Model Compounds for Iron Proteins. Structures and Magnetic, Spectroscopic, and Redox Properties of Fe(III)M(II) and [Co(III)Fe(III)](2)O Complexes with (&mgr;-Carboxylato)bis(&mgr;-phenoxo)dimetalate and (&mgr;-Oxo)diiron(III) Cores

A series of heterobimetallic complexes of the type [Fe(III)M(II)L(&mgr;-OAc)(OAc)(H(2)O)](ClO(4)).nH(2)O (2-5) and [{Fe(III)Co(III)L(&mgr;-OAc)(OAc)}(2)(&mgr;-O)](ClO(4))(2).3H(2)O (6) where H(2)L is a tetraaminodiphenol macrocyclic ligand and M(II) = Zn(2), Ni(3), Co(4), and Mn(5) have been synthesized and characterized. The (1)H NMR spectrum of 6 exhibits all the resonances between 1 and 12 ppm. The IR and UV-vis spectra of 2-5 indicate that in all the cases the metal ions have similar coordination environments. A disordered crystal structure determined for 3 reveals the presence of a (&mgr;-acetate)bis(&mgr;-phenoxide)-Ni(II)Fe(III) core, in which the two metal ions have 6-fold coordination geometry and each have two amino nitrogens and two phenolate oxygens as the in-plane donors; aside from the axial bridging acetate, the sixth coordination site of nickel(II) is occupied by the unidentate acetate and that of iron(III) by a water molecule. The crystal structure determination of 6 shows that the two heterobinuclear Co(III)Fe(III) units are bound by an Fe-O-Fe linkage. 6 crystallizes in the orthorhombic space group Ibca with a = 17.577(4) ?, b = 27.282(7) ?, c = 28.647(6) ?, and Z = 8. The two iron(III) centers in 6 are strongly antiferromagnetically coupled, J = -100 cm(-1) (H = -2JS(1).S(2)), whereas the other two S(1) = S(2) = (5)/(2) systems, viz. [Fe(2)(III)(HL)(2)(&mgr;-OH)(2)](ClO(4))(2) (1) and the Fe(III)Mn(II) complex (5), exhibit weak antiferromagnetic exchange coupling with J = -4.5 cm(-1) (1) and -1.8 cm(-1) (5). The Fe(III)Ni(II) (3) and Fe(III)Co(II) (4) systems, however, exhibit weak ferromagnetic behavior with J = 1.7 cm(-1) (3) and 4.2 cm(-1) (4). The iron(III) center in 2-5 exhibits quasi-reversible redox behavior between -0.44 and -0.48 V vs Ag/AgCl associated with reduction to iron(II). The oxidation of cobalt(II) in 4 occurs quasi-reversibly at 0.74 V, while both nickel(II) and manganese(II) in 3 and 5 undergo irreversible oxidation at 0.85 V. The electrochemical reduction of 6 leads to the generation of 4.     

Spectrofluorimetric determination of molybdenum in some real and environmental samples

A very simple, highly-sensitive and selective quenchofluorimetric method for the rapid determination of molybdenum(VI) in aqueous media is described. The method is based on the instantaneous quenching action by the metal-ion upon the native fluorescence of bathophenanthrolinedisulphonate (4,7-diphenyl-1,10-phenanthrolinedisulphonate) solution [lambda(ex) (max) 288 nm; lambda(em) (max) 444.8 nm] in the optimum pH-range of 3.0-3.7 at room temperature (25 +/- 5 degrees ). The fluorescence quenching is co-linear in the range of 0.01-1.0 ppm molybdenum. Large excesses of over 50 cations, anions and some common complexing agents were found to have no interference. Cu, Ni, Co, Fe and V can be tolerated only up to the corresponding amount of molybdenum. Interference from greater amounts can however be removed by a one-step ion-exchange separation process. The developed method was successfully tested over several standard alloys, synthetic mixtures of various compositions, factory effluents and in spiked environmental waters.     

Adsorption of several tracer cations and separation of234Th from238U and113mIn from113Sn on tin dioxide

The uptake of 22 cations at tracer concentrations has been studied over hydrous tin dioxide exchanger material. A granular variety of tin dioxide was prepared from the reaction of tin(IV) chloride with NaOH solution, and the formula of the material was ascertained to be SnO₂·1.7 H₂O. Radiochemical separation of carrier-free²³⁴Th from²³⁸U and^113mIn from¹¹³Sn was achieved over a tin dioxide column. The separated products were of high radionuclidic purity. The overall separation procedures are very simple and quick with quantitative yield.     

Simple methods for the direct assembly, functionalization, and patterning of acid-terminated monolayers on Si111

This article describes mild methods to directly assemble, functionalize, and pattern monolayers of undecylenic acid on hydrogen-terminated Si(111). These monolayers were assembled under very mild conditions from a neat solution of undecylenic acid containing 0.1 mol % 4-(decanoate)-2,2,6,6-tetramethylpiperidinooxy at room temperature without the need for UV light. Because of these mild conditions, monolayers exposing carboxylic acids could be assembled in one step without the need to protect the acid prior to its assembly. The monolayers were extensively characterized by horizontal attenuated total reflection infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle goniometry. The monolayers bonded to the silicon surface preferentially through the olefin with no detectable bonds between the carboxylic acids and silicon. The crystallinity of the monolayer was studied by infrared spectroscopy through the antisymmetric--v(a)(CH(2))--and symmetric--v(s)(CH(2))--stretches for methylene. Because it is important for future applications to assemble functional surfaces, methods to react the acid-terminated monolayers with trifluoroacetic anhydride and triethylamine to yield a symmetric anhydride on the monolayer were studied. These anhydrides were reacted with a variety of milligram-quantity amines to yield amide-terminated surfaces. This method was general, and a variety of amines could be bonded to the monolayer. The stabilities of these monolayers upon exposure to ambient conditions and under a variety of solvents were described. Because patterned monolayers have found wide applications, we have developed methods to pattern 1-octadecylamine and poly(ethylenimine) on the micrometer scale using soft lithography. In addition, polymer brushes of polynorbornene with thicknesses from 32 to 150 nm were grown from monolayers patterned with the Grubbs' catalyst. The patterned surfaces were imaged by scanning electron microscopy, scanning probe microscopy, and ellipsometry to determine the thicknesses of the patterns and the fidelity of the method.     

A facile one‐pot synthesis of novel substituted 1,2,3,4‐tetrahydropyrimidine,part 2: Synthesis of 1‐(aralkyl/aryl)‐3‐(alkyl/aralkyl/aryl)‐5‐aroyl‐1,2,3,4‐tetrahydropyrimidines

1‐(Aralkyl/aryl)‐3‐(alkyyaralkyl)‐5‐aroyl‐1,2,3,4‐tetrahydropyrimidines ( 2a‐c ) have been synthesized by dethiomethylation of 5‐aroyl‐6‐methylthio‐1,2,3,4‐tetrahydropyrimidines ( 1a‐c ). An alternative one‐pot synthetic strategy has been developed for the title compounds 2a‐t by the reaction of enaminones 3 with pri mary amine and formaldehyde in refluxing methanol in good yields.     

Nuclear moments and the change in the mean square charge radius of neutron deficient thallium isotopes

The hyperfine structure, isotope and isomeric shifts in the atomic transition 6p ² P _3/2–7s ² S _1/2, =535 nm have been measured for theI=7 andI=2 states of^{190, 192, 194, 196}Tl; theI=1/2 andI=9/2 states of¹⁹¹Tl and the I=7 isomer of¹⁸⁸Tl. The thallium isotopes were prepared as fast atomic beams at the GSI on-line mass separator following fusion reactions and — in some cases — subsequent-decay. The nuclear dipole moments, electric quadrupole moments and the change in the nuclear mean square charge radius are evaluated. Theuu-isotopes show an isomeric shift which changes sign between¹⁹²Tl and¹⁹⁴Tl.Dedicated to P. Armbruster on the occasion of his 60th birthday     

Oxygen binding to sulfur in nitrosylated iron--thiolate complexes: relevance to the Fe-containing nitrile hydratases

Iron-nitrosyl complex containing S-bonded monosulfinate [PPN][(NO)Fe(S,SO2-C6H4)(S,S-C6H4)] (3) has been isolated from sulfur oxygenation of complex [PPN][(NO)Fe(S,S-C6H4)2] (2) which is obtained from addition of NO molecule to [PPN][(C4H8O)Fe(S,S-C6H4)2] (1) in organic solvents. This result reveals that binding of NO to the iron center promotes sulfur oxygenation of iron dithiolates by dioxygen and stabilizes the S-bonded sulfinate iron species. Analysis of the bond angles for complexes 2 and 3 reveals that iron is best described as existing in a distorted trigonal bipyramidal coordination environment surrounded by one NO, three thiolates, and one sulfinate in complex 3, whereas the distorted square pyramidal geometry is adopted in complex 2. Complex 3 further reacts in organic solvents with molecular oxygen in the presence of [PPN][NO2] to produce the dinuclear bis(sulfinate) complex [PPN]2[(NO)Fe(SO2,SO2-C6H4)(S,S-C6H4)]2 (4). Complex 3 showed reaction with PPh3 in THF/CH2Cl2 to yield complex 2 and Ph3PO. Upon photolysis of CH2Cl2 solution of complex 3 under N2 purge at ambient temperature, the UV-vis and IR spectra consistent with the formation of complex 2 demonstrate that complex 2 and 3 are photochemically interconvertible. Obviously, complex 3 is thermally quite stable but is photochemically active toward [O] release. Also described are the X-ray crystal structures of 3 and 4.     

Size controlled synthesis of ZnO nanoparticles via electric field assisted continuous spray pyrolysis (EACoSP) reactor

ZnO nanoparticles were synthesized by the continuous spray pyrolysis technique (CoSP) and the effect of applied voltage across the spray nozzle and an annular ground electrode during spray has been studied. X-ray diffraction and transmission electron microscopy studies showed that the product has (hexagonal) wurtzite structure with the average particle size decreasing from 18.5?nm to 12.9?nm in the presence of a high DC voltage (1?kV). The higher value of the absorption peak for the nanoparticles synthesized without voltage is supportive of this behavior. The films deposited by spin coating using these nanoparticles can be used for a variety of applications, particularly as photoelectrodes for dye-sensitized solar cells.