IR spectroscopy of protonated leu-enkephalin and its 18-crown-6 complex embedded in helium droplets

Flórez, Astrid Carolina; Ahn, Doo‐Sik; Gewinner, Sandy; Schöllkopf, Wieland; Helden, Gert von

doi:10.1039/c5cp02172c

Cited by 50 publications

(57 citation statements)

References 32 publications

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“…While the mechanism of the ejection process is not entirely understood, the technique itself is pivotal for ion spectroscopy. Recent experiments revealed that the intensity of the ejection signal rises faster than linear with the laser pulse energy [198]. This effect indicates a nonlinear character of the ejection, and may potentially complicate the interpretation of the results.…”

Section: Molecular Ionsmentioning

confidence: 99%

“…While resonance multiphoton ionization is only feasible with specific molecules, electrospray ionization (ESI) provides a universal technique for bringing large ions, such as proteins, into the gas phase [195,196,[198][199][200]. However, the low density of ions in electrospray has warranted a considerable modification of the pickup technique which involves ion traps.…”

Section: Molecular Ionsmentioning

confidence: 99%

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Infrared spectroscopy in superfluid helium droplets

Verma

Tanyag

O’Connell

et al. 2018

Advances in Physics: X

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For more than two decades, encapsulation in superfluid helium nanodroplets has served as a reliable technique for probing the structure and dynamics of molecules and clusters at a low temperature of ≈0.37 K. Due to weak interactions between molecules and the host liquid helium, good spectral resolution can usually be achieved, making helium droplets an ideal matrix for spectroscopy in a wide spectral range from infrared to ultraviolet. Furthermore, rotational structure in the spectra of small molecules provides a unique probe for interactions with the superfluid on an atomic scale. This review presents a summary of results and a discussion of recent experimental developments in helium droplet spectroscopy with the emphasis laid on infrared studies. Initially, studies focused on single molecules and have been expanded to larger species, such as metal-molecular clusters, biomolecules, free radicals, ions, and proteins. ARTICLE HISTORY

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Section: Molecular Ionsmentioning

confidence: 99%

Section: Molecular Ionsmentioning

confidence: 99%

Infrared spectroscopy in superfluid helium droplets

Verma

Tanyag

O’Connell

et al. 2018

Advances in Physics: X

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“…Here alignment refers to confinement of molecular axes to axes fixed in the laboratory frame -typically defined by the polarization vectors of the laser pulses employed [5,6]. The transfer of laser-induced alignment techniques from gas-phase molecules to molecules in He droplets opens new opportunities such as extending the range of molecular systems amenable to alignment -notably to larger molecules, clusters and complexes [7][8][9], conducting experiments on aligned molecules in the presence of a dissipative environment [1,10,11] and possibly using controlled rotation of molecules [12] to study the properties of He droplets [13].…”

Section: Introductionmentioning

confidence: 99%

Strongly aligned molecules inside helium droplets in the near-adiabatic regime

Shepperson

Chatterley

Søndergaard

et al. 2017

The Journal of Chemical Physics

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Iodine (I 2 ) molecules embedded in He nanodroplets are aligned by a 160 ps long laser pulse. The highest degree of alignment, occurring at the peak of the pulse and quantified by cos 2 θ2D , is measured as a function of the laser intensity. The results are well described by cos 2 θ2D calculated for a gas of isolated molecules each with an effective rotational constant of 0.6 times the gas-phase value, and at a temperature of 0.4 K. Theoretical analysis using the angulon quasiparticle to describe rotating molecules in superfluid helium rationalizes why the alignment mechanism is similar to that of isolated molecules with an effective rotational constant. A major advantage of molecules in He droplets is that their 0.4 K temperature leads to stronger alignment than what can generally be achieved for gas phase molecules -here demonstrated by a direct comparison of the droplet results to measurements on a ∼ 1 K supersonic beam of isolated molecules. This point is further illustrated for more complex system by measurements on 1,4-diiodobenzene and 1,4-dibromobenzene. For all three molecular species studied the highest values of cos 2 θ2D achieved in He droplets exceed 0.96.

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“…Thereafter, Florez et al recorded the vibrational spectra of [Leu-Enk + H] + and its complex with crown-16 [Leu-Enk + CE + H] + embedded in helium droplets. 16 Based on the small spectral shift, the authors confirmed the weak interaction between the dopant – albeit charged – with the helium environment. Our group has examined the effects of kinetic energy and droplet size on the doping efficiency using a different approach.…”

Section: Introductionmentioning

confidence: 92%

Doping of Green Fluorescent Protein into Superfluid Helium Droplets: Size and Velocity of Doped Droplets

et al. 2017

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We report doping of green fluorescent protein from an electrospray ionization (ESI) source into superfluid helium droplets. From analyses of the time profiles of the doped droplets, we identify two distinct groups of droplets. The faster group has a smaller average size, on the order of 106 helium atoms/droplet, and the slower group is much larger, by at least an order of magnitude. The relative populations of these two groups depend on the temperature of the droplet source: from 11 K to 5 K, the signal intensity of the slower droplet group gradually increases, from near the detection limit to comparable to that of the faster group. We postulate that the smaller droplets are formed via condensation of gaseous helium upon expansion from the pulsed valve, while the larger droplets develop from fragmentation of ejected liquid helium. Our results on the size and velocity of the condensation peak at higher source temperatures (> 7 K) agree with previous reports, but those at lower temperatures (< 7 K) seem to be off. We attribute this discrepancy to the masking effect of the exceedingly large droplets from the fragmentation peak in previous measurements of droplet sizes. Within the temperature range of our investigation, although the expansion condition changes from subcritical to supercritical, there is no abrupt change in either the velocity distribution or the size distribution of the condensation peak, and the most salient effect is in the increasing intensity of the fragmentation peak. The absolute doping efficiency, as expressed by the ratio of ion doped droplets over the total number of ions from the ESI source, is on the order of 10−4, while only hundreds of doped ions have been detected. Further improvements in the ESI source are key to extending the technology for future experiments. On the other hand, the separation of the two groups of droplets in velocity is beneficial for size selection of only the smaller droplets for future experiments of electron diffraction.

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IR spectroscopy of protonated leu-enkephalin and its 18-crown-6 complex embedded in helium droplets

Cited by 50 publications

References 32 publications

Infrared spectroscopy in superfluid helium droplets

Infrared spectroscopy in superfluid helium droplets

Strongly aligned molecules inside helium droplets in the near-adiabatic regime

Doping of Green Fluorescent Protein into Superfluid Helium Droplets: Size and Velocity of Doped Droplets

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