Influences of land use on water quality of a diverse New England watershed.

Analysis of variations in major ion chemistry in the Mill River watershed reveals the importance of anthropogenic activities in controlling streamwater chemistry. Average concentrations of NO3- and SO4(2-) show a positive correlation with percent catchment area altered by human land uses, and concentrations of Cl- increase with road density. Water removal from municipal reservoirs increases the downstream concentration of NO3- and SO4(2-) over that predicted by land use changes, showing that removal of high quality upstream water concentrates pollutants downstream. In salt-impacted streams, Cl- exceeds Na- by 10-15% due to cation exchange reactions that bind Na+ to soil. The net effect of nonpoint source pollution is to elevate ANC in the most developed areas, which impacts the natural acidity of a large swamp. The sum of base cations (C(B)) exceeds ANC for all samples. Plotting C(B) against ANC and subtracting Cl- quantifies the impact of road salt from the impact of the addition of strong acids.

308 nm excimer laser ablation of cartilage.

This article reports the investigation of the XeCl excimer laser as a cutting-ablating tool for human fibrocartilage and hyaline cartilage. Quantitative measurements were made of tissue ablation rates as a function of fluence in meniscal fibrocartilage and articular hyaline cartilage. A force of 1.47 Newtons was applied to an 800-microns fiber with the laser delivering a range of fluences (40-190 mJ/mm2) firing at a frequency of 5 Hz. To assess the effect of repetition rate on depth per pulse, a set of measurements was made at a constant fluence of 60 mJ/mm2, with the repetition rate varying from 10 to 40 Hz. Histologic and morphometric analysis of preserved specimens was performed using light microscopy. The results of these studies revealed that the ablation rate was directly proportional to fluence over the range tested. Fibrocartilage was ablated at a rate 2.56 times faster than hyaline cartilage. Repetition rate had no effect on the penetration per pulse. Adjacent tissue damage was noted to be minimal (10-70 microns). The excimer laser achieved ablation rates adequate for arthroscopic applications.

Design, synthesis, and biological evaluation of DNA sequence and minor groove selective alkylating agents.

The syntheses of oligoimidazolecarboxamido analogues of distamycin wherein the N-terminus contains either a benzyl-mustard 8 or chlorambucil moiety 9-11 are reported. Based on data from an ethidium displacement assay and CD studies, these compounds, along with the N-benzoyl mustards 6 and 7, were shown to have increased acceptance of GC-rich sequences over distamycin. Compounds 8-11 which contain an electron-donating group (sigma < 0) para to the bischloroethylamino moiety, were found to have significantly enhanced reactivity with DNA compared to the benzoyl mustards 6 and 7. Through dialysis experiments, the benzyl and chlorambucil mustards were shown to alkylate calf thymus DNA more readily than the benzoyl mustards, presumably due to destabilization of the aziridinium intermediate by the electron-withdrawing (sigma > 0) carboxamido group of the benzoyl compounds. Compounds 8-11 were found to alkylate guanine-N7 in the major groove, while compounds 6 and 7 did not, suggesting that they may have different modes of DNA interaction. Mustards 8-11 were also more efficient than 6 and 7 at producing DNA interstrand cross-links in isolated DNA. In general, for these compounds, the cytotoxicity against human chronic myeloid leukemia K562 cells and the panel of human tumor cell lines of the National Cancer Institute increased with the number of imidazole moieties. The IC50 values of compounds 7 and 8 were similar, even though the latter compound was at least 100-fold more efficient at forming DNA cross-links in isolated DNA. Similarly, compounds 9-11 were less cytotoxic than 6 and 7, although they were more efficient cross-linkers in isolated DNA. A direct comparison of the three imidazole-containing benzoyl mustard 7 with the corresponding chlorambucil-containing 11 for their ability to form interstrand cross-links in cells revealed that the former compound showed no cross-linking even at doses in excess of the IC50, whereas the latter produced extensive cross-linking. This further suggests that these compounds exert their biological activity through different mechanisms. It is proposed that the aromatic moiety of compounds 8-11, which bind to the minor groove, may be able to intercalate between GC base pairs and the protruding bischloroethylamino group would be positioned to alkylate and cross-link at guanine-N7 sites in the major groove. However, the benzoyl mustards, which have a rigid amino linkage between the imidazole and aromatic-mustard moieties, do not have the flexibility to intercalate into the DNA.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro cytotoxicity of GC sequence directed alkylating agents related to distamycin.

Imidazole containing analogues 7, 10, and 17 of distamycin wherein the C-terminus contain a dimethylamino moiety have been shown to selectively bind to the minor groove of GC-rich sequences. Accordingly, these agents were employed as vectors for the delivery of a variety of alkylating agents to GC-rich sequences. The alkylating agents are attached to the N-terminus of these vectors thus providing the benzoyl N-mustards (8, 15, and 18 that contain one, two, and three imidazole units, respectively) and substituted acetamides 11-14. Results from the ethidium displacement assay for the formamides 7, 10, and 17 and mustards 15 and 18 showed that these agents bind to calf thymus DNA, poly(dA.dT), poly(dG.dC), and also to coliphage T4 DNA, thus confirming their binding in the minor groove. The reduced binding constants of these compounds for poly(dA.dT) while still binding as strongly, or more strongly, to poly(dG.dC) than distamycin provided evidence for their acceptance of GC sequences. Selectivity for GC-rich sequences was also indicated by CD titration studies. Titration of 10, 15, 17, and 18 to poly(dA.dT) produced weak drug-induced CD bands at approximately 330 nm; however, interaction of these agents to poly(dG.dC) in equimolar drug concentrations gave strong bands in this region. Results from dialysis and cross-link gel experiments provided evidence of alkylation and cross-linking of DNA by the mustards which could explain their enhanced cytotoxicity over the formamido analogues. The bifunctional N-mustard-containing analogues 15 and 18 are significantly more cytotoxic than the monoalkylating acetamides 11-14. The mustards also exhibited significant activity against cell lines derived from solid tumors such as melanomas, ovarian cancers, CNS cancers, and small cell lung cancer.

GC base sequence recognition by oligo(imidazolecarboxamide) and C-terminus-modified analogues of distamycin deduced from circular dichroism, proton nuclear magnetic resonance, and methidiumpropylethylenediaminetetraacetate-iron(II) footprinting studies.

The DNA binding properties of a series of imidazole-containing and C-terminus-modified analogues 4-7 of distamycin are described. These analogues contain one to four imidazole units, respectively. Data from the ethidium displacement assay showed that these compounds bind in the minor groove of DNA, with the relative order of binding constants of 6 (Im3) > 7 (Im4) > 5 (Im2) > 4 (Im1). The reduced binding constants of these compounds for poly(dA-dT) relative to distamycin, while they still interact strongly with poly(dG-dC), provided evidence of GC sequence acceptance. The preferences for GC-rich sequences by these compounds were established from a combination of circular dichroism (CD) titration, proton nuclear magnetic resonance (1H-NMR), and methidiumpropylethylenediaminetetraacetate-iron(II) [MPE.Fe-(II)] footprinting studies. In the CD studies, these compounds produced significantly larger DNA-induced ligand bands with poly(dG-dC) than poly(dA-dT) at comparable ligand concentrations. 1H-NMR studies of the binding of 5 to d-[CATGGCCATG]2 provided further evidence of the recognition of GC sequences by these compounds, and suggested that the ligand was located on the underlined sequence in the minor groove with the C-terminus oriented over the T residue. MPE footprinting studies on a GC-rich BamHI/SalI fragment of pBR322 provided unambiguous evidence for the GC sequence selectivity for some of these compounds. Compounds 4 and 7 produced poor footprints on the gels; however, analogues 5 and 6 gave strong footprints.(ABSTRACT TRUNCATED AT 250 WORDS)