Cd-content and temperature dependences of hyperfine fields in CdxFe3-xO4

Cd-content and temperature dependences of hyperfine fields in CdxFe3-xO4 (0 ≤ x ≤ 0.5) were investigated by means of time-differential perturbed angular correlation spectroscopy with the 111Cd(←111In) probe. It was found that Cd2+ ions selectively occupy the tetrahedral A site in the spinel structure in all the range of the present Cd content x. The magnetic transition temperature TC becomes lower with increasing x due to the interference of the long-range ordering of Fe spins as a result of expansion of the lattice constants by Cd doping. The measurement of room-temperature hyperfine fields at different x shows that the supertransferred magnetic hyperfine field (SMHF) at the probe decreases as x increases in the range of 0 ≤ x ≤ 0.5. Isothermal measurements at 15 K revealed a contrastive phenomenon for the Cd contents up to x = 0.4: the SMHF becomes great with increasing x; however, this increasing trend of the SMHF turns to reduction at x = 0.46. These observations can be explained based on the effect of Cd doping on the antiferromagnetic coupling between Fe ions in the A and B sites.

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 α4β2 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. Interactions between the guest nicotinoid and the amino acids of the binding pocket were found to be mainly classical in nature, except for those between the nicotinoid and Trp156. The larger pockets were found to model binding structures more accurately and predicted the addictive character of all nicotinoids, while smaller models, which are more computationally feasible, would only predict the addictive character of nicotinoids that are similar to nicotine. The present study identifies the binding affinity of the guest nicotinoid to the host binding pocket as a strong descriptor of the nicotinoid's addiction potential, and as such it can be employed as a fast-screening technique for the potential addiction of nicotine analogs.

Similarity scores of vibrational spectra reveal the atomistic structure of pentapeptides in multiple basins

Vibrational spectroscopy combined with theoretical calculations is a powerful tool for analyzing the interaction and conformation of peptides at the atomistic level. Nonetheless, identifying the structure becomes increasingly difficult as the peptide size grows large. One example is acetyl-SIVSF-N-methylamide, a capped pentapeptide, whose atomistic structure has remained unknown since its first observation [T. Sekiguchi, M. Tamura, H. Oba, P. Çarçarbal, R. R. Lozada-Garcia, A. Zehnacker-Rentien, G. Grégoire, S. Ishiuchi and M. Fujii, Angew. Chem., Int. Ed., 2018, 57, 5626-5629]. Here, we propose a novel conformational search method, which exploits the structure-spectrum correlation using a similarity score that measures the agreement of theoretical and experimental spectra. Surprisingly, the two conformers have distinctly different energy and geometry. The second conformer is 25 kJ mol-1 higher in energy than the other, lowest-energy conformer. The result implies that there are multiple pathways in the early stage of the folding process: one to the global minimum and the other to a different basin. Once such a structure is established, the second conformer is unlikely to overcome the barrier to produce the most stable structure due to a vastly different hydrogen bond network of the backbone. Our proposed method can characterize the lowest-energy conformer and kinetically trapped, high-energy conformers of complex biomolecules.

Transition from vehicle to Grotthuss proton transfer in a nanosized flask: cryogenic ion spectroscopy of protonated p-aminobenzoic acid solvated with D2O

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. Herein we show by infrared spectroscopy that a vehicle-type PT occurs in the penta- and hexahydrated clusters of protonated p-aminobenzoic acid, while Grotthuss-type PT is observed in heptahydrated clusters, indicating a change in the PT mechanism depending on the degree of hydration. These findings emphasize the importance of the usually ignored vehicle mechanism as well as the degree of hydration. It highlights the possibility of controlling the PT mechanism by the number of water molecules in chemical and biological environments.

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 ab initio calculations, is facilitated via a Grotthuss instead of a bimolecular proton transfer (vehicle) mechanism at the experimental temperature (T = 130 K) as unambiguously confirmed by experiments with deuterated water. In contrast, the bimolecular vehicle mechanism is preferred at higher temperatures (T = 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. Theoretical analysis suggests that the concerted proton transfer occurs via hydrogen-bonded bridges consisting of a 3 water molecule "core" that connects the pyridine protonated (Pyri-H+) with the pyrrolidine-protonated (Pyrro-H+) protomers. Additional water molecules attached as acceptors to the hydrogen-bonded "core" bridge result in lowering the reaction barrier of the concerted proton transfer down to less than 6 kcal/mol, which is consistent with the experimental observations.

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. Almost all bands observed in the spectral region of 35 550-36 500 cm-1 in the LIF excitation spectrum were successfully assigned with the DF and the IR-UV hole-burning spectra coupled with the quantum chemical calculation at M06-2x/6-311G and MP2/6-311G levels. Five conformers were found in the LIF excitation spectrum. The most stable conformer was Ggπ, and the second most stable conformer was Ggπ' (the trans rotamer of the methoxy group for Ggπ). Ggπ and Ggπ' had the OH group directed toward the π electron system of the benzene ring. The OH stretching frequency of Ggπ/Ggπ' of MPE in the IR dip spectra was red-shifted against that of Ggπ of phenylethanol, indicating that the introduction of the methoxy group would enhance the intramolecular OH/π interaction. In addition, the torsional vibration between the benzene ring and the side chain (-CH2CH2OH) (mode 63) was observed in the DF spectra of the Ggπ-00 and Ggπ'-00 band excitation, but their intensities were rather different, resulting from the different orientation of the OH group for each conformer toward the π electron system. The methoxy group would increase the negative charge on the benzene ring and would enhance the intramolecular OH/π interaction through the electrostatic interaction.

Electronic and vibrational spectroscopies of aromatic clusters with He in a supersonic jet: The case of neutral and cationic phenol-Hen (n = 1 and 2)

Van der Waals clusters composed of He and aromatic molecules provide fundamental information about intermolecular interactions in weakly bound systems. In this study, phenol-helium clusters (PhOH-Hen with n ≤ 2) are characterized for the first time by UV and IR spectroscopies. The S1 ← S0 origin and ionization energy both show small but additive shifts, suggesting π-bound structures of these clusters, a conclusion supported by rotational contour analyses of the S1 origin bands. The OH stretching vibrations of the PhOH moiety in the clusters match with those of bare PhOH in both the S0 and D0 states, illustrating the negligible perturbation of the He atoms on the molecular vibration. Matrix shifts induced by He attachment are discussed based on the observed band positions with the help of complementary quantum chemical calculations. For comparison, the UV and ionization spectra of PhOH-Ne are reported as well.

Ramucirumab plus FOLFIRI as second-line treatment for patients with RAS wild-type metastatic colorectal cancer previously treated with anti-EGFR antibody: JACCRO CC-16

BACKGROUND

Chemotherapy in combination with anti-epidermal growth factor receptor (EGFR) antibody is considered a first-line treatment regimen for RAS wild-type and left-sided metastatic colorectal cancer (mCRC), whereas second-line treatment regimens have not yet been established. Few studies have prospectively evaluated second-line treatment with anti-vascular endothelial growth factor antibody after first-line anti-EGFR antibody therapy for RAS wild-type mCRC.

PATIENTS AND METHODS

This non-randomized phase II trial investigated the clinical outcomes of second-line ramucirumab (RAM) plus fluorouracil, levofolinate, and irinotecan (FOLFIRI) after first-line anti-EGFR antibody in combination with doublet or triplet regimen in patients with RAS wild-type mCRC. The primary endpoint was the 6-month progression-free survival (PFS) rate. The secondary endpoints were PFS, overall survival (OS), objective response rate (ORR), rate of early tumor shrinkage (ETS), and safety. We hypothesized a threshold 6-month PFS rate of 30% and an expected 6-month PFS rate of 45%. Treatment was considered effective if the lower limit of the 90% confidence interval (CI) of the 6-month PFS rate was >0.30.

RESULTS

Ninety-two patients were enrolled in the study. The primary tumor was located on the left side in 86 (95.6%) patients. Twenty (22.0%) patients had received triplet plus cetuximab as previous therapy. Six-month PFS rate was 58.2% (90% CI 49.3% to 66.2%) with a median PFS of 7.0 months (95% CI 5.7-7.6 months). Median OS was 23.6 months (95% CI 16.5-26.3 months). The ORR and ETS rate were 10.7% and 16.9%, respectively, in 83 patients with measurable lesions. The 6-month PFS rate was comparable between patients previously treated with doublet and triplet regimens; however, median PFS was longer for the doublet regimen (7.4 versus 6.4 months, P = 0.036).

CONCLUSIONS

Our study demonstrated prospectively that RAM plus FOLFIRI is an effective second-line treatment after anti-EGFR antibody-containing first-line therapy in RAS wild-type and left-sided mCRC. Furthermore, the results were similar for patients who were previously treated with triplet regimen.

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. For residues of identical chirality, the cation interacts with one amide oxygen and one of the aromatic rings only; the distance between the aromatic rings does not change with the nature of the metal. In contrast, for residues of opposite chirality, the metal cation is located in between the two aromatic rings and interacts with both of them. The distance between the two aromatic rings strongly depends on the metal. Electronic spectra obtained by Ultra Violet Photodissociation (UVPD) spectroscopy and analysis of the UV photo-fragments shed light on the excited state deactivation processes, which depend on both the chirality of the residue and that of the metal ion core. Na+ stands out by the presence of low-lying charge transfer states resulting in the broadening of the electronic spectrum.

Stepwise hydration of [CH3COOMg]+ studied by cold ion trap infrared spectroscopy: insights into interactions in the magnesium channel selection filters

The magnesium channel controls Mg2+ concentration in the cell and plays an indispensable role in biological functions. The crystal structure of the Magnesium Transport E channel suggested that Mg2+ hydrated by 6 water molecules is transported through a selection filter consisting of COO- groups on two Asp residues. This Mg2+ motion implies successive pairing with -OOC-R and dissociation mediated by water molecules. For another divalent ion, however, it is known that RCOO-⋯Ca2+ cannot be separated even with 12 water molecules. From this discrepancy, we probe the structure of Mg2+(CH3COO-)(H2O)4-17 clusters by measuring the infrared spectra and monitoring the vibrational frequencies of COO- with the help of quantum chemistry calculations. The hydration by (H2O)6 is not enough to induce ion separation, and partially-separated or separated pairs are formed from 10 water molecules at least. These results suggest that the ion separation between Mg2+ and carboxylate ions in the selection-filter of the MgtE channel not only results from water molecules in their first hydration shell, but also from additional factors including water molecules and protein groups in the second solvation shell of Mg2+.

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 (M2+) is yet to be established due to inconsistent results from condensed phase experiments. Based on fluorescence quenching rates, Ca2+ appears to be preferred while extraction experiments favor Mg2+. In this study, we apply cold ion trap─infrared spectroscopy to Bv-M2+ coupled with electrospray ionization mass spectrometry. The mass spectrum shows that Bv favors binding to physiologically active ions Mg2+ and Ca2+ although it can form complexes with all four alkaline earth metal ions. Infrared spectroscopy, as measured by the H2 tag technique, reveals that Bv binds Mg2+ and Ca2+ ions by six carbonyl oxygens in the center of its cavity. This observation is supported by theoretical calculations. Other alkaline earth metal ions are bound by three carbonyl groups at the amide face. This difference in configuration is consistent with the binding preferences for the alkaline earth metal ions.

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 Na⁺VM complex with 1-10 water molecules using cryogenic ion trap infrared spectroscopy with computational calculations. It shows that the water molecule penetrates the cavity of VM deeply enough to distort the C₃-symmetric structure of gas-phase Na⁺VM, in stark contrast to hydrated clusters of K⁺VM with C₃-symmetric structure, where H₂O is located outside the cavity. The high affinity to K⁺ would be ascribed to minimal hydration-induced structural deformation of K⁺VM compared to Na⁺VM. This study highlights a novel cooperative hydration effect on the K⁺ selectivity and will provide an updated understanding of its ionophoric properties beyond the traditional size-matching model.

Hydration rearrangement in the 4-aminobenzonitrile-(H2O)2 cluster induced by photoionization: The effect of solvent-solvent interactions

The interplay between solute-solvent and solvent-solvent interactions plays an essential role in solvation dynamics that has important effects on the mechanism and dynamics of chemical reactions in solution. In this study, the rearrangement of the hydration shell induced by photoionization of a solute molecule is probed in a state- and isomer-specific manner by resonant multiphoton ionization detected IR spectroscopy of the prototypical 4-aminobenzonitrile-(H2O)2 cluster produced in a molecular beam. IR spectra reveal that the water molecules form a cyclic solvent network around the CN group in the initial neutral state (S0). Different from the singly-hydrated cluster, in which either the CN or the NH2 group is hydrated, hydration of the NH2 group is not observed in the dihydrated cluster. IR spectra obtained after ionizing the solute molecule into the cation ground state (D0) exhibit features ascribed to both NH-bound and CN-bound isomers, indicating that water molecules migrate from the CN to the NH site upon ionization with a yield depending on the ionization excess energy. Analysis of the IR spectra as a function of the excess energy shows that migration produces two different NH2 solvated structures, namely (i) the most stable structure in which both N-H bonds are singly hydrated.

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. The addition of a channel inhibitor (4-aminopyridine) to modulate the Ag⁺ uptake could support this view. However, the inhibitor enhances the uptake of Ag⁺, the opposite result. We have applied cold ion trap infrared laser spectroscopy to complexes of Ag⁺ and Ac-Tyr-NHMe (a model for GYG) which is a portion of the selectivity filter in the K⁺ channel to consider the question of permeation. With support from quantum chemical calculations, we have determined the stable conformations of the complex. The conformations strongly suggest that Ag⁺ would not readily permeate the K⁺ channel. The mechanism of the unexpected enhancement by the inhibitor is discussed.

Cryogenic Ion Spectroscopy of Protonated and Sodiated Methyladenine Derivatives

Ultraviolet photodissociation (UVPD) spectra of protonated 9-methyladenine (H⁺9MA), protonated 7-methyl adenine (H⁺7MA), protonated 3-methyladenine (H⁺3MA), and sodiated 7-methyladenine (Na⁺7MA) near the origin bands of the S₀-S₁ transition were obtained using cryogenic ion spectroscopy. The UV-UV hole burning, infrared (IR) ion-dip, and IR-UV double resonance spectra showed that all the ions were present as single isomers in a cryogenic ion trap. The UVPD spectrum of H⁺9MA exhibited only a broad absorption band, whereas the spectra of H⁺7MA, H⁺3MA, and Na⁺7MA displayed moderately or well-resolved vibronic bands. Potential energy profiles were computed to understand the reason for the different bandwidths of the vibronic bands in the spectra. The broadening of the bands was correlated with the slopes between the Franck-Condon point and the conical intersection between the S₁ and S₀ states in the potential energy profiles, thus reflecting the deactivation rates in the S₁ state.

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

Para-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. However, the threshold size has remained ambiguous because the arrival time distributions in the IMS experiments exhibit multiple peaks. On the other hand, IRPD spectroscopy could not detect the N-protomer for smaller hydrated clusters because of broad background due to annealing required to reduce kinetic trapping. Herein, we report the threshold size for O → N protomer switching without ambiguity using IR spectroscopy in a double ion trap spectrometer from 1300 to 1800 cm^-1. The pure O-protomer is prepared by electrospray, and size-specific hydrated clusters are formed in a reaction ion trap. The resulting clusters are transferred into a second cryogenic ion trap and the distribution of O- and N-protomers is determined by mid-IR spectroscopy without broadening. The threshold to promote O → N protomer switching is indeed five water molecules. It is smaller than the value reported previously, and as a result, its pentahydrated structure does not support the Grotthuss mechanism proposed previously. The extent of O → N proton transfer is evaluated by collision-assisted stripping IR spectroscopy, and the N-protomer population increases with the number of water molecules. This result is consistent with the dominant population of the N-protomer in aqueous solution.

Conformer-selective Photodynamics of TrpH+ -H2 O

The photodynamics of protonated tryptophan and its mono hydrated complex TrpH⁺ -H₂ 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⁺ -H₂ 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. The two experimentally observed conformers of TrpH⁺ -H₂ O have been assigned. A striking result arises from the conformer-selective photodynamics of TrpH⁺ -H₂ O, in which a single water molecule inserted in between the ammonium and the indole ring hinders the barrierless ESPT reaction responsible for the ultra-fast deactivation process observed in the other conformer and in bare TrpH⁺ .

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 C₃-symmetric β-turn-like backbone. Although the binding affinity is drastically decreased for the VM-sodium (Na⁺VM) complex with respect to K⁺VM, VM holds relatively high affinity to Rb⁺ and Cs⁺. The high affinity for larger ions irrespective of ionic size seems to conflict with the expected optimal size matching model and raises questions on what factors determine ion selectivity. A combination of infrared spectroscopy with supporting computational calculations reveals that VM can accommodate larger Rb⁺ and Cs⁺ by flexibly changing its cavity size with the elongation of its folded β-turn-like backbone. The high affinity to Rb⁺ and Cs⁺ can be ascribed to a size-dependent cavity expansion. These findings provide a new perspective on molecular recognition and selectivity beyond the conventional size matching model.

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. Mass spectrometry shows Bv readily binds all five alkali ions; however, the complex with Na⁺ is the most abundant species, indicating a strong binding preference. Gas phase infrared spectroscopy and theoretical calculations show that Li⁺, K⁺, Rb⁺, and Cs⁺ are coordinated by three amide carbonyl oxygens on the N-methylamino-l-phenylalanyl face. Selectivity for Na⁺ is achieved as Bv sequesters Na⁺ in the center of its cavity formed by three amide carbonyl and three ester carbonyl groups, a configuration unique among alkali metal ions. This finding provides insight into the correlation between selectivity and conformation of Bv, essential for development of this mycotoxin.

Bi-directional relationships of arterial stiffness with hypertension and diabetes mellitus from the early pathophysiological stages: a 16-year prospective observational study

Background

Hypertension and diabetes mellitus frequently coexist; however, it has not yet been clarified if the bidirectional longitudinal relationships between arterial stiffness and hypertension are independent of those between arterial stiffness and diabetes mellitus.

Methods

In this 16-year prospective observational study, 3960 middle-aged employees of a Japanese company without hypertension/diabetes mellitus at the study baseline underwent annual repeated measurements of the blood pressure, serum glycosylated hemoglobin A1c levels (HbA1c), and brachial-ankle pulse wave velocity (baPWV).

Results

By the end of the study period, 664, 779, 154, and 406 subjects developed hypertension, prehypertension, diabetes mellitus, and prediabetes, respectively. Increased baPWV at the baseline was associated with a significant odds ratio (per 1 standard deviation increase) for new onset of prehypertension/hypertension with (2.45/3.28, P<0.01) or without (2.49/2.76, P<0.01) coexisting prediabetes/diabetes mellitus, but not for new onset of prediabetes/diabetes mellitus without coexisting hypertension. Analyses using the latent growth curve model confirmed the bidirectional relationships between baPWV and hypertension, but no such relationship was observed between baPWV and abnormal glucose metabolism. Moreover, after the adjustments, higher mean blood pressure at baseline accelerated the increases in the baPWV over follow-up (unstandardized coefficient [B] = 0.39, standard error [SE] = 0.05x10–1, P<0.01). Similarly, higher baPWV at baseline accelerated the increases in mean blood pressure over follow-up (B = 0.02x10–1, SE = 0.01x10–1, P<0.01) (Figure 1). On the other hands, higher HbA1c levels at baseline accelerated the increases in the baPWV over follow-up (B = 0.43, SE = 0.05x10–1, P<0.01), but higher baPWV at baseline did not accelerate the increases in HbA1c levels over follow-up (B <0.01, SE <0.01, P=0.52) (Figure 2).

Conclusions

In middle-aged employees of a Japanese company, in contrast to the bidirectional relationships that exist between arterial stiffness and hypertension, increased arterial stiffness preceding the development of diabetes mellitus may represent that associated with the development of hypertension, as it is observed only in cases of diabetes mellitus coexisting with hypertension. Therefore, arterial stiffness may be associated to a greater degree with the development of hypertension than with the development of diabetes mellitus.

Funding Acknowledgement

Type of funding sources: Private company. Main funding source(s): Omron Health Care Company (Kyoto, Japan),Teijin Pharma Company (Tokyo, Japan)

Age-related differences in longitudinal associations between alcohol intake and arterial stiffness, pressure wave reflection, and inflammation in male employees

Backgrounds

While arterial stiffness and abnormal pressure wave reflection are independent cardiovascular risk, the difference of their association with alcohol intake have not been fully clarified.

Aim

This prospective observational study, which utilized repeated annual measurements performed over a 9-year period, applied mixed model analyses to examine age-related differences in longitudinal associations between alcohol intake and arterial stiffness, pressure wave reflection, and inflammation.

Methods

In 4016 middle-aged (43±9 years) healthy Japanese male employees, alcohol intake, brachial-ankle pulse wave velocity (baPWV), radial augmentation index (rAI), and serum C-reactive protein (CRP) levels were measured annually during a 9-year study period. Based on the questionnaire, alcohol intake was classified as non-drinker, mild-moderate drinker (ethanol 1–20 g/day) and heavy drinker (>20 g/day).

Results

The estimated marginal mean baPWV (non-drinkers = 1306 cm/s, mild-moderate drinkers = 1311 cm/s, and heavy drinkers = 1337 cm/s, P<0.01) and that of rAI showed significant stepped increases in an alcohol dose-dependent manner in the entire cohort, but an increase in rAI was not observed in subjects aged ≥50 years. The estimated slope of the annual increase in baPWV, but not rAI, was higher for heavy drinkers than for non-drinkers (slope difference, 2.73; P<0.01), especially for subjects aged <50 years. The estimated marginal mean of the serum CRP levels was lower for drinkers than for non-drinkers.

Conclusion

In middle-aged male Japanese employees, alcohol intake may attenuate inflammatory activity. While alcohol intake may exacerbate the progression of arterial stiffening in a dose-dependent manner without mediating inflammation, especially in subjects under 50 years of age, it may promote pressure wave reflection abnormalities with aging at earlier ages without further exacerbation at older ages.

Funding Acknowledgement

Type of funding sources: Private company. Main funding source(s): Omroncarpis

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). In the protonated form, the strength of the OH⁺···π interaction is different for the two diastereomers, resulting in a ∼110 cm^-1 difference in the ν(OH⁺) frequency and a smaller but clearly identifiable difference in the protonated amide ν(NH) frequency. Stereochemical effects are therefore still evidenced despite the strong perturbation due to the excess charge.

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., tryptophan). Our temperature-controlled double ion trap infrared spectroscopic experiments assisted by the collisional stripping method and high-level theoretical calculations yield the protonation ratio of Pyri:Pyrro = 8:2 at 240 K for the gas phase NICH⁺···(H₂O) complex, which resembles the molecular cluster present in the AChBP. Therefore, a single water molecule in the gas phase enhances this ratio in NICH⁺ relative to the 3:2 for the nonhydrated gas phase NICH⁺ in a trend that contrasts with the almost exclusive presence of Pyrro-NICH⁺ in aqueous solution. In contrast, the Pyri-NORH⁺ protomer is exclusively observed, a fact that may correlate with its weaker biological activity.

A bottom-up approach to the ion recognition mechanism of K+ channels from laser spectroscopy of hydrated partial peptide-alkali metal ion complexes

K⁺ channels allow selective permeation of K⁺, but not physiologically abundant Na⁺, at almost diffusion limit rates. The conduction mechanism of K⁺ channels is still controversial, with experimental and computation studies supporting two distinct conduction mechanisms: either with or without water inside the channel. Here, we employ a bottom-up approach on hydrated alkali metal complexes of a model peptide of K⁺ channels, Ac-Tyr-NHMe, to characterize metal-peptide, metal-water, and water-peptide interactions that govern the selectivity of K⁺ channels at a molecular level. Both the extension to the series of alkali metal ions and to temperature-dependent studies (approaching physiological values) have revealed the clear difference between permeable and non-permeable ions in the spectral features of the ion complexes. Furthermore, the impact of hydration is discussed in relation to the K⁺ channels by comparisons of the non-hydrated and hydrated complexes.

O-288 Association of initial zygote cleavage, compaction pattern and euploidy rates: possible implications for embryo correction mechanisms

Study question

Is the morula compaction pattern associated with early zygote cleavage anomalies and euploidy rates? Can it represent a possible mechanism of embryonic correction?

Summary answer

Abnormalities in the first divisions give rise to dysfunctional blastomeres, which were excluded from compaction process. This process represent a possible embryonic correction mechanism.

What is known already

IVF embryos have historically been analyzed based on morphological characteristics focusing on days 2/3 (cleavage stage) and 5/6 (blastocyst). The morula stage, usually reached on day 4, represent a transitional phase resulting from the embryonic genome activation and has received little attention in clinical embryology. However, during this crucial stage, cell differentiation begins, metabolism reaches higher levels, changes in cell shape and cell-destination mechanisms are enhanced, providing opportunities for “quality control”. At morula stage, embryos with severe genetic abnormalities are sorted out by natural selection or possibly self-correction events may occurs, reducing the load of aneuploid cells in mosaic embryos.

Study design, size, duration

We evaluated laboratory and clinical outcomes of 836 blastocysts (195 ICSI cycles) cultured in a time-lapse system and biopsied for preimplantation genetic testing for aneuploidy (PGT-A), from April-2018 to June-2020. Time-lapse videos were retrospectively analyzed to assess morphokinetic parameters of initial zygote cleavages and morula compaction. These parameters were evaluated and associated to genetic and embryonic outcomes. Blastocyst outcomes were also assessed according to maternal age <35 (n = 140), 35-37 (n = 175), 38-40 (n = 314) and >40 (n = 207).

Participants/materials, setting, methods

The zygote initial cleavages were classified as normal (1-2-4 cleavage) or anomalous: 1-3 cleavage (zygote splits directly into three blastomeres); 1-2-3 cleavage (2-3 in < 3h); and 1-2-5 cleavage (after the first normal cleavage, one blastomere splits directly into three blastomeres). Morula were classified as: Fully Compacted Morulae (FCM); Partially Compacted Morulae (PCM). The PCM could have cells excluded from the compaction process (Exc-PCM), extruded from an already compacted morula (Ext-PCM), or both situations (Exc/Ext-PCM).

Main results and the role of chance

Most blastocysts showed normal zygotic cleavage (83.3%). Anomalous cleavage such as 1-3 (0.8%), 1-2-3 (7.2%) and 2-5 (8.7%) were less prevalent and no differences were observed according to female age (p = 0.268). Overall, FCM (61.0%) was a more frequent pattern than PCM (39.0%). According to compaction pattern of PCM, Exc-PCM (25.1%) was more prevalent than Ext-PCM (11.5%) and Exc/Ext-PCM (2.4%). There was also no difference in the prevalence of the morulae compaction pattern according to female age (p = 0.124). FCM occurred in 511 embryos (73.4%) from zygotes with normal cleavage (n = 696), but no FCM was observed among anomalous cleaved zygotes (p < 0.001). Genetic and embryonic outcomes were displayed as follows: normal cleavage and FCM (NC-FCM, n = 511), normal cleavage and PCM (NC-PCM, n = 185), and anomalous cleavage and PCM (AC-PCM, n = 140). NC-FCM and AC-PCM groups showed statistically similar euploidy rates (39.3% and 38.6%, p = 0.870), that were both significantly higher than the NC-PCM group euploidy rate (23.8%, p < 0.001). However, morphokinetic scores (KidScore) and percentage of top-quality blastocysts at morphological evaluation were discordant: NC-FCM (6.4±1.7; 81.4%), NC-PCM (5.0±1.8; 47.6%) and AC-PCM (4.3±2.0; 37.9%). Euploidy rate decreased with female age for all groups: NC-FCM (<35:54.7%, 35-37:56.0%, 38-40:33.3%, >40:24.1%); NC-PCM (<35:37.5%, 35-37:19.0%, 38-40:25.0%, >40:19.0%); AC-PCM (<35:66.7%, 35-37:48.5%, 38-40:39.0%, >40:3.7%).

Limitations, reasons for caution

The retrospective design of the study represents a general limitation. In addition, this study evaluated only embryos that reached the blastocyst stage and showed enough quality to be biopsied. Therefore, the association between anomalies in the first and second mitotic cleavages and the embryonic development could not be evaluated.

Wider implications of the findings

Similar euploidy rates among NC-FCM and AC-PCM support the hypothesis that cell exclusion/extrusion in compaction stage of anomalous-cleaved zygotes can represent a potential correction mechanism, even though lower morphological/morphokinetic scores are seen on AC-PCM. That process is supposed to rescue embryos from the mosaic aneuploidy which occurs after abnormal cleavage.

Trial registration number

not applicable

Dynamic changes in RAS gene status in circulating tumour DNA: a phase II trial of first-line FOLFOXIRI plus bevacizumab for RAS-mutant metastatic colorectal cancer (JACCRO CC-11)

Background

Few prospective studies have used liquid biopsy testing in RAS-mutant metastatic colorectal cancer (mCRC), and its clinical significance remains unknown. Therefore, this study aimed to carry out a biomarker analysis by liquid biopsy using updated data of the phase II trial of FOLFOXIRI plus bevacizumab as first-line chemotherapy for RAS-mutant mCRC.

Materials and methods

A total of 64 patients who received modified FOLFOXIRI regimen (irinotecan 150 mg/m², oxaliplatin 85 mg/m², levofolinate 200 mg/m², and fluorouracil 2400 mg/m²) plus bevacizumab biweekly were enrolled. The primary endpoint was the objective response rate (ORR). Plasma samples were collected at pre-treatment, 8 weeks after treatment, and progression in participants included in the biomarker study. The levels of circulating tumour DNA (ctDNA) and specific KRAS and NRAS variants were evaluated using real-time PCR assays.

Results

There were 62 patients (median age: 62.5 years, 92% performance status 0, 27% right side) who were assessable for efficacy and 51 for biomarker analysis. ORR was 75.8% (95% confidence interval 65.1% to 86.5%). The median progression-free survival was 12.1 months, and the median overall survival (OS) was 30.2 months. In 78% of patients, RAS mutations disappeared in the ctDNA at 8 weeks after treatment; these patients tended to have better outcomes than those with RAS mutations. Interestingly, RAS mutations remained undetectable during progression in 62% of patients. Survival analysis indicated that the median OS from progression was significantly longer in patients with RAS mutation clearance than in those with RAS mutation in the ctDNA at disease progression (15.1 versus 7.3 months, hazard ratio: 0.21, P = 0.0046).

Conclusions

Our biomarker study demonstrated no RAS mutations in ctDNA at disease progression in 62% of patients with RAS-mutant mCRC. Both OS and post-progression survival were better in patients with clearance of RAS mutations in ctDNA after triplet-based chemotherapy.

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First-line FOLFOXIRI plus bevacizumab is effective for RAS-mutant mCRC with comparable efficacy in elderly patients.

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RAS mutations disappeared in ctDNA after intensive chemotherapy in 62% of patients with mCRC with RAS-mutant tumours.

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Survival time was longer in patients with RAS mutation clearance than in those with RAS mutations in ctDNA.

Stepwise dissociation of ion pairs by water molecules: cation-dependent separation mechanisms between carboxylate and alkali-earth metal ions

Microhydrated H₂-tagged ion pairs (Ca²⁺, AcO^-)(H₂O)_n=0-8 and (Ba²⁺, AcO^-)(H₂O)_n=0-5 are investigated by IR photodissociation laser spectroscopy and DFT-D frequency calculations. The detailed picture of the first steps of ion dissociation reveals two mechanisms, where water molecules promote dissociation either directly or indirectly depending on the nature of the cation.

Excited state dynamics of protonated dopamine: hydration and conformation effects

Electronic and vibrational spectroscopy in a cryogenic ion trap has been applied to protonated dopamine water clusters and assigned with the help of quantum chemistry calculations performed in the ground and electronic excited states. A dramatic hydration effect is observed when dopamine is solvated by three water molecules. The broad electronic spectra recorded for the bare and small water clusters containing protonated dopamine turn to sharp, well-resolved vibronic transitions in the 1-3 complex. This reflects the change induced by hydration in the photodynamics of protonated dopamine which is initially controlled by an excited state proton transfer (ESPT) reaction from the ammonium group toward the catechol ring. Interestingly, conformer selectivity is revealed in the 1-3 complex which shows two low lying energy conformers for which the ESPT reaction is prevented or not depending on the H-bond network formed between the dopamine and water molecules.

Collision-assisted stripping for determination of microsolvation-dependent protonation sites in hydrated clusters by cryogenic ion trap infrared spectroscopy: the case of benzocaineH+(H2O)n

The protonation site of molecules can be varied by their surrounding environment. Gas-phase studies, including the popular techniques of infrared spectroscopy and ion mobility spectrometry, are a powerful tool for the determination of protonation sites in solvated clusters but often suffer from inherent limits for larger hydrated clusters. Here, we present collision-assisted stripping infrared (CAS-IR) spectroscopy as a new technique to overcome these problems and apply it in a proof-of-principle experiment to hydrated clusters of protonated benzocaine (H⁺BC), which shows protonation-site switching depending on the degree of hydration. The most stable protomer of H⁺BC in the gas phase (O-protonated) is interconverted into its most stable protomer in aqueous solution (N-protonated) upon hydration with three water molecules. CAS-IR spectroscopy enables us to unambiguously assign protonation sites and quantitatively determine the relative abundance of various protomers.

Gas phase protonated nicotine is a mixture of pyridine- and pyrrolidine-protonated conformers: implications for its native structure in the nicotinic acetylcholine receptor

The infrared (IR) spectra of gas phase protonated nicotine has been measured in the never-before probed N-H "fingerprint region" (3200-3500 cm^-1). The protonated molecules generated by an electrospray source are thermalized in the first ion trap with water vapor and He gas at a pre-determined temperature prior to being probed by IR spectroscopy in the second ion trap at 4 K. The IR spectra exhibit two N-H stretching bands which are assigned to the pyridine and pyrrolidine protomers with the aid of high-level electronic structure calculations. This finding is in sharp contrast to previous spectroscopic studies that suggested a single population of the pyridine protomer. The relative populations of the two protomers vary by changing the temperature of the thermalizing trap from 180-300 K. The relative conformer populations at 240 K and 300 K are well reproduced by the theoretical calculations, unequivocally determining that gas phase nicotine is a 3 : 2 mixture of both pyridine and pyrrolidine protomers at room temperature. The thermalizing anhydrous vapor does not result in any population change. It rather demonstrates the catalytic role of water in achieving equilibrium between the two protomers. The combination of IR spectroscopy and electronic structure calculations establish the small energy difference between the pyridine and pyrrolidine protomers in nicotine. One of the gas phase nicotine pyrrolidine protomers has the closest conformational resemblance among all low-lying energy isomers with the X-ray structure of nicotine in the nicotinic acetylcholine receptor (nAChR).

Isomer-Selective Spectroscopy and Dynamics of Phenol-Arn (n ≤ 5) Clusters

Structures and ionization-induced solvation dynamics of phenol-(argon)_n clusters, PhOH-Ar_n (n ≤ 5), were studied by using a variety of isomer-selective photoionization and vibrational spectroscopic techniques. Several higher-energy isomers were found and assigned for the first time by systematically controlling the experimental conditions of the supersonic expansion. This behavior is also confirmed for the PhOH-Kr₂ cluster. Solvation structures are elucidated by evaluating systematic shifts in the S₁ ← S₀ origin and ionization energies obtained by resonance-enhanced photoionization, in addition to the OH stretching frequency obtained by IR photodissociation. Isomer-selective picosecond time-resolved IR spectroscopy for the n = 2 clusters revealed that the dynamics for the ionization-induced intermolecular π → H site-switching reaction strongly depends on the initial isomeric structure. In particular, the reaction time for the (1|1) isomer is 7 ps, while that for (2|0) is <3 ps. This difference shows that the switching time is determined by the distance of the reaction coordinate between the initial π-site and the final OH-site.

Double Ion Trap Laser Spectroscopy of Alkali Metal Ion Complexes with a Partial Peptide of the Selectivity Filter in K+ Channels─Temperature Effect and Barrier for Conformational Conversions

Potassium ion channels selectively permeate K⁺, as well as Rb⁺ and Cs⁺ to some degree, while excluding Na⁺ and Li⁺. Conformations of alkali metal complexes of Ac-Tyr-NHMe, a model peptide of the selectivity filter in a K⁺ channel, were previously found to correlate with the permeability of alkali metal ions to a K⁺ channel by cold ion trap infrared spectroscopy. With an additional temperature-controlled ion trap, we examined the conformations of the alkali metal complexes, allowing the ions to collide with a He buffer gas at different temperatures, prior to spectroscopic investigation. The conformational distribution of the K⁺-peptide complex shows the most significant variation with temperature, which suggests that this complex has more flexibility when complexed with K⁺ and suggests lower barrier heights than other metal-peptide complexes. The variability of the conformational distribution with temperature for the ions follows the same order of ion permeability of a K⁺ channel. This work demonstrates that the additional temperature-controlled ion trap is a powerful tool to explore the conformational landscape of flexible molecular systems.

Hydration-controlled excited-state relaxation in protonated dopamine studied by cryogenic ion spectroscopy

Ultraviolet (UV) and infrared (IR) spectra of protonated dopamine (DAH⁺) and its hydrated clusters DAH⁺(H₂O)_1-3 are measured by cryogenic ion spectroscopy. DAH⁺ monomer and hydrated clusters with up to two water molecules show a broad UV spectrum, while it turns to a sharp, well-resolved one for DAH⁺-(H₂O)₃. Excited state calculations of DAH⁺(H₂O)₃ reproduce these spectral features. The conformer-selected IR spectrum of DAH⁺(H₂O)₃ is measured by IR dip spectroscopy, and its structure is assigned with the help of quantum chemical calculations. The excited state lifetime of DAH⁺ is much shorter than 20 ps, the cross correlation of the ps lasers, revealing a fast relaxation dynamics. The minimal energy path along the NH → π proton transfer coordinate exhibits a low energy barrier in the monomer, while this path is blocked by the high energy barrier in DAH⁺(H₂O)₃. It is concluded that the excited state proton transfer in DAH⁺ is inhibited by water-insertion.

Real-time observation of photoionization-induced water migration dynamics in 4-methylformanilide-water by picosecond time-resolved infrared spectroscopy and ab initio molecular dynamics simulations

A novel time-resolved pump-probe spectroscopic approach that enables to keep high resolution in both the time and energy domain, nanosecond excitation-picosecond ionization-picosecond infrared probe (ns-ps-ps TRIR) spectroscopy, has been applied to the trans-4-methylformanilide-water (4MetFA-W) cluster. Water migration dynamics from the CO to the NH binding site in a peptide linkage triggered by photoionization of 4MetFA-W is directly monitored by the ps time evolution of IR spectra, and the presence of an intermediate state is revealed. The time evolution is analyzed by rate equations based on a four-state model of the migration dynamics. Time constants for the initial to the intermediate and hot product and to the final product are obtained. The acceleration of the dynamics by methyl substitution and the strong contribution of intracluster vibrational energy redistribution in the termination of the solvation dynamics is suggested. This picture is well confirmed by the ab initio on-the-fly molecular dynamics simulations. Vibrational assignments of 4MetFA and 4MetFA-W in the neutral (S₀ and S₁) and ionic (D₀) electronic states measured by ns IR dip and electron-impact IR photodissociation spectroscopy are also discussed prior to the results of time-resolved spectroscopy.

Potassium and sodium ion complexes with a partial peptide of the selectivity filter in K+ channels studied by cold ion trap infrared spectroscopy: the effect of hydration

Potassium channels allow K+ to rapidly diffuse, while the selectivity filter (SF) actively blocks Na+. The presence of water in the SF during ion translocation remains under debate due to the experimental and computational challenges in characterizing the interactions between water, ions, and the SF. Our bottom-up approach has been applied to a system composed of a partial peptide of the SF (Ac-tyrosine-NHMe) with a metal ion and a single water molecule to probe these interactions. The IR photodissociation spectra of M+Ac-tyrosine-NHMe(H2O) (M = Na, K) combined with quantum chemical calculations revealed that the water molecule binding sites are ion-dependent. In addition, the ion-peptide distances are elongated significantly for the K+ complex in comparison to the Na+ complex by the addition of a single water molecule. This striking structural difference with the water molecule is discussed in relation to ion selectivity and translocation within the K+ channel.

Cryogenic ion spectroscopy of adenine complexes containing alkali metal cations

Cryogenic ion spectroscopy was used to characterize adenine complexes containing alkali metal cations (M⁺A, M = Cs, Rb, K, Na, and Li) produced by electrospray ionization. The ultraviolet (UV) photodissociation spectra of the complexes stored in a cryogenic ion trap exhibited well-resolved vibronic bands near their origin bands of the S₀-S₁ transition. The UV-UV hole-burning and infrared ion-dip spectra showed that all the M⁺A ions in the ion trap were single isomers of M⁺A7a, where the M⁺ ion was not bound to canonical 9H-adenine (A9) but bound to a rare tautomer, 7H-adenine (A7). Density functional theory calculations showed lower tautomerization barriers for M⁺A9 than for bare A9 in aqueous solution. We suggest that M⁺ ions not only play a catalytic role in the tautomerization of A9 to A7 but also increase the tautomerization yield by forming stable M⁺A7a isomers.

Rethinking Ion Transport by Ionophores: Experimental and Computational Investigation of Single Water Hydration in Valinomycin-K+ Complexes

Valinomycin is a macrocyclic ionophore that transports K⁺ across hydrophobic membranes. Its function depends on selectivity, capture, transport, and release of the ion. While thermodynamics clearly indicate that valinomycin binds K⁺ preferentially over all other alkali ions, characterizing the capture/transport/release of K⁺ by valinomycin at the molecular level remains a challenge. The bracelet-like structure of valinomycin-K⁺ (K⁺VM) has the ion completely enveloped, facilitating transport through the cell membrane. We report that hydration by a single water molecule, (K⁺VM)(H₂O), produces three different conformers, identified by infrared spectroscopy and supporting computational studies. For two minor conformers, the water prevents the ionophore from closing, a conformation that would inhibit diffusion through the membrane. However, the dominant conformer encloses both the ion and the water, replicating the bracelet-like K⁺VM and arguably enhancing diffusion through the membrane. This potential for active participation of water in transport through the hydrophobic cellular membrane has never been previously considered.

Revealing the role of excited state proton transfer (ESPT) in excited state hydrogen transfer (ESHT): systematic study in phenol-(NH3) n clusters

Excited State Hydrogen Transfer (ESHT), proposed at the end of the 20th century by the corresponding authors, has been observed in many neutral or protonated molecules and become a new paradigm to understand excited state dynamics/photochemistry of aromatic molecules. For example, a significant number of photoinduced proton-transfer reactions from X–H bonds have been re-defined as ESHT, including those of phenol, indole, tryptophan, aromatic amino acid cations and so on. Photo-protection mechanisms of biomolecules, such as isolated nucleic acids of DNA, are also discussed in terms of ESHT. Therefore, a systematic and up-to-date description of ESHT mechanism is important for researchers in chemistry, biology and related fields. In this review, we will present a general model of ESHT which unifies the excited state proton transfer (ESPT) and the ESHT mechanisms and reveals the hidden role of ESPT in controlling the reaction rate of ESHT. For this purpose, we give an overview of experimental and theoretical work on the excited state dynamics of phenol–(NH₃)_n clusters and related molecular systems. The dynamics has a significant dependence on the number of solvent molecules in the molecular cluster. Three-color picosecond time-resolved IR/near IR spectroscopy has revealed that ESHT becomes an electron transfer followed by a proton transfer in highly solvated clusters. The systematic change from ESHT to decoupled electron/proton transfer according to the number of solvent molecules is rationalized by a general model of ESHT including the role of ESPT.

A general model of excited state hydrogen transfer (ESHT) which unifies ESHT and the excited state proton transfer (ESPT) is presented from experimental and theoretical works on phenol–(NH₃)_n. The hidden role of ESPT is revealed.