A New Route to Macrocycles Possessing the 2,6-Pyridino Subunit via Bis-1,3-Dithianes [1]

Two rigid crown ethers 12 , which possess a terpyridine subunit, are herein prepared by the construction of the middle pyridine moiety via a bis-dithiane precursor. The intermediate diketone and derivatives are sufficiently mobile to permit macrocyclization; then their irreversible conversion to a pyridine nucleus circumvents the inherent structural constraints associated with the synthesis of these macromolecules.     

The cerebral neurobiology of hope and hopelessness

Hope and hopelessness are useful constructs that have been employed by clinicians in theory making regarding the pathogenesis and course of disease and in the application of various psychological and medical treatments to illness. French (1952) and Frank (1968) viewed hope as a necessary motivating force in influencing an individual to try to overcome inner psychological conflicts and seek to resolve a psychoneurosis. Melges and Bowlby (1969) classified the types of hopelessness in psychopathological processes. Perley et al. (1971), using an objective method for content analysis of small samples of speech (Gottschalk 1974), found that elevated hope scores predicted continuation of psychiatric treatment rather than dropping out. Gottschalk et al. (1967, 1969) found that hope scores derived from verbal samples predicted the duration of survival of patients with terminal cancer receiving irradiation treatment (1969) and predicted relatively favorable outcome in psychotherapy (1967).     

Binding and selectivity aspects of an expanded azamacrocycle for anions

An expanded azamacrocycle L, containing four secondary and two tertiary amines was synthesized, and its binding ability towards chloride, bromide, iodide, sulfate, nitrate and perchlorate were determined by (1)H NMR titrations in D(2)O at pH 1.7. The results suggest that the ligand is capable of forming a complex with each of the anions examined, showing the selectivity for sulfate in water. X-ray diffraction analysis of the perchlorate complex of L suggests that the ligand is tetraprotonated and is involved in interacting anions from both sides forming a ditopic complex with strong NH···O bonds. In the packing diagram, the macrocycles and external perchlorates are alternatively linked though hydrogen bonding to form a 1D chain.     

Effects of Temperature and UV Light on Degradation of α-Tocopherol in Free and Dissolved Form

The effects of heat and UV exposure on the degradation of free α-tocopherol (oil form), α-tocopherol dissolved in methanol, and α-tocopherol dissolved in hexane were measured. Results showed that degradation of free α-tocopherol due to heat followed first order kinetics, with the samples held at 180 °C showing the greatest degradation rate. Free α-tocopherol degraded faster at high temperatures than dissolved α-tocopherol. In contrast, free α-tocopherol did not degrade when exposed to UV light for as long as 6 h, but the hexane and methanol samples degraded significantly as a matter of time. The α-tocopherol dissolved in hexane and methanol degraded by 20 and 70%, respectively over this time span. A mechanism for degradation of α-tocopherol was proposed to explain the higher degradation rate of α-tocopherol in methanol, as compared to hexane for times longer than 180 min. Knowledge of degradation kinetics of pure α-tocopherol as a result of temperature or exposure to UVA light whether in free or dissolved form is critically needed to understand how different processing parameters affect the amount of α-tocopherol during extraction, stabilization, storage or encapsulation processes.     

GR 24 enantiomers: synthesis, NMR spectroscopy, X-ray crystallography, and separation by chiral electrokinetic capillary chromatography

Chiral discrimination of enantiomers of 2-methyl-4-(2-oxo-2,3,3a,8b-tetrahydro-4H-indeno[1,2b]furan-3-yl-iden emethoxy)but-2-en-4-olide (commonly referred to as GR 24) by three polymeric chiral surfactants (PCS) is studied by use of chiral polymeric surfactant capillary electrophoresis (CPSCE). The CPSCE results indicate that the optical configurations of valine residues on the PCS backbone affect chiral resolution and elution order of GR24 stereoisomers. The L- and D-forms of poly(sodium N-undecanoyl valinate) provide baseline separation of all four enantiomers while the DL-form separates diastereomers of GR 24 (1). A model is presented rationalizing the migration behavior and chiral resolution of 1 in CPSCE. The actual configuration of the stereogenic centers of GR 24 and 3-[(2,5-dihydro-3-methyl-2-oxo-5-furanyl)oxo]-methylene-3,3a,6,6a-tetrah ydro-2H-cyclopenta[b]furan-2-one (GR 7) is established by a concerted application of high-resolution nuclear magnetic resonance spectroscopy and X-ray crystallography.     

Asymmetric hydrogenations of diketopiperazines

The dehydrodiketopiperazines 6 undergo face selective hydrogenation with a 5% palladium on carbon catalyst to give the diketopiperazines 7 in high yield with excellent diastereoisomeric ratios (>97%). This revised version was published online in June 2006 with corrections to the Cover Date.