Solvent effect on the relative quantum yield and fluorescence quenching of a newly synthesized coumarin derivative

Fluorescent bioinspired albumin/polydopamine nanoparticles and their interactions with Escherichia coli cells

Inspired by the eumelanin aggregates in human skin, polydopamine nanoparticles (PDA NPs) are promising nanovectors for biomedical applications, especially because of their biocompatibility. We synthesized and characterized fluorescent PDA NPs of 10-25 nm diameter based on a protein containing a lysine-glutamate diad (bovine serum albumin, BSA) and determined whether they can penetrate and accumulate in bacterial cells to serve as a marker or drug nanocarrier. Three fluorescent PDA NPs were designed to allow for tracking in three different wavelength ranges by oxidizing BSA/PDA NPs (Ox-BSA/PDA NPs) or labelling with fluorescein 5-isothiocyanate (FITC-BSA/PDA NPs) or rhodamine B isothiocyanate (RhBITC-BSA/PDA NPs). FITC-BSA/PDA NPs and RhBITC-BSA/PDA NPs penetrated and accumulated in both cell wall and inner compartments of Escherichia coli (E. coli) cells. The fluorescence signals were diffuse or displayed aggregate-like patterns with both labelled NPs and free dyes. RhBITC-BSA/PDA NPs led to the most intense fluorescence in cells. Penetration and accumulation of NPs was not accompanied by a bactericidal or inhibitory effect of growth as demonstrated with the Gram-negative E. coli species and confirmed with a Gram-positive bacterial species (Staphylococcus aureus). Altogether, these results allow us to envisage the use of labelled BSA/PDA NPs to track bacteria and carry drugs in the core of bacterial cells.

Molecular machines stimulate intercellular calcium waves and cause muscle contraction

Intercellular calcium waves (ICW) are complex signalling phenomena that control many essential biological activities, including smooth muscle contraction, vesicle secretion, gene expression and changes in neuronal excitability. Accordingly, the remote stimulation of ICW could result in versatile biomodulation and therapeutic strategies. Here we demonstrate that light-activated molecular machines (MM)-molecules that perform mechanical work on the molecular scale-can remotely stimulate ICW. MM consist of a polycyclic rotor and stator that rotate around a central alkene when activated with visible light. Live-cell calcium-tracking and pharmacological experiments reveal that MM-induced ICW are driven by the activation of inositol-triphosphate-mediated signalling pathways by unidirectional, fast-rotating MM. Our data suggest that MM-induced ICW can control muscle contraction in vitro in cardiomyocytes and animal behaviour in vivo in Hydra vulgaris. This work demonstrates a strategy for directly controlling cell signalling and downstream biological function using molecular-scale devices.

Oxyethylated Fluoresceine-(thia)calix[4]arene Conjugates: Synthesis and Visible-Light Photoredox Catalysis in Water-Organic Media

Fluorescent derivatives attract the attention of researchers for their use as sensors, photocatalysts and for the creation of functional materials. In order to create amphiphilic fluorescent derivatives of calixarenes, a fluorescein derivative containing oligoethylene glycol and propargyl groups was obtained. The resulting fluorescein derivative was introduced into three different (thia)calix[4]arene azide derivatives. For all synthesized compounds, the luminescence quantum yields have been established in different solvents. Using UV-visible spectroscopy, dynamic light scattering, as well as transmission and confocal microscopy, aggregation of macrocycles was studied. It was evaluated that calixarene derivatives with alkyl substituents form spherical aggregates, while symmetrical tetrafluorescein-containing thiacalix[4]arene forms extended worm-like aggregates. The macrocycle containing tetradecyl fragments was found to be the most efficient in photoredox ipso-oxidation of phenylboronic acid. In addition, it was shown that in a number of different electron donors (NEt₃, DABCO and iPr₂EtN), the photoredox ipso-oxidation proceeds best with triethylamine. It has been shown that a low molecular weight surfactant Triton-X100 can also improve the photocatalytic abilities of an oligoethylene glycol fluorescein derivative, thus showing the importance of a combination of micellar and photoredox catalysis.

Synthesis of blue light emitting heterocycles via cyclization of 2-pyridine derived 4-azido-r1,2,3-triazoles

An efficient synthesis of 2-pyridine derived 4-azido-1,2,3-triazoles was elaborated using the corresponding dichlorodiazadienes as precursors. The reaction of the prepared 2-azine substituted diazadienes with sodium azide permits the preparation of target triazoles isolated in up to 92% yield. Subsequent thermal cyclization was studied. Elimination of molecular nitrogen promoted the cyclization of nitrene at the azine nitrogen. As a result, a family of 2H-[1,2,3]triazolo[4',5':3,4]pyrazolo[1,5-a]pyridin-5-ium-4-ides was prepared. The synthesized compounds are members of a new heterocyclic system. Moreover, these compounds are new attractive blue light emitting molecules.

Re-usage of the Waste Drug as Molecular Chemosensor for Fe3+ Ion: Application towards Fluorescent Ink

Herein, a novel notion is used to reuse an expired drug namely Telmisartan (Sensor 2) to optically sense the Fe³⁺ metal ion. Direct re-usage of the drug avoided wearisome procedures of synthesis, hence proved the method as simple and economic. Sensor 2 found highly stable in the temperature range 25-75 °C. Relative fluorescence was almost the same even after 35 days of observation. There were no significant changes in wavelength even after adding different concentrations of FeCl₃, which shows the high stability of the compound. The value of Limit of Detection (LOD) observed was 34.2 nM. FTIR studies confirmed the presence of carboxylic group. The method of fluorescence quenching was used to detect the Fe³⁺ ion. The association between Sensor 2 and Fe³⁺ was analyzed using Benesi-Hildebrand relation. Positive deviation from the linearity of S-V plots suggested that the quenching was not purely dynamic. Further, this deviation was analyzed by the sphere of action quenching model. To investigate whether the quenching is diffusion limited, we applied the finite sink approximation model and deduced that quenching is due to both static and dynamic processes. Due to the high fluorescence property of the molecule, it was successfully tested to be used as fluorescent ink.

Evaluation of polyvinylpyrrolidone and block copolymer micelle encapsulation of serine chlorin e6 and chlorin e4 on their reactivity towards albumin and transferrin and their cell uptake

Encapsulation of porphyrinic photosensitizers (PSs) into polymeric carriers plays an important role in enhancing their efficiency as drugs in photodynamic therapy (PDT). Porphyrin aggregation and low solubility as well as the preservation of the advantageous photophysical properties pose a challenge on the design of efficient PS-carrier systems. Block copolymer micelles (BCMs) and polyvinylpyrrolidone (PVP) are promising drug delivery vehicles for physical entrapment of PSs. BCMs exhibit enhanced dynamics as compared to the less flexible PVP network. In the current work the question is addressed how these different dynamics affect PS encapsulation, release from the carrier, reaction with serum proteins, and cellular uptake. The porphyrinic compounds serine-amide of chlorin e6 (SerCE) and chlorin e4 (CE4) were used as model PSs with different lipophilicity and aggregation properties. ¹H NMR and fluorescence spectroscopy were applied to study their interactions with PVP and BCMs consisting of Kolliphor P188 (KP). Both chlorins were well encapsulated by the carriers and had improved photophysical properties. Compared to SerCE, the more lipophilic CE4 exhibited stronger hydrophobic interactions with the BCM core, stabilizing the system and preventing exchange with the surrounding medium as was shown by NMR NOESY and DOSY experiments. PVP and BCMs protected the encapsulated chlorins against interaction with human transferrin (Tf). However, SerCE and CE4 were released from BCMs in favor of binding to human serum albumin (HSA) while PVP prevented interaction with HSA. Fluorescence spectroscopic studies revealed that HSA binds to the surface of PVP forming a protein corona. PVP and BCMs reduced cellular uptake of the chlorins. However, encapsulation into BCMs resulted in more efficient cell internalization for CE4 than for SerCE. HSA significantly lowered both, free and carrier-mediated cell uptake for CE4 and SerCE. In conclusion, PVP appears as the more universal delivery system covering a broad range of host molecules with respect to polarity, whereas BCMs require a higher drug-carrier compatibility. Poorly soluble hydrophobic PSs benefit stronger from BCM-type carriers due to enhanced bioavailability through disaggregation and solubilization allowing for more efficient cell uptake. In addition, increased PS-carrier hydrophobic interactions have a stabilizing effect. For more hydrophilic PSs, the main advantage of polymeric carriers like PVP or poloxamer micelles lies in their protection during the transport through the bloodstream. HSA binding plays an important role for drug release and cell uptake in carrier-mediated delivery to the target tissue.

Utility of Europium ion characteristic peak for quantitation of Fenoterol hydrobromide and Salmeterol xinafoate in different matrices; application to stability studies

A simple selective luminescent dependent approach was established for quantitation of two selective β₂ agonists namely; Fenoterol hydrobromide (FEN) and Salmeterol xinafoate (SAL). This approach utilizes the capability of the cited drugs to undergo a complexation reaction with Europium ion (Eu³⁺) in the presence of 1,10-phenanthroline as a co-ligand. The resultant complex leads to a hypersensitive transition and enhancement of the Eu³⁺ emission peak at 615nm (279nm excitation). Under the optimized conditions, the rectilinear concentration plots of both drugs were (70-1500ngmL^-1) and (100-2000ngmL^-1) with limit of quantitation 51.3 and 84.4ngmL^-1 for FEN and SAL, respectively. The luminescence properties of the complex and its optimum formation conditions were carefully investigated according to the regulations of ICH and the method was successfully applied in plasma. The good accuracy and selectivity of the suggested method allowed extending the proposed protocol into stability study of the cited drugs.

Hyperbranched conjugated polymers containing 1,3-butadiene units: metal-free catalyzed synthesis and selective chemosensors for Fe3+ ions

Hyperbranched polymers containing 1,3-butadiene units in main chain were synthesized by transition-metal-free catalysis and investigated as chemosensors for Fe³⁺ ions.

Synthesis of platinum-containing poly(phenyleneethynylene)s having various chromophores: aggregation and optical properties

Various platinum-containing phenylene–ethynylene–arylene polymers were synthesized, and the relationships between the optical properties and aggregation behaviour were examined.