Thomas L. Netzel

Picosecond spectroscopic studies of (d8-d8) binuclear rhodium and iridium complexes: a comparison of 1B2 and 3B2 reactivity in bis(1,5-cyclooctadiene)bis(.mu.-pyrazolyl)diiridium(I)

Picosecond transient kinetics and difference spectra have been recorded for the singlet and triplet (dsigma*psigma) excited states in the d/sup 8/-d/sup 8/ dimers Rh/sub 2/(TMB)/sub 4//sup 2 +/ (TMB = 2,5-dimethyl-2,5-diisocyanohexane) and (Ir(..mu..-pz)(COD))/sub 2/ (pz = pyrazolyl, COD = 1,5-cyclooctadiene). The singlet excited state in the rhodium dimer (tau=- 820 ps) displays a strong transient absorption feature maximizing at 440 nm that is not present in the spectrum of the triplet excited state. This intense absorption feature, characteristic of a /sup 1/(dsigma-psigma) electronic configuration, is assigned to a /sup 1/(dsigma*psigma) ..-->.. /sup 1/(psigma/sup 2/) excitation. This singlet excited state lifetime of the iridium dimer in cyclohexane is less than 20 ps. Though the solvent 1,2-dichloroethane (DCE) quenches luminescence from both singlet and triplet excited states in (Ir(..mu..-pz)(COD))/sub 2/ and oxidatively adds to the dimer upon steady-state illumination, picosecond spectroscopy finds no evidence for any chemical reactivity of the very short-lived singlet excited state. The quenching of (Ir(..mu..-pz)(COD))/sub 2/ singlet luminescence in DCE appears to result from enhanced singlet ..-->.. triplet intersystem crossing in DCE relative to that in cyclohexane. Also, the invariance of triplet yield in these two solvents indicates that the efficiency of intersystem crossing is near unity.

SYNTHESIS OF 5-(2,2′-BIPYRIDINYL AND 2,2′-BIPYRIDINEDIIUMYL)-2′-DEOXYURIDINE NUCLEOSIDES: PRECURSORS TO METALLO-DNA CONJUGATES

ABSTRACT The synthesis of 2,2′-bipyridinyl-2′-deoxyuridine metal-chelator nucleosides (Bipy-dU) with either ethynyl or ethylenyl linkers was now been accomplished. These new nucleosides will permit the construction of a number of corresponding metallo-DNA conjugates where many types of metals can be complexed to the 2,2′-bipyridinyl chelator group and the resulting metallo-dU conjugates incorporated into DNA oligonucleotides. Additionally this paper also reports the synthesis of a di-N-alkylated bipyridinediiumyl-2′-deoxyuridine nucleoside (Bipy2+-dU) with an ethylenyl linker. The Bipy2+-dU nucleoside was found to decompose under basic conditions precluding its use in standard automated DNA-synthesis by the phosphoramidite method. No such restrictions apply to the two Bipy-dU nucleosides reported here for use as metal chelators.

Synthesis of two 8-[(anthraquinone-2-yl)-linked]-2'-deoxyadenosine 3'-benzyl hydrogen phosphates for studies of photoinduced hole transport in DNA.

The challenge in working with anthraquinone-2′-deoxyadenosine (AQ-dA) conjugates is that they are insoluble in water and only sparingly soluble in most organic solvents. However, water-soluble AQ-dA conjugates with short linkers are required for study of their electrochemical and intramolecular electron transfer properties in this solvent prior to their use in laser kinetics investigations of photoinduced hole (cation) transport in DNA. This article first describes the synthesis of a water-soluble, ethynyl-linked AQ-dA conjugate, 8-[(anthraquinone-2-yl)ethynyl]-2′-deoxyadenosine 3′-benzyl hydrogen phosphate, based on initial formation of a 5′-O-(4,4′-dimethoxytrityl) (5′-O-DMTr) intermediate. Because intended H2 over Pd/C reduction of the ethynyl linker in 5′-O-DMTr–protected 2′-deoxyadenosines cleaves the DMTr protecting group and precipitates multiple side products, this work also describes the synthesis of an ethylenyl-linked AQ-dA conjugate, 8-[2-(anthraquinone-2-yl)ethyl]-2′-deoxyadenosine 3′-benzyl hydrogen phosphate, starting with a 5′-O-tert-butyldiphenylsilyl protecting group.

Synthesis of N,N-Dialkylaniline-2′-deoxyuridine Conjugates for DNA-Mediated Electron Transfer Studies

Abstract Syntheses of two analogs of deoxyuridine with N,N-dialkylaniline chromophores are reported. 5-[3-(N-methylphenylamino)propanoyl]-2′-deoxyuridine (1) and 5-[2-(4-N,N-dimethylaminophenyl)ethyl)]-2′-deoxyuridine (2) are prepared by palladium-mediated coupling. Preparation of 2 was facilitated by in situ transient O4-trimethylsilyl protection during alkynylation which suppressed secondary cyclization of the coupling adduct.

SYNTHESIS OF 5-(PYRIDINYL AND PYRIDINIUMYL)-2′-DEOXYURIDINE NUCLEOSIDES: REVERSIBLE ELECTRON TRAPS FOR DNA

The desire to produce reversible electron traps for direct, room temperature studies of excess electron transport in DNA duplexes and hairpins motivated our efforts first to link pyridines to 2′-deoxyuridine (pyridinyl-dU) and then to convert these new conjugates into pyridiniumyl-dU nucleosides. Base sensitivity studies presented here rule out general use of bipyridinediiumyl compounds, but show that pyridiniumyl compounds are suitable for use under the strand cleavage and base deprotection procedures required for automated solid-phase oligonucleotide synthesis. This paper presents the synthesis of four 5′-O-DMT-protected 5-(N-methylpyridiniumyl)-dU conjugates using either ethynyl or ethylenyl linkers to join the pyridiniumyl and dU subunits.

Synthesis, Electrochemistry, and Hydrolysis of Anthraquinone Derivatives

Abstract Anthraquinone (AQ) derivatives, including members of the anthraquinone imide (AQI) family, have been synthesized to afford good candidates for electron-transfer studies in DNA. Electron-withdrawing groups on the AQ ring give a less negative reduction potential, as desired. As expected, the AQI derivatives have less negative reduction potentials than AQ derivatives. The AQI ring system has a half-life for hydrolysis of about 75 min in a 3:7 MeCN and 0.005 M K2CO3 in MeOH.

Dynamic behavior in the light and dark phases of alkane photochemical functionalization by [W10O32]4−

Picosecond irradiation of [W10O32]4−,1, indicates that this complex forms a ligand-to-metal charge-transfer (LMCT) excited state that decays withτ<30 ps to another much longer lived species (>15 ns) that is responsible for attack on alkane substrate and is distinguishable from the reduced complex, [W10O32]5−. Kinetics of production of reduced complex and the organic product (ethylalkane) in the presence of ethylene indicate that the role of1 in production of this product is not simply as an initiator of radical chain ethylene addition.