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Biofloc technology is much highlighted these days because of its tremendous effects on aquaculture. Microbes were enriched on cheapest organic carbon source i. e., powdered banana peels and were incorporated in different aquaria rearing grass carp fingerlings under different C/N treatments (10:1, 15:1 and 20:1) and 10% water daily water exchange. The initial growth of fingerlings was recorded. The experiment was settled in triplicates for 60 days and run parallel to control group provided with commercial feed and daily water exchange. Its effect was evaluated by measuring the growth of fingerlings and water parameters of each aquarium. The average % gain in weight and length of fingerlings was obtained significantly highest (28.12 ± 0.30g and 17.29 ± 0.46cm respectively) in aquaria containing pure powdered banana peels with 10% water exchange and C/N ratio was adjusted at 20: 1 (T3) than other treatments and control. Ammonia and other water parameters were also under control in T3 than other experimental and control groups. By all counts, it was concluded that the highest C/N ratio in biofloc system had the potential to increment C. idella growth rate by reducing toxicity and could be used as fish meal substitute. Resumo A tecnologia Biofloc é muito destacada hoje em dia por causa de seus tremendos efeitos na aquicultura. Os micróbios foram enriquecidos com a fonte de carbono orgânico mais barata, i. e., cascas de banana em pó, e foram incorporadas em diferentes aquários de criação de alevinos de carpa-capim sob diferentes tratamentos C/N (10: 1, 15: 1 e 20: 1) e 10% de troca diária de água. O crescimento inicial dos alevinos foi registrado. O experimento foi resolvido em triplicatas por 60 dias e executado paralelamente ao grupo controle fornecido com ração comercial e troca diária de água. Seu efeito foi avaliado medindo o crescimento dos alevinos e os parâmetros da água de cada aquário. O% de ganho médio em peso e comprimento dos alevinos foi obtido significativamente mais alto (28,12 ± 0,30g e 17,29 ± 0,46 cm respectivamente) em aquários contendo cascas de banana em pó puro com 10% de troca de água e a relação C/N foi ajustada em 20: 1 (T3) do que outros tratamentos e controle. A amônia e outros parâmetros da água também estavam sob controle no T3 mais do que nos outros grupos experimentais e de controle. Por todas as contagens, concluiu-se que a maior razão C/N no sistema de bioflocos tem o potencial de incrementar a taxa de crescimento de C. idella reduzindo a toxicidade e pode ser usada como substituto da farinha de peixe.

This research aimed to elucidate the effect of Chlorella sp. addition on biofloc quality and growth of Macrobrachium rosenbergii juveniles in biofloc systems. Four treatments of freshwater prawn nursery culture systems were tested, i.e., control system with clear water system at a regular water exchange at about 50% every 2 weeks; control system with Chlorella sp. addition with regular water exchange and weekly addition of Chlorella sp.; biofloc system without Chlorella sp. addition; and biofloc system with Chlorella sp. addition. Freshwater prawn juvenile at an average initial body weight of 0.25 g was randomly distributed into 16 units of aquarium with a working volume of 100 L at a density of 20 prawn/aquarium (50 prawn/m2). Molasses was added every day into biofloc treatments at an estimated C/N ratio of 6.25. Chlorella sp. was added into the microalgae treatments at the initiation of the experiment and every 2 weeks at 10% of the total volume to reach an estimated final density of about 105/mL. Microbial aggregation was inhibited by vanillin (a quorum sensing inhibitor) addition regardless the presence of Chlorella sp. The microalgae addition resulted in biofloc with higher density, larger particle size, and higher protein content. Different amino acid and fatty acid profiles of biofloc were observed between the biofloc treatments. Essential amino acid index of biofloc with the addition of Chlorella sp. was about 39% higher compared to that of biofloc without Chlorella sp. addition. The growth of freshwater prawn in biofloc systems was generally higher than those of the control with and without Chlorella sp. addition. In conclusion, the addition of Chlorella sp. could improve biofloc quality and the growth performance of freshwater prawn juveniles.

Se evaluó el efecto de las tasas de recambio sobre las características físico-químicas del agua, rendimiento productivo y modelo de ajuste de crecimiento de juveniles de tilapia roja (Oreochromis spp.). Se utilizaron 15 acuarios de 53 L con 10 juveniles cada uno bajo los siguientes tratamientos; recambio de agua 25% diario, 50% cada 7 días y sin recambio, cada tratamiento con 5 réplicas, en el diseño completamente aleatorizado. Los acuarios fueron colmados con agua proveniente de tanques de cultivo de peces del laboratorio. Se utilizaron 150 juveniles entre 6 y 8 cm de longitud total, alimentados a una tasa de 8% de la biomasa. Los peces se distribuyeron de manera aleatoria en grupos de diez por acuario o unidad experimental. Se cuantificaron las variables masa y longitud total; se midió la temperatura, el oxígeno disuelto, pH, amonio no ionizado y nitratos en el agua de los acuarios y sus valores comparados por la prueba LSD (p≤0,05); de manera similar, se evalúo el grado de ajuste de la masa y longitud con diferentes modelos de crecimiento. Se concluyó que el recambio diario de 25% del agua favoreció el crecimiento de los juveniles de tilapia roja, en masa y longitud final de 12,16 g y 8,81 cm, respectivamente. De manera similar, en este tratamiento se observó los menores valores promedios de temperatura y nitratos, y los más elevados de oxígeno disuelto y amonio no ionizado. El modelo exponencial presentó el mejor ajuste para la masa y longitud total de los juveniles de tilapia roja.

This review deals with the influence of gold nanoparticles on physiological processes (responses) in higher plants. Gold nanoparticles can affect a lot of processes in the plant organism, including growth rate, parameters of water exchange, activity of the photosynthetic apparatus and the antioxidant system, and expression of some genes important for the functioning of plants under optimal and adverse conditions, which was shown in plants belonging to different taxonomic groups. Analysis of literature data suggests that gold nanoparticles may be used not only as stimulators of growth and development but also as adaptogens improving plant resistance to various adverse influences.

PURPOSE To develop and evaluate a flexible, Bloch-equation based framework for retrospective T2∗ correction to the arterial input function (AIF) obtained with quantitative cardiac perfusion pulse sequences. METHODS Our framework initially calculates the gadolinium concentration [Gd] based on T1 measurements alone. Next, T2∗ is estimated from this initial calculation of [Gd] while assuming fast water exchange and using the literature native T2 and static magnetic field variation (ΔB0 ) values. Finally, the [Gd] is recalculated after performing T2∗ correction to the Bloch equation signal model. Using this approach, we performed T2∗ correction to historical phantom and in vivo, dual-imaging perfusion data sets from 3 different patient groups obtained using different pulse sequences and imaging parameters. Images were processed to quantify both the AIF and resting myocardial blood flow (MBF). We also performed a sensitivity analysis of our T2∗ correction to ±20% variations in native T2 and ΔB0 . RESULTS Compared with the ground truth [Gd] of phantom, the normalized root-means-square-error (NRMSE) in measured [Gd] was 5.1%, 1.3%, and 0.6% for uncorrected, our corrected, and Kellman's corrected, respectively. For in vivo data, both the peak AIF (7.0 ± 3.0 mM vs. 8.6 ± 7.1 mM, 7.2 ± 0.9 mM vs. 8.6 ± 1.7 mM, 7.7 ± 1.8 mM vs. 10.3 ± 5.1 mM, P < .001) and resting MBF (1.3 ± 0.1 mL/g/min vs. 1.1 ± 0.1 mL/g/min, 1.3 ± 0.1 mL/g/min vs. 1.1 ± 0.1 mL/g/min, 1.2 ± 0.1 mL/g/min vs. 0.9 ± 0.1 mL/g/min, P < .001) values were significantly different between uncorrected and corrected for all 3 patient groups. Both the peak AIF and resting MBF values varied by

The present study was designed to display the integrated model of nitrogen discharge process (i.e. nitrites and nitrates; ammonia; chlorophyll and dissolved nitrogen, dissolved oxygen) which is part of the complete model of shrimp aquaculture of an Integrated Shrimp Aquaculture Park (i-Sharp) ecosystem in System Dynamic Model Aquaculture-System Policy (SD-AQEP). This study offers a comprehensive elaboration concerning the long-term process of nitrogen accumulation, as well as its effects on shrimp activities. Furthermore, the analysis of the model and the simulation results also show the conditions of nitrogen with several strategies for control and manipulation. For example, in situations where mixing of stock density is high and providing feed into ponds supplies is excessive, the nitrogen dynamic rapidly hits alarming levels. Aforementioned, the typical strategy in this setting such as stocking density and the best time to harvest could be established. Additionally, the model structure represents the discharge derived from the nitrogen process on varied settings of variables in aquaculture development. In conclusion, this model provides an experimental simulation platform that can be implemented by policy makers on long-term strategic management for developing or maintaining large-scale aquaculture development projects in the future.

This report deals with a comparison of experimentally obtained kinetic and activation parameter data, and theoretical DFT computations, in terms of mechanistic information on the water exchange and water displacement reactions by thiourea for a series of complexes of the type [RuII(terpy)(N^N)(H2O)]2+, where terpy = 2,2′:6′,2″-terpyridine and N^N represents ethylenediamine (en), 2-(aminomethyl)pyridine (ampy), 2,2′-bipyridine (bipy), 1,10-phenantroline (phen), and N,N,N′,N′-tetramethylethylenediamine (tmen). The complexes were all isolated in the form of [Ru(terpy)(N^N)Cl]X (X = Cl– or ClO4–) compounds and fully characterized in both the solid state and in solution. The DFT calculations revealed further mechanistic insight into the water exchange reactions as well as the water displacement reactions by thiourea. Both the experimental activation parameters and the DFT calculations suggest the operation of an associative interchange (Ia) mechanism for both reaction types studied.

Thermodynamic modeling with the HCh software complex was applied to analyze the probability of acid drainage formation during the evolution of a copper–ore deposit in low-temperature conditions (5°C) with various water levels. During the modeling, three main factors were taken into account: the percentage of pyrite in rocks, the availability of oxygen in the air, and the water content of the rocks (the relative rate of water exchange). It was found that the increase in the content of pyrite sulfur in the rock and an increase in the ratio of the rock–water mass (decrease in water exchange) lead to an increase in mineralization and a decrease in the pH of the drainage solution. The openness of the system to atmospheric gases (in particular, to O2) increases the acidification effect. The most environmentally unfavorable rocks at the deposit are mudstones, siltstones, and silt-sandstones.

Nanobubbles have been reported to have many novel applications due to their unique physicochemical properties. Ethanol-water exchange is regarded as one of the most convenient methods for producing nanobubbles; however, it is still questioned whether this method can produce bulk nanobubbles or not. In this paper, we present a method to monitor the ethanol-water exchange process based on a setup that combines the equipment of the ethanol-water exchange with an apparatus for dynamic light scattering. In contrast to the previous works where the measurements were performed after the exchanges were completed, our method measures the intensity of the scattered light from the beginning of the process to the end. We found that three different stages of the exchange process can be easily distinguished and that the diameters of the particles produced decrease as the exchange time increases. Furthermore, the measured diameters agree very well with a theoretical model presented very recently for the stability of the bulk nanobubbles in the liquid. Based on these findings, we believe that the products of the ethanol-water exchange are bulk nanobubbles. In addition, since our experimental setup provides the details of the ethanol-water exchange process, it can be used to investigate how to control the parameters of the final nanobubbles, such as their size, concentration, etc., which might promote the potential applications of bulk nanobubbles.

Partial water exchange is one of the most common conventional methods used to maintain water quality and aesthetic beauty in recirculating aquarium systems (RASs). However, this method uses substantial amount of water. The ozone-down-flow hanging sponge-up-flow sludge blanket (ozone-DHS-USB) system attempts to be a more responsible method for aquarium maintenance. It eliminates the necessity for water exchange in aquarium by maintaining nitrogen concentrations at a safe level and by reducing yellow substances. Also, the impact of O

The influences of freezing pretreatment, thermal pretreatments (water blanching and steam blanching) and their combinations on hot-air drying kinetics of Vaccinium bracteatum Thunb (VBT) leaves at 60 °C and key quality attributes were investigated. Generally, all the applied pretreatments accelerated VBT leaf drying process. The sequential freezing (8 h) and water blanching (1 min) pretreatments shortened the drying time by 65.5%. The diffusion modeling results revealed that all the pretreatments intensified water diffusion and external water exchange with hot air during drying. Freezing pretreatments had no preservative effect on phenolics, iridoids, and antioxidant capacity of VBT leaves after dehydration, whereas both thermal pretreatments significantly improved dried VBT leaf quality in these three aspects. On the contrary, thermal pretreatments had destructive effects on activities of polyphenol oxidase and β-glucosidase. Due to the low β-glucosidase activity in dried VBT leaves with thermal pretreatments that participated in the transformation of iridoids to generate dark colorants eventually, the extracts from dried VBT leaves with only thermal pretreatments had weak ability to dye glutinous rice. However, this problem was fixed once extra β-glucosidase was added before rice cooking. Overall, the obtained results can provide guidance for the preservation and drying of VBT leaves that has been poorly studied.

The results of the study of the water regime characteristics (without and taking into account the indicators of oxidative stress) of triticale shoots under conditions of short-term NaCl stress were analyzed with the principal component analysis (PCA). It is shown that the water content is the most stable indicator of triticale shoots under experimental conditions. The results of the analysis led to the conclusion that its value is not determined by the value of stomatal conductivity and/or transpiration. Determination of the correlation coefficients between the studied characteristics yielded negative values between the water content and other indicators of the water regime, as well as oxidative stress, except for the value of lipid peroxidation (LPO) (0.67). Despite the closest relationship between the water content and the osmotic potential according to the results of cluster analysis, the correlation between them was negative (-0.76). This can be explained by different physiological and biochemical mechanisms that support each of these indicators. It is also shown that manifestations of oxidative stress are closely related to the osmotic potential and water content. In this case, the formation of a first-order cluster was observed between the content of water and hydrogen peroxide. This is not unexpected, but the correlation coefficient between them was only 0.018. This value can be interpreted in such a way that water is needed for the formation of hydrogen peroxide, but their quantitative ratio (water : hydrogen peroxide) in the shoots of triticale is significantly different. The inclusion in the analysis of the results of the accumulation of salt ions showed a closer relationship between the increase in the content of salt ions and the change in transpiration, stomatal conductivity and the content of proline than with the water content in the shoots of triticale under experimental conditions.

Smart/intelligent contrast agent candidates for MRI based on Mn(II) ion are rare, as it usually forms labile complexes with polyaminocarboxylate-type ligands. Here, we report the first example of a Mn(II) complex that can be activated by changing the pH of its local environment. The PC2A-EA ligand with an ethylamine pendant arm was found to form a thermodynamically stable (log KMnL = 19.01, pMn = 9.27) and kinetically inert complex with Mn(II) with respect to trans-chelation with a metal ion such as Cu(II). The [MnH(PCA2-EA)] complex displays a relatively slow water exchange rate ((4.0 ± 0.2) × 107 s-1), but the pH-dependent coordination of the ethylamine moiety occurs in the pH range of 6-8 (log KMnLH = 6.88), enabling the complex to exhibit pH-sensitive relaxivity in the biologically relevant pH range.

Changes in the deformability of red blood cells can reveal a range of pathologies. For example, cells which have been stored for transfusion are known to exhibit progressively impaired deformability. Thus, this aspect of red blood cells has been characterized previously using a range of techniques. In this paper, we show a novel approach for examining the biophysical response of the cells with quantitative phase imaging. Specifically, optical volume changes are observed as the cells transit restrictive channels of a microfluidic chip in a high refractive index medium. The optical volume changes indicate an increase of cell’s internal density, ostensibly due to water displacement. Here, we characterize these changes over time for red blood cells from two subjects. By storage day 29, a significant decrease in the magnitude of optical volume change in response to mechanical stress was witnessed. The exchange of water with the environment due to mechanical stress is seen to modulate with storage time, suggesting a potential means for studying cell storage., Sensors: Measuring blood cell deformability A team at Duke University in the United States led by Han Sang Park has developed a novel approach to investigate the deformability of cells. The technique uses quantitative phase microscopy to measure optical volume as cells are squeezed through a constriction. The team used this approach to study changes in red blood cells that had been stored for up to 29 days. The older cells had a larger volume before constriction, and their volume changed less when they were squeezed. The increased optical volume may be due to changes in hemoglobin concentration during storage, while the smaller change in volume may be because of less water exchange during constriction of older cells. Further investigation will reveal how these biophysical properties change during storage, affecting how readily cells can pass through narrow blood vessels.

The study of brain clearance mechanisms is an active area of research. While we know that the cerebrospinal fluid (CSF) plays a central role in one of the main existing clearance pathways, the exact processes for the secretion of CSF and the removal of waste products from tissue are under debate. CSF is thought to be created by the exchange of water and ions from the blood, which is believed to mainly occur in the choroid plexus. This exchange has not been thoroughly studied in vivo. We propose a modified arterial spin labeling (ASL) MRI sequence and image analysis to track blood water as it is transported to the CSF, and to characterize its exchange from blood to CSF. We acquired six pseudo-continuous ASL sequences with varying labeling duration (LD) and post-labeling delay (PLD) and a segmented 3D-GRASE readout with a long echo train (8 echo times (TE)) which allowed separation of the very long-T2 CSF signal. ASL signal was observed at long TEs (793 ms and higher), indicating presence of labeled water transported from blood to CSF. This signal appeared both in the CSF proximal to the choroid plexus and in the subarachnoid space surrounding the cortex. ASL signal was separated into its blood, gray matter and CSF components by fitting a triexponential function with T2s taken from literature. A two-compartment dynamic model was introduced to describe the exchange of water through time and TE. From this, a water exchange time from the blood to the CSF (Tbl->CSF) was mapped, with an order of magnitude of approximately 60 s.

PURPOSE To develop phase alternate labeling with null recovery (PALAN) MRI methods for the quantification of the water exchange between cerebrospinal fluid (CSF) and other surrounding tissues in the brain. METHOD In both T1 -PALAN and apparent diffusion coefficient (ADC)-PALAN MRI methods, the cerebrospinal fluid signal was nulled, whereas the partial recovery of other tissues with shorter T1 (T1 -PALAN) or lower ADC values (ADC-PALAN) was labeled by alternating the phase of pulses. The water exchange was extracted from the difference between the recovery curves of CSF with and without labeling. RESULTS Both T1 -PALAN and ADC-PALAN observed a rapid occurrence of CSF water exchange with the surrounding tissues at 67 ± 56 ms and 13 ± 2 ms transit times, respectively. The T1 and ADC-PALAN signal peaked at 1.5 s. The CSF water exchange was 1153 ± 270 mL/100 mL/min with T1 -PALAN in the third and lateral ventricles, which was higher than 891 ± 60 mL/100 mL/min obtained by ADC-PALAN. T1 -PALAN ∆S values for the rostral and caudal ventricles are 0.015 ± 0.013 and 0.034 ± 0.01 (p = 0.022, n = 5), whereas similar ΔS values in both rostral and caudal lateral ventricles were observed by ADC-PALAN (3.9 ± 1.9 × 10-3 vs 4.4 ± 1.4 × 10-3 ; p = 0.66 and n = 5). CONCLUSION The PALAN methods are suitable tools to study CSF water exchange across different compartments in the brain.

it has been learned features of water exchange during the wax ripeness phase of wheat varieties in soil climatic condition in surkhandarya region

We derive a model that provides an exact solution to the substrate-water exchange kinetics in a double-conformation system and use this model to interpret recently published data for Ca(2+)- and Sr(2+)-containing PSII in the S(2) state, in which the g = 2.0 and g = 4.1 conformations coexist. The component concentrations derived from the kinetic model provide an analytic description of the substrate-water exchange kinetics, allowing us to more accurately interpret the results. Based on this model and the previously reported data on the S(2) state g = 2.0 conformation, we obtain the substrate-water exchange rates of the g = 4.1 conformation and the conformational change rates. Two conclusions are made from the analyses. First, contrary to previous reports, there is no significant effect of substituting Sr(2+) for Ca(2+) on any of the exchange rate constants. Second, the exchange rate of the slowly-exchanging water (W(s)) in the S(2) state g = 4.1 conformation is much faster than that in the S(2) state g = 2.0 conformation. The second conclusion is consistent with the assignment of W(s) to W1 or W2 bound as terminal ligands to Mn4; Mn4 has been proposed to undergo an oxidation state change from Mn(IV) in the g = 2.0 conformation to Mn(III) in the g = 4.1 conformation.

The contents of artificial and natural radionuclides of 137Cs, 90Sr, 226Ra, 232Th, and 40K had been investigated in muscle and bone tissues, gill petals, and scales of common perch Perca fluviatilis and pikeperch Sander lucioperca from two fishing areas of the Dnipro (Zaporizhzhia) Reservoir. The specific radionuclide activities were measured with the SEG-001 “AKP-C” and SEB-01-150 scintillation spectrometers of gamma- and beta-radiation energy in Bq/kg of wet weight. The radioactive elements of both natural and artificial origins were concentrated greatly in common perch tissues compared to pikeperch. The bone and muscle tissues contained the maximal levels of radionuclides, while respectively smaller amounts of radionuclides were found in gills and scales. The radionuclide levels in the tissues of investigated fish species were significantly higher in the Dnipro Reservoir area with weak flowage and slow water exchange. Keywords: artificial radionuclides; natural radionuclides; common perch; pikeperch; specific activity; the Dnipro (Zaporizhzhia) Reservoir

Biofloc technology degrades waste into useful resources exploiting microbes and can be used in zero‐water exchange systems. To study the effect of different biofloc systems on haematological and metabolic response of Labeo rohita fingerlings, a 60‐days experiment was conducted using four long lasting carbon sources. Seven hundred and fifty fingerlings having mean weight of 4.80 ± 0.12 g were randomly distributed into 15 tanks (n = 50 per tank). Five experimental groups were set in triplicate; T1 (Tapioca), T2 (Wheat), T3 (Corn) T4 (Sugar bagasse) and control (clear water). In‐situ biofloc was developed in 300 L fibre‐reinforced plastic (FRP) tanks and a C/N ratio of 15 was maintained. Water quality variables indicated ammonia immobilization by heterotrophic bacteria, as the dominant mechanism for the removal of toxic‐nitrogenous compounds in the biofloc systems. Results exhibited significantly higher floc volume (53.33 ± 7.88 ml/L), haemoglobin content (6.61 ± 0.03 g/dl) and total leucocyte count (109.66 ± 0.06 thousand cells/mm³) in tapioca biofloc system. Furthermore, the digestive and anti‐oxidative enzymes activities were also significantly higher in tapioca biofloc system. The lactate dehydrogenase and malate dehydrogenase enzyme assays showed a decreased level in tapioca biofloc system as compared with other biofloc systems and control group. Our observations indicate that tapioca biofloc system could improve the water quality, haematological and anti‐stress responses of L. rohita fingerlings in biofloc systems and thus can effectively replace other carbohydrate sources for the biofloc system.

This article deals with spatio-temporal changes in methane emission from the surface of the Mozhaisk reservoir. Seasonal changes in methane content and flux were revealed for different morphological areas of the reservoir, based on field observation data obtained in 2015–2018. In the low-flow Mozhaisk reservoir, the methane content in the boundary and bottom layers of the deep-water areas at the end of the summer stratification period may differ by three orders of magnitude. According to results from measuring with floating chambers in the central area of the reservoir from early June to the end of the period of direct stratification (August–September) the total methane flux increased from less than 1 to 16 mgC-CH4/(m2/hr). Time-coincident measurements with floating chambers of two types revealed characteristic values of the methane flux components and their change over the sampling period. It was found that at the period of stratification the diffusive flux predominates with the mean values 0.2 mgC-CH4/(m2/hr). A further increase in the total methane flux is associated with an increase of its bubble component. According to calculations, the diffusive flux reaches its maximum values in late summer in the shallow zone of the reservoir. It is established that a significant increase of the values of the total methane flux is observed when the upper boundary of the oxygen-free zone reaches the lower boundary of the epilimnion. The methane flux density reaches its largest values prior to destruction of the direct stratification. Comparison of field measurements with literature data showed that the magnitude of emission from reservoirs with a slow water exchange in the temperate zone can be underestimated in the evaluation of global methane emission.

The metal composition of water and bottom sediments of the southern tributaries of Lake Baikal has been studied, and the water migration coefficients have been calculated. A regional zoning scheme is compiled according to the ability to supply a given composition of waters. Significant differentiation of the Baikal waters and its main tributaries by mineralization, the predominant macro-, and trace elements is found. The comparison of coefficients of aquatic migration based on metal composition of waters and sediments shows that the coefficient values calculated for macro elements are close in the southern and main tributaries, and the values calculated for microelements differ sharply. The reason is the presence of sources of solutes (rocks and deep groundwater) with a composition uncharacteristic for the respective landscapes. The contribution of southern tributaries to the macro element composition of the water of Lake Baikal is 7–15%, and the contribution to the micro element composition cannot be assessed due to their much higher concentrations in river waters. The reason for these differences is the migration of trace elements in the form of organic matter, which, due to the extended time of water exchange in Baikal, precipitates or destroys, contributing to the removal of trace elements from the solution.

Проведена классификация факторов водообильности пород водоносных комплексов зоны активного водообмена. На территориях со слабой гидрогеологической изученностью предложено использовать знания о их геологическом строении, геоморфологии и гидрометеорологические данные для выделения участков с различной водообильностью пород, а на территориях с хорошей гидрогеологической изученностью – данные о водообильности пород для характеристики их структурно-тектонического строения.

The Mumbai Harbour Bay (MHB), Mumbai, India houses a large number of ports, industrial units and urban settlements thus the groundwater may be highly contaminated. In the present study short lived Ra isotopes (223Ra and 224Ra) input sources (viz. water exchange from Arabian Sea, input from Rivers and wastewater discharge, Diffusion of Ra from bottom sediments and desorption from suspended particles) and pathways of removal (radioactive decay and export during the low tide) were estimated in MHB individually. A mass balance for 223Ra and 224Ra in the bay indicated an imbalance of 53.38% and 71.68% respectively. The imbalance was assigned to contribution from submarine groundwater discharge (SGD) and using the concentration in the shallow groundwater (at 2 m depth) of 223Ra and 224Ra the SGD were estimated. Based on 223Ra and 224Ra, the SGD was estimated and found to be 33.4 × 109 L day−1 and 64.9 × 109 L day−1 respectively.

This study assessed the effects of three levels of water exchange during the start-up of recirculating aquaculture systems (RAS) on the growth and protein productive value (PPV) of pikeperch (Sander lucioperca) and on water quality parameters. The experiment was conducted in twelve independent RAS stocked with pikeperch (average body weight 247.4 g). The start-up phase of the RAS was described via the accumulating feed burden (AFB). Different water exchange levels were tested in quadruplicates as low AFB (final AFB of 1000 mg L−1 achieved through a water exchange of 1000 L per kg feed), medium AFB (final AFB of 1958 mg L−1 achieved through a water exchange of 500 L per kg feed) and high AFB (final AFB of 4422 mg L−1 achieved through a water exchange of 200 L per kg feed). Fish were fed daily at 0.9% biomass (BM) with a commercial diet (ALLER Metabolica) and individual body weight was assessed after 14, 35 and 56 feeding days. Protein productive value was significantly affected by water exchange rate after 2 months, while no differences in end weight were observed and no mortalities occurred during the experiment. A segmented linear regression analysis was used to identify the AFB induced effect on the fish approximated by the use of the specific growth rate (SGR). Pikeperch exhibited positive growth up to AFB values of 4000 mg L−1 but the threshold value for an AFB induced effect on SGR was identified at 1953 ± 613 mg L−1. As expected, the following water quality parameters showed a linear correlation with AFB: nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N), total ammonia-nitrogen (TAN), total organic carbon (TOC), total carbon (TC) and total suspended solids (TSS) over the course of the experiment. Analysis of heavy metals and trace elements showed a linear correlation between AFB and phosphorus, arsenic, copper and potassium at the end of the experiment. The study quantified the functional relationship between AFB and water quality, as well as SGR. Additionally the present study was able to calculate the concentration of individual water quality parameters concomitant to the identified optimal AFB in order to provide reference points for future experiments as well as an approximation for commercial RAS for NO3-N, NO2-N, TAN, TOC, TC and TSS.

The rooting zone water storage capacity (S) defines the total amount of water available to plants for transpiration during rain-free periods. Thereby, S determines the sensitivity of carbon and water exchanges between the land surface and the atmosphere, controls the sensitivity of ecosystem functioning to progressive drought conditions, and mediates feedbacks between soil moisture and near-surface air temperatures. While being a central quantity for water-carbon-climate coupling, S is inherently difficult to observe. Notwithstanding scarcity of observations, terrestrial biosphere and Earth system models rely on the specification of S either directly or indirectly through assuming plant rooting depth.Here, we model S based on the assumption that plants size their rooting depth to maintain function under the expected maximum cumulative water deficit (CWD), occurring with a return period of 40 years (CWDX40), following Gao et al. (2014). CWDX40 is “translated” into a rooting depth by accounting for the soil texture. CWD is defined as the cumulative evapotranspiration (ET) minus precipitation, where ET is estimated based on thermal infrared remote sensing (ALEXI-ET), and precipitation is from WATCH-WFDEI, modified by accounting for snow accumulation and melt. In contrast to other satellite remote sensing-based ET products, ALEXI-ET makes no a priori assumption about S and, as our evaluation shows, exhibits no systematic bias with increasing CWD. It thus provides a robust observation of surface water loss and enables estimation of S with global coverage at 0.05° (~5 km) resolution.Modelled S and its variations across biomes is largely consistent with observed rooting depth, provided as ecosystem-level maximum estimates by Schenk et al. (2002), and a recently compiled comprehensive plant-level dataset. In spite of the general agreement of modelled and observed rooting depth across large climatic gradients, comparisons between local observations and global model predictions are mired by a scale mismatch that is particularly relevant for plant rooting depth, for which the small-scale topographical setting and hydrological conditions, in particular the water table depth, pose strong controls.To resolve this limitation, we investigate the sensitivity of photosynthesis (estimated by sun-induced fluorescence, SIF), and of the evaporative fraction (EF, defined as ET over net radiation) to CWD. By employing first principles for the constraint of rooting zone water availability on ET and photosynthesis, it can be derived how their sensitivity to the increasing CWD relates to S. We make use of this relationship to provide an alternative and independent estimate of S (SdSIF and SdEF), informed by Earth observation data, to which S, modelled using CWDX40, can be compared. Our comparison reveals a strong correlation (R2=0.54) and tight consistency in magnitude between the two approaches for estimating S. Our analysis suggests adaptation of plant structure to prevailing climatic conditions and drought regimes across the globe and at catchment scale and demonstrates its implications for land-atmosphere exchange. Our global high-resolution mapping of S reveals contrasts between plant growth forms (grasslands vs. forests) and a discrepant importance across the landscape of plants’ access to water stored at depth, and enables an observation-informed specification of S in global models.

The complexes described here serve as contrast agents for magnetic resonance imaging thermometry. The complexes differentially enhance contrast between 275 and 325 K. The basis of the temperature response of the fluorinated contrast complex is the modulation of water exchange caused by trifluoromethyl groups that can be chemically controlled.

Gadolinium contrast agents that bind to human serum albumin (HSA) can achieve significantly higher relaxivity values and show improved vascular retention time. Most contrast agents of this design are linear agents, which have demonstrated lower kinetic stability and can cause gadolinium deposition. However, the macrocyclic agent Gd-HPDO3A has been found to display the lowest levels of gadolinium retention in the body and therefore demonstrates a useful contrast agent scaffold. We studied the properties of the first Gd-HPDO3A HSA-binding contrast agent, including analysis of isomer composition, water-exchange rates, relaxivity profiles, and in vivo distribution. The relaxivity values of the complex were found to be limited by the slow water exchange rate and reduced hydration state of the albumin-bound complex, compared to previous albumin-binding agents. However, the complex displayed significantly enhanced vascular retention time, which allows for a longer imaging window, and showed enhanced contrast efficiency in a murine tumor model and in mouse models for stable and vulnerable atherosclerotic plaques. This complex therefore presents the opportunity to utilise the benefits of the Gd-HPDO3A structure in blood-pool imaging.

Fish farmers utilize the reversibility of the bioconcentration process to depurate geosmin and other off- flavour causing chemicals from their fish by placing them in clean water just before harvest. To better understand and improve this process, we investigated effects of temperature and water exchange of depuration tanks on geosmin elimination from Atlantic salmon (Salmo salar). Fish loaded with geosmin were depurated for 144 h during which they were subjected to combinations of water exchange (stagnant water or a water exchange rate of ~1200 L/kg fish/d) and temperature (~11.5 or ~14.5 °C) treatments. Model predictions indicated enhanced depuration by water exchange, elevated temperature and interactive effects of these two factors, plus geosmin accumulation in the depuration tank water. The latter was predicted but not observed in the experiment. Furthermore the elevated temperature did not enhance geosmin elimination from Atlantic salmon, possibly because in the tanks with water exchange, temperature treatments did not cause differences in oxygen levels and thus gill ventilation rates. The water exchange significantly increased geosmin elimination from Atlantic salmon, indicating that removal of excreted geosmin from the direct environment of this fish is needed to obtain maximal geosmin elimination from the fish.

International audience; The reactivity of water with Li-rich layered Li2RuO3 and partial exchange of Li2O with H2O within the structure is studied under aqueous (electro)chemical conditions. Upon slow delithiation in water over long time periods, micron-sized Li2RuO3 particles structurally transform from an O3 structure to an O1 structure with a corresponding loss of 1.25 Li ions per formula unit. The O1 stacking of the honeycomb Ru layers is imaged using high-resolution high-angle annular dark-field scanning transmission electron microscopy, and the resulting structure is solved by X-ray powder diffraction and electron diffraction. In situ X-ray absorption spectroscopy suggests that reversible oxidation/reduction of bulk Ru sites is realized on potential cycling between 0.4 and 1.25 VRHE in basic solutions. In addition to surface redox pseudocapacitance, the partially delithiated phase of Li2RuO3 shows high capacity, which can be attributed to bulk Ru redox in the structure. This work demonstrates that the interaction of aqueous electrolytes with Li-rich layered oxides can result in the formation of new phases with (electro)chemical properties that are distinct from the parent material. This understanding is important for the design of aqueous batteries, electrochemical capacitors, and chemically stable cathode materials for Li-ion batteries.

Background: Dynamic contrast-enhanced (DCE) MRI using intravenous injection of gadolinium-based contrast agents (GBCAs) is commonly used for imaging blood-brain barrier (BBB) permeability. Water is an alternative endogenous tracer with limited exchange rate across the BBB. A direct comparison between BBB water exchange rate and BBB permeability to GBCA is missing. The purpose of this study was to directly compare BBB permeability to GBCA (Ktrans and kGad = Ktrans/Vp) and water exchange rate (kw) in a cohort of elderly subjects at risk of cerebral small vessel disease (cSVD).Methods: Ktrans/kGad and kw were measured by DCE-MRI and diffusion prepared pseudo-continuous arterial spin labeling (DP-pCASL), respectively, at 3 Tesla in 16 elderly subjects (3 male, age = 67.9 ± 3.0 yrs) at risk of cSVD. The test-retest reproducibility of kw measurements was evaluated with repeated scans ~6 weeks apart. Mixed effects linear regression was performed in the whole brain, gray matter (GM), white matter (WM), and 6 subcortical brain regions to investigate associations between Ktrans/kGad and test-retest kw. In addition, kw and Ktrans/kGad were compared in normal appearing white matter (NAWM), white matter hyperintensity (WMH) lesions and penumbra.Results: Significant correlation was found between kw and Ktrans only in WM (β = 6.7 × 104, P = 0.036), caudate (β = 8.6 × 104, P = 0.029), and middle cerebral artery (MCA) perforator territory (β = 6.9 × 104, P = 0.009), but not in the whole brain, GM or rest 5 brain regions. Significant correlation was found between kw and kGad in MCA perforator territory (β = 1.5 × 103, P = 0.049), medial-temporal lobe (β = 3.5 × 103, P = 0.032), and hippocampus (β = 3.4 × 103, P = 0.038), but not in the rest brain regions. Good reproducibility of kw measurements (ICC=0.75) was achieved. Ktrans was significantly lower inside WMH than WMH penumbra (16.2%, P = 0.026), and kGad was significantly lower in NAWM than in the WMH penumbra (20.8%, P < 0.001).Conclusion: kw provides a measure of water exchange rate across the BBB with good test-retest reproducibility. The BBB mechanism underlying kw and Ktrans/kGad is likely to be different, as manifested by correlations in only three brain regions for each pair of comparison between kw and Ktrans or kGad.

PURPOSE: To assess the feasibility of using diffusion-time-dependent diffusional kurtosis imaging (tDKI) to measure cellular-interstitial water exchange time (τ(ex)) in tumors, both in animals and in humans. METHODS: Preclinical tDKI studies at 7 T were performed with the GL261 glioma model and the 4T1 mammary tumor model injected into the mouse brain. Clinical studies were performed at 3 T with women who had biopsy-proven invasive ductal carcinoma. tDKI measurement was conducted using a diffusion-weighted STEAM pulse sequence with multiple diffusion times (20–800 ms) at a fixed echo time, while keeping the b-values the same (0–3000 s/mm(2)) by adjusting the diffusion gradient strength. The tDKI data at each diffusion time t were used for a weighted linear least-squares fit method to estimate the diffusion-time-dependent diffusivity, D(t), and diffusional kurtosis, K(t). RESULTS: Both preclinical and clinical studies showed that, when diffusion time t ≥ 200 ms, D(t) did not have a noticeable change while K(t) decreased monotonically with increasing diffusion time in tumors and t ≥ 100 ms for the cortical ribbon of the mouse brain. The estimated τ(ex) averaged median and interquartile range (IQR) of GL261 and 4T1 tumors were 93 (IQR = 89) ms and 68 (78) ms, respectively. For the cortical ribbon, the estimated τ(ex) averaged median and IQR were 41 (34) ms for C57BL/6 and 30 (17) ms for BALB/c. For invasive ductal carcinoma, the estimated τ(ex) median and IQR of the two breast cancers were 70 (94) and 106 (92) ms. CONCLUSION: The results of this proof-of-concept study substantiate the feasibility of using tDKI to measure cellular-interstitial water exchange time without using an exogenous contrast agent.

Transmembrane water exchange, including intra-to-extravascular and intra-to-extracellular ones, are potential biomarkers in the diagnosis and understanding of cancers, brain disorders, and other diseases. Filter-exchange imaging (FEXI), a special case of diffusion exchange spectroscopy (DEXSY) adapted for clinical applications, has the potential to reveal different physiological water exchange processes using the same MRI sequence. In this study, we aim to explore the feasibility of FEXI in measuring different water exchange processes by modulating the diffusion filter (bf) and detection blocks in FEXI. Two FEXI protocols were implemented on a 3T MRI clinical scanner and reveal distinct apparent exchange rate (AXR) contrast in brain tissues in seven healthy volunteers. AXR estimated from a FEXI protocol with bf ​= ​250 ​s/mm2, which is expected to filter out the vascular water specifically, are significantly larger than those of a FEXI protocol with bf ​= ​900 ​s/mm2. Besides, the filter efficiency of FEXI with bf ​= ​250 ​s/mm2 shows a strong correlation with vascular density, a metric estimated as the fraction of water exhibiting intravoxel incoherent motion (IVIM). AXR of FEXI with bf ​= ​250 ​s/mm2 agrees with the vascular water efflux rate constants reported by other independent measurements, although the physiological basis of the AXR of FEXI with bf ​= ​900 ​s/mm2 is not clear yet. Collectively, our current results demonstrate the feasibility of FEXI in measuring different water exchange processes in vivo, and that FEXI targeting the vascular water could help characterize the intra-to-extravascular water exchange process.

Bridged polymacrocyclic ligands featured by structurally different cages offer the possibility of coordinating multiple trivalent lanthanide ions, giving rise to the exploitation of their different physicochemical properties, e.g., multimodal detection for molecular imaging purposes. Intrigued by the complementary properties of optical and MR-based image capturing modalities, we report the synthesis and characterization of the polymetallic Ln(III)-based chelate comprised of two DOTA-amide-based ligands (DOTA&mdash, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) bridged via 1,10-diaza-18-crown-6 (DA18C6) motif. The DOTA-amide moieties and the DA18C6 were used to chelate two Eu(III) ions and one Tb(III) ion, respectively, resulting in a multinuclear heterometallic complex Eu2LTb. The bimetallic complex without Tb(III), Eu2L, displayed a strong paramagnetic chemical exchange saturation transfer (paraCEST) effect. Notably, the luminescence spectra of Eu2LTb featured mixed emission including the characteristic bands of Eu(III) and Tb(III). The advantageous features of the complex Eu2LTb opens new possibilities for the future design of bimodal probes and their potential applicability in CEST MR and optical imaging.

Relaxometric analyses and in particular the use of fast-field cycling techniques have become routine in the study of paramagnetic metal complexes. The field dependence of the solvent proton relaxation properties (nuclear magnetic relaxation dispersion, NMRD) can provide unparalleled insights into the chemistry of these complexes. However, analyzing NMRD data is a multiparametric problem, and some sets of variables are mutually compensatory. Specifically, when fitting NMRD profiles, the metal–proton distance and the rotational correlation time constant have a push–pull relationship in which a change to one causes a predictable compensation in the other. A relaxometric analysis of four isomeric chelates highlights the pitfalls that await when fitting the NMRD profiles of chelates for which dissociative water exchange is extremely rapid. In the absence of independently verified values for one of these parameters, NMRD profiles can be fitted to multiple parameter sets. This means that NMRD fitting can inadvertently be used to buttress a preconceived notion of how the complex should behave when a different parameter set may more accurately describe the actual behavior. These findings explain why the effect of very rapid dissociative exchange on the hydration state of Gd(3+) has remained obscured until only recently.

Postlarvae (PL) nutrition and adequate oxygenation and mixing of the culture medium are all factors that have a major impact on shrimp performance in any culture systems and more so in intensive zero-exchange, biofloc-dominated production systems. Feeding of properly formulated high quality liquid or dry feed can be more convenient and cost-effective than live Artemia-based diets. However, offering the PL with the correct feed quality, quantity, and the particle-size for their body size is a prerequisite for PL performance especially in intensive nursery systems where availability of natural food is limited. The high shrimp performance, low green colony forming units Vibrio concentrations, and comparatively lower ammonia, and nitrite concentrations observed in these trials may demonstrate the benefits from using inoculum of nitrifying-rich water, probiotic, and nitrifying bacteria during the nursery phase of this species.

Introduccion: la insuflacion de dioxido de carbono (CO2) durante la enteroscopia reduce el tiempo del procedimiento y los sintomas posteriores al mismo e incrementa la profundidad de insercion comparado con aire ambiente. En colonoscopia, la tecnica de intercambio de agua (IA) se asocia a menor dolor en comparacion con la insuflacion de CO2. La tecnica IA no esta bien estudiada en enteroscopia. El objetivo de este estudio es comparar la seguridad y eficacia de la enteroscopia con IA y la enteroscopia con CO2. Metodos: estudio prospectivo, comparativo y observacional, que incluyo enteroscopias de doble balon (EDB) que fueron aleatorizadas en dos grupos: el primero con IA y el segundo con insuflacion de CO2. Los datos recopilados se evaluaron mediante analisis univariado y una regresion logistica multiple (variables con p ≤ 0.10 en analisis univariado). Resultados: se incluyeron 46 EDB (23 por brazo; mediana de edad 63,5 anos, 37% mujeres). No hubo diferencias estadisticas en la via de acceso, los hallazgos, la terapeutica y las complicaciones entre grupos. Cuatro pacientes (20%) en el grupo de CO2 tuvieron eventos adversos (distension abdominal y dolor) y uno en el grupo IA (nauseas) sin diferencia estadistica. La mediana de profundidad de insercion fue mayor en el grupo de CO2 (260 cm vs. 160 cm; p = 0,048). La regresion logistica multiple mostro una diferencia estadistica en la profundidad de insercion utilizando insuflacion de CO2 (OR 1,009, 1,001-1,017; p = 0,034). Conclusiones: las EDB con tecnica de insuflacion de CO2 y con IA son seguras con una mayor profundidad de insercion con CO2.

Purpose Malaria is a global health problem with the most malignant form caused by Plasmodium falciparum (P. falciparum). Parasite maturation in red blood cells (RBCs) is accompanied by changes including the formation of paramagnetic hemozoin (HZ) nanocrystals, and increased metabolism and variation in membrane lipid composition. Herein, MR relaxometry (MRR) was applied to investigate water exchange across RBCs' membrane and HZ formation in parasitized RBCs. Methods Transverse water protons relaxation rate constants (R2 = 1/T2 ) were measured for assessing HZ formation in P. falciparum-parasitized human RBCs. Moreover, water exchange lifetimes across the RBC membrane (τi ) were assessed by measuring longitudinal relaxation rate constants (R1 = 1/T1 ) at 21.5 MHz in the presence of a gadolinium complex dissolved in the suspension medium. Results τi increased after invasion of parasites (ring stage, mean τi / τ i 0 = 1.234 ± 0.022) and decreased during maturation to late trophozoite (mean τi / τ i 0 = 0.960 ± 0.075) and schizont stages (mean τi / τ i 0 = 1.019 ± 0.065). The HZ accumulation in advanced stages was revealed by T2 -shortening. The curves reporting R2 (1/T2 ) vs. magnetic field showed different slopes for non-parasitized RBCs (npRBCs) and parasitized RBCs (pRBCs), namely 0.003 ± 0.001 for npRBCs, 0.009 ± 0.002, 0.028 ± 0.004 and 0.055 ± 0.002 for pRBCs at ring-, early trophozoite-, and late trophozoite stage, respectively. Antimalarial molecules dihydroartemisinin and chloroquine elicited measurable changes in parasitized RBCs, namely dihydroartemisinin modified τi , whereas the interference of chloroquine with HZ formation was detectable by a significant T2 increase. Conclusions MRR can be considered a useful tool for reporting on P. falciparum blood stages and for screening potential antimalarial molecules.

Non-invasive assessment of intercompartment water exchange may be of importance to characterize pathologies which are subject to changes in membrane permeability either caused by the malignancy or as an effect of intervention. Conventional diffusion MRI is not specific to water exchange since it cannot separate the effects of exchange and restricted diffusion. For this purpose, advanced diffusion strategies based on a double-diffusion encoding have been developed to disentangle them. In this work, diffusion-based magnetic resonance methods and applications for the measurement of intercompartment exchange are reviewed.

This study evaluated different artificial substrates during pre-nursery of Pacific white shrimp in a biofloc system. Post-larvae (PL 5–80 PL L−1) were raised in 60 L tanks filled with 52 L of chlorinated seawater (35‰) and 6 L of the microalga Chaetoceros muelleri. Four treatments were performed, including control (no artificial substrate), Bidim® (geotextile), mosquito net screen (2 mm mesh) and Needlona® (polyester fiber). The total surface area of artificial substrate comprised 100% of the tank area (0.89 m2). PLs were fed nine times a day using commercial feed. Molasses was added in all treatments four times a day at an average carbon:nitrogen ratio of 14.7:1. The experiment was carried out until the PLs reached PL20, and during this time, water quality, survival, weight gain and survival to salinity stress were all evaluated. Water quality parameters remained within the accepted levels for shrimp rearing, with the exception of total suspended solids (TSS) in mosquito net screen and control, which had the highest values (507 ± 5.50 mg L−1 and 565 ± 23.46 mg L−1, respectively). Using Needlona® as artificial substrate increased the survival rate (91 ± 11.6%) and reduced TSS (42%) when compared to the control. No significant differences were observed in final weight and survival to salinity stress. Among the different substrates, Needlona® was the most suitable for application in Pacific white shrimp prenursery in the biofloc system, essentially because it could maintain levels of solids suspended in water without the use of clarifiers or water exchange, resulting in higher survival.

The annual regimes of estimated rates of oxygen and carbon dioxide exchange between water surface and the atmosphere was compared for two water bodies with different sizes and hydroecological conditions: the deep oligotrophic Lake Baikal and the small mesotrophic–eutrophic Mozhaisk Reservoir with water exchange rate 150 times greater than that of Baikal. The obtained, very large, differences between the rates of gas evasions and invasions in the lake and the reservoir allow the rates of these processes to be used as integral characteristics for the parameterization of the self-purification capacity of freshwater bodies from organic pollutants.

Equilibrium, kinetic (solvent exchange and dissociation of the complex) and relaxometric studies (1H and 17O NMR) have been performed with the [M(II)(c-cdta)]2− complexes (c-cdta = cis-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, M(II) = Mn(II), Zn(II), Cu(II),Ca(II), Mg(II)) and the physico-chemical data are compared to the isomeric complexes with trans-1,2-cdta (t-cdta) with the aim of searching appropriate ligands for Mn(II) complexation for safe MRI contrast agents. The total basicity (Σ log KiH) of the c-cdta ligand appears to be very similar to that of the trans-derivative under the conditions applied (I = 0.15 M NaCl and 25 °C), but the first two protonation constants notably differ. log K1H is 1.5 log units higher, while the log K2H is 0.8 log units lower than those determined for the trans-derivative. Similar basicity of the ligands results in similar complex stability (log K[Mn(L)] values are 14.19(2) and 14.32), whereas the conditional stabilities near to physiological pH are different (pMn values are 7.82 and 8.68) for the [Mn(c-cdta)]2− and the [Mn(t-cdta)]2− derivatives, respectively. Dissociation kinetic studies revealed that the [Mn(c-cdta)]2− dissociates 250 times faster than the [Mn(t-cdta)]2− complex. The water exchange rate (kex298) of [Mn(c-cdta)]2− is ca. 60% higher than that of [Mn(t-cdta)]2−. The differences can likely be attributed to the different distances between the individual donor atoms, and the arrangement of the donor atoms around the metal ions in the cis- and trans- isomers. Interestingly, the relaxivity values of the Mn(II) complexes are very close (r1p = 3.79 mM−1 s−1 and 3.62 mM−1 s−1; 20 MHz, 25 °C for the cis- and trans-isomers, respectively). DFT calculations were used to gain insight into the different properties of the [Mn(c-cdta)]2− and the [Mn(t-cdta)]2− complexes. The results gained in our studies confirm that the trans-1,2-cyclohexanediamine “building block” displays better features for further ligand development.

The water exchange reaction of the neptunyl(VI) and -(V) aqua ions was investigated with quantum chemical methods. Associative ( a) and dissociative ( d) exchange mechanisms were studied. The geometries and vibrational frequencies were computed with density functional theory (DFT) and multiconfiguration self-consistent field (MCSCF) methods. The Gibbs activation energies (Δ G

International audience; The geometric features of two pyclen-based ligands possessing identical donor atoms but different site organization have a profound impact in their complexation properties toward lanthanide ions. The ligand containing two acetate groups and a picolinate arm arranged in a symmetrical fashion (L1) forms a Gd3+ complex being two orders of magnitude less stable than its dissymmetric analogue GdL2. Besides, GdL1 experiences a much faster dissociation following the acid-catalyzed mechanism than GdL2. On the contrary, GdL1 exhibits a lower exchange rate of the coordinated water molecule compared to GdL2. These very different properties are related to different strengths of the Gd ligand bonds associated to steric effects, which hinder the coordination of a water molecule in GdL2 and the binding of acetate groups in GdL1.