Diffusion Of Ammonia Research Articles

A study of acetoacetoxyethyl methacrylate hydrolysis in acrylic latex polymers as a function of pH

Acetoacetoxyethyl methacrylate (AAEM) is an ambient crosslinking monomer that, when incorporated into architectural coatings binders, provides coatings with improved hardness, scrub, stain, and dirt pick-up resistance. This study details the use of NMR spectroscopy to explore the hydrolysis profile of AAEM as a function of pH, type of neutralizer, and glass transition temperature of the binder. We have determined that AAEM has a hydrolysis profile that is independent of latex polymer pH relevant to coatings (pH 7–10). Lower Tg latex polymers enable the diffusion of ammonia into the binder nanoparticles converting a larger amount of the acetoacetoxy moiety to the enamine form; this approach also allows for measuring the distribution of enamine and AAEM form in the latex polymer particle. The consequence of these findings is that AAEM may be utilized at a lower pH than previously envisioned without consequence to the hydrolysis profile of the acetoacetoxy functionality.

ChemInform Abstract: The Interpenetrated Three‐Dimensional Framework of a New Mixed Lithium/Ammonium Perchlorate Growth in a Gel Medium.

AbstractLi9.41(NH4)0.59ClO4 is synthesized by slow diffusion of aqueous lithium oxalate and ammonium oxalate dissolved in perchloric acid through agar agar gel at ambient temperature.

Spherical Crystallization: A Novel Drug Delivery Approach

Spherical crystallization is a fast developing technique of particle design in which crystallization and agglomeration can be achieved simultaneously in one step. It has been successfully utilized for improvement of flow ability and compactability of crystalline drugs. The principle steps involved in the process of spherical crystallization are flocculation zone, zero growth zone, fast growth zone and constant size zone. General methods of spherical crystallization are emulsion solvent diffusion, spherical agglomeration, ammonia diffusion method and neutralization method. Factors controlling the process of agglomeration are solubility profile, mode and intensity of agitation, temperature of the system and residence time. Characterization of spherical crystals can be carried out using Optical Microscopy, Scanning Electron Microscopy, X-ray Powder Diffraction, Fourier Transform Infrared spectroscopy, Differential Scanning Calorimetry and Thin layer Chromatography.

Update on cerebral uptake of blood ammonia

Ammonia is believed to play a key role in the development of hepatic encephalopathy (HE) with increased formation of glutamine playing a central role. It has been debated whether blood ammonia enters the brain by passive diffusion and/or active transport by ion-transporters and that changes in blood pH could affect the blood-to-brain transfer of ammonia. It has also been proposed that the permeability-surface area product for ammonia across the blood-brain barrier (PSBBB) should be increased in cirrhosis and HE. In the present paper it is argued that changes in blood pH does not alter PSBBB for ammonia and the question of passive diffusion versus active transport of ammonia remains unresolved. Furthermore, recent studies do not find evidence for increased PSBBB for ammonia in cirrhosis. The main determent for cerebral uptake of blood ammonia (i.e. flux) is the arterial blood ammonia concentration. This means that the only way to protect the brain from hyperammonemia is by lowering blood ammonia, inhibit cerebral uptake of ammonia, or by manipulating cerebral ammonia metabolism so that less glutamine is produced.

Two Distinct Transport Mechanisms in AmtB and RhCG Proteins

The Amt/Rh family of membrane proteins facilitates the diffusion of ammonium across cellular membranes. Functional data show that Amt proteins, notably found in plants, transport ammonium ion (NH4+) while human rhesus (Rh) proteins transport ammonia (NH3). Comparison between the X-ray structures of the prokaryotic AmtB and the human RhCG reveals important differences at the level of their pore. Despite these important functional and structural differences between Amt and Rh proteins, studies of the AmtB transporter have led to the conclusion that proteins of both sub-families work according to the same mechanism and all transport ammonia. We performed molecular dynamics simulations of the AmtB and RhCG proteins under different conditions. Our free energy calculations suggest that the probability of finding NH3 molecules in the pore of AmtB is negligible in comparison to water and refute a single file diffusion of ammonia in AmtB. The pore lumen of RhCG is found to be more hydrophobic due to the presence of a phenylalanine conserved among Rh proteins. Simulations of RhCG also reveal that one of the signature histidine residues is occasionally exposed to the extra-cellular bulk, which is never observed in AmtB. These quite different hydration patterns are consistent with the idea that permeation in Amt and Rh proteins are not functionally equivalent and take place according to two distinct mechanisms. In both cases, after binding to the histidine dyad, ammonium deprotonates and diffuse down the pore as ammonia. Hydration of the pore in Amt proteins allows proton diffusion, which results in electrogenic transport. Such mechanism cannot take place in Rh proteins due to lack of pore hydration. Our QM/MM simulations rather show that the excess proton is released back to the extracellular bulk through a network of H-bonds, resulting in net NH3 transport.

Elucidating Mechanisms of Diffusion‐Based Calcium Carbonate Synthesis Leads to Controlled Mesocrystal Formation

AbstractAggregation‐based crystal growth often gives rise to crystals with complex morphologies which cannot be generated via classical growth processes. Despite this, understanding of the mechanism is rather poor, particularly when organic additives or amorphous precursor phases are present. In this work, advantage is taken of the observation that aggregation‐based growth of calcium carbonate, and indeed many other minerals, is most often observed using diffusion‐based synthetic methods. By fully characterizing the widely used ammonia diffusion method (ADM)–which is currently used as a “black box”–the solution and supersaturation conditions which accompany CaCO3 precipitation using this method are identified and insight is gained into the nucleation and growth processes which generate calcite mesocrystals. This reveals that the distinguishing feature of the ADM is that the initial nucleation burst consumes only a small quantity of the available ions, and the supersaturation then remains relatively constant, and well above the solubility of amorphous calcium carbonate (ACC), until the reaction is almost complete. New material is thus generated over the entire course of the precipitation, a feature which appears to be fundamental to the formation of complex, aggregation‐based morphologies. Finally, the importance of this understanding is demonstrated using the identified carbonate and supersaturation profiles to perfectly replicate CaCO3 mesocrystals through slow addition of reagents to a bulk solution. This approach overcomes many of the inherent problems of the ADM by offering excellent reproducibility, enabling the synthesis of such CaCO3 structures in large‐scale and continuous‐flow systems, and ultimately facilitating in situ studies of assembly‐based crystallization mechanisms.

Growth process and crystallographic properties of ammonia-induced vaterite

Metastable vaterite crystals were synthesized by increasing the pH and consequently the saturation states of Ca2+- and CO2-3-containing solutions using an ammonia diffusion method. SEM and TEM analyses indicate that vaterite grains produced by this method are polycrystalline aggregates with a final morphology that has a sixfold-symmetry. The primary structure develops within an hour and is almost a spherical assemblage of nanoparticles (5-10 nm) with random orientation, followed by the formation of hexagonal platelets (1-2 μm), which are first composed of nanoparticles and that develop further into single crystals. As determined using transmission electron microscopy, these hexagonal crystallites are terminated by (001) surfaces and are bounded by {110} edges. The hexagonal crystals subsequently stack to form the “petals” (20 μm wide, 1 μm thick) of the final “flower-like” vaterite morphology. The large flakes gradually tilt toward the center as growth progresses so that their positions become more and more vertical, which eventually leads to a depression in the center. Since this sequence encompasses several morphologies observed in previous studies (spheres, hexagons, flowers etc.), they may actually represent different stages of growth rather than equilibrium morphologies for specific growth conditions.

Spherical crystallization of drugs

Spherical crystallization of drugs is the process of obtaining larger particles by agglomeration during crystallization. The most common techniques used to obtain such particles are spherical agglomeration and quasi-emulsion solvent diffusion. Ammonia diffusion systems and crystallo-co-agglomeration are extensions of these techniques. By controlling process parameters during crystallization, such as temperature, stirring rate, type and amount of solvents, or excipient selection, it is possible to control the formation of agglomerates and obtain spherical particles of the desired size, porosity, or hardness. Researchers have reported that the particles produced have improved micromeritic, physical, and mechanical properties, which make them suitable for direct compression. In some cases, when additional excipients are incorporated during spherical crystallization, biopharmaceutical parameters including the bioavailability of drugs can also be tailored.

Ammonium recovery and energy production from urine by a microbial fuel cell

Nitrogen recovery through NH3 stripping is energy intensive and requires large amounts of chemicals. Therefore, a microbial fuel cell was developed to simultaneously produce energy and recover ammonium. The applied microbial fuel cell used a gas diffusion cathode. The ammonium transport to the cathode occurred due to migration of ammonium and diffusion of ammonia. In the cathode chamber ionic ammonium was converted to volatile ammonia due to the high pH. Ammonia was recovered from the liquid–gas boundary via volatilization and subsequent absorption into an acid solution. An ammonium recovery rate of 3.29 gN d−1 m−2 (vs. membrane surface area) was achieved at a current density of 0.50 A m−2 (vs. membrane surface area). The energy balance showed a surplus of energy 3.46 kJ gN−1, which means more energy was produced than needed for the ammonium recovery. Hence, ammonium recovery and simultaneous energy production from urine was proven possible by this novel approach.

Zinc(II) Complexes with Asymmetric 3,5‐Substituted 1H‐Pyrazoles

AbstractTwo new pyrazolate‐based ligands, N′‐[1‐(3‐acetyl‐4‐methyl‐1H‐pyrazol‐5‐yl)ethylidene]‐2‐(hydroxyimino)propanehydrazide (L1) and 5‐[(E)‐1‐(2‐{(E)‐2‐(hydroxyimino}propanoyl}hydrazono)ethyl]‐4‐methyl‐1H‐pyrazole‐3‐carboxylic acid (L2), were synthesized and studied for zinc(II) complexation. A set of pH‐dependent UV/Vis measurements has been performed to determine the complex formation properties of L2. According to the calculations, in solution, L2 forms variously protonated mononuclear (ZnII/L2 = 1:1) and dinuclear (ZnII/L2 = 2:1) complexes. The reaction of the deprotonated ligands with hydrated ZnII salts and slow diffusion of ammonia into the reaction mixtures gave mononuclear [Zn(L1‐2H)(NH3)2]·DMF (1) and trinuclear μ‐pyrazolato‐bridged [Zn3(L2‐3H)2(NH3)5]·4H2O (3). In both complexes, the zinc ions are in the same distorted trigonal‐bipyramidal environment, coordinated to two nitrogen atoms of the ammonia and one oxygen and two nitrogen atoms of the pyrazolate and hydrazide groups. The molecular structures of all of the ligands and complexes have been elucidated by X‐ray crystallography.

Measuring nitrification in sediments – comparison of two techniques and three 15NO measurement methods

Nitrification is a crucial process in sediment nitrogen cycling. We compared two 15N tracer-based nitrification measurement techniques (isotope pairing technique (IPT) combined with 15N nitrate pool dilution and 15N ammonium oxidation) and three different 15N analyses from bottom water nitrate (ammonia diffusion, denitrifier and SPINMAS) in a sediment mesocosm. The 15N nitrate pool dilution technique combined with IPT can be used to quantify the in situ nitrification, but the minimum detection limit for the total nitrification is higher than that in the 15N ammonium oxidation technique. The 15N ammonium oxidation technique, however, is not applicable for sediments that have high ammonium content. If nitrate concentration and the amount of 15N label in the sample are low, the 15N nitrate analysis should be done with the denitrifier method. In higher 15N concentrations, the less sensitive SPINMAS method can also be applied. The ammonia diffusion method is not suitable for bottom water 15N nitrate analyses.

PHARMACEUTICAL OVERVIEW OF SPHERICAL CRYSTALLIZATION

Spherical crystallization is a particle design technique, by which crystallization and agglomeration can be carried out simultaneously in one step and which has been successfully utilized for improvement of flowability, compactability and bioavailability of crystalline drugs. General methods of spherical crystallization are spherical agglomeration, emulsion solvent diffusion and ammonia diffusion method. The principle steps involved in the process of spherical crystallization are flocculation zone, zero growth zone, fast growth zone and constant size zone. Spherical crystallization is having wide applications in pharmaceuticals like improvement of flowability and compressibility of poorly compressible drugs, masking bitter taste of drugs and improving the solubility and dissolution rate of poorly soluble drug.

Nitrogen transformations in a through‐flow wetland revealed using whole‐ecosystem pulsed 15N additions

We used pulsed and continuous additions of 15N together with whole‐ecosystem metabolism measurements to elucidate the mechanisms of nitrogen (N) transformations in a small (1170 m2) through‐flow wetland situated along a stream. From measurements of the wetland inflow and outflow, we observed a consistent decrease in nitrate (by 10% of inflow concentrations), while ammonium increased by an order of magnitude. Outflow ammonium concentrations oscillated in a diel cycle, inverse to the concentration of dissolved oxygen (i.e., greater ammonium export at night). The pulsed 15N additions showed little uptake of nitrate over time in the wetland and rapid daytime uptake of ammonium from the water column (rate constant, kt = 0.11 h−1). A steady‐state 15N‐ammonium addition demonstrated a similar rate of ammonium uptake (kt = 0.067 h−1), no detectable nitrification, and highlighted the spatial pattern of ammonium and nitrate uptake within the wetland. Porewater concentration profiles suggest high rates of net ammonium diffusion from the sediments. Ecosystem metabolism measurements indicate that release was attenuated during the day by autotrophic uptake, resulting in lower ammonium export during the day. Denitrification rates were modeled from dissolved N2 : Ar ratios, but they were not sufficient to account for the observed loss in nitrate. Nitrate was removed near the pond inflow but not actively cycled throughout the pond, while the balance between sediment release and subsequent uptake of ammonium from the water‐column dominated N cycling in this wetland.

Vapour phase diffusion of ammonia on the first row transition metal series and its effect on the crystallization process: A structural investigation

The diffusion of ammonia vapors to the magnesium/manganese/nickel nitrate solution results in the formation of their respective metal hydroxides, while the diffusion of ammonia vapors to copper and zinc nitrate solutions results in the crystallization of layered hydroxysalts. The PXRD patterns show that highly crystalline phases of samples are obtained. Infrared spectra were used to get information on the local coordination of ions. The thermogravimetric analysis justifies the phases concluded from powder X-ray diffraction and infrared spectroscopy. This clearly demonstrates that the crystal structure is mainly dictated by the nature of the metal ion, its site selectivity and specificity under identical synthesis conditions.

Soil Ammonium Diffusion Constraints Contribute to Large Differences in Nitrogen Supply to Rice in the Southern United States

This study was to determine if diffusion of soil ammonium may explain why many sandy soils have greater nitrogen (N)–supplying capacity to rice than clay soils. A laboratory procedure using transient-state methods measured the linear movement of soil ammonium (NH4) in tubes packed with five field soils under aerobic conditions. Ammonium diffusion was measured by sectioning tubes after 48 h of equilibration and then measuring NH4 by steam distillation. Effective diffusion coefficients, De, and NH4 diffusion distance, d, per day ranged from De = 4.6 × 10−5 cm2 d−1 and 1.5 cm d−1 for Katy sandy loam to De = 2.9 × 10−7 cm2 d−1 and 0.11 cm d−1 for League clay. Ammonium diffusion distance d was strongly related to soil clay content and hence was predicted by d = Y × {[100/(% clay)] − 1}, where Y is set to 0.1. Predicted d and measured d were highly related (R2 = 0.99).

Low temperature, pH-triggered synthesis of collagen–chitosan–hydroxyapatite nanocomposites as potential bone grafting substitutes

A pH-triggered synthesis strategy at low temperature was developed to initiate collagen self-assembly, chitosan precipitation and hydroxyapatite synthesis by ammonia diffusion into the acidic homogeneous stock solution for preparing bone-like nanocomposites. FTIR and XRD analyses were used to confirm the molecular interactions and the formation of bone-like hydroxyapatite in collagen–chitosan–hydroxyapatite nanocomposites. A facile modulation of hydroxyapatite content in the obtained nanocomposites was further validated by thermogravimetric analysis. SEM observations revealed that the unique microstructure of obtained nanocomposites was composed of collagen fibrils and nano needle-like objects dependent upon the relative ratio of inorganic to organic components. This strategy is convenient and also feasible to prepare collagen based bone-like nanocomposites.

Synthesis of Fe3O4 Nanoparticles Using Controlled Ammonia Vapor Diffusion under Ultrasonic Irradiation

Fe3O4 nanoparticles were synthesized for the first time via an ammonia vapor diffusion process under ultrasonic irradiation. The possible ultrasound mechanism and the process of ammonia diffusion and reaction has been deduced. Influences of experiment parameters such as reaction time, temperature on the morphology, and size of products were also investigated in detail. Morphology and magnetic properties of products were carefully studied by Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), Scanning electron microscopes (SEM), and vibrating sample magnetometer (VSM). The synthesized Fe3O4 nanoparticles possess superparamagnetic properties at room temperature, and the saturation magnetization is 70.5 emu/g.

Development of a sequential injection gas diffusion system for the determination of ammonium in transitional and coastal waters

This work describes the development of a sequential injection system for the ammonium determination in transitional and coastal waters with a wide salinity range. Estuarine waters are rather complex matrices as their characteristics change considerably along the salinity gradient, as well as the ammonium levels. The developed system effectively solves these issues by converting ammonium into ammonia and using a gas diffusion unit (GDU) for matrix removal. The ammonium determination in a wide quantification range (0.1–5.0 mg L−1) was obtained with small changes in the protocol sequence and was applied, not only to estuarine samples, but also well water samples (low salinity) and coastal waters (higher salinity). Spectrophotometry was the chosen detection system to measure the absorbance change in the bromothymol blue acid base indicator caused by the diffusion of ammonia through the GDU. Additionally, the developed system used a green chemistry approach, as there was no indicator reagent consumption per determination, still maintaining a good precision (relative standard deviation lower than 2%) and a low detection limit, 27 μg L−1 (1.5 μM).

Analytical Techniques for Quantifying 15N/14N of Nitrate, Nitrite, Total Dissolved Nitrogen and Ammonium in Environmental Samples Using a Gas Chromatograph Equipped with a Quadrupole Mass Spectrometer

The measurement of (15)N concentrations in environmental samples requires sophisticated pretreatment devices and expensive isotope-ratio mass spectrometry (IRMS). This report describes the use of a gas chromatograph equipped with a quadrupole-type mass spectrometer (GC/MS) to measure (15)N concentrations of ammonium, nitrate, nitrite, and total dissolved nitrogen (TDN) in distilled water, a 2 M KCl solution and a 0.5 M K(2)SO(4) solution. The system measures nitrous oxide (N(2)O) that is ultimately converted from the target N compound, requiring no special apparatus such as a purge-and-trap pretreatment device. It uses a denitrifier lacking N(2)O reductase, which produces N(2)O from nitrate. Persulfate oxidation was applied to convert TDN to nitrate, while additional pretreatment with ammonia diffusion was required for ammonium prior to the persulfate oxidation. Up to 100 samples can be measured daily using the system. We can generally run (15)N measurements with only 1-10 mL of sample for each chemical species of N, a volume 1/10-1/100 times smaller than the amount necessary for conventional methods. Our method is useful for measuring (15)N with GC/MS, offering greater convenience than IRMS.

Ammonia redistribution from the gastrointestinal tract to general circulation after intraperitoneal injection of cyclophosphamide to rats

Ammonia level in the blood increased within 3 h after intraperitoneal injection of cyclophosphamide in doses of 200, 600, and 1000 mg/kg: by 1.4, 1.8, and 2.5 times in the blood from v. portae, by 1.5, 2.1, and 3.3 times in the blood from v. cava caud. caudally to vv. renales orifice, and by 1.8, 2.7, and 4.2 times, respectively, in the same vein cranially to vv. hepaticae. A positive portocaval gradient of ammonia concentration was abolished. Blood concentrations of glutamine and urea increased less markedly than those of ammonia. Ammonia and glutamine accumulation in isotonic saline injected to animals intraperitoneally 2.5 h after cyclophosphamide was stimulated depending on the drug dose. Blood concentrations of cytolysis markers (lactate dehydrogenase and alanine and aspartate transaminases) increased. Ammonia, glutamine, and urea concentrations in the blood remained high 18 h after injection of cyclophosphamide, the glutamine/ammonia ratio increased. These data indicate that a single intraperitoneal injection of cyclophosphamide to rats in doses of 200-1000 mg/kg disorders detoxification and stimulates transperitoneal diffusion of ammonia from the digestive tract to the posterior vena cava basin with the development of hyperammoniemia.