Kinetic Study of the Interaction of Three Glycine-Containing Dipeptides with Hydroxopentaaquarhodium(III) Ion in Aqueous Medium

The kinetics of the interaction of three glycine-containing dipeptides, namely, glycyl-L-valine (L¹-L??H), glycyl-glycine (L²-L??H) and glycyl-L-glutamine (L³-L??H), with [Rh(H₂O)₅OH]²⁺ has been studied spectrophotometrically in aqueous medium as a function of the Rh(H₂O)₅OH²⁺ and dipeptide concentrations, pH and temperature, at constant ionic strength. At pH = 4.3, the substrate complex exists predominantly as the hydroxopentaaqua species and dipeptides as zwitterions. The reaction has been found to proceed via two parallel paths: both processes are ligand dependent. The rate constants for the processes are of the order: k ₁??10^?3 s^?1 and k ₂??10^?5 s^?1. The activation parameters for both steps were evaluated from Eyring plots. Based on the kinetic and activation parameters an associative interchange mechanism is proposed for both of the interaction processes. The low $\Delta H_{1}^{\neq}$ and $\Delta H_{2}^{\neq}$ values and large negative values of $\Delta S_{1}^{\neq}$ and $\Delta S_{2}^{\neq}$ support the associative mode of activation for both processes. The product of the reaction has been characterized using IR and ESI-mass spectroscopic analysis.     

Combinatorial proofs of some determinantal identities

In this paper, we give combinatorial proofs of some determinantal identities. In fact, we give a combinatorial proof of a theorem of R. P. Stanley regarding the enumeration of paths in acyclic digraphs along with some interesting applications. We also give an almost visual proof of a recent result of Oliver Knill, namely ‘The generalized Cauchy–Binet Theorem.’     

The g-value of the 2E state of K3CR(CN)6 and the lower symmetry field

The ⁴A₂ → ²E transition of potassium chromicyanide has been studied under magnetic field. It has been found that the g-value is nearly isotropic, quite unlike the case of ruby. An attempt has been made to explain the zero-field splittings of ^2E, ²T₁ and ²T₂ states and the g-value of the ²E state on the assumption that the distant ions are mainly responsible for lowering of symmetry of the crystal field from O_h. A reasonable choice of parameters can make the calculated values agree with the observed ones.     

Spectrophotometric determination of palladium with 2-mercaptomethyl-benzimidazole

Summary A spectrophotometric method has been developed for the determination of palladium with 2-mercaptomethyl-benzimidazole. This involves extraction of the palladium complex into iso-amyl alcohol in presence of 0.3 to 2N hydrochloric acid and 0.45 to 1.4M ammonium sulfate. The color is very stable and is highly selective for palladium. At 380 nm it obeys Berr's law in the concentration range of 1 to 9g of Pd per ml; the optimum range being 4 to 8g. The sensitivity and molar absorptivity of the reaction are 0.019g of palladium per cm² and 5600±70 respectively. The continuous variation and molar ratio methods indicate that palladium forms 12 complex with the ligand.

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Zusammenfassung Eine spektrophotometrische Methode zur Bestimmung von Palladium mit 2-Merkaptomethylbenzimidazol wurde ausgearbeitet. Der Palladiumkomplex wird mit Isoamylalkohol in Gegenwart von 0,3- bis 2-n Salzsäure und von 0,45- bis 1,4-m Ammoniumsulfat extrahiert. Die Farbe ist sehr beständig und sehr selektiv für Palladium. Bei 380 nm entspricht die Färbung dem Beerschen Gesetz zwischen 1 und 9g Pd/ml; der optimale Konzentrationsbereich liegt zwischen 4 und 8g. Die Empfindlichkeit der Reaktion beträgt 0,019g Pd/cm²und die molare Absorption 5600±70. Die Untersuchung nachJob ergab für den Komplex das Molverhältnis Pd: Reagens= 12.

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Résumé On a mis au point une méthode spectrophotométrique pour le dosage du palladium par le mercaptométhyl-2 benzimidazole. Elle met en jeu l'extraction du complexe du palladium par l'alcool isoamylique en présence d'acide chlorhydrique 0,3 à 2N et de sulfate d'ammonium 0,45 à 1,4M. La coloration est très stable et bien sélective pour le palladium. A 380 nm, elle suit la loi de Beer dans le domaine de concentration de 1 à 9g de Pd par ml; le meilleur domaine s'étend de 4 à 8g. La sensibilité et l'absorbance molaire de la réaction sont respectivement de 0,019g de palladium par cm² et 5600±70. Les méthodes des variations continues et du rapport molaire indiquent que le palladium forme un complexe 1,2 avec le coordinat.

     

Structural characterization, magnetic properties, and electrospray mass spectrometry of two Jahn-Teller isomers of the single-molecule magnet [Mn12O12(CF3COO)16(H2O)4

The syntheses and characterization of two new, highly soluble, single-molecule magnets [Mn12O12(CF3COO16(H2O)4].2CF3COOH.4H2O (1) and Mn12O12(CF3COO16(H2O)4].CF3COOH.7H2O (2) are reported. Compound 1 was isolated from the reaction of Mn12O12(CF3COO16(H2O)4] with trifluoroacetic acid in CH2Cl2. Compound 1 crystallizes in the tetragonal space group Ifourmacr; (No. 82) with unit cell parameters a = b = 18.128(3) A, c = 13.048(3) A, V = 4287.9(19) A3, Z = 2 and is isostructural to [Mn12O12(CH3COO)16(H2O)4]. Compound 2 was prepared from the reaction of Mn12O12(CF3COO16(H2O)4] with neat trifluoroacetic acid, and crystallizes in the monoclinic space group P2(1)/n (No. 14) with unit cell parameters a = 15.221(8) A, b = 21.870(12) A, c = 27.217(15) A, beta = 90.53(1) degrees, V = 9060(9) A3, and Z = 4. The dc magnetic susceptibility measurements in the 2-300 K temperature range support a high-spin ground state. The magnetization data collected in the 1-7 T field range from 1.8 to 4.0 K were best fit to the parameters S = 10, g = 2.15, D = -0.65 cm(-1), and E = 0 cm(-1) for 1 and S = 10, g = 1.87, D = -0.34 cm(-1), and E = -0.10 cm(-1) for 2. The ac susceptibility data for compound 1 reveal out-of-phase (chi(m)") signals in the 4-7 K temperature range, whereas the chi(m)" signals for compound 2 appear below temperatures of 4 K. This variation in blocking temperatures is a consequence of the two different crystallographic forms of compounds 1 and 2. Compound 1 exhibits the same structural geometry and distortions found in [Mn12O12(CH3COO)16(H2O)4], while compound 2 is of lower molecular symmetry with two Jahn-Teller axes of distortion being oriented along oxide ligands. This different structural arrangement facilitates a different tunneling pathway that leads to a lower effective barrier for magnetization reorientation for compound 2. The substitution of the acetate ligands by trifluoroacetic acid was monitored by mass spectrometry, which is a convenient tool for judging completion of the substitution process.     

The optimal sequential and parallel algorithms to compute all hinge vertices on interval graphs

If the distance between two vertices becomes longer after the removal of a vertexu, thenu is called a hinge vertex. In this paper, a linear time sequential algorithm is presented to find all hinge vertices of an interval graph. Also, a parallel algorithm is presented which takesO(n/P + logn) time usingP processors on an EREW PRAM.     

Influence of Chemical Reaction on Stability of Thermo-Solutal Convection of Couple-Stress Fluid in a Horizontal Porous Layer

We consider the onset of thermo-solutal convection in a couple-stress fluid-saturated anisotropic porous medium, where the chemical equilibrium on the bounding surfaces and the solubility of the dissolved components depend on temperature. The entire study has been spilt into two parts: (i) linear stability analysis (ii) weakly non-linear stability analysis. Stationary case of linear stability analysis is discussed for two modes of bounding surfaces (a) realistic bounding surfaces i.e. Rigid-Rigid and Rigid-Free (R/R and R/F), (b) non-realistic bounding surfaces i.e. Free-Free (F/F). Howsoever, investigation of oscillatory state and weakly non-linear stability are restricted to F/F case. Galerkin method is used to solve the eigenvalue problem for R/R and R/F cases, whereas, exact solutions are obtained for F/F case.A comparative study among flow stability for above different cases is made as function of ratio of viscosities ( i.e., couple-stress viscosity to fluid viscosity which is defined as couple-stress parameter, $(C)$ ) and effective chemical reaction (i.e. chemical reaction parameter, $(\chi )$ ). It has been found that increasing viscosity of the couple-stress fluid, in terms of increasing $C$ , increases flow stability in all three cases, but among all cases its stabilization effect for R/R is maximum. However, in the absence of couple-stress parameter the maximum stability of flow is observed for F/F. Apart from this, the chemical reaction stabilizes the flow for all the three cases. Furthermore, stability analysis for F/F case indicates that couple-stress parameter stabilizes the system in all modes (stationary, oscillatory and finite amplitude) of convection.Damköhler number $(\chi )$ is found to delay the stationary convection, however, it speeds up the onset of oscillatory convection. The non-linear theory based on truncated representation of Fourier series method predicts the occurrence of sub-critical instability in the form of finite amplitude motion. The effect of $C$ and $\chi $ on heat and mass transfer is also examined.     

Shift of millimeterwave window frequencies in relation to tropospheric radio meteorological parameters

In view of wide application areas of the millimeterwave frequency band (18–300 GHz) in recent years for various civil and defence applications including radar and communications, remote sensing and radio astronomy, we were prompted to undertake a theoretical estimate of the variation of specific attenuation (dB/Km) with radio meteorological parameters in clear weather conditions. The results of the estimation of the attenuation in this frequency band for some major locations in India from available radio meteorological data from NOAA, USA are presented in this paper. An appreciable amount of shift, which is mainly a function of the atmospheric pressure, temperature and relative humidity was noticeable in each of the window frequencies around 35, 94, 140 GHz and 220 GHz.     

Optical absorption and photoluminescence spectroscopy of the growth of silver nanoparticles

Results obtained from the optical absorption and photoluminescence (PL) spectroscopy experiments have shown the formation of excitons in the silver-exchanged glass samples. These findings are reported here for the first time. Further, we investigate the dramatic changes in the photoemission properties of the silver-exchanged glass samples as a function of postannealing temperature. Observed changes are thought to be due to the structural rearrangements of silver and oxygen bonding during the heat treatments of the glass matrix. In fact, photoelectron spectroscopy does reveal these chemical transformations of silver-exchanged soda glass samples caused by the thermal effects of annealing in a high vacuum atmosphere. An important correlation between temperature-induced changes of the PL intensity and thermal growth of the silver nanoparticles has been established in this Letter through precise spectroscopic studies.