13C-13C rotational resonance width distance measurements in uniformly 13C-labeled peptides

The rotational resonance width (R2W) experiment is a constant-time version of the rotational resonance (R2) experiment, in which the magnetization exchange is measured as a function of sample spinning frequency rather than the mixing time. The significant advantage of this experiment over conventional R2 is that both the dipolar coupling and the relaxation parameters can be independently and unambiguously extracted from the magnetization exchange profile. In this paper, we combine R2W with two-dimensional 13C-13C chemical shift correlation spectroscopy and demonstrate the utility of this technique for the site-specific measurement of multiple 13C-13C distances in uniformly labeled solids. The dipolar truncation effects, usually associated with distance measurements in uniformly labeled solids, are considerably attenuated in R2W experiments. Thus, R2W experiments are applicable to uniformly labeled biological systems. To validate this statement, multiple 13C-13C distances (in the range of 3-6 A) were determined in N-acetyl-[U-13C,15N]l-Val-l-Leu with an average precision of +/-0.5 A. Furthermore, the distance constraints extracted using a two-spin model agree well with the X-ray crystallographic data.     

Topochemical models for prediction of anti-tumor activity of 3-aminopyrazoles

Relationship between topochemical indices and inhibition of CDK2/cyclin A by 3-aminopyrazoles was investigated using a data set comprising of 42 3-aminopyrazoles. Three topochemical indices--the Wiener's topochemical index--a distance based topochemical index, atomic molecular connectivity index--an adjacency based topochemical index and superadjacency topochemical index--an adjacency-cum-distance based topochemical index were used for the present investigations. The values of Wiener's topochemical index, atomic molecular connectivity index and superadjacency topochemical index for each of the 42 compounds comprising the data set were computed using an in-house computer program. Resultant data was subsequently analyzed and suitable models were developed after identification of the active ranges. Subsequently, a biological activity was assigned to each of the compounds using these models, which was then compared with the reported CDK2/cyclin A inhibitory activity. High accuracy of prediction ranging from 86 to 89% was observed using these models.     

MHNAMT,a new locating and chelating agent in thin-layer chromatographic determination of Cu(II), Co(II), Ni(II), Pd(II), Pt(IV), and Rh(III)

Summary Synthesis of MHNAMT [3-methyl-4-(2-hydroxy-1 naphthalideneamino)-5-mercapto-1,2,4-triazole] and its IR and NMR spectral data are reported. The high stability of the characteristically coloured chelates with Cu(II), Co(II), Ni(II), Pd(II), Pt(IV) and Rh(III) has been made the basis for their efficient ascending TLC separations on silica gel G layers, when present together. Results of three different solvent systems are included to assess efficient resolution of the chelates.     

Heat transport in turbulent rayleigh-Benard convection

We present measurements of the Nusselt number N as a function of the Rayleigh number R in cylindrical cells with aspect ratios 0. 510(7) they are consistent with N = asigma-1/12R1/4+bsigma-1/7R3/7 as proposed by Grossmann and Lohse for sigma greater, similar2.     

Intensity-reversal in the donor bound exciton luminescence of GaAs

A self-reversal model is presented to explain the luminescence dependence of the donor bound exciton intensity. The line broadening mechanism is attributed to rotational interaction with non-rigid rotator states. Line reversal results from absorption by non-broadened states near the crystal surface. The absence of a similar excitation intensity dependence for acceptor bound excitons is explained.     

Photoluminescence studies of the amphoteric behavior of carbon and germanium in GaAs

Recombination radiation due to an exciton bound to neutral donors and neutral acceptors in high purity vapor phase epitaxial GaAs is investigated using high resolution photoluminescence spectroscopy at liquid helium temperatures. It is found that those samples which show the presence of germanium acceptors also exhibit a strong residual donor referred to in the literature as X₃. Samples containing carbon acceptors however, do not show the presence of X₃. In the past X₃ has been identified by some groups as due to carbon on the gallium site. The work presented here sugests that the X₃ donor is associated with germanium. This identification of the X₃ donor is in agreement with a recent assignment based on the far infrared study of neutron transmuted GaAs.     

The stereochemistry of allohimachalol

Allohimachalol, an unusual rearranged sesquiterpene from the essential oil of $\text{Cedrus}$$\text{deodara}$ Loud., is shown to have structure 3.     

Pion scattering from a bound nucleon at medium energies

In order to examine the validity of the impulse approximation for pion-nucleus scattering in the 33-resonance energy region, we consider pion-scattering from a “nucleus” which consists of a single nucleon bound in a harmonic oscillator potential. A separable πN interaction is assumed. The oscillator parameter is chosen such that the nuclear sizes are fitted for ⁴He ～ ¹⁶O. The binding effect is found to result in a downward shift of the resonance energy (by about 20 MeV), and an increase (by 50 ～ 70%) of the total cross section near the resonance. The angular distribution is also strongly modified. In connection with the binding effect, the importance of a careful treatment of nucleon recoil is emphasized. It is pointed out that the closure approximation which is often used to sum over intermediate nuclear states leads to very misleading results. The effect of the Pauli principle is also examined by excluding some intermediate states.