Sensing of Double‐Stranded DNA/RNA Secondary Structures by Water Soluble Homochiral Perylene Bisimide Dyes

A broad series of homochiral perylene bisimide (PBI) dyes were synthesized that are appended with amino acids and cationic side chains at the imide positions. Self‐assembly behavior of these ionic PBIs has been studied in aqueous media by UV/Vis spectroscopy, revealing formation of excitonically coupled H‐type aggregates. The interactions of these ionic PBIs with different ds‐DNA and ds‐RNA have been explored by thermal denaturation, fluorimetric titration and circular dichroism (CD) experiments. These PBIs strongly stabilized ds‐DNA/RNA against thermal denaturation as revealed by high melting temperatures of the formed PBI/polynucleotide complexes. Fluorimetric titrations showed that these PBIs bind to ds‐DNA/RNA with high binding constants depending on the number of the positive charges in the side chains. Thus, spermine‐containing PBIs with six positive charges each showed higher binding constants (logK_s=9.2–9.8) than their dioxa analogues (logK_s=6.5–7.9) having two positive charges each. Induced circular dichroism (ICD) of PBI assemblies created within DNA/RNA grooves was observed. These ICD profiles are strongly dependent on the steric demand of the chiral substituents of the amino acid units and the secondary structure of the DNA or RNA. The observed ICD effects can be explained by non‐covalent binding of excitonically coupled PBI dimer aggregates into the minor groove of DNA and major groove of RNA which is further supported by molecular modeling studies.     

Mammalian plasma membrane proteins as potential biomarkers and drug targets

Defining the plasma membrane proteome is crucial to understand the role of plasma membrane in fundamental biological processes. Change in membrane proteins is one of the first events that take place under pathological conditions, making plasma membrane proteins a likely source of potential disease biomarkers with prognostic or diagnostic potential. Membrane proteins are also potential targets for monoclonal antibodies and other drugs that block receptors or inhibit enzymes essential to the disease progress. Despite several advanced methods recently developed for the analysis of hydrophobic proteins and proteins with posttranslational modifications, integral membrane proteins are still under-represented in plasma membrane proteome. Recent advances in proteomic investigation of plasma membrane proteins, defining their roles as diagnostic and prognostic disease biomarkers and as target molecules in disease treatment, are presented.     

5,10-A2B2-type meso-substituted porphyrins--a unique class of porphyrins with a realigned dipole moment

Current applications in porphyrin chemistry require the use of unsymmetrically substituted porphyrins. Many current industrial interests in optics and biomedicine require systems with either push-pull (electron-donating and -withdrawing groups) or amphiphilic systems (hydrophobic and hydrophilic groups). In this context we present the class of 5,10-A(2)B(2)-type porphyrins for which two different substituents are positioned in diagonally opposite meso positions. Thus, the intramolecular dipole moment in these tetrapyrroles is positioned along a β-β vector passing through two pyrrole rings. This is opposite to the situation of the frequently used 5,15-A(2)BC porphyrins for which the dipole moment is oriented along a meso-meso axis. We have elaborated syntheses of the 5,10-A(2)B(2) porphyrins by using transition-metal-catalyzed transformations of 5,10-A(2) porphyrins or direct substitutions reactions thereof; this gives the target molecules in 22-77% overall yields. The compounds exhibit interesting structural, spectroscopic, and optical features and can serve as building blocks for new porphyrin arrays and applications.     

Antiradical, chelating and antioxidant activities of hydroxamic acids and hydroxyureas

Reactive oxygen species, along with reactive nitrogen species, may play an important role in the pathogenesis and progress of many diseases, including cancer, diabetes and sickle cell disease. It has been postulated that hydroxyurea, one of the main treatments in sickle cell disease, achieves its activity partly also through its antioxidant properties. A series of hydroxyurea derivatives of L- and D-amino acid amides and cycloalkyl-N-aryl-hydroxamic acids was synthesized and investigated for their radical scavenging activity, chelating properties and antioxidant activity. All the compounds showed exceptional antiradical activities. For example, free radical scavenging activities of investigated hydroxyureas were higher than the activity of standard antioxidant, butylated hydroxyanisole (BHA). Moreover, most of the investigated hydroxamic acids were stronger Fe2? ion chelators than quercetin. In addition, the investigated compounds, especially hydroxamic acids, were proven to be excellent antioxidants. They were as effective as BHA in inhibiting β-carotene-linoleic acid coupled oxidation. It is reasonable to assume that the antioxidant activity of the investigated compounds could contribute to their previously proven biological properties as cytostatic and antiviral agents.     

On the Evaluation of Antenna-Mode Currents Along Transmission Lines

In this paper, we derive an integral equation describing the antenna-mode currents along a two-wire transmission line (TL). We show that when the cross-sectional dimensions of the line are electrically small, the integral equation reduces to a pair of TL-like equations with equivalent line parameters (inductance and capacitance). The derived equations make it possible to compute the antenna-mode currents using any traditional TL coupling code with appropriate parameters. The derived equations are tested against numerical results obtained using numerical electromagnetics code (NEC), and reasonably good agreement is found     

Salting-out effects in aqueous ionic liquid solutions: cloud-point temperature shifts

The effects of the addition of three inorganic salts, namely, NaCl, Na(2)SO(4), and Na(3)PO(4), on the liquid-liquid (L-L) phase diagram of aqueous solutions containing the model ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF(4)], were investigated. All three inorganic salts trigger salting-out effects, leading to significant upward shifts of the L-L demixing temperatures of the systems. The magnitude of the shifts depends on both the water-structuring nature of the salt and its concentration; that is, the effects are correlated with the ionic strength of the solution and the Gibbs free energy of hydration of the inorganic salt. The pH effect and the occurrence of salt precipitation in concentrated solutions are also discussed.     

Spectroscopic characterization, crystal structure determination and interaction with DNA of novel cyano substituted benzimidazole derivative

Novel cyano-substituted benzimidazole derivatives 3 and 4 were synthesized from 4-N,N-dimethylamino-benzaldehyde and 2-cyanomethyl-benzimidazole. 2-(1H-benzimidazol-2-yl)-3-(4-N,N-dimethylamino-phenyl)-acrylonitrile hydrochloride monohydrate 4 has been studied by ¹H and ¹³C NMR, IR, MS, UV/Vis and fluorescence spectroscopy and confirmed by X-ray crystal structure analysis. The interaction of 4 with ct-DNA has also been investigated by fluorescence spectroscopy and melting temperature determination experiment. According to the emission spectra recorded in the absence and presence of ct-DNA at different ratios r ([compound]/[polynucleotide]), 4 showed marked decrease in the fluorescence intensity and very strong hypochromic effect. Melting temperature experiment showed weak stabilization of double helix. To determine binding mode of 4, other additional experiments are necessary. The molecules of 4 are almost planar with the dihedral angle between benzimidazole and phenyl rings of 6.99(6)°. The protonation of nitrogen atom of benzimidazole ring is followed by π-electrons delocalization in the region resulting in C–N bond distances equality [1.341(2) and 1.337(2) Å]. Both NH groups of benzimidazole ring form intermolecular hydrogen bonds, one with the oxygen atom of water molecule [N···O 2.689(2) Å] and the other with Cl^? ion (N···Cl^? 3.051(1) Å). Except proton acceptor, water molecule acts as double proton donor in the formation of intermolecular hydrogen bonds with Cl^? ion [O···Cl^? 3.126(2) and 3.169(2) Å]. In that way, infinite chains along [110] direction are formed.     

NMR and HPLC study of chiral selectors with naphthyl unit

Doubling of resonances in NMR spectra of chiral selectors with naphthyl group attached to the tertiary amide nitrogen atom has been noticed what revealed the presence of two isomers. To test the enantiorecognition ability of these chiral selectors they are covalently bonded to the HPLC silica gel. Those kind of chiral stationary phases were compared with analogous commercial leucine chiral stationary phase. They exhibit the better enantioseparation results which indicate that the existence of cis/trans isomers does not have the negative influence on their enantioselective ability.