Laser desorption jet-cooling of organic molecules

Meijer, Gerard; Vries, Mattanjah S. de; Hunziker, H. E.; Wendt, Hartmut

doi:10.1007/bf00329101

Cited by 176 publications

(117 citation statements)

References 19 publications

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“…We placed DNA bases in the gas phase by pulsed laser desorption followed by entrainment in a supersonic expansion of argon (11). This jet cooling served two purposes: (i) The resulting internal temperature of 10-20 K allowed us to perform highresolution spectroscopy both in the UV and in the IR wavelength ranges.…”

Section: Methodsmentioning

confidence: 99%

“…Twenty lowest-energy hydrogen-bonded GC structures. Stabilization energy for each is indicated in kcal͞mol relative to that of the lowest-energy configuration, the WC structure (11). Blue circles indicate structures that are not possible with 1-substituted cytosine, and gray circles indicate structures that are not possible with 9-substituted guanine.…”

Section: Methodsmentioning

confidence: 99%

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Photochemical selectivity in guanine–cytosine base-pair structures

Abo-Riziq

Grace

Nir

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

248

284

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Prebiotic chemistry presumably took place before formation of an oxygen-rich atmosphere and thus under conditions of intense short wavelength UV irradiation. Therefore, the UV photochemical stability of the molecular building blocks of life may have been an important selective factor in determining the eventual chemical makeup of critical biomolecules. To investigate the role of UV irradiation in base-pairing we have studied guanine (G) and cytosine (C) base pairs in the absence of the RNA backbone. We distinguished base-pair structures by IR-UV hole-burning spectroscopy as well as by high-level correlated ab initio calculations. The Watson-Crick structure exhibits broad UV absorption, in stark contrast to other GC structures and other base-pair structures. This broad absorption may be explained by a rapid internal conversion that makes this specific base pair arrangement uniquely photochemically stable.ab initio computation ͉ DNA base pairs ͉ IR-UV spectroscopy ͉ jet cooling ͉ photochemistry T he DNA bases involved in reproduction have short S 1 excited state lifetimes, of the order of 1 ps or less (1-7). It has been argued that this phenomenon serves to protect these bases against photochemical damage, because after excitation they do not cross to the reactive triplet state; instead, they rapidly internally convert to the electronic ground state (8). This mechanism may have been particularly significant under the conditions of the early earth, when purines and pyrimidines presumably were assembled into the first macromolecular structures, producing RNA. At that time, the earth was exposed to shorter wavelength UV radiation than it is today. For an analysis of possible prebiotic chemistry, it is necessary not only to consider the individual bases but also to study them as they interact and to do so without the RNA backbone (9). We achieve such an analysis by studying clusters of guanine (G) and cytosine (C) in the gas phase by using double resonant laser spectroscopy techniques. The experimental studies are accompanied by stateof-the-art quantum chemical and molecular dynamics calculations of the pairing of G and C. These two bases can form many different hydrogen-bonded structures, of which at least 20 are within 12 kcal͞mol of the global minimum. Thus, the familiar Watson-Crick (WC) structure may not be unique, based on energies alone. Here, we report a remarkable difference in excited state properties among the WC structure and other structures. The former exhibits broad UV absorption features; this is in contrast with the sharp UV spectra exhibited by non-WC structures. The broad absorption can be explained by recent theoretical results, predicting a pathway for rapid internal conversion (10). If the difference is solely due to lifetime broadening, these results correspond to a lifetime for the WC structures that is at least 2 orders of magnitude shorter than those of observed non-WC structures. Thus, it appears possible that the WC recognition mechanism involves a structure that was significantly more stab...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Photochemical selectivity in guanine–cytosine base-pair structures

Abo-Riziq

Grace

Nir

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

248

284

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“…The use of activated carbon yields a stable source of DPA for many hours of operation. 8,10 Accurate positioning of the desorption substrate relative to the nozzle opening as well as accurate alignment of the desorption laser spot along the molecular beam axis is needed for optimum beam intensity. The laser de-sorbed molecules are entrained in the Ar gas pulse and are internally cooled by multiple collisions with the carrier gas atoms.…”

Section: Methodsmentioning

confidence: 99%

“…This cooling process can be as efficient as in conventional seeding experiments provided the desorption takes place very close to the nozzle ͑within two nozzle diameters͒ and rotational temperatures down to 5 K have been demonstrated using this approach. 8 The pulse of laser desorbed molecules travels along the molecular beam axis through the skimmer into the differentially pumped detection chamber.…”

Section: Methodsmentioning

confidence: 99%

“…[5][6][7] It has been demonstrated by various groups that the detection sensitivity of such a laser desorption jetcooling molecular beam spectrometer is such that femtograms of material are sufficient for a mass-spectrometric analysis, and that mass-resolved wavelength spectra can already be recorded using picograms of material. 8 In many cases, however, the amount of material that is available for spectroscopic characterization is not limited to picograms, and one would therefore like to know what the optimum beam intensity is that one can reach following the laser desorption approach. This beam intensity can then be compared to the typical beam intensities that one can reach when conventional seeding techniques are being used.…”

Section: Introductionmentioning

confidence: 99%

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Measurement of the beam intensity in a laser desorption jet-cooling mass spectrometer

Boogaarts

Meijer

1995

The Journal of Chemical Physics

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In a laser desorption jet-cooling molecular beam spectrometer the concentration of translationally and internally cooled laser desorbed organic molecules that can be achieved is experimentally determined. Sensitive direct absorption detection of laser desorbed jet-cooled diphenylamine ͑DPA͒ via cavity ring down ͑CRD͒ spectroscopy on the S 1 ←S 0 transition around 308 nm is used to measure the line-integrated absolute absorption of the pulse of laser desorbed DPA molecules. The absolute cross section for the various vibrational bands of the electronic transition that is used, is determined in a separate two-color ionization experiment. It is concluded that the optimum beam intensity that is obtained with laser desorption is comparable to the beam intensity that is obtained in the same spectrometer by conventional seeding of the desired species at a partial pressure of 10 Ϫ4 .

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