Diazabicyclooctane Research Articles

Electron Transfer Studies in C78 (C2v‘), C76 (D2), C70 (D5h), and C60 (Ih) Surfactant Aqueous Solutions

C60 (Ih) and several higher fullerenes, namely, C70 (D5h), C76 (D2), and C78 (C2v‘), have been solubilized via capping with suitable surfactants. Excited states and reduced states of these surfactant systems were probed by photolytic and radiolytic techniques. Flash photolytic irradiation at 355 nm of surfactant solutions of C60, C70, C76, and C78 revealed the rapid grow-in of transient (*S1 → *Sn) absorptions with λmax at 920, 660, 650, and 890 nm, respectively. The associated intersystem crossing rates to the energetically lower lying excited triplet states are typically on the order of 9.0 × 108 s-1. Reductive quenching of the excited triplet states by diazabicyclooctane (DABCO) occurs with (0.8−7.4) × 107 M-1 s-1 and yields the fullerene π-radical anions. Direct reduction of surfactant capped fullerene monomers have been studied by means of time-resolved pulse radiolysis with measurements being conducted in the near-IR region. Radiolytic reduction of (C76)surfactant and (C78)surfactant resulted in the...

ChemInform Abstract: Enantiomerically Pure Cage‐Shaped (1S,4S,5R)‐4‐Hydroxy‐2,6‐ diazabicyclo(3.3.0)octane and (1S,4R,5R)‐4‐Hydroxy‐2‐oxa‐6‐azabicyclo( 3.3.0)octane: Synthesis and Test for Enantioselective Catalysis.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Direct synthesis and crystal structure of zinc thiocyanate complexes with 1,4diazabicyclo(2,2,2)octane

A direct method of synthesis of zinc thiocyanate complexes with 1,4-diazabicyclo(2,2,2) octane (or triethylenediamine, Ten) is reported. The main peculiarities of interaction of zinc oxide with non-aqueous (methanol, acetonitrile, N,N-dimethylformamide = DMF, dimethylsulfoxide = DMSO) solutions of ammonium thiocyanate in the presence of Ten were investigated. The crystal structures of the compounds [Zn 2(NCS) 4(NH 3) 2Ten] ( I), (HTen) 2[Zn(NCS) 4] ( II) and [Zn(NCS) 2(Ten)DMSO] ( III) were determined by X-ray diffraction. The complexes contain four ( I) and five ( III) coordinate zinc atoms linked by μ 2-bridging nitrogen atoms of Ten forming the dimeric and polymeric molecules respectively; the complex ( II) has an ionic-type crystal lattice with (HTen) + cations and [Zn(NCS) 4] 2− anions.

Excitation of C 60, solubilized in water by triton X-100 and γ-cyclodextrin, and subsequent charge separation via reductive quenching

The excitation of C 60 incorporated in triton X-100 micelles has been studied by laser flash photolysis. Reductive quenching of triplet-excited 3C 60 by diazabicyclooctane (DABCO) has been established in the micellar assembly, in aqueous solution of the fullerene embedded in γ-cyclodextrin, in alcohols and non-polar toluene. In aqueous media potassium hexacyanoferrate(II) and potassium iodide have been employed in the reductive quenching process as well. The C 60 − radical anion in all investigations has been characterized by its IR absorption. The formation and the half-life of C 60 − have been shown to be strongly dependent on the polarity of the environment. By utilizing DABCO as a quencher a half-life of 440 μs has been observed in the micellar assembly, while the respective values in propan-2-ol and butan-1-ol are 110 and 98 μs, respectively. In aqueous solution the radical anion γ-CD/C 60 − decays with a half-life of 59 μs and, in contrast, in the non-polar toluene no formation of any C 60 −. could be detected. The results are consistent with a charge-separated 3C 60-quencher contact pair.

Solvent induced photophysics and photochemistry of the (2p3s) Rydberg state of diazabicyclooctane: intersystem crossing, electron transfer, and energy transfer

Solvent induced singlet (2p3s) RydBerg state relaxation dynamics of diazabicyclooctane (DABCO) are studied in van der Waals clusters generated in a supersonic jet expansion. The excited-state decay is determined by a pump (excitation)/probe (ionization) mass selective technique. Solvents employed for these cluster studies include rare gases, saturated hydrocarbons and fluorocarbons, amines, ethers, methyl sulfide, acetonitrile, and aromatics. The nature of the intermediate states to which the nascent singlet (2p3s) Rydberg state decays is determined based on excited-state lifetimes, cluster dissociation products, and ionization energies

Charge recombination reactions in photoexcited fullerene C60-amine complexes studied by picosecond pump probe spectroscopy

Photoexcitation of complexes between fullerence C[sub 60] and organic amines in benzene solutions is known to result in charge separation (CS) and subsequent charge recombination (CR) reactions, which lead to varying yields of fullerence triplet formation. Picosecond flash photolysis studies are carried out on C[sub 60]-diphenylamine (DPA), C[sub 60]-triethylamine (TEA), C[sub 60]-diazabicyclooctane (DABCO), and C[sub 60]-triphenylamine (TPA) systems to find out mechanistic details of the triplet formation on CR by inducing heavy atom and polarity effects by using suitable solvents. It is found that in the case of C[sub 60]-DPA, C[sub 60]-TEA, and C[sub 60]-DABCO systems proton transfer from the amine cation to the C[sub 60] anion in the ion pair state dominates, leading to poor triplet yields, which improve in heavy atom containing solvents. In TPA, proton transfer is not possible and hence fullerene triplet yields are high. Increase of solvent polarity for this system results in decreased C[sub 60] triplet yields with a consequent increase in the ion dissociation yield. A suitable reaction scheme is proposed to explain the results obtained. 34 refs., 5 figs., 2 tabs.

Selection rule and efficiency for autoionization of diazabicyclooctane as studied by two-color double-resonance spectroscopy

Photoelectron spectra due to autoionization for two series of high Rydberg states have been observed for diazabicyclooctane (DABCO) in a supersonic jet. The selection rule of the autoionization has been found to be ..delta..v = -1 for each vibrational mode involved in the Rydberg states, consistent with Berry's theory available for the vibrational autoionization of a polyatomic molecule. The relative autoionization efficiencies Phi/sub a/ for the high Rydberg series have also been determined from two-color MPI and fluorescence dip spectra. The irregular variation of Phi/sub a/ with the principal quantum number n has been found for the two Rydberg series, suggesting the irregular variation in their nonradiative rates

ChemInform Abstract: Charge‐Transfer Interactions of Amines with Tetrahalomethanes. X‐Ray Crystal Structures of the Donor‐Acceptor Complexes of Quinuclidine and Diazabicyclo(2.2.2)octane with Carbon Tetrabromide.

ChemInformVolume 18, Issue 40 Physical Organic Chemistry ChemInform Abstract: Charge-Transfer Interactions of Amines with Tetrahalomethanes. X-Ray Crystal Structures of the Donor-Acceptor Complexes of Quinuclidine and Diazabicyclo(2.2.2)octane with Carbon Tetrabromide. S. C. BLACKSTOCK, S. C. BLACKSTOCK Chem. Lab., Calif. Inst. Technol., Pasadena, CA 91125, USASearch for more papers by this authorJ. P. LORAND, J. P. LORAND Chem. Lab., Calif. Inst. Technol., Pasadena, CA 91125, USASearch for more papers by this authorJ. K. KOCHI, J. K. KOCHI Chem. Lab., Calif. Inst. Technol., Pasadena, CA 91125, USASearch for more papers by this author S. C. BLACKSTOCK, S. C. BLACKSTOCK Chem. Lab., Calif. Inst. Technol., Pasadena, CA 91125, USASearch for more papers by this authorJ. P. LORAND, J. P. LORAND Chem. Lab., Calif. Inst. Technol., Pasadena, CA 91125, USASearch for more papers by this authorJ. K. KOCHI, J. K. KOCHI Chem. Lab., Calif. Inst. Technol., Pasadena, CA 91125, USASearch for more papers by this author First published: October 6, 1987 https://doi.org/10.1002/chin.198740054AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume18, Issue40October 6, 1987 RelatedInformation

Photo-induced oxidative activation of the antitumor drug 2N-methyl-9-hydroxyellipticinium in vitro.

Abstract— The phenolic antitumor drug 2N‐methyl‐9‐hydroxyellipticine (NMHE) has been found to undergo oxidative activation upon irradiation with near‐UV light at 365 nm (UVA) in aqueous medium. In the presence of leucine used as biological nucleophile, UVA‐induced activation of NMHE results in covalent binding as shown by the generation of the corresponding adduct isobutyl‐oxazolopyridocarbazole (IB‐OPC). The reaction involves as the initial step the one‐electron transfer from the drug to molecular oxygen yielding superoxide anion (O2‐) whereas the generation of IB‐OPC may proceed either through a free radical reaction or a Michael addition reaction. The UVA light‐induced production of IB‐OPC is markedly increased by superoxide dismutase (SOD) and by the singlet oxygen quencher diazabicyclooctane (DABCO) but not affected by β‐carotene. It is concluded that UVA induces the oxidation of NMHE through an oxidasic process which may result in the covalent binding of the drug to biological nucleophiles. This finding leads to further investigation of the photodynamic action of NMHE in tumor cells.

Synthesis of [3‐11C]phenylpyruvic acid and its use in an enzymatic transamination to [3‐11C]phenylalanine

AbstractThe synthesis of [3‐11C]phenylpyruvic acid, starting with 11CO2, is reported. This α‐keto acid was prepared via a condensation reaction, using [11C]benzaldehyde (prepared as described elsewhere), and 2‐phenyl‐5‐oxazolone, using diazabicyclooctane (DABCO) as a base. The condensation product, [α‐11C]‐4‐benzylidene‐2‐phenyl‐5‐oxazolone, was converted by basic hydrolysis to give [3‐11C]phenylpyruvic acid in 40 % radiochemical yield, starting with 11CO2, within 40 min. The potential of [3‐11C]phenylpyruvic acid in enzymatic transamination, catalyzed by glutamic/oxaloacetic acid transaminase (GOT) (Ee 2.6.1.1) immobilized on CNBr‐activated Sepharose was also studied.

Asymmetric synthesis of l-[3- 11C]phenylalanine using chiral hydrogenation catalysts

The seven-step synthesis of L-[3- 11C]phenylalanine using chiral diphosphines as ligands in rhodium catalysts is reported. [ 11C]Benzaldehyde, prepared in a three-step reaction from [ 11C]carbon dioxide, as reported elsewhere, (1) was reacted with 2-phenyl-5-oxazolone or 2-(4-chloro)phenyl-5-oxazolone in the presence of the tertiary amine diazabicyclooctane (DABCO). The resultant [α- 11C]-4-arylene-2-aryl-5-oxazolones were hydrogenated after ring opening, using the chiral rhodium complex of (R)-1,2-bis(diphenylphosphino)propane [(R)-PROPHOS] or (+)-2,3-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane [(+)-DIOP]. After removal of the amino protecting group, the labelled amino acid was obtained on purification by preparative LC in 10–15% radiochemical yield, and radiochemical purity higher than 95%, from [ 11C]carbon dioxide within 60 min. The optical purity of the products determined by the tRNA method and capillary GC, was 80 and 60% e.e., respectively (i.e. L/D = 90 10 and 80 20 ).

Two-color multiphoton ionization of diazabicyclooctane in a supersonic free jet

Two-color multiphoton ionization (MPI) spectroscopy has been applied for diazabicyclooctane (DABCO) in a supersonic free jet. The MPI spectra due to transitions from the various vibronic levels of the S 1 (3s Rydberg) state which were excited by the first laser revealed the high Rydberg states above the adiabatic ionization potential. The ionization process and the vibrational potential of the ion are discussed.

Resonance Raman spectra of transient free radicals using stopped flow multichannel and rapid scan methods

AbstractChemical oxidations of 1,4‐dimethoxybenzene (DMOB) and diazabicyclooctane (DABCO) in solution result in the generation of short‐lived free radical cations which have strong visible absorptions. These have been used for the excitation of resonance‐enhanced Raman spectra. The DMOB+˙ radicals were produced in a stopped‐flow apparatus linked with an optical multichannel Raman instrument. The DABCO+˙ species was produced by rapid mixing and its spectrum determined by rapid scanning of a conventional spectrometer. Both kinetic data and vibrational spectra are produced by these methods.

The Reaction of Biadamantylidene with Singlet Oxygen in the Presence of Dyes [1

AbstractSinglet oxygen, generated chemically or photogenetically, reacts with biadamantylidene to give the corresponding dioxetane and epoxide only. When methylene blue (MB) or meso‐tetraphenylporphin (m‐TPP) is used as sensitizer the normal reaction course occurs giving dioxetane as the preponderant product in 2‐propanol, ethyl acetate, acetone, pinacolone, methylene chloride, chloroform, carbon tetrachloride and benzene, although in the last two solvents some 10–25% of epoxide is formed. When erythrosin and rose bengal (RB) are used, epoxide becomes the main product (70–95%). Epoxide does not derive from chemical reaction with the solvent. Pinacolone, for example, is not oxidized to t‐butyl acetate.The rose bengal reaction involves both singlet oxygen and radicals, since diazabicyclooctane (DABCO) and di‐t‐butyl‐p‐cresol interfere with the oxidation. A mechanistic scheme is proposed in which sensitizer and oxygen combine to produce sensitizer radical cation and superoxide radical anion. Subsequently, hydroperoxy radical, deriving from superoxide, reacts with substrate to give epoxide and hydroxy radicals. The latter adds to substrate to give a new radical which captures triplet oxygen. Epoxide is formed by loss of hydroperoxy radical and the chain starts anew. The dioxetane is formed separately either by [2+2]‐cycloaddition or stepwise addition.

BILIRUBIN‐SENSITIZED PHOTOINACTIVATION OF ENZYMES IN THE ISOLATED MEMBRANE OF THE HUMAN ERYTHROCYTE*

Abstract— Bilirubin has been found to sensitize the photodynamic inactivation of several enzymes in the isolated membrane (ghost) of the human red cell. When ghosts (pH 8.0, 10°C) + bilirubin (0.1 mM) were irradiated with blue light (350 Wm‐2), the activity of glyceraldehyde 3‐phosphate dehydrogenase decayed with t1/2≃ 15 min. No effect was observed in the absence of pigment or with incident yellow light. Diazabicyclo‐octane (DABCO) sharply reduced the inactivation rate, suggesting that 1O2 is involved. Sodium dodecyl sulfate‐gel electrophoresis of ghosts containing fully inactivated glyceraldehyde 3‐phosphate dehydrogenase revealed no change in the polypeptide band corresponding to the subunit of the enzyme. Solubilized enzyme, which was similarly photosensitive, could be partially protected by nicotinamide adenine dinucleotide or glyceraldehyde 3‐phosphate. The integral enzymes Mg2+‐ATPase, Na+, K+‐ATPase, and acetylcholinesterase were also affected. Under the above conditions and bilirubin = 0.37 mM, these enzymes were photoinactivated in first‐order fashion, k≃ 2, 1.2 and 0.2 h‐1, respectively. The rate of decay of total ATPase was found to vary as the square root of the bilirubin concentration over the range 7–370 μM. At a fixed bilirubin concentration (0.37 mM), this rate was also shown to be directly proportional to light intensity. Inasmuch as the —SH content of bilirubin‐containing ghosts diminished during irradiation, oxidation of essential cysteine residues could be responsible for the inactivation of some of the enzymes studied.