Ion-pair Research Articles

Preparation and Properties of Crosslinked Quaternized Chitosan-Based Hydrogel Films Ionically Bonded with Acetylsalicylic Acid for Biomedical Materials.

The aim of the current study is to develop chitosan-based biomaterials which can sustainably release acetylsalicylic acid while presenting significant biological activity. Herein, an innovative ionic bonding strategy between hydroxypropyl trimethyl ammonium chloride chitosan (HACC) and acetylsalicylic acid (AA) was proposed, skillfully utilizing the electrostatic attraction of the ionic bond to achieve the controlled release of drugs. Based on this point, six crosslinked N-[(2-hydroxy-3-trimethylammonium)propyl]chitosan acetylsalicylic acid salt (CHACAA) hydrogel films with varying acetylsalicylic acid contents were prepared by a crosslinking reaction. The results of 1H nuclear magnetic resonance spectroscopy (1H NMR) and scanning electron morphology (SEM) confirmed the crosslinked structure, while the obtained hydrogel films possessed favorable thermal stability, mechanical properties, and swelling ability. In addition, the drug release behavior of the hydrogel films was also investigated. As expected, the prepared hydrogel films demonstrated the capability for the sustainable release of acetylsalicylic acid due to ion pair attraction dynamics. Furthermore, the bioactivities of CHACAA-3 and CHACAA-4 hydrogel films with acetylsalicylic acid molar equivalents of 1.25 and 1.5 times those of HACC were particularly pronounced, which not only exhibited an excellent drug sustained-release ability and antibacterial effect, but also had a higher potential for binding and scavenging inflammatory factors, including NO and TNF-α. These findings suggest that CHACAA-3 and CHACAA-4 hydrogel films hold great potential for applications in wound dressing, tissue engineering scaffolds, and drug carriers.

Electrolyte Solvation Engineering Stabilizing Anode-Free Sodium Metal Battery With 4.0V-Class Layered Oxide Cathode.

Anode-free sodium metal batteries (AFSMBs) are regarded as the "ceiling" for current sodium-based batteries. However, their practical application is hindered by the unstable electrolyte and interfacial chemistry at the high-voltage cathode and anode-free side, especially under extreme temperature conditions. Here, an advanced electrolyte design strategy based on electrolyte solvation engineering is presented, which shapes a weakly solvating anion-stabilized (WSAS) electrolyte by balancing the interaction between the Na+-solvent and Na+-anion. The special interaction constructs rich contact ion pairs (CIPs) /aggregates (AGGs) clusters at the electrode/electrolyte interface during the dynamic solvation process which facilitates the formation of a uniform and stable interfacial layer, enabling highly stable cycling of 4.0V-class layered oxide cathode from -40°C to 60°C and excellent reversibility of Na plating/stripping with an ultrahigh average CE of 99.89%. Ultimately, industrial multi-layer anode-free pouch cells using the WSAS electrolyte achieve 80% capacity remaining after 50 cycles and even deliver 74.3% capacity at -30°C. This work takes a pivotal step for the further development of high-energy-density Na batteries.

Determination of valsartan drug by ion pair complex formation method in tablet form

A rapid, simple, sensitive, spectroscopic, ion pair complex method was developed for valsartan (VAL ) in pharmaceutical forms. Resazurin dye was used to form an ion pairing complex with the drug valsartan. analytical characteristics of the proposed method are Beer’s law range =10-60 (μg/mL), correlation coefficient (R2) = 0.9976 , limit of detection (LOD) = 0.1076(µg/mL), limit of quantification (LOQ) = 0.3261 (µg/mL), recovery percentage (%Rec) = (101.9626% - 95.6074%), relative standard deviation (%RSD)= 0.6188% - 0.7148%, Molar absorption (ε)= 4659.85(L/mol.cm), Sandell's index(S) = 0.093458(μg/cm2),at wavelength 495 nm . The results showed high accuracy and precision of the proposed quantification method for the valsartan drug , and it was of high accuracy and consistent.

(1,2,5,6-η)-Cyclo-octa-1,5-diene](1-ethyl-4-iso-butyl-1,2,4-triazol-5-yl-idene)(tri-phenyl-phosphane)iridium(I) tetra-fluorido-borate di-chloro-methane hemisolvate.

A new triazole-based N-heterocyclic carbene IrI cationic complex with a tetra-fluorido-borate counter-anion and hemi-solvating di-chloro-methane, [Ir(C8H12)(C8H15N3)(C18H15P)]BF4·0.5CH2Cl2, has been synthesized and structurally characterized. There are two independent ion pairs in the asymmetric unit and one di-chloro-methane solvent mol-ecule per two ion pairs. The cationic complex exhibits a distorted square-planar conformation around the IrI atom, formed by a bidentate cyclo-octa-1,5,diene (COD) ligand, a tri-phenyl-phosphane ligand, and an N-heterocyclic carbene (NHC). There are several close non-standard H⋯F hydrogen-bonding inter-actions that orient the tetra-fluorido-borate anions with respect to the IrI complex mol-ecules. The complex shows promising catalytic activity in transfer hydrogenation reactions. The structure was refined as a non-merohedral twin, and one of the COD mol-ecules is statistically disordered.

The Interaction Of Homodimer Styrylcyanine Dyes With Sodium Dodecyl Sulfate And Triton X-100.

Solubilization of the styrylcyanine dye Sbt ((E)-2-(4-(dimethylamino)styryl)-3-methylbenzo[d]thiazol-3-ium iodide) and its homodimers Dbt-5 and Dbt-10 in aqueous solution of sodium dodecyl sulfate and Triton X-100 has been studied by steady state and picosecond time-resolved fluorescence spectroscopy. At low concentration of sodium dodecyl sulfate in solution, between Sbt, Dbt-5 dyes molecules and surfactant ion pairs are formed followed by the formation non-luminescent H-aggregates. The nature of the interaction between molecules of dyes and surfactants has been revealed. The binding constants Ks of the dyes to the surfactants, free energy changes (ΔG0), the number of dye molecules (n) included in a single micelle and photophysical parameters have been determined. The degree of solubilization of dyes in micellar solution of Triton X-100 is higher as compared to sodium dodecyl sulfate and depends on the molecular weight and size of both dye molecules and micelles.

Diphosphonic ionic liquids as anion-exchangers for palladium(II) and platinum(IV): Synthesis, complexation and selective extraction from hydrochloric solutions

The demand for platinum group metals (PGMs) continues to grow. To reduce the negative environmental impact, it is necessary to switch to secondary sources of PGMs and to improve the separation and purification processes of these metals. In this work, new phosphonium-based ionic liquids (diphosphonium salts) were synthesized as extractants for the selective recovery of palladium(II) and platinum(IV) from hydrochloric acid solutions. Substances synthesized contain a doubly-charged cation, which significantly affects the selectivity of extraction compared to singly charged phosphonium extractants. It was found that diphosphonium salts have a high extraction efficiency of metallic ions that form stable doubly-charged chloride anionic complexes. Thus, solutions of synthesized ionic liquids in 3-nitrobenzotrifluoride can selectively extract palladium(II) and platinum(IV) in the presence of all d‐metal ions studied, which are contained in PGMs secondary sources. The extraction efficiency under optimal conditions is 99.6 % and 98.5 % for palladium(II) and platinum(IV), respectively. The extraction mechanism has been investigated by X-ray diffraction, DFT calculations and 31P, 111Cd NMR spectroscopy. Extraction proceeds through the anion-exchange mechanism, however, in the case of the studied compounds, the significant role of bromide as a counterion of ligands was shown. It was found that bromide is likely included in the extracted ion pair, displacing chloride ions from anionic metal complexes during extraction.

Counterion Blockade in a Heterogeneously Charged Single-File Water Channel.

The Possion-Nernst-Planck theories fail to describe the ionic transport in Angstrom channels, where conduction deviates from Ohm's law, which is attributed to the dehydration/self-energy barrier and dissociation of Bjerrum ion pairs in previous work. Here, we find that the cations can be strongly bound to the surface charge, which blocks the ionic transport in a single-file water channel, causing nonlinear current-voltage curves. The presence of free ions significantly increases the probability of bound ions being released, resulting in an ionic current. We find that ionic conduction gradually becomes Ohmic as the surface charge density increases, but the conduction amplitude decreases due to the increased friction from the bound ions. We rationalize the ionic transport using 1D Kramers' escape theory framework, which describes nonlinear ionic current and the impact of surface charge density on the I-V curves. Our results show that the strong Coulomb interaction between the counterion and surface charge may cause ionic blockade in Angstrom channels.

Ion‐Pairing Chromonic Liquid Crystals via Alternately Stacked Assembly of Amphiphilic Charged π‐Electronic Systems

In this study, a new assembly strategy for lyotropic chromonic liquid crystals (LCLCs) is proposed using iπ–iπ interactions, mainly comprising electrostatic and dispersion forces, between charged π‐electronic systems to form stacking structures supported by the hydration of triethylene glycol (TEG) units. Meso‐TEG‐aryl‐substituted porphyrin AuIII complex, an amphiphilic π‐electronic cation, showed diverse states and assembly modes in ion pairs depending on the coexisting counteranions. The PCCp– ion pair formed a hexagonal columnar (Colh) LC phase based on a charge‐by‐charge assembly, suggesting the formation of an ordered arrangement of charged p‐electronic systems through iπ–iπ interactions, with reduced interactions between the TEG chains. Furthermore, in the presence of water, LCLC behaviors in the Colh and nematic columnar phases according to the amount of water were observed for the PCCp– ion pair via iπ–iπ interactions. Magnetic‐field‐induced orientation of the charge‐by‐charge columnar structures upon dehydration was observed. Furthermore, single‐stranded charge‐by‐charge columnar structures, as components of the LCLCs, were observed using transmission electron microscopy (TEM).

Weakly Solvating Ether‐Based Electrolyte Constructing Anion‐Derived Solid Electrolyte Interface in Graphite Anode toward High‐Stable Potassium‐Ion Batteries

AbstractLow‐cost graphite has emerged as the most promising anode material for potassium‐ion batteries (PIBs). Constructing the inorganic‐rich solid electrolyte interface (SEI) on the surface of graphite anode is crucial for achieving superior electrochemical performance of PIBs. However, the compositions of SEI formed by conventional strongly solvating electrolytes are mainly organic, leading to the SEI structure being thick and causing the co‐intercalation behavior of ions with the solvent. Herein, a weakly solvating electrolyte is applied to weaken the cation‐solvent interaction and alter the cation solvation sheath structures, conducing to the inorganic composition derived from anions also participating in the formation of SEI, together with forming a uniformly shaped SEI with superior mechanical properties, and thus improving the overall performance of PIBs. The electrolyte solvation structure rich in aggregated ion pairs (AGGs) (69%) enables remarkable potassium‐ion intercalation behavior at the graphite anode (reversible capacity of 269 mAh g−1) and highly stable plating/stripping of potassium metal anode (96.5%). As a practical device application, the assembled potassium‐ion full‐battery (PTCDA//Graphite) displays superior cycle stability. The optimizing strategy of cation solvation sheath structures offers a promising approach for developing high‐performance electrolytes and beyond.

Facile heterolytic bond splitting of molecular chlorine upon reactions with Lewis bases: Comparison with ICl and I2

AbstractFormation of molecular complexes and subsequent heterolytic halogen‐halogen bond splitting upon reactions of molecular Cl2 with nitrogen‐containing Lewis bases (LB) are computationally studied at M06‐2X/def2‐TZVPD and for selected compounds at CCSD(T)/aug‐cc‐pvtz//CCSD/aug‐cc‐pvtz levels of theory. Obtained results are compared with data for ICl and I2 molecules. Reaction pathways indicate, that in case of Cl2∙LB complexes the activation energies for the heterolytic Cl‐Cl bond splitting are lower than the activation energies of the homolytic splitting of Cl2 molecule into chlorine radicals. The heterolytic halogen splitting of molecular complexes of X2∙Py with formation of [XPy2]+… contact ion pairs in the gas phase is slightly endothermic in case of Cl2 and I2, but slightly exothermic in the case of ICl. Formation of {[ClPy2]+…}2 dimers makes the overall process exothermic. Taking into account that polar solvents favor ionic species, generation of donor‐stabilized Cl+ in the presence of the Lewis bases is expected to be favorable. Thus, in polar solvents the oxidation pathway via donor‐stabilized Cl+ species is viable alternative to the homolytic Cl‐Cl bond breaking.

Development of levamlodipine long-acting patches based on an ion-pair strategy: Investigation of the mechanism for reducing skin irritation

The aim of this study was to develop a long-acting transdermal patch of levamlodipine (LAM) using an ion-pair strategy to reduce the skin irritation induced by topical application of LAM and explore the mechanism underlying the improvement of skin irritation. The formulation was optimized through porcine in vitro transdermal experiments and rabbit in vivo skin irritation tests. The obtained formulation consisted of poly (2-Ethylhexyl acrylate-co-N-Vinyl-2-pyrrolidone-co-N-(2-Hydroxyethyl) acrylamide) (PENH) as the adhesive matrix, 13.00 % levamlodipine-sorbic acid ion-pair complex (LAM-SA) (w/w), and 10 % isopropyl myristate (IPM) (w/w), with a patch thickness of 70 μm, achieving an erythema index of 188 for rabbit skin and 117–187 for human skin (264 for rabbit skin and 110–260 for human skin in the absence of sorbic acid (SA)). In vivo rabbit and human skin erythema analysis and H&E staining verified that the optimized ion-pair patch effectively reduced skin irritation. Drug distribution experiments in the skin, ATR-FTIR, and molecular simulation were used to characterize the mechanism by which the ion-pair reduced skin irritation. Excessive accumulation of LAM in the epidermis induced secondary structural changes in keratin, resulting in skin barrier damage and inflammatory response. The formation of the LAM-SA ion pair altered physicochemical properties of LAM, reducing drug retention in the epidermis and, thereby, reducing skin irritation. This study demonstrated the potential of the ion-pair strategy to improve the safety of transdermal drug delivery system (TDDS) and provided a means for reducing skin irritation caused by the active pharmaceutical ingredient (API) itself.

A green and sensitive electromembrane extraction (EME) method for the determination of dialkylphosphates in maternal urine and amniotic fluid

Organophosphates compounds are extensively used pesticides, whose metabolites, dialkyl phosphates, are considered as bioindicators of human exposure. Recently, research has indicated that they can affect thyroid endocrine function. Pregnant women are a particularly vulnerable cohort to these effects due to concerns about prenatal exposure to environmental pollutants. For the first time an electromembrane microextraction method is proposed for the simultaneous determination of seven dialkylphosphate metabolites in maternal urine and amniotic fluid, which is compatible with mass spectrometry detection and achieves highly sensitive levels of quantitation. Dialkylphosphates were extracted from a 10 mL donor solution at pH 7 into a 50 µL acceptor solution at pH 12 using 1-octanol as the supported liquid membrane and applying 60 V for 10 min at 600 rpm. The obtained extracts were analysed by ion pair liquid chromatography coupled to a triple quadrupole mass spectrometer, using an Acquity UPLC® BEH C18 column (100 mm × 2.1 mm i.d., 1.7 µm particle size) at 30 °C. Under optimal extraction conditions, the preconcentration factors were achieved were up to 178-fold, allowing for high sensitivity levels, in the order of ng mL−1. The limits of quantitation were within 0.075 ng mL−1 (diethyl thiophosphate) and 1.67 ng mL−1 (dimethyl phosphate) in maternal urine samples and within 0.015 ng mL−1 (diethyl thiophosphate) and 0.5 ng mL−1 (dimethyl dithiophosphate) in amniotic fluid samples. The comparative study revealed a significant improvement in terms of analysis time, sensitivity, greenness, and practicality. Finally, the applicability of the method for the determination of selected dialkylphosphates was demonstrated in paired maternal urine and amniotic fluid samples. These results suggest potential placental transfer to the offspring.

Hydronium Ion Transport across the Liquid/Liquid Interface Assisted by a Phase-Transfer Catalyst: Structure and Thermodynamics Using Molecular Dynamics Simulation.

Molecular dynamics simulations are used to examine the thermodynamic and structural aspects of the transfer of the classical hydronium ion (H3O+) across a water/1,2-dichloroethane (DCE) interface assisted by the phase-transfer catalyst (PTC) tetrakis(pentafluorophenyl) borate anion (TPFB-). The free energy of transfer from water to DCE of the H3O+-TPFB- ion pair is calculated to be 6 ± 1 kcal/mol, significantly less than that of the free hydronium ion (17 ± 1 kcal/mol). The ion pair is relatively stable at the interface and in the organic phase when it is accompanied by three water molecules with a small barrier to dissociation that supports its utility as a PTC. An examination of the hydration structure that accompanies the transfer of the ion pair shows that the ion pair, like the free hydronium ion, is transferred with the assistance of a finger-like water structure.

Mechanochemically accelerated deconstruction of chemically recyclable plastics.

Plastics redesign for circularity has primarily focused on monomer chemistries enabling faster deconstruction rates concomitant with high monomer yields. Yet, during deconstruction, polymer chains interact with their reaction medium, which remains underexplored in polymer reactivity. Here, we show that, when plastics are deconstructed in reaction media that promote swelling, initial rates are accelerated by over sixfold beyond those in small-molecule analogs. This unexpected acceleration is primarily tied to mechanochemical activation of strained polymer chains; however, changes in the activity of water under polymer confinement and bond activation in solvent-separated ion pairs are also important. Together, deconstruction times can be shortened by seven times by codesigning plastics and their deconstruction processes.

C-C Bonding in Molecular Systems via Cross-Coupling-like Reactions Involving Noncovalently Bound Constituent Ions.

Carbon-based molecules are of universal importance for a huge variety of chemical and biological processes. The complication of the structure of such molecules proceeds via the bonding of carbon atoms. An efficient mechanism for such reactions proceeds via cross-coupling, related to the association of bond-terminating counter-ions. Here, an uncommon version of such a process is investigated, with at least some ions bound in the system noncovalently and/or switching the bonding mode in due course. The analyzed sample reactions involve a single C-C bond formation in environmentally relevant halocarbon species and involve alkali-halide ion-pair components. A consistent ab initio computational study predicts the related energy barriers to alter significantly in the presence of the ion pair. Different channels are checked, with the carbon-halogen bond cleavage preceding or following the actual C-C bonding and with the counter-ions located closely or farther apart. The relative heights of the corresponding energy barriers are found to be switched by the ion pair. The above results suggest a possibility of facilitating such reactions without expensive catalysts.

Rotaxane Formation from Borate Ion-Containing Crown Ether and Ammonium Ion: Enhancement of Their Association through Ion-Pairing.

We synthesized [2]rotaxanes featuring a catechol borate ion-containing crown ether and secondary ammonium ions. These rotaxane components show both ion-ion interactions and hydrogen bonds. X-ray crystallography and NMR spectroscopy allowed elucidation of the rotaxane structure. Moreover, 1H NMR spectroscopy revealed the rotaxane synthesis can be thermodynamically controlled. The binding affinity between the borate-containing crown ether and ammonium ions is enhanced by ion-pairing.

Implicit Solvent with Explicit Ions Generalized Born Model in Molecular Dynamics: Application to DNA.

The ion atmosphere surrounding highly charged biomolecules, such as nucleic acids, is crucial for their dynamics, structure, and interactions. Here, we develop an approach for the explicit treatment of ions within an implicit solvent framework suitable for atomistic simulations of biomolecules. The proposed implicit solvent/explicit ions model, GBION, is based on a modified generalized Born (GB) model; it includes separate, modified GB terms for solute-ion and ion-ion interactions. The model is implemented in the AMBER package (version 24), and its performance is thoroughly investigated in atomistic molecular dynamics (MD) simulations of double-stranded DNA on a microsecond time scale. The aggregate characteristics of monovalent (Na+ and K+) and trivalent (Cobalt Hexammine, CoHex3+) counterion distributions around double-stranded DNA predicted by the model are in reasonable agreement with the experiment (where available), all-atom explicit water MD simulations, and the expectation from the Manning condensation theory. The radial distributions of monovalent cations around DNA are reasonably close to the ones obtained using the explicit water model: expressed in units of energy, the maximum deviations of local ion concentrations from the explicit solvent reference are within 1 kBT, comparable to the corresponding deviations expected between different established explicit water models. The proposed GBION model is able to simulate DNA fragments in a large volume of solvent with explicit ions with little additional computational overhead compared with the fully implicit GB treatment of ions. Ions simulated using the developed model explore conformational space at least 2 orders of magnitude faster than in the explicit solvent. These advantages allowed us to observe and explore an unexpected "stacking" mode of DNA condensation in the presence of trivalent counterions (CoHex3+) that was revealed by recent experiments.

Towards a universal method for middle-down analysis of antibodies via proton transfer charge reduction-Orbitrap mass spectrometry.

Modern mass spectrometry technology allows for extensive sequencing of the ~ 25kDa subunits of monoclonal antibodies (mAbs) produced by IdeS proteolysis followed by disulfide bond reduction, an approach known as middle-down mass spectrometry (MD MS). However, the spectral congestion of tandem mass spectra of large polypeptides dramatically complicates fragment ion assignment. Here, we report the development and benchmark of an MD MS strategy based on the combination of different ion fragmentation techniques with proton transfer charge reduction (PTCR) to simplify the gas-phase sequencing of mAb subunits. Applied on the liquid chromatography time scale using an Orbitrap Tribrid mass spectrometer, PTCR produces easy-to-interpret mass spectra with limited ion signal overlap. We demonstrate that the accurate estimation of the number of charges submitted to the Orbitrap mass analyzer after PTCR allows for the detection of charge-reduced product ions over a wide mass-over-charge (m/z) window with low parts per million m/z accuracy. Therefore, PTCR-based MD MS analysis increases not only sequence coverage, number of uniquely identified fragments, and number of assigned complementary ion pairs, but also the general confidence in the assignment of subunit fragments. This data acquisition method can be readily applied to any class of mAbs without an apparent need for optimization, and benefits from the high resolving power of the Orbitrap mass analyzer to return sequence coverage of individual subunits exceeding 80% in a single run, and > 90% when just two experiments are combined.

Separation and identification of oligonucleotides impurities and degradation products by reversed phase ultra-high performance liquid chromatography using phenyl-bonded stationary phases without ion pairs - A step towards sustainability

This manuscript discusses the development of a reversed-phase ultra high-performance liquid chromatography (RP UHPLC) method based on phenyl-bonded stationary phases without ion-pairs for the separation and identification of oligonucleotides. The elimination of ion-pair reagents makes the proposed protocol as more compliant to the principles of green chemistry, compared to the traditional ion-pair reversed-phase liquid chromatography methods (IP RP LC). In detail, three phenyl-based stationary phases were tested, namely a C18/AR (a C18 stationary phase with the addition of aromatic groups), a Phenyl-hexyl, and a Diphenyl. Generally, the retention of oligonucleotides increases with the increase of salt concentration and the decrease of the pH, thus confirming the significant impact of van der Waals interactions, salting-out effect, and π-electrons interactions in the retention mechanism. The highest retention and best peak symmetry were observed for the C18/AR stationary phase, while the lowest retention for the Phenyl-hexyl, with retention influenced by the type of salt in the mobile phase. The obtained methods using C18/AR stationary phases allow for the effective separations of positional isomers and for identifying impurities and degradation products using RP UHPLC Q-TOF-MS in a comparatively short time. The application of RP UHPLC Q-TOF-MS provides reasonable selectivity for the resolution of 33 impurities and two degradation products. Both groups of compounds are mainly 3′N and 5′N-shortmers, but in the case of impurities, modifications of cyclic phosphate and phosphate groups were also identified. Nevertheless, Diphenyl and Phenyl-Hexyl may be applied to separate modified oligonucleotides with higher salt concentrations. The proposed separation methods without ion-pair reagents contribute to a more sustainable approach in oligonucleotide analysis.

Mass Spectrometry Imaging for the Characterization of C═C Localization in Unsaturated Lipid Isomers at the Single-Cell Level.

Unsaturated lipids with carbon-carbon double bonds (C═C) have been implicated in the pathogenesis of various diseases. While mass spectrometry imaging (MSI) has been employed to map the distribution of lipid isomers in tissue sections, the identification of lipid C═C positional isomers at the single-cell level using MSI poses a significant challenge. In this study, we developed a novel approach utilizing ToF-SIMS in conjunction with the Paternò-Büchi (P-B) photochemical reaction to characterize the C═C localization in unsaturated lipid isomers at the single-cell level. The P-B reaction was employed to produce adduct products, which were subsequently subjected to collision-induced dissociation by the primary ion beam of ToF-SIMS to generate characteristic ion pairs indicative of the presence of C═C bonds. Utilizing this approach, lipid isomers in brain and skeletal tissues from mice, as well as different cell lines, were visualized at single-cell resolution. Furthermore, distinct variations in the composition of FA 18:1 isomers across different microregions and cell types were revealed. Our P-B ToF-SIMS approach enables the accurate identification and characterization of complex lipid structures with remarkable spatial resolution and can be helpful in understanding the physiological role of these C═C positional isomers.