Photoprocesses of excited molecules in confined liquid environments: An overview

Simple naturally occurring β-carboline alkaloids – role in sustainable theranostics

This review is a brief treatise on some simple β-carboline alkaloids that are abundantly available in plants, animals and foodstuff. These alkaloids are well known for their pharmacological action as well as their allelopathic behaviour. The focus of this review is on sustainable use of naturally occurring compounds in safeguarding human health and protecting our environment at large i.e. the prospective applications of these molecules for Sustainable Theranostics. The review commences with an initial introduction to the β-carboline alkaloids, followed by an outlay of their geographical distribution and natural abundance, then the basic structure and building units of the simplest β-carboline alkaloids have been mentioned. This is followed by a discussion on the important methods of extraction from natural sources both plants and animals. Then the foundation for the use of these alkaloids in Sustainable Theranostics has been built by discussing their interesting photophysics, interactions with important biological molecules and an extensive survey of their therapeutic potential and allelopathic behaviour. Finally the review ends with a silver lining mentioning the future prospective applications of these alkaloids with special relevance to sustainability issues.

Fluorescence Sensors Based on Hydroxycarbazole for the Determination of Neurodegeneration-Related Halide Anions

The environmental presence of anions of natural origin or anthropogenic origin is gradually increasing. As a tool to tackle this problem, carbazole derivatives are an attractive gateway to the development of luminescent chemosensors. Considering the different mechanisms proposed for anion recognition, the fluorescence properties and anion-binding response of several newly synthesised carbazole derivatives were studied. Potential anion sensors were designed so that they combined the native fluorescence of carbazole with the presence of hydrogen bonding donor groups in critical positions for anion recognition. These compounds were synthesised by a feasible and non-expensive procedure using palladium-promoted cyclodehydrogenation of suitable diarylamine under microwave irradiation. In comparison to the other carbazole derivatives studied, 1-hydroxycarbazole proved to be useful as a fluorescent sensor for anions, as it was able to sensitively recognise fluoride and chloride anions by establishing hydrogen bond interactions through the hydrogen atoms on the pyrrolic nitrogen and the hydroxy group. Solvent effects and excited-state proton transfer (ESPT) of the carbazole derivatives are described to discard the role of the anions as Brönsted bases on the observed fluorescence behaviour of the sensors. The anion-sensor interaction was confirmed by 1H-NMR. Molecular modelling was employed to propose a mode of recognition of the sensor in terms of complex stability and interatomic distances. 1-hydroxycarbazole was employed for the quantitation of fluoride and chloride anions in commercially available medicinal spring water and mouthwash samples.

Pivotal role of water molecules in the photodegradation of pymetrozine: New insights for developing green pesticides

Photodegradation of the insecticide pymetrozine (PYM) was studied on surface of wax films, and in aqueous and nonaqueous phase. The half-life of PYM on the wax surface was approximately 250 times longer than in water. Scavenging experiments, laser flash photolysis, and spectra analysis indicated the first singlet excited state of PYM (S1 *_PYM) to be the most important photoinduced species initiating the photodegradation. Quantum chemistry calculations identified significant molecular torsion and changes in the structure C-CN-N of S1 *_PYM, and the absolute charges of the CN atoms increased and the bond strength weakened. Free energy surface analysis, and O¹⁸ labeling experiments further confirmed that the mechanism was two-step photoinduced hydrolysis. The first step is the hydrolysis of S1 *_PYM at CN upon reaction with 2-3 water molecules (one H₂O molecule as the catalyst). The second step is an intramolecular hydrogen transfer coupled with the cleavage of C-N bond and formation of two cyclic products. During the interactions, water molecules experience catalytic activation by transferring protons, while there is a negligible solvent effect. Clarifying the detailed photodegradation mechanisms of PYM is beneficial for the development of green pesticides that are photostable and effective on leaf surfaces, and photolabile and detoxified in the aquatic environment.

Ultrafast Excited-State Proton Transfer of a Cationic Superphotoacid in a Nanoscopic Water Pool

The excited-state proton transfer (ESPT) of a cationic superphotoacid, N-methyl-7-hydroxyquinolium, was studied within the water pool of an anionic aerosol-OT (AOT), bis(2-ethylhexyl) sulfosuccinate, reverse micelle (RM). Previously, we had found that the cationic photoacid residing at the anionic AOT interface was conducive to ESPT to the bound water having concentric heterogeneity on the time scale of hundreds of picoseconds to nanoseconds. In our present study, on the time scale of hundreds of femtoseconds to a few tens of picoseconds, the photoacid underwent an ultrafast ESPT influenced by mobile water constituting the core of the RM. The two subpopulations of the core water molecules that determine the ultrafast biphasic deprotonation of the photoacid on time scales differing by an order of magnitude were identified. The core water molecules solvating the counteranion of the photoacid showed a higher basicity than typical water clusters in bulk resulting in ESPT on a subpicosecond time scale. Bare water clusters sensed by the photoacid showed a slower ESPT, over several picoseconds, as typically limited by the rotational motion of water molecules for similar types of the photoacid.

Visual pH Sensors: From a Chemical Perspective to New Bioengineered Materials

Many human activities and cellular functions depend upon precise pH values, and pH monitoring is considered a fundamental task. Colorimetric and fluorescence sensors for pH measurements are chemical and biochemical tools able to sense protons and produce a visible signal. These pH sensors are gaining widespread attention as non-destructive tools, visible to the human eye, that are capable of a real-time and in-situ response. Optical “visual” sensors are expanding researchers’ interests in many chemical contexts and are routinely used for biological, environmental, and medical applications. In this review we provide an overview of trending colorimetric, fluorescent, or dual-mode responsive visual pH sensors. These sensors include molecular synthetic organic sensors, metal organic frameworks (MOF), engineered sensing nanomaterials, and bioengineered sensors. We review different typological chemical entities of visual pH sensors, three-dimensional structures, and signaling mechanisms for pH sensing and applications; developed in the past five years. The progression of this review from simple organic molecules to biological macromolecules seeks to benefit beginners and scientists embarking on a project of pH sensing development, who needs background information and a quick update on advances in the field. Lessons learned from these tools will aid pH determination projects and provide new ways of thinking for cell bioimaging or other cutting-edge in vivo applications.

Hydrogen bond regulated hydrogen sulfate ion recognition: an overview

Hydrogen sulfate possesses substantial biological importance, having a colossal impact on physiological and environmental events. Therefore, several scientific groups have devoted serious effort to the development of versatile colorimetric and fluorimetric HSO4- sensors. Along with the scope, challenges, and significance, this review emphasizes the advancement of the optical recognition of HSO4- based on hydrogen bonding during the past two decades. Moreover, hydrogen-bond-driven proton transfer, ESIPT, ICT, PET, CHEF, and TBET mechanisms that allow for the optical detection of HSO4- are also discussed concisely. The foundation of this review includes the key points of the sensing process, like the nature of spectroscopic changes, selectivity and sensitivity, naked-eye color changes, the reusability of sensors, and the in vivo detection of HSO4-, if any. Special attention is focused on the correlation between the photophysical changes and the underlying interaction mechanisms that triggered the recognition aspect.

Role of Different States of Solubilized Water on Solvation Dynamics and Rotational Relaxation of Coumarin 490 in Reverse Micelles of Gemini Surfactants, Water/12-s-12.2Br- (s = 5, 6, 8)/n-Propanol/Cyclohexane

The present study demonstrates how the different states of solubilized water viz. quaternary ammonium headgroup-bound, bulklike, counterion-bound, and free water in reverse micelles of a series of cationic gemini surfactants, water/12-s-12 (s = 5, 6, 8).2Br^-/n-propanol/cyclohexane, control the solvation dynamics and rotational relaxation of Coumarin 490 (C-490) and microenvironment of the reverse micelles. The relative number of solubilized water molecules of a given state per surfactant molecule decides major and minor components. A rapid increase in the number of bulklike water molecules per surfactant molecule as compared to the slow increase in the number of each of headgroup- and counterion-bound water molecules per surfactant molecule with increasing water content (W _o) in a given reverse micellar system is responsible for the increase in the rate of solvation and rotational relaxation of C-490. The increase in the number of counterion-bound water molecules per surfactant molecule and the concomitant decrease in the number of bulklike water molecules per surfactant molecule with increasing spacer chain length of gemini surfactants at a given W _o are ascribed to the slower rates of both solvation and rotational relaxation. Relative abundances of different states of water have a role on the microenvironment of the reverse micelles as well. Thus, a comprehensive effect of different states of water on dynamics in complex biomimicking systems has been presented here.

Photochemical study of the highly used corticosteroids dexamethasone and prednisone. Effects of micellar confinement and cytotoxicity analysis of photoproducts

Photodegradation of dexamethasone (Dexa) and prednisone (Pred) occurs by a combination of ROS attack and unimolecular photodegradation reactions. The photoproducts obtained are more cytotoxic than the parent compounds.

Factors for the emission enhancement of dimidium in specific media such as in DNA and on a clay surface

Dimidium (3,8-diamino-5-methyl-6-phenylphenanthridinium: NH2PhP) is a well-known fluorophore as a DNA probe, although its fluorescence enhancement mechanism is not clear. In this study, we investigated the fluorescence enhancement mechanism of NH2PhP on a clay surface by observing the fluorescence behavior. Four systematically selected phenanthridinium derivatives (PDs): NH2PhP, 3,8-bisdimethylamino-5-methyl-6-phenylphenanthridinium (NMe2PhP), 5-methyl-6-phenylphenanthridinium (PhP) and 5-methylphenanthridinium (P) and synthetic clay were used as guest and host materials, respectively. It was revealed that the suppression of hydrogen bonding with water (N-HOH or NH-OH2) is the dominant factor for the fluorescence enhancement on the clay surface for NH2PhP and NMe2PhP. In addition, judging from the fluorescence enhancement for NH2PhP, NMe2PhP and PhP and no fluorescence enhancement for P on the clay surface, the suppression of rotation of the phenyl ring was indicated to make a partial contribution to the fluorescence enhancement mechanism. Because the fluorescence enhancement behavior was quite similar on the clay surface and in DNA, the obtained results afford an important clue to discuss the fluorescence enhancement mechanism of NH2PhP in DNA.

Excited state proton transfer based fluorescent molecular probes and their application in studying lipid bilayer membranes

The distribution and prototropic equilibria of 1-naphthol (NpOH) in lipid bilayer membrane.

Influence of Branched Polyester Chains on the Emission Behavior of Dipyridamole Molecule and Its Biosensing Ability

Toward the development of the smart biosensing drug carrier, integration of dye molecules with polymeric chain has been an emerging method in recent years. In this perspective, dipyridamole (Dip)-based branched poly(l-lactide) (PLLA) and branched polycaprolactone (PCL) have been synthesized by ring-opening polymerization. After polymerization, the influence of the polyester chains on the Dip emission behavior has been studied systematically in this work. Dip-PLLA has undergone C=O···N=C interaction in ground stage, leading to intramolecular charge transfer in the excited state. Limited availability of the C=O in PCL chains resists such interactions with Dip molecule. So, this structural availability of the C=O group in the polymeric chains influences the color change between Dip-PLLA (green fluorescence) and Dip-PCL (blue fluorescence). To visualize the biosensing ability of Dip-PLLA and Dip-PCL, hollow microspheres have been prepared by the double-emulsion solvent evaporation method, and the prepared microspheres cells uptake has been visualized by fluorescence imaging.

Modulation of the Excited-State Proton Transfer Rate of d-luciferin in Mixed Reverse Micellar Systems

The excited-state proton transfer (ESPT) rate of photo-acids in a confined medium depends on several physical parameters of the immediate environment. We introduce a new parameter in the form of charge type at the interface of reverse micellar (RM) systems to modulate the ESPT rate. We investigate the ESPT reaction of d-luciferin in mixed RM systems composed of nonionic polyoxyethylene(5)nonylphenylether (Igepal CO-520) with cationic didodecyldimethylammonium bromide (DDAB) and anionic sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in cyclohexane (Cy) at different mole fractions of Ig (X _Ig) and fixed hydration. ESPT is feeble in AOT RM, whereas it is favorable in the other two RMs. Addition of Ig is observed to facilitate ESPT in AOT RM linearly, whereas in DDAB, it shows a synergistic effect. The various physical parameters of water in the mixed RM water pool have been investigated using dynamic light scattering, Fourier transform infrared, and time-resolved fluorescence spectroscopy measurements to underline the ESPT mechanism in these mixed RMs.

Circularly Polarized Luminescence from a Pyrene-Cyclodextrin Supra-Dendron

Soft nanomaterials with circularly polarized luminescence (CPL) have been currently attracting great interest. Here, we report a pyrene-containing π-peptide dendron hydrogel, which shows 1D and 2D nanostructures with varied CPL activities. It was found that the individual dendrons formed hydrogels in a wide pH range (3-12) and self-assembled into helices with pH-tuned pitches. Through chirality transfer, the pyrene unit could show CPL originated from both the monomer and excimer bands. When cyclodextrin was introduced, different supra-dendrons were obtained with β-cyclodextrin (PGAc@β-CD) and γ-cyclodextrin (PGAc@γ-CD) through host-guest interactions, respectively. Interestingly, the PGAc@β-CD and PGAc@γ-CD supra-dendrons self-assembled into 2D nanosheet and entangled nanofibers, respectively, showing cyclodextrin induced circularly polarized emission from both the monomer and excimer bands of the pyrene moiety. Thus, through a simple host-guest interaction, both the nanostructures and the chiroptical activities could be modulated.

Application of Fluorescence Emission for Characterization of Albendazole and Ricobendazole Micellar Systems: Elucidation of the Molecular Mechanism of Drug Solubilization Process

Albendazole (ABZ) and ricobendazole (RBZ) are referred to as class II compounds in the Biopharmaceutical Classification System. These drugs exhibit poor solubility, which profoundly affects their oral bioavailability. Micellar systems are excellent pharmaceutical tools to enhance solubilization and absorption of poorly soluble compounds. Polysorbate 80 (P80), poloxamer 407 (P407), sodium cholate (Na-C), and sodium deoxycholate (Na-DC) have been selected as surfactants to study the solubilization process of these drugs. Fluorescence emission was applied in order to obtain surfactant/fluorophore (S/F) ratio, critical micellar concentration, protection efficiency of micelles, and thermodynamic parameters. Systems were characterized by their size and zeta potential. A blue shift from 350 to 345 nm was observed when ABZ was included in P80, Na-DC, and Na-C micelles, while RBZ showed a slight change in the fluorescence band. P80 showed a significant solubilization capacity: S/F values were 688 for ABZ at pH 4 and 656 for RBZ at pH 6. Additionally, P80 micellar systems presented the smallest size (10 nm) and their size was not affected by pH change. S/F ratio for bile salts was tenfold higher than for the other surfactants. Quenching plots were linear and their constant values (2.17/M for ABZ and 2.29/M for RBZ) decreased with the addition of the surfactants, indicating a protective effect of the micelles. Na-DC showed better protective efficacy for ABZ and RBZ than the other surfactants (constant values 0.54 and 1.57/M, respectively), showing the drug inclusion into the micelles. Entropic parameters were negative in agreement with micelle formation.

Three-Dimensional Printing of Photoresponsive Biomaterials for Control of Bacterial Microenvironments

Advances in microscopic three-dimensional (μ3D) printing provide a means to microfabricate an almost limitless range of arbitrary geometries, offering new opportunities to rapidly prototype complex architectures for microfluidic and cellular applications. Such 3D lithographic capabilities present a tantalizing prospect for engineering micromechanical components, for example, pumps and valves, for cellular environments composed of smart materials whose size, shape, permeability, stiffness, and other attributes might be modified in real time to precisely manipulate ultralow-volume samples. Unfortunately, most materials produced using μ3D printing are synthetic polymers that are inert to biologically tolerated chemical and light-based triggers and provide low compatibility as materials for cell culture and encapsulation applications. We previously demonstrated feasibility for μ3D printing environmentally sensitive, microstructured protein hydrogels that undergo volume changes in response to pH, ionic strength, and thermal triggers, cues that may be incompatible with sensitive chemical and biological systems. Here, we report the systematic investigation of photoillumination as a minimally invasive and remotely applied means to trigger morphological change in protein-based μ3D-printed smart materials. Detailed knowledge of material responsiveness is exploited to develop individually addressable "smart" valves that can be used to capture, "farm", and then dilute motile bacteria at specified times in multichamber picoliter edifices, capabilities that offer new opportunities for studying cell-cell interactions in ultralow-volume environments.

Dual emission from 2-(4'-N,N-dimethylaminophenyl)pyridoimidazole-nanoparticle composite: effect of β-cyclodextrin

The interactions of the silver nanoparticles with 2-(4'-N,N-dimethylaminophenyl)benzimidazole and its nitrogen substituted analogues, 2-(4'-N,N-dimethylaminophenyl)pyridoimidazoles are investigated by absorption, steady-state and time resolved fluorescence, field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) techniques. The surface plasmon resonance band, the FESEM and the TEM images of the particles suggest that the fluorophores can stabilize the nanoparticles even in the absence of any other stabilizing agent. On the other hand, in the absence of fluorophores the nanoparticles are unstable and coagulate. In contrary to the earlier literature reports that interactions of nanoparticles with intramolecular charge transfer (ICT) or twisted intramolecular charge transfer (TICT) species quenches their fluorescence, to the best of our knowledge, the first ever formation of TICT state by interactions of nanoparticles with the fluorophores is observed. The formation of TICT state in 2-(4'-N,N-dimethylaminophenyl)pyridoimidazoles results in dual emission. The TICT emissions from the nanoparticle-fluorophore complexes are weak. But the emissions become prominent upon complexation with β-cyclodextrin.

Dual-sensor fluorescent probes of surfactant-induced unfolding of human serum albumin

Two extrinsic fluorescent probes, 3-(dimethylamino)-8,9,10,11-tetrahydro-7H-cyclohepta[a]naphthalen-7-one (1) and 7-(dimethylamino)-2,3-dihydrophenanthren-4(1H)-one (2), are used to probe the unfolding of human serum albumin by sodium dodecyl sulfate (SDS). These probes respond separately to the polarity and H-bond-donating ability of their surroundings. Competitive binding experiments show that fluorophore 1 binds to site I (domain IIA) and 2 binds to site II (domain IIIA). The local acidity of 1 in site I is out of the sensing range of 1, whereas the local acidity of 2 in site II is calculated to be nearly zero on Catalan's solvent acidity index. Both probes show that the first two equivalents of bound SDS result in a decrease in the local polarity of the binding sites. Each subsequent equivalent of SDS gives rise to a dramatic increase in polarity until HSA is saturated with seven molecules of SDS at the end of the specific binding domain. Compound 2 experiences an increase of acidity of 0.10 on Catalan's solvent acidity index through seven equivalents of SDS, but the local acidity for 1 is still out of range. The increase in acidity experienced by 2 is greater than the increase in polarity. This result is consistent with greater exposure of the carbonyl group in 2, but not the bulk of 2, to the aqueous solvent in site II of the SDS-saturated HSA complex.

Spectrofluorimetric determination of zearalenone using dispersive liquid–liquid microextraction coupled to micro-solid phase extraction onto magnetic nanoparticles

A new and sensitive method using dispersive liquid–liquid microextraction (DLLME) coupled to micro-solid phase extraction (μ-SPE) onto magnetic nanoparticles was developed for spectrofluorimetric determination of zearalenone (ZEN) in corn samples.

Interaction between holo transferrin and HSA-PPIX complex in the presence of lomefloxacin: an evaluation of PPIX aggregation in protein-protein interactions

Human serum albumin (HSA) and holo transferrin (TF) are two serum carrier proteins that are able to interact with each other, thereby altering their binding behavior toward their ligands. During the course of this study, the interaction between HSA-PPIX and TF, in the presence and absence of lomefloxacin (LMF), was for the first time investigated using different spectroscopic and molecular modeling techniques. Fluorescence spectroscopy experiments were performed in order to study conformational changes of proteins. The RLS technique was utilized to investigate the effect of LMF on J-aggregation of PPIX, which is the first report of its kind. Our findings present clear-cut evidence for the alteration of interactions between HSA and TF in the presence of PPIX and changes in drug-binding to HSA and HSA-PPIX complex upon interaction with TF. Moreover, molecular modeling studies suggested that the binding site for LMF became switched in the presence of PPIX, and that LMF bound to the site IIA of HSA. The obtained results should give new insight into research in this field and may cast some light on the dynamics of drugs in biological systems.

Photophysical processes of an intramolecular charge transfer fluorescent dye with carbazole units

A carbazole-based compound with intramolecular charge transfer (ICT) characteristics, 3,6-bis-((N-ethylcarbazole-3-)-propene-1-keto)-N-ethylcarbazole (BCzPCz) was synthesized by N-alkylation, acetylation and aldol condensation. BCzPCz was further confirmed by IR and (1)H NMR. The central N-ethylcarbazole was connected with two N-ethylcarbazole units through the propenone group in BCzPCz. N-ethylcarbazole and carbonyl groups were electron donors (D) and acceptors (A), respectively. The UV-vis absorption and fluorescence characteristics of BCzPCz were also investigated in different solvents. Solvatochromism was attributed to ICT complex formation in singlet excited state. Magnitude of the change in the dipole moment was 24.78 D according to Lippert-Mataga equation. Fluorescence of BCzPCz was significantly affected by pH and was quenched in acidic medium. Fluorescence quantum yield of BCzPCz was 0.516 in ethanol. Experimental results showed its potential use as a fluorescence probe and as two-photon absorption material.

Physicochemical perspective of cyclodextrin nano and microaggregates

''Chemistry beyond the molecule'' is the nickname for supramolecular chemistry. This branch of study is based on molecular recognition that is host-guest chemistry. A number of potential hosts have been defined and applied in scores of studies. Among all potential hosts, cyclodextrins occupy a high position due to their characteristic solubilisation capability and biocompatibility. In the present article we are revisiting the host-guest aspects of cyclodextrins from a physicochemical perspective. We present details of formation and applications of cyclodextrin nanoaggregates induced by guest molecules, the concerned thermodynamics behind the process and also the effect of concentration of the guest molecules on the morphology of the aggregates. This article reviews the topic mainly from the spectroscopic point of view.

Quenching of the triplet state of Safranine-O by aliphatic amines in AOT reverse micelles studied by transient absorption spectroscopy

The photophysics of Safranine-O (3,6-diamino-2,7-dimethyl-5 phenyl phenazinium chloride) (SfH(+)Cl(-)) was investigated in reverse micelles (RMs) of AOT (sodium bis(2-ethylhexyl)sulfosuccinate) with special emphasis on the triplet state processes. The triplet is formed in its monoprotonated form, independently of the pH of the water used to prepare the RMs. While the intersystem crossing quantum yields in RMs are similar to those in organic solvents, the triplet lifetime is much longer. Since the pH in the water pool of AOT RMs is close to 5 and the triplet state of the dye is subjected to proton quenching, the long lifetime indicates that the dye resides in a region where it cannot be reached by protons during its lifetime. All the measurements indicate that the dye is localized in the interface, sensing a medium of micropolarity similar to EtOH : water (3:1) mixtures. The quenching by aliphatic amines was also investigated. While the quenching by the hydrophobic tributylamine is similar to that in methanol, the hydro-soluble triethanolamine is one order of magnitude more effective in RMs than in homogeneous solution. In the latter case the quenching process is interpreted by a very fast intramicellar quenching, the overall kinetics being controlled by the exchange of amine molecules between RMs. Semireduced dye is formed in the quenching process in RMs in the di-protonated state with a comparable quantum yield to the monoprotonated state formed in homogeneous solvents. The results point to the advantage of the reverse micellar system for the generation of active radicals for the initiation of vinyl polymerization, since a much lower concentration of amine can be employed with similar quantum yields.

The design, synthesis and photochemical study of a biomimetic cyclodextrin model of photoactive yellow protein (PYP)

The design, synthesis and study of the photophysical and photochemical properties of the first biomimetic cyclodextrin (CD) model of photoactive yellow protein (PYP) are described. This model bears a deprotonated trans-p-coumaric acid chromophore, covalently linked via a cysteine moiety to a permethylated 6-monoamino β-CD. NMR and UV/Visible spectroscopy studies showed the formation of strong self-inclusion complexes in water at basic pH. Steady-state photolysis demonstrated that, unlike the free chromophore in solution, excitation of the model molecule leads to the formation of a photoproduct identified as the cis isomer by NMR spectroscopy. These observations provide evidence that the restricted CD cavity offers a promising framework for the design of biomimetic models of the PYP hydrophobic pocket.