Bildungskonstanten von Komplexen der 3-Hydroxynaphthalin-2-carbonsäure mit Pr(III), Nd(III), Gd(III), Dy(III), Er(III) und Yb(III)

The stability constants of the complexes of 3-hydroxynaphthalene-2-carboxylic acid with some lanthanides have been obtained potentiometrically in aqueous dioxane (50%,V/V) at three temperatures and keeping the ionic strength at 0.1M (KNO₃), usingIrving-Rossotti titration technique. The values of overall changes in G°, H°, and S° have also been evaluated.     

Complexes of metal ions with phosphorus or arsenic containing ligands,part XX. Chelates ofo-phenylenebis(diarylarsines) with palladium(II) and platinum(II) halides,pseudohalides and perchlorates

Summary Two ditertiaryarsines,o-phenylenebis(diphenylarsine), (pdpa) ando-phenylenebis(di-p-tolylarsine), (pdta) yield some new complexes of palladium(II) and platinum(II). These are: square planar M(pdta)X₂ · nCH₂Cl₂, [M = Pd, X = Cl, Br or NCS; M = Pt, X = Cl]; [Pt(A-A)₂] X₂ · nCH₂Cl₂, [(A-A) = pdta, X = Cl, NCS or ClO₄; (A-A) = pdpa, X=ClO₄] and [M₂(A-A)₂(NCS)₂] (ClO₄)₂ · nCH₂Cl₂, [M = Pd, (A-A) = pdta; M = Pt, (A-A) = pdpa]; distorted octahedral M(pdta)₂-X₂nCH₂Cl₂, [M = Pd, X = I; M = Pt, X = Br or I] and [Pd(pdta)₂(H₂O)₂](ClO₄)₂, and five coordinate [M(A-A)₂X] ClO₄ · nCH₂Cl₂, [M = Pd, Pt, (A-A) = pdta, X = I; M = Pt, (A-A) = pdpa, X = Br or I]. The [M₂(A-A)₂(NCS)₂] (ClO₄)₂ · nCH₂Cl₂ complexes are novel in the sense that they contain bridging thiocyanate together with ionic perchlorate. The stereochemical assignments have been made on the basis of i.r. and u.v. spectra as well as conductance data.     

Experimental evaluation of multiple Compton backscattering of gamma rays in copper

The gamma ray photons continue to soften in energy as the number of scatterings increases in thick target, and results in the generation of singly and multiply scattered events. The number of these multiply scattered events increases with an increase in target thickness and saturates beyond a particular target thickness known as saturation depth. The present experiment is undertaken to study the saturation depth for 279 and 320 keV incident gamma ray photons multiply backscattered from copper targets of varying thickness. The backscattered photons are detected by a Nal(Tl) gamma detector whose pulse-height distribution is converted into a photon spectrum with the help of an inverse matrix approach. To extract the contribution of multiply backscattered photons only, the spectrum of singly scattered photon is reconstructed analytically. We observe that the numbers of multiply scattered events increases with an increase in target thickness and then saturate. The saturation depth is found to be decreasing with increase in incident gamma energy.     

Effect of neutron-irradiation on optical properties of SiO2-Na2O-MgO-Al2O3 glasses

Silica based glasses are used as nuclear shielding materials. The effect of radiation on these glasses varies as per the constituents used in these glasses. Glasses of different composition of SiO₂-Na₂OMgO-Al₂O₃ were made by melt casting techniques. These glasses were irradiated with neutrons of different fluences. Optical absorption measurements of neutron-irradiated silica based glasses were performed at room temperature (RT) to detect and characterize the induced radiation damage in these materials. The absorption band found for neutron-irradiated glasses are induced by hole type color centers related to non-bridging oxygen ions (NBO) located in different surroundings of glass matrix. Decrease in the transmittance indicates the formation of color-center defects. Values for band gap energy and the width of the energy tail above the mobility gap have been measured before and after irradiation. The band gap energy has been found to decrease with increasing fluence while the Urbach energy shows an increase. The effects of the composition of the glasses on these parameters have been discussed in detail in this paper.      

Studies on uracils: A facile one‐pot synthesis of pyrazolo[3,4‐d]pyrimidines

The reaction of 6‐hydrazino uracils 1 and nitrones 2 result in an efficient one‐pot synthesis of pyrazolo[3,4‐d]pyrimidines 3 in excellent yields. The isolation of the by‐product aniline from the reaction mixture supported the plausible mechanism for the formation of pyrazolo[3,4‐d]pyrimidines.     

Pseudo-conservation laws in cyclic-service systems with a class of limited service policies

This paper considers a cyclic-service system with a class of limited service policies that consists of exhaustive limited, gated limited and general decrementing policies. Under these policies, the number of customers served consecutively during a server visit is limited by a vector of integers. The major results in this paper are derivations of expected amount of work left in the queues at the server departures for these three policies. Exact expressions of weighted sum of mean waiting times, known as pseudo-conservation laws, are subsequently obtained. The conservation laws for this class of policies contain unknown boundary probabilities. We estimate these probabilities using corresponding server vacation models. Numerical results presented for the exhaustive limited policy are noted to be very accurate compared with simulation results. Moreover, we have obtained analytical bounds for the weighted sums. Finally, we present a conservation law with mixed service policies, and mean waiting times for symmetric systems.This work was completed while the author was in the Ph.D. program at Rensselaer Polytechnic Institute.This work was partially supported by the Center for Advanced Technologies of the New York State.     

Preparation and characterization of diphenyllead(IV) and triphenyllead(IV) complexes with N-protected amino-acids and the dipeptides

The diphenyllead(IV) derivatives of N-benzoyl-(glycine, DL -alanine); N-formyl and N-acetyl-L -phenylalanine; N-monochloroacetyl-L -phenylalanine; N-benzoyl-(glycylglycine, DL -alanylglycine), and N-formyl- N-acetyl- and N-monochloroacetyl-(L -phenylalanylglycine) have been prepared in 1:2 molar ratio by reaction of diphenyllead dichloride with the appropriate amino-acid or dipeptide. Corresponding triphenyllead(IV) derivatives have been prepared in 1:1 molar ratio by reaction of triphenyllead chloride with the thallium(I) salts of the amino-acid or the dipeptide. These complexes have been characterized by elemental analysis, IR and ¹H NMR spectral studies. A polymeric hexacoordinated octahedral structure for diphenyllead(IV), and a five-coordinated distorted trigonalbipyramidal chain-type structure for triphenyllead(IV), complexes is confirmed by IR spectra. The carboxylate group acts in a bidentate manner, not as in diorgano and triorganotin(IV) complexes with these acids, where it is monodentate. The available bonding sites such as amide and peptide carbonyl (CO) and amide and peptide nitrogen atoms are not involved in bonding with lead (IV) and thus are available for bonding with the biological systems. The presence of different N-protecting groups does not affect the coordination sites around lead(IV). The triphenyllead(IV) compounds are relatively more stable than the diphenyllead(IV) compounds.     

Nucleophilic additions of phosphines to a π-cyclobutadiene ligand

Nucleophilic addition of phosphines to the cyclobutadiene ring in [(h⁴-C₄H₄)Fe(CO)₂ NO]⁺PF₆^? leads to the formation of (exo-phosphonium-h³-cyclobutenyl) dicarbonylnitrosyliron hexafluorophosphate.     

Complexation reaction of metal ions with peptide systems. Part IV. A potentiometric study of rare earth complexes of glycyl-L-proline

Amino acids and dipeptides are of biological importance and therefore their metal complexes are of special interest. Many workers have studied the complexes of various peptides with different transition metals in solution^{1 – 5}. Although the stability of complexes of lanthanum with amino acids has been studied^{6 – 11}, no work appears to have been done with dipeptide systems. In continuation to our previous work^{12, 13} on the complexation reactions of lanthanides with dipeptide systems, the present communication reports the stability constants and thermodynamic functions of Y(III), La(III), Ce(III), Pr(III) and Nd(III) with glycyl-L-proline in aqueous medium at 25, 35 and 45°C at 0.15 M (KNO₃) ionic strength. The Calvin—Bjerrum titration technique^{14, 15} as modified by Irving and Rossotti¹⁶ was used.