Anharmonic behavior in the multisubunit protein apoferritin as revealed by quasi-elastic neutron scattering

Quasi-elastic neutron scattering (QENS) has been used to study the deviation from Debye-law harmonic behavior in lyophilized and hydrated apoferritin, a naturally occurring, multisubunit protein. Whereas analysis of the measured mean squared displacement (msd) parameter reveals a hydration-dependent inflection above 240 K, characteristic of diffusive motion, a hydration-independent inflection is observed at 100 K. The mechanism responsible for this low-temperature anharmonic response is further investigated, via analysis of the elastic incoherent neutron scattering intensity, by applying models developed to describe side-group motion in glassy polymers. Our results suggest that the deviation from harmonic behavior is due to the onset of methyl group rotations which exhibit a broad distribution of activated processes ( E a,ave = 12.2 kJ.mol (-1), sigma = 5.0 kJ x mol (-1)). Our results are likened to those reported for other proteins.     

Thioflavin T hydroxylation at basic pH and its effect on amyloid fibril detection

The fluorescent dye thioflavin T (ThT) is commonly used for in situ amyloid fibril detection. In this work, we focused on the spectroscopic properties and chemical stability of ThT in aqueous solution as a function of pH, temperature, and dye concentration. A reversible hydroxylation process occurs in alkaline solutions, which was characterized using a combination of UV-vis absorption spectroscopy, proton NMR, and density functional theory (DFT). On the basis of these studies, we propose a chemical structure for the hydroxylated form. Finally, by means of fluorescence spectroscopy, ThT hydroxylation effects on in situ amyloid detection have been investigated, providing new insights on the efficiency of the ThT assay for quantitative fibril evaluation at basic pH.     

Comparison of the effectiveness of solid-phase and ultrasound-mediated liquid-liquid extractions to determine the volatile compounds of wine

Two ultrasound-assisted liquid–liquid extraction (LLE-I, LLE-II) methods were compared to a solid-phase extraction (SPE) protocol to assess their effectiveness for the analysis of up to 44 volatile compounds in a synthetic and several commercial white, red and “cream” wines produced in the southwest of Spain. Regardless of the extraction protocol used the highest recoveries corresponded to acids and terpene alcohols and the lowest to lactones and alcohols. In any case, it was concluded that one of the liquid–liquid extraction protocols evaluated led to higher recoveries for a greater number of odorants that could be implicated in the aroma of the wines than the solid-phase extraction. However, the SPE method also presented some advantages that should not be overlooked, like higher repeatability and throughput and lower solvent consumption.     

Homophymine A, an anti-HIV cyclodepsipeptide from the sponge Homophymia sp

A new anti-HIV cyclodepsipeptide, homophymine A, was isolated from a New Caledonian collection of the marine sponge Homophymia sp. The structure of homophymine A was determined by interpretation of spectroscopic data, acid hydrolysis, and LC-MS analysis. Homophymine A contains 11 amino acid residues and an amide-linked 3-hydroxy-2,4,6-trimethyloctanoic acid moiety. Along with four D-, two L-, and one N-methyl amino acids, it also contains four unusual amino acid residues: (2S,3S,4R)-3,4-diMe-Gln, (2R,3R,4S)-4-amino-2,3-dihydroxy-1,7-heptandioic acid, L-ThrOMe, and (2R,3R,4R)-2-amino-3-hydroxy-4,5-dimethylhexanoic acid. In a cell-based XTT assay, homophymine A exhibited cytoprotective activity against HIV-1 infection with a IC50 of 75 nM.     

Pentakis(trifluoromethyl)phenyl, a sterically crowded and electron-withdrawing group: synthesis and acidity of pentakis(trifluoromethyl)benzene, -toluene, -phenol, and -aniline

A general route to functionalized pentakis(trifluoromethyl)phenyl (C6(CF3)5) derivatives, promising building blocks for designing novel stable carbenes, radical species, superacids, weakly coordinating anions and other practically and theoretically useful species, is presented. This pertrifluoromethylation route proceeds via conveniently pregenerated (trifluoromethyl)copper (CF3Cu) species in DMF, stabilized by addition of 1,3-dimethyl-2-imidazolidinone (DMI). These species react with hexaiodobenzene at ambient temperature to give the potassium pentakis(trifluoromethyl)phenoxide along with hexakis(trifluoromethyl)benzene and pentakis(trifluoromethyl)benzene in a combined yield of 80%. A possible reaction pathway explaining the formation of pentakis(trifluoromethyl)phenoxide is proposed. Pentakis(trifluoromethyl)phenol gives rise to easily functionalized pentakis(trifluoromethyl)chlorobenzene and pentakis(trifluoromethyl)aniline. Pertrifluoromethylation of pentaiodochlorobenzene and pentaiodotoluene allows straightforward access to pentakis(trifluoromethyl)chlorobenzene and pentakis(trifluoromethyl)toluene, respectively. XRD structures of several C6(CF3)5 derivatives were determined and compared with the calculated structures. Due to the steric crowding the aromatic rings in all C6(CF3)5 derivatives are significantly distorted. The gas-phase acidities (Delta Gacid) and pKa values in different solvents (acetonitrile (AN), DMSO, water) for the title compounds and a number of related compounds have been measured. The origin of the acidifying effect of the C6(CF3)5 group has been explored using the isodesmic reactions approach.     

Glycolipids from sponges. 20. J-Coupling analysis for stereochemical assignments in furanosides: structure elucidation of vesparioside B, a glycosphingolipid from the marine sponge Spheciospongia vesparia

Reinvestigation of the glycosphingolipid composition of the marine sponge Spheciospongia vesparia revealed the presence of vesparioside B ( 2a), a new furanose-rich hexaglycosylated glycosphingolipid that is the most complex glycosphingolipid isolated from a marine sponge to date. The structure of the new compound was elucidated using extensive 2D NMR studies and chemical degradation. Particularly useful for structure elucidation of vesparioside B was a quantum mechanical computational study, showing that in furanosides a vicinal coupling constant <2.0 Hz (for H-1/H-2 or H-3/H-4) or <3.5 Hz (for H-2/H-3) is a proof of the trans orientation of the relevant protons. This general rule, combined with ROE data, allowed us to elucidate the relative stereochemistry (including anomeric configuration) of the three furanose five-membered rings.     

Inclusion complexes of 5-flucytosine with β-cyclodextrin and hydroxypropyl-β-cyclodextrin: characterization in aqueous solution and in solid state

Complexation between 5-flucytosine (5-FC), a cytosine analogue with in vitro antifungal and antiyeast activity, and β-cyclodextrins (β-cyclodextrin and hydroxypropyl-β-cyclodextrin) was studied in solution and in solid states. Complexation in solution was evaluated using solubility studies, UV–vis and ¹H-NMR. In the solid state, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), FT-IR and X-ray diffraction studies were used. UV–vis, FT-IR and ¹H-NMR spectroscopy studies showed that the complex formed occurs by complexation of piridinique base analogue into inner cavity. DSC studies showed the existence of a complex of 5-FC with β-CDs. X-ray studies confirmed the DSC results of the complex existence. Solubility studies showed that the complexed drug is forty times more soluble than free 5-FC, indicating the obtained systems as future, promising drug carriers.     

Nematic and columnar ordering of a PEG-peptide conjugate in aqueous solution

The self-assembly in aqueous solution of a PEG-peptide conjugate is studied by spectroscopy, electron microscopy, rheology and small-angle X-ray and neutron scattering (SAXS and SANS). The peptide fragment, FFKLVFF is based on fragment KLVFF of the amyloid beta-peptide, Abeta(16-20), extended by two hydrophobic phenylalanine units. This is conjugated to PEG which confers water solubility and leads to distinct self-assembled structures. Small-angle scattering reveals the formation of cylindrical fibrils comprising a peptide core and PEG corona. This constrained structure leads to a model parallel beta-sheet self-assembled structure with a radial arrangement of beta sheets. On increasing concentration, successively nematic and hexagonal columnar phases are formed. The flow-induced alignment of both structures was studied in situ by SANS using a Couette cell. Shear-induced alignment is responsible for the shear thinning behaviour observed by dynamic shear rheometry. Incomplete recovery of moduli after cessation of shear is consistent with the observation from SANS of retained orientation in the sample.     

Second-order advantage from kinetic-spectroscopic data matrices in the presence of extreme spectral overlapping A multivariate curve resolution--alternating least-squares approach

Multivariate curve resolution coupled to alternating least-squares (MCR-ALS) has been employed to model kinetic-spectroscopic second-order data, with focus on the achievement of the important second-order advantage, under conditions of extreme spectral overlapping among sample components. A series of simulated examples shows that MCR-ALS can conveniently handle the studied analytical problem unlike other second-order multivariate calibration algorithms, provided matrix augmentation is implemented in the spectral mode instead of in the usual kinetic mode. The approach has also been applied to three experimental examples, which involve the determination of: (1) the antiparkinsonian carbidopa (analyte) in the presence of levodopa as a potential interferent, both reacting with cerium (IV) to produce the fluorescent species cerium (III) with different kinetics; (2) Fe(II) (analyte) in the presence of the interferent Zn(II), both catalyzing the oxidation of methyl orange with potassium bromate; and (3) tartrazine (analyte) in the presence of the interferent brilliant blue, both oxidized with potassium bromate, with the interferent leading to a product with an absorption spectrum very similar to tartrazine. The results indicate good analytical performance towards the analytes, despite the intense spectral overlapping and the presence of unexpected constituents in the test samples.     

Spectrofluorimetric determination of benzoimidazolic pesticides: effect of p-sulfonatocalix[6]arene and cyclodextrins

The effect of the addition of a macrocyclic host (H) such as p-sulfonatocalix[6]arene (C6S), native and modified cyclodextrins (CDs), on the fluorescence of benzoimidazolic fungicides (P), like Benomyl (BY) and Carbendazim (CZ), has been studied. The fluorescence of BY in water at pH 1.000 and 25.0 degrees C was increased in the presence of C6S, alphaCD and hydroxypropyl-beta-CD (HPCD). The association constants determined by fluorescence enhancement showed weak interactions (K(A) approximately 10(1) to 10(2) M(-1)) between the fungicide with both CDs, whereas they were stronger with C6S (K(A) approximately 10(5) M(-1)). Molecular recognition of BY for C6S was mainly attributed to electrostatic interactions, and for CDs to the hydrophobic effect and hydrogen bond formation. On the other hand, the fluorescent behaviour of CZ in the presence of C6S at pH 6.994 was interpreted as the formation of two complexes with 1:1 (P:H) and 1:2 (P:H(2)) stoichiometry, the latter being less fluorescent than the free analyte. Relative fluorescence quantum yield ratios between the complexed and free BY (phi(P:H)/phi(P)) were 2.00+/-0.05, 1.40+/-0.03 and 2.8+/-0.4 for C6S, alphaCD and HPCD, respectively. The analytical parameters improved in the presence of C6S and CDs. The best limit of detection (L(D), ng mL(-1)) was 17.4+/-0.8 with HPCD. The proposed method with C6S and HPCD was successfully applied to fortified samples of tap water and orange flesh extract with good recoveries (91-106%) and R.S.D. (< or = 2%) by triplicate analysis. The method is rapid, direct and simple and needs no previous degradation or derivatization reaction.