Significant Activity Research Articles

Unravelling the role of work function difference on supported Ru nanoclusters for alkaline hydrogen evolution reaction

Fine tuning the work function difference (ΔΦ) between support and Ru which in turn affects the electron distribution of Ru is an effective method for the design of high-performance alkaline hydrogen evolution reaction (HER) catalysts. However, it remains a challenge to understand the intrinsic relationship between HER activity and ΔΦ at the atomic level. Herein, taking N doped graphene supported Ru nanoclusters (Ru/CxNy) as the theoretical model, we demonstrate that the HER activity can be correlated with the variation of ΔΦ. For Ru/C50 with smaller ΔΦ, we find that the Ru atoms located at the top layer of Ru nanoclusters (Ru-t) with lower coordination numbers are the main reaction sites. For Ru/C30N20 with larger ΔΦ, the stronger charge redistributions of Ru is observed, and the electron-deficient Ru atoms closing to the interface (Ru-i) are the main reaction sites with significant improvement HER activity. Our findings demonstrate the role of ΔΦ on Ru/CxNy systems for the alkaline HER, which can provide valuable theoretical guidance for the design of high efficient HER catalysts.

Chemical composition and bioactivities of the methanol root extracts of Saussurea costus

Abstract Saussurea costus (S. costus) is a medicinal plant from the Asteraceae family that is widely used in traditional medicine in Saudi Arabia. This study examines S. costus root extract for its chemical composition and its antioxidant, anti-cancer, and antibacterial properties. The results of the study on the methanol root extract of S. costus reveal a rich chemical composition, as identified by GC-MS/FID analysis. The extract also showed high levels of total phenolic content (188.2 ± 2.1 mg GAE/g DM) and total flavonoid content (129 ± 2.6 mg QE/g DM). In antioxidant tests, the extract exhibited strong activity, with the half-maximal inhibitory concentration (IC50) values of 137.15 μg/mL for ABTS and 175.5 μg/mL for DPPH as compared to positive control’s IC50 values of 45.5 ± 0.3 μg/mL for ABTS and 55.3 ± 0.1 μg/mL for DPPH. The cytotoxic assessment against MCF-7 and A549 cell lines showed notable effects, particularly at higher concentrations. Additionally, the extract induced apoptosis in these cell lines, evidenced by changes in gene expression. Antibacterial tests revealed significant activity against various strains, with MIC values ranging from 7.81 to 125 μg/mL. The study underscores the importance of plant extracts in modern healthcare and suggests future research directions, including clinical applications and compound identification.

Syntheses, Crystal Structures and Antimicrobial Activity of Zinc(II) Complexes Derived from 5-Bromo-2- (((2-piperazin-1-yl)ethyl)imino)methyl)phenol

Three new zinc(II) complexes, [ZnCl2L]·CH3OH (1), [ZnClL(NCS)]·2CH3OH·0.5H2O (2), and [ZnL(NCS)2]·CH3OH·H2O (3), where L is the zwitterionic form of 5-bromo-2-(((2-piperazin-1-yl)ethyl)imino)methyl)phenol, NCS is thiocyanate anion, were facile prepared by reaction of different molar ratio of L, zinc chloride and ammonium thiocyanate in methanol. The complexes were characterized by IR and UV-Vis spectroscopy. Detailed structures of the three complexes were confirmed by single crystal X-ray determination. The Zn atoms in the complexes are in tetrahedral coordination. The Schiff base ligand coordinates to Zn atom through phenolate oxygen atom and amino and imino nitrogen atoms. The remaining two sites are occupied by two Cl for 1, one Cl and one NCS for 2, and two NCS for 3. The compounds show significant antimicrobial activities.

Exploring sustainable management by using green nano-silver to combat three post-harvest pathogenic fungi in crops

Global crop protection and food security have become critical issues to achieve the ‘Zero Hunger’ goal in recent years, as significant crop damage is primarily caused by biotic factors. Applying nanoparticles in agriculture could enhance crop yield. Nano-silver, or AgNPs, have colossal importance in many fields like biomedical, agriculture, and the environment due to their antimicrobial potential. In this context, nano-silver was fabricated by Citrus medica L. (Cm) fruit juice, detected visually and by UV–Vis spectrophotometric analysis. Further, AgNPs were characterized by advanced techniques. UV–Vis spectroscopic analysis revealed absorbance spectra at around 487 nm. The zeta potential measurement value was noted as -23.7 mV. Spectral analysis by FT-IR proved the capping of the acidic groups. In contrast, the XRD analysis showed the Miller indices like the face-centered cubic (fcc) crystalline structure. NTA revealed a mean size of 35 nm for nano-silver with a 2.4 × 108 particles mL−1 concentration. TEM analysis demonstrated spherical Cm-AgNPs with 20–30 nm sizes. The focus of this research was to evaluate the antifungal activity of biogenic AgNPs against post-harvest pathogenic fungi, including Aspergillus niger, A. flavus, and Alternaria alternata. The Cm-AgNPs showed significant antifungal activity in the order of A. niger > A. flavus > A. alternata. The biogenic Cm-AgNPs can be used for the inhibition of toxigenic fungi.

Efficacy of the induced pluripotent stem cell derived and engineered CD276-targeted CAR-NK cells against human esophageal squamous cell carcinoma.

Chimeric antigen receptor natural killer (CAR-NK) cells have been found to be successful in treating hematologic malignancies and present potential for usage in solid tumors. In this study, we created CD276-targeted CAR-expressing NK cells from pluripotent stem cells (iPSC CD276-targeted CAR-NK cells) and evaluated their cytotoxicity against esophageal squamous cell carcinoma (ESCC) using patient-specific organoid (PSO) models comprising of both CD276-positive and CD276-negative adjacent epithelium PSO models (normal control PSO, NC PSO) as well as primary culture of ESCC cell models. In addition, in vitro and in vivo models such as KYSE-150 were also examined. iPSC NK cells and NK-free media were used as the CAR-free and NK-free controls, respectively. The positive CD276 staining was specifically detected on the ESCC membrane in 51.43% (54/105) of the patients of all stages, and in 51.35% (38/74) of stages III and IV. The iPS CD276-targeted CAR-NK cells, comparing with the iPS NK cells and the NK-free medium, exhibited specific and significant cytotoxic activity against CD276-positive ESCC PSO rather than CD276-negative NC PSO, and exhibited significant cytotoxicity against CD276-expressing cultured ESCC cells, as well as against CD276-expressing KYSE-150 in vitro and in BNDG mouse xenograft. The efficacy of the iPSC CD276-targeted CAR-NK cells demonstrated by their successful treatment of CD276-expressing ESCC in a multitude of pre-clinical models implied that they hold tremendous therapeutic potential for treating patients with CD276-expressing ESCC.

Flavonoids from Liriodendron chinense Leaves Alleviate Oxidative Activity in Vitro and D-galactose-induced Brain Injury via AMPK/SIRT1 Pathway in Vivo

The exploration of active ingredients and new activities of industrial crops could expand their scope of applications. Liriodendron chinense (L. chinense), an important ornamental and economic forest tree in China, has been widely used in timber, medicine and landscape. Flavonoids are major constituents of L. chinense leaves, while their effects of preventing brain damage are still unclear. In this study, flavonoids from L. chinense leaves (LCLF) were obtained through AB-8 resin chromatography and UPLC-MS/MS assay indicated that 16 compounds were identified from LCLF. LCLF treatment showed significant scavenging activities against DPPH•, ABTS•+, •OH, FRAP and total reducing power. D-galactose-impaired exploratory behaviors, cognitive functions and histopathological alterations in hippocampus of mice were obviously recovered by LCLF administration. Network pharmacology results demonstrated that LCLF could produce the healing efficacy through multiple pathways, mostly related to oxidative stress and inflammation. Further in vivo experiments revealed that LCLF treatment could regulated MDA content, SOD, CAT and GSH-Px activity, as well as the production of inflammatory factors (NO, IL-1β and IL-6). The underlying mechanisms of LCLF were probably related to Nrf2/HO-1, NF-κB and AMPK/SIRT1 pathways. Molecular docking results and surface plasmon resonance analysis validated that especially hesperidin in LCLF had strong binding activities with all 8 genes in the mentioned pathways. Our study revealed the beneficial effects of LCLF on oxidative activity and D-galactose-induced brain injury, offering experimental support for its potential application in pharmaceutical and other industries.

Identification of Quality Markers in Schisandra chinensis (Turcz.) Baill. Using UPLC-Q-Extractive Orbitrap/MS, Chemometric Analysis, and Network Pharmacology

Chemical composition is a critical factor for determining the efficacy of any traditional Chinese medicine (TCM) and can be used as an indicator of commercial quality. To develop a new strategy for discovering potential quality markers (Q-markers) of TCM by integrating ultra-performance liquid chromatography-Q-extractive orbitrap/mass spectrometry (UPLC-Q-Extractive Orbitrap/MS), chemometric analysis, and network pharmacology, using Schisandra chinensis (Turcz.) Baill. (S. chinensis) as an example. The chemical profiling of S. chinensis was performed using UPLC-Q-Extractive Orbitrap/MS, followed by identification of hepatoprotective Q-markers through a comprehensive understanding of chemometric analysis and virtual target prediction of network pharmacology. Six compounds were considered potent candidates for Q-markers, which were identified as schisandrol A (6), angeloylgomisin H (10), schisantherin A (17), schisantherin B (18), schisandrin A (23), and schisandrin C (26). All Q-markers exhibited significant hepatoprotective activity, as evidenced by in vitro experiments. Subsequently, a method for simultaneous quantification was established and employed to analyse seven batches of S. chinensis. Therefore, the integrated approach of UPLC-Q-Extractive Orbitrap/MS, chemometrics, and network pharmacology proved to be an effective strategy for the discovery of Q-markers that can assist in assessing the overall chemical consistency of samples and provide a basis for quality evaluation of the material basis of S. chinensis.

Synthesis and evaluation of amylose-mefenamic acid conjugates as colon-targeting prodrugs.

Aim: Amide-linked amylose-based prodrugs were developed for colon-targeted release of mefenamic acid. Materials & methods: Activation of prodrug was studied spectrophotometrically, enzyme-linked immunosorbent assay appraised cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) inhibition at different concentrations of the prodrug, the behavior of prodrug under physiological conditions was monitored by scanning electron microscopy. Results: Prodrug was poorly activated in the enzyme-free simulated gastric media and simulated intestinal media (SIM) but preincubation in pancreatin followed by treatment in aminopeptidase containing SIM led to a significant activation of prodrug. Conclusion: Amide-linked amylose-mefenamic acid conjugates showed a slow release in simulated gastric media and a controlled release in SIM with pancreatin playing an important role in drug release.

Identification of a Novel Selective CDK9 Inhibitor for the Treatment of CRC: Design, Synthesis, and Biological Activity Evaluation.

Cyclin-dependent kinase 9 (CDK9) is a member of the transcription CDK subfamily. In this work, we preliminarily demonstrated the feasibility of CDK9 as a potent target of treatment for colorectal cancer, and a series of novel CDK9 inhibitors were rationally designed and synthesized based on the structure of AZD5438 (a pan CDKs inhibitor reported by AstraZeneca). A novel selective CDK9 inhibitor named CLZX-205, which possessed significant CDK9 inhibitory activity (IC50 = 2.9 nM) with acceptable pharmacokinetic properties and antitumor efficacy in vitro and in vivo, was developed. Research on the mechanism indicated that CLZX-205 could induce apoptosis in the HCT116 cell line by inhibiting phosphorylation of RNA polymerase II at Ser2, which resulted in the inhibition of apoptosis-related genes and proteins expression, and these results were validated at the cellular and tumor tissue levels. Currently, CLZX-205 is undergoing further research as a promising candidate for CRC treatment.

Direct Activation of Nucleobases with Small Molecules for the Conditional Control of Antisense Function.

Conditionally controlled antisense oligonucleotides provide precise interrogation of gene function at different developmental stages in animal models. Only one example of small molecule-induced activation of antisense function exist. This has been restricted to cyclic caged morpholinos that, based on sequence, can have significant background activity in the absence of the trigger. Here, we provide a new approach using azido-caged nucleobases that are site-specifically introduced into antisense morpholinos. The caging group design is a simple azidomethylene (Azm) group that, despite its very small size, efficiently blocks Watson-Crick base pairing in a programmable fashion. Furthermore, it undergoes facile decaging via Staudinger reduction when exposed to a small molecule phosphine, generating the native antisense oligonucleotide under conditions compatible with biological environments. We demonstrated small molecule-induced gene knockdown in mammalian cells, zebrafish embryos, and frog embryos. We validated the general applicability of this approach by targeting three different genes.

Direct Activation of Nucleobases with Small Molecules for the Conditional Control of Antisense Function

AbstractConditionally controlled antisense oligonucleotides provide precise interrogation of gene function at different developmental stages in animal models. Only one example of small molecule‐induced activation of antisense function exist. This has been restricted to cyclic caged morpholinos that, based on sequence, can have significant background activity in the absence of the trigger. Here, we provide a new approach using azido‐caged nucleobases that are site‐specifically introduced into antisense morpholinos. The caging group design is a simple azidomethylene (Azm) group that, despite its very small size, efficiently blocks Watson–Crick base pairing in a programmable fashion. Furthermore, it undergoes facile decaging via Staudinger reduction when exposed to a small molecule phosphine, generating the native antisense oligonucleotide under conditions compatible with biological environments. We demonstrated small molecule‐induced gene knockdown in mammalian cells, zebrafish embryos, and frog embryos. We validated the general applicability of this approach by targeting three different genes.

Determination of the proteolytic profile in Balaustium murorum (Hermann, 1804) (Acari: Prostigmata: Erythraeidae)

ABSTRACT Balaustium murorum (Acariformes: Erythraeidae) is a pollen feeder and predatory mite that occasionally causes dermatitis. We sought to determine the protease profile in the whole-mite extract of B. murorum using general and specific substrates as well as inhibitors. The pH profiles using two general substrates, azacasein and haemoglobin, revealed an optimal pH of 6 for both substrates. Specific trypsin inhibitor TLCK showed no influence activity towards BApNA; however, TPCK and AEBSF inhibited chymotrypsin and elastase, respectively. Specific cysteine protease inhibitors Cystatin and E-64 influenced both types of cathepsins B and L, while DTT as a specific activator increased the enzymatic activities. Only aminopeptidase showed significant activity and inhibition using negative control and phenanthroline. Chymotrypsin and elastase had the highest activity at pH of 9–10 and 10, respectively, by using both substrates alone and substrates along with specific inhibitors. Cathepsins B and L had pH optima of 6. Aminopeptidase revealed a broad pH optimum of 5–7 on both substrates HA and HPA alone and substrate along with inhibitor phenanthroline. Finally, different concentrations of each inhibitor were used to find IC50 values of TPCK, AEBSF, cystatin, E-64, DTT and phenanthroline required to inhibit half of enzyme activity.

Invitro antibacterial activity of bark, leaf and root extracts of combretum molle plant against streptococcus equi isolated from clinical cases of strangles in donkeys and horses

BackgroundEffective therapy for many infections is becoming difficult due to the evolutionary development of drug resistance, and hence, the development of alternative treatment options mainly from herbs is crucial. The objective of this study was to investigate the antibacterial effects of ethanol extracts of stem bark, leaves and roots of Combretum molle against Streptococcus equi isolated from clinical cases of strangles using in vitro tests.MethodsPlant extraction was performed using a maceration technique with 80% ethanol. The mean zone of inhibition was determined using the agar well diffusion method. Six serial dilutions with different concentrations (10%, 5%, 2.5%, 1.25%, 0.625% and 0.3125%) of each plant extract were prepared using dimethyl sulfoxide (DMSO). A modified agar microdilution method was used to determine the minimum inhibitory concentration (MICs) of the extracts.ResultsThe results revealed that all plant extracts showed significant antibacterial activity. The root extract showed the best antibacterial effect compared to the others at all concentrations, with MZI values of 27.5, 23.225, 20.5, 17.9, 15.65 and 12.25 for the respective concentrations mentioned above and an MIC of 250 µg/ml. It was followed by the stem bark extract, which had MZI values of 24.67, 22.35, 18.225, 16.175, 11.125 and 8.2 millimeters and an MIC of 375 µg/ml. The leaf extract also had significant activity, with MZI values of 20.175, 18.25, 15.7, 13.125, 9.4 and 6.75 in millimeters and an MIC of 500 µg/ml. There was a direct relationship between the concentrations of the plant extracts and the level of inhibition.ConclusionThe test plant extracts were compared with the conventional antibiotic penicillin G, and the results indicated that the parts of the test plant have significant antibacterial activity, which may support traditional claims and could be candidates for alternative drug discoveries.

Synthesis of biologically active Shiga toxins in cell-free systems

Shiga toxins (Stx) produced by pathogenic bacteria can cause mild to severe diseases in humans. Thus, the analysis of such toxins is of utmost importance. As an AB5 toxin, Stx consist of a catalytic A-subunit acting as a ribosome-inactivating protein (RIP) and a B-pentamer binding domain. In this study we synthesized the subunits and holotoxins from Stx and Stx2a using different cell-free systems, namely an E. coli- and CHO-based cell-free protein synthesis (CFPS) system. The functional activity of the protein toxins was analyzed in two ways. First, activity of the A-subunits was assessed using an in vitro protein inhibition assay. StxA produced in an E. coli cell-free system showed significant RIP activity at concentrations of 0.02 nM, whereas toxins synthesized in a CHO cell-free system revealed significant activity at concentrations of 0.2 nM. Cell-free synthesized StxA2a was compared to StxA2a expressed in E. coli cells. Cell-based StxA2a had to be added at concentrations of 20 to 200 nM to yield a significant RIP activity. Furthermore, holotoxin analysis on cultured HeLa cells using an O-propargyl-puromycin assay showed significant protein translation reduction at concentrations of 10 nM and 5 nM for cell-free synthesized toxins derived from E. coli and CHO systems, respectively. Overall, these results show that Stx can be synthesized using different cell-free systems while remaining functionally active. In addition, we were able to use CFPS to assess the activity of different Stx variants which can further be used for RIPs in general.

Enhancing bactericidal activities of ciprofloxacin by targeting the trans-translation system that is involved in stress responses in Klebsiella pneumoniae.

Although the trans-translation system is a promising target for antcibiotic development, its antibacterial mechanism in Klebsiella pneumoniae (KP) is unclear. Considering that tmRNA was the core component of trans-translation, this study firstly investigated phenotypic changes caused by various environmental stresses in KP lacking trans-translation activities (tmRNA-deleted), and then aimed to evaluate antibacterial activities of the trans-translation-targeting antibiotic combination (tobramycin/ciprofloxacin) in clinical KP isolates based on inhibition activities of aminoglycosides against trans-translation. We found that the tmRNA-deleted strain P4325/ΔssrA was significantly more susceptible than the wild-type KP strain P4325 under environments with hypertonicity (0.5 and 1M NaCl), hydrogen peroxide (40mM), and UV irradiation. No significant differences in biofilm formation and survivals under human serum were observed between P4325/ΔssrA and P4325. tmRNA deletion caused twofold lower MIC values for aminoglycosides. As for the membrane permeability, tmRNA deletion increased ethidium bromide (EtBr) uptake of KP in the presence or absence of verapamil and carbonyl cyanide-m-chlorophenylhydrazone (CCCP), decreased EtBr uptake in presence of reserpine in P4325/ΔssrA, and reduced EtBr efflux in P4325/ΔssrA in the presence of CCCP. The time-kill curve and in vitro experiments revealed significant bactericidal activities of the tmRNA-targeting aminoglycoside-based antibiotic combination (tobramycin/ciprofloxacin). Thus, the corresponding tmRNA-targeting antibiotic combinations (aminoglycoside-based) might be effective and promising treatment options against multi-drug resistant KP.

Anti-Inflammatory Sesquiterpenes from Fruiting Bodies of Schizophyllum commune.

Schizophyllum commune, a fleshy fungus, is an important medicinal and food-homologous mushroom in China. In this work, eight undescribed sesquiterpenes schizomycins A-H (1-8) and one new meroterpenoid schizomycin I (9) together with three known analogues (10-12) were isolated from fruiting bodies of S. commune. Their planar structures were established by extensive spectroscopic and mass spectrometric data. The absolute configurations of compounds 1, 2, and 4 were determined by single crystal X-ray diffraction, and compounds 3 and 5-9 were confirmed by electronic circular dichroism calculations. Anti-inflammatory activities of all isolated compounds were evaluated for their inhibitory effects on IL-6 and IL-1β production in RAW 264.7 cells. Among them, compound 7 exhibited significant IL-6 inhibitory activity with an IC50 value of 3.6 μM. The results of molecular docking showed that compound 7 interacts with amino acid residues (Gly117, Lys118, Asp120, Thr166, and Try168) of the IL-6 receptor protein through hydrogen bonding.

Isolation and characterization of Paenibacillus peoriae JC-3jx from Dendrobium nobile.

Dendrobium is a rich source of high-value natural components. Endophytic fungi are well studied, yet bacteria research is limited. In this study, endophytic bacteria from Dendrobium nobile were isolated using an improved method, showing inhibition of pathogens and growth promotion. JC-3jx, identified as Paenibacillus peoriae, exhibited significant inhibitory activity against tested fungi and bacteria, including Escherichia coli. JC-3jx also promoted corn seed rooting and Dendrobium growth, highlighting its excellent biocontrol and growth-promoting potential.

Phase-Tunable Molybdenum Boride Ceramics as an Emerging Sensitive and Reliable SERS Platform in Harsh Environments.

Traditional surface-enhanced Raman scattering (SERS) sensors rely heavily on the use of plasmonic noble metals, which have limitations due to their high cost and lack of physical and chemical stability. Hence, it is imperative to explore new materials as SERS platforms that can withstand high temperatures and harsh conditions. In this study, the SERS effect of molybdenum boride ceramic powders is presented with an enhancement factor of 5 orders, which is comparable to conventional noble metal substrates. The molybdenum boride powders synthesized through liquid-phase precursor and carbothermal reduction have β-MoB, MoB2 , and Mo2 B5 phases. Among these phases, β-MoB demonstrates the most significant SERS activity, with a detection limit for rhodamine 6G (R6G) molecules of 10-9 m. The impressive SERS enhancement can be attributed to strong molecule interactions and prominent charge interactions between R6G and the various phases of molybdenum boride, as supported by theoretical calculations. Additionally, Raman measurements show that the SERS activity remains intact after exposure to high temperature, strong acids, and alkalis. This research introduces a novel molybdenum boride all-ceramic SERS platform capable of functioning in harsh conditions, thereby showing the promising of boride ultrahigh-temperature ceramics for detection applications in extreme environments.

UHPLC-MS/MS and GC-MS Metabolic Profiling of a Medicinal Flourensia Fiebrigii Chemotype.

The comparative metabolic profiling and their biological properties of eight extracts obtained from diverse parts (leaves, flowers, roots) of the medicinal plant Flourensia fiebrigii S.F. Blake, a chemotype growing in highland areas (2750 m a.s.l.) of northwest Argentina, were investigated. The extracts were analysed by GC-MS and UHPLC-MS/MS. GC-MS analysis revealed the presence of encecalin (relative content: 24.86 %) in ethereal flower extract (EF) and this benzopyran (5.93 %) together sitosterol (11.35 %) in the bioactive ethereal leaf exudate (ELE). By UHPLC-MS/MS the main compounds identified in both samples were: limocitrin, (22.31 %), (2Z)-4,6-dihydroxy-2-[(4-hydroxy-3,5-dimethoxyphenyl)methylidene]-1-benzofuran-3-one (21.31 %), isobavachin (14.47 %), naringenin (13.50 %), and sternbin, (12.49 %). Phytocomplexes derived from aerial parts exhibited significant activity against biofilm production of Pseudomonas aeruginosa and Staphylococcus aureus, reaching inhibitions of 74.7-99.9 % with ELE (50 μg/mL). Notably, the extracts did not affect nutraceutical and environmental bacteria, suggesting a selective activity. ELE also showed the highest reactive species scavenging ability. This study provides valuable insights into the potential applications of this chemotype.

Co(II) Substitution Enhances the Esterase Activity of a de Novo Designed Zn(II) Carbonic Anhydrase.

Carbonic Anhydrases (CAs) have been a target for de novo protein designers due to the simplicity of the active site and rapid rate of the reaction. The first reported mimic contained a Zn(II) bound to three histidine imidazole nitrogens and an exogenous water molecule, hence closely mimicking the native enzymes' first coordination sphere. Co(II) has served as an alternative metal to interrogate CAs due to its d7 electronic configuration for more detailed solution characterization. We present here the Co(II) substituted [Co(II)(H2O/OH-)]N(TRIL2WL23H)3 n+ that behaves similarly to native Co(II) substituted human-CAs. Like the Zn(II) analogue, the cobalt-derivative at slightly basic pH is incapable of hydrolyzing p-nitrophenylacetate (pNPA); however, as the pH is increased a significant activity develops, which at pH values above 10 eventually yields a catalytic efficiency that exceeds that of the [Zn(II)(OH-)]N(TRIL2WL23H)3 + peptide complex. X-ray absorption analysis is consistent with an octahedral species at pH 7.5 that converts to a 5-coordinate species by pH 11. UV-vis spectroscopy can monitor this transition, giving a pKa for the conversion of 10.3. We assign this conversion to the formation of a 5-coordinate Co(II)(Nimid)3(OH)(H2O) species. The pH dependent kinetic analysis indicates the maximal rate (kcat), and thus the catalytic efficiency (kcat/Km), follow the same pH profile as the spectroscopic conversion to the pentacoordinate species. This correlation suggests that the chemically irreversible ester hydrolysis corresponds to the rate determining process.