gamma-tocopherol traps mutagenic electrophiles such as NO(X) and complements alpha-tocopherol: physiological implications

Peroxynitrite, a powerful mutagenic oxidant and nitrating species, is formed by the near diffusion-limited reaction of .NO and O2.- during activation of phagocytes. Chronic inflammation induced by phagocytes is a major contributor to cancer and other degenerative diseases. We examined how gamma-tocopherol (gammaT), the principal form of vitamin E in the United States diet, and alpha-tocopherol (alphaT), the major form in supplements, protect against peroxynitrite-induced lipid oxidation. Lipid hydroperoxide formation in liposomes (but not isolated low-density lipoprotein) exposed to peroxynitrite or the .NO and O2.- generator SIN-1 (3-morpholinosydnonimine) was inhibited more effectively by gammaT than alphaT. More importantly, nitration of gammaT at the nucleophilic 5-position, which proceeded in both liposomes and human low density lipoprotein at yields of approximately 50% and approximately 75%, respectively, was not affected by the presence of alphaT. These results suggest that despite alphaT's action as an antioxidant gammaT is required to effectively remove the peroxynitrite-derived nitrating species. We postulate that gammaT acts in vivo as a trap for membrane-soluble electrophilic nitrogen oxides and other electrophilic mutagens, forming stable carbon-centered adducts through the nucleophilic 5-position, which is blocked in alphaT. Because large doses of dietary alphaT displace gammaT in plasma and other tissues, the current wisdom of vitamin E supplementation with primarily alphaT should be reconsidered.

Manipulation of energy transfer processes in nanochannels

The realisation of molecular assemblies featuring specific macroscopic properties is a prime example for the versatility of supramolecular organisation. Microporous materials such as zeolite L are well suited for the preparation of host-guest composites containing dyes, complexes, or clusters. This short tutorial focuses on the possibilities offered by zeolite L to study and influence Förster resonance energy transfer inside of its nanochannels. The highly organised host-guest materials can in turn be structured on a larger scale to form macroscopic patterns, making it possible to create large-scale structures from small, highly organised building blocks for novel optical applications.

Acetaldehyde as an underestimated risk factor for cancer development: role of genetics in ethanol metabolism

Chronic ethanol consumption is a strong risk factor for the development of certain types of cancer including those of the upper aerodigestive tract, the liver, the large intestine and the female breast. Multiple mechanisms are involved in alcohol-mediated carcinogenesis. Among those the action of acetaldehyde (AA), the first metabolite of ethanol oxidation is of particular interest. AA is toxic, mutagenic and carcinogenic in animal experiments. AA binds to DNA and forms carcinogenic adducts. Direct evidence of the role of AA in alcohol-associated carcinogenesis derived from genetic linkage studies in alcoholics. Polymorphisms or mutations of genes coding for AA generation or detoxifying enzymes resulting in elevated AA concentrations are associated with increased cancer risk. Approximately 40% of Japanese, Koreans or Chinese carry the AA dehydrogenase 2*2 (ALDH2*2) allele in its heterozygous form. This allele codes for an ALDH2 enzyme with little activity leading to high AA concentrations after the consumption of even small amounts of alcohol. When individuals with this allele consume ethanol chronically, a significant increased risk for upper alimentary tract and colorectal cancer is noted. In Caucasians, alcohol dehydrogenase 1C*1 (ADH1C*1) allele encodes for an ADH isoenzyme which produces 2.5 times more AA than the corresponding allele ADH1C*2. In studies with moderate to high alcohol intake, ADH1C*1 allele frequency and rate of homozygosity was found to be significantly associated with an increased risk for cancer of the upper aerodigestive tract, the liver, the colon and the female breast. These studies underline the important role of acetaldehyde in ethanol-mediated carcinogenesis.

Ethanol-induced cytochrome P4502E1 causes carcinogenic etheno-DNA lesions in alcoholic liver disease

Oxidative stress is thought to play a major role in the pathogenesis of hepatocellular cancer (HCC), a frequent complication of alcoholic liver disease (ALD). However, the underlying mechanisms are poorly understood. In hepatocytes of ALD patients, we recently detected by immunohistochemistry significantly increased levels of carcinogenic etheno-DNA adducts that are formed by the reaction of the major lipid peroxidation product, 4-hydroxynonenal (4-HNE) with nucleobases. In the current study, we show that protein-bound 4-HNE and etheno-DNA adducts both strongly correlate with cytochrome P450 2E1 (CYP2E1) expression in patients with ALD (r = 0.9, P < 0.01). Increased levels of etheno-DNA adducts were also detected in the liver of alcohol-fed lean (Fa/?) and obese (fa/fa) Zucker rats. The number of nuclei in hepatocytes stained positively for etheno-DNA adducts correlated significantly with CYP2E1 expression (r = 0.6, P = 0.03). To further assess the role of CYP2E1 in the formation of etheno-DNA adducts, HepG2 cells stably transfected with human CYP2E1 were exposed to ethanol with or without chlormethiazole (CMZ), a specific CYP2E1 inhibitor. Ethanol increased etheno-DNA adducts in the nuclei of CYP2E1-transfected HepG2 cells in a concentration-dependent and time-dependent manner, but not in vector mock-transfected control cells. CMZ blocked the generation of etheno-DNA adducts by 70%-90% (P < 0.01). CONCLUSION: Our data support the assumption that ethanol-mediated induction of hepatic CYP2E1 leading inter alia to highly miscoding lipid peroxidation-derived DNA lesions may play a central role in hepatocarcinogenesis in patients with ALD.

DNA-multiporhyrinic systems: promising objects for materials science

Porphyrin-containing materials are attractive objects for advanced light-harvesting systems [1]. Despite existence of numerous approaches to arrange porphyrines in a controlled and programmed way and therefore mimic natural photosynthetic systems, the problem of porphyrin`s arraying remains challenging [2]. Herein, we present an approach based on using DNA as a scaffold to hold porphyrines together. The whole spectroscopic investigation of the compounds containing several porphyrines and a possibility of their usage as molecular blocks for functional supramolecular architectures is discussed [3].

OMA and OPA—Software-Supported Mass Spectra Analysis of Native and Modified Nucleic Acids

The platform-independent software package consisting of the oligonucleotide mass assembler (OMA) and the oligonucleotide peak analyzer (OPA) was created to support the analysis of oligonucleotide mass spectra. It calculates all theoretically possible fragments of a given input sequence and annotates it to an experimental spectrum, thus, saving a large amount of manual processing time. The software performs analysis of precursor and product ion spectra of oligonucleotides and their analogues comprising user-defined modifications of the backbone, the nucleobases, or the sugar moiety, as well as adducts with metal ions or drugs. The ability to expand the library of building blocks and to implement individual structural variations makes it extremely useful for supporting the analysis of therapeutically active compounds. The functionality of the software tool is demonstrated on the examples of a platinated doublestranded oligonucleotide and a modified RNA sequence. Experiments also reveal the unique dissociation behavior of platinated higher-order DNA structures.

Observation of the rare chrysene excimer

Formation of the so far elusive chrysene excimer in solution is achieved by using DNA as a supramolecular scaffold. Oligonucleotides possessing one or two chrysene building blocks have been synthesized. Chrysene excimer fluorescence has been unambiguously observed in DNA double strands, as well as in single strands containing two neighbouring chrysenes.

Monitoring of alcohol markers by capillary electrophoresis.

Work dealing with the monitoring of alcohol markers by CE performed during the past two decades led to the development of assays for carbohydrate-deficient transferrin (CDT), ethyl sulfate, ethyl glucuronide, and phosphatidylethanol in body fluids and first attempts for the detection of the urinary 5-hydroxytryptophol/5-hydroxyindoleacetic acid ratio and stable hemoglobin acetaldehyde adducts. Most notably are assays for CDT that have been commercialized and are being used in many laboratories under routine conditions. This paper provides insight into the development, specifications, and use of the currently known CE-based assays suitable to detect alcohol markers. The achievements reached so far indicate that CE is an attractive technology for monitoring alcohol markers. This is particularly seen with the CDT assays that do not require an elaborate sample pretreatment and thus could be fully automated for high-throughput analyses on multicapillary instruments.

Highlights in Analytical Chemistry in Switzerland: OMA & OPA - A Software Tool for Mass Spectrometric Sequencing of Nucleic Acids

Oligonucleotides comprising unnatural building blocks, which interfere with the translation machinery, have gained increased attention for the treatment of gene-related diseases (e.g. antisense, RNAi). Due to structural modifications, synthetic oligonucleotides exhibit increased biostability and bioavailability upon administration. Consequently, classical enzyme-based sequencing methods are not applicable to their sequence elucidation and verification. Tandem mass spectrometry is the method of choice for performing such tasks, since gas-phase dissociation is not restricted to natural nucleic acids. However, tandem mass spectrometric analysis can generate product ion spectra of tremendous complexity, as the number of possible fragments grows rapidly with increasing sequence length. The fact that structural modifications affect the dissociation pathways greatly increases the variety of analytically valuable fragment ions. The gas-phase dissociation of oligonucleotides is characterized by the cleavage of one of the four bonds along the phosphodiester chain, by the accompanying loss of nucleases, and by the generation of internal fragments due to secondary backbone cleavage. For example, an 18-mer oligonucleotide yields a total number of 272’920 theoretical fragment ions. In contrast to the processing of peptide product ion spectra, which nowadays is highly automated, there is a lack of tools assisting the interpretation of oligonucleotide data. The existing web-based and stand-alone software applications are primarily designed for the sequence analysis of natural nucleic acids, but do not account for chemical modifications and adducts. Consequently, we developed a software to support the interpretation of mass spectrometric data of natural and modified nucleic acids and their adducts with chemotherapeutic agents.

Reactivity of hexanuclear ruthenium metallaprisms towards nucleotides and a DNA decamer

The reactivity of three hexacationic arene ruthenium metallaprisms towards isolated nucleotides and a short DNA strand was investigated using NMR spectroscopy, ESI mass spectrometry, UV/Vis and circular dichroism spectroscopy. The metallaprism built from oxalato-bridging ligands reacts rapidly in the presence of deoxyguanosine monophosphate (dGMP) and deoxyadenosine monophosphate, while the benzoquinonato derivative only reacts with dGMP. On the other hand, the larger metallaprism incorporating naphtoquinonato bridges remains stable in the presence of nucleotides. The reactivity of the three hexacationic metallaprisms with the decameric oligonucleotide d(CGCGATCGCG)2 was also investigated. Analysis of the NMR, MS, UV/Vis and CD data suggests that no adducts are formed between the oligonucleotide and the metallaprisms, but electrostatic interactions, leading to partial unwinding of the double-stranded oligonucleotide, were evidenced

The Exploitation of Versatile Building Blocks for the Self-Assembly of Novel Molecular Magnets

Using molecular building blocks to self-assemble lattices supporting long-range magnetic order is currently an active area of solid-state chemistry. Consequently, it is the realm of supramolecular chemistry that synthetic chemists are turning to in order to develop techniques for the synthesis of structurally well-defined supramolecular materials. In recent years we have investigated the versatility and usefulness of two classes of molecular building blocks, namely, tris-oxalato transition-metal (M. Pilkington and S. Decurtins, in “Magnetoscience—From Molecules to Materials,” Wiley–VCH, 2000), and octacyanometalate complexes (Pilkington and Decurtins, Chimia 54, 593 (2001)), for applications in the field of molecule-based magnets. Anionic, tris-chelated oxalato building blocks are able to build up two-dimensional honeycomb-layered structural motifs as well as three-dimensional decagon frameworks. The discrimination between the crystallization of the two- or three-dimensional structures relies on the choice of the templating counterions (Decurtins, Chimia 52, 539 (1998); Decurtins et al. Mol. Cryst. Liq. Cryst. 273, 167 (1995); New J. Chem. 117 (1998)). These structural types display a range of ferro, ferri, and antiferromagnetic properties (Pilkington and Decurtins, in “Magnetoscience—From Molecules to Materials”). Octacyanometalate building blocks self-assemble to afford two new classes of cyano-bridged compounds namely, molecular clusters and extended three dimensional networks (J. Larionova et al., Angew. Chem. Int. Ed. 39, 1605 (2000); Pilkington et al., in preparation). The molecular cluster with a MnII9MoV6 core has the highest ground state spin value, S=51/2, reported to-date (Larionova et al., Angew. Chem. Int. Ed. 39, 1605 (2000)). In the high-temperature regime, the magnetic properties are characterized by ferromagnetic intracluster coupling. In the magnetic range below 44 K, the magnetic cluster signature is lost as possibly a bulk behavior starts to emerge. The three-dimensional networks exhibit both paramagnetic and ferromagnetic behavior, since the magnetic properties of these materials directly reflect the electronic configuration of the metal ion incorporated into the octacyanometalate building blocks (Pilkington et al., in preparation). For both the oxalate- and cyanide-bridged materials, we are able to manipulate the magnetic properties of the supramolecular assemblies by tuning the electronic configurations of the metal ions incorporated into the appropriate molecular building blocks (Pilkington and Decurtins, in “Magnetoscience—From Molecules to Materials,” Chimia 54, 593 (2000)).

The Design and Synthesis of Versatile Molecular Building Blocks: Working Towards the Controlled Self-Assembly of Novel Functional Materials

Our research goals are focused on the preparation of novel molecule-based materials that possess specifically designed properties in solution or in the solid state e.g. self-assembly, magnetism, conductivity and spin crossover phenomena. Most of our systems incorporate paramagnetic transition metal ions and the search for new molecule-based magnetic materials is a prominent theme. Specific areas of research include the preparation and study of oxalate based 2D and 3D magnets, probing the versatility of octacyanometalate building blocks as precursors for new molecular magnets, and the preparation of new tetrathiafulvalene (TIF) derivatives for applications in molecular and supramolecular chemistry.

Multifunctional Coordination Compounds: Design and Properties

Cleverly designed molecular building blocks provide chemists with the tools of a powerful molecular-scale construction set. They enable them to engineer materials having a predictable order and useful solid-state properties. Hence, it is in the realm of supramolecular chemistry to follow a strategy for synthesizing materials which combine a selected set of properties, for instance from the areas of magnetism, photophysics and electronics. As a successful approach, host/guest solids which are based on extended anionic, homo- and bimetallic oxalato-bridged transition-metal compounds with two-and three-dimensional connectivities have been investigated. In this report, a brief review is given on the structural aspects of this class of compounds followed by a presentation of a thermal and magnetic study for two distinct, heterometallic oxalato-bridged layer compounds.

Stabilisation of precipitates of pedogenic dissolved organic matter by multivalent cations

Purpose Precipitation of dissolved organic matter (DOM) by multivalent cations is important for biogeochemical cycling of organic carbon. We investigated to which extent cation bridges are involved in DOM precipitation and how cross-links by cations and water molecule bridges (WaMB) stabilise the matrix of precipitated DOM. Materials and methods DOM was precipitated from the aqueous extract of a forest floor layer adding solutions of Ca(NO3)2, Al(NO3)3 and Pb(NO3)2 with different initial metal cation/C (Me/C) ratios. Precipitates were investigated by differential scanning calorimetry before and after ageing to detect cation bridges, WaMB and restructuring of supramolecular structure. Results and discussion Twenty-five to sixty-seven per cent of the dissolved organic carbon was precipitated. The precipitation efficiency of cations increased in the order Ca < Al < Pb, while the cation content of precipitates increased in the order Pb < Ca < Al. The different order and the decrease in the WaMB transition temperature (T*) for Al/C > 3 is explained by additional formation of small AlOOH particles. Thermal analysis indicated WaMB and their disruption at T* of 53–65 °C. Like cation content, T* increased with increasing Me/C ratio and in the order Ca < Pb < Al for low Me/C. This supports the general assumption that cross-linking ability increases in the order Ca < Pb < Al. The low T* for high initial Me/C suggests less stable and less cross-linked precipitates than for low Me/C ratios. Conclusions Our results suggest a very similar thermal behaviour of OM bound in precipitates compared with soil organic matter and confirms the relevance of WaMB in stabilisation of the supramolecular structure of cation-DOM precipitates. Thus, stabilisation of the supramolecular structure of the DOM precipitates is subjected to dynamics in soils.