Examining the impact of ancillary ligand basicity on copper(I)–ethylene binding interactions: a DFT study

A theoretical investigation at the density functional theory level (B3LYP) has been conducted to elucidate the impact of ligand basicity on the binding interactions between ethylene and copper(I) ions in [Cu(?? ²-C₂H₄)]⁺ and a series of [Cu(L)(?? ²-C₂H₄)]⁺ complexes, where L?=?substituted 1,10-phenanthroline ligands. Molecular orbital analysis shows that binding in [Cu(?? ²-C₂H₄)]⁺ primarily involves interaction between the filled ethylene ??-bonding orbital and the empty Cu(4s) and Cu(4p) orbitals, with less interaction observed between the low energy Cu(3d) orbitals and the empty ethylene ??*-orbital. The presence of electron-donating ligands in the [Cu(L)(?? ²-C₂H₄)]⁺ complexes destabilizes the predominantly Cu(3d)-character filled frontier orbital of the [Cu(L)]⁺ fragment, promoting better overlap with the vacant ethylene ??*-orbital and increasing Cu????ethylene ??-backbonding. Moreover, the energy of the filled [Cu(L)]⁺ frontier orbital and mixing with the ethylene ??*-orbital increase with increasing pK _a of the 1,10-phenanthroline ligand. Natural bond orbital analysis reveals an increase in Cu????ethylene electron donation with addition of ligands to [Cu(?? ²-C₂H₄)]⁺ and an increase in backbonding with increasing ligand pK _a in the [Cu(L)(?? ²-C₂H₄)]⁺ complexes. Energy decomposition analysis (ALMO-EDA) calculations show that, while Cu????ethylene charge transfer (CT) increases with more basic ligands, ethylene????Cu CT and non-CT frozen density and polarization effects become less favorable, yielding little change in copper(I)?Cethylene binding energy with ligand pK _a. ALMO-EDA calculations on related [Cu(L)(NCCH₃)]⁺ complexes and calculated free energy changes for the displacement of acetonitrile by ethylene reveal a direct correlation between increasing ligand pK _a and the favorability of ethylene binding, consistent with experimental observations.     

Helical‐Ribbon Formation by a β‐Amino Acid Modified Amyloid β‐Peptide Fragment

An addition to the family : The introduction of β‐amino acid residues into a modified amyloid β peptide fragment resulted in well‐defined helical nanoribbons (see cryo‐TEM image) comprising β strands mainly oriented perpendicular to the ribbon axis. The nanoribbons order into a flow‐aligning nematic phase at higher concentration. The β‐strand nanoribbon structure is an addition to the known set of secondary structures adopted by β‐peptides.

     

Development and validation of a rapid and efficient method for simultaneous determination of methylxanthines and their metabolites in urine using monolithic HPLC columns

A new rapid, sensitive and validated HPLC method has been developed for the determination of methylxanthines and their metabolites in asthmatic patients. The method was initiated by using spiked urine samples on a silica monolithic column as a novel packing material. The mobile phase consisted of 10 mM potassium dihydrogen phosphate buffer/methanol (87.5:12.5 v/v), at a flow rate 1 mL/min. Detection was set at 274 nm. The LOQ for all the compounds ranged from 14 to 41 ng/mL. Excellent linearity was achieved over the studied range of concentration with correlation coefficients 0.9991–0.9998 (n = 6). The developed method was validated by precision and accuracy with RSD <2.55%. On extraction of the drugs and metabolites from the urine samples high recoveries were achieved ranging from 82.06 to 98.34% w/w on RP18 cartridges and methanol/chloroform (20:80 v/v) as the extraction solvent. This method has advantages over other methods using conventional C18 packings.