Protein kinase CK2 inhibitors, polyhalogenated benzimidazoles, have been studied experimentally in solid state by NMR-NQR double resonance and X-ray and theoretically by the density functional theory (DFT). Six resonance frequencies on (14)N have been detected and assigned to particular nitrogen sites in each polyhalogenated benzimidazole molecule. The effects of prototropic annular tautomerism and polymorphism related to stable cluster formation due to intermolecular hydrogen bonding interactions on the (14)N NQR parameters have been analyzed within the DFT and AIM (atoms in molecules) formalism. The studies suggest that all polyhalogenobenzimidazoles are isostructural and can exhibit polymorphism and that (14)N NQR is very sensitive to hydrogen bondings but less sensitive to the specific arrangement of the hydrogen bonded molecules. NQDR and DFT results suggest the presence of the prototropic annular tautomerism 50:50, which is in a good agreement with the X-ray and (1)H NMR data.

Two antibacterial and antifungal agents, chloroxylenol (4-chloro-3,5-dimethyl-phenol) and triclosan (5-chloro-2-(2',4'-dichlorophenoxy)-phenol), were studied experimentally in solid state with an X-ray, (35)Cl-nuclear quadrupole resonance (NQR) and (17)O-nuclear quadrupole double resonance (NQDR) spectroscopies and, theoretically, with the density functional theory/quantum theory of atoms in molecules (DFT/QTAIM). The crystallographic structure of triclosan, which crystallises in space group P31 with one molecule in the asymmetric unit [a = 12.64100(10), b = 12.64100(10), c = 6.71630(10) Å], was solved with an X-ray and refined to a final R-factor of 2.81% at room temperature. The NQR frequencies of (35)Cl and (17)O were detected with the help of the density functional theory (DFT) assigned to particular chlorine and oxygen sites in the molecules of both compounds. The NQR frequencies at (35)Cl sites in chloroxylenol and triclosan were found to be more differentiated than frequencies at the (17)O site. The former better describes the substituent withdrawing effects connected to π-electron delocalization within the benzene rings and the influence of temperature; whereas, those at the (17)O site provide more information on O-H bond and intermolecular interactions pattern. The conformation adopted by diphenyl ether of triclosan in solid state was found to be typical of diphenyl ethers, but the opposite to those adopted when it was bound to different inhibitors. According to an X-ray study, temperature had no effect on the conformation of the diphenyl ring of triclosan, which was the same at 90 K and at room temperature (RT). The scattering of NQR frequencies reproduced by the DFT under assumption of the X-ray data at 90 K and RT is found to be a good indicator of the quality of resolution of the crystallographic structure.

the overall survival time increased significantly, especially in high-developed countries, but in fact the metastases, not the cancer itself, are the major cause of death. In 1971, only 50% of people diagnosed with the cancer went on to live at least five years, while nowadays, the fiveyear survival rate is 63% [2]. However if a cancer has spread the chances of survival are only scarcely better than in the 1970s. These numbers indicate that although the knowledge about cancer in the last two decades raised, even to a larger degree than in all preceding centuries, but the problem of cancer diseases persists and our knowledge is still insufficient to solve it. Despite the remarkable progress in cancer prevention, early detection, and treatment, made during the last few decades, the methods of cancer diagnosis and treatment are still not sufficiently specific and effective thus cancer still takes a heavy toll.Not so long ago in the beginning of 20 th century, neither carcinogens nor cellular targets were identified while the treatment was carried out exclusively by surgeries or natural products selected by trial and error. Modern cancer therapy based on the so-called holistic approachthe combined use of surgical methods, radiotherapy, chemotherapy, hormonal therapy and immunotherapy -is applied in the treatment of cancer at most stages. In fact this approach originated from the ancient Sumerian, Akkadian, Babylonian, Assyrian and Egyptian medicine, and was largely influenced by the Roman and Greek ideas concerning anatomy, physiology as well as the achievements of practical medicine and natural science. The chemotherapy, hormonal therapy, immunotherapy and radiotherapy as the methods of cancer treatment joined to the oldest surgical one only in the 20 th c. An important component of the combined therapy, but sometimes when cancer had already metastasised, the only available therapeutic method, is chemotherapy using natural or synthetic anticancer drugs and treated as curative, palliative, adjuvant or neoadjuvant. Over the centuries anticancer drugs evolved from natural products, discovered mainly from green plants and minerals to fully chemically synthesized chemotherapeutic agents. However, even today drugs of natural origin play an important role in the treatment of cancer as 14 of them were on the list of the top 35 drugs worldwide sales [4]. The process of anticancer drug discovery leading from natural products to chemotherapeutic agents, often illicitly limited only to cytostatic and antiproliferative, has evolved from serendipity to rational design based on advances in chemistry, physics and biology in a long and complicated process. Nowadays both cancer itself and anticancer drugs are investigated at the molecular level thus methods of drug discovery have changed diametrically. The dominant direction of contemporary aniticancer drug discovery is the search for the possibilities to influence the pathogenetic mechanisms specific of the tumour structures at the cellular and molecular levels, which require the kn...

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