Crystal structure, Hirshfeld surface analysis and computational study of a rhodamine B-salicyl-aldehyde Schiff base derivative.

The mol-ecular structure of the title compound {systematic name: 3',6'-bis(di-ethyl-amino)-2-[(2-hy-droxy-benzyl-idene)amino]-spiro-[isoindoline-1,9'-xan-then]-3-one}, C35H36N4O3 or RbSa, can be seen as being composed of two parts sharing a central quaternary carbon atom. Both the xanthene and iso-indole moieties are nearly planar: 14 atoms in the former moiety show an r.m.s. deviation of 0.0411 Šand eleven atoms in the latter moiety show an r.m.s. deviation of 0.0545 Å. These two planes are almost perpendicular to each other, the angle between the mean planes being 87.71 (2)°. The title compound appears to be in its enol form. The corresponding H atom was located and freely refined at a distance of 1.02 (3) Šfrom the O atom and 1.72 (2) Šfrom the N atom. The strong intra-molecular hydrogen bond O-H⋯N bridging the hydroxyl group and its neighboring nitro-gen atom forms an S(6) graph-set motif. Apart from the intra-molecular O-H⋯N hydrogen bond, C-H⋯O inter-actions are observed between two neighbouring RbSa mol-ecules related by an inversion center. The C-O donor-acceptor distance is 3.474 (2) Å. Moreover, C-H⋯π inter-actions are observed between the C-H bond of one of the ethyl groups and the centroid of the benzene ring of the iso-indole moiety. The C⋯centroid distance is 3.8191 (15) Å. No π-π inter-actions are observed in the crystal structure as the shortest distance between ring centroids is more than 4 Å. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H, C⋯H/H⋯C, O⋯H/H⋯O and N⋯H/H⋯N inter-actions. DFT calculations at the CAM-B3LYP/6-31 G(d) level were carried out to gain a better understanding of the relative energies and the tautomerization process between two possible conformers (keto and enol), as well as the transition state of the title compound.

Synthesis and Characterization of ROSA Dye - A Rhodamine B-type Fluorophore, Suitable for Bioconjugation and Fluorescence Studies in Live Cells.

BACKGROUND: Herein we report the multigram-scale synthesis, characterization and application of a rhodamine B-based fluorophore (ROSA) suitable for fluorescent studies in biological applications. This fluorophore is devoid of rhodamine spirolactone formation and furthermore characterized by a high molar extinction coefficient (ϵ=87250 ± 1630 M-1cm-1) and quantum yield (φ) of 0.589 ± 0.070 in water. Reported here is also the application of ROSA towards synthesis of a ROSA-PEG-GRGDS-NH2 fluorescent probe suitable for live cell imaging of αvß3 integrins for in vitro assays. OBJECTIVES: The main objective of this study is to efficiently prepare rhodamine B derivative, devoid of spirolactone formation that would be suitable for bioconjugation and subsequent bioimaging. METHODS: Rhodamine B was transformed into rhodamine B succinimide ester (RhoB-OSu) using N-hydroxysuccinimide. RhoB-OSu was further coupled to sarcosine to obtain rhodamine Bsarcosine dye (ROSA) in good yield. The ROSA dye was then coupled to a αvß3 integrin binding sequence using standard solid-phase conditions. Resulting ROSA-PEG-GRGDS-NH2 probe was used to image integrins on cancer cells. RESULTS: The rhodamine B-sarcosine dye (ROSA) was obtained in multigram scale in good total yield of 47%. Unlike rhodamine B, the ROSA dye does not undergo pH-dependent spirolactone/spirolactam formation as compared with rhodamine B-glycine. It is also characterized by excellent quantum yield (φ) of 0.589 ± 0.070 in water and high molar extinction coefficient of 87250 ± 1630 M-1cm-1. ROSA coupling to the RGD-like peptide was proved to be efficient and straightforward. Imaging using standard filters on multimode plate reader and confocal microscope was performed. The αvß3 integrins present on the surface of live WM-266-4 (melanoma) and MCF- 7 (breast cancer) cells were successfully imaged. CONCLUSION: We successfully derivatized rhodamine B to create an inexpensive, stable and convenient to use fluorescent probe. The obtained derivative has excellent photochemical properties and it is suitable for bioconjugation and many imaging applications.

TBET-based ratiometric fluorescent probe for Hg2+ with large pseudo-Stokes shift and emission shift in aqueous media and intracellular colorimetric imaging in live Hela cells.

The detection of Hg2+ in biological systems and its imaging is of highly importance. In this work, a novel ratiometric fluorescence probe is developed based on through-bond energy transfer (TBET) with a 2-(2-hydroxyphenyl)benzoxazole (HBO) as donor and a Rhodamine derivative-Hg conjugate (RDM-Hg) as acceptor. Hg2+ weakens the fluorescence of HBO at 430 nm and meanwhile interacts with Rhodamine B derivative to form a fluorescent conjugate (RDM-Hg) giving rise to emission at 597 nm with a 167 nm red-shift. Further, the difference 282 nm between the donor absorption (315 nm) and the accepter emission (597 nm) for 1+Hg2+ is comparable to the highest value of the Stokes shift (282 nm) reported earlier for other reported TBET-based cassette. Through-bond energy transfer from HBO to RDM-Hg is triggered by Hg2+ resulting in concentration-dependent variation of fluorescence ratio I597/I430. A linear calibration of I597/I430versus Hg2+ concentration is obtained within 0-5 µM, along with the lowest detection limit being found to be as low as 1.31 × 10-9 mol·L-1 (~ 0.26 ppb) for Hg2+. This feature is further demonstrated by colorimetric imaging of test strip and intracellular Hg2+. On the other hand, the HBO/RDM TBET sensing system is characterized by a combination of high sensitivity and selectivity. The present study provides an approach for further development of ratiometric probes dedicated to selective in vitro or in vivo sensing some species of biologically interest.

A Rhodamine B-based fluorescent probe for imaging Cu2+ in maize roots.

A new Rhodamine B-based fluorescent probe (RBO) is successfully designed and synthesized, which is a higher selective and sensitive chemosensor for Cu2+ than other ions. Under physiological conditions (pH = 7.0), the non emission RBO displays a rapid fluorescence increase together with a color change after addition of Cu2+ and the detection limit is down to 28nM, which can clearly illustrate the distribution of Cu2+ with the help of laser scanning confocal microscope in plant tissues. Eventually, it confirmed that the Cu2+ accumulates mostly in the vascular cylinder and very less in the epidermal cells of maize roots, which is important to understand how the plants take up, transport and store in the Cu2+.

Rhodamine-Functionalized Graphene Quantum Dots for Detection of Fe(3+) in Cancer Stem Cells.

A turn-on orange-red fluorescent nanosensor based on rhodamine B derivative-functionalized graphene quantum dots (RBD-GQDs) has been successfully synthesized for Fe(3+) detection with high sensitivity and selectivity. By connecting with GQDs, the water solubility, sensitivity, photostability, and biocompatibility of RBD are drastically improved. The most distinctive feature of the RBD-GQDs, which sets them apart from other previously reported fluorophores or GQDs, is that they with the detection limits as low as 0.02 µM are demonstrated as a Fe(3+) turn-on fluorescent nanosensor in cancer stem cells. Fe(3+) binding to such GQDs (RBD-GQDs-Fe(3+)) with orange-red fluorescence of 43% quantum yield were demonstrated to be the biomarkers for cancer stem cell imaging.

Synthesis and evaluation of a new Rhodamine B and Di(2-picolyl)amine conjugate as a highly sensitive and selective chemosensor for Al3+ and its application in living-cell imaging.

A new Rhodamine B derivative (RBDPA), namely, N(1)-(2-(3',6'-bis(diethylamino)-3-oxospiro[isoindoline-1,9'-xanthen]-2-yl)ethyl)-N(4),N(4)-bis(pyridin-2-ylmethyl)succinamide, was designed, synthesized and structurally characterized to develop a chemosensor. The studies show that RBDPA exhibits high sensitivity and selectivity toward Al(3+) among many other metal cations in an ethanol/H2O (1:1, v/v, pH=7.2, HEPES buffer, 0.1mM) solution. Fluorescence microscopy experiments further demonstrate that RBDPA can be used as a fluorescent probe to detect Al(3+) in living cells.

A new Rhodamine B-based 'on-off' chemical sensor with high selectivity and sensitivity toward Fe(3+) and its imaging in living cells.

A new fluorescent chemosensor based on a Rhodamine B and pyrrole conjugate (RBPY) has been designed and synthesized. UV-vis absorption and fluorescence spectroscopic studies show that RBPY exhibits a high selectivity and sensitivity toward Fe(3+) among many other metal cations in a MeOH/H2O solution (3:2, v/v, pH 7.10, HEPES buffer, 0.1mM) by forming a 1:1 complex with Fe(3+). Furthermore, results reveal that the formation of the RBPY-Fe(3+) complex is fully reversible in the presence of sulfide anions and could also be used as an efficient sensor for S(2-). Importantly, fluorescence microscopy experiments further demonstrated that RBPY can be utilized as a fluorescent probe for the detection of Fe(3+) in human liver (L-02) cells.

A highly selective fluorescent probe for Cu2+ based on rhodamine B derivative.

A new fluorescent probe 1 for Cu(2+) based on a rhodamine B derivative was designed and synthesized. Probe 1 displays high sensitivity toward Cu(2+) and about a 37-fold increase in fluorescence emission intensity is observed upon the addition of 10 equiv. Cu(2+) in 50% water/ethanol buffered at pH 7.10. Besides, upon binding Cu(2+) a remarkable color change from colorless to pink was easily observed by the naked eyes. The reversible dual chromo- and fluorogenic response toward Cu(2+) is likely due to the chelation-induced ring-opening of rhodamine spirolactam. The linear response range covers a concentration range of Cu(2+) from 8.0×10(-7) to 1.0×10(-4) mol/L and the detection limit is 3.0×10(-7) mol/L. Except Co(2+), the probe exhibits high selectivity for Cu(2+) over a large number of cations such as alkaline, alkaline earth and transitional metal ions. The accuracy and precision of the method were evaluated by the analysis of the standard reference material, copper in water (1.0 mol/L HNO3). The proposed probe has been used for direct measurement of Cu(2+) content in river water samples and imaging of Cu(2+) in living cells with satisfying results, which further demonstrates its value of practical applications in environmental and biological systems.

Analytical method to evaluate chelating capacity of constituents in decoction of Chinese materia medica with free iron ions / 中草药

Objective: To establish the in vitro screening method for determining what kinds of Chinese materia medica (CMM) and which main constituents in the medicine used for the treatment of Alzheimer's disease, Parkinson's disease, and osteoporosis can chelate with free iron ions (Fe3+) and evaluating the chelating strength. Methods: Based on the catalytic effect of Fe3+ on the spirolactam (nonfluorescence) to ring-open amide reaction (fluorescence), the catalytic spectrophotometric method was established to determine the free Fe3+ in the decoction of CMM, by adding a certain amount of iron ion and determinig the chelating level to evaluate the chelating strength of the constituents in CMM. Results: The chelating strength of kidney-tonifying CMM is stronger. The catalytic spectrophotometric method could be used to determine the free Fe3+ in the decoction of CMM and the linearity was good in the range of 1.68-22.4 mg/L, r = 0.999 0. The average recovery was between 90.45% and 104.11% with RSD < 5%. Conclusion: This method can be used to evaluate the chelating capacity of constituents in CMM with Fe3+.