Martin Breza

Bio: Martin Breza is an academic researcher from Slovak University of Technology in Bratislava. The author has contributed to research in topics: Molecular orbital & Ab initio. The author has an hindex of 19, co-authored 185 publications receiving 1507 citations. Previous affiliations of Martin Breza include Liverpool John Moores University.

Role of Radicals and Singlet Oxygen in Photoactivated DNA Cleavage by the Anticancer Drug Camptothecin: An Electron Paramagnetic Resonance Study

Abstract: Camptothecin (CPT) is an anticancer drug that inhibits topoisomerase I (Topo I), an enzyme closely linked to cell division, by forming a ternary DNA−CPT−Topo I complex. However, it has been shown that UVA-irradiated CPT in the absence of Topo I produces DNA damage. It has been proposed that free radicals are the key species responsible for the DNA cleavage. It has also been shown that the presence of metal ions enhances the activity of several anticancer drugs. Therefore, we attempt here to explore and identify free radicals generated in these processes. We describe a detailed spectroscopic study of UVA-irradiated CPT and the Cu(II)−CPT complex. From the low-temperature EPR spectrum of the Cu(II)−CPT complex, a proximity between the Cu(II) ion and the 20-hydroxy group of the lactone E ring of CPT is proposed. Upon irradiation (λ = 365 nm) of the Cu(II)−CPT complex in deoxygenated dimethyl sulfoxide (DMSO), the EPR signal of Cu(II) measured in situ at room temperature shows formal first-order exponential d...

Copper(II) Complexes with Schiff Bases Containing a Disiloxane Unit: Synthesis, Structure, Bonding Features and Catalytic Activity for Aerobic Oxidation of Benzyl Alcohol

Abstract: Mononuclear copper(II) salen-type Schiff base complexes, CuIIL1–5 [H2L1 to H2L5 = tetradentate N,N,O,O ligands derived from 2-hydroxybenzaldehyde, 2,4-dihydroxybenzaldehyde, 3,5-dibromo-2-hydroxybenzaldehyde, 2-hydroxy-5-nitrobenzaldehyde, 5-chloro-2-hydroxybenzaldehyde and 1,3-bis(3-aminopropyl)tetramethyldisiloxane, respectively] were prepared in situ in the presence of a copper(II) salt or by direct complexation between a copper(II) salt and a presynthesised Schiff base. The compounds {CuL1, CuL1·0.5Py, CuL2·0.375CH2Cl2, (CuL3)[Cu(4-Me-Py)4Cl]Cl·2H2O, CuL4, CuL4·CHCl3 and CuL5, as well as the isolated ligand H2L3} were characterised by elemental analysis, spectroscopic methods (IR, UV/Vis, 1H NMR, EPR) and X-ray crystallography. The formation of a 12-membered central chelate ring in these complexes is effected by the tetramethyldisiloxane unit, which separates the aliphatic chains, thus significantly reducing the mechanical strain in such a chelate ring. We dub this a “shoulder yoke effect” by analogy with the load-spreading ability of such an ancient device. The coordination geometry of copper(II) in CuIIL1–5 can be described as tetrahedrally distorted square-planar. Maximum tetrahedral distortion of the coordination geometry expressed by the parameter τ4 was observed for CuL1 (0.460), while distortion was minimal for the two crystallographically independent molecules of CuL2 (0.219 and 0.284). The Si–O–Si bond angle varies markedly between 169.75(2)° for CuL1 and 154.2(3)° for CuL4·CHCl3. Charge-density and DFT calculations on CuL1 indicate high ionic character of the Si–O bonds in the tetramethyldisiloxane fragment. The new copper(II) complexes bearing the disiloxane moiety have been shown to act as catalyst precursors for the aerobic oxidation of benzyl alcohol to benzaldehyde mediated by the TEMPO radical, reaching yields and TONs up to 99 % and 990, respectively, under mild and environmentally friendly conditions (50 °C; MeCN/H2O, 1:1).

Syntheses, Electronic Structures, and EPR/UV−Vis−NIR Spectroelectrochemistry of Nickel(II), Copper(II), and Zinc(II) Complexes with a Tetradentate Ligand Based on S-Methylisothiosemicarbazide

Abstract: Template condensation of 3,5-di-tert-butyl-2-hydroxybenzaldehyde S-methylisothiosemicarbazone with pentane-2,4-dione and triethyl orthoformate at elevated temperatures resulted in metal complexes of the type M(II)L, where M = Ni and Cu and H(2)L = a novel tetradentate ligand. These complexes are relevant to the active site of the copper enzymes galactose oxidase and glyoxal oxidase. Demetalation of Ni(II)L with gaseous hydrogen chloride in chloroform afforded the metal-free ligand H(2)L. Then by the reaction of H(2)L with Zn(CH(3)COO)(2)·2H(2)O in a 1:1 molar ratio in 1:2 chloroform/methanol, the complex Zn(II)L(CH(3)OH) was prepared. The three metal complexes and the prepared ligand were characterized by spectroscopic methods (IR, UV-vis, and NMR spectroscopy), X-ray crystallography, and DFT calculations. Electrochemically generated one-electron oxidized metal complexes [NiL](+), [CuL](+), and [ZnL(CH(3)OH)](+) and the metal-free ligand cation radical [H(2)L](+•) were studied by EPR/UV-vis-NIR and DFT calculations. These studies demonstrated the interaction between the metal ion and the phenoxyl radical.

Vanadium(V) Complexes with Substituted 1,5-bis(2-hydroxybenzaldehyde)carbohydrazones and Their Use As Catalyst Precursors in Oxidation of Cyclohexane

Abstract: Six dinuclear vanadium(V) complexes have been synthesized: NH4[(VO2)2(HLH)] (NH4[1]), NH4[(VO2)2(t-BuLH)] (NH4[2]), NH4[(VO2)2(ClLH)] (NH4[3]), [(VO2)(VO)(HLH)(CH3O)] (4), [(VO2)(VO)(t-BuLH)(C2H5O)] (5), and [(VO2)(VO)(ClLH)(CH3O)(CH3OH/H2O)] (6) (where HLH4 = 1,5-bis(2-hydroxybenzaldehyde)carbohydrazone, t-BuLH4 = 1,5-bis(3,5-di-tert-butyl-2-hydroxybenzaldehyde)carbohydrazone, and ClLH4 = 1,5-bis(3,5-dichloro-2-hydroxybenzaldehyde)carbohydrazone). The structures of NH4[1] and 4–6 have been determined by X-ray diffraction (XRD) analysis. In all complexes, the triply deprotonated ligand accommodates two V ions, using two different binding sites ONN and ONO separated by a diazine unit −N–N–. In two pockets of NH4[1], two identical VO2+ entities are present, whereas, in those of 4–6, two different VO2+ and VO3+ are bound. The highest oxidation state of V ions was corroborated by X-ray data, indicating the presence of alkoxido ligand bound to VO3+ in 4–6, charge density measurements on 4, magnetic susceptibil...

Spectroscopic and Computational Studies of Spin States of Iron(IV) Nitrido and Imido Complexes.

Abstract: High-oxidation-state metal complexes with multiply bonded ligands are of great interest for both their reactivity as well as their fundamental bonding properties. This paper reports a combined spectroscopic and theoretical investigation into the effect of the apical multiply bonded ligand on the spin-state preferences of threefold symmetric iron(IV) complexes with tris(carbene) donor ligands. Specifically, singlet (S = 0) nitrido [{PhB(ImR)3}FeN], R = tBu (1), Mes (mesityl, 2) and the related triplet (S = 1) imido complexes, [{PhB(ImR)3}Fe(NR′)]+, R = Mes, R′ = 1-adamantyl (3), tBu (4), were investigated by electronic absorption and Mossbauer effect spectroscopies. For comparison, two other Fe(IV) nitrido complexes, [(TIMENAr)FeN]+ (TIMENAr = tris[2-(3-aryl-imidazol-2-ylidene)ethyl]amine; Ar = Xyl (xylyl), Mes), were investigated by 57Fe Mossbauer spectroscopy, including applied-field measurements. The paramagnetic imido complexes 3 and 4 were also studied by magnetic susceptibility measurements (for 3) a...

Review of progress in shape-memory polymers

Abstract: Shape-memory polymers (SMPs) have attracted significant attention from both industrial and academic researchers due to their useful and fascinating functionality. This review thoroughly examines progress in shape-memory polymers, including the very recent past, achieved by numerous groups around the world and our own research group. Considering all of the shape-memory polymers reviewed, we identify a classification scheme wherein nearly all SMPs may be associated with one of four classes in accordance with their shape fixing and recovering mechanisms and as dictated by macromolecular details. We discuss how the described shape-memory polymers show great potential for diverse applications, including in the medical arena, sensors, and actuators.

Role of oxygen radicals in DNA damage and cancer incidence

Abstract: The development of cancer in humans and animals is a multistep process. The complex series of cellular and molecular changes participating in cancer development are mediated by a diversity of endogenous and exogenous stimuli. One type of endogenous damage is that arising from intermediates of oxygen (dioxygen) reduction - oxygen-free radicals (OFR), which attacks not only the bases but also the deoxyribosyl backbone of DNA. Thanks to improvements in analytical techniques, a major achievement in the understanding of carcinogenesis in the past two decades has been the identification and quantification of various adducts of OFR with DNA. OFR are also known to attack other cellular components such as lipids, leaving behind reactive species that in turn can couple to DNA bases. Endogenous DNA lesions are genotoxic and induce mutations. The most extensively studied lesion is the formation of 8-OH-dG. This lesion is important because it is relatively easily formed and is mutagenic and therefore is a potential biomarker of carcinogenesis. Mutations that may arise from formation of 8-OH-dG involve GC --> TA transversions. In view of these findings, OFR are considered as an important class of carcinogens. The effect of OFR is balanced by the antioxidant action of non-enzymatic antioxidants as well as antioxidant enzymes. Non-enzymatic antioxidants involve vitamin C, vitamin E, carotenoids (CAR), selenium and others. However, under certain conditions, some antioxidants can also exhibit a pro-oxidant mechanism of action. For example, beta-carotene at high concentration and with increased partial pressure of dioxygen is known to behave as a pro-oxidant. Some concerns have also been raised over the potentially deleterious transition metal ion-mediated (iron, copper) pro-oxidant effect of vitamin C. Clinical studies mapping the effect of preventive antioxidants have shown surprisingly little or no effect on cancer incidence. The epidemiological trials together with in vitro experiments suggest that the optimal approach is to reduce endogenous and exogenous sources of oxidative stress, rather than increase intake of anti-oxidants. In this review, we highlight some major achievements in the study of DNA damage caused by OFR and the role in carcinogenesis played by oxidatively damaged DNA. The protective effect of antioxidants against free radicals is also discussed.

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg