Environmentally sensitive fluorescence of the topical retinoid adapalene

Intrinsic fluorescence of drugs brings valuable information on their localization in the organism and their interaction with key biomolecules. In this work, we investigate the absorption and emission properties of the topical retinoid adapalene in different solvents and biological media. While the UVA/UVB absorption band does not exhibit any significant solvent-dependent behavior, a strong positive solvatochromism is observed for the emission. These results are in line with molecular modeling and simulations that show the presence of two quasi-degenerate states, i.e., a local π-π* and an intermolecular charge-transfer (ICT) state. However, molecular modeling also revealed that, whatever the solvent, at the corresponding equilibrium geometry the lowest and emissive excited state is the local π-π*. Finally, the potential of adapalene to act as a biological probe is demonstrated using albumin, DNA and micelles.

A symmetric bis(salamo)-like fluorescent chemosensor for identifying HCO3- and CO32- and its application

In this work, we successfully designed and synthesized a methoxydisubstituted bis(salamo)-type fluorescent chemical sensor BS, which can be applied as a highly sensitive and selective fluorescence probe for HCO3- and CO32- detection. The LODs of HCO3- and CO32- were experimentally calculated to be 5.4068 × 10-8 M and 4.4517 × 10-8 M, respectively. After relevant experiments, the sensing mechanism was investigated. Moreover, the application of the sensor in practice is explored, and the sensor BS can be loaded on portable test strips for ion detection. In the field of ion detection, salamo-like chemical sensors have been less studied compared to other sensor molecules, especially for the recognition and detection of anions. Therefore, this study will to some extent contribute to expanding the application of salamo-like compounds.

"Click" Reaction-Mediated Silk Fibroin-Functionalized Thiol-Branched Graphene Oxide Quantum Dots for Smart Sensing of Tetracycline

The abuse of tetracycline (TC) antibiotics causes the accumulation of their residue in the environment, which has an irreversible impact on food safety and human health. In light of this, it is vital to offer a portable, quick, efficient, and selective sensing platform to detect TC instantly. Herein, we have successfully developed a sensor using silk fibroin-decorated thiol-branched graphene oxide quantum dots through a well-known thiol-ene click reaction. It is applied to ratiometric fluorescence sensing of TC in real samples in the linear range of 0-90 nM, with the detection limit of 49.69, 47.76, 55.25, 47.90, and 45.78 nM for deionized water, chicken sample, fish sample, human blood serum, and honey sample, respectively. With the gradual addition of TC to the liquid media, the sensor develops a synergetic luminous effect in which the fluorescence intensity of the nanoprobe steadily declines at 413 nm, while the intensity of a newly emerging peak increases at 528 nm, maintaining a ratio that is dependent on the analyte concentration. The increase of luminescence properties in the liquid media is clearly visible by naked eyes in the presence of 365 nm UV light. The result helps us in building a filter paper strip-based portable smart sensor using an electric circuit comprising a 365 nm LED (light-emitting diode) powered by a mobile phone battery which is attached just below the rear camera of a smartphone. The camera of the smartphone captures the color changes that occur throughout the sensing process and translates into readable RGB data. The dependency of color intensity with respect to the concentration of TC was evaluated by deducing a calibration curve from where the limit of detection was calculated and found to be 0.125 μM. These kinds of gadgets are important for the possible real-time, on-the-spot, quick detection of analytes in situations where high-end approaches are not easily accessible.

Subtle Ligand Spacer Change in 2D Metal-Organic Framework Sheets for Dual Turn-On/Turn-Off Sensing of Acetylacetone and Turn-On Sensing of Water in Organic Solvents

Metal-organic framework (MOF)-based sensors for the detection of various analyte molecules has been a subject of absolute importance. However, most of these sensors rely on the turn-off (quenching) transduction response, while those reporting turn-on response are very rare. In this article, we have synthesized two new MOF-based sensors, {[Zn₂(oxdz)₂(tpbn)]·14H₂O}_n (1) and {[Zn₂(oxdz)₂(tpxn)]·10H₂O·2C₂H₅OH}_n (2), via the self-assembly of Zn(II) metal ions, a fluorogenic oxdz^2- linker, and bis(tridentate) ligands (tpbn and tpxn) under ambient conditions. Their formation from such a self-assembly process has been evaluated on the basis of the geometry around the five-coordinated Zn(II), preferential meridional binding of the bis(tridentate) ligands, and diverse binding of the carboxylate groups in oxdz^2-. Although 1 and 2 are isostructural, a difference in the transduction mechanism for the sensing of acetylacetone in organic solvents (turn-on for 1 and turn-off for 2) is observed and can be attributed to the spacer in the bis(tridentate) ligands. We have demonstrated the competing effect of the nonradiative interactions and photoinduced electron transfer toward the sensing mechanism. The results are well-supported by the Fourier transform infrared spectroscopy study, intensity versus concentration plots, spectral overlap measurements, time-resolved fluorescence studies, and MM2 and density functional theory calculations. Furthermore, we have showcased the utilization of 1 for the sensing of trace amounts of water in organic solvents.

β-Cyclodextrin-capped ZnO-doped carbon dot as an advanced fluorescent probe for selective detection of dopamine

Selective and sensitive detection of dopamine in presence of other interfering biomolecules using β-cyclodextrin-capped ZnO-doped carbon dot.

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.

Domain-Specific Stabilization of Structural and Dynamic Responses of Human Serum Albumin by Sucrose

Background:

Human Serum Albumin (HSA) is the most abundant protein present in human blood plasma. It is a large multi-domain protein with 585 amino acid residues. Due to its importance in human body, studies on the interaction of HSA with different external agent is of vital interest. The denaturation and renaturation of HSA in presence of external agents are of particular interest as they affect the biological activity of the protein.

Objective:

The objective of this work is to study the domain-specific and overall structural and dynamical changes occurring to HSA in the presence of a denaturing agent, urea and a renaturing agent, sucrose.

Methods:

In order to carry out the domain-specific studies, HSA has been tagged using N-(7- dimethylamino-4-methylcoumarin-3-yl) iodoacetamide (DACIA) at Cys-34 of domain-I and pnitrophenyl coumarin ester (NPCE) at Tyr-411 site in domain-III, separately. Steady-state absorption, emission and solvation dynamic measurements have been carried out in order to monitor the domain-specific alteration of HSA caused by the external agents. The overall structural change of HSA have been monitored using circular dichroism spectroscopy.

Results:

The α-helicity of HSA was found to decrease from 65% to 11% in presence of urea and was found to further increase to 25% when sucrose is added, manifesting the denaturing and renaturing effects of urea and sucrose, respectively. The steady state studies show that domain-III is more labile towards denaturation as compared to domain-I. The presence of an intermediate state is observed during the denaturation process. The stabilization of this intermediate state in presence of sucrose is attributed as the reason for the stabilization of HSA by sucrose. From solvation dynamics studies, it could be seen that the solvation time of DACIA inside domain-I of HSA decreases and increases regularly with increasing concentrations of urea and sucrose, respectively, while in the case of NPCE-tagged domain-III, the effect of sucrose on solvation time is evident only at high concentrations of urea.

Conclusion:

The denaturing and renaturing effects of urea and sucrose could be clearly seen from the steady state studies and circular dichroism spectroscopy measurements. A regular change in solvation time could only be observed in the case of domain-I and not in domain-III. The results indicate that the renaturing effect of sucrose on domain-III is not very evident when protein is in its native state, but is evident in when the protein is denatured.</P>

Interaction rule and mechanism of perfluoroalkyl sulfonates containing different carbon chains with human serum albumin

All three PFASs bind to HSA mainly through electrostatic forces and the toxicity decreases with the shortening of the carbon chain.

Ionic complex of a rhodamine dye with aggregation-induced emission properties

An AIE-active rhodamine based luminogen was prepared via a complexation reaction between non-emissive rhodamine hydrazide (RdH) and bulky camphorsulfonic acid (CSA). Besides acting to open the spirolactam ring of RdH, CSA also imposes a rotational restriction on the resultant ionic complex, RdH(CSA)_x. Without CSA, the analogous complex RdH(HCl)₃ is a luminogen with aggregation-caused quenching (ACQ) properties. The ionic bonds of RdH(CSA)₃ are sensitive to several external stimuli and therefore it is a luminescent sensor for metal ions, organic amines and the blood protein bovine serum albumin (BSA). Besides being a sensor for BSA, the ionic RdH(CSA)₃ is also a denaturant capable of uncoiling the peptide chain of BSA.

Multiple-responsive ionic complex luminogen of quinine and camphorsulfonic acid with aggregation-induced emission

Bulky camphorsulfonic acid (CSA) was used to complex with quinine (Qu) to impose restricted intramolecular rotation (RIR) required for aggregation-induced emission (AIE) properties.

New fluorescence probes for biomolecules

Steady state fluorescence measurements have been used for the investigation of interaction between the bovine serum albumin (BSA) and fluorescence probes: 3-hydroxy-2,4-bis[(3-methyl-1,3-benzoxazol-2(3H)-ylidene)methyl]cyclobut-2-en-1-one (SQ6), 3-hydroxy-2,4-bis[(3-methyl-1,3-benzothiazol-2(3H)-ylidene)methyl]cyclobut-2-en-1-one (SQ7) and 3-hydroxy-2,4-bis[(1,3,3-trimethyl-1,3-dihydro-2H-indol-2-ylidene)methyl]cyclobut-2-en-1-one (SQ8). The binding constant between bovine serum albumin and squarine dyes has been determined by using both the Benesi-Hildebrand and Stern-Volmer equations. The negative value of free energy change indicates the existence of a spontaneous complexation process of BSA with squarine dyes.

Interaction between the Natural Components in Danhong Injection (DHI) with Serum Albumin (SA) and the Influence of the Coexisting Multi-Components on the SaB-BSA Binding System: Fluorescence and Molecular Docking Studies

Danhong injection (DHI) is a widely used Chinese Materia Medica standardized product for the clinical treatment of ischemic encephalopathy and coronary heart disease. The bindings of eight natural components in DHI between bovine serum albumin (BSA) were studied by fluorescence spectroscopy technology and molecular docking. According to the results, the quenching process of salvianolic acid B and hydroxysafflor yellow A was a static quenching procedure through the analysis of quenching data by the Stern-Volmer equation, the modified Stern-Volmer equation, and the modified Scatchard equation. Meanwhile, syringin (Syr) enhanced the fluorescence of BSA, and the data were analyzed using the Lineweaver-Burk equation. Molecular docking suggested that all of these natural components bind to serum albumin at the site I location. Further competitive experiments of SaB confirmed the result of molecular docking studies duo to the displacement of warfarin by SaB. Base on these studies, we selected SaB as a research target because it presented the strongest binding ability to BSA and investigated the influence of the multi-components coexisting in DHI on the interaction between the components of the SaB-BSA binding system. The participation of these natural components in DHI affected the interaction between the components of the SaB-BSA system. Therefore, when DHI is used in mammals, SaB is released from serum albumin more quickly than it is used alone. This work would provide a new experiment basis for revealing the scientific principle of compatibility for Traditional Chinese Medicine.

Charge invariant protein-water relaxation in GB1 via ultrafast tryptophan fluorescence

The protein–water interface is a critical determinant of protein structure and function, yet the precise nature of dynamics in this complex system remains elusive. Tryptophan fluorescence has become the probe of choice for such dynamics on the picosecond time scale (especially via fluorescence “upconversion”). In the absence of ultrafast (“quasi-static”) quenching from nearby groups, the TDFSS (time-dependent fluorescence Stokes shift) for exposed Trp directly reports on dipolar relaxation near the interface (both water and polypeptide). The small protein GB1 contains a single Trp (W43) of this type, and its structure is refractory to pH above 3. Thus, it can be used to examine the dependence of dipolar relaxation upon charge reconfiguration with titration. Somewhat surprisingly, the dipolar dynamics in the 100 fs to 100 ps range were unchanged with pH, although nanosecond yield, rates, and access all changed. These results were rationalized with the help of molecular dynamics (including QM-MM) simulations that reveal a balancing, sometimes even countervailing influence of protein and water dipoles. Interestingly, these simulations also showed the dominant influence of water molecules which are associated with the protein interface for up to 30 ps yet free to rotate at approximately “bulk” water rates.

Charge-transfer interactions for the fabrication of multifunctional viral nanoparticles

In this paper, a facile strategy to fabricate multifunctional viral nanoparticles was described by introducing charge-transfer interactions between a pyrenyl motif with dinitrophenyl and pyridinium-contained guest molecules.

Modulated photophysics of a cationic DNA-staining dye inside protein bovine serum albumin: study of binding interaction and structural changes of protein

The binding affinity of cationic DNA-staining dye, propidium iodide, with transport protein, bovine serum albumin, has been explored using UV-vis absorption, fluorescence, and circular dichroism spectroscopy. Steady state and time resolved fluorescence studies authenticate that fluorescence quenching of bovine serum albumin by propidium iodide is due to bovine serum albumin-propidium iodide complex formation. Thermodynamic parameters obtained from temperature dependent spectral studies cast light on binding interaction between the probe and protein. Site marker competitive binding has been encountered using phenylbutazone and flufenamic acid for site I and site II, respectively. Energy transfer efficiency and distance between bovine serum albumin and propidium iodide have been determined using Förster mechanism. Structural stabilization or destabilization of protein by propidium iodide has been investigated by urea denaturation study. The circular dichroism study as well as FT-IR measurement demonstrates some configurational changes of the protein in presence of the dye. Docking studies support the experimental data thereby reinforcing the binding site of the probe to the subdomain IIA of bovine serum albumin.

Studies of the fluorescence light-up effect of amino-substituted benzo[b]quinolizinium derivatives in the presence of biomacromolecules

A comparative study of the ability of amino-substituted benzo[b]quinolizinium derivatives to act as DNA- or protein-sensitive fluorescent probes is presented. Spectrophotometric titrations, DNA denaturation studies and viscometric titrations showed that all tested aminobenzo[b]quinolizinium derivatives intercalate into DNA with binding constants K(b) = 10(4)-10(5) M(-1). The intense fluorescence of the 9-aminobenzo[b]quinolizinium (Φ(fl) = 0.41) as well as the intrinsically very weak emission of the 7-aminobenzo[b]quinolizinium (Φ(fl) < 0.005) are quenched by the addition of DNA, most likely caused by a photoinduced electron transfer (PET) between the excited intercalated ligand and the DNA bases. The 6-aminobenzo[b]quinolizinium (1b) and the 6-amino-9-bromobenzo[b]quinolizinium (1c) exhibit very low fluorescence intensity in water (Φ(fl) < 0.005). However, in water-glycerol mixtures the emission intensity increases by factors of 56 (1b) and 27 (1c) with increasing glycerol content of the solution (0-100 wt%), which indicates the radiationless deactivation of the excited state of 1b and 1c due to a torsional relaxation, i.e. rotation about the exocyclic C(ar)-NH(2) bond. In the case of the bromo-substituted derivative 1c, a viscosity-independent heavy-atom-effect of the bromo substituent leads to additional quenching. The association of 1b and 1c with ds DNA leads to a restricted conformational flexibility of the intercalated ligand and results in an increase of fluorescence intensity. This effect is particularly strong in the presence of poly[dA-dT]-poly[dA-dT]. Upon association with ct DNA or poly[dG-dC]-poly[dG-dC] only very small enhancement of emission intensity (1b) or even a slight quenching (1c) of the fluorescence was observed because of the interfering PET reaction with the guanine residues. Preliminary experiments reveal that the 6-aminobenzo[b]quinolizinium derivatives 1b and 1c may also be employed as protein-sensitive probes, because their emission intensity increases upon association with selected albumins.

Quantitation, visualization, and monitoring of conformational transitions of human serum albumin by a tetraphenylethene derivative with aggregation-induced emission characteristics

Human serum albumin (HSA) is a major protein component of blood plasma, and its assay is of obvious value to biological research. We, herein, present a readily accessible fluorescent bioprobe for HSA detection and quantitation. A nonemissive tetraphenylethene derivative named sodium 1,2-bis[4-(3-sulfonatopropoxyl)phenyl]-1,2-diphenylethene (BSPOTPE) is induced to emit by HSA, showing a novel phenomenon of aggregation-induced emission (AIE). The AIE bioprobe enjoys a broad working range (0-100 nM), a low detection limit (down to 1 nM), and a superior selectivity to albumins. The fluorescent bioassay is unperturbed by the miscellaneous bioelectrolytes in the artificial urine. The AIE luminogen can also be used as a rapid and sensitive protein stain in gel electrophoresis for HSA visualization. Utilizing the AIE feature of BSPOTPE and the Forster resonance energy transfer from HSA to BSPOTPE, the unfolding process of HSA induced by guanidine hydrochloride is monitored, which reveals a multistep transition with the involvement of molten globule intermediates. Computational modeling suggests that the AIE luminogens dock in the hydrophobic cleft between subdomains IIA and IIIA of HSA with the aid of hydrophobic effect, charge neutralization, and hydrogen bonding interactions, offering mechanistic insight into the microenvironment inside the hydrophobic cavity.