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PubMed2000

Attenuation mechanisms of N-nitrosodimethylamine at an operating intercept and treat groundwater remediation system.

The North Boundary Containment System (NBCS), an intercept-and-treat system, was established at Rocky Mountain Arsenal (RMA), Commerce City, CO, to remove low-level organic contaminants from a groundwater plume exiting RMA to the north and northwest. N-nitrosodimethylamine (NDMA) was detected in groundwater collected from the dewatering and recharge zones of the NBCS system. Concern over the fate of NDMA, in terms of potentially exiting the boundaries of the arsenal, prompted an investigation to evaluate potential attenuation mechanisms for NDMA within the alluvial aquifer system and within the NBCS itself. Groundwater, soil, and granular activated carbon (GAC) samples were taken from key locations in the NBCS system. Soil and GAC samples were assayed for sorption kinetics and for adsorption and desorption properties using 14C-labeled NDMA. NDMA biodegradation experiments were conducted by following 14CO(2) evolution from 14C-labeled NDMA in soils and GAC samples under aerobic and anaerobic conditions. The sorptive capacity of the site soils for NDMA was insignificant. Furthermore, the adsorption of the NDMA by the soil was almost completely reversible. Evaluation of the degradation potential of the native microbial consortia indicated a high level of NDMA mineralization when measured using bench-scale microcosms. The native consortia had capability to mineralize the NDMA under both aerobic and anaerobic incubations, indicating facultative characteristics. Testing of the local groundwater chemistry revealed that the area of the aquifer of interest was microaerobic and neutral in pH. These conditions were optimal for NDMA removal. While sorption was insignificant, degradation was a significant attenuation mechanism, which may be the reason that no NDMA has migrated off-site. This gives rise to the potential of a long-term sink for attenuating NDMA within the recharge zone of the treatment system.

Adsorption↗
PubMed2006

Intercepting palladacycles derived by C-H insertion. A mechanism-driven entry to heterocyclic tetraphenylenes.

Mechanistic support for the intermediacy of a palladacycle, which has been implicated in the crossover Heck reaction, has been obtained by intercepting this species using biphenylene. This leads to the formation of heterocyclic tetraphenylene derivatives. Three examples of this process are reported, and in two cases, the product structures have been confirmed by X-ray crystallographic analysis.

Journal Article↗
PubMed2000

Ru(II)- and Pt(II)-catalyzed cycloisomerization of omega-aryl-1-alkynes. Generation Of carbocationic species from alkynes and transition metal halides and its interception by an aromatic ring

The treatment of aryl-1-alkynes, such as 4-aryl-1-butyne, 5-aryl-1-pentyne, and 6-aryl-1-hexyne, with catalytic amounts of transition metal chlorides, such as PtCl(2) and [RuCl(2)(CO)(3)](2), at 80 degrees C in toluene results in cycloisomerization to give dihydronaphthalenes or dihydrobenzocycloheptenes, in which the cyclization mode is dependent on the length of the tethers. The reaction is limited to substrates containing terminal alkynes. A key step of the reaction is the intramolecular interception by an aromatic ring of the vinylmetal complex 2, which contains a cation center at the beta-position, generated from the electrophilic addition of transition metal halides toward an alkyne. The more electron-rich aryl systems are more reactive.

Journal Article↗
PubMed2005

Studies on taxadiene synthase: interception of the cyclization cascade at the isocembrene stage with GGPP analogues.

[reaction: see text] The cyclization of GGPP to taxadiene, catalyzed by taxadiene synthase, has been suggested to proceed through a series of monocyclic isocembrenyl- and bicyclic verticillyl-carbocationic intermediary stages. A set of GGPP analogues with abolished or perturbed pi-nucleophilicity at the delta10 double bond (GGPP numbering) was synthesized and incubated with taxadiene synthase to intercept the cyclization cascade at the monocyclic stage. Each analogue was transformed by taxadiene synthase in vitro to hydrocarbon products in varying yields, and the structures of the major product in each reaction were solved by GCEIMS and one- and two-dimensional (1H and 13C) NMR and found to be 14-membered monocyclic isocembrenyl diterpenes, indicating that the first C-C bond formation catalyzed by taxadiene synthase could be uncoupled from the other subsequent bond formation events by using suitably designed substrate analogues. The formation and isolation of these isocembrenyl diterpene products using taxadiene synthase supports proposals that the isocembrenyl cation is an intermediate in the cyclization of GGPP to taxadiene.

Alkenes↗
PubMed2006

Ortho effect in the Bergman cyclization: interception of p-benzyne intermediate by intramolecular hydrogen abstraction.

Intramolecular hydrogen atom (H-atom) abstraction from the o-OCH3 group effectively intercepts the p-benzyne intermediate in the Bergman cycloaromatization of 2,3-diethynyl-1-methoxybenzene (1) before this intermediate undergoes either retro-Bergman ring opening or external H-atom abstraction. This process leads to the formation of a new diradical and renders the cyclization step essentially irreversible. Chemical and kinetic consequences of this phenomenon were investigated through the combination of computational and experimental studies.

Journal Article↗
PubMed2000

Interception of Deaminatively Generated Benzyl Carbenium Ions by Acetone.

Essentially free benzyl carbenium ions were generated via protonation of phenyldiazomethane with benzoic acid in acetone. Interestingly, no proton transfer occurred below -20 degrees C. After protonation and dediazoniation of the diazoalkane at -20 degrees C, the solvent was found to intercept the deaminatively generated carbocations to yield initially the corresponding O-benzyl oxonium ion and benzyl benzoate. The onium ion, however, was labile under the reaction conditions, and decomposed into a cascade of products whose concentrations as a function of time were used to trace the reaction pathway. Thus, the O-benzyl oxonium ion reacted with benzoate ion to yield (2-benzyloxy)isopropyl benzoate; subsequent decomposition of this O-benzyl-O-benzoyl ketal produced 2,2-dibenzyloxypropane (a dibenzyl ketal), 2-benzyloxypropene, and benzyl alcohol. In a related study, benzyl cations were generated via thermolyses of N-benzyl-N-nitroso-O-benzoyl hydroxylamine at 0 and -70 degrees C. The product distributions were found to be temperature-dependent and different from that in the PhCHN(2) + PhCO(2)H case.

Journal Article↗
PubMed2006

Lateral interception II: predicting hand movements.

D. M. Jacobs and C. F. Michaels (2006) concluded that aspects of hand movements in lateral catching were predicted by the ratio of lateral optical velocity to expansion velocity. Their conclusions were based partly on a modified version of the required velocity model of catching (C. E. Peper, R. J. Bootsma, D. R. Mestre, & F. C. Bakker, 1994). The present article considers this optical ratio in detail and asks whether it, together with a control law, predicts the (often curious) hand trajectories observed in lateral interception. The optical ratio was used to create a succession of target-position inputs for the vector integration to endpoint model of hand movements (D. Bullock & S. Grossberg, 1988). The model used this succession, initial hand position, and model parameters (fit to 60 trials) to predict hand trajectories on each trial. Predicted trajectories were then compared with observed hand trajectories. Hand movements were predicted accurately, especially in the binocular condition, and were superior to predictions based on lateral ball position, the input variable of the required velocity model. The authors concluded, as did C. E. Peper et al. (1994), that perceivers continuously couple movements to optics.

Attention↗
PubMed2002

The mechanism of nitrogen monoxide (NO)-mediated iron mobilization from cells. NO intercepts iron before incorporation into ferritin and indirectly mobilizes iron from ferritin in a glutathione-dependent manner.

Nitrogen monoxide (NO) is a cytotoxic effector molecule produced by macrophages that results in Fe mobilization from tumour target cells which inhibits DNA synthesis and mitochondrial respiration. It is well known that NO has a high affinity for Fe, and we showed that NO-mediated Fe mobilization is markedly potentiated by glutathione (GSH) generated by the hexose monophosphate shunt [Watts, R.N. & Richardson, D.R. (2001) J. Biol. Chem. 276, 4724-4732]. We hypothesized that GSH completes the coordination shell of an NO[bond]Fe complex that is released from the cell. In this report we have extended our studies to further characterize the mechanism of NO-mediated Fe mobilization. Native PAGE 59Fe-autoradiography shows that NO decreased ferritin-59Fe levels in cells prelabelled with [59Fe]transferrin. In prelabelled cells, ferritin-59Fe levels increased 3.5-fold when cells were reincubated with control media between 30 and 240 min. In contrast, when cells were reincubated with NO, ferritin-59Fe levels decreased 10-fold compared with control cells after a 240-min reincubation. However, NO could not remove Fe from ferritin in cell lysates. Our data suggest that NO intercepts 59Fe on route to ferritin, and indirectly facilitates removal of 59Fe from the protein. Studies using the GSH-depleting agent, L-buthionine-(S,R)-sulphoximine, indicated that the reduction in ferritin-59Fe levels via NO was GSH-dependent. Competition experiments with NO and permeable chelators demonstrated that both bind a similar Fe pool. We suggest that NO requires cellular metabolism in order to effect Fe mobilization and this does not occur via passive diffusion down a concentration gradient. Based on our results, we propose a model of glucose-dependent NO-mediated Fe mobilization.

Adenocarcinoma↗
PubMed1983

STS 557 as an interceptive in baboons.

STS 557 (17 alpha-cyanomethyl-17 beta-hydroxy-estra-4, 9-dien-3-one) or levonorgestrel was given orally as a single dose of 0.4 mg per animal. Treatment was performed immediately after the 18 h or 6 h mating period. Regarding the 18 h mating period, in 30 control cycles (20 animals) 11 pregnancies (36.7%) and in 20 cycles (16 animals) with levonorgestrel treatment 2 pregnancies (10.0%) were observed. In 80 cycles (31 animals) with STS 557 treatment 7 pregnancies occurred (8.7%). With regard to the 6 h mating period, in 30 control cycles (18 animals) 9 pregnancies (30%) and in 26 cycles (17 animals) with levonorgestrel administration 3 pregnancies were recorded (11.5%). In 50 cycles (21 animals) with postcoital administration of STS 557 only two pregnancies occurred (4%). Therefore, after the 6 h mating period STS 557 showed high interceptive activities in this non-human primate model. In comparison with controls, STS 557 did not decrease the postovulatory rise of plasma progesterone. This finding demonstrates that postcoital STS 557 in the chosen dosage does not suppress ovulation. Repeated STS 557 administration starting early in the follicular phase was without marked influence on cycle characteristics. On the other hand, treatment start in the middle or at the end of the cycle caused cycle lengthening and reduced progesterone levels in some animals.

Animals↗
PubMed1996

The Y-intercept of the maximal work-duration regression and field tests of anaerobic capacity in cyclists.

The purpose of the present study was to provide initial data upon which field tests of anaerobic capacity for cyclists might be developed, by examining the relationships between the y-intercept of the maximal work-duration regression (Y-int) and cycle performance variables in fifteen well-trained male cyclists (mass = 73.3 +/- 8.6 kg; VO2peak = 4.93 +/- 0.70 l.min-1). The Y-int was determined from three maximal supra-VO2peak cycle bouts varying in duration from 195 to 369 s. Each cyclist performed two performance tests: 1) an all-out cycle sprint over 1000 m (AOS) during which the accumulated time over intervals of 125 m (e.g., AOS125, AOS250, etc. was recorded; 2) a 2-by-2000 m ride from which an "anaerobic distance" (Anl) was determined as the product of anaerobic speed (i.e. average speed during a second, maximal 2000 m time-trial minus the average speed during a 20 km time-trial) and time taken to complete the maximal 2000 m ride. The frontal area (FA) of each cyclist and common values for air density, work efficiency and the drag coefficient were used to estimate the energy equivalent of Anl. The Y-int was 20.0 +/- 9.4 kJ or 278 +/- 128 J.kg-1. The Y-int (J.FA-1) was correlated (p < or = 0.05) with AOS250 (r = -0.50), AOS375 (r = -0.53) and AOS625 (r = -0.50) which were 21.5 +/- 1.1 s, 30.1 +/- 1.3 s and 47.5 +/- 1.9 s long, respectively. The Y-int (kJ) was also correlated with AOS375 (r = -0.51), but Y-int (kJ) was not correlated with a performance variable lasting longer than approximately 30 s. The energy equivalent of Anl (91.5 +/- 26.0 kJ) was similar to the energy equivalent for Y-int (90.9 +/- 43 kJ), although these two variables were not significantly correlated. However, given the potential sources of variance in determining both of these variables, their quantitative similarity provides limited evidence supporting the use of Anl to estimate anaerobic capacity. The results also support the use of an all-out sprint performance lasting between 20-30 s to best reflect anaerobic work capacity in cyclists.

Adult↗
PubMed1998

Fast-reacting thiols in rat hemoglobins can intercept damaging species in erythrocytes more efficiently than glutathione.

The S-conjugation rates of the free-reacting thiols present on each component of rat hemoglobin with 5,5-dithio-bis(2,2-nitrobenzoic acid) (DTNB) have been studied under a variety of conditions. On the basis of their reactivity with DTNB (0.5 mM), three classes of thiols have been defined as follows: fast reacting (fHbSH), with t1/2 <100 ms; slow reacting (sHbSH), with t1/2 30-50 s; and very slow reacting (vsHbSH), with t1/2 180-270 s. Under paraphysiological conditions, fHbSH (identified with Cys-125beta(H3)) conjugates with DTNB 100 times faster than glutathione and approximately 4000 times more rapidly than (v)sHbSH (Cys-13alpha(A11) and Cys-93beta(F9)). Such characteristics of fHbSH reactivity that are independent of the quaternary state of hemoglobin are mainly due to the following: (i) its low pK (approximately 6.9, the cysteinyl anion being stabilized by a hydrogen bond with Ser-123beta(H1)) and (ii) the large exposure to the solvent (as measured by analysis of a model of the molecular surface) and make these thiols the kinetically preferred groups in rat erythrocytes for S-conjugation. In addition, because of the high cellular concentration (8 mM, i.e. four times that of glutathione), fHbSHs are expected to intercept damaging species in erythrocytes more efficiently than glutathione, thus adding a new physiopathological role (direct involvement in cellular strategies of antioxidant defense) to cysteinyl residues in proteins.

Animals↗
PubMed2006

Food-purchasing patterns for home: a grocery store-intercept survey.

OBJECTIVES: To identify the most common frequency of food-purchasing patterns and relate this pattern to characteristics of individuals and families. DESIGN: A customer-intercept survey was conducted in the greater Houston area, Texas, USA, in 2002. The frequency of food shopping at supermarkets, convenience stores and restaurants to buy food for eating at home was assessed. SUBJECTS: A total of 823 adults (78.5% female; mean age 37.4 years) who went to any of several grocery or convenience stores, including European, Hispanic and African Americans, and Asian/Pacific Islanders. RESULTS: Major food-shopping patterns were a weekly big trip with a few small trips (34.9%), biweekly big trips with a few small trips (21.9%), no big shopping trips (15.4%), a weekly big trip without small trips (13.9%), a monthly big trip (8.3%), and biweekly big trips without small trips (6.4%). While 61.1% of participants never went to convenience stores to buy fruit and vegetables (F&V) for eating at home, 67% went to restaurants for F&V. African American families shopped for food least frequently, while Asian American families shopped for food most frequently. Educational level was negatively associated with the use of convenience stores and positively associated with take-away from restaurants. CONCLUSIONS: There is substantial variability in the frequency of food shopping. Future research on food shopping should incorporate this variable.

Adult↗
PubMed1999

Intercepting Moving Objects During Self-Motion.

It is generally assumed that in catching a fly ball, an efficient strategy for dealing with the horizontal component of the ball's trajectory is for the observer to keep the angular position of the ball constant with respect to his head. That strategy is called the constant bearing angle or CBA strategy. Maintenance of angular constancy results in the simultaneous arrival of both observer and ball at the landing spot. The authors analyzed the approach behavior of 26 subjects in a ball-interception task with straight paths for both the subjects and the ball. Subjects moved at a velocity that maintained a close-to-constant horizontal angular position of the ball with respect to the end effector throughout the approach phase rather than a constant bearing angle with respect to their head. Velocity adaptations occurred as a function of the changes in the angular velocity of the ball in such a way that a positive or negative angular velocity was canceled. Thus, an actor following the CBA strategy does not need to know where and when the ball will arrive (i.e., a predictive strategy), because reliance on the CBA strategy ensures that he will make the appropriate adaptations that enable him to arrive at the right place in the right time.

Journal Article↗
PubMed2005

The continuous nature of timing reprogramming in an interceptive task.

The time course of movement timing reprogramming was examined in a task requiring temporal coincidence of the conclusion of a forehand drive with the arrival of a moving luminous target at the end of an electronic trackway. The moving target departed from one end of the trackway at a constant velocity of 2 m (.) s(-1), and for a part of the trials its velocity was increased to 3 m (.) s(-1). Target velocity was modified at different moments during stimulus displacement, producing times-to-arrival after velocity increment (TAVIs) from 100 to 600 ms. The effect of specific practice on movement reprogramming was also examined. The results showed early adjustments to the action (TAVIs = 100 - 200 ms) that seemed to be stereotyped, while feedback-based corrections were implemented only at TAVIs of 300 ms or longer. Temporal accuracy was progressively increased as longer TAVIs were provided up to 600 ms. Skill training led to an overall increment of temporal accuracy, but no effect of specific practice was found. The results indicate that timing reprogramming in interceptive actions is a continuous process limited mainly by intrinsic factors: latency to initiate more effective adjustments to the action, and rate-of-movement timing reprogramming.

Adaptation, Physiological↗
PubMed2002

Age-related differences in vision and proprioception in a lower limb interceptive task: the effects of skill level and practice.

This study examined age-related differences in the role of visual proprioception during a lower limb interceptive action and how this varies as a function of skill and practice. In Experiment 1, skilled and less-skilled 8-, 10-, and 12-year-old boys controlled a soccer ball using their preferred foot under full vision and when sight of the effector was occluded. With the exception of the high-skilled 12-year-olds and low-skilled 8-year-olds, participants showed a decrement in peformance when denied access to visual proprioception. In Experiment 2, the effect of practicing under different informational constraints was examined for 12 year-old boys. Children performed varying amounts of practice under full vision, or in a condition where sight of the foot was occluded, before being transferred to the alternative viewing condition. Participants who practiced under occluded viewing conditions showed greater relative improvement in performance over practice and transfer sessions compared with a full vision control group. Some support is provided for the manipulation of visual informational constraints as an effective pedagogical approach to motor learning.

Age Factors↗
PubMed1993

Illicit drug use by young people in sydney: results of a street intercept survey.

To complement existing institution-based drug use surveys, a street intercept survey of 581 young illicit drug users was conducted in Sydney, Australia. Patterns of use, reasons for use and awareness of the health risks associated with use were investigated. The most commonly used illicit drug type, after marijuana, was amphetamines. The least popular illicit drug was heroin. Most of the sample used occasionally, exhibiting a controlled pattern of use with a low prevalence of problems associated with use. Heroin users, in contrast, were often frequent users and reported a higher prevalence of associated problems. The majority of the sample reported excessive drinking patterns, indicating that the current policy of emphasis on alcohol misuse rather than illicit drug use amongst youth is appropriate.

Journal Article↗
PubMed2006

Mixture of normal distributions in multivariate null intercept measurement error model.

In this paper we propose the use of a multivariate null intercept measurement error model, where the true unobserved value of the covariate follows a mixture of two normal distributions. The proposed model is applied to a dental clinical trial presented in Hadgu and Koch (1999). A Bayesian approach is considered and a Gibbs Sampler is used to perform the computations.

Algorithms↗
PubMed2005

Visual perception and interception of falling objects: a review of evidence for an internal model of gravity.

Prevailing views on how we time the interception of a moving object assume that the visual inputs are informationally sufficient to estimate the time-to-contact from the object's kinematics. However, there are limitations in the visual system that raise questions about the general validity of these theories. Most notably, vision is poorly sensitive to arbitrary accelerations. How then does the brain deal with the motion of objects accelerated by Earth's gravity? Here we review evidence in favor of the view that the brain makes the best estimate about target motion based on visually measured kinematics and an a priori guess about the causes of motion. According to this theory, a predictive model is used to extrapolate time-to-contact from the expected kinetics in the Earth's gravitational field.

Adaptation, Physiological↗