Solvatochromic and Fluorogenic Dyes as Environment-Sensitive Probes: Design and Biological Applications.

Fluorescent environment-sensitive probes are specially designed dyes that change their fluorescence intensity (fluorogenic dyes) or color (e.g., solvatochromic dyes) in response to change in their microenvironment polarity, viscosity, and molecular order. The studies of the past decade, including those of our group, have shown that these molecules become universal tools in fluorescence sensing and imaging. In fact, any biomolecular interaction or change in biomolecular organization results in modification of the local microenvironment, which can be directly monitored by these types of probes. In this Account, the main examples of environment-sensitive probes are summarized according to their design concepts. Solvatochromic dyes constitute a large class of environment-sensitive probes which change their color in response to polarity. Generally, they are push-pull dyes undergoing intramolecular charge transfer. Emission of their highly polarized excited state shifts to the red in more polar solvents. Excited-state intramolecular proton transfer is the second key concept to design efficient solvatochromic dyes, which respond to the microenvironment by changing relative intensity of the two emissive tautomeric forms. Due to their sensitivity to polarity and hydration, solvatochromic dyes have been successfully applied to biological membranes for studying lipid domains (rafts), apoptosis and endocytosis. As fluorescent labels, solvatochromic dyes can detect practically any type of biomolecular interactions, involving proteins, nucleic acids and biomembranes, because the binding event excludes local water molecules from the interaction site. On the other hand, fluorogenic probes usually exploit intramolecular rotation (conformation change) as a design concept, with molecular rotors being main representatives. These probes were particularly efficient for imaging viscosity and lipid order in biomembranes as well as to light up biomolecular targets, such as antibodies, aptamers and receptors. The emerging concepts to achieve fluorogenic response to the microenvironment include ground-state isomerization, aggregation-caused quenching, and aggregation-induced emission. The ground-state isomerization exploits, for instance, polarity-dependent spiro-lactone formation in silica-rhodamines. The aggregation-caused quenching uses disruption of the self-quenched dimers and nanoassemblies of dyes in less polar environments of lipid membranes and biomolecules. The aggregation-induced emission couples target recognition with formation of highly fluorescent dye aggregates. Overall, solvatochromic and fluorogenic probes enable background-free bioimaging in wash-free conditions as well as quantitative analysis when combined with advanced microscopy, such as fluorescence lifetime (FLIM) and ratiometric imaging. Further development of fluorescent environment-sensitive probes should address some remaining problems: (i) improving their optical properties, especially brightness, photostability, and far-red to near-infrared operating range; (ii) minimizing nonspecific interactions of the probes in biological systems; (iii) their adaptation for advanced microscopies, notably for superresolution and in vivo imaging.journal article2017 Feb 212017 01 09importe

Characterization of Coupled Ground State and Excited State Equilibria by Fluorescence Spectral Deconvolution

Fluorescence probes with multiparametric response based on the relative variation in the intensities of several emission bands are of great general utility. An accurate interpretation of the system requires the determination of the number, positions and intensities of the spectral components. We have developed a new algorithm for spectral deconvolution that is applicable to fluorescence probes exhibiting a two-state ground-state equilibrium and a two-state excited-state reaction. Three distinct fluorescence emission bands are resolved, with a distribution of intensities that is excitation-wavelength-dependent. The deconvolution of the spectrum into individual components is based on their representation as asymmetric Siano-Metzler log-normal functions. The application of the algorithm to the solvation response of a 3-hydroxychromone (3HC) derivative that exhibits an H-bonding-dependent excited-state intramolecular proton transfer (ESIPT) reaction allowed the separation of the spectral signatures characteristic of polarity and hydrogen bonding. This example demonstrates the ability of the method to characterize two potentially uncorrelated parameters characterizing dye environment and interactions

Characterizing Counterion-Dependent Aggregation of Rhodamine B by Classical Molecular Dynamics Simulations

The aggregation in a solution of charged dyes such as Rhodamine B (RB) is significantly affected by the type of counterion, which can determine the self-assembled structure that in turn modulates the optical properties. RB aggregation can be boosted by hydrophobic and bulky fluorinated tetraphenylborate counterions, such as F5TPB, with the formation of nanoparticles whose fluorescence quantum yield (FQY) is affected by the degree of fluorination. Here, we developed a classical force field (FF) based on the standard generalized Amber parameters that allows modeling the self-assembling process of RB/F5TPB systems in water, consistent with experimental evidence. Namely, the classical MD simulations employing the re-parametrized FF reproduce the formation of nanoparticles in the RB/F5TPB system, while in the presence of iodide counterions, only RB dimeric species can be formed. Within the large, self-assembled RB/F5TPB aggregates, the occurrence of an H-type RB-RB dimer can be observed, a species that is expected to quench RB fluorescence, in agreement with the experimental data of FQY. The outcome provides atomistic details on the role of the bulky F5TPB counterion as a spacer, with the developed classical FF representing a step towards reliable modeling of dye aggregation in RB-based materials

Ca-NIR: a ratiometric near-infrared calcium probe based on a dihydroxanthene-hemicyanine fluorophore.

Fluorescent calcium probes are essential tools for studying the fluctuation of calcium ions in cells. Herein, we developed Ca-NIR, the first ratiometric calcium probe emitting in the near infrared region. This probe arose from the fusion of a BAPTA chelator and a dihydroxanthene-hemicyanine fluorophore. It is efficiently excited with common 630-640 nm lasers and displays two distinct emission bands depending on the calcium concentration (Kd = ∼8 μM). The physicochemical and spectroscopic properties of Ca-NIR allowed for ratiometric imaging of calcium distribution in live cells.journal article2017 Jun 01imported"Supporting information" disponible sur le site de l'éditeu

Two-Dimensional Molecular Patterning by Surface-Enhanced Zn-Porphyrin Coordination

In this contribution, we show how zinc-5,10,15,20-meso-tetradodecylporphyrins (Zn-TDPs) self-assemble into stable organized arrays on the surface of graphite, thus positioning their metal center at regular distances from each other, creating a molecular pattern, while retaining the possibility to coordinate additional ligands. We also demonstrate that Zn-TDPs coordinated to 3-nitropyridine display a higher tendency to be adsorbed at the surface of highly oriented pyrolytic graphite (HOPG) than noncoordinated ones. In order to investigate the two-dimensional (2D) self-assembly of coordinated Zn-TDPs, solutions with different relative concentrations of 3-nitropyridine and Zn-TDP were prepared and deposited on the surface of HOPG. STM measurements at the liquid-solid interface reveal that the ratio of coordinated Zn-TDPs over noncoordinated Zn-TDPs is higher at the n-tetradecane/HOPG interface than in n-tetradecane solution. This enhanced binding of the axial ligand at the liquid/solid interface is likely related to the fact that physisorbed Zn-TDPs are better binding sites for nitropyridines.

Комплексоутворення калікс[4]аренгідроксиметил-фосфонової кислоти з триптофаном та N-aцетил-триптофанамідом

The Host-Guest complexation of calixarene hydroxymethylphosphonic acid with tryptophan and N-acetyltryptophan amide has been investigated by the RP HPLC method in H2O/MeCN (99/1) solution (column support Hypersil CN, UV-detector, λ = 254 nm). Adsorption of calixarene hydroxymethylphosphonic acid on the Hypersil CN surface has been studied. It has been found that hydroxymethylphosphonic acid is characterized by reversible sorption on the Hypersil CN surface. The binding constants (KA = 23000 M-1 and 39000 M-1 for tryptophan and N-acetyltryptophan amide, respectively) of the supramolecular complexes have been calculated from the ratio between the capacity factors k’ of the Guest and the calixarene hydroxymethylphosphonic acid Host concentration in the mobile phase. The Gibbs free energies of the tryptophan and N-acetyltryptophan amide complexes are -24.84 and -26.15 kJ/mol, respectively. The molecular modelling of calixarene hydroxymethylphosphonic acid and its complexes with tryptophan and N-acetyltryptophan amide (Hyper Chem, version 8, force field PM3) has indicated that the complexes are stabilized by hydrogen bonds, electrostatic, π-π, and solvatophobic interactions. The geometric parameters of the energy minimized calixarene macrocycle and its complexes with tryptophan and N-acetyltryptophan amide have been calculated. According to the calculations it has been shown that the Host-Guest complexation does not change the flattened-cone conformation of calixarene. Finally, the inverse correlation has been found between the KA values of the complexes and the Log P values of the guest molecules.Методом ОФ ВЭЖХ исследован процесс комплексообразования типа Хозяин-Гость каликсаренгидроксиметилфосфоновой кислоты с триптофаном и N-aцетил-триптофанамидом в растворе H2O/MeCN (99/1) (насадка Hypersil CN, УФ-детектор, λ = 254 нм). Исследовано взаимодействие каликсаренгидроксиметилфосфоновой кислоты с поверхностью хроматографической насадки Hypersil CN. Установлено, что каликсаренгидроксиметилфосфоновая кислота характеризуется обратимой сорбцией на поверхности Hypersil CN. Константы связывания супрамолекулярных комплексов (23000 M-1 и 39000 M-1 для триптофана и N-aцетилтриптофанамида, соответственно) были рассчитаны из соотношения меж- ду коэффициентом емкости k’ молекулы Гостя и концентрацией каликсаренгидроксиметилфосфо­новой кислоты Хозяина в подвижной фазе. Значения свободных энергий Гиббса комплексов каликса­ренгидроксиметилфосфоновой кислоты с триптофаном и N-aцетил-триптофанамидом составили -24.84 и -26.15 кДж/моль, соответственно. Проведено молекулярное моделирование каликсаренгидрокси- метилфосфоновой кислоты и ее комплексов с триптофаном и N-aцетилтриптофанамидом (Hyper Chem, версия 8, силовое поле PM3). Отмечается, что супрамолекулярные комплексы могут стабилизироваться водородными связями, а также электростатическими, π-π, и сольватофобными взаимодействиями. Рассчитаны геометрические параметры энергетически минимизированных структур каликсаренгидроксиметилфосфоновой кислоты и ее комплексов с триптофаном и N-aцетилтриптофанамидом. Согласно расчетам показано, что процесс комплексообразования не меняет конформацию макроциклического остова каликсарена. Установлено, что значения KA повышаются со снижением Log P молекул Гостей.Методом ОФ ВЕРХ досліджено процес комплексоутворення типу Господар-Гість каліксаренгідрокси- метилфосфонової кислоти з триптофаном та N-aцетилтриптофанамідом у розчині H2O/MeCN (99/1) (насадка Hypersil CN, УФ-детектор, λ = 254 нм). Досліджено взаємодію каліксаренгідроксиметилфосфонової кислоти з поверхнею хроматографічної насадки Hypersil CN. Встановлено, що каліксаренгідроксиметилфосфонова кислота характеризується оберненою сорбцією на поверхні Hypersil CN. Кон- станти зв’язування супрамолекулярних комплексів (23000 M-1 і 39000 M-1 для триптофану і N-aцетилтриптофанаміду, відповідно) були розраховані із співвідношення між коефіцієнтом ємкості k’ молекули Гостя і концентрацією каліксаренгідроксиметилфосфонової кислоти Господаря в рухомій фазі. Значення вільних энергій Гіббса комплексів каліксаренгідроксиметилфосфонової кислоти з триптофаном і N-aце- тилтриптофанамідом складає -24.84 і -26.15 кДж/моль, відповідно. Здійснено молекулярне моделювання каліксаренгідроксиметилфосфонової кислоти і її комплексів з триптофаном і N-aцетилтриптофанамідом (Hyper Chem, версія 8, силове поле PM3). Супрамолекулярні комплекси можуть стабілізуватись водневими зв’язками, а також електростатичними, π-π, і сольватофобними взаємодіями. Розраховані геометричні параметри энергетично мінімізованих структур каліксаренгідроксиметилфосфонової кис- лоти та її комплексів з триптофаном і N-aцетилтриптофанамідом. Показано, що значення KA зрос­тають зі зниженням Log P молекул субстратів, а процес комплексоутворення не змінює конформації макроциклічного кістяка каліксарену

Simultaneous computer-assisted assessment of mucosal and serosal perfusion in a model of segmental colonic ischemia

BACKGROUND: Fluorescence-based enhanced reality (FLER) enables the quantification of fluorescence signal dynamics, which can be superimposed onto real-time laparoscopic images by using a virtual perfusion cartogram. The current practice of perfusion assessment relies on visualizing the bowel serosa. The aim of this experimental study was to quantify potential differences in mucosal and serosal perfusion levels in an ischemic colon segment. METHODS: An ischemic colon segment was created in 12 pigs. Simultaneous quantitative mucosal and serosal fluorescence imaging was obtained via intravenous indocyanine green injection (0.2 mg/kg), using two near-infrared camera systems, and computer-assisted FLER analysis. Lactate levels were measured in capillary blood of the colonic wall at seven regions of interest (ROIs) as determined with FLER perfusion cartography: the ischemic zone (I), the proximal and distal vascularized areas (PV, DV), and the 50% perfusion threshold proximally and distally at the mucosal and serosal side (P50M, P50S, D50M, D50S). RESULTS: The mean ischemic zone as measured (mm) for the mucosal side was significantly larger than the serosal one (56.3 ± 21.3 vs. 40.8 ± 14.9, p = 0.001) with significantly lower lactate values at the mucosal ROIs. There was a significant weak inverse correlation between lactate and slope values for the defined ROIs (r = - 0.2452, p = 0.0246). CONCLUSIONS: Mucosal ischemic zones were larger than serosal zones. These results suggest that an assessment of bowel perfusion from the serosal side only can underestimate the extent of ischemia. Further studies are required to predict the optimal resection margin and anastomotic site

Photopolymerized micelles of diacetylene amphiphile: physical characterization and cell delivery properties:

A series of polydiacetylene (PDA) - based micelles were prepared from diacetylenic surfactant bearing polyethylene glycol, by increasing UV-irradiation times. These polymeric lipid micelles were analyzed by physicochemical methods, electron microscopy and NMR analysis. Cellular delivery of fluorescent dye suggests that adjusting the polymerization state is vital to reach the full in vitro potential of PDA-based delivery system

Non-coordinating anions assemble cyanine amphiphiles into ultra-small fluorescent nanoparticles

A non-coordinating anion, fluorinated tetraphenylborate, assembles specially designed cationic cyanine amphiphiles into 7–8 nm fluorescent nanoparticles that are >40-fold brighter than a single cyanine dye. This kind of anion, combining hydrophobic and electrostatic forces in aqueous media, constitutes promising building blocks in the self-assembly of functional nanomaterials