Enantioselective Hydroaminations Catalyzed by Yttrium(III)-Bis(sulfoximine) Complexes.

Bis(sulfoximine) yttrium complexes as catalysts for enantioselective intramolecular hydroaminations were prepared for the first time and characterized by a multinuclear NMR study including the nuclei 1H, 13C, 15N and 89Y. The stoichiometries of the complexes were confirmed by a Job plot. In addition to the experimental results, the 89Y NMR shifts and the complex structures were elucidated by DFT calculations.

Pyridine-2,6-Dicarboxylic Acid As a Facile and Highly Selective "Turn-Off" Fluorimetric Chemosensor for Detection of Cu (II) Ions in Aqueous Media.

Copper metal is third most abundant trace element in human body. Determination of Cu (II) ions is a burning topic in field of environment protection and food safety because of its significant impact on ecosystem. In this study, 2,6-pyridine dicarboxylic acid (PDA) has been explored as "turn-off" florescent probe for florescent detection of Cu (II) ions. This sensor showed highly selective complexing ability towards Cu (II) ions. Addition of aqueous solution of Cu (II) ions remarkably quenched the fluorescence intensity of PDA while, on contrary, there was no any prominent fluorescence quenching interference on addition of various metal ions. The binding mode of PDA and Cu (II) ions was determined as stoichiometry of 1:1 and it was further confirmed by single crystal XRD analysis. Mechanisms of static and dynamic quenching were confirmed by stern-volmer plot. Limit of detection (LOD) and limit of quantification (LOQ) for Cu (II) ions was calculated as 3.6 µM and 1.23 µM respectively, which is far below the acceptable value (31.5µM) according to the World Health Organization. The use of the sensor for detection of Cu (II) ions in real samples in aqueous media was also performed.

Cyclodextrin-Enabled Enantioselective Complexation Study of Cathinone Analogs.

The characteristic alkaloid component of the leaves of the catnip shrub (Catha edulis) is cathinone, and its synthetic analogs form a major group of recreational drugs. Cathinone derivatives are chiral compounds. In the literature, several chiral methods using cyclodextrins (CDs) have been achieved so far for diverse sets of analogs; however, a comprehensive investigation of the stability of their CD complexes has not been performed yet. To characterize the enantioselective complex formation, a systematic experimental design was developed in which a total number of 40 neutral, positively, and negatively charged CD derivatives were screened by affinity capillary electrophoresis and compared according to their cavity size, substituent type, and location. The functional groups responsible for the favorable interactions were identified in the case of para-substituted cathinone analog mephedrone, flephedrone, and 4-methylethcathinone (4-MEC) and in the case of 3,4-methylendioxy derivative butylone and methylenedioxypyrovalerone (MDPV). The succinylated-ß-CD and subetadex exhibited the highest complex stabilities among the studied drugs. The complex stoichiometry was determined using the Job's plot method, and the complex structures were further studied using ROESY NMR measurements. The results of our enantioselective complex formation study can facilitate chiral method development and may lead to evaluate potential CD-based antidotes for cathinone analogs.

An Isoniazid Based Schiff Base Sensor for Selective Detection of Pd2+ Ions.

Here, we developed a novel isoniazid based fluorescent probe (E)-N'-(thiophen-2-ylmethylene)isonicotinohydrazide (TINH) through simple condensation reaction and employed for selective detection of Pd2+ ions with a low detection limit of 4.102 × 10-11 M. Among the many existing cations, TINH bound Pd2+ ions with an association affinity of 9.794 × 105 M-1. Adding Pd2+ ions to ligand solution increased the absorption intensity in UV-Visible and quenched the emission intensity in fluorescence spectroscopic experiments. More importantly, this TINH complexed to Pd2+ ions in 1:1 stoichiometric ratio. To evaluate the stability of complexed system, pH experiments has been performed. The binding insights among the ligand and Pd2+ ions has been confirmed by IR spectroscopic and MASS spectrometric methods. Additionally, TINH also applied to real water samples for the identification and measurement of Pd2+ ions. Hence, this system could be highly applicable for detection of Pd2+ ions in environmental and industrial samples with in low detection range.

Nanoparticle-Protein Interaction: Demystifying the Correlation between Protein Corona and Aggregation Phenomena.

Protein corona formation and nanoparticles' aggregation have been heavily discussed over the past years since the lack of fine-mapping of these two combined effects has hindered the targeted delivery evolution and the personalized nanomedicine development. We present a multitechnique approach that combines dynamic light and small-angle X-ray scattering techniques with cryotransmission electron microscopy in a given fashion that efficiently distinguishes protein corona from aggregates formation. This methodology was tested using ∼25 nm model silica nanoparticles incubated with either model proteins or biologically relevant proteomes (such as fetal bovine serum and human plasma) in low and high ionic strength buffers to precisely tune particle-to-protein interactions. In this work, we were able to differentiate protein corona, small aggregates formation, and massive aggregation, as well as obtain fractal information on the aggregates reliably and straightforwardly. The strategy presented here can be expanded to other particle-to-protein mixtures and might be employed as a quality control platform for samples that undergo biological tests.

Bis(thiophen-2-yl-methylene) Benzene-1, 4-Diamine as Fluorescent Probe for the Detection of Fe3+ in Aqueous Samples.

A Schiff base bis(thiophen-2-yl-methylene)benzene-1, 4-diamine (L) was synthesized and used for selective and sensitive detection of Fe3+. L exhibited enhanced fluorescence response at excitation of 365 nm and emission wavelength of 440 nm for Fe3+. The formation of a 1:1 complex between L and Fe3+ was suggested by Job's plot by fluorescence titration and from optimized structures using Density functional theory (DFT). The fluorescence intensity was directly proportional to concentration of Fe3+ (R2 = 0.999) with the detection limit of 3.8 × 10-7 M and the binding constant of 1.20 × 104 M-1 at pH = 6.0. The probe was used to detect Fe3+ in different water samples with the percentage recovery of 99.7-103%. The interference of the other cations are < 5%.

BODIPY-Hg2+ Complex: A Fluorescence "Turn-ON" Sensor for Cysteine Detection.

A BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) based pioneering sensing material (HLPy) having 2-amino pyridine as receptor was synthesized and used for the selective detection of Hg2+ ions. The synthesized HLPy features a high affinity towards Hg2+ (ka = 2.04 × 105 M-1), accompanied by effective quenching of fluorescence in DMF:H2O (1:9 v/v, 10 mM HEPES buffer, pH 7.4) with 54 nM limit of detection (LOD). The emission titration experiments (Job's plot) in the presence of varying mole-fraction of Hg2+ ions reveals the formation of non-fluorescent 2:1 coordination complex [Hg(LPy)2]. The resulting non-fluorescent [Hg(LPy)2] was thoroughly characterized using various spectroscopic techniques and analyses. Interestingly, the non-fluorescent complex [Hg(LPy)2] is able to specifically respond towards Cys over other biothiols and amino acids through a reversible de-complexation mechanism. As a result, the remarkable recovery of the fluorescence can be observed. The limit of detection (LOD) for Cys detection is estimated to be 29 nM in DMF:H2O (1:9 v/v, 10 mM HEPES buffer, pH 8.0). The reversibility and reusability of [Hg(LPy)2] were achieved by the sequential addition of Cys and Hg2+ ions up to five cycles. Moreover, the removal of Hg2+ ions up to 89% from aqueous samples using HLPy was successfully demonstrated.

Malonyl-based Chemosensors: Selective Detection of Fe3+ Ion in Aqueous Medium.

Two novel malonyl-based chemosensors, N,N'-bis(ethyl-4'-benzoate)-1,3-propanediamide (1) and N,N'-bis(ethyl-3'-benzoate)-1,3-propanediamide (2), have been synthesized and screened towards various biologically important metal ions such as Na+, Mg2+, K+, Ca2+, Al3+, Cr3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Ag+, Cd2+, Hg2+, Ti3+, and Pb2+. The emission spectral studies of both 1 and 2 displayed 84 - 91% turn-off emission responses selectively with Fe3+ ion in aqueous buffer (MeCN/H2O, 1:4, v/v, pH = 7.4) solution. Chemosensors 1 and 2 exhibited remarkable sensing ability towards Fe3+ ion over other metal ions with limit of detection (LOD) of 4.28 and 4.33 µM, respectively. The binding stoichiometry of 1 and 2 with Fe3+ ion was studied by Benesi-Hildebrand fitting, Stern-Volmer plot and Job's plots, revealing that both chemosensors (1 - 2) bind with Fe3+ metal ion in 1:1 stoichiometric ratio with the apparent association constant (Ka) 8.90 × 103 and 11.16 × 103 M-1, respectively. Furthermore, the interactions of chemosensors (1 - 2) with metal ion were also investigated by using density functional theory (DFT) at B3LYP hybrid functional using 6-31G and LanL2DZ basis sets.

Complexes of the Mycotoxins Citrinin and Ochratoxin A with Aluminum Ions and their Spectroscopic Properties.

The sensitive detection of the mycotoxin citrinin (CIT) utilizing its fluorescence requires approaches to enhance the emission. In this respect, we studied the complexation of CIT and ochratoxin A (OTA) with Al3+ in methanol using absorption and fluorescence spectroscopy. In this context, an isocratic high performance liquid chromatography (HPLC) method using a polymer column and a fluorescence detector was also developed that enables the separation of the metal ion complexes from the free ligands and non-complexed Al3+. CIT and OTA showed distinct changes in their absorption and fluorescence properties upon Al3+-coordination, and the fluorescence of CIT was considerably enhanced. Analysis of the photometrically assessed titration of CIT and OTA with Al3+ using the Job plot method revealed 1:2 and 1:1 stoichiometries for the Al3+ complexes of CIT (Al:CIT) and OTA (Al:OTA), respectively. In the case of CIT, only one ß-diketone moiety participates in Al3+ coordination. These findings can be elegantly exploited for signal amplification and provide the base to reduce the limit of detection for CIT quantification by about an order of magnitude, as revealed by HPLC measurements using a fluorescence detector.

Investigation of inclusion behaviour of gefitinib with epichlorohydrin-ß-cyclodextrin polymer: preparation of binary complex, stoichiometric determination and characterization.

Gefitinib is anticancer drug which is sparingly soluble in water. This limits its dissolution and bioavailability. Binary inclusion complex of gefitinib with Epi-ß-CD was prepared by freeze-drying method. Stoichiometric ratio of 1:1 M was established by continuous variation (Job's) plot. The stability constant of complex as determined by phase solubility study was found to be 15,871.3 M-1. Complex was characterized by FTIR, DSC, DTA and dissolution study. Results revealed that in complex the drug no longer exist in crystalline state and is converted into amorphous form; which shows higher dissolution efficiency as compared to crystalline drug. The solubilizing efficiency for freeze dried complex was found to be 175.57 and the relative drug crystallinity degree was 87.91% as estimated by thermal analysis. Complexation led to decrease in surface tension; from 54.8 dynes/cm (pure gefitinib) to 40.3 dynes/cm (FD complex) due to adsorption phenomenon. The results obtained in this study confirmed that complexation of gefitinib with Epi-ß-CD is a prominent approach and suitable tool for tailoring the issue related to its delivery and can be explored for development of an effective delivery system.

FRET-based Stoichiometry Measurements of Protein Complexes in vitro.

For a complete understanding of biochemical reactions, information on complex stoichiometry is essential. However, measuring stoichiometry is experimentally challenging. Our lab has developed a FRET-based assay to study protein complex stoichiometry in vitro. This assay, also known as Job plot, is set up as a continuous variation of the molar ratio between the two species, kept at constant total concentration. The FRET (Fluorescence Resonance Energy Transfer) between the two fluorescently-labeled proteins is measured and the stoichiometry is inferred from the sample with highest FRET signal. This approach allows us to assess complex stoichiometry in solution.

Study on inclusion behavior and properties of tetrahydropalmatine with β-cyclodextrin and its derivatives / 中草药

Objective: To prepare tetrahydropalmatine (THP) and β-cyclodextrin (β-CD) and its derivatives inclusion complexes (HP-β-CD, DM-β-CD, and TM-β-CD and explore their inclusion behavior and properties. Methods: The inclusion complexes of THP with β-CD, HP-β-CD, DM-β-CD, and TM-β-CD were prepared by saturated solution. The inclusion ratio and stability constant of inclusion complexes were determined with the Job plot and UV-vis spectroscopy. The THP/CDs complexes were characterized and determinated by means of XRD, TG, and SEM. The molecular simulation was processed to investigate the inclusion behavior of THP and different CDs. The water solubility of the inclusion complexes was measured and the stability test was conducted in the simulated human gastric juice and intestinal fluid environment. Results: Job plot and UV-vis spectroscopy showed that inclusion ratio of host-guest inclusion complexes was 1:1. Molecular docking showed that the entire THP entered the macrophage port and run through the cavities of β-CD and DM-β-CD, with the two aromatic rings located at the large and small mouth, respectively. For HP-β-CD and TM-β-CD, the two nitrogen heterocycle of THP were “V” shaped inlaid into the CD cavity, and both aromatic rings were located at the large end of the CDs. Conclusion: The solubility of tetrahydropalmatine was increased from 0.30 mg/mL to 1.60, 3.40, 9.13, and 4.02 mg/mL for β-CD, HP-β-CD, DM-β-CD, and TM-β-CD, respectively. The thermal stability and biological environment stability had been significantly improved.

Biochemical and Biophysical Methods for Analysis of Poly(ADP-Ribose) Polymerase 1 and Its Interactions with Chromatin.

Poly (ADP-Ribose) Polymerase I (PARP-1) is a first responder to DNA damage and participates in the regulation of gene expression. The interaction of PARP-1 with chromatin and DNA is complex and involves at least two different modes of interaction. In its enzymatically inactive state, PARP-1 binds native chromatin with similar affinity as it binds free DNA ends. Automodification of PARP-1 affects interaction with chromatin and DNA to different extents. Here we describe a series of biochemical and biophysical techniques to quantify and dissect the different binding modes of PARP-1 with its various substrates. The techniques listed here allow for high throughput and quantitative measurements of the interaction of different PARP-1 constructs (inactive and automodified) with chromatin and DNA damage models.

Raman and NMR kinetics study of the formation of amidoamines containing N-hydroxyethyl groups and investigations on their Cu(II) complexes in water.

Three amidoamines containing the N-hydroxyethyl group (HOEt), namely (HOEt)2N(CH2)2C(O)NH2 (1), [(HOEt)2N(CH2)2C(O)NH]2CH2 (2) and HOEtN[(CH2)2C(O)NH2]2 (3) have been synthesized by reacting diethanolamine HOEt2NH with acrylamide and N,N'-methylenebisacrylamide (respectively 1 and 2) and ethanolamine HOEtNH2 with acrylamide (3). Four other compounds corresponding to 1 and 2, but derived from sec-amines Me2NH (4 and 5) and Et2NH (6 and 7) have been prepared for the sake of comparison of the spectroscopic features. All compounds have been obtained by the well-known aza-Michael addition between an N-nucleophile and an activated vinyl group. The reaction in water between diethanolamine and acrylamide leading to 1 has been monitored in situ by Raman and NMR spectroscopy, both techniques confirming second order kinetics and giving values for kinetic constants in excellent agreement. The coordination ability of 1 and 2 towards Cu2+ in water has been studied by the Job's plot method. Spectroscopic data indicate that ligand 1 prevalently forms a 4:1 Ligand/Metal complex with a (N,O3) coordination set on the equatorial plane of Cu2+, whereas ligand 2, containing two amide functionalities bridged by a methylene group, appears able to form a 1:1 Ligand/Metal chelate species, again with a (N,O3) donor set around copper.

A Novel Cr(3+) Fluorescence Turn-On Probe Based on Rhodamine and Isatin Framework.

A novel turn-on fluorescent dye (E)-3',6'-bis(diethylamino)-2-((1-(naphthalen-2-ylmethyl)-2-oxoindolin-3-ylidene)amino)spiro[isoindoline-1,9'-xanthen]-3-one (RBNI) based on a rhodamine-isatin hybrid molecular architecture was synthesized by condensation of isatin derivative with rhodamine hydrazide. The dye RBNI is selective and sensitive for recognition of Cr(3+) ion in aqueous CH3CN media over other tested metal ions. The sensor shows large fluorescence enhancement upon complexation with Cr(3+) and simultaneous color change occurs from colorless to pink-red. Spectroscopic study predicted 1:1 binding stoichiometry between RBNI and Cr(3+) ion and this was again verified through ESI-MS (Electrospray Ionisation Mass Spectrometry). Detection limit of Cr(3+) ion by this dye was calculated to be 2.4 µM. Furthermore, the potential application of this dye for the monitoring of Cr(3+) ions in pond water and tap water samples was demonstrated.

A highly selective dual mode detection of Fe3+ ion sensing based on 1,5-dihydroxyanthraquinone in the presence of ß-cyclodextrin.

1,5-Dihydroxyanthraquinone (1,5-DHAQ) and in the presence of ß-cyclodextrin (ß-CD) has been used to find Fe(3+) ion in aqueous solution by UV-visible and fluorescence spectroscopy. The chromo-fluorogenic probe undergoes absorption and emission intensity enhancement upon binding to Fe(3+) ion in pH~7 aqueous solutions. The enhancement of the chemosensor probe is attributed to a 1:1 inclusion complex formation between ß-CD and 1,5-DHAQ, which has been utilized as the basis for selective detection of Fe(3+) ion. The chemosensors can be applied to the selectivity and sensitivity analysis which showed that the remarkable sensing limit of detection (LOD) was 7.3∗10(-7)M (ß-CD/1,5-DHAQ:Fe(3+)). The proposed chemosensors based on 1,5-DHAQ and in the presence of ß-CD has a good selectivity, sensitivity and potential application to the determination of Fe(3+) ion in environmental and biological systems.

Pyrazolone as a recognition site: Rhodamine 6G-based fluorescent probe for the selective recognition of Fe3+ in acetonitrile-aqueous solution.

Two novel Rhodamine-pyrazolone-based colorimetric off-on fluorescent chemosensors for Fe(3+) ions were designed and synthesized using pyrazolone as the recognition moiety and Rhodamine 6G as the signalling moiety. The photophysical properties and Fe(3+) -binding properties of sensors L(1) and L(2) in acetonitrile-aqueous solution were also investigated. Both sensors successfully exhibit a remarkably 'turn-on' response, toward Fe(3+) , which was attributed to 1: 2 complex formation between Fe(3+) and L(1) /L(2) . The fluorescent and colorimetric response to Fe(3+) can be detected by the naked eye, which provides a facile method for the visual detection of Fe(3+) .

A characterization study of resveratrol/sulfobutyl ether-ß-cyclodextrin inclusion complex and in vitro anticancer activity.

A resveratrol/sulfobutylether-ß-cyclodextrin inclusion complex was prepared using the freeze-drying method and characterized in solution through UV-vis spectroscopy, solubility phase studies and Job's plot methods. At the solid state it was characterized using the FTIR-ATR technique. Sulfobutylether-ß-cyclodextrin has a high affinity for the drug, and forms an inclusion complex with a 1:1 molar ratio both in solution and as a solid sample. It also has a high stability constant (Kc, 10,114 M(-1)). Complexation strongly increases the water solubility of resveratrol (from 0.03 mg/ml to 1.1 mg/ml, at 25 °C) and positively influences its in vitro anticancer activity which was observed on a human breast cancer cell line (MCF-7). In solid phase, FTIR-ATR revealed itself as being a useful technique in elucidating the complexation mechanism, which it did by emphasizing the functional groups involved in the activation of non-covalent "host-guest" interactions.