A Dimethylaminophenyl-Substituted Naphtho[1,2-b]quinolizinium as a Multicolor NIR Probe for the Fluorimetric Detection of Intracellular Nucleic Acids and Proteins

AbstractThe dye 3‐(4‐(N,N‐dimethylamino)phenyl)naphtho[1,2‐b]quinolizinium was synthesized by means of a Suzuki–Miyaura reaction in good yield, and its binding properties with duplex DNA, quadruplex DNA (G4‐DNA), RNA, and bovine serum albumin (BSA) were investigated by photometric, fluorimetric and polarimetric titrations and DNA denaturation analysis. The compound intercalates into DNA and RNA, associates in binding site I of BSA, and binds to G4‐DNA by terminal π stacking. The ligand exhibits a fluorescence light‐up effect upon complexation to these biomacromolecules, which is more pronounced and blue shifted in the presence of BSA (Φfl=0.29, λfl=627 nm) than with the nucleic acids (Φfl=0.01–0.05, λfl=725–750 nm). Furthermore, the triple‐exponential fluorescence decay of the probe when bound to biomacromolecules in a cell enables their visualization in this medium and the differential labeling of cellular components

Ultrafast photoinduced relaxation dynamics of the indoline dye D149 in organic solvents

The relaxation dynamics of the indoline dye D149, a well-known sensitizer for photoelectrochemical solar cells, have been extensively characterized in various organic solvents by combining results from ultrafast pump–supercontinuum probe (PSCP) spectroscopy, transient UV-pump VIS-probe spectroscopy, time-correlated single-photon counting (TCSPC) measurements as well as steady-state absorption and fluorescence. In the steady-state spectra, the position of the absorption maximum shows only a weak solvent dependence, whereas the fluorescence Stokes shift Δ[small nu, Greek, tilde]F correlates with solvent polarity. Photoexcitation at around 480 nm provides access to the S1 state of D149 which exhibits solvation dynamics on characteristic timescales, as monitored by a red-shift of the stimulated emission and spectral development of the excited-state absorption in the transient PSCP spectra. In all cases, the spectral dynamics can be modeled by a global kinetic analysis using a time-dependent S1spectrum. The lifetime τ1 of the S1 state roughly correlates with polarity [acetonitrile (280 ps) < acetone (540 ps) < THF (720 ps) < chloroform (800 ps)], yet in alcohols it is much shorter [methanol (99 ps) < ethanol (178 ps) < acetonitrile (280 ps)], suggesting an appreciable influence of hydrogen bonding on the dynamics. A minor component with a characteristic time constant in the range 19–30 ps, readily observed in the PSCP spectra of D149 in acetonitrile and THF, is likely due to removal of vibrational excess energy from the S1 state by collisions with solvent molecules. Additional weak fluorescence in the range 390–500 nm is observed upon excitation in the S0 → S2 band, which contains short-lived S2 → S0 emission of D149. Transient absorption signals after excitation at 377.5 nm yield an additional time constant in the subpicosecond range, representing the lifetime of the S2 state. S2 excitation also produces photoproducts

Search for rare or forbidden decays of the D0 meson

We present a search for nine lepton-number-violating and three lepton-flavor-violating neutral charm decays of the type D0→h'−h−ℓ'+ℓ+ and D0→h'−h+ℓ'±ℓ∓, where h and h′ represent a K or π meson and ℓ and ℓ′ an electron or muon. The analysis is based on 468 fb−1 of e+e− annihilation data collected at or close to the Υ(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the twelve modes, and we establish 90% confidence level upper limits on the branching fractions in the range (1.0–30.6)×10−7. The limits are between 1 and 3 orders of magnitude more stringent than previous measurements.publishedVersio

Measurements of the absolute branching fractions of B± →k±Xc c

A study of the two-body decays B±→Xc¯cK±, where Xc¯c refers to one charmonium state, is reported by the BABAR Collaboration using a data sample of 424 fb−1. The absolute determination of branching fractions for these decays are significantly improved compared to previous BABAR measurements. Evidence is found for the decay B+→X(3872)K+ at the 3σ level. The absolute branching fraction B[B+→X(3872)K+]=[2.1±0.6(stat)±0.3(syst)]×10−4 is measured for the first time. It follows that B[X(3872)→J/ψπ+π−]=(4.1±1.3)%, supporting the hypothesis of a molecular component for this resonance.publishedVersio

Light meson spectroscopy from Dalitz plot analyses of ηc decays to η0 K+K− , η0 π + π − , and ηπ + π − produced in two-photon interactions

We study the processes γγ→ηc→η′K+K−, η′π+π−, and ηπ+π− using a data sample of 519  fb−1 recorded with the BABAR detector operating at the SLAC PEP-II asymmetric-energy e+e− collider at center-of-mass energies at and near the Υ(nS) (n=2, 3, 4) resonances. This is the first observation of the decay ηc→η′K+K− and we measure the branching fraction Γ(ηc→η′K+K−)/(Γ(ηc→η′π+π−)=0.644±0.039stat±0.032sys. Significant interference is observed between γγ→ηc→ηπ+π− and the nonresonant two-photon process γγ→ηπ+π−. A Dalitz plot analysis is performed of ηc decays to η′K+K−, η′π+π−, and ηπ+π−. Combined with our previous analysis of ηc→K¯Kπ, we measure the K∗0(1430) parameters and the ratio between its η′K and πK couplings. The decay ηc→η′π+π− is dominated by the f0(2100) resonance, also observed in J/ψ radiative decays. A new a0(1700)→ηπ resonance is observed in the ηc→ηπ+π− channel. We also compare ηc decays to η and η′ final states in association with scalar mesons as they relate to the identification of the scalar glueball.publishedVersio

Intramolecular Charge Transfer with Crystal Violet Lactone in Acetonitrile As a Function of Temperature: Reaction Is Not Solvent-Controlled

Intramolecular charge transfer (ICT) with crystal violet lactone (CVL) in the excited singlet state takes place in solvents more polar than <i>n</i>-hexane, such as ethyl acetate, tetrahydrofuran, and acetonitrile (MeCN). In these solvents, the fluorescence spectrum of CVL consists of two emission bands, from a locally excited (LE) and an ICT state. The dominant deactivation channel of the lowest excited singlet state is internal conversion, as the quantum yields of fluorescence (0.007) and intersystem crossing (0.015) in MeCN at 25 °C are very small. CVL is a weakly coupled electron donor/acceptor (D/A) molecule, similar to an exciplex ¹(A^–D⁺). A solvatochromic treatment of the LE and ICT emission maxima results in the dipole moments μ_e(LE) = 17 D and μ_e(ICT) = 33 D, much larger than those previously reported. This discrepancy is attributed to different Onsager radii and spectral fluorimeter calibration. The LE and ICT fluorescence decays of CVL in MeCN are double exponential. As determined by global analysis, the LE and ICT decays at 25 °C have the times τ₂ = 9.2 ps and τ₁ = 1180 ps, with an amplitude ratio of 35.3 for LE. From these parameters, the rate constants <i>k</i>_a = 106 × 10⁹ s^–1 and <i>k</i>_d = 3.0 × 10⁹ s^–1 of the forward and backward reaction in the LE ⇄ ICT equilibrium are calculated, resulting in a free enthalpy difference Δ<i>G</i> of −8.9 kJ/mol. The amplitude ratio of the ICT fluorescence decay equals −1.0, which signifies that the ICT state is not prepared by light absorption in the S₀ ground state, but originates exclusively from the directly excited LE precursor. From the temperature dependence of the fluorescence decays of CVL in MeCN (−45 to 75 °C), activation energies <i>E</i>_a = 3.9 kJ/mol (LE → ICT) and <i>E</i>_d = 23.6 kJ/mol (ICT → LE) are obtained, giving an enthalpy difference Δ<i>H</i> (= <i>E</i>_a – <i>E</i>_d) of −19.7 kJ/mol, and an entropy difference Δ<i>S</i> = −35.5 J mol^–1 K^–1. These data show that the ICT reaction of CVL in MeCN is not barrierless. The ICT reaction time of 9.2 ps is much longer than the mean solvent relaxation time of MeCN (0.26 ps), indicating, in contrast with earlier reports in the literature, that the reaction is not solvent controlled. This conclusion is supported by the observation of double exponential LE and ICT fluorescence with the same decay times

Absence of Intramolecular Charge Transfer with 4‑Fluoro‑<i>N</i>,<i>N</i>‑dimethylaniline (DMA4F), Contrary to an Experimental Report Supported by Computations

With 4-fluoro-<i>N</i>,<i>N</i>-dimethylaniline (DMA4F), only a single fluorescence from a locally excited (LE) state is observed, irrespective of solvent polarity, temperature, and excitation wavelength. The relatively small excited state dipole moment μ_e = 7.3 D confirms the identification as LE. The single exponential fluorescence decays in the nonpolar <i>n</i>-hexane (2.04 ns) and in the strongly polar acetonitrile (5.73 ns) are a further support. Similar results are obtained with 4-chloro-<i>N</i>,<i>N</i>-dimethylaniline (DMA4Cl), having a chlorobenzene subgroup, a somewhat better electron acceptor than the fluorobenzene moiety in DMA4F. The absence of intramolecular charge transfer (ICT) with DMA4F is in accord with its large energy gap Δ<i>E</i>(S₁,S₂) of 8300 cm^–1 in <i>n</i>-hexane between the two lowest singlet excited states, which is even larger than that (6300 cm^–1) of <i>N</i>,<i>N</i>-dimethylaniline (DMA), for which an LE → ICT reaction likewise does not occur. The results with DMA4F are in contradiction with a publication by Fujiwara et al. (Chem. Phys. Lett. 2013, 586, 70), in which the appearance of dual LE + ICT emission is reported for DMA4F in <i>n</i>-hexane and MeCN at room temperature. The ICT/LE fluorescence quantum yield ratio Φ′(ICT)/Φ­(LE) reached a maximum value of ∼2, in <i>n</i>-hexane and surprisingly also in MeCN, as the excitation wavelength approaches the red-edge of the absorption spectrum. These, in our opinion, erroneous observations were supported by time-dependent density functional theory (TDDFT) calculations, which compute a perpendicularly twisted lowest ICT state (TICT) state. This is a further example of the general tendency of computations to find a TICT conformation for the lowest excited singlet state of electron donor/acceptor molecules such as <i>p</i>-substituted anilines