Second Dissociation Constant of Bis-[(2-hydroxyethyl)amino]acetic Acid (BICINE) and pH of Its Buffer Solutions from 5 to 55 °C

The values of the second dissociation constant, K ₂, and related thermodynamic quantities of the ampholyte bis[(2-hydroxyethyl)amino]acetic acid (BICINE) have been determined at temperatures from 5 to 55 ^∘C. The pH values of six equimolal buffer solutions, and four buffer solutions having ionic strengths (I = 0.16 mol⋅kg⁻¹) similar to those in blood plasma, have been evaluated at 12 temperatures from 5 to 55 ^∘C using the Bates–Guggenheim convention. The liquid junction potentials (E _j ) between the buffer solutions of BICINE and saturated KCl solution of the calomel electrode at 25 and 37 ^∘C have been estimated by measurement with a flowing junction cell. These values of E _j have been used to ascertain the operational pH values at 25 and 37 ^∘C. The pK ₂ values at 25 and 37 ^∘C are 8.333 and 8.156, respectively. The thermodynamic quantities associated with the second acid dissociation have been calculated from the values of pK ₂ as a function of temperature. The zwitterionic buffer BICINE was shown to be useful as a pH standard in the region close to that of blood serum.     

Efficient Method for Demethylation of Aryl Methyl Ether Using Aliquat-336

A rapid method for selective cleavage of aryl methylethers can be achieved in the presence of a protic acid and a catalytic amount of phase-transfer catalyst (Aliquat-336). Aliquat-336 accelerates the rate of reaction and affords the corresponding phenols in excellent to good yields on a wide variety of substrates.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

On the static Lovelock black holes

We consider static spherically symmetric Lovelock black holes and generalize the dimensionally continued black holes in such a way that they asymptotically for large $r$ go over to the d-dimensional Schwarzschild black hole in dS/AdS spacetime. This means that the master algebraic polynomial is not degenerate but instead its derivative is degenerate. This family of solutions contains an interesting class of pure Lovelock black holes which are the $N$ th order Lovelock $\Lambda $ -vacuum solutions having the remarkable property that their thermodynamical parameters have the universal character in terms of the event horizon radius. This is in fact a characterizing property of pure Lovelock theories. We also demonstrate the universality of the asymptotic Einstein limit for the Lovelock black holes in general.     

Assembling metals (Co II and Mn II) with pyridylcarboxylates in the presence of azide: synthesis, structural aspects and magnetic behavior of three coordination polymers

The reaction between Co(NO3)2.6H2O and substituted pyridylcarboxylic acid [nicotinic acid (Hnic) or trans-3-pyridylacrylic acid (Htpa)] in the presence of NaN3 under hydrothermal conditions yielded [Co(1.5)(nic)2 (Hnic)(N3)]n (1) and [Co(1.5)(tpa)2 (N3)(H2O)]n (2), respectively. Single crystal structure analyses reveal that both complexes are 3D complicated coordination polymers. The basic repeating units in both of the complexes are Co(3) trinuclear clusters containing syn-syn bridging carboxylate and end-on azido linker. A similar reaction using MnCl2.4H2O in presence of equimolar amounts of Htpa and NaN3 yielded a 2D corrugated sheet [Mn(tpa)2]n (3) containing no azide. Complex 3 can also be synthesized under hydrothermal conditions using Natpa in the absence of NaN3. Surprisingly, the same reaction at room temperature yielded a known mononuclear complex [Mn(tpa)2(H2O)4]. Variable temperature magnetic studies down to 2 K revealed the dominant antiferromagnetic nature of the first two complexes with a ferrimagnetic type of behavior despite the facts that they are homometallic and homospin systems. The susceptibility data in both cases were analyzed by a Co3 trinuclear model as well as considering inter-trimer interactions. Complex 3 is weakly antiferromagnetic in nature with an exchange parameter of J = -2 cm(-1) through the syn-anti bridging carboxylate pathway.     

Stability and bonding of carbon(0)-iron−N2 complexes relevant to nitrogenase co-factor: EDA-NOCV analyses

The factors/structural features which are responsible for the binding, activation and reduction of N₂ to NH₃ by FeMoco of nitrogenase have not been completely understood well. Several relevant model complexes by Holland et al. and Peters et al. have been synthesized, characterized and studied by theoretical calculations. For a matter of fact, those complexes are much different than real active N₂-binding Fe-sites of FeMoco, which possesses a central C(4-) ion having an eight valence electrons as an μ₆-bridge. Here, a series of [(S₃C(0))Fe(II/I/0)-N₂]^n- complexes in different charged/spin states containing a coordinated σ- and π-donor C(0)-atom which possesses eight outer shell electrons [carbone, (Ph₃P)₂C(0); Ph₃P→C(0)←PPh₃] and three S-donor sites (i.e. ^-S-Ar), have been studied by DFT, QTAIM, and EDA-NOCV calculations. The effect of the weak field ligand on Fe-centres and the subsequent N₂-binding has been studied by EDA-NOCV analysis. The role of the oxidation state of Fe and N₂-binding in different charged and spin states of the complex have been investigated by EDA-NOCV analyses. The intrinsic interaction energies of the Fe−N₂ bond are in the range from −42/−35 to −67 kcal/mol in their corresponding ground states. The S₃C(0) donor set is argued here to be closer to the actual coordination environment of one of the six Fe-centres of nitrogenase. In comparison, the captivating model complexes reported by Holland et al. and Peter et al. possess a stronger π-acceptor C-ring (S₂C_ring donor, π-C donor) and stronger donor set like CP₃ (σ-C donor) ligands, respectively.     

Three new Cu-azido polymers and their systematic interconversion: role of the amount of the blocking amine on the structural diversity and magnetic behavior

Three new coordination polymers [Cu5(N3)10(en)2]n (1), [Cu6(N3)12(en)4]n (2), and [Cu4(N3)8(en)4]n (3) have been synthesized in a controlled manner by treatment of a 1:2 mixture of Cu(NO3)2 and NaN3 with varying amount of ethylenediamine (en). Single-crystal structure analyses clearly indicated that the puckered Cu4 biscubane unit in 1 gradually opens to a slightly more open Cu4 macrocyclic unit in 2 when more en approaches to the Cu4 core. Upon addition of further en, an open Cu4 linear secondary building unit was obtained in complex 3. Complex 1 contains four different kinds of bridging modes of the azide anion and is a complicated 3D polymer. Similarly, complexes 2 and 3 are 3D and 2D polymers, respectively, containing three different kinds of bridging azides. Complex 3 contains two very rare cis end-to-end (EE) and single-end-on (EO) azido modes. Structural transformation from 1 to 3 was monitored and explained qualitatively. Variable-temperature magnetic studies in the temperature range of 300-2 K reveal the existence of dominant ferromagnetic behavior in all the three cases with a metamagnetic-type behavior in complex 1 with the critical field of transition at 0.8 T. The purity of all the complexes were established by elemental analyses, as well as by the powder XRD patterns that matched well with the expected patterns from the single-crystal structure analysis.     

Quasi-static response and texture evolution of α- and γ-RDX: a comparative study

In this paper, we undertake a comparative study of the stress–strain response and slip activity of α- and γ-polymorph of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) under pressure loading using a rate-dependent single-crystal plasticity model. Texture evolution studies are performed to further understand the effects of the dominant slip systems. The simulations indicate that the difference in elastic moduli and lattice parameters for α- and γ-RDX lead to different elastic–plastic constitutive response in the two polymorphs. γ-RDX exhibits more plastic slip compared to α-RDX for loading on (1 1 1) plane and the two polymorphs have different sets of dominant slip systems. We observe that the high-pressure slip system (0 0 1)[0 1 0] that is determined using molecular dynamics simulations is the most dominant slip system for this orientation. Whereas, for loading on (2 1 0) plane, α-RDX has marginally higher plastic slip than γ-RDX, though the same slip system is dominant for both the polymorphs. The texture evolution for loading on (1 1 1) and (2 1 0) planes follow the path towards the most dominant slip systems for both the polymorphs. We predict that the larger plastic slip in γ-RDX for loading on (1 1 1) plane might play an important role in understanding the reduced sensitivity for shock loading on (1 1 1) plane, when compared to (2 1 0) for which γ-RDX has lesser plastic slip, and (1 0 0) which is purely elastic.