The abasic site (apurinic/apyrimidinic site) is the most common lesion in DNA and is suggested to be an important intermediate in mutagenesis and carcinogenesis. We have recently reported a novel assay for the detection and quantitation of abasic sites in DNA [Kubo, K., Ide, H., Wallace, S. S., & Kow, Y. W. (1992) Biochemistry 31, 3703-3708]. In this assay, the aldehyde group in an abasic site is first modified by a probe bearing a biotin residue, called the Aldehyde Reactive Probe (ARP) and then the tagged biotin is quantified by an ELISA-like assay. However, in the previous study, ARP was prepared only in a crude form, and no solid chemical data concerning the structure and specificity of ARP were reported. In this study, an improved method for the preparative synthesis of ARP has been established, and its structure has been unambiguously characterized using spectroscopic means. In order to elucidate the specificity of ARP to DNA damages, ARP was incubated with a variety of damaged bases or nucleosides and the reaction mixtures were analyzed by HPLC. Of the 14 compounds tested for their reactivity to ARP, 2-deoxyribose (a model compound for an abasic site) and 5-formyluracil reacted with ARP. Interestingly, compounds bearing a formamide group such as formamidopyrimidine and deoxyribosylformamide did not react with ARP, indicating that ARP is specific to damages having an alkyl or allyl aldehyde group. Furthermore, the ability of ARP synthesized by the defined chemical route to detect abasic sites has been substantiated using natural DNA containing abasic sites. Potential applications and limitations of the ARP assay are discussed.

Unique styrene polymerization behavior of bis(phenoxy-imine) Ti complexes (Ti-FI catalysts) combined with dried MAO (DMAO) was revealed. Upon activation with DMAO at 20 °C, non-fluorinated Ti-FI catalysts 1 and 2 produce highly syndiotactic polystyrene (sPS, T m 275 °C (1), 279 °C (2)), whereas fluorinated Ti-FI catalysts 3 and 4 form highly isotactic PS (iPS, T m 224 °C (3), 213 °C (4)). Interestingly, the fluorinated Ti-FI catalysts can produce an iPS/sPS mixture by varying polymerization conditions.

Interaction of p‐tert‐butylcalix[8]areneH8 (L8H8) with [NaVO(OtBu)4] (formed in situ from VOCl3) afforded the complex [Na(NCMe)5][(VO)2L8H]⋅4 MeCN (1⋅4 MeCN). Increasing [NaVO(OtBu)4] to 4 equiv led to [Na(NCMe)6]2[(Na(VO)4L8)(Na(NCMe))3]2⋅10 MeCN (2⋅10 MeCN). With adventitious oxygen, reaction of 4 equiv of [VO(OtBu)3] with L8H8 afforded the alkali‐metal‐free complex [(VO)4L8(μ3‐O)2] (3); solvates 3⋅3 MeCN and 3⋅3 CH2Cl2 were isolated. For the lithium analogue, the order of addition had to be reversed such that lithium tert‐butoxide was added to L8H8 and then treated with 2 equiv of VOCl3; crystallisation afforded [(VO2)2Li6[L8](thf)2(OtBu)2(Et2O)2]⋅Et2O (4⋅Et2O). Upon extraction into acetonitrile, [Li(NCMe)4][(VO)2L8H]⋅8 MeCN (5⋅8 MeCN) was formed. Use of the imido precursors [V(NtBu)(OtBu)3] and [V(Np‐tolyl)(OtBu)3] and L8H8, afforded [tBuNH3][{V(p‐tolylN)}2L8H]⋅3 1/2 MeCN (6⋅3 1/2 MeCN). The molecular structures of 1 to 6 are reported. Complexes 1, 3, and 4 were screened as precatalysts for the polymerisation of ethylene in the presence of cocatalysts at various temperatures and for the copolymerisation of ethylene with propylene. Activities as high as 136 000 g (mmol(V) h)−1 were sometimes achieved; higher molecular weight polymers could be obtained versus the benchmark [VO(OEt)Cl2]. For copolymerisation, incorporation of propylene was 7.1–10.9 mol % (compare 10 mol % for [VO(OEt)Cl2]), although catalytic activities were lower than [VO(OEt)Cl2].

The synthesis, molecular structures, and olefin polymerization behavior of the sterically crowded tris(pyrazolyl)borate complexes Tp Ms ZrCl 3 (2a; Tp Ms ) HB(3-mesitylpyrazolyl) 3 -), Tp Ms* ZrCl 3 (2b; Tp Ms* ) HB(3-mesitylpyrazolyl) 2 (5-mesitylpyrazolyl) -), (Tp Ms** ZrCl 2 ) 2 (µ-O) (2c; Tp Ms** ) HB(3-mesitylpyrazolyl)(5-mesitylpyrazolyl) 2 -), and Tp Ms* HfCl 3 (3b) are described. The molecular structures of TlTp Ms (1a) and TlTp Ms* (1b), the reagents used to prepare 2a-c and 3b, are also described. The core structures of 1a,b, and of 2a-c and 3b, are very similar, but the steric properties of these compounds differ markedly due to the different placements of the mesityl substituents on the tris(pyrazolyl)borate ligands. Under MAO activation conditions at low catalyst concentrations, 2a exhibits extremely high activity for ethylene polymerization and ethylene/hexene copolymerization. 2a/MAO produces ultrahigh-molecular-weight polyethylene and ethylene/hexene copolymers (up to 27% hexene) with narrow molecular weight distributions (M w /M n ) 1.8-2.3), characteristic of single-site catalysis. 2a/MAO is more active for ethylene polymerization than the less crowded analogues 2b/MAO and 2c/MAO.

Treatment of p-tert-butylcalix[6]areneH6 (L(6)H6) with in situ [LiVO(Ot-Bu)4] afforded, after work-up, the dark green complex [Li(MeCN)4][V2(O)2Li(MeCN)(L(6)H2)2]·8MeCN (1·8MeCN). On one occasion, the reaction led to the formation of a mixture of products, the bulk of which differing from 1 only in the amount of solvate, viz.2·9.67MeCN. The second minor, yellow product has the formula {[(VO2)2(L(6)H2)(Li(MeCN)2)2]·2MeCN}n (3·2MeCN), and comprises a 1D polymeric structure with links through the L(6)H2 ligand and Li2O2 units. When the reverse order of addition was employed such that lithium tert-butoxide (7.5 equivalents) was added to L(6)H6, and subsequently treated with VOCl3 (2 equiv.), the complex {[VO(THF)][VO(μ-O)]2Li(THF)(Et2O)][L(6)]}·2Et2O·0.5THF (4·2Et2O·0.5THF), which contains a trinuclear motif possessing a central, octahedral vanadyl centre linked via oxo bridges to two tetrahedral (C3v) vanadyl centres, was isolated. The calix[6]arene in 4 is severely twisted and adopts a ‘down, down, down, down, out, out’ conformation. Use of excess lithium tert-butoxide led to a complex very similar to 4, differing only in the solvent of crystallization, namely 5·Et2O·2THF. The ability of 1 and 5 to act as pre-catalysts for ethylene polymerization in the presence of a variety of co-catalysts and under various conditions has been investigated. Co-polymerization of ethylene with propylene and with 1-hexene have also been conducted; results are compared versus VO(OEt)Cl2.