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Introduction: Biological nitrogen fixation (BNF), an unparalleled metabolic novelty among living microorganisms on earth, globally contributes ~88-101 Tg N year-1 to natural ecosystems, ~56% sourced from symbiotic BNF while ~22-45% derived from free-living nitrogen fixers (FLNF). The success of symbiotic BNF is largely dependent on its interaction with host-plant, however ubiquitous environmental heterotrophic FLNFs face many limitations in their immediate ecological niches to sustain unhindered BNF. The autotrophic FLNFs like cyanobacteria and oceanic heterotrophic diazotrophs have been well studied about their contrivances acclimated/adapted by these organisms to outwit the environmental constraints for functional diazotrophy. However, FLNF heterotrophs face more adversity in executing BNF under stressful estuarine/marine/aquatic habitats. Methods: In this study a large-scale cultivation-dependent investigation was accomplished with 190 NCBI accessioned and 45 non-accessioned heterotrophic FLNF cultivable bacterial isolates (total 235) from halophilic estuarine intertidal mangrove niches of Indian Sundarbans, a Ramsar site and UNESCO proclaimed World Heritage Site. Assuming ~1% culturability of the microbial community, the respective niches were also studied for representing actual bacterial diversity via cultivation-independent next-generation sequencing of V3-V4 rRNA regions. Results: Both the studies revealed a higher abundance of culturable Gammaproteobacteria followed by Firmicutes, the majority of 235 FLNFs studied belonging to these two classes. The FLNFs displayed comparable selection potential in media for free nitrogen fixers and iron-oxidizing bacteria, linking diazotrophy with iron oxidation, siderophore production, phosphorus solubilization, phosphorus uptake and accumulation as well as denitrification. Discussion: This observation validated the hypothesis that under extreme estuarine mangrove niches, diazotrophs are naturally selected as a specialized multidimensional entity, to expedite BNF and survive. Earlier metagenome data from mangrove niches demonstrated a microbial metabolic coupling among C, N, P, S, and Fe cycling in mangrove sediments, as an adaptive trait, evident with the co-abundant respective functional genes, which corroborates our findings in cultivation mode for multiple interrelated metabolic potential facilitating BNF in a challenging intertidal mangrove environment.
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Cancer is recognized as one of the major causes of mortality, however, early-stage detection can increase the survival chance greatly. It is recognized that folate receptors are gradually overexpressed in the cellular membrane with the progress of cancer from stage 1 to stage 4. Utilizing the fact, herein, developed a porous silica nanoparticle system C1@SiO2-FA-NP; A) impregnated with thermodynamically stable Mn(II) complex (1) molecules within the core of the nanoparticle, and B) surface functionalized with folate units. It exhibited a high longitudinal relaxivity value r1 = 21.45 mM-1s-1 that substantially increased to r1 = 40.97 mM-1s-1 in the presence of 0.67 mM concentration of BSA under the physiological condition. The in vitro fluorescent images after surface conjugation of C1@SiO2-FA-NP with FITC (fluorescein isothiocyanate) buttressed the inclusion of the nanoparticle exclusively within the cancerous HeLa cells than that of healthy HEK293 cells. The importance of the surface-bound folate unit in the nanoparticle is further established by comparing the fluorescent images of HeLa cells in the absence of the group. Finally, the applicability of C1@SiO2-FA-NP as the T1-weighted MRI contrast agent for early-stage cancer diagnosis is established within C57BL/6 mice after infecting the mice with HeLa cells.
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BACKGROUND: Aniline serves as a pivotal precursor in many industries such as pesticides, pharmaceuticals, and chemicals. However, its ingestion can lead to severe health consequences, including the potential to induce cancer, respiratory tract irritation, and adverse effects on the nervous and digestive systems in the human body. The widespread use of aniline in industrial processes, coupled with inadequate wastewater management that allows for the direct release of aniline into the environment, leads to surface and groundwater contamination. Therefore, it becomes crucial to devise a reliable electrochemical sensor capable of detecting even trace amounts of aniline. RESULTS: This study presents a modified polyol synthesis method for producing silver nanorods (AgNRs, length: 861-1345 nm, diameter: 66-107 nm) with preferential growth along the (111) crystal plane. Immobilizing AgNRs on a glassy carbon (GC) electrode with Nafion as a binder decreases its charge transfer resistance from 3040 to 129 kΩ and increases its electroactive area from 0.034 to 0.101 cm2. AgNRs/GC electrode exhibited an aniline detection limit of 0.032 µM and sensitivity of 1.4841 µA.M-1cm-2 within a linear range of 0-10 µM using square wave voltammetry (SWV). The reaction rate constant of aniline sensing was determined to be 0.08697 s-1. Chlorobenzene, acephate, and chlorpyrifos could not interfere aniline detection, and 26 % decrease in peak response was observed after the 10th cycle of aniline sensing. The sensor demonstrated â¼100 % recovery for aniline, comparable to the performance of high-performance liquid chromatography when applied to real-world samples like tap and river water. SIGNIFICANCE: The electrochemical sensing of aniline is notably efficient in tap and river water within the acceptable limit, by utilizing one dimensional AgNRs functionalized GC electrode. Importantly, the presence of interferents does not compromise the sensitivity of the sensor. Therefore, one dimensional AgNRs synthesized via a modified polyol route emerge as a promising electrocatalyst for the in-situ detection and determination of aniline.
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Since the finding of nephrogenic systemic fibrosis (NFS) in patients with renal impairment and the long-term accumulation of Gd(III) ions in the central nervous system, the search for nongadolinium ion-based MRI contrast agents made of nutrient metal ions has drawn paramount attention. In this context, the development of Mn(II)-based MRI contrast agents has been a subject of interest for the last few decades. Herein, we report a pentadentate ligand (Li2[BenzPic2]) composed of two picolinate moieties and a rigid 1,2,3,4-tetrahydroquinazoline unit and the corresponding bis(aquated) Mn(II) complex (Complex 1). The complex exhibited high thermodynamic stability (log Kcond = 11.62) and kinetic inertness similar to that of the clinically approved Gd(III)-based contrast agent Magnevist. Complex 1 exerted longitudinal relaxivity (r1) of 5.32 mM-1 s-1 at 1.41 T, 37 °C, pH 7.4, and it increased by 3.6-fold in the presence of serum albumin protein, confirming a substantial rigidifying interaction (albumin association constant KA = 1.66 × 103 M-1) between the protein and the amphiphilic (log P = -0.45) contrast agent. An intravenous dose of 0.08 mmol/kg in a healthy mouse, excellent MRI signal intensity enhancement in the vasculature of the mouse liver, and brightened images of the gallbladder, kidney, and liver were realized.
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Meios de Contraste , Gadolínio DTPA , Humanos , Animais , Camundongos , Albuminas , Imageamento por Ressonância Magnética , ÍonsRESUMO
Type-1 and type-2 diabetes mellitus are metabolic disorders governed by the functional efficiency of pancreatic ß-cells. The activities of the cells toward insulin production, storage, and secretion are accompanied by Zn(II) ions. Thus, for non-invasive pathology of the cell, developing Zn(II) ion-responsive MRI-contrast agents has earned considerable interest. In this report, we have synthesized a seven-coordinate, mono(aquated) Mn(II) complex (1), which is impregnated within a porous silica nanosphere of size 13.2 nm to engender the Mn(II)-based MRI contrast agent, complex 1@SiO2NP. The surface functionalization of the nanosphere by the Py2Pic organic moiety for the selective binding of Zn(II)-ions yields complex 1@SiO2-Py2PicNP, which exhibits r1 = 13.19 mM-1 s-1. The relaxivity value elevates to 20.38 mM-1 s-1 in the presence of 0.6 mM BSA protein at pH 7.4. Gratifyingly, r1 increases linearly with the increase of Zn(II) ion concentration and reaches 39.01 mM-1 s-1 in the presence of a 40 fold excess of the ions. Thus, Zn(II)-responsive contrast enhancement in vivo is envisaged by employing the nanoparticle. Indeed, a contrast enhancement in the pancreas is observed when complex 1@SiO2-Py2PicNP and a glucose stimulus are administered in fasted healthy C57BL/6 mice at 7 T.
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Nanopartículas , Dióxido de Silício , Camundongos , Animais , Dióxido de Silício/metabolismo , Meios de Contraste/metabolismo , Porosidade , Camundongos Endogâmicos C57BL , Imageamento por Ressonância Magnética/métodos , Pâncreas/metabolismo , Zinco/metabolismo , Íons/metabolismoRESUMO
The tridentate pincer ligand [LONS]3- with the ONS donor set was generated in situ by cleaving the disulfane linkage of the pristine redox-active H4Sar(AP/AP) ligand during the complexation reaction with Co(II) and Mn(II) salts in the presence of air and Et3N. X-ray crystal structure analysis of the Co complex (1) and Mn complex (2) revealed that both the complexes were neutral in charge and six-coordinate with the meridional coordination of the two pincer [LONS]n- ligands. The Co ion was in the trivalent state, while the Mn ion was in the tetravalent state. Thus, the generated two pincer [LONS]3- ligands were non-innocent and cumulatively were in trinegative and tetranegative charges for the respective complexes. The intraligand bond distances of the coordinating ligands in each complex were similar, implying the same oxidation/electronic structure of the two ligating units. Variable-temperature magnetic susceptibility measurements revealed an S = 1/2 ground state for each complex. X-band EPR measurements unambiguously established the presence of a ligand-based unpaired electron in complex 1, and in complex 2, the unpaired electron was at the Mn centre. DFT-based theoretical calculations suggested the three-electron oxidation of the two ligating units in complex 1. Two iminosemiquinone radicals were of opposite spins (α-spin and ß-spin) and a thiyl radical in either α-spin or ß-spin was delocalized between two sulfur atoms. Thus, the antiferromagnetic coupling among the two opposite spins provided an S = 1/2 ground state and resulted in the radical-based EPR spectrum. In complex 2, each ligating pincer unit contained an iminosemiquinone radical that interacted antiferromagnetically with the Mn(IV)-based three unpaired electrons. This rendered a doublet ground state with the residual electron density located at the Mn center.
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Contrast-agent enhanced magnetic resonance imaging (MRI) has been under continuous investigation for the conspicuous imaging of lesions and the early-stage detection of tumors. To achieve the development of a T1-weighted contrast agent with a high relaxivity value, herein, porous silica nanoparticles that had internalized about 20 aquated cationic Gd(III) complexes (1) of the hexadentate hydroxyethyl-appended picolinate-based ligand H2hbda were demonstrated. Complex 1 exhibited a longitudinal relaxivity value per mM Gd(III) ions, r1, of 9.05 mM-1 s-1 (pH 7.4, 37 °C, 1.41 T), which increased to 86.41 mM-1 s-1 because of the grafting of complex 1 in the inner core of porous silica nanospheres through electrostatic interactions between the anionic silica surface and the cationic complex 1 molecules. A further augmentation in the relaxivity value to 118.32 mM-1 s-1 was realized because of the interaction of the complex 1@SiO2NPs with serum albumin protein. The synthesized nanosystem was impervious to physiologically available anions (HPO42- and HCO31-) and also kinetically inert, as evidenced via a transmetallation experiment in the presence of Zn(II) ions. The developed complex-incorporated nanomaterial was bio- and hemo-compatible. Cellular uptake measurements employing HeLa cells and the concentration-dependent enhancement in the brightness of in vitro phantom images, recorded under a clinical scanner at 1.5 T, demonstrated that the developed biocompatible 1@SiO2NP complex has promising diagnostic applications as a T1-weighted MRI contrast agent.
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Meios de Contraste , Nanopartículas , Meios de Contraste/química , Células HeLa , Humanos , Ligantes , Imageamento por Ressonância Magnética/métodos , Nanopartículas/química , Porosidade , Albumina Sérica , Dióxido de Silício/química , Eletricidade EstáticaRESUMO
Ligand H2LAP comprises a non-innocent 2-aminophenol unit and an innocent bis(pyridin-2-ylmethyl)amine unit. The ligand, upon reaction with an equivalent amount of Mn(ClO4)2·6H2O in the presence of Et3N under air in MeOH, provided a mono(oxo)-bridged dinuclear Mn2 complex ({[(LISQ)MnIII-O-MnIII(LISQ)][(ClO4)]2}; 1). X-ray crystal structure analysis of complex 1 revealed that in the dicationic unit, the physical oxidation state of each Mn ion was +III and the 2-aminophenol unit of ligand H2LAP was in its one-electron oxidized iminobenzosemiquinone form. 1H-NMR measurement of complex 1 confirmed that the complex acquired a diamagnetic ground state (St = 0). Thus, antiferromagnetic couplings among the paramagnetic centers were realized. The UV-Vis-NIR spectrum of complex 1 was consisted of ligand-to-metal charge-transfer transitions in the visible region, while ligand-to-metal and metal-to-ligand charge-transfer transitions were noticed in the near-infrared region due to the presence of iminobenzosemiquinone radical units. The cyclic voltammogram of the complex showed three one-electron oxidation waves and two one-electron reduction waves. While the first two oxidation processes were metal-based, the two successive reductions were ligand-centered. DFT-based theoretical studies confirmed the assignment.
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An elusive aminyl radical and an iminosemiquinone radical-coordinated square pyramidal Cu(ii) complex (1) have been isolated by the reaction between the noninnocent ligand H4LPy(AP) and Cu(ClO4)2·6H2O in the presence of Et3N and air as the sole oxidant. The geometry and electronic structure of the complex were concluded by X-ray crystallography, magnetic and EPR measurements, and density functional theory (DFT) calculations. This work reports the first crystallographic example of the two different types of radicals co-existing in a stable complex.
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Magnetic resonance imaging has emerged as an indispensable imaging modality for the early-stage diagnosis of many diseases. The imaging in the presence of a contrast agent is always advantageous, as it mitigates the low-sensitivity issue of the measurements and provides excellent contrast in the acquired images even in a short acquisition time. However, the stability and high relaxivity of the contrast agents remained a challenge. Here, molecules of a mononuclear, mono(aquated), thermodynamically stable [log KMnL = 14.80(7) and pMn = 8.97] Mn(II)-complex (1), based on a hexadentate pyridine-picolinate unit-containing ligand (H2PyDPA), were confined within a porous silica nanosphere in a noncovalent fashion to render a stable nanosystem, complex 1@SiO2NP. The entrapped complex 1 (complex 1@SiO2) exhibited r1 = 8.46 mM-1 s-1 and r2 = 33.15 mM-1 s-1 at pH = 7.4, 25 °C, and 1.41 T in N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid buffer. The values were about 2.9 times higher compared to the free (unentrapped)-complex 1 molecules. The synthesized complex 1@SiO2NP interacted significantly with albumin protein and consequently boosted both the relaxivity values to r1 = 24.76 mM-1 s-1 and r2 = 63.96 mM-1 s-1 at pH = 7.4, 37 °C, and 1.41 T. The kinetic inertness of the entrapped molecules was established by recognizing no appreciable change in the r1 value upon challenging complex 1@SiO2NP with 30 and 40 times excess of Zn(II) ions at pH 6 and 25 °C. The water molecule coordinated to the Mn(II) ion in complex 1@SiO2 was also impervious to the physiologically relevant anions (bicarbonate, biphosphate, and citrate) and pH of the medium. Thus, it ensured the availability of the inner-coordination site of complex 1 for the coordination of water molecules in the biological media. The concentration-dependent changes in image intensities in T1- and T2-weighted phantom images and uptake of the nanoparticles by the HeLa cell put forward the biocompatible complex 1@SiO2NP as a potential dual-mode MRI contrast agent, an alternative to Gd(III)-containing contrast agents.
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Meios de Contraste , Nanosferas , Meios de Contraste/química , Células HeLa , Humanos , Imageamento por Ressonância Magnética/métodos , Manganês/química , Porosidade , Dióxido de Silício , Água/químicaRESUMO
Long-range antiferromagnetic coupling impeded electron flow through the hexaradical-containing tetranuclear CoIII4 complex (1), while the nonradical-containing tetranuclear CoIII4 complex (2), with no paramagnetic centres, was a semiconductor and sensed NH3 efficiently at room temperature (25 °C).
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Sundarbans mangrove forest, the world's largest continuous mangrove forests expanding across India and Bangladesh, in recent times, is immensely threatened by degradation stress due to natural stressors and anthropogenic disturbances. The degradation across the 19 mangrove forests in Indian Sundarbans was evaluated by eight environmental criteria typical to mangrove ecosystem. In an attempt to find competent predictors for mangrove ecosystem degradation, key eco-physiological resilience trait complex specific for mangroves from 4922 individuals for physiological analyses with gene expression and 603 individuals for leaf tissue distributions from 16 mangroves and 15 associate species was assessed along the degradation gradient. The degradation data was apparently categorized into four and CDFA discriminates 97% of the eco-physiological resilience data into corresponding four groups. Predictive Bayesian regression models and mixed effects models indicate osmolyte accumulation and thickness of water storage tissue as primary predictors of each of the degradation criteria that appraise the degradation status of mangrove ecosystem. RDA analyses well represented response variables of degradation explained by explanatory resilience variables. We hypothesize that with the help of our predictive models the policy makers could trace even the cryptic process of mangrove degradation and save the respective forests in time by proposing appropriate action plans.
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Conservação dos Recursos Naturais , Previsões , Áreas Alagadas , Teorema de Bayes , Geografia , Índia , Modelos Lineares , Modelos Teóricos , Análise de RegressãoRESUMO
Bacterial Pho regulon is a key regulator component in biological phosphorus-uptake. Poly-phosphate accumulating bacteria used in enhanced biological phosphorus removal (EBPR) system encounter negative regulation of the Pho regulon, resulting in reduced phosphorus-uptake from phosphorus-replete waste effluents. This study demonstrates possible trends of overcoming the PhoU negative regulation, resulting in excessive PO4 3--P uptake at varying concentrations of NO3 --N through denitrifying phosphorus removal process. We investigated the Pho regulon gene expression pattern and kinetic studies of P-removal by denitrifying phosphate accumulating organisms (DPAOs) which are able to remove both PO4 3--P and NO3 --N in single anoxic stage with the utilization of external carbon sources, without the use of stored polyhydroxyalkanoate (PHA) and without any anaerobic-aerobic or anaerobic-anoxic switches. Our study establishes that a minimum addition of 100 ppm NO3 --N leads to the withdrawal of the negative regulation of Pho regulon and results in â¼100% P-removal with concomitant escalated poly-phosphate accumulation by our established DPAO isolates and their artificially made consortium, isolated from sludge sample of PO4 3- -rich parboiled rice mill effluent, in a settling tank within 12 h of treatment. The same results were obtained when a phosphate rich effluent (stillage from distillery) mixed with a nitrate rich effluent (from explosive industry) was treated together in a single phase anoxic batch reactor, eliminating the need for alternating anaerobic/aerobic or anaerobic/anoxic switches for removing both the pollutants simultaneously. The highest poly-phosphate accumulation was observed to be more than 17% of cell dry weight. Our studies unequivocally establish that nitrate induction of Pho regulon is parallely associated with the repression of PhoU gene transcription, which is the negative regulator of Pho regulon. Based on earlier observations where similar nitrate mediated transcriptional repression was cited, we hypothesize the possible involvement of NarL/NarP transcriptional regulator proteins in PhoU repression. At present, we propose this denitrifying phosphorus removal endeavor as an innovative methodology to overcome the negative regulation of Pho regulon for accelerated unhindered phosphorus remediation from phosphate rich wastewater in India and the developing world where the stringency of EBPR and other reactors prevent their use due to financial reasons.
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The noninnocent ligand H2LAP(Ph) contained a bulky phenyl substituent at the ortho position to the aniline moiety. The ligand reacted with 0.5 equiv of CuCl2·2H2O in the presence of Et3N under air and provided the corresponding Cu(II)-bis(imonosemiquinone) complex (1). The complex upon oxidation by a stoichiometric amount of ferrocenium hexafluorophosphate (FcPF6) yielded the four-coordinate [Cu(II)-(imonosemiquinone)(iminoquinone)]PF6 complex (3), while the oxidation by an equivalent amount of CuCl2·2H2O produced the five-coordinate Cu(I)-bis(iminoquinone)Cl complex (2). Thus, a ligand-based oxidation followed by ligand-to-metal electron-transfer was realized for the latter oxidation process. Removal of the Cl- ion from complex 2 rendered the four-coordinate complex 4. The oxidation state of both Cu(I) and iminoquinone moieties remained unaltered upon the change in the coordination number. All the complexes were characterized by X-ray crystallography. Complexes 2, 3, and 4 were diamagnetic with an St = 0 ground state as evident by electron paramagnetic resonance (EPR) and 1H NMR measurements. The UV-vis-NIR spectra of all the complexes were dominated by charge-transfer transitions. Two oxidations and two reductions waves were noticed in the cyclic voltammogram (CV) of complex 1. Complex 2 and complex 3 underwent one oxidation and three reductions. Unlike complex 3, which experienced ligand-based oxidation, in complex 2 the oxidation was metal-centered [oxidation of Cu(I)-to-Cu(II)]. UV-vis-NIR spectral changes during the fixed-potential coulometric one-electron oxidation and thereafter EPR analysis consolidated the metal-based oxidation in complex 2. Complex 2 was air stable; however, it oxidized KO2 to oxygen molecule, and complex 1 was formed in due course as evident by UV-vis-NIR spectral changes and EPR measurements. Time dependent density functional theory calculations have been incorporated to assign the transitions that appeared in the UV-vis-NIR spectra of the complexes.
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In the presence of FeCl3 and Et3N, a ligand H4Ldtda(AP) underwent S-S bond cleavage and generated a pincer non-innocent H3LONS ligand, which formed a homoleptic, six-coordinate, low-spin Fe(iii) complex (1). The complex comprised two 2-iminobenzosemiquinone (1-) π-radicals and one thiyl π-radical.
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Disclosed here are a piperazine, a pyridine, and two carboxylate groups containing pentadentate ligand H2pmpa and its corresponding water-soluble Mn(II) complex (1). DFT-based structural optimization implied that the complex had pentagonal bipyramidal geometry where the axial positions were occupied by two water molecules, and the equatorial plane was constituted by the ligand ON3O donor set. Thus, a bis(aquated) disc-like Mn(II) complex has been synthesized. The complex showed higher stability compared with Mn(II)-EDTA complex [log KMnL = 14.29(3)] and showed a very high r1 relaxivity value of 5.88 mM-1 s-1 at 1.41 T, 25 °C, and pH = 7.4. The relaxivity value remained almost unaffected by the pH of the medium in the range of 6-10. Although the presence of 200 equiv of fluoride and bicarbonate anions did not affect the relaxivity value appreciably, an increase in the value was noticed in the presence of phosphate anion due to slow tumbling of the complex. Cell viability measurements, as well as phantom MR images using clinical MRI imager, consolidated the possible candidature of complex 1 as a positive contrast agent.
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Meios de Contraste/química , Complexos de Coordenação/química , Gadolínio/química , Imageamento por Ressonância Magnética , Manganês/química , Sobrevivência Celular/efeitos dos fármacos , Meios de Contraste/síntese química , Meios de Contraste/farmacologia , Complexos de Coordenação/síntese química , Complexos de Coordenação/farmacologia , Relação Dose-Resposta a Droga , Gadolínio/farmacologia , Células HeLa , Humanos , Concentração de Íons de Hidrogênio , Manganês/farmacologia , Estrutura Molecular , Teoria Quântica , Relação Estrutura-AtividadeRESUMO
To attain high relaxivity as well as stability, a new water-soluble, water-coordinated Gd(iii) complex, which was synthesised by reacting equimolar amounts of picolinate-based ligand H4peada and GdCl3·xH2O at pH â¼ 6.5, was examined. The number of inner sphere water molecules (q) in the complex was found to be 1.7 ± 0.1 from luminescence lifetime measurements of its Tb(iii) congener, complex 2. At 1.41 T, 25 °C, and pH = 7.4, the longitudinal relaxivity (r1) value of the complex was found to be 6.08 mM-1 s-1, which remained almost constant in the pH range 4-10. The r1 relaxivity value has not been affected in the presence of a 100 fold excess of bicarbonate and phosphate anions, whereas in the case of fluoride ions, the value dropped to 4.6 mM-1 s-1 due to a binding interaction of fluoride ions by replacing inner sphere water molecules of the complex. From the potentiometric titration method, the stability constant of the complex was found to be log KGdL = 17.0 ± 0.08 (in 0.15 M KCl and 25 °C). At pH = 7.4, the pGd value of ligand H4peada was found to be 14.01 which was comparable to the commercially available MRI contrast agent Omniscan®. Phantom MR images of the complex under a clinical MR scanner at 1.5 T also demonstrated the usefulness of complex 1 as a potential MRI contrast agent.
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Single-molecule magnets (SMMs) retain a magnetization without applied magnetic field for a decent time due to an energy barrier U for spin-reversal. Despite the success to increase U, the difficult to control magnetic quantum tunneling often leads to a decreased effective barrier Ueff and a fast relaxation. Here, we demonstrate the influence of the exchange coupling on the tunneling probability in two heptanuclear SMMs hosting the same spin-system with the same high spin ground state St = 21/2. A chirality-induced symmetry reduction leads to a switch of the MnIII-MnIII exchange from antiferromagnetic in the achiral SMM [MnIII6CrIII]3+ to ferromagnetic in the new chiral SMM RR[MnIII6CrIII]3+. Multispin Hamiltonian analysis by full-matrix diagonalization demonstrates that the ferromagnetic interactions in RR[MnIII6CrIII]3+ enforce a well-defined St = 21/2 ground state with substantially less mixing of MS substates in contrast to [MnIII6CrIII]3+ and no tunneling pathways below the top of the energy barrier. This is experimentally verified as Ueff is smaller than the calculated energy barrier U in [MnIII6CrIII]3+ due to tunneling pathways, whereas Ueff equals U in RR[MnIII6CrIII]3+ demonstrating the absence of quantum tunneling.
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The synthesized lithium (S)-6,6'-(1-carboxyethylazanediyl)bis(methylene)dipicolinate (Li3cbda) is a new chiral, alanine-based ligand bearing two picolinate functionalities. The trianionic form of the ligand [(cbda)3-] constitutes a seven-coordinate, water-soluble, pentagonal bipyramidal Mn(ii) complex (1). The structural analysis reveals the presence of a water coordinating site in the complex. The complex is thermodynamically very stable, and the stability is not affected by the presence of physiological anions (HCO3-, PO43-, and F-). The pH of the medium exerts a small effect on the stability of the complex. The r1 relaxivity of 3.02 mM-1 s-1 is exhibited by the complex at 1.41 T, pH â¼7.4, and 25 °C. Phantom images obtained via a clinical MRI BRIVO MR355 system established concentration-dependent signal enhancement by the complex. The cytotoxicity test confirmed complex 1 as a biocompatible potential T1-weighted MRI contrast agent.
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Alanina/química , Meios de Contraste/química , Complexos de Coordenação/química , Imageamento por Ressonância Magnética , Manganês/química , Estabilidade de MedicamentosRESUMO
Four-coordinate, monoradical-containing Co(iii) complexes participated in the non-innocent ligand driven homolytic cleavage of S-S and Se-Se bonds and catalyzed the conversion of RNCO (R = phenyl and naphthyl) to the corresponding urea derivatives (TON 480) in dry CH2Cl2 under sunlight stimulus.