Transition metal chemistry of oxime-containing ligands,VI: magnetic and structural properties of mono (pyridine-2-aldoxime) dithiocyanato iron (II) and mono (6-methylpyridine-2-aldoxime) dithiocyanato iron (II) complexes

The complexes of pyridine-2-aldoxime (HPOX) and 6-methylpyridine-2-aldoxime (HMPX) with iron (II) thiocyanate of the type [Fe(L)(NCS)₂] (L=HPOX and HMPX) have been prepared and characterized. A study of X-ray, magnetic, vibrational spectra (conventional and far-infrared), electronic spectra andMössbauer spectra has indicated that these complexes have polymeric, pseudo octahedral, coordination geometry with linear bridging thiocyanate ligands. The electronic spectra of mono complexes show a larger, low symmetry, ligand field than that present in [Fe(L)₂(NCS)₂] complexes. UnperturbedMössbauer spectra show a large quadrupole splitting, E _Q, and smaller isomer shift values in these iron (II) thiocyanate complexes. The magnetically perturbedMössbauer spectra of these iron(II) thiocyanate complexes at room temperature show that the principal component of the electric field gradient tensor is positive and corresponds to ad _xy (⁵B₂) ground state.With 2 Figures     

Stability of AQUO-organic silver iodide sol

Summary The coagulation concentration for silver iodide sol, both in presence of pyridine and dioxane, increases for mono- and bivalent coagulating electrolyte. In presence of a mixture of pyridine and dioxane in equal volume, the coagulation concentration assumes an intermediate value, which is nearer to dioxane. However, in presence of dioxane more bivalent electrolyte is needed than in presence of pyridine. If a bivalent coagulating electrolyte is added to a sol containing a mixture of pyridine and dioxane, the amount of electrolyte required to coagulate is less than pyridine and greater than dioxane. Thus silver iodide sol is more stable toward mono- and bivalent coagulating electrolytes. The degree of stabilization increases with the decrease of the dielectric constant of the dispersing medium. The intermediate values for dioxane pyridine mixture is accountable by the fact that dioxane acts as a solvent for pyridine. The PH value of the sol increases up to the coagulation point. Beyond this, there is an abrupt decrease. When the particles settle down completely a rise in PH is again noted on the further addition of electrolytes. The increase in the electrical conductance is more significant after coagulation. These changes have been explained by adsorption of the ions and due to the release of ions from the electrical double layer.

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Zusammenfassung Die Koagulationskonzentration für Silberjodidsol in Gegenwart von Pyridin und Dioxan steigt für ein- und zweiwertige Elektrolyte an. In Gegenwart einer Mischung zu gleichen Volumen erh?lt man mittlere Werte, n?her denen zu Dioxan. Für Koagulation in Gegenwart von Dioxan ist jedoch mehr zweiwertiger Elektrolyt notwendig als in Gegenwart von Pyridin. Bei Koagulation mit zweiwertigem Elektrolyt verbraucht ein Sol mit der Mischung von Pyridin und Dioxan weniger als für Pyridin und mehr als für Dioxan. Daher ist das Silbersol gegenüber ein- und zweiwertigen Elektrolyten stabiler. Der Grad der Stabilisierung w?chst mit abnehmender Dielektrizit?tskonstante des Dispersionsmediums. Die Zwischenwerte der Dioxan-Pyridin-Mischungen lassen sich verstehen durch die Tatsache, da? Dioxan als L?sungsmittel für Pyridin wirkt. Der PH-Wert des Sols w?chst bis zum Koagulationspunkt, darüberhinaus erfolgt ein steiler Abfall. Wenn die Teilchen vollst?ndig absetzen, ist bei weiterer Zugabe von Elektrolyt ein erneuter Anstieg im PH feststellbar. Der Anstieg der elektrolytischen Leitf?higkeit wird nach der Koagulation ausgepr?gter. Diese ?nderungen lassen sich durch Ionenadsorption und Freiwerden von Ionen aus der elektrischen Doppelschicht erkl?ren.

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Our thanks are due to Prof. R. C. Mehrotra for providing all the facilities for this work and to Prof. S. Ghosh of Allahabad University for helpful discussions. Thanks are also due to the University Grants Commission, Government of India, for the award of a research scholarship to one of us (V. K. S.).     

Biocompatible hydrogels based on chitosan,cellulose/starch,PVA and PEDOT:PSS with high flexibility and high mechanical strength

Fabricating mechanically strong hydrogels that can withstand the conditions in internal tissues is a challenging task. We have designed hydrogels based on multicomponent systems by combining chitosan, starch/cellulose, PVA, and PEDOT:PSS via one-pot synthesis. The starch-based hydrogels were homogeneous, while the cellulose-based hydrogels showed the presence of cellulose micro- and nanofibers. The cellulose-based hydrogels demonstrated a swelling ratio between 121 and 156%, while the starch-based hydrogels showed higher values, from 234 to 280%. Tensile tests indicated that the presence of starch in the hydrogels provided high flexibility (strain at break?>?300%), while combination with cellulose led to the formation of stiffer hydrogels (elastic moduli 3.9–6.6 MPa). The ultimate tensile strength for both types of hydrogels was similar (2.8–3.9 MPa). The adhesion and growth of human osteoblast-like SAOS-2 cells was higher on hydrogels with cellulose than on hydrogels with starch, and was higher on hydrogels with PEDOT:PSS than on hydrogels without this polymer. The metabolic activity of cells cultivated for 3 days in the hydrogel infusions indicated that no acutely toxic compounds were released. This is promising for further possible applications of these hydrogels in tissue engineering or in wound dressings.

Graphical abstract

     

Direct determination of the complete set of iron normal modes in a porphyrin-imidazole model for carbonmonoxy-heme proteins: [Fe(TPP)(CO)(1-MeIm)

Detailed Fe vibrational spectra have been obtained for the heme model complex [Fe(TPP)(CO)(1-MeIm)] using a new, highly selective and quantitative technique, Nuclear Resonance Vibrational Spectroscopy (NRVS). This spectroscopy measures the complete vibrational density of states for iron atoms, from which normal modes can be calculated via refinement of the force constants. These data and mode assignments can reveal previously undetected vibrations and are useful for validating predictions based on optical spectroscopies and density functional theory, for example. Vibrational modes of the iron porphyrin-imidazole compound [Fe(TPP)(CO)(1-MeIm)] have been determined by refining normal mode calculations to NRVS data obtained at an X-ray synchrotron source. Iron dynamics of this compound, which serves as a useful model for the active site in the six-coordinate heme protein, carbonmonoxy-myoglobin, are discussed in relation to recently determined dynamics of a five-coordinate deoxy-myoglobin model, [Fe(TPP)(2-MeHIm)]. For the first time in a six-coordinate heme system, the iron-imidazole stretch mode has been observed, at 226 cm(-)(1). The heme in-plane modes with large contributions from the nu(42), nu(49), nu(50), and nu(53) modes of the core porphyrin are identified. In general, the iron modes can be attributed to coupling with the porphyrin core, the CO ligand, the imidazole ring, and/or the phenyl rings. Other significant findings are the observation that the porphyrin ring peripheral substituents are strongly coupled to the iron doming mode and that the Fe-C-O tilting and bending modes are related by a negative interaction force constant.     

Thermodynamic model for the solubility of NdPO4(c) in the aqueous Na+-H+-H2PO4–HPO42–OH–Cl–H2O system

The solubility of NdPO₄(c) was studied at 23±2 °C from both the over and undersaturation directions, with pH ranging from 0 to 9, P concentrations ranging from 0.0003 to 1.00M, and equilibration periods ranging from 6 to 57 days. Equilibrium was reached in <6 days. From the H⁺, Nd, and P concentrations in equilibrated solutions, the logarithm of the thermodynamic equilibrium constant for the reaction (NdPO₄(c) Nd³⁺+PO₄ ^3-) was calculated to be -24.65±0.23 and the value of the Pitzer ion-interaction parameter ⁽²⁾for Nd³⁺-H₂PO₄ ^- was determined to be -92.9. Predictions based on these thermodynamic quantities were in excellent agreement with the experimental data.     

The circular chemistry conceptual framework: A way forward to sustainability in industry 4.0

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Vibrational spectrum of glycine molecule

The infrared and Raman spectra of glycine molecule has been studied in spectral region 400-4000 cm(-1) in solid form as well as in water. The vibrational frequencies for the fundamental modes of the glycine in neutral and its zwitterionic form have also been calculated using AM1 semiempirical method as well as ab initio method with minimal basis set. The reliability of the minimal basis set and AM1 method with higher basis sets, for IR spectra of the neutral glycine conformers were examined. We find that the 6-21G basis set calculation yields structural parameters, rotational constant and dipole moment of glycine conformers, which are very similar to those obtained from extended basis set calculation as well as experimental values. IR frequencies for glycine conformer I are also calculated in water using SCRF=PCM model and compared with experimental values. A comparison between calculated frequencies for neutral glycine, and its zwitterionic form with observed IR and Raman bands have been made. The total energies for gas phase glycine and its zwitterionic form along with those of hydrated forms were also calculated. It is found from the calculations that in the gas phase neutral glycine is more stable as compared to its zwitterionic form.     

X-band e.p.r. spectra of mixed-ligand copper(II) complexes

E.p.r. spectra of [Cu(et2dtc)2], Na[Cu(asp/glut)(et2dtc)] and Na2[Cu(asp/glut)(et2dtc)2] in the polycrystalline state have been recorded and discussed. The complexes display an antiferromagnetic exchange interaction, increasing in the order: Na2[Cu(asp/glut)(et2dtc)2] < Na[Cu(asp/glut)(et2dtc)] < [Cu(et2dtc)2] This revised version was published online in June 2006 with corrections to the Cover Date.     

A note on a characterization of P-matrices

In this note we show that the characterization results for P-matrices due to K.G. Murty and A. Tamir which state that a given square matrixM of ordern is a P-matrix if and only if the linear complementarity problem (q, M) has a unique solution for allq in a specified finite subset of ⁿ depending onM are incorrect whenn > 3.Research supported by Dr. K.S. Krishnan (DAE) fellowship for research in Mathematics and Computer Science, Bombay, India.     

A characterization based on the equidistribution of the first two spacings of record values

Summary For a sequence {X _n:n=0, 1, 2,...} of i.i.d. discrete random variables let X ₀ denote the zeroeth record value and X _L(1), the first record value. It is shown that X ₀ and X _L(1) –X ₀ are identically distributed if and only if X ₀ has the geometric distribution over the lattice k :k=1, 2,... for some >0.