Surface chemical analysis of raw cotton fibres and associated materials

The surface chemical composition of raw unscoured cotton was successfully investigated by the surface analytical techniques X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The presence of non-cellulosic material at the fibre surface was established and determined to be a complex mixture of fatty acids, alcohols, alkanes, esters and glycerides. The effect of scouring and bleaching was to reduce the surface concentration of these materials but even after aqueous processing some non-cellulosic material residue was still detected at the fibre surface.     

Rotational barrier for 1-acetyl-2-(p-methoxy benzyl)-3-pyrroline

Calculation of the rotational barriers for the trans- and cis-forms of 2-(p-methoxy)-1-acetyl-pyrroline are presented in this paper. It is found that thetrans-isomer is slightly more favourable energetically, while the rotations of the cis-form are highly impeded. Hence the relevant rotations are in thetrans-form which stabilizes its energy by forming a weak inner proton bond between the carbonyl oxygen and the pyrroline ring. The acetyl rotational barrier is of the order of 8 kcal, which is well in accord with experimental data reported in the literature for other acetyl-amide derivatives.[/p]Work supported in part by Instituto Mexicano del Petróleo.     

Can magnetic circular dichroism tackle the problem of site symmetry in solutions?

A new approach to unravel the site symmetry of lanthanides in solutions is presented. The magnetic circular dichroism spectra of Eu³⁺ in the symmetries D_3h, C_4v and D_2d are simulated. In these simulations, the main idea is to introduce the magnetic field along a 3-fold axis, being the resultant of the three equivalent X-, Y- and Z-direction of a cube. This implies that the parallel and perpendicular Zeeman effects are taken into account simultaneously.     

Electronic structure of the enolate anion of chlorophyll b

The enolate anion of chlorophyll b (Chl b) has been synthesized under deoxygenated conditions and its electronic structure characterized for the first time by ¹H NMR and electronic absorption spectroscopy. The formation of the enolate anion caused a marked perturbation to the 18 π-electron [18]diazaannulene aromatic pathway of Chl b. This perturbation appeared as noticeable upfield shifts, exceeding 1 ppm, for the meso-CH protons of the Chl b enolate anion. Nevertheless, the enolate anion remained diatropic, maintaining aromaticity in its delocalized macrocycle.     

Stereochemistry of [4 + 2] Cycloadditions of Perfluorinated Selenocarbonyls to 1, 3‐Dienes

In completely stereospecific [4+2] cycloadditions, the perfluorinated selenocarbonyls 1 and 2 react both with trans‐trans‐2, 4‐hexadiene and cis‐trans‐2, 4‐hexadiene to yield 3, 6‐dihydro‐cis‐3, 6‐dimethyl‐2H‐selenapyrans 3 , 4a and 4b . The observed stereoselectivity leads to the conclusion, that the [4+2] cycloaddition of perfluorinated selenocarbonyls follows a concerted pathway. An identical mixture of isomers was isolated when using the precursor for 2 , trimethylstannyl (pentafluoroethyl)selane, which reacts with both 1, 3‐dienes over several weeks to form a mixture of syn‐2‐fluoro‐3, 6‐dihydro‐cis‐3, 6‐dimethyl‐2‐trifluoromethyl‐2H‐selenapyran ( 4a ) and anti‐2‐fluoro‐3, 6‐dihydro‐cis‐3, 6‐dimethyl‐2‐trifluoromethyl‐2H‐selenapyran ( 4b ) in the same ratio as found for 2 , thus proving the intermediate formation of Se=C(F)CF₃ ( 2 ). Complex 2D NMR experiments were used to distinguish the isomers 4a and 4b and to assign the ¹H, ¹³C and ¹⁹F NMR data of the selenaheterocycles.     

Synthesis and Conformational Analysis of 1′‐ and 3′‐Substituted 2‐Deoxy‐2‐fluoro‐D‐ribofuranosyl Nucleosides

Convergent syntheses of the 9‐(3‐X‐2,3‐dideoxy‐2‐fluoro‐β‐D ‐ribofuranosyl)adenines 5 (X=N₃) and 7 (X=NH₂), as well as of their respective α‐anomers 6 and 8 , are described, using methyl 2‐azido‐5‐O‐benzoyl‐2,3‐dideoxy‐2‐fluoro‐β‐D ‐ribofuranoside ( 4 ) as glycosylating agent. Methyl 5‐O‐benzoyl‐2,3‐dideoxy‐2,3‐difluoro‐β‐D ‐ribofuranoside ( 12 ) was prepared starting from two precursors, and coupled with silylated N⁶‐benzoyladenine to afford, after deprotection, 2′,3′‐dideoxy‐2′,3′‐difluoroadenosine ( 13 ). Condensation of 1‐O‐acetyl‐3,5‐di‐O‐benzoyl‐2‐deoxy‐2‐fluoro‐β‐D ‐ribofuranose ( 14 ) with silylated N²‐palmitoylguanine gave, after chromatographic separation and deacylation, the N⁷‐β‐anomer 17 as the main product, along with 2′‐deoxy‐2′‐fluoroguanosine ( 15 ) and its N⁹‐α‐anomer 16 in a ratio of ca. 42 : 24 : 10. An in‐depth conformational analysis of a number of 2,3‐dideoxy‐2‐fluoro‐3‐X‐D ‐ribofuranosides (X=F, N₃, NH₂, H) as well as of purine and pyrimidine 2‐deoxy‐2‐fluoro‐D ‐ribofuranosyl nucleosides was performed using the PSEUROT (version 6.3) software in combination with NMR studies.     

Synthesis, structure and properties of SrAu3In3 and EuAu3In3—New indides with gold zig-zag chains

New indides SrAu₃In₃ and EuAu₃In₃ were synthesized by induction melting of the elements in sealed tantalum tubes. Both indides were characterized by X-ray diffraction on powders and single crystals. They crystallize with a new orthorhombic structure type: Pmmn, Z=2, a=455.26(9), b=775.9(2), c=904.9(2) pm, wR2=0.0425, 485 F² values for SrAu₃In₃ and a=454.2(2), b=768.1(6), c=907.3(6) pm, wR2=0.0495, 551 F² values for EuAu₃In₃ with 26 variables for each refinement. The gold and indium atoms build up three-dimensional [Au₃In₃] polyanionic networks, which leave distorted hexagonal channels for the strontium and europium atoms. Within the networks one observes Au2 atoms without Au-Au contacts and gold zig-zag chains (279 pm Au1-Au1 in EuAu₃In₃). The Au-In and In-In distances in EuAu₃In₃ range from 270 to 290 and from 305 to 355 pm. The europium atoms within the distorted hexagonal channels have coordination number 14 (8 Au+6 In). EuAu₃In₃ shows Curie-Weiss behavior above 50 K with an experimental magnetic moment of 8.1(1) μB/Eu atom. ¹⁵¹Eu Mössbauer spectra show a single signal at δ=−11.31(1) mm/s, compatible with divalent europium. No magnetic ordering was detected down to 3 K.     

A fluorescence spectroscopic study of the interaction between epristeride and bovin serum albumine and its analytical application

A new spectrofluorimetric method to determine epristeride (EP) has been developed, which based on the EP has a strong ability to quench the intrinsic fluorescence of bovine serum albumin (BSA). There was the relationship between the fluorescence quenching intensity of BSA (ΔF = F_BSA − F_BSA-EP) and the concentration EP. The quenching mechanism was investigated with the quenching type, the association constants, the number of binding sites and basic thermodynamic parameters. The method had been successfully applied to the analysis of EP in real samples and the obtained results were in good agreement with the results of official method-HPLC.     

Platination of [3-X-7,8-Ph2-7,8-nido-C2B9H8] (X=Et, F): Synthesis and characterisation of slipped and 1,2→1,7 isomerised products

The reaction of the labelled carborane ligand [3-Et-7,8-Ph₂-7,8-nido-C₂B₉H₈]²⁻ with a source of {Pt(PMe₂Ph)₂}²⁺ affords non-isomerised 1,2-Ph₂-3,3-(PMe₂Ph)₂-6-Et-3,1,2-closo-PtC₂B₉H₈ (1). The analogous reaction between [3-F-7,8-Ph₂-7,8-nido-C₂B₉H₈]²⁻ and {Pt(PMe₂Ph)₂}²⁺ yields 1,8-Ph₂-2,2-(PMe₂Ph)₂-4-F-2,1,8-closo-PtC₂B₉H₈ (3). Compound 1 has a heavily slipped structure (Δ 0.72 Å), which to some degree obviates the need for C atom isomerisation. However, that it is a kinetic product of the reaction is evident from the fact that it reverts to isomerised 1,8-Ph₂-2,2-(PMe₂Ph)₂-4-Et-2,1,8-closo-PtC₂B₉H₈ (2) slowly at room temperature but more rapidly with gentle warming. The heteroatom and labelled-B atom positions in the isomerised compounds 2 and 3 may be explained most simply by the rotation of a CB₂ face of an intermediate based on the structure of 1. Compounds 1–3 were characterised by a combination of spectroscopic and crystallographic techniques.