Triple oxygen isotope analysis of nitrate using the denitrifier method and thermal decomposition of N2O

Interaction with ozone transfers its anomalous (non-mass-dependent) 17O enrichment to atmospheric nitrogen oxides and nitrate. The 17O anomaly (Delta17O) in nitrate can be used to identify atmospheric nitrate inputs into terrestrial and aquatic environments as well as to study the role of ozone in the atmosphere's reactive nitrogen cycle. We report here on an online method for analysis of the 17O anomaly, using a strain of denitrifiers to convert nitrate to N2O, which decomposes quantitatively to N2 and O2 in a gold furnace at 800 degrees C, followed by gas chromatographic separation and isotope analysis of O2. This method requires approximately 50 nmol of nitrate, 2-3 orders of magnitude less than previous offline thermal decomposition methods to achieve a similar analytical precision of 0.5 per thousand for Delta17O. There is no significant memory effect, but calibration via nitrate or N2O reference materials is required for scale normalization. The N2O decomposition method is shown to be well-suited for nitrate analysis in freshwater and seawater samples from various environments.     

Individualization of gasoline samples by covariance mapping and gas chromatography/mass spectrometry

A set of 10 fresh (unevaporated) gasoline samples from a single metropolitan area were differentiated based on a covariance mapping method combined with a t-test statistic. The covariance matrix for each sample was calculated from the retention time-ion abundance data set obtained by gas chromatography/mass spectrometry analysis. Distance metrics were calculated between the covariance matrices from replicate analyses of the same sample and between the replicate analyses of different samples. The distance metric for the same-sample comparisons were shown to constitute a population significantly different from the distance metric for the different-sample comparisons. A power analysis was performed to estimate the number of analyses needed to discriminate between two samples while maintaining a probability of type II error, beta, below 1%, e.g., a test power greater than 99%. Triplicate analyses of two gasoline samples was shown to be sufficient to discriminate between the two using a t-test, while keeping beta<0.01 at a significance level, alpha, of 0.05. Analysis of the 45 possible pairwise comparisons between samples found that 100% of the samples were statistically distinguishable, and no type II errors occurred. Blind tests were conducted wherein 2 of the 10 gasoline samples where presented as unknowns. One of the unknowns was found to be indistinguishable from the original source, and one unknown was determined to be statistically different from the original source, constituting a type I error. The effects of evaporation on sample comparison are not addressed in this paper. The results from this study demonstrate a statistically acceptable method of physical evidence comparison in forensic casework.     

Infant attention in relation to intellectual abilities in childhood.

Infant attention was observed at term and 4 mo of age in 93 preterm infants who were tested with the Wechsler Intelligence Scale for Children—Revised (WISC—R) at 8 yrs of age. Results show that for the term measure, total fixation time on the first 1-min trial to a repeated 2 by 2 checkerboard was negatively related to the childhood intelligence assessments for the entire sample and for the subset of Ss (n?=?61) from English-speaking families. For the 4-mo measure, the percentage of decrement in 1st fixation time over 1 min of repeated presentations of a 24 by 24 checkerboard was positively correlated with IQ scores for the English-speaking subsample. It is concluded that preterm infants who continued to fixate an unchanging stimulus for protracted periods of time were less intellectually able in childhood. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modeling longitudinal change in the language abilities of children with autism: Parent behaviors and child characteristics as predictors of change.

The objective of the current study was to evaluate the patterns of longitudinal change in the language abilities of 28 children with autism during early and middle childhood. Results from fitting a series of multilevel models showed that children's rate of language growth was independently predicted by (a) children's responsiveness to others' bids for joint attention and (b) parents' responsiveness to their children's attention and activity during play. Both predictive relations could not be explained by initial variation in global developmental characteristics, such as IQ, mental age, or language abilities. These findings support a social?pragmatic view on language acquisition, which emphasizes the collaborative process through which children and their parents negotiate shared meaning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterizing interactions between anxious mothers and their children.

The present study assessed interactions between anxious mothers and their children, using observational techniques to elucidate potential mechanisms of anxiety transmission. Results revealed that anxious mothers were less warm and positive in their interactions with their children, less granting of autonomy, and more critical and catastrophizing in comparison with normal control mothers. Maternal anxiety status appeared to be the primary predictor of maternal warmth during interactions. Child anxiety status was most predictive of maternal granting of autonomy behavior. Maternal behaviors exhibited during interactions were the most salient predictors of child anxiety. Interventions focusing on family interactions that take into account the contributions of both members of the dyad may be more effective in curbing transmission than interventions that solely address maternal or child symptomatology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Imparting catalyst control upon classical palladium-catalyzed alkenyl C-H bond functionalization reactions

The functional group transformations carried out by the palladium-catalyzed Wacker and Heck reactions are radically different, but they are both alkenyl C-H bond functionalization reactions that have found extensive use in organic synthesis. The synthetic community depends heavily on these important reactions, but selectivity issues arising from control by the substrate, rather than control by the catalyst, have prevented the realization of their full potential. Because of important similarities in the respective selectivity-determining nucleopalladation and β-hydride elimination steps of these processes, we posit that the mechanistic insight garnered through the development of one of these catalytic reactions may be applied to the other. In this Account, we detail our efforts to develop catalyst-controlled variants of both the Wacker oxidation and the Heck reaction to address synthetic limitations and provide mechanistic insight into the underlying organometallic processes of these reactions. In contrast to previous reports, we discovered that electrophilic palladium catalysts with noncoordinating counterions allowed for the use of a Lewis basic ligand to efficiently promote tert-butylhydroperoxide (TBHP)-mediated Wacker oxidation reactions of styrenes. This discovery led to the mechanistically guided development of a Wacker reaction catalyzed by a palladium complex with a bidentate ligand. This ligation may prohibit coordination of allylic heteroatoms, thereby allowing for the application of the Wacker oxidation to substrates that were poorly behaved under classical conditions. Likewise, we unexpectedly discovered that electrophilic Pd-σ-alkyl intermediates are capable of distinguishing between electronically inequivalent C-H bonds during β-hydride elimination. As a result, we have developed E-styrenyl selective oxidative Heck reactions of previously unsuccessful electronically nonbiased alkene substrates using arylboronic acid derivatives. The mechanistic insight gained from the development of this chemistry allowed for the rational design of a similarly E-styrenyl selective classical Heck reaction using aryldiazonium salts and a broad range of alkene substrates. The key mechanistic findings from the development of these reactions provide new insight into how to predictably impart catalyst control in organometallic processes that would otherwise afford complex product mixtures. Given our new understanding, we are optimistic that reactions that introduce increased complexity relative to simple classical processes may now be developed based on our ability to predict the selectivity-determining nucleopalladation and β-hydride elimination steps through catalyst design.     

Engineering of DNA binding proteins into site-specific cutters: reactivity of Trp repressor-1,10-phenanthroline chimeras

Trp repressor (TrpR) can be converted into a site-specific nucleateby chemical modification of the cysteine mutants TrpR D46C orTrpR E49C with 5-iodoacetamido-l,10-phenanthroline (OP). Inthe presence of cupric ion and 3-mercaptopropionic acid, TrpR-regulatedoperators are cleaved. The properties of these semisyntheticscission reagents have been compared. The E49C construct cleavesefficiently at two sites within the operator and the D46C cleavesat multiple sites. Molecular modeling indicates that the reasonfor the focused reactivity of E49C is that the OP is rigidlyoriented in the protein-DNA complexes whereas the OP can adoptseveral orientations in TrpR D46C. Mutations and reaction conditionsthat increase the affinity of the repressor enhance the scissionefficiency which approaches 100% within the acrylamide matrix.TrpR E49C-OP smoothly cleaves the trpEDCBA operator in a plasmidin a reaction dependent on the corepressor L-tryptophan. Inthe absence of tryptophan, non-specific cleavage of the plasmidis observed under the same conditions. Therefore, tryptophannot only directs cleavage to a specific site but also blocksit at non-specific sites. The analysis of the cleavage patternof the trpEDCBA operator provides strong evidence for the tandembinding model in which protein-protein interactions stabilizebinding on the DNA. TrpR E49C-OP should serve as the basis forthe engineering of a family of highly specific semisyntheticscission reagents.