P-nitroaniline In Water Research Articles

Multilevel CC2 and CCSD Methods with Correlated Natural Transition Orbitals.

In the multilevel coupled cluster approach, an active orbital space is treated at a higher level of coupled cluster theory than the remaining inactive orbitals. We introduce the multilevel CC2 method where CC2 is used for the active orbital space. Furthermore, we present a simplified formulation of the multilevel CCSD method where CCSD is used for the active space. The simplification lies in the evaluation of the CC2 amplitudes in the inactive space; these CC2 amplitudes have previously been determined iteratively. We use correlated natural transition orbitals to determine the active orbital spaces. The convergence of the multilevel CC2 and multilevel CCSD valence excitation energies is established with proof-of-concept calculations. The methods are also applied to two larger systems: p-nitroaniline in water and amoxicillin. The calculations on the p-nitroaniline-water system illustrate the usefulness of multilevel coupled cluster methods for molecules in solution and for charge transfer excitations.

Electron binding energies and the fundamental gap of a push-pull dye in a polar environment: p-nitroaniline in liquid water

The outer valence electron binding energies and the fundamental gap of p-nitroaniline (PNA) in water were determined by electron propagator theory. The adopted methodology relies on the calculation of electron binding energies by using configurations generated by Born-Oppenheimer molecular dynamics of PNA in water. The fundamental gap (Eg) of PNA in water was estimated from the first ionisation energy (IE) and the first vertical electron affinity VEA (Eg=IE-VEA). In liquid water Eg is predicted to be 6.5±0.5eV (OVGF), which is ∼3.3eV greater than the experimental optical gap (3.25eV).

A First-Principles Approach to the Dynamics and Electronic Properties of p-Nitroaniline in Water.

Born-Oppenheimer molecular dynamics of p-nitroaniline (PNA) in water was carried out and the electronic structure was investigated by time-dependent density functional theory. Hydrogen bonding involving the PNA nitro and amine groups and the water molecules leads to an ∼160 cm(-1) red shift of the ν(N-O) and ν(N-H) stretching frequencies relative to the gas phase species. Our estimate for the peak position of the charge transfer (CT) band in the absorption spectrum of PNA in water (∼3.5 eV) is in good agreement with experimental data (3.3 eV). We have investigated the specific role played by local hydrogen bonding and electrostatic interactions on the electronic absorption spectrum. It is shown that although electrostatic interactions play a major role for explaining the structure of the PNA CT band in water, the theoretical prediction of the observed red shift is improved by the explicit consideration of local hydrogen bonding of PNA to water. For isolated PNA, we predict that the dipole moment of the second excited state (S2) is 9.6 D greater than ground state (S0) dipole, which is in good agreement with experimental information (8.2-9.3 D). Calculation of charge transfer indexes for the two first excitations of PNA in water indicates that despite the feature that a small fraction of S1 states (<5%) may exhibit some CT character, CT states in solution are mainly associated with S2 ← S0 transitions.

Electron Transfer Reaction Dynamics of p-Nitroaniline in Water from Liquid to Supercritical Conditions

Photoexcitation dynamics of p-nitroaniline (pNA) have been investigated by femto-second transient absorption spectroscopy in water from liquid to supercritical conditions; along the isochoric line from the ambient condition to 664 K at 40.1 MPa and along the isothermal line from 40.1 to 36.1 MPa at 664 K. The rates of the back electron transfer reaction from the photoexcited charge transfer state to the electronic ground state was determined by the bleach recovery of the ground state absorption, and the successive vibrational relaxation in the electronic ground state was determined by the hot-band decay which was apparent at the red edge of the absorption. The variation of the back electron transfer rate was compared with the prediction based on the electron transfer theory including the Franck-Condon active vibrational modes. The results indicated that both the free energy change of the reaction and the change of the intramolecular vibrational reorganization energy cause the characteristic density (or temperature) dependence of the back electron transfer rate. The density dependence of the vibrational relaxation rate was compared with the collision frequency and the coordination number of the solvent molecule around the solute estimated by the molecular dynamics simulations. The density dependence of the coordination of a water oxygen atom to an amino hydrogen atom of pNA was found to be correlated with the density dependence of vibrational relaxation rate.

Oxidative decomposition of p-nitroaniline in water by solar photo-Fenton advanced oxidation process

The degradation of p-nitroaniline (PNA) in water by solar photo-Fenton advanced oxidation process was investigated in this study. The effects of different reaction parameters including pH value of solutions, dosages of hydrogen peroxide and ferrous ion, initial PNA concentration and temperature on the degradation of PNA have been studied. The optimum conditions for the degradation of PNA in water were considered to be: the pH value at 3.0, 10 mmol L −1 H 2O 2, 0.05 mmol L −1 Fe 2+, 0.072–0.217 mmol L −1 PNA and temperature at 20 °C. Under the optimum conditions, the degradation efficiencies of PNA were more than 98% within 30 min reaction. The degradation characteristic of PNA showed that the conjugated π systems of the aromatic ring in PNA molecules were effectively destructed. The experimental results indicated solar photo-Fenton process has more advantages compared with classical Fenton process, such as higher oxidation power, wider working pH range, lower ferrous ion usage, etc. Furthermore, the present study showed the potential use of solar photo-Fenton process for PNA containing wastewater treatment.

Cooling dynamics of an optically excited molecular probe in solution from femtosecond broadband transient absorption spectroscopy

The cooling of p-nitroaniline (PNA), dimethylamino-p-nitroaniline (DPNA) and trans-stilbene (t-stilbene) in solution is studied experimentally and theoretically. Using the pump–supercontinuum probe (PSCP) technique we observed the complete spectral evolution of hot absorption induced by femtosecond optical pumping. In t-stilbene the hot S1 state results from Sn→S1 internal conversion with 50 fs characteristic time. The time constant of intramolecular thermalization or intramolecular vibrational redistribution (IVR) in S1 is estimated as τIVR≪100 fs. In PNA and DPNA the hot ground state is prepared by S1→S0 relaxation with characteristic time 0.3–1.0 ps. The initial molecular temperature is 1300 K for PNA and 860 K for t-stilbene. The subsequent cooling dynamics (vibrational cooling) is deduced from the transient spectra by assuming: (i) a Gaussian shape for the hot absorption band, (ii) a linear dependence of its peak frequency νm and width square Γ2 on molecular temperature T. Within this framework we derive analytic expressions for the differential absorption signal ΔOD(T(t),ν). After calibration with stationary absorption spectra in a low temperature range, the solute temperature T(t) may be evaluated from a transient absorption experiment. For highly polar PNA and DPNA, T(t) is well described by a biexponential decay which reflects local heating effects, while for nonpolar t-stilbene the local heating is negligible and the cooling proceeds monoexponentially. To rationalize this behavior, an analytic model is developed, which considers energy flow from the hot solute to a first solvent shell and then to the bulk solvent. Fastest cooling is found for PNA in water: a time constant of 0.64 ps (68%) corresponds to solute–solvent energy transfer while 2.0 ps (32%) characterizes the cooling of the first shell. In aprotic solvents cooling is slower than in alcohols and slows down further with decreasing solvent polarity. This contrasts with nonpolar t-stilbene which cools down with 8.5 ps both in acetonitrile and cyclohexane. Comparison of the cooling kinetics for PNA in water with those for DPNA in water-acetonitrile mixtures suggests that the solute–solvent energy transfer proceeds mainly through hydrogen bonds.

Ionic solvation in water + cosolvent mixtures. Part 9.—Free energies of transfer of single ions from water into water + ethanol mixtures

Values for the free energy of transfer of the proton ΔG°t(H+) have been determined experimentally using spectrophotometric measurements on p-nitroaniline in water + ethanol employing the method previously used for other cosolvents mixed with water. Values for ΔG°t(i) for other individual ions, i= anion X–, have been determined by combining these values for ΔG°t(H+) with values for ΔG°t(HX) calculated from electrochemical data. These values for ΔG°t(X–) are subsequently used with values for ΔGot(MX) and ΔG°t(MX2) derived from electrochemical and solubility data to provide values for ΔG°t(M+) and ΔG°t(M2+). ΔG°t(X–) and ΔG°t(X2–) for anions where ΔG°t(HX) and ΔG°t(H2X) are not available are calculated from ΔG°t(MX) and ΔG°t(M2X) obtained from solubility measurements and the above values for ΔG°t(cation).

ChemInform Abstract: SOLUBILITY OF P‐NITROANILINE IN WATER AND HEXAMETHYLPHOSPHOROTRIAMIDE (HMPT) MIXTURES AND FUNCTIONS OF TRANSFER FROM WATER TO THESE MIXTURES

Chemischer InformationsdienstVolume 13, Issue 37 Article ChemInform Abstract: SOLUBILITY OF P-NITROANILINE IN WATER AND HEXAMETHYLPHOSPHOROTRIAMIDE (HMPT) MIXTURES AND FUNCTIONS OF TRANSFER FROM WATER TO THESE MIXTURES H. CHEBIB, H. CHEBIBSearch for more papers by this authorC. JAMBON, C. JAMBONSearch for more papers by this authorJ.-C. MERLIN, J.-C. MERLINSearch for more papers by this author H. CHEBIB, H. CHEBIBSearch for more papers by this authorC. JAMBON, C. JAMBONSearch for more papers by this authorJ.-C. MERLIN, J.-C. MERLINSearch for more papers by this author First published: September 14, 1982 https://doi.org/10.1002/chin.198237080AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue37September 14, 1982 RelatedInformation