Unique Aggregation of Sterigmatocystin in Water Yields Strong and Specific Circular Dichroism Response Allowing Highly Sensitive and Selective Monitoring of Bio-Relevant Interactions.

We demonstrated the hitherto unknown property of the mycotoxin sterigmatocystin (STC) to provide homogeneous solutions in aqueous medium by forming a unique aggregate type (not formed by analogous aflatoxins), characterized by exceptionally strong circular dichroism (CD) bands in the 300-400 nm range. Results showed that these CD bands do not originate from intrinsic STC chirality but are a specific property of a peculiar aggregation process similar to psi-DNA CD response. Transmission electron microscopy (TEM) experiments revealed a fine fiber network resembling a supramolecular gel structure with helical fibers. Thermodynamic studies of aggregates by differential scanning calorimetry (DSC) revealed high reversibility of the dominant aggregation process. We demonstrated that the novel STC psi-CD band at 345 nm could be applied at biorelevant conditions (100 nanomolar concentration) and even in marine-salt content conditions for specific and quantitative monitoring of STC. Also, we showed that STC strongly non-covalently interacts with ds-DNA with likely toxic effects, thus contrary to the previous belief requiring prior enzyme epoxidation.

Synthesis of Glycomimetics by Diastereoselective Passerini Reaction.

We describe the utilization of bis-isopropylidene-protected d-fructose-derived aldehyde in the Passerini reaction with various acids and isocyanides. A library of densely functionalized glycomimetics bearing up to 3 carbohydrate units was obtained in high yields and diastereoselectivities. The configuration of the newly formed stereocenter was determined and the diastereoselectivity was rationalized by DFT calculations.

Supramolecular Ionic-Liquid Gels with High Ionic Conductivity.

Supramolecular ionogels were prepared by the gelation of room-temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4 ]) with (S,S)-bis(leucinol)oxalamide. Remarkably, the ionic conductivity of solutions and ionogels with low gelator concentrations is higher than that of neat [BMIm][BF4 ]. On the basis of molecular dynamics simulations and quantum mechanical calculations, the origin of this phenomenon is attributed to the higher affinity of gelator molecules towards [BF4 ](-) ions, which reduces the electrostatic attraction between [BMIm](+) and [BF4 ](-) and thus increases their mobility. With increasing gelator concentration, the ionic conductivity decreases due to the formation of a denser gelator matrix, which hinders the pathways for ionic transport. However, even for very dense ionogels, this decrease is less than one order of magnitude relative to neat [BMIm][BF4 ], and thus they can be classified as highly conductive materials with strong potential for application as functional electrolytes.

Dibenzotetraaza[14]annulene-adenine conjugate recognizes complementary poly dT among ss-DNA/ss-RNA sequences.

Among three novel DBTAA derivatives only the DBTAA-propyl-adenine conjugate showed recognition of the consecutive oligo dT sequence by increased affinity and specific induced chirooptical response in comparison to other single stranded RNA and DNA; whereby of particular importance is the up until now unique efficient differentiation between dT and rU. At variance, its close analogue DBTAA-hexyl-adenine did not reveal any selectivity between ss-DNA/RNA pointing out the important role of steric factors (linker length); moreover non-selectivity of the reference compound (, lacking adenine) stressed the importance of adenine interactions in the selectivity.

Determination of (3)J((1)H3'-(31)P) couplings in a DNA oligomer with enhanced sensitivity employing a constant-time TOCSY difference experiment.

A constant-time TOCSY difference experiment for the determination of (3)J((1)H3'-(31)P) coupling constants in non-isotope-labelled DNA oligonucleotides is presented. The method is tested on a DNA octamer and compared with the established constant-time NOESY difference method. Each (3)J((1)H3'-(31)P) coupling constant is determined from amplitude changes caused by phosphorous decoupling, which are observable on multiple cross-peaks, thus leading to a high accuracy of the value of the (3)J((1)H3'-(31)P) coupling constant. The new experiment delivers up to three times the sensitivity compared with previously reported methods.

A ferrocene-based pseudopeptide chiroptical switch.

We present a double-stranded ferrocene pseudopeptide 2b which exhibits stimuli responsive chirality inversion triggered by solvent exchange or acid addition. Compound 2b exists as a mixture of self-assembled fast exchanging oligomers which macroscopically behave as a chiroptical switch with two stable states. The ferrocene group inversion results in a distinct CD signal in the visible part of the spectrum. The inversion is accomplished through a conformational change due to a rearrangement of hydrogen bonding forcing the rotation of ferrocene rings.

Comparative study on the antioxidant and biological activities of carvacrol, thymol, and eugenol derivatives.

Four derivatives of thymol, carvacrol, and eugenol were synthesized: 4-(hydroxymethyl)-5-isopropyl-2-methylphenol, 4,4'-methylenebis(5-isopropyl-2-methyl)phenol, 4-allyl-6-(hydroxymethyl)-2-methoxyphenol, and 4-(hydroxymethyl)-2-isopropyl-5-methylphenol. The obtained derivatives showed remarkably better antioxidative properties according to 1,1-diphenyl-2-picrylhydrazyl assay (50% inhibitory concentrations = 4-156 microg/mL) and Rancimat assay (protection factors = 1.55-5.84) when compared with parent compounds and values similar to or better than those of butylated hydroxytoluene and vitamin C. At concentrations of 10 mM carvacrol derivatives had no toxic effect on viability of Escherichia coli K-12 (determined by minimum inhibitory concentrations). Other phenol derivatives showed reduced cytotoxic effect on E. coli K-12 at concentrations of 2-5 mM on the basis of 50% lethal dose measurements. In comparison with the parent compounds, phenol derivatives showed reduced cytotoxic effect for Saccharomyces cerevisiae cells (determined by yeast colony reduction). On the other hand, the majority of synthesized compounds had dose-dependent antiproliferative effects on human uterine carcinoma cells (HeLa), which makes them potentially interesting for the adjuvant experimental cancer treatments. The 4,4'-methylenebis(5-isopropyl-2-methyl)phenol derivative of carvacrol showed lower inhibiting capacity also for the HeLa cells, which makes this particular derivative attractive as an efficient antioxidant with negligible cytotoxic effects.

The secondary cell wall polymer of Geobacillus tepidamans GS5-97T: structure of different glycoforms.

Nuclear magnetic resonance spectroscopic studies of the strain-specific secondary cell wall polymer (SCWP) of the Gram-positive, moderately thermophilic organism Geobacillus tepidamans GS5-97T reveal two glycoforms consisting of identical tetrasaccharide repeating units with different chemical modifications of the amide moieties. On the basis of sugar analyses along with 1D and 2D 1H, 13C, 15N, and 31P NMR spectroscopy at natural isotope abundance, the basic backbone structure of the SCWP was established to be [beta-D-Manp-2,3-diNAcANH2-(1-->6)-alpha-D-Glcp-(1-->4)-beta-D-Manp-2,3-diNAcANH2-(1-->3)-alpha-D-GlcpNAc-(1-->]6-(1-->O)-PO2-(O-->6)-MurNAc-, with modifications of the amide groups. In one glycoform, all beta-D-Manp-2,3-diNAcANH2 (2,3-diacetamido-2,3-dideoxy-beta-D-mannopyranuronamide, ManpANH2) residues are substituted with two acetyl groups (glycoform I) at the amide group at C-6; in the other glycoform (glycoform II), only one proton of this amide group is substituted by an acetyl group. The ratio between both the glycoforms approximates 1:1.

Extraction of multiple pure component 1H and 13C NMR spectra from two mixtures: novel solution obtained by sparse component analysis-based blind decomposition.

Sparse component analysis (SCA) is demonstrated for blind extraction of three pure component spectra from only two measured mixed spectra in (13)C and (1)H nuclear magnetic resonance (NMR) spectroscopy. This appears to be the first time to report such results and that is the first novelty of the paper. Presented concept is general and directly applicable to experimental scenarios that possibly would require use of more than two mixtures. However, it is important to emphasize that number of required mixtures is always less than number of components present in these mixtures. The second novelty is formulation of blind NMR spectra decomposition exploiting sparseness of the pure components in the wavelet basis defined by either Morlet or Mexican hat wavelet. This enabled accurate estimation of the concentration matrix and number of pure components by means of data clustering algorithm and pure components spectra by means of linear programming with constraints from both (1)H and (13)C NMR experimental data. The third novelty is capability of proposed method to estimate number of pure components in demanding underdetermined blind source separation (uBSS) scenario. This is in contrast to majority of the BSS algorithms that assume this information to be known in advance. Presented results are important for the NMR spectroscopy-associated data analysis in pharmaceutical industry, medicine diagnostics and natural products research.

Non-linearity and frequency shifts of nuclear magnetic spin-noise.

We have systematically investigated the line shapes observed in proton nuclear spin-noise spectra which depend in a complex way on the properties of the resonance circuit, the number of spins present, transverse relaxation, inhomogeneous broadening, and radiation damping. Using highly sensitive high resolution probes these dependencies are investigated by way of high resolution (1)H noise power NMR spectra of liquid samples. Significant deviations from intuitive expectations are observed. Simulations based on an adapted Nyquist noise equation are used to understand and interpret the experimental findings.

Fructose-induced N-terminal glycation of enkephalins and related peptides.

The formation of glycation products in model systems consisting of fructose and the endogenous opioid peptides not containing lysine residue, such as Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu) and Met-enkephalin (Tyr-Gly-Gly-Phe-Met), or of their fragments, Tyr-Gly-Gly-Phe and Tyr-Gly-Gly, was examined. N-(2-Deoxy-aldos-2-yl)-peptides (Heyns compounds) as well as diastereoisomeric imidazolidinone compounds were identified as reaction products of N-terminal amino group glycation for each of the peptides studied. The structure of the glycation products and relative configuration of C-2 substituents on the imidazolidinone ring in diastereoisomers were determined by NMR experiments. The chemical and enzymatic stability of the fructose-derived glycated products of Leu- and Met-enkephalin was studied in phosphate-buffered saline (pH 7.4) and in human serum at 37 degrees C. The obtained results revealed that glycation increases the stability of the parent peptide to enzymatic degradation. As a result of different configuration at the newly formed stereogenic center, large stability differences in the 2S* and 2R* isomers of the imidazolidinone compounds were observed.

Homonuclear long-range correlation spectra from HMBC experiments by covariance processing.

We present a new application of covariance nuclear magnetic resonance processing based on 1H--13C-HMBC experiments which provides an effective way for establishing indirect 1H--1H and 13C--13C nuclear spin connectivity at natural isotope abundance. The method, which identifies correlated spin networks in terms of covariance between one-dimensional traces from a single decoupled HMBC experiment, derives 13C--13C as well as 1H--1H spin connectivity maps from the two-dimensional frequency domain heteronuclear long-range correlation data matrix. The potential and limitations of this novel covariance NMR application are demonstrated on two compounds: eugenyl-beta-D-glucopyranoside and an emodin-derivative.

Sugar pucker modulates the cross-correlated relaxation rates across the glycosidic bond in DNA.

The dependence of N1/9 and C1' chemical shielding (CS) tensors on the glycosidic bond orientation (chi) and sugar pucker (P) in the DNA nucleosides 2'-deoxyadenosine, 2'-deoxyguanosine, 2'-deoxycytidine, and 2'-deoxythymidine was studied using the calculation methods of quantum chemistry. The results indicate that these CS-tensors exhibit a significant degree of conformational dependence on chi and P structural parameters. The presented data test underlying assumptions of currently established methods for interpretation of cross-correlated relaxation rates between the N1/9 chemical shielding tensor and C1'-H1' dipole-dipole (Ravindranathan et al. J. Biomol. NMR 2003, 27, 365-75. Duchardt et al. J. Am. Chem. Soc. 2004, 126, 1962-70) and highlight possible limitations of these methods when applied to DNA.