Orientation dependent far-infrared terahertz absorptions in single crystal pentaerythritol tetranitrate (PETN) using terahertz time-domain spectroscopy

Terahertz time-domain spectroscopy (THZ-TDS) has been used to measure the absorption spectra in the range 7-100 cm(-1) (0.2-3 THz) of single crystal pentaerythritol tetranitrate (PETN). Absorption was measured in transmission mode as a function of incident polarization with the incident and transmitted wave vectors oriented along the crystallographic directions [100], <10(a/c)(2)>, and <110>. Samples were rotated with respect to the incident polarization while absorption was measured at both 300 and 20 K. Comparatively minor differences were observed among the three orientations. Two broad absorptions at 72 and >90 cm(-1), and several weaker absorptions at 36, 55, 80, and 82 cm(-1), have been observed at cryogenic temperatures.     

Bernstein's asymptotic best bound for the Kth derivative of a polynomial

A complete proof, which yields an error term showing a dependence on n and x, is given for Bernstein's result that the best bound on the kth derivative on polynomials of degree less than or equal to n, at a point x in ( ?1, 1), is asymptotic to $\text{(}\text{n}\text{√1 ? x}{}^2\text{)}{}^{\mathrm{k}}$ as n tends to infinity.     

Cyclopropene-carbene rearrangements at low temperatures. Generation and trapping of 1,2-dichloro-3-methylbut-2-en-1-ylidene

Reaction of (5, X = H, Cl, Br) with methyl lithium in ether in the presence alkenes leads to cyclopropanes, e g.(6), apparently derived by trapping of an intermediate carbene (4); in the case of (5, X = Br), the precursor of the carbene, a cyclopropene (1, X=Y=Cl, Z=Me), may be trapped by addition of bromine at ?90°C.     

A Three‐Site Mechanism for Agonist/Antagonist Selective Binding to Vasopressin Receptors

Molecular‐dynamics simulations with metadynamics enhanced sampling reveal three distinct binding sites for arginine vasopressin (AVP) within its V₂‐receptor (V₂R). Two of these, the vestibule and intermediate sites, block (antagonize) the receptor, and the third is the orthosteric activation (agonist) site. The contacts found for the orthosteric site satisfy all the requirements deduced from mutagenesis experiments. Metadynamics simulations for V₂R and its V_1aR‐analog give an excellent correlation with experimental binding free energies by assuming that the most stable binding site in the simulations corresponds to the experimental binding free energy in each case. The resulting three‐site mechanism separates agonists from antagonists and explains subtype selectivity.     

Untersuchung von Wasser

Ohne Zusammenfassung     

A general complex variable boundary element method

The solution to any 2‐dimensional potential problem, with continuous data given on the boundary of a bounded domain with connected complement, can be approximated by sums Re Σ c_n f(α_n z + z₀), where f is any preassigned non‐polynomial analytic function. © 2001 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 17:332–335, 2001     

Metalations utilizing aryllithiums; ortho-functionalization of p-bromoanisole (pBrA)

An ortho-metalation protocol has been developed, which permits the survival of a bromine substituent in p-bromoanisole. Eight derivatives of the generated ortho-lithiated intermediate have been prepared. A neglected metalation concept is being explored here; one which proposes that minimizing the pK_a difference between the aryl substrate and the conjugate acid of the metalating agent will lead to a regiospecific and selective metalation process.