pH Plots Research Articles

Synthesis and optimization of chitosan-incorporated semisynthetic polymer/α-Fe2O3 nanoparticle hybrid polymer to explore optimal efficacy of fluorescence resonance energy transfer/charge transfer for Co(II) and Ni(II) sensing

Initially, four synthetic fluorescent polymers (SFPs) are synthesized from α-methacrylic acid and methanolacrylamide monomers carrying –C(=O)OH and –C(=O)NH subfluorophores, respectively. Among SFPs, ∼1:1 incorporation of subfluorophores in the optimum SFP3 is explored by spectroscopic analyses. Subsequently, chitosan is incorporated in SFP3 to produce five semi-synthetic fluorescent polymers (SSFPs). The maximum incorporation of chitosan in SSFP4 is supported by different spectroscopies. In SSFP4, strong electrostatic interactions among polar functionalities of chitosan and synthetic polymer favor resonance-associated charge transfer (RCT) from SSFP4-(amide) to SSFP4-(canonical). Finally, three hybrid fluorescent polymers (HFPs) are fabricated encapsulating iron-oxide nanoparticle within SSFP4. The maximum proportion of hematite (α-Fe2O3) phase in HFPs is explored by spectroscopic, magnetometric, microscopic, and light scattering studies. HFP2 shows local/RCT/fluorescence resonance energy transfer (FRET) emission at 393/460/570 nm. In HFP2, FRET, RCT, and ratiometric pH-sensing within 3.0–6.5 phenomena are explored by solvent polarity effects, time-correlated single photon counting, quantum yield measurements, alongside I431/I460 vs pH plots. RCT and FRET emissions of HFP2 are utilized for selective sensing of Co(II)/Ni(II) with limits of detection of 4.990 ppb (460 nm)/4.353 ppb (570 nm) and 45.041 ppb (428 nm)/29.617 ppb (527 nm) in organic and aqueous solutions, respectively.

Future proofing a long-term agricultural experiment for decades to come: Relocation and redesign

We took land encroachment for urban development that threatened a 60-year-old field experiment as an opportunity to transport and redesign an entire experiment to more effectively address contemporary challenges. The field experiment comprised long-term pH plots, established for agronomic demonstration in 1961, but used over the years for both applied and fundamental research. We redesigned the experimental layout to add strength to the statistical design through randomisation. Continuation and enrichment of the long-term pH experimental platform lends a unique resource for microbiome research per se. Here we have provided a rationale for why the decision was made to move the soils from the former Woodlands Field pH experiment. Moving soil on the scale of a field experiment requires costs and benefits to be weighed up in that the realisation of the transfer costs and the costs for the ongoing maintenance can outweigh the costs of a new experimental set up or indeed closing the experiment and walking away. It is important to recognise that much of the value is in assets that are not monetary. Considerations include the availability of a site suitable from a biophysical perspective but also considering ownership and future access. The topsoil (0–20 cm to plough depth) was moved to a new location in a similar environment and within the same soil association. The soil was disturbed under very dry conditions and placed back into the earth in the new location within 90 minutes, and thus as near to normal cultivation as possible. Additional plots were added to the experiment that will be amended to the pH treatments in the long-term experiment providing an exciting opportunity to assess how soil microbial communities change over time. Soil samples taken 2 years after the relocation of the soils indicate that the soil pH gradient (4.5–7.5) has been maintained. Safeguarding this long-term resource on soil pH helps us to predict the impacts of changed practice with regard to liming on productivity and also to address wider contemporary and future issues surrounding net zero, food security and soil protection.

Electrochemical proton-coupled electron transfer processes to form neutral radicals of azaphenalenes: pKa values of protonated radicals

Azaphenalenes are nitrogen substituted analogues of the phenalene ring system, and their radicals have attracted significant attention because of the novel electronic and magnetic properties. In the previous study, the neutral tris(tert-butyl) 1,3-diazaphenalenyl radical has been synthesized by chemical oxidation of the parent compound with PbO2. In this study, we focused on electrochemical proton-coupled electron transfer (PCET) process leading to the formation of neutral unsubstituted 1,3-diazaphenalenyl radical from 1,3-diazaphenalene (DAP) in solution. Additionally, this electrochemical approach was extended to study the redox behavior of newly synthesized 1,4,7-triazaphenalene (TAP) giving the access to the 1,4,7-triazaphenalenyl radical. Electrochemical oxidation potentials vs. pH plots (Pourbaix diagram) for DAP and TAP revealed that their one-electron oxidation to the corresponding neutral radicals occurred by a PCET process over a wide pH range. From the analysis of Pourbaix diagrams, the pKa values of the protonated radicals were determined to be pKa = 2.57 and 2.39 for the DAP and TAP radicals, respectively. Cyclic voltammograms of azaphenalenes in MeCN and MeCN/buffer solutions showed a characteristic ECE process, in which electrochemical oxidative dimerization took place following the electron transfer. The dimerization reaction pathway was rationalized by the digital simulations, DFT calculations and crystallization of a DAP dimer after chemical oxidation with PbO2. The spectroscopic properties of azaphenalenes and their dimerized products were characterized by in-situ UV–Vis and EPR spectroelectrochemistry techniques. The fundamental information about the pKa and redox potentials for a series of azaphenalenes (DAP, TAP, as well as 1,3,4,6,7,9-hexaazaphenalene, HAP) could be fed back into the molecular design of redox-active conductive coordination networks based on multi-interactive ligands.

Fine-scale evaluation of two standard 16S rRNA gene amplicon primer pairs for analysis of total prokaryotes and archaeal nitrifiers in differently managed soils.

The advance of high-throughput molecular biology tools allows in-depth profiling of microbial communities in soils, which possess a high diversity of prokaryotic microorganisms. Amplicon-based sequencing of 16S rRNA genes is the most common approach to studying the richness and composition of soil prokaryotes. To reliably detect different taxonomic lineages of microorganisms in a single soil sample, an adequate pipeline including DNA isolation, primer selection, PCR amplification, library preparation, DNA sequencing, and bioinformatic post-processing is required. Besides DNA sequencing quality and depth, the selection of PCR primers and PCR amplification reactions arguably have the largest influence on the results. This study tested the performance and potential bias of two primer pairs, i.e., 515F (Parada)-806R (Apprill) and 515F (Parada)-926R (Quince) in the standard pipelines of 16S rRNA gene Illumina amplicon sequencing protocol developed by the Earth Microbiome Project (EMP), against shotgun metagenome-based 16S rRNA gene reads. The evaluation was conducted using five differently managed soils. We observed a higher richness of soil total prokaryotes by using reverse primer 806R compared to 926R, contradicting to in silico evaluation results. Both primer pairs revealed various degrees of taxon-specific bias compared to metagenome-derived 16S rRNA gene reads. Nonetheless, we found consistent patterns of microbial community variation associated with different land uses, irrespective of primers used. Total microbial communities, as well as ammonia oxidizing archaea (AOA), the predominant ammonia oxidizers in these soils, shifted along with increased soil pH due to agricultural management. In the unmanaged low pH plot abundance of AOA was dominated by the acid-tolerant NS-Gamma clade, whereas limed agricultural plots were dominated by neutral-alkaliphilic NS-Delta/NS-Alpha clades. This study stresses how primer selection influences community composition and highlights the importance of primer selection for comparative and integrative studies, and that conclusions must be drawn with caution if data from different sequencing pipelines are to be compared.

Exploring the potential of the novel imidazole-4,5-dicarboxyamide chemical exchange saturation transfer scaffold for pH and perfusion imaging.

Here, we describe and assess the potential of 14 newly synthesized imidazole-4,5-dicarboxyamides (I45DCs) for pH and perfusion imaging. A number of these aromatic compounds possess large labile proton chemical shifts (up to 7.7ppm from water) because of their intramolecular hydrogen bonds and a second labile proton to allow for chemical exchange saturation transfer (CEST) signal ratio-based pH measurements. We have found that the contrast produced is strong for a wide range of substitutions and that the inflection points in the CEST signal ratio versus pH plots used to generate concentration-independent pH maps can be adjusted based on these subsitutions to tune the pH range that can be measured. These I45DC CEST agents have advantages over the triiodobenzenes currently employed for tumor and kidney pH mapping, both preclinically and in initial human studies. Finally, as CEST MRI combined with exogenous contrast has the potential to detect functional changes in the kidneys, we evaluated our highest performing anionic compound (I45DC-diGlu) on a unilateral urinary obstruction mouse model and observed lower contrast uptake in the obstructed kidney compared with the unobstructed kidney and that the unobstructed kidney displayed a pH of ~6.5 while the obstructed kidney had elevated pH and an increased range in pH values. Based on this, we conclude that the I45DCs have excellent imaging properties and hold promise for a variety of medical imaging applications, particularly renal imaging.

Separation of intact proteins by capillary electrophoresis.

This work introduces novel and universal workflows for the analysis of intact proteins by capillary electrophoresis and presents guidelines for the targeted selection of appropriate background electrolytes (BGEs) by consideration of the target proteins' isoelectric point (pI). The suitability of neutral dimethyl polysiloxane (PDMS) capillaries with dynamic coatings of cationic cetyltrimethylammonium bromide (CTAB) or anionic sodium dodecyl sulfate (SDS), and bare fused silica (BFS) capillaries were systematically evaluated for the analysis of histidine and seven model proteins in six BGEs with pH values between 3.0 and 9.6. Multiple capillary and BGE combinations were suitable for the analysis of all proteins with molecular weights ranging from 13.7-150 kDa, and pIs between 4.7 and 9.6. The CTAB-PDMS capillary was best suited for low pH BGEs, while the SDS-PDMS and BFS capillary were superior for high pH BGEs. These combinations consistently resulted in sharp peak shapes and rapid migration times. pH values of BGEs closer to the proteins' pI produced poorer peak shapes and decreased effective mobilities due to suppressed ionisation. Plots of mobility vs. pH crossed at approximately the pI of the protein in most cases. The workflow was applied to the analysis of caseins and whey proteins in milk for the separation of the seven most abundant proteins, including the isoforms of A1 and A2 β-casein and β-lactoglobulin A and B.

Thermodynamic analysis of primary and secondary minerals stability in melilite-nephelinite tuff with Australopithecus Afarensis footprints, Laetoli, Tanzania

The Laetoli area in northern Tanzania is an important palaeo-anthropological site, where the oldest footprints of Australopithecus afarensis reside. Aeolian tuffs are the major rock type at Laetoli and they are divided into Lower and Upper Laetolil Beds that were deposited at an interval of 4.36 and 3.63 million years. The Upper Laetolil Beds contain eight layers of air-fall tuffs known as marker tuffs. The Australopithecus afarensis footprints are observed on the surface of the white tuff, which is a part of the Upper Laetolil marker tuff 7, also known as the “Footprint Tuff.” The interpolated age of the marker tuff 7 is 3.66 million years. Two mineral assemblages are distinguished in the Upper Laetolil marker tuffs. The first assemblage consists of primary tuff minerals and includes clinopyroxene (diopside, augite, aegirine-augite), nepheline, melilite (åkermanite and alumoåkermanite), garnet (andradite and schorlomite), magnetite, and others. The second mineral assemblage consists of secondary minerals, montmorillonite, calcite, and phillipsite. They were formed during replacement of the primary minerals, volcanic glass, and ash cementation. Thermodynamic calculations show that the major primary tuff minerals (melilite and nepheline) are stable at variable sodium activity and pH values. Replacement of melilite and nepheline by montmorillonite is caused by a decrease of sodium activity in slightly alkaline, neutral and acidic conditions (рН < 10). Montmorillonite is not present in the altered nephelinitic tuff of the Sadiman volcano (which is considered as a source of the Laetolil Beds) where kaolinite is the major secondary mineral. This is explained by the difference in H2O fugacity with higher lgfH2O values in Sadiman and lower values in Laetoli. Relationships between primary and secondary tuffs minerals on the lgaHCO3 vs pH plot suggest mineral transformation within the Laetolil Beds in slightly acid and neutral con- ditions (рН = 5–7) compared with more alkaline conditions at Sadiman (рН > 10).

Rosaniline Hydrochloride Encapsulated MCM-48: Fluorescent and Electrochemical Sensor for Dopamine.

The dye Rosaniline hydrochloride (RANH) has been successfully incorporated in MCM-48 (designated as RANH@MCM-48) and characterized by various spectroscopic methods including FT-IR, SEM, EDX and N2 adsorption-desorption isotherm. RANH@MCM-48 in aqueous medium acts as fluorescence "on" sensor for neurotransmitter dopamine (DA) in presence of its main biological interfering agent ascorbic acid or vitamin c (AA) along with Glucose, Cholesterol and Uric acid (UA). The limits of detection (LOD) were found to be 65nM and 51nM respectively in absence and in presence of AA. The interaction of DA to RANH@MCM-48 is found to be reversible with respect to EDTA2-. The fluorescence intensity vs. pH plot shows a narrow fluorescence window of 7.2 to 8.8. RANH@MCM-48 has been successfully applied for DA detection in artificial cerebrospinal fluid (ACF) and bovine serum albumin (BSA) with LOD values 27nM and 22.5nM respectively. Platinum disc electrode has been modified with RANH@MCM-48 which showed distinct oxidation peaks with a separation of 0.188V in cyclic voltammetry (CV). The LOD for DA in presence of AA determined from oxidation current is 77.5nM. The voltammetric detection of DA is found to be free from common interfering species Na+, K+, Ca2+, Fe2+, UA, Cholesterol and Glucose. RANH@MCM-48 has been found to be a very effective fluorescence and voltammetric sensor for DA with very low LOD.

Accelerated vegetation succession but no hydrological change in a boreal fen during 20years of recent climate change.

Northern mires (fens and bogs) have significant climate feedbacks and contribute to biodiversity, providing habitats to specialized biota. Many studies have found drying and degradation of bogs in response to climate change, while northern fens have received less attention. Rich fens are particularly important to biodiversity, but subject to global climate change, fen ecosystems may change via direct response of vegetation or indirectly by hydrological changes. With repeated sampling over the past 20 years, we aim to reveal trends in hydrology and vegetation in a pristine boreal fen with gradient from rich to poor fen and bog vegetation. We resampled 203 semi‐permanent plots and compared water‐table depth (WTD), pH, concentrations of mineral elements, and dissolved organic carbon (DOC), plant species occurrences, community structure, and vegetation types between 1998 and 2018. In the study area, the annual mean temperature rose by 1.0°C and precipitation by 46 mm, in 20‐year periods prior to sampling occasions. We found that wet fen vegetation decreased, while bog and poor fen vegetation increased significantly. This reflected a trend of increasing abundance of common, generalist hummock species at the expense of fen specialist species. Changes were the most pronounced in high pH plots, where Sphagnum mosses had significantly increased in plot frequency, cover, and species richness. Changes of water chemistry were mainly insignificant in concentration levels and spatial patterns. Although indications toward drier conditions were found in vegetation, WTD had not consistently increased, instead, our results revealed complex dynamics of WTD as depending on vegetation changes. Overall, we found significant trend in vegetation, conforming to common succession pattern from rich to poor fen and bog vegetation. Our results suggest that responses intrinsic to vegetation, such as increased productivity or altered species interactions, may be more significant than indirect effects via local hydrology to the ecosystem response to climate warming.

Speeding up the Development of 5-[(4-Chlorophenoxy)-Methyl]-1,3,4-Oxadiazole-2-Thiol as Successful Oral Drug Candidate Based on Physicochemical Characteristics

The present paper describes for the first time the oral-drug-qualifying predictors, anti-acetylcholinesterase activity, and molecular docking of a new compound, 5-[(4-chlorophenoxy)-methyl]-1,3,4-oxadiazole-2-thiol. The oral bioavailability predictors such as lipophilicity (logP), ionization constant (pKa), solubility (logS) and permeability (logD) were predicted using computational tools. Then, a UV spectrophotometric method was developed to verify the predicted properties and determine stability of the proposed compound in the presence of various stressors. The predicted logP and pKa values were very close to the measured values, while, the computed aqueous solubility (6.46 μg/mL) was lower than that found experimentally (65.00 μg/mL). The logS versus pH and logD versus pH plots indicated that the compound migrated to hydrophilic compartment on increasing pH. The compound remained stable under various photolytic and pH stress conditions. However, the compound exhibited degradation under oxidative and thermal stress. The results of the present study indicate that the proposed compound absorbs well from the oral route and remains stable at ambient temperature and physiological pH. The observed remarkable dose-dependent anti-acetylcholinesterase activity indicates that the compound may be a drug candidate for treating neurodegenerative disorders.

Biohydrogen fermentation from Pistia stratiotes (aquatic weed) using mixed and pure bacterial cultures

In this study, mixed and pure bacterial cultures are inoculated in a dark-fermentation process for hydrogen production from Pistia stratiotes hydrolysate. The maximum hydrogen yield (HY) of 2.3 molH₂/molglucose (energy yield 0.3 kJ/gDW) is obtained at pH 5.5, fermentation time 6.7 h, substrate-to-biomass ratio (S/X) 0.5 gCOD/gVSS, and 25 °C using a mixed culture system. The plots of HY versus pH and time result in quadratic linear concave-up curves, whereas the effects of S/X and temperature on HY cause quadratic concave-up and flat curves, respectively. Fluorescent in situ hybridization (FISH) indicates that the mixed culture contains multiple H2-producers including Enterobacteriaceae, Gammaproteobacteria, Betaproteobacteria, and Clostridium histolyticum. Three isolates belonging to Bacillus cereus, Bacillus anthracis, and Enterobacter cloacae are used as pure cultures, achieving HYs of 2.21, 1.10, and 1.97 molH₂/molglucose, respectively. Accordingly, the mixed culture inoculum subjected to thermal treatment at 100 °C for 30 min can deliver higher HYs than pure cultures.

Distribution of Some Diamondoids in Crude Oils from Niger Delta Basin

Some Niger Delta oils were studied for the presence of diamondoids in the oils. Oils were obtained from a well each from their respective oil fields. The objectives of the study include identification of diamondoids in the oils, use of parametric ratios to delineate biodegradation and maturity of the oils. The m/z 136 show the presence of Adamantane and the m/z135 showed the presence of 1-Methyladamantane, 2–Methyladamantane, 1–Ethyladamantane and 2-Ethyladamantanein the oils. The nC17/Pr and nC17+nC18/(Pr+Ph) showed good biodegradation trend for the oils. 1MA/nC11 and nC17+nC18/(Pr+Ph plot did not show a good biodegradation gradient though of similar trend. 1MA/ nC11 showed a restricted spread. The plot 1MA/nC11 and 1MA+2MA/A showed a better spread for 1MA+2MA/A. The1MA/1MA+2MA (Methyladamantane index) showed a better maturity gradient and is good for the Nigerian oils but the 1EA/1EA+2EA (Ethyladamantane index) showed restricted spread for a good maturity gradient and may be better for higher matured oils than the Niger delta Oils.

Hydrogeo-morphological influences for arsenic release and fate in the central Gangetic Basin, India

Geochemical influences on arsenic (As) and other solutes along with regional groundwater flow path were inferred in parts of the central Gangetic Basin. The median concentration of As in groundwater was higher (0.046 mg/L) in Piedmont and (0.006 mg/L) in younger alluvium while very low (0.002 mg/L) in older alluvium. The median As concentrations in core sediments of Piedmont, older alluvium and younger alluvium were observed as 5.12, 11.2 and 11.6 mg/kg, respectively. Approximately 70% of the samples fell in As(OH)3 or As(III) field and 30% samples fell in HAsO42− or field of As(V) in Eh–pH plots. In contrast ∼60% of the samples fell in the FeOOH field and 40% in Fe(II) field in the Eh–pH plots. Cation exchange in Piedmont and older alluvium, while carbonate dissolution in younger alluvium controlling the groundwater major solute chemistry. The predictive outputs of inverse modelling congruence with predicted/ hypothetical groundwater flow directions. It was observed that geomorphology and the groundwater flow path also have substantial influence on solute chemistry and As distribution. Redox controlled adsorption/ desorption of Fe–Mn (oxyhydr)oxide was suggested as the probable mechanisms for As liberation in Piedmont, while multiple processes control the mobilization and presence of As in the younger alluvium. Study also concluded that the shallow aquifers of Piedmont and younger alluvium are contaminated with As while aquifers of older alluvium having low As contamination, could be the safe alternate for the residing people.

Galena Non-oxidative Dissolution Kinetics in Seawater

The rate of non-oxidative galena dissolution in seawater compositions over the pH range of 2–4.5 was determined from batch reactor experiments. The derivative at zero time of a polynomial fit of the Pb concentration versus time data for the first 30 min was used to determine the rate. A plot of RGn (rate of galena dissolution) versus pH for data from six experiments is linear (R2 = 0.96), with a slope of 0.5. The rate equation describing the rate of galena dissolution as a function of hydrogen ion activity is $$R_{\text{Gn}} = - \,10^{ - 10.72} \left( {a_{{{\text{H}}^{ + } }} } \right)^{0.50}$$ Varying the concentration of dissolved oxygen produced no significant effect on the measured rates. The activation energy, based on four experiments carried out over the temperature range of 7–30 °C, is 61.1 kJ/mol.

Artificial intelligence, regression model, and cost estimation for removal of chlorothalonil pesticide by activated carbon prepared from casuarina charcoal

Abstract Chlorothalonil is a pesticide that can contaminate water bodies, detriment aquatic organisms, and cause cancers of the forestomach and kidney. In this study, a powdered activated carbon prepared from casuarina wood was used for the adsorption of chlorothalonil from aqueous solutions. Based on Scanning Electron microscopy and Fourier Transform Infrared Spectroscopy analyses, the adsorbent material comprised pores and multiple functional groups that favored the entrapment of chlorothalonil onto its surface. At initial chlorothalonil concentration of 480 mg L−1, the equilibrium uptake capacity was 187 mg g−1 at pH: 7, adsorbent dosage: 0.5 g L−1, contact time: 40 min, and room temperature (25 ± 4 °C). The kinetic and isotherm studies indicated that the rate constant of pseudo-second-order model (k2) was 0.003 g mg−1 min−1, and the monolayer adsorption capacity was 192 mg g−1. Results from a quadratic model demonstrated that the plot of adsorption capacity versus pH, chlorothalonil concentration, adsorbent dosage, and contact time caused quadratic-concave, linear-up, flat, and quadratic-linear concave up curves, respectively. An artificial neural network with a structure of 4–5–1 was able to predict the adsorption capacity (R2: 0.982), and the sensitivity analysis using connection weights showed that pH was the most influential factor. An economic estimation using amortization and operating costs revealed that an adsorption unit subjected to 100 m3 d−1 containing chlorothalonil concentration of 250 ± 50 mg L−1 could cost 1.18 $ m−3.

Kinetics of Forward Extraction of V(V) in V(V)-NO<sub>3</sub><sup>-</sup> (H<sup>+</sup>, Na<sup>+</sup>)-TOA-Kerosene System using Single Drop Technique

The titled system has been investigated using a single drop technique and flux (F) method of data treatment. In calculating fluxes, the time for drop formation and coalescence (?t = 0.75 s) is considered. At lower concentration region of vanadium, V(V), the rate of V(V) transfer is directly proportional to its concentration. With the increase in [V(V)], slowly extractable V(V) species are formed gradually resulting in decrease in rate. Rate is directly proportional to the square root of [TOA]. It is reported that the most favorable extractable V(V) species exists in maximum amount at pH 2, and so, log F vs pH plots show a maximum at pH~2. The flux of V(V) transfer in most cases is found to be decreased with increasing [NO3-]. Reaction orders with respect to [V(V)], pH and [NO3-] have been attempted to be estimated, but in vein due to non-linearity of plots in most cases. Activation energies for the present system is ~ -12 kJ/mol. This is unexpected but explained. Due to irregular variation of the composition of extractable species with [V(V)], [H+]; as well as temperature; it is not possible to elucidate the value of rate constant (k) and mechanism in simple way.

Solvent extraction: fundamental equilibrium studies of neodymium and DEHPA

This article presents equilibrium studies into the NdCl3 –HCl (or NaOH)–H2 O–DEHPA (di-(2-ethylhexyl) phosphoric acid)–kerosene system. The system plays a role in solvent extraction of rare earth elements from aqueous chloride solutions. Thereby neodymium is transferred into the organic phase consisting of DEHPA solved in kerosene. Measurements were taken at DEHPA concentrations between 1 and 40 vol.% and at concentrations of neodymium which prevent a gelatinous organic phase. Results are presented in tables. Three charts of process variables were evaluated which, under the assumption of ideal behaviour, should lead to slopes of 3 in double logarithmic scale in all three cases. Since the actual slopes of measured variables were 2.4, 2.5 and 3.8, ideal behaviour is only a first approximation, and non-ideal aspects need to be further studied. The plot of percentage extraction versus pH shows that neodymium is completely extracted at pH values above 1.

Kinetics of the Anaerobic Reaction of para‐Substituted Phenols with Nitrogen Dioxide

ABSTRACTpara‐Substituted phenols in aqueous solution under anaerobic conditions readily react with nitrogen dioxide (NO2●) over a wide range of experimental conditions. The rate and rate law of the process were dependent on phenol concentration and solution pH. The kinetic order in phenol changed from one (low concentration) to zero (high concentration), a result attributable to total NO2● capture. Initial consumption rate (r0) of phenols versus pH plots showed parabolic behavior with a minimum rate at pH ca. 5. On the other hand, the maximum rate took place at high pH (pH>10) and involved the protonated phenols. The reaction rate of para‐substituted phenols with NO2● correlated with the bond dissociation energy and with Hammett's parameter. Based on such results and also supported by analysis of products carried out by HPLC‐MS/MS, our data conclusively show that, in spite of the fast acid–base interchanges of phenols and the interconversion of the different nitrogen oxides, the mechanisms of phenols nitration mediated by NO2● or HONO are clearly different.

Changes of weed infestation under long-term effect of different soil pH levels and amount of phosphorus:potassium

ABSTRACTThe aim of the present study was to investigate changes of weed species density as a result of long-term (1976–2005) exposure to different soil pH levels, and P2O5:K2O amount in soil created by initial and subsequent periodical liming, and fertilization. As a result of liming during the period 1976–2005, average soil pH levels at the start of the sixth crop rotation (2001–2005) ranged from 4.1 (unlimed) to 6.6. And in each pH plot were four sub-plots with a different amount of mobile phosphorus:potassium. In acid soil (pH 4.1), in spring oilseed rape and in spring barley crops, the dominant weed Spergula arvensis density decreased significantly at a pH of 5.1 or higher. With increasing amount of P2O5:K2O in soil, the abundance of S. arvensis in spring rape and spring barley crops was reduced at all soil pH levels. At pH 5.1, Chenopodium album and Tripleurospermum perforatum were prominent. Elytrigia repens tended to decrease with increased alkalinity and nutrient amount in soil. With reduction of soil acidity from pH 4.1 to 6.6, the total weed infestation consistently declined in all crops. A low amount of P2O5:K2O in soil caused the decline in the abundance of S. arvensis, E. repens and increase in C. album and T. perforatum.

Square Wave Voltammetric Determination of Fomesafen Herbicide Using Modified Nanostructure Carbon Paste Electrode as a Sensor and Application to Food Samples

Cyclic and square wave voltammetric measurements were performed to deduce the electrochemical behavior of fomesafen herbicide on the prepared carbon nanotube paste electrodes. Fomesafen has created a well-defined cathodic peak at −540 mV (vs. Ag/AgCl), but no corresponding oxidation peak has appeared on the reverse scan. The influence of the pH on the electro-reduction peak was tested at various pH values, and the Ep versus pH plot suggested that protons are involved in reduction process. Electrochemical studies showed that –NO2 group was responsible for the reduction process. A linear relationship has been constructed in the concentration range of 0.30–40 mg/L. The limits of detection and quantification values were obtained as 0.089 and 0.297 mg/L, respectively. Fomesafen was determined in the presence of some well-known pesticides, and the extent of recoveries of 5 mg/L fomesafen in the presence of equal amounts of pesticides anilazine, pymetrozine, and triflumizole was 103.7 ± 0.9, 94.3 ± 0.4, and 97.9 ± 0.5 %, respectively (n = 3). The accuracy of the recommended method was further proved by the determination of fomesafen in spiked real samples such as apricot juice, cherry juice, and lake water with a relative error of −4.2, −2.8, and −1.8 %, respectively. The obtained results suggest that the recommended method is sufficiently accurate, selective, and precise.