Combination of Negative Electrospray Ionization and Positive Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry as a Quantitative Approach of Acid Species in Crude Oils

Crude oils differ from one another in numerous chemical and physical properties, many of which play an important role in defining their quality and price. Generally, statistical analysis of price differentials has focused on two main properties: density and sulfur content. However, the growing significance of high total acid number (TAN) crude oils, especially from developing countries, has aroused the necessity for extending these models. Consequently, refineries must obtain real and exact information regarding crude oil quality to achieve optimal crude oil selection and processing decisions. This could be attained when a detailed molecular-level characterization is performed. The present work presents the combination of negative electrospray ionization [(−)­ESI] and positive atmospheric pressure photoionization [(+)­APPI] Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, as a prominent approach to semi-quantify the acid species comprised in crude oils. A novel polarity index is proposed that corrects the relative abundances of (−)­ESI classes, where mainly acid species are detected. By consideration of different indexes, it was possible to enhance the correlation coefficients (<i>R</i>²) from 0.579 to 0.986 between the percentage of acid compounds and TAN of crude oils, where most of the samples stand close to a linear tendency. These results avoid the deviations observed in previous works on the correlations between relative abundances of the O2 class through (−)­ESI and TAN and could support achieving optimal crude oil selection and defining their quality and price

Electrostatic Control of Peptide Side-Chain Reactivity Using Amphiphilic Homopolymer-Based Supramolecular Assemblies

Supramolecular assemblies formed by amphiphilic homopolymers with negatively charged groups in the hydrophilic segment have been designed to enable high labeling selectivity toward reactive side chain functional groups in peptides. The negatively charged interiors of the supramolecular assemblies are found to block the reactivity of protonated amines that would otherwise be reactive in aqueous solution, while maintaining the reactivity of nonprotonated amines. Simple changes to the pH of the assemblies’ interiors allow control over the reactivity of different functional groups in a manner that is dependent on the p<i>K</i>_a of a given peptide functional group. The labeling studies carried out in positively charged supramolecular assemblies and free buffer solution show that, even when the amine is protonated, labeling selectivity exists only when complementary electrostatic interactions are present, thereby demonstrating the electrostatically controlled nature of these reactions

Composition to Interfacial Activity Relationship Approach of Petroleum Sulfonates by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

In the present work, petroleum sulfonates were obtained from three atmospheric residues (ARs) and characterized by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry [(−) ESI FT-ICR MS], looking for an approach to establish a relationship between molecular composition and interfacial activity for chemical enhanced oil recovery (CEOR) formulations. From the correlation of the (−) ESI FT-ICR MS data and the interfacial tension measurements, it was possible to infer that the composition and some characteristics, such as aromatic and/or naphthenic condensation, must be taken into account to understand the performance of petroleum sulfonates. Obtained sulfonates contained mainly O3S, NO3S, O3S2, and O4S compounds, but the relative abundance of each class depended directly upon the chemical composition of the raw AR. Both carbon number (CN) and double bound equivalent (DBE) distributions of the main classes provided a way to explain the lipophilicity and interfacial activity of the sulfonates. This information can be useful to establish the initial characteristics desired in ARs to produce petroleum sulfonates with appropriate capabilities for CEOR applications