Radical intermediates in the addition of OH to propene: photolytic precursors and angular momentum effects.

We investigate the photolytic production of two radical intermediates in the reaction of OH with propene, one from addition of the hydroxyl radical to the terminal carbon and the other from addition to the center carbon. In a collision-free environment, we photodissociate a mixture of 1-bromo-2-propanol and 2-bromo-1-propanol at 193 nm to produce these radical intermediates. The data show two primary photolytic processes occur: C-Br photofission and HBr photoelimination. Using a velocity map imaging apparatus, we measured the speed distribution of the recoiling bromine atoms, yielding the distribution of kinetic energies of the nascent C3H6OH radicals + Br. Resolving the velocity distributions of Br((2)P(1/2)) and Br((2)P(3/2)) separately with 2 + 1 REMPI allows us to determine the total (vibrational + rotational) internal energy distribution in the nascent radicals. Using an impulsive model to estimate the rotational energy imparted to the nascent C3H6OH radicals, we predict the percentage of radicals having vibrational energy above and below the lowest dissociation barrier, that to OH + propene; it accurately predicts the measured velocity distribution of the stable C3H6OH radicals. In addition, we use photofragment translational spectroscopy to detect several dissociation products of the unstable C3H6OH radicals: OH + propene, methyl + acetaldehyde, and ethyl + formaldehyde. We also use the angular momenta of the unstable radicals and the tensor of inertia of each to predict the recoil kinetic energy and angular distributions when they dissociate to OH + propene; the prediction gives an excellent fit to the data.

Modeling the rovibrationally excited C2H4OH radicals from the photodissociation of 2-bromoethanol at 193 nm.

This study photolytically generates, from 2-bromoethanol photodissociation, the 2-hydroxyethyl radical intermediate of the OH + ethene reaction and measures the velocity distribution of the stable radicals. We introduce an impulsive model to characterize the partitioning of internal energy in the C(2)H(4)OH fragment. It accounts for zero-point and thermal vibrational motion to determine the vibrational energy distribution of the nascent C(2)H(4)OH radicals and the distribution of total angular momentum, J, as a function of the total recoil kinetic energy imparted in the photodissociation. We render this system useful for the study of the subsequent dissociation of the 2-hydroxyethyl radical to the possible asymptotic channels of the OH + ethene reaction. The competition between these channels depends on the internal energy and the J distribution of the radicals. First, we use velocity map imaging to separately resolve the C(2)H(4)OH + Br((2)P(3/2)) and C(2)H(4)OH + Br((2)P(1/2)) photodissociation channels, allowing us to account for the 10.54 kcal/mol partitioned to the Br((2)P(1/2)) cofragment. We determine an improved resonance enhanced multiphoton ionization (REMPI) line strength for the Br transitions at 233.681 nm (5p (4)P(1/2) <-- 4p (2)P(3/2)) and 234.021 nm (5p (2)S(1/2) <-- 4p (2)P(1/2)) and obtain a spin-orbit branching ratio for Br((2)P(1/2)):Br((2)P(3/2)) of 0.26 +/- 0.03:1. Energy and momentum conservation give the distribution of total internal energy, rotational and vibrational, in the C(2)H(4)OH radicals. Then, using 10.5 eV photoionization, we measure the velocity distribution of the radicals that are stable to subsequent dissociation. The onset of dissociation occurs at internal energies much higher than those predicted by theoretical methods and reflects the significant amount of rotational energy imparted to the C(2)H(4)OH photofragment. Instead of estimating the mean rotational energy with an impulsive model from the equilibrium geometry of 2-bromoethanol, our model explicitly includes weighting over geometries across the quantum wave function with zero, one, and two quanta in the harmonic mode that most strongly alters the exit impact parameter. The model gives a nearly perfect prediction of the measured velocity distribution of stable radicals near the dissociation onset using a G4 prediction of the C-Br bond energy and the dissociation barrier for the OH + ethene channel calculated by Senosiain et al. (J. Phys. Chem. A 2006, 110, 6960). The model also indicates that the excited state dissociation proceeds primarily from a conformer of 2-bromoethanol that is trans across the C-C bond. We discuss the possible extensions of our model and the effect of the radical intermediate's J-distribution on the branching between the OH + ethene product channels.

Sleep and activity rhythms are related to circadian phase in the blind.

STUDY OBJECTIVES: Sleep is controlled by both circadian and homeostatic mechanisms. As the light-dark cycle is the most important time cue in humans, blind individuals may have circadian rhythm disorders including sleep. The aim of the study was to assess sleep with simultaneous measurement of an endogenous marker of the circadian clock, namely 6-sulphatoxymelatonin (aMT6s). SETTING AND PARTICIPANTS: 59 registered blind subjects were studied in their own homes. DESIGN: Subjects completed daily sleep and nap diaries for at least four weeks, wore activity monitors continuously, and collected urine samples over 48 hours each week for 3-5 weeks for assessment of aMT6s rhythms. RESULTS: The most sensitive indicator of a circadian rhythm disorder was day-time napping. Subjects with normally entrained (NE) aMT6s rhythms had fewer naps of a shorter duration than abnormally entrained (AE) or free-running (FR) subjects. The timing of these naps was not random; significantly more naps occurred within a five-hour range before and after the aMT6s acrophase (phi (phi)) than outside this range. Disorders in the timing and duration of night sleep in AE subjects manifested as either a permanent advance (advanced sleep phase syndrome, ASPS) or delay (delayed sleep phase syndrome, DSPS). In FR subjects there were transient advances and delays in sleep timing that paralleled aMT6s timing with increased night sleep duration and reduced number and duration of day-time naps associated with a normal aMT6s phase. CONCLUSIONS: Changes in sleep and activity rhythms reflect changes in circadian phase.

Teamwork in pediatric trauma centers.

Various models have been proposed for optimal care of children in the trauma centers of general hospitals. The authors discuss the determinants of successful pediatric trauma care. In-house trauma surgeons, a consensus protocol for the first 20 minutes of resuscitation, real-time involvement of radiologists as part of the trauma team, and professional respect are the basis of teamwork.

Moving toward policy development on assigning publication credit for oncology nurses' contributions to scholarly and scientific work.

The policy implications of a 1996 national nursing survey on the allocation of publication credit form of this paper. An earlier article (Butler & Ginn, 1997) describes and analyzes the outcome of the survey; the purpose here is to draw on that analysis, and on the relevant literature, to propose a starting place for discussion within the specialty of oncology and the nursing profession regarding assignment of credit for various contributions to collaborative scholarly work. After identifying the growing need for such a discussion and briefly highlighting the findings of the survey, the paper goes on to examine unacceptable practices in scholarly work and identify issues which should be resolved before collaborative work is undertaken. The final portion of the paper makes tentative suggestions as to principles and guidelines which might be applied to avoid disputes about the value of different contributions to a collaborative project. It is emphasized that the intention is not to advocate acceptance of the guidelines suggested here, but to create sufficient interest so that an approach to allocation of publication credit may be developed which will be consistent and relevant to the needs of the nursing profession.

Providing care to patients with pancreatic cancer: a retrospective chart review.

Pancreatic cancer may be considered rare, yet in Canada it is the fourth leading cause of death by cancer in the elderly. This study was conducted in a large tertiary centre to determine the symptoms experienced by patients and the response by health professionals in providing supportive care. This paper reports the results of a retrospective review of health records from patients diagnosed with pancreatic cancer (n = 99). Results indicate that pain, nausea, vomiting, and anorexia were frequently reported. There was a lack of consistency in the documentation of nursing care and little evidence of an organized, planned approach for care delivery. The role of the interdisciplinary health care team and its members in managing this devastating disease and its impact on patient quality of life was difficult to ascertain. The development of an integrated approach to the care of patients with pancreatic cancer is presented.

Determining the partial photoionization cross-sections of ethyl radicals.

Using a crossed laser-molecular beam scattering apparatus, these experiments photodissociate ethyl chloride at 193 nm and detect the Cl and ethyl products, resolved by their center-of-mass recoil velocities, with vacuum ultraviolet photoionization. The data determine the relative partial cross-sections for the photoionization of ethyl radicals to form C2H5+, C2H4+, and C2H3+ at 12.1 and 13.8 eV. The data also determine the internal energy distribution of the ethyl radical prior to photoionization, so we can assess the internal energy dependence of the photoionization cross-sections. The results show that the C2H4++H and C2H3++H2 dissociative photoionization cross-sections strongly depend on the photoionization energy. Calibrating the ethyl radical partial photoionization cross-sections relative to the bandwidth-averaged photoionization cross-section of Cl atoms near 13.8 eV allows us to use these data in conjunction with literature estimates of the Cl atom photoionization cross-sections to put the present bandwidth-averaged cross-sections on an absolute scale. The resulting bandwidth-averaged cross-section for the photoionization of ethyl radicals to C2H5+ near 13.8 eV is 8+/-2 Mb. Comparison of our 12.1 eV data with high-resolution ethyl radical photoionization spectra allows us to roughly put the high-resolution spectrum on the same absolute scale. Thus, one obtains the photoionization cross-section of ethyl radicals to C2H5+ from threshold to 12.1 eV. The data show that the onset of the C2H4++H dissociative photoionization channel is above 12.1 eV; this result offers a simple way to determine whether the signal observed in photoionization experiments on complex mixtures is due to ethyl radicals. We discuss an application of the results for resolving the product branching in the O+allyl bimolecular reaction.

Characterization of the methoxy carbonyl radical formed via photolysis of methyl chloroformate at 193.3 nm.

This study investigates two features of interest in recent work on the photolytic production of the methoxy carbonyl radical and its subsequent unimolecular dissociation channels. Earlier studies used methyl chloroformate as a photolytic precursor for the CH3OCO, methoxy carbonyl (or methoxy formyl) radical, which is an intermediate in many reactions that are relevant to combustion and atmospheric chemistry. That work evidenced two competing C-Cl bond fission channels, tentatively assigning them as producing ground- and excited-state methoxy carbonyl radicals. In this study, we measure the photofragment angular distributions for each C-Cl bond fission channel and the spin-orbit state of the Cl atoms produced. The data shows bond fission leading to the production of ground-state methoxy carbonyl radicals with a high kinetic energy release and an angular distribution characterized by an anisotropy parameter, beta, of between 0.37 and 0.64. The bond fission that leads to the production of excited-state radicals, with a low kinetic energy release, has an angular distribution best described by a negative anisotropy parameter. The very different angular distributions suggest that two different excited states of methyl chloroformate lead to the formation of ground- and excited-state methoxy carbonyl products. Moreover, with these measurements we were able to refine the product branching fractions to 82% of the C-Cl bond fission resulting in ground-state radicals and 18% resulting in excited-state radicals. The maximum kinetic energy release of 12 kcal/mol measured for the channel producing excited-state radicals suggests that the adiabatic excitation energy of the radical is less than or equal to 55 kcal/mol, which is lower than the 67.8 kcal/mol calculated by UCCSD(T) methods in this study. The low-lying excited states of methylchloroformate are also considered here to understand the observed angular distributions. Finally, the mechanism for the unimolecular dissociation of the methoxy carbonyl radical to CH3 + CO2, which can occur through a transition state with either cis or, with a much higher barrier, trans geometry, was investigated with natural bond orbital computations. The results suggest donation of electron density from the nonbonding C radical orbital to the sigma* orbital of the breaking C-O bond accounts for the additional stability of the cis transition state.

Probing the barrier for CH2CHCO --> CH2CH + CO by the velocity map imaging method.

This work determines the dissociation barrier height for CH2CHCO --> CH2CH + CO using two-dimensional product velocity map imaging. The CH2CHCO radical is prepared under collision-free conditions from C-Cl bond fission in the photodissociation of acryloyl chloride at 235 nm. The nascent CH2CHCO radicals that do not dissociate to CH2CH + CO, about 73% of all the radicals produced, are detected using 157-nm photoionization. The Cl(2P(3/2)) and Cl(2P(1/2)) atomic fragments, momentum matched to both the stable and unstable radicals, are detected state selectively by resonance-enhanced multiphoton ionization at 235 nm. By comparing the total translational energy release distribution P(E(T)) derived from the measured recoil velocities of the Cl atoms with that derived from the momentum-matched radical cophotofragments which do not dissociate, the energy threshold at which the CH2CHCO radicals begin to dissociate is determined. Based on this energy threshold and conservation of energy, and using calculated C-Cl bond energies for the precursor to produce CH2CHC*O or C*H2CHCO, respectively, we have determined the forward dissociation barriers for the radical to dissociate to vinyl + CO. The experimentally determined barrier for CH2CHC*O --> CH2CH + CO is 21+/-2 kcal mol(-1), and the computed energy difference between the CH2CHC*O and the C*H2CHCO forms of the radical gives the corresponding barrier for C*H2CHCO --> CH2CH + CO to be 23+/-2 kcal mol(-1). This experimental determination is compared with predictions from electronic structure methods, including coupled-cluster, density-functional, and composite Gaussian-3-based methods. The comparison shows that density-functional theory predicts too low an energy for the C*H2CHCO radical, and thus too high a barrier energy, whereas both the Gaussian-3 and the coupled-cluster methods yield predictions in good agreement with experiment. The experiment also shows that acryloyl chloride can be used as a photolytic precursor at 235 nm of thermodynamically stable CH2CHC*O radicals, most with an internal energy distribution ranging from approximately 3 to approximately 21 kcal mol(-1). We discuss the results with respect to the prior work on the O(3P) + propargyl reaction and the analogous O(3P) + allyl system.

Chemical reaction dynamics beyond the Born-Oppenheimer approximation.

To predict the branching between energetically allowed product channels, chemists often rely on statistical transition state theories or exact quantum scattering calculations on a single adiabatic potential energy surface. The potential energy surface gives the energetic barriers to each chemical reaction and allows prediction of the reaction rates. Yet, chemical reactions evolve on a single potential energy surface only if, in simple terms, the electronic wavefunction can evolve from the reactant electronic configuration to the product electronic configuration on a time scale that is fast compared to the nuclear dynamics through the transition state. The experiments reviewed here investigate how the breakdown of the Born-Oppenheimer approximation at a barrier along an adiabatic reaction coordinate can alter the dynamics of and the expected branching between molecular dissociation pathways. The work reviewed focuses on three questions that have come to the forefront with recent theory and experiments: Which classes of chemical reactions evidence dramatic nonadiabatic behavior that influences the branching between energetically allowed reaction pathways? How do the intramolecular distance and orientation between the electronic orbitals involved influence the nonadiabaticity in the reaction? How can the detailed nuclear dynamics mediate the effective nonadiabatic coupling encountered in a chemical reaction?

A rapid modified fluorescence-plus-Giemsa technique for sister chromatid exchanges and DNA replication patterns.

Five different fluorochromes were tested, in a revised fluorescence-plus-Giemsa technique, for their ability to give good quality permanent preparations. Hoechst 33342 was found to give the best results. Slides were stained with Hoechst 33342, followed by exposure to long wavelength UV light with a simultaneous incubation in a hot alkaline solution, and then were Giemsa stained. This technique gives good quality preparations, in approximately 1 h, of sister chromatid exchanges or DNA replication patterns.

Automatic analysis of G-banded human chromosomes by fast scanning microscope photometry. 2. Practical applications.

The practical applications and improvements to a fast scanning microscope photometer system are described. The production of a density profile is demonstrated which, when taken in conjunction with the chromosome scan, allows more information to be extracted from the data than was previously possible. This enables a more accurate correlation to be made between phenotype and karyotype. The system is demonstrated on preparations of known cytogenetically abnormal individuals, showing the range of problems which can be tackled.

Classification of Y chromosome polymorphisms by DNA content and C-banding.

A system has been developed using a microscope photometer to measure the DNA content of individual chromosomes. After correcting for the systematic and statistical errors the measured values are highly reproducible. Data are presented of measurements of human Y chromosomes from a cytogenetically normal population. When compared with the C-banding pattern from the same specimens the DNA content is found to change in discrete steps of 1.36 x 10(-14)g or 13.26 x 10(6) bp for each of the Y chromosome polymorphic types.

A child trisomic for the distal part of chromosome 14q.

A child is described with multiple congenital abnormalities including microcephaly, odd facies, Fallot's tetralogy, and absent parathyroids. These were associated with partial trisomy for the distal half of the long arm of chromosome 14, the extra segment being translocated to the short arms of No 10. The main clinical problems were those related to the congenital heart disease and hypocalcaemia.

Automatic analysis of G-banded human chromosomes by fast scanning microscope photometry. I. Basic principles and computer control.

A high resolution scanning microscope photometry system has been developed for use with standard G-banded chromosome preparations. Various alternative scanning methods and their limitations are reviewed. The computer algorithms which we use are described for the manipulation of the digitized image as produced by the microscope photometer; these include noise reduction and contrast enhancement as well as altering the orientation of the chromosome.

Partial trisomy 3q causing mild Cornelia de Lange phenotype.

A brother and sister are reported with developmental delay and facial features suggestive of the Cornelia de Lange syndrome. Cytogenetic analysis showed them to be trisomic for the region 3q25.1-26.2 because of the inheritance of an unbalanced interchromosomal insertion from their father, who was a balanced insertion carrier. The clinical phenotype and cytogenetic analysis (including chromosome painting studies) in relation to the possible localisation of the Cornelia de Lange gene are discussed.

The trisomy (5)(q31-qter) syndrome: study of a family with a t(5:14) translocation.

We report a child with multiple malformations caused by trisomy for the distal part of the long arm of chromosome No 5. A neonatal diagnosis of Down's syndrome had previously been made on the basis of clinical examination and the detection of an additional chromosome not unlike No 21. A subsequent clinical re-evaluation, with the cooperation of the parents who permitted further studies, led to the confirmation of the true diagnosis. The mother was the carrier of a balanced translocation between chromosome No 5 and No 14. The child had severe growth and psychomotor retardation and characteristic features: microcephaly, antimongoloid slant, epicanthus, low set ears, down-turned mouth, and long upper lip. She was hypertonic and a congenital heart disease (atrial septal defect) was present. We have compared this case with others known to be trisomic for segment 5q31-qter.

A new interstitial deletion of chromosome No. 4 del(4) (q22::q25).

A female child is described with multiple anomalies including epicanthus, frontal bossing, short sternum, polydactyly, cleft of the larynx, renal cysts, and unusual dermatoglyphics. She died aged 3 months and was found to have a unique de novo deletion of chromosome No. 4 (q22-q25). This case is compared with other long arm deletions of 4q and reference made to assignment of genetic markers to chromosome No. 4.

193-nm photodissociation of acryloyl chloride to probe the unimolecular dissociation of CH2CHCO radicals and CH2CCO.

The work presented here uses photofragment translational spectroscopy to investigate the primary and secondary dissociation channels of acryloyl chloride (CH2==CHCOCl) excited at 193 nm. Three primary channels were observed. Two C-Cl fission channels occur, one producing fragments with high kinetic recoil energies and the other producing fragments with low translational energies. These channels produced nascent CH2CHCO radicals with internal energies ranging from 23 to 66 kcal/mol for the high-translational-energy channel and from 50 to 68 kcal/mol for the low-translational-energy channel. We found that all nascent CH2CHCO radicals were unstable to CH2CH + CO formation, in agreement with the G3//B3LYP barrier height of 22.4 kcal/mol to within experimental and computational uncertainties. The third primary channel is HCl elimination. All of the nascent CH2CCO coproducts were found to have enough internal energy to dissociate, producing CH2C: + CO, in qualitative agreement with the G3//B3LYP barrier of 39.5 kcal/mol. We derive from the experimental results an upper limit of 23 +/- 3 kcal/mol for the zero-point-corrected barrier to the unimolecular dissociation of the CH2CHCO radical to form CH2CH + CO.