Showing papers on "Water cluster published in 2021"

Confinement effects and acid strength in zeolites

Abstract: Chemical reactivity and sorption in zeolites are coupled to confinement and—to a lesser extent—to the acid strength of Bronsted acid sites (BAS). In presence of water the zeolite Bronsted acid sites eventually convert into hydronium ions. The gradual transition from zeolite Bronsted acid sites to hydronium ions in zeolites of varying pore size is examined by ab initio molecular dynamics combined with enhanced sampling based on Well-Tempered Metadynamics and a recently developed set of collective variables. While at low water content (1–2 water/BAS) the acidic protons prefer to be shared between zeolites and water, higher water contents (n > 2) invariably lead to solvation of the protons within a localized water cluster adjacent to the BAS. At low water loadings the standard free energy of the formed complexes is dominated by enthalpy and is associated with the acid strength of the BAS and the space around the site. Conversely, the entropy increases linearly with the concentration of waters in the pores, favors proton solvation and is independent of the pore size/shape. The structure of water around Bronsted acid sites in zeolites is shown to influence their catalytic activity. Here the authors shed light on confinement effects in different pores zeolites/water interfaces acidic strength by means of ab-initio molecular dynamics and enhanced sampling metadynamics techniques.

Water cluster in hydrophobic crystalline porous covalent organic frameworks.

Abstract: Progress over the past decades in water confinement has generated a variety of polymers and porous materials. However, most studies are based on a preconception that small hydrophobic pores eventually repulse water molecules, which precludes the exploration of hydrophobic microporous materials for water confinement. Here, we demonstrate water confinement across hydrophobic microporous channels in crystalline covalent organic frameworks. The frameworks are designed to constitute dense, aligned and one-dimensional polygonal channels that are open and accessible to water molecules. The hydrophobic microporous frameworks achieve full occupation of pores by water via synergistic nucleation and capillary condensation and deliver quick water exchange at low pressures. Water confinement experiments with large-pore frameworks pinpoint thresholds of pore size where confinement becomes dominated by high uptake pressure and large exchange hysteresis. Our results reveal a platform based on microporous hydrophobic covalent organic frameworks for water confinement.

Towards complete assignment of the infrared spectrum of the protonated water cluster H+(H2O)21.

Abstract: The spectroscopic features of protonated water species in dilute acid solutions have been long sought after for understanding the microscopic behavior of the proton in water with gas-phase water clusters H+(H2O)n extensively studied as bottom-up model systems. We present a new protocol for the calculation of the infrared (IR) spectra of complex systems, which combines the fragment-based Coupled Cluster method and anharmonic vibrational quasi-degenerate perturbation theory, and demonstrate its accuracy towards the complete and accurate assignment of the IR spectrum of the H+(H2O)21 cluster. The site-specific IR spectral signatures reveal two distinct structures for the internal and surface four-coordinated water molecules, which are ice-like and liquid-like, respectively. The effect of inter-molecular interaction between water molecules is addressed, and the vibrational resonance is found between the O-H stretching fundamental and the bending overtone of the nearest neighboring water molecule. The revelation of the spectral signature of the excess proton offers deeper insight into the nature of charge accommodation in the extended hydrogen-bonding network underpinning this aqueous cluster. Protonated water species have been the subject of numerous experimental and computational studies. Here the authors provide a nearly complete assignment of the experimental IR spectrum of the H+(H2O)21 water cluster based on high-level wavefunction theory and anharmonic vibrational quasi-degenerate perturbation theory.

A Molecular Model of PEMFC Catalyst Layer: Simulation on Reactant Transport and Thermal Conduction.

Abstract: Minimizing platinum (Pt) loading while reserving high reaction efficiency in the catalyst layer (CL) has been confirmed as one of the key issues in improving the performance and application of proton exchange membrane fuel cells (PEMFCs). To enhance the reaction efficiency of Pt catalyst in CL, the interfacial interactions in the three-phase interface, i.e., carbon, Pt, and ionomer should be first clarified. In this study, a molecular model containing carbon, Pt, and ionomer compositions is built and the radial distribution functions (RDFs), diffusion coefficient, water cluster morphology, and thermal conductivity are investigated after the equilibrium molecular dynamics (MD) and nonequilibrium MD simulations. The results indicate that increasing water content improves water aggregation and cluster interconnection, both of which benefit the transport of oxygen and proton in the CL. The growing amount of ionomer promotes proton transport but generates additional resistance to oxygen. Both the increase of water and ionomer improve the thermal conductivity of the C. The above-mentioned findings are expected to help design catalyst layers with optimized Pt content and enhanced reaction efficiency, and further improve the performance of PEMFCs.

The Many-Body Expansion for Aqueous Systems Revisited: II. Alkali Metal and Halide Ion-Water Interactions.

Abstract: We present a detailed study of the many-body expansion (MBE) for alkali metal and halide ion-water interactions and quantify the effect of these ions on the strength of the surrounding aqueous hydrogen bonding environment. Building on our previous work on neutral water clusters [J. P. Heindel and S. S. Xantheas, J. Chem. Theor. Comput.16 (11), 6843-6855 (2020)], we carry out the MBE for the alkali metal and halide ion-water clusters, Z+/-(H2O)9, where Z = Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I- and compare them with the results for a pure water cluster with the same number of "bodies", viz., (H2O)10. The 2-B ion-water (I-W) interaction accounts for a larger percentage of the total cluster binding energy compared to a pure water cluster of the same size, with the total 3-B term being smaller and of opposite sign (repulsive), whereas higher order terms are essentially negligible. The same oscillating behavior around zero for the MBE terms higher than the 5-B with a basis set that was reported for water clusters is also observed for the ion-water clusters considered here, with the basis set superposition error (BSSE) corrections amending this as in the water cluster case. A remarkable, linear anticorrelation between the total 2-B (I-W), the total 2-B (W-W), and also the 3-B (W-W-W) interactions is found, quantifying the effect of the different ions in disrupting and altering (weakening) the neighboring hydrogen bonded water network: stronger (I-W) interactions result in weaker (W-W) interactions. Additional linear correlations across the two series of alkali metals and halide ions were found between the 3-B (I-W-W) and the 2-B (I-W) as well as between the 3-B (I-W-W) and the 3-B (W-W-W) interactions, suggesting the existence of previously unrealized underlying physics governing these 2-B intermolecular and 3-B collective interactions. Our results further suggest a universal behavior of the two different families of ions (alkali metals and halides) for both the correlations of the various components of the total binding energies and the estimate of the 2-B BSSE correction, which is reported to follow a common profile for ion-water and water-water interactions when cast in terms of reduced distances and energies of the respective dimers. We expect the current results that quantify the interplay between ion-water and water-water interactions in aqueous clusters to impact the development of classical, ab initio-based force fields for monatomic ion solvation, whereas the insights into the nature of the BSSE to be critical in future ab initio-based, many-body molecular dynamics studies.

Hydroxy Channels-Adaptive Pathways for Selective Water Cluster Permeation.

Abstract: Artificial water channels (AWCs) are known to selectively transport water, with ion exclusion. Similarly to natural porins, AWCs encapsulate water wires or clusters, offering continuous and iterative H-bonding that plays a vital role in their stabilization. Herein, we report octyl-ureido-polyol AWCs capable of self-assembly into hydrophilic hydroxy channels. Variants of ethanol, propanediol, and trimethanol are used as head groups to modulate the water transport permeabilities, with rejection of ions. The hydroxy channels achieve a single-channel permeability of 2.33 × 108 water molecules per second, which is within the same order of magnitude as the transport rates for aquaporins. Depending on their concentration in the membrane, adaptive channels are observed in the membrane. Over increased concentrations, a significant shift occurs, initiating unexpected higher water permeation. Molecular simulations probe that spongelike or cylindrical aggregates can form to generate transient cluster water pathways through the bilayer. Altogether, the adaptive self-assembly is a key feature influencing channel efficiency. The adaptive channels described here may be considered an important milestone contributing to the systematic discovery of artificial water channels for water desalination.

Operando liquid pressure determination in polymer electrolyte fuel cells

Abstract: Extending the operating range of fuel cells to higher current densities is limited by the ability of the cell to remove the water produced by the electrochemical reaction, avoiding flooding of the gas diffusion layers. It is therefore of great interest to understand the complex and dynamic mechanisms of water cluster formation in an operando fuel cell setting as this can elucidate necessary changes to the gas diffusion layer properties with the goal of minimizing the number, size, and instability of the water clusters formed. In this study, we investigate the cluster formation process using X-ray tomographic microscopy at 1 Hz frequency combined with interfacial curvature analysis and volume-of-fluid simulations to assess the pressure evolution in the water phase. This made it possible to observe the increase in capillary pressure when the advancing water front had to overcome a throat between two neighboring pores and the nuanced interactions of volume and pressure evolution during the droplet formation and its feeding path instability. A 2 kPa higher breakthrough pressure compared to static ex situ capillary pressure versus saturation evaluations was observed, which suggests a rethinking of the dynamic liquid water invasion process in polymer electrolyte fuel cell gas diffusion layers.

Mechanistic Insight into the Synergetic Interaction of Ammonia Borane and Water on ZIF-67-Derived Co@Porous Carbon for Controlled Generation of Dihydrogen.

Abstract: Regarding dihydrogen as a clean and renewable energy source, ammonia borane (NH3BH3, AB) was considered as a chemical H2-storage and H2-delivery material due to its high storage capacity of dihydrogen (19.6 wt %) and stability at room temperature. To advance the development of efficient and recyclable catalysts for hydrolytic dehydrogenation of AB with parallel insight into the reaction mechanism, herein, ZIF-67-derived fcc-Co@porous carbon nano/microparticles (cZIF-67_nm/cZIF-67_μm) were explored to promote catalytic dehydrogenation of AB and generation of H2(g). According to kinetic and computational studies, zero-order dependence on the concentration of AB, first-order dependence on the concentration of cZIF-67_nm (or cZIF-67_μm), and a kinetic isotope effect value of 2.45 (or 2.64) for H2O/D2O identify the Co-catalyzed cleavage of the H-OH bond, instead of the H-BH2NH3 bond, as the rate-determining step in the hydrolytic dehydrogenation of AB. Despite the absent evolution of H2(g) in the reaction of cZIF-67 and AB in the organic solvents (i.e., THF or CH3OH) or in the reaction of cZIF-67 and water, Co-mediated activation of AB and formation of a Co-H intermediate were evidenced by theoretical calculation, infrared spectroscopy in combination with an isotope-labeling experiment, and reactivity study toward CO2-to-formate/H2O-to-H2 conversion. Moreover, the computational study discovers a synergistic interaction between AB and the water cluster (H2O)9 on fcc-Co, which shifts the splitting of water into an exergonic process and lowers the thermodynamic barrier for the generation and desorption of H2(g) from the Co-H intermediates. With the kinetic and mechanistic study of ZIF-67-derived Co@porous carbon for catalytic hydrolysis of AB, the spatiotemporal control on the generation of H2(g) for the treatment of inflammatory diseases will be further investigated in the near future.

The many-body expansion for aqueous systems revisited: III. Hofmeister ion–water interactions

Abstract: We report a Many Body Energy (MBE) analysis of aqueous ionic clusters containing anions and cations at the two opposite ends of the Hofmeister series, viz. the kosmotropes Ca2+ and SO42− and the chaotropes NH4+ and ClO4−, with 9 water molecules to quantify how these ions alter the interaction between the water molecules in their immediate surroundings. We specifically aim at quantifying how various ions (depending on their position in the Hofmeister series) affect the interaction between the surrounding water molecules and probe whether there is a qualitatively different behavior between kosmotropic vs. chaotropic ions. The current results when compared to the ones reported earlier for water clusters [J. P. Heindel and S. S. Xantheas, J. Chem. Theor. Comput., 2020, 16, 6843–6855] as well as for alkali metal and halide ion aqueous clusters of the same size [J. P. Heindel and S. S. Xantheas, J. Chem. Theor. Comput., 2021, 17, 2200–2216], which lie in the middle of the Hofmeister series, offer a complete account of the effect an ion across the Hofmeister series from “kosmotropes” to “chaotropes” has on the interaction between the neighboring water molecules. Through this analysis, noteworthy differences between the MBE of kosmotropes and chaotropes were identified. The MBE of kosmotropes is dominated by ion–water interactions that extend beyond the 4-body term, the rank at which the MBE of pure water converges. The percentage contribution of the 2-B term to the total cluster binding energy is noticeably larger. The disruption of the hydrogen bonded network due to the dominant ion–water interactions results in weak, unfavorable water–water interactions. The MBE for chaotropes, on the other hand, was found to converge more quickly as it more closely resembles that of pure water clusters. Chaotropes exhibit weaker overall binding energies and weaker ion–water interactions in favor of water–water interactions, somewhat recovering the pattern of the 2-4 body terms exemplified by pure water clusters. A remarkable anti-correlation between the 2-B ion–water (I–W) and water–water (W–W) interactions as well as between the 3-B (I–W–W) and (I–W) interactions was found for both kosmotropic and chaotropic ions. This anti-correlation is linear for both monatomic anions and monatomic cations, suggesting the existence of underlying physical mechanisms that were previously unexplored. The consideration of two different structural arrangements (ion inside and outside of a water cluster) suggests that fully solvated (ion inside) chaotropes disrupt the hydrogen bonding network in a similar manner to partially solvated (ion outside) kosmotropes and offers useful insights into the modeling requirements of bulk vs. interfacial ion solvation. It is noteworthy that the 2-B contribution to the total Basis Set Superposition Error (BSSE) correction for both kosmotropic and chaotropic ions follows the universal erf profile vs. intermolecular distance previously reported for pure water, halide ion–water and alkali metal ion–water clusters. When scaled for the corresponding dimer energies and distances, a single profile fits the current results together with all previously reported ones for pure water and halide water clusters. This finding lends further support to schemes for accurately estimating the 2-B BSSE correction in condensed environments.

Unlocking the Water Trimer Loop: Isotopic Study of Benzophenone‐(H2O)1‐3 Clusters with Rotational Spectroscopy

Abstract: Examined here are the structures of complexes of benzophenone microsolvated with up to three water molecules by using broadband rotational spectroscopy and the cold conditions of a molecular jet. The analysis shows that the water molecules dock sideways on benzophenone for the water monomer and dimer moieties, and they move above one of the aromatic rings when the water cluster grows to the trimer. The rotational spectra shows that the water trimer moiety in the complex adopts an open-loop arrangement. Ab initio calculations face a dilemma of identifying the global minimum between the open loop and the closed loop, which is only solved when zero-point vibrational energy correction is applied. An OH⋅⋅⋅π bond and a Burgi-Dunitz interaction between benzophenone and the water trimer are present in the cluster. This work shows the subtle balance between water-water and water-solute interactions when the solute molecule offers several different anchor sites for water molecules.

Directional Proton Transfer in the Reaction of the Simplest Criegee Intermediate with Water Involving the Formation of Transient H3O.

Abstract: The reaction of Criegee intermediates with water vapor has been widely known as a key Criegee reaction in the troposphere. Herein, we investigated the reaction of the smallest Criegee intermediate, CH2OO, with a water cluster through fragment-based ab initio molecular dynamics simulations at the MP2/aug-cc-pVDZ level. Our results show that the CH2OO-water reaction could occur not only at the air/water interface but also inside the water cluster. Moreover, more than one reactive water molecules are required for the CH2OO-water reaction, which is always initiated from the Criegee carbon atom and ends at the terminal Criegee oxygen atom via a directional proton transfer process. The observed reaction pathways include the loop-structure-mediated and stepwise mechanisms, and the latter involves the formation of transient H3O+. The lifetime of transient H3O+ is on the order of a few picoseconds, which may impact the atmospheric budget of the other trace gases in the actual atmosphere.

Computational Study of Hydrogen Bond Interactions in Water Cluster-Organic Molecule Complexes

Abstract: We analyzed the interactions present in complexes that acetone, azomethane, dimethylamine, dimethyl ether, methyl acetate, and oxirane form with 39 different (H2O)n clusters (n = 1-10). A random generation of configurations and a subsequent screening procedure were employed to sample representative interactions. Using quantum chemical computations, we calculated the associated binding energies, which range from -0.19 to -10.76 kcal/mol at the DLPNO-CCSD(T)/CBS level. It was found that the binding energies can be understood in terms of various factors, including the water cluster size, the nature of the organic molecule, and the type of hydrogen bond donor. We find that the most stable complexes often arise from a combination of a strong hydrogen bond plus a secondary interaction between the organic molecule and the water cluster.

A computational study of water in UiO-66 Zr-MOFs: Diffusion, hydrogen bonding network, and confinement effect

Abstract: For chemical warfare agent removal, the humidity emerges as an unavoidable challenge that significantly affects the performance of metal–organic frameworks. In this work, via density functional the ...

Molecular properties affecting the hydration of acid–base clusters

Abstract: In the atmosphere, water in all phases is ubiquitous and plays important roles in catalyzing atmospheric chemical reactions, participating in cluster formation and affecting the composition of aerosol particles. Direct measurements of water-containing clusters are limited because water is likely to evaporate before detection, and therefore, theoretical tools are needed to study hydration in the atmosphere. We have studied thermodynamics and population dynamics of the hydration of different atmospherically relevant base monomers as well as sulfuric acid–base pairs. The hydration ability of a base seems to follow in the order of gas-phase base strength whereas hydration ability of acid–base pairs, and thus clusters, is related to the number of hydrogen binding sites. Proton transfer reactions at water–air interfaces are important in many environmental and biological systems, but a deeper understanding of their mechanisms remain elusive. By studying thermodynamics of proton transfer reactions in clusters containing up to 20 water molecules and a base molecule, we found that that the ability of a base to accept a proton in a water cluster is related to the aqueous-phase basicity. We also studied the second deprotonation reaction of a sulfuric acid in hydrated acid–base clusters and found that sulfate formation is most favorable in the presence of dimethylamine. Molecular properties related to the proton transfer ability in water clusters are discussed.

Nickel(II) di-aqua complex containing a water cluster: synthesis, X-ray structure and catecholase activity

Abstract: A trans-diaquanickel(II) complex of the type [(L2−)NiII(H2O)2]·nH2O (1·nH2O) was isolated, where LH2 is (E)-2-(2-((2-hydroxyphenylimino)methyl)phenoxy)acetic acid (LH2), a tetradentate ligand. The molecular geometry of 1·nH2O was confirmed by single crystal X-ray structure determination. It is observed that in the crystal, coordinated water, bulk water and ligand oxygen atoms form six membered water clusters by OH⋯H interactions. 1·nH2O has emerged as a catalyst for the oxidation of 3,5-di-tert-butylcatecholto 3,5-di-tert-butyl-o-benzoquinone with a turnover number (kcat) of 4.46 × 102 h−1 in CH3OH. During oxidation, the coordination of catechol to the nickel(II) centre and the formation of an o-benzosemiquinone intermediate were confirmed by a nickel based EPR signal, ESI mass spectrometry and UV-vis spectra. 1·nH2O exhibits an irreversible anodic peak at 0.83 V versus the Fc+/Fc couple due to the phenoxyl/phenolato redox couple, authenticated by DFT calculations.

Hydroxyl Group-Directed Solvation of Excited-State Intramolecular Proton Transfer Probes in Water: A Demonstration from the Fluorescence Anisotropy of Hydroxyflavones.

Abstract: Formation of a probe-solvent network resulting in unusually high fluorescence anisotropy (FA) of an excited-state intramolecular proton transfer (ESIPT) probe, 3-hydroxyflavone (3HF), in water prompted us to explore the solvation patterns on its 7-hydroxy (7HF) and 6-hydroxy (6HF) positional analogues. In the present study, it was observed that 7HF exhibits a lower FA than 3HF does in water, implying that the volume of the 7HF-water cluster is less than that of the 3HF-water cluster. Experimental and computational results led us to propose that 7HF forms its water cluster at the molecular periphery in contrast to the projected-out structure in case of the 3HF-water cluster. Density functional theory (DFT)-based quantum chemical calculations provide an approach for the differential solvation patterns of 3HF and 7HF. 6HF, a non-ESIPT probe, exhibits very low FA in water compared with both 3HF and 7HF. This study demonstrates that proper positioning of the hydroxyl group and its participation in the extended π-conjugation within the molecule dictate the formation of the solvated cluster endorsing directed solvation.

Correction: Mirror twin boundaries in MoSe2 monolayers as one dimensional nanotemplates for selective water adsorption.

Abstract: Water adsorption on transition metal dichalcogenides and other 2D materials is generally governed by weak van der Waals interactions. This results in a hydrophobic character of the basal planes, and defects may play a significant role in water adsorption and water cluster nucleation. However, there is a lack of detailed experimental investigations on water adsorption on defective 2D materials. Here, by combining low-temperature scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations, we study in that context the well-defined mirror twin boundary (MTB) networks separating mirror-grains in 2D MoSe2. These MTBs are dangling bond-free extended crystal modifications with metallic electronic states embedded in the 2D semiconducting matrix of MoSe2. Our DFT calculations indicate that molecular water also interacts similarly weak with these MTBs as with the defect-free basal plane of MoSe2. However, in low temperature STM experiments, nanoscopic water structures are observed that selectively decorate the MTB network. This localized adsorption of water is facilitated by functionalization of the MTBs by hydroxyls formed by dissociated water. Hydroxyls may form by dissociating of water at undercoordinated defects or adsorbing of radicals from the gas phase in the UHV chamber. Our DFT analysis indicates that the metallic MTBs adsorb these radicals much stronger than on the basal plane due to charge transfer from the metallic states into the molecular orbitals of the OH groups. Once the MTBs are functionalized with hydroxyls, molecular water can attach to them, forming water channels along the MTBs. This study demonstrates the role metallic defect states play in the adsorption of water even in the absence of unsaturated bonds that have been so far considered to be crucial for adsorption of hydroxyls or water.

Molecular Adsorption on Cold Gas-Phase Hydrogen-Bonded Clusters of Chiral Molecules

Abstract: Gas-phase molecular adsorption was investigated as a model for molecular cloud formation. Molecular adsorption on cold gas-phase hydrogen-bonded clusters containing protonated tryptophan (Trp) enantiomers and monosaccharides such as methyl-α-D-glucoside, D-ribose, and D-arabinose was detected using a tandem mass spectrometer equipped with an electrospray ionization source and cold ion trap. The adsorption sites on the surface of cold gas-phase hydrogen-bonded cluster ions were quantified using gas-phase N2 adsorption-mass spectrometry. The gas-phase N2 adsorption experiments indicated that the number of adsorption sites on the surface of the hydrogen-bonded heterochiral clusters containing L-Trp and D-monosaccharides exceeded the number of adsorption sites on the homochiral clusters containing D-Trp and D-monosaccharides. H2O molecules were preferentially adsorbed on the heterochiral clusters, and larger water clusters were formed in the gas phase. Physical and chemical properties of cold gas-phase hydrogen-bonded clusters containing biological molecules were useful for investigating enantiomer selectivity and chemical evolution in interstellar molecular clouds.

Discrete-Particle Model to Optimize Operational Conditions of Proton-Exchange Membrane Fuel-Cell Gas Channels.

Abstract: Operation of proton-exchange membrane fuel cells is highly deteriorated by mass transfer loss, which is a result of spatial and temporal interaction between airflow, water flow, channel geometry, and its wettability. Prediction of two-phase flow dynamics in gas channels is essential for the optimization of the design and operating of fuel cells. We propose a mechanistic discrete particle model (DPM) to delineate dynamic water distribution in fuel cell gas channels and optimize the operating conditions. Similar to the experimental observations, the model predicts seven types of flow regimes from isolated, side wall, corner, slug, film, and plug flow droplets for industrial temporal and spatial scales. Consequently, two-phase flow regime maps are proposed. The results suggest that an increase in water accumulation in the channel is related to the increase in the water cluster density emerging from the gas diffusion layer rather than the increased water flow rate through constant water pathways. From a modeling perspective, the DPM replicated well volume-of-fluid channel simulation results in terms of saturation, water coverage ratio, and interface locations with an estimated 5 orders of magnitude increase in calculation speed.

(CO2)n+, (H2O)n+, and (H2O)n+ (CO2) gas cluster ion beam secondary ion mass spectrometry: analysis of lipid extracts, cells, and Alzheimer’s model mouse brain tissue

Abstract: This work assesses the potential of new water cluster-based ion beams for improving the capabilities of secondary ion mass spectrometry (SIMS) for in situ lipidomics. The effect of water clusters was compared to carbon dioxide clusters, along with the effect of using pure water clusters compared to mixed water and carbon dioxide clusters. A signal increase was found when using pure water clusters. However, when analyzing cells, a more substantial signal increase was found in positive ion mode when the water clusters also contained carbon dioxide, suggesting that additional reactions are in play. The effects of using a water primary ion beam on a more complex sample were investigated by analyzing brain tissue from an Alzheimer’s disease transgenic mouse model. The results indicate that the ToF-SIMS results are approaching those from MALDI as ToF-SIMS was able to image lyso-phosphocholine (LPC) lipids, a lipid class that for a long time has eluded detection during SIMS analyses. Gangliosides, sulfatides, and cholesterol were also imaged.