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.

The role of an L-leucine residue on the conformations of glycyl-L-leucine oligomers and its N- or C-terminal dependence: infrared absorption and Raman scattering studies.

The conformations of glycyl-L-leucine oligomers (GnL, residue number n = 3, 4, and 5) in the solid state were found to be similar to that of a polyglycine II (PGII). However, for L-leucyl-glycine oligomers (LGn; n = 3, 4, 5) in the solid state, LG3 and LG4 have already been confirmed to take a reverse-turn structure (LG3-type reverse-turn) while LG5 adopts a PGII-type helix. The present results provide evidence that the conformations of L-leucine-containing glycine oligomers depend strongly upon whether the L-leucine residue is placed in the N- or C-terminal position. For the aqueous G3L and G4L samples, we assumed that reverse-turn structures similar to the type II ß-turn, rather than the LG3-type reverse-turn, are stabilized in concentrated solution, probably as the result of aggregation. Models to explain the mechanism of these phenomena are presented.

Aggregate structures of asymmetric di-alkyl phosphate anions and the role of conformations about the polar region: SANS, cryo-TEM, Raman scattering, 13C NMR, and selective NOE studies.

The aggregate structures of two di-n-alkyl-phosphate anions (di-n-alkyl: n-butyl(n-dodecyl)(BDoP) and n-hexyl(n-dodecyl)(HDoP)) in water were studied by the use of SANS, cryo-TEM, Raman scattering, (13)C NMR, and selective NOE ((1)H{(1)H}) techniques. The results of SANS indicated that the different -CH(2)- lengths of the short chain led to a marked difference in the aggregational behavior of BDoP and HDoP. Cryo-TEM added direct images to support the average aggregation size and shape predicted by the SANS analyses. Raman scattering, (13)C NMR, and selective NOE results provided further evidence that variation of molecular conformations strongly contributed to variation in the shape of the aggregates. In particular, selective NOE was a powerful technique for investigating the dynamic structures of the hydrocarbon chains during growth of the micelles.

Concentration-resolved 2D correlation gel permeation chromatography study of aggregate-aggregate interactions in the polymerization products of triethoxysilyl-terminated polystyrene silane-coupling agent.

Concentration-resolved 2D correlation gel permeation chromatography (GPC) has been used to examine the intricate details of the HCl-catalyzed polymerization of a polymeric silane-coupling agent (SCA), triethoxysilyl-terminated polystyrene (TESiPS). The concentration-resolved 2D correlation GPC maps directly reflect the marked difference in the aggregate-aggregate interactions of dilute and concentrated monomeric units, which govern the differences in the polymerized products. There is an optimum concentration of SCA for the enhancement of interfacial strength and subsequent polymerization. Thus, the concentration-resolved 2D correlation GPC technique can be used as a powerful tool for elucidation of aggregate-aggregate interactions and reaction mechanisms in a surface- or interface-enhanced reaction system. It has been shown that the yield value of polymerization products can be improved to a marked extent by choosing a high initial monomer concentration, due to the increase in the production of oligomers. Multiple reaction processes are promoted by the self-assembly of the monomeric and oligomeric components.

Folded structures of L-leucylglycine oligopeptides and their aggregational behavior in aqueous solution: Raman scattering spectra and proton NMR spin-lattice relaxation studies.

The aggregational behavior of three L-leucylglycine oligopeptides (residue numbers of glycine are 3, 4, and 5) in aqueous solution was investigated by the use of Raman scattering and 1H NMR spin-lattice relaxation methods. The results indicate that their oligopeptides take up a folded structure to form dimeric aggregates above their critical aggregation concentration. The application of one-dimensional aggregate theory to these systems provides the following prediction. Elongation up to 6 glycine residues makes it possible to form dimeric aggregates, but further elongation (up to 7 glycine residues) makes the aggregates very unstable, and up to 8 or 9 glycine residues makes the formation of dimeric aggregates very difficult. The one-dimensional aggregate theory may be used to predict the existence of peptide aggregates through intermolecular hydrogen bonding.

Effect of apple cell walls and their extracts on the activity of dietary antioxidants.

The effect of dietary fiber in the form of apple cell walls and pectin extracts on natural antioxidants was examined. Cell walls (CW), isolated from apples ( Malus domestica Borkh. cv. "Pacific Rose"), were incubated with ascorbic acid (AA) or quercetin in N-2-hydroxyethylpiperazine- N'-2-ethanesulfonic acid (HEPES) buffer (pH 6.5) at 37 degrees C for 2 h. The resulting supernatants were characterized by a ferric reducing antioxidant power (FRAP) assay and cyclic voltammetry (CV). The experiments were repeated with pectin isolated from the apple cell walls and commercial pectins and showed that polysaccharide preparations stabilized AA effectively but offered little protection against quercetin oxidation. The water-soluble components from cell walls appeared to be responsible for the observed effects of cell-wall polysaccharide preparations on antioxidant activity.

The products from lipase-catalysed hydrolysis of bovine milkfat kill Helicobacter pylori in vitro.

Free fatty acids and monoglycerides released from milkfat by partial pregastric lipase-catalysed hydrolysis are bactericidal towards Helicobacter pylori. Two milkfat preparations were investigated: a normal bovine milkfat, and a fractionated milkfat preparation, termed ModFat, enriched in triglycerides containing short- and medium-chain fatty acids. The released products were tested for bactericidal potency against H. pylori. The potencies of the respective preparations were consistent with expected potencies calculated from individual free fatty acid and monoglyceride concentrations and their lauric acid equivalence factors (Ki). ModFat products were more bactericidal, in accordance with release of free fatty acid types of high potency, and addition of the surfactant Tween 80 to the hydrolysed lipid increased potency eight times more than did addition of lecithin. Tween 80 micelles have smaller aggregation numbers, and the mixed micelles of Tween 80/free fatty acids would be more likely to expose the bacteria to higher apparent free fatty acid concentrations.

Application of emulsifiers/stabilizers in dairy products of high rheology.

The role played by low molecular weight emulsifiers (mono- and di-glycerides) and non-dairy stabilizers (alginates, carrageenans, gums and gelatins) in the formation and stabilization of liquid milk (and specifically a functionalized milk containing omega-3), yoghurt and ice cream has been reviewed. Attention is given to the interactions that may occur between the reactive sites on polysaccharide stabilizers and milk proteins and other milk components, and to the desirable characteristics, e.g., viscosity/consistency, appearance and mouthfeel, body and texture, imparted to yoghurt and ice cream by addition of emulsifiers and gums.

Antibacterial actions of fatty acids and monoglycerides against Helicobacter pylori.

The bactericidal potencies of saturated and unsaturated fatty acids (FAs) and monoglycerides (MGs) against Helicobacter pylori were determined following short incubations with freshly harvested cells over a range of pHs. FAs and their derivatives with an equivalent-carbon number of 12 were the most potent: lauric acid had a minimum bactericidal concentration (MBC) at pH 7.4 of 1 mM, myristoleic and linolenic acid were the most potent unsaturated FAs (MBCs of 0.5 mM, pH 7.4), and monolaurin was the most potent MG (MBC 0.5 mM). Potencies of saturated FAs were increased sharply by lowering pH, and a decrease of only 0.5 pH units can cause a change from non-lethal to lethal conditions. Conversely, the bactericidal action of monolaurin was not pH-dependent. The bactericidal potencies of unsaturated FAs increased with degree of unsaturation. When more than one FA or FA plus MGs were present, their combined action was additive. Urea and endogenous urease did not protect H. pylori from the bactericidal action of FAs. These results suggest that H. pylori present in the stomach contents (but not necessarily within the mucus barrier) should be rapidly killed by the millimolar concentrations of FAs and MGs that are produced by pre-intestinal lipase(s) acting on suitable triglycerides such as milk fat.

Fourier transform IR study of aggregational behavior of N-acetyl-L- and N-butyloxycarbonyl-L-glutamic acid oligomeric benzyl esters in dioxane and benzene: beta-turn --> antiparallel beta-sheet transition.

Oligomeric N-acetyl-L-glutamic acid benzyl esters (AN(p)Z) with exact residue numbers (N(p) = 2, 3, 4, and 5) and N-butyloxycarbonyl-L-glutamic acid benzyl esters (BOCN(p)Z) with exact residue numbers (N(p) = 4, 5, 6, and 8) are synthesized by a stepwise procedure in a liquid phase. The aggregational behavior of these oligomeric molecules in dioxane and benzene is examined by Fourier transform IR spectra. In particular, the concentration dependence of the IR spectra for the AN(p)Z solutions with N(p) values of 4 (A4Z) and 5 (A5Z) shows that the predominant antiparallel beta-sheet structure is stabilized above the critical aggregation concentration (cac), while other conformations including beta-turns may coexist below the cac. This fact provides evidence that aggregation induces the conformational transition from other conformers (probably beta-turns) to an antiparallel beta-sheet form. The IR results for the A3Z and A2Z solutions indicate that specific conformers (beta-turns), which are different from the beta-sheet structure, may be preferentially stabilized upon aggregation. Thus, the critical residue number of the AN(p)Z oligopeptides, which is essential for formation of a rodlike aggregate in dioxane and benzene, is 4 or 5.

The antimicrobial properties of milkfat after partial hydrolysis by calf pregastric lipase.

Studies on the kinetic characteristics of calf pregastric lipase (EC 3.1.1.3) have shown that it preferentially releases short chain fatty acids (SCFAs) from bovine milkfat. The released fatty acids form mixed micelle structures. The aim of this investigation has been to test whether hydrolysed milkfat is antimicrobial, and how the state of the emulsion alters the bactericidal or bacteriostatic effects. Partial hydrolysis of milkfat by pregastric lipase was carried out in two types of emulsion systems, containing either Triton X-100 or casein/lecithin, plus milkfat in citrate/phosphate buffer (pH 5.0-6.0). The concentrations and compositions of fatty acids were determined by gas chromatography. The minimum percentages of hydrolysed milkfat which affected growth and survival of selected Gram-positive and Gram-negative bacteria were measured. The bacterial experiments were repeated using pure fatty acids at similar concentrations. Lauric acid (C12:0) was found to be the most potent bactericidal fatty acid against Enterococcae (Gram-positive), and caprylic acid (C8:0) was the most potent against coliforms (Gram-negative). Use of Triton X-100 for milkfat emulsification provided a more compatible medium for studying bacterial growth in the hydrolysed milkfat than did use of casein/lecithin. The results also show that the antimicrobial effects of individual fatty acids released from hydrolysed milkfat were at least additive and suggest that hydrolysis of milkfat may be a significant factor in controlling growth of organisms imbibed with food in pre-weaned animals. The amount of pregastric catalyzed triglyceride hydrolysis in the digestive tract is sufficient to produce an antibacterial concentration of fatty acids and monoglycerides.

Early weaning of calves using feedstuffs. A rationalization based on inhibition of lipolysis.

The ability of broll (a combination of the wheat-milling byproducts bran and pollard, i.e., a mixture of wheat bran, husk, and flour) and blackstrap molasses (an ingredient of calf feed) to inhibit calf pregastric lipase (CPGL)-catalyzed hydrolysis of tributyrylglycerol (TBG) has been studied in vitro. Lipolysis was measured at pH 6.5 and 37 degrees C (CPGL at 0.02 mg/mL) with stirring at 300 rpm. The broll soaked in Bis-Tris buffer (50 mM, pH 6.5) at 4 degrees C for either 24 h or 15 min, and then added to an emulsion containing TBG, before initiation of the reaction by addition of CPGL, exhibited 22% inhibitory effect. A solution of blackstrap molasses (50%, v/v) exhibited inhibitory effects of 50% in the absence and 45% in the presence of Bis-Tris buffer. The initial rate of lipolysis in the presence of the dialyzed molasses retentate (10%, v/v) increased a little, compared with the same amount of crude molasses, from a mean value of 69% to a mean value of 74%. The results have been discussed in terms of the chemical nature and composition of broll and molasses and their roles as components of feedstuffs used in development of the rumen in early weaning of calves.