Fluorescence spectroscopy of monoclonal antibodies produced against the fluorescyl hapten conjugated through the xanthene ring

Two mouse anti-fluorescyl monoclonal antibodies (mAb), clones FL43.1 and FL55.3, were produced to the fluorescein hapten, which was conjugated to the carrier protein through the 4 position of the xanthene ring. Association constants (K _A) and thermodynamic parameters for both mAb were ascertained by monitoring the steady-state intrinsic and fluorescein fluorescence. Both techniques were in good agreement and gaveK _A values in the 10⁹ M ^–1 range. Ligand-induced intrinsic fluorescence quenching showed a hypsochromic shift for mAb FL43.1, but not for FL55.3, suggesting that the ligand interacts with different tryptophan residues in each mAb. Because these mAb are directed toward the phenylcarboxylate portion of fluorescein, the different ionic and structural forms should be useful as indicators of antibody binding site pH and buffering capacity near the binding site.     

Absorption and Fluorescence Emission Attributes of a Fluorescent dye: 2,3,5,6-Tetracyano-p-Hydroquinone

Four cyano groups have been substituted on the aromatic ring of p-hydroquinone (2,3,5,6-tetracyanohydroquinone) in order to study the enhanced photoacidity of this molecule. The acid-base equilibria have been studied using absorption (for ground state pK_a) and fluorescence (excited state pK_a) spectra. Three distinct species (neutral, anionic and dianionic forms) were observed in the ground state and only two species (anionic and dianionic forms) were found in the excited state when studied at different pH/H_o in water. Absorption and emission characteristics were studied in various organic solvents, including protic and aprotic solvents. Deprotonation was also investigated using binary mixtures. It has been revealed that absorption and emission spectra are considerably changed with change in media. Proton transfer to the solvent has been observed in various solvents.     

Fluorescence Properties of Dibenzofluorescein in Aqueous Solution

The deprotonation of dibenzofluorescein (DBFL), a long wavelength fluorescence probe, results in the simultaneous occurrence of neutral form, monoanion and dianion under physiological conditions. The fluorescence properties of the former two cannot be measured directly because they are always coexistent with some other species. By measuring the fluorescence under various pHs we computed the fluorescence parameters for each species involved in the prototropic equilibria of DBFL, including each species’ emission spectrum, excitation spectrum, emission and excitation maximum, fluorescence quantum yield and lifetime. It was found that the monoanion is the most fluorescent chromospheres (Φ _f = 0.66, compared to Φ _f = 0.25 for dianion, 0.18 for cation and 0.0 for the neutral form). Together with the computed pK _as, we are able to suggest that the monoanion plays a major role under physiological conditions when DBFL is used as a fluorescence probe, contrary to the assumption in literature.     

Fiber-Optic pH Sensor

The new enhancement in the determination of pH using optical fiber system is described here. This work uses the membrane made of cellulose acetate membrane for reagent immobilization and congo red (pK _a 3.7) and neutral red (pK _a 7.2) as pH indicators. An effective covalent chemical binding procedure is used to immobilize the indicators. The response time, reversibility, linear range, reproducibility, and long-term stability of fiber optic sensor with congo red as well as neutral red have been determined. The linear range measured for the sensor based on the congo red and neutral red is 4.2–6.3 and 4.1–9.0, respectively. The response time of sensor membrane is measured by varying the substance pH values between 11.0 and 2.0.     

Influence of Sr doping on the free carrier absorption in high-T c superconductors La2−x SrxCuO4

The reflectance spectra of polycrystalline La_2–x Sr _x CuO₄ samples were investigated in the energy range between 50 meV and 4 eV in dependence of the Sr content. The spectra are attributed to free carrier absorption of the Drude type, superimposed by optical phonon excitations below 0.1 eV and intrinsic absorption above 1 eV. From the influence of Sr doping onto the plasma energy it is deduced that La_2–x Sr _x CuO₄ is ap-type conductor with a maximum carrier concentration of 2.0×10²¹ cm^–3 forx=0.15. The results are interpreted in terms of a Hubbard model with an empty upper and ap-doped lower Hubbard band with a width of 1.9 eV.     

Jet Spectroscopy of theD12B1–D01B1Transition of thep-Cyanobenzyl Radical

We have generated thep-cyanobenzyl radical in supersonic free expansion, and measured the vibrationally and rotationally resolved laser induced fluorescence (LIF) excitation spectra and the LIF dispersed spectra from the single vibronic levels (SVL) in the green-blue region. The lowest energy band at 20 738 cm⁻¹with the strongest intensity in the excitation spectrum has been assigned to the 0⁰₀band of the visible spectrum, on the basis of the vibronic structures in the SVL dispersed spectra. Based on the band type of the 0⁰₀band,a-type, determined from the rotationally resolved LIF excitation spectrum, we have definitely assigned the visible band to theD₁2²B₁–D₀1²B₁electronic transition. We have found, on the grounds of the vibrational analysis of the dispersed spectra, that the vibronic structure of the 2²B₁–1²B₁electronic transition of the benzyl type is characterized by totally symmetric fundamental modes, 1, 8a, and 9a.     

Effects of S incorporation on Ag substitutional acceptors in ZnO:(Ag, S) thin films

Ag–S codoped ZnO thin films have been fabricated on Si substrates by radio frequency (RF) magnetron sputtering using a thermal oxidation method. XRD and SEM measurements showed that the sample has hexagonal wurtzite structure with a preferential (002) orientation and the surface is composed of compact and uniform grains. Ag_Zn–nS_O defect complexes were observed in the Ag–S codoped ZnO films by XPS analysis. Low temperature PL spectra showed neutral acceptor bound exciton emission related to Ag_Zn–nS_O. The corresponding acceptor ionization energy of 150 meV is much lower than that of monodoped Ag (246 meV), which is favorable for p-type doping of ZnO.     

The pH dependence of fluorescein fluorescence

Fluorescence quantum yields Φ_f and corrected fluorescence spectra were determined for fluorescein over a wide pH range (10 M H₂SO₄ to 0.01 M NaOH) in aqueous solution. The results were interpreted by comparison with those obtained for the very similar dye 6-hydroxy-9-phenyl-fluoron (HPF) which lacks the fluorescein carboxyl group. We find for the fluorescein cation Φ_f = 0.9−1, for the neutral molecule Φ_f = 0.20−0.25, and for the monoanion Φ_f = 0.25−0.35. The neutral molecule and monoanion have identical fluorescence spectra: an emission with maximum at 515 nm, extending to about 700 nm. (The dianion also has a maximum at 515 nm but has a more narrow emission band.) The fluorescein cation dissociates in the excited state at an acidity corresponding to that of ≈3 M H₂SO₄. A detailed scheme of the protolytic reactions of fluorescein in the excited state is presented.     

Fluorescent properties of thiochrome in solvents of different polarity

Spectral and fluorescent properties of thiochrome in solvents of different polarity were studied. It was found that the pK_a value of the transition between the cationic and neutral forms of thiochrome in aqueous solutions increased from ∼5.5 to 9.7 upon photoexcitation. It is supposed that protonation takes place in the excited state of the molecule resulting in fluorescence quenching of the thiochrome neutral form in aqueous solutions at neutral pH values. The fluorescence quantum yield of thiochrome increased by ∼2.2 times upon the transition from aqueous solutions to alcohols or polar aprotic solvents. It was found that an increase of the solvent polarity led to an increase in the Stokes shift from 3200 to 4200 cm⁻¹ for the thiochrome neutral form emission. The change in the dipole moment upon excitation into the S1-state was estimated to be less than 3D.     

Sources of atomic vapor for laser isotope separation

Conclusions Thus, our experimental investigations of the methods of obtaining a vapor of neutral atoms of the refractory and chemically active rare element (Gd) have shown that both investigated methods — electron-beam evaporation and cathode sputtering — are promising. The fact that the levela ⁹D₅ is equally singled out in the electron-beam evaporation and in the cathode sputtering is evidence of the decisive importance of the processes of establishment of the distribution of the populations over the sublevels of the ground state of the evaporated atoms. It is obvious here that the determination of the properties of this distribution for other elements calls for investigations similar to those described above.The question of the choice of source of neutral atoms should be solved separately for each chosen laser isotope separation scheme.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva Akademii Nauk SSSR, Vol. 114, pp. 24–37 (1979)     

Rotational Spectrum of Vinylarsine

The rotational spectrum of vinylarsine in the ground state has been studied in the range 7–320 GHz. The spectra of asynconformer and agaucheconformer have been unambiguously assigned on the basis of the existence of ab-type or ac-type spectrum. Rotational constants, quartic, and some sextic centrifugal distortion constants were derived. For thesynform, measurements of lowJ^aR_0,1transitions in a pulsed-nozzle Fourier transform microwave spectrometer (FTMWS) enabled the determination of the diagonal elements of the quadrupole tensor, as well as two spin–rotation constants.Ab initiocalculations performed at the MP2 level using the 6-311++G(3df, 3pd) basis set reproduced experimental rotational constants within 0.2%.     

Cycloaddition of 2′-azidoethyl glycosides to fullerene[C60] under ultrasonic irradiation

The reactions of fullerene[C₆₀] with 2′-azidoethyl 2,3,4,6-tetra-O-acetyl-α-d-mannopyranoside (2a) and 2′-azidoethyl 2,3,4,6-tetra-O-acetyl-β-d-galactopyranoside (2b) under ultrasonic irradiation cause the cycloaddition of 2′-azidoethyl glycosides to fullerene[C₆₀] and lead to d-glycosyl fullerene[C₆₀] derivatives 3a and 3b, respectively. The glycosyl fullerene[C₆₀] derivatives were characterized by ¹H and ¹³C NMR, UV–vis, FAB-MS, FT-IR spectra and were a 1:1 glycoside fullerene [C₆₀]-adduct.     

Rate of abstraction of hydrogen atoms from ethane by muonium

Thermal reaction rates for the gas-phase reaction Mu+C₂H₆MuH+C₂H₅ have been measured bySR over the temperature range 510–730 K. The usual Arrhenius expression,k=Aexp(–E _a /RT), fits the data well, giving parametersA=1.0×10^–9 cm³ molecule^–1 s^–1 andE _a =15.35 kcal/mol. The activation energyE _a is 5.5 kcal/mol higher than for the H atom variant of this reaction, indicating a marked difference in reaction dynamics. Preliminary analysis indicates a still greater difference between Mu and H for the corresponding CH₄ reaction.     

The experimental and theoretical investigation of vibration spectra in ferroelectric semiconductor SbSBrxI1−x crystals

The vapor grown SbSBr_xI_1−x (x=0.1; 0.5; 0.9) crystals with clear mirror surfaces have been used for infrared reflection measurements with Fourier spectrometer. The vibration frequencies along c(z)-axis have been derived from Kramers–Kroning and optical parameters fitting analysis of the experimental reflectivity spectra at T=300 K. The theoretical vibration spectra of SbSBr_xS_1−x (x=0.1; 0.5; 0.9) crystals in paraelectric phase (T=300 K) along c(z)-axis have been determined in quasiharmonic approximation by diagonalization of dynamical matrix. The theoretical vibration spectra of these crystals in a–b(x−y) plane have been determined in harmonic approximation. In this work we discuss the nature of anharmonism in SbSBr_xI_1−x crystals along the c(z)-axis.     

Ab Initio Study of the Phosphorescence of Nitrite Ions

In order to interpret the phosphorescence spectra of NaNO₂ and similar single crystals, we performed MCSCF geometry optimization in the ground singlet (X ¹ A ₁) and in the first excited triplet (a ³ B ₁) states of the NO ₂ ^- ion and MCSCF quadratic response (QR) calculation of the a ³ B ₁–X ¹ A ₁ transition probability at different bending angles and asymmetric stretch modes. The complete form of the spin–orbit coupling (SOC) operator is accounted for in the QR procedure. Dunning's correlation-consistent polarized valence double- (cc-pVDZ) and triple- (cc-pVTZ) basis sets are imployed. The electric-dipole transition moment from the T ^z spin sublevel (z is the C ₂ axis) oriented along the y direction (the other in-plane axis) is found to be 5 times higher than that from the T ^y sublevel in the ground-state geometry. This is in agreement with polarization measurements and with optical detection of ESR spectra. The T ^z–S ₀ transition moment decreases almost linearly with an increase in the ONO bond angle. The so-called non-Condon effects in the phosphorescence spectra of NaNO₂ crystals are explained on these backgrounds. The long progression of the bending vibrations (v ₂, a ₁) with an anomolous intensity distribution in the T ^z–S ₀ transition and additional involvement of the asymmetric stretch mode (v ₃, b ₂) in the T ^y–S ₀ transition are interpreted by force field and SOC calculations in the MCSCF-response technique. Configuration interaction (CI) calculations of the spin-allowed electric dipole transitions in NO ₂ ^- ions with effective one-electron SOC operator matrix element estimations were done for comparison with the results of the quadratic and linear response methods. Other T _n–S ₀ transitions are also studied. Finally, a short discussion of nonradiative processes is presented.     

Rotational spectrum of the Ar–dimethyl sulfide complex

The rotational spectra of three isotopomers of the Ar–dimethyl sulfide (DMS) complex – normal, ³⁴S, and ¹³C species – were measured in the frequency region from 3.7 up to 24.1 GHz by Fourier transform microwave spectroscopy. The normal species yielded 43 a-type and 79 c-type transitions. No Ar tunneling splitting was observed, while many transitions were split by the internal rotation of the two methyl tops of the DMS unit. In cases where the K-type splitting was close to that due to methyl internal-rotation, several forbidden transitions were observed that followed b-type selection rules. All of the observed transition frequencies were analyzed simultaneously using a phenomenological Hamiltonian also used in previously published work describing the Ar–dimethyl ether (DME) and Ne–DME complexes. The rotational and centrifugal distortion constants and the potential barrier height to methyl-top internal rotation, V₃, were determined. The rotational constants were consistent with an Ar–DMS center of mass (cm) distance of 3.796 (3) Å and a S–cm–Ar angle of 104.8 (2)°. The V₃ potential barrier obtained, 736.17 (32) cm⁻¹, was 97.8% of the DMS monomer barrier. By assuming a Lennard–Jones-type potential, the dissociation energy was estimated to be 2.4 kJ mol⁻¹, which was close to the value for Ar–DME, 2.5 kJ mol⁻¹.     

Photophysical characterization of pyrazino[2,3-c]-1,2,6-thiadiazine 2,2-dioxides in DMSO and acetonitrile solutions

Photophysical characterization of some pyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxides derivatives in DMSO and acetonitrile has been carried out. Acid-base processes have been found to occur in the ground and excited states. In DMSO and acetonitrile equilibrium between the neutral and deprotonated molecules is established in the ground state. In acetonitrile, a second equilibrium between the neutral and protonated form is also present at a lower pH, and can be treated independently of the first one. Absorption, emission, and excitation spectra of the species involved have been measured; data analysis allows us to calculate pK _aand quantum efficiencies. The change of the decay lifetimes with pH, along with steady state fluorescence measurements show the existence of communication between the excited states and enable us to estimate the excited state kinetic rate constants.A discussion about their possible use as laser dyes based on the energy threshold condition is also given.     

Continuum electrostatic calculations of the pK<Subscript>a</Subscript> of ionizable residues in an ion channel: Dynamic vs. static input structure

We have computed the pK_a’s of the ionizable residues of a protein ion channel, the Staphylococcus aureus toxin a \alpha -hemolysin, by using two types of input structures, namely the crystal structure of the heptameric a \alpha -hemolysin and a set of over four hundred snapshots from a 4.38ns Molecular Dynamics simulation of the protein inserted in a phospholipid planar bilayer. The comparison of the dynamic picture provided by the Molecular Simulation with the static one based on the X-ray crystal structure of the protein embedded in a lipid membrane allows analyzing the influence of the fluctuations in the protein structure on its ionization properties. We find that the use of the dynamic structure provides interesting information about the sensitivity of the computed pK_a of a given residue to small changes in the local structure. The calculated pK_a are consistent with previous indirect estimations obtained from single-channel conductance and selectivity measurements.     

Experimental and computational study on the aqueous acidity constants of some new aminobenzoic acid compounds

The acidity constants of three new aminobenzoic acid derivatives were determined using potentiometric and spectrophotometric methods in 0.10 M aqueous potassium nitrate solution as supporting electrolyte. The potentiometric data and UV–Vis absorption spectra of solutions were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants, concentration distribution diagrams and number of components involved have been calculated. The relative pK_a values for three acids were also calculated using ab initio quantum mechanical method at the HF/6-31G** level of theory in combination with CPCM continuum solvation method. The influence of substituents on the ionization constants of the studied molecular structures was investigated. The satisfactory agreement between the experimentally derived and theoretically calculated pK_a values provides solid support for the acid–base reactions proposed in this work.