RESUMO
Olefin metathesis has become an efficient tool in synthetic organic chemistry to build carbon-carbon bonds, thanks to the development of Grubbs- and Schrock-type catalysts. Olefin coordination, a key and often rate-determining elementary step for d0 Schrock-type catalysts, has been rarely explored due to the lack of accessible relevant molecular analogues. Herein, we present a fully characterized surrogate of this key olefin-coordination intermediate, namely, a cationic d0 tungsten oxo-methylidene complex bearing two N-heterocyclic carbene ligandsâ[WO(CH2)Cl(IMes)2](OTf) (1) (IMes = 1,3-dimesitylimidazole-2-ylidene, OTf-triflate counteranion), resulting in a trigonal bipyramidal (TBP) geometry, along with its neutral octahedral analogue [WO(CH2)Cl2(IMes)2] (2)âand an isostructural oxo-methylidyne derivative [WO(CH)Cl(IMes)2] (3). The analysis of their solid-state 13C and 183W MAS NMR signatures, along with computed 17O NMR parameters, helps to correlate their electronic structures with NMR patterns and evidences the importance of the competition among the three equatorial ligands in the TBP complexes. Anchored on experimentally obtained NMR parameters for 1, computational analysis of a series of olefin coordination intermediates highlights the interplay between σ- and π-donating ligands in modulating their stability and further paralleling their reactivity. NMR spectroscopy descriptors reveal the origin for the advantage of the dissymmetry in σ-donating abilities of ancillary ligands in Schrock-type catalysts: weak σ-donors avoid the orbital-competition with the oxo ligand upon formation of a TBP olefin-coordination intermediate, while stronger σ-donors compromise M≡O triple bonding and thus render olefin coordination step energy demanding.
RESUMO
Treatment of Ziegler-Natta (ZN) catalysts with BCl3 improves their activity by increasing the number of active sites. Here we show how 47/49Ti solid-state nuclear magnetic resonance (NMR) spectroscopy enables us to understand the electronic structure of the Ti surface sites present in such treated ZN pre-catalysts, prior to activation with alkyl aluminum. High-field (21.1 T) and low-temperature (â¼100 K) NMR augmented by DFT modeling on the pre-catalyst and corresponding molecular analogues enables the detection of 47/49Ti NMR signatures and a molecular level understanding of the electronic structure of Ti surface sites. The associated Ti surface sites exhibit 49Ti NMR signatures (δiso, exp = -170 ppm; CQ, exp = 9.3 MHz; κ = 0.05) corresponding to well-defined fully chlorinated hexacoordinated Ti sites adsorbed on a distorted surface of the MgCl2 support, formed upon post-treatment with BCl3 and removal of the alkoxo ligands, paralleling the increased polymerization activity.
RESUMO
Molecular-level understanding of the acid/base properties of heterogeneous catalysts requires the development of selective spectroscopic probes to establish structure-activity relationships. In this work we show that substituting the surface protons in oxide supports by isolobal N-heterocyclic carbene (NHC) Ag cations and measuring their 109Ag nuclear magnetic resonance (NMR) signatures enables to probe the speciation and to evaluate the corresponding Brønsted acidity of the substituted OH surface sites. Specifically, a series of silver N-heterocyclic carbene (NHC) Ag(i) complexes of general formula [(NHC)AgX] are synthesized and characterized, showing that the 109Ag NMR chemical shift of the series correlates with the Brønsted acidity of the conjugate acid of X- (i.e., HX), thus establishing an acidity scale based on 109Ag NMR chemical shift. The methodology is then used to evaluate the Brønsted acidity of the OH sites of representative oxide materials using Dynamic Nuclear Polarization (DNP-)enhanced solid-state NMR spectroscopy.
RESUMO
The OCT4 transcription factor is necessary to maintain cell stemness in the early stages of embryogenesis and is involved in the formation of induced pluripotent stem cells, but its role in oncogenesis is not yet entirely clear. In this work, OCT4 expression was investigated in malignant gliomas. Twenty glioma cell lines and a sample of normal adult brain tissue were used. OCT4 expression was found in all studied glioma cell lines but was not detected in normal adult brain tissue. For one of these lines, OCT4 knockdown caused tumor cell death. By varying the culture conditions of these cells, we unexpectedly found that OCT4 expression increased when cells were incubated in serum-free medium, and this effect was significantly enhanced in serum-free and L-glutamine-free medium. L-glutamine and the Krebs cycle, which is slowed down in serum-free medium according to our NMR data, are sources of α-KG. Thus, our data indicate that OCT4 expression in gliomas may be regulated by the α-KG-dependent metabolic reprogramming of cells.
RESUMO
Since its emergence over 50 years ago, the structure of surface sites in Ziegler-Natta catalysts, which are responsible for a major fraction of the world's supply of polyethylene (PE) and polypropylene (PP), has remained elusive. This is in part due to the complexity of these systems that involve multiple synthetic steps and components, namely, the MgCl2 support, a transition-metal chloride, and several organic modifiers, known as donors, that are used prior and in some instances during the activation step with alkyl aluminum. Due to the favorable nuclear magnetic resonance (NMR) properties of V and its use in Ziegler-Natta catalysts, we utilize 51V solid-state NMR spectroscopy to investigate the structure of VOCl3 on MgCl2(thf)1.5. The resulting catalyst shows ethylene polymerization activity similar to that of its Ti analogues. Using carefully benchmarked density functional theory (DFT) calculations, the experimental 51V NMR signature was analyzed to elucidate the structure of the surface sites. Using this approach, we demonstrate that the 51V NMR signature contains information about the coordination environment, i.e., the type of ancillary ligand, and the morphology of the MgCl2 support. Analysis of the NMR signature shows that the adsorption of VOCl3 on MgCl2(thf)1.5 generates a well-defined hexacoordinated V-oxo species containing one alkoxy and four chloride ligands, whose local geometry results from the interaction with an amorphous MgCl2 surface. This study illustrates how NMR spectroscopy, which is highly sensitive to the local environment of the investigated nuclei, here V, enables us to identify the exact coordination sphere and to address the effect of the support morphology on surface site structures.
RESUMO
Gallia-based shells with a thickness varying from a submonolayer to ca. 2.5 nm were prepared by atomic layer deposition (ALD) using trimethylgallium, ozone, and partially dehydroxylated silica, followed by calcination at 500 °C. Insight into the atomic-scale structure of these shells was obtained by high-field 71Ga solid-state nuclear magnetic resonance (NMR) experiments and the modeling of X-ray differential pair distribution function data, complemented by Ga K-edge X-ray absorption spectroscopy and 29Si dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) studies. When applying one ALD cycle, the grown submonolayer contains mostly tetracoordinate Ga sites with Si atoms in the second coordination sphere ([4]Ga(Si)) and, according to 15N DNP SENS using pyridine as the probe molecule, both strong Lewis acid sites (LAS) and strong Brønsted acid sites (BAS), consistent with the formation of gallosilicate Ga-O-Si and Ga-µ2-OH-Si species. The shells obtained using five and ten ALD cycles display characteristics of amorphous gallia (GaOx), i.e., an increased relative fraction of pentacoordinate sites ([5]Ga(Ga)), the presence of mild LAS, and a decreased relative abundance of strong BAS. The prepared Ga1-, Ga5-, and Ga10-SiO2-500 materials catalyze the dehydrogenation of isobutane to isobutene, and their catalytic performance correlates with the relative abundance and strength of LAS and BAS, viz., Ga1-SiO2-500, a material with a higher relative fraction of strong LAS, is more active and stable compared to Ga5- and Ga10-SiO2-500. In contrast, related ALD-derived Al1-, Al5-, and Al10-SiO2-500 materials do not catalyze the dehydrogenation of isobutane and this correlates with the lack of strong LAS in these materials that instead feature abundant strong BAS formed via the atomic-scale mixing of Al sites with silica, leading to Al-µ2-OH-Si sites. Our results suggest that [4]Ga(Si) sites provide strong Lewis acidity and drive the dehydrogenation activity, while the appearance of [5]Ga(Ga) sites with mild Lewis activity is associated with catalyst deactivation through coking. Overall, the atomic-level insights into the structure of the GaOx-based materials prepared in this work provide a guide to design active Ga-based catalysts by a rational tailoring of Lewis and Brønsted acidity (nature, strength, and abundance).
RESUMO
Converting colloidal nanocrystals (NCs) into devices for various applications is facilitated by designing and controlling their surface properties. One key strategy for tailoring surface properties is thus to choose tailored surface ligands. In that context, amines have been universally used, with the goal to improve NCs synthesis, processing and performances. However, understanding the nature of surface sites in amine-capped NCs remains challenging, due to the complex surface compositions as well as surface ligands dynamic. Here, we investigate both surface sites and amine ligation in CdSe NCs by combining advanced NMR spectroscopy and computational modelling. Notably, dynamic nuclear polarization (DNP) enhanced 113 Cd and 77 Se 1D NMR helps to identify both bulk and surface sites of NCs, while 113 Cd 2D NMR spectroscopy enables to resolve amines terminated sites on both Se-rich and nonpolar surfaces. In addition to directly bonding to surface sites, amines are shown to also interact through hydrogen-bonding with absorbed water as revealed by 15 N NMR, augmented with computations. The characterization methodology developed for this work provides unique molecular-level insight into the surface sites of a range of amine-capped CdSe NCs, and paves the way to identify structure-function relationships and rational approaches towards colloidal NCs with tailored properties.
RESUMO
The optimization of the air-solid contactor is critical to improve the efficiency of the direct air capture (DAC) process. To enable comparison of contactors and therefore a step toward optimization, two contactors are prepared in the form of pellets and wash-coated honeycomb monoliths. The desired amine functionalities are successfully incorporated onto these industrially relevant pellets by means of a procedure developed for powders, providing materials with a CO2 uptake not influenced by the morphology and the structure of the materials according to the sorption measurements. Furthermore, the amine functionalities are incorporated onto alumina wash-coated monoliths that provide a similar CO2 uptake compared to the pellets. Using breakthrough measurements, dry CO2 uptakes of 0.44 and 0.4 mmol gsorbent-1 are measured for pellets and for a monolith, respectively. NMR and IR studies of CO2 uptake show that the CO2 adsorbs mainly in the form of ammonium carbamate. Both contactors are characterized by estimated Toth isotherm parameters and linear driving force (LDF) coefficients to enable an initial comparison and provide information for further studies of the two contactors. LDF coefficients of 1.5 × 10-4 and of 1.2 × 10-3 s-1 are estimated for the pellets and for a monolith, respectively. In comparison to the pellets, the monolith therefore exhibits particularly promising results in terms of adsorption kinetics due to its hierarchical pore structure. This is reflected in the productivity of the adsorption step of 6.48 mol m-3 h-1 for the pellets compared to 7.56 mol m-3 h-1 for the monolith at a pressure drop approximately 1 order of magnitude lower, making the monoliths prime candidates to enhance the efficiency of DAC processes.
RESUMO
Although titanosilicalite-1 (TS-1) is among the most successful oxidation catalysts used in industry, its active site structure is still debated. Recent efforts have mostly focused on understanding the role of defect sites and extraframework Ti. Here, we report the 47/49Ti signature of TS-1 and molecular analogues [Ti(OTBOS)4] and [Ti(OTBOS)3(OiPr)] using novel MAS CryoProbe to enhance the sensitivity. While the dehydrated TS-1 displays chemical shifts similar to those of molecular homologues, confirming the tetrahedral environment of Ti consistent with X-ray absorption spectroscopy, it is associated with a distribution of larger quadrupolar coupling constants, indicating an asymmetric environment. Detailed computational studies on cluster models highlights the high sensitivity of the NMR signatures (chemical shift and quadrupolar coupling constant) to small local structural changes. These calculations show that, while it will be difficult to distinguish mono- vs dinuclear sites, the sensitivity of the 47/49Ti NMR signature should enable distinguishing the Ti location among specific T site positions.
RESUMO
Streptomycetes produce a huge variety of bioactive metabolites, including antibiotics, enzyme inhibitors, pesticides and herbicides, which offer promise for applications in agriculture as plant protection and plant growth-promoting products. The aim of this report was to characterize the biological activities of strain Streptomyces sp. P-56, previously isolated from soil as an insecticidal bacterium. The metabolic complex was obtained from liquid culture of Streptomyces sp. P-56 as dried ethanol extract (DEE) and possessed insecticidal activity against vetch aphid (Medoura viciae Buckt.), cotton aphid (Aphis gossypii Glov.), green peach aphid (Myzus persicae Sulz.), pea aphid (Acyrthosiphon pisum Harr.) and crescent-marked lily aphid (Neomyzus circumflexus Buckt.), as well as two-spotted spider mite (Tetranychus urticae). Insecticidal activity was associated with production of nonactin, which was purified and identified using HPLC-MS and crystallographic techniques. Strain Streptomyces sp. P-56 also showed antibacterial and antifungal activity against various phytopathogenic bacteria and fungi (mostly for Clavibacfer michiganense, Alternaria solani and Sclerotinia libertiana), and possessed a set of plant growth-promoting traits, such as auxin production, ACC deaminase and phosphate solubilization. The possibilities for using this strain as a biopesticide producer and/or biocontrol and a plant growth-promoting microorganism are discussed.
RESUMO
Advances in solid-state nuclear magnetic resonance (NMR) methods and hardware offer expanding opportunities for analysis of materials, interfaces, and surfaces. Here, we demonstrate the application of a very high magnetic field strength of 28.2 T and fast magic-angle-spinning rates (MAS, >40 kHz) to surface species relevant to catalysis. Specifically, we present as case studies the 1D and 2D solid-state NMR spectra of important catalyst and support materials, ranging from a well-defined silica-supported organometallic catalyst to dehydroxylated γ-alumina and zeolite solid acids. The high field and fast-MAS measurement conditions substantially improve spectral resolution and narrow NMR signals, which is particularly beneficial for solid-state 1D and 2D NMR analysis of 1H and quadrupolar nuclei such as 27Al at surfaces.
RESUMO
Stacking disorder and polymorphism in zeolite and zeolite-like materials hinder their structural characterization. In this work, we propose an advanced approach based on applying "pure shift" solid-state 29Si nuclear magnetic resonance (NMR) spectroscopy for the structural investigation of zeolitic materials containing intergrown polymorphs. The approach developed in the case study of zeolite beta allows for the resolution of 21 29Si signals, attributing them to non-equivalent T sites in polymorphs A, B, and C, reconstruction of individual 29Si magic angle spinning NMR spectra for each polymorph, and determination of the polymorph composition with higher accuracy than X-ray diffraction. The results reveal that two widely used synthetic routes for zeolite beta, alkaline and fluoride synthesis, lead to different polymorph compositions. These findings indicate that "pure shift" solid-state 29Si NMR can serve as a superior tool for the elucidation of polymorphism in zeolites.
RESUMO
Nicotinamide riboside (NR) is an effective precursor of nicotinamide adenine dinucleotide (NAD) in human and animal cells. NR supplementation can increase the level of NAD in various tissues and thereby improve physiological functions that are weakened or lost in experimental models of aging or various human pathologies. However, there are also reports questioning the efficacy of NR supplementation. Indeed, the mechanisms of its utilization by cells are not fully understood. Herein, we investigated the role of purine nucleoside phosphorylase (PNP) in NR metabolism in mammalian cells. Using both PNP overexpression and genetic knockout, we show that after being imported into cells by members of the equilibrative nucleoside transporter family, NR is predominantly metabolized by PNP, resulting in nicotinamide (Nam) accumulation. Intracellular cleavage of NR to Nam is prevented by the potent PNP inhibitor Immucillin H in various types of mammalian cells. In turn, suppression of PNP activity potentiates NAD synthesis from NR. Combining pharmacological inhibition of PNP with NR supplementation in mice, we demonstrate that the cleavage of the riboside to Nam is strongly diminished, maintaining high levels of NR in blood, kidney, and liver. Moreover, we show that PNP inhibition stimulates Nam mononucleotide and NAD+ synthesis from NR in vivo, in particular, in the kidney. Thus, we establish PNP as a major regulator of NR metabolism in mammals and provide evidence that the health benefits of NR supplementation could be greatly enhanced by concomitant downregulation of PNP activity.
Assuntos
NAD , Purina-Núcleosídeo Fosforilase , Humanos , Camundongos , Animais , NAD/metabolismo , Purina-Núcleosídeo Fosforilase/genética , Purina-Núcleosídeo Fosforilase/metabolismo , Niacinamida/farmacologia , Niacinamida/metabolismo , Compostos de Piridínio , Mamíferos/metabolismoRESUMO
This work explores how H2 pretreatment at 550 °C induces structural transformation of two gallia-based propane dehydrogenation (PDH) catalysts, viz. nanocrystalline γ/ß-Ga2O3 and amorphous Ga2O3 (GaO x ) supported on silica (γ-Ga2O3/SiO2 and Ga/SiO2, respectively) and how it affects their activity, propene selectivity and stability with time on stream (TOS). Ga/SiO2-H2 shows poor activity and propene selectivity, no coking and no deactivation with TOS, similar to Ga/SiO2. In contrast, the high initial activity and propene selectivity of γ-Ga2O3/SiO2-H2 decline with TOS but to a lesser extent than in calcined γ-Ga2O3/SiO2. In addition, γ-Ga2O3/SiO2-H2 cokes less than γ-Ga2O3/SiO2. Ga K-edge X-ray absorption spectroscopy suggests an increased disorder of the nanocrystalline γ/ß-Ga2O3 phases in γ-Ga2O3/SiO2-H2 and the emergence of additional tetrahedral Ga sites (GaIV). Such GaIV sites are strong Lewis acid sites (LAS) according to studies using adsorbed pyridine and CO probe molecules, i.e., the abundance of strong LAS is higher in γ-Ga2O3/SiO2-H2 compared to γ-Ga2O3/SiO2 but lower than in Ga/SiO2 and Ga/SiO2-H2. Dissociation of H2 on the Ga-O linkages in γ-Ga2O3/SiO2-H2 yields high-frequency Ga-H bands that are observed in Ga/SiO2 and Ga/SiO2-H2 but not detected in γ-Ga2O3/SiO2. We attribute the increased amount of GaIV sites in γ-Ga2O3/SiO2-H2 mostly to an increased disorder in γ/ß-Ga2O3. X-ray photoelectron spectroscopy detects the formation of Ga+ and Ga0 species in both Ga/SiO2-H2 and γ-Ga2O3/SiO2-H2. Therefore, it is likely that a minor amount of GaIV sites also forms through the interaction of Ga+ (such as Ga2O) and/or Ga0 with silanol groups of SiO2.
RESUMO
The ability to tailor the properties of metal centers in single-atom heterogeneous catalysts depends on the availability of advanced approaches for characterization of their structure. Except for specific host materials with well-defined metal adsorption sites, determining the local atomic environment remains a crucial challenge, often relying heavily on simulations. This article reports an advanced analysis of platinum atoms stabilized on poly(triazine imide), a nanocrystalline form of carbon nitride. The approach discriminates the distribution of surface coordination sites in the host, the evolution of metal coordination at different stages during the synthesis of the material, and the potential locations of metal atoms within the lattice. Consistent with density functional theory predictions, simultaneous high-resolution imaging in high-angle annular dark field and bright field modes experimentally confirms the preferred localization of platinum in-plane in the corners of the triangular cavities. X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and dynamic nuclear polarization enhanced 15 N nuclear magnetic resonance (DNP-NMR) spectroscopies coupled with density functional theory (DFT) simulations reveal that the predominant metal species comprise Pt(II) bound to three nitrogen atoms and one chlorine atom inside the coordination sites. The findings, which narrow the gap between experimental and theoretical elucidation, contribute to the improved structural understanding and provide a benchmark for exploring the speciation of single-atom catalysts based on carbon nitrides.
RESUMO
Zeolites, although key materials used in industrial processes, remain poorly understood on a molecular level despite their well-defined crystal lattices. In fact, obtaining a direct spectroscopic signatures and resolving the structure of Lewis acid sites (LAS) has remained a challenge. In this work, thanks to 1D and 2D 1H, 15N, and 27Al MAS NMR spectroscopy, carried out at different temperatures (from 298 down to 107 K), we were able to obtain the NMR spectroscopic signatures of LAS and Brønsted acid sites (BAS) in mordenite zeolite in the presence and the absence of adsorbed pyridine (Py). Combined with DFT modeling, this information enabled the structure of LAS to be revealed, namely (≡SiO)3Al sites interacting with pyridine, thus indicating that the corresponding base-free framework-associated sites are pseudo tricoordinated Al sites, namely tricoordinated Al sites interacting with an additional coordinated adjacent siloxane bridge. With this information in hand, we propose a molecular-level understanding on how the AlIV and AlVI framework and framework-associated sites evolve upon dehydration and exposure to Py into BAS and LAS, and their associated Py adducts. By measuring and analyzing the changes in quadrupolar coupling constants (CQ) that reflect electrical charge distribution around the nuclei, we further show that the lower CQ values observed at 298 K are due to residual dynamics that makes the electric field around aluminum nuclei more symmetric. Thus, NMR spectroscopic signatures of 27Al greatly vary with temperature; this information illustrates the importance of accounting for the temperature effect when confronting experimental and calculated CQ values of the corresponding aluminum sites in zeolites in order to obtain accurate structural assessment.
RESUMO
RecA protein mediates homologous recombination repair in bacteria through assembly of long helical filaments on ssDNA in an ATP-dependent manner. RecX, an important negative regulator of RecA, is known to inhibit RecA activity by stimulating the disassembly of RecA nucleoprotein filaments. Here we use a single-molecule approach to address the regulation of (Escherichia coli) RecA-ssDNA filaments by RecX (E. coli) within the framework of distinct conformational states of RecA-ssDNA filament. Our findings revealed that RecX effectively binds the inactive conformation of RecA-ssDNA filaments and slows down the transition to the active state. Results of this work provide new mechanistic insights into the RecX-RecA interactions and highlight the importance of conformational transitions of RecA filaments as an additional level of regulation of its biological activity.
Assuntos
Proteínas de Escherichia coli , Escherichia coli , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , DNA de Cadeia Simples/metabolismo , Escherichia coli/genética , Proteínas de Escherichia coli/genética , Proteínas de Escherichia coli/metabolismo , Recombinases Rec ARESUMO
The development of an efficient heterogeneous catalyst for storing H2 into CO2 and releasing it from the produced formic acid, when needed, is a crucial target for overcoming some intrinsic criticalities of green hydrogen exploitation, such as high flammability, low density, and handling. Herein, we report an efficient heterogeneous catalyst for both reactions prepared by immobilizing a molecular iridium organometallic catalyst onto a high-surface mesoporous silica, through a sol-gel methodology. The presence of tailored single-metal catalytic sites, derived by a suitable choice of ligands with desired steric and electronic characteristics, in combination with optimized support features, makes the immobilized catalyst highly active. Furthermore, the information derived from multinuclear DNP-enhanced NMR spectroscopy, elemental analysis, and Ir L3-edge XAS indicates the formation of cationic iridium sites. It is quite remarkable to note that the immobilized catalyst shows essentially the same catalytic activity as its molecular analogue in the hydrogenation of CO2. In the reverse reaction of HCOOH dehydrogenation, it is approximately twice less active but has no induction period.
Assuntos
Dióxido de Carbono , Irídio , Dióxido de Carbono/química , Formiatos , Hidrogenação , Irídio/química , Ácidos Picolínicos , Dióxido de SilícioRESUMO
RecA is a central enzyme of homologous recombination in bacteria, which plays a major role in DNA repair, natural transformation and SOS-response activation. RecA forms nucleoprotein filaments on single-stranded DNA with a highly conserved architecture that is also shared by eukaryotic recombinases. One of the key features of these filaments is the ability to switch between stretched and compressed conformations in response to ATP binding and hydrolysis. However, the functional role of such conformational changes is not fully understood. Structural data revealed that in the absence of ATP RecA binds DNA with the stoichiometry of 5 nucleotides per one monomer, while in the presence of ATP the binding stoichiometry is 3:1. Such differences suggest incompatibility of the active and inactive conformations, yet dynamic single-molecule studies demonstrated that ATP and apo conformations can be directly interconvertible. In the present work we use a single-molecule approach to address the features of inactive RecA nucleoprotein filaments formed de novo in the absence of nucleotide cofactors. We show that compressed RecA-DNA filaments can exist with both 5:1 and 3:1 binding stoichiometry which is determined by conditions of the filament assembly. However, only a 3:1 stoichiometry allows direct interconvertibility with the active ATP-bound conformation.
Assuntos
Nucleoproteínas , Recombinases Rec A , Trifosfato de Adenosina/metabolismo , DNA/metabolismo , DNA de Cadeia Simples , Nucleoproteínas/metabolismo , Nucleotídeos , Recombinases Rec A/metabolismoRESUMO
Antibiotic resistance is acquired in response to antibiotic therapy by activating SOS-depended mutagenesis and horizontal gene transfer pathways. Compounds able to inhibit SOS response are extremely important to develop new combinatorial strategies aimed to block mutagenesis. The regulators of homologous recombination involved in the processes of DNA repair should be considered as potential targets for blocking. This review highlights the current knowledge of the protein targets for the evolution of antibiotic resistance and the inhibitory effects of some new compounds on this pathway.