P-nitroaniline Molecules Research Articles

High-performance detection of p-nitroaniline on defect-graphene SERS substrate utilizing molecular imprinting technique

We report a novel surface-enhanced Raman scattering (SERS) substrate for detecting p-nitroaniline (PNA) in real water samples, which possesses excellent sensitivity, good selectivity, and high SERS activity. Specifically, the uniform distribution structure of defect-graphene/Ag (DG/Ag) is obtained by acid etching graphene loading silver nanoparticles. The Molecularly imprinted polymer (MIP) film is copolymerized on the surface of DG/Ag by function monomer, crosslinker and template of PNA. A DG/Ag-MIP SERS substrate is obtained through polymerization of molecular imprinted polymer (MIP) on defect-graphene/Ag (DG/Ag) supporting materials. Our results signify that this new SERS substrate reveals excellent performance for PNA with an enhancement factor of 2.42 × 107. Moreover, DG/Ag-MIP substrate exhibits outstanding capability to detect PNA molecules with detection limit approximately reaching 1.0 × 10−14 M. These experimental results imply that the DG/Ag-MIP SERS substrate possesses potential application for sensing detection of PNA in environment.

Orientation correlation of p-nitroaniline molecules in acetone solution observed by hyper-Rayleigh scattering

Measurements of the polarization dependence of hyper-Rayleigh scattering (HRS) by solutions of p-nitroaniline (PNA) in acetone-d6 were used to study molecular orientation correlations. The HRS observations were analyzed in terms of short range direct dipole-dipole correlations between the PNA molecules, a long range transverse polar mode for the PNA molecules, and a long range ion-induced longitudinal polar mode. The conclusion that long range correlations are present is opposite to that in previous work, due to previous neglect of the ion-induced contribution. Depolarized HRS not explained by local correlations appears above 0.1 M PNA concentration, and analysis of the HRS observations indicates strong orientation correlations with a range of 10 nm for the PNA molecules.

Study of the pair correlations between p-nitroaniline molecules in solution by depolarized hyper-Rayleigh scattering

The concentration dependence of the hyper-Rayleigh scattering depolarization ratios of p-nitroaniline in solution was obtained and the results were compared with theory. It was found that the experimental data can be theoretically accounted for by using a pair distribution function that includes only direct correlation, with the molecules interact through a dipolar hard-sphere potential. The results show that short-range dipole-dipole interactions are responsible for the correlation between pairs of p-nitroaniline molecules in solution.

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.

Nonempirical calculations of nonlinear optical properties of p‐nitroaniline in acetone: Comparison of supermolecule and semicontinuum approaches

AbstractThe comparison of the conventional continuum, supermolecule, and semicontinuum models for the description of solvent effect on the (hyper)polarizability of p‐nitroaniline (PNA) in acetone is performed. The supermolecule approach is used for the clusters containing PNA and one or two acetone molecules. The account of the specific solute–solvent interactions via the hydrogen bonds formation is shown to result in the enhancement of (hyper)polarizability values. The continuum approach exploited in the framework of polarizable continuum model (PCM) was shown to describe mainly the solvent effect on (hyper)polarizability. The semicontinuum approach, accounting explicitly the interaction between PNA and solvent molecules and treating the rest of the solvent as a continuum, results in a moderate increase of the (hyper)polarizability values compared to those obtained within the conventional PCM approach. All the calculations of (hyper)polarizabilities are performed at the Hartree–Fock level in the aug‐cc‐pVDZ' Dunning basis set. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Experimental (FT-IR) and theoretical (DFT) studies on the adsorption behavior of p-nitroaniline (PNA) on gold nanoparticales

This paper reports the studies on the adsorption behavior of p-nitroaniline (PNA) on gold nanoparticales by experiment (FT-IR) and theory (DFT). On dried filter paper coated with gold nanoparticles and in gold aqueous colloids, surface-enhanced Raman scattering (SERS) spectra of p-nitroaniline (PNA) are studied by FT-IR excitation. The Raman frequencies of these two models for the p-nitroaniline (PNA) molecules on different substrate using DFT-B3PW91 with lanl2dz are calculated. Here it is demonstrated the calculated Raman frequencies are in good agreement with experimental values. Experimental (FT-IR) and theoretical (DFT) studies indicate that the adsorption behaviors of PNA molecules are different on these two substrates: in gold aqueous colloids, PNA molecules are adsorbed through the nitro group; while on the gold-coated filter paper, they are titled and there is a certain angle between the benzene rings and the surfaces of gold nanoparticles.

Solid-state NMR study on dynamics of p-nitroaniline molecules in FSM-type mesoporous silicas at high loading levels

We have investigated dynamics of deuterated p-nitroaniline (pNA- d) molecules in FSM-16 mesoporous silica (FSM) and FSM modified with trimethylethoxysilane (C1FSM) with different loading amounts ranging from 10 to 50 mass% by means of solid-state NMR. We have measured temperature dependence of 2H NMR spectra and spin-lattice relaxation times ( T 1) as well as 13C magic-angle-spinning (MAS) NMR spectra. The 2H and 13C MAS NMR spectra indicate that there are two modes of motions; an isotropic motion and a fast wobbling one. The rates of the wobbling motion are estimated from the 2H T 1 results. pNA- d molecules in the FSM/pNA- d sample of 10 mass% undergo the wobbling motion at the low temperatures, whereas the isotropic motion is relatively suppressed at the high temperatures. In the samples of 20 and 30 mass% the wobbling motion is suppressed at the low temperatures, whereas the isotropic motion is enhanced at the high temperatures. The above changes further proceed in the sample of 50 mass%. The temperature dependences of 2H spectra in C1FSM/pNA- d of 13 and 20 mass% are similar to those of FSM/pNA- d of 20 and 30 mass%. C1FSM/pNA- d of 30 mass% shows spectra intermediate between FSM/pNA- d of 30 mass% and FSM/pNA- d of 50 mass%. We have proposed “three-layer model” to explain the above NMR results.

Dynamics of p-Nitroaniline Molecules in Micoporous Aluminophosphate AlPO4-5 Studied by Solid-State NMR

Dynamics of deuterated p-nitroaniline (pNA-d) molecules in the micropores of AlPO4-5 has been investigated by means of solid-state NMR. The adsorbed amounts of pNA-d were 5.0 and 10.1 mass % of the total mass. We have measured 13C magic-angle-spinning (MAS) and 2H NMR spectra of the guest molecules and 31P and 27Al MAS NMR spectra of the host framework. The pNA-d molecules distribute rather inhomogeneously in the channel, and do not coordinate to Al strongly like H2O. The intermolecular hydrogen bonds are formed between a part of the guest molecules only when the loading level is high. The 2H NMR spectra are successfully analyzed, elucidating the orientation and the motion of the guest molecules. The molecular axis of pNA-d is inclined to the channel axis, and the molecular plane is perpendicular to the inner wall. The guest molecule jumps among 12 sites or 12 orientations. This motion is faster in the sample of 5.0 mass % than in the sample of 10.1 mass %, suggesting that the guest-guest interaction hinders the motion. The mean residence times of the molecules are estimated from the analysis of the 2H NMR spectra, which are affected by the size of the nanospace as well as the property of the adsorbed site.

Effects of Na+ on Dynamics of p-Nitroaniline Molecules in Zeolite ZSM-5 Studied by Solid-State NMR

Abstract The dynamics of deuterated p-nitroaniline (pNA-d) molecules in zeolite ZSM-5 including Na+ (NaZSM-5) were investigated by means of 2H and 13C solid-state NMR to clarify the effects of Na+ and hydrated Na+. The adsorbed amount of pNA-d was four molecules per unit cell of NaZSM-5. 2H NMR spectra of a dehydrated sample indicated that the motion of pNA-d in the micropore is a 180°flip-flop around the C2 axis of the molecule. Another species with a faster flip-flop motion was distinguishable and assigned to pNA-d on the outer surface. When the sample adsorbed water molecules, 2H spectra showed that the flip-flop motion of pNA-d was largely suppressed in the micropore and that pNA-d on the outer surface underwent an isotropic motion. These results indicated that the dynamics of pNA-d in NaZSM-5 depended on the interactions with Na+ and hydrated Na+ as well as on the location.

Assembly of p-Nitroaniline Molecule in the Channel of Zeolite MFI Large Single Crystal for NLO Material

A large high-quality zeolite MFI single crystal 3.0 × 1.5 × 1.5 mm3 in size was synthesized by means of a nutrition supplemental method and a p-nitroaniline (PNA)/MFI single crystal was prepared via physical vapor deposition. The light yellow PNA/MFI single crystal changed to green when irradiated by 1062 nm fundamental wavelength from a Nd:YAG pulse laser, and the transmitted light includes the SHG wavelength 527 nm. Both C−H−N analysis and molecular mechanics suggested that there were five PNA molecules encapsulated in each MFI unit cell, and the structure of the PNA molecule within the MFI microporous system is noncentrosymmetric. The PNA/MFI single crystal would be potentially applied as a NLO material.

Dynamics of p-nitroaniline molecules in FSM-type mesoporous silicas studied by solid-state NMR

Dynamics of p-nitroaniline (pNA) in FSM-type mesoporous silicas was investigated by means of 2H and 13C solid-state NMR. Deuterated pNA (pNA-d) was loaded to FSM-16 (FSM) and modified FSM samples which were prepared by reactions of FSM with trimethylethoxysilane (C1FSM), n-octyltriethoxysilane (C8FSM) and 3-aminopropyltriethoxysilane (NH 2FSM). 13C MAS NMR spectra of the samples at room temperature showed four sharp signals assigned to pNA-d, indicating a fast motion of pNA-d at room temperature. Temperature dependence of 2H NMR spectra exhibited the presence of two modes of motions, the isotropic motion and another motion such as a wobbling one (Motion I). Analysis of spin-lattice relaxation times ( T 1) for 2H spins demonstrated that the apparent activation energies of Motion I were 20 kJ mol −1 for FSM and 31–32 kJ mol −1 for C1FSM and NH 2FSM. On the other hand, temperature dependence of T 1 of Motion I in C8FSM was complicated presumably because of the motion of alkyl chains of the reacted silylating agent. These results indicated that the dynamics of pNA molecules was varied with the surface properties of the mesopores.

Dynamics of p-nitroaniline molecules in siliceous ZSM-5 studied by solid-state NMR

Sites and dynamics of p-nitroaniline (pNA) molecules in the micropores of siliceous ZSM-5 zeolite have been investigated by means of solid-state NMR. The adsorbed amounts of pNA studied were about 1.5, 4 and 6 molecules per unit cell of ZSM-5. 2H NMR and 13C NMR revealed that the motion of pNA was a 180° flip-flop around the C2 axis of the molecule when the adsorbed amount was less than four molecules per unit cell. The rate of the motion was about 50 kHz at 297 K, and the apparent activation energy was 57±17 kJ mol−1. 13C NMR confirmed the presence of different adsorbed states of pNA when the adsorbed amount was more than four molecules. Furthermore, 2H NMR revealed that the flip-flop motion of pNA was largely suppressed. These results indicate that the motion of pNA in the micropores of ZSM-5 depended on the adsorbed amount of pNA, and that the interaction between the guest molecules influenced the dynamics of the guest molecules.

Mechanistic relationships between polymer microstructure and drug release kinetics in bioerodible polyanhydrides

This work investigates the relationship between polymer microstructure and drug release kinetics in the bioerodible polyanhydride system, poly[(1,6-bis- p-carboxyphenoxy hexane)–co-(sebacic anhydride)] (CPH–SA). Model drugs, p-nitroaniline (PNA) and disperse yellow 3 (DY), were selected based on compatibility with CPH and SA, respectively. The polymer microstructure and compatibility of the drug with the constituent monomers were determined to have significant influence over the release kinetics of the drugs studied. Polymer systems with homogeneous microstructure, poly(SA) and 50:50 CPH–SA, showed simultaneous polymer degradation and drug release, although the solubility of the drug in the polymer influenced the shape of the release profiles. For the heterogeneous copolymers, 20:80 and 80:20 CPH–SA, individual monomer release kinetics demonstrated the effects of drug partitioning within a phase-separated microstructure. The PNA molecules partition preferentially into the CPH microdomains in the 20:80 CPH–SA copolymer while the DY molecules partition preferentially into the SA microdomains in the 80:20 CPH–SA copolymer. These studies suggest that the drug release mechanism is driven by polymer microstructure, compatibility of the drug with the constituent polymer phases, and solubility of the drug within the polymer. A thorough understanding of drug–polymer interactions as well as the polymer microstructure will pave the way for more accurate predictions of drug release from bioerodible polyanhydrides.

Hyper-Rayleigh scattering in p-nitroaniline with excited states obtained by 355 nm optical pump

We report what we believe to be the first experimental demonstration of the dependence of hyper-Rayleigh scattering (HRS) (fundamental wavelength of 1064 nm) and, hence, the first hyperpolarizability in optically pumped p-nitroaniline (PNA) molecules on the energy of pump photons.

Interpenetration of covalent and noncovalent networks in the crystal structures of {[M(4,4′-bipyridine) 2(NO 3) 2]⋅2p-nitroaniline} n where M=Co, 1, Ni, 2, Zn, 3

The synthesis and crystal structures of {[M(4,4′-bipyridine) 2(NO 3) 2]⋅2p-nitroaniline} n, M=Co, 1, Ni, 2, Zn, 3, are described. 1, 2 and 3 crystallize in the form of compounds that can be described as interpenetrating covalent and noncovalent networks. Analysis of the crystal packing in these compounds reveals that the p-nitroaniline molecules form a noncovalent network that is complementary from a topological perspective with [M(4,4′-bipyridine) 2(NO 3) 2] networks, which exist as square grids. These structures are interpreted in the broader perspective of crystal engineering strategies and development of new hybrid materials.

Solid-state NMR and X-ray diffraction structural investigations of the p-nitroaniline/ZSM-5 complex

The complex of zeolite ZSM-5 loaded with p-nitroaniline to four molecules per unit cell is of current interest as a potential non-linear optical material. A previous single crystal X-ray diffraction (XRD) investigation has claimed that the p-nitroaniline molecules line up as oriented dipole chains inside the channels of ZSM-5, and it was concluded that this ordering explains how second harmonic generation arises. In another XRD study, it was not possible to distinguish between order and disorder of the p-nitroaniline molecules. The present results from solid-state NMR and single crystal XRD experiments indicate that the p-nitroaniline molecules are disordered in the ZSM-5 channels, i.e., they do not form ordered dipole chains throughout the entire crystal. The quantitative 29Si-MAS spectrum at room temperature shows 48 peaks of equal intensity indicating disorder of the guest molecules, and the 15N-MAS spectrum at 180 K of the 15N-labeled p-nitroaniline in ZSM-5 shows a splitting of the NO 2 resonance, which also implies disorder. The single crystal XRD results show that the p-nitroaniline molecules are disordered over four-sites at the channel intersection even when refined in the less symmetric Pn2 1a space group. The final structure was refined in the orthorhombic Pnma space group to R=0.0465. The nature of this disorder is discussed. In particular, the possibilities of disorder arising from the average of polar domains or local disorder are examined in the light of the solid-state NMR results. That the p-nitroaniline molecules are disordered in ZSM-5 implies that the mechanism by which second harmonic generation arises may be more complex than is presently assumed.

Polar Growth and Directional Adsorption of Large AlPO4-5 Crystals Determined by Scanning Pyroelectric Microscopy

Scanning pyroelectric microscopy on large crystals reveals the three-dimensional polarization distribution in AlPO4-5 crystals. AlPO4-5 probably grows in such a way that one particular absolute configuration is formed. In general twinned crystals are formed. The twin domains exhibit an opposite polarization. A single domain is found when crystals are grown from a substrate. In some cases the crystals show a more complex domain structure, which can be attributed to specific growth conditions. From the polarization distribution the history of the crystal growth can be retrieved. A mechanism for the adsorption of p-nitroaniline molecules is proposed on the basis of the polarization distribution in AlPO4-5 crystals and earlier observed preferential orientation of this guest molecule in the host structure.

An acentric arrangement of p-nitroaniline molecules between the layers of kaolinite†

p-Nitroaniline molecules were intercalated between the layers of kaolinite, and an acentric arrangement of p-nitroaniline induced by the asymmteric environment of the interlayer region was accomplished.

Combination of single crystal zeolites and microfabrication: Two applications towards zeolite nanodevices

We present two novel approaches to using zeolite crystals for ‘nanodevices’. First, single crystal zeolites have been aligned within the grooves of micromachined silicon wafers for a three-dimensional ordering of dye molecules ( p-nitroaniline). The orientation of p-nitroaniline molecules absorbed within the channel system of the aligned zeolites by steric constraints provides an opportunity to study the optical properties of the composite. Second, zeolites with their high surface-to-mass ratio and selectivity are ideal materials to enhance the sensitivity of micron scale sensor devices to loading. As an example, experimental data on humidity sensing using a few single crystal zeolites attached to a cantilever sensor is presented.

Solubilities of p-nitroanilines in various classes of solvents. Specific solute-solvent interactions

The solubilities ф B in volume fractions of p-nitroaniline (PNA) and N,N-dimethyl p-nitroaniline (N,N-PNA) were determined near 25°C in some 40 solvents belonging to different classes using a thermoturbidimetric method. The ratio between the solubilities of the two compounds can be corrected for the differences in the melting characteristics determined from DSC measurements. The solubilities at 25°C of N,N-PNA have then to be multiplied by the factor 2.72. The corrected ratios ф PNA ф∗ N,N-PNA give indications on the formation of H-bonds between the solvent molecules and the NH groups of PNA. This is observed in solvent classes with electron donor oxygens like sulfoxides, ketones, esters and cyclic ethers. However, the ratio ф PNA ф∗ N,N-PNA decreases in an homologous series when the molar volume of the solvent increases, indicating that the formation of H-bonds by PNA depends also on the concentration of the active sites in the solvent and that not all the PNA molecules are involved in H-bonding. ф PNA ф∗ N,N-PNA is also markedly larger than 2 in the lower alcohols demonstrating the formation of N-HO hydrogen bonds at the end of the self-association chains. The fraction γ of the PNA molecules escaping from H-bonding in the electron donor solvents and in alcohols is quantitatively estimated from the solubility using the equations of the theory of the mobile order and disorder of Huyskens and Ruelle. In nitriles a weak formation of N-HHC bonds is observed. In contrast H-bonds are not observed in nitroalkanes. Unexpectedly the ratio's ф PNA ф∗ N,N-PNA are much smaller than 1 in chloro alkanes. The formation of EDA bonds between N,N-PNA and these solvents acting as Lewis acids is therefore probable.