Bathochromic Spectral Shift Research Articles

A novel NIR fluorescent probe for visualizing hydrogen sulfide in Alzheimer's disease.

Alzheimer's disease (AD) represents a devastating form of neurodegeneration, hallmarked by a relentless erosion of memory and cognitive faculties. One key player in this complex pathology is hydrogen sulfide (H2S), a gaseous neurotransmitter that is highly concentrated in the brain. Its fluctuating levels have been compellingly linked to the onset and progression of AD. Despite the availability of numerous fluorescent probes for detecting H2S, targeted imaging of this neurotransmitter within AD models remains underexplored. To bridge this gap, we have engineered an innovative near-infrared (NIR) "turn-on" fluorescent probe, designated as probe 1. Crafted around a dicyanoisophorone scaffold, the probe incorporates a strategic methoxy modification to facilitate a bathochromic spectral shift. Impressively, upon binding with H2S, probe 1 exhibited a robust 46-fold enhancement in fluorescence at a wavelength of 680 nm. We successfully deployed this probe to visualize both exogenous and endogenous H2S in living cells and zebrafish. Further, our pathogenic investigations have corroborated that diminished H2S levels are intricately linked to an escalation in amyloid plaque formation. Most crucially, we employed probe 1 to capture real-time images of H2S concentrations within the hippocampal tissue of AD mouse models. This revealed a significant depletion in H2S levels, thereby underscoring the probe's immense potential as an effective tool for the diagnosis and prevention of Alzheimer's disease.

Acidic pH-Triggered Live-Cell Lysosome Specific Tracking, Ratiometric pH Sensing, and Multicolor Imaging by Visible to NIR Switchable Cy-7 Dyes.

We have demonstrated an efficient synthetic route with crystal structures for the construction of acidic pH-triggered visible-to-NIR interchangeable ratiometric fluorescent pH sensors. This bioresponsive probe exhibits pH-sensitive reversible absorption/emission features, low cytotoxicity, a huge 322 nm bathochromic spectral shift with augmented quantum yield from neutral to acidic pH, high sensitivity and selective targeting ability of live-cell lysosomes with ideal pKa , off-to-on narrow NIR absorption/fluorescence signals with high molar absorption coefficient at acidic lysosomal lumen, and in-situ live-cell pH-activated ratiometric imaging of lysosomal pH. Selective staining and ratiometric pH imaging in human carcinoma live-cell lysosomes were monitored by dual-channel confocal laser scanning microscope using a pH-activatable organic fluorescent dye comprising a morpholine moiety for lysosome targeting and an acidic pH openable oxazolidine ring. Moreover, real-time tracking of lysosomes, 3D, and multicolor live-cell imaging have been achieved using the synthesized pH-activatable probe.

Tetraphenylethylene-Arylamine Derivatives as Hole Transporting Materials for Perovskite Solar Cells.

A series of hole transporting materials (HTMs) with fused tetraphenylethylene cores (9,9'-bifluorenylidene and dibenzo[g,p]chrysene) as well as different substitution positions of arylamine side arms has been designed and synthesized. A reference HTM with a non-fused tetraphenylethylene core is also prepared for a comparative study. It is noted that fused tetraphenylethylene molecules show a bathochromic spectral shift, electronegative character, and lower reorganization energies than the non-fused ones. Furthermore, the molecules with side arms located on the meta-position on the tetraphenylethylene core in terms of a double bond exhibit a deeper highest occupied molecular orbital level than those of the para-position-based ones whether tetraphenylethylene is fused or not. Moreover, the reorganization energies of fused meta-position-based HTMs are lower than those of para-position-based HTMs. Fused tetraphenylethylene HTMs own a better hole-extraction capability than the non-fused ones. When used in perovskite solar cells, all devices with fused tetraphenylethylene HTMs display better performance than those of the non-fused ones. The HTMs based on dibenzo[g,p]chrysene exhibit better performance than those of bifluorenylidene. Moreover, the devices with HTMs with side arms located on the meta-position on the tetraphenylethylene core display higher power conversion efficiency than those of the para-position-based ones. The results give some new insight and reference to develop ideal HTMs for perovskite solar cells.

Photo-Physics of Föster Resonance Energy Transfer to Enhance the Sensitivity of Co-Polymer Towards Nitro-Compounds

Föster Resonance Energy Transfer (FRET) is a powerful technique used to probe close-range molecular interactions. Physically, the FRET phenomenon manifests as a dipole–dipole interaction between closely juxtaposed fluorescent molecules (10–100 Å). For instance, after photoexcitation, a fluorophore may de-excite through direct emission with a bathochromic spectral shift. However, in the presence of a nearby acceptor, the donor non-radiatively transfers energy to the acceptor molecule, resulting in quenched donor fluorescence. With the advent of genetically encoded fluorescent molecules, this method has found widespread biological applications as a spectroscopic atomic-scale ruler, biochemical reaction kinetics and chemical sensor. [1] Our effort is to employ this FRET technique to make a prototype device for highly sensitive detection of environment pollutant.Among the most common environmental pollutants, nitroaromatic compounds (NACs) are of particular interest because of their durability and toxicity. That’s why, sensitive and selective detection of small amounts of nitroaromatic explosives, in particular, 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP) has been a key challenge due to the increasing threat of explosive-based terrorism and the need of environmental monitoring of drinking and waste water. In addition, the excessive utilization of TNP in several other areas such as burn ointment, pesticides, glass and the leather industry resulted in environmental accumulation, and is eventually contaminating the soil and aquatic systems. To the date, A great number of elegant methods, including fluorimetry, gas chromatography, mass, ion-mobility and Raman spectrometry have been successfully applied for explosive detection. Among these efforts, fluorescence-quenching methods based on the mechanism of FRET show good assembly flexibility, high selectivity and sensitivity. [2]Recently, our group has reported a highly fluorescent dansyl copolymer poly[(Methyl methacrylate)-co-(Dansyl-alanine methacryloyloxyethyl ester)], P[(MMA-co-(Dansyl-Ala-HEMA)], DCP for sensitive detection of NACs. [3] Here our alternative approach to increase fluorescence sensing efficiency by exciting the fluorophore DCP through Förster resonance energy transfer (FRET). In this paper, we report a polymer-polymer FRET-based sensor system for the highly selective detection of NACs, such as TNP, DNT and TNT. The sensor system is composed of a copolymer Poly[(N,N-dimethylacrylamide)-co-(Boc-Trp-EMA)] (RP) bearing tryptophan derivative in the side chain as donor and dansyl tagged copolymer P(MMA-co-Dansyl-Ala-HEMA) (DCP) as an acceptor. Initially, the inherent fluorescence of RP copolymer is quenched by non-radiative energy transfer to DCP which only happens once the two molecules are within Förster critical distance (R0). The excellent spectral overlap (Jλ= 6.08×1014 nm4M-1cm-1) between donors’ (RP) emission profile and acceptors’ (DCP) absorption profile makes them an exciting and efficient FRET pair i.e. further confirmed by the high rate of energy transfer from RP to DCP i.e. 0.87 ns-1 and lifetime measurement by time correlated single photon counting (TCSPC) to validate the 64% FRET efficiency. This FRET pair exhibited a specific fluorescence response to NACs such as DNT, TNT and TNP with 5.4, 2.3 and 0.4 mM LODs, respectively. The detection of NACs occurs with high sensitivity by photoluminescence quenching of FRET signal induced by photo-induced electron transfer (PET) from electron-rich FRET pair to electron-deficient NAC molecules. The estimated stern-volmer constant (KSV ) values for DNT, TNT and TNP are 6.3 × 103, 7.6 × 103 and 2.2 × 104 M-1, respectively, this is approximately 6 orders of higher magnitude than the previous report. [3] The mechanistic details of molecular interactions are established by time-resolved fluorescence, steady state fluorescence and absorption spectroscopy confirmed that the sensing process is of mixed type, i.e. both dynamic and static quenching as lifetime of FRET system (0.73 ns) is reduced to 0.55, 0.57 and 0.61 ns DNT, TNT and TNP, respectively.Consequently, our results suggest a promising and potential approach to use FRET- and PET-based fluorescent probe to detect NACs with higher sensitivity. It’s simple and rich methodology opens up the possibility of designing optical sensor of various NACs in one single platform for designing multimodal sensor for environmental monitoring and future field based study.Reference: 1. Jares-Erijman, E.A. et al. Nat. Biotechnol. 2003, 21, 1387.2. Sun, X. et al. Chem. Soc. Rev. 2015, 44, 8019.3. Kumar, V. et al. Sci. Rep. 2019, 9 (1), 7269. Figure 1

Luminescent mechanochromism of gold N-heterocyclic carbene complexes with hypso- and bathochromic spectral shifts.

Two gold N-heterocyclic carbene complexes show contrasting luminescent mechanochromism behavior with hypso- and bathochromic spectral shifts. The distinct emission shifts upon mechanical stimulation can be explained by the aggregate-to-monomer transformation and intensified intermolecular interactions, respectively.

Interpretation of Absorption Spectra of Some Bisazomethine Dyes in a Crystalline State in Terms of Conformational Change and Exciton Interaction

Abstract Absorption properties of 13 bisazomethine dyes in a crystalline state were studied by optical waveguide spectroscopy. Their solid-state absorption spectra were found to shift bathochromically relative to those in solution with no remarkable change in a spectral shape. The observed spectral shifts were characterized in terms of two intermolecular interactions, conformational change and exciton interaction, on the basis of the crystal structure. Solid-state fluorescence properties of the diethylamino derivatives were also examined for their electronic characterization. The characteristic two-dimensional staircase structure, one of the proposed structures of J-aggregates, was found to play a significant role in the bathochromic spectral shift of all the bisazomethine derivatives.

Fluorescence-based logic gate for sensing of Ca2+ and F- ions using PVP crowned chrysene nanoparticles in aqueous medium.

Polyvinyl pyrrolidone (PVP) crowned chrysene nanoparticles (CHYNPs) were prepared by using a reprecipitation method. Dynamic light scattering (DLS) and scanning electron microscope (SEM) studies indicate that the monodispersed spherical nanoparticles bear a negative charge on their surfaces. The bathochromic spectral shift in the UV-visible and fluorescence spectrum of CHYNPs from chrysene (CHY) in acetone solution supports the J- type aggregation of nanoparticles. The aggregation-induced enhanced emission of CHYNPs at 486 and 522nm decreases by increasing the concentration of the Ca2+ ion solution. It can display an ON-OFF type fluorescence response with high selectivity towards Ca2+ ions aqueous medium. Furthermore, the in situ generated PVP-CHYNPs-Ca2+ ensemble could recover the quenched fluorescence upon the addition of fluoride anions resulting in an OFF-ON type sensor. The present method has a correlation coefficient R2 = 0.988 with a detection limit of 1.22μg/mL for Ca2+ in the aqueous medium. The fluorescence changes of PVP crowned CHYNPs upon the addition of Ca2+ and F- can be utilized as an INHIBIT logic gate at the molecular level, using Ca2+ and F- chemical inputs and the fluorescence intensity signal as output.

Synthesis of an oxadiazole through an indole mediated single step procedure for selective optical recognition of Cu2+ ions

An unusual dimerization of 1-nitroso-2-naphthol mediated by indole afforded a substituted oxadiazole, which was characterized by NMR, HR-MS and single crystal X-ray crystallography. The reaction represents a new method for the synthesis of five membered heterocyclic rings. Owing to the presence of suitably positioned donor atoms, the oxadiazole was screened for affinity towards transition metal ions in aqueous solution. The addition of an aqueous solution of copper ions to a solution of the oxadiazole resulted in a bathochromic spectral shift along with the color change from colorless to yellow visible to the naked eye. The receptor also displayed selective fluorescence “turn-off” response towards Cu2+ ions in aqueous medium. An excellent detection limit value (0.47μM) was observed using fluorescence spectroscopy. The DFT calculations were performed to investigate the experimental processes.

Co-pigmentation of pelargonidin derivatives in strawberry and red radish model solutions by the addition of phenolic fractions from mango peels

Pelargonidin-based colors suffer from notorious instability. A phenolic mango peel extract and defined phenolic fractions thereof were shown to effectively modulate the visible absorption of anthocyanins from strawberry (Fragaria x ananassa Duch.) and red radish (Raphanus sativus L.) by intermolecular co-pigmentation. Consistently, non-acylated pelargonidin derivatives from strawberry exerted significantly greater hyper- and bathochromic spectral shifts than their acylated counterparts from red radish. The addition of low molecular-weight co-pigments such as gallic acid and monogalloyl glucoses to strawberry anthocyanins led to strong hyperchromic shifts from 30% to 48%, while gallotannins (>six galloyl units) exerted smaller co-pigmentation effects (36±2%; Δλmax 13nm), possibly due to steric hindrances. In contrast, penta- and hexa-O-galloyl-glucose induced greatest and most stable co-pigmentation effects (53±2%; Δλmax 13nm). Irrespective of the underlying mechanisms and the responsible compounds, phenolic mango peel extracts might represent suitable color enhancers for coloring foodstuff, particularly for those containing non-acylated pelargonidin derivatives.

Rigidified malononitrile- and ketone-merocyanines in rigid environments

<p class="03Abstract">Two merocyanine dyes containing a malononitrile or a ketone functional group as electron-acceptors, and a piperidine group as electron-donor were synthetized and crystallized as pigments. The electron-donor and -acceptor moieties are linked <em>via</em> an octahydroanthracene skeleton, forming an electronic push-pull molecular system. The crystal structure of the malononitrile compound was solved <em>ab initio</em> from X-ray powder diffraction data, complementing the reported structure of the ketone pigment. Both compounds show similar molecular structures in the solid state, yet with completely different crystal packing schemes. The crystal structures were analysed with inspecting the Hirshfeld surfaces. IR spectroscopy was applied to complement the crystallographic study. The absorption characteristics of both pigments emerge from the push-pull chemical structure, which was visualized by plotting the electrostatic potentials, calculated using molecular geometries as observed in the solid state. The solid state UV-vis spectra showed peak broadening and bathochromic spectral shift as compared to the spectra recorded in solution, depending on the polarity of the solvent molecules: The largest shifts of the spectra of solid state pigments were observed with respect to the spectra recorded in toluene solution, whether the smallest to those in ethanol. </p>

Optical Properties of Three Differently Colored Crystal Modifications of a 2,3-Dicyanopyrazine Dye

Abstract Optical properties of three crystal modifications of 5-t-butyl-2,3-dicyano-6-[4-(dimethylamino)styryl]pyrazine having different color appearances were measured and interpreted on the basis of crystal structure analysis. Two of the three modifications exhibited a bathochromic spectral shift both in absorption and fluorescence compared with those in a toluene solution of the dye. The crystal structure analysis revealed that a two-dimensional brick-wall structure is formed in both modifications. In contrast, the third modification showed a hypsochromic absorption shift with a large bathochromic fluorescence shift. The crystal structure of this modification was characterized by a one-dimensional stacked molecular column. The optical characteristics of the three modifications were qualitatively interpreted in terms of excitonic intermolecular interaction on the basis of their crystal structures.

J-aggregate structure in a chloroform solvate of a 2,3-dicyanopyrazine dye – Separation of two-dimensional stacking dye layers by solvate formation

Here, we report the J-aggregate structure of a chloroform solvate of 5-t-butyl-2,3-dicyano-6-[4-(dimethylamino)styryl]-pyrazine with a strong intramolecular charge transfer system. The dye was found to form a two-dimensional brick-wall structure separated by chloroform molecules in the solvated crystals, which exhibited intense red fluorescence. The absorption maximum of the solvate was also found to show a bathochromic spectral shift. These observed optical characteristics were interpreted in terms of excitonic intermolecular interaction based on two-dimensional brick-wall structure which is one of the proposed structures for J-aggregates.

Colorimetric detection of aliphatic primary amines and a molecular logic gate based on a photochromic phenoxyquinone derivative

A photochromic phenoxyquinone-based, sensor for aliphatic primary amine was developed. An efficient trans-to-ana photoisomerization was occurred when 6-(4′-methoxyphenoxy)-5,12-naphthacenequinone in acetonitrile was irradiated with 365 nm UV light. The photochemically generated “ana” quinone intermediate was found to undergo nucleophilic substitution reactions by aliphatic primary amines to afford a large bathochromic shift in the absorption spectra, allowing colorimetric detection of the aliphatic primary amines. Neither aromatic nor secondary and tertiary amines were able to promote the bathochromic spectral shift of the phenoxyquinone. Removal of the phenoxy group by a primary amine was confirmed by using 1H NMR analysis and a preparative scale reaction. In addition, colorimetric detection of the aliphatic primary amine was demonstrated to be feasible with phenoxyquinone-containing PDMS films. Since the large bathochromic shift occurs only in the presence of UV light and aliphatic primary amine, the sensor system functions a molecular AND logic gate.

Revisit of 4,4′-Diaminodiphenyl Sulfone Photophysics in Different Solvents

This paper aims at getting the origin of dual emission of 4,4′-diaminodiphenyl sulfone (Dapsone) in various solvents using steady state and time-resolved emission spectroscopy in conjunction with ground and excited state optimized geometry calculations in gaseous phase and in solvents. The dual fluorescence in different solvents and a distinctive bathochromic spectral shift of the low energy band in polar solvents indicate the possibility of intramolecular charge transfer (ICT) from the donor site (−NH2) to the acceptor moiety in the excited state. Time-resolved emission spectra (TRES) and more precisely time-resolved area normalized emission spectra (TRANES) depict the evolution of the dynamics of excited state species and the charge transfer. Hindrance of rotational relaxation in restricted environments causes intensified charge transfer emission quantum yield. A plausible model for excited state deactivation through ICT has been proposed on the basis of both theoretical and experimental findings. The o...

Intermolecularly hydrogen-bonded dimeric helices: tripyrrindiones

A rare and unusual class of tripyrrolic compounds, violet-colored tripyrrin-1,14-diones, can be prepared easily and in moderately high yields from base (piperidine)-catalyzed condensation of 3-pyrrolin-2-ones with 2,5-diformylpyrroles. Dipyrrinones adopt the all- syn- Z conformation leading to helical, lock-washer like structures, which form dimers that are held together by intermolecular hydrogen bonds in nonpolar solvents and in the crystal. Strong bathochromic spectral shifts of the tripyrrindione ∼480 nm long wavelength UV–visible absorption band are seen with added base: DBU, 615 nm; TFA, 573 nm; and Zn(OAc) 2, 586 nm.

Aromatic Monoazines as Fluorescent Sensors for Photoacid Generation in Thin Polymer Films

This paper reports a novel approach to monitor photoinduced acid generation in polymer films of the type used in microlithography. We have employed fluorescent acid-sensitive sensors to monitor the progress of photoacid generation in solution and in thin polymer films. We have studied the effect of p-toluenesulfonic acid on the spectral properties of 2-phenylpyridine, 2-phenylquinoline, and acridine in diglyme solution and in poly(methyl methacrylate) (PMMA) films using absorption and fluorescence spectroscopy. In both cases a bathochromic spectral shift and an increase in fluorescence quantum yield are observed upon protonation. In samples containing a photoacid generator, the acid production upon irradiation could be monitored by observing the increase in fluorescence intensity with proceeding irradiation time in both solution and PMMA films. This new acid-monitoring method may find application in the study of diffusional processes in polymer films.

Crustacyanin, the lobster carapace astaxanthin-protein: effects of modification of tyrosine residues of apocrustacyanin with tetranitromethane on the ability of the protein to reconstitute with astaxanthin

The effects of modification of apocrustacyanin with the tyrosine-specific reagent, tetanitromethane, on the ability of the protein to reconstitute with astaxanthin is investigated. Modification of an average three to six tyrosine residues per apoprotein molecule destroys the specific carotenoid binding responsible for the bathochromic spectral shift of the native carotenoprotein. The reaction is accompanied by intermolecular cross-linking of the protein, giving polymeric, polydisperse material which associates with carotenoid micelles. The loss of the carotenoid binding in this case may be due to general protein unfolding rather than alteration of specific tyrosine residues at the ligand binding sites. At lower levels of tyrosine modification (two to three tyrosine/subunit) intermolecular cross-linking is still evident but the monomeric and cross-linked dimeric apoprotein have reduced affinity for astaxanthin. Treatment of the separate apoprotein, A 2, with low levels of tetranitromethane modifying less than three tyrosine on average/subunit results, partly, in the formation of intermolecular cross-linked dimers and lesser amounts of higher molecular sized oligomers. The remaining apoprotein monomer (and the cross-linked dimers) shows a reduced ability to bind astaxanthin. It is concluded that tyrosine residues may be of importance for the interaction between carotenoid and apoprotein or for maintaining the integrity of the carotenoid binding sites.

Enhancement by Artificial Electron Acceptors of Thylakoid Lumen Acidification and Zeaxanthin Formation

In chloroplasts the enzyme violaxanthin de-epoxidase is responsible for the transformation of violaxanthin (Vio) to zeaxanthin (Zea) in the presence of ascorbate (Asc). The enzyme is mobile within the thylakoid lumen and becomes bound to the membrane in its active state. It is characterized by a narrow pH optimum at 5.2 and is presumed to be activated by the photosynthetic electron transport via the acidification of the lumenal pH of the thylakoid vesicles. Correlations between the pH of the lumen and the formation of Zea were studied using isolated thylakoids and leaf disks from Spinacia oleracea L. The alterations of the lumenal pH were measured by a photometric method using neutral red as indicator. A so far not documented bathochromic spectral shift of the protonated dye in the thylakoid lumen was taken into consideration. The xanthophylls were quantified by HPLC. In vitro , when using thylakoids that had been illuminated by red light at pH 7.5, artificial electron acceptors (such as methyl viologen (MV) or menadione (MD)) increased both the light-dependent H + -accumulation within the thylakoid lumen and the transformation of Vio to Zea. In vivo , after infiltration in leaf disks, MV was also effective. In its presence a 5-min illumination of these disks increased the Zea content by about 100 % in comparison with the MV-free control. Moreover, in isolated preilluminated Zea-containing thylakoids MD strongly inhibited the epoxidation of Zea to Vio, which is catalyzed by a mixed-function oxygenase in the presence of the cosubstrates O 2 and NAD(P)H at pH 7.5 in the dark. This inhibition was the result of an oxidation of NAD(P)H by MD catalyzed by an undefined thylakoid enzyme. The decreased level of (reduced) NAD(P)H and the fact that the reduced MD cannot substitute for NAD(P)H in the epoxidation reaction caused the diminished Zea epoxidation. The results demonstrate that under the influence of artificial electron acceptors an increased formation of Zea in the thylakoid membrane is strictly correlated with an increased light-dependent H + concentration in the thylakoid lumen.

Solvatochromic Response of an Aminobenzoxazinone in the Visible Region

Solvatochromic Response of an Aminobenzoxazinone in the Visible Region

Introduction of hydroxyl-bearing amino acids causes bathochromic spectral shifts in rhodopsin. Amino acid substitutions responsible for red-green color pigment spectral tuning.

Comparisons of the deduced amino acid sequences of eight primate photopigment genes led to the proposal that three amino acid substitutions produce the approximately 1,000 cm-1 difference in the absorption maxima of human red and green pigments (Neitz, M., Neitz, J., and Jacobs, G.H. (1991) Science 252, 971-974). We tested this proposal by mutating these three residues in rhodopsin and evaluating the effects on spectral properties. Nonpolar residues normally present in rhodopsin and in the green pigment were substituted by hydroxyl-bearing residues normally present in the red pigment. Two of these substitutions (Phe-261 to Tyr or Ala-269 to Thr) caused significant red shifts in the absorption maxima of the resulting mutant pigments. A third substitution (Ala-164 to Ser) caused only a slight effect. Combinations of substitutions caused additive shifts in absorption maxima. A double mutant (Phe-261 to Tyr/Ala-269 to Thr) displayed an absorption maximum that was red-shifted by 775 cm-1. Wavelength modulation in the visual pigments responsible for red-green color vision is likely to be governed by retinal-protein interactions involving primarily these two amino acid residues. Furthermore, interactions of hydroxyl-bearing amino acids with the chromophore may be a general mechanism of the opsin shift in visual pigments.