The Effects of Substituents and Solvents on the Ground‐State π‐Electronic Structure and Electronic Absorption Spectra of a Series of Model Merocyanine Dyes and Their Theoretical Interpretation

Two series of new merocyanine dyes have been synthesised and the dependence of their electronic structure on substituents and solvents has been studied by NMR spectroscopy, by using both the NMR ¹³C chemical shifts between adjacent C atoms in the polymethine chain and the ³J(H,H) coupling constants for trans‐vicinal protons. The widely used valence bond (VB) model based on two contributing structures cannot account theoretically for the observed alternating π‐electron density in the polymethine chain. In addition, the prediction of zero‐π‐bond order alternation (or zero‐bond length alternation) by this model is also incorrect. However, the results are consistent with the predictions of a qualitative VB model which considers the resonance of a positive charge throughout the whole polymethine chain. Based on this model and the Franck‐Condon principle the effect of substituents and solvents on the fine structure of the electronic spectra of these dyes can be explained as vibronic transitions from the vibrational state v=0 to v′, where v is the vibrational quantum number of the totally symmetric C?C valence vibration of the polymethine chain in the electronic ground state and v′ is that in the electronic excited state. In contrast, neither the effects of substituents or solvents on the electronic structure of merocyanines and their electronic spectra can be accounted for by the simple two state VB model.     

Recovery of neptunium from highly radioactive waste solutions of PUREX origin using CMPO

The partitioning and recovery of²³⁷Np from three types of simulated high level waste solutions originating from PUREX processing of spent nuclear fuels such as sulfate bearing high level waste (SB-HLW), HLW from a pressurised heavy water reactor (PHWR-HLW) and from a fast breeder reactor (FBR-HLW) have been carried out using a mixture of 0.2M CMPO and 1.2M TBP in dodecane. Quantitative extraction of neptunium was possible by either oxidizing it to the hexavalent state keeping K₂Cr₂O₇ at 0.01M concentration or by reducing it to tetravalent state keeping Fe²⁺ at 0.02M concentration. Stripping of neptunium was carried out using different reagents, such as dilute nitric acid, oxalic acid and sodium carbonate. Almost quantitative recovery of neptunium has been achieved during these studies.     

The solvent extraction of some thallium(I) chelates

Fourteen different chelating reagents have been investigated, as possible extradants for radioiabelled 10^-6M thallium(I) from aqueous solutions into chloroform. The data have beun analyzed theoretically to identify the predominant species involved and to estimate association and distribution constanta.     

Synthesis,stability in solutions,and spectral and thermal properties of alkyl-substituted 3,3′-bis(dipyrromethene) hydrobromides

3,3′-Bis(dipyrromethene) dihydrobromides (H₂L · 2HBr) with various types of alkylation have been synthesized. On the basis of IR, ¹H NMR, and electronic absorption spectra, spectrophotometric titration, and thermogravimetry, conclusions have been drawn about the influence of structural factors on the optical and thermal properties and salt stability in solutions. An increase in the degree of alkylation causes a significant high-frequency shift of the N-H stretching vibration band in the IR spectra, an upfield shift of the ¹H NMR signals of NH protons, a decrease in the auxochromic effects of protons on the aromatic system of the chromophore, and an increase in the salt stability in solutions in the presence of nucleophilic reagents and in the thermal stability in air and argon.     

Deeply colored anionic polymethine dyes derived from bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9 H-fluorene-2,7-disulfonate

Anionic symmetric polymethine dyes have been synthesized based on bis(2,2,3,3,4,4,5,5-octafluoropentyl) 9H-fluorene-2,7-disulfonate, which exhibit intensive absorption in the near IR region of the spectrum: pentamethine with an open polymethine chain (⋉_max = 790 nm) and nonamethine with six- and five-membered saturated rings at δ-positions of the chain (@#@ ⋉_max = 1044 and 1086 nm, respectively). To make comparisons, anionic dyes with analogous structure of the polymethine chain, viz., 1,3-dimethylbarbituric and 1,3-diethylthiobarbituric acid derivatives, have been also synthesized. Quantum chemical analysis of the electron structure of the dyes has been performed. Their solvatochromism in polar solvents depends weakly on electrophilicity and nucleophilicity of the medium and is primarily determined by universal interactions. This is the reason that they, in contrast to cationic dyes, retain a high selectivity of absorption (sharp absorption bands) and universal contour of electronic bands in strong polar solvents even with the long polymethine chain. Special solvatochromic effects of the anionic dyes in weakly polar media have been revealed and interpreted. The role of a counterion in these effects has been analyzed.     

Length of Soliton Wave in the Excited State in the Cations of Symmetrical Pyridocyanines and Their Carbo and Hetero Analogs

Quantum-chemical calculations in the AM1 approximation were undertaken for the optimized geometry of the cations of polymethine dyes [R⁺—(CH=CH) _n —CH=R], where R represents phenyl substituents or pyridinium, pyrylium, and thiopyrylium groups and n = 1-6, in the ground state and for the electron density distribution in the Frank – Condon excited state. It was found that excitation of the molecule by a light quantum leads to a decrease in the length of the charge wave (soliton). It was shown that the length of the soliton depends on the electron-donating character of the terminal groups R and on the length of the conjugated chain, while shortening of the soliton in the thiopyrylocyanines leads to disruption of its symmetry.     

Development and Optimization of Twenty-Four Hour Manual Methods for the Collection and Colorimetric Analysis of Atmospheric NO2

Abstract

Manual twenty-four hour colorimetric procedures for the determination of atmospheric NO₂ are described. The methods are based on collecting NO₂ by bubbling ambient air for twenty-four hours through reagents that form stable nitrite solutions. The reagents described have a 93 % collection efficiency over the range of 20 to 750 μg/m³ NO₂ with no apparent interferences. The inadequacies' of the former reference or alkaline method¹ are also described.     

Effects of supercharging reagents on noncovalent complex structure in electrospray ionization from aqueous solutions

The effects of two supercharging reagents, m-nitrobenzyl alcohol (m-NBA) and sulfolane, on the charge-state distributions and conformations of myoglobin ions formed by electrospray ionization were investigated. Addition of 0.4% m-NBA to aqueous ammonium acetate solutions of myoglobin results in an increase in the maximum charge state from 9+ to 19+, and an increase in the average charge state from 7.9+ to 11.7+, compared with solutions without m-NBA. The extent of supercharging with sulfolane on a per mole basis is lower than that with m-NBA, but comparable charging was obtained at higher concentration. Arrival time distributions obtained from traveling wave ion mobility spectrometry show that the higher charge state ions that are formed with these supercharging reagents are significantly more unfolded than lower charge state ions. Results from circular dichroism spectroscopy show that sulfolane can act as chemical denaturant, destabilizing myoglobin by ∼1.5 kcal/mol/M at 25 °C. Because these supercharging reagents have low vapor pressures, aqueous droplets are preferentially enriched in these reagents as evaporation occurs. Less evaporative cooling will occur after the droplets are substantially enriched in the low volatility supercharging reagent, and the droplet temperature should be higher compared with when these reagents are not present. Protein unfolding induced by chemical and/or thermal denaturation in the electrospray droplet appears to be the primary origin of the enhanced charging observed for noncovalent protein complexes formed from aqueous solutions that contain these supercharging reagents, although other factors almost certainly influence the extent of charging as well.     

Reaction of polymethine dyes with hydroperoxides and free radicals

The interaction kinetics of the cationic and anionic polymethine dyes with radicals has been studied. Azoinitiator AAPH, as well as tert-butyl hydroperoxide, and hydrogen peroxide were used as radical initiators in water and buffer solutions at 37 °C. It is shown that the dyes are active scavengers of peroxyl radicals. It is found that reactivity and behavior of dyes in relation to the peroxides are strongly dependent on the structure of lateral substituents in polymethine chains.     

The Fluorination of C−H Bonds: Developments and Perspectives

This Review summarizes advances in fluorination by C(sp²)?H and C(sp³)?H activation. Transition‐metal‐catalyzed approaches championed by palladium have allowed the installation of a fluorine substituent at C(sp²) and C(sp³) sites, exploiting the reactivity of high‐oxidation‐state transition‐metal fluoride complexes combined with the use of directing groups (some transient) to control site and stereoselectivity. The large majority of known methods employ electrophilic fluorination reagents, but methods combining a nucleophilic fluoride source with an oxidant have appeared. External ligands have proven to be effective for C(sp³)?H fluorination directed by weakly coordinating auxiliaries, thereby enabling control over reactivity. Methods relying on the formation of radical intermediates are complementary to transition‐metal‐catalyzed processes as they allow for undirected C(sp³)?H fluorination. To date, radical C?H fluorinations mainly employ electrophilic N?F fluorination reagents but a unique Mn^III‐catalyzed oxidative C?H fluorination using fluoride has been developed. Overall, the field of late‐stage nucleophilic C?H fluorination has progressed much more slowly, a state of play explaining why C?H ¹⁸F‐fluorination is still in its infancy.     

New reagents for increasing ESI multiple charging of proteins and protein complexes

The addition of m-nitrobenzyl alcohol (m-NBA) was shown previously (Lomeli et al., J. Am. Soc. Mass Spectrom. 2009, 20, 593–596) to enhance multiple charging of native proteins and noncovalent protein complexes in electrospray ionization (ESI) mass spectra. Additional new reagents have been found to “supercharge” proteins from nondenaturing solutions; several of these reagents are shown to be more effective than m-NBA for increasing positive charging. Using the myoglobin protein-protoporphyrin IX (heme) complex, the following reagents were shown to increase ESI charging: benzyl alcohol, m-nitroacetophenone, m-nitrobenzonitrile, o-NBA, m-NBA, p-NBA, m-nitrophenyl ethanol, sulfolane (tetramethylene sulfone), and m-(trifluoromethyl)-benzyl alcohol. Based on average charge state, sulfolane displayed a greater charge increase (61%) than m-NBA (21%) for myoglobin in aqueous solutions. The reagents that promote higher ESI charging appear to have low solution-phase basicities and relatively low gas-phase basicities, and are less volatile than water. Another feature of mass spectra from some of the active reagents is that adducts are present on higher charge states, suggesting that a mechanism by which proteins acquire additional charge involves direct interaction with the reagent, in addition to other factors such as surface tension and protein denaturation.     

Interaction of radium with freshwater sediments and their mineral components. I.

The radiotracer method has been used for investigation of the adsorption and desorption of traces of radium on ferric hydroxide and quartz under conditions similar to those prevailing in waste and surface waters. The effects of pH, liquid to solid ratio, ionic strength and presence of Ca²⁺ or SO ₄ ^2- ions have been studied. It has been concluded that at pH less than 7 and at concentration of suspended sediments (of common composition) less than 100 mg·1^–1 ferric hydroxide and quartz have negligible effect on the state and migration of radium in surface waters. Radium adsorbed on quartz can be easily desorbed with dilute solutions of hydrochloric acid or sodium chloride.     

A theoretical study on the ground and excited state behaviors of TTBC related carbocyanine dyes

The effects of functional groups on the benzimidazole rings, length of the conjugated chain and alkyl groups bonded to the nitrogen atoms on the ground and excited state behaviors of the 1,1′,3,3′-tetraethyl-5,5′,6,6′-tetrachlorobenzimidazolocarbocyanine (TTBC or JC-1) have been analyzed via quantum chemical methods. DFT and TDDFT with B3LYP/6-31G(d,p) level of theory were used for the ground and excited state calculations, respectively. It has been found that TTBC has a very rigid geometry; no significant effect of functional groups has been predicted either as donor or acceptor on its optimum structure. However, the length of alkyl groups changes the structure of the molecule. It is possible to increase λ_max of TTBC based carbocyanine dye with NH₂, butyl/propyl and increasing polymethine chain length.     

Synthesis,spectral properties,and solvatochromism of merocyanine dyes based on bis(2,2,3,3,4,4,5,5-octafluoropentyl)-4,5-dinitro-9H-fluorene-2,7-disulfonate

Di-, tetra-, and hexamethine merocyanines containing heterocyclic fragments with different electron-donor abilities have been synthesized on the basis of bis(2,2,3,3,4,4,5,5-octafluoropentyl)-4,5-dinitro-9H-fluorene-2,7-disulfonate. Their electronic absorption spectra in solvents with different polarities have been studied, and their electronic structure and electronic transitions have been analyzed by DFT and TDDFT quantum chemical calculations using B3LYP functional and 6-31G(d,p) basis set. The electronic structure of the synthesized merocyanines changes from neutral polyene to polymethine and dipolar polyene, depending on the electron-donor ability of the heterocyclic fragment, length of the polymethine chain, and solvent polarity. Therefore, these merocyanines display positive, negative, and reverse solvatochromism.     

Unstable reagents in flow analysis

Investigations on the analytical applications of unstable oxidizing and reducing agents in aqueous solutions in flow analysis are reviewed. The generation of these unstable reagents in flow eliminates the disadvantages of their application in batch, i.e., frequent standardization, difficulties with storage and time consumption. The advantages of flow analysis (speed, ease of operation and good precision) remain. Limits of determination of 10^?5?10^?6 mol l^?1 can be achieved in several cases with spectrophotometric or amperometric detection. Uranium(III) and silver(II) are especially promising reagents. Possibilities for future work are discussed.     

Photophysics of Silicon Phthalocyanines in Aqueous Media

Phthalocyanines have been used as photodynamic therapy (PDT) agents because of their uniquely favorable optical properties and high photostability. They have been shown to be highly successful for the treatment of cancer through efficient singlet‐oxygen (¹O₂) production. However, due to their hydrophobic properties, the considerations of solubility and cellular location have made understanding their photophysics in vitro and in vivo difficult. Indeed, many quantitative assessments of PDT reagents are undertaken in purely organic solvents, presenting challenges for interpreting observations during practical application in vivo. With steady‐state and time‐resolved laser spectroscopy, we show that for axial ligated silicon phthalocyanines in aqueous media, both the water:lipophile ratio and the pH have drastic effects on their photophysics, and ultimately dictate their functionality as PDT drugs. We suggest that considering the presented photophysics for PDT drugs in aqueous solutions leads to guidelines for a next generation of even more potent PDT agents.     

Association constants and enthalpies of formation of heteroassociates of anions of cresol red and thymol blue

The tendency of anions of sulfophthaleine dyes to heteroassociation was studied in aqueous solutions of phenol red, cresol red, thymol blue, and non-substituted phenol red. It was spectrophotometrically determined that single (HAn⁻) and doubly charged anions (An²⁻) of sulfophthaleines can form stable heteroassociates of the composition Ct⁺ · HAn⁻ and (Ct⁺)₂ · An²⁻ with cations (Ct⁺) of polymethine dyes, pinacyanol, and quinaldine red. The values of enthalpy formation of ions of dyes and heteroassociates were calculated semi-empirically and compared with experimentally determined values of the equilibrium association constants.     

The effects of substituents and solvents on the ground-state π-electronic structure and electronic absorption spectra of a series of model merocyanine dyes and their theoretical interpretation

Two series of new merocyanine dyes have been synthesised and the dependence of their electronic structure on substituents and solvents has been studied by NMR spectroscopy, by using both the NMR (13)C chemical shifts between adjacent C atoms in the polymethine chain and the (3)J(H,H) coupling constants for trans-vicinal protons. The widely used valence bond (VB) model based on two contributing structures cannot account theoretically for the observed alternating π-electron density in the polymethine chain. In addition, the prediction of zero-π-bond order alternation (or zero-bond length alternation) by this model is also incorrect. However, the results are consistent with the predictions of a qualitative VB model which considers the resonance of a positive charge throughout the whole polymethine chain. Based on this model and the Franck-Condon principle the effect of substituents and solvents on the fine structure of the electronic spectra of these dyes can be explained as vibronic transitions from the vibrational state v = 0 to v', where v is the vibrational quantum number of the totally symmetric C=C valence vibration of the polymethine chain in the electronic ground state and v' is that in the electronic excited state. In contrast, neither the effects of substituents or solvents on the electronic structure of merocyanines and their electronic spectra can be accounted for by the simple two state VB model.     

Investigation of the distribution of the negative charge in anionic cyanine dyes by means of lanthanide shift reagents

It was established by PMR with lanthanide shift reagents that the charge in anionic cyanine dyes with a linear chromophore is concentrated at the ends of the polymethine chain, while in compounds containing a vinylene group in the chromophore it is concentrated in the region of the five-membered ring. The results are compared with the data from¹³C NMR spectroscopy and relaxation measurements in the presence of Gd(fod)₃. The validity of the conclusions is also considered.Kiev University. Institute of Organic Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya, Vol. 27, No. 2, pp. 197–201, March–April, 1991. Original article submitted December 20, 1989.     

Study of the reaction Fe(CN)4(bpy)2− + S2O82− in Sulfobetaine Aqueous Micellar Solutions

The reaction Fe(CN)₄(bpy)^2? + S₂O₈^2? has been studied in aqueous micellar solutions of N‐tetradecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propanesulfonate, SB3‐14. The influence of changes in the surfactant concentration as well as in the peroxodisulfate ions concentration on k_obs was investigated. Spectroscopic and conductivity measurements have given information about the distribution of both anionic reagents between the aqueous and micellar pseudophases of the SB3‐14 micellar solutions. A discussion about the adequacy of various equations based on the pseudophase model to rationalize kinetic micellar effects for anion‐anion reactions in sulfobetaine micellar solutions has been done. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 225–231, 2001