A red emissive donor-acceptor fluorophore as protein sensor: Synthesis, characterization and binding study

In situ generation of a Zwitterionic fluorescent probe for detection of human serum albumin protein

In this article, a new approach for human serum albumin selective fluorophore design has been reported. The fluorophore reported here comprises a substituted phenol donor and a cationic benzo[e]indolium acceptor connected with a π bond. Originally, the cationic fluorophore did not bind with human serum albumin. Upon deprotonation of the phenolic-OH by a water molecule the cationic form was transformed into an active zwitterionic form. Spectroscopic studies and theoretical calculations revealed that the new active form remained in a zwitterionic state in neutral aqueous solution, and it formed a strong supramolecular complex with human serum albumin. The spontaneous complexation resulted multi-fold increase of fluorescence intensity which increased linearly with the concentrations of the protein, thus giving an analytical tool to monitor human serum albumin in aqueous samples. We believe, this simple strategy applied on appropriate fluorogenic scaffolds would prove useful to develop new and improved turn-on fluorescent probes for pH regulated biological applications.

Evaluating the Merit of a Syringol Derived Fluorophore as a Charge Transfer Probe for Detection of Serum Albumins

In this article a syringol-π-benz[e]indolium based donor-acceptor fluorophore has been reported. The fluorophore shows a solvent polarity dependent change in the absorption and emission spectra in solution. A combined spectroscopic and time dependent density functional theory (TDDFT) studies reveal higher dipole moment of the fluorophore in the excited state, resulting positive solvatochromism. In physiological pH, the phenol group in the fluorophore is easily deprotonated owing to the electron pulling effect of the substituents. Consequently, the phenolate (PhO-) becomes a strong active donor in the new donor-acceptor pair. In aqueous solution, the new phenolate fluorochrome shows negligible fluorescence due to energy loss via non-radiative pathways from the low-lying polar excited states. The fluorochrome can detect human and bovine serum albumins in physiological buffer solution with high selectivity. The underlying mechanism of human serum albumin (HSA) detection was estimated to be strong (1.46 × 105 M-1, ΔG = -7.05 kcal/mol) supramolecular complexation between the fluorophore and albumin in hydrophobic binding site III-B. The linear relationship between fluorescence intensity and HSA concentration extends from 40 mg/L to an impressive upper limit (540 mg/L), thereby opening an opportunity for albumin detection in a broad range of health conditions. The practical applicability of the fluorophore was tested in spiked urine samples and a good correlation was observed between fluorescence intensity and the concentration of human serum albumin in neutral aqueous samples.

Dual luminescent charge transfer probe for quantitative detection of serum albumin in aqueous samples

In diagnostic medicine serum albumin is considered as an important biomarker for assessment of cardiovascular functions and diagnosis of renal diseases. Herein, we report a novel donor-π-π-acceptor fluorophore for selective detection of serum albumin in urine samples. In our design, a phenolic donor was conjugated with a tricyanofuran (TCF) acceptor through a dimethine bridge via a simple condensation reaction. The stereoelectronic effects of the incorporated methoxy (-OCH3) groups and the TCF moiety-in conjunction with the extended π-electron conjugation-led to dual red and NIR-I absorption/emission in water. Moreover, due to superior electron transfer between a phenolate donor and the TCF acceptor and the subsequent energy decay from the charge transfer states, the fluorophore displayed negligible fluorescence emission in water and other polar solvents. Consequently, we have been able to utilize the fluorophore for quantitative estimation of serum albumin both in the red (<700 nm) and NIR-I (700-900 nm) regions of the electromagnetic spectrum with excellent reproducibility. The fluorophore selectively recognized human serum albumin over other proteins and enzymes with a limit of detection of 10 mg/L and 20 mg/L in simulated urine samples at red and NIR-I emission window of the spectrum, respectively. By molecular docking analysis and experimental displacement assays, we have shown that the selective response of the fluorophore toward human serum albumin is due to tighter supramolecular complexation between the fluorophore and the protein at subdomain IB, and the origin of the NIR-I (780 nm) emission was attributed to a twisted conformer of phenolate-π-π-TCF system in aqueous solution. These findings indicate that the fluorophore could be utilized for quantitative detection of human serum albumin in urine samples for clinical diagnosis of albuminuria.

Selective Detection of Human Serum Albumin by Near Infrared Emissive Fluorophores: Insights into Structure-property Relationship

Two donor-acceptor fluorophores were prepared and tested for quantitative determination of HSA in aqueous samples. Fluorophores were non-emissive in polar solvents due to energy loss via non-radiative decays. Complexation of the fluorophores with HSA resulted multi-fold enhancement of emission in the red-near infrared (NIR) region. The emission intensity was linearly correlated to the amount of protein in the solution, which enabled us to develop calibration graphs for quantitative estimation of HSA in synthetic urine samples. Between the two fluorophores, the methoxy substituted fluorophore 1 selectively recognized HSA. It exhibited remarkable fluorescence enhancement with HSA over bovine serum albumin (BSA) and other globular proteins. The selective sensing aptitude of 1 was attributed to its restricted motions in the protein's microenvironment due to multiple non-covalent interactions, preventing energy loss by radiationless decay. The different recognition properties of the fluorophores were estimated by the steady-state fluorescence and molecular docking studies. These findings indicate that this class of fluorophores can be useful for quantitative estimation of HSA in biological urine and blood samples in clinical practice.

First representatives of functionalized D–π–A chromophores containing a tunable hydroxytricyanopyrrole (HTCP) acceptor and N,N-disubstituted aminophenyl donor

D–π–A chromophores based on a hydroxytricyanopyrrole (HTCP) acceptor and N,N-disubstituted aminophenyl donor are described for the first time. Their absorption properties were thoroughly studied.