A calorimetric study of simple bases in H-ZSM-5: a comparison with gas-phase and solution-phase acidities

Verteporfin, a free base benzoporphyrin derivative monoacid ring A, is a photosensitizing drug for photodynamic therapy (PDT) used in the treatment of the wet form of macular degeneration and activated by red light of 689 nm. Here, we present the first direct study of its photofragmentation channels in the gas phase, conducted using a laser interfaced mass spectrometer across a broad photoexcitation range from 250 to 790 nm. The photofragmentation channels are compared with the collision-induced dissociation (CID) products revealing similar dissociation pathways characterized by the loss of the carboxyl and ester groups. Complementary solution-phase photolysis experiments indicate that photobleaching occurs in verteporfin in acetonitrile; a notable conclusion, as photoinduced activity in Verteporfin was not thought to occur in homogenous solvent conditions. These results provide unique new information on the thermal break-down products and photoproducts of this light-triggered drug.

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Do electrospray mass spectra reflect the ligand binding state of proteins in solution?

Canadian Journal of Chemistry ◽

10.1139/v05-194 ◽

2005 ◽

Vol 83 (11) ◽

pp. 1953-1960 ◽

Cited By ~ 13

Author(s):

Belal M Hossain ◽

Douglas A Simmons ◽

Lars Konermann

Keyword(s):

Mass Spectrometry ◽

Gas Phase ◽

Protein Interactions ◽

Noncovalent Complex ◽

Deuterium Exchange ◽

Solution Phase ◽

Hydrogen Deuterium Exchange ◽

Esi Ms ◽

Protein Ions ◽

Hydrogen Deuterium

Electrospray ionization (ESI) mass spectrometry (MS) has become a popular tool for monitoring ligandprotein and proteinprotein interactions. Due to the "gentle" nature of the ionization process, it is often possible to transfer weakly bound complexes into the gas phase, thus making them amenable to MS detection. One problem with this technique is the potential occurrence of fragmentation events during ESI. Also, some analytes tend to cluster together during ionization, thus forming nonspecific gas-phase assemblies that do not represent solution-phase complexes. In this work, we implemented a hydrogendeuterium exchange (HDX) approach that can reveal whether or not the free and (or) bound constituents of a complex observed in ESI-MS reflect the binding situation in solution. Proteins are subjected to ESI immediately following an isotopic labeling pulse; only ligand-free and ligand-bound protein ions that were formed directly from the corresponding solution-phase species showed different HDX levels. Using myoglobin as a model system, it is demonstrated that this approach can readily distinguish scenarios where the hemeprotein interactions were disrupted in solution from those where dissociation of the complex occurred in the gas phase. Experiments on cytochrome c strongly suggest that dimeric protein ions observed in ESI-MS reflect aggregates that were formed in solution.Key words: electrospray mass spectrometry, ligandprotein interaction, noncovalent complex, hydrogendeuterium exchange, protein folding.

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Studies on the structure and conformational flexibility of secondary structures in amyloid beta — A quantum chemical study

Journal of Theoretical and Computational Chemistry ◽

10.1142/s0219633620500145 ◽

2020 ◽

Vol 19 (06) ◽

pp. 2050014

Author(s):

Mahendiraprabu Ganesan ◽

Selvarengan Paranthaman

Keyword(s):

Gas Phase ◽

Amyloid Beta ◽

Density Functional ◽

Conformational Transition ◽

Intermolecular Hydrogen Bond ◽

Quantum Chemical Study ◽

Chemical Study ◽

Secondary Structures ◽

Conformational Flexibility ◽

Solution Phase

Density functional theory (DFT) calculations are performed to study the conformational flexibility of secondary structures in amyloid beta (A[Formula: see text]) polypeptide. In DFT, M06-2X/6-31[Formula: see text]G(d, p) method is used to optimize the secondary structures of 2LFM and 2BEG in gas phase and in solution phase. Our calculations show that the secondary structures are energetically more stable in solution phase than in gas phase. This is due to the presence of strong solvent interaction with the secondary structures considered in this study. Among the backbone [Formula: see text] and [Formula: see text] dihedral angles, [Formula: see text] varies significantly in sheet structure. This is due to the absence of intermolecular hydrogen bond (H-bond) interactions in sheets considered in this study. Our calculations show that the conformational transition of helix/coil to sheet or vice-versa is due to the floppiness of the amino acid residues. This is observed from the Ramachandran map of the studied secondary structures. Further, it is noted that the intramolecular H-bond interactions play a significant role in the conformational transition of secondary structures of A[Formula: see text].

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Bond-dissociation enthalpies in the gas phase and in organic solvents: Making ends meet

Pure and Applied Chemistry ◽

10.1351/pac200779081369 ◽

2007 ◽

Vol 79 (8) ◽

pp. 1369-1382 ◽

Cited By ~ 8

Author(s):

Rui M. Borges dos Santos ◽

Benedito J. Costa Cabral ◽

José A. Martinho Simões

Keyword(s):

Gas Phase ◽

Organic Solvents ◽

Solvent Effects ◽

Solution Phase ◽

Parent Molecule ◽

Solvent Interaction ◽

Solvation Effects ◽

Bond Dissociation ◽

The Difference

Solvent effects are responsible for the difference between gas- and solution-phase bond-dissociation enthalpies (BDEs), and are thus crucial for understanding reactivity in solution. While solvation effects can be negligible (e.g., in reactions involving carbon-centered radicals), they may be rather significant (e.g., when oxygen-centered radicals are formed). This paper reviews a number of models which have been proposed to deal with the difference between the solvation energetics of a radical and its parent molecule. It is concluded that the radical-solvent interaction may be larger than previously anticipated.

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