Use of heterodifunctional ligands to bridge “early” and “late” transition metals. Construction and chemistry of complexes containing indirectly linked cobalt carbonyl and zirconocene units

Four zirconocene systems, each containing tertiary phosphine functionality indirectly linked to either or both cyclopentadienyl rings, are described. Unlike the phosphinomethylzirconocenes, in which the metal and the phosphine strongly influence each other's basic chemistry, it has been found that a variety of transformations may be carried out at either site on the more indirectly linked systems without interference from the other. Thus reduction and hydrozirconation proceed normally at the Zr center, and quaternization and complexation to a second metal may be achieved at the phosphine. Two “early-late” multimetallic systems containing Zr and Co have been prepared. Reduction and acylation at Co proceed without interference from Zr; however, attempts to generate hydrides at Zr in the bimetallic systems were unsuccessful.     

Preparation and properties of poly(urethane-imide)s derived from amine-blocked-polyurethane prepolymer and pyromellitic dianhydride

Poly(urethane-imide)s were prepared using amine-blocked-polyurethane (PU) prepolymer and pyromellitic dianhydride. The PU prepolymers were prepared by the reaction of different diols (polypropyleneoxy glycol, polytetramethyleneoxy glycol, polycaprolactonediol and hydroxyl terminated polybutadiene) and different diisocyanates (2,4-tolylene diisocyanate, 1,4-phenelene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate and 4,4^′-methylenebis(cyclohexyl)isocyanate) and end capped with N-methylaniline. The polymerization was faster with aromatic isocyanates than with aliphatic isocyanates. The effect of imide content on the thermal and mechanical properties was studied. The poly(urethane-imide)s were characterized by FTIR, GPC, TGA and for dynamic and static mechanical properties. Weight average molecular weight (M_w) of the polymers did not vary significantly with change in -NCO/-OH ratio where as number average molecular weight (M_n) increased with increasing -NCO/-OH ratio, correspondingly, the dispersity (PD) decreased. Polymers with higher hard segment content exhibited higher glass transition temperature. The thermal stability of the PU was found to increase significantly by the introduction of imide component.     

5-Hydroxy-pyrrolone based building blocks as maleimide alternatives for protein bioconjugation and single-site multi-functionalization

Recent dramatic expansion in potential uses of protein conjugates has fueled the development of a wide range of protein modification methods; however, the desirable single-site multi-functionalization of proteins has remained a particularly intransigent challenge. Herein, we present the application of 5-hydroxy-1,5-dihydro-2H-pyrrol-2-ones (5HP2Os) as advantageous alternatives to widely used maleimides for the chemo- and site-selective labeling of cysteine residues within proteins. A variety of 5HP2O building blocks have been synthesized using a one-pot photooxidation reaction starting from simple and readily accessible furans and using visible light and oxygen. These novel reagents display excellent cysteine selectivity and also yield thiol conjugates with superior stability. 5HP2O building blocks offer a unique opportunity to introduce multiple new functionalities into a protein at a single site and in a single step, thus, significantly enhancing the resultant conjugate''s properties.

Recent expansion in potential uses of protein conjugates has fueled the development of a range of protein modification methods; however, the desirable single-site multi-functionalization of proteins has remained a particularly intransigent challenge.     

Kinetics and mechanism of oxidation of S-phenylthioacetic acids by Ce(IV)

The kinetics of oxidation of several S-phenylthioacetic acids by ceric ammonium nitrate (CAN) in presence of perchloric acid has been studied spectrophoto- metrically in 50 %(v/v) aqueous acetic acid. The order with respect to Ce(IV) is one and the order with respect to S-phenylthioacetic acid is found to be 0.8. A linear plot of k_obs⁻¹ vs [substrate]⁻¹ with an intercept on the rate of axis suggests the formation of an equilibrium complex between the reactants prior to the rate determining step. The added acrylonitrile retards the reaction rate considerably suggesting that the oxidation process may involve a free radical mechanism. Electron-releasing substituents generally accelerate the rate, while electron-withdrawing groups retard the rate. A good correlation is found to exist between log k_1.8 and Hammett σ constants.     

Ultraviolet-A induced changes in photosystem II of thylakoids: effects of senescence and high growth temperature

Ultraviolet-A (UV-A) radiation induced changes in photosystem II (PS II) of senescing leaves of wheat seedlings were investigated. UV-A radiation did not show any significant effect on the level of photosynthetic pigments. However, the decline in F(v)/F(m) and oxygen evolution rate indicated the damaging effect of the radiation on primary photochemistry of PS II. Modification at the Q(B)-binding site was inferred from the observed downshift of peak temperature of thermoluminescence (TL) B-bands. The UV-A induced changes in PS II of chloroplasts from senescing leaves were found to be synergistically accelerated by high growth temperature.     

Separation of heavier rare earths from neutron irradiated uranium targets

A radiochemical method is described for the separation of heavier rare earths from the fission of uranium. The method is particularly suitable for the separation of low yield (10⁻⁵%–10⁻⁷%), highly asymmetric rare earth fission products viz.^179,177Lu,¹⁷⁵Yb,¹⁷³Tm,^172,171Er,¹⁶⁷Ho and^161,160Tb in the neutron induced fission of natural and depleted uranium targets. Additional separation steps have been incorporated for decontamination from²³⁹Np (an activation product) and^93-90Y (a high fission-yield product) which show similar chemical behaviour to rare earths. Separation of individual rare earths is achieved by a cation exchange method performed at 80°C by elution with α-hydroxyisobutyric acid (α-HIBA).     

Long-range deuterium isotope effects on fluorine-19 chemical shifts of 4-substituted bicyclo[2.2.2]octyl- and bicyclo[2.2.1]heptyl-1-fluorides : Deuterium as a substituent

²H/¹H isotope effects on the ¹⁹F chemical shifts of 4-substituted bicyclo[2.2.2]oct-1-yl and bicyclo[2.2.1]hept-1-yl fluoride are significantly shielding and deshielding, respectively. This result is consistent with deuterium being viewed as an $\text{electronegative}$ substituent relative to hydrogen when attached to an sp³ hybridised carbon.     

Speciation and estimation of radioiodine in reactor coolant water

The species of radioiodine in the primary coolant water of the heavy water moderated, heavy water cooled 100 MW research reactor have been identified. It was observed that IO ₃ ^? was the major species in the reactor coolant during reactor operation and I^? was the major species during shutdown. Organic and elemental forms amount only to less than 2% of total radioiodine. A simple method was developed for the estimation of gross iodine activity in reactor coolant water. The method involves the separation of all inorganic forms of iodine into a photographic film consisting of a thin layer of silver halide. The iodine in the film was estimated by gross counting of the film in a Geiger-Müller counter. Gross iodine activity in the reactor coolant samples estimated by the present method were in agreement with that obtained by direct γ-spectrometry with a Ge detector. It is concluded that the method can be used for the routine estimation of radioiodine in reactor coolant water.¹³³I/¹³¹I and¹³⁵I/¹³¹I ratios in the film were estimated and found to be useful in identifying split rod conditions in the reactor.     

Application of two-tracer isotope dilution mass spectrometry in the determination of uranium in geological samples

The determination of the uranium concentration in mineral samples using two tracer (²³³U and ²³⁵U) mass spectrometric isotope dilution techniques is described. The precision and accuracy are discussed and results are compared with those obtained by x-ray fluorescence and instrumental neutron activation methods. Based on the two independent values obtained for the same dilution, parameters such as the chemical procedures adopted, effect of mass fractionation and uranium distribution in minerals are evaluated. The ability of the method to distinguish between the analytical errors and heterogeneous distribution of uranium is discussed.     

A Novel Test Strategy for Fine Pitch Wafer-Level Packaged Devices

This paper describes an innovative test strategy comprising a compliant elastomer mesh for testing fine pitch wafer-level package (WLP) devices. The test probe, hardware, and sample preparation processes are detailed. The components of the test hardware socket such as the SMA connectors, coplanar transmission lines on the PCB, via, off-chip interconnect, and elastomer mesh probe have been modeled. A complete system-level model, with off-chip interconnects on the WLP device pads, has been developed. The measurement and model demonstrate that the prototype test socket performs at 5 GHz with an insertion loss of about 3 dB. WLP device with Bed-of-Nail interconnects are characterized. Functional test features of the system are also addressed.