Absorption Spectra Of Aqueous Solutions Research Articles

Resolution of absorption spectra of rhodamine 6G aggregates in aqueous solution using the law of mass action

There is striking dissimilarity among the absorption spectra of rhodamine dimers reported by different authors. To address this issue, we measured the absorption spectra of aqueous solutions of rhodamine 6G over a wide range of concentrations. The lack of an isosbestic point near 508 nm indicates the presence of at least three species. Data analysis using the program spectrabind described in [D. Toptygin, L. Brand, Anal. Biochem. 222 (1995) 330] confirms the presence of trimers and tetramers in addition to dimers and monomers. The absorption peaks of the monomer, dimer, trimer, and tetramer are at 526, 498, 485, and 475 nm, respectively.

Interaction of chromophores in dissimilar associates of cationic and anionic polymethine dyes in water

A strong interaction between chromophores of cationic and anionic components was found based on the analysis of electronic absorption spectra of aqueous solutions of mixtures of cationic indopolycarbocyanines with anionic cyanines. Strong dissimilar 1∶1 associates are formed. Association constants were estimated spectrophotometrically. The main factors determining the degree of interaction of chromophores were revealed.

水溶液中でのアクリジンオレンジ会合体の構造と解離平衡

The aggregate states of Acridine Orange bimolecular probe in aqueous solution and micelle media were strudied by absorption spectroscopy. The absorption spectra of the solutions involving Acridine Orange (AO) change with their concentrations. On the basis of Kasha's theory on the difference spectrum between the solution of the AO monomer and that of dimer, the averaged distance between molecular planes of AO's and the dihedral angle in dimer molecules were estimated as 4.4 A and 80°, respectively.It was also shown that the AO dimer dissociates by the addition of surfactant to AO aqueous solution. Dissociation equilibrium of bimolecular associates (dimer) of AO was studied thermodynamically. At the temperature of 30-60°C, absorption spectra of aqueous solutions of AO showed only monomer and dimer bands. Spectral changes with varying temperature suggested that a simple equilibrium between AO dimer and monomer. The values of dissociation constant K and dissociation enthalpy δH were estimated to be 4.24-6.45×10-5 mol dm-3 in the range from 40 to 60°C, and 4.16 kcal mol-1, respectively.

Preparation and Resolution of a Series of Cobalt(III) Complexes Containing 2,2′-Biimidazole and Ethylenediamine

Abstract A new series of cobalt(III) complexes of the type [Co(H2biim)n(en)3−n]3+ (H2biim = 2,2′-biimidazole; n = 1—3) was obtained. All of the complexes were resolved into their antipodes by SP-Sephadex column chromatography. The absorption, circular dichroism, and 1H NMR spectra of the complexes in aqueous solutions were dependent on the pH due to deprotonation of the imino protons of H2biim. The pKa1 and pKa2 values for [Co(H2biim)(en)2]3+ were obtained as 5.9 and 9.9, respectively, from the absorption spectra in aqueous solutions. The optically active deprotonated complexes, (−)589-[Co(Hbiim)3]·2H2O and (−)589-Ba1.5[Co(biim)3]·2H2O, were also isolated from weakly and strongly basic aqueous solutions, respectively, of (−)589-[Co(H2biim)3](NO3)3·H2O.

Deterministic resolution of molecular absorption spectra of aqueous solutions: environmental applications

Direct absorptiometric measurement of aqueous solutions in the UV-visible region is simple but often of little interest because of the featureless shape of the spectra. Automatic resolution methods for deconvolution of the signal are thus required. The choice of the basis of reference spectra is very important and the most appropriate methods use a deterministic approach. These procedures can be added to the software of many new instruments. Some environmental applications are presented.

Coordination equilibria and water exchange kinetics of lanthanide(III) propylenediaminetetraacetates and other magnetic resonance imaging related complexes

The UV-Vis absorption spectra of aqueous solutions of Eu 3+ complexes with the hexadentate polyaminocarboxylate ligands EDTA 4−, CDTA 4−, HDTA 3− and PDTA 4− were measured as a function of temperature and pressure in the frequency region corresponding to the 7F 0→ 5D 0 transition of Eu 3+. The results can be explained in terms of equilibria between nine-coordinate and eight-coordinate species where the eight-coordinate species contain one less inner sphere water molecule than the nine-coordinate species. The thermodynamic parameters, including the reaction volume, for these equilibria were determined. 17O NMR transverse relaxation rates and chemical shifts were measured for aqueous solutions of the eight-coordinate complexes [Ln(PDTA)(H 2O) 2] − (LnTb, Dy, Er, Tm, Yb) and [Er(EDTA)(H 2O) 2] − as a function of temperature, pressure and magnetic field. The results were analysed in terms of the water exchange kinetics on the complexes. The water exchange rate on [Ln(PDTA)(H 2O) 2] − decreases dramatically with decreasing ionic radius across the lanthanide series from k ex 298 = (2.4±0.1)×10 7 s −1 for LnTb to k ex 298 = (2.8±0.3)×10 5 s −1 for LnYb. The activation volumes show that this is accompanied by a change of exchange mechanism from associatively activated for LnTb ( ΔV # = −7.6±0.3 cm 3 mol −1) to dissociatively activated for LnYb ( ΔV # = +7.4±0.8 cm 3 mol −1). Water exchange on [Er(EDTA)(H 2O) 2] − ( k ex 298 = (9.8±1.9)×10 6 s −1) is more than an order of magnitude faster than on [Er(PDTA)(H 2O) 2] − ( k ex 298 = (5.6±0.5)×10 5 s −1). These kinetic results can be interpreted in terms of the equilibria measured by UV-Vis spectrophotometry. The implications of these observations for the design of new MRI contrast agents are discussed.

Aggregation Behaviour of Some Reactive Dyes

The absorption spectra of aqueous solutions of monochlorotriazine reactive dyes, C.I. Reactive Red 9 and Reactive Orange 13 were measured in the presence of 5, 10, 25 and 50% (v/v) of ethanol, pyridine and dioxane-water mixtures and in varied concentrations of KCl, NaCl and LiCl. The varying position, intensity and shape of absorption bands are interpreted in terms of aggregation and disaggregation of dyes in solutions. The aggregation behaviour of the reactive dyes in solutions and in the presence of additives is related to their apparent deviations from Beer's law and aggregation numbers (N). The aggregation constant (K.) of the monomer/dimer equilibrium is calculated. Dyes in ethanol-water mixtures record a larger aggregation number and aggregation constant than in the presence of pyridine. Dioxane is classified as anon-polar solvent and hence has a more disaggregating influence. The value of the aggregation number and constant are increased with increasing salt conentration and the order of degree of aggregation is KCl > NaCl > LiCl related to the order of ionic radii of K+, Na+ and Li+ ions.

On the infrared absorption of acidified water

We have investigated some of the electro-optic properties of ions solvated in a structured liquid. In particular, we have looked at the origin of a dynamic polarizability which we show can be quite large. This frequency dependent polarizability can make a substantial contribution to the observed absorption spectra of aqueous solutions in those regions where continua are observed. Our model also produces a possible mechanism for the hydrophobic interaction of nonpolar molecules in polar solutes.

Far infrared absorption by electrolyte solutions

The far infrared absorption spectra of aqueous solution of LiCl have been investigated in a frequency range 8–40 cm−1 at room temperature. In low frequency range (8–20 cm−1), the absorption is mainly controlled by Debye relaxation of the electric dipole rotation, and the absorption decreases with the increase of concentration.

Synthesis and characterisation of carboxylic acid and diphenylphosphine derivatives in the 1,3‐diyne series: Spectral properties of polydiacetylene carboxylates

AbstractSymmetrically substituted 1,3‐diynes containing hydroxyalkyl (1a‐d), bromoalkyl (1e‐h) (diphenylphosphinyl) (1i‐k) and carboxyalkyl (2a‐d) substituents have been prepared and characterised; the phosphine derivative (1k) has been converted with alkyl iodides (RI; R = Me, Et) into bis(phosphonium) salts (1l and m). During preparation of the diynedioic acid. (2a), the non‐centrosymmetrical diyne, HO2CCH2CC—CC(CH2)2OH (3), was also isolated. 60Co γ‐Irradiation of diacetylene monomers (2a–d) and 10,12‐tricosadiyn‐1‐oic acid gave the corresponding polydiacetylene derivatives (4a–d and 5), respectively. Rubidium salts of (4c) and (4d), a barium salt of (4c), and a potassium salt of (5) were prepared and isolated; soluble potassium salts of the carboxylic acid polymers (4) were generated in aqueous solution. The effects of changes in pH on the UV/visible absorption spectra of aqueous solutions of selected carboxylic acid polydiacetylenes have been recorded, and are discussed.

Effects of Ring Size on Spectral Properties of Copper(II)-Diaminodiamide Complexes in Aqueous Solution

The electronic absorption spectra of aqueous solutions containing copper(II) ion and N, N′-bis(carbamoylmethyl)trimethylenediamine(L-1, 3, 1) at 25.0 ± 0.1°C and 0.10 mol L−1 NaClO4, were measured as a function of pH. The absorption maxima and the molar absorptivities of [Cu(L-l, 3, l)]2+, [Cu(H.1L-1, 3, 1)]+, and [Cu(H-2L-l, 3, l)] were calculated from these spectra. A comparison of the spectral parameters of these complexes with those of the copper(lI)-diaminodiamide complexes containing 6, 5, 6-and 6, 6, 6-membered ring systems indicates that the chelate ring size has significant effects on these spectral parameters.

Novel colloidal polyaniline fibrils made by template guided chemical polymerization

The colloidal fibrils of polyaniline–poly(acrylic acid) complex were first synthesized by template guided chemical polymerization; their morphology and the electronic absorption spectra in aqueous solution are reported.

１‐Ｍｅｔｈｙｌ‐４‐（４‐ｄｉｅｔｈｙｌａｍｉｎｏｐｈｅｎｙｌａｚｏ）ｐｙｒｉｄｉｎｉｕｍ ｉｏｄｉｄｅの水溶液および吸着分子層の電子吸収スペクトル

１‐Ｍｅｔｈｙｌ‐４‐（４‐ｄｉｅｔｈｙｌａｍｉｎｏｐｈｅｎｙｌａｚｏ）ｐｙｒｉｄｉｎｉｕｍ ｉｏｄｉｄｅの水溶液および吸着分子層の電子吸収スペクトル

TRANSIENTS OF URACIL and THYMINE DERIVATIVES and THE QUANTUM YIELDS OF ELECTRON EJECTION and INTERSYSTEM CROSSING UPON 20 ns PHOTOLYSIS AT 248 nm

Transients of uracil and a series of 17 correlated pyrimidines, e.g. methylated bases, nucleosides, nucleotides, and polyuridylic acid [poly(U)] were studied after 248 nm excitation by 20 ns laser pulses. The transient absorption spectra in aqueous solution at room temperature reveal the triplet state and the hydrated electron (e-aq), while the corresponding radical cation could not be observed at pH 6-7. Fast loss of the chromophore in the 260-290 nm range within 0.1 microsecond was observed in aqueous solution in some cases [e.g. poly(U), 5'-UMP, uridine, uracil] and in others (thymine, thymidine) virtually not. This photobleaching is assigned to formation of the photohydrate. The concentration of e-aq shows a quadratic dependence on the laser pulse intensity (IL) in the range (0.2-2) x 10(7) W cm-2 and the quantum yield of electron ejection (phi c-) thus depends linearly on IL. This behaviour, suggesting that the photoionization involves a two-step absorption process, was found for poly(U) and all pyrimidine monomers examined. At a constant IL value of 2 x 10(7) W cm-2, phi c- ranges from 3 x 10(-3) for 1,3-dimethylthymine to 4 x 10(-2) for poly(U). The triplet state shows a much larger transient absorbance (delta A, typically in a broad range, e.g. 290-500 nm) than that of the neutral radical resulting from the radical cation. The triplet state in organic solvents (acetonitrile and ethanol) shows generally a significantly larger delta A value than in aqueous solution. The estimated quantum yields of intersystem crossing at room temperature are compared with those of phosphorescence at -196 degrees C.

Internal heavy-atom effect on the photophysics and photochemistry of 2-styrylanthracene

Abstract The nature and identification of the excited states and of the reactive intermediates resulting from the absorption of UV by components of nucleic acids is relevant in understanding the photobiological effects of UV radiation. The transient absorption spectra of aqueous solutions of guanine, 9-methylguanine, 7-methylguanine, guanosine, 2′-deoxyguanosine, guanosine-5′-phosphate, and 2′-deoxyguanosine-5′-phosphate have been determined at several pH values for the different charged species of these molecules using laser flash photolysis. Reactive intermediates resulting from the absorption of 266 nm (60 mJ) radiation by these molecules present similar initial absorption spectra: a higher intensity band in the visible region with a maximum around 700 nm, which extends into the 400 nm wavelength region and decays within the first few microseconds, and a lower intensity band in the UV region which lasts for longer observation times. After the disappearance of the visible band, the spectra consist of a band commencing around 550 – 650 nm and extending into the UV region. The fast-decaying visible band is attributed to the hydrated electron which decays following pseudo-first-order kinetics. Almost diffusion-controlled rate constants were determined for the reaction of the electron with the guanines. The UV band has contributions from absorptions by the cation radical, anion radical and/or radicals resulting from neutralization reactions of these charged radicals. The cation radical was also produced by radiolytically generating the azide radical. Except for 7-methylguanine and 9-methylguanine, there is no evidence of the participation of the triplet state in the photochemical processes of the other guanine derivatives since the changes in the transient spectrum caused by the presence of oxygen or other triplet quenchers are explained in terms of their reaction with the hydrated electron. The neutral and charged forms of the guanine derivatives photoionize from a singlet state. Substitution of a ribose by a deoxyribose, or the incorporation of a phosphate group, does not produce an effect on the type of transient intermediate resulting from the primary photochemical processes of these guanine derivatives.

Coordination Chemistry of F430: Axial ligation equilibrium between square-planar and bis-aquo species in aqueous solution

Abstract X-ray absorption spectroscopic characterization of axial ligand coordination to factor F430, the nickel-tetrapyrrole cofactor of the S-methyl-coenzyme M (CH3SCoM) methyl reductase enzyme from methanogenic bacteria, is presented. The nickel of isolated F430 is hexacoordinate at 10 K in aqueous solution (as is the enzyme-bound cofactor), whereas the epimerized and ring-oxidized derivatives of F430 have four-coordinate nickel. Reduction of the ring-oxidized derivative, F560, with dithionite yields F430 in its native configuration, with axial ligands indistinguishable from those present when the cofactor is obtained directly from the holoenzyme. Thus, we conclude that the axial ligands to F430 in aqueous solution are water molecules. Analysis of the nickel extended x-ray absorption fine structure is consistent with this conclusion. Resonance Raman spectra obtained at room temperature contain features characteristic of both 4- and 6-coordinate forms of the cofactor. We have found that the resonance Raman, optical, and x-ray absorption spectra of aqueous solutions of F430 are temperature-dependent due to a ligand-binding equilibrium involving the square-planar and 6-coordinate bis-aquo forms of the cofactor. At low temperatures (less than 250 K) the 6-coordinate form predominates, whereas higher temperature solutions contain both 4- and 6-coordinate species in a dynamic equilibrium. Similar behavior is observed in other weakly coordinating solvents such as methanol and ethanol. The 4-coordinate form is predominant in solvents with strong electron-withdrawing substituents such as 2,2,2-trifluoroethanol and 2-mercaptoethanol. The relevance of this facile ligand exchange to the active site structure and enzymatic mechanism of the parent enzyme is discussed.

Effect of micelle formation on the absorption spectra of a functionalized detergent with the anthraquinone moiety

Measurements of the absorption spectra of aqueous solutions of (2-anthraquinonylmethyl)dodecyldimethylammonium (AQD+) bromide have been performed. From the concentration dependence of the molar absorption coefficient at λmax= 330 nm (εapp), the c.m.c. and the molar absorption coefficient of AQD+ participating in its micelle formation were calculated by assuming a micellar pseudo-phase model. The change in εapp above the c.m.c. was found to be due to interactions of the anthraquinone moieties, by studying the effect of the addition of hexadecyltrimethylammonium bromide (CTAB) to the AQD+ micellar solution. The effect of the addition of CTAB to the AQD+ monomer solution was also examined, but the spectra of the AQD+ monomer were little affected by the addition of CTAB. Measurements of the absorption spectra of aqueous solutions of the monomeric AQD+ and sodium dodecylsulphate (SDS) point to the formation of a stable ion-pair complex between them. On further addition of SDS, the complex disappeared above the c.m.c. of SDS. This amphiphatic anthraquinone derivative serves as a probe for determining the c.m.c. of SDS in the absence and presence of electrolyte because the molar absorption coefficient at 290 nm changes by a factor of 7 above and below the c.m.c. of the host surfactant.

８‐アミノ‐３，６‐ジアザオクタノアトコバルト（ＩＩＩ）錯体の研究 ＶＩＩ β‐ｍｅｒ（Ｎ）‐ｔｒａｎｓ（Ｏ）‐（８‐ａｍｉｎｏ‐３，６‐ｄｉａｚａｏｃｔａｎｏａｔｏ）‐（Ｌ‐ｐｈｅｎｙｌａｌａｎｉｎａｔｏ）ｃｏｂａｌｔ（ＩＩＩ）ジアステレオ異性体の合成と円偏光二色性スペクトル

In order to isolate the diastereoisomers (abbreviated as isomers below) in [Co(adao)(L-phe)]+(adao: -OOCCH2NH2(CH2)2NH(CH2)2NH2; L-phe: C6H5CH2CH(NH2)C00-) and to clarify their structures, the liquid chromatographic separation was carried out on the reaction products from β-mer(N)-[Co(adao)Cl(H2O)]ClO4 and L-phenylalaninate ion. Two isomers were successfully isolated as the crystals from two eluates (EI and EII). The elemental analyses indicated that the crystals had the compositions of [Co(adao)(L-phe)]X⋅nH2O { (X, n) = (I, 2), (ClO4, 1)}, respectively. Their absorption spectra in aqueous solution showed that both crystals are trans(O) isomers. As shown in Fig., 1, it is apparent that adao in the trans(O)isomers coordinates with the β-mer(N) coordination mode. By using the circular dichroism (CD) spectra of two isomers, the configurational effective CD curves and the vicinal effective CD curve of L-phenylalanine were calculated. On the basis of the configurational CD curve for the trans(O) isomer from EI, it has been deduced that this isomer has the Δ(ΔΔΔΔ)-β-mer(N)-trans(O) structure. Therefore, the isomer from Elf has been assigned to the Δ(ΔΔΔΔ)-β-mer(N)-trans(O) one.

ChemInform Abstract: The Two‐Electron Oxidation of Methyl Viologen. Detection and Analysis of Two Fluorescing Products.

The oxidation of methyl viologen, 1,1′-dimethyl-4,4′-bipyridylium chloride (MV2+), in aqueous solution has been carried out γ-radiolytically and photocatalytically (in the presence of colloidal titanium dioxide). Two strongly fluorescing products have been observed, separated and identified: the 1′,2′-dihydro-1,1′-dimethyl-2′-oxo-4,4′-bipyridylium cation [‘2-one’, λflmax(H2O)= 516 nm] and the 3,4-dihydro-1,1′-dimethyl-3-oxo-4,4′-bipyridylium cation [‘3-one’, λflmax(H2O)= 528 nm]. Both compounds exhibit characteristic u.v.–visible absorption spectra in aqueous solution with maxima at 222, 260 and 347 nm (Iµ= 14800, 20200 and 2400 dm3 mol–1 cm–1) or 236, 260 (shoulder) and 390 nm (Iµ= 12000, 5800 and 3700 dm3 mol–1 cm–1) for the 2-one or 3-one, respectively. Their relative abundance in the radiolysis experiments is strongly dependent on the absence or presence of secondary oxidants, e.g. dioxygen and ferric ions. The overall low G-values in the radiation chemical studies [Gmax(2-one)= 0.04, Gmax(3-one)= 0.11] indicates the formation of other as yet unidentified oxidation products. Comparatively high quantum yields are observed for both products upon ultra-bandgap irradiation of aqueous colloidal suspensions of TiO2[ϕ(2-one)= 0.032, ϕ(3-one)= 0.01], suggesting a simultaneous or consecutive two-hole transfer mechanism rather than a homogeneous free radical pathway is involved. Probable mechanisms of the ·OH-induced oxidation of methyl viologen are discussed as well as the possible implication of these results on the use of MV2+ as an electron relay in solar energy devices.

UV resonance raman and UV-VIS absorption spectra of aqueous solutions of an azobenzene-containing ammonium amphiphile

UV resonance Raman and UV-VIS absorption spectra of aqueous solutions of an azobenzene-containing, single-chain amphiphile have been measured over wide ranges of temperature and concentration. Below the gel- or coagel-liquid crystalline phase transition temperature ( T c), the aqueous solution gives a doublet absorption band at 375 and 393 nm due to a J-like bilayer aggregate. Above T c, on the other hand, it shows a single broad band at 345 nm suggesting the liquid crystalline state. With a further increase in temperature, the absorption band shifts to 355 nm, indicating that a molecularly dispersed state is attained. The intensity ratios of the two intense Raman bands at 1458 and 1413 cm −1 of the aqueous solution are found to change upon the melting of ice surrounding the amphiphile. With dilution of the aqueous solution below and above T c, spectral changes due to the gel-molecularly dispersed state transition and the liquid crystalline-molecularly dispersed state transition are observed at 2 x 10 −5 and 4 x 10 −5 M, respectively.