Scale inhibitors are widely used to prevent mineral scale deposition and precipitation in industrial processes. In this study, the performance of scale inhibitors is systematically investigated in a flow loop apparatus, designed to mimic the barite deposition in pipelines. The inhibitors are tested in tubing with and without a precovered barite scale layer. DTPMP (diethylenetriamine-pentamethylene phosphonic acid), PPCA (phosphinopoly carboxylic acid), and SPCA (sulfonated poly­(carboxylic acid)) are the main inhibitors tested in this work. The heterogeneous deposition rate constants at 120 °C in a clean tubing in the presence of 0.25 ppm of DTPMP/PPCA/SPCA are 0.00, 10.3 × 10–5, and 32.1 × 10–5 cm/s, respectively. The deposition rate constants at 120 °C in a tubing fully covered with barite in the presence of 2.0 ppm of DTPMP, PPCA, or SPCA are 5.97 × 10–5, 36.8 × 10–5, and 28.0 × 10–5 cm/s, respectively. In tubing fully covered with barite, all three inhibitors require a higher concentration to reach the same level of inhibition as observed in the uncoated tubing. The experiments in fully covered tubing were conducted in a wide temperature range (50–150 °C) with various dosages of inhibitors (0.02–40 ppm). The impact of inhibitors on deposition rate constants is modeled with a Langmuir-type equation by using an adsorption equilibrium constant K eq, fractional occupancy θ, and unoccupiable fraction θ0 in the fully covered tubing. θ represents the fraction of active sites occupied by the inhibitors, and θ0 represents the fraction that cannot be occupied by the inhibitors. The adsorption isosteric enthalpies of functional groups on the inhibitor molecules are calculated from the fitted associate equilibrium constants. A kink site adsorption mechanism has been proposed as the inhibition mechanism.

Ribonuclease III is a conserved bacterial endonuclease that cleaves double-stranded(ds) structures in diverse coding and noncoding RNAs. RNase III is subject to multiple levels of control that in turn confer global post-transcriptional regulation. The Escherichia coli macrodomain protein YmdB directly interacts with RNase III, and an increase in YmdB amount in vivo correlates with a reduction in RNase III activity. Here, a computational-based structural analysis was performed to identify atomic-level features of the YmdB-RNase III interaction. The docking of monomeric E. coli YmdB with a homology model of the E. coli RNase III homodimer yields a complex that exhibits an interaction of the conserved YmdB residue R40 with specific RNase III residues at the subunit interface. Surface Plasmon Resonance (SPR) analysis provided a KD of 61 nM for the complex, corresponding to a binding free energy (ΔG) of −9.9 kcal/mol. YmdB R40 and RNase III D128 were identified by in silico alanine mutagenesis as thermodynamically important interacting partners. Consistent with the prediction, the YmdB R40A mutation causes a 16-fold increase in KD (ΔΔG = +1.8 kcal/mol), as measured by SPR, and the D128A mutation in both RNase III subunits (D128A/D128'A) causes an 83-fold increase in KD (ΔΔG = +2.7 kcal/mol). The greater effect of the D128A/D128'A mutation may reflect an altered RNase III secondary structure, as revealed by CD spectroscopy, which also may explain the significant reduction in catalytic activity in vitro. The features of the modeled complex relevant to potential RNase III regulatory mechanisms are discussed.

Barium sulfate deposition is one of the most serious problems in the flow assurance issues in the industry. The kinetics of barium sulfate deposition inside the flowing tubing has been studied. The deposition process can be divided into two phases: the growth phase, where the deposition rate constant increases with time, and the steady-state phase, wherein the deposition rate remains constant. The result suggests that the barite deposition is governed by a surface-controlled process followed by a mass transport-controlled process. The measured deposition rate along the tubing can be successfully modeled via a heterogeneous reaction equation. Furthermore, the deposition rate constants match well with the coupled-ion diffusion-controlled rate constants, which suggest that the kinetics of barite deposition can be predicted from the fundamental diffusion theory. The measured sizes and crystal number densities follow the predictions of the classical nucleation theory. This result indicates that nucleation is also involved in the scale deposition process. In tubing partially covered with barite, the deposition rate constants ranged from (2.17 to 3.53) × 10–4 cm/s at 50–120 °C. The deposition rate constants increase in the tubing fully covered with barite and become (2.38–9.55) × 10–4 cm/s over the same temperature range. By comparison with the Graetz–Nusselt theory, the deposition rate constants in the partially covered tubing correspond well with the coupled-ion diffusion control rate constants (1.89–4.41) × 10–4 cm/s at 50–120 °C, which suggest that the barite deposition in the flowing pipe can be described as the coupled-ion diffusion process. The higher deposition rate constants in the fully covered tubing correspond to an increased barite crystal surface area covering the tubing.

Ribonuclease III (RNase III) is a conserved, gene-regulatory bacterial endonuclease that cleaves double-helical structures in diverse coding and noncoding RNAs. RNase III is subject to multiple levels of control, reflective of its global regulatory functions. Escherichia coli (Ec) RNase III catalytic activity is known to increase during bacteriophage T7 infection, reflecting the expression of the phage-encoded protein kinase, T7PK. However, the mechanism of catalytic enhancement is unknown. This study shows that Ec-RNase III is phosphorylated on serine in vitro by purified T7PK, and identifies the targets as Ser33 and Ser34 in the N-terminal catalytic domain. Kinetic experiments reveal a 5-fold increase in kcat and a 1.4-fold decrease in Km following phosphorylation, providing a 7.4–fold increase in catalytic efficiency. Phosphorylation does not change the rate of substrate cleavage under single-turnover conditions, indicating that phosphorylation enhances product release, which also is the rate-limiting step in the steady-state. Molecular dynamics simulations provide a mechanism for facilitated product release, in which the Ser33 phosphomonoester forms a salt bridge with the Arg95 guanidinium group, thereby weakening RNase III engagement of product. The simulations also show why glutamic acid substitution at either serine does not confer enhancement, thus underscoring the specific requirement for a phosphomonoester.

In oil and gas industry, scaling prevention is one of the most important problems. While with more aggressive drilling and exploitation, scale control for the unconventional scale under complex water chemistry becomes more challenging. There are more chances to encountering with high temperature, high pressure, high TDS and some unconventional scale conditions. The modeling of the sulfide scale is notoriously difficult due to the extremely low solubility and complex water chemistry. Thus, the thermodynamic data is rare for sulfide minerals. Metal-sulfide-bisulfide complexes bring a large uncertainty for scale prediction. Another challenge is scale prediction in brine with high TDS, especially with high calcium concentration. Thermodynamic data with common ions Ca2+ and SO42- is needed to improve thermodynamic models. The objective of this paper is to extend our knowledge for these exotic scale solubility predictions with both experimental studies and model validation. Some remaining questions in Pitzer theory framework have been thoroughly reviewed and discussed to improve the scale prediction for iron sulfide and high calcium condition. The newly derived models are able to predict the saturation index (SI) within ±0.3 unit for iron sulfide and ±0.15 units for common sulfate scales, respectively. These developed models have been incorporated into ScaleSoftPitzer for practical use in the oil and gas production.