Photoinduced Carbon Dioxide Release via a Metastable Photoacid in a Nonaqueous Environment.

Capturing carbon dioxide (CO) from the atmosphere is a scientific and technological challenge. CO can be captured by forming carbamate bonds with amines, most notably monoethanolamine (MEA). Regenerating MEA by releasing captured CO requires that the carbamate solution be heated.

Intra-cluster Charge Migration upon Hydration of Protonated Formic Acid Revealed by Anharmonic Analysis of Cold Ion Vibrational Spectra.

The rates of many chemical reactions are accelerated when carried out in micron-sized droplets, but the molecular origin of the rate acceleration remains unclear. One example is the condensation reaction of 1,2-diaminobenzene with formic acid to yield benzimidazole. The observed rate enhancements have been rationalized by invoking enhanced acidity at the surface of methanol solvent droplets with low water content to enable protonation of formic acid to generate a cationic species (protonated formic acid or PFA) formed by attachment of a proton to the neutral acid.

Observation of Slow Eigen-Zundel Interconversion in H(HO) Clusters upon Isomer-Selective Vibrational Excitation and Buffer Gas Cooling in a Cryogenic Ion Trap.

The formation of isomers when trapping floppy cluster ions in a temperature-controlled ion trap is a generally observed phenomenon. This involves collisional quenching of the ions initially formed at high temperature by buffer gas cooling until their internal energies fall below the barriers in the potential energy surface that separate them. Here we explore the kinetics at play in the case of the two isomers adopted by the H(HO) cluster ion that differ in the proton accommodation motif.

Microhydration of the metastable N-protomer of 4-aminobenzoic acid by condensation at 80 K: H/D exchange without conversion to the more stable O-protomer.

4-aminobenzoic acid (4ABA) is a model scaffold for studying solvent-mediated proton transfer. Although protonation at the carboxylic group (O-protomer) is energetically favored in the gas phase, the N-protomer, where the proton remains on the amino group, can be kinetically trapped by electrospray ionization of 4ABA in an aprotic solvent such as acetonitrile. Here, we report the formation of the hydrated deuterium isotopologues of the N-protomers, RND ·(HO), (R = CHCOOD), which are generated by condensing water molecules onto the bare N-protomers in a liquid nitrogen cooled, radiofrequency octopole ion trap at 80 K.

Electronic and mechanical anharmonicities in the vibrational spectra of the H-bonded, cryogenically cooled X · HOCl (X=Cl, Br, I) complexes: Characterization of the strong anionic H-bond to an acidic OH group.

We report vibrational spectra of the H-tagged, cryogenically cooled X · HOCl (X = Cl, Br, and I) ion-molecule complexes and analyze the resulting band patterns with electronic structure calculations and an anharmonic theoretical treatment of nuclear motions on extended potential energy surfaces. The complexes are formed by "ligand exchange" reactions of X · (HO) clusters with HOCl molecules at low pressure (∼10 mbar) in a radio frequency ion guide. The spectra generally feature many bands in addition to the fundamentals expected at the double harmonic level.

Preparation and Characterization of the Halogen-Bonding Motif in the Isolated Cl·IOH Complex with Cryogenic Ion Vibrational Spectroscopy.

In the presence of a halide ion, hypohalous acids can adopt two binding motifs upon formation of the ion-molecule complexes [XHOY] (X, Y = Cl, Br, I): a hydrogen (HB) bond to the acid OH group and a halogen (XB) bond between the anion and the acid halogen. Here we isolate the X-bonded Cl·IOH ion-molecule complex by collisions of I·(HO) clusters with HOCl vapor and measure its vibrational spectrum by IR photodissociation of the H-tagged complex. Anharmonic analysis of its vibrational band pattern reveals that formation of the XB complex results in dramatic lowering of the HOI bending fundamental frequency and elongation of the O-I bond (by 168 cm and 0.

Vibrational Signatures of HNO Acidity When Complexed with Microhydrated Alkali Metal Ions, M·(HNO)(HO) (M = Li, K, Na, Rb, Cs), at 20 K.

The speciation of strong acids like HNO under conditions of restricted hydration is an important factor in the rates of chemical reactions at the air-water interface. Here, we explore the trade-offs at play when HNO is attached to alkali ions (Li-Cs) with four water molecules in their primary hydration shells. This is achieved by analyzing the vibrational spectra of the M·(HNO)(HO) clusters cooled to about 20 K in a cryogenic photofragmentation mass spectrometer.

On the Hydrogen Oxalate Binding Motifs onto Dinuclear Cu and Ag Metal Phosphine Complexes.

We report the binding geometries of the isomers that are formed when the hydrogen oxalate ((CO ) H=HOx) anion attaches to dinuclear coinage metal phosphine complexes of the form [M M dcpm (HOx)] with M=Cu, Ag and dcpm=bis(dicyclohexylphosphino)methane, abbreviated [MM] . These structures are established by comparison of isomer-selective experimental vibrational band patterns displayed by the cryogenically cooled and N -tagged cations with DFT calculations of the predicted spectra for various local minima. Two isomeric classes are identified that feature either attachment of the carboxylate oxygen atoms to the two metal centers (end-on docking) or attachment of oxygen atoms on different carbon atoms asymmetrically to the metal ions (side-on docking).

Ionic Liquid Clusters Generated from Electrospray Thrusters: Cold Ion Spectroscopic Signatures of Size-Dependent Acid-Base Interactions.

We determine the intramolecular distortions at play in the 2-hydroxyethylhydrazinium nitrate (HEHN) ionic liquid (IL) propellant, which presents the interesting case that the HEH cation has multiple sites (i.e., hydroxy, primary amine, and secondary ammonium groups) available for H-bonding with the nitrate anion.

Isolating the Contributions of Specific Network Sites to the Diffuse Vibrational Spectrum of Interfacial Water with Isotopomer-Selective Spectroscopy of Cold Clusters.

Decoding the structural information contained in the interfacial vibrational spectrum of water requires understanding how the spectral signatures of individual water molecules respond to their local hydrogen bonding environments. In this study, we isolated the contributions for the five classes of sites that differ according to the number of donor (D) and acceptor (A) hydrogen bonds that characterize each site. These patterns were measured by exploiting the unique properties of the water cluster cage structures formed in the gas phase upon hydration of a series of cations M·(HO) (M = Li, Na, Cs, NH, CHNH, HO, and = 5, 20-22).

Vibrational spectroscopy of the cryogenically cooled O- and N-protomers of 4-Aminobenzoic acid: Tag effects, isotopic labels, and identification of the isomer of the O-protomer.

4-Aminobenzoic acid (4ABA) is a biologically relevant, small organic molecule with two protonation sites: the amino group (N-protomer) and the carboxyl group (O-protomer). The O-protomer is energetically preferred in the gas-phase, while the higher energy N-protomer can be trapped using aprotic solvents such as acetonitrile during electrospray ionization. Here, we focus on the structure of the O-protomer, which can occur in three low-lying isomeric forms that result from different orientations of the OH groups relative to the benzene ring.

Characterization of the alkali metal oxalates (MCO) and their formation by CO reduction via the alkali metal carbonites (MCO).

The reduction of carbon dioxide to oxalate has been studied by experimental Collisionally Induced Dissociation (CID) and vibrational characterization of the alkali metal oxalates, supplemented by theoretical electronic structure calculations. The critical step in the reductive process is the coordination of CO2 to an alkali metal anion, forming a metal carbonite MCO2- able to subsequently receive a second CO2 molecule. While the energetic demand for these reactions is generally low, we find that the degree of activation of CO2 in terms of charge transfer and transition state energies is the highest for lithium and systematically decreases down the group (M = Li-Cs).

Multimodal Prussian blue analogs as contrast agents for X-ray computed tomography.

Prussian blue analogs (PBAs) are versatile materials with a wide range of applications. Due to their tunability, intrinsic biocompatibility, as well as low toxicity, these nanoscale coordination polymers have been successfully studied as multimodal contrast agents for multiple imaging techniques. Herein, we report the expanded biomedical application of PBAs to X-ray computed tomography (CT).

Matrix Isolation Spectroscopy: Aqueous p-Toluenesulfonic Acid Solvation.

Interaction between p-toluenesulfonic acid (pTSA) and water is studied at -20 °C in a CCl matrix. In CCl water exists as monomers with restricted rotational motion about its symmetry axis. Additionally, CCl is transparent in the hydrogen-bonded region; CCl thus constitutes an excellent ambient thermal energy matrix isolation medium for diagnosing interactions with water.

Structural and Functional Characterization of Human Stem-Cell-Derived Retinal Organoids by Live Imaging.

Purpose: Human pluripotent stem cell (hPSC)-derived retinal organoids are a platform for investigating retinal development, pathophysiology, and cellular therapies. In contrast to histologic analysis in which multiple specimens fixed at different times are used to reconstruct developmental processes, repeated analysis of the same living organoids provides a more direct means to characterize changes. New live imaging modalities can provide insights into retinal organoid structure and metabolic function during in vitro growth.

Intestinal adaptation in proximal and distal segments: Two epithelial responses diverge after intestinal separation.

Background: In short bowel syndrome, luminal factors influence adaptation in which the truncated intestine increases villus lengths and crypt depths to increase nutrient absorption. No study has evaluated the effect of adaptation within the distal intestine after intestinal separation. We evaluated multiple conditions, including Igf1r inhibition, in proximal and distal segments after intestinal resection to evaluate the epithelial effects of the absence of mechanoluminal stimulation.