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1.
J Am Chem Soc ; 146(18): 12401-12409, 2024 May 08.
Artículo en Inglés | MEDLINE | ID: mdl-38652043

RESUMEN

Ion receptors are molecular hosts that bind ionic guests, often with great selectivity. The interplay of solvation and ion binding in anion host-guest complexes in solution governs the binding efficiency and selectivity of such ion receptors. To gain molecular-level insight into the intrinsic binding properties of octamethyl calix[4]pyrrole (omC4P) host molecules with halide guest ions, we performed cryogenic ion vibrational spectroscopy (CIVS) of omC4P in complexes with fluoride, chloride, and bromide ions. We interpret the spectra using density functional theory, describing the infrared spectra of these complexes with both harmonic and anharmonic second-order vibrational perturbation theory (VPT2) calculations. The NH stretching modes of the pyrrole moieties serve as sensitive probes of the ion binding properties, as their frequencies encode the ion-receptor interactions. While scaled harmonic spectra reproduce the experimental NH stretching modes of the chloride and bromide complexes in broad strokes, the high proton affinity of fluoride introduces strong anharmonic effects. As a result, the spectrum of F-·omC4P is not even qualitatively captured by harmonic calculations, but it is recovered very well by VPT2 calculations. In addition, the VPT2 calculations recover the intricate coupling of the NH stretching modes with overtones and combination bands of CH stretching and NH bending modes and with low-frequency vibrations of the omC4P macrocycle, which are apparent for all of the halide ion complexes investigated here. A comparison of the CIVS spectra with infrared spectra of solutions of the same ion-receptor complexes in d3-acetonitrile and d6-acetone shows how ion solvation changes the ion-receptor interactions for the different halide ions.

2.
J Phys Chem A ; 127(25): 5374-5381, 2023 Jun 29.
Artículo en Inglés | MEDLINE | ID: mdl-37310223

RESUMEN

We investigate the microhydration structures of complexes of alkaline earth dications and ethylenediaminetetraacetic acid (EDTA) for up to two water molecules, using cryogenic ion vibrational spectroscopy in concert with density functional theory (DFT). The interaction with water shows a clear dependence on the chemical identity of the bound ion. For Mg2+, microhydration mostly involves the carboxylate groups of EDTA and does not entail direct contact with the dication. In contrast, the larger ions (Ca2+, Sr2+, and Ba2+) interact electrostatically with the microhydration environment, and this interaction increases in importance with the size of the ion. This trend reflects the ion position in the EDTA binding pocket, which comes closer to the rim of the pocket with increasing ion size.

3.
J Phys Chem A ; 127(36): 7586-7593, 2023 Sep 14.
Artículo en Inglés | MEDLINE | ID: mdl-37647595

RESUMEN

We present the vibrational spectra of a series of dicationic, organometallic complexes consisting of a transition metal center (Co, Ni, or Cu) coordinated by 4,4'-di(tert-butyl)-2,2'-bipyridine (DTBbpy) ligands and a formate adduct. Spectral features are analyzed and assigned through comparison with density functional theory calculations, and structures are reported. Natural population analysis shows that the DTBbpy ligands serve as flexible charge reservoirs in each complex. Shifts in the vibrational signatures of the formate moiety reveal that the nature of the metal center plays a crucial role in the charge distribution and formate-metal binding motif in each complex, illustrating the impact of the metal center on the structural and electronic properties of these complexes.

4.
J Phys Chem A ; 127(46): 9717-9722, 2023 Nov 23.
Artículo en Inglés | MEDLINE | ID: mdl-37944122

RESUMEN

The symmetric (νs) and antisymmetric (νas) O-C-O stretching modes of CO2-containing compounds encode structural information that can be difficult to decipher, due to the sensitivity of these spectral features to small shifts in charge distribution and structure, as well as the anharmonicities of these two vibrational modes. In this work, we discuss the relation between the frequency of these modes and the geometry of the O-C-O group, showing that the splitting between νs and νas (Δνas-s = νas - νs) can be predicted based only on the O-C-O bond angle obtained from quantum chemical calculations with reasonable accuracy (±46 cm-1, R2 = 0.994). The relationship is shown to hold for the infrared spectra of a variety of CO2-containing molecules measured in vacuo. The origins of this model are discussed in the framework of elementary mode analysis.

5.
J Phys Chem A ; 127(10): 2258-2264, 2023 Mar 16.
Artículo en Inglés | MEDLINE | ID: mdl-36877889

RESUMEN

The vibrational spectra of cold complexes of ethylenediaminetetraacetic acid (EDTA) with transition metal dications in vacuo show how the electronic structure of the metal provides a geometric template for interaction with the functional groups of the binding pocket. The OCO stretching modes of the carboxylate groups of EDTA serve as structural probes, informing on the spin state of the ion as well as the coordination number in the complex. The results highlight the flexibility of EDTA in accepting a large range of metal cations in its binding site.

6.
J Phys Chem A ; 125(33): 7297-7302, 2021 Aug 26.
Artículo en Inglés | MEDLINE | ID: mdl-34396777

RESUMEN

We report the vibrational spectrum of a metal-organic complex consisting of a Co center surrounded by two bipyridine-based ligands and explore the change of the spectrum upon addition of a formate ligand to the complex. We assign the spectra using density functional theory. The infrared response encodes the binding motif of the formate to the metal, and the calculated charge distributions highlight the ability of the organic ligand framework to act as charge reservoirs modulating the redox properties of the metal center.

7.
Phys Chem Chem Phys ; 22(36): 20295-20302, 2020 Sep 23.
Artículo en Inglés | MEDLINE | ID: mdl-32966432

RESUMEN

We present electronic spectra containing the Qx and Qy absorption bands of singly and doubly deprotonated protoporphyrin IX, prepared as mass selected ions in vacuo at cryogenic temperatures, revealing vibronic structure in both bands. We assign the vibronic progression of the Qx band using a Frank-Condon-Herzberg-Teller simulation based on time-dependent density functional theory, comparing the observed bands with those calculated for porphine. A comparison of the electronic spectra of the two charge states allows investigation of the electronic Stark effect with an electric field strength beyond the capabilities of typical laboratory setups. We analyze the differences in the electronic spectra of the two charge states using n-electron valence perturbation theory (NEVPT2) and simulated charge distributions.

8.
J Phys Chem A ; 124(38): 7827-7831, 2020 Sep 24.
Artículo en Inglés | MEDLINE | ID: mdl-32866387

RESUMEN

We report infrared spectra of a model chromophore of green fluorescent protein, prepared in an ion trap at temperatures ranging from 30 K to room temperature. We compare the changes in the infrared spectrum with predicted infrared spectra for the Z and E isomers of this molecule, and we confirm that the molecule exists as the Z isomer at low temperatures. We revisit the question whether or not it can thermally isomerize in the temperature range of this experiment, and we find no evidence for isomerization.


Asunto(s)
Proteínas Fluorescentes Verdes/química , Imidazolinas/química , Temperatura , Isomerismo , Estructura Molecular , Espectrofotometría Infrarroja
10.
J Phys Chem Lett ; 15(37): 9481-9486, 2024 Sep 19.
Artículo en Inglés | MEDLINE | ID: mdl-39254991

RESUMEN

We present cryogenic ion vibrational spectroscopy of complexes of the anion receptor octamethyl calix[4]pyrrole (omC4P) with nitrate in vacuo. We compare the resulting vibrational spectrum with that in deuterated acetonitrile solution, and we interpret the results using density functional theory. Nitrate binds to omC4P through hydrogen bonds between the four NH groups of the receptor and a single NO group of the nitrate ion. The shape of the ion breaks the C4v symmetry of the receptor, and this symmetry lowering is encoded in the pattern of the NH stretching modes of omC4P. We compare the spectrum of nitrate-omC4P with that of chloride-omC4P to discuss effects of ion size, shape, and solvent interaction on the ion binding behavior.

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