Roman S. Czernuszewicz

Interaction of doxorubicin and its derivatives with DNA: Elucidation by resonance Raman and surface-enhanced resonance Raman spectroscopy

The interactions of doxorubicin and its derivatives, hydroxyrubicin and adriamycinone, with DNA were studied by resonance Raman (RR) and surface-enhanced resonance Raman scattering (SERRS) spectroscopy. The π-π interaction between the chromophore of the drug and DNA base pairs has been shown to downshift the skeletal stretching mode ∼ 1440 cm−1 by 8, 5, and 4 cm−1 for doxorubicin, hydroxyrubicin, and adriamycinone, respectively. The additional effects of intercalation with DNA on the RR and SERRS spectra for hydroxyrubicin are similar to those for doxorubicin. However, different effects are observed for adriamycinone. These results indicate that the sugar moiety is necessary to maintain the maximum van der Waals contact between the chromophore and the DNA base pairs and that the amine group in the amino sugar is more favored than the hydroxyl group.

Structural and spectroscopic models of the manganese catalase active site. Isolation and structures of the asymmetric [(H2O)MnIII(μ-O)-(μ-O2CR)2MnIII(L)] (L Cr2O72−, CH3OH) cores: Analogs of a substrate-bound catalase active site intermediate

Abstract The isolation and structural characterization are reported for two new unsymmetrical (μ-oxo)bis(μ-carboxylato)dimanganese(III) complexes, [Mn2O(O2CC2H5)2(H2O)(Cr2O7)(bpy)2] (1) and [Mn2O(O2CCH2Cl)2(H2O)(CH2OH)(bpy)2]2− (2) (bpy = 2,2′-bipyridine) that mimic end-on substrate and/or inhibitor coordination to only one manganese atom of the dimeric active site in bacterial manganese catalases. Crystals of 1 were self assembled spontaneously in aqueous medium following treatment of equimolar Mn(II) and bpy with K2Cr2O, in propionic acid rich solution. Complex 2 was synthesized by oxidation of Mn(II) with KMnO4 in pure methanol in the presence of bpy, chloroacetic acid, and sodium chloroacetate. X-ray crystallographic studied of 1 and 2 establish the presence of a similar triply bridged dimanganese core with distinct manganese sites in which one manganese atom contains an axial water molecule and the other is bonded to a terminal oxygen atom of dichromate anion (1), or to the oxygen atom of methanol (2), a neutral substrate. Complex 1 represents the first structurally characterized instance in which the dichromate acts as a monodentate ligand, the Mnue5f8O(dichromate) bond of 2.132(23) A indicating strong anion coordination. Isolation of these model complexes and their structural characteristics suggest a preference of the [Mn2O(O2CR)2(H2O)2]2− core towards a replacement of one water molecule only a feature that is suspected to operate in hydroperoxide binding to a dimanganese site of catalases. The resonance Raman signatures with visible excitation (406.7–501.7 nm) were obtained for a series of catalase model complexes containing dimanganese cores bridged by one or two μ-oxo groups, including (μ-oxo)bis(μ-carboxylato) Mn(III.III), and mixed-valent bis (μ-oxo) and bis (μ-oxo)mono(μ-carboxylato)Mn(III.IV) dimers. The two structural types, which model the oxidized Mn(III,III) and superoxidized Mn(III,IV) forms of catalase, are distinguished readily by the uniquely resonance-enhanced μ-18O-sensitive Mnue5f8O(oxo) stretching bands at ≈ 560 and ≈ 700 cm, respectively.

Fingerprinting petroporphyrin structures with vibrational spectroscopy: II. Resonance Raman marker bands for the exocyclic rings of nickel tetrahydrobenzoporphyrins and nickel cycloalkanoporphyrins

Abstract The Q-band excited (568.2 nm) resonance Raman (RR) spectra are reported for a series of geologically significant nickel(II) complexes of etio-, cycloalkano-, and tetrahydro-benzoporphyrins in the frequency range from 600 to 1200 cm−1. Several patterns in the RR spectra of these complexes can be utilized as signatures for each petroporphyrin family. Useful marker bands for these classes of petroporphyrins are identified and distinguishing features of the spectra are given which can differentiate closely related isomers within a given class.

Geochemistry of porphyrins: biological, industrial and environmental aspects

The existence of metalloporphyrins in geological materials was established by Alfred Treibs in the 1930s. This discovery provided definitive evidence that organic matter in fossil fuels is largely of biological origin and laid the foundation for the modern science of porphyrin geochemistry. This overview covers to some degree biological, industrial, and environmental topics in the geochemistry of nickel and vanadyl porphyrins in fossil fuels, principally petroleum.

One-equivalent oxidative charge storage on an [Mn2O2]3+ core: Synthesis, crystal structure and resonance Raman spectra of [Mn2O2(pbz)4]n+ (n = 3, 4)

Abstract Complexes similar in structure but with a higher oxidation state of the metal center mimic charge-storage processes observed in biological systems. An oxomanganese system based on the ligand 2(2′-pyridyl)benzimidazole, [Mn 2 O 2 (pbz) 4 ] 3+ , which contains the biologically relevant mixed-valent di-μ-oxo Mn(III,IV) unit capable of undergoing a pH controlled one-electron redox conversion to the Mn(IV,IV) state, is described. The [Mn 2 O 2 (pbz) 4 ] 4+ and [Mn 2 O 2 (pbz) 4 ] 3+ complexes have both been isolated and structurally characterized by X-ray crystallography and UV-Vis, EPR and resonance Raman spectroscopic methods. A characteristic Mn(IV)-O stretching mode of the (di-μ-oxo)dimanganese core in these complexes at ∼695 cm −1 provides a useful reference probe for structural characterization of Mn containing active sites involving two oxo bridges.

Fingerprinting petroporphyrin structures with vibrational spectroscopy: resonance Raman spectra of nickel and vanadyl etioporphyrins I and III

Abstract A study has been initiated which utilizes the sensitivity and selectivity of resonance Raman (RR) scattering to establish vibrational “structure-marker” frequencies for petroporphyrins in crude oils and tar balls as an empirical tool in the determination and differentiation of numerous porphyrins known to exist in these complex matrices. The RR spectra with variable-wavelength excitation are reported for nickel and vanadyl etioporphyrins I and III. Essentially all in-plane porphyrin skeletal modes and their assignments are catalogued. Among these, many (VO)Etio high-frequency vibrations (> 1400 cm −1 ) associated mainly with pyrrole C s C s and methine bridge C α C m stretching modes are 14–28 cm −1 lower in frequency than their corresponding modes in NiEtios, enabling the two metalloporphyrin families to be readily distinguished. The strongest band with the Soret-band excitation of vanadyl etioporphyrins arises from the characteristic VO stretch at 991 cm −1 . The RR spectra of two isomers, Etio-I and Etio-III, show significant differences in the 750–1050 cm −1 alkyl substituent vibrations which should allow qualitative identification of particular position isomers and perhaps quantitative analysis of isomeric mixtures.

Fingerprinting petroporphyrin structures with vibrational spectroscopy. Part 6: resonance Raman characterization of regioisomers of nickel(II) benzoetioporphyrin

Abstract Nickel(II) complexes of the geochemically significant four regioisomers of benzoetioporphyrin, Ni(BP–A–D), which contain a benzene ring fused onto the C β atoms of a pyrrole ring, have been synthesized and structurally characterized by resonance Raman spectroscopy. Laser excitations in resonance with the porphyrin Soret (406.7 nm) and Q (530.9 and 568.2 nm) electronic absorption bands exposed nearly all Raman active vibrations in the fingerprint region (100–1700 cm −1 ). The porphyrin skeletal vibrations above 1300 cm –1 are largely unaffected by the different location of the β,β-benzo exocyclic ring, but their frequencies indicate slightly more planar structures in solution for Ni(BP) porphyrins relative to nickel tetrahydrobenzo- and etioporphyrins. Several unique marker bands are also found for vibrations of the β,β-benzo substituent, especially in the Soret-band resonant spectra. Alkyl substituent and porphyrin skeletal vibrations in the low- (350–550 cm −1 ) and mid-frequency (750–1300 cm −1 ) regions show striking sensitivity to small conformational changes in the porphyrin, allowing the four Ni(BP) regioisomers to be readily distinguished.

Fingerprinting petroporphyrin structures with vibrational spectroscopy. Part 5. Structural influences of the porphyrin 13-alkyl substituent on resonance Raman scattering from nickel(II) cycloalkanoporphyrins

Resonance Raman (RR) spectroscopy is exploited in the structural identification of geochemically important nickel(II) complexes of six and seven membered ring cycloalkanoporphyrins (CAPs). The CAP6s and CAP7s of interest contain variable porphyrin 13-alkyl substituents (H, Me and Et) that are commonly found in crude oil and tar balls. Multiple polarized RR experiments of variable laser excitation combining near resonant porphyrin Soret (406.7 nm) and Q (530.9 and 568.2 nm) electronic bands exposed nearly all of the Raman active vibrations in the fingerprint region (150–1700 cm−1). Many of these vibrations conform to classical porphyrin skeletal CβCβ and CαCm pyrrole stretching, alkyl CH2 rocking, C–C exocyclic ring stretching and Cβ–C1 bending/metal–pyrrole breathing modes which show striking sensitivity in the RR spectra to small conformational changes in the porphyrin. This report becomes of particular interest in the study of the origin of petroleum and is potentially useful in oil exploration where the porphyrins may serve as markers of different crude oils.

Redox thermodynamics of mutant forms of the rubredoxin from Clostridiumpasteurianum: identification of a stable Fe(III)(S-Cys)3(OH) centre in the C6S mutant.

AbstractRedox thermodynamic data provide a detailed insight into control of the reduction potential E°′ of the [Fe(S-Cys)4] site in rubredoxin. Mutant forms were studied in which specific structural changes were made in both the primary and secondary coordination spheres. Those changes have been probed by resonance Raman spectroscopy. The decrease of ~200 mV in E°′ observed for the [Fe(S-Cys)3(O-Ser)]–/2– couples in the surface ligand mutants C9S and C42S is essentially enthalpic in origin and associated with the substitution of ligand thiolate by ligand olate. However, the pH dependence of the potentials below characteristic pKared≈7 is an entropic contribution, plausibly associated with increased conformational flexibility induced by a longer FeII-O(H)-Ser bond in the reduced form. The presence of a second surface Ser ligand in the new double mutant protein C9S/C42S affects the enthalpic term primarily for pH>pKared≥9.3, but for pH<pKared the entropic term again becomes significant. The available data for the internal ligand mutant C39S appear to follow those for the surface ligand mutants. A longer FeIII-O-Ser link in the oxidized form is expected from structural considerations and a smaller decrease of ~100 mV in E°′ is observed for this particular [Fe(S-Cys)3(O-Ser)]–/2– couple. The reduced form is particularly susceptible to hydrolysis with consequent irreversible electrochemistry, an apparent consequence of an even longer FeII-O(H)-Ser bond. The second internal ligand mutant C6S exhibits starkly different behaviour. The cause was traced to the presence of a FeIII(S-Cys)3(OH)– centre in the oxidized form. Resonance Raman spectroscopy on 54Fe-, H218O- and D2O-enriched samples supports the presence of an iron hydroxyl group that donates a hydrogen bond to the OH group of the free S6 side chain and/or a cluster of bound water molecules. The thermodynamic parameters can then be rationalized in terms of the following processes: pH>pKa∼9: [FeIII(S-Cys)3(OH)]– + e– → [FeII(S-Cys)3(OH)]2–n pH<pKa: [FeIII(S-Cys)3(OH)]– + H+ + e– → [FeII(S-Cys)3(OH2)]–

Removal of a cysteine ligand from rubredoxin: assembly of Fe2S2 and Fe(S-Cys)3(OH) centres

Abstract. The electron transfer protein rubredoxin from Clostridiumpasteurianum contains an Fe(S-Cys)4 active site. Mutant proteins C9G, C9A, C42G and C42A, in which cysteine ligands are replaced by non-ligating Gly or Ala residues, have been expressed in Escherichiacoli. The C42A protein expresses with a FeIII2S2 cluster in place. In contrast, the other proteins are isolated in colourless forms, although a FeIII2S2 cluster may be assembled in the C42G protein via incubation with FeIII and sulfide. The four mutant proteins were isolated as stable mononuclear HgII forms which were converted to unstable mononuclear FeIII preparations that contain both holo and apo protein. The FeIII systems were characterized by metal analysis and mass spectrometry and by electronic, electron paramagnetic resonance, X-ray absorption and resonance Raman spectroscopies. The dominant FeIII form in the C9A preparation is a Fe(S-Cys)3(OH) centre, similar to that observed previously in the C6S mutant protein. Related centres are present in the proteins NifU and IscU responsible for assembly and repair of iron-sulfur clusters in both prokaryotic and eukaryotic cells. In addition to Fe(S-Cys)3(OH) centres, the C9G, C42G and C42A preparations contain a second four-coordinate FeIII form in which a ligand appears to be supplied by the protein chain. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00775-002-0355-1.