Size-exclusion chromatography in 1,1,1,3,3,3-hexafluoro-2-propanol

Two molecularly imprinted polymers (MIPs) have been synthesised for the selective extraction of 4-nitrophenol (4-NP) from water samples. One polymer was synthesised via a non-covalent approach and the other via a semi-covalent approach. The selectivity of the polymers for 4-NP was evaluated when these polymers were applied in on-line solid-phase extraction (MISPE) coupled to reversed-phase HPLC. The MISPE conditions for both MIPs were optimised and a clean-up step was included to eliminate non-specific interactions. Differences between the two MIPs were observed with the non-covalent MIP being the more selective of the two, whereas the recoveries were slightly higher for the semi-covalent MIP. The performance of the imprinted polymers in the MISPE of real water samples was also evaluated.     

Polystyrene-supported phosphine oxide-catalysed Beckmann rearrangement of ketoximes in 1,1,1,3,3,3-hexafluoro-2-propanol

A polystyrene-supported phosphine oxide-catalysed Beckmann rearrangement of ketoximes in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) has been developed. Good substrate compatibility, mild reaction conditions, good yields as well as the reusability of the catalyst/solvent made this procedure more environmentally benign.     

Lewis acid catalyst free synthesis of benzimidazoles and formamidines in 1,1,1,3,3,3-hexafluoro-2-propanol

A simple, inexpensive, environmentally friendly and efficient route for the synthesis of benzimidazole and formamidine derivatives by the reaction of O-phenylenediamines or amines with orthoesters using hexafluoroisopropanol as a solvent/catalyst is described.     

The conductance of electrolytes in acetone-2-propanol and acetone-1,1,1,3,3,3-hexafluoro-2-propanol mixtures at 25°C1

Precise conductance measurements are reported for tetrabutylammonium chloride, bromide, iodie, and perchlorate and lithium chloride in acetone-2-propanol (2-PrOH) and acetone-1,1,1,3,3,3-hexafluoro-2-propanol (HFP) mixtures at 25°C. Densities, viscosities and dielectric constants of the mixtures were determined. The dielectric constant vs mole % acetone curve for the acetone (ε=19.4)-2-propanol (ε=20.5) goes through a minimum at 40% acetone (ε=17.4), while that for acetone-HFP (ε=16.8) goes through a maximum at 50% acetone (ε=26.87). The variations ofK _A with ε in acetone-HFP are in accord with the predictions of electrostatic theory, while those for acetone-2-PrOH show more complex behavior. Ionic association in these mixtures is discussed in terms of an interplay between solvent structure and a multiple-step association process.     

Harnessing the catalytic behaviour of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP): An expeditious synthesis of thioesters

A novel, efficient, metal-, base- and acid-free straightforward protocol has been developed for the construction of useful thioesters. The immense catalytic potential of HFIP for promoting the thiocarbonylation of acyl halides and thiols is disclosed. HFIP was recovered with ease and reused for further reactions without any loss of reactivity. Both aryl and alkyl thiols bearing electron-donating and electron-withdrawing groups as well as aryl- and alkyl acyl halides worked well in this reaction. Inexpensive precursors, short reaction time, obviating workup, high atom economy, and gram-scale preparation are the significant features of the developed eco-friendly route for S-carbonylation of thiols.     

Rapid and efficient thiocyanation of phenols,indoles, and anilines in 1,1,1,3,3,3-hexafluoro-2-propanol under ultrasound irradiation

An efficient ultrasound-promoted thiocyanation of phenols, indoles, and anilines in the presence of N-chlorosuccinimide and NH₄SCN using 1,1,1,3,3,3-hexafluoro-2-propanol as the solvent has been developed. The major features of the present protocol include the mild reaction conditions, short reaction times, good to excellent yields, and broad substrate scope. Moreover, scale-up synthesis can be achieved and the solvent can be easily recovered and reused.     

Convenient syntheses of 1,1,1,3,3,3-hexafluoro-2-organyl-propan-2-ols and the corresponding trimethylsilyl ethers

A new convenient synthetic procedure to obtain various 1,1,1,3,3,3-hexafluoro-2-organyl-propan-2-ols and the corresponding trimethylsilyl ethers has been worked out starting from anhydrides or activated esters of carboxylic acids and trimethyl(trifluoromethyl)silane in the presence of tetramethylammonium fluoride. Conditions for the selective formation of 1,1,1,3,3,3-hexafluoro-2-organyl-propan-2-ols as well as the trimethylsilyl derivatives have been found.     

Irreversible thermal denaturation of cytochrome c studied by electrospray mass spectrometry

This work uses electrospray ionization mass spectrometry (ESI-MS) in conjunction with hydrogen/deuterium exchange (HDX) and optical spectroscopy for characterizing the solution-phase properties of cytochrome c (cyt c) after heat exposure. Previous work demonstrated that heating results in irreversible denaturation for a subpopulation of proteins in the sample. However, that study did not investigate the physical reasons underlying this interesting effect. Here we report that the formation of oxidative modifications at elevated temperature plays a key role for the observed behavior. Tryptic digestion followed by tandem mass spectrometry is used to identify individual oxidation sites. Trp59 and Met80 are among the modified amino acids. In native cyt c both of these residues are buried deep within the protein structure, such that covalent modifications would be expected to be particularly disruptive. ESI-MS analysis after heat exposure results in a bimodal charge-state distribution. Oxidized protein appears predominantly in charge states around 11+, whereas a considerably lower degree of oxidation is observed for the 7+ and 8+ peaks. This finding confirms that different oxidation levels are associated with different solution-phase conformations. HDX measurements for different charge states are complicated by peak distortions arising from oxygen adduction. Nonetheless, comparison with simulated peak shapes clearly shows that the HDX properties are different for high- and low-charge states, confirming that interconversion between unfolded and folded conformers is blocked in solution. In addition to oxidation, partial aggregation upon heat exposure likely contributes to the formation of irreversibly denatured protein.     

A study of the thermal denaturation of ribonuclease S by electrospray ionization mass spectrometry

The thermal stability of ribonuclease S (RNase S), an enzymatically active noncovalent complex composed of a 2166-u peptide (S-peptide) and a 11,534-u protein (S-protein), was investigated by electrospray ionization mass spectrometry (ESI-MS) and capillary electrophoresis ESI-MS (CE-ESI-MS). The intensities of peaks corresponding to the RNase S complex were inversely related to both the applied nozzle-skimmer (or capillary-skimmer) voltage bias in the atmosphere-vacuum interface and the temperature of the RNase S solution. By using a heated metal capillary-skimmer interface and a room temperature solution of RNase S, the intensities of RNase S molecular ion peaks were observed to decrease with increasing metal capillary temperature. Mass spectrometric studies with both the nozzle-skimmer and capillary-skimmer interface designs allowed determination of phenomenological enthalpies for dissociation of the RNase S complex in both solution and for the electrosprayed microdroplet-gas phase species. Intact RNase S complex could also be detected with CE-ESI-MS separations by using a 10-mM ammonium bicarbonate (pH 7.9) solution as the electrophoretic buffer. These studies provide new insights into the stability of multiply charged noncovalent complexes in the gas phase and the mass spectrometric conditions required for such studies, and suggest that information regarding solution properties can be obtained by ESI-MS.     

Radiolysis of 2-propanol in presence of 2-hexanoylfuran

2-hexanoyl-5-(2-hydroxy 2-propyl)furan (HHPF), has been investigated as the principal product of radiolysis of 2-hexanoyl-furan (HF) in 2-propanol. The effect of absorbed dose on the product yields has been examined. Possible mechanisms for the formation of radiolytic products are discussed.     

Intramolecular cross-linking experiments on cytochrome c and ribonuclease A using an isotope multiplet method.

Mass spectral analysis of tryptic digests of cross-linked proteins offers considerable promise as a simple technique to probe protein structure and study protein-protein interactions. We describe the use of a 1:1 mixture of isotopically labeled and unlabeled cross-linkers, disuccinimidyladipate (DSA) and dimethyladipimidate (DMA), to enhance visualization of cross-linked peptides in a tryptic digest. Optimized intramolecular reactions of cytochrome c and ribonuclease A (RNase A) with DSA yielded an average of two cross-links per protein molecule. After digestion of the cross-linked cytochrome c with trypsin and analysis by liquid chromatography/mass spectrometry (LC/MS) and matrix-assisted laser desorption/ionization (MALDI), eight modified peptides, five cross-linked and two end-capped, were detected by virtue of their doublet character. An eighth modified peptide's identity remained ambiguous because of its inability to fragment. The lysine-lysine distance constraints obtained are discussed in the context of the known NMR and X-ray structures of cytochrome c. Analysis of cross-linked RNase A by LC/MS and MALDI yielded nine modified peptides, four of which were modified twice, as indicated by the isotopic triplets. Although seven of these peptides contained cross-links, few distance constraints were gained due to the fact that the cross-linked products were variations of modification of the same three lysine residues.     

Peroxidase-like activity of cytochrome c in the presence of anionic surfactants

Peroxidase-like activity of cytochrome c is significantly higher in the presence of anionic surfactants, sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and sodium n-dodecyl sulphate (SDS). The enhancement is due to the higher reaction rate of the cytochrome c with H₂O₂, which is the rate determining step in the peroxidase cycle of cytochrome c. An intermediate formed in the cycle rapidly oxidizes the substrates or reacts with further molecule(s) of H₂O₂, causing heme degradation. Thus, the specific microenvironment provided by anionic surfactants facilitates also degradation of heme iron by H₂O₂.     

A comparison of the thermal and photochemical oxidation of 2-propanol by two peroxoanions

The chain length (i.e., relative quantum yield) for the oxidation of 2-propanol by peroxodisulfate ion at 25°C has been studied. A number of initial experiments were carried out in order to clarify the influence of dissolved oxygen, light intensity, cupric ion, and acetone absorption. After these problems were understood, conditions satisfactory for evaluation of chain length were chosen. The chain length was found to be 500 (to within ±100). The difference between this value and the thermal oxidation chain length of 1800 at 60° is, in both direction and magnitude, as expected for a common mechanism and a low activation energy for the propagation steps. A remarkable difference is seen for comparable reactions of peroxodisulfate and peroxodiphosphate anions.     

Novel titanium(iv) complexes with 2,4-di-tert-butyl-6-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)phenol in ethene polymerization

Dinuclear (2) and mononuclear dichloride complexes (3) of titanium(iv) isopropoxide with a bidentate phenol alcohol ligand, viz., 2,4-di-tert-butyl-6-(1,1,1,3,3,3-hexafluoro-2-hydroxy-propan-2-yl)phenol, were obtained. The structures of the complexes were confirmed by X-ray diffraction. The dimeric structure of complex 2 is typical of alkoxy compounds and contains the bridging fragment Ti(??-OPrⁱ)₂Ti; the coordination polyhedron of the Ti atom is a distorted tetragonal pyramid. In complex 3, the Ti atom has a distorted octahedral environment made up of the O atoms of the ligand, the Cl atoms, and the O atoms of two coordinated propan-2-ol molecules. The catalytic properties of complexes 2 and 3 in ethene polymerization were studied with such promoters as polymethylaluminoxane (MAO), trimethylaluminum, triisobutylaluminum, diethylaluminum chloride, and Et₂AlCl-MgBu₂. Both the complexes were catalytically active (635 and 540 kg of polyethylene (PE)/(mol of Ti) h atm, respectively) only in the presence of the binary promoter Et₂AlCl-MgBu₂. The dichloride complexes obtained from a lithium or magnesium salt of the same ligand and TiCl₄ without separation from lithium and magnesium chlorides formed as by-products were catalytically active in the presence of MAO, Buⁱ ₃Al, and Me₃Al. For the catalytic system containing the dichloride complex and MgCl₂, the best promoter is Me₃Al (1082 kg of PE/(mol of Ti) h atm). The polymer obtained on all the catalytic systems is linear polyethylene characterized by high molecular weight (M_w = = 593900?C2000000 g mol^?1) and high polydispersity indices (M_w/M_n = 2.8?C15). Various conjectures were made about why lithium and magnesium chlorides have the promoting effects.     

Thermodynamic study of the thermal denaturation of a globular protein in the presence of different ligands

By means of difference UV-Vis spectra, the thermal denaturation of catalase has been studied in the presence of different surfactants: sodium perfluorooctanoate, sodium octanoate and sodium dodecanoate. These results indicate that hydrogenated surfactants play two opposite roles in the folding and stability of catalase, they act as a structure stabiliser at a low molar concentrations (enhancing T _m) and as a destabilizer at a higher concentrations (diminishing T _m). Meanwhile sodium perfluorooctanoate enhances T _m in the whole concentration range. An approach for the determination of the heat capacity, enthalpy and entropy has been made, finding that for the three studied surfactants, at all concentrations, the enthalpy term dominates the entropy term.     

Synthesis of poly[1,1,1,3,3,3-hexafluoro-2-(pentafluorophenyl)propan-2-yl methacrylate]: Thermal and optical properties of the copolymers with methyl methacrylate

Poly[1,1,1,3,3,3-hexafluoro-2-(pentafluorophenyl)propan-2-yl methacrylate (I)] was synthesized, and the copolymers of the monomer I with various compositions of methyl methacrylate (MMA) were prepared and characterized. The glass transition temperature values obtained for the copolymers were between 120 and 150 °C. The refractive indices of the copolymers were in the range of 1.4350-1.4872 at 532 nm. They were thermally stable (up to 297-323 °C), and their water absorptive properties were greatly decreased, compared with pure PMMA.     

Ligand-induced biphasic thermal denaturation of RNAase A

DSC measurements have been accomplished in aqueous solutions of bovine pancreatic ribonuclease A (RNAase A) in the presence of subsaturating amounts of 3′ cytidine monophosphate (3′ CMP) and 2′ cytidine monophosphate (2′ CMP) atpH 5.0 and 5.5. In these conditions the experimental profiles do not conform to a one-step unfolding process. It can be emphasized, as a general phenomenon, that a strong linkage between the temperature-induced protein unfolding and the ligand binding, when the ligand is less than the saturation level, causes marked distortions from a two-state transition. A purely equilibrium thermodynamic analysis gives a correct account of this behaviour and allows to simulate calorimetric curves. It is thus possible to obtain, in an indirect manner, information about the thermodynamic parameters concerning the binding process, namely the association constant and the binding enthalpy. The values ofKb and Δ_b H for 3′CMP and 2′CMP, so determined, are consistent with the literature data.