-MeVDC, Fig. 2 spectrum C) gave spectra with distinct hyperfine interactions. The observed g-tensors and A-tensors are summarized in Table 1. The observed difference’s in spectrum patterns can only be explained in one way. Samples of compounds 3 and 6 have not been magnetically diluted, because they are not true inclusion compounds. The α-CD forms with vanadocene dichlorides 1 and 2 are only fine dispersion mixtures. In contrast, cyclodextrines with larger cavities (β-CD and γ- CD) produced with the vanadocene dichlorides 1 and 2, are true inclusion compounds (see scheme). The inclusion of a paramagnetic compound into the cavity of cyclodextrine causes a dilution of the paramagnetic centers. The obtained spectra have similar patterns to the EPR spectra of the frozen solutions and to the solid EPR spectra in isostructural diamagnetic matrix. Table 2 summarizes the results of microbiological studies and gives the minimum inhibitory concentrations (MIC), effective concentration as well as the relative amounts of elongated cells (in %) and maximal elongation at the most effective concentration. All studied complexes are effective in the cell division and embodies a strong inhibition of bacterial growth. From the obtained data, it can be estimated that complexes 1 and J. Vinkl´arek et al. / Central European Journal of Chemistry 3(1) 2005 72–81 75 Fig. 1 EPR spectra of compounds: (A) α-CD-VDC (3), (B) β-CD-VDC (4),γ-CD-VDC (5); ν0= 9.544 GHz. 2 are more effective than the antitumor agent TDC [22], which has undergone clinical testing before [4,23]. The true inclusion compounds 4, 5, 7 and 8 show similar biological activity as free vanadocene complexes 1 and 2. The minimum inhibitory concentrations (MIC) were found to be 4.5 mmol/l and the effective concentration was in the range 0.25 - 1.8 mmol/l for all studied compounds. It was shown that inclusion into the cavity of cyclodextrine does not adversely influence the germicidal activity and nor probably the cytostatic activity. MICa Effective conc. Rel. % Max. elong. (mmol/l) (mmol/l) elong. cells 1 4.5 1.34-0.28 25-50 80x 2 4.5 1.03-0.33 20-40 60x 4 4.5 1.13-0.24 25-40 70x 5 4.5 1.79-0.24 25-50 70x 7 4.5 1.13-0.28 25-50 60x 8 4.5 1.82-0.28 25-45 70x a minimum inhibitory concentration. Table 2 Microbiological activity of compounds 1, 2, 4, 5, 7 and 8. 76 J. Vinkl´arek et al. / Central European Journal of Chemistry 3(1) 2005 72–81 Fig. 2 EPR spectra of compounds: (A) α-CD-MeVDC (6), (B) β-CD-MeVDC (7),γ-CD- MeVDC (8); (ν0= 9.544 GHz).
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