Range Of Rate Constants Research Articles

Novel Catalyst-free Activation of Chlorine by Visible Light for Micropollutant Abatement

This study systematically investigated the direct activation of chlorine by visible light emitting diode (Vis-LED). Vis-LED could effectively activate chlorine to degrade micropollutants with degradation efficiency and pseudo-first-order degradation rate constant range of 64.3%-100% and 0.0340-0.195min-1, respectively. Quenching experiments and modeling results suggested that reactive chlorine species (RCS, including ClO•, Cl2•-, and Cl•) and hydroxyl radical (•OH) were involved in the degradation of atenolol (ATL). The contribution ratio of ClO•, free available chlorine, Cl•, Cl2•-, and •OH to ATL degradation were 58.7%, 17.4%, 15.6%, 1.8%, and 5.9%, respectively, in Vis-LED448/chlorine process. Moreover, the innate quantum yields of HClO and ClO- decreased from 0.229 and 0.0206 to 0.0489 and 0.0109mol·Einstein-1, respectively, as the wavelength increased from 448 to 513nm, leading to a decrease in ATL degradation, which was consistent with the model results. Experimental and modeling results have confirmed that ATL degradation decreased when pH increased from 4.0 to 9.0. Cl- had little effect on the degradation of ATL, while HA and HCO3- affected ATL degradation by scavenging reactive species and/or shielding effect. The concentration of disinfection by-products decreased with the increase of wavelength and pH. In summary, Vis-LED/chlorine is an efficient water treatment process even without a catalyst.

A comparative analysis of square-wave voltammetry and multi-frequency electrochemical Faradaic spectroscopy for kinetic characterisation

A rigorous comparison between square-wave voltammetry (SWV) and the recently proposed multi-frequency electrochemical Faradaic spectroscopy (MEFS) is presented for both a quasireversible electrode reaction of a dissolved redox couple at a planar macroscopic electrode and a catalytic regenerative electrode mechanism (EC′ reaction scheme) by means of numerical simulations. MEFS offers fast kinetic characterisation with a minimal set of experiments, as the system is interrogated with a range of SW frequencies in a single experiment. By changing the mid-potential Em, a critical parameter of MEFS, a broad range of standard rate constants for the heterogeneous interfacial electron transfer is accessible, ranging between 0.006 and 0.12 cm s−1. In the case of the EC′ mechanism, features of the current components in both SWV and MEFS reflect the involvement of the follow-up regenerative chemical reaction (i.e. C′ catalytic step). However, for the kinetic characterisation of the EC′ mechanism, the comparative analysis suggests that SWV should be the main operating technique.

Estimation of the rate constants for the radical addition of a trifluoromethyl radical to aryl-substituted vinyl triflates

Abstract The rate constants for the radical addition of a trifluoromethyl radical to aryl-substituted vinyl triflates have been determined by applying competition kinetics at a single concentration point. The rate constants range from 4.1× 106 to 5.6× 106 M−1 s−1 and depend on the electronic properties of the benzene rings on the aryl-substituted vinyl triflates.

Simultaneous Cr(VI) Reduction and Dexamethasone Phosphate Oxidation with Organo-metallic Sludge Formation Under UV Irradiation: Kinetics, Degradation Pathways, and Mechanism

In this study, we investigated the concurrent elimination of two distinct contaminants: organic matter in the form of dexamethasone phosphate (DexP) and an inorganic substance, chromium (Cr), employing UV irradiation. UV irradiation serves as a potent tool for breaking down organic materials, leading to the production of benign by-products, namely CO2 and H2O. Under optimal conditions characterized by a 30:1 DexP/Cr molar ratio and a pH level of 9, remarkable removal efficiencies were attained. In a mere 20 min, approximately 100% of DexP and 82.73% of Cr were effectively removed. Intriguingly, the removal of Cr exhibited an initially sluggish rate, with deposition commencing only after the breakdown of the DexP structure. This transformation was accompanied by the emergence of various sludge forms, each possessing unique characteristics. Utilizing Fourier-transform infrared (FTIR) analysis, we identified these sludge forms as chromium(III) hydroxide (green sludge), chromium(III) hydroxide (brown sludge), chromium(III) oxide (tiny green crystals), chromium(II) acetate chromium trioxide (red brick), and chromium oxide (black sludge). Further experimentation with varying concentrations of Cr and DexP, ranging from 50 to 150 mg L−1, yielded a range of rate constants (kobs) from 0.33 to 0.15 and removal efficiencies (robs) from 16.8 to 23.4% in the UV/DexP/Cr process. Energy efficiency output (EEO) calculations revealed that Cr precipitation ranged from 24.65 to 5.74 kW h m−3, whereas DexP EEO ranged from 12.54 to 4.73 kW h m−3. Of significant importance is the observation that when these two contaminants are removed simultaneously, the overall energy consumption is substantially lower compared to the scenario where pollutants are addressed individually. This finding underscores the efficiency and potential energy cost savings achievable through the concurrent removal of DexP and Cr using UV irradiation, making it a promising approach for environmental remediation.

Effect of pH on UV/H2O2-mediated removal of single, mixed and halogenated parabens from water

Adjusting pH values in aqueous environments can significantly improve the efficiency by which parabens and halo-parabens are removed. In this study, 20 neutral and deprotonated species were selected as models to investigate their pH-dependent removal mechanisms and kinetics by a UV/H2O2 process using density functional theory (DFT). Compared to neutral species, deprotonated species exhibit higher reactivity to HO• due to their high electron cloud density. H atom abstraction (HAA) reactions on the substitution groups are the most favorable pathways for neutral species, while radical adduct formation (RAF) reactions are the most favorable for deprotonated species. Single electron transfer (SET) reactions can be neglected for neutral species, while these reactions become a viable route for deprotonated molecules. The total reaction rate constants range from 1.63 × 109 to 3.74 × 1010 M− 1 s− 1 at pH 7.0, confirming the experimental results. Neutral and weakly alkaline conditions are favorable for the degradation of MeP and halo-parabens in the UV/H2O2 process. The order of removal efficiency at optimum pH is dihalo-parabens > mono-halo-parabens ≈ F, F-MeP > MeP. Furthermore, the transformation products must undergo oxidative degradation due to their high toxicity. Our findings provide new insights into the removal of parabens and their halogenated derivatives from wastewater.

Use of Inner/Outer Sphere Terminology in Electrochemistry—A Hexacyanoferrate II/III Case Study

Salts of hexacyanoferrate II/III anions have been widely used as redox couple probe molecules to determine the characteristics of electrode surfaces. Examples include the assessment of electrocatalysts for energy applications and electrocatalysts for the detection of biological or chemical species, as well as the determination of electrochemically active surface areas. An examination of the electrochemical literature, based largely on cyclic voltammetric investigations, reveals a wide range of peak separation and/or heterogeneous electron transfer rate constants, classified sometimes as inner or outer sphere electron transfer processes. Originally developed for the mechanistic interpretation of inorganic transition metal compounds in solution, this terminology has since been extended to account for heterogeneous electron transfer occurring at electrodes. In the case of the hexacyanoferrate II/III anions, there can be a number of reasons why it sometimes behaves as an outer sphere probe and at other times displays inner sphere electron transfer characteristics. After examining some of the structural and chemical properties of the hexacyanoferrate II/III species, the methods used to determine such classifications are described. The most common method involves measuring peak-to-peak separation in a cyclic voltammogram to ascertain a heterogeneous rate constant, but it has inherent flaws. This paper reviews the reasons for the classification disparity, including the effects of various oxygen surface species, the influence of organic surface films, the nature of the cation counter-ion, surface adsorption and surface hydrophilicity/hydrophobicity. Other surface interactions may also take place, such as those occurring with Au corrosion or pH effects. These can impact the electrical double layer and thus may affect the electron transfer process. Consequently, it is recommended that hexacyanoferrate II/III should be considered a multi-sphere or alternatively a surface-sensitive electron transfer species.

Electroosmotic Perfusion, External Microdialysis: Simulation and Experiment.

Information about the rates of hydrolysis of neuropeptides by extracellular peptidases can lead to a quantitative understanding of how the steady-state and transient concentrations of neuropeptides are controlled. We have created a small microfluidic device that electroosmotically infuses peptides into, through, and out of the tissue to a microdialysis probe outside the head. The device is created by two-photon polymerization (Nanoscribe). Inferring quantitative estimates of a rate process from the change in concentration of a substrate that has passed through tissue is challenging for two reasons. One is that diffusion is significant, so there is a distribution of peptide substrate residence times in the tissue. This affects the product yield. The other is that there are multiple paths taken by the substrate as it passes through tissue, so there is a distribution of residence times and thus reaction times. Simulation of the process is essential. The simulations presented here imply that a range of first order rate constants of more than 3 orders of magnitude is measurable and that 5-10 min is required to reach a steady state value of product concentration following initiation of substrate infusion. Experiments using a peptidase-resistant d-amino acid pentapeptide, yaGfl, agree with simulations.

Evaporation of the tramp element antimony from molten steel under reduced pressure treatment

ABSTRACT The evaporation of antimony (Sb) in molten steel under reduced pressure is investigated with the gas phase pressure of 19–670 Pa, smelting temperature of 1823–1973 K and initial Sb content of 0.033–0.1 wt%. The findings indicate that Sb removal efficiency increases when smelting temperature rises or gas phase pressure decreases. However, the initial Sb content has little effect on the Sb removal. The Sb removal ratio can reach 94.1% within 40 min of treatment. The range of the apparent evaporation rate constant, k Sb, is 0.61 × 10−5 to 29.13 × 10−5 m s−1. The evaporation of Sb is limited by the gas phase mass transfer at 1903 K and 19–670 Pa. Additionally, the apparent activation energy of Sb evaporation, E Sb, is 128 kJ mol−1 at 226 Pa and 1823–1973 K, and the rate of the interfacial reaction severely restricts the evaporation of Sb.

Stabilising Effects of Lumped Integration Schemes for the Simulation of Metal-Electrolyte Reactions

Computational modelling of metal-electrolyte reactions is central to the understanding and prediction of a wide range of physical phenomena, yet this is often challenging owing to the presence of numerical oscillations that arise due to dissimilar reaction rates. The ingress of hydrogen into metals is a paradigmatic example of a technologically-relevant phenomenon whose simulation is compromised by the stiffness of the reaction terms, as reaction rates vary over orders of magnitude and this significantly limits the time increment size. In this work, we present a lumped integration scheme for electro-chemical interface reactions that does not suffer from numerical oscillations. The scheme integrates the reactions in a consistent manner, while it also decouples neighbouring nodes and allows for larger time increments to be used without oscillations or convergence issues. The stability and potential of our scheme is demonstrated by simulating hydrogen ingress over a wide range of reaction rate constants and environmental conditions. While previous hydrogen uptake predictions were limited to time scales of minutes, the present lumped integration scheme enables conducting simulations over tens of years, allowing us to reach steady state conditions and quantify hydrogen ingress for time scales relevant to practical applications.

Adsorption of Methylene Blue on Nano-Crystal Cellulose of Oil Palm Trunk: Kinetic and Thermodynamic Studies

The adsorption kinetic study of methylene blue using nano-crystal cellulose made from oil palm trunk was investigated. A sample of 0.08 g of nano-crystal cellulose was used to adsorb 300 mL of methylene blue solution, with a varied stirring speed at 100, 200, and 300 rpm. Meanwhile, the concentration of methylene blue was varied at 1, 2, and 3 mg/L. The experimental results showed that the range of adsorption rate constant was 0.0007–0.0130 m/min. For the thermodynamic study, adsorption temperature was varied at 303, 308, 313, and 318 K. The adsorption capacity values for such temperatures were 10.3389, 10.3802, 10.3614, and 10.3464 mg/g, respectively. It was found that ΔH° value of 0.00742 kJ/mol, ΔS° of 0.7758 kJ/mol K and ΔG° value of −242.81 kJ/mol. Based on the curve-fitting using the Henry, Langmuir, and Freundlich isotherm models, this adsorption tended to the Langmuir isotherm model, where the adsorption formed a monolayer covering the surface of the adsorbent. It was also found that the Langmuir affinity constant (KL) value was 4.560 L/mg, and the maximum adsorption capacity (qm) was 8.590 mg/g.

Degradation of sulfonamide antibiotics and a structurally related compound by chlorine dioxide: Efficiency, kinetics, potential products and pathways

Sulfonamides (SAs) detected in all kinds of environmental water matrix may cause potential risk for aquatic environment and organisms. In this research, the oxidation of three SAs of sulfamethoxazole (SMX), sulfadiazine (SD) and sulfaguanidine (SGD), and a structurally related compound of 4-methylsulfonylaniline (MSA) by chlorine dioxide (ClO2) was investigated to identify removal efficiency, kinetics, potential products and pathways. At pH 7.0, the highest removal rates of 99.36 %, 100 % and 97.29 % were acquired for SMX, SD and SGD at the initial ClO2 concentration of 50 μM, while that of MSA was only 48.25 %. The difference among three SAs and MSA can be explained by structural influences of substituent attached to the sulfonyl amido-nitrogen. The reactions of SMX, SD and SGD with ClO2 followed the second-order kinetic model (R2 greater than 0.98) with the apparent second-order rate constants range of 5.60 × 102 to 2.73 × 103 M−1 s−1 at pH 7.0 and 25 ℃. The reaction rates were highly dependent on the pH and the trend of activation energy was SGD > SMX > SD at pH 7.0. Products evaluation indicated that the main potential degradation pathways of three SAs were the cleavage of SN and SC bonds, deamination and hydroxylation of aniline group. The sulfonyl amido-nitrogen and aniline amino-nitrogen were prone to be attacked by ClO2. Aniline and sulfanilic acid were found to be the common products of three SAs degradation. The results suggest that ClO2 has the potential to serve as a chemical oxidant for removing sulfonamides in practical water treatment conditions.

Influence of time, temperature, and UV light on stability and degradation kinetics of fortificants in sattu beverage during storage

The stability and degradation of fortificants in beverages has been stated as major hurdle in fortification. The fortificants tend to degrade during the storage and cause quality loss in beverages. The sattu beverage fortified with rutin-loaded pectin nanoparticles (RLPN) and riboflavin was evaluated for the stability and kinetics of degradation of fortificants. The loading stability of fortificant was determined to evaluate the stability of the RLPN. The Fourier transform infrared (FTIR) analysis showed the loading of rutin over pectin nanoparticles. The turbidity, cloudiness, and turbidity loss rate were also determined at an interval of 7 days during 56 days of storage. The turbidity and cloudiness of the beverage increased during storage while the fortification was helpful to maintain the turbidity loss rate. The degradation kinetics and half-life of RLPN and riboflavin were calculated for the same period. The range of rate constant of RLPN and riboflavin were 5.12 × 10−2 to 6.11 × 10−2 s−1 and 2.76 × 10−2 to 4.73 × 10−2 s−1, respectively. The study on the effect of UV light showed that the stability of riboflavin was complemented by RLPN (RLPN was found to be self-stable). The color analysis of fortified beverage samples showed that the UV light did not have significant effect on the stability and degradation of fortificants. The addition of RLPN in sattu beverage was found to enhance the stability of riboflavin. The data obtained from this research work can be used to scale-up the processing of fortified sattu beverage to commercial scale. Practical application The sustainability of fortificants is easily affected by different parameters (time and temperature) applied during food processing. The present study deals with the challenges encountered during processing and storage of fortified beverage. The temperature and time period applied in this study are commonly used for beverages and drinks. The study of kinetics can help to understand the degradation and loss behavior of fortificants in fortified beverage at commercial or industrial scale. The study also helps to understand the mechanism behind the appearance (turbidity, cloudiness, turbidity loss ratio, and color) change in fortified beverages during storage. The knowledge obtained from this research might be helpful in developing fortified sattu beverage in industry.

Measurements of SARS-CoV-2 antibody dissociation rate constant by chaotrope-free biolayer interferometry in serum of COVID-19 convalescent patients

Kinetics measurements of antigen-antibody binding interactions are critical to understanding the functional efficiency of SARS-CoV-2 antibodies. Previously reported chaotrope-based avidity assays that rely on artificial disruption of binding do not reflect the natural binding kinetics. This study developed a chaotrope- and label-free biolayer interferometry (BLI) assay for the real-time monitoring of receptor binding domain (RBD) binding kinetics with SARS-CoV-2 spike protein in convalescent COVID-19 patients. An improved conjugation biosensor probe coated with streptavidin-polysaccharide (SA-PS) led to a six-fold increase of signal intensities and two-fold reduction of non-specific binding (NSB) compared to streptavidin only probe. Furthermore, by utilizing a separate reference probe and biotin-human serum albumin (B-HSA) blocking process to subtracted NSB signal in serum, this BLI biosensor can measure a wide range of the dissociation rate constant (koff), which can be measured without knowledge of the specific antibody concentrations. The clinical utility of this improved BLI kinetics assay was demonstrated by analyzing the koff values in sera of 24 pediatric (≤18 years old) and 63 adult (>18 years old) COVID-19 convalescent patients. Lower koff values for SARS-CoV-2 serum antibodies binding to RBD were measured in samples from children. This rapid, easy to operate and chaotrope-free BLI assay is suitable for clinical use and can be readily adapted to characterize SARS-CoV-2 antibodies developed by COVID-19 patients and vaccines.

UV/Chlorine Process: An Efficient Advanced Oxidation Process with Multiple Radicals and Functions in Water Treatment.

Because of the deterioration of global water quality, the occurrence of chemical and microbial contaminants in water raises serious concerns for the health of the population. Identifying and developing effective and environmentally friendly water treatment technologies are critical to obtain clean water. Among the various technologies for the purification of water, ultraviolet photolysis of chlorine (UV/chlorine), an emerging advanced oxidation process (AOP), has multiple functions for the control of contaminants via the production of hydroxyl radicals (HO·) and reactive chlorine species (RCS), such as Cl·, ClO·, and Cl2·-.This Account centers around the radical chemistry of RCS and HO· in different water matrices and their roles and mechanisms in the abatement of contaminants. The concentrations of Cl·, ClO·, and Cl2·- are comparable to or higher than those of HO· (10-14 to 10-13 M). The reactivities of RCS are more selective than HO· with a broader range of second-order rate constants (k). The k values of Cl· toward most aromatics are higher or similar as compared to those of HO·, while those of Cl2·- and ClO· are less reactive but more selective toward aromatics containing electron-donating functional groups. Their major reaction mechanisms with Cl· are electron transfer and addition, while those with ClO· and Cl2·- primarily involve electron transfer. As for aliphatics, their reactivities with both HO· and RCS are much lower than those of aromatics. The reaction mechanisms for most of them with Cl· and Cl2·- are hydrogen abstraction, except for olefins, which are addition. In addition, RCS greatly contribute to the inactivation of microbial contaminants.Toward future application, the UV/chlorine process has both pros and cons. Compared with the traditional HO·-based AOP of UV/H2O2, UV/chlorine is more efficient and energy-saving for oxidation and disinfection, and its efficiency is less affected by water matrix components. However, the formation of toxic byproducts in UV/chlorine limits its application scenarios. In dissolved organic matter (DOM)-rich water, the formation of halogenated byproducts is enhanced in UV/chlorine. In the presence of ammonia, reactive nitrogen species (RNS) (e.g., ·NO and ·NO2) are involved, and highly toxic nitro(so) products such as nitro(so)-phenolics and N-nitrosodimethylamine are generated. For a niche application, the UV/chlorine process is recommended to be utilized in water with low levels of DOM and ammonia.Strategies should be developed to make full use of highly reactive species (RCS and HO·) for the abatement of target contaminants and to reduce the formation of toxic byproducts. For example, the UV/chlorine process can be used in tandem with other treatments to create multiple barriers for the production of safe water. In addition, halogen radicals are very important in ecosystems as well as other areas such as medical therapy and organic synthesis. UV/chlorine is the most efficient homogeneous system to generate halogen radicals, and thus it provides a perfect system to investigate the fates of halogen radicals for interdisciplinary research.

Kinetic investigation of the polymerase and exonuclease activities of human DNA polymerase ε holoenzyme

In eukaryotic DNA replication, DNA polymerase ε (Polε) is responsible for leading strand synthesis, whereas DNA polymerases α and δ synthesize the lagging strand. The human Polε (hPolε) holoenzyme is comprised of the catalytic p261 subunit and the noncatalytic p59, p17, and p12 small subunits. So far, the contribution of the noncatalytic subunits to hPolε function is not well understood. Using pre-steady-state kinetic methods, we established a minimal kinetic mechanism for DNA polymerization and editing catalyzed by the hPolε holoenzyme. Compared with the 140-kDa N-terminal catalytic fragment of p261 (p261N), which we kinetically characterized in our earlier studies, the presence of the p261 C-terminal domain (p261C) and the three small subunits increased the DNA binding affinity and the base substitution fidelity. Although the small subunits enhanced correct nucleotide incorporation efficiency, there was a wide range of rate constants when incorporating a correct nucleotide over a single-base mismatch. Surprisingly, the 3'→5' exonuclease activity of the hPolε holoenzyme was significantly slower than that of p261N when editing both matched and mismatched DNA substrates. This suggests that the presence of p261C and the three small subunits regulates the 3'→5' exonuclease activity of the hPolε holoenzyme. Together, the 3'→5' exonuclease activity and the variable mismatch extension activity modulate the overall fidelity of the hPolε holoenzyme by up to 3 orders of magnitude. Thus, the presence of p261C and the three noncatalytic subunits optimizes the dual enzymatic activities of the catalytic p261 subunit and makes the hPolε holoenzyme an efficient and faithful replicative DNA polymerase.

Kinetics and pathways of the degradation of PPCPs by carbonate radicals in advanced oxidation processes

The carbonate radical (CO3•−) is a typical secondary radical observed in engineering and natural aquatic systems. This study investigated the degradation kinetics of 20 pharmaceuticals and personal care products (PPCPs) by CO3•− and the transformation pathways of a typical PPCP (naproxen) that is susceptible to CO3•−. CO3•− is highly selective for compounds containing aniline and phenolic hydroxyl groups as well as naphthalene rings, such as sulfamethoxazole, sulfamethazine, salbutamol, propranolol, naproxen, and macrolide antibiotics such as azithromycin, for which the second-order rate constants range from 5.6 × 107 M−1s−1 to 2.96 × 108 M−1s−1. A good linear relationship is observed between the natural logarithms of kCO3•− and the negative values of the Hammett Σσp+ constant for aromatic PPCPs, indicating that electron-donating groups promote the attack of benzene derivatives by CO3•−. The contribution of CO3•− to naproxen degradation is significant in different processes such as UV/H2O2, UV/persulfate, UV/chlorine, and UV/monochloramine, in the presence of HCO3−, which compensates for the decreased contributions of primary radicals. In particular, the formation of CO3•− increases the first-order rate constant of naproxen by 127% in UV/monochloramine in the presence of 50 mM HCO3− compared to that without HCO3−. Natural organic matter (NOM) exerts a slight scavenging effect on CO3•−, decreasing the inhibition effect of NOM on the degradation of naproxen by UV/H2O2 in the presence of HCO3−. The pathways involved in the transformation of naproxen by CO3•− include decarboxylation, hydroxylation, ketonization, demethylation and aldolization. In addition, the alteration of the genotoxicity during naproxen degradation by CO3•− was negligible.

Slow Molecular Recognition by RNA

Molecular recognition is fundamental to life as demonstrated by the remarkable specificity observed in biological processes mediated by proteins and RNAs. Nevertheless, the most accurate process is of no value to biology if it cannot be carried out rapidly. Proteins associate with ligands with a wide range of association rate constants, with maximal values matching the theoretical limit set by the rate of diffusional collision. As less is known about RNA association, we recently compiled association rate constants for all RNA/ligand complexes that we could find in the literature. Our analysis indicates that RNAs, like proteins, exhibit a wide range of association rate constants. However, the fastest RNA association rates are considerably slower than those of the fastest protein associations and fall well below the diffusional limit. The apparently general observation of slow association with RNAs presumably reflects basic physical properties of RNA and has implications for evolution and for modern‐day biology. We also discuss potential strategies for increasing RNA association kinetics, such as the use of electrostatic forces to accelerate binding, which may provide broadly applicable strategies for developing fast‐binding RNA ligands as well as RNA‐targeted therapeutics.

Kinetics and morphological characteristics of struvite (MgNH4PO4.6H2O) under the influence of maleic acid.

This work reports a stirred-batch lab crystallization to examine the influence of maleic acid (HO2CCHCHCO2H), and temperatures (30 and 40 °C) on crystallization kinetics and morphology of struvite. The crystallization was followed by measuring the pH change up to 70 min. The pH decreased drastically for the first 5 min of the run, then started to tail off. It was found that the crystallization rate constants range from 1.608 to 6.534 per hour, which agrees with the most published value. Higher maleic acid concentrations resulted in greater growth retardation; the highest retardation was 74.21%, which was achieved for 30 °C with 20.00 ppm maleic acid. SEM imaging of the obtained precipitates showed irregular prismatic morphology, and the associated EDX confirmed that the precipitates were struvite (MgNH4PO4⋅6H2O). As checked through XRD, the crystalline nature of the struvite was further confirmed, and that co-precipitation of struvite with struvite-K was observed. The co-precipitation was the result of K+ adsorption onto the crystal surface. Temperatures had less influence on struvite crystallization. At 40oC and 20.00 ppm the rate constant was 1.332 per hour; whereas at 30oC and 0.00 ppm) the corresponding was 1.776 per hour, indicating the retardation of about 25%. Thus, the temperature effect is only 1/3 of the maleic acid effect. The current findings suggest that the presence of maleic acid can be used to elucidate the mechanism of crystallization as well as the crystalline phase transformation of struvite. In practical terms, maleic acid could be potential as a scale inhibitor.

The Dynamics of Cytoplasmic mRNA Metabolism.

For all but a few mRNAs, the dynamics of metabolism are unknown. Here, we developed an experimental and analytical framework for examining these dynamics for mRNAs from thousands of genes. mRNAs of mouse fibroblasts exit the nucleus with diverse intragenic and intergenic poly(A)-tail lengths. Once in the cytoplasm, they have a broad (1000-fold) range of deadenylation rate constants, which correspond to cytoplasmic lifetimes. Indeed, with few exceptions, degradation appears to occur primarily through deadenylation-linked mechanisms, with little contribution from either endonucleolytic cleavage or deadenylation-independent decapping. Most mRNA molecules degrade only after their tail lengths fall below 25 nt. Decay rate constants of short-tailed mRNAs vary broadly (1000-fold) and are larger for short-tailed mRNAs that have previously undergone more rapid deadenylation. This coupling helps clear rapidly deadenylated mRNAs, enabling the large range in deadenylation rate constants to impart a similarly large range in stabilities.

Kinetics of the formation and degradation of carbonaceous and nitrogenous disinfection by-products in Bangkok and Songkhla source waters

The kinetics of the formation and degradation of disinfection by-products (DBPs) in the treated water from the Bangkhen and Hatyai water treatment plants in Thailand were investigated. The DBPs studied included trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), and trichloronitromethane (TCNM). When the chlorination time was increased, the levels of TCM, BDCM, DBCM, and TCNM increased, while the levels of TCAN, DCAN, and BCAN decreased. The kinetic rates of DBPs’ formation were assessed based on the formation and degradation rates, which were best described by first-order kinetics. TCM had the highest formation rate with a range of rate constants from 5.5 × 10−3 to 7.3 × 10−3 h−1. TCAN had the lowest degradation rate with a range of rate constants from 0.6 × 10−3 to 2.9 × 10−3 h−1. Good correlations were observed between chlorination time and DBPs’ formation normalized by LC50, lowest cytotoxicity, and lowest genotoxicity. A high formation rate of TCM and a low degradation rate of TCAN normalized by their toxicity were observed. The optimal retention time providing low DBPs’ formation together with high DBPs’ degradation was determined. The retention time of three days decreased the sum of the DBPs/LC50, DBPs/lowest cytotoxicity, and DBPs/lowest genotoxicity from a retention time of one day by 40–60%, 45–65%, and 25–36%, respectively.