New hydroxyl protecting groups of a safety-catch type removable by reductive acidolysis.

New hydroxyl protecting groups of a safety-catch type, i.e., 4-methylsulfinylbenzyl-oxycarbonyl (Msz) group for Tyr and 4-methylsulfinylbenzyl (Msob) ether for Thr, have been developed. O-Msz and O-Msob groups are stable under both acidic and basic conditions and can be removed by a one-pot reaction involving reductive acidolysis using tetrachlorosilane-trifluoroacetic acid (TFA)-scavengers. Using these new protecting groups, a 17 residue-peptide, gamma-endorphin, was successfully synthesized by the efficient solid phase method.     

Small-Angle electron scattering and electron density in carbon dioxide

The total (elastic and inelastic) intensity of electrons scattered by CO₂ was measured in the s range of 1 to 12 Å^?1 and compared with the theoretical intensity calculated from the Hartree-Fock molecular wave function and those calculated for the independent-atom-model (IAM ) molecule. In the range of s ? 4 Å^?1 the electron correlation effect on the total scattered intensity was found to be represented by that for the IAM molecule.     

Preconcentration of trace elements from pure manganese and manganese compounds with activated carbon as collector

A method is described for separation of traces of Bi, Cd, Co, Cu, Fe, In, Ni. Pb, Tl, and Zn from pure manganese and manganese compounds and their determination by flame a.a.s. After the metal or manganese dioxide samples have been dissolved in acid (and manganese salts in water) the trace elements are compleed with potassium xanthogenate. The solution is then filtered through a small filter paper covered with activated carbon, whereby complex compounds are separated from the matrix. When the charcoal is treated with acid, a trace concentrate is obtained which is nearly free of manganese. The detection limits for the analysis of 10-g samples of manganese metal are <0.5 p.p.m., and for 30-g samples of MnCl₂-4H₂O are ? 0.1 p.p.m. The relative standard deviation, in general,is lower than 5%.     

Refining Cosmetatos' Approximation for the Mean Waiting Time in the M/D/s Queue

This paper deals with refining Cosmetatos's approximation for the mean waiting time in an M/D/s queue. Although his approximation performs quite well in heavy traffic, it overestimates the true value when the number of servers is large or the traffic is light. We first focus on a normalized quantity that is a ratio of the mean waiting times for the M/D/s and M/M/s queues. Using some asymptotic properties of the quantity, we modify Cosmetatos's approximation to obtain better accuracy both for large s and in light traffic. To see the quality of our approximation, we compare it with the exact value and some previous approximations. Extensive numerical tests indicate that the relative percentage error is less than 1% for almost all cases with s ≤ 20 and at most 5% for other cases.     

Approximating the Mean Waiting Time in the <Emphasis Type="Italic">GI/G/s</Emphasis> Queue

We provide two distribution-dependent approximations for the mean waiting time in a GI/G/s queue. Both approximations are weighted combinations of the exact mean waiting times for the GI/M/s and M/D/s queues each of which has the same mean service time and traffic intensity as in the approximating GI/G/s queue. The weights in the approximations are expressed by the service-time c.d.f. and the first two moments of interarrival and service times. To examine the performance of our approximations, they are numerically compared with exact solutions and previous two-moment approximations for various cases. Extensive numerical comparisons indicate that the relative percentage errors of the approximations are of the order of 5% in moderate traffic and 1% in heavy traffic, except for extreme cases.     

An analysis of the through-bond interaction using the localized molecular orbitals—IV: Long-range proton hyperfine coupling in exo- and endo-hydrogens in bicyclo[2.1.1]hex-5-yl radical

The INDO calculations were performed on bicyclo[2.1.1]hex-5-yl radical. From these calculations, it was confirmed that the hyperfine coupling constants depend largely on the geometry of the α hydrogen. The localized MO's were obtained from the canonical MO's calculated by using the INDO method. With the use of the localized MO's thus obtained, the variation in the hyperfine coupling constants at the 6exo- and 6endo-protons in this radical was explained in terms of the through-bond and/or the through-space interactions according to the procedure which we proposed previously. That is by the procedure we can selectively pick up a particular interaction between the specified localized MO's. The hyperfine coupling constant in this radical can be expressed by the summation of several interaction terms. The difference in the hyperfine spin coupling constants of the H_6exo and H_6endo in the radical now concerned has been attempted to explain using MO coefficients of the occupied orbitals.     

Cardiac glycosides: 3. synthesis of β-D-digitoxose analogues

Earlier studies have shown that the β-D-digitoxose (2,6-dideoxy-β-D-mannopyranose) directly attached to the cardiac glycoside steroid C3 has the greatest effect on biological activity. This report describes the synthesis of eight digitoxosides (2a-9a), with widely varying cyclic and acyclic C17β-side groups, and the corresponding C3',C4'-acetonides (2b-9b). NMR analysis of conformational strain introduced by the acetonide groups is supported by crystallographic analysis of the sugars' torsion angles.     

ESR Study of a Nitroxide Radical in Sol-Gel Glasses

A spin probe TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy) was dissolved in a tetraethyl orthosilicate sol-gel reaction system and measured by electron spin resonance spectroscopy at 295 K. The nitrogen hyperfine coupling constant was from 1.64–1.66 mT in the sol-gel solutions. The values were sensitive to the ethanol-to-water ratio of the solutions. The hyperfine coupling constant in the xerogels was 1.70 mT, which was almost the same as that in water, indicating that the probe molecules were trapped in silica pores with water adsorbed on the silica surfaces. The motion of TEMPOL in the xerogels was considerably slower than in the sol-gel solutions. The local viscosity estimated was from 70–90 cP. The ESR spectra of TEMPOL were altered during the sol-gel process, indicating that adsorbed water on the silicas surfaces has an important role for trapping organic molecules in sol-gel glasses.