Observation of Enhanced Dissociative Photochemistry in the Non-Native Nucleobase 2-Thiouracil.

We present the first study to measure the dissociative photochemistry of 2-thiouracil (2-TU), an important nucleobase analogue with applications in molecular biology and pharmacology. Laser photodissociation spectroscopy is applied to the deprotonated and protonated forms of 2-TU, which are produced in the gas-phase using electrospray ionization mass spectrometry. Our results show that the deprotonated form of 2-thiouracil ([2-TU-H]) decays predominantly by electron ejection and hence concomitant production of the [2-TU-H]· free-radical species, following photoexcitation across the UVA-UVC region.

Auto-titrating CPAP for the treatment of obstructive sleep apnea in children.

Study Objectives: In-laboratory titration polysomnography (PSG) is standard to determine optimal therapeutic continuous positive airway pressure (CPAP) in children with obstructive sleep apnea (OSA). The use of auto-titrating CPAP devices (autoCPAP) as an alternative to CPAP titration has not been well studied in children. We hypothesized that autoCPAP-derived pressures (P, P, P) would be similar to titration PSG pressure (P).

Mapping the intrinsic absorption properties and photodegradation pathways of the protonated and deprotonated forms of the sunscreen oxybenzone.

Sunscreens provide vital protection against the photodamaging effects of UV radiation, however, many fundamental questions remain about the detailed mechanisms by which they dissipate UV energy. One such issue is the extent to which the pH environment of an organic sunscreen molecule alters its effectiveness, both in terms of ability to absorb UV radiation, and also its potential to photodegrade. Here, we use gas-phase laser photodissociation spectroscopy for the first time to measure the intrinsic UVA-UVC absorption spectra and associated photodegradation products of protonated and deprotonated oxybenzone, away from the complications of bulk mixtures.

Observation of Near-Threshold Resonances in the Flavin Chromophore Anions Alloxazine and Lumichrome.

Lumichrome (LC) is the chromophore of the flavin family of photoactive biomolecules, where key biochemical activity involves interplay between redox and photophysical events. Questions remain about the relationship between the redox status of the ground and excited states and demand an improved understanding of the intrinsic photochemistry. Using anion photodissociation spectroscopy, we have measured the intrinsic electronic spectroscopy (564-220 nm) and accompanying photodegradation pathways of the deprotonated anionic form of LC.

Protomer-Dependent Electronic Spectroscopy and Photochemistry of the Model Flavin Chromophore Alloxazine.

Flavin chromophores play key roles in a wide range of photoactive proteins, but key questions exist in relation to their fundamental spectroscopic and photochemical properties. In this work, we report the first gas-phase spectroscopy study of protonated alloxazine (AL∙H⁺), a model flavin chromophore. Laser photodissociation is employed across a wide range (2.

Photoexcitation of iodide ion-pyrimidine clusters above the electron detachment threshold: Intracluster electron transfer versus nucleobase-centred excitations.

Laser photodissociation spectroscopy of the I·thymine (I·T) and I·cytosine (I·C) nucleobase clusters has been conducted for the first time across the regions above the electron detachment thresholds to explore the excited states and photodissociation channels. Although photodepletion is strong, only weak ionic photofragment signals are observed, indicating that the clusters decay predominantly by electron detachment. The photodepletion spectra of the I·T and I·C clusters display a prominent dipole-bound excited state (I) in the vicinity of the vertical detachment energy (∼4.

Experiment and theory confirm that UV laser photodissociation spectroscopy can distinguish protomers formed via electrospray.

The identification of protonation sites in electrosprayed molecules remains a challenge in contemporary physical science. We present the first demonstration that low-resolution, UV laser photodissociation spectroscopy can be applied in situ to identify the protomers of para-aminobenzoic acid (PABA) formed via electrospray from a single solution. Electronic absorption spectra are recorded via photodepletion and photofragmentation for PABA electrosprayed from solutions of water and acetonitrile.

Self-Efficacy and Short-Term Adherence to Continuous Positive Airway Pressure Treatment in Children.

Study Objectives: Infants, children, and adolescents are increasingly being prescribed continuous positive airway pressure (CPAP) for treatment of obstructive sleep apnea syndrome (OSAS), yet adherence is often poor. The purpose of this study was to examine the relationship between caregiver and patient-reported health cognitions about CPAP prior to starting CPAP and CPAP adherence at 1 month. We hypothesized that greater caregiver-reported self-efficacy would be positively associated with CPAP adherence in children.

Photoexcitation of Adenosine 5'-Triphosphate Anions in Vacuo: Probing the Influence of Charge State on the UV Photophysics of Adenine.

We report the first UV laser photodissociation spectra (4.0-5.8 eV) of gas-phase deprotonated adenosine 5'-triphosphate, diphosphate and monophosphate anions.

Financial Analysis of an Intensive Pediatric Continuous Positive Airway Pressure Program.

Study Objectives: Continuous positive airway pressure (CPAP) is effective in treating obstructive sleep apnea in children, but adherence to therapy is low. Our center created an intensive program that aimed to improve adherence. Our objective was to estimate the program's efficacy, cost, revenue and break-even point in a generalizable manner relative to a standard approach.

ON or OFF?: Modulating the N-Methyl-D-Aspartate Receptor in Major Depression.

Since the discovery that a single dose of ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist, had rapid and long-lasting antidepressant effects, there has been increased interest in using NMDAR modulators in the pharmacotherapy of depression. Ketamine's efficacy seems to imply that depression is a disorder of NMDAR hyperfunctionality. However, studies showing that not all NMDAR antagonists are able to act as antidepressants challenge this notion.

Photodissociation dynamics of the iodide-uracil (I(-)U) complex.

Photofragment action spectroscopy and femtosecond time-resolved photoelectron imaging are utilized to probe the dissociation channels in iodide-uracil (I(-) ⋅ U) binary clusters upon photoexcitation. The photofragment action spectra show strong I(-) and weak [U-H](-) ion signal upon photoexcitation. The action spectra show two bands for I(-) and [U-H](-) production peaking around 4.

UV laser photoactivation of hexachloroplatinate bound to individual nucleobases in vacuo as molecular level probes of a model photopharmaceutical.

Isolated molecular clusters of adenine, cytosine, thymine and uracil bound to hexachloroplatinate, PtCl6(2-), have been studied using laser electronic photodissociation spectroscopy to investigate photoactivation of a platinum complex in the vicinity of a nucleobase. These metal complex-nucleobase clusters represent model systems for identifying the fundamental photochemical processes occurring in photodynamic platinum drug therapies that target DNA. This is the first study to explore the specific role of a strongly photoactive platinum compound in the aggregate complex.

Photoelectron spectroscopy of hexachloroplatinate-nucleobase complexes: Nucleobase excited state decay observed via delayed electron emission.

We report low-temperature photoelectron spectra of isolated gas-phase complexes of the hexachloroplatinate dianion bound to the nucleobases uracil, thymine, cytosine, and adenine. The spectra display well-resolved, distinct peaks that are consistent with complexes where the hexachloroplatinate dianion is largely intact. Adiabatic electron detachment energies for the hexachloroplatinate-nucleobase complexes are measured as 2.

Cerebral Blood Flow Response to Hypercapnia in Children with Obstructive Sleep Apnea Syndrome.

Study Objectives: Children with obstructive sleep apnea syndrome (OSAS) often experience periods of hypercapnia during sleep, a potent stimulator of cerebral blood flow (CBF). Considering this hypercapnia exposure during sleep, it is possible that children with OSAS have abnormal CBF responses to hypercapnia even during wakefulness. Therefore, we hypothesized that children with OSAS have blunted CBF response to hypercapnia during wakefulness, compared to snorers and controls.

Inhibitors of the gamma-aminobutyric acid transporter 1 (GAT1) do not reveal a channel mode of conduction.

We expressed the gamma-aminobutyric acid (GABA) transporter GAT1 (SLC6A1) in Xenopus laevis oocytes and performed GABA uptake experiments under voltage clamp at different membrane potentials as well as in the presence of the specific GAT1 inhibitors SKF-89976A and NO-711. In the absence of the inhibitors, GAT1 mediated the inward translocation of 2 net positive charges across the plasma membrane for every GABA molecule transported into the cell. This 2:1 charge flux/GABA flux ratio was the same over a wide range of membrane potentials from -110 mV to +10 mV.

Safety of hematopoietic stem cell transplantation in children less than three years of age.

Allogeneic hematopoietic stem cell transplantation (HSCT) is a standard treatment for a variety of hematologic conditions. However, very young children may experience different complications of HSCT compared to older patients. The authors retrospectively analyzed the results of 51 transplants performed on children less than 3 years of age between June 1987 and October 2005.

Control of exposure to mite allergen and allergen-impermeable bed covers for adults with asthma.

Background: The effectiveness of avoidance of house-dust-mite allergen (Dermatophagoides pteronyssinus 1 [Der p1]) in the management of asthma is uncertain.

Methods: We conducted a double-blind, randomized, placebo-controlled study of allergen-impermeable bed covers involving 1122 adults with asthma. The primary outcomes were the mean morning peak expiratory flow rate over a four-week period during the run-in phase and at six months and the proportion of patients who discontinued inhaled corticosteroid therapy as part of a phased-reduction program during months 7 through 12.