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Papers by Luiz Alberto Beraldo Moraes

Research paper thumbnail of ChemInform Abstract: Dehydrobenzoyl Cations: Distonic Ions with Dual Free Radical and Acylium Ion Reactivity

Research paper thumbnail of Gas-Phase Synthesis and Characterization of an Azaphosphirenium Ion: The First N,P-Analogue of the Aromatic Cyclopropenyl Cation

Organometallics, Oct 13, 2001

Research paper thumbnail of Dehydrobenzoyl Cations: Distonic Ions with Dual Free Radical and Acylium Ion Reactivity

Journal of the American Chemical Society, Oct 17, 1998

Research paper thumbnail of Structurally diagnostic ion-molecule reactions: acylium ions with ?-, ?- and ?-hydroxy ketones

Journal of Mass Spectrometry, 2002

Research paper thumbnail of Gas-phase chemistry of acylium ions. Seven-to-five ring contraction of 1,3-dioxepane and 1,3-dioxep-5-ene

Journal of Mass Spectrometry, Jun 1, 1999

ABSTRACT

Research paper thumbnail of Transacetalization of 1,3-dioxane with acylium and sulfinyl cations in the gas phase

Journal of the Chemical Society, 1997

Research paper thumbnail of Acyclic distonic acylium ions: Dual free radical and acylium ion reactivity in a single molecule

Journal of the American Society for Mass Spectrometry, Aug 1, 2000

Research paper thumbnail of The First Nonclassical Distonic Ion

Journal of the American Chemical Society, Jul 28, 2000

Research paper thumbnail of Ketalization of gaseous acylium ions

Journal of the American Society for Mass Spectrometry, Feb 1, 2001

Research paper thumbnail of Novel Ketalization Reaction of Acylium Ions with Diols and Analogues in the Gas Phase

Journal of Organic Chemistry, 1996

Research paper thumbnail of Transacetalization with Acylium Ions. A Structurally Diagnostic Ion/Molecule Reaction for Cyclic Acetals and Ketals in the Gas Phase

Journal of Organic Chemistry, Jul 1, 1997

Research paper thumbnail of A new method for the selective quantitation of cyanogenic glycosides by membrane introduction mass spectrometry

Research paper thumbnail of Electron ionization mass spectra of bis-1,2,4-oxadiazoles: tandem mass spectrometry and accurate mass measurements

Rapid Communications in Mass Spectrometry, 2001

Research paper thumbnail of The use of electrospray ionization tandem mass spectrometry on the structural characterization of novel asymmetric metallo-organic supermolecules, based on pentafluorophenylporphyrins and ruthenium complexes

Research paper thumbnail of Direct sampling tandem mass spectrometry (MS/MS) and multiway calibration for isomer quantitation

Research paper thumbnail of The Gas-Phase Meerwein Reaction

Chemistry: A European Journal, Mar 3, 2000

A systematic investigation of a novel epoxide and thioepoxide ring expansion reaction promoted by... more A systematic investigation of a novel epoxide and thioepoxide ring expansion reaction promoted by gaseous acylium and thioacylium ions is reported. As ab initio calculations predict, and 18O-labeling and MS3 pentaquadrupole experiments demonstrate, the reaction proceeds by initial O(S)-acylation of the (thio)epoxides followed by rapid intramolecular nucleophilic attack that results in three-to-five-membered ring expansion, and forms cyclic 1,3-dioxolanylium, 1,3-oxathiolanylium, or 1,3-dithiolanylium ions. This gas-phase reaction is analogous to a condensed-phase reaction long since described by H. Meerwein (Chem. Ber. 1955, 67, 374), and is termed as "the gas-phase Meerwein reaction"; it occurs often to great extents or even exclusively, but in some cases, particularly for the most basic (thio)epoxides and the most acidic (thio)acylium ions, proton transfer (eventually hydride abstraction) competes efficiently, or even dominates. When (thio)epoxides react with (thio)-acylium ions, the reaction promotes O(S)-scrambling; when epoxides react with thioacylium ions and the adducts are dissociated, it promotes S/O replacement. An analogous four-to-six-membered ring expansion also occurs predominantly in reactions of trimethylene oxide with acylium and thioacylium ions.

Research paper thumbnail of Production and chemical characterization of pigments in filamentous fungi

Research paper thumbnail of Enhanced xyloglucan-specific endo-β-1,4-glucanase efficiency in an engineered CBM44-XegA chimera

Applied microbiology and biotechnology, Jan 22, 2015

Xyloglucan-specific endo-β-1,4-glucanases (Xegs, EC 3.2.1.151) exhibit high catalytic specificity... more Xyloglucan-specific endo-β-1,4-glucanases (Xegs, EC 3.2.1.151) exhibit high catalytic specificity for β-1,4 linkages of xyloglucan, a branched hemicellulosic polysaccharide abundant in dicot primary cell walls and present in many monocot species. In nature, GH12 Xegs are not associated with carbohydrate-binding modules (CBMs), and here, we have investigated the effect of the fusion of the xyloglucan-specific CBM44 on the structure and function of a GH12 Xeg from Aspergillus niveus (XegA). This fusion presented enhanced catalytic properties and conferred superior thermal stability on the XegA. An increased k cat (chimera, 177.03 s(-1); XegA, 144.31 s(-1)) and reduced KM (chimera, 1.30 mg mL(-1); XegA, 1.50 mg mL(-1)) resulted in a 1.3-fold increase in catalytic efficiency of the chimera over the parental XegA. Although both parental and chimeric enzymes presented catalytic optima at pH 5.5 and 60 °C, the thermostabilitiy of the chimera at 60 °C was greater than the parental XegA. Mor...

Research paper thumbnail of Naphthoquinone derivatives as potential immunomodulators: prospective for COVID-19 treatment

Research paper thumbnail of Characterization of lipopeptides from Paenibacillus sp. (IIRAC30) suppressing Rhizoctonia solani

World Journal of Microbiology & Biotechnology, May 22, 2010

Research paper thumbnail of ChemInform Abstract: Dehydrobenzoyl Cations: Distonic Ions with Dual Free Radical and Acylium Ion Reactivity

Research paper thumbnail of Gas-Phase Synthesis and Characterization of an Azaphosphirenium Ion: The First N,P-Analogue of the Aromatic Cyclopropenyl Cation

Organometallics, Oct 13, 2001

Research paper thumbnail of Dehydrobenzoyl Cations: Distonic Ions with Dual Free Radical and Acylium Ion Reactivity

Journal of the American Chemical Society, Oct 17, 1998

Research paper thumbnail of Structurally diagnostic ion-molecule reactions: acylium ions with ?-, ?- and ?-hydroxy ketones

Journal of Mass Spectrometry, 2002

Research paper thumbnail of Gas-phase chemistry of acylium ions. Seven-to-five ring contraction of 1,3-dioxepane and 1,3-dioxep-5-ene

Journal of Mass Spectrometry, Jun 1, 1999

ABSTRACT

Research paper thumbnail of Transacetalization of 1,3-dioxane with acylium and sulfinyl cations in the gas phase

Journal of the Chemical Society, 1997

Research paper thumbnail of Acyclic distonic acylium ions: Dual free radical and acylium ion reactivity in a single molecule

Journal of the American Society for Mass Spectrometry, Aug 1, 2000

Research paper thumbnail of The First Nonclassical Distonic Ion

Journal of the American Chemical Society, Jul 28, 2000

Research paper thumbnail of Ketalization of gaseous acylium ions

Journal of the American Society for Mass Spectrometry, Feb 1, 2001

Research paper thumbnail of Novel Ketalization Reaction of Acylium Ions with Diols and Analogues in the Gas Phase

Journal of Organic Chemistry, 1996

Research paper thumbnail of Transacetalization with Acylium Ions. A Structurally Diagnostic Ion/Molecule Reaction for Cyclic Acetals and Ketals in the Gas Phase

Journal of Organic Chemistry, Jul 1, 1997

Research paper thumbnail of A new method for the selective quantitation of cyanogenic glycosides by membrane introduction mass spectrometry

Research paper thumbnail of Electron ionization mass spectra of bis-1,2,4-oxadiazoles: tandem mass spectrometry and accurate mass measurements

Rapid Communications in Mass Spectrometry, 2001

Research paper thumbnail of The use of electrospray ionization tandem mass spectrometry on the structural characterization of novel asymmetric metallo-organic supermolecules, based on pentafluorophenylporphyrins and ruthenium complexes

Research paper thumbnail of Direct sampling tandem mass spectrometry (MS/MS) and multiway calibration for isomer quantitation

Research paper thumbnail of The Gas-Phase Meerwein Reaction

Chemistry: A European Journal, Mar 3, 2000

A systematic investigation of a novel epoxide and thioepoxide ring expansion reaction promoted by... more A systematic investigation of a novel epoxide and thioepoxide ring expansion reaction promoted by gaseous acylium and thioacylium ions is reported. As ab initio calculations predict, and 18O-labeling and MS3 pentaquadrupole experiments demonstrate, the reaction proceeds by initial O(S)-acylation of the (thio)epoxides followed by rapid intramolecular nucleophilic attack that results in three-to-five-membered ring expansion, and forms cyclic 1,3-dioxolanylium, 1,3-oxathiolanylium, or 1,3-dithiolanylium ions. This gas-phase reaction is analogous to a condensed-phase reaction long since described by H. Meerwein (Chem. Ber. 1955, 67, 374), and is termed as "the gas-phase Meerwein reaction"; it occurs often to great extents or even exclusively, but in some cases, particularly for the most basic (thio)epoxides and the most acidic (thio)acylium ions, proton transfer (eventually hydride abstraction) competes efficiently, or even dominates. When (thio)epoxides react with (thio)-acylium ions, the reaction promotes O(S)-scrambling; when epoxides react with thioacylium ions and the adducts are dissociated, it promotes S/O replacement. An analogous four-to-six-membered ring expansion also occurs predominantly in reactions of trimethylene oxide with acylium and thioacylium ions.

Research paper thumbnail of Production and chemical characterization of pigments in filamentous fungi

Research paper thumbnail of Enhanced xyloglucan-specific endo-β-1,4-glucanase efficiency in an engineered CBM44-XegA chimera

Applied microbiology and biotechnology, Jan 22, 2015

Xyloglucan-specific endo-β-1,4-glucanases (Xegs, EC 3.2.1.151) exhibit high catalytic specificity... more Xyloglucan-specific endo-β-1,4-glucanases (Xegs, EC 3.2.1.151) exhibit high catalytic specificity for β-1,4 linkages of xyloglucan, a branched hemicellulosic polysaccharide abundant in dicot primary cell walls and present in many monocot species. In nature, GH12 Xegs are not associated with carbohydrate-binding modules (CBMs), and here, we have investigated the effect of the fusion of the xyloglucan-specific CBM44 on the structure and function of a GH12 Xeg from Aspergillus niveus (XegA). This fusion presented enhanced catalytic properties and conferred superior thermal stability on the XegA. An increased k cat (chimera, 177.03 s(-1); XegA, 144.31 s(-1)) and reduced KM (chimera, 1.30 mg mL(-1); XegA, 1.50 mg mL(-1)) resulted in a 1.3-fold increase in catalytic efficiency of the chimera over the parental XegA. Although both parental and chimeric enzymes presented catalytic optima at pH 5.5 and 60 °C, the thermostabilitiy of the chimera at 60 °C was greater than the parental XegA. Mor...

Research paper thumbnail of Naphthoquinone derivatives as potential immunomodulators: prospective for COVID-19 treatment

Research paper thumbnail of Characterization of lipopeptides from Paenibacillus sp. (IIRAC30) suppressing Rhizoctonia solani

World Journal of Microbiology & Biotechnology, May 22, 2010