Dimer Bands Research Articles

Interaction between TCNQ and Surfactant. III. The Effect of Light on the Spectra of TCNQ Solubilized in Surfactant Solutions

Abstract The absorption spectra of 7,7,8,8-tetracyanoquinodimethane (TCNQ) solubilized in surfactant solutions were found to be influenced by day light (hereafter referred to as light). The formation of the monomer band of TCNQ, anion radical in the aqueous solution of DPCl (dodecylpyridinium chloride), DPBr (dodecylpyridinium bromide) and C12E8 (homogeneous octaethylene glycol dodecylether) were enhanced by light. On the other hand, the spectra of TCNQ solubilized in surfactant micelle in the dark suggested that TCNQ exists as dimer anion radical form (TCNQ)2\ewdot. Thus, in solubilized state of TCNQ in micelle there is an equilibrium between monomer TCNQ\ewdot and dimer (TCNQ)2\ewdot, which seems to be easily influenced by light and surfactant. Appearance of a monomer radical band was remarkable in DPCl, DPBr, and C12E8 but only the dimer band was found in SDS even in the light.

Thallous Ion Dimer Center in Alkali Halide Crystals

Absorption, emission and excitation spectra of KI-Tl, KBr-Tl, KCl-Tl and KCl-In crystals have been investigated from 15°K to 300°K. Five absorption band, which are ascribed to the Tl + dimer center, are observed in addition to the Tl + monomer absorption bands in highly doped crystal (>0.01 mole %). Optical properties of the five bands are explained in terms of energy level diagram. The diagram is constructed from (Tl + ) 2 pseudo-molecular model where two Tl + ions are coupled weakly together. It is shown that of the five dimer bands, two are related to the A band, one is to the B band, and two are to the C band.

Dye aggregations or crystals within the void places of viscose film

The visible absorption spectra of the cross-sections of dyed viscose films were measured by means of a microspectrophotometer. We found that the spectra of Acridine Orange in the cross-sections of films showed a high maximum at 475 mμ, which would be referred to as β-band (a monomer peak at 497 mμ). It was explained from microscopic photographs and electron microscopic photographs that the dimer band arises from dye aggregates or crystals at the void places of viscose film.

Some physicochemical aspects of L-asparaginase therapy.

Clinical trials of E. coli asparaginase have been carried out with enzymes supplied by several companies [1–4]. The length of time the enzyme remains in the circulation of the host, is apparently a function of the source of the preparation [5]. In early attempts to detect the difference between two such samples (one from Bayer and one from Squibb), each was subjected to gel filtration on a G-200 Sephadex column. Identical activity patterns were obtained with each sample being divided into two peaks of activity. On disc electrophoresis the activity was separated into three bands which seem to represent a major band of monomer, an intermediate band of dimer, and a small band of trimer at the top of the gel. Each enzyme preparation was also subjected to isoelectric focusing, a procedure which separates compounds through a pH gradient according to their isoelectric point regardless of molecular size. Suprisingly, very different patterns of activity were obtained (Fig. 1).KeywordsIsoelectric PointPolyaspartic AcidHeart PunctureGlutaminase ActivityErwinia CAROTOVORAThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The dependence of excimer formation of polystyrene solutions on solvent and concentration

AbstractThe fluorescence spectra of polystyrene solutions have been measured in various solvents. The ratio of the intensity ID of the excimer (short living excited dimer) band to the intensity IM of the monomer band depends on the solvent. The values extrapolated to diluted solutions may be related to the average density of segments in a polymer molecule. Above concentrations of 0.1 g/100 ml, the ratio ID/IM increases with increasing concentration, and the peak position of the excimer band shifts to a longer wavelength.

ANALYSIS OF GENES CONTROLLING PEROXIDASE ISOZYMES IN <i>ORYZA SATIVA</i> AND <i>O. PERENNIS</i>

Eight strains belonging to Oryza sativa and O. perennis (Asian form) were intercrossed, and the hybrid plants were observed for peroxidase isozymes of the leaf blades by starch-gel electrophoresis method. Band 4C was found to be specified by an active gene, Pe4C. Bands 2A and 4A were specified by allelic genes, Pe2A and Pe4A, respectively. Their heterozygotes produced a hybrid dimer band, 3A, between 2A and 4A. Further, diallel crosses were made among ten plants randomly chosen from a population of O. perennis. The data suggested that there might be a regulatory gene, R4C, repressing band 4C. The loci of Pe4C, R4C and Pe2A/Pe4A appeared to be independent of one another.

Absorption spectra of dimer cations. Part 2.—Benzene derivatives

Radical cations of benzene, fluorobenzene, toluene, m-xylene, mesitylene, hexamethyl-benzene and p-tert-butyl-toluene have been prepared by γ-radiolysis of glassy solutions in a mixture of isopentane and n-butyl chloride at 77 K. The effects of concentration and of slight warming are used to assign the absorption bands to monomeric and dimeric species (M+ and M+2); the latter presumably have “sandwich” configurations like excimers. The assignments are supported by the resemblance of the dimer bands to those of para-cyclophane : some α,ω-diphenyl alkanes were also studied. Attempts at preparing “dimer anions” were unsuccessful, except with para-cyclophane. The spectra of the cations of the methyl-benzenes showed extra peaks, probably due to carbonium ions formed by hydrogen-atom transfer.

TRIPLET BEHAVIOR OF ORGANIC COMPOUNDS

Abstract— The rates of phosphorescence decay of nine compounds in frozen glass were measured. Six of the nine compounds decay exponentially, indicating that previously reported non‐exponential decay of some of them may have resulted from impurities, probably in the solvent.Three compounds – acetophenone, phenanthrene, and acridine orange–have unusual decay kinetics. Acetophenone has no wavelength–dependence of rate, but the decay is non‐exponential at all observed stages. The effect is believed due to a multiplicity of metastable excited states, all of which ultimately decay through a common lowest triplet. The delayed emission of phenanthrene in frozen glass consists of phosphorescence and a P‐type delayed fluorescence in the dimer band only. The ratio of the rates of decay of phosphorescence and delayed fluorescence is nearly the same in frozen glass as it is in liquid solution. It is suggested that excimers can be formed by molecules up to 100 A apart, and that the description ‘excited dimer’ is misleading. Finally, acridine orange has a P‐Type delayed fluorescence which decays initially with second‐order kinetics. The first‐order kinetics generally observed in P‐type delayed fluorescence are merely the result of the relative importance of competitive unimolecular reactions in depopulation of the triplet state.

A New Interpretation of the Anomalous Magnetic and Optical Behavior of Copper Acetate Monohydrate

Interpretation of the extensive magnetic and optical measurements of copper acetate monohydrate on the basis of a C4v symmetry of the complex by different workers are, to some extent, incomplete and often lead to contradictions. Starting with the electronic states of each half of the complex, assumed to have a C2v symmetry as shown by ESR. data, we find that the bonding between the two halves is a mixture of σ- and δ-type as against a pure σ or δ bonding for a C4v symmetry. Operation of H=Hex+HLS+βH(L+2S) on the valence bond states of the whole complex by usual perturbation technique then gives us the expressions for the singlet-triplet separation (J), the spectroscopic splitting factors and the magnetic susceptibilities. It is found that the last two quantities and the optical absorption data can be correlated to a good extent and the ligand field parameters obtained in the process yield a value of − 138 cm−1 for J, which is fair enough under the approximations employed. In this calculation we have found it necessary to consider the dimeric band at 28 000 cm−1 to be a Laporte forbidden type under a strong anisotropic ligand field.

Dimerization of p-substituted benzoic acids

Infrared spectroscopic studies have been carried out to determine the type and extent of hydrogen bond formation occurring in dilute solutions of benzoic, p-toluic, p-chlorobenzoic, p-iodobenzoic and p-fluorobenzoic acids in CCl 4 solution. Association constants were calculated separately from absorbance-concentration data using (a) the free—OH band, (b) the carbonyl dimer band, (c) the carbonyl monomer band, and (d) data from both carbonyl monomer and dimer bands. Results of the different methods of calculation did not differ significantly. At concentrations below 10 −3 M, the primary process is self-association to form cyclic dimers. The individual association constants of the various acids did not differ significantly. For the process 2 monomer ⇌ dimer, the average equilibrium constant is 5.89 × 10 3 M −1 at 25°, and 2.33 × 10 3 M −1 at 45°. The enthalpy of dimerization is −9.0 kcal/mole of dimer.

Hydrogen Bonding of Hydrazoic Acid in Solid Nitrogen

The infrared spectrum of hydrogen bonded HN3 dimers in solid nitrogen has been determined. A dimer band at 387 cm−1, assigned to the torsional distortion of the hydrogen bond, indicates the dimer has an open, not a cyclic structure. The hydrogen bond bending force constant is 0.09 mdyn/Å. The hydrogen bond frequency shift in the N–H stretching mode is 150 cm−1, which, by comparison to similar systems, suggests a hydrogen bond energy of about 2 kcal/mole. The infrared spectrum of monomeric HN3 casts doubt upon the earlier gas-phase assignment of ν6. According to the matrix spectrum, the band center is more likely to be near 588 cm−1.

Microwave Rotation Spectra of Hydrogen-Bonded Molecules

The pure rotation spectra have been observed for the hydrogen-bonded bimolecules CF3COOH–HCOOH, CF3COOH–CH3COOH, and CF3COOH–CH2FCOOH. For CF3COOH–HCOOH, the O···O distance RH was found to be 2.69±0.02 Å. The O···O distance becomes 0.011 Å longer when D is substituted for H in the hydrogen bond, i.e., RD—RH=0.011 Å. The heat of formation was found to be —ΔH=15.8 kcal/mole. Similar values, RH=2.67 Å and RD—RH=0.012 Å, were obtained for CF3COOH–CH3COOH, but in this molecule the spectrum of the singly deuterated species shows that the D atom tunnels between the two partners in the bimolecule at a rate faster than the rotational frequency. For a symmetric double minimum potential function the barrier to tunneling is found to be less than 5000 cm—1. The rapid tunneling also implies that only a sixfold barrier to the internal rotation of the CF3 and CH3 groups can exist, and therefore the nearly free rotation of these groups in the bimolecules and in dimers can be expected. This free rotation would explain the failure to detect the low K lines in the pure rotation spectra. The rapid tunneling of the D (and H) atoms in the hydrogen bond also implies an inversion doubling which would contribute to the width of the v(OH) bands in the carboxylic acid dimer infrared spectra. The difference RD—RH predicts a shortening of the O···O distance of 0.073 Å when the O–H vibration is excited, which provides a mechanism to couple the low hydrogen-bond stretching frequency and the v(OH) frequency to produce the broad dimer bands.

Delayed fluorescence from naphthalene solutions

Abstract The delayed emission spectra from solutions of naphthalene at low temperature show the presence of the dimer band which was previously observed by Doller and Forster in the normal fluorescence spectra of concentrated solutions. The relative intensities of the monomer and dimer bands in both the normal and delayed emission spectra of naphthalene solutions at low temperature are qualitatively similar to those observed with pyrene solutions at room temperature. They have been interpreted by a similar mechanism involving triplet-triplet quenching. Approximate values for the triplet formation efficiency of naphthalene have been derived.

Delayed Fluorescence Spectrum of Pyrene Solutions at Low Temperatures

Parker and Hatchard1 have convincingly demonstrated that delayed fluorescence exhibited by dissolved aromatic hydrocarbons A originates in the interaction of two triplet states, and that at low light intensities the overall process 1, followed by 2, is controlled by the first-order process 3 which is almost entirely responsible for triplet state decay under these conditions. To account for the presence of the dimer band in the delayed fluorescence spectrum of pyrene2, these authors3 suggest that process 1 involves Colpa's doubly-excited state 1A2 ** and the excimer 1A2* as intermediates, that is: where the energy-dependent process 1c competes with excimer fluorescence, process (4). This mechanism accounts for the observation3 that the ratio of intensities ID/IM of dimer to monomer bands in the delayed spectrum approaches a limiting non-zero value at zero concentration of A at room temperature; moreover, it requires a negative temperature coefficient of ID/IM which is indeed observed above 0° C as shown in Fig. 1.

Hydrogen-bond energies of acetic and n-butyric acids in the vapour phase by infra-red spectroscopy

Infra-red intensities at different temperatures were related to vapour-phase equilibrium conditions between monomers and dimers of acetic and of n-butyric acids. The van't Hoff equation was used to calculate the heats of dimerization which gave hydrogen-bond energies. The intensities of monomer and dimer bands in the carbonyl region (with a CaF 2 prism) and in the hydroxyl region (with a LiF prism) provided two independent measurements for each compound. The average values found for the hydrogen-bond energies were 8.5 ± 0.4 and 8.6 ± 0.4 kcal mole , respectively

The infra-red intensities of the carbonyl band in halogenated derivatives of acetic acid

The intrinsic intensity of the C=0 infra-red band has been measured for various halogenated acetic acid derivatives dissolved in carbon tetrachloride. For reference purposes, formic and acetic acids were studied. D-Carboxydichloroacetic acid was also measured. For measurement of the intensity, Wilson-Wells extrapolation was used and a correction of the “wings” was made by Ramsay's method. Even in dilute solutions of carboxylic acids the C=O band is double. The more intense maximum in our solutions corresponds to the dimer and lies at lower frequency than that corresponding to the monomer. It was not possible to eliminate the monomer although in some cases its absorption was in the range of only 1 per cent of the dimer. Since the effect of hydrogen bonding on the intensity of the carbonyl band in this case is expected to be small, the total intensity was measured for both bands. On the other hand, the overlap of the monomer band was negligible at the concentrations used and it was possible to measure the area of the dimer band without any considerable error. The monomer and dimer concentrations required for calculating the intensities were determined, approximately, on the basis of the optical densities at the maximal absorptions. With these data, the maximal molecular extinction coefficients and the intensities of the dimer bands were calculated. The intensity values were related to the chemical reactivity by using the Taft polar parameters.

The overlapping hydrogen fluoride monomer-dimer spectra

It is shown that the data of Kuipers on the absorption of the HF monomer lines can be interpreted if the line contour is expressed in a modified Lorentz form α=α 0a 2p 2[(v−v 0) 1.8+a 2p 2] −1 The apparent absorbance at the line centers has been measured under such circumstances that the temperature variation of α 0 a 2 can be obtained. It is shown that the line breadth parameter, a, has the temperature variation expected if resonant dipole intermolecular forces are for the most part responsible for the line breadth. The absorption computed from the modified Lorentz expression between the monomer lines is sometimes considerably less than the absorption that is measured. The difference is attributed to HF dimer. There result three dimer bands. The strongest is broad and featureless with a peak near 3857 cm −1, the two other bands have PQR structures with Q branch peaks at 3895 and 3965 cm −1. The temperature dependence of the dimer absorption indicates a heat of decomposition of about 6 kcal/mole.

Molecular Structure and Vibrational Spectra of Alkali Halide Dimers

The molecular structure and infrared-active vibrational frequencies of alkali-halide dimer molecules have been calculated, assuming an ionic model similar to that used for alkali halide diatomic molecules and crystals. The results of the calculation provide further evidence for the presence of large concentrations of lithium halide dimers. The previous identification of infrared bands with monomeric alkali halides is verified and several alternatives are then suggested for the absence of dimer bands. Some inconsistencies in the dimerization energies obtained from molecular beam studies also become apparent by this treatment.

Infra-red spectroscopic studies of hydrogen bonding in methanol, ethanol, and t-butanol

The infra-red spectra of methanol, ethanol and t-butanol have been investigated in the 3 μ, region (fundamental frequency of the OH stretching vibration). The alcohols were studied in CCl 4 solution over a concentration range 0.005–1.0 M and a temperature range − 15° to +60°C. Quantitative measurements of the intensity of the sharp OH band near 3630 cm −1 yielded values for the equilibrium constants and the following values for the enthalpies of dimer formation: methanol, 9.2 ± 2.5; ethanol, 7.2 ± 1.6; t-butanol, 4.8 ± 1.1 kcal/mole of dimer. Integrated intensities are given for the dimer band near 3500 cm −1 and the polymer band near 3350 cm −1. The high values of ΔH, together with the frequency shift and intensity data, suggest that the alcohol dimer is cyclic with two non-linear hydrogen bonds.