Calibration of Circular Dichrometers in the Visible Region

Abstract

The cesium salt of R, R-(-)-trans-l, 2-cyclohexane-diaminetetraacetatocobaltate(III), Δ-(+)₅₄₆-Cs[Co(R, R(-)-CDTA)], Δ-Cs[Co(R, R(-)CDTA)]), provides a compound which can be used for calibration of circular dichrometers in the visible region. Δ-Cs[Co(R, R(-)CDTA)] has three major circular dichroism (CD) maxima at 593 nm, 527 nm, and 240 nm. The molecular ellipticities, [θ], at 593 nm, 527 nm, and 240 nm are -4490 ± 40, 5720 ± 40, and -47, 900 ± 300 deg cm² dmol^?1, respectively. The CD maxima in terms of Δε at 593, 527, and 240 nm are -1.36 ± 0.01, 1.73 ± 0.01, and -14.5 ± 0.1 l cm^?1 mol^?1, respectively. Optical rotatory dispersion (ORD) and ultraviolet-visible absorption data has also been obtained for this compound.     

Two-Point Calibration of Circular Dichrometer with d-10-Camphorsulfonic Acid

Abstract

The circular dichroism (CD) of d-10-camphorsulfonic acid (CSA) in terms of ?_L - ?_R is 2.36 and -4.72 cm² mmol^?1 at 290.5 and 192.5 nm, respectively. The corresponding molar ellipticities, [?], are 7,800 and -15,600 deg cm² dmol^?1. A ratio of -2.00 for the negative and positive bands provides a simple two-point calibration. If a standardized spectropolarimeter is available, the ratio of [?]_290.5/[M]₃₀₆ = 1.75 to 1.76 or [?]_290.5/([M]₃₀₆?[M]₂₇₀) = 0.77 at the extrema is recommended for CD calibration at the 290 nm region, which is unaffected by the presence of optically inactive impurities such as water. Alternately, CSA has a molar absorption coefficient of 34.5 cm² mmol^?1 at 285 nm, which can be used for concentration determination. This leads to (?_L??_R)_290.5/?₂₈₅ = 0.068 or [?]_290.5/?₂₈₅ = 226. However, CSA must be purified to remove any impurities that are optically active or absorb light or both in the UV region.     

Spectrophotometric Determination of Diphenadione Via its Metal Complexes

Abstract

Spectrophotometric procedure is described for the quantitative determination of diphenadione [2-(diphenylacetyl)-1,3-indandione], based on direct spectrophotometric measurements of the absorbances of its iron (III), iron (II) and cobalt (II), metal complexes at 488 nm, 505 nm and (334 nm, 372 nm), respectively. The drug reacts with metals in the ratio of 3:1 and 2:1 for iron (III) and for both iron (II) and cobalt (II) respectively. The obtained complexes have apparent molar absorptivities of 1.48 × 10³ 1 mol^?1 cm^?1, 0.714 × 10³ 1 mol^?1cm^?1 and (1.70 × 10³ 1 mol^?1cm^?1, 1.93 × 10³ 1 mol^?1cm^?1) for iron (III), iron (II) and cobalt (II) complexes, respectively. The procedure is suggested for the determination of 51–400 μg.ml^?1 diphenadione via the iron (II) complex and 35–170 μg.ml^?1 diphenadione via both cobalt (II) and iron (III) complexes. The suggested procedure has accuracies of 99.79 ± 0.67%, 99.64 ± 0.37% and (100.09 ± 0.53%, 99.99 ± 0.42%) for the metal complexes of iron (III), iron (II) and cobalt (II), respectively.     

Laser flash photolysis of aqueous acetaminophen solutions

The N-acetyl-4-aminophenoxyl radical, a supposed intermediate of the enzymatic oxidation of acetaminophen in living organisms, was prepared and studied by means of nanosecond laser flash photolysis. A number of important spectral-kinetic parameters of this species were determined, namely, the absorption coefficient at 440 nm ((4.2±0.2)×10³ l mol^?1cm^?1), the quantum yield of acetaminophen photoionization at 266 nm (φ= 0.03), and the rate constants for recombination (2k= (2.4±0.3))×10⁹ l mol^?1s^?1) and the reaction with the superoxide radical (k= (9±2))×10⁹ l mol^?1s^?1).     

The synthesis of poly(phenylacetylene)s with bulky chiral silyl groups and the thermal stability of their helical conformation

The polymerization of (−)‐p‐[(tert‐butylmethylphenyl)silyl]phenylacetylene (t‐BuMePhSi*PA) and (+)‐p‐[{methyl(α‐naphthyl)phenyl}silyl]phenylacetylene (MeNpPhSi*PA) with the [(nbd)RhCl]₂ Et₃N catalyst yielded polymers with very high molecular weights over 2 × 10⁶ in high yields. The optical rotations of the formed poly(t‐BuMePhSi*PA) and poly(MeNpPhSi*PA) were as high as −356 and −150° (c = 0.11 g/dL in CHCl₃), respectively. The circular dichroism (CD) spectrum of poly(t‐BuMePhSi*PA) in CHCl₃ exhibited very large molar ellipticities ([θ]) in the UV region: [θ]_max = 9.2 × 10⁴ ° · cm² · dmol⁻¹ at 330 nm and −8.0 × 10⁴ ° · cm² · dmol⁻¹ at 370 nm. The [θ]_max values of poly(MeNpPhSi*PA) were also fairly large: [θ]_max = 7.1 × 10⁴ ° · cm² · dmol⁻¹ at 330 nm and −5.3 × 10⁴ ° · cm² · dmol⁻¹ at 370 nm. The optical rotations of poly(t‐BuMePhSi*PA) and poly(MeNpPhSi*PA), measured in tetrahydrofuran, chloroform, and toluene solutions, were hardly dependent on temperature in the range 22–65 °C. The CD effects of these polymers hardly changed in the temperature range 28–80 °C, either. These results indicate that the helical structures of these polymers are thermally appreciably stable. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 71–77, 2001     

A consistent model for the thermal decomposition of NCN3 and the singlet– triplet relaxation of NCN

The thermal decomposition of cyanogen azide (NCN₃) and the subsequent collision‐induced intersystem crossing (CIISC) process of cyanonitrene (NCN) have been investigated by monitoring excited electronic state ¹NCN and ground state ³NCN radicals. NCN was generated by the pyrolysis of NCN₃ behind shock waves and by the photolysis of NCN₃ at room temperature. Falloff rate constants of the thermal unimolecular decomposition of NCN₃ in argon have been extracted from ¹NCN concentration–time profiles in the temperature range 617 K <T< 927 K and at two different total densities: k(ρ ≈ 3 × 10^?6 mol/cm³)/s^?1=4.9 × 10⁹ × exp (?71±14 kJ mol^?1/RT) (± 30%); k(ρ ≈ 6 × 10^?6 mol/cm³)/s^?1=7.5 × 10⁹ × exp (‐71±14 kJ mol^?1/RT) (± 30%). In addition, high‐temperature ¹NCN absorption cross sections have been determined in the temperature range 618 K <T< 1231 K and can be expressed by σ /(cm²/mol)= 1.0 × 10⁸ ?6.3 × 10⁴ K^?1 × T (± 50%). Rate constants for the CIISC process have been measured by monitoring ³NCN in the temperature range 701 K <T< 1256 K resulting in k_CIISC (ρ ≈ 1.8 ×10^?6 mol/cm³)/ s^?1=2.6 × 10⁶× exp (‐36±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 3.5×10^?6 mol/cm³)/ s^?1 = 2.0 × 10⁶ × exp (?31±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 7.0×10^?6 mol/cm³)/ s^?1=1.4 × 10⁶ × exp (?25±10 kJ mol^?1/RT) (± 20%). These values are in good agreement with CIISC rate constants extracted from corresponding ¹NCN measurements. The observed nonlinear pressure dependences reveal a pressure saturation effect of the CIISC process. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 30–40, 2013     

Spectrophotometric study of complexes of mercury(II) with mono- and dithiosemicarbazones

The formation of complexes at pH 4.7 of the Hg(II) with five monothiosemicarbazone and two dithiosemicarbazone has been studied. The mercury(II) reacts with monothiosemicarbazones of salicylaldehyde (λ_max = 363 nm, E = 1.69 × 10⁴liters · mol^?1cm^?1), pi-colinadehyde (λ_max = 363 nm, E = 2.38 × 10⁴liters · mol^?1cm^?1), 6-methyl-picolinaldehyde (λ_max = 363 nm, E = 2.28 × 10⁴liters · mol^?1cm^?1), di-2-pyridylketone (λ_max = 380 nm, E = 2.08 × 10⁴liters · mol^?1cm^?1), and o-naphthoquinone (λ_max = 540 nm, E = 1.03 × 10⁴liters · mol^?1cm^?1) and with dithiosemicarbazones of 1,4-dihydroxyphthalimide (λ_max = 430 nm, E = 2.56 × 10⁴liters · mol^?1cm^?1) and dipyridylglyoxal (λ_max = 363 nm, E = 2.37 × 10⁴liters · mol^?1cm^?1). A critical comparison of the stoichiometry and apparent stability constant of complexes with mono- and dithiosemicarbazones is given.     

DI-2-Pyridyl ketone thiosemicarbazone as an analytical reagent

The synthesis, characteristics and analytical reactions of di-2-pyridyl ketone thiosemicarbazone are described. This compound reacts with iron(II) (λ_max=410mm, ε = 9.3 · 10³ 1 mol^?1 cm^?1), nickel(II) (λ_max =395 mm ε =19.6·10³ 10 mol ^?1 cm ^-1), cobalt(II) (λ_max = 415 nm. ε = 1.0 · 10⁴ mol^?1 cm^?1 ) and copper(I) (λmax =395mm ε = 11.3 · 10³ mol^?1 cm^?1) A critical comparison of di-2-pyridyl ketone, picolinaldehyde and bipyridylglyoxal thiosemicarbazones as analytical reagents is given.     

Spectrophotometric determination of vanadium in petroleum crudes and derivatives

The spectrophotometric study of the complexation reaction between 5,5′methylenedisalicylhydroxamic acid and V(V) shows that two complexes are formed, the 1:1 (? = 5100 liters mol^?1 cm^?1 at 490 nm, log K_est = 5.8 ± 0.1) and the 1:2 (L:V) (? = 6250 liters mol^?1 cm^?1 at 600 nm, log K_est = 6.1 ± 0.1). A spectrophotometric method is developed for the determination of vanadium (2–9 ppm) at 2 N HCl and 495 nm, which allows its determination in petroleum crude oils with a series of advantages over the ASTM D-1548-63 method.     

铝(Ⅲ)与脱铁伴清蛋白结合的紫外差光谱研究

在 pH7.4、 0.1mol· L~(－1)N-2-羟乙基哌嗪- N′-2-乙磺酸（ Hepes）及室温条件下,使用紫外吸收差光谱进行了铝(Ⅲ)对脱铁伴清蛋白的滴定。结果表明铝(Ⅲ)与脱铁伴清蛋白结合后其紫外差光谱在 238nm和 291nm处出现吸收峰。在 238nm处铝(Ⅲ)-脱铁伴清蛋白配合物的摩尔吸光系数是 (1.52± 0.04)× 10~4cm~(－1)· mol~(－1)· L。铝(Ⅲ)可占据脱铁伴清蛋白的两个金属离子结合部位,条件稳定常数是 lgK_N=11.21± 0.12,lgKC=9.53± 0.24。 N-端单铁伴清蛋白的紫外差光谱滴定表明,铝 ?优先占据脱铁伴清蛋白的 N端结合部位。     

2,2′-Dihydroxybenzophenone thiosemicarbazone as a spectrophotometric reagent for the determination of copper,cobalt, nickel,and iron trace amounts in mixtures without previous separations

2,2′-Dihydroxybenzophenone thiosemicarbazone forms complexes with Cu(II) (λ_max = 385 nm, ? = 8.60 × 10³ liter · mol^?1 · cm^?1); Ni(II) (λ_max = 380 nm, ? = 15.4 × 10³ liter · mol^?1 · cm^?1); Co(II) (λ_max = 380 nm, ? = 12.3 × 10³ liter · mol^? · cm^?1); and Fe(III) (λ_max = 365 nm, ? = 7.9 × 10³ liter · mol^?1 · cm^?1) and have been applied to the analysis of these metal ions in binary, ternary, and quaternary mixtures. The determination procedures are based exclusively on the different pH values of the formation complexes, hence the extraction step is not necessary.     

A pulse radiolysis study of the reactions of the hydrated electron and hydroxyl radical with the oxalate ion in neutral aqueous solution

The rate constants of the reactions of e _aq ^? and the OH^· radical with the oxalate ion in a neutral aqueous solution were measured by means of the pulse radiolysis technique. They were found to be (3.5 ± 0.5) × 10⁷ and (1.5 ± 0.2) × 10⁷ l mol^?1 s^?1, respectively. The radical anion ^?OOC-C^·OO^2? is characterized by an optical absorption band that has a maximum at 270 nm and a molar absorption coefficient of (2400 ± 200) l mol^?1 cm^?1. The radical anion ^·OOC-COO^?, the product of the reaction with the OH^· radical, exhibits absorption that has no maximum and increases in intensity with a decrease in the wavelength extending to the UV region (?₂₂₀ = 1800 l mol^?1 cm^?1). The mechanism of radiation-chemical transformations in aqueous oxalate solutions is discussed.     

Volumes of activation for the reactions of Pentacyanocobaltate(III) Complexes in aqueous solution

The volumes of activation in cm³ mol^?1 for the aquation of Co(CN)₅X^3? were determined at 40°C and μ = 1 M (NaClO₄) to be + 7.8 ± 0.5 for X = Cl^?, + 7.6 ± 0.6 for X = Br^?, + 14.0 ± 0.7 for X = I^?, and + 16.8 ± 0.5 for X = N₃^? (0.1 M HClO₄), respectively. The volumes of activation for the aquation of Co(CN)₅Cl^3? at μ = 0.1 M are + 10.0 ± 0.6 cm³ mol^?1 and ± 9.1 ± 0.3 cm³ mol^?1 at 40°C and 25°C, respectively. The corresponding values for the anation of Co(CN)₅OH₂^2? (at 40°C) and μ = 1 M by Br^?, I^?, and NCS^? are +8.4 ± 1.0, +9.4 ± 1.6, and +8.2 ± 0.9 cm³ mol^?1, respectively. These data are discussed in terms of a dissociative (D) mechanism.     

PRIMARY INTERMEDIATES IN THE PULSED IRRADIATION OF RETINOIDS

Abstract Laser flash photolysis and pulse radiolysis have led to the characterisation of several shortlived intermediates formed after irradiation of retinoic acid and retinyl acetate in hexane or methanol. For retinoic acid, the triplet state, wavelength maximum 440 nm, extinction coefficient 7.3 × 10⁴ dm³ mol^?1 cm^?1, decay constant 6.2 × 10⁵ s^?1, is formed with a quantum yield of 0.012 for 347 nm excitation. The radical cation, absorption maximum 590 nm, extinction coefficient ～7 × 10⁴ dm³mol^?1 cm^?1, is formed in a biphotonic process. The radical anion, absorption maximum 510nm in hexane, 480 nm in methanol where its extinction coefficient is 1.2 × 10⁵ dm³mol^?1 cm^?1, appears to decay partially in methanol into another longer-lived neutral radical, wavelength maximum 420 nm, by loss of OH^?. For retinyl acetate, the triplet state, absorption maximum 395 nm, extinction coefficient 7.9 × 10⁴dm³mol^?1 cm^?1, decay constant 1.2 × 10⁶s^?1 is formed with a quantum yield of 0.025 for 347 nm excitation. Monophotonic photoelimination of OCOCH₃? in methanol produces the retinylic carbenium ion, wavelength maximum 590 nm, whose decay is enhanced by ammonia, k ～ 2 × 10⁶ dm³ mol^?1 s^?1 and retarded by water. The radical cation also has a wavelength maximum at 590 nm, its extinction coefficient being ～ 1.0 × 10⁵ dm³mol¹ cm^?1. The long-lived transient absorption with maximum at 385 nm, extinction coefficient 1.0 × 10⁵ dm³mol^?1 cm^?1, obtained from the reaction of the solvated electron with retinyl acetate in methanol may be due to either the radical anion itself or more likely the radical resulting from elimination of OCOCH₃? from this anion. These results suggest that skin photosensitivity caused by retinyl acetate might be greater than that due to retinoic acid.     

THE pKa OF DIPROTONATED SEMIMETHYLENE BLUE, IN 5% ETHANOL AND 50% ACETONITRILE AQUEOUS SOLUTIONS

Abstract— Semimethylene blue was generated by reductive quenching of triplet methylene blue, ³MBH²⁺, with diphenylamine at pH 0.62–3.4. A Q-switched ruby laser flash-photolysis-kinetic spectro-photometric apparatus was used to characterize the absorption spectrum of semimethylene blue from 350 to 900 nm and a number of physical constants at 25°C with μ= 0.4 M and Cl^? as the anion. The specific rate of quenching of ³MBH²⁺ by DPA is 2.8 × 10⁹M^?1 s^?1 in 5% EtOH-95% water and 1.2×10⁹M^?1 s^?1 in 50 v/v% aq. CH₃CN. Corresponding efficiencies of net electron transfer are, respectively, 0.15 and 0.62. Spectral characteristics in 5% EtOH are, for MBH²₂±, λ_max= 375 nm, ε₃₇₅= 9000 M^?1 cm^?1; λ_max= 880 nm, ε₈₈₀= 12700 M^?1 cm^?1; for MBH±, λ_max= 410 nm, ε₄₁₀= 9800 M^?1 cm^?1, λ_max= 880 nm, ε₈₈₀= 33000 M^?1 cm^?1; for MBH± in 50 v/v% AN, λ_max= 400 nm, ε₄₀₀= 11000 M^?1 cm^?1 and λ_max= 880 nm,ε₈₈₀= 39000 M^?1 cm^?1. The pK_a of MBH²₂ε calculated from the pH dependence of the absorption spectrum is 1.86 × 0.04 in 5% EtOH and 1.15 in 50 v/v% AN. Rate constants, k_decay, for reaction DPAH±⁺ with MBH²₂ε and MBH± in 5% EtOH are, respectively, 3.9 × 10⁹ and 9.5 × 10⁹M^?1 s^?1. The value of pK_a of MBH²₂ε calculated from the dependence of k_decay on pH is 1.75 in 5% EtOH.     

Calcichrome: a re-examination of its structure and chemical properties by solid- and liquid-state NMR,infrared spectroscopy,and selective chemical degradation

Nuclear magnetic resonance and infrared spectroscopies were used to unravel the controversies regarding the structures of calcichrome and calcion. Together with the identification of the products from selective chemical cleavage reactions, these data indicate that structures of both compounds are equivalent with a molecular formula of C₂₀H₁₄N₂O₁₅S₄·3H₂O (2,8,8′-trihydroxy-1,1′-azonaphthelene-3,6,3′,6′-tetrasulfonic acid). The compound has two titratable phenolic protons in aqueous solution with pK_a values of 7.19 ± 0.05 and 11.63 ± 0.05 at 25 ° C. As a ligand, the compound forms a colored complex with calcium(II) at a 1:1 stoichiometric ratio (pH 12.3) with a formation constant of 8.0 × 10³ at 25 ° C. The free form of the ligand at pH 12.3 has a molar maximum molar absorptivity of 1.44 × 10⁴ l mol^?1 cm^?1 at 599 nm, whereas the complexed form has a maximum molar absorptivity of 1.37 × 10⁴ l mol^? cm^?1 at 522 nm.     

Complexation equilibria and spectrophotometric determination of zinc (II) with 2-(4′-methyl-2′-thiazolylazo)-4,6-dimethylphenol

2-(4′-methyl-2′-thiazolylazo)-4,6-dimethylphenol has been synthesized and its acid—base behaviour (pK_a1=0.03 ± 0.01, pK_a2=9.70±0.09) and complexation equilibria with zinc (logβ₁₀₁=6.70±0.04, logβ₁₀₂ = 13.70±0.02) studied in a 40% (v / v) ethanol—water medium at I=0.25 M NaClO₄. A spectrophotometric method for the determination of 0.2–1.5 ppm of zinc has been developed (ε=1.83 × 10⁴ 1. mol⁻¹ cm⁻¹ at 590 nm) and applied to its determination in lubricating oils.     

Micro-determination of gold using N-cyanoacylacetaldehyde hydrazone

A reliable and rapid procedure for the flotation and micro-determination of Au(III) using N-cyanoacylacetaldehyde hydrazone (CyAH) is proposed. CyAH forms a blue 1:1 complex (K_f=4.1×10⁵ mol^?1l^?1) with Au(III) at pH 3–7. The maximum absorbance is obtained after 7 min; instantaneously by adding 3.3×10^?3 mol/l H₃PO₄ or by heating to 55°C. Beer's law is obeyed for 1–30 ppm of Au(III) with a molar absorptivity of 0.3×10⁴ l mol^?1 cm^?1 at 550 nm.     

Sensitive spectrophotometric determination of La(III) with 1-(2-pyridylazo)-2-naphthol

A simple and sensitive method for spectrophotometric determination of lanthanum has been developed. At pH 9.6, in presence of 50% ethanol, lanthanum reacts with 1-(-2-pyridylazo)-2-naphthol (PAN) to form a red complex which has two absorption maxima, at 545 and 510 nm. The molar absorptivity at 545 nm is 0.55 × 10⁴ liters · mol^?1 cm^?1. On the other hand, lanthanum reacts with PAN in pure ethanol to form a red complex at 530 nm, with high molar absorptivity (8 × 10⁴ liters · mol^?1 cm^?1).     

1,3-Cyclopentanedione bis(4-methylthiosemicarbazone) monohydrochloride as a spectrophotometric reagent for the determination of lodate in acetic and perchloric acid media

1,3-Cyclopentanedione bis(4-methylthiosemicarbazone) monohydrochloride produces colored solutions with iodate ions in acid medium. The yellow color obtained has been used to proposed Spectrophotometric methods for determination of IO₃^? in the concentration range 1.0–11.0 ppm in acetic acid medium (molar absorptivity 1.08 × 10⁴ liters mol^?1 cm^?1 at a wavelength of 415 nm) and 0.5–8.0 ppm in perchloric acid medium (molar absorptivity 2.05 × 10⁴ liters mol^?1 cm^?1 at a wavelength of 400 nm).