Multifunctional water-soluble molecular capsules based on p-phosphonic acid calix[5]arene

p-Phosphonic acid calix[5]arene forms molecular capsules in water based on two of the molecules, which can be loaded with carboplatin using intense shearing, and attached to single wall carbon nano-tubes. Spin coating of the capsules onto a substrate affords 2 nm fibres of stacked calixarenes, with the self-assembly understood using molecular modelling.     

Macropolyhedral boron-containing cluster chemistry. A synthetic approach via the auto-fusion of [6,9-(SMe2)2-arachno-B10H12

In an attempt to build up borane-based multicluster assemblies, thermolysis of [6,9-(SMe2)2-arachno-B10H12] 1 in inert hydrocarbon solution, followed by chromatographic separation, has resulted in the isolation not only of the previously established single-cluster product from this reaction, [5-(SMe2)-nido-B10H12] 2 (30%), but also the two two-cluster species [6,9-(SMe2)2-arachno-B10H11-1-(6-nido-B10H13)] 3 (20%) and [1,6-(nido-B10H13)2] 6 (ca. 0.5%) and the two three-cluster species [6,9-(SMe2)2-arachno-B10H10-1,5-(6-nido-B10H13)2] 4 (5%), characterized crystallographically, and [6,9-(SMe2)2-arachno-B10H10-1,3-(6-nido-B10H13)2] 5 (<1%), identified by NMR spectroscopy. An improved crystallographic investigation of [5-(SMe2)-nido-B10H12] 2 is also presented. The feasibility of the stability of species resulting from multiple adjacent substitution of nido-decaboranyl units on the [6,9-(SMe2)2-arachno-B10H12] skeleton is tested by DFT calculations. In an extension, to attempt the use of pre--linked two-cluster compounds as starting substrates, two-cluster [5-(SMe2)-4-(2-nido-B10H13)-nido-B10H11] 7 (0.6%) has been isolated from the reaction of SMe2 with [1,5-(nido-B10H13)2], other identified products being compound 1 (39%) and compound 3 (10.5%).     

Optimization of an electrolytic conductivity detector for determination of toxic nitrogen-containing food contaminants separated by open tubular column gas chromatography

The combination of open tubular column gas chromatography with electrolytic conductivity detection has been evaluated for the determination of nitrogen-containing pesticide residues in food extracts. Optimization of the column position at the column-detector interface was crucial to the successful operation of the detector. The signal-to-noise ratio and response stability of the detector are greatly influenced by the composition of the electrolyte solvent. Large volume splitless injections using retention gaps and optimized detector operating conditions enabled pesticide residues in food extracts to be determined at sub parts-per-million levels. Although the electrolytic conductivity detector is less sensitive than the thermionic ionization detector, its greater nitrogen selectivity can he crucial to the determination of nitrogen-containing contaminants in food extracts, particularly in complex mixtures where phosphorus-containing contaminants or matrix compounds are also present.     

Photoreactive surfactants: a facile and clean route to oxide and metal nanoparticles in reverse micelles

A new class of photoreactive surfactants (PRSs) is presented here, consisting of amphiphiles that can also act as reagents in photochemical reactions. An example PRS is cobalt 2-ethylhexanoate (Co(EH)(2)), which forms reverse micelles (RMs) in a hydrocarbon solvent, as well as mixed reversed micelles with the standard surfactant Aerosol-OT (AOT). Small-angle neutron scattering (SANS) data show that mixed AOT/PRS RMs have a spherical structure and size similar to that of pure AOT micelles. Excitation of the ligand-to-metal charge transfer (LMCT) band in the PRSs promotes electron transfer from PRS to associated metal counterions, leading to the generation of metal and metal-oxide nanoparticles inside the RMs. This work presents proof of concept for employing PRSs as precursors to obtain nearly monodisperse inorganic nanoparticles: here both Co(3)O(4) and Bi nanoparticles have been synthesized at high metal concentration (10(-2) M) by simply irradiating the RMs. These results point toward a new approach of photoreactive self-assembly, which represents a clean and straightforward route to the generation of nanomaterials.     

Rates of base-catalysed cleavage of pyridyl-, quinolyl-, picolyl- and (quinolylmethyl)-trimethylsilanes

Rates of cleavage of some picoyl- and (quinolylmethyl)-trimethylsilanes (RSiMe₃, where R = PyCH₂ or QnCH₂SiMe₃) have been measured in “90%” aqueous methanolic sodium methoxide at 50°C. Relative reactivities are: 2-PyCH₂, 1.0; 3-PyCH₂, 0.030; 4-PyCH₂, 8.9; 2-QnCH₂, 41; 3-QnCH₂, 0.161; 4-QnCH₂, 37. The rates correlate well with those for base-catalysed hydrogen-exchange in the parent carbon acids RH. Approximate pK_a's (based on the scale of ion-pair acidities in CsNHC₆H₁₁H₂NC₆H₁₁, with pK_a of 9-phenylfluorene = 18.6) for the carbon acids, RH, can be derived as follows: 2-PyCH₃, 29.5; 3-PyCH₃, 34; 4-PyCH₃, 27; 2-QnCH₃, 25; 3-QnCH₃, 32; 4-QnCH₃, 25.Rates of cleavage of pyridyl- and quinolyl-trimethylsilanes (PySiMe₃ and QnSiMe₃) by sodium hydroxide in 4 : 1 v/v Me₂SO/H₂O at 50°C have also been measured; and the relative reactivities are: 2-Py, 1.0; 3-Py, 2.9; 4-Py, 8.4; 2-Qn, 15.9; 3-Qn, 12.7; 4-Qn, 184. The sequence of reactivity differes from that for base-catalysed hydrogen-exchange at the relevant positions of pyridine and quinoline, indicating that the reactivities are not determined in both cases (if in either) solely by the stabilities of the corresponding carbanions.     

Anticancer agent development: X-ray crystal structure and keto-enol tautomerism of dimethyl 1-hydroxy-6,7-methylenedioxy-4-(3′,4′,5′-trimethoxyphenyl-trans-3,4-dihydronaphthalene-2,3-dicarboxylate

Structural and conformational information obtained from the crystal structure and solution¹H nmr investigations of the title compound are compared. The 4-aryltetralone, C₂₄H₂₄O₁₀, crystallizes as a chloroform solvate in the monoclinic space group, P2₁/n, witha=12.519(4),b=17.938(6),c=12.534(9)Å,=111.90(5)°, and D_calc=1.51 g cm^–3 forZ=4. The data for this compound were collected at –150°C. Least-squares refinement of 2796 observed [F _o5(F _o)] reflections led to the final agreement index ofR=0.062. A threefold static disorder was observed for one of the carboxyl groups. The second carboxyl group participates in an intramolecular hydrogen bond and is thus ordered. The¹H nmr spectrum revealed the title compound to exist as a keto-enol tautomeric mixture in solution. Vicinal hydrogen coupling constant analysis proved reliable in ascertaining B-ring stereochemistry of 2,3-disubstituted-4-aryltetralones.     

Gas-liquid chromatography of fecal neutral steriods.

A method is described for the analysis of fecal neutral steriods with a dual-column gas-liquid chromatography (GLC) system. After saponification of the fecal slurry, the neutral steroids were extracted with hexane. The GLC separation of the compounds and quantitation were achieved by simultaneous injection of the derivatized and derivatized aliquots of the extract onto dual colmuns under identical conditions. The neutral steroids of interest were than identified by matching the retention times with those of known standards, and identification was confirmed by use of an interfaced GLC high-resolution mass spectrometry system. The detection limit was 0.003 mg of steroid/g of fecal slurry. The pricision of the method is illustrated by a relative standard diviation of 2-10% and a recovery of neutral steroids from 73-96%. The method was applied to the determination of fecal neutral steroids in a "High protein diet in colon cancer study". A considerably larger level of coprostanone than of coprostanol was observed. Data on neutral steroids in fecal samples from subjects on different diets are the subject of a separate publication.     

X=Y=ZH Systems as potential 1,3-dipoles. Part 58: Cycloaddition route to chiral conformationally constrained (R)-pro-(S)-pro peptidomimetics

Imines of (1S,9S)-t-butyl-9-amino-octahydro-6,10-dioxo-6H-pyridazino[1,2-a][1,2]diazepine-1-carboxylate undergo thermal (toluene, 110°C) or LiBr-DBU catalysed (MeCN, room temperature) regio- and stereo-specific cycloaddition to a range of chiral dipolarophiles giving enantiopure spiro-cycloadducts in excellent yield. The reactions proceed via intermediate NH azomethine ylides and litho azomethine ylides, respectively and results in the multiplication of chiral centres from 2 (one of which is lost in the process) to 5.     

Resolution, enantiomerization kinetics, and chiroptical properties of 7,7'-dihydroxy-8,8'-biquinolyl

(+/-)-7,7'-Dihydroxy-8,8'-biquinolyl (6) was resolved into its enantiomorphic atropisomers via reverse phase (C18) chromatographic separation of epimeric bismenthyl carbonates, (-)-lk-9 and (+)-ul-9, derived from 6 and (+)-menthyl chloroformate. The faster eluting diastereoisomer, (-)-lk-9, was revealed to possess an (aS)-configurated biaryl axis by X-ray crystallographic analysis. Saponification of the separated bismenthyl carbonates gave enantioenriched samples of biquinolyl 6, and absolute stereochemical configurations were assigned to the two optical isomers as (-)-(aS)-6 and (+)-(aR)-6 by correlation with their respective progenitors, (-)-lk-9 and (+)-ul-9. First-order rate constants for the enantiomerization of 6 in water were obtained over the temperature range 316-366 K, and activation parameters were determined as DeltaH(++) = 34.0 kcal mol(-1) and DeltaS(++) = 18.7 cal mol(-1) K(-1) by Eyring plot analysis. A low level (AM1) computational study of the rotational dynamics of 6 showed excellent agreement with kinetic experimental data and suggested that enantiomerization occurs preferentially via a syn pathway. In common with (-)-(aS)-1,1'-bi-2-naphthol (BINOL), (-)-(aS)-6 showed positive exciton chirality in its electronic circular dichroism (CD) spectrum and gave a characteristic couplet composed of a positive maximum Cotton effect at 250 nm and a negative minimum at 234 nm (Delta Delta epsilon = +40 M(-1) cm(-1) at 64% ee).     

A universal temperature controlled membrane interface for the analysis of volatile and semi-volatile organic compounds

A universal temperature controlled membrane interface (TCMI) has been constructed for hollow-fibre membranes. The membrane temperature is controllable in the range -70 to 250 degrees C using an electric heater and a flow of cooled nitrogen or helium gas. Volatile and semi-volatile organic compounds may be detected either by continuous diffusion across the membrane or by in-membrane pre-concentration followed by thermal desorption into the detector. The TCMI interface is demonstrated in combination with mass spectrometry and GC-MS, for the determination of VOCs and SVOCs in aqueous and air samples and for the on-line monitoring of a bioreactor.