Copper(II)-peptides are widely used as industrial catalysts such as in the aerobic oxidation of organic molecules, formation of new C-H bonds and in the azide-alkyne cycloaddition reaction. The length of peptides and the effect of adding copper metal into peptides were questioned in their field of applications. Five novel histidine-based tetrapeptides with the sequences HAAD (P1), HAFD (P2), HAVD (P3), AGHD (P4) and PGHD (P5) were synthesized using the solid phase peptide scheme and analysed with high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) with percentage purities as high as 99.5%. All the peptides were positively charged (+1) and the molecular weight calculated from m/z values of MS results coincided with the theoretical molecular weight of the peptides. Copper(II)-peptides derived from these peptides and copper(II) acetate monohydrate (CuP1-CuP5) in a 1 : 2 ratio was synthesised, purified and characterised by ultravioletvisible spectroscopy (UV-Vis), ultraviolet-fluorescence spectroscopy (fluorescence) and fourier transform infrared spectroscopy (FTIR), circular dichroism spectroscopy (CD) and optical rotation polarimetry. It provided the necessary information on the secondary structure and the successful binding of copper(II) to the specific amino acids, hence leading to the putative geometry of copper(II)-peptides and the difference in the chirality of amino acids, peptides and copper(II)-peptides. The catalytic activities of the synthesised complexes were evaluated. CuP1 & CuP3 catalysed both the asymmetric aldol reactions with high enantioselectivity of p-nitrobenzaldehyde with cyclohexanone (% ee ¼ 87. 3 & 80.3, respectively) and of p-anisaldehyde with cyclohexanone (% ee ¼ 95.5 & 90.9, respectively).

In the title di­thio­carbazate compound, C17H19N3S2, the central CN2S2 residue is essentially planar (r.m.s. deviation = 0.0288 Å) and forms dihedral angles of 9.77 (8) and 77.47 (7)° with the substituted-pyridyl and p-tolyl rings, respectively, indicating a highly twisted mol­ecule; the dihedral angle between the rings is 85.56 (8)°. The configuration about the C=N bond is Z, which allows for the formation of an intra­molecular N—H⋯N(pyrid­yl) hydrogen bond. The packing features tolyl-methyl-C—H⋯N(imine), pyridyl-C—H⋯π(tol­yl) and π–π inter­actions [between pyridyl rings with a distance = 3.7946 (13) Å], which generates jagged supra­molecular layers that stack along the b axis with no directional inter­actions between them.

Laccases, oxidative copper-enzymes found in fungi and bacteria were used as the basis in the design of nona- and tetrapeptides. Laccases are known to be excellent catalysts for the degradation of phenolic xenobiotic waste. However, since solvent extraction of laccases is environmentally-unfriendly and yields obtained are low, they are less preferred compared to synthetic catalysts. The histidine rich peptides were designed based on the active site of laccase extracted from Trametes versicolor through RCSB Protein Data Bank, LOMETS and PyMol software. The peptides were synthesized using Fmoc-solid phase peptide synthesis (SPPS) with 30–40% yield. These peptides were purified and characterized using LC-MS (purities >75%), FTIR and NMR spectroscopy. Synthesized copper(II)-peptides were crystallized and then analyzed spectroscopically. Their structures were elucidated using 1D and 2D NMR. Standards ( o , m , p -cresol, 2,4-dichlorophenol) catalysed using laccase from Trametes versicolor (0.66 U/mg) were screened under different temperatures and stirring rate conditions. After optimizing the degradation of the standards with the best reaction conditions reported herein, medications with phenolic and aromatic structures such as ibuprofen, paracetamol (acetaminophen), salbutamol, erythromycin and insulin were screened using laccase (positive control), apo-peptides and copper-peptides. Their activities evaluated using GC-MS, were compared with those of peptide and copper-peptide catalysts. The tetrapeptide was found to have the higher degradation activity towards salbutamol (96.8%) compared with laccase at 42.8%. Ibuprofen (35.1%), salbutamol (52.9%) and erythromycin (49.7%) were reported to have the highest degradation activities using Cu-tetrapeptide as catalyst when compared with the other medications. Consequently, o -cresol (84%) was oxidized by Tp-Cu while the apo-peptides failed to oxidize the cresols. Copper(II)-peptides were observed to have higher catalytic activity compared to their parent peptides and the enzyme laccase for xenobiotic degradation.

Five different histidine and aspartic acid based tetrapeptides were designed using LOMETS and PyMol. They were chemically synthesized following the solid phase Fmoc-peptide synthesis protocols and were analysed using the reverse-phase High Performance Liquid Chromatography (HPLC) C 18 analytical column for the purity. The peptides were further analysed by Liquid Chromatography Mass Spectrometry (LCMS) to see if the desired peptides were synthesized systematically. Copper(II) acetate monohydrate was bound to the peptides and the best molar ratio for the binding of these metal salts to peptides was 2:1. These observations were monitored through several spectroscopic techniques. The first physical observations for the successful synthesis of metallopeptides were the colour change, the melting/decomposition points and the solubility of these metallopeptides. Due to the visible colour change of the peptides to metallopeptides, UV-Visible spectroscopy and UVFluorescence spectroscopy were used as a qualitative analysis tests and the results were in agreement with other researchers' data from similar researches.Keywords: copper(II), histidine, aspartic acid, tetrapeptides, spectroscopic Abstrak Lima tetrapeptida berbeza yang mempunyai histidine dan asid aspartik direkabentuk oleh LOMETS dan PyMol. Tetrapeptida ini disintesis mengikut skim fasa pepejal peptida dan dianalisis menggunakan fasa sonsang Kromatografi Cecair Berprestasi Tinggi (HPLC) C 18 turus analisis untuk mengetahui keaslian peptida. Kesemua peptida ini dianalisis mengunakan Kromatografi CecairSpektrometer Jisim (LC-MS) untuk mengkaji sintesis peptida secara sistematik. Kuprum(II) asetat monohidrat terikat kepada peptida dan nisbah mol yang terbaik untuk mengikat garam logam ini kepada peptida adalah 2:1. Cerapan ini telah dipantau melalui beberapa teknik spektroskopi. Pemerhatian fizikal pertama untuk logam peptida yang berjaya disintesis ialah perubahan warna, takat lebur/penguraian dan kebolehlarutan peptida logam ini. Oleh kerana perubahan warna yang nyata dalam dari peptida kepada logam peptida, spektroskopi Ultralembayung-tampak (UV-Vis) dan spektroskopi Ultralembayung-Pendafluor (UVFluorescence) digunakan sebagai ujian analisis kuantatif dan data yang diperolehi adalah setara dengan perolehan data bagi penyelidikan yang serupa.Kata kunci: Kuprum(II), histidin, asid aspartik, tetrapeptida, spektroskopi ISSN -2506 Mohd. Basyaruddin et al: SPECTROSCOPIC CHARACTERIZATION OF COPPER(II)-BASED TETRAPEPTIDES 736Introduction Metallopeptides that are easier and cheaper to synthesise when compared to metalloproteins have caught the attention of many researchers. Metallopeptides, synthesized from metal salt and peptides, are known as pseudoproteins. They imitate the applications of large proteins especially in the industrial field of catalysis as well as in biological applications [1]. Metallopeptides are hybrid structures that combine peptides and metal and in this project, the transition metal copper(II) was used, that has various roles when used as b...