Verification of a model to predict the influence of particle inertia and gravity on a decaying turbulent particle-laden flow

In an earlier publication some of the authors presented a theoretical model for the calculation of the influence of particle inertia and gravity on the turbulence in a stationary particle-laden flow. In the present publication the model is extended for application to a decaying suspension. Also a comparison is given between predictions made with the model and experimental data (own data and data reported in the literature) on a decaying turbulent flow with particles in a water tunnel or in a wind tunnel. For most of the experiments a prediction with reasonable accuracy and an interpretation is possible by means of the model.     

Analysis of O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX) and its degradation products by packed capillary liquid chromatography-electrospray mass spectrometry

Packed capillary column liquid chromatography (LC)-electrospray mass spectrometry (ESI-MS) was used for the first time to detect and identify O-ethyl, S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX) and its degradation products, including compounds containing a P-CH3 bond, bis(diisopropylamino)thioalkanes and ureas commonly employed as VX stabilizers. The reported ESI-MS data were generally acquired with a higher sampling cone voltage, a setting that promoted collisionally activated dissociation, and resulted in the acquisition in informative mass spectra containing both molecular and product ion information. The developed method appears to be an attractive alternative to GC-MS for the analysis of aqueous sample containing the degradation products of VX, since they may be analysed directly with little risk of thermal decomposition and without the need for additional sample handling or derivatization. Application of this method to a degraded VX sample resulted in the detection of a number of novel polar and higher-molecular-mass degradation products, not previously associated with VX during GC-MS analysis.     

266 nm photolysis of CF3I and C2F5I studied by diode laser gain FM spectroscopy

Frequency modulated diode laser based absorption at 1.315 microm has been used to measure the Doppler lineshapes of the I((2)P(1/2)-(2)P(3/2)) transition in atomic iodine produced from the 266 nm photolysis of both CF(3)I and C(2)F(5)I. Wavelength resolved laser gain is seen following photolysis as excited iodine atoms ((2)P(1/2)) are produced with a quantum yield close to unity from photolysis of both parent molecules. Time resolved measurements were made and the nascent speed distribution and translational anisotropy parameter, beta were determined. Mean atomic speeds of 800 and 850 ms(-1), which correspond to 83 and 68% of the maximum possible kinetic energy release into the iodine photofragment, were determined for photolysis of CF(3)I and C(2)F(5)I, respectively. The nascent translational anisotropy parameter was found to be beta = 1.77 +/- 0.05 for CF(3)I and beta = 1.69 +/- 0.05 for C(2)F(5)I. These values are explicable in terms of parent rotational motion and non-adiabatic processes in the exit channel.     

N,N'-Ethylenedi-L-cysteine (EC) and Its Metal Complexes: Synthesis, Characterization, Crystal Structures, and Equilibrium Constants

N,N'-ethylenedi-L-cysteine (EC) and its indium(III) and gallium(III) complexes have been synthesized and characterized. The crystal structures of the ligand and the complexes have been determined by single-crystal X-ray diffraction. EC.2HBr.2H(2)O (C(8)H(22)Br(2)N(2)O(6)S(2)) crystallizes in the orthorhombic space group P2(1)2(1)2 with a = 12.776(3) ?, b = 13.735(2) ?, c = 5.1340 (10) ?, Z = 2, and V = 900.9(3) ?(3). The complexes Na[M(III)EC].2H(2)O (C(8)H(16)MN(2)O(6)S(2)Na) are isostructural for M = In and Ga, crystallizing in the tetragonal space group P4(2)2(1)2 with the following lattice constants for In, (Ga): a = 10.068(2) ?, (9.802(2) ?), b = 10.068(2) ?, (9.802(2) ?), c = 14.932(2) ?, (15.170(11) ?), Z = 4 (4), and V = 1513.6(5) ?(3), (1457.5(11) ?(3)). In both metal complexes, the metal atoms (In and Ga) are coordinated by six donor atoms (N(2)S(2)O(2)) in distorted octahedral coordination geometries in which two sulfur atoms and two nitrogen atoms occupy the equatorial positions, and the axial positions are occupied by two oxygen atoms of two carboxylate groups. The structures of the complexes previously predicted by molecular mechanics are compared with the crystal structures of the Ga(III) and In(III) complexes obtained experimentally. In contrast to the oxygen donors in phenolate-containing ligands, such as 1,2-ethylenebis((o-hydroxyphenyl)glycine) (EHPG) and N,N'-bis(o-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED), the thiolate donors of EC enhances affinity for In(III) relative to Ga(III). The following stability sequence has been obtained: In(III) > Ga(III) > Ni(II) > Zn(II) > Cd(II) > Pb(II) > Co(II). Evidence was also obtained for several protonated and hydroxo species of the complexes of both divalent and trivalent metals, where the corresponding protonation constants (K(MHL)) decrease with increasing stability of the chelate, ML(n)(-)(4), where M(n)()(+) represent the metal ion.     

Use of high-performance capillary electrophoresis to monitor charge heterogeneity in recombinant-DNA derived proteins

The separation of charge variants of recombinant DNA-derived (rDNA) proteins by high-performance capillary electrophoresis (HPCE) has been explored with the following examples: human growth hormone (rhGH), a soluble form of a T4 receptor protein (rCD4) and tissue plasminogen activator (rt-PA). The separation of rhGH and deamidated variants were examined over the range of low pH (less than 2.5) to high pH (8.0) on a coated silica capillary. No resolution was observed at pH 2.5 while at pH values of 6.5 or greater the deamidated species were separated. At pH 3.5 the variant was partially resolved but no detector signal was observed at pH 4.5 and 5.0. HPCE was also used to monitor a glycoprotein (rt-PA) with charge heterogeneity presumably due to variable sialic acid content. At a pH value of 4.5, the charge heterogeneity was only observed as peak broadening. For rCD4 multiple peaks were observed at pH 5.5 but no signal was observed at pH 6.5 or above (the pI of rCD4 is 8). These results suggest that HPCE will prove to be a valuable technique for the analysis of charged variants present in rDNA products either as a consequence of natural microheterogeneity or due to degradative processes such as deamidation.     

Hydrolysis of 4-nitrophenyl acetate by a (N2S(thiolate))zinc hydroxide complex: a model of the catalytically active intermediate for the zinc form of peptide deformylase

A novel zinc(II) hydroxide complex with a rare alkylthiolate donor in the coordination sphere is formed in aqueous solution from the dissolution of the zinc alkyl precursor complex (PATH)ZnCH(3) (PATH = 2-methyl-1-[methyl(2-pyridin-2-ylethyl)amino]propane-2-thiolate) in H(2)O and protonolysis of the Zn-C bond to give (PATH)ZnOH (1). The (PATH)ZnOH complex has been shown to promote the hydrolysis of 4-nitrophenyl acetate (4-NA) by a detailed kinetic study and is the first functional model for the zinc form of the enzyme peptide deformylase. From a fit of the sigmoidal pH-rate profile a kinetic pK(a) of 8.05(5) and a pH-independent second-order rate constant (k" max)) of 0.089(3) M(-1) s(-1) have been obtained. The kinetic pK(a) is similar to the pK(a) of 7.7(1) determined by a potentiometric study (25 degrees C, I = 0.1 (NaNO3)). Observation of both rate enhancement and turnover shows that 1 acts as a catalyst for the hydrolysis of 4-NA, although the turnovers are modest. Activation parameters have been obtained from a temperature-dependence study of the rate constants (E(a) = 54.8 kJ mol(-1), DeltaH++ = 52.4 kJ mol(-1), and DeltaS++ = -90.0 J mol(-1) K(-1)), and support a reaction mechanism which depends on nucleophilic attack of 1 in the rate-determining step. This is the first kinetic and thermodynamic study of a 4-coordinate zinc hydroxide complex containing a thiolate donor. In addition it is only the second time that a complete set of activation parameters have been obtained for the zinc-promoted hydrolysis of a carboxylic ester. This study puts the basicity and nucleophilicity of a (N(2)S)ZnOH complex in context with those of other L(n)()ZnOH complexes and enzymes.     

Observation of the enhancement in enantioselectivity with conversion for the aziridination of styrene using copper bis(oxazoline) complexes

During the aziridination of styrene using copper bis(oxazoline) complexes the ee increases with conversion due to further reactions of the product.     

Effects of steric constraint on chromium(III) complexes of tetraazamacrocycles, 2. Comparison of the chemistry and photobehavior of the trans-dichloro- and trans-dicyano- complexes of cyclam, 1,4-C2-cyclam, and 1,11-C3-cyclam

The synthesis and characterization of several Cr(III) complexes of the constrained macrocyclic ligand 1,11-C3-cyclam (1,4,8,11-tetraazabicyclo[9.3.3]heptadecane) is reported. Only trans complexes are formed, and the structure of trans-[Cr(1,11-C3-cyclam)Cl2]PF6 is presented. The chemical and photophysical behavior of the 1,11-C3-cyclam complexes are compared with those of the corresponding cyclam (1,4,8,11 tetraazacyclotetradecane) and 1,4-C2-cyclam (1,4,8,11-tetraazabicyclo[10.2.2]hexadecane) complexes. The aquation rate of trans-[Cr(1,11-C3-cyclam)Cl2]+ is similar to that of the corresponding 1,4-C2-cyclam complex and is more than 5 orders of magnitude faster than the cyclam counterpart. A monotonic increase in the extinction coefficient is observed on going from the cyclam complexes to the 1,11-C3-cyclam complexes to the 1,4-C2-cyclam complexes, and this is related to the degree of centrosymmetry in each complex. The trans-[Cr(1,11-C3-cyclam)(CN)2]+ complex is a weak emitter in aqueous solution with a room-temperature emission maximum at 724 nm (tau=23 micros). Like the corresponding 1,4-C2-cyclam complex (tau=0.24 micros), the 1,11-C3-cyclam complex shows no deuterium-isotope effect in room-temperature solution. This is in marked contrast to the corresponding cyclam complex which has an emission lifetime of 335 micros and a significant deuterium isotope effect in room-temperature solution. Low temperature (77K) data are also presented in an attempt to understand the differences in photophysical behavior.     

π-Interaction in metal Β-ketoenolates

The available data (supplemented where necessary) on the electronic, nuclear magnetic resonance and vibrational spectra of metal -ketoenolates has been analysed to assess the relative contributions of donor and acceptor metal-ligand -bonding in the first transition period metal (III) -ketoenolates. The effects of the metal ion and the ligand substituent on the -interaction in the -ketoenolate ring are discussed in terms of established theoretical concepts.

---

Zusammenfassung Die bekannten Daten (ergÄnzt, falls notwendig) der elektronischen und kernmagnetischen Resonanz sowie der Schwingungsspektren von Metall--ketoenolaten wurden analysiert, um die relativen BeitrÄge von Donor- und Akzeptor (Metall-Ligand) -Bindung in Metall(III)ketoenoIaten der ersten übergangsperiode zu ermitteln. Die Einwirkung des Metallions und des Ligandsubstituenten auf die -Bindung im -Ketoenolatring werden diskutiert auf der Grundlage von bekannten theoretischen Prinzipien.

---

Résumé L'examen des résultats antérieurement publiés (supplementés ou nécessaire) des spectres électroniques, résonance nucléaire magnétiques et vibrationnel nous a amenés à préciser les contributions relatifs de liaison- donneur et accepteur entre métal et ligand de la première période transitionelle métal(III) -kétoénolates. Les effects de l'ion métallique et du ligand substituent exercés sur l'interaction- dans le noyau -kétoénolate sont discutés selon les idées théoriques déjà établies.

---

---

This work was supported by University of Cape Town and C.S.I.R. Research Grants. We thank the National Institute for Metallurgy for a bursary (to R.D.H.).