title: Raman and surface-enhanced Raman spectroscopy investigation of vasopressin analogues containing 1-aminocyclohexane-1-carboxylic acid residue.
abstract: In this work, Raman spectroscopy (RS) was employed to characterize molecular structures of [Arg8]vasopressin (AVP) and its [Acc2,D-Arg8]AVP, [Acc3]AVP, and [Cpa1, Acc3]AVP analogues. The RS band assignments have been proposed. To determine the mechanism of adsorption of the above-mentioned compounds adsorbed on a colloidal silver surface, surface-enhanced Raman spectra (SERS) were measured. The SERS spectra were used to determine relative proximity of the adsorbed functional groups of [corrected] investigated peptides and their orientation on the silver surface. The AVP and [Acc3]AVP SERS spectra (Acc: 1-aminocyclohexane-1-carboxylic acid) show that the L-tyrosine (Tyr) lies far from the metal surface, whereas the [Cpa1,Acc3]AVP spectrum (Cpa: 1-mercaptocyclohexaneacetic acid) provides evidence that Tyr interacts with the silver surface. These results suggest that [corrected] the binding of the Tyr-ionized phenolic group might be responsible for the selectivity of the analogues. We show that the aromatic ring of L-phenylalanine (Phe) of AVP and [Acc2,D-Arg8]AVP interacts with the silver surface. The strength of this interaction is considerably weaker for [Acc2,D-Arg8]AVP than for AVP. This might be due either to a longer distance between the Phe ring and the silver surface, or to the almost perpendicular orientation of the Phe ring towards the surface. The carbonyl group of the L-glutamine [corrected] (Gln) or L-asparagine [corrected](Asn) of AVP, [Acc2,D-Arg8]AVP, and [Acc3]AVP is strongly bound to the silver surface. We have also found that all peptides adsorb on the silver surface via sulfur atoms of the disulfide bridge, adopting a "GGG" conformation, except [Cpa1,Acc3]AVP, which accepts a "TGG" geometry.
authors.affiliation: Laser Raman Laboratory, Regional Laboratory of Physicochemical Analysis and Structural Research, Jagiellonian University, Ingardena 3 Str., 30-060 Kraków, Poland.
authors.forename: Edyta
authors.initials: E
authors.lastname: Podstawka
authors.forename: Emilia
authors.initials: E
authors.lastname: Sikorska
authors.forename: Leonard M
authors.initials: LM
authors.lastname: Proniewicz
authors.forename: Bernard
authors.initials: B
authors.lastname: Lammek
mesh_terms: D000598:Amino Acids, Cyclic / Q000737:chemistry*; D001127:Arginine Vasopressin / Q000031:analogs & derivatives* / Q000737:chemistry*; D003102:Colloids / Q000737:chemistry; D003509:Cyclohexanecarboxylic Acids / Q000737:chemistry*; D011487:Protein Conformation; D012680:Sensitivity and Specificity; D012834:Silver / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D014443:Tyrosine / Q000737:chemistry
chemical_list: D000598:Amino Acids, Cyclic; D003102:Colloids; D003509:Cyclohexanecarboxylic Acids; D001127:Arginine Vasopressin; C014966:1-aminocyclohexanecarboxylic acid; D012834:Silver; D014443:Tyrosine