The Green Fluorescent Protein (GFP) is one of the most widely used fluorescent markers in bioimaging, and much work has been dedicated to understanding the electronic structure of its anionic chromophore in solution, protein, and in vacuo. A model for this chromophore (deprotonated p-hydroxybenzylidene-2,3-dimethylimidazolinone, HBDI , see Figure 1) contains the complete conjugated system, and replaces the linkers to the protein structure with methyl groups. Previous work by many groups has established that the initial photophysics of the chromophore upon excitation is likely to be similar in the protein and in vacuo, but quite different from aqueous solution.S. Brøndsted Nielsen, A. Lapierre, J. U. Andersen, U. V. Pedersen, S. Tomita, L.H. Andersen, Phys. Rev. Lett. 87 (2001) 228102 W. Zagorec-Marks, M. M. Foreman, J. R. R. Verlet, J. M. Weber, J. Phys. Chem. Lett. 10 (2019) 7817-7822 All previous spectroscopy in vacuo has been performed at room temperature, which introduces spectral congestion through hot bands. By studying this chromophore as a cryogenically prepared, mass-selected ion, we are able to provide unprecedented resolution in the electronic band origin region of the S₁ ← S₀ electronic transition. Figure Figure 1: Structure of HBDI⁻.

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S. Brøndsted Nielsen, A. Lapierre, J. U. Andersen, U. V. Pedersen, S. Tomita, L.H. Andersen, Phys. Rev. Lett. 87 (2001) 228102

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Solvation plays an important role in the function of fluorescent proteins. Many of these proteins contain a functional water molecule in the chromophore pocket, which can influence the electronic properties of the chromophore. In the case of the Green Fluorescent Protein (GFP), a single water molecule is coordinated to the phenolate group of the chromophore, raising questions about the effect this has on the electronic spectrum of GFP. Here, we present the electronic and infrared spectra of a model system for the GFP chromophore in complexes with up to two water molecules.

Polycyclic aromatic hydrocarbons (PAH) are some of the most abundant complex molecules in the interstellar medium. In their anionic forms, these molecules can exist either as a radical anion or a singly deprotonated species. These deprotonated varieties have been proposed as key intermediates in the formation of much larger interstellar molecules such as C60. Previous work has used anion slow-electron velocity map imaging (SEVI) to study the naphthyl and anthracenyl anions and the corresponding neutral radicalJ. Am. Chem. Soc. 2015, 137, 4, 1420–1423 PNAS February 16, 2016 113 (7) 1698-1705. Here, we extend this work to the larger tetracenyl anions and radical. For the 9-tetracenyl radical, we report an electron affinity value of 1.8457(5)eV which differs from the previously published result of 2.6(2)eVPhys. Chem. Chem. Phys., 2015,17, 32464-32471 but is more consistent with the values for the smaller deprotonated PAHs. We also report the first anion photoelectron spectra of 1 and 2-tetracenyl isomers, yielding electron affinity values of 1.623(2) and 1.547(2) eV, respectively. Interestingly, the ordering of electron affinities of these isomers differs from the anthracenyl radical. The most active vibrations in these spectra involve displacements near the deprotonation site. In order to explain high intensity of very low kinetic energy electrons in multiple SEVI images, we have acquired the action photoelectron spectra of the 9-tetracenyl radical. This spectrum reveals an anion excited state about 2000 cm⁻¹above the detachment threshold with peak widths that suggest lifetimes on the order of 4.5ps. The primary pathway to detachment from this anion excited state is via thermionic emission, in agreement with previously published results. Implications for possible detection in astrochemical data will be discussed.

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J. Am. Chem. Soc. 2015, 137, 4, 1420–1423

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Phys. Chem. Chem. Phys., 2015,17, 32464-32471,

With the detection of C₆₀, C₇₀ and C₆₀⁺, the fullerenes constitute by far the largest molecular species individually identified in the interstellar medium (ISM). Proton affinities of C₆₀ and C₇₀ are significant which support the hypothesis that protonated fullerenes may also be abundant in the ISM. We present the experimental vibrational spectra of gaseous C₆₀H⁺ and C₇₀H⁺. Protonation of the highly symmetrical molecules causes a drastic symmetry lowering resulting in a rich vibrational spectrum. As compared to C₆₀, where all C-atoms are equivalent due to the icosahedral symmetry, C₇₀ belongs to the D_5h point group and has five non-equivalent C-atoms, which are available as protonation sites. Combined analysis of the experimental spectrum and spectra computed at the density functional theory level enables us to evaluate the protonation isomers being formed. We compare the IR spectra of C₆₀H⁺ and C₇₀H⁺ to IR emission spectra from planetary nebulae, which suggests that a mixture of these fullerene analogues could contribute to their IR emission.

Porphyrins are ubiquitous macrocycles in biology, where they perform a variety of functions ranging from behaving as chromophores in proteins to molecular/electron shuttles. Porphyrins often incorporate a metal center and have substituents on the macrocycle periphery to allow this versatility. These species have been studied for decades, using many techniques primarily focused on solution and solid phase environments. While such techniques yield much useful information, the chemical environment and the temperatures involved in such studies usually lead to solvatochromic shifts, broadening of spectral lines, and spectral congestion. Even spectra obtained in cryogenic matrices exhibit shifts whose magnitude and even direction are hard to predict. As a consequence, the intrinsic photophysical properties of these molecules, i.e., in the absence of effects caused by chemical environments, have been elusive. We are able to circumvent these difficulties by studying cryogenically prepared, mass selected ions. Here we report the electronic and infrared spectra of metal free protoporphyrin mono- and dianions. We interpret the experimental data in the framework of quantum chemical calculations.

Catalytic reduction of CO₂ to produce chemical fuels is a viable strategy for meeting the growing demand for renewable energy, but better catalysts are needed to perform this chemistry on an industrial scale. The first step in designing improved catalysts is understanding key molecular properties of existing catalysts, which includes characterizing the structures and intramolecular forces of species in the catalytic cycle. Metal bipyridine complexes have been shown to efficiently reduce CO₂ with long catalyst lifetimes

Flavonoids constitute a family of natural compounds found in a large number of fruits and vegetables being responsible for many of their vivid colours. Flavonoids are the largest group of phytonutrients, with more than 6,000 types. Flavone (2-Phenylchromone) and flavanone (2,3-Dihydroflavone) define the basic units for whole families of these compounds, anthoxantines and flavanones respectively. Due to their biological activity, their structure–activity relationships are of interest also for medicine and biochemistry. In this work, we present the first study of the microwave spectra of both flavone and flavanone. The spectra of these two molecules have been observed using a CP-FTMW spectrometer with two vaporization methods: conventional heating and a laser ablation (LA) system recently implemented. A conformational search was done for each compound using DFT, corrected with empirical dispersion terms, and MP2 methods. We have observed only one conformer of each system and their monohydrated complexes. Flavanone is a case where DFT and MP2 methods diverge in predicting the global minimum being the experimental data in agreement with the DFT predictions.

The phenomena of valence tautomerism consists in a particular intramolecular process involving just one reactive species where an intramolecular bond migrates raising to a sometimes different, but not always, molecular structure. In this context, barbaralones, widely well-known fluxional molecules, have been deeply ingrained in the understanding of the phenomena of valence tautomerism. They can undergo low energy [3, 3]-sigmatropic process, where the number of constitutional isomers depends on the presence and chemical nature of any possible substituent that induces isomerization restrictions. We have laser-ablated 1-(4-tert-Butyl)phenyl)tricyclo[3.3.1.0^2,8]nona-3,6-dien-9-one, a large fluxional molecule that is central to the understanding of the phenomena of valence tautomerism, and one conformer has been characterized using chirped-pulse Fourier transform microwave LA-CP-FTMW spectroscopy. This precise structural data should be useful in future studies as a reference point in the characterization of new fluxional molecules.

• Acknowledgments: The authors thank the financial fundings from Ministerio de Ciencia e Innovacion (CTQ2016-76393-P and PID2019-111396GB-I00), Junta de Castilla y Leon (VA077U16 and VA244P20) and European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC-2013-SyG, Grant Agreement n. 610256 NANOCOSMOS, are gratefully acknowledged. E.R.A. acknowledges MINECO for a Juan de la Cierva postdoctoral fellowship and the Fundación Biofísica Bizkaia (Spain). M.S.N. acknowledges funding from the Spanish "Ministerio de Ciencia, Innovación y Universidades" under predoctoral FPU Grant (FPU17/02987).

We describe a new interactive program (DAPPERS: Data Analysis Package for Productive and Enthusiastic Rotational Spectroscopists) for the rapid processing of dense rotational spectra of asymmetric rotors. DAPPERS is based on an intelligent algorithm that quickly and accurately locates spectral progressions with user-identified quantum number identities and then seamlessly integrates with Pickett’s SPCAT and SPFIT programs to allow complete assignment and fitting. The program has been shown to be proficient across the full range of asymmetry parameters and can produce final fits containing hundreds of transitions of any type (a, b, or c) or branch (P, Q, or R) in just a few minutes. The software interacts with the user through a simple graphical user interface, and includes a peak-finder with adjustable baseline drift compensation, as well as a number of visualization features. It is designed for easy installation and use, with special attention given to the design of a single executable file platform. It is available for download, together with extensive documentation, at www.chem.umn.edu/groups/kleopold.

Microwave spectra for a series of carboxylic acid anhydrides derived from acetic acid, pivalic acid, benzoic acid, and trifluoroacetic acid are reported. All semi-rigid rotor spectra, including those of the A states of species with a single methyl rotor, were quickly assigned using the new rotational spectral fitting program, DAPPERS. The observed internal rotor states of the single-rotor anhydrides and the double rotor spectra of parent and D-6 acetic anhydride were fit using XIAM. The aid of closed loops in the assignment of the acetic anhydride spectrum will be briefly discussed along with remaining challenges in the spectral analysis. The heavy atom structure of pivalic anhydride and pivalic trifluoroacetic anhydride were determined through isotopic substitution and Kraitchman analysis. Trends of the dihedral angle between anhydride carbonyls are studied through an analysis of M06-2X/6-311++G(d,p) computational values, which are shown to be in good agreement with those experimentally determined for pivalic and pivalic trifluoroacetic anhydrides. The V₃ barriers measured for acetic anhydride, acetic trifluoroacetic anhydride, and acetic pivalic anhydride are compared with those for a wide variety of molecules exhibiting methyl group internal rotation in an acetate functionality. A straightforward synthesis for mixed carboxylic anhydrides will also be described.

Microwave studies of hydrated acid anhydrides (RCOOCOR-H₂O) provide an interesting venue for characterizing local minima on the potential energy landscape of reactive systems. This talk reports the microwave spectra of the monohydrates of pivalic anhydride (R = R' = C(CH₃)₃), trifluoracetic anhydride (R = R' = CF₃), and the mixed pivalic-trifluoroacetic anhydride (R = C(CH₃)₃, R' = CF₃). While the ultimate fate of these species in bulk aqueous solution is hydrolysis to form the parent acids, this work captures the precursor complexes and investigates the effect of R and R' on the geometry of the monohydrate. Microwave spectra of the parent species and their D₂O and DOH isotopologues are reported, as is an in-depth computational analysis at different levels of theory. Calculated structures show varying degrees of hydrogen bonding and electrophilic-nucleophilic interaction, depending on the particular combination of R and R' groups. Additionally, closely spaced pairs of tunneling states arising from internal water motion were observed in the monohydrate spectra except in the case where R = R' = CF₃.

Chemical models and experiments indicate that interstellar dust grains and their ice mantles play an important role in the production of complex organic molecules (COMs). The meeting of chemical species adsorbed from the gas phase onto the grain/ice surface allows reactions to occur efficiently, and leads to the emergence of the ice mantles as a major reservoir of volatile species. To date, the most complex solid-phase molecule detected with certainty in the ISM is methanol (CH₃OH), but it is hoped that the upcoming James Webb Space Telescope (JWST), aided by new laboratory data, will be able to identify yet larger organic species. In this study, we use a coupled chemo-dynamical model to predict new candidate species for JWST detection toward the young star-forming core Cha-MMS1, combining the gas-grain chemical kinetic model MAGICKAL with a 1-D radiative hydrodynamics (RHD) simulation. The abundances of the main ice constituents with respect to water in the model match well with observational values. The model also predicts high solid-phase abundances of intermediate radicals associated with the hydrogenation of CO to methanol ( > 0.1 % with respect to water ice). Four oxygen-bearing COMs (ethanol C₂H₅OH, dimethyl ether CH₃OCH₃, methyl formate CH₃OCHO, and acetaldehyde CH₃CHO) as well as formic acid (HCOOH), show abundances as high as > 0.01 % with respect to water ice. N-bearing COMs are generally less abundant than O-bearing ones, suggesting methylamine (CH₃NH₂) as the only N-bearing solid-phase COM candidate for JWST detection.