Study on various fluorescein derivatives as pH sensors

Various fluorescein derivatives were examined as fluorescent pH sensors. Fluorescein derivatives bearing benzylic amine moieties displayed opposite fluorescent changes compared to those of simple fluorescein derivatives upon pH changes. Photo-induced electron transfer (PET) mechanism controls the fluorescent changes of these derivatives. In this Letter, modulations of pK_a values were successfully demonstrated through variations of substituent groups.     

Photoinduced intramolecular electron transfer between fluorescein and carbazole

Several dyads consisting of a fluoreseein covalently linked with a carhazole at site 2 or site 6 have been synthesized and characterized.Studies of absorption spectra,emission spectra and fluorescence lifetime quern hing Indicate that the ground-state interaction between fluorescein and carhazole in dyads is negligible and the intramolecular electron transfer (ET) reactions are mainly of dynamic process.Moreover,the efficiency and raie conslam of lectron transfer reactions in ZFO4 (carbazole linked at site 2'of fluorescein) are larg er than those in 4FOZ (carbazole linked at site 6 of fluorescein) 0 74; KET 11×108S-1),because the mutual orientation of donor and acceptor in ZFO4 is nearly face-to-face,which is more favorable to the process than the shoulder-to-shoulder mutual orientation in 4FOZ.Estimations are also formed of the free energy change of the photomduced electron transfer and the back reactions in the dyads.     

NMR-spektroskopische Untersuchungen an Mercaptophosphazenen. I. Verlauf der Reaktion von Natriumethylmercaptid mit Hexachlorocyclotriphosphazatrien bzw. Octachlorocyclotetraphosphazatetraen

N.M.R. Spectroscopic Investigations of Thiophosphazenes. I. Reactions of Sodium Ethylthiolate with Hexachlorocyclotriphosphazatriene and Octachlorocyclotetraphosphazatetraene By reactions of hexachlorocyclotriphosphazatriene with an excess of sodium ethylthiolate as a suspension in ether all of the possible geminal derivatives N₃P₃Cl_6?n(SEt)_n; n = 1–6, are formed in different quantities. Products from reactions of octachlorocyclotetraphosphazatetraene with sodium ethylthiolate, N₄P₄Cl_8?n(SEt)_n, likewise contain all of the geminally substituted derivatives up to n = 8 with the exception of the derivatives with n = 1 and n = 7. Compounds with n = 3, 4, or 5 exist in two geminal isomers respectively. Nongeminal ethylthiochlorophosphazenes were not found by any reaction. The formed compounds were isolated by chromatographic methods and studied by ³¹P n.m.r. spectroscopy.     

Simple and ecofriendly synthesis of dihydropyrimidinones (thiones), dihydropyridines,and pyridines using 3‐formylchromones as substrates assisted by a recyclable Preyssler heteropolyacid

Several dihydropyrimidinones/thiones, 1,4‐dihydropyridines, and pyridine derivatives were prepared in very good yields and purity values. The corresponding reactions were carried out by employing a bulk Preyssler heteropolyacid H₁₄[NaP₅W₂₉MoO₁₁₀] as an efficient and recyclable catalyst. The preparation of pyridine derivatives was carried out not through a usual procedure, i.e., the opening of the γ‐pyrone ring of 3‐formylchromone. In general, reactions took place in solvent‐free conditions at 80°C during short reaction times.     

λ-radiolysis of mitomycin c derivatives

The λ-Radiolysis reactions of mitomycin C ( 1 ) and its derivatives were studied in the hope of developing a radiation-induced drug (RID). The λ-radiolysis reactions were carried out in aqueous solutions under the condition where hydrated electron (e^?_aq) was generated as a principal reactive species. The competitive λ-radiolysis studies revealed that the rate constants for the reactions of 1 with e^?_aq at room temperature was 3.6 × 10¹⁰ dm³ mol^?1s^?1. Among mitomycin C derivatives, the 5H-6-alkoxyimino derivatives 11 and 12 , and compound 13 in which ring A of 1 has the 4-hydroxy-6-hydroxyimino structure cleaved to give 1 . The mechanic aspect of these λ-radiolysis reactions is discussed.     

New 4-pentafluorosulfanyl and 4-perfluoroalkylthio derivatives of 1-chloro-2-nitro- and 1-chloro-2,6-dinitrobenzenes

New 4-pentafluorosulfanyl and 4-perfluoroalkylthio derivatives of 1-chloro-2-nitrobenzene and 1-chloro-2,6-dinitrobenzene were prepared from the corresponding bis(4-chloro-3-nitrophenyl)disulfide and bis(4-chloro-3,5-dinitrophenyl)disulfide, respectively. The SF₅ derivatives were obtained by fluorination of the disulfides with AgF₂ according to Sheppard’s method, while perfluoroalkylation was carried out by means of thermolytic reactions with xenon(II) bis(perfluoroalkylcarboxylates). The introduction of fluorine-containing, electron-withdrawing substituents into the aromatic ring (in the presence of other deactivating groups) reinforces the activation of the halogen substituent towards nucleophilic attack. Several nucleophilic substitution reactions have been carried out with these compounds, and as a result, some N- and S-containing groups were introduced in the benzene ring. For example, the previously unknown SF₅, CF₃S, and C₂F₅S analogues of trifluralin (Treflan^®) were prepared and characterized. Additional synthetic possibilities for heterocyclic chemistry are presented on the basis of reactions of the new 1-chloro-2,6-dinitrobenzene derivatives with ethyl thioglycolate wherein fluorine-containing derivatives of benzothiazole N-oxide were obtained as the main products.     

Rh(I)-catalyzed addition of alkenylzirconocene chlorides to aldimine derivatives

[RhCl(COD)]₂ (2 mol%) catalyzed reactions of alkenylzirconocene chloride complexes to N-Ts, -PO(OEt)₂ and COOR aldimine derivatives were efficiently carried out in dioxane at room temperature to give allylic amine derivatives in excellent yields. This is the first example of the catalytic addition reactions of alkenylzirconocene chloride complexes to aldimine derivatives.     

Quantum-chemical simulation of unit process for the oxidation reactions of ethylene and its derivatives invoving <Superscript>1</Superscript>O<Subscript>2</Subscript> (<Superscript>1</Superscript>Δg)

The results of simulation of oxidation reactions of ethylene derivatives with different substituents (F atoms, CH₃O and CH₃ groups) and butadiene molecule with participation of ¹O₂ (¹Δg) have shown the possibility to realize different routes for the majority of the considered reactions. The largest product variety is obtained for butadiene and CH₃ derivatives of ethylene. For butadiene, along with 1,2-cycloaddition reactions resulting in four-membered dioxetane (which is realized in all cases), the possibility to form six-membered cyclic epidioxides (1,4-addition) and diepoxide products with two three-membered rings (epoxidation) has been found. The formation of hydroperoxide forms along with 1,2-addition reactions is also possible for all CH₃ derivatives of ethylene. Formation conditions and relative stability of the noted products have been analyzed for each case and certain features of the revealed reaction pathways with the transfer of two oxygen atoms have been discussed.     

Ruthenium‐catalyzed carbonylative cycloaddition reactions involving carbonyl and imino groups as assembling units

This paper describes carbonylative cycloaddition reactions catalyzed by Ru₃(CO)₁₂. Ru₃(CO)₁₂ was found to catalyze an intramolecular Pauson–Khand‐type reaction. Carbonylative cycloaddition reactions involving a carbonyl group in aldehydes, ketones, and esters as a two‐atom assembling unit were also achieved in the presence of Ru₃(CO)₁₂ as the catalyst. The reaction of 5‐hexyn‐1‐al and 6‐heptyn‐1‐al derivatives with CO in the presence of Ru₃(CO)₁₂ resulted in cyclocarbonylation from which bicyclic α, β‐unsaturated lactones were obtained. Intermolecular [2 + 2 + 1] carbonylative cycloaddition of alkenes, ketones, and CO was also catalyzed by Ru₃(CO)₁₂ as the catalyst to give saturated γ‐lactone derivatives. Simple ketones were not applicable, but ketones having a C?O or C?N group at the α‐position served as a good substrate. These reactions could be extended to carbonylative cycloaddition of the corresponding imines leading to γ‐butyrolactam derivatives. The [4 + 1] carbonylative addition of α,β‐unsaturated imines leading to unsaturated γ‐lactams was achieved with Ru₃(CO)₁₂. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 201–212; 2008: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20149     

Acid-base and tautomeric equilibria of fluorescein dyes in water micellar solutions of zwitterionic sulfobetaine surfactant

Ionization constants of fluorescein and six its derivatives in water micellar solutions of zwitterionic surfactant, N-cetyl-N,N-dimethyl-3-ammonium-1-propanesulfonate were evaluated spectrophotometrically. On the basis of absorption spectra of dyes conclusions concerning the tautomerism of molecular and ionic forms were made and the relationships between the pK _a values were explained.     

Rhenium-catalyzed synthesis of naphthalene derivatives via insertion of aldehydes into a C-H bond

A rhenium complex, [ReBr(CO)₃(THF)]₂, catalyzed reactions of aromatic ketimines and aldehydes with dienophiles, followed by dehydration, to give naphthalene derivatives in good to excellent yields. This reaction proceeds via C-H bond activation, insertion of an aldehyde, intramolecular nucleophilic cyclization, reductive elimination, elimination of aniline and Diels-Alder reaction. After dehydration, naphthalene derivatives were formed.     

Ureas as a New Nucleophilic Reagents for SNAr Amination and Carbamoyl Amination Reactions in 1,3,7‐Triazapyrene Series

The ability of urea anions to react as nucleophiles with alkoxy derivatives of 1,3,7‐triazapyrenes has been investigated. It was found that against all expectations, the products of the substitution of an alkoxy groups (S_N^ipso ) by amino group were isolated in good yields. The reactions proceed in anhydrous dimethyl sulfoxide solution at room temperature. But when anions of the mono‐substituted ureas containing bulky substituents were used, the first products of the earlier unknown S_NAr reactions of alkyl carbamoyl amination were obtained.     

Cluster Chemistry: XVII.Radical ion-initiated synthesis of ruthenium cluster carbonyls containing tertiary phosphines,phosphites, arsines,SbPh3, or isocyanides

The syntheses of over sixty known and new derivatives of Ru₃(CO)₁₂ and H₄Ru₄(CO)₁₂ by substitution reactions initiated by sodium diphenylketyl are described. The range of ligands studied includes isocyanides, tertiary phosphines and phosphites, tertiary arsines and SbPh₃. The reactions are characterised by high degrees of specificity and conversion: under mild conditions up to four ligands can be introduced. Comparisons with the corresponding thermally induced reactions are made in several cases. The reactions provide routes to mixed ligand derivatives of the cluster carbonyls, although account of relative Lewis base strengths of the ligands may have to be taken. Possible mechanisms of these reactions are discussed briefly, as are the IR ν (CO) spectra of the Ru₃ (CO)_12-nL_n complexes.     

Ruthenium carbonyl complexes with α-substituted oxime derivatives of terpenes as ligands

The reactions of Ru₃(CO)₁₂ with oximes of α-substituted caran-4-one, lemonen-5- and pinan-3-one derivatives were studied. The reactions at elevated temperatures yield binu-clear complexes Ru₂(CO)₄L₂, with two ruthenium atoms bridging two terpenoid ligands (L) through the oxime groups and coordinated additionally to a nitrogen or sulfur atom of the NR₂ or SR groups respectively. The reactions carried out at room temperature in the presense of Me₃NO yield trinuclear complexes Ru₃(CO)₈L₂ with analogous coordination of the terpenoid ligands. In a solution at room temperature these clusters readily transform to binuclear complexes. The NMR spectroscopy shows the stereochemical nonrigidity of the complexes with the S-CH₂-Ph fragment: at room temperature in a solution the benzyl radical undergoes slow rotation about the S-C bond and a change of the conformation of carane and pinane carbocycles occurs more rapidly. The reactions with pinane and carane derivatives are stereospecific yielding only one of the possible diastereoisomers. More flexible limonene derivative form both diastereoisomers.     

Synthesis of coumarin derivatives in a microfluidic flow system employing the Pechmann condensation: A case study

For the synthesis of coumarin derivatives using the Pechmann condensation scheme, an acidic ionic liquid catalyst, abbreviated as [EBsImH][HSO ₄ ] , was prepared from the ring opening of 1,4-butanesultone by 1-ethylimidazole, followed by the addition of 1 equiv. H₂SO₄(c). The [EBsImH][HSO ₄ ] -catalyzed Pechmann condensation reactions proceeded smoothly in a batch setup, with recyclable [EBsImH][HSO ₄ ] showing great catalytic activity. The acidic ionic liquid catalyst [EBsImH][HSO ₄ ] was recovered from EtOAc/H₂O extraction of the product mixture, where the H₂O layer was worked up and dried for reuse in consecutive runs of the Pechmann condensation reactions, maintaining >85% conversion for four times. The catalytic reactions were also carried out in a microfluidic flow setup. The flow parameters, the reactant molar amounts, and the additional H₂SO₄ as a modifying acid catalyst were optimized in the current case study. A minimum conversion rate of 2.8 g/hr of coumarin derivatives was demonstrated.     

Reactions of alkoxy and peroxy radicals formed upon the decomposition of hydroxyperoxide groups in the artemisinin derivatives

The enthalpies of intramolecular reactions of alkoxy and peroxy radicals formed from polyatomic artemisinin hydroperoxides and of their bimolecular reactions with C—H, S—H, and O—H bonds of biological substrates were calculated. The activation energies and rate constants of these reactions were calculated using the intersecting parabolas method. The decomposition of artemisinin hydroperoxides can initiate the cascade of intramolecular oxidation reactions involving radicals R·, RO·, HO·, HO₂·, and RO₂·. The main sequences of transformation of these radicals were established. The oxidative destruction of the artemisinin peroxy derivatives generates radicals RO₂·, HO·, and HO₂· in an amount of 4.5 radicals per peroxide derivative molecule on the average. The kinetic scheme of oxidative transformations of the hydroperoxide with four OOH groups and radicals formed from it was constructed using this radical as an example.     

One-pot synthesis of 1,2,4,5-tetrahydro-2,4-dioxobenzo[b][1,4]diazepine and malonamide derivatives using multi-component reactions

In this work, a new series of 1,2,4,5-tetrahydro-2,4-dioxobenzo[b][1,4]diazepine and malonamide derivatives have been synthesized using an aromatic 1,2-diamine, Meldrum's acid, an isocyanide, and an arylidene malononitrile (or an aldehyde and malononitrile instead of an arylidene malononitrile) in CH₂Cl₂ at ambient temperature. Synthesis of 1,2,4,5-tetrahydro-2,4-dioxobenzo[b][1,4]diazepine proceeded via four- and five-component reactions; while the synthesis of malonamide derivatives was performed using five- and six-component reactions. In addition, a new series of the malonamide derivatives have been prepared using an aldehyde, malononitrile, Meldrum's acid, an isocyanide, and two molecules of 1,4-diamine via a six-component reaction. These procedures provide alternative methods to the synthesis of a new series of 1,2,4,5-tetrahydro-2,4-dioxobenzo[b][1,4]diazepine and malonamide derivatives.     

Assessment of amination reactions via nucleophilic aromatic substitution using conventional and eco-friendly energies

The efficiency of conventional heating energy source compared with Infrared (IR), Ultrasound (US), Microwave and the simultaneous combination US–IR eco-friendly approaches for preparation of new N-(5-R¹ _-amino-2-nitrophenyl)acetamides and 5-R¹-amino-2-nitroaniline by Nucleophilic Aromatic Substitution (S_NAr) via addition–elimination reactions on the halogens F, Cl, Br, I, employing amines as nucleophiles were explored. Moreover, phenyldiazenyl derivatives in good yields by an oxidative one-pot S_NAr-based amination reaction from an unusual oxidation of 2-phenylhydrazinyl derivatives in DMSO was prepared.     

Methyl-and tert-butyl-substituted hydroquinones and semiquinone radicals: Bond strength estimates, enthalpy of formation, and the rate constants of their reactions with peroxy radicals

The strength of the O-H bonds (D) in hydroquinone (HQH) and its alkyl derivatives has been estimated by the intersecting parabolas method using rate constants known for the reactions of these compounds with the styrene peroxy radical. For unsubstituted HQH, D = 352.6 kJ/mol; for substituted HQH derivatives, D = 349.9 (Me), 346.9 (2,5-Me₂), 343.0 (Me₃), 347.6 (CMe₃), and 340.2 (2,5-(CMe₃)₂) kJ/mol. The enthalpies of formation of these HQH derivatives have been calculated. The O-H bond strengths in the semiquinone radicals (HQ^.) resulting from the above HQH derivatives have been calculated using a thermochemical equation to be $D_{HQ^. } $ = 236.7, 237.4, 239.8, 244.7, 240.1, and 247.5 kJ/mol, respectively. Rate constants have been determined for the reactions of the hydroquinones with tertiary and secondary peroxy radicals and HOO^. at 323 K. The rate constants of the reactions between HOO^. and benzoquinones and the relative reactivities of the HQ^. radicals in their reactions with ROO^. have been estimated.     

Photoinitiated Free-Radical Polymerization of 4,5,6,7-Tetrahalogenated Fluoresceins

We demonstrated the photoredox catalytic performances of fluorescein derivatives, bearing heavy halogen atoms (Br or I) on a benzoic acid group, using photoinitiated free-radical polymerization. 4,5,6,7-Tetrabromofluorescein and 4,5,6,7-tetraiodofluorescein were used as visible-light-photoredox catalysts to initiate polymerization of poly(ethylene glycol) diacrylate and N-vinylpyrrolidone in the presence of triethanolamine under aerobic conditions. Their photocatalytic performances were evaluated by the hydrogelation of photopolymerization both on the surface of an agarose film and in a liquid solution. The polymerization degree increased considerably in the following order: tetraiodofluorescein<tetrabromofluorescein<fluorescein. This result was different from fluorescein derivatives containing the heavy halogen atoms on a xanthene core ring. Consequently, the location of the heavy halogen atoms was crucial in the photocatalytic performance of fluorescein derivatives.