Flavin Molecules Research Articles

Deciphering the Two-Step Hydride Mechanism of Monoamine Oxidase Flavoenzymes.

The complete two-step hydride transfer mechanism of amine oxidation involved in the metabolism of monoamine neurotransmitters was scrutinized by DFT calculations. In living organisms, this process is catalyzed by monoamine oxidase enzymes. Herein, we focus on some intriguing aspects of the reaction that may have been previously noticed but have not been clarified to date. The first step of the reaction includes the C-H bond cleavage on the methylene group vicinal to the amino group of the monoamine substrate and the subsequent transfer of hydrogen to the N5 atom of the flavin prosthetic group of the enzyme. We confirmed the nature of this step to be hydride transfer by evaluation of the pertinent HOMO-LUMO gap together with analysis of orbital contours alongside the intrinsic reaction coordinate profile. Next, we investigated the rather peculiar intermediate adduct that may form between the amine substrate and the flavin molecule, featuring an unusually long C-N bond of ∼1.62 Å. Although this bond is quite stable in the gas phase, the presence of just a few explicit water molecules facilitates its dissociation almost without energy input so that the amine-flavin intermediate can form an ionic pair instead. We attribute the existence of the unusual C-N bond to a fragile balance between opposing electronic structure effects, as evaluated by the natural bond orbital analysis. In line with this, the intermediate in the solution or in the enzyme active site can exist in two energetically almost equivalent forms, namely, as a covalently bound complex or as an ion pair, as suggested by previous studies. Finally, we characterized the transformation of the intermediate to the fully reduced flavin and imine products via proton transfer from the amino group to the flavin N1 atom, completing the reductive part of the catalytic cycle. Although we found that explicit solvation substantially boosts the kinetics of this step, the corresponding barrier is significantly lower than that in the hydride transfer step, confirming hydrogen abstraction as the rate-limiting step of amine oxidation and validating the two-step hydride transfer mechanism of monoamine oxidases.

Redox Properties of Flavin in BLUF and LOV Photoreceptor Proteins from Hybrid QM/MM Molecular Dynamics Simulation.

Flavins play an important role in many oxidation and reduction processes in biological systems. For example, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) are common cofactors found in enzymatic proteins that use the special redox properties of these flavin molecules for their catalytic or photoactive functions. The redox potential of the flavin is strongly affected by its (protein) environment; however, the underlying molecular interactions of this effect are still unknown. Using hybrid quantum mechanics/molecular mechanics (QM/MM) simulation techniques, we have studied the redox properties of flavin in the gas phase, aqueous solution, and two different protein environments, in particular, a BLUF and a LOV photoreceptor domain. By mapping the changes in electrostatic potential and solvent structure, we gain insight into how specific polarization of the flavin by its environment tunes the reduction potential. We find also that accurate calculation of the reduction potentials of these systems by using the hybrid QM/MM approach is hampered by a too limited sampling of the counterion configurations and by artifacts at the QM/MM boundary. We make suggestions for how these issues can be overcome.

Enhanced Solid-State Fluorescence of Flavin Derivatives by Incorporation in the Metal-Organic Frameworks MIL-53(Al) and MOF-5.

The flavin derivatives 10-methyl-isoalloxazine (MIA) and 6-fluoro-10-methyl-isoalloxazine (6F-MIA) were incorporated in two alternative metal-organic frameworks, (MOFs) MIL-53(Al) and MOF-5. We used a post-synthetic, diffusion-based incorporation into microcrystalline MIL-53 powders with one-dimensional (1D) pores and an in-situ approach during the synthesis of MOF-5 with its 3D channel network. The maximum amount of flavin dye incorporation is 3.9 wt% for MIA@MIL-53(Al) and 1.5 wt% for 6F-MIA@MIL-53(Al), 0.85 wt% for MIA@MOF-5 and 5.2 wt% for 6F-MIA@MOF-5. For the high incorporation yields the probability to have more than one dye molecule in a pore volume is significant. As compared to the flavins in solution, the fluorescence spectrum of these flavin@MOF composites is broadened at the bathocromic side especially for MIA. Time-resolved spectroscopy showed that multi-exponential fluorescence lifetimes were needed to describe the decays. The fluorescence-weighted lifetime of flavin@MOF of 4 ± 1 ns also corresponds to those in solution but is significantly prolonged compared to the solid flavin dyes with less than 1 ns, thereby confirming the concept of "solid solutions" for dye@MOF composites. The fluorescence quantum yield (ΦF) of the flavin@MOF composites is about half of the solution but is significantly higher compared to the solid flavin dyes. Both the fluorescence lifetime and quantum yield of flavin@MOF decrease with the flavin loading in MIL-53 due to the formation of various J-aggregates. Theoretical calculations using plane-wave and QM/MM methods are in good correspondence with the experimental results and explain the electronic structures as well as the photophysical properties of crystalline MIA and the flavin@MOF composites. In the solid flavins, π-stacking interactions of the molecules lead to a charge transfer state with low oscillator strength resulting in aggregation-caused quenching (ACQ) with low lifetimes and quantum yields. In the MOF pores, single flavin molecules represent a major population and the computed MIA@MOF structures do not find π-stacking interactions with the pore walls but only weak van-der-Waals contacts which reasons the enhanced fluorescence lifetime and quantum yield of the flavins in the composites compared to their neat solid state. To analyze the orientation of flavins in MOFs, we measured fluorescence anisotropy images of single flavin@MOF-5 crystals and a static ensemble flavin@MIL53 microcrystals, respectively. Based on image information, anisotropy distributions and overall curve of the time-resolved anisotropy curves combined with theoretical calculations, we can prove that all fluorescent flavins species have a defined and rather homogeneous orientation in the MOF framework. In MIL-53, the transition dipole moments of flavins are orientated along the 1D channel axis, whereas in MOF-5 we resolved an average orientation that is tilted with respect to the cubic crystal lattice. Notably, the more hydrophobic 6F-MIA exhibits a higher degree order than MIA. The flexible MOF MIL-53(Al) was optimized essentially to the experimental large-pore form in the guest-free state with QuantumEspresso (QE) and with MIA molecules in the pores the structure contracted to close to the experimental narrow-pore form which was also confirmed by PXRD. In summary, the incorporation of flavins in MOFs yields solid-state materials with enhanced rigidity, stabilized conformation, defined orientation and reduced aggregations of the flavins, leading to increased fluorescence lifetime and quantum yield as controllable photo-luminescent and photo-physical properties.

Surface-Enhanced Raman Spectroscopic Analysis of Flavoenzyme Cofactors: Guidance for Flavin-Related Bio- and Chemo- Sensors

Flavin mononucleotides (FMNs) and flavin adenine nucleotide (FAD) play vital roles in the electron-transfer processes in diverse enzymatic reactions. Owing to the isoalloxazine chromophore, flavins are easily detectable by surface-enhanced Raman spectroscopy (SERS), a surface-sensitive technique. However, the details of the adsorption of flavins on SERS-active materials have never been investigated. In this study, a comprehensive SERS analysis of flavins containing lumichrome and lumiflavin on silver nanoparticles was conducted. With the aid of density-functional-theory calculations, our results suggested that the flavin molecules were adsorbed on the silver nanoparticles via the N3 site of the isoalloxazine moiety, which had a stronger adsorption ability than the adenine moiety in the FAD. The SERS spectra of the flavins at different pH values also supported this conclusion. This study demonstrated the feasibility of SERS for the structural characterization of flavins, paving the way for the functional exploration of flavin-labeled detection sensors and flavoprotein researches.

Immobilization of a flavin molecule onto poly(methacrylic acid)s and its application in aerobic oxidation catalysis: effect of polymer stereoregularity.

The isoalloxazine ring system, called flavin, was successfully immobilized on poly(methacrylic acid)s, PMAAs, with different tacticity via post-polymerization modification under suitable conditions. The resulting flavin-containing polymers showed catalytic activity for aerobic oxidation reactions, in which the polymer stereoregularity clearly influenced their catalytic activity.

Insights into Flavoenzymes: Structure, classification and potential biotechnological applications

Flavoenzymes are the diverse enzymes that use the flavin cofactors for their catalysis. They are widespread from bacteria to humans and have various biological role. This review provides a comprehensive overview about the flavoenzymes, classification, catalysis mechanism and their applications. The transfer of electrons between the flavin molecule which possess basically the isoalloxazine chromophore comprises of 7,8-dimethylbenzene moiety and the hydrophilic pyrimidine ring combine to form the amphipathic molecule, and the substrate which forms the valuable products by undergone chemical transformation which also provides basis for their classification. Here mainly, dehydrogenases, flavoprotein oxidases, monooxygenases and reductases classes are explained with examples along with their many physiological roles, showcasing their involvement in essential cellular functions. However, some additional redox centers flavoproteins, metal-containg, flavocytochromes and disulphide oxidoreductases are also mentioned here. Beside that they have many other tremendous applications including in disease diagnosis, treatments, novel drugs and therapeutic approaches for various diseases, biosensors, industrial, various biotechnological applications and some recent achieved advancements are discussed in detail. This study aims to advance knowledge of these unique enzymes by providing an extensive analysis of the classification, processes, and uses of flavoenzymes. Further study of flavoenzyme catalysis is required to unveil exciting avenues for future study and invention.

Vibrationally resolved absorption and fluorescence spectra of flavins: A theoretical simulation in the gas phase

AbstractFlavin is involved in a wide range of life processes. Flavin can exist in different forms due to its ability to transfer electron(s) in different physiological conditions. It is difficult to experimentally obtain the absorption and fluorescence spectra at the vibrational level. A systematically theoretical simulation is a necessary way to explore the fine structure of these spectra of all forms of flavin molecules. In this study, the vibrationally resolved absorption spectra and fluorescence spectra of five forms of flavins (fully oxidized form , neutral radical form , anionic radical form , neutral reduced form , and anionic reduced form ) are simulated by adiabatic or vertical methods combined with time‐dependent or time‐independent (TD/TI) formalisms, with displace, Duschinsky, and Herzberg−Teller (HT) effects under the framework of the Franck‐Condon approximation. The statistical vibronic transition analysis reveals the unity of the spectrum transition property, the relevant normal modes, and the primary geometrical variations. The correlation between geometry and spectral calculation is explained.

Thiolumazines as Heavy-Atom-Free Photosensitizers for Applications in Daylight Photodynamic Therapy: Insights from Ultrafast Excited-State Dynamics.

Finding appropriate photosensitizers (PSs) for daylight photodynamic therapy (dPDT) applications is extremely challenging, even though heavy-atom-free photosensitizers (HAFPSs) such as thiocarbonyl-modified nucleobases have shown a ray of hope. Few attempts have been made to find alternative natural products for dPDT applications. Pteridine heterocycles consisting of a pyrazine ring and a pyrimidine ring, such as lumazine, which exhibit many structural similarities to the alloxazine ring of the flavin molecule, could be an option for HAFPSs. The photophysical and quantum mechanical studies of the thio-modified lumazines revealed that sequential thiomodifications in lumazine result in a bathochromic shift. Additionally, higher tissue penetration depths were observed for thiolumazines. The fluorescence quenching in the case of thiomodified lumazines was explained using triplet state formation, whereas the contribution from the photoinduced electron transfer process cannot be ignored. It was also noticed that a strong one-photon absorption influenced the two-photon absorption (TPA) process, leading to a self-focusing effect in the visible spectral region. The higher tissue penetration and larger TPA cross section are the hallmark characteristics of the thiolumazines to be considered as potential HAFPSs for dPDT applications.

Exploration of bifurcated electron transfer mechanism in Bacillus cereus for enhanced power generation in double-chambered microbial fuel cells

Extracellular Electron Transfer (EET) is considered as the communication bridge between bacterial cells and outer electron acceptors. Apart from a few model microorganisms conventionally studied, the literature regarding the EET mechanism in Gram-positive bacteria and its conductive interaction is sparse. In the present study, proteolytic Gram-positive bacteria - Bacillus cereus is explored for enhancement of power generation in Microbial Fuel Cells (MFC). A low zeta potential (−0.1 V) of B. cereus, enables it to release electrons and protons much faster. We achieve a power density as high as 400 mW m−2 with a current density of ~5.8 mA cm−2 by inoculating an MFC with B. cereus. A genome wide transcriptome analysis by RNA-seq is used to categorize the genes and the significant pathways potentially involved in EET in B. cereus. The expression of gene cluster encodes for PTS (Phosphotransferase system) that catalyzes and transport phosphorylation of disaccharide present in the medium. This plays a regulatory role in biofilm formation. Simultaneously the secretion and assembly of extracellular flavin molecules by B. cereus, shuttle and mediate electron to the extracellular acceptor. In short, B. cereus uses bifurcated pathway i.e., directly by aligning the cytochrome complex and indirectly by secreting flavins molecules to promote electron transfer. These findings reveal its significant functional role in MFCs’ electrode community for sustainable bioenergy production.

Selective prototropism of lumichrome in the liposome/graphene oxide interface: A detailed spectroscopic study

The interactions of the biologically active fluorophores like flavins and biomolecules with nano carriers are very much important to produce targeted drug delivery systems. Also studying the interaction of graphene oxide (GO) with liposomes is essential for surface science and which have various applications. Herein, we have reported the interaction of a biologically active flavin molecule lumichrome (LU) with GO, in the absence and presence of zwitterionic 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposome by employing different spectroscopic techniques. These study also shows the prototropic tautomerization of LU, when it interacted with GO in the absence and presence of DMPC liposome. We have found that GO interacted with LU differently in the absence and presence of DMPC liposome. In the absence of DMPC liposome, LU molecules were directly adsorbed on the GO surface involving both edges and basal planes of GO via hydrogen bonding, π-π stacking between aromatic ring of LU and GO, and as a result we observe higher fluorescence quenching of LU. However, in the presence of DMPC liposome, LU molecules were partitioned inside the vesicle and in the presence of GO whole vesicle (in which LU molecules were partitioned) was placed on the edges of GO and here π-π stacking between aromatic ring of LU and GO is not possible, and as a result we observe moderate fluorescence quenching of LU. This study also indicates that zwitterionic DMPC liposome retained its structure when it interacts with GO. We have also found that in LU + GO complex, due to the direct adsorption of LU in GO surface, the prototropic tautomerization of LU is not possible, only the alloxazine form of LU exist. However, in LU + DMPC + GO complex when LU is incorporate inside the vesicle both alloxazine and isoalloxazine form of LU co-exist, indicates the prototropic tautomerization of LU in LU + DMPC + GO complex.

Extracellular riboflavin induces anaerobic biofilm formation in Shewanella oneidensis

BackgroundSome microorganisms can respire with extracellular electron acceptors using an extended electron transport chain to the cell surface. This process can be applied in bioelectrochemical systems in which the organisms produce an electrical current by respiring with an anode as electron acceptor. These organisms apply flavin molecules as cofactors to facilitate one-electron transfer catalyzed by the terminal reductases and in some cases as endogenous electron shuttles.ResultsIn the model organism Shewanella oneidensis, riboflavin production and excretion trigger a specific biofilm formation response that is initiated at a specific threshold concentration, similar to canonical quorum-sensing molecules. Riboflavin-mediated messaging is based on the overexpression of the gene encoding the putrescine decarboxylase speC which leads to posttranscriptional overproduction of proteins involved in biofilm formation. Using a model of growth-dependent riboflavin production under batch and biofilm growth conditions, the number of cells necessary to produce the threshold concentration per time was deduced. Furthermore, our results indicate that specific retention of riboflavin in the biofilm matrix leads to localized concentrations, which by far exceed the necessary threshold value.ConclusionThis study describes a new quorum-sensing mechanism in S. oneidensis. Biofilm formation of S. oneidensis is induced by low concentrations of riboflavin resulting in an upregulation of the ornithine-decarboxylase speC. The results can be applied for the development of strains catalyzing increased current densities in bioelectrochemical systems.

Preconditioning of AISI 304 stainless steel surfaces in the presence of flavins—Part II: Effect on biofilm formation and microbially influenced corrosion processes

AbstractBiofilm formation and microbially influenced corrosion of the iron‐reducing microorganism Shewanella putrefaciens were investigated on stainless steel surfaces preconditioned in the absence and presence of flavin molecules by means of XANES (X‐ray absorption near‐edge structure) analysis and electrochemical methods. The results indicate that biofilm formation was promoted on samples preconditioned in electrolytes containing minute amounts of flavins. On the basis of the XANES results, the corrosion processes are controlled by the iron‐rich outer layer of the passive film. Biofilm formation resulted in a cathodic shift of the open circuit potential and a protective effect in terms of pitting corrosion. The samples preconditioned in the absence of flavins have shown delayed pitting and the samples preconditioned in the presence of flavins did not show any pitting in a window of −0.3‐ to +0.0‐V overpotential in the bacterial medium. The results indicate that changes in the passive film chemistry induced by the presence of minute amounts of flavins during a mild anodic polarization can change the susceptibility of stainless steel surfaces to microbially influenced corrosion.

Photoinduced electron transfer in host-guest interactions of lumichrome with p-sulfonatocalix[6]arene

This study explores the complexation and fluorescence quenching of lumichrome (LC), a structural analogue of the biologically important flavin molecules, with a macrocyclic host, p-sulfonatocalix[6]arene (SCX6). It is revealed that the fluorescence quenching involves both static and dynamic interactions and occurs due to photoinduced electron transfer (PET) from the SCX6 host to the excited LC guest. The static quenching constant obtained from the modified Stern-Volmer relationship is in good agreement with the binding affinity of SCX6 with LC. Thermodynamic parameters obtained from the binding isotherms reveal that the SCX6-LC interaction is accompanied by entropy loss, which is consistent with the restriction imposed on the flexibility of the host and guest due to complex formation. Laser flash photolysis studies indicate that PET from SCX6 to LC is followed by proton abstraction by LC from the host or from the medium, to generate the corresponding radical species. The present results help in understanding the fluorescence quenching effect of p-sulfonatocalix[n]arene hosts that is widely exploited in designing fluorescence-based assays. Further, the prolonged lifetimes of the radicals in the SCX6-LC system underlines the notable role of macrocycles in the stabilization of radical intermediates in solution.

Sublimable Surfactant for Carbon Nanotube Dispersion: Study on a Flavin Compound

We describe the sublimation property of a flavin molecule as a solution to the surfactant residue problem of single-walled carbon nanotubes. Thermogravimetric analysis, UV-vis spectroscopy, and NMR...

Functional dynamics of a single tryptophan residue in a BLUF protein revealed by fluorescence spectroscopy

Blue Light Using Flavin (BLUF) domains are increasingly being adopted for use in optogenetic constructs. Despite this, much remains to be resolved on the mechanism of their activation. The advent of unnatural amino acid mutagenesis opens up a new toolbox for the study of protein structural dynamics. The tryptophan analogue, 7-aza-Trp (7AW) was incorporated in the BLUF domain of the Activation of Photopigment and pucA (AppA) photoreceptor in order to investigate the functional dynamics of the crucial W104 residue during photoactivation of the protein. The 7-aza modification to Trp makes selective excitation possible using 310 nm excitation and 380 nm emission, separating the signals of interest from other Trp and Tyr residues. We used Förster energy transfer (FRET) between 7AW and the flavin to estimate the distance between Trp and flavin in both the light- and dark-adapted states in solution. Nanosecond fluorescence anisotropy decay and picosecond fluorescence lifetime measurements for the flavin revealed a rather dynamic picture for the tryptophan residue. In the dark-adapted state, the major population of W104 is pointing away from the flavin and can move freely, in contrast to previous results reported in the literature. Upon blue-light excitation, the dominant tryptophan population is reorganized, moves closer to the flavin occupying a rigidly bound state participating in the hydrogen-bond network around the flavin molecule.

Microscopic Picture of the Solvent Reorganization During Electron Transfer to Flavin in Water.

The redox potential of molecular species is largely modulated by its molecular environment so that a change of the environment will lead to a different redox potential. However, a detailed molecular picture of reorganization of the environment upon reduction is still unclear. To unravel the details of the solvent reorganization during electron transfer, we have performed density functional theory-based molecular dynamics (DFT-MD) and hybrid quantum mechanics/molecular mechanics (QM/MM) simulations of the reduction of lumiflavin. Previously, we have calculated the reduction free energy curves of the redox half reactions of lumiflavin in water as a function of the instantaneous gap energy (ΔE) ( J. Chem. Theory Comput. 2013 , 9 , 3889 - 3899 ). In this work, we focus on finding the changes in the solvent environment that correlate with this ΔE reaction coordinate. Comparing the QM/MM simulations, in which the solvent is modeled with an empirical force field, with the (full) DFT-MD simulations, we find that the response through electronic polarization plays a significant role in the latter case. Also a small charge transfer between flavin and solvent is observed in the full DFT treatment. As a result, we find only in the case of the QM/MM model a strong correlation between ΔE and the (pairwise computed) electrostatic potential (ESP) at the flavin due to the solvent. By analyzing the contribution of the ESP at the flavin per solvent molecule, we cannot only distinguish between the different modes of hydration by solvent molecules that coordinate at the hydrophilic and hydrophobic sides of the flavin molecule but also quantify their contribution to the reorganization free energy by measuring the ESP fluctuations per solvent molecule.

Individual Solubilization Behavior of Single-Walled Carbon Nanotubes by Riboflavin (Vitamin B2) in Water and Its Analyses Using Regression Approach and Computational Simulations

Abstract Flavin analogues are dispersants of carbon nanotubes. We report the finding that riboflavin, which is a nutrient that is much less expensive than a flavin mononucleotide, is a good SWNT dispersant in water. We carried out a temperature dependence test of the solubilization of SWNTs, and propose a possible solubilization mechanism based on a regression analysis. We assume that the linear and lognormal components for the solubilized SWNTs can be explained by nonspecific and specific interactions between the riboflavin and the SWNTs, respectively. We also carried out computational calculations (molecular dynamics simulations) on this SWNT solubilization by which we proposed a suitable complex structure of the SWNT that provided the number of adsorbed flavin molecules via hydrogen bonding on the tubes.

Spectro-Electrochemical Investigation of the Effects of Flavin Electron Transporters in Artificial and Bacterial Biofilms

Bacterial biofilms have the capacity to develop and thrive in virtually all circumstances and surfaces, even in the most challenging environmental conditions. The pervasive and recalcitrant existence of biofilms renders them to be a significant safety risk and economical encumbrance in a wide array of industries and technologies, and therefore is a priority area of research. It is essential to develop an improved understanding of the mechanisms implicated during biofilm formation, such as in the case of the diffusion of bacterial-secreted extracellular electron transporters, which are purported to play an important role during biocorrosion by exoelectrogenic bacteria. Hence, a fundamental understanding of electron transfer mechanisms between bacteria and extracellular electron acceptors will contribute insight to our understanding of charge transport and chemistry at the biofilm – external insoluble electron acceptor interface. In the present work, Attenuated Total Reflection - Fourier transform-infrared (ATR-FTIR) spectroscopy has been coupled to electrochemical techniques for the nondestructive, in situ spectro-electrochemical monitoring of biofilms in real-time. Shewanella sp. have been selected for this investigation due to their adaptable exoelectrogenic respiratory capacities and their notable ability to reduce metals via several different mechanisms of extracellular electron transfer mechanisms, including self-secreted flavin shuttles. Gold-thin film model substrates have been used due to their inert nature and for their ability to permit precise manipulation of the substrate surface polarization. Additionally, hydrogels comprised of calcium cross-linked alginate have been used to mimic the architectural features of extracellular polymeric substances which are integral to a bacterial biofilm, to allow the study of electron-transporting flavin molecules in an artificial biofilm. The results will demonstrate patterns of diffusion, akin to how flavins would diffuse in a naturally occurring biofilm, and how polarization affects this process. Furthermore, insight will be gained on how the redox behavior of flavins can influence the development and evolution of a biofilm. This interdisciplinary approach should shed light on bacterial electron transfer mechanisms which could contribute towards emerging technologies which seek to better understand such mechanisms for novel antifouling strategies, renewable energies, and bioremediation.

(Invited) Facile Isolation of Semiconducting Single-Walled Carbon Nanotubes By Flavin-Based Supramolecular Chemistry

The separation/purification of semiconducting single-walled carbon nanotubes (sem-SWNTs) with high quality is one of the most important issues in the science and technology of carbon nanotubes[1-4]. We have already reported that supramolecular coordination polymer [1] and hydrogen bonding systems [2] as well as use of a flavin molecule [3] are powerful methods for highly efficient adsorbent-free sem-SWNT separation. Here, we designed and synthesized a flavin with thioalkyl substituent at 7- and 8 positions, then examined its selective sem-SWNT sorting behavior. We have found that the addition of a metal ion formed a complex with the flavin, which enhanced selective (8,6)SWNT sorting.

Investigation of Different Prototropic Forms of Biologically Active Flavin Lumichrome in the Presence of Liposome.

Herein, we reported the photophysical behavior of lumichrome (LC), one of the biologically active flavin molecules, in the presence of small unilamellar vesicle of anionic lipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). With the help of different spectroscopic techniques, we have proposed that anionic DMPC liposome interacts with the cationic form LC in ground state and in excited state and modulate the spectral properties of LC. Photophysical study reveals that different prototropic forms of LC are present in DMPC liposome medium. In the presence of DMPC liposome, fluorescence emission properties of LC vary with change in excitation and emission wavelengths. This indicates switch over between different structural forms of LC. From fluorescence lifetime measurements and fluorescence lifetime imaging (FLIM) study, it was revealed that emission decay profile of LC was fitted biexponentially in the presence of liposome. It suggests that in the presence of liposome, more than one form of LC is present. We have constructed the time-resolved area-normalized emission spectra (TRANES) of LC in the liposome and found one isoemissive point. This confirmed that two emissive species of LC are present in liposome. FLIM study and FE-SEM study give an idea about the structural feature of the complex between LC and liposome.