Complexation between α-alkenylaluminum compounds and diisobutylaluminum hydride: The nature of organoaluminum intermediates responsible for the inhibited hydralumination of alkynes

In order to understand the nature of organoaluminum intermediates encountered in the hydralumination of alkynes, NMR spectral and kinetic studies have been carried out on the alkenyl(dialkyl)aluminum systems (I) resulting from the addition of diisobutylaluminum hydride to 4-octyne and to di-t-butylacetylene. A kinetic study of the reaction of a 1/1 mixture of I and diisobutylaluminum hydride with 5-decyne at 50° followed the rate expression v = k(5-decyne)^1.0 (AlH)^0.5. The E^X (apparent) was 23.0 kcal/mole.The aluminum adducts of 4-octyne with one or two equivalents of diisobutylaluminum hydride did not show any temperature-dependence in their NMR spectra. However, those derived from di-t-butylacetylene did reveal the existence of several components, both for the alkenyl(dialkyl)aluminum itself, as well as for the 1/1 admixture of the alkenyl(dialkyl)aluminum with diisobutylaluminum hydride. However, in the temperature range of hydralumination, namely 50°, the diisobutyl(E-4-octenyl)aluminum was shown to be in equilibrium, with triisobutylaluminum.A proposed rationale for the NMR spectral data, formulated with the aid of data from model systems such as bis(E-4-octenyl)aluminum hydride, also offers an insight into the nature and kinetic behavior of organoaluminum intermediates in the hydralumination reaction.     

Hierarchical assembly of model cell surfaces: synthesis of mucin mimetic polymers and their display on supported bilayers

Molecular level analysis of cell-surface phenomena could benefit from model systems comprising structurally defined components. Here we present the first step toward bottom-up assembly of model cell surfaces-the synthesis of mucin mimetics and their incorporation into artificial membranes. Natural mucins are densely glycosylated O-linked glycoproteins that serve numerous functions on cell surfaces. Their large size and extensive glycosylation makes the synthesis of these biopolymers impractical. We designed synthetically tractable glycosylated polymers that possess rodlike extended conformations similar to natural mucins. The glycosylated polymers were end-functionalized with lipid groups and embedded into supported lipid bilayers where they interact with protein receptors in a structure-dependent manner. Furthermore, their dynamic behavior in synthetic membranes mirrored that of natural biomolecules. This system provides a unique framework with which to study the behavior of mucin-like macromolecules in a controlled, cell surface-mimetic environment.     

Importance of Debye and Keesom interactions in separating m-xylene and p-xylene in GC-MS analysis utilizing PEG stationary phase

In electron impact gas chromatography (GC)-mass spectrometry analysis of a complex mixture, such as gasoline, two coeluting solutes can be distinguished if each has a unique major ion. The boiling-point difference between m-xylene and p-xylene, which also has identical major ions (mz-1: 91 and 106 Da), is 0.77 degrees C. These cannot be separated even on a crossed-linked polydimethylsiloxane capillary column, which has a minimum of 5000 plates/m. They are separated on a crossed-linked polar polyethylene glycol (PEG) capillary column. GC separation on a stationary phase depends on the relative strengths of solute-solute, stationary phase-stationary phase, and solute-stationary phase interactions. Although the calculated molar electronic polarization and refractivity factor of Lorenz-Lorentz equation for m-xylene and p-xylene are nearly equal because of its greater dipole moment difference (0.30 and 0.02), the calculated orientation polarization of m-xylene is 80 times greater than p-xylene. This implies the dipole reinforcement through inductive polarization by the hydroxyl of PEG stationary phase molecules is greater on m-xylene than p-xylene. In addition, as the permanent dipole moment of m-xylene is 15 times greater than p-xylene, m-xylene has a stronger Keesom interaction with PEG. In order for m-xylene and p-xylene to solvate in PEG, analytes must overcome the PEG-PEG Keesom/hydrogen bonding interaction forces. Physical and chemical parameters indicate that compared with p-xylene, m-xylene has a greater Debye-Keesom interaction tendency with PEG molecules. This is supported by the 0.12-min. retention-time difference between them.     

Flow and heat/mass transfer in a wavy duct with various corrugation angles in two dimensional flow regimes

In this study, two dimensional heat/mass transfer characteristics and flow features were investigated in a rectangular wavy duct with various corrugation angles. The test duct had a width of 7.3 mm and a large aspect ratio of 7.3 to simulate two dimensional characteristics. The corrugation angles used were 100°, 115°, 130°, and 145°. Numerical analysis using the commercial code FLUENT, was used to analyze the flow features. In addition, the oil-lamp black method was used for flow visualization. Local heat/mass transfer coefficients on the corrugated walls were measured using a naphthalene sublimation technique. The Reynolds number, based on the duct hydraulic diameter, was varied from 700 to 5,000. The experimental results and numerical analysis showed interesting and detailed features in the wavy duct. Main flow impinged on upstream of a pressure wall, and the flow greatly enhanced heat/mass transfer. On a suction wall, however, flow separation and reattachment dominantly affected the heat/mass transfer characteristics on the wall. As the corrugation angle decreased (it means the duct has more sharp turn), the region of flow stagnation at the front part of the pressure wall became wider. Also, the position of flow reattachment on the suction wall moved upstream as the corrugation angle decreased. A high heat transfer rate appeared at the front part of the pressure wall due to main-flow impingement, and at the front part of the suction wall due to flow reattachment. The high heat/mass transfer region by the main-flow impingement and the circulation flow induced at a valley between the pressure and suction walls changed with the corrugation angle and the Reynolds number. As the corrugation angle decreased, the flow in the wavy duct changed to transition to turbulent flow earlier.     

Pd-Catalyzed Synthesis of Vinyl Arenes from Aryl Halides and Acrylic Acid

Acrylic acid is presented as an inexpensive, non-volatile vinylating agent in a palladium-catalyzed decarboxylative vinylation of aryl halides. The reaction proceeds through a Heck reaction of acrylic acid, immediately followed by protodecarboxylation of the cinnamic acid intermediate. The use of the carboxylate group as a deciduous directing group ensures high selectivity for monoarylated products. The vinylation process is generally applicable to diversely substituted substrates. Its utility is shown by the synthesis of drug-like molecules and the gram-scale preparation of key intermediates in drug synthesis.     

Effects of Sleep Deprivation on the Sedation of Pediatric Patients Undergoing MRI Examinations

Sedation is an essential factor for pediatric magnetic resonance imaging (MRI) procedure. A long-term failure of sedation has a detrimental effect on a 1 day test plan. Given this background, this study examined the effects of sedation using a sleep deprivation method in pediatric patients scheduled to undergo an MRI examination. The current study examined 54 patients (36 boys and 18 girls) with diseases, such as epilepsy, brain tumor, development delay, mental retardation, and cerebral infarction, who were treated at our medical institution from December 2009 to March 2010. The patients were classified into two groups: group A (n = 27) with sleep deprivation, and group B (n = 27) without sleep deprivation. The mean age of these patients was 4.2 years. Comparative analysis of groups A and B was performed to assess the success rate of pediatric sedation, the time elapsed until complete sedation had been achieved, and the frequency at which patients took Pocral syrup (chloral hydrate). In group A, patients were allowed to start sleep 1 hr later and were woken 1 hr earlier than their mean sleep time. According to this pretreatment, the rate of successful sedation, frequency of the administration of Pocral syrup, and the time elapsed until deep sedation had been achieved were measured. In group A, the rate of successful sedation was 100%, the mean time elapsed until deep sedation had been achieved was 23 min, and the mean frequency of Pocral syrup administration was 1.2 times. In addition, the proportions of patients who had achieved successful sedation after one-time use and two-time use of Pocral syrup were 77.8% and 22.2%, respectively. In group B, successful sedation was achieved in 89%, and the mean time elapsed until deep sedation was 39 min. The mean frequency of Pocral syrup administration was 1.5 times. The proportions of patients who had achieved successful sedation after one-time use and two-time use of Pocral syrup were 51.9% and 48.12%, respectively. The statistical significance was tested using a nonparametric analysis, Mann–Whitney U Test (p < 0.05). Other studies have reported that sleep deprivation had no significant effects. An actual comparison of the sleep-deprived and other patients showed that sleep deprivation affected the rate of successful sedation, the frequency of Pocral syrup administration, and the time elapsed until the patients were sedated. The rate of successful sedation was significantly higher in group A than in group B. The time elapsed until deep sedation had been achieved was also significantly shorter in group A than in group B. In addition, the frequency of Pocral syrup administration (administration dose) was significantly lower in group A than in group B. In conclusion, sleep deprivation increases the effectiveness of pediatric sedation in an MRI examination of pediatric patients and might assist in performing an MRI examination more efficiently in pediatric patients.