Amide Derivatives of DMABN: A New Class of Dual Fluorescent Compounds

Smart fluorescent polysaccharides: Recent developments and applications

Polysaccharides are ubiquitous, generally benign in nature, and compatible with many tissues in biomedical situations, making them appealing candidates for new materials such as therapeutic agents and sensors. Fluorescent labeling can create the ability to sensitively monitor distribution and transport of polysaccharide-based materials, which can for example further illuminate drug-delivery mechanisms and therefore improve design of delivery systems. Herein, we review fluorophore selection and ways of appending polysaccharides, utility of the product fluorescent polysaccharides as new smart materials, and their stimulus-responsive nature, with focus on their biomedical applications as environment-sensitive biosensors, imaging, and as molecular rulers. Further, we discuss the advantages and disadvantages of these methods, and future prospects for creation and use of these self-reporting materials.

Comparative DFT Computational Studies with Experimental Investigations for Novel Synthesized Fluorescent Pyrazoline Derivatives

A novel series of pyrazoline derivatives were synthesized and their spectral properties were characterized via FT-IR, ¹H, and ¹³C NMR. The electronic transitions and fluorescence properties were tracked via UV-Vis and emission spectrometry. The density functional theory (DFT) calculations have been also computed to get spot onto the geometry, electronic transitions and spectroscopic properties theoretically that has been compared with the encountered experimental ones. Moreover, the dipole moment, optimized energy, HOMO - LUMO energies and band gaps were calculated for novel candidates pyrazoline derivatives with highly fluorescence quantum yield.

New highly selective turn-on fluorescence receptor for the detection of copper (II)

Three new receptors (1a-c) bearing a p-dimethylaminobenzamide fluorophore have been synthesized and evaluated in terms of their fluoroionophoric properties towards various metal ions. Notably, receptors 1a and 1c exhibited dramatic fluorescent enhancement towards Cu²⁺ in acetonitrile. Subsequent investigations revealed that the highly selective behavior of these receptors towards Cu²⁺ could be attributed to the Cu²⁺-mediated oxidative cyclization of these compounds to the corresponding 1,3,4-oxadiazoles. Solvent effects and quantum calculations indicated that 1a and 1c both possessed an intramolecular charge transfer channel, which could be obstructed by the oxidative cyclization of these receptors. Receptor 1a was successfully applied to the determination of the Cu²⁺ in drug sample with a low detection limit of 2.2×10^-8molL^-1.

Positional impact of fluorescently modified G-tetrads within polymorphic human telomeric G-quadruplex structures

Emissive C8-aryl-2'-deoxyguanosines placed within G-tetrads of G-quadruplex structures are useful probes for distinguishing G-quadruplexes from duplex structures using fluorescence spectroscopy. Here, we report the positional impact of C8-furyl-dG ((Fur)dG) on G-quadruplex folding in the human telomere 22-mer oligonucleotide (HTelo22, (d[AG3(T2AG3)3])). The (Fur)dG probe was inserted into four different positions within the three unique G-tetrads of HTelo22, and G-quadruplex folding was monitored by UV-vis thermal denaturation, circular dichroism, and fluorescence spectroscopy. Our studies demonstrate the impacts of C8-aryl-dG adduct formation on G-quadruplex polymorphism in K(+) solution and in the presence of the additives and cosolutes, CH3CN, polyethylene glycol (PEG-600), and N-methyl mesoporphyrin IX (NMM). Our experiments predict that C8-aryl-dG derivatives can serve as useful tools for various in vitro studies aimed at understanding both the implications of DNA adduct formation within G-quadruplex structures and the unique implications imposed by various folding topologies on biological function/recognition.

Pyridinium-fused pyridinone: a novel "turn-on" fluorescent chemodosimeter for cyanide

A new chemodosimeter based on pyridinium-fused pyridinone iodide (PI) has been obtained through a "clean reaction" method. This compound can detect CN(-) in aqueous solution with a high selectivity and rapid response. The detection of CN(-) occurs through the nucleophilic attack of CN(-) on the C=N bond, which induces the destruction of the π-conjugation on the pyridinium ring. Support of this detection mechanism was obtained by (1)H NMR titration, HR-MS, and DFT calculations. Upon the addition of 10 equivalents CN(-) to a solution of PI in THF/H2 O (1:1, v/v), a 57-fold enhancement in fluorescence intensity was observed at the maximum emission wavelength of 457 nm. Meanwhile, the maximum absorption wavelength was also blue-shifted from 447 nm to 355 nm. Other common anions such as BF4(-), PF6(-), F(-), Cl(-), Br(-), I(-), H2PO4(-), ClO4(-), CH3 COO(-) , NO2 (-) , N3 (-) , and SCN(-) had little effect on the detection of CN(-). The response time of PI for CN(-) was less than 5 seconds. The detection limit was calculated to be 5.4×10(-8) M, which is lower than the maximum permission concentration in drinking water (1.9 μM) set by the World Health Organization (WHO).

Effect of nitro groups on the photo physical properties of benzimidazolone: a solvatochromic study

Electronic absorption and fluorescence spectra of mono, di, and tri-nitro benzimidazolones are measured at room temperature (298 K) in nine solvents with different polarities and the observed shifts are compared with benzimidazolone. Ground and excited state electric dipole moments are determined using the solvatochromic method based on the bulk solvent properties, F(1)(ε, n) and F(2)(ε, n). A reasonable agreement is observed between the experimental and ab initio dipole moments. Change in dipole moment is also determined using the solvatochromic method based on the microscopic solvent polarity parameter, (E(T)(N)), which considers the polarization changes due to hydrogen bonding in different solvents. It has been observed that the correlation of the solvatochromic Stokes shifts with the parameter (E(T)(N)), is superior to that derived using bulk solvent polarity functions for all the benzimidazolones reported in the present study. Calculated difference between excited state and ground state dipole moments seems to be a good measure of the effect of nitro group when correlated with (E(T)(N)).

Solvent-dependent intramolecular charge transfer dual fluorescence of p-dimethylaminobenzanilide bearing steric ortho,ortho-dimethyl substituents at amido aniline

Intramolecular charge transfer (ICT) dual fluorescence was observed in various organic solvents with p-dimethylaminobenzanilide (DMBA) derivatives bearing ortho-methyl (DMOMBA) and ortho,ortho-dimethyl (DMDMBA) substituents at amido aniline moiety. Ab initio calculation and absorption spectral data indicated that high steric hindrance was introduced by the ortho,ortho-dimethyl substitutions. It was found that, with DMDMBA, the CT emission initially shifted to the red with increasing solvent polarity from cyclohexane (CHX, 480 nm) to diethyl ether (DEE, 520 nm), similar to those of DMBA derivatives with the ortho-, meta- or para-methyl substitutions at amido aniline moiety. However, there is a characteristic blue-shift of the long wavelength emission between DEE and tetrahydrofuran (THF, 424 nm) then a bathochromic shift again in highly polar solvent acetonitrile (ACN, 484 nm). The unusual solvent-dependent CT emission was ascribed to two competitive CT channels. One is benzanilide (BA)-like CT, whose CT reaction occurs from amido aniline to benzoyl moiety in nonpolar solvent CHX and DEE; the other one is p-dimethylaminobenzamide (DMABA)-like, whose CT reaction occurs from dimethylamino to benzanilide moiety in highly polar solvent THF and ACN. These findings revealed the steric effect plays an important role in the ICT process, which may alter the properties of the electron donor and/or acceptor, but also change the reaction potential.

Microwave-induced facile synthesis of water-soluble fluorogenic alginic acid derivatives

A facile microwave-induced method was developed for synthesizing water-soluble fluorescent derivatives of alginic acid (ALG) with four different diamines, hydrazine (HY), ethylenediamine (EDA), 1,6-hexanediamine (HDA), and 1,4-cyclohexanediamine (CHDA), followed by a cross-linking reaction with a natural cross linker genipin. The ethylenediamine derivative of alginic acid (ALG-EDA) exhibited good fluorescent activity, which upon cross linking was enhanced threefold. The other amide derivatives, for example, ALG-HY, ALG-HDA, and ALG-CHDA, were not fluorescent, but their respective crosslinked products exhibited excellent fluorescent activity. The fluorescence intensity had an inverse correlation with the number of carbon atoms present in the amine, which in turn was a function of degree of substitution (DS). These fluorescent polysaccharide derivatives are of potential utility in the domain of sensor applications.

Photophysical and complexation properties of benzenesulfonamide derivatives with different donor and acceptor moieties

Pyrrolobenzosulfonamide, indolobenzosulfonamide and carbazolobenzosulfonamide derivatives with different acceptor groups were synthesized and their photophysical properties were compared. The electron donor linking sites are found to influence the emission characteristics of these compounds while acceptor linking sites have no noticeable effects on the spectral properties. P2-A5 which is a C-C linked pyrrole derivative exhibited different spectral properties from the C-N linked pyrrole derivatives. The complexation properties of the molecules were also investigated employing Na (I), Ca (II), Li (I), Mg (II), Zn (II) and Cu (II) ions.

Novel chiral fluorescent chemosensors for malate and acidic amino acids based on two-arm thiourea and amide

The charge neutral anthracene based chiral fluorescent receptors 4a and 4b containing thiourea and amide groups were synthesized by simple steps in good yields, and their enantioselective recognition for chiral dicarboxylic anions (L/D-malate, L/D-aspartate, and L/D-glutamate) were examined by UV–vis, fluorescence, and 1H NMR spectroscopy. The sensor 4a exhibited an excellent enantioselective recognition ability towards malate (Kass (L)/Kass (D) = 9.65).Key words: enantioselective recognition, chiral chemosensor, fluorescence, malate.

Study on the fluorescence properties of a new intramolecular charge transfer compound 1,5-diphenyl-3-(N-ethylcarbazole-3-yl)-2-pyrazoline

The fluorescence properties of a newly synthesized compound, 1,5-diphenyl-3-(N-ethylcarbazole-3-yl)-2-pyrazoline (DEP) have been studied. On excitation at 352 nm, the fluorescence spectrum exhibits a large red shift with an increase in the polarity of solvents. The intensity of the band is different in different solvents as well. The change in the dipole moment in various solvents at room temperature has been characterized by the absorption and steady state fluorescence techniques and calculated based on the Lippert-Mataga equation. DEP has an increase of dipole moment of 2.83 D units on excitation to the lowest singlet state. It is concluded that photo-induced charge transfer from N (1) to C (3) actually exists in the excited state of the pyrazoline moiety. Its fluorescence property is relative to viscosity and temperature of solvents. The phi(f) of DEP in neutral medium or basic medium is higher than acidic medium. In addition, when the concentration of DEP is higher than 10(-3) M, its fluorescence is quenched by the collision of each molecule. The red shift of the maximum emission of DEP attributes to the formation of aggregates and the conjugate system is strengthened.

Stereoselective syntheses of fluorescent non-natural aromatic amino acids based on asymmetric Michael additions

Four fluorescent non-natural aromatic amino acids have been synthesized based on a key stereoselective Michael addition reaction. S-1-phenylethylamine was employed as both the source of amine and the stereoselectivity controller. The overall yields were moderate (30-50%). Fluorescent properties of some of the fluorophores were also investigated. It was found that compounds with a dimethylamino group bonded to the aromatic ring display intramolecular charge transfer fluorescence.

CT-Operated Bifunctional Fluorescent Probe Based on a Pretwisted Donor–Donor–Biphenyl

Taking into account the structural requirements for TICT-type sensor molecules, a general synthetic route to derive pH and cation-responsive pretwisted donor (D)-donor (D) biphenyls (b) equipped with donor receptors is developed and a first model compound containing a mono aza-15-crown-5 and a DMA receptor is synthesized, see Scheme 1. The spectroscopic properties of this new bifunctional D-D biphenyl are studied in the non-polar and polar solvents cyclohexane, acetonitrile, and methanol. Protonation as well as complexation studies are performed with the representative metal ions Na(I), K(I), Ca(II), Ag(I), Zn(II), Cd(II), Hg(II), and Pb(II) to reveal the potential of this molecule for communication of whether none, only one, or both binding sites are engaged in analyte coordination by spectroscopically distinguishable outputs. The results are compared to those obtained with closely related donor (D)-acceptor (A) substituted biphenyl-type sensor molecules and are discussed within the framework of neutral and ionic D-A biphenyls.

A unique NH-spacer for N-benzamidothiourea based anion sensors. Substituent effect on anion sensing of the ICT dual fluorescent N-(p-dimethylaminobenzamido)-N′-arylthioureas

A series of N-(p-dimethylaminobenzamido)-N'-(substituted-phenyl)thioureas (substituent = p-CH3, H, p-Cl, p-Br, m-Br, m-NO2, and p-NO2) were designed as anion sensors in order to better understand the -NH-spacer via a substituent effect investigation. In these molecules the dual fluorescent intramolecular charge transfer (ICT) fluorophore p-dimethylaminobenzamide as the signal reporter was linked to the anion-binding site, the thiourea moiety, via an N-N single bond. Correlation of the NMR signals of the aromatic and -NH protons with substituents in these molecules indicated that the N-N single bond stopped the ground-state electronic communication between the signal reporter and the anion-binding site. Dual fluorescence was observed in highly polar solvents such as acetonitrile with the former five derivatives. The fact that the CT emission wavelength and the CT to LE emission intensity ratio of the sensors were independent of the substituent existing in the anion-binding moiety suggested that the substituent electronic effect could not be communicated to the CT fluorophore in the excited-state either. Yet in acetonitrile both the CT dual fluorescence and the absorption of the sensors were found to be highly sensitive toward anions. A conformation change around the N-N bond in the sensor molecules was suggested to occur upon anion binding that established the electronic communication between the signal reporter and the anion-binding site. The anion binding constants of the N-(p-dimethylaminobenzamido)thiourea sensors were found higher than those of the corresponding traditional N-phenylthiourea counterparts and the substituent effect on the anion binding constant was much higher than that in the latter. "-NH-" was shown to be a unique spacer that affords N-benzamidothiourea allosteric anion sensors.

A highly selective charge transfer fluoroionophore for Cu2+

A dual fluorescent charge transfer fluoroionophore (1) with its ionophore incorporated in the electron acceptor was developed and was found to show a highly selective fluorescent response to Cu2+ with a dramatic enhancement in its CT emission.

Rational Design of a Chromo- and Fluorogenic Hybrid Chemosensor Material for the Detection of Long-Chain Carboxylates

A strategy for the rational design of a new optical sensor material for the selective recognition of long-chain carboxylates in water is presented. The approach relies on the combination of structure-property relationships to single out the optimal molecular sensor unit and the tuning of the sensing characteristics of an inorganic support material. A spacer-substituted 7-urea-phenoxazin-3-one was employed as the signaling moiety and a mesoporous trimethylsilylated UVM-7 (MCM-41 type) material served as the solid support. The sensor material shows the advantageous features of both modules that is absorption and emission in the visible spectral range, a fluorescence red-shift and enhancement upon analyte coordination, and the amplification of noncovalent (binding) and hydrogen-bonding (recognition) interactions in the detection event. Besides these basic results that are related to the design and performance of the sensor material, the paper discusses general aspects of amido-substituted phenoxazinone photophysics and addresses some general features of molecular anion recognition chemistry in aqueous vs nonaqueous media, utilizing steady-state and time-resolved optical as well as NMR spectroscopies. Detailed studies on potentially competing biochemical species and a first access to the schematic model of the response of the sensor material as obtained by a combination of fluorescence lifetime distribution analysis and Langmuir-type fitting of the gross binding constants complement the key issues of the paper.

Selenoxanthones via directed metalations in 2-arylselenobenzamide derivatives

The reaction of N, N-diethyl 4-(N', N'-dimethylamino)-2-phenylselenobenzamide (7a), N, N-diethyl 4-methoxy-2-phenylselenobenzamide (7b), N, N-diethyl 4-(N', N'-dimethylamino)-2-[(3-(N, N-dimethylamino)phenylseleno]benzamide (7c), and N, N-diethyl 4-methoxy-2-(3-methoxyphenylseleno)-benzamide (7d) with excess lithium diisopropylamide (LDA) gave 2-N, N-(dimethylamino)-9H-selenoxanthone (9a), 2-methoxy-9H-selenoxanthone (9b), 2,7-bis-N, N-(dimethylamino)-9H-selenoxanthone (9c), and 2,5-dimethoxy-9H-selenoxanthone (9d) in 70%, 59%, 23%, and 90% isolated yields, respectively. N, N-Diethyl 2-phenylselenobenzamide (2-Se) gave no reaction with LDA, t-BuLi, MeLi, or lithium 2,2,6,6-tetramethylpiperidide as base. Electron donation from the 4-substituent of benzamide derivatives 7a-7d may increase the directing ability of the carbonyl oxygen to metalate the 2-position of the arylseleno group.

Tripodal ligand incorporating dual fluorescent ionophore: a coordinative control of photoinduced electron transfer

p-(N,N-Dimethylamino)benzenesulfonamide (DMABSA), a dual fluorescent fluorophore, has been derivatized into two new fluoroionophores for transition metal cations. The electron-acceptor sulfonamide group has been N-substituted by a 2-pyridylmethylene group to lead to a bidentate ligand which forms a 2:1 complex with Cu(II). The crystal structure of the copper(II) complex is reported. The Cu(II) is coordinated through the pyridine N- and sulfonamide N-deprotonated atom which account for the blue-shift of the absorption and the partly quenched fluorescence. When DMABSA was incorporated into the tris(2-aminoethyl)amine (tren), a tripodal, dual-fluorescent ligand, is obtained which shows higher binding affinity for Zn(II) than for Cu(II). Furthermore, the large increase of the short wavelength emission and the disappearance of the TICT emission, upon Zn complexation, allow measurements of the Zn(II) concentration from relative fluorescence intensity at two wavelengths.

A novel thiourea-based dual fluorescent anion receptor with a rigid hydrazine spacer

[structure: see text] A neutral receptor with a rigid hydrazine spacer, N-p-(dimethylamino)benzamido-N'-phenylthiourea, was prepared, and its dual fluorescence in acetonitrile was found to show response toward the presence of anions such as AcO(-), H(2)PO(4)(-), HSO(4)(-), Br(-), Cl(-), F(-), and ClO(4)(-) with high sensitivity and selectivity toward AcO(-).

Unique dual fluorescence of sterically congested hexaalkyl benzenehexacarboxylates: mechanism and application to viscosity probing

The static and dynamic fluorescence behavior of a series of hexaalkyl benzenehexacarboxylates (R(6)BHC; R = methyl (Me), tert-butyl (tBu), (-)-menthyl (Men), (-)-bornyl (Bor), (-)-1-methylheptyl (MHp), neopentyl (neoPn), and 2-adamantyl (Ad)) was studied by steady-state and time-resolved fluorescence spectroscopy. Dual fluorescence from both the partially relaxed metastable Franck-Condon-like (FC') and the fully relaxed (RX) state was observed for tBu(6)BHC, Men(6)BHC, Bor(6)BHC, MHp(6)BHC, neoPn(6)BHC, and Ad(6)BHC, whereas only single fluorescence from the RX state was observed for Me(6)BHC. Picosecond time-resolved fluorescence spectroscopic measurements clearly demonstrated that the initially formed Franck-Condon (FC) state sequentially converts to the FC' and then to RX state, with the relaxation hindered to such an extent that it shows variation with the steric bulk of the R groups. Thus, the fluorescence lifetimes (tau's) of FC' and RX are critically dependent on the bulkiness of the R groups, varying from 17 to 130 ps and from 0.6 to 1.1 ns, respectively. The relative intensity of FC' and RX fluorescence (I(RX)/I(FC)(')) was found to be dependent on the excitation wavelength, suggesting that the conformational relaxation from the FC' to RX state can compete with the vibrational relaxation of the FC' state. The temperature and pressure dependences were studied by steady-state fluorescence spectroscopy to give the activation energies of 1-3 kcal/mol for the FC'-to-RX relaxation of congested R(6)BHCs, as well as the activation volumes of 2.0, -0.62, and 7.4 mL/mol for tBu(6)BHC, Men(6)BHC, and Bor(6)BHC at room temperature. The fluorescence anisotropy (rho), as a measure of molecular motion, was also determined to be in the ranges of 0.03-0.3 for FC' and 0.003-0.01 for RX. The much larger rho's for the FC' fluorescence by a factor of 2-100 are attributed to the shorter tau's. The I(RX)/I(F' ratio was found to be insensitive to solvent polarity, but critically dependent on solvent viscosity, exhibiting an excellent linear relationship with the reciprocal viscosity. The potential use of these sterically congested R(6)BHCs as microenvironmental viscosity probes is proposed.