Synthesis and structural characterization of bi- and trimetallic octacyanometalate(IV) complexes: [Delta,Lambda-MII(en)3][cis-MII(en)2(OH2)][MIV(CN)8].2H2O and [cis-MII(en)2(OH2)]2[(mu-NC)2MIV(CN)6].4H2O (MII = Mn, Co, Ni; MIV = Mo, W)

Treatment of [M(II)(en)(3)][OTs](2) or methanolic ethylenediamine solutions containing transition metal p-toluenesulfonates (M(II) = Mn, Co) with aqueous K(4)M(IV)(CN)(8).2H(2)O or Cs(3)M(V)(CN)(8) (M(IV) = Mo, W; M(V) = Mo) affords crystalline clusters of [M(II)(en)(3)][cis-M(II)(en)(2)(OH(2))(mu-NC)M(IV)(CN)(7)].2H(2)O (M(IV) = Mo; M(II) = Mn, 1; Ni, 5; M(IV) = W; M(II) = Mn, 2; Ni, 6) and [cis-M(II)(en)(2)(OH(2))](2)[(mu-NC)(2)M(IV)(CN)(6)].4H(2)O (M(IV) = Mo; M(II) = Co, 3; Ni, 7; M(IV) = W; M(II) = Co, 4) stoichiometry. Each cluster contains cis-M(II)(en)(2)(OH(2))(mu-NC)(2+) units that likely result from dissociative loss of en from [M(II)(en)(3)](2+), affording cis-M(II)(en)(2)(OH(2))(2)(2+) intermediates that are trapped by M(IV)(CN)(8)(4-).     

Central limit theorems for dependent variables,II

Summary Two families of measures of the dependence between two random variables (rv's) are introduced. They include the strong-mixing ‘distance’. Two Central Limit Theorems (CLT's) are proved for dependent samples or processes where the dependence of the ‘past’ is not too strong. Tightness of the empirical process is shown to hold under conditions involving only the four-dimensional marginals of the sample.     

Gas phase noncovalent protein complexes that retain solution binding properties: Binding of xylobiose inhibitors to the β-1, 4 exoglucanase from <Emphasis Type="Italic">Cellulomonas fimi</Emphasis>

Tandem mass spectrometry has been used to compare gas-phase and solution binding of three small-molecule inhibitors to the wild type and three mutant forms of the catalytic domain of Cex, an enzyme that hydrolyses xylan and xylo-oligosaccharides. The inhibitors, xylobiosyl-deoxynojirimycin, xylobiosyl-isofagomine lactam, and xylobiosyl-isofagomine consist of a common distal xylose linked to different proximal aza-sugars. The three mutant forms of the enzyme contain the substitutions Asn44Ala, Gln87Met, and Gln87Tyr that alter the binding interactions between Cex and the distal sugar of each inhibitor. An electrospray ionization (ESI) triple quadrupole MS/MS system is used to measure the internal energies, DeltaE(int), that must be added to gas-phase ions to cause dissociation of the noncovalent enzyme-inhibitor complexes. Collision cross sections of ions of the apo-enzyme and enzyme-inhibitor complexes, which are required for the calculations of DeltaE(int), have also been measured. The results show that, in the gas phase, enzyme-inhibitor complexes have more compact, folded conformations than the corresponding apo-enzyme ions. With the mutant enzymes, the effects of substituting a single residue can be detected. The energies required to dissociate the gas-phase complexes follow the same trend as the values of DeltaG0 for dissociation of the complexes in solution. This trend is observed both with different inhibitors, which probe binding to the proximal sugar, and with mutants of Cex, which probe binding to the distal sugar. Thus the gas-phase complexes appear to retain much of their solution binding characteristics.     

An optical fibre sensor for the measurement of pressure

This paper describes the design, construction and testing of a fibre optic pressure sensor based on a reflecting Fabry-Perot etalon. The etalon comprised one fixed mirror and a second mirror designed to flex under the action of the pressure being monitored. A single multimode fibre was used to connect the passive, remote sensor to the transmitter/receiver section, and dual wavelength referencing was used to eliminate the effects of bending-induced attenuation in the fibre.     

Central Limit Theorems for dependent variables. I

Summary This paper gives a flexible approach to proving the Central Limit Theorem (C.L.T.) for triangular arrays of dependent random variables (r.v.s) which satisfy a weak mixing condition called -mixing. Roughly speaking, an array of real r.v.s is said to be -mixing if linear combinations of its past and future are asymptotically independent. All the usual mixing conditions (such as strong mixing, absolute regularity, uniform mixing, -mixing and -mixing) are special cases of -mixing. Linear processes are shown to be -mixing under weak conditions. The main result makes no assumption of stationarity. A secondary result generalises a C.L.T. that Rosenblatt gave for strong mixing samples which are nearly second order stationary.     

D-Gluconhydroximo-1,5-lactam and Related N-Arylcarbamates Theoretical Calculations,Structure, Synthesis,and Inhibitory Effect on β-Glucosidases

The known D -gluconhydroximo-1,5-lactam (= D -glucono-1,5-lactam oxime) 7a , its nitrogen isotopomers 7b and 7c , and the N-arylcarbamates 26–29 were synthesized from 2,3,4,6-tetra-O-benzyl-D -glucono-1,5-lactam ( 11a ) and its nitrogen isotopomer 11b to establish the controversial structure of 7a and to study the inhibition of β-glucosidases by the N-arylcarbamates 26–29 . Conversion of 11a with Lawesson's reagent yielded a mixture of the thionolactam 15a and its manno-configurated isomer 16a , which was transformed into a mixture of the benzylated hydroximo-lactam 13a and the manno-isomer 17a . Debenzylation (Na/NH₃) and acetylation of this mixture led to the gluco-configurated pentaacetate 14a and the manno-isomer 18a . Treatment of 11a with Et₃O·BF₄ and then with H₂NOH gave exclusively the benzylated D -gluconhydroximo-1,5-lactam (benzylated D-nojirilactam oxime) 13a , which was transformed into 14a . Deacetylation of 14a yielded the hydroximo-lactam 7a . The isotopomers 7b and 7c were obtained by analogous reaction sequences, using either ¹⁵NH₃ or ¹⁵NH₂OHHCl. To prepare the acetylated N-arylcarbamates 20–25 , 13a was debenzylated and acetylated (→ 14a ), followed by selective deacetylation to the tetraacetate 19a and treatment with the appropriate isocyanates. The structure of the 2-chlorophenyl carbamate 21 was established by X-ray analysis. Deacetylation of 20–23 led to the N-arylcarbamates 26–29 . The ¹⁵N-NMR spectra of 7b , 7c , and of their precursors 13b , 13c , 14b , and 14c , show that the C?N bond in all these lactam oximes is exocyclic as predicted from semiempirical and ab initio SCF-MO calculations on the structure of acetamide oxime and 5-pentanelactam oxime. According to these calculations, 5-pentanelactam oxime is a (Z)-configurated, flattened chair. X-ray analysis established the structure of D -glucono-1,5-lactam oxime ( 7a ) in the solid state, where it adopts a conformation between ⁴C₁ and ⁴H₃. In H₂O, 7a is a flattened ⁴C₁. The calculations also predict that protonation at the exocyclic N-atom strengthens the conjugation between the endocyclic N-atom and the hydroxyimino group, and leads to a half-chair conformation. This is evidenced by the chemical shift differences in the ¹⁵N-NMR spectra observed upon protonation of 7b and 7c . The hydroximolactam 7a and the N-arylcarbamates 26–29 are competitive inhibitors of the β-glucosidases from sweet almond (emulsin) and from Agrobacterium faecalis (= Abg), with K_I values between 8 and 21·10^?6M against emulsin (at pH 6.8) and between 0.15 and 1.2·10^?6M against Abg (at pH 7.0).     

The synthesis of carboxymethyl derivatives of purines and pyrimidines and their condensation with naturally occurring macromolecules

1-Carboxymethylthymine, 1-carboxymethylcytosine and 9-carboxymethyladenine were obtained by the direct carboxymethylation of the appropriate bases. In addition a small amount of 3-carboxymethyladenine was obtained. 9-Carboxymethylhypoxanthine was obtained by deamination of 9-carboxymethyladenine. 1-Carboxymethyluracil, 1-carboxymethylthymine and 9-carboxymethyl-hypoxanthine were each condensed with protamine and with dextran to give water-soluble, base-substituted polymers. The 1-carboxymethylthymine-dextran showed a slow decrease in optical density at 268 nm in 2 × SSC at 20°, of 30%. This did not occur in 7M urea. 1-Carboxymethylthymine-dextran gave an additional hypochromic effect with polyadenylic acid in 2 × SSC at 4° or 14° of 13% and 9% respectively. The ratio of thymine: adenine residues at the point of maximum hypochromicity was 3:1. The other dextran derivatives did not show similar hypochromic effects. The 1-carboxy-methylthymine-protamine gave a precipitate with polyadenylic acid probably due to electrostatic interaction.     

Structural, mechanistic, and computational analysis of the effects of anomeric fluorines on anomeric fluoride departure in 5-fluoroxylosyl fluorides

The effects of fluorine substitution at the C-5 center of pyranosyl fluorides on the reactivity at the C-1 anomeric center was probed by studying a series of 5-fluoroxylosyl fluoride derivatives. X-ray structures of their per-O-acetates detailed the effects on the ground-state structures. First-order rate constants for spontaneous hydrolysis, in conjunction with computational studies, revealed that changes in the stereochemistry of the 5-fluorine had minimal effects on the solvolysis rate constants and that the observed rate reductions were broadly similar to those caused by additional fluorine substitution at C-1 but significantly less than those due to substitution at C-2. Differences in the trapping behavior of 5- versus 2-fluoro-substituted glycosyl fluorides with α- and β-glycosidases arise more from differences in steric effects and hydrogen-bonding interactions than from intrinsic reactivity differences.     

Elucidation of the mechanism of polysaccharide cleavage by chondroitin AC lyase from Flavobacterium heparinum

Chondroitin AC lyase from Flavobacterium heparinum degrades chondroitin sulfate glycosaminoglycans via an elimination mechanism resulting in disaccharides or oligosaccharides with delta4,5-unsaturated uronic acid residues at their nonreducing end. Mechanistic details concerning the ordering of the bond-breaking and -forming steps of this enzymatic reaction are nonexistent, mainly due to the inhomogeneous nature of the polymeric substrates. The creation of a new class of synthetic substrates for this enzyme has allowed the measurement of defined and reproducible k(cat) and K(m) values and has expanded the range of mechanistic studies that can be performed. The primary deuterium kinetic isotope effect upon k(cat)/K(m) for the abstraction of the proton alpha to the carboxylic acid was measured to be 1.67 +/- 0.07, showing that deprotonation occurs in a rate-limiting step. Using substrates with leaving groups of differing reactivity, a flat linear free energy relationship was produced, indicating that the C4-O4 bond is not broken in a rate-determining step. Taken together, these results strongly suggest a stepwise mechanism. Consistent with this was the measurement of a secondary deuterium kinetic isotope effect upon k(cat)/K(m) of 1.01 +/- 0.03 on a 4-[(2)H]-substrate, indicating that no sp2 character is developed at C4 during the rate-limiting step, thereby ruling out a concerted syn-elimination.