Competing Insertion and External Binding Motifs in Hydrated Neurotransmitters: Infrared Spectra of Protonated Phenylethylamine Monohydrate

Bouchet, Aude; Schütz, Markus; Dopfer, Otto

doi:10.1002/cphc.201500939

Cited by 29 publications

(36 citation statements)

References 86 publications

(105 reference statements)

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“…Similar to H + PEA, the calculations reveal two stable isomers for p F‐H + PEA, with the side chain either in gauche (G) or anti (A) conformation with respect to the phenyl ring. Fluorine substitution at the para position has only little influence on the geometry of the side chain and the energetic properties (Table ).…”

Section: Resultsmentioning

confidence: 86%

“…The IRMPD spectrum of H + PEA shown in Figure a has been analyzed in detail before and is included here for comparison. Briefly, the IR spectrum calculated for H + PEA(G) and H + PEA(A) mainly differ in the ranges around 850 and 1100 cm −1 , and comparison with the IRMPD spectrum, in particular bands J and G, indicates that the experimental spectrum is clearly dominated by the significantly more stable G isomer.…”

Section: Resultsmentioning

confidence: 99%

“…To obtain a more realistic description of these biomolecules as they are found in a physiological medium, protonation has to be taken into account . Aromatic ethylamino neurotransmitters are mostly protonated at the terminal amino group of the side chain, as it has been observed for dopamine, serotonin, tryptamine, ethanolamine, 2‐amino‐1‐phenylethanol, and more generally for phenylalkylamines …”

Section: Introductionmentioning

confidence: 99%

“…In protonated PEA (H + PEA), the flexible ethylamino side chain can adopt either a folded gauche or an extended anti conformation. The single gauche conformer is substantially stabilized with respect to the anti isomer by the additional intramolecular NH + ⋅⋅⋅π (cation–π) interaction between the positively charged ammonium group and the highly polarizable π electrons of the aromatic phenyl ring . For this reason, only the gauche conformer is populated in the gas phase, both in a cold molecular beam and at room temperature, that is, the cation–π interaction completely locks H + PEA in the gauche configuration, in stark contrast to neutral PEA (and o F‐PEA).…”

Section: Introductionmentioning

confidence: 99%

“…The comparison between PEA and H + PEA has revealed major modifications of the conformational landscape of PEA induced by protonation, in particular by locking of the side‐chain conformation by the strong NH + ⋅⋅⋅π interaction between the ammonium group and the aromatic ring . This work aims now at addressing the effect of aromatic fluorination on the structural and electronic properties of H + PEA.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Aromatic Fluorine Substitution on Protonated Neurotransmitters: The Case of 2‐Phenylethylamine

Schütz

Bouchet

Chiavarino

et al. 2016

Chemistry A European J

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Fluorination of pharmaceutical compounds is a common tool to modulate their physiochemical properties. We determine the effects of site-specific aromatic fluorine substitution on the geometric, energetic, vibrational, and electronic properties of the protonated neurotransmitter 2-phenylethylamine (xF-H(+) PEA, x=ortho, meta, para) by infrared multiphoton photodissociation (IRMPD) in the fingerprint range (600-1750 cm(-1) ) and quantum chemical calculations at the B3LYP-D3/aug-cc-pVTZ level. The IRMPD spectra of all ions are assigned to their folded gauche conformers stabilized by intramolecular NH(+) ⋅⋅⋅π hydrogen bonds (H-bonds) between the protonated amino group and the aromatic ring. H→F substitution reduces the symmetry and allows for additional NH(+) ⋅⋅⋅F interactions in oF-H(+) PEA, leading to three distinct gauche conformers. In comparison to oF-H(+) PEA, the fluorination effects on the energy landscape (energy ordering and isomerization barriers) in pF-H(+) PEA and mF-H(+) PEA with one and two gauche conformers are less pronounced. The strengths of the intramolecular NH(+) ⋅⋅⋅F and NH(+) ⋅⋅⋅π bonds are analyzed by the noncovalent interaction (NCI) method.

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Section: Resultsmentioning

confidence: 86%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of Aromatic Fluorine Substitution on Protonated Neurotransmitters: The Case of 2‐Phenylethylamine

Schütz

Bouchet

Chiavarino

et al. 2016

Chemistry A European J

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Aromatic Charge Resonance Interaction Probed by Infrared Spectroscopy

2018

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Charge resonance is as trong attractive intermolecular force in aromatic dimer radical ions.D espite its importance,this fundamental interaction has not been characterized at high resolution by spectroscopyo fi solated dimers.W e employv ibrational infrared spectroscopyo fc old aromatic pyrrole dimer cations to precisely probe the charge distribution by measuring the frequency of the isolated N À Hstretch mode (n NH ). We observe al inear correlation between n NH and the partial charge qo nt he pyrrole molecule in different environments.S ubtle effects of symmetry reduction, such as substitution of functional groups (here pyrrole replaced by Nmethylpyrrole) or asymmetric solvation (here by an inert N 2 ligand), shift the charge distribution towardt he moiety with lower ionization energy.T his general approach provides ap recise experimental probe of the asymmetry of the charge distribution in such aromatic homo-and heterodimer cations.The intermolecular interactions of aromatic p electrons are important for chemical and biological recognition. [1] Radical ions of arenes are involved in chemical reaction mechanisms, charge transport of modern (bio-)organic materials (organic electronics), and radiation damage in DNAand proteins. [2] In addition to p H-bonding,c ation/anion-p,a nd p-p stacking interactions, [3] the charge-resonance (CR) interaction is af undamental and very strong force in charged arene dimers. [4] Forc ations,t his stabilization arises from sharing the positive charge between two identical or different molecules with the same or comparable ionization energies in a p-stacked dimer.I nahomodimer cation (A 2 + ), the positive charge is equally shared between both molecules, while in ah eterodimer (AB + )t he partner with the lower ionization energy (IE) carries more positive charge.I nt he simplest description, the CR interaction in A 2 + causes as plitting between the two electronic states described by Y AE = Y(A + )Y(A) AE Y(A)Y(A + ); the symmetric Y + ground state is stable and the destabilized antisymmetric Y À state is repulsive.The splitting between both electronic states is twice the stabilization energy of the ground state (ca. 50-100 kJ mol À1 ). Thei nteraction is strongest for A 2 + homodim-ers,a nd decreases in AB + as the difference in the IEs of the two molecules increases (DIE = IE A ÀIE B ). This description of the CR interaction in arene dimer ions is similar to the one employed for odd electron chemical bonds in radical ions (hemibonds) [5] and exciton splitting in delocalized electronic excitation in neutral dimers. [6] In the condensed phase, p-stacked dimer cations of aromatic and polycyclic aromatic hydrocarbons were first detected by electron spin resonance [7] and optical absorption spectroscopy of the intense and broad CR transition connecting the two Y AE states. [7d, 8] Thelatter electronic transition occurs in the low-energy part of the optical spectrum (in the red to near-infrared near 1 mm) and provides adirect measure for the CR splitting.Inthe gas phase,the binding e...

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