•Cr(R-pic)3 (R = H, 5-Br, 5-CF3, 4-Cl, 5-COOH, 3-CH3, 5-OH, 3-OH) were obtained.•Fenton-like reaction and oxidation mechanism were investigated.•No obvious cellular damage and tissue injury (acute toxicity) were observed.•Cr(R-pic)3 have not significant influence than CrCl3 on hypoglycemic activity.The worldwide use of chromium(III) picolinate Cr(pic)3 as nutrition additives has aroused more and more controversies. To reevaluate the safety and validity of Cr(pic)3, seven new derivatives Cr(R-pic)3 (pic = picolinic acid, R = H (1), 5-Br (2), 5-CF3 (3), 4-Cl (4), 5-COOH (5), 3-CH3 (6), 5-OH (7), 3-OH (8)) were synthesized and characterized by X-ray crystal diffraction, ESI-MS, IR and elemental analysis. It was found that different substituent group affected physicochemical activities of the complex such as the Fenton-like reaction and oxidation reaction. Especially, –OH group derivatives lose their hydroxyl radical-generation and Cr(VI)-generation abilities comparing with halogen group in tube experiment. Even so, these differences in chemistry properties may be ignored in live cells and animal tests: no obvious cellular damage (MTT assay) and tissue injury (acute toxicity study) were observed for both Cr(pic)3 and its derivatives. In addition, hypoglycemic activity study indicated that these Cr(III) complexes have no significant influence than CrCl3 salt on the blood glucose, serum insulin, total cholesterol, triglyceride, high density lipoprotein and low density lipoprotein of diabetic mice through two months’ study. Therefore, these substituent group is unable to improve the biological activities of Cr(pic)3 obviously and the validity of Cr(pic)3 used as a nutrition additives is doubted.Seven new Cr(R-pic)3 (pic = picolinic acid, R = H (1), 5-Br (2), 5-CF3 (3), 4-Cl (4), 5-COOH (5), 3-CH3 (6), 5-OH (7), 3-OH (8)) were synthesized, the structure, redox properties, cytotoxicity, acute toxicity and hypoglycemic activity were fully studied.Download high-res image (93KB)Download full-size image

•Three Cr(pic)3 derivatives [Cr(R-pic)2(H2O)2]NO3·H2O were synthesized.•Decomposition in PBS, apo-ovotransferrin and EDTA were measured.•The redox potential of Cr(III)/Cr(II) by cyclic voltammetry were studied.•OH-generation by complexes was determined by Fenton-like reaction.Complexes [Cr(3-CH3-pic)2(H2O)2]NO3·H2O (1), [Cr(5-Br-pic)2(H2O)2]NO3·H2O (2) and [Cr(5-CF3-pic)2(H2O)2]NO3·H2O (3) were synthesized (pic = pyridine-2-carboxylic acid) and characterized by X-ray crystal diffraction. Crystal structure indicates that two bidentate ligands occupy equatorial position and two H2O occupy axial positions in trans-configuration. (i) Decomposition of complexes 1, 2 and 3 in different medium (phosphate buffered saline (PBS), apo-ovotransferrin (apootf) and EDTA) indicates that decomposition rate constants of these complexes follow the sequence of 1 < 2 < 3. (ii) The redox potential of Cr(III)/Cr(II) by cyclic voltammetry follows the sequence of 1 (−1.20 V) > 3 (−1.29 V) > 2 (−1.31 V). (iii) In addition, ·OH-generation of the new synthesized complexes was determined by Fenton-like reaction in comparison with Cr(pic)3, and it may be related to the reduction potential of the complexes. (iv) Moreover, Hammett substituent constants σp (inductive) and σm (resonance) (R = 3-CH3, 5-Br, 5-CF3) were introduced to evaluate the impact of substituent groups on the bond length and decomposition kinetics. The substituent group on the ligand has great effect on the properties of the complexes.Download high-res image (251KB)Download full-size image

•AIE of salen is observed in H2O and crystal state with green fluorescence.•[Al(salen)(H2O)2]+ exhibits an assembly phenomenon in H2O and crystal state.•Green in hydrophilic and blue in hydrophobicity region of cell for Al-salen.•Fluorescence of salen and [Al(salen)(H2O)2]+ were certified by calculation.Salen demonstrates aggregation-induced emission (AIE) effect in aqueous solution and solid state with green fluorescence (salen = N,N′-Ethylenebis(salicylimine)). The reaction of salen with Al3+ results in [Al(salen)(H2O)2]+ directly. [Al(salen)(H2O)2]+ exhibits an obvious assembly phenomenon: monomer exists in organic solution with blue fluorescence while self-assembly polymer forms in aqueous solution and crystal state emitting green fluorescence, we rename it as Restriction of Coordinated Water Motions (RCWM) effect. Moreover, the self-assembly of [Al(salen)(H2O)2]+ has been observed in different part of cells: green fluorescence in hydrophilic region and blue fluorescence in hydrophobicity region in the same time. The photophysical processes are verified by fluorescence spectra, ESI–MS, X-ray diffractometer. ESIPT effect of salen and fluorescence spectra of [Al(salen)(H2O)2]+ have been certified by theoretical calculation. Therefore, salen and [Al(salen)(H2O)2]+ can act as an ideal model for the combination of organic AIEgen and metal complex self-assembly both in aqueous solution and crystal state.

•Chromium picolinate derivatives and its X-ray crystal structures•Dynamics stability, electrochemical potential and hydroxyl radical experiment•Cytotoxic tests and sub-chronic oral toxicity study are studied.As a man-made additive, chromium picolinate Cr(pic)3 has become a popular dietary supplement worldwide. In this paper Cr(pic)3 and its new derivatives Cr(6-CH3-pic)3 (1), [Cr(6-NH2-pic)2(H2O)2]NO3 (2) and Cr(3-NH2-pic)3 (3) were synthesized, and complexes 1 and 2 were characterized by X-ray crystal structure (where pic = 2-carboxypyridine). The relationship between the chemical properties and biotoxicity of these complexes was fully discussed: (1) The dynamics stability of chromium picolinate complexes mainly depends on the CrN bonds length. (2) There is a positive correlation between the dynamics stability, electrochemical potentials and generation of reactive oxygen species through Fenton-like reaction. (3) However, no biological toxicity was observed through MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and sub-chronic oral toxicity study for these chromium picolinate compounds. Together, our findings establish a framework for understanding the structure-property-toxicity relationships of the chromium picolinate complexes.Cr(pic)3 and its derivatives Cr(6-CH3-pic)3, [Cr(6-NH2-pic)2(H2O)2]NO3 and Cr(3-NH2-pic)3 were synthesized (pic = 2-carboxypyridine). The different electronic effects on the metal center, the chemical properties and biotoxicity of these complexes were discussed.

•Three naphthol Schiff base-type fluorescent sensors have been compared.•Coordination with Al3 + inhibited the CN isomerization of Schiff base•L3 had higher sensitivity selectivity for Al3 + in HEPES buffer than L1 and L2•L3 was applied as an excellent fluorescence probe for Al3 + in living cell.Three naphthol Schiff base-type fluorescent sensors, 1,3-Bis(2-hydroxy-1-naphthylideneamino)propane (L1), 1,3-Bis(1-naphthylideneamino)-2-hydroxypropane (L2) and 1,3-Bis(2-hydroxy-1-naphthylideneamino)-2-hydroxypropane (L3), have been synthesized. Their recognition abilities for Al3 + are studied by fluorescence spectra. Coordination with Al3 + inhibited the CN isomerization of Schiff base which intensely increase the fluorescence of L1–L3. Possessing a suitable space coordination structure, L3 is a best selective probe for Al3 + over other metal ions in MeOH–HEPES buffer (3/7, V/V, pH = 6.6, 25 °C, λem = 435 nm). A turn-on ratio over 140-fold is triggered with the addition of 1.0 equiv. Al3 + to L3. The binding constant Ka of L3-Al3 + is found to be 1.01 × 106.5 M− 1 in a 1:1 complex mode. The detection limit for Al3 + is 0.05 μM. Theoretical calculations have also been included in support of the configuration of the L3-Al3 + complex. Importantly, the probe L3 has been successfully used for fluorescence imaging in colon cancer SW480 cells.

•One fluorescent probe L for Cr(III) was developed.•Cr(VI) is easily taken inside cells and rapidly reduced to Cr(III) in cells.•Cr(VI) metabolism in vivo is primarily driven by Vc and GSH.•The resulted Cr(III) can be captured and imaged timely by L in cells.Cellular uptake of Cr(VI), followed by its reduction to Cr(III) with the formation of kinetically inert Cr(III) complexes, is a complex process. To better understand its physiological and pathological functions, efficient methods for the monitoring of Cr(VI) are desired. In this paper a selective fluorescent probe L, rhodamine hydrazide bearing a benzo[b]furan-2-carboxaldehyde group, was demonstrated as a red chemosensor for Cr(III) at about 586 nm. This probe has been used to probe Cr(III) which is reduced from Cr(VI) by reductants such as glutathione (GSH), vitamin C, cysteine (Cys), H2O2 and Dithiothreitol (DTT) by fluorescence spectra. Cr(VI) metabolism in vivo is primarily driven by Vc and GSH. Vc could reduce CrO42 − to Cr(III) in a faster rate than GSH. The indirectly detection limit for Cr(VI) by L + GSH system was determined to be 0.06 μM at pH = 6.2. Moreover, the confocal microscopy image experiments indicated that Cr(VI) can be reduced to Cr(III) inside cells rapidly and the resulted Cr(III) can be captured and imaged timely by L.Cr(VI) is easily taken inside cells and rapidly reduced to Cr(III) in cells by cellular reductants. The resulted Cr(III) is able to be detected by probe L with off–on red fluorescence emissions timely.

•The probe (1) was developed as a Hg(II)-selective green fluorescence agent.•1-Hg2+ can be quenched severely by Cys but not for GSH and HCY.•Aggregations were proved to be the crucial factor for the green emitting.•Sequential switching effect for Hg(II) and then Cys was achieved in bioimaging.Many rhodamine B probes for metal ions and anions showing “orange” fluorescent have attracted a tremendous amount of attention. Herein a rhodamine B-based fluorescent probe 1 showing “green” fluorescence emission in the presence of Hg2+ was first reported. Self-assembled aggregation was proved to be the crucial factor for the green emitting fluorescence by means of resonance light scattering spectra, fluorescence spectra, ESI mass spectral analysis and SEM image. The probe 1 was developed as a excellent Hg(II)-selective green fluorescence agent in ethanol/HEPES buffer media (v/v = 3:7, pH 7.3) with a detection limit of 0.09 μM. Meanwhile, the green fluorescence of 1-Hg2+ can be quenched severely by Cys but not for GSH, S2−, SO42−, SO32−, CN−, CO32− and HCY. The sequential switching effect for Hg2+ and then Cys has been achieved in aqueous media and bioimaging with satisfactory results.

•Synthesis of salicylate chromium(III) complexes with different ammonium ligands•Complex 2 is the most instable one in the presence of EDTA.•Only complex 2 efficiently cleaves DNA in the absence of any added cofactor.Complexes [Cr(III)(SA)(en)2]+ (1), [Cr(III)(SA)(DETA)(H2O)]+ (2) and [Cr(III)(SA)(TETA)]+ (3) were synthesized (H2SA = salicylic acid, en = ethylenediamine, DETA = diethylenetriamine, TETA = triethylenetetramine). Kinetics studies show that 2 is the most instable one among these complexes. In addition, only 2 is found to be a very efficient catalyst of the cleavage of PBR322 DNA in the absence of any added cofactor. The degradation rate from supercoiled form to nicked form was 1.05 ± 0.081 h− 1 (10− 5 M) at pH 7.4 and 37 °C. Thiobarbituric acid-reactive substances assay shows 2 fail to produce OH causing any degradation of deoxyribose ring even in the presence of ascorbic acid. Ethidium bromide displacement assay suggests that only 2 can kick out EB from the groove of DNA. The interaction with DNA causes a blue shift of the d → d transition spectra of 2.Salicylate chromium(III) complex with diethylenetriamine ligand [Cr(III)(SA)(DETA)(H2O)]+ (2) can efficiently cleavage of PBR322 DNA in the absence of any added cofactor.