The Enhanced Proton-Accepting Ability of Bound Water in Poly(vinyl alcohol) Films

Poly(vinyl alcohol) (PVA) films have been widely used as flexible matrixes in advanced optical materials. Most studies concern the rigidification strategy of PVA films, while the physicochemical properties of inside bound water are ignored. In this study, we have employed lumichrome as the fluorescent probe to explore the acid-base property of bound water, which was demonstrated to exhibit an enhanced proton-accepting ability than bulk water, evidenced by the promoted deprotonation of lumichrome in the ground state. Decreasing the water content in a PVA film is demonstrated to further improve the proton-accepting ability. Different from that in bulk solution, a selective prototropism of lumichrome is determined in PVA films, which is induced by the formation of an anchored lumichrome-PVA complex through three hydrogen bonds. This work first points out the enhanced proton-accepting ability of bound water in PVA films, opening a new avenue for the development of flexible optical materials based on proton transfer.

Photodynamics of biological active flavin in the presence of zwitterionic surfactants

In the flavin family of photoactive biomolecules, lumichrome (LM) is a very important compound. It contains a tri-cyclic structure with methyl groups at two sides. It formed by the partial decomposition and biodegradation of riboflavin in both acidic as well as in neutral medium. Herein, we have studied the photophysical properties of LM in the presence of two zwitterionic surfactants, namely dodecyldimethyl(3-sulfopropyl) ammonium hydroxide inner salt (DSB), and tetradecyldimethyl(3-sulfopropyl) ammonium hydroxide inner salt (TSB), having the same head group but a different tail part. We have used steady-state absorption, fluorescence emission, and time-resolved fluorescence emission measurements. We observed that in the presence of zwitterionic surfactant aggregates LM shows excitation and emission wavelength dependent emission properties, which demonstrate the structural changes that take place from one form to another prototropic form of LM molecule. The higher rotational relaxation time of LM in the case of DSB compared to TSB demonstrated that LM is facing more rigid environment in DSB micelles compared to TSB micelles.

Structural transition dynamics of biologically active flavins in alkylglucoside surfactants aggregates

The photophysics and structural transition dynamics of a bio-active flavin lumichrome (LM) entrapped in two sugars based neutral surfactants were reported. Sugar-based surfactants, which were used for research purpose are potential environmentally friendly, green alternative amphiphilic surface active substance compared to other kinds of common surfactants. Here, two alkyl glucoside surfactants n-octyl-β-D-glucopyranoside (OBG) and n-octyl-β-D-thioglucopyranoside (OBTG) were used. This work is carried out by using steady-state absorption and fluorescence emission spectroscopy along with time-resolved fluorescence emission techniques. Photophysics of LM was modulated several folds in these two sugar-based neutral micelles. LM exhibits excitation and emission wavelength dependent fluorescence properties in these two sugars based neutral micelles. LM confined in the micellar environments exhibited structural transition dynamism, i.e. different kinds of conformers are equilibrated. Herein, different conformers of LM are identified and explained with the help of spectroscopic methods. From the fluorescence anisotropy measurement, it was found that the rotational relaxation time of LM in OBG micelle was more compared to that in OBTG micelle, which indicates that the LM molecule faced much more constrained environment in OBG micellar media.

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.

K. P, Pal H, Dutta Choudhury S. An insight into the molecular and surface state photoluminescence of carbon dots revealed through solvent-induced modulations in their excitation wavelength dependent emission properties

Solvent environment can uniquely alter excitation wavelength dependent photoluminescence of carbon dots.

Interaction of Biologically Active Flavins inside Bile Salt Aggregates: Molecular Level Investigation

In this work we have studied the photophysics of biologically active flavin molecule lumichrome (LCM) in different bile-salt aggregates. With alteration of the functional groups of the bile salts, the photophysics of confined fluorophore is largely affected and shows difference in their spectral behavior. This study also reveals the selective prototropic species of LCM present in bile salt aggregates. In the presence of the bile salt aggregates, LCM molecule shows excitation and emission wavelength-dependent emission properties, indicating switch over of the structural change of different prototropic form of the LCM molecule. The observation of higher rotational relaxation time in NaDC aggregates compared to NaTC aggregates clearly reflects that NaDC aggregates are more rigid due to its greater hydrophobicity and large in size, which is capable to bind the guest molecule more into their nanoconfined medium. Moreover, due to less acidic nature, NaDC aggregates have more ability to accept hydrogen bond from the LCM molecule and show the selective formation of isoalloxazine N10 anion (A1 monoanionic form) of LCM.