Unbuckling the 18-Crown-6 Ether Belt Around Metal Ions: Forging the Connection to the Condensed Phase.

Crown ethers are central to supramolecular chemistry, recognizing and binding specific ions in solution. The most well-known, 18-Crown-6 (18C6), preferentially captures K in an aqueous solution, while gas phase binding of 18C6 with alkali metal ions decreases linearly with an increasing ionic radius. Why the high affinity for Li and Na in the gas phase is dramatically reduced with hydration remains an open question in understanding the K selectivity in the aqueous phase.

Releasing Preferentially Sequestered Na from Its Confinement by Beauvericin: A Single Water Molecule is the Accomplice.

Beauvericin (Bv) is a natural ionophore capable of transporting ions across biological membranes. Mass spectrometry and infrared spectroscopy show that Bv specifically captures sodium ions with a unique 6-fold coordination in its cavity, which illustrates how ions are carried through the membrane. But with no reports on how ions are released from Bv at the interface, a complete picture of the ion transport process has yet to be established.

Water-Induced Dissociative Mechanism of Carboxylate and Divalent Calcium Ions Revealed by IR Laser Spectroscopy.

The dissociation of carboxylate and divalent calcium ions is investigated at the molecular level in microsolvation experiments by gradually increasing the number of water molecules around the ions. IR photodissociation (IRPD) laser spectroscopy of H-tagged (Ca, AcO)(HO) clusters in the ν(CO) spectral range combined with RI-B97-D3-BJ-abc/TZVPPD frequency calculations is used to identify the type of ion pairs involved in this process. These results reveal that the ion dissociation follows a multistep mechanism involving in particular pseudobridged monodentate contact ion pairs (CIPs), which are found to be the first intermediate species formed from bidentate CIPs along the ion dissociation path.

Micro Solvation Effect of Methanol on Excited-State Dynamics of Protonated Tryptophan and Dopamine.

The electronic and vibrational cryogenic ion spectroscopy of protonated tryptophan (TrpH) and dopamine (DAH) complexed with methanol has been recorded. These two biological chromophores exhibit ultrafast photochemistry due to excited-state proton transfer (ESPT). We have established the relationship between the structure of the complexes and their photodynamics and compared them with recent results obtained in hydrated complexes.

The Gas Phase Protonation Sites of Six Naturally Occurring Nicotinoids.

The gas phase protonation sites of six naturally occurring nicotinoids, namely nicotine (NIC), nornicotine (NOR), anabasine (ANB), anatabine (ANT), cotinine (COT), and myosmine (MYO), consisting of a common Pyridine and differing -Pyridine rings, have been determined for the first time at the physiological temperature from cryogenic ion trap infrared spectroscopy and electronic structure calculations. The protonation site on either of these two rings is related to the nicotinoid's biological activity. At room temperature, NIC is a mixture of Pyridine and Pyrrolidine (-Pyridine) protomers, whereas NOR, ANB, ANT, and COT are pure Pyridine protomers and finally MYO is mostly a Pyroline (-Pyridine) protomer.

Affinity of Nicotinoids to a Model Nicotinic Acetylcholine Receptor (nAChR) Binding Pocket in the Human Brain.

The binding affinity of nicotinoids to the binding residues of the αβ variant of the nicotinic acetylcholine receptor (nAChR) was identified as a strong predictor of the nicotinoid's addictive character. Using ab initio calculations for model binding pockets of increasing size composed of 3, 6, and 14 amino acids (3AA, 6AA, and 14AA) that are derived from the crystal structure, the differences in binding affinity of 6 nicotinoids, namely, nicotine (NIC), nornicotine (NOR), anabasine (ANB), anatabine (ANT), myosmine (MYO), and cotinine (COT) were correlated to their previously reported doses required for increases in intracranial self-stimulation (ICSS) thresholds, a metric for their addictive function. By employing the many-body decomposition, the differences in the binding affinities of the various nicotinoids could be attributed mainly to the proton exchange energy between the pyridine and non-pyridine rings of the nicotinoids and the interactions between them and a handful of proximal amino acids, namely Trp156, Trpβ57, Tyr100, and Tyr204.

Transition from vehicle to Grotthuss proton transfer in a nanosized flask: cryogenic ion spectroscopy of protonated -aminobenzoic acid solvated with DO.

Proton transfer (PT) is one of the most ubiquitous reactions in chemistry and life science. The unique nature of PT has been rationalized not by the transport of a solvated proton (vehicle mechanism) but by the Grotthuss mechanism in which a proton is transported to the nearest proton acceptor along a hydrogen-bonded network. However, clear experimental evidence of the Grotthuss mechanism has not been reported yet.

Switching of Protonation Sites in Hydrated Nicotine via a Grotthuss Mechanism.

The switching of the protonation sites in hydrated nicotine, probed by experimental infrared (IR) spectroscopy and theoretical calculations, is facilitated via a Grotthuss instead of a bimolecular proton transfer (vehicle) mechanism at the experimental temperature ( = 130 K) as unambiguously confirmed by experiments with deuterated water. In contrast, the bimolecular vehicle mechanism is preferred at higher temperatures ( = 300 K) as determined by theory. The Grotthuss mechanism for the concerted proton transfer results in the production of nicotine's bioactive and addictive pyrrolidine-protonated (Pyrro-H) protomer with just 5 water molecules.

Conformational preference of 2-(4-methoxyphenyl)ethanol studied by supersonic jet spectroscopy: Intramolecular OH/π interaction.

A π-type hydrogen bonding between the OH group and the π electron is a crucial factor for the conformational preference of the molecular structure with a flexible group. However, the information on the effect of the substituent on the OH/π interaction is insufficient. The laser-induced fluorescence (LIF) excitation, the dispersed fluorescence (DF), the IR-UV hole-burning, and the IR dip spectra of jet-cooled 2-(4-methoxyphenyl)ethanol were measured for the first time.

Development of CuSe/Ag(S,Se)-Based Monolithic Thermoelectric Generators for Low-Grade Waste Heat Energy Harvesting.

With the ongoing climate and energy crises, thermoelectric conversion has slowly emerged as a clean and reliable alternative energy source for small Internet of Things (IoT) devices. Commercially available thermoelectric generators (TEGs) are typically composed of expensive and toxic BiTe-based thermoelectric materials and require complicated and energy-intensive device assembly processes. As an alternative solution, we have developed a Ag- and Cu-chalcogenide-based monolithic TEG using simple, quick, and low-energy-cost device fabrication processes for low-grade waste heat recovery for energy harvesting.

Stepwise hydration of [CHCOOMg] studied by cold ion trap infrared spectroscopy: insights into interactions in the magnesium channel selection filters.

The magnesium channel controls Mg concentration in the cell and plays an indispensable role in biological functions. The crystal structure of the Magnesium Transport E channel suggested that Mg hydrated by 6 water molecules is transported through a selection filter consisting of COO groups on two Asp residues. This Mg motion implies successive pairing with OOC-R and dissociation mediated by water molecules.

Infrared Spectra of Beauvericin-Alkaline Earth Metal Ion Complexes─Ion Preference to Physiological Ions.

Beauvericin (Bv) is a naturally occurring ionophore that selectively transports ions through cell membranes. However, the intrinsic ion selectivity of Bv for alkaline earth metal ions (M) is yet to be established due to inconsistent results from condensed phase experiments. Based on fluorescence quenching rates, Ca appears to be preferred while extraction experiments favor Mg.

Does Chiral Sensitivity of a Structure Depend on the Metal Core? Alkali Ion Complexes of Cyclo(Tyr-Tyr).

Alkali metal complexes of cyclic dipeptide cyclo Tyr-Tyr have been studied under cryogenic ion trap conditions. Their structure was obtained by combining Infra-Red Photo-Dissociation (IRPD) and quantum chemical calculations. The structural motif strongly depends on the relative chirality of the tyrosine residues.

Ion Recognition beyond Size Matching: Cooperative Hydration Effect on the K Selectivity of Valinomycin over Na Revealed by Cryogenic Double Ion Trap Infrared Spectroscopy.

The naturally occurring ionophore valinomycin (VM) selectively transports K across the biological membrane, which makes VM a plausible antivirus and antibacterial candidate. The K selectivity of VM was rationalized based on a size-matching model despite structural inconsistency between experiments and computations. In this study, we investigated the conformations of the NaVM complex with 1-10 water molecules using cryogenic ion trap infrared spectroscopy with computational calculations.

Muscle co-activation in the elderly contributes to control of hip and knee joint torque and endpoint force.

We investigated the coordinated activity patterns of muscles based on cosine tuning in the elderly during an isometric force exertion task. We also clarified whether these coordinated activity patterns contribute to the control of hip and knee joint torque and endpoint force as co-activation. Preferred direction (PD) of activity for each muscle in 10 young and 8 older males was calculated from the lower limb muscle activity during isometric force exertion task in various directions.

Can Ag Permeate through a Potassium Ion Channel? A Bottom-Up Approach by Infrared Spectroscopy of the Ag Complex with the Partial Peptide of a Selectivity Filter.

Silver and silver ions have a long history of antimicrobial activity and medical applications. Nevertheless, the activity of Ag against bacteria, how it enters a cell, has not yet been established. The K channel, a membrane protein, is a possible route.

Movement-synchronized cerebellum rhythm coordinates multi-joint movements in young and elderly adults.

Rhythmic limb multi-joint movement like locomotion is controlled by intralimb coordination. Intralimb coordination changes entail immediate alterations in movement patterns and be related with cerebellum function. Synchronized cerebellum activity has known to modulate the frequency of walking, but not known the effect of only intralimb coordination.

Compensatory relationship of mechanical energy in paretic limb during sit-to-stand motion of stroke survivors.

The sit-to-stand motion is a prerequisite for walking and is therefore frequently performed in daily life. Diseases such as stroke often make performing it challenging. Even the stroke survivors who can stand up, the number of sit-to-stand motions they perform each day is lower than that of healthy adults.

Cation-responsive cavity expansion of valinomycin revealed by cryogenic ion trap infrared spectroscopy.

Valinomycin (VM) is a natural K-selective ionophore that transports K through the cell membrane. VM captures K in its central cavity with a -symmetric β-turn-like backbone. Although the binding affinity is drastically decreased for the VM-sodium (NaVM) complex with respect to KVM, VM holds relatively high affinity to Rb and Cs.

Hydration-induced protomer switching in -aminobenzoic acid studied by cold double ion trap infrared spectroscopy.

-Aminobenzoic acid (PABA) is a benchmark molecule to study solvent-induced proton site switching. Protonation of the carboxy and amino groups of PABA generates O- and N-protomers of PABAH, respectively. Ion mobility mass spectrometry (IMS) and infrared photodissociation (IRPD) studies have claimed that the O-protomer most stable in the gas phase is converted to the N-protomer most stable in solution upon hydration with six water molecules in the gas-phase cluster.

Na Selective Binding by Beauvericin and Its Mechanism Studied by Mass-Coupled Cold Ion Trap Infrared Spectroscopy.

Beauvericin (Bv) is a cyclic hexadepsipeptide mycotoxin that selectively transports ions across cell membranes. Characterization of its intrinsic ion affinity has been complicated by different previous results in condensed phases and biological membranes. We report the marked specificity between alkali metal ions by Bv using experimental and computational methods.

Conformer-selective Photodynamics of TrpH -H O.

The photodynamics of protonated tryptophan and its mono hydrated complex TrpH -H O has been revisited. A combination of steady-state IR and UV cryogenic ion spectroscopies with picosecond pump-probe photodissociation experiments sheds new lights on the deactivation processes of TrpH and conformer-selected TrpH -H O complex, supported by quantum chemistry calculations at the DFT and coupled-cluster levels for the ground and excited states, respectively. TrpH excited at the band origin exhibits a transient of less than 100 ps, assigned to the lifetime of the excited state proton transfer (ESPT) structure.

Do Stereochemical Effects Overcome a Charge-Induced Perturbation in Isolated Protonated Cyclo(Tyr-Tyr)?

Two diastereomers of the protonated diketopiperazine (DKP) dipeptide cyclo(Tyr-Tyr), namely, cyclo(LTyr-LTyr)H and cyclo(LTyr-DTyr)H, are studied in a cryogenic ion trap by means of IR photodissociation spectroscopy combined with quantum chemical calculations. The two diastereomers have similar structures in which one of the rings is folded over the DKP ring and the other one is extended in a trans geometry, allowing a strong OH···π interaction to take place. This contrasts to the observation of a stacked geometry for neutral cyclo(LTyr-LTyr) only under supersonic expansion conditions that do not exist for cyclo(LTyr-DTyr).

Structure of Gas Phase Monohydrated Nicotine: Implications for Nicotine's Native Structure in the Acetylcholine Binding Protein.

We report a joint experimental-theoretical study of the never reported before structure and infrared spectra of gas phase monohydrated nicotine (NIC) and nornicotine (NOR) and use them to assign their protonation sites. NIC's biological activity is strongly affected by its protonation site, namely, the pyrrolidine (Pyrro-NICH, anticipated active form) and pyridine (Pyri-NICH) forms; however, these have yet to be directly experimentally determined in either the nicotinic acetylcholine receptor (nAChR, no water present) or the acetylcholine-binding protein (AChBP, a single water molecule is present) but can only be inferred to be Pyrro-NICH from the intermolecular distance to the neighboring residues (i.e.