Charmian J. O’Connor

An NMR assay for quantitating lipase activity in biphasic macroemulsions

A novel nuclear magnetic resonance (NMR) assay has been developed to monitor lipase-catalyzed esterification reactions without the need to extract and purify the individual components. The technique measures ratios of ester:alcohol signals and has been shown to be both efficient and reproducible. The assay has proven useful as a quick screen for the effect of varying conditions on the extent of esterification in various biphasic solvent systems and can be applied to both saturated and unsaturated long-chain fatty acid and alcohol substrates. The NMR ratio technique has been used to quantitate the extent of reaction in theCandida cylindracea lipase-catalyzed synthesis of oleyl palmitate, stearyl palmitate, oleyl oleate, oleylgamma-linolenate and oleyl linoleate. The identity of these products was confirmed by high-resolution mass spectrometry.

Leaving group effects in reductively triggered fragmentation of 4-nitrobenzyl carbamates

The rates and extent of release of a series of substituted anilines from 4-nitrobenzyl carbamates, following nitro group reduction by radiolytic, enzymic and chemical methods, are reported. The yield of released anilines decreased over the pH range 4–7, but was independent of the basicity of the leaving aniline. Detailed studies of the fragmentation of one example identified the 4-hydroxylamine as the key intermediate. At pH greater than 5 the released aniline 3b condenses with a reactive 4-iminoquinomethane intermediate 4a to give amine 26, thus depleting the measurable amount of aniline 3b released. At pH less than 5 the release of amine proceeds to completion. The efficiency of reductively triggered release of anilines 7 varied with small changes in the leaving group, but this was not uniformly related to aniline basicity. The competing reaction of the released aniline 3b to form amine 26 lowers the efficiency of release of 3b. This reaction occurs at the relatively high concentrations (50 μM) used in the study and indicates the released effector amine should be toxic at concentrations considerably lower than 50 μM. This highlights the need for prodrugs of very potent cytotoxic effectors to be used in tumour-directed nitroreductase enzyme-prodrug therapy.

FTIR evidence for antiparallel β-sheet structures of long oligomeric N-acetyl-l-glutamic acid benzyl esters

Abstract Relatively long oligomeric N -acetyl- l -glutamic acid benzyl esters, with exact residue numbers, have been synthesized by a stepwise procedure and their infrared (IR) spectra in the solid state and in dioxane solution have been examined. The results show that these oligomeric molecules take up an antiparallel β-sheet structure in the solid state and that this structure is preferentially stabilized upon aggregation in dioxane.

Aggregate structures of asymmetric di-alkylphosphate anions in concentrated aqueous solutions and the role of the short chain: X-ray diffraction and Raman scattering studies

The microstructures of concentrated aqueous solutions of n-butyl(n-dodecyl)phosphate (BDoP) and n-hexyl(n-dodecyl)phosphate (HDoP) anions, as asymmetric double-chain surfactants, were studied using X-ray diffraction and Raman scattering techniques. The results indicated a marked difference in the aggregate behavior between BDoP and HDoP, attributed to the difference in the extent of the steric effect of the two short chains. The Raman scattering spectra provided direct evidence of the steric effect. This marked difference in the steric effect is clearly reflected in the phase structures of the BDoP and HDoP water binary systems.

Long acyl chain induces conformational changes in oligomeric N-acyl-l-proline anions: a FTIR study

Abstract The potassium salts of N-octanoyl, N-decanoyl- and N-dodecanoyl- l -proline oligopeptides with exact residue numbers equal to 3 and 6 have been synthesized by a stepwise procedure. The conformations of the oligopeptide portions in the solid state and in aqueous solution have been examined by use of infrared absorption spectroscopy. The results have shown that the conformation of the peptide portions, which is similar to that of poly- l -proline I with a right-handed helical structure, is stabilized by the long acyl chain effect both in the solid state and in aqueous solution.

Design, synthesis and evaluation of two diastereoisomeric phosphonate inhibitors of lamb pregastric lipase

A mixture of the two diastereoisomers of (2R)-1,2-di-O-butyl-sn-glycerol-3-O-p-nitrophenyl-n-propylphosphonate, varying only in their configuration at phosphorus, was synthesised from (R)-3-O-benzyl-sn-glycerol. The diastereoisomers were separated by normal phase HPLC and fully characterised. Both diastereoisomers were irreversible inhibitors of the activity of lamb pregastric lipase (LPGL), although the isomer which eluted first in the HPLC separation was significantly more effective.

Complex, Dynamic Behavior of Extremely Asymmetric Di-n-Alkylphosphate-Anion Aggregates, the Long-Chain Effect and the Role of a Limiting Size: Cryo-TEM, SANS, and X-Ray Diffraction Studies

For extremely asymmetric n-hexyl(n-decyl)phosphate (HDeP), n-hexyl(n-dodecyl)phosphate (HDoP), and n-hexyl(n-cetyl)phosphate (HCeP), the effect of the long-chains on the dynamic behavior of their aggregate structures in water was examined by cryo-TEM imaging, SANS, and X-ray diffraction techniques. The cryo-TEM images demonstrated the complex and dynamic behavior of the aggregates, and its dependence on the length of the long-chain. Application of the one-dimensional aggregate theory to the SANS results led to the conclusion that the existence of a limiting size also depended on the length of the main long-hydrocarbon chain and affected strongly the dynamic behavior of the aggregates, causing breakage of thread-like micelles or ribbon-like aggregates. The X-ray diffraction patterns of the lyotropic liquid crystalline samples of HDeP and HCeP were used to estimate the aggregate structures of this limited size.

Time-resolved near IR and 2D-correlation spectroscopic studies of the polymerization process of 3-aminopropyltriethoxysilane

The polymerization behavior of 3-aminopropyltriethoxysilane, a process initiated by water molecules, has been examined using time-resolved Near IR and 2D Near IR correlation spectra. In the time-resolved Near IR spectra, the bands at 5184 and 5300 cm−1 have been assigned to water molecules and the silanol (SiOH) group, respectively. The intensities of the two Near IR bands decrease markedly as the reaction proceeds, indicating that water molecules and the SiOH groups are utilized in hydrolysis of the ethoxy groups and formation of a siloxane bond, respectively. It has also been found that this polymerization process is distinctly reflected in the 2D Near IR correlation spectra.

Interactions Between Steroidal Surfactants and Human Milk Lipase

The pseudo first-order rate constants of hydrolysis of 4-nitrophenylacetate, in the presence of bile salt-stimulated human milk lipase, have been measured in Bistris buffer at pH 6.5, T 310.5 K. Sodium cholate, deoxycholate and chenodeoxycholate and their taurine and glycine conjugates have been used as cofactors in the enzymic esterolytic reaction.

Kinetic Concepts in Reversed Micellar Systems

Reversed micellar systems have borrowed extensively from the nomenclature and concepts used in aqueous detergent systems, and much of the early work on surfactant aggregates in nonpolar solvents arose from the concept of modelling the active site of proteolytic enzymes. Moreover, the readiness with which quite large concentrations of water and substrate were solubilized in the polar interior of reversed micelles led to the attractive possibility of determining reaction order with respect to water.