Small molecule–biopolymer interactions: Ultraviolet–visible and fluorescence spectroscopy and chemometrics

Interaction of normelinonine F and related N-methyl-β-carbolines derivatives with bovine serum albumin. Spectroscopic profiles, multivariate analysis and theoretical calculations

β-carbolines (βCs) represent a large family of bioactive alkaloids, including norharmane and normelinonine F, known for their diverse pharmacological activities. The effects of these alkaloids may depend, among other factors, on their delivery, accumulation in different subcellular compartments, and interactions with biomacromolecules such as serum albumins. In this study, we investigated the pH dependence of the interactions between bovine serum albumin (BSA) and four βCs (norharmane, normelinonine F, and their corresponding N(9)-methyl derivatives) using UV-vis and fluorescence spectroscopy, combined with multivariate analysis and molecular docking. This selected set of N-methyl derivatives provides valuable insights into molecular-level binding interactions, clarifying aspects observed in previous studies. The results reveal a distinct spectroscopic interaction pattern for quaternary βCs compared to derivatives with a free N(2)-pyridinic nitrogen. Specifically, normelinonine F and N(9)-methyl-normelinonine F exhibited weak interactions, likely with external sites (site 3, subdomain IB) and/or the protein surface. In contrast, for N(2)-unsubstituted derivatives such as norharmane and N(9)-methyl-norharmane, stronger interactions and internalization into less polar and/or hydrophobic BSA sites predominate across the investigated pH-range (4 < pH < 9), likely site 2 (subdomain IIIA). However, the interaction of the corresponding cationic species of norharmane and N(9)-methyl-norharmane with BSA remains unclear due to low interaction levels and similar UV-vis absorption and emission spectra between free and BSA-bound species.

Chemometrics in investigation of small molecule-biomacromolecule interactions: A review

Chemometrics is chemical discipline in which mathematical and statistical methods are coupled with chemical data to extract useful information which cannot be extracted by the use of conventional methods. When experimental techniques are assisted by chemometric methods, very interesting studies will be performed which enable us to obtain valuable information about the system under our study. Chemico-biological interactions are very useful studies which are performed to obtain information about binding of small molecules with biological macromolecules. Recently, these studies have been assisted by chemometric methods to perform advanced studies which can help us to have a deep insight to them. Literature survey showed us that multivariate analysis of the chemico-biological interactions is becoming popular and nowadays, chemometricians are using multivariate chemometric methods for resolving chemico-biological interactions. This article focuses on the works published in the literature to provide a background for those who are interested to work in this field and finally, the results will be discussed and concluded.

Interaction of Aldehyde dehydrogenase with acetaminophen as examined by spectroscopies and molecular docking

The interaction of acetaminophen, a non-substrate anionic ligand, with Aldehyde Dehydrogenase was studied by fluorescence, UV-Vis absorption, and circular dichroism spectroscopies under simulated physiological conditions. The fluorescence spectra and data generated showed that acetaminophen binding to ALDH is purely dynamic quenching mechanism. The acetaminophen-ALDH is kinetically rapid reversible interaction with a binding constant, Ka, of 4.91×103 L mol-1. There was an existence of second binding site of ALDH for acetaminophen at saturating acetaminophen concentration. The binding sites were non-cooperative. The thermodynamic parameters obtained suggest that Van der Waal force and hydrogen bonding played a major role in the binding of acetaminophen to ALDH. The interaction caused perturbation of the ALDH structures with an obvious reduction in the α-helix. The binding distance of 4.43 nm was obtained between Acetaminophen and ALDH. Using Ficoll 400 as macro-viscosogen and glycerol as micro-viscosogen, Stoke-Einstein empirical plot demonstrated that acetaminophen-ALDH binding was diffusion controlled. Molecular docking showed the participation of some amino acids in the complex formation with -5.3 kcal binding energy. With these, ALDH might not an excipient detoxifier of acetaminophen but could be involved in its pegylation/encapsulation.

Competitive interactions of ionic surfactants with salbutamol and bovine serum albumin: a molecular spectroscopy study with implications for salbutamol in food analysis

The effect of ionic surfactants, sodium dodecyl sulfate (SDS) and N-cetyl-N,N,N-trimethylammonium bromide (CTAB), on the interaction between β-agonist salbutamol (SAL) and bovine serum albumin (BSA) was investigated with the use of fluorescence spectroscopy (FLS) and chemometrics methods [multivariate curve resolution-alternating least-squares (MCR-ALS) and parallel factor analysis algorithm (PARAFAC)]. It was found that the binding constant of SAL to BSA in the presence of CTAB was much larger than that without this ligand. The ligand/BSA stoichiometry was 4:1, that is, (CTAB)4-BSA, and was 2:1 with the ligand, that is, (SAL)2-BSA. These results were obtained from the concentration profiles extracted by MCR-ALS for all three reactants. Quantitative information on the complex CTAB-BSA-SAL species was obtained with the resolution of the excitation-emission fluorescence three-way data matrices by PARAFAC. This research has implications for the analysis of SAL in food and might be performed in laboratories associated with organizations such as the U.S. Food and Drug Administration (FDA) and the International Olympic Committee (IOC).

Enantioselective binding interaction of the metolachlor pesticide enatiomers with bovine serum albumin--a spectroscopic analysis study

Enantioselective binding interaction of the pesticides, metolachlor (RAC-metolachlor) and its S-enantiomer (S-metolachlor), with bovine serum albumin (BSA) was investigated by fluorescence and UV-vis absorption spectroscopy. Both RAC- and S-metolachlors quenched the intrinsic fluorescence of BSA via a static mechanism, and various binding parameters indicated that electrostatic forces were involved in the binding of both of these compounds. Site marker competitive experiments demonstrated that S-metolachlor bound to site I of BSA, while R-metolachlor bound to site II, indicating the importance of enantiomeric factors for binding site selection. Further experiments showed that S-metolachlor had a higher binding affinity to BSA than R-metolachlor. The obtained spectral data were resolved with use of the multivariate curve resolution-alternating least squares method (MCR-ALS), and the extracted concentration profiles of the reacting species in the interaction were obtained. These profiles indicated that S-metolachlor was the main active constituent of RAC-metolachlor for binding with BSA, and these findings have significant implications in providing an explanation why S-metolachlor is the preferred herbicide in practice than RAC-metolachlor.