Molecular recognition and supramolecular chemistry in the gas phase

We report on the first observation of isolated large neutral metal amino acid complexes such as TrpnMek, with Me == Ca, Ba, Sr, cluster combinations covering n = 1. ..33, k = 0..2 and masses beyond 6500 u. The cluster beam is generated using UV laser desorption from a mixed powder of alkaline-earth metal salts and tryptophan inside a cluster mixing chalU1el. The particles are detected using VUV photoionization followed by time-of-flight mass spectroscopy. The enhanced stability of metal amino acid clusters over pure amino acid clusters is substantiated in molecular dynamics simulations by determining the gain in binding energy related to the inclusion of the metal atoms. . The majority of studies so far focused on the generation and use of ionic species. Our work, presented here, focuses on the gas-phase formation of neutral biomolecular clusters as did already some very early studies in the field [1]. Such experiments are often motivated by the desire to better identify the role of solvation and desolvation for the relative importance of various binding forces in organic clusters and molecules [5].The particle's neutrality is also an important criterion in efforts to establish new beam methods for quantum interferometry with molecular matter waves [6-9] as well as for precision metrology on large molecules [10][11][12]. Neutral molecules are much better isolated from any electromagnetic environment and they may therefore propagate coherently, without noticeable perturbation, even in a rather noisy field environment.Biomolecular clusters are exciting study objects for future matter wave experiments as they permit one to scale the mass in well-defined steps, while at the same time changing the internal properties in an intriguing way: the number of possible conformations as well as the number of allowed configurational and vibrational transitions scales exponentially with the size of the cluster [13], and it is still an open question how this will affect de Broglie interferometry [14], which formally considers only the center of mass motion alone. (19]. But it has still remained a challenge to find reproducible methods for photoionizing biomolecules and complexes with masses exceeding 3000 u [17,20,21].The formation and photo-detection of small amino acid [22] and nucleotide clusters [23], both hydrated and solvent-free, were already reported for objects up to 1400 u. Ultracold small bioclusters can be formed by pick-up in helium nano-droplets [24]. Complexes formed between metal atoms and amino acids were also studied to understand their structure [25], their fragmentation pathways [26,27], and metal ion affinities [28].Here we extend these investigations to much larger organometallic complexes composed of up to more than 30 tryptophan molecules with masses exceeding 6500 u, that can still be detected using VUV photoionization and time-of-flight mass spectrometry. ExperimentalWe generate the molecular macroclusters using pulsed laser evaporation and collisional cooling: the pulsed beam of aNd:YAG laser (Quantel...

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confidence: 99%

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confidence: 99%

Gas-phase formation of large neutral alkaline-earth metal tryptophan complexes

Marksteiner

Haslinger

Sclafani

et al. 2008

“…Mass spectrometry (MS) with a soft ionization technique such as electrospray ionization (ESI) [19 -22] is nowadays challenging these more traditional methods in the study of host-guest interactions [23,24]. As a technique, ESI-MS is positioned somewhere between the solution state and the gas phase.…”

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confidence: 99%

ESI-FTICR mass spectrometric study of alcohol complexation properties of mono- and diphosphonate-bridged cavitands

Ventola

Vainiotalo

Suman

et al. 2006

Alcohol complexation properties of eight mono-and diphenyl phosphonate-bridged cavitands (Scheme 1). were studied by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR) and theoretical calculations. The cavitands varied in number and position of phenyl phosphonate bridges and their orientation with respect to the cavity, length of the lower rim alkyl chains, and substituents at apical positions of the resorcarene skeleton. The specificities of the different cavitands toward primary, secondary, and tertiary alcohols varying long of the alkyl chain were investigated, together with the stabilities of the formed complexes. The number, position, and orientation of the P ϭ O moieties affected the complex formation of the cavitands and stability of the complexes dramatically. Methyl groups at apical positions of the resorcarene skeleton also affected the complexation properties. Although length and branching of the alkyl chain of the alcohol influenced the complex formation, the effect on stability of the complexes was negligible. (J Am Soc Mass Spectrom 2006, 17, 213-221)

“…The anionic supramolecular complexes Inorganic ions with small mass-to-charge ratios are typically analyzed by other techniques, such as ion chromatography and capillary electrophoresis, because under normal MS ionization conditions many compounds can produce small ions that can interfere with their detection. There are, however, some notable examples [7,8] that demonstrate the potential of soft ionization methods [9], such as atmospheric pressure chemical ionization mass spectrometry (APCI-MS) and electrospray ionization mass spectrometry (ESI-MS)[10] for analysis of inorganic ions, and ion pairs, such as ammonium nitrate [11].Increased sensitivity for MS analysis of inorganic ions has been achieved by a relatively new and promising strategy, which bridges the fields of mass spectrometry and supramolecular chemistry [12][13][14]. This approach is based on selective host molecules for specific cationic or anionic guests, which can form ionic adducts with higher molecular mass.…”

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confidence: 99%

“…Increased sensitivity for MS analysis of inorganic ions has been achieved by a relatively new and promising strategy, which bridges the fields of mass spectrometry and supramolecular chemistry [12][13][14]. This approach is based on selective host molecules for specific cationic or anionic guests, which can form ionic adducts with higher molecular mass.…”

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confidence: 99%

Identification of Anionic Supramolecular Complexes of Sulfonamide Receptors with Cl⁻, NO₃⁻, Br⁻, and I⁻ by APCI-MS

Kavallieratos

Sabucedo

Pau

et al. 2005

As part of a mass spectrometric investigation of the binding properties of sulfonamide anion receptors, an atmospheric pressure chemical ionization mass spectrometric (APCI-MS) method involving direct infusion followed by thermal desorption was employed for identification of anionic supramolecular complexes in dichloromethane (CH 2 Cl 2 ). Specifically, the dansylamide derivative of tris(2-aminoethyl)amine (tren) (1), the chiral 1,3-benzenesulfonamide derivatives of (1R,2S)-(ϩ)-cis-1-amino-2-indanol (2), and (R)-(ϩ)-bornylamine, (3), were shown to bind halide and nitrate ions in the presence of (nϪBu) Solutions of receptors and anions in CH 2 Cl 2 were combined to form the anionic supramolecular complexes, which were subsequently introduced into the mass spectrometer via direct infusion followed by thermal desorption. The anionic supramolecular complexes Inorganic ions with small mass-to-charge ratios are typically analyzed by other techniques, such as ion chromatography and capillary electrophoresis, because under normal MS ionization conditions many compounds can produce small ions that can interfere with their detection. There are, however, some notable examples [7,8] that demonstrate the potential of soft ionization methods [9], such as atmospheric pressure chemical ionization mass spectrometry (APCI-MS) and electrospray ionization mass spectrometry (ESI-MS)[10] for analysis of inorganic ions, and ion pairs, such as ammonium nitrate [11].Increased sensitivity for MS analysis of inorganic ions has been achieved by a relatively new and promising strategy, which bridges the fields of mass spectrometry and supramolecular chemistry [12][13][14]. This approach is based on selective host molecules for specific cationic or anionic guests, which can form ionic adducts with higher molecular mass. Most of the supramolecular complexes investigated by MS involve macrocycles, such as crown ethers and cryptands, which form cationic metal-receptor complexes detectable in positive ion mode [15][16][17][18][19]. Anion supramolecular chemistry [20] is relatively less well developed and oftentimes anion receptors are not as strong as cation receptors in terms of thermodynamic binding constants. Moreover, negative ionization is more susceptible to corona discharge [21,22]. Therefore, negative-ion mode MS detection of noncovalent anion-receptor complexes is less common than positive-ion mode, with the examples reported [23][24][25][26][27][28] for the detection of organic explosives. APCI presents some advantages compared with ESI in quantitative analysis such as higher dynamic range, and is considered rugged, easy to operate, and more tolerant of higher buffer concentrations (fewer matrix effects) [31]. Multiply charged species are typically not observed in APCI-MS spectra [1]. Even though APCI is considered a soft ionization method, it has not found the same application in anion supramolecular chemistry as ESI because the larger supramolecular ions are generally not observed. Therefore, successful identification of noncova...