We report the use of scanning electrochemical microscopy (SECM) in determining the heterogeneous electron transfer and homogeneous comproportionation kinetics of tetracyanoquinodimethane (TCNQ) in acetonitrile at Pt tip UMEs (radius 12.5–1 μm). TCNQ undergoes two consecutive one-electron reductions with comproportionation occurring between TCNQ2–, the product of the second reduction, and bulk TCNQ to produce TCNQ–. A standard rate constant, k(1)(0) = 2.9 ± 0.5 cm/s, for the first reduction was determined by tip voltammetry with total positive feedback and a large Pt substrate. A comparatively smaller rate constant, k(2)(0) = 0.44 ± 0.05 cm/s, for the second reduction was determined in the absence of comproportionation by tip voltammetry with the tip shielded from the bulk TCNQ solution by the TCNQ– diffusion layer of the large Pt substrate. A comproportionation rate constant, k(comp) = 1 × 10(6) M(–1) s(–1), was determined by tip pulse chronoamperometry at coaxially aligned tip and substrate UMEs of the same radius. Diffusion coefficients of the TCNQ species and standard potentials for the reductions were also determined. Experimental results were compared with 2D transient axisymmetric simulations and reported analytical equations.

ABSTRACT:Tetramethylthiuram disulfide is a widely used pesticide and a soil treatment agent in the agricultural sector. Consequently, its detection in the environment and investigation of the distribution between the aqueous and soil phases would be of highly importance. In this study, the detection of tetramethylthiuram disulfide in CHCl 3 was successfully achieved through absorbance measurements at 280 nm, which resulted in linear calibration curves. This detection method was extended for the determination of the partition coefficient (K D ) of tetramethylthiuram disulfide between CHCl 3 and H 2 O phases at ambient temperature. The partition coefficient was subsequently used to determine the apparent partition coefficient (K D ) of tetramethylthiuram disulfide between sieved soil of diamater < 2.0 mm used for agricultural practices and water where by the quantification of tetramethylthiuram disulfide in water after adsorption equilibrium with soil was achieved through a solvent extraction step of tetramethylthiuram disulfide-contaminated water into CHCl 3 . The K D determined for an initial tetramethylthiuram disulfide concentration ranging from 3.00 ppm to 10.00 ppm showed a decreasing trend, which leveled off at high concentrations, indicating the strong irreversible adsorption behavior of tetramethylthiuram disulfide on soil at low concentrations. The proposed detection method would have the potential to determine the extent of adsorption of tetramethylthiuram disulfide in soil or its levels in water when tetramethylthiuram disulfide is introduced to soil systems for agricultural practices.

1. Resource partitioning is a critical component in competing species that coexist in a community. The biting behaviour of coexisting frog‐biting mosquito species associated with a tropical anuran community is investigated. 2. Monthly samplings were taken for 2 years at two study sites in central Sri Lanka to collect frog‐biting mosquitoes, anuran abundance, environmental data, and interactions between mosquitoes and anuran hosts. Mosquitoes were collected using mouth‐operated aspirators and sound traps broadcasting anuran calls. Mosquitoes were identified using taxonomic keys and DNA barcodes. 3. A total of 1079 frog‐biting mosquitoes from four species belonging to two genera were collected [Uranotaenia rutherfordi (5%), Ur. morphotype 1 (67%), Ur. morphotype 2 (21%), and Mansonia uniformis (7%)]. Species‐specific interactions between Uranotaenia mosquitoes and their anuran host were found. Uranotaenia morphotype 1, the most common species, was mainly attracted (99%) to Duttaphrynus melanostictus. Uranotaenia rutherfordi was mainly attracted (95%) to Pseudophilautus rus, while Ur. morphotype 2 was attracted (97%) to Polypedates cruciger. These Uranotaenia species are active at different hours at night that correspond to the peak calling activity of their anuran host. Each Uranotaenia species was active at heights that coincide with the calling sites of their host. In contrast, Ma. uniformis was non‐specific in host choice and was equally distributed in space and time with respect to host feeding. 4. Here, previously unknown feeding patterns of co‐occurring frog‐biting mosquito species and their interactions with anurans present in their community are reported, highlighting the existence of complex behavioural patterns of these mosquito communities.

In honor of Wolfgang Schuhmanns60 th birthday 1Introduction Hydroxyquinones are of interest both chemically [1][2][3][4][5][6][7] and biologically [8][9][10][11][12],i na ddition to being used in syntheses of anticancer agents [13,14].D ihydroxyanthraquinones are reducede lectrochemicallyu nder reversible conditions to the anion and di-anion radicals,w hich undergo comproportionation with the neutral quinone. Dependingo ns olution conditions, the anion radicals may also interactw ith an eutral molecule through intermolecular hydrogen bondinga nd undergo an associationr eaction [1,6,7].A nthrarufin (HQ), 1,5-dihydroxy-9,10-anthracenedione( SchemeS1o ft he Supporting Information), is ad ihydroxyd erivative of anthraquinone and electrochemically undergoes at wo-step reduction, first formingaradical anion followed by dianion formation. An association reaction takes place in solution by bonding an eutral anthrarufin molecule with ar adical anion. In contrast,d ianionf ormation opens the pathway for ac omproportionation reaction. Thus,a nthrarufin reduction is accompanied by two heterogeneous asw ell as two homogeneous reactions.A ssociation reactions are driven forwardb yt he formation of the radical anion from the comproportionation reaction[ 1].HQ þ e À ! HQ À first e À transfer ð1ÞHQ þ 2e À ! HQ 2À net reaction ð3ÞIn comparison to electrochemical investigationsi nvolving hydroxyquinonesi ng eneral [ 1-3, 6, 7, 13],f ew studies have been devoted specifically to anthrarufin [1,7].I nt he most recent study, experimentalcyclic voltammograms recorded at am acro-size glassy carbon electrode for the anthrarufinr eductionw ere compared with simulatedc urves, where the best fit was obtained only after introduction of the association reaction( eq. 4) in the simulation mechanism [11].R eported values from that studyf or diffusion Abstract:W er eport the use of scanning electrochemical microscopy( SECM)i nd etermining the heterogeneous electront ransfer and homogeneousa ssociation and comproportionation kinetics of anthrarufin (HQ) in acetonitrile at aP tt ip UME (radius 12.5 mm). HQ undergoes two consecutiveo ne-electron reductionsw ith comproportionationo ccurring between HQ 2À ,t he product of the second reduction, and bulk HQ to produce HQ À and association occurring between HQ À and bulk HQ to produce an electroinactive species.S tandard rate constants, k 1 0 = 5.1 AE 0.4 cm/s,f or the first reduction, and ac omparatively smaller ratec onstant, k 2 0 = 0.37 AE 0.03 cm/s,f or the second reduction, were determined by tip voltammetry over al arge Pt substrate.A na ssociation rate constant, k assoc = 2.9 10 2 M À1 s À1 ,w as determined using positive feedback approachc urveso ver co-axially aligned tip and substrateU MEs of the same radius.Acomproportionation rate constant, k comp = 7.1 10 1 M À1 s À1 ,w as determined in the presence of the associationr eaction by tip pulse chronoamperometry at the same co-axially alignedt ip and substrateU MEs. Diffusion coefficients of the HQ species and standard potentials for the reductio...

Electrochemical investigation of 3,4dichlorophenylamine (3,4-dicholoroaniline or 3,4-DCA), the principal degraded product of propanil, in aqueous medium reveals that the most intense peak appears at +0.75 V vs. saturated calomel reference electrode (SCE). The diffusioncontrolled behaviour of this peak enables direct detection of 3,4-DCA in the environment, which can be extended for investigation of the fate of propanil. Rice cultivation grown in three beds of equal dimensions prepared in a polytunnel, an effective simulated environment to which the recommended dose of propanil was applied, was used for this study. Determination of the concentrations of 3,4-DCA throughout the rice cultivation cycle indicated that the concentration of 3,4-DCA initially increases up to 4 days followed by a decrease up to 10 days, and finally reaches a plateau. The concentration-time relationships of 3,4-DCA suggest that the initial degradation of propanil and subsequent degradation of 3,4-DCA follow the mechanism of consecutive reactions, where the product of the first step becomes the reactant of the second step. Further, comparison of kinetic data with integrated rate law expressions and the mathematical model of consecutive first order reactions indicated that the degradation of both processes is of first order with relatively low rate constants, being the degradation of 3,4-DCA as the rate limiting step.