MONITORING LIGHT-INDUCED CHANGES IN ISOLATED, INTACT EYE LENSES

Fluorescence spectral changes occurring upon irradiation with 300 nm light have been monitored in situ in isolated, intact, whole lenses from the eyes of several species. The findings corroborate observations on other individual constituent protein molecules in the solution state, and also reveal features attributable to the supramolecular protein assembly that exists in the whole lens. Irradiation of the lens with 300 nm light causes red shifts in the tryptophan emission spectrum, suggesting alterations in the protein packing in the lens. Intermolecular energy transfer from tryptophan to one of the photoproducts, presumably N-formylkynurenine (N-FK), occurs in the condensed-phase sample. The N-FK formed is photodegraded efficiently in the lens, indicating that the photodynamic effects of endogenous N-FK might not be as severe as has been thought. Species variation in the photoevents are evident, particularly in avian lenses that contain the variant δ-crystallin as the core protein. The photoinduced changes in the near-UV circular dichroism of δ-crystallin (which is α-helical, as opposed to the β-sheet structure of α-, β-, and -γ-crystallins), isolated from chicken lenses, are remarkably different from other crystallins. Irradiation of δ-crystallin leads to a drastic reduction of circular dichroism intensity in the 250–300 nm region, whereas no changes are seen in the peptide absorption band.     

Novel Synthesis of Mafenide and Other Amino Sulfonamides by Electrochemical Reduction of Cyano Sulfonamides

Both aliphatic and aromatic amino sulfonamides such as mafenide ( 1a ) were synthesized in good yields (80–86%) by direct electrochemical hydrogenation of the corresponding nitriles in an undivided cell containing a Ni cathode, a Pt anode, and Raney Ni as catalyst (Table 1). The reaction can be performed without external supply of pressurized gas by in situ generation of H₂. Slightly elevated temperatures (45°) and low current densities (10 mA/cm²) are favorable conditions for this type of electrochemical nitrile hydrogenation. Our synthetic protocol does not require high‐pressure equipment or chemical hazards, is environmentally very friendly, and more economical than traditional methods. The concentration of adsorbed H^. radicals on the catalyst surface can be easily controlled by adjusting the electric potential, which may lead to improved product selectivity and, at the same time, reduces the risk of explosion and fire.     

Mixed valency in the high-temperature phases of transition metal molybdates, A MoO4 ( A =Fe, Co, Ni)

Transition metal molybdates of the formulaAMoO₄ whereA=Fe, Co or Ni exhibit a first-order phase transition between 670K–970K. An investigation of the lowtemperature (lt) and high-temperature (ht) phases by x-ray photoelectron spectroscopy, x-ray absorption spectroscopy, magnetic susceptibility and other physical methods shows that the phase transition is associated with a valence change of the typeA ²⁺+Mo⁶⁺αA ³⁺+Mo⁵⁺ in the cases of iron and cobalt molybdates. Contribution No. 311 from the Solid State and Structural Chemistry Unit.     

Development of a method for recovery of 233U from thorium oxalate cake in reconversion step of reprocessing of irradiated thorium rods

A method is developed for the selective leaching of ²³³U from a thorium oxalate cake. The leaching capacity of ammonium carbonate and nitric acid have been investigated, showing that (NH₄)₂CO₃ leads to higher recovery. The maximum leaching efficiency is obtained using 0.5% ammonium carbonate, with a minimal thorium pick-up. A uranium recovery of 94% is obtained after three consecutive contact experiments in carbonate media, with minimal thorium uptake in the leachate. This process was applied to an actual plant stream, allowing the reduction of the ²³³U -activity from 5.64 to 0.3 Ci/g of thorium oxalate cake.     

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     

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.

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

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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.     

Preconcentration of trace metals on Amberlite XAD-4 resin coated with dithiocarbamates and determination by inductively coupled plasma-atomic emission spectrometry in saline matrices

Preconcentration of Cd(II), Cu(II), Mn(II), Ni(II), Pb(II) and Zn(II) in saline matrices on Amberlite XAD-4 resins coated with ammonium pyrrolidine dithiocarbamate (APDC) and piperidine dithiocarbamate (pipDTC) and subsequent determination by inductively coupled plasma atomic emission spectrometry were studied. Parameters such as effect of pH, effect of HNO(3) concentration on elution of metals from resin were studied. The results show that Amberlite XAD-4 coated with APDC was more efficient in the recovery of metal ions compared with Amberlite XAD-4 coated with pipDTC, in the concentration range of 0.1-200 mug l(-1), for 1 g of Amberlite XAD-4 coated resin. The detection limits for Cd(II), Cu(II), Mn(II), Ni(II), Pb(II), Zn(II) are 0.1, 0.4, 0.3, 0.4, 0.6, 0.5 mug l(-1), respectively, for resin coated with APDC and 0.7, 1.0, 0.8, 0.9, 1.7 and 1.2 mug l(-1) for resin coated with pipDTC. The effect of diverse ions on the determination of aforesaid metals was studied. The method was applied for the determination of trace metal ions in artificial sea water and natural water samples. The results were compared with extraction AAS method.