Luiz Alberto Beraldo Moraes - Academia.edu (original) (raw)

Papers by Luiz Alberto Beraldo Moraes

Organometallics, Oct 13, 2001

Journal of the American Chemical Society, Oct 17, 1998

In the gas phase, m-and p-dehydrobenzoyl cations display strong duality of chemical behavior. The... more In the gas phase, m-and p-dehydrobenzoyl cations display strong duality of chemical behavior. The ions react selectively as either free radicals or acylium ions, depending on the choice of the neutral reaction partner. Transacetalization with 2-methyl-1,3-dioxolane, ketalization with 2-methoxyethanol, and epoxide ring expansion with epichlorohydrin demonstrate their acylium ion reactivity, whereas • SCH 3 abstraction with dimethyl disulfide demonstrates their free radical reactivity. In one-pot reactions with gaseous mixtures of epichlorohydrin and dimethyl disulfide, the m-and p-dehydrobenzoyl cations react selectively at either site to form the two monoderivatized ions in variable but controlled yields; further reaction at either the remaining radical or the acylium charge site forms a single biderivatized ion as the final product. The o-dehydrobenzoyl cation also displays the expected radical and acylium ion reactivities. But for the ortho isomer, binding of the nucleophilic neutral to the free or derivatized C + dO group facilitates reactions at the radical site. Hence, the ortho isomer displays a unique behavior; its acylium ion reactions either occur simultaneously with, or are followed by, H-abstraction radical reactions. As shown by ab initio calculations, the three isomers display σ-localized odd-spin and π-delocalized charge densities, which characterize distonic structures with molecular orbital-separated radical and charge sites. The dehydrobenzoyl cations are also, according to the calculations, the most stable among 19 of the most feasible C 7 H 4 O +• isomers.

Journal of Mass Spectrometry, 2002

Journal of Mass Spectrometry, Jun 1, 1999

ABSTRACT

Journal of the Chemical Society, 1997

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

Journal of the American Chemical Society, Jul 28, 2000

The gaseous and ionized prototype carbonyl ylide, the distonic ion + CH 2-O-CH 2 • , is found to ... more The gaseous and ionized prototype carbonyl ylide, the distonic ion + CH 2-O-CH 2 • , is found to transfer ionized methylene to 1-adamantylphosphaacetylene (1-Ad-CtP), a kinetically stabilized phosphaalkyne, thus forming the 1-adamantylphosphaacetylenium P-methylide ion, 1-Ad-C + dP-CH 2 • , a novel phosphorus, and the first nonclassical distonic ion. The ion abstracts CH 3 S • from CH 3 SSCH 3 and both Br • and C 3 H 5 • from allyl bromide, and this characteristic reactivity demonstrates its distonic character. MO calculations at the Becke3LYP/6-311G(d,p) and MCSCF [CAS(3,3)] levels confirm that 1-Ad-C + dP-CH 2 • bears spatially separated charge and odd spin sites. They also reveal for the ion a phosphaallylic radical structure that stabilizes the radical site, and a σ-bridged structure with three-center two-electron bonds that stabilizes the charge site. This unique electronic structure characterizes 1-Ad-C + dP-CH 2 • as the first nonclassical distonic ion.

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

Journal of Organic Chemistry, 1996

Journal of Organic Chemistry, Jul 1, 1997

Rapid Communications in Mass Spectrometry, 2001

Polyhedron, Aug 1, 2008

The novel asymmetric metallo-organic triads cis-and trans-[B(4-py)BPFPH 2 {Ru 3 O(Ac) 6 (py) 2 }{... more The novel asymmetric metallo-organic triads cis-and trans-[B(4-py)BPFPH 2 {Ru 3 O(Ac) 6 (py) 2 }{Ru-(bpy) 2 Cl}](PF 6) 2 (5a,b) for which cis-and trans-B(4-py)BPFPH 2 = 5,10-bis(pentafluorophenyl)-15,20bis(4-pyridyl)porphyrin and 5,15-bis(pentafluorophenyl)-10,20-bis(4-pyridyl)porphyrin, respectively; Ac = acetate; py = pyridine and bpy = 2,2 0-bipyridine, as well as their corresponding monosubstituted dyads cis-and trans-[B(4-py)BPFPH 2 {Ru 3 O(Ac) 6 (py) 2 }]PF 6 (4a,b) have been structurally characterized via electrospray ionization mass spectrometry (ESI-MS and ESI-MS/MS). The ESI-MS of dyads 4a,b display two characteristic Ru-multicomponent clusters of isotopologue ions corresponding to singly charged ions 4a,b + of m/z 1629 and doubly charged ions [4a,b+H] 2+ of m/z 815 and the triads 5a,b are detected by ESI-MS as the intact doubly charged cluster of isotopologue ions of m/z 1039 [5a,b] 2+. The ESI-MS/MS of 4a,b + , [4a,b+H] 2+ and [5a,b] 2+ reveal characteristic dissociation pathways, which confirm the structural assignments providing additional information on the intrinsic binding strengths of the gaseous ions. Although the gas-phase behavior of each pair of isomers was rather similar, the less symmetric dyads 4a,b are distinguished via the 1 H NMR spectral profile of the pyrrolic signals. Exploratory photophysical assays have shown that both modifying motifs alter the porphyrinic core emission profile, opening the possibility to use these asymmetric systems as photophysical devices.

Analyst, Jun 26, 2002

Direct sampling tandem mass spectrometry (MS/MS) was used for the quantitation of mixtures of the... more Direct sampling tandem mass spectrometry (MS/MS) was used for the quantitation of mixtures of the isomers 2-, 3-and 4-ethyl pyridine. The similarity between the analytes and the second-order nature of MS/MS data require the use of multivariate calibration techniques capable of handling multiway data. Multilinear PLS (N-PLS) was applied here, as well as the alternative technique of unfolding the data and using standard two-way PLS. Particular attention was paid to the optimal type of spectral preprocessing. Due to the presence of heteroscedastic noise the logarithmic transform of the spectra prior to calibration gives the best results. Predictions errors of the order of 10-15% were obtained, which compare well with other results found in the literature.

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.

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...

RSC advances, 2024

Inflammation plays a crucial role in COVID-19, and when it becomes dysregulated, it can lead to s... more Inflammation plays a crucial role in COVID-19, and when it becomes dysregulated, it can lead to severe outcomes, including death. Naphthoquinones, a class of cyclic organic compounds widely distributed in nature, have attracted significant interest due to their potential biological benefits. One such naphthoquinone is 3,5,8-trihydroxy-6-methoxy-2-(5-oxohexa-1,3-dienyl)-naphthanthene-1,4-dione (3,5,8-TMON), a compound produced by fungi. Despite its structural similarity to shikonin, limited research has been conducted to investigate its biological properties. Therefore, the objective of this study was to evaluate the effects of 3,5,8-TMON and its synthetic derivatives in the context of inflammation induced by lipopolysaccharide (LPS) and SARS-CoV-2 infection in vitro using cell cultures. 3,5,8-TMON was obtained by acid treatment of crude extracts of fermentation medium from Cordyceps sp., and two derivatives were accessed by reaction with phenylhydrazine under different conditions. The results revealed that the crude extract of the fungi (C. Ex) inhibited the activity of transcription factor NF-kB, as well as the production of nitric oxide (NO) and interleukin-6 (IL-6) when LPS induced it in RAW 264.7 cells. This inhibitory effect was observed at effective concentrations of 12.5 and 3.12 mg mL −1. In parallel, 3,5,8-TMON and the new derivatives 3 and 4 demonstrated the ability to decrease IL-6 production while increasing TNF, with a specific effect depending on the concentration. These concentration-dependent agonist and antagonist effects were observed in THP-1 cells. Furthermore, 3,5,8-TMON inhibited IL-6 production at concentrations of 12.5 and 3.12 mg mL −1 in Calu-3 cells during SARS-CoV-2 viral infection. These findings present promising opportunities for further research into the therapeutic potential of this class of naphthoquinone in the management of inflammation and viral infections.

World Journal of Microbiology & Biotechnology, May 22, 2010

The main aim was to identify the active compound against Rhizoctonia solani produced by the cassa... more The main aim was to identify the active compound against Rhizoctonia solani produced by the cassava endophyte Paenibacillus sp. IIRAC-30. The compounds produced were extracted with ethyl acetate and purified by Sephadex column prior to analysis by Q-TOF mass spectrometry. A C 15-lipopeptide with an estimated molecular weight of 1036 Da and homologues were identified. The lipopeptide had a cyclic structure, which was deduced by interpreting the ESI-MS/MS spectra of main protonated homologues containing 15:0 FA, and the amino acid composition was Glu-Leu-Leu-Val-Asp-Leu-Leu. Therefore, the lipopeptides produced by isolate IIRAC-30 was characterized as a surfactin series. Thus, the main mechanism used by Paenibacillus sp. IIRAC-30 to suppress R. solani was elucidated. Furthermore, because lipopeptides active against phytopathogens generally show low toxicity to humans and the environment, the positive findings presented here suggest that the isolate IIRAC-30 could be a possible candidate for biocontrol of R. solani.