Fluorogenic properties of 4-dimethylaminocinnamaldehyde (DMACA) enable high resolution imaging of cell-wall-bound proanthocyanidins in plant root tissues

Proanthocyanidins (PAs) are polymeric phenolic compounds found in plants and used in many industrial applications. Despite strong evidence of herbivore and pathogen resistance-related properties of PAs, their in planta function is not fully understood. Determining the location and dynamics of PAs in plant tissues and cellular compartments is crucial to understand their mode of action. Such an approach requires microscopic localization with fluorescent dyes that specifically bind to PAs. Such dyes have hitherto been lacking. Here, we show that 4-dimethylaminocinnamaldehyde (DMACA) can be used as a PA-specific fluorescent dye that allows localization of PAs at high resolution in cell walls and inside cells using confocal microscopy, revealing features of previously unreported wall-bound PAs. We demonstrate several novel usages of DMACA as a fluorophore by taking advantage of its double staining compatibility with other fluorescent dyes. We illustrate the use of the dye alone and its co-localization with cell wall polymers in different Populus root tissues. The easy-to-use fluorescent staining method, together with its high photostability and compatibility with other fluorogenic dyes, makes DMACA a valuable tool for uncovering the biological function of PAs at a cellular level in plant tissues. DMACA can also be used in other plant tissues than roots, however care needs to be taken when tissues contain compounds that autofluoresce in the red spectral region which can be confounded with the PA-specific DMACA signal.

Solvent Effects on the Photophysical Properties of a Donor-acceptor Based Schiff Base

In this work, a donor-acceptor substituted aromatic system ((E)-N-((E)-3-(4 (dimethylamino)phenyl) allylidene)-4-(trifluoromethyl) benzenamine (DPATB) has been synthesized and its detailed photophysics of intramolecular charge transfer process have been explored on the basis of steady state absorption, fluorescence and time resolved spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring from the donor group to the acceptor moiety in the excited state. Effect on addition of acid and pH on steady state spectral properties further reveals excited state charge transfer character. Quantum chemical calculations were performed in order to study the conformation and polarity of DPATB at their ground as well as excited electronic states. The HOMO and LUMO molecular orbital pictures are obtained at DFT level using B3LYP functional and 6-311 + g(d,p) basis set which clearly support excited state intramolecular charge transfer process. The molecular electrostatic potential maps for the optimized ground state, donor twisted and acceptor twisted geometry shed insight on the electrostatic potential and charge distribution in a system which gives information about the reacting site of the probe and nature of the reaction. In this work, detailed photophysics of excited state intramolecular charge transfer process in donor-acceptor system (DPATB) was evaluated using steady state and time-resolved fluorescence spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring in DPATB. Molecular orbital pictures as obtained from DFT based computational analysis reveals a significant change in the distribution of electron density upon transition from HOMO to LUMO which confirms an ICT process occurring from the donor group to the acceptor moiety in the excited state.

Entrapment in micellar assemblies switches the excimer population of potential therapeutic luminophore azapodophyllotoxin

Azapodophyllotoxin is a new class of anti-tumor agent with brilliant therapeutic activity and understanding its physicochemical nature in bio-mimetic microenvironments may provide substantial importance in context of its intercellular localization, efficacy as well as delivery. The present work epitomizes environment-sensitive fluorescence modulation of a prodigy, 4-(2-Hydroxyethyl)-10-phenyl-3,4,6,7,8,10- hexahydro-1H-cyclopenta[g]furo[3,4-b]quinoline-1-one (HPFQ) from the class of anti-cancer agent Azapodophyllotoxin, in differently charged model bio-mimetic micellar microenvironment of cationic CTAB, anionic SDS and neutral Triton X-100 using UV-visible absorption, steady state fluorescence, time-resolved fluorescence and fluorescence anisotropy studies. As a distinct phenomenon, anticancer HPFQ exhibits prolific fluorescence in solvents of varying polarity, originating from a mixed contribution of locally excited, charge transfer and excimer emission. A dramatic modulation in the photophysics of HPFQ has been observed in two types of surfactant consortiums: pre-micellar and post-micellar at physiological and anoxic pH. On photo-excitation, anti-cancer HPFQ exists in monomer-excimer equilibrium with varying ratios in different polarity regions. The marked enhancement in fluorescence intensity of HPFQ in post-micellar region of the surfactant under study probably arises due to regeneration of the monomer from its excimer. This reoccurrence reduces the possibility of Förster resonance energy transfer (FRET) from monomer to excimer, which essentially increases the desired emission intensity. Localization of HPFQ in micellar systems highly depends on polarity gradient inside the micelle, electrostatic, hydrophobic and intermolecular hydrogen bonding interactions. Further corroboration with the polarity sensitive experiments in dioxane-water mixture indicates towards spatial localization of the probe molecule in the stern layer of cationic CTAB, sheer surface of neutral TX100 and outer Gouy-Chapman layer in anionic SDS micelles. A molecular binary logic gate correlates the dominance of micellization over the polarity factor, which enhances the fluorescence response of HPFQ. The enhancement of the emissive potential of anti-cancer HPFQ in biomimetic environments by switching its excimer population may have an immense importance to achieve the status of a dual therapeutic and imaging agent altogether in progressive biomedical research.

Time-dependent density functional theory study on excited-state spectral and dynamic properties of hydrogen-bonded complexes formed by DMACA and water

Excited-state spectral and dynamic properties of hydrogen-bonded complexes formed by 4-(dimethylamino)cinnamic acid with water molecules were studied using the TDDFT method.

Interaction of cinnamic acid derivatives with serum albumins: a fluorescence spectroscopic study

Cinnamic acid (CA) derivatives are known to possess broad therapeutic applications including anti-tumor activity. The present study was designed to determine the underlying mechanism and thermodynamic parameters for the binding of two CA based intramolecular charge transfer (ICT) fluorescent probes, namely, 4-(dimethylamino) cinnamic acid (DMACA) and trans-ethyl p-(dimethylamino) cinnamate (EDAC), with albumins by fluorescence spectroscopy. Stern-Volmer analysis of the tryptophan fluorescence quenching data in presence of the added ligand reveals fluorescence quenching constant (κ(q)), Stern-Volmer constant (K(SV)) and also the ligand-protein association constant (K(a)). The thermodynamic parameters like enthalpy (ΔH) and entropy (ΔS) change corresponding to the ligand binding process were also estimated. The results show that the ligands bind into the sub-domain IIA of the proteins in 1:1 stoichiometry with an apparent binding constant value in the range of 10(4) dm(3) mol(-1). In both the cases, the spontaneous ligand binding to the proteins occur through entropy driven mechanism, although the interaction of DMACA is relatively stronger in comparison with EDAC. The temperature dependence of the binding constant indicates the induced change in protein secondary structure.

Effect of solvent hydrogen bonding on the photophysical properties of intramolecular charge transfer probe trans-ethyl p-(dimethylamino) cinamate and its derivative

Intramolecular charge transfer (ICT) behavior of trans-ethyl p-(dimethylamino) cinamate (EDAC) and 4-(dimethylamino) cinnamic acid (DMACA) were studied by steady state absorption and emission, picosecond time-resolved fluorescence experiments in various pure and mixed solvent systems. The large fluorescence spectral shift in more polar solvents indicates an efficient charge transfer from the donor site to the acceptor moiety in the excited state compared to the ground state. The energy for 0,0 transition (nu(0,0)) for EDAC shows very good linear correlation with static solvent dielectric property; however, fluorescence emission maximum, stokes shift and fluorescence quantum yield show significant deviation from linearity in polar protic solvents, indicating a large contribution of solvent hydrogen bonding on the excited state relaxation mechanism. A quantitative estimation of contribution from different solvatochromic parameters was made using linear free energy relationship based on Kamlet-Taft equation.