Intrinsically chiral thiolate-protected gold clusters were recently separated into their enantiomers, and their circular dichroism (CD) spectra were measured. Introduction of the chiral R-1,1′-binaphthyl-2,2′-dithiol (BINAS) into the ligand layer of rac-Au38(2-PET)24 clusters (2-PET: 2-phenylethylthiolate, SCH2CH2Ph) was shown to be diastereoselective. In this contribution, we isolated and characterized the diastereomeric reaction products of the first exchange step, A-Au38(2-PET)22(R-BINAS)1 and C-Au38(2-PET)22(R-BINAS)1 (A/C, anticlockwise/clockwise) and the second exchange product, A-Au38(2-PET)20(R-BINAS)2. The absorption spectra show minor, but significant influence of the BINAS ligand. Overall, the spectra are less defined as compared to Au38(2-PET)24, which is ascribed to symmetry breaking. The CD spectra are similar to those of the parent Au38(2-PET)24 enantiomers, readily allowing the assignment of handedness of the ligand layer. Nevertheless, some characteristic differences are found between the diastereomers. The anisotropy factors are slightly lower after ligand exchange. The second exchange step seems to confirm the trend. Inversion experiments were performed and compared to the racemization of Au38(2-PET)24. It was found that the introduction of the BINAS ligand effectively stabilizes the cluster against inversion, which involves a rearrangement of the thiolates on the cluster surface. It therefore seems that introduction of the dithiol reduces the flexibility of the gold–sulfur interface.

There is little information on how neuropeptide Y (NPY) proteolysis by peptidases occurs in serum, in part because reliable techniques are lacking to distinguish different NPY immunoreactive forms and also because the factors affecting the expression of these enzymes have been poorly studied. In the present study, LC-MS/MS was used to identify and quantify NPY fragments resulting from peptidolytic cleavage of NPY Neuropeptide Y (NPY)2 is a 36-amino acid peptide involved in the central and peripheral control of blood pressure (1-4) and in feeding behavior and obesity (5-9). NPY stimulates at least 6 types of receptors, called Y1, Y2, Y3, Y4, Y5, and y6 (10 -12). The Y1 receptor has high affinity for full-length NPY, while Y2 and Y5 receptors bind and are stimulated by fulllength and N-terminally truncated NPY. The physiological effects associated to the Y1 and Y2 receptors are the best known; exposure to a Y1 agonist causes an increase in blood pressure and potentiates postsynaptically the action of other vasoactive substances (1, 4, 13), whereas Y2 receptors are mainly located presynaptically, and upon stimulation mediate the inhibition of neurotransmitter release (14,15). NPY is a prototype of peptide whose function can be altered by proteases. Among peptidases displaying a high affinity for NPY, the primary role appears to be played by dipeptidyl peptidase IV (DPPIV, EC 3.4.14.5), a serine-type protease, also known as CD26, that releases an N-terminal dipeptide, Xaa-Xab--Xac, preferentially when Xab is a proline or an alanine residue (16). By cleaving the Tyr-Pro dipeptide off the NPY N-terminal extremity, DPPIV generates NPY 3-36 , a truncated form that loses its affinity for the Y1 receptor and becomes a Y2/Y5 receptor agonist (17, 18).NPY can also be degraded by aminopeptidase P (AmP, EC 3.4.11.9), a metalloprotease that hydrolyzes the peptide bond between the first and the second amino acid residue at the N terminus of proteins, if the second amino acid is a proline (19). AmP removes the N-terminal tyrosine from NPY to generate NPY 2-36 , a selective Y2 agonist (18,20). There is little information on how NPY cleavage by these enzymes occurs in serum, in part because reliable techniques are lacking to distinguish different NPY immunoreactive (NPYir) forms and also because the factors affecting the expression of these enzymes have been poorly studied. Recently, Frerker et al. (21) reported by MALDI-TOF mass spectrometry that NPY 1-36 is exclusively degraded by DPPIV into NPY 3-36 in EDTA-plasma but they did not provide kinetics of NPY cleavage efficiency of DPPIV. BeckSickinger and co-workers (22) studied with the same technique the metabolic stability of fluorescent N-terminally labeled NPY analogues incubated in human plasma and found that the 36th, 35th, and 33rd residues of NPY analogues may also be removed by unknown carboxypeptidases.We have set up a method using liquid chromatography coupled with tandem mass spectrometry (LC-MS n ) to selectively quantify NPY and its C-terminal fragments NPY 2-36 an...

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