Metal complexes of penicillins and cephalosporins (Review)

Attaching Metal-Containing Moieties to β-Lactam Antibiotics: The Case of Penicillin and Cephalosporin

Procedures for the preparation of transition metal complexes having intact bicyclic cepham or penam systems as ligands have been developed. Starting from readily available 4-azido-2-azetidinones, a synthetic approach has been tuned using a copper-catalyzed azide-alkyne cycloaddition between 3-azido-2-azetinones and alkynes, followed by methylation and transmetalation to Au(I) and Ir(III) complexes from the mesoionic carbene Ag(I) complexes. This methodology was applied to 6-azido penam and 7-azido cepham derivatives to build 6-(1,2,3-triazolyl)penam and 7-(1,2,3-triazolyl)cepham proligands, which upon methylation and metalation with Au(I) and Ir(III) complexes yielded products derived from the coordination of the metal to the penam C6 and cepham C7 positions, preserving intact the bicyclic structure of the penicillin and cephalosporin scaffolds. The crystal structure of complex 28b, which has an Ir atom directly bonded to the intact penicillin bicycle, was determined by X-ray diffraction. This is the first structural report of a penicillin-transition-metal complex having the bicyclic system of these antibiotics intact. The selectivity of the coordination processes was interpreted using DFT calculations.

Nitrogen and Sulfur co-doped Carbon dots as an "on-off-on" Fluorescent Sensor for the Detection of Hg2+ and Ampicillin

Herein, a fluorescent "on-off-on" nanosensor based on N,S-CDs was developed for highly precise and sensitive recognition of Hg2+ and ampicillin (AMP). Nitrogen and sulfur co-doped carbon dots with blue fluorescence were synthesized by one-pot hydrothermal method using ammonium citrate and DL-methionine as precursors. N,S-CDs exhibited a surface abundant in -OH, -COOH, and -NH2 groups, aiding in creating non-fluorescent ground state complexes when combined with Hg2+, leading to the suppression of N,S-CDs' fluorescence. Subsequent to additional AMP application, the mixed system's fluorescence was restored. Based on this N,S-CDs sensing system, the thresholds for detection for AMP and Hg2+ were discovered to be 0.121 µM and 0.493 µM, respectively. Furthermore, this methodology proved effective in identifying AMP in real samples of tap and lake water, yielding satisfactory results. Consequently, in the area of bioanalysis in intricate environmental sample work, the sensing system showed tremendous promise.

Efficient removal of antibiotics from water by highly crosslinked metal-alginate particles: Preparation, isotherms, kinetics, and microbiological assay

Traces of antibiotics reaching aquatic environment lead to the emergence of antimicrobial resistance (AMR). The efficient removal of antibiotics (ATBs) traces from wastewater is essential to tackle the AMR. In this study, a novel solid-state crosslinking method of alginate (ALG) was developed and applied to specifically remove ATBs from water. A wide range of crosslinkers (Ca2+, Zn2+, Cu2+, Ni2+, Fe3+ and Al3+) was used and the crosslinking nature, density, and distribution were evidenced by FTIR, ICP-MS, and SEM-EDS. Compared with ionotropic gelation, the novel solid-state crosslinking method proved superior in term of ease of production, high crosslinking degree, and ATBs removal capacity. Fe-ALG and Zn-ALG showed high removal capacity of ciprofloxacin (356.5 mg/g and 928.6 mg/g) and doxycycline (90 mg/g and 690 mg/g), however, they were less effective toward amoxicillin (11.5 mg/g and 6 mg/g). Removal isotherms and kinetics followed type I and pseudo-second order suggesting a chemisorption removal mechanism. Fe-ALG was successfully regenerated with no loss in ATB removal capacity. The microbiological assay showed significant reductions of antibacterial activities after ATBs removal from water. Overall, metal-ALG systems obtained by solid-state crosslinking are promising for ATBs removal from wastewater giving the ease of production, high efficiency, regenerability, and scalability potential.

Imipenem-metal complexes: Computational analysis and toxicity studies with wastewater model microorganisms

The occurrence of antibiotic residues in diverse water sources has long been acknowledged as a potential health concern due to the emergence and spread of antibiotic-resistant bacteria and genes. However, there have been limited studies into the presence of antibiotic-metal complexes (AMCs) in real-time wastewater matrices, and their impact on wastewater microbial communities. The present work, in this regard, investigated the stability of Imipenem-metal complexes (Me = Mg (II), Ca (II), Fe (II), Cu (II), and Al (III)) with computational studies, stoichiometry with potentiometric measurements, and their antibacterial activity towards wastewater model microorganisms- Bacillus subtilis (B. subtilis) and Escherichia coli (E. Coli) by Colony Forming Unit (CFU) method. The lower energy of Imipenem-metal complexes than the parent antibiotic- Imipenem, during energy optimization using density functional (DFT) methods, revealed that metal interactions of Imipenem stabilize the drug by minimizing its energy. Further, CFU studies indicated that these complexes display higher antimicrobial activity than parent antibiotics. The electron delocalization over the entire chelated system (AMCs) reduces polarity and increases the lipophilicity of the complexes, thereby facilitating stronger interaction between AMCs and the bacterial cell membrane. Results indicate increased antibacterial activity of Imipenem-metal complexes for both E. coli and B. subtilis. The antibacterial activity, was however, more pronounced in B. subtilis, with >97% growth inhibition for metal complexes of Imipenem (at a Minimum Inhibitory Concentration of 20 nM or 6 ppb (i.e., MIC90)), for both the stoichiometric ratios (metal to ligand) ratios (M: L 1: 1 and 2: 1). All around, with increased stability and toxicity, AMCs are emerging as contaminants of concern and demand immediate attention to devise methods for their removal.

Insights into the formation of environmentally persistent free radicals during photocatalytic degradation processes of ceftriaxone sodium by ZnO/ZnIn2S4

At present, the researches on photocatalysis were mainly focused on the design, improvement and development of catalysts, and less attention was paid to the existing characteristics of environmentally persistent free radicals (EPFRs) during the process of photocatalytic oxidation. In this study, A flower-like Z-type heterojunction ZnO/ZnIn₂S₄ (ZnO/ZIS) and typical antibiotic ceftriaxone sodium (CS) were taken as study objects, concentrating on the generation characteristics of EPFRs during the degradation of CS by ZnO/ZIS, and clarifying the degradation mechanism of CS in which EPFRs participated. The results showed that the degradation efficiency of 10 mg/L CS by 0.40 g/L ZnO/ZIS reached 85.3% in 150 min under the irradiation of 500 W xenon lamp. It was clear that ·O₂^- and h⁺ play major roles in CS degradation by ZnO/ZIS under visible light, and ·OH plays an auxiliary role. Furthermore, the formation mechanism of EPFRs during photocatalytic degradation processes of CS by ZnO/ZIS were first investigated thoroughly via experimental analysis and density functional theory (DFT) calculations. The concentration level of EPFRs centered on oxygen atoms is 10¹¹ spin/mm³, which were generated in the process of degradation of CS by ZnO/ZIS under visible light. The production of EPFRs chiefly includes two procedures: chemical adsorption and transfer of electrons. The adsorption energy of precursor P8 on ZnIn₂S₄ side is -1.91 eV, the electrons transferred from precursor P8 and P11 to ZnO/ZnIn₂S₄ heterojunction. Surprisingly, EPFRs have little negative effects on the degradation process of CS by ZnO/ZIS. The study was not only a key field in the development of photocatalysis technology, but also a new way to study the removal mechanism of antibiotics.

Improvement of the QuEChERS extraction step by matrix-dispersion effect and application on beta-lactams analysis in wastewater sludge by LC-MS/MS

In the last decade, beta-lactams use in veterinary and human medicine increased to represent today about 15% of the overall consumption. Beta-lactams tend to degrade and metabolize in the environment. Therefore, analytical methods must be sensitive enough to quantify low concentrations of the parent molecules and also allow detection of metabolites. This study presents the development of a modified QuEChERS method for the extraction of seven beta-lactams and one degradation product (Amoxicillin, Ampicillin, Cefapirin, Cefoperazone, Cefquinome, Ceftiofur, Cloxacillin, and Amoxicillin-Diketopiperazine) from sewage treatment plant sludge and their analysis by liquid chromatography coupled with tandem mass spectrometry. Before the QuEChERS extraction, a dispersion step of the sample with EDTA-treated sand was optimized and added, allowing to facilitate the exchanges between the matrix and the extraction solvent. Then, to decrease the interferences present in the extract, a fast and efficient pass-through SPE was implemented. The optimized method was validated and showed satisfactory performances, in adequacy with the analysis of beta-lactams in solid environmental matrices. Limits of quantification lower than 20 ng.g^-1 for all analytes, high accuracy (96%-114% quantification on spiked samples nominal concentration) and interday precision (2%-12% RSD) were obtained. This method was then applied to eight sludge samples. Cefapirin and amoxicillin-diketopiperazine were detected in four samples each, at concentrations of 10.2-53.3 ng.g^-1 and 3.0-9.5 ng.g^-1 respectively. Thus, the developed method is very effective for the extraction of beta-lactams from environmental solid matrices.

Selective toxicity of antibacterial agents-still a valid concept or do we miss chances and ignore risks?

BACKGROUND

Selective toxicity antibacteribiotics is considered to be due to interactions with targets either being unique to bacteria or being characterized by a dichotomy between pro- and eukaryotic pathways with high affinities of agents to bacterial- rather than eukaryotic targets. However, the theory of selective toxicity oversimplifies the complex modes of action of antibiotics in pro- and eukaryotes.

METHODS AND OBJECTIVE

This review summarizes data describing multiple modes of action of antibiotics in eukaryotes.

RESULTS

Aminoglycosides, macrolides, oxazolidinones, chloramphenicol, clindamycin, tetracyclines, glycylcyclines, fluoroquinolones, rifampicin, bedaquillin, ß-lactams inhibited mitochondrial translation either due to binding to mitosomes, inhibition of mitochondrial RNA-polymerase-, topoisomerase 2ß-, ATP-synthesis, transporter activities. Oxazolidinones, tetracyclines, vancomycin, ß-lactams, bacitracin, isoniazid, nitroxoline inhibited matrix-metalloproteinases (MMP) due to chelation with zinc and calcium, whereas fluoroquinols fluoroquinolones and chloramphenicol chelated with these cations, too, but increased MMP activities. MMP-inhibition supported clinical efficacies of ß-lactams and daptomycin in skin-infections, and of macrolides, tetracyclines in respiratory-diseases. Chelation may have contributed to neuroprotection by ß-lactams and fluoroquinolones. Aminoglycosides, macrolides, chloramphenicol, oxazolidins oxazolidinones, tetracyclines caused read-through of premature stop codons. Several additional targets for antibiotics in human cells have been identified like interaction of fluoroquinolones with DNA damage repair in eukaryotes, or inhibition of mucin overproduction by oxazolidinones.

CONCLUSION

The effects of antibiotics on eukaryotes are due to identical mechanisms as their antibacterial activities because of structural and functional homologies of pro- and eukaryotic targets, so that the effects of antibiotics on mammals are integral parts of their overall mechanisms of action.

β-lactam antibiotics to tame down molecular pathways of Alzheimer's disease

Alzheimer's disease is a multifactorial disorder characterized by extracellular accumulation of amyloid-β (Aβ) and intracellular accumulations of neurofibrillary tangles. Numerous drug targets have been explored for therapeutic efficacy but failed to deliver successful treatments clinically. However, over the years our understanding of the disease pathophysiology increased significantly. Many of the novel targets which can cure or modify disease pathology are being explored preclinically as well as clinically. On contrarily, the drug discovery and development process is lengthy and the cost involved makes it difficult for faster translation of therapeutic outcomes. Therefore, repurposing existing drugs for a new therapeutic indication is considered a better approach and helps in the fast translation of therapeutic information. The existing drugs have well-proven records on their safety, pharmacokinetics, etc. In recent years, beta (β)-lactam antibiotics have been repurposed for the management of neurodegenerative pathologies. Here in the current review, we have explored β-lactam antibiotics, their target sites, molecular mechanisms, and their therapeutic potential in Alzheimer's disease.

Complexation Enhances Cu(II)-Activated Peroxydisulfate: A Novel Activation Mechanism and Cu(III) Contribution

While aqueous free Cu(II) ion is known to be ineffective to activate peroxydisulfate (PDS), here we report for the first time that Cu(II) complexes are potentially effective activators for PDS when the coordination involves suitable ligands. Using cefalexin (CFX) as a representative, studies show that the complex of Cu(II) with CFX can efficiently activate PDS to induce rapid degradation of CFX. Transformation products of CFX by PDS/Cu(II) differ substantially from those generated from the typical radical oxidation process, for example, PDS/Ag(I), but quite resemble the products from oxidation of CFX by Cu(III). Complexation with CFX increases the electron density of Cu(II), favoring electron transfer from Cu(II) to PDS to generate radicals and Cu(III). The produced Cu(III), rather than radicals, plays the primary role in the overall CFX degradation and regenerates Cu(II) in a catalytic cycle. This novel activation process can occur for a wide range of contaminants (cephalosporin, penicillin, and tetracycline antibiotics) and ligands when coordinated with Cu(II), and N-containing functional groups (e.g. amines) were found to form effective Cu(II) complexes for PDS activation. The new findings of this study further broaden the knowledge on PDS activation by aqueous Cu(II), and verify the contribution of Cu(III) to contaminant elimination.

Bio-Organometallic Derivatives of Antibacterial Drugs

Overuse and misuse of antibacterial drugs has resulted in bacteria resistance and in an increase in mortality rates due to bacterial infections. Therefore, there is an imperative necessity of new antibacterial drugs. Bio-organometallic derivatives of antibacterial agents offer an opportunity to discover new active antibacterial drugs. These compounds are well-characterized products and, in several examples, their antibacterial activities have been studied. Both inhibition of the antibacterial activity and strong increase in the antibiotic activity of the parent drug have been found. The synthesis of the main classes of bio-organometallic derivatives of these drugs, as well as examples of the use of structure-activity relation (SAR) studies to increase the activity and to understand the mode of action of bio-organometallic antimicrobial peptides (BOAMPs) and platensimicyn bio-organometallic mimics is presented in this article.

Copper Influences the Antibacterial Outcomes of a β-Lactamase-Activated Prochelator against Drug-Resistant Bacteria

The unabated rise in bacterial resistance to conventional antibiotics, coupled with collateral damage to normal flora incurred by overuse of broad-spectrum antibiotics, necessitates the development of new antimicrobials targeted against pathogenic organisms. Here, we explore the antibacterial outcomes and mode of action of a prochelator that exploits the production of β-lactamase enzymes by drug-resistant bacteria to convert a nontoxic compound into a metal-binding antimicrobial agent directly within the microenvironment of pathogenic organisms. Compound PcephPT (phenylacetamido-cephem-pyrithione) contains a cephalosporin core linked to 2-mercaptopyridine N-oxide (pyrithione) via one of its metal-chelating atoms, which minimizes its preactivation interaction with metal ions and its cytotoxicity. Spectroscopic and chromatographic assays indicate that PcephPT releases pyrithione in the presence of β-lactamase-producing bacteria. The prochelator shows enhanced antibacterial activity against strains expressing β-lactamases, with bactericidal efficacy improved by the presence of low-micromolar copper in the growth medium. Metal analysis shows that cell-associated copper accumulation by the prochelator is significantly lower than that induced by pyrithione itself, suggesting that the location of pyrithione release influences biological outcomes. Low-micromolar (4-8 μg/mL) minimum inhibitory concentration (MIC) values of PcephPT in ceftriaxone-resistant bacteria compared with median lethal dose (LD50) values greater than 250 μM in mammalian cells suggests favorable selectivity. Further investigation into the mechanisms of prochelators will provide insight for the design of new antibacterial agents that manipulate cellular metallobiology as a strategy against infection.

Detection of the iron complexes with hydrolysis products of cephalexin and cefradine upon high-performance liquid chromatography/electrospray ionization mass spectrometry analysis

RATIONALE

Cephalosporins (e.g. cephalexin, cefradine) are a major group of widely used β-lactam antibiotics. Hydrolysis of the β-lactam ring is an important reaction (often undesired) which leads to deactivation of β-lactams. To the best of our knowledge there is no electrospray ionization mass spectrometry (ESI-MS) data reported concerning the products of hydrolysis of cephalosporins.

METHODS

The hydrolysis of cephalexin and cefradine was performed in aqueous NaOH solutions. After the process the solutions were analyzed by high-performance liquid chromatography (HPLC)/ESI-MS. The elemental compositions of the ions discussed were confirmed by the accurate mass measurements on a quadrupole time-of-flight (QTOF) mass spectrometer.

RESULTS

Unexpectedly, complexes between the hydrolysis products of cephalexin and cefradine (CFL_h and CFR_h ) and iron cation were detected upon HPLC/ESI-MS analysis, namely the ions [(CFL_h -H)₂ +Fe]⁺ and [(CFR_h -H)₂ +Fe]⁺ , although iron was not added to the analyzed solutions or to the mobile phase. These ions were found to be very stable in the gas phase.

CONCLUSIONS

The detection of the complexes between the hydrolysis products of cephalosporins and iron may have a positive impact on the sensitivity and specificity of HPLC/ESI-MS analyses of the hydrolysis products of some cephalosporins.

Cu(II)-catalyzed degradation of ampicillin: effect of pH and dissolved oxygen

Cu(II)-catalyzed hydrolysis of β-lactam antibiotics has been well-identified and recognized as the key mechanism of antibiotic degradation. However, the overlooked Cu(II) oxidation susceptibly also plays an important role comparably with hydrolysis. This study evaluated the roles of hydrolysis and oxidation in Cu(II)-catalyzed degraded ampicillin (AMP), as a typical β-lactam antibiotic, under relevant environmental conditions (pH 5.0, 7.0, and 9.0; oxygen 0.2 and 6.2 mg/L). Under AMP and Cu(II) molar ratio of 1:1, AMP degradation was the fastest at pH 9.0, followed by pH 5.0 and pH 7.0. The facilitation of oxygen on AMP degradation was notable at pH 5.0 and 7.0 rather than pH 9.0. AMP degradation rate increased from 21.8% in 0.2 mg/L O₂ solution to 85.9% in 6.2 mg/L O₂ solution at pH 7.0 after 4-h reaction. AMP oxidation was attributed to both oxygen-derived Cu(I)/Cu(II) cycle and intermediate reactive oxygen species (HO^. and O₂^.-). Several intermediate and final products in AMP degradation were firstly identified by LC-quadrupole time-of-flight-MS analysis. Phenylglycine primary amine on the AMP structure was the essential complexation site to proceed with the oxidation reaction. The oxidation of AMP preferentially occurred on the β-lactam structure. The inherent mechanisms related to pH and oxygen conditions were firstly investigated, which could enhance the understanding of both oxidation and hydrolysis mechanisms in AMP degradation. This study not only has an important implication in predicting β-lactam antibiotic transformation and fate in natural environment but also benefits the developing of strategies of antibiotic control to reduce the environmental risk.

The interactions of cephalosporins on polyol pathway enzymes from sheep kidney

CONTEXT

Cephalosporins are derived from the fungus Acremonium. Due to their strong bactericidal ability, these drugs have to a wide usage in medicine.

OBJECTIVE

An investigation of the effects on sheep renal aldose reductase (AR) and sorbitol dehydrogenase (SDH) of cefoperazone, cefazolin, cefuroxime, ceftazidime and ceftriaxone as cephalosporin drugs was carried out in the present study.

METHODS

AR and SDH were purified from sheep kidney by ion exchange, gel filtration and affinity methods with approximately 219- and 484-fold, respectively. Some kinetic properties of the enzymes were determined such as optimal pH, optimal ionic strength, optimal temperature, stable pH, K_m and V_max. IC₅₀ values of the drugs were found for each enzyme.

RESULTS

While the AR was inhibited by all drugs, SDH enzyme was inhibited by only CXM (IC₅₀ 8.10 mM). Interestingly, CZO activated SDH enzyme. This result was evaluated as important for the flow of the polyol reactions. K_i values and inhibition types were determined for AR. However, these values could not have determined for SDH, due to insufficient inhibition.

CONCLUSIONS

From these results, it was concluded that cephalosporins may have an important effect on flow of the polyol metabolism.

Fe(III)-promoted transformation of β-lactam antibiotics: Hydrolysis vs oxidation

The widely used β-lactam antibiotics are susceptible to oxidative and/or hydrolytic degradation promoted by some metal ions (e.g., Cu(II)). Ferric ions (Fe(III)) are among the most common metal ions, but their role in the environmental transformation and fate of β-lactam antibiotics is still unknown. This study elucidates that Fe(III) can promote degradation of β-lactam antibiotics under environmental aquatic conditions. Degradation rate constants of ampicillin (AMP) linearly increased with increasing Fe(III) concentration, but were independent of AMP concentration when AMP was higher than Fe(III) concentration. Neutral pH was most favorable for Fe(III)-promoted degradation of AMP, and the promoted degradation was also significant in real surface water and wastewater matrix. Among the various β-lactam antibiotics, Fe(III)-promoted degradation of penicillins was faster than that of cephalosporins. Product analysis indicated that only two isomers of hydrolysis products were observed without detection of oxidation products. The Fe(III)-promoted degradation likely occurred via complexation of β-lactam antibiotics with carboxyl group and tertiary nitrogen, and then enhancing the hydrolytic cleavage of β-lactam ring. This study is among the first to identify the role of Fe(III) in the degradation of β-lactam antibiotics and elucidate the mechanism. The new findings indicate iron species are among the factors affecting the environmental fate of β-lactam antibiotics.

Potentiometric, UV and 1H NMR study on the interaction of Cu2+ with ampicillin and amoxicillin in aqueous solution

A potentiometric, UV and ¹H NMR study on Cu²⁺-ampicillin [(2S,5R,6R)-6-([(2R)-2-amino-2-phenylacetyl]amino)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid] and -amoxicillin [(2S,5R,6R)-6-{[(2R)-2-amino-2-(4-hydroxyphenyl)-acetyl]amino}-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-24-carboxylic acid] systems in NaCl aqueous solution at I=0.15molL^-1 and t=25°C is reported. On the basis of potentiometric results two speciation models were proposed for each system. It was found that spectrophotometric and ¹H NMR measurements are essential for selecting the most reliable speciation models. They included ML, MLOH and ML(OH)₂ species in both systems and, only for Cu²⁺-ampicillin, also MLH species. The stability constants obtained by UV and ¹H NMR titrations were comparable to the ones calculated by potentiometry. The sequestering ability of the ligands under study towards Cu²⁺ by pL_0.5 empiric parameter (ligand concentration required to sequester 50% of the metal cation present in traces) at several pH values was calculated as well. For ampicillin and amoxicillin, pL_0.5=7.19 and 6.67, respectively, at physiological pH, I=0.15molL^-1 and t=25°C were obtained.

Potentiometric, UV and 1H NMR study on the interaction of penicillin derivatives with Zn(II) in aqueous solution

The interaction of Zn(II) with ampicillin [(2S,5R,6R)-6-([(2R)-2-amino-2-phenylacetyl]amino)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2- carboxylic acid] and amoxicillin [(2S,5R,6R)-6-{[(2R)-2-amino-2-(4-hydroxyphenyl)-acetyl]amino}-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-24-carboxylic acid] in NaCl aqueous solution at different ionic strengths and at t=25°C was investigated by potentiometric, UV and ¹H NMR techniques. Fairly similar speciation models were obtained for the two systems. At I=0.15molL^-1, two different sets of measurements, at low and high concentrations, were carried out. For the Zn²⁺-amoxicillin system, the Zn₂L₂(OH)₂ species was obtained in the set of measurements at high concentration. The spectrophotometric and ¹H NMR results thus obtained are fully consistent with the speciation models found from potentiometric investigations, confirming the formation as well as the relative stability of the complex species. The dependence of the stability constants on the ionic strength was modeled by means of the Debye-Hückel and SIT (Specific ion Interaction Theory) approaches, and the parameter that accounts for the variation of the stability constants with the ionic strength and the specific ion interaction parameters were determined for all the ionic species. The sequestering ability of the ligands towards Zn²⁺ was evaluated by determining the pL_0.5 parameter at different ionic strengths. It resulted that the sequestering ability of ampicillin is higher of ~0.5 order of magnitude with respect to amoxicillin.

Multiple Roles of Cu(II) in Catalyzing Hydrolysis and Oxidation of β-Lactam Antibiotics

The widely used β-lactam antibiotics such as penicillins and cephalosporins are known to be susceptible to Cu^II-catalyzed hydrolysis at their four-membered β-lactam ring. However, this study elucidates that Cu^II can in fact play multiple roles in promoting the hydrolysis and/or oxidation of β-lactam antibiotics under environmental aquatic conditions (pH 5.0-9.0 and 22 °C), depending on β-lactams' structural characteristics and solution pH. Most significantly, the β-lactam antibiotics that contain a phenylglycine primary amine group on the side chain can undergo direct oxidation by Cu^II via this functional group. On the other hand, the β-lactam ring of penicillins is susceptible to Cu^II-catalyzed hydrolysis, followed by oxidation of the hydrolysis product by Cu^II. In contrast, the β-lactam ring of cephalosporins is susceptible to Cu^II-catalyzed hydrolysis only. Solution pH influences the Cu^II-promoted transformation by affecting the β-lactam and Cu^II complexation through protonation/deprotonation of critical organic functional groups. When Cu^II acts as an oxidant to promote the transformation of β-lactam antibiotics to yield Cu^I, the overall role of Cu^II appears catalytic if the reaction occurs under ambient atmospheric condition, due to quick oxidation of Cu^I by oxygen to regenerate Cu^II. Compared to earlier literature that largely assumed only the hydrolytic catalyst role of Cu^II in promoting degradation of β-lactam antibiotics, the oxidative roles of Cu^II identified by this study mark important contributions to a more accurate mechanistic understanding.

Cu(II)-catalyzed transformation of benzylpenicillin revisited: the overlooked oxidation

Penicillins, a class of widely used β-lactam antibiotics, are known to be susceptible to catalyzed hydrolysis by metal ions such as Cu(II). However, new results in this study strongly indicate that the role of Cu(II) is not merely a hydrolysis catalyst but also an oxidant. When benzylpenicillin (i.e., penicillin G (PG)) was exposed to Cu(II) ion at an equal molar ratio and pH 7, degradation of PG occurred rapidly in the oxygen-rich solution but gradually slowed down to a halt in the oxygen-limited solution. In-depth studies revealed that Cu(II) catalyzed hydrolysis of PG to benzylpenicilloic acid (PA) and oxidized PA to yield phenylacetamide and other products. The availability of oxygen played the role in reoxidizing Cu(I) back to Cu(II), which sustained fast degradation of PG over time. The overall reaction was also influenced by pH, with Cu(II)-catalyzed hydrolysis of PG occurring throughout pH 5, 7 and 9, while Cu(II) oxidation of PA occurring at pH 7 and 9. Note that the potential of Cu(II) to oxidize penicillins was largely overlooked in the previous literature, and catalyzed hydrolysis was frequently assumed as the only reaction. This study is among the first to identify the dual roles of Cu(II) in the entire degradation process of PG and systematically investigate the overlooked oxidation reaction to elucidate the mechanism. The new mechanistic knowledge has important implications for many other β-lactam antibiotics for their interactions with Cu(II), and significantly improves the ability to predict the environmental fate and transformation products of PG and related penicillins in systems where Cu(II) species are also present.