Anion Band Research Articles

Hofmeister anion effects on aqueous solutions of poly(ethylene oxide) studied by attenuated total reflectance FT-IR spectroscopy

FT-IR–ATR spectra have been measured for ternary solutions of poly(ethylene oxide)/electrolyte/H2O over a temperature range of approximately 60°C, each solution spectrum being referenced to a background spectrum from pure water at the same temperature. For solutions containing sodium phosphate or sodium thiosulfate, an increase in the intensity of the PEO bands relative to the intensity of the anion bands was observed with increasing temperature. At temperatures close to the cloud points of the solutions, the PEO/anion intensity ratio was higher than its value at ambient temperature by a factor of 4–5. In contrast, for solutions containing sodium thiocyanate for which the experimental temperatures were much below the cloud point no change was observed in the PEO/anion intensity ratio, as expected. These observations are interpreted in terms of the build-up of a polymer-rich, salt-deficient layer on the hydrophobic surface of the ZnSe ATR crystal. The different behaviour of the sodium thiocyanate solutions is consistent with the ‘structure-breaking’ status of the thiocyanate anion in the Hofmeister series as compared to the ‘structure-making’ status of phosphate and thiosulfate anions.

Experimental and Theoretical Characterization of the Optical Properties of CeO2, SrCeO3, and Sr2CeO4 Containing Ce4+ (f0) Ions

In an effort to find new UV absorbers, the optical properties of CeO2, SrCeO3, and Sr2CeO4 were examined by UV−visible diffuse reflectance measurements and electron energy-loss spectroscopy (EELS), and their electronic structures were investigated on the basis of first-principles density functional theory (DFT) calculations. The extinction coefficient k and the refractive index n determined from the loss function Im(−1/e) by EELS were compared with the corresponding quantities calculated from DFT calculations. The UV absorption thresholds of these materials were determined by the electron excitation from the O 2p anionic band to the empty Ce 4f orbitals. The calculated and measured refractive indices were in satisfactory agreement. The applicability of CeO2, SrCeO3, and Sr2CeO4 as potential UV absorbers was assessed.

Two dimensional metal–oxianion surface complexes formation during the upd process on a Au(1 1 1) electrode studied by in situ surface X-ray diffraction and infrared reflection absorption spectroscopy

Throughout the whole potential ranges where underpotential deposition (upd) proceeds, the stretching absorption bands of both sulfate and phosphate anions (vSO and vPO) do not change at all with regard to band-center position. Sulfate and phosphate anions are combined with copper or zinc ions to form surface metal complexes on a Au(111) electrode surface, respectively: transition metal–oxianion (sulfate and phosphate) pseudo-complexes are formed in the course of upd processes. The surface structure of the Au(111) electrode in the topmost layer is the same as the bulk structure (1×1), and lifting of surface reconstruction takes place in the case of Cu-upd where Cu(I)2SO4 and Cu(I)3SO4 pseudo-complexes extend on the surface, while surface reconstruction of a Au(111) electrode continues to occur in the case of Zn-upd where the Zn(I)2PO4 or Zn(I)3PO4 pseudo-complex locates.

Photoinduced Electron Transfer from Tetrathienylethylenes to Fullerenes (C60/C70): Tetrathienylethylene-Dendrimer Effect

Abstract Photoinduced electron-transfer processes between C60/C70 and tetrathienylethylenes (TTE’s) in benzonitrile have been studied by measuring the transient absorption spectra in the Vis/NIR regions using nanosecond laser photolysis. The absorption bands of the radical anions of C60/C70 (C60•−/C70•−) and radical cations of TTE’s (TTE’s•+) were observed with the decay of the triplet states of C60/C70 (3C60*/3C70*), indicating that electron transfer takes place via 3C60*/3C70*. In addition, formation of the dication of TTE (TTE2+) was confirmed by its characteristic absorption band at 680 nm. The TTE2+ is formed by the stepwise collision of TTE with 3C60*/3C70*. By the substitutions with the MeS groups at the thienyl rings of TTE, the efficiencies and rates of the electron-transfer processes became higher than those of TTE with the PhS groups. For dendrimer TTE’s, the photoinduced electron-transfer processes also took place via 3C60*/3C70*, although the efficiencies and rates were decreased with an increase in the dendrimer generation. After forward electron transfer, the back electron transfer processes were observed between separately solvated C60•−/C70•− and TTE’s•+ even for the dendrimer TTE’s, which suggest that outer-sphere back electron-transfer took place in the backward processes.

Primary quinone (QA) binding site of bacterial photosynthetic reaction centers: mutations at residue M265 probed by FTIR spectroscopy.

In the primary quinone (Q(A)) binding site of Rb. sphaeroides reaction centers (RCs), isoleucine M265 is in extensive van der Waals contact with the ubiquinone headgroup. Substitution of threonine or serine for this residue (mutants M265IT and M265IS), but not valine (mutant M265IV), lowers the redox midpoint potential of Q(A) by about 100 mV (Takahashi et al. (2001) Biochemistry 40, 1020-1028). The unexpectedly large effect of the polar substitutions is not due to reorientation of the methoxy groups as similar redox potential changes are seen for these mutants with either ubiquinone or anthraquinone as Q(A). Using FTIR spectroscopy to compare Q(A)(-)/Q(A) IR difference spectra for wild type and the M265 mutant RCs, we found changes in the polar mutants (M265IT and M265IS) in the quinone C[double bond]O and C[double bond]C stretching region (1600-1660 cm(-1)) and in the semiquinone anion band (1440-1490 cm(-1)), as well as in protein modes. Modeling the mutations into the X-ray structure of the wild-type RC indicates that the hydroxyl group of the mutant polar residues, Thr and Ser, is hydrogen bonded to the peptide C[double bond]O of Thr(M261). It is suggested that the mutational effect is exerted through the extended backbone region that includes Ala(M260), the hydrogen bonding partner to the C1 carbonyl of the quinone headgroup. The resulting structural perturbations are likely to include lengthening of the hydrogen bond between the quinone C1[double bond]O and the peptide NH of Ala(M260). Possible origins of the IR spectroscopic and redox potential effects are discussed.

A crystallographic and vibrational study of cesium di-μ-aqua bis[tetraaquasodium(I)] decavanadate, Cs4[Na2(H2O)10](V10O28)

The title compound crystallizes in the triclinic space group \(P\bar 1\), with a = 8.6161(4) A, b = 10.591(1) A, c = 11.406(1) A, α = 67.976(7)°, β = 86.868(6)°, γ = 67.798(6)°, and Z = 1. The structure was refined to R1 = 0.0413. The decavanadate anion V10O286− and the [Na2(H2O)10]2+ bridged cation are located at inversion centers. Partial deuteration of the substance indicates that the coordinated water molecules are strongly asymmetric, forming weak hydrogen bonds with acceptor oxygen atoms from the decavanadate anion. The infrared and Raman spectra are dominated by the water and decavanadate anion bands.

Homoleptic tetrahydrometalate anions MH(4)(-) (M = Sc, Y, La). Matrix infrared spectra and DFT calculations.

Laser-ablated Sc, Y, and La atoms react with molecular hydrogen upon condensation in excess argon, neon, and deuterium to produce the metal dihydride molecules and dihydrogen complexes MH(2) and (H(2))MH(2). The homoleptic tetrahydrometalate anions ScH(4)(-), YH(4)(-), and LaH(4)(-) are formed by electron capture and identified by isotopic substitution (D(2), HD, and H(2) + D(2) mixtures). Doping with CCl(4) to serve as an electron trap virtually eliminates the anion bands, and further supports the anion identifications. The observed vibrational frequencies are in agreement with the results of density functional theory calculations, which predict electron affinities in the 2.8-2.4 eV range for the (H(2))ScH(2), (H(2))YH(2), and (H(2))LaH(2) complexes, and indicate high stability for the MH(4)(-) (M = Sc, La, Y) anions and suggest the promise of synthesis on a larger scale for use as reducing agents.

Electrochemical reduction of p-nitrothiophenol-self-assembled monolayer films on Au( [formula omitted]) surface and coadsorption of anions and water molecules

Electrochemical reduction of p-nitrothiophenol (PNTP)-self-assembled monolayer (SAM) films on Au(1 1 1) surface was studied using attenuated total reflection-IR spectroscopy. The reduction potential was evaluated from the spectral changes, which depended on pH in electrolyte solutions, e.g. +0.05 V (pH 0.45), −0.55 V (pH 5.5) or −0.55 V (pH 13) (vs. Ag/AgCl) in accordance with voltammetric results. We found that the IR absorption bands of anions and water increases upon reduction in acidic solution at pH<p K a of p-aminothiophenol (PATP), while those for hydroxide anions decreases in alkaline solution. The observations result from the electrostatic interaction of these anions with partial charge at the PNTP- and PATP-SAM films on Au(1 1 1) surface. It suggests that the pKa of the PNTP-SAM film on the Au electrode can be evaluated from the IR spectral changes with the potential. Pronounced IR background shift observed during the PNTP reduction was discussed based on the superimposed changes from molecular structure, orientation of the SAM film and coadsorption of the anions.

Probing M-Branch Electron Transfer and Cofactor Environment in the Bacterial Photosynthetic Reaction Center by Addition of a Hydrogen Bond to the M-Side Bacteriopheophytin

Subpicosecond time-resolved absorption and steady-state resonance Raman (RR) studies are reported for Rhodobacter capsulatus reaction centers (RCs) that incorporate an Asp in place of Val M131 near the ring V keto group of the M-side bacteriopheophytin (BPh M ). The L-side C 2 -symmetry analogue of residue M131 is Glu L104, which is known to form a hydrogen bond to the ring V keto group of BPh L in the wild-type RC. The effects of the V(M131)D mutation were probed in the triple mutant V(M131)D/G(M201)D/L(M212)H, which also incorporates an Asp at M201 near the L-side bacteriochlorophyll (BChl L ) as well as the beta mutation L(M212)H that results in replacement of the native BPh L with a Bchl molecule (denoted β). The primary photochemistry in the triple mutant (denoted V(M131)D-DH) is similar to that reported previously for the G(M201)D/L(M212)H double mutant (denoted DH). Upon excitation, P* decays with a time constant of 15 ps via a combination of electron transfer to the L side (70%), decay to the ground state (15%), and electron transfer to the M side to form P + BPh M - (15%). The bleaching of the Qx ground-state absorption band of BPh M observed upon formation of P + BPh M - is red shifted 1-2 nm from ∼527 nm in the DH RC to ∼529 nm in the V(M131)D-DH mutant, and the BPh M anion band is shifted 20 nm from 645 to 665 nm. RR experiments reveal that the ring V keto vibration of BPh M at 1705 cm - 1 in the wild-type RC downshifts to 1697 cm - 1 in the V(M131)D mutant. Collectively, these results indicate that the Asp introduced at M131 forms a hydrogen bond to the ring V keto group of BPh M in both ground (neutral) and anionic states of this cofactor, and further demonstrate that M-side electron transfer to form P + BPh M - occurs in both mutants. Comparison of the effects engendered by the addition of the hydrogen to BPh M with those found previously upon removal of the Glu L104 hydrogen bond to BPh L give insights into specific and global effects of the protein on the properties of these symmetry-related cofactors.

Electron energy loss and dissociative electron attachment spectroscopy of methyl vinyl ether and related compounds

The triplet and singlet excited states of methyl vinyl ether have been characterized by electron energy loss spectroscopy and multireference density functional theory with configuration interaction (DFT/MRCI). The electron attachment energy was determined from the excitation functions for vibrational excitation to be 2.3 eV. Dissociative electron attachment spectra have been measured with a mass spectrometer having a trochoidal monochromator in the incident electron beam. Fragment anion bands peaking at 3 eV, 6.5 eV and 9.5 eV have been found in methyl vinyl ether. The first band is assigned to the 2(π∗) shape resonance, the second band to a resonance where an electron is loosely bound by dipole and polarization forces to the target molecule in its valence excited 1(π, π∗) state, and the third band to Feshbach resonances with occupation of Rydberg orbitals. CH 3O − and H 2CC − are formed at 3 eV, CH 3O − and HCC − at 6.5 and 9.5 eV. The fragmentation pattern of ethyl vinyl ether at 3 eV is similar, yielding ethanolate and vinylidene anions, but with the unexpected addition of the deprotonated acetaldehyde anion CH 2CHO −. The fragmentation patterns of methyl allyl ether and benzyl methyl ether are dominated by the methanolate anions with high intensity, indicating that dissociation of C–O bond in unsaturated ethers is much faster if this bond does not lie in the plane of the π system.

IR spectra and microstructure of electrolyte solutions. Dependence of spectroscopic characteristics of solvated molecules on composition of solvates in the system CH3CN–Mg(ClO4)2–DMF

The integrated intensities of the ν(CC) and ν(CN) stretching vibration bands of acetonitrile (CH3CN) molecules, the δ(OCN) bending vibration band of N,N-dimethylformamide (DMF) molecules, and the ν3 and ν4 bands of perchlorate anions (ClO4−) in ternary CH3CN–Mg(ClO4)2–DMF solutions were measured. The obtained experimental data show that DMF molecules have a greater ability to solvate cations than CH3CN molecules. The spectroscopic properties of CH3CN and DMF molecules located in the first coordination sphere of a cation depend on the composition of the solvate: the absolute intensities of the ν(CC) and ν(CN) bands of CH3CN molecules and of the δ(OCN) band of DMF molecules decrease when the number of DMF molecules in the first solvation shell of the cations increases. Electron transfer from the solvent molecules to the cations is discussed. The influence of the electrostatic field of the cations on the electro-optical parameters of the bonds of the solvated molecules decreases due to this effect.

DNA, peroxidase profile, and biochemical composition changes during the treatment in vitro of pollen of Argemone mexicana L. with SO 2

The allergenic pollen of Argemone mexicana L. a common road-side weed was subjected to artificial SO 2 fumigation at a concentration of 100ppm for 24 hours, 48 hours and 72 hours and its effect on the total carbohydrate, lipid, free amino acid, DNA and RNA content as well as peroxidase isozyme and DNA profile studied. In comparison to the control (pollen exposed to charcoal-filtered air), the carbohydrate, lipid, DNA and RNA content decreased with the increase in the time of exposure to SO 2 , where as the percentage composition of free amino acid increased. Contrary, to this, the activity of peroxidase was found to increase with a change in the iso-peroxidase zymogram showing three new anionic isozyme bands. SO 2 affected the total DNA profile leading to the gradual breakdown of DNA with several bands observed on agarose gel electrophoresis with an increase in the time of fumigation.

Formation of Bacteriochlorophyll Anion Band at 1020 nm Produced by Nuclear Wavepacket Motion in Bacterial Reaction Centers

AbstractFormation of a nuclear wavepacket on the potential energy surface of the primary electron donor P* induced by 30‐fs excitation of pheophytin‐modified Rhodobacter sphaeroides R‐26 reaction centers leads to a reversible and irreversible appearance of the state P+BA− monitored by the measurements of the 1020‐nm band which is characteristic of the radical anion band of bacteriochlorophyll monomer BA−. The reversible appearance of the state P+BA− is characterized by two (130 and 320 cm−1) vibration modes and related to the creation of maximal value of the Franck‐Condon factor when the wavepacket is near an intersection of the P* and P+BA− potential energy surfaces. The irreversible formation of the state P+BA− with a time constant of 3 ps is accompanied by oscillations with frequencies of 9 and 33 cm−1. These results show that the nuclear vibration modes (9 and 3 3 cm−1) on the P* potential energy surface have near their bottom the intersection with the P+BA− surface as well. The electron transfer time between P* and BA was estimated to be in the range of 700 fs. This is larger than the wavepacket intersection time for the 130 cm−1 mode (∼100 fs) and comparable with that for the 33 cm−1 mode (∼600 fs). Therefore the reversible electron transfer with small amplitude can be observed for the 130 cm−1 mode, while the irreversible one is allowed for the 33 cm−1 mode that is probably important for the primary charge separation.

Nuclear wavepacket motion producing a reversible charge separation in bacterial reaction centers

The excitation of bacterial reaction centers (RCs) at 870 nm by 30 fs pulses induces the nuclear wavepacket motions on the potential energy surface of the primary electron donor excited state P*, which lead to the fs oscillations in stimulated emission from P* [M.H. Vos, M.R. Jones, C.N. Hunter, J. Breton, J.-C. Lambry and J.-L. Martin (1994) Biochemistry 33, 6750–6757] and in Q Y absorption band of the primary electron acceptor, bacteriochlorophyll monomer B A [A.M. Streltsov, S.I.E. Vulto, A.Y. Shkuropatov, A.J. Hoff, T.J. Aartsma and V.A. Shuvalov (1998) J. Phys. Chem. B 102, 7293–7298] with a set of fundamental frequencies in the range of 10–300 cm −1. We have found that in pheophytin-modified RCs, the fs oscillations with frequency around 130 cm −1 observed in the P*-stimulated emission as well as in the B A absorption band at 800 nm are accompanied by remarkable and reversible formation of the 1020 nm absorption band which is characteristic of the radical anion band of bacteriochlorophyll monomer B A −. These results are discussed in terms of a reversible electron transfer between P* and B A induced by a motion of the wavepacket near the intersection of potential energy surfaces of P* and P +B A −, when a maximal value of the Franck–Condon factor is created.

Effects of chromophore interaction in photophysics and photochemistry of cyanine dyes

Spectral and fluorescent properties of ketocyanine dyes (polyenic bis‐ω, ω′‐aminoketones) and cation‐anionic polymethine dyes of various structures were studied. The symmetric ketocyanines were shown to have a long‐wavelength absorption band bathochromically shifted in comparison with that of the asymmetric ketocyanines with the same total length of the polyenic chain. The nonlinear ketocyanines exhibit the additional short‐wavelength band in their absorption spectra, which can be more intense than the longwavelength band. The absorption spectra of ion pairs of cation‐anionic dyes with overlapping cation and anion bands contain a new intense short‐wavelength band inactive in fluorescence excitation. These spectral peculiarities are explained on the basis of chromophore interaction model. It has also been shown that the T1 levels of ketocyanine chromophores do not essentially interact with each other in a ketocyanine molecule in nonpolar solvents; in polar solvents this interaction becomes appreciable due to lowering the potential barrier for conjugation.

FT-Raman and powder XRD analysis of the Ba(SO 4) x(CrO 4) 1− x solid solution

The Ba(SO 4) x (CrO 4) 1-x solid solution has been described in nature, forming the mineral Hashemite. From the geochemical point of view, however, anionic solid solutions have much interest because they are suitable systems to probe order–disorder phenomena. The solid solution analysed in the present study has, moreover, a special incentive in its possible use for the extraction from water, and immobilisation, of the pollutant Cr(VI) ion. The orthorhombic (space group Pnma) unit cell parameters of the solid solution change linearly with the mole fraction of both anions, decreasing with increase in the sulfate anion concentration. The vibrational spectroscopic study is centred on the behaviour of the anionic symmetric stretching band (ν 1, A 1), whose characteristics are examined in detail. While the chromate anion band retains its wavenumber along the full compositional range, the sulfate anion band is shifted toward lower wavenumbers with decrease in the corresponding mole fraction. The positional disorder induced by the random anionic substitution results in strong increase of the halfwidth in both bands, which becomes greatest in the central member of the series.

Photochemistry of “Super”-Photoacids. Solvent Effects

We study steady-state and time-resolved fluorescence of 5-cyano-2-naphthol in various pure solvents. To some of these, excited-state proton transfer occurs within the excited-state lifetime of the chromophore. Solvatochromic shifts in the acid and anion bands are analyzed using the empirical Kamlet−Taft approach. The hydrogen-bond donated from the OH group to basic solvents accounts for most of the shift in the excitation spectra. This bond produces considerably larger shifts in the emission spectra, suggesting that it strengthens in the excited state. In contrast, the hydrogen bond donated from protic solvents to the hydroxyl oxygen is cleaved following photoexcitation. This bond (and not the change in dielectric constant) is responsible for the solvent-induced blue shift in anion fluorescence. Hence it must re-form simultaneously with the proton-transfer event. Our time-resolved fluorescence data fit the solution of the Debye−Smoluchowski equation for reversible geminate recombination in a field of force, provided that the difference in excited-state lifetimes and contact quenching are taken into account. An extended theory of reversible geminate recombination provides an accurate description of the asymptotic behavior in this case. The quenching processes correlate with the solvent hydrogen-bond donation ability, implicating the involvement of hydrogen-bonded pathways.

M-side electron transfer in reaction center mutants with a lysine near the nonphotoactive bacteriochlorophyll.

We report the primary charge separation events in a series of Rhodobacter capsulatus reaction centers (RCs) that have been genetically modified to contain a lysine near the bacteriochlorophyll molecule, BChl(M), on the nonphotoactive M-side of the RC. Using wild type and previously constructed mutants as templates, we substituted Lys for the native Ser residue at position 178 on the L polypeptide to make the S(L178)K single mutant, the S(L178)K/G(M201)D and S(L178)K/L(M212)H double mutants, and the S(L178)K/G(M201)D/L(M212)H triple mutant. In the triple mutant, the decay of the photoexcited primary electron donor (P) occurs with a time constant of 15 ps and is accompanied by 15% return to the ground state, 62% electron transfer to the L-side bacteriopheophytin, BPh(L), and 23% electron transfer to the M-side analogue, BPh(M). The data supporting electron transfer to the M-side include bleaching of the Q(X) band of BPh(M) at 528 nm and a spectrally and kinetically resolved anion band with a maximum at 640 nm assigned to BPh(M)(-). The decay of these features and concomitant approximately 20% decay of bleaching of the 850 nm band of P give a P(+)BPh(M)(-) lifetime on the order of 1-2 ns that reflects deactivation to give the ground state. These data and additional findings are compared to those from parallel experiments on the G(M201)D/L(M212)H double mutant, in which 15% electron transfer to BPh(M) has been reported previously and is reproduced here. We also compare the above results with the primary electron-transfer processes in S(L178)K, S(L178)K/G(M201)D, and S(L178)K /L(M212)H RCs and with those for the L(M212)H and G(M201)D single mutants and wild-type RCs. The comparison of extensive results that track the primary events in these eight RCs helps to elucidate key factors underlying the directionality and high yield of charge separation in the bacterial photosynthetic RC.

Optical and Electronic Properties of Polysilane Radical Anions

Analyses of the electronic absorption spectra and their polarization spectra of the radical anions of permethylated hexa- and octasilane and poly(cyclohexylmethylsilane) in the mixed solvents of nonpolar methylcyclohexane and polar 2-methyltetrahydrofuran at 77 K have revealed that the orbitals of the excess electrons in the radical anions are antibonding pseudo-π composed of Si 3py atomic orbitals bisecting the Si−Si−Si planes. The near-IR and UV bands of the radical anions are assigned as being due to the excitation of an electron from the SOMO pseudo-π(3py) to pseudo-π*(3py) and from the HOMO pseudo-π(3px) to antibonding-σ(3s), respectively. The near-IR band of the polysilane radical anion shows strong solvatochromic shift, which arises from the localization of the excess electron on a part of the main chain. Localization of the excess electron is proposed to be due to Anderson localization which is induced by the fluctuation of pseudo-π conjugation arising from the irregularity of the torsional angles...

High density lipoprotein (HDL), and not albumin, is the major palmitate binding protein in New Zealand long-finned ( Anguilla dieffenbachii) and short-finned eel ( Anguilla australis schmidtii) plasma

Plasma from two members of the teleost Anguillidae family, the New Zealand long-finned ( Anguilla dieffenbachii) and short-finned eels ( Anguilla australis schmidtii), were examined. Agarose gel electrophoresis showed both species had a major anionic diffuse protein band migrating at approximately the same position as human albumin, and autoradiography showed this protein bound [ 14C]palmitic acid, but not 63Ni 2+. Cellulose acetate electrophoresis followed by Oil Red O staining suggested that this band was a lipoprotein. Two-dimensional electrophoresis of plasma showed the absence of a significant albumin band at approx. 65 kDa, and that the palmitate binding band appeared to be composed of at least three proteins, with the major protein running at 30 kDa. N-Terminal sequencing of the palmitate binding band indicated major sequences of DAPAPP(S)QLED- for long-finned eel and DAPAPPSQLEHV- for short-finned eel, confirming their identities as apo-AI, the major apolipoprotein of high density lipoprotein (HDL). When ultracentrifugation was used to separate the lipoproteins of each species, the anionic palmitate binding protein was found solely in the lipoprotein fractions. There was no evidence of albumin in plasma from either eel, and it appears that in its absence HDL takes on the role of fatty acid transport.