Predictors of dropout in university students participating in an 8-week e-mail-based cognitive-behavioral therapy for insomnia intervention.

PURPOSE: We conducted an exploratory study to identify risk factors of dropout in an 8-week e-mail-based cognitive-behavioral therapy for insomnia (REFRESH) to improve sleep among university students with insomnia symptoms. METHODS: University and graduate students in Hong Kong and Korea who scored higher than 10 on the Insomnia Severity Index participated in REFRESH. RESULTS: Of 158 participants from Hong Kong (n = 43) and Korea (n = 115), 90 (57%) did not complete all 7 sessions, while 52 of 90 (57.8%) dropped out prior to the fourth session. ROC analysis was conducted on the entire sample of 158 participants with intervention completion vs. dropout (non-completion) as the outcome variable. Predictors of dropout were wake time after sleep onset (WASO) < 7.1 min on the weekly sleep diary and expectations for sleep (a subscale of dysfunctional beliefs and attitudes about sleep; DBAS) < 18 at baseline. CONCLUSIONS: These findings indicate that shorter WASO and less expectations for sleep at baseline were associated with risk of dropout from e-mail delivered self-help CBT-I-based intervention. Our results highlight the importance of identifying and tailoring treatment formats to students based on their presenting sleep characteristics.

Femtosecond decay dynamics of intact adenine and thymine base pairs in a supersonic jet.

We investigated the decay dynamics of the DNA base pairs adenine-adenine (A(2)), adenine-thymine (AT), and thymine-thymine (T(2)) produced in a supersonic jet by femtosecond (fs) time-resolved photoionization spectroscopy. The base pair was excited by a fs pump pulse at 267 nm and the population change of its excited state was monitored by non-resonant three-photon ionization using a fs probe pulse at 800 nm after a certain time delay. All of the transients recorded in the mass channel of the parent ion exhibited a tri-exponential decay, with time constants ranging from 100 fs to longer than 100 ps. Most of these time constants coincide well with the previous values deduced indirectly from the transients of protonated adenine (AH(+)) and thymine (TH(+)), which were assumed to be produced by fragmentation of the base-pair ions. Notably, for the transient of T(2), we observed a new decay component with a time constant of 2.3 ps, which was absent in the transient of TH(+). We suggest that the new decay component arises from the decay of stacked T(2) dimers that are mostly ionized to T(2)(+), whereas the decay signal recorded in the mass channel of TH(+) is merely from the relaxation of hydrogen-bonded T(2) dimers. From the amplitude of the new decay component, the population of the stacked T(2) dimers relative to the hydrogen-bonded dimers was estimated to be ∼2 % in the supersonic jet, which is about fifteen times higher than the theoretical value.

Conformationally resolved structures of jet-cooled acetaminophen by UV-UV hole-burning spectroscopy.

The conformational structures of jet-cooled acetaminophen were investigated in the gas phase by resonant 2-photon ionization and UV-UV hole-burning spectroscopy. In contrast to the results from a previous study, two nearly isoenergetic conformers were distinctly found in a supersonic molecular beam expansion and positively identified as the cis and trans isomers of acetaminophen by UV-UV hole-burning spectroscopy. The 0-0 bands of the cis and trans isomers were found at 33518.7 and 33485.6 cm(-1), respectively. The vibronic bands of the two isomers are close-lying and/or partially overlapping due to the small energy difference (33 cm(-1)) between the two 0-0 bands. As a consequence, the recorded resonant 2-photon ionization spectrum is highly congested in the low excitation energy region, which develops continuously into a featureless, broadened spectrum in the high energy region.

Excited-state lifetime of adenine near the first electronic band origin.

The excited-state lifetime of supersonically cooled adenine was measured in the gas phase by femtosecond pump-probe transient ionization as a function of excitation energy between 36 100 and 37 500cm(-1). The excited-state lifetime of adenine is ∼2ps around the 0-0 band of the (1)L(b) ππ(∗) state (36 105cm(-1)). The lifetime drops to ∼1ps when adenine is excited to the (1)L(a) ππ(∗) state with the pump energy at 36 800cm(-1) and above. The excited-state lifetimes of (1)L(a) and (1)L(b) ππ(∗) states are differentiated in accordance with previous frequency-resolved and computational studies.

Fusion step-specific influence of cholesterol on SNARE-mediated membrane fusion.

Cholesterol is a major component of biological membranes and is known to affect vesicle fusion. However, the mechanism by which cholesterol modulates SNARE-dependent intracellular fusion is not well understood. Using the fluorescence assay and dye-labeled SNAREs and the fluorescent lipids, we dissected cholesterol effects on individual fusion steps including SNARE complex formation, hemifusion, pore formation, and pore dilation. At physiological high concentrations, cholesterol stimulated hemifusion as much as 30-fold, but its stimulatory effect diminished to 10-fold and three-fold for subsequent pore formation and pore expansion at 40 mol %, respectively. The results show that cholesterol serves as a strong stimulator for hemifusion but acts as mild stimulators for pore opening and expansion. Strong stimulation of hemifusion and mild stimulation of pore formation are consistent with the fusion model based on the intrinsic negative curvature of cholesterol. However, even a milder effect of cholesterol on pore expansion is contradictory to such a simple curvature-based prediction. Thus, we speculate that cholesterol also affects the conformation of the transmembrane domains of SNAREs, which modulates the fusion kinetics.

Direct observation of an intermediate state for a surface photochemical reaction initiated by hot electron transfer.

The photoinduced charge transfer that had been suggested to result in the dissociation of phenol on Ag(111) was investigated by two-photon photoemission spectroscopy. An unoccupied intermediate state was positively identified, which was found to be located 3.22 eV above the Fermi level. From the photoelectron energy dispersion, the effective mass of the intermediate state was determined to be (15 +/- 10)m(e) for a 1 ML coverage of phenol. This implies that the excited electron is localized mainly on the adsorbed phenol, forming a molecular resonance state. Polarization dependence of the photoelectron intensity suggested that the initial photoexcitation of the substrate produces hot electrons that scatter into the molecular resonance state, leading ultimately to the dissociation of the adsorbate. These results are the first two-photon photoemission study to characterize the transient anionic state involved in photodissociation of a molecule adsorbed on a metal surface.

Dynamics of solvated electron transfer in thin ice film leading to a large enhancement in photodissociation of CFCl3.

Solvation and transfer dynamics of photoinjected electrons in thin ice film coadsorbed with CFCl3 were investigated by two-photon photoemission spectroscopy. Water molecules were found to solvate the photoinjected electrons within the first several hundred femtoseconds, thus stabilizing the electron with a lifetime of ca. 120 fs for 5 ML ice film grown on Ag(111). The significant lifetime decrease upon adsorption of CFCl3 on the ice film was attributed to dissociative electron transfer of the solvated electron based on the observed scission of the C-Cl bonds. Furthermore, the photodissociation rate of CFCl3 adsorbed directly on Ag(111) was observed to increase drastically owing to the transfer of the solvated electron when ice film was overlaid.

Interfacial electron dynamics and hot-electron-driven surface photochemistry of carbon tetrachloride on Ag(111).

We used time-resolved two-photon photoemission (2PPE) spectroscopy to investigate the photochemical behavior, the interfacial electronic structure, and the fate of photogenerated hot electron for carbon tetrachloride adsorbed on Ag(111). The photodissociation cross section was determined over a wide range of photon energy from 1.62 to 5.69 eV, which suggested a low-lying electron affinity level of adsorbed CCl4. A CCl4-derived unoccupied state located at 3.41 eV above the Fermi level was attributed to an image potential (IP) state based on its binding energy and effective mass. Polarization dependence of the 2PPE signal revealed that the IP state was populated by an indirect excitation process involving scattering of photoexcited hot electrons rather than direct electronic transition from a bulk band. The lifetime of the IP state was much shorter on the CCl4-covered Ag(111) surface than on the clean one, implying that the electron in the IP state is scavenged effectively by CCl4, probably through dissociative attachment to it. These results are significant in the sense that they provide dynamical evidence for a new relaxation pathway of the IP state in addition to the more common pathway involving back transfer of electron to the substrate.