Aqueous NH4Cl Research Articles

Precision measurement of ternary diffusion coefficients and implications for protein crystal growth: lysozyme chloride in aqueous ammonium chloride at 25°C

Isothermal ternary diffusion coefficients for the system lysozyme chloride (1)+NH 4Cl (2)+H 2O at 25°C and pH 4.5 have been measured interferometrically for five mean NH 4Cl concentrations, C 2=0.25, 0.5, 0.9, 1.2 and 1.5 M, with C 1=0.6 mM. The main-term diffusion coefficient ( D 11) v varies slowly with C 2. The main-term ( D 22) v increases with increasing NH 4Cl concentration, as does the binary D v in aqueous NH 4Cl, but the ( D 22) v values are lower in the ternary system. The cross-term ( D 21) v, which relates the coupled flow of NH 4Cl to the protein concentration gradient, increases sharply with increasing salt concentration, and is 19 times larger than ( D 22) v at the highest concentration. The values of ( D 12) v are smaller than the corresponding values previously obtained for the lysozyme chloride+NaCl+H 2O system over the whole range of salt concentration studied. Using equations based on the Onsager Reciprocal Relations, we have calculated the derivative of the chemical potential of lysozyme chloride with respect to the NH 4Cl concentration, and have estimated the protein cation charge. Integration with respect to the NH 4Cl concentration gives the dependence of the chemical potential of lysozyme chloride on NH 4Cl concentration, providing information about the driving force for nucleation and crystal growth of lysozyme chloride.

A Remarkable Photoreaction of 3-O-Benzylhypericin

Irradiation of 3-O-benzylhypericin dissolved together with at least 1 equiv. of `proton sponge' in benzene was shown, by means of UV/VIS, 1H-NMR, and mass spectrometric measurements, to produce the rearranged blepharismin-analogous 11-phenyl-11H-benz[4,10]anthra[2,1,9,8-nopqa]pleiadene system. The latter compound yielded hypericin when treated with light and oxygen in acetone solution, followed by aqueous NH4Cl. This reaction is considered to proceed via the oxybleopharismin-analog 3,4-benzal acetal of hypericin. The implications of the novel phototransformation for synthesis and biosynthesis of the natural products, as well as the structural peculiarities of the photoproducts, are discussed.

Density and viscosity studies of glucose and fructose solutions in aqueous and 0.5 mol dm3 aqueous NH 4Cl

Abstract Densities and viscosities of glucose and fructose solutions in water and in aqueous 0.5 mol dm−3 NH4Cl have been measured at 298.15, 303.15, 308.15 and 313.15 K. From density data, apparent molar volumes at infinite dilution (φ ;°v) and from viscosity data, the B-coefficients are calculated. Glucose and fructose are found to be structure promoters in water as well as in aqueous 0.5 mol dm−3 NH4Cl solutions.

Synthesis of two pentaarylated [60]fullerene derivatives Ar5C60‐H (Ar = p‐MeC6H4, m‐MeC6H4) and their novel electrochemical properties

AbstractThrough one pot reaction of C60 with organocopper/magnesium reagent ( p‐MeC6H4 )2 CuMgBr or ( m ‐ MeC6 H4 )2‐CuMgBr prepared from CuBr‐Me2S and p‐MeC6H4MgBr or m‐MeC6H4 MgBr and subsequent quenching with aqueous NH4Cl, two pentaarylated [ 60 ] fullerene derivatives (p‐MeC6H4)5 C60H (1) and (m‐MeC6H4)5 C60H (2) have been synthesized in 94% and 96% yields, respectively. While known compound 1 prepared via this improved method is unambiguously identified, new compound 2 is fully characterized by elemental analysis, IR, UV‐vis, 1H NMR and 13C NMR spectroscopies. Additionally, electrochemical study shows that the two [60] fullerene derivatives 1 and 2 in dichloromethane solution display two sequential one‐electron reductions which are shifted by about 0.4 V towards more negative potential values with respect to free C60. Such remarkable cathodic shift is attributed to the multiple breakage of the double‐bond conjugation within the Fullerene core.

Kinetic growth characteristics of a single dendrite during crystallization from a solution

The behavior kinetics of the transition rate during free quasitwo-dimensional growth of a single dendrite from an aqueous NH4Cl solution is studied experimentally. It is established that the integral curves are described by a Weibull distribution and the possibility of applying the Kolmogorov-Avrami theory to describe the kinetics of dendritic crystallization is discussed. Small-amplitude oscillations of the growing dendrite mass are observed against the background trend, having a quasiperiodic nature with a frequency around 0.1 Hz. The nature of these oscillations is related to the interaction between the diffusion fields of existing and newly forming secondary branches.

Numerical calculation of the permeability in a dendritic mushy zone

An averaging procedure applied to the local Stokes equations in a columnar dendritic-like porous structure yields the heterogeneous form of Darcy’s law, with three Brinkman correction terms explicitly involving gradients of the liquid volume fraction. Because of these extra terms, the associated closure problem leading to the determination of the permeability becomes very complex, and the full solution is still out of reach. However, in some cases, a simplified closure problem can be used to physically describe the spatial evolution of the permeability components in the columnar dendritic mushy zone. From digitized images of dendritic structures observed experimentally during solidification of a 26 wt pct solution of aqueous NH4Cl and succinonitrile-4 wt pct acetone, components of the permeability tensor in a direction parallel and normal to the primary dendrite arm are numerically calculated. Comparisons to experimental correlations and physical models show that the closure problem provides a more realistic physical description of the structure, especially in the vicinity of the tip of the dendrites. Finally, numerical calculations performed on a schematic dendritic structure point out that the permeability for flow parallel to the primary dendritic arms is hardly dependent on the secondary arm spacing (d 2).

Hydrothermal Synthesis and Characterization ofM2Te3O8(M=Mn, Co, Ni, Cu, Zn): A Series of Compounds with the Spiroffite Structure

Several compounds isotypic to the mineral spiroffite were obtained as high quality single crystals via hydrothermal reactions. These materials, which have the general formulaM2Te3O8, crystallize in the monoclinic space groupC2/cand contain divalent transition metal ions and tellurite building blocks. Typical synthetic conditions for the preparation of these materials are 375°C for 3–5 days in an aqueous NH4Cl solution. This structure type is based on slabs containing Te2O6groups joined byMcations. These Te2O6groups are made up of two edge-sharing TeO3+1polyhedra. The metal tellurite slabs are connected to one another through tellurium(IV) atoms, which are coordinated by four oxygen atoms in a regular TeO4trigonal bipyramidal configuration. A detailed structural characterization via single crystal X-ray diffraction was performed on four compounds (Co2Te3O8:a=12.690(1) Å,b=5.211(2) Å,c=11.632(2) Å,β=98.98(1)°,V=759.7(3) Å3,R(Rw)=0.023 (0.046); Ni2Te3O8:a=12.407(1) Å,b=5.207(1)Å,c=11.509(1) Å,β=98.723(9)°,V=735.0(2) Å3,R(Rw)=0.025 (0.033); Cu2Te3O8:a=11.8368(8) Å,b=5.266(2) Å,c=12.2419(8) Å,β=100.316(6)°,V=750.7(2) Å3,R(Rw)=0.025 (0.032); Zn2Te3O8:a=12.681(2) Å,b=5.200(2) Å,c=11.786(2) Å,β=99.60(1)°,V=766.3(3) Å3,R(Rw)=0.031 (0.041)). The manganese analog (a=12.896(5) Å,b=5.398(2) Å,c=11.907(5) Å,β= 98.14(4)°) was identified via powder diffraction patterns. The cobalt, nickel, and copper compounds were observed to have an antiferromagnetic transition by DC magnetic susceptibility measurements. The band gaps were obtained by optical diffuse reflectance spectroscopy and show that these compounds are all wide band gap materials.

Well-dispersed perovskite-type oxidation catalysts

A novel technique for the preparation of highly dispersed rare-earth perovskite LaCoO 3 catalysts was developed. Using the conventional complexation and pyrolysis methods, an etchable component, zinc oxide (ZnO), was introduced into the precursor by adding zinc nitrate during preparation. After calcination, the independent ZnO phase was extracted by an aqueous NH 4Cl solution, resulting in well-dispersed LaCoO 3 catalysts with a surface area of over 30 m 2/g. DTA-reaction tests using CO oxidation as the model reaction were performed as a quick means to illustrate the higher catalytic oxidation activities of the prepared LaCoO 3 catalysts mainly due to their high surface area.

The correlation between electrochemical impedance spectra and voltammograms of PB films in aqueous NH 4Cl and CsCl

Voltammetric curves of reduction of Prussian Blue Films to the Everitt’s Salt form and oxidation to the Prussian Yellow form show important differences depending on the supporting electrolyte countercation. The rate of the overall electron-hopping depends on the countercation. Apparent diffusion coefficients are evaluated from impedance spectra at different stabilization potentials. The dependence of the apparent diffusion coefficients on the stabilization potential can help understand the dependence of the voltammograms shape on the countercation nature.

Generation and Decomposition of a Pentacoordinate Spirobis[1,2-oxasiletanide

Sequential treatment of diphenylbis((phenylthio)methyl)silane with lithium naphthalenide, hexafluoroacetone, and then aqueous NH4Cl gave the (β-hydroxyalkyl)diphenyl((phenylthio)methyl)silane 8, Ph2Si(CH2SPh)CH2C(CF3)2OH, a hydroxyl group of which was protected with methoxymethyl to afford the corresponding methoxymethyl ether 9a. Similarly, the reaction of 9a with hexafluoroacetone followed by deprotection of the methoxymethyl group yielded the diphenylbis(β-hydroxyalkyl)silane 11, Ph2Si[CH2C(CF3)2OH]2. Sequential treatment of 11 with trifluorormethanesulfonic acid in CDCl3 and with 2 mol equiv of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) gave almost quantitatively [DBU·H]+, phenylbis[1,1,1-trifluoro-2-(trifluoromethyl)-2-propanolate(2−)-C3,O]silicate(−1) (6) along with [DBU·H]+ triflate at low temperature (−20 °C). The 29Si NMR, which showed a signal at δSi −61.75, as well as other NMR analyses indicate that 6 is a pentacoordinate silicate with two 1,2-oxasiletanide rings. Compound 6 decomposed at room t...

A Grignard-like Organic Reaction in Water

The addition of a Grignard reagent to a carbonyl-containing compound to form an alcohol is an important reaction to demonstrate in organic chemistry laboratory courses. However, the reaction presents several practical problems for the lab instructor including the need for anhydrous solvents (e.g., ether), dry glassware, and the occasional problem of slow reaction initiation. We have scaled, and tested, a known Grignard-like reaction between allyl bromide and benzaldehyde mediated by zinc metal in aqueous media. The procedure retains the desirable features of the traditional Grignard reaction, while eliminating some of the commonly encountered difficulties. Thus, addition of allyl bromide (1.2 eq) to benzaldehyde and zinc in a two-phase mixture of THF and saturated aqueous NH4Cl afforded addition product 1-phenyl-3-buten-1-ol in 70-85% yields.

Reaction of SilyLketenes with Carbanions: Simple Preparation of .ALPHA.-SilyLketones Using Organocerium Reagents.

Preparation of α-silylketones 1 by the reaction of three kinds of silylketenes 3a-c with various organometallic reagents 4 was studied. Although the use of n-BuLi, MeMgBr, Me2CuLi, Et3Al, and Et2Zn resulted in complicated reactions, organocerium reagents 4 (M=CeCl2) added selectively to the carbonyl carbon of 3 to generate enolate anions A, which were treated with aqueous NH4Cl or alkyl halides 5 to give 1. Seventeen α-silylketones 1a-q were prepared in 31-99% yields from three components, 3, alkyl- or arylcerium reagents 4, and proton or alkyl halides 5. This method was applied to a regiocontrolled preparation of two isomeric α-silylketones 1r, s.

Regioselective synthesis of 1,8-dihydroxytetralins through a tandem reduction/intramolecular hydroxyalkylation of 4-(3-hydroxyphenyl)alkanoates

A series of 4-(3-hydroxyphenyl)butanoates 3 has been prepared and transformed into 1,8-dihydroxytetralins of general formula 2 by treatment with 2 equivalents of DIBALH followed by quenching with aqueous NH 4Cl. A possible mechanism for this novel totally regioselective intramolecular hydroxyalkylation is suggested and the factors affecting the stability of 1,8-dihydroxytetralins 2 are also discussed.

THREE-DIMENSIONAL CONSIDERATIONS OF UNIDIRECTIONAL SOLIDIFICATION IN A BINARY LIQUID

Unidirectional solidification of an aqueous NH4Cl solution has been simulated using a fully three-dimensional model for the strongly coupled transport of momentum, energy, and species in the mushy and melt regions of the solution. The predictions reveal the nucleation and development of pencil-like vertical channels in the mushy region and the complex, three-dimensional flow and thermosolutal conditions associated with channel formation. The number of channels is at a maximum shortly after nucleation and thereafter decreases with increasing time, as solidification progresses. Favorable agreement is obtained between three- and two-dimensional predictions of global parameters such as heat rate and mass fraction of solid formation.

Studies of the electrodeposition of palladium from baths based on [Pd(NH3)2X2] salts. I. [Pd(NH3)2Cl2] baths

Spectroscopic techniques are used to confirm the chemistry of solutions of [Pd(NH3)2Cl2] in aqueous NH4Cl at various pH. In addition, potential sweep and step methods at rotating and stationary disc electrodes (both vitreous carbon and freshly plated palladium) are used to investigate palladium deposition from a standard electroplating bath, [Pd(NH3)2Cl2] in NH4Cl/NH3 (pH 8.9). The relative importance of oxygen reduction, hydrogen absorption and hydrogen evolution as competing cathode reactions under various conditions is defined and the advantage of strong convection for high rate plating is demonstrated.

NUMERICAL ANALYSIS OF BINARY SOLID-LIQUID PHASE CHANGE WITH BUOYANCY AND SURFACE TENSION DRIVEN CONVECTION

The effects of thermo/diffusocapillary convection on the solidification of aqueous NH4Cl in a rectangular cavity have been simulated numerically using a newly developed continuum model. Diffusocaptttary convection is negligible relative to thermocapillary convection, and for a 20 × 20 mm cavity in a one-gravity environment, thermocapillary effects are most pronounced during the early stages of solidification, when flow conditions are characterized by three major cells. One cell, driven by solutal buoyancy forces, extends from the mushy region to the melt and separates top and bottom melt region cells driven primarily by surface tension and buoyancy forces, respectively. With increasing time, however, the top cell strengthens and eventually envelops the entire melt. In terms of the strength of the flow, the liquidus front morphology, and the amount of solid formed, final conditions differ only slightly from those predicted for pure thermal/solutal convection.

The forces between mica surfaces in ammonium chloride solutions

The total interaction forces between two molecularly smooth mica crystals have been measured in a range of aqueous NH 4Cl solutions. The NH 4 + ion was found to adsorb onto the mica basal plane with a binding energy similar to that of the original lattice ion, K +. The charging properties at the mica/water interface were analyzed using a model previously developed by one of us which gives an estimated exclusion area of the adsorbed NH 4 + ion of about 0.52 nm 2. At low concentrations the measured interaction forces were, at all distances, found to be in good agreement with DLVO theory, whereas at concentrations above about 10 −3 M, a short-range (<1.5 nm) repulsion was measured. This was oscillatory with a periodicity of about 0.4 nm. This short-range solvation force was most likely caused by a combination of the hydrated state of the adsorbed NH 4 + ion and the molecular packing properties of water in thin films.

Evaporation kinetics of ammonium chloride solution droplets in water vapor

The evaporation kinetics of aqueous NH 4Cl droplets have been measured in a single-particle suspension apparatus in conjunction with Mie resonance spectroscopy. Evaporation coefficients for NH 3 and HCl, heretofore inaccessible to any measurements, have been deduced from the droplet evaporation rate data using a mathematical model considering equal-molar evaporation of the solute gases. The values are 0.29 ± 0.03 for NH 3 and 0.45 ± 0.04 for HCl, based on the partial pressures of the solute gases estimated from the best available thermodynamic properties.

Viscosity of aqueous NH4Cl and tracer diffusion coefficients of ions, water and non-electrolytes in aqueous NH4Cl, KI, and MgCl2 at 25�C

Viscosities for aqueous NH4Cl and tracer diffusion coefficients for22Na+,36Cl−, HTO, and CH3OH, acetone and dimethylformamide (all14C-labelled) in NH4Cl supporting electrolyte are reported for 25°, together with tracer diffusion coefficients for22Na+,36Cl−, and14CH3OH in 1M KI, and for14CH3OH in 1M MgCl2. The diffusion coefficient of HTO in NH4Cl solutions is slightly larger, for most of the concentration range investigated (0.05 to 4.5 M), than the value for pure water and is almost unaffected by the supporting electrolyte up to about 4M. Similar behavior is shown by CH3OH, acetone and dimethylformamide in NH4Cl solutions. Onsager limiting law behavior is approached by Cl− at NH4Cl concentrations in the 0.05–0.1M region but at much lower concentrations by Na+.

Synthesis of homoallylic alcohols via palladium-catalyzed coupling of organomercurials and vinylic oxetanes

The reaction of aryl- and vinylmercurials, cupric chloride, 5% aqueous NH 4Cl, oxygen, catalytic amounts of Li2pPdCl4 and vinylic oxetanes affords an excellent route to functionally-substituted homoallylic alcohols.