A new method of removing excess of reagent from organic phases in the solvent extraction of metal complex anions with quaternary ammonium salts: Spectrophotometric determination of micro amounts of cobalt with 2-nitroso-1-naphthol-4-sulfonic acid

The removal of excess reagent extracted into an organic phase in the solvent extraction of a metal complex anion with a quaternary ammonium ion is discussed. With a given chelating ligand (HO—R—SO₃H), the order of extractability is HO—R—SO₃^- > M(OR—SO₃)^n- > X^- > ^-O—R—SO₃^- when an anion such as nitrate or halide is added. If suitable amounts of the anion are added, only the excess of reagent can be removed. The principle is applied to the extraction with zephiramine of the cobalt complex anion formed with 2-nitroso-1-naphthol-4-sulfonic acid. Micro amounts of cobalt in pure nickel salts were determined spectrophotometrically.     

Determination of sulfate in river water by flow injection analysis

Sulfate ion in river water is determined by flow injection analysis at a rate of 30 samples per hour; the sulfate contents are typically less than 30 ppm. The reagent solution contains dimethylsulfonazo-III, barium chloride, potassium nitrate and chloroacetate buffer in 70% ($\text{v}\text{v}$) ethanol, and is saturated with barium sulfate. The aqueous carrier stream is also saturated with barium sulfate. The sample is filtered and treated with Amberlite IR120-B cation-exchanger before injection into the carrier stream, and the decoloration of the barium—dimethylsulfonazo-III complex by sulfate is measured at 662 nm. The calibration graph is linear over the range 0–30 μg ml^-1 for sulfate in water.     

Modification de la position 8 des purines nucleosides et de l'adenosine monophosphate cyclique-3′,5′. Reactions de couplage catalytique des organo-magnesiens avec les bromo-8 purines ribosides et bromo-8 adenosine monophosphate cyclique-3′,5′ silyles en presence de dichloro-bis-triphenylphosphine palladium

The palladium catalysed condensation of Grignard reagents with silyl derivatives of 8-bromopurine nucleosides and 8-bromoadenosine-3′,5′ cyclic monophosphate is a convenient method for the preparation of free 8-alkylpurine nucleosides and 8-alkyladenosine-3′,5′ cyclic monophosphate.     

The practical synthesis of a novel and highly potent analogue of bryostatin

Macrocycle 1 is a new highly potent analogue of bryostatin 1, a promising anti-cancer agent currently in human clinical trials. In vitro, 1 displays picomolar affinity for PKC and exhibits over 100-fold greater potency than bryostatin 1 when tested against various human cancer cell lines. Macrocycle 1 can be generated in clinically required amounts by chemical synthesis in only 19 steps (LLS) and represents a new clinical lead for the treatment of cancer.     

Novel heteroleptic cis-(C--N)2Pd(II) chelates for the preparation of enantiopure planar chiral cyclopalladated 2-[tricarbonyl(eta6-phenyl)chromium]pyridine

In the presence of large amounts of [Me4N]Cl, the reaction of ortho-chloromercurated 2-[(eta6-phenyl)tricarbonylchromium]pyridine with mu-chloro cyclopalladated aromatic compounds yields a series of new heteroleptic heterodinuclear cis-(C--N)2Pd(II) complexes, which are valuable precursors of planar chiral cyclopalladated (eta6-arene)Cr(CO)3 complexes.     

Actinide heterobimetallic oxides (Th, U): reduction studies

In our laboratories we have been studying the synthesis and reactivity of binary actinide and lanthanide intermetallic compounds. In this work, the air-oxidation of ThCu₂ and AnNi₂ (An = Th, U) was followed by thermogravimetry (TG) and the products were characterized by X-ray powder diffraction (XRD). The heterobimetallic oxides obtained are described by the formulas 2MO·ThO₂ (M = Cu, Ni) and 2NiO·UO₃. The thermogravimetric analysis under hydrogen of these heterobimetallic oxides show one mass loss for 2MO·ThO₂ and two mass losses for 2NiO·UO₃ over a wide range of temperature (293–1273 K). The characterization by XRD shows that the reduction products are 2M·ThO₂ (M = Cu, Ni) and 2Ni·UO₂, with all the actinides in the 4+ oxidation state. The actinide heterobimetallic oxides were described as copper or nickel supported catalysts.     

Coordination solids via assembly of adaptable components: systematic structural variation in alkaline earth organosulfonate networks

A family of alkaline earth organosulfonate coordination solids is reported. In contrast to more typical crystal engineering approaches, these solids are sustained by the assembly of building blocks that are coordinatively adaptable rather than rigid in their bonding preferences. The ligand, 4,5-dihydroxybenzene-1,3-disulfonate, L, progressively evolves from a 0D, 1D, 2D, to a 3D microporous network with the Group II cations Mg(2+), Ca(2+), Sr(2+), and Ba(2+), (compounds 1-4), respectively. This trend in dimensionality can be explained by considering factors such as hard-soft acid-base principles and cation radii, a rationalization which follows salient crystal engineering principles. The selective gas sorption properties of the microporous 3D network [Ba(L)(H(2)O)].H(2)O, 4, with different gaseous guests are also presented.     

Quantum mechanical valence study of a bond-breaking–bond-forming process in triatomic systems

The recently introduced set of the quadratic, two-electron covalent and ionic valence indices is used to investigate the bond-breaking–bond-forming (BB-BF ) process in an atom exchange reaction between H₂ and X (X = H, F—I) as well as in the O₂—H system. Valence changes accompanying selected charge reorganizations are examined within the three-orbital model and valence diagrams for symmetric transition states (TS s) are given. The UHF valence data for Li₂O and CO₂ and the H—H—X, O—O—H, and O—H—O (ABC) TS s (collinear and angular) are reported and compared to valence data in the separated fragments limits (SFL ), AB and BC. The overall valence, ν(ABC), and the total (ionic plus covalent) diatomic valences, ν_AB and ν_BC, are used as measures of the overall bond-order in a concerted BB–BF reaction, to test the postulate of the bond-energy–bond-order (BEBO ) model. In collinear TS s of H₂X, ν ? ?1, i.e., one bonding electron pari, is found to be roughly preserved, whereas in the angular H₂X and in collinear O—H—O TS s, the effect of increased valence at the saddle-point is observed, relative to that of diatomic fragments (reactiants or products). For the angular O—O—H TS , a similar increase in | ν (ABC)| relative to both O₂ and OH SFL s is detected; smaller changes relative to the O₂ data are found in the collinear TS . This observation is in agreement with earlier predictions from the intersecting-state model. The relative diatomic valences, ν/ν and ν/ν, are shown to conserve the overall relative bond multiplicity around 1 in both collinear and angular TS s of the H₂—X systems. © 1994 John Wiley & Sons, Inc.     

Determination of ambroxol in an automated multi-pumping pulsed flow system.

A new flow methodology exploiting the multi-pumping approach was developed for the spectrophotometric determination of ambroxol hydrochloride in pharmaceutical preparations. The flow manifold was implemented by using, exclusively, multiple solenoid-actuated micro-pumps, which acted simultaneously as sample insertion, solutions propelling and reagents commutation units. Linear calibration plots were obtained over an ambroxol concentration ranging from 10 to 200 mg l(-1) (r.s.d. < 0.5%, n = 15) and a sampling rate of about 60 samples per hour (flow rate = 1.92 ml min(-1), sample volume = 80 microl).     

Reversal of diastereofacial selectivity in the intramolecular michael addition of -α-carbamoyloxy-α,β-unsaturated esters. Synthesis of N-benzoyl-D,L-daunosamine

Contrary to the precedents, 1,3-anti stereoselection was found in the intramolecular Michael addition of ethyl $\text{threo}$,5-carbamoyloxy-4-trialkylsilyloxy-2-hexenoate to culminate in a synthesis of N-benzoyl-$\text{D}$,$\text{L}$-daunosomine. The antiperiplanar effect due to the group at 4-position was revealed to play a major role in the stereoselection in this type of reactions. N-benzoyl-$\text{D}$,$\text{L}$-3-epidaunosamine was also synthesized by 1,2-syn asymmetric induction.