Rate Constants For Hydrolysis Research Articles

Synthesis and hydrolysis of aryl fluoroglycosides

In this work, we have used a new approach for the synthesis of aryl fluoroglycoside analogues. This strategy used a simple metal-mediated anomeric arylation leading to phenolic fluoroglycosides. Moreover, we determined the rate constants of the acid-catalyzed hydrolysis of original and known mono- and polyfluorinated aryl O- and S-glycosides. For simple phenyl O-fluoroglucosides, the pseudo-first order rate constant for acid-catalyzed hydrolysis was smaller for the β anomer than for the α anomer. As for 4-carboxyphenyl O-galactosides, the rate constant varies as follows: nonfluorinated > 6-deoxy-6-fluoro > 3-deoxy-3-fluoro ≈ 4-deoxy-4-fluoro > 2-deoxy-2-fluoro > polyfluorinated. Finally, we observed a diminution in the hydrolysis rate constant with an increase in the number of integrated fluorine atoms as compared to the native carbohydrate.

Self-catalyst degradation of amoxicillin in alkaline condition driven by superoxide radical

We studied the rate of amoxicillin (AMX) degradation in oxygen-contained (OCG) and oxygen-free (OFG) groups under alkaline conditions by comparing the molecular structure of AMX with penicillin (PG) and penicillin V potassium (PV) resulting from measuring the hydrolysis rate, performing quenching experiments, and analyzing the products of AMX. The pseudo first-order rate constants of AMX hydrolysis were 0.003 h−1 and 0.032 h−1 (pH = 9, 25 ℃) in OCG and OFG, respectively, with both dissolved oxygen and OH− radicals playing important roles in AMX hydrolysis in OCG. According to the quenching experiments, the signal intensity of O2− in OCG appeared after 3 h and increased consistently, which confirmed that the participation of dissolved oxygen in AMX degradation accelerates the reaction and O2− generate from the reaction between dissolved oxygen and the hydrolysis products of AMX. The phenol group was the key functional group involved in the O2− reaction when comparing the molecular structure differences between PG, PV, and AMX. In total, 30 degradation products of AMX were found by liquid-chromatography triple-quadrupole mass spectrometry. Five degradation pathways of AMX were suggested, which are similar to those of photodegradation. Among them, path 3, which involves phenol (phenol, p-carboxyphenol, etc.) reactions, contained reactions with both dissolved oxygen and OH−. Considering there were no extra reagents added to the reaction system, the degradation of AMX in OCG appeared to be a self-catalytic reaction.

Pig slurry organic matter transformation and methanogenesis at ambient storage temperatures.

Manure management is a significant source of global methane emissions, and there is an increased interest in understanding and predicting emissions. The hydrolysis rate of manure organic matter is critical for understanding and predicting methane emissions. We estimated hydrolysis rate constants of crude protein, fibers, and lipids and used the Arrhenius equation to describe its dependency on temperature. Simultaneously, measurements of methane emission, 13/12 C isotope ratios, and methanogen community were conducted. This was achieved by incubating fresh pig manure without inoculum at 10°C, 15°C, 20°C, and 25°C for 85 days in a lab-scale setup. Hydrolysis of hemicellulose and cellulose increased more with temperature than crude protein, but still, hydrolysis rate of crude protein was highest at all temperatures. Results suggested that crude protein consisted of multiple substrate groups displaying large differences in degradability. Lipids and lignin were not hydrolyzed during incubations. Cumulative methane emissions were 7.13±2.69, 24.6±8.00, 66.7±4.8, and 105.7±7.14 gCH4 kgVS -1 at 10°C, 15°C, 20°C, and 25°C, respectively, and methanogenic community shifted from Methanosphaera toward Methanocorpusculum over time and more quickly at higher temperatures. This study provides important parameter estimates and dependencies on temperature, which is important in mechanistic methane emission models. Further work should focus on characterizing quickly degradable substrate pools in the manure organic matter as they might be the main carbon source of methane emission from manure management.

Analyzing disinfection by-products yield and mechanisms in UV/Cl2 using response surface methodology and quantitative structure-activity relationship models

The study aimed to investigate the formation of halogenated disinfection byproducts (DBPs) during applying UV/chlorine (UV/Cl2) and unravel the interactive impacts of critical operational parameters and the mechanisms behind DBPs formation. Response surface methodology and quantitative structure-activity relationship models were developed to evaluate the contribution of electrophilic, nucleophilic, and free radical reactions to the formation of DBPs in UV/Cl2. The study found that Cl2 and its interactions dominated the total DBPs and non-Br-DBPs formation, while Br− and the Cl2–Br− interaction played a decisive role in the Br-DBPs formation. The study also observed significant interactions of Br, Cl2, and pH on chloroform, bromodichloromethane, dichloroacetonitrile, 1,1-dichloro-2-propanone, trichloroactic acid, and chlorodibromoacetic acid formations, while no evident interaction on chloral hydrate, dibromochloromethane, trichloroacetone, dibromoacetic acid, and bromodichloroacetic acid formations. The electrophilic substitution of HOBr mainly controlled the formation of trihalomethanes, and the contribution of nucleophilic, electrophilic, and free radical (•OH, Cl•, Cl2•- and ClO•) reactions depended on the molar ratio of Cl2 to Br, and pH-determined hydrolysis rate constants of DBPs and the types of free radicals. Overall, the response surface methodology and quantitative structure-activity relationship models provided a reference for revealing DBPs formation mechanisms in other disinfection processes.

Construction of imidazole@defective hierarchical porous UiO-66 and fibrous composites for rapid and nonbuffered catalytic hydrolysis of organophosphorus nerve agents

Hydrolytic destruction of toxic organophosphorus nerve agents by metal-organic framework (MOF) catalysts is commonly reliant on bulk water and volatile liquid base, preventing real-world implementation. Poor accessibility to MOF-based active sites in heterogeneous catalysis is also a crucial factor since reactants diffusion is limited by inherently small micropores. To overcome these practical limitations, a ligand-selective pyrolysis strategy was used to construct unsaturated Zr defects and additional mesopores in UiO-66(Zr). Owing to synergistic effect of Zr defects and hierarchical pores, hydrolysis rate constant (k) of nerve agent simulant DMNP (dimethyl 4-nitrophenyl phosphate) on optimal DHP-UiO-30% (defective hierarchical porous UiO-66) is 3.2 times higher than counterpart UiO-30% in N-ethylmorpholine buffer. Encapsulating imidazole (Im) into DHP-UiO-30% affords Im@DHP-UiO, mimicking phosphotriesterase. Im-72@DHP-UiO exhibits rapid DMNP detoxification with 99% conversion in 12 min and initial half-life (t1/2) of 1.8 min in nonbuffered water. As the first example of ‘three-in-one’ detoxifier, Im@DHP-UiO is further integrated onto nonwoven fabric to construct Im@DHP/Fiber, achieving solid-phase detoxification at ambient humidity with t1/2 of 19.6 min and final conversion of 91%. This is comparable to many powdered catalysts in aqueous solution buffered by volatile bases. This unified strategy is critical and viable to efficiently hydrolyze nerve agents in practical settings.

Nonenzymatic hydrolysis of 1,2:3,4‐diepoxybutane: A kinetic study including pH, temperature, and ion effects

Abstract1,3‐Butadiene is a carcinogenic and mutagenic air pollutant metabolized to butane epoxides, among which 1,2:3,4‐diepoxybutane (DEB) exhibits the highest genotoxicity. DEB is also formed by 1,3‐butadiene oxidation in the air, producing a direct environmental and occupational exposure. In this paper, we studied the kinetics of the nonenzymatic hydrolysis of DEB at a wide range of pH and temperature, including the catalytic effect of ionic species. The compound degradation involved a general and specific acid‐base catalysis of the epoxide ring hydrolysis. DEB had the greatest stability at pH 5–9, when the rates of acid‐catalyzed and base‐catalyzed hydrolysis are negligible and the neutral hydrolysis predominates. The capability of the buffer anions to accelerate the DEB decay increased in the order H2PO4− < HCO3− < CH3COO− < HPO42− < and CO32−. The Arrhenius equation well described the influence of temperature on the acid‐catalyzed, base‐catalyzed, and neutral hydrolysis rate constants. According to the obtained hydrolysis model coupled with the found thermodynamic parameters, the half‐life of DEB in natural fresh waters spans from 2 days at 30°C to 31 days at 0°C, but in the laboratory waste adjusted to pH 1or 13, the half‐life shortens to 2–3 h at 20°C. Therefore, the results of the paper help to assess the risk of exposure to the genotoxic action of DEB.

Modeling of the Peptide Release during Proteolysis of β-Lactoglobulin by Trypsin with Consideration of Peptide Bond Demasking.

Prospects for predicting the fragmentation of polypeptide chains during their enzymatic hydrolysis using proteolysis models are considered. The opening of the protein substrate during proteolysis and the exposure of its internal peptide bonds for a successful enzymatic attack, the so-called demasking process, were taken into account. The two-step proteolysis model was used, including the parameters of demasking and the rate constants of hydrolysis of enzyme-specific peptide bonds. Herein, we have presented an algorithm for calculating the concentrations of intermediate and final peptide fragments depending on the time of hydrolysis or the degree of hydrolysis. The intermediate peptide fragments with two or one internal specific peptide bond were considered. The fragmentation of β-lactoglobulin (β-LG) by trypsin was predicted, and the calculated concentration curves for peptide fragments were compared with the experimental dependences of the concentrations on the degree of hydrolysis. Numerical parameters were proposed that characterize the concentration curves for intermediate and final peptide fragments, and they were used to compare the calculated and experimental dependences. The predicted distribution of the peptide fragments corresponded to the experimental data on the peptide release during the proteolysis of β-LG by trypsin.

Enhanced anaerobic digestion of waste activated sludge by alkaline protease-catalyzing hydrolysis: Role and significance of initial pH adjustment

Anaerobic digestion has been regarded as a preferred technology for carbon/energy recovery from waste activated sludge via volatile fatty acids (VFAs) and methane production. Although the enzyme pretreatment has been investigated, specific roles of initial pH adjustment on alkaline protease (AP) catalysis and its influence on anaerobic digestion have been rarely reported. This work demonstrated that the increasing initial pH displayed positive mutual promotion of AP-catalyzing hydrolysis for facilitating sludge solid reduction and biodegradable organic matter solubilization. The release of carbon source and phosphorus were also promoted, while the soluble NH4+-N content was decreased at increasing alkaline conditions, which was beneficial for hydrolysate bio-utilization. Nevertheless, initial pH = 10 was the optimum condition for maximizing VFAs and methane recovery after AP-catalyzing sludge hydrolysis. Under such condition, the sludge solid reduction and sludge hydrolysis rate constants were 0.7981 h−1 and 1.1288 h−1, respectively, which were 6.40 and 2.45 times higher than those in the control. Meanwhile, the biochemical acidogenic potential of 447.0 mg COD VFAs/g VSS and the estimated biochemical methane potential of 437.6 mL CH4/g VSS were achievable. The identification of the mutual promotion distribution revealed that initial pH adjustment presented more close association with anaerobic digestion than AP catalysis and its contribution was amplified with increasing pH. Apparently, such AP catalysis with initial pH adjustment is a promising technology for sustainable sludge management with economic benefits and carbon-emission reduction.

Kinetic Study on Alkaline Hydrolysis of an Ester to Correlate the Solvent Effect with Some Thermodynamic Functions

In the present research paper, second-order rate constants for the alkaline hydrolysis of ethyl benzoate and of ethyl p-nitrobenzoate in ethanol–water mixtures in the ethanol mol fraction range 0.16–0.72 and at 278.15– 318.15 K measured by a specially developed titrimetric technique. The results show interesting variations in the rate constants with ethanol content at the various temperatures, especially over the mol fraction ranges 0.16–0.25 and 0.4–0.5. The rate constant (k2) data, the Arrhenius activation energy (EA) and preexponential factor (A) for ethyl benzoate and the parameters of the fitted polynomials from which other derived thermodynamic functions may be calculated are provided as supplementary material.

Postharvest ripening of newly harvested corn: Structural, rheological, and digestive characteristics of starch

Newly harvested corn was stored at 25 °C and 55% relative humidity, the changes in the structure, rheological and digestive properties of corn starch during postharvest ripening were studied. The postharvest ripening process of corn resulted in a reduction in the content of amylose and an increase in the proportion of double-helical structures, short-range orderliness and relative crystallinity. These structural changes significantly improved the thermal stability of the starch and its ability to form gels. The lowest hydrolysis rate constant was demonstrated for corn starch at 30 days, indicating that proper post-ripening could help corn starch to form a stronger gel network structure and slow down the digestibility. The results of the study will contribute to a better understanding of the changes in the structure and properties of corn starch during the postharvest ripening, which provided a pathway for the rational processing and utilization of corn starch and even corn food at different postharvest ripening stages.

Impact of UV-C pretreatment on β-lactoglobulin hydrolysis by trypsin: Production and bioavailability of bioactive peptides

The effects of UV-C light irradiation and low-temperature long-time (LTLT) pasteurization on protein structural changes, degree of hydrolysis (DH) by trypsin, peptide profile of tryptic hydrolysates by MALDI-TOF/TOF-MS, and bioavailability of β-lactoglobulin were compared. Compared with native or LTLT pasteurised samples, the hydrolysis rate constant of β-lactoglobulin treated with UV-C increased significantly, implying that the protein backbone cleavage sites became more accessible, whereas thermal treatment produced aggregates that impede trypsin activity. Tryptic hydrolyses of UV-C light treated β-lactoglobulin yielded more peptides and a more diverse peptide mass profile. Six bioactive peptides were revealed in β-LG tryptic hydrolysates of UV-C-treated protein; transepithelial transport in Caco-2 cell monolayers showed intermediate in vivo transport and absorption for three (β-LG f87–91, β-LG f91–99, and β-LG f158–164). The moderate allergen peptide LSFNPTQLEEQCHI β-LG was absent after tryptic hydrolysis of UV-C-treated protein, indicating that UV-C photolysis may be a useful tool for allergenicity reduction.

A multiple linear regression approach to the estimation of carboxylic acid ester and lactone alkaline hydrolysis rate constants

ABSTRACT Pesticides, pharmaceuticals, and other organic contaminants often undergo hydrolysis when released into the environment; therefore, measured or estimated hydrolysis rates are needed to assess their environmental persistence. An intuitive multiple linear regression (MLR) approach was used to develop robust QSARs for predicting base-catalyzed rate constants of carboxylic acid esters (CAEs) and lactones. We explored various combinations of independent descriptors, resulting in four primary models (two for lactones and two for CAEs), with a total of 15 and 11 parameters included in the CAE and lactone QSAR models, respectively. The most significant descriptors include pK a, electronegativity, charge density, and steric parameters. Model performance is assessed using Drug Theoretics and Cheminformatics Laboratory’s DTC-QSAR tool, demonstrating high accuracy for both internal validation (r 2 = 0.93 and RMSE = 0.41–0.43 for CAEs; r 2 = 0.90–0.93 and RMSE = 0.38–0.46 for lactones) and external validation (r 2 = 0.93 and RMSE = 0.43–0.45 for CAEs; r 2 = 0.94–0.98 and RMSE = 0.33–0.41 for lactones). The developed models require only low-cost computational resources and have substantially improved performance compared to existing hydrolysis rate prediction models (HYDROWIN and SPARC).

Weak Temperature Dependence of the Relative Rates of Chlorination and Hydrolysis of N2O5 in NaCl–Water Solutions

We have measured the temperature dependence of the ClNO2 product yield in competition with hydrolysis following N2O5 uptake to aqueous NaCl solutions. For NaCl-D2O solutions spanning 0.0054-0.21 M, the ClNO2 product yield decreases on average by only 4 ± 3% from 5 to 25 °C. Less reproducible measurements at 0.54-2.4 M NaCl also fall within this range. The ratio of the rate constants for chlorination and hydrolysis of N2O5 in D2O is determined on average to be 1150 ± 90 at 25 °C up to 0.21 M NaCl, favoring chlorination. This ratio is observed to decrease significantly at the two highest concentrations. An Arrhenius analysis reveals that the activation energy for hydrolysis is just 3.0 ± 1.5 kJ/mol larger than for chlorination up to 0.21 M, indicating that Cl- and D2O attack on N2O5 has similar energetic barriers despite the differences in charge and complexity of these reactants. In combination with the measured preexponential ratio favoring chlorination of 300-200+400, we conclude that the strong preference of N2O5 to undergo chlorination over hydrolysis is driven by dynamic and entropic, rather than enthalpic, factors. Molecular dynamics simulations elucidate the distinct solvation between strongly hydrated Cl- and the hydrophobically solvated N2O5. Combining this molecular picture with the Arrhenius analysis implicates the role of water in mediating interactions between such distinctly solvated species and suggests a role for diffusion limitations on the chlorination reaction.

Electrochemical fingerprinting of cephalosporin antibiotics and its applications for investigations of hydrolysis behavior

Cephalosporin, as one of the most widely used antibiotics, study of its hydrolysis process is important for predicting their environmental persistence. Two critical factors are considered has the first priority, which are hydrolysis rate constant (kh) and half-life (t1/2). To date, many efforts have been made by using various analytical techniques to obtain the data for calculating kh and t1/2. However, the typical techniques such as UV/vis spectrophotometry and liquid chromatography are of significant challenges like low accuracy and timely operations. Herein, we explored an electrochemical method by identifying the characteristic peaks with the same parent nuclear structure through square wave voltammetry (SWV). This proposed electrochemical fingerprinting was able to track the hydrolysis of intact cephalosporin molecules, β-lactam ring, and transformation product. The kh and t1/2 of cefadroxil (CDX) under pH = 7 and 25 °C by electrochemical (0.0640 d−1 and 11.0 d) were consistent with those of high-performance liquid chromatography-UV/vis (HPLC-UV/vis) (0.0660 d−1 and 10.7 d). The t1/2 ranged from 3.40 to 36.2 d, 7.33 d–43.7 d and 9.63 d–45.3 d for base-catalyzed, neutral pH and acid-catalyzed hydrolysis hydrolyzed, respectively, indicating that base-catalyzed hydrolysis rates were the greatest under alkaline conditions. Meanwhile, hydrolysis rates increased 2.50–3.60-fold for every 10 °C raise in temperature. Besides, the electrochemical fingerprinting could realize cephalosporin and β-lactam ring hydrolysis rates close to 100% in-situ hydrolysis process monitoring. This present work provides a powerful technology for understanding the environmental fate and predicting the environmental behavior of antibiotics with fast, high accuracy, specific recognition, and in situ monitoring.

High temperatures and CO2 dissolution can cause nitrogen losses from urine stabilized with base

Human urine is rich in valuable nitrogen which can easily be lost due to biological urea hydrolysis and subsequent ammonia volatilization. While this enzymatic reaction can be prevented by alkalizing the urine, recent studies suggest that chemical urea hydrolysis can result in substantial nitrogen losses when drying alkalinized urine at high temperatures. Furthermore, it was previously suggested that CO2 dissolution from the air used to evaporate water from alkalinized urine could result in a pH decrease to values which allows for biological urea hydrolysis and subsequent ammonia losses. This study aimed to determine the kinetics of chemical urea hydrolysis in alkalinized human urine and confirm the effect of CO2 dissolution with controlled laboratory experiments. We measured the change in urea concentration at different temperatures and pH values for real human urine and determined the corresponding rate constants for chemical urea hydrolysis. We showed that the rate constant increases as a function of temperature and that pH has a negligible effect on the rate of chemical urea hydrolysis in the high pH range of alkalized urine (>11). The rate constants for chemical urea hydrolysis in a saturated calcium hydroxide solution were found to be 0.00147 d−1, 0.00595 d−1, 0.0204 d−1 and 0.0848 d−1 for temperatures of 25°C, 40°C, 55°C and 70°C, respectively. The effect of CO2 dissolution on urea hydrolysis was determined by aerating human urine alkalinized with calcium hydroxide (Ca(OH)2). In order to represent biological urea hydrolysis, urease was added to the solution. The computer simulations of the experimental results showed that CO2 dissolution and the subsequent dissociation of carbonic acid to carbonate ions, bicarbonate ions and protons is the main cause of the pH decrease, but CaCO3 precipitation, and NH3 volatilization foster the pH decrease. However, biological urea hydrolysis prevents the pH from decreasing below 9. Residual undissolved Ca(OH)2 was shown to substantially delay the pH decrease. Overall, this work provides valuable insights into the mechanisms of urea hydrolysis in alkalinized urine during dehydration, which can be used to design more efficient decentralized sanitation systems and minimize nitrogen losses.

Isolation and Purification of Bacillus amyloliquefaciens D1 Protease and Its Application in the Fermentation of Soybean Milk to Produce Large Amounts of Free Amino Acids.

In this study, a strain of Bacillus amyloliquefaciens D1, with a notably high production of neutral protease, was isolated from Morchella crassipes. The protease was purified to 10.4-fold with a specific activity of 4542.9 U/mg and 2.7% recovery. The enzyme was purified by 70% (NH4)2SO4 and DEAE-Cellulose-52 column. The estimated molecular mass of the purified protease obtained by SDS-PAGE was approximately 40kDa. The enzyme was optimally active at pH 6.0 and 50°C. Furthermore, the maximum hydrolysis rate (Vmax) and apparent Michaelis-Menten constant (Km) values of the purified protease were 8.2mg/mL and 65.7µg/(min mL). The enzymatic properties and rapid and efficient purification of Bacillus amyloliquefaciens D1 provide the basis for its potential commercialization and industrial development. Moreover, more essential amino acids, such as isoleucine, leucine, and phenylalanine, would be released when the strain fermented soybean milk, and then a better amino acid profile would be formed in soybean milk. Results suggest that this strain exhibits great potential in fermented soybean milk, and the enzyme could lay a foundation for its industrial application and further research.

Degradation kinetics of artesunate for the development of an ex-tempore intravenous injection

BackgroundArtesunate is recommended by the World Health Organization (WHO) for parenteral treatment of severe Plasmodium falciparum malaria. However, artesunate is inherently unstable in an aqueous solution and hydrolyses rapidly after its preparation for injection. Therefore, the aim of the study was to evaluate the stabilizing effects of phosphate buffer and mannitol against short-term (ex-tempore) artesunate hydrolysis.MethodsA HPLC–UV isocratic method was developed using a reversed-phase fused core column (HALO RP-C18) and a mobile phase consisting of a mixture of 45% ammonium formate 10 mM in water (pH 4.5) and 55% methanol. Artesunate was formulated as aqueous solutions using a design of experiment (DOE) to investigate the artesunate stabilizing effects of pH (8–10), phosphate buffer strength (0.3–0.5 M), and mannitol (0–0.22 mmol/mL). The solutions were incubated at predefined temperatures (5, 25, and 40 °C) with subsequent analysis. Arrhenius equation was applied to model and evaluate the stability results.ResultsThe developed HPLC-based method using fused-core stationary phase allowed to selectively quantify artesunate in the presence of its main hydrolysis degradants; namely β-dihydroartemisinin (β-DHA) and α-dihydroartemisinin (α-DHA) within 10 min. By applying the Arrhenius equation, the rate of hydrolysis of the drug increased approximately by 3.4 as the temperature raised by 10 °C. Buffer strength was found to be the main factor affecting the hydrolysis rate constants at 5 and 25 °C (p < 0.05), the activation energy (p = 0.009), and the frequency factor (p = 0.045). However, the effect of the buffer was predominant on the activation energy and hydrolysis rate constants, revealing its stabilizing effect on the drug at lower buffer strength (0.3 M). Within the investigated range (pH = 8–10), pH was found to influence the activation energy, with a positive stabilizing effect in the pH range of 8–9. The addition of mannitol as stabilizing agent into artesunate aqueous formulation did not show an improved response.ConclusionPhosphate buffer was the main stability determining factor of artesunate in the aqueous intravenous (i.v.) formulation and was found to be more effective in stabilizing artesunate at a buffer strength of 0.3 M in pH 8–9, while mannitol lacked stabilizing effect.

Spent coffee grounds anaerobic digestion: Investigating substrate to inoculum ratio and dilute acid thermal pretreatment

Spent coffee grounds have the potential of being used in further bioprocesses to produce materials and fuels. In Norway, the relative abundance and ease of collection of this waste substrate make it a candidate for investigation. For this study, the substrate-to-inoculum ratio as well as a combined dilute acid-thermal pretreatment were assessed by a series of biochemical methane potential assays using spent coffee grounds as a substrate. Reactors with substrate-to-inoculum ratio 2 demonstrated a relatively low hydrolysis rate constant (kh) and comparatively high volatile fatty acids/alkalinity concentrations rendering them inapt to produce bio-CH4. Pretreatment was conducted over varying contact times (15–45 min), dilute acid concentrations (1.5–2.5 %, v/v), and liquid-to-solid ratios (10–20 %, v/w) and evaluated using response surface methodology. To determine bio-CH4 yield, pretreatment time and the interaction between acid concentration and liquid-to-solid ratio are considered significant variables, suggesting a shared importance. Chemical oxygen demandremoval is primarily contingent upon changes in liquid-to-solid ratio. Finally, Fourier-transform infrared spectroscopy of the discarded solid phase showed that the major functional groups are still widely present in the coffee grounds even after pretreatment was applied. A better understanding of the biodegradability profile of spent coffee grounds as a function of substrate-to-inoculum ratio is achieved.

Effects of First‐Coordination Sphere and Buffers on the Nitrosyl‐Nitrite Conversion Rate in Ru(II) Complexes

AbstractNitrogen oxide derivative ruthenium compounds can deliver nitric oxide (NO) by chemical, electrochemical, or photochemical processes. Among these compounds, nitrosyl ruthenium complexes have been one of the most studied species. The σ‐ and π‐character of the co‐ligand L in [RuL5(NO)]n+ exerts a unique and determining effect on the structure of the complex and the NO delivery mode. We have found inconsistencies in this assertion. How the buffer medium influences the hydrolysis rate constant of nitrosyl ruthenium complexes such as cis‐[Ru(NO)(bpy)2L]3++(L=4‐pic; py; isn and 4‐acpy) has been evaluated in biphthalate, phosphate, and imidazole buffer solutions. For the studied ruthenium complexes, hydrolysis depended on the π‐acceptor character of ligand “L”, with kobs increasing in the following order: 4‐pic&lt;py&lt;isn&lt;4‐acpy. For nitrite conversion, the relative efficiency of the buffers increased in the order: biphthalate&lt;phosphate&lt;imidazole for all the studied nitrosyl ruthenium complexes. On the basis of these findings, we hypothesized that the second‐coordination sphere interacts with the ruthenium complexes. By conducting theoretical modeling studies, we have elucidated the potential contribution of this interaction to nitrosyl/nitrite interconversion.

Hydrolysis rate constants of ATP determined in situ at elevated temperatures

Life can be found even in extreme environments, e.g., near black smokers on the ocean floor at temperatures up to ca. 120 °C and hydrostatic pressures of 40 MPa. To maintain vital reactions under these hostile conditions, extremophiles are interacting with the surrounding geochemical system. In this context, the stabilities of the essential energy-storing adenosine triphosphate (ATP) and adenosine diphosphate (ADP) are of fundamental importance because reactions involving adenosine phosphates constrain the conditions at which carbon-based life can exist and might be also crucial information for the search of extra-terrestrial life. Adenosine phosphates react by non-enzymatic hydrolysis, which is kinetically enhanced at high temperatures. If these abiotic hydrolysis processes are too rapid, they will most likely prevent metabolisms from relying on ATP.Here, we report on an approach used in experimental geochemistry, i.e., in situ Raman spectroscopic analyses of a fluid phase at high temperature using a hydrothermal diamond anvil cell. This combination allowed the investigation of the hydrolysis of Adenosine Tri-Phosphate (ATP) in aqueous solution at pH 3 and 7 and at temperatures of 80, 100 and 120 °C, extending the so far measured temperature range substantially. We observed Arrhenian behaviour over this temperature interval. The rate constants at 120 °C were 4.34 × 10−3 s−1 at pH 3 and 2.91 × 10−3 s−1 at pH 7. This corresponds to ATP half-lives of a few minutes. These high decomposition rates of ATP suggest that organisms must have developed a mechanism to counteract this fast reaction at high temperatures to maintain the vital processes.