Liquid-Crystal Monolayers in High Magnetic-Fields - a second-Harmonic Generation Study

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Magnetization-Induced Optical 2nd-Harmonic Generation from Magnetic Multilayers

The optical 2nd-harmonic intensity generated by magnetic multilayers appears to depend strongly on the magnetization. Combining interface and magnetic sensitivity, magnetization-induced optical 2nd-harmonic generation provides a unique tool to study magnetic interface properties. The underlying theor. anal. is given and illustrated with an example and expts. on Co/Au multilayers. [on SciFinder (R)

SELDI-TOF-MS as a rapid tool to study food related protein–peptide interactions

The use of SELDI-TOF-MS was investigated as a rapid tool to detect peptides present in a crude protein hydrolysate, which are capable to bind to intact food proteins. A purified and well characterized ß-lactoglobulin preparation was extensively hydrolyzed by the Glu-specific enzyme V8 from Staphylococcus aureus. Characterization of this hydrolysate by SELDI-TOF-MS and MALDI-TOF-MS resulted in sixteen identified peptides, which covered 98% of the primary sequence of ß-lactoglobulin. To identify peptides capable to bind non-covalently to intact proteins, the complete hydrolysate was applied to covalently bound ovalbumin, glycinin, ß-lactoglobulin and ß-casein on a SELDI ProteinChip PS-20. Six peptides (AB [f29–45], AB [f90–108], AB [f138–158], B [f63–89], AB [f1–45], AB [f135–162] bound to these four different proteins with decreasing affinity to glycinin > ovalbumin > ß-lactoglobulin > ß-casein. Peptides, which bound to these proteins were AB [f1–45] and AB [f135–158]. Using different concentrations of Triton X-100 (up to 2%) as a washing step prior to MS detection, enabled a rapid distinction between the peptides bound with respect to protein binding capacity

Separation of Interface and Bulk Contributions in 2nd-Harmonic Generation from Magnetic and Nonmagnetic Multilayers

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Protein–Peptide Interaction: Study of Heat-Induced Aggregation and Gelation of ß-Lactoglobulin in the Presence of Two Peptides from Its Own Hydrolysate

Two peptides, [f135–158] and [f135–162]-SH, were used to study the binding of the peptides to native ß-lactolobulin, as well as the subsequent effects on aggregation and gelation of ß-lactoglobulin. The binding of the peptide [f135–158] to ß-lactoglobulin at room temperature was confirmed by SELDI-TOF-MS. It was further illustrated by increased turbidity of mixed solutions of peptide and protein (at pH 7), indicating association of proteins and peptides in larger complexes. At pH below the isoelectric point of the protein, the presence of peptides did not lead to an increased turbidity, showing the absence of complexation. The protein–peptide complexes formed at pH 7 were found to dissociate directly upon heating. After prolonged heating, extensive aggregation was observed, whereas no aggregation was seen for the pure protein or pure peptide solutions. The presence of the free sulfhydryl group in [f135–162]-SH resulted in a 10 times increase in the amount of aggregation of ß-lactoglobulin upon heating, illustrating the additional effect of the free sulfhydryl group. Subsequent studies on the gel strength of heat-induced gels also showed a clear difference between these two peptides. The replacement of additional ß-lactoglobulin by [f135–158] resulted in a decrease in gel strength, whereas replacement by peptide [f135–162]-SH increased gel strength

Characteristics and Effects of Specific Peptides on Heat-Induced Aggregation of ß-Lactoglobulin

A bovine ß-lactoglobulin hydrolysate, obtained by the hydrolysis by the Glu specific enzyme Bacillus licheniformis protease (BLP), was fractionated at pH 7.0 into a soluble and an insoluble fraction and characterized by LC-MS. From the 26 peptides identified in the soluble fraction, five peptides (A[f97–112] = [f115–128], AB[f1–45], AB[f135–157], AB[f135–158], and AB[f138–162]) bound to ß-lactoglobulin at room temperature. After heating of ß-lactoglobulin in the presence of peptides, eight peptides were identified in the pellet formed, three of them belonging to the previously mentioned peptides. Principle component analysis revealed that the binding at room temperature (to ß-lactoglobulin) was related to the total hydrophobicity and the total charge of the peptides. The binding to the unfolded protein could not be attributed to distinct properties of the peptides. The presence of the peptides caused a 50% decrease in denaturation enthalpy (from 148 ± 3 kJ/mol for the protein alone to 74 ± 2 kJ/mol in the presence of peptides), while no change in secondary structure or denaturation temperature was observed. At temperature

Interface Magnetism and Possible Quantum-Well Oscillations in Ultrathin Co/Cu Films Observed by Magnetization Induced second Harmonic Generation

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