A Student-Centered, Entrepreneurship Development (ASCEND) Undergraduate Summer Research Program: Foundational Training for Health Research.

Increasing the participation of students of African descent and other minoritized populations in the scientific workforce is imperative in generating a more equitable biomedical research infrastructure and increasing national research creativity and productivity. Undergraduate research training programs have shown to be essential tools in retaining underrepresented minority (URM) students in the sciences and attracting them into STEM and biomedical careers. This paper describes an innovative approach to harness students' entrepreneurial desire for autonomy and creativity in a Summer Research Institute (SRI) that has served as an entry point into a multiyear, National Institutes of Health Building Infrastructure Leading to Diversity (NIH BUILD)-funded research training program. The SRI was designed as an 8-week, student-centered and course-based research model in which students select their own research topics. We test here the effects of SRI training on students' science self-efficacy and science identity, along with several other constructs often associated with academic outcomes in the sciences. The data shown here comprise analysis of four different training cohorts throughout four subsequent summers. We show significant gains in students' science self-efficacy and science identity at the conclusion of SRI training, as well as academic adjustment and sense of belonging. SRI participants also displayed substantially improved retention in their science majors and graduation rates.

Trapping of a cross-link formed by a major purine adduct of a metabolite of the carcinogen N-nitrosomorpholine by inorganic and biological reductants.

3-Hydroperoxy-N-nitrosomorpholine in buffered aqueous media in the presence of calf thymus DNA was treated with a phosphine reductant to generate the transient α-hydroxynitrosamine and subsequent diazonium ion that alkylated the DNA, as previously reported. Subsequent addition of hydride donors, for 30 min, followed by acid hydrolysis of the mixture allowed detection and quantification of 6-(2-{2-[(9H-purin-6-yl)amino]ethoxy}ethoxy)-9H-purin-2-amine, the reduced cross-link formed from deposition, via the diazonium ion, of a 3-oxapentanal fragment on O(6)-Gua, and condensation with N(6)-Ade, presumably in the vicinity. Decreasing the temperature of the reaction mixtures and decreasing the pH modestly increased the yields of the trapped cross-link. Among three borohydride reductants, NaNCBH3 is superior, being ∼4 times more effective on a molar basis, as opposed to a hydride equivalent basis, than NaBH4 or Na(AcO)3BH. For trapping with NaNCBH3, it is deduced that the reaction likely occurs with the iminium ion that is in protonic equilibrium with its conjugate base imine. In an experiment in which the hydroperoxide was decomposed and NaNCBH3 was introduced after various periods of time, the amount of cross-link was observed to increase, nearly linearly, by ∼4-fold over 1 week. These data indicate that there are a minimum of two populations of cross-links, one that forms rapidly, in minutes, and another that grows in with time, over days. Reduced nicotinamide cofactors and ascorbate are observed to effect reduction (over 3 days) of the cross-links, confirming the possibility that otherwise reversible cross-links might be immortalized under biological conditions.

Lactone metabolite common to the carcinogens dioxane, diethylene glycol, and N-nitrosomorpholine: aqueous chemistry and failure to mediate liver carcinogenesis in the F344 rat.

1,4-Dioxan-2-one, 1, was synthesized, and the equilibrium constant between it and the hydrolysis product 2-(2-hydroxyethoxy) acetic acid, 2, was determined as K(O) = 70 ± 4 in acidic aqueous media, 25 °C, ionic strength 1 M (KCl), and 5% by volume acetonitrile. The carboxylic acid dissociation constant of 2 was determined under the same conditions to be pK(a) = 3.31 ± 0.02. On the basis of these two determinations, the equilibrium constant between 1 and carboxylic acid anion, 3, and the proton was calculated to be K(OA) = 0.034 ± 0.002 M. The stability of 1 was determined in the range of pH between 1 and 8.5 in buffered aqueous solutions under the conditions above by UV spectrophotometric methods and exhibited simple first order kinetics of decay. On the basis of buffer dilution plots, the values of k(o), the rate constant for solvent mediated decomposition, were determined. The plot of log k(o) against pH is consistent with a three term rate law for solvolysis with a hydrogen ion catalyzed rate constant k(H+) = 1.1 (±0.1) M(-1) min(-1), a water catalyzed rate constant, k(w) = 9.9 (±0.5) × 10(-4) min(-1), and a hydroxide ion catalyzed rate constant, k(OH) = 4.1 (±0.3) × 10(4) M(-1) min(-1). The t(1/2) for decay at pH 7.0, at 25 °C, is ∼2 h. Treatment of F344 rats with aflatoxin B(1) (AFB(1)) (positive control) elicited the expected preneoplastic foci in the livers of each rat tested, while subsequent administration of 1 (a total of 1.32 g over 12 weeks) failed to statistically increase focal number or focal volume percent. In 8 rats administered 1 (1.32 g, 12 weeks) alone, no increase above background foci was detected. This study does not support compound 1 as a common carcinogen.

Synthesis of modified nucleosides for incorporation of formyletheno and carboxyetheno adducts of adenine nucleosides into oligonucleotides.

Three protected derivatives of 1,N(6)-ethenoadenine nucleosides, viz. 3-[5-O-(4,4'-dimethoxytrityl) of 7-formyl-(1) and 7-(1,2-diacetyloxypropyl)-2'-deoxyadenosine (2), and 3-[5-O-(4,4'-dimethoxytrityl)-2-O-(tert-butyldimethylsilyl)-7-(ethoxycarbonyl)adenosine (3), expected to allow introduction of formyletheno and carboxyethenoadenine adducts into oligonucleotides by the conventional phosphoramidite chemistry, have been synthesized.

Reactions of 9-substituted guanines with bromomalondialdehyde in aqueous solution predominantly yield glyoxal-derived adducts.

Reactions of 9-ethylguanine, 2'-deoxyguanosine and guanosine with bromomalondialdehyde in aqueous buffers over a wide pH-range were studied. The main products were isolated and characterized by (1)H and (13)C NMR and mass spectroscopy. The final products formed under acidic and basic conditions were different, but they shared the common feature of being derived from glyoxal. Among the 1 : 1 adducts, 1,N(2)-(trans-1,2-dihydroxyethano)guanine adduct (6) predominated at pH < 6 and N(2)-carboxymethylguanine adduct (10a,b) at pH > 7. In addition to these, an N(2)-(4,5-dihydroxy-1,3-dioxolan-2-yl)methylene adduct (11a,b) and an N(2)-carboxymethyl-1,N(2)-(trans-1,2-dihydroxyethano)guanine adduct (12) were obtained at pH 10. The results of kinetic experiments suggest that bromomalondialdehyde is significantly decomposed to formic acid and glycolaldehyde under the conditions required to obtain guanine adducts. Glycolaldehyde is oxidized to glyoxal, which then modifies the guanine base more readily than bromomalondialdehyde. Besides the glyoxal-derived adducts, 1,N(2)-ethenoguanine (5a-c) and N(2),3-ethenoguanine adducts (4a-c) were formed as minor products, and a transient accumulation of two unstable intermediates, tentatively identified as 1,N(2)-(1,2,2,3-tetrahydroxypropano)(8) and 1,N(2)-(2-formyl-1,2,3-trihydroxypropano)(9) adducts, was observed.

Synthesis of an oligonucleotide analogue of ethenoadenosine.

A phosphoramidite building block derived from 11-carboxy-1,N6-ethenoadenosine has been prepared to be used in a solid supported oligonucleotide synthesis.