G-quadruplex formation of thrombin-binding aptamer detected by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry detected the formation of the G-quadruplex structure of the thrombin-binding aptamer, d(GGTTGGTGTGGTTGG), and established its specific interaction with metal ions. One piece of evidence that the bonding in the gas phase is via the G-quadruplex form is the enhanced binding, with respect to other metal ions, of the aptamer with Sr2+, Pb2+, Ba2+, and K+, which are of similar size. Another is the lack of specific binding with controls in which the G's are replaced with A's. The most convincing evidence is the extent of H/D exchange of the gas-phase aptamer as compared to that bound to K+ and Sr2+. The latter two complexes exchange six and nine fewer H's, indicating a significant increase in protection upon binding to the metals. Mass spectrometry will be an important tool in understanding G-quadruplexes, which are particularly important in DNA telomers.     

Estimation of third virial coefficients at low reduced temperatures

We use the Clausius–Clapeyron equation to calculate third virial coefficients at low reduced temperatures. This procedure gives an alternative to predict third virial coefficients in a region where the third virial coefficient is difficult to measure. We compare the results of this method with published third virial coefficient data. Calculated third virial coefficients have average percentage deviations within 5% of the experimental values at reduced temperatures between 0.8 and 1.0.     

Methanofullerene Molecular Scaffolding: Towards C60-substituted poly(triacetylenes) and expanded radialenes,preparation of a C60–C70 hybrid derivative,and a novel macrocyclization reaction

The synthesis of (E)-hex-3-ene-l, 5-diynes and 3-methylidenepenta-1, 4-diynes with pendant methano[60]-fullerene moieties as precursors to C₆₀-substituted poly(triacetylenes) (PTAs, Fig. 1) and expanded radialenes (Fig. 2) is described. The Bingel reaction of diethyl (E)-2, 3-dialkynylbut-2-ene-1, 4-diyl bis(2-bromopropane-dioates) 5 and 6 with two C₆₀ molecules (Scheme 2) afforded the monomeric, silyl-protected PTA precursors 9 and 10 which, however, could not be effectively desilylated (Scheme 4). Also formed during the synthesis of 9 and 10 , as well as during the reaction of C₆₀ with thedesilylated analogue 16 (Scheme 5 ), were the macrocyclic products 11, 12 , and 17 , respectively, resulting from double Bingel addition to one C-sphere. Rigorous analysis revealed that this novel macrocyclization reaction proceeds with complete regio- and diastereoselectivity. The second approach to a suitable PTA monomer attempted N, N′-dicyclohexylcarbodiimide(DCC)-mediated esterification of (E)-2, 3-diethynylbut-2-ene-l, 4-diol ( 18 , Scheme 6) with mono-esterified methanofullerene-dicarboxylic acid 23 ; however, this synthesis yielded only the corresponding decarboxylated methanofullerene-carboxylic ester 27 (Scheme 7). To prevent decarboxylation, a spacer was inserted between the reacting carboxylic-acid moiety and the methane C-atom in carboxymethyl ethyl 1, 2-methano[60]fullerene-61, 61-dicarboxylate ( 28 , Scheme 8), and DCC-mediated esterification with diol 18 afforded PTA monomer 32 in good yield. The formation of a suitable monomeric precursor 38 to C₆₀-substituted expanded radialenes was achieved in 5 steps starting from dihydroxyacetone (Schemes 9 and 10), with the final step consisting of the DCC-mediated esterification of 28 with 2-[1-ethynyl(prop-2-ynylidene)]propane-1, 3-diol ( 33 ). The first mixed C₆₀-C₇₀ fullerene derivative 49 , consisting of two methano[60]fullerenes attached to a methano[70]fullerene, was also prepared and fully characterized (Scheme 13). The C_s-symmetrical hybrid compound was obtained by DCC-mediated esterification of bis[2-(2-hydroxy-ethoxy)ethyl] 1, 2-methano[70]fullerene-71, 71-dicarboxylate ( 46 ) with an excess of the C₆₀-carboxylic acid 28 . The presence of two different fullerenes in the same molecule was reflected by its UV/VIS spectrum, which displayed the characteristic absorption bands of both the C₇₀ and C₆₀ mono-adducts, but at the same time indicated no electronic interaction between the different fullerene moieties. Cyclic voltammetry showed two reversible reduction steps for 49 , and comparison with the corresponding C₇₀ and C₆₀ mono-adducts 46 and 30 indicated that the three fullerenes in the composite fullerene compound behave as independent redox centers.     

Growth and characterization of Mn- and Co-doped ZnO nanowires

A flow injection chemiluminescence method is proposed for the determination of cobalt, based on the strong catalytic effect of Cobalt(II) (1,10-phenanthroline)₃ complex on the lucigenin-periodate reaction in alkaline medium. Under the optimum experimental conditions, the chemiluminescence signal responded linearly to the concentration of cobalt(II) in the 1.0 × 10⁻⁹–3.0 × 10⁻⁷ g mL⁻¹ range with a detection limit of 4.4 × 10⁻¹⁰ g mL⁻¹ cobalt(II). The relative standard deviation for the determination of 5.0 × 10⁻⁸ g mL⁻¹ of cobalt was 2.3% in eleven replicated measurements. The method was successfully applied to the determination of cobalt(II) in pharmaceutical preparations.     

Characterization of the triplet state of tris(8-hydroxyquinoline)aluminium(III) in benzene solution

The lowest triplet state of tris(8-hydroxyquinoline)aluminium(III) (Alq3) has been prepared by pulse radiolysis/energy transfer from appropriate donors in benzene solutions and has an absorption maximum around 510 nm with a lifetime of about 50 mus. It is quenched by molecular oxygen, leading to singlet oxygen formation. From flash photolysis and singlet oxygen formation measurements, a quantum yield of triplet formation of 0.24 was determined for direct photolysis of the complex. A value of 2.10 +/- 0.10 eV was determined for the energy of the lowest triplet state by energy transfer studies and was confirmed by phosphorescence measurements on Alq3, either in the heavy atom solvent ethyl iodide or photosensitized by benzophenone in benzene. Dexter (exchange) energy transfer was observed from triplet Alq3 to platinum(II) octaethylporphyrin.     

Isolation of selenium organic species from antarctic krill after enzymatic hydrolysis

Total selenium content and its distribution in the soluble and insoluble protein-bound fractions obtained after aqueous extraction of antarctic krill samples were determined. About 26% of the total selenium (2.4 g g^–1 dry weight) was found in the supernatant; the rest was in the pellet. Isolation of low molecular selenium-containing fractions was also performed by enzymatic digestion of the protein, followed by size-exclusion chromatography in conjunction with atomic absorption spectrometry. From the applied various proteinases (pronase E, subtilisin Carlsberg, trypsin, chymotrypsin, proteinase and proteinase N from Bacillus subtilis and Novo 0.6 MPX enzyme), the treatment with pronase E led to best recovery of selenium. About 96% of the total Se was found in the hydrolysate, mainly in low molecular weight fractions. Eighty percent of the Se species were in fractions with molecular weights in the range of amino acids and short peptides. High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC-ICP-MS) allowed the identification of selenomethionine and the assumption that selenocystine or its derivatives were the main species in these fractions.     

Four isomers of [C3H8O]+˙ distinguished by collisional activation

Collisional activation of the molecular ions of 1-propanol, 2-propanol and methyl ethyl ether, and of the m/z 60 ion from 1,2-dimethoxyethane provides evidence for four distinct forms of [C₃H₈O]^+˙. Collision induced decompositions may be explained either by simple cleavages, by cyclic processes involving adjacent substituents, or by bicyclic processes of adjacent substituents. Evidence for a form of [C₃H₈O]^+˙ in which charge and radical site are separate is assembled from the spectra.     

Multiple scattering in random media I. Restricted two-body additive approximation

We present a microscopic theory of the problem of finding the properties of a particle interacting with potentials located at random sites. The sites are governed by a general probability distribution. The starting point is the multiple scattering equations for the amplitude k ₁|T |k ₂ in terms of the individual scattering amplitudes k ₁|T |k ₂. We work with quantitiesA defined by k ₁|T |k ₂=k ₁|T |k ₂exp[i(k ₁–k ₂)R ]. The theory is based on a splitting of the fundamental equation forA into equations for the mean A and the fluctuationsAA . Neglect of the fluctuations yields the quasicrystalline approximation. We rearrange the equation forAA to isolate the collective part of the fluctuations. We then make the simplest microscopic truncation which is thatAA is a restricted two-body additive function of the site positions. With the contribution of the collective fluctuations, this yields results forA that are accurate to ordert ⁴.Work supported in part by the National Science Foundation under Contract No. NSF DMRWork supported in part by the National Science Foundation under Contract No. NSF DMR     

Photophysical Properties of Some Flavones Probes in Homogeneous Media

Photophysical properties of five hydroxyflavones (HF) (some typical models of flavonols), (3 - HF, 6 - HF, 7-HF, 3, 6 - diHF and 3, 7 - diHF) were studied in homogeneous media by means of UV–vis and steady-state and time resolved fluorescence spectroscopies. Their absorption and fluorescence characteristics based on the flavonols structure are presented and discussed. It was found that the fluorescence of the flavonols depends on the nature of the solvent and on their molecular structure, especially on the position and the number of the -OH groups of the substituted phenyl ring. Attention is paid to the number of the -OH groups that influence the excited-state intramolecular proton transfer (ESIPT) process. The fluorescence quantum yield and the lifetime of the flavonols in heterogeneous media have been also determined. The results are discussed with relevance to the flavonols as sensitive fluorescence probe and to their microenvironments in the systems of biological interest and especially in a typical protein environment.