UV-vis Electronic Absorption Research Articles

Decomposition of Monolayer Coverage on Gold Nanoparticles by UV/ozone Treatment

Abstract Au nanoparticles, covered with cationic dichain surfactant on the whole surface, were treated with UV/ozone. FT-IR spectra of the Au nanoparticles with bottom-, upper-, and fully covered surfactant monolayers revealed a variable decomposition rate. The sum frequency generation spectra of the treated nanoparticles showed that the surface coverage of gold nanoparticles lose the centrosymmetric structure, implying asymmetric distribution of the protected surfactant molecules. The UV–vis electronic absorption spectra suggested stable nanoparticle monolayer film structure after UV/ozone irradiation.

Activation of CdS nanoparticles by metallic ions and their selective interactions with PAMAM dendrimers

CdS nanoparticles (NPs) in colloidal dispersion were activated by metallic ions [Mn(II) and Cu(II)], employing a simple method under mild conditions. These metallic ions on the surface of the CdS NPs quench the red-shifted defect emission, and efficiently promote near band gap emission; they also enhance the photo stability and dispersability of the suspensions. Taking advantage of the chemical affinity of Mn(II) and Cu(II) for the CdS surface, we carried out a study of the interaction between [CdS-M(II) n] NPs and polyamidoamine dendrimers of 1 and 2.5 generations (G1=8 amino, and G2.5=32 carboxylic end-groups, respectively). The strong interaction between these two chemical species results in the formation of new [CdS-M(II) n G n] nanocomposites. All colloidal systems were monitored by UV-visible electronic absorption and emission spectroscopies, and electronic paramagnetic resonance. The crystal structures of the nanocomposites, as well as their average diameters (2.0–3.3 nm), were determined by high-resolution transmission electron microscopy images.

Vibrational and thermal studies of p-methylaniline complexes with Ni(II), Zn(II) and Cd(II) iodides

The complexes of general formula [MI 2( p-methylaniline) n ] ( n=2, M=Zn and Cd; n=4, M=Ni) have been prepared and characterized by their FT-infrared (IR) spectra, FT-Raman spectra, thermal analyses, elemental analyses and UV-Vis electronic absorption spectra. The observed IR and Raman bands of the complexes have been assigned as compared with the free p-methylaniline (pMA). The influence of the transition metals on the pMA vibrational bands has been investigated. The results of thermogravimetry (TG) and differential scanning calorimeter (DSC) have been discussed. The IR and Raman spectral studies and the energy minimization studies with B88-PW91/DZVP level density functional theory (DFT) and semiempirical MNDO/d calculations show that the four-coordinate [ZnI 2(pMA) 2] and [CdI 2(pMA) 2] complexes belong to C 2v point group.

Studies on molecular structure of Schiff base derivatives in LB films

The present paper investigated the molecular configurations of the two novel amphiphiles with Schiff base moiety as headgroup in LB films. FTIR-ATR spectra and UV–vis electronic absorption spectra revealed the different isomers between the two amphiphiles LB film. Since OH groups situate in different position of the aromic rings in Schiff base amphiphiles, the proton transfer by different ways leads to different isomers, which were reflected by monolayer and LB films behavior.

Energetics, structures, vibrational frequencies, vibrational absorption, vibrationalcircular dichroism and Raman intensities of Leu-enkephalin

Here we present several low energy conformers of Leu-enkephalin(LeuE) calculated with the density functional theory usingthe Becke 3LYP hybrid functional and the 6-31G*basis set. The structures, conformational energies, vibrational frequencies, vibrationalabsorption (VA) intensities, vibrational circular dichroism (VCD) intensities andRaman scattering intensities are reported for the conformers of LeuE which areexpected to be populated at room temperature. The species of LeuE present innon-polar solvents is the neutral non-ionic species with the NH2 andCO2Hgroups, in contrast to the zwitterionic neutral species with the NH3+ andCO2−groups which predominates in aqueous solution and in the crystal. All of ourattempts to find the zwitterionic species in the isolated state failed, with theresult that a hydrogen atom from the positively charged N-terminus ammoniumgroup transferred either to one of the oxygens of the carboxylate group of theC-terminus or to the oxygen of the amide group of one of the other residues.Hence we conclude that the zwitterionic species of LeuE is not stable in theisolated state. Spectral simulations of the species expected to be found in theisolated state can be compared to the measured VA, VCD and Raman spectra ofLeuE in non-polar solvents to identify which conformer or conformers of LeuE arepresent in these media. Characteristic features in the VCD spectra are moresensitive to conformational changes than those in either the VA or Ramanspectra, similar to the characteristic features in electronic circular dichroismspectra with respect to those in the UV–vis electronic absorption spectra. Finally,we have also attempted to stabilize the zwitterionic species by treatingthe aqueous environment by using a continuum solvent approach, theOnsager model. Here we found that the zwitterionic species is now stable.The neutral species in an aqueous environment was also modelled by thecontinuum solvent approaches to determine the relative stability of these twospecies in this new aqueous environment. Here the relative energy of thezwitterionic species is higher than neutral species, in contradiction toexperiment. Hence the use of explicit water molecules plus either this or anothercontinuum model to treat the bulk water environment is necessary tomake the zwitterionic species more stable than the neutral species. We arepursuing explicit water molecules to treat LeuE in this environment.

Expression of recombinant Pseudomonas stutzeri di-heme cytochrome c4 by high-cell-density fed-batch cultivation of Pseudomonas putida

The gene of the di-heme protein cytochrome c 4 from Pseudomonas stutzeri was expressed in Pseudomonas putida. High-yield expression of the protein was achieved by high-cell-density fed-batch cultivation using an exponential glucose feeding strategy. The recombinant cytochrome c 4 protein was purified to apparent homogeneity and analyzed by electronic absorption spectroscopy, nanoflow electrospray ionization time-of-flight mass spectrometry, and electrochemistry. Cyclic voltammograms and UV–vis electronic absorption spectra were indistinguishable from the equivalent data of native P. stutzeri cytochrome c 4. Furthermore, the calculated and experimentally determined molecular masses of recombinant cytochrome c 4 were identical. Biochemical characterization of both wild-type and mutant derivatives of the protein will be greatly enhanced and facilitated by the described high-yield fermentation and rapid isolation procedure.

Spectroscopic investigation of tetracycline interaction with phospholipid Langmuir–Blodgett films

A widely used veterinary antibiotic, tetracycline (TC), has been incorporated in Langmuir–Blodgett (LB) films of dipalmitoylphosphatidic acid (DPPA) by means of two different procedures: co-transfer and incubation in solution. The resulting structures were characterized by means of contact angle and ellipsometric measurements. The presence of the antibiotic in the phospholipid film was evidenced by means of UV–Vis electronic absorption and infrared vibrational spectroscopy. The two sets of measurements unambiguously indicated the presence of the drug in the LB layer films obtained with both methods, although incubation led to a smaller content of immobilized tetracycline. In both cases, the drug was found to reside in the hydrophilic portion of the layers due to specific interactions of the dimethylamino group of the molecule with the polar head groups of the phospholipid.

Reaction of carbon monoxide with the reduced active site of bacterial nitric oxide reductase.

Bacterial nitric oxide reductase (NOR), a member of the superfamily of heme-copper oxidases, catalyzes the two-electron reduction of nitric oxide to nitrous oxide. The key feature that distinguishes NOR from the typical heme-copper oxidases is the elemental composition of the dinuclear center, which contains non-heme iron (FeB) rather than copper (CuB). UV-vis electronic absorption and room-temperature magnetic circular dichroism (RT-MCD) spectroscopies showed that CO binds to Fe(II) heme b3 to yield a low-spin six-coordinate species. Photolysis of the Fe(II)-CO bond is followed by CO recombination (k(on) = 1.7 x 10(8) M(-1) x s(-1)) that is approximately 3 orders of magnitude faster than CO recombination to the active site of typical heme-copper oxidases (k(on) = 7 x 10(4) M(-1)x s(-1)). This rapid rate of CO recombination suggests an unimpeded pathway to the active site that may account for the enzyme's high affinity for substrate, essential for maintaining denitrification at low concentrations of NO. In contrast, the initial binding of CO to reduced heme b3 measured by stopped-flow spectroscopy is much slower (k(on) = 1.2 x 10(5) M(-1) x s(-1)). This suggests that an existing heme distal ligand (water/OH-) may be displaced to elicit the spin-state change observed in the RT-MCD spectrum.

Studies on charge transfer properties from mixture of Schiff base and zinc complex in Langmuir–Blodgett film by UV–vis absorption and Fourier transform infrared spectroscopy

A novel mixed Langmuir–Blodgett (LB) film based on a 1:1 (molar ratio) mixture of a non-amphiphile complex (Et 4N) 2[Zn(dmit) 2] (H 2dmit=4,5-dimercapto-1,3-dithiole-2-thione) and Schiff base amphiphile 2,4-dihydroxy- N-octadecylbenzylideneamine (SBC 18) was constructed and characterized by Fourier transform infrared (FTIR) spectra and UV–vis electronic absorption spectra. After iodine was doped in situ, magnitude of charge transfer increases, which was demonstrated by FTIR and UV–vis absorption spectral analysis.

Structure Studies on Ion Coordination in 2,4-Dihydroxy-N-Octadecybenzylideneamine LB Films by UV–Vis Absorption and FTIR Spectroscopy

The coordination reaction of Cu2+ ions with the Schiff base amphiphile 2,4-dihydroxy-N-octadecylbenzylideneamine in ultrathin organic LB films was probed by Fourier transform infrared (FTIR) transmission spectroscopy and UV–Vis electronic absorption spectroscopy. FTIR spectral changes owing to LB films of 2,4-dihydroxy-N-octadecylbenzylideneamine contacting aqueous Cu(OAC)2 solution suggest the formation of ion-coordination films, which is corroborated by UV–Vis absorption spectra. The coordination reaction of the annealing film at different temperatures suggests that the microstructure of LB films had an important effect on the reaction rate. Detailed analysis shows that ion-coordination films take an isotropic unaxial orientation and exhibit phase transition behavior, which is determined by the different complex structures of headgroups and of subphase and surface film.

Influence of d- p π-conjugate interaction upon electronic spectra in some cluster compounds

The UV-vis electronic absorption spectra of the clusters Mo 2S 4(dtp) 2 and Mo 3S 4(dtp) 4·Py have been observed, and the electronic excitation energies have been calculated using the INDO/S-CI method. Comparing the calculated values with the observed results, the absorption bands have been assigned. The influence of d- p π-conjugate interaction strength upon the electronic absorption spectrum is discussed in the clusters Mo 2S 4(dtp) 2 ( 1), Mo 3S 4(dtp) 4·Py ( 2), Mo 3O 4(H 2O) 9 4+ ( 3) and Mo 3S 4(H 2O) 9 4+ ( 4) [dtp = S 2P(OC 2H 5), Py = pyridine]. It has been found that the absorption bands of clusters 2 and 4, with larger d- p π-conjugate interaction over rings, causes a red-shift compared with those of clusters 1 and 3, with a smaller d- p π-conjugate interaction.

Synthesis and spectral and electrochemical properties of 2,3,9,10,16,17,23,24-octabutylthiophthalocyaninatozinc(II)

The title Zn(II) complex was synthesized, and its UV-Vis electronic absorption spectrum and cyclic voltammograms in N, N-dimethylformamide were measured. The Q and B bands appear around 704 and 370 nm, respectively. The two redox couples indicating reversible one-electron transfer processes appear in the reduction side of the cyclic voltammogram. Adsorption on an electrode surface and irreversible oxidation with decomposition of the complex molecule were confirmed by a controlled-potential electrolysis experiment. The Q and B bands, reduction potentials and oxidation potential of the present complex shift to longer wavelength, positive direction and negative direction, respectively, compared with those of 2,3,9,10,16,17,23,24-octabutoxyphthalocyaninatozinc(II).

Electrochemical behavior of [octaethylporphyrin iron(III)-σ-bonded pyrrole] and its electrocatalytic activity for the reduction of dioxygen

The electrochemistry of [octaethylporphyrin iron(III)-σ-bonded pyrrole] (abbreviated as (OEP)Fe III(Pyr)) was investigated in CH 2Cl 2 + TBAP solution by cyclic voltammetry (CV) and in situ UV-visible electronic absorption spectrometry. It was found that (OEP)Fe III(Pyr) can undergo a quasi-reversible one-electron reduction step to form (OEP)Fe II(Pyr), and two sorts of irreversible one-electron oxidation step: one was the formation of [(OEP)Fe III(Pyr)] + firstly, followed by loss of the σ-bonded pyrrole to produce [(OEP)Fe III] +; the other was probably the direct formation of [(OEP)Fe III] + with simultaneous loss of the σ-bonded pyrrole. It was also found that (OEP)Fe III(Pyr) adsorbed on the surface of glassy cardon (GC) exhibited high activity for the electrocatalytic reduction of dioxygen, but this activity was not stable. However, this catalyst can be buried in polypyrrole (PPyr) film, resulting in more stable activity. Rotation ring-disk experiments (RRDE) demonstrated that (OEP)Fe III(Pyr) whether adsorbed on a GC surface or buried in PPyr film could catalyze the reduction of dioxygen to give water predominantly. In these two cases, the catalytic mechanisms were found to be the same and the water production efficiencies were nearly 90% in the potential region −0.30 to 0.35 V (vs. SCE) in O 2 saturated 0.05 M H 2 SO 4 solution. The slope of the Tafel curve suggested that the one-electron transfer from [(OEP)Fe II(Pyr)O 2] to [(OEP)Fe III(Pyr)O 2 −] was the rate-controlling step before the limiting disk current was reached. 1. (i) The electrochemistry and in situ UV-visible absorption spectra suggested that the electrochemical oxidation of (OEP)Fe III(Pyr) might produce the porphyrin ring cation with the loss of its σ-bonded pyrrole, resulting in irreversible oxidation of (OEP)Fe III(Pyr) to form [(OEP)Fe III] + species. The electrochemical reduction of (OEP)Fe III(Pyr) seems to be a reversible process in which the porphyrin ring anion is formed first, followed by electron transfer from the porphyrin ring to the central iron to yield (OEP)Fe II(Pyr). 2. (ii) There may be two different forms of (OEP) Fe III(Pyr) adsorbed on the GC surface. The so-called “different adsorption form” is resulted probably from the different distance between the active sites on which (OEP)Fe III(Pyr) could adsorb. This might lead to a different interaction pattern of bonding with dioxygen. For type I sites (as described in Section 3.3.4) perhaps the side-on and/or end-on interactions occurred favorably, whereas for type II sites perhaps the bridge interaction was predominant [36,37]. 3. (iii) Burying (OEP)Fe III(Pyr) in PPyr film might proceed only at the beginning of the electrochemical polymerization of pyrrole monomers. The concentration of (OEP)Fe III(Pyr) buried in the PPyr film appeared to be independent of the thickness of the film. (OEP)Fe III(Pyr), whether buried in PPyr film or adsorbed on the GC surface, exhibited a similar electrocatalytic activity for dioxygen reduction. The catalytic mechanisms were found to be the same. Furthermore, the burying method clearly could increase the stability of this activity. 4. (iv) In the low polarization region where the potential is higher than −0.120 V, the catalytic reduction of dioxygen by (OEP)Fe(Pyr)] ad/GC underwent successive 2e − reduction steps to form water, whereas in the higher polarization region, the direct 4e − reduction occurred to give water predominantly. The Tafel slope in the kinetic controlled region suggested that the reaction rate was controlled by the first one-electron transfer step. In the more negative potential region, the reaction rate was controlled by the diffusion of dioxygen in solution phase. Thus, (OEP)Fe III(Pyr) has a high activity for the electrocatalytic reduction of dioxygen with an efficiency of water production of 75%–90%, which is close to the activity observed on a Pt electrode. This activity appeared very unstable, probably resulting from the loss of (OEP)Fe III(Pyr) from the GC surface. However, it was satisfactory to find that the burying method, for example burying (OEP)Fe III(Pyr) in a PPyr film, could increase the catalytic activity and its stability markedly. Furthermore, it was interesting to find that this kind of σ-bonded metalloporphyrin could be used as the cathodic catalyst in a full cell if further research into increasing its stability were accomplished, according to the conditions for practical use.

Characterization of the r-state insulin hexamer and its derivatives. The hexamer is stabilized by heterotropic ligand binding interactions

1H NMR and UV-visible electronic absorption studies have been performed to investigate the effects of anions and cyclic organic molecules on the interconversion of the T- and R-conformational states (Kaarsholm et al., 1989) of hexameric M (II)-substituted insulin in solution (M = Zn or Co.). Two ligand binding processes that stabilize the R-state conformation of the M(II)-substituted insulin hexamer [M(II)-R6] have been distinguished: (i) The binding of neutral organic molecules to the six, crystallographically identified, protein pockets in the Zn(II)-R6 insulin hexamer (Derewenda et al. 1989) generate homotropic site-site interactions that stabilize the R-state. Cyclohexanol, phenol, 4-nitrophenol, and 4-hydroxymethylbenzoate are shown to bind at these sites. (ii) The coordination of singly charged anions that are able to gain access to the two HisB10 coordinated metal ions of the M(II)-R6 hexamer stabilizes the R-state. Adducts of the M(II)-R6 hexamer are formed, thereby, in which the solvent-accessible fourth coordination position of the M(II) ion is replaced by a competing anion. Binding to these two classes of sites introduces strong heterotropic interactions that stabilize the R-state. UV-visible spectral data and apparent affinity constants for the adducts formed by the Co(II)-R6 hexamer with a wide range of anionic ligands are presented. The Co(II)-R6 adducts have a strong preference for the formation of pseudotetrahedral Co(II) centers. The HCO3- and pyridine-2-thiolate ions form Co(II)-R6 adducts that are proposed to possess pentacoordinate Co(II) geometries. The relevance of the Co(II)-R6 complexes to carbonic anhydrase catalysis and zinc enzyme model systems is discussed.

Catalytic properties of erbium oxide in dehydration of alcohols and in dehydrogenation of alcohols and tetralin

The UV–visible electronic absorption spectra, molar absorptivity, fluorescence spectra, fluorescence quantum yield and excited state lifetime of 1,4-bis [2-(2-pyridyl) vinyl] benzene P2VB were measured in different solvents. The fluorescence quenching of P2VB by molecular oxygen was also studied using lifetime measurements. A 2 × 10−4 mol dm−3 solution of P2VB in dimethyl formamide (DMF) gave amplified spontaneous emission (ASE) in blue spectral region with emission maximum at 420 nm upon pumping by 337.1 nitrogen laser pulse. The photochemical quantum yields (ϕc) of trans–cis photoisomerization of P2VB were calculated in different organic solvents. The photoreactivity of P2VB are also studied PMMA matrix.