Corrosion Inhibition of Carbon Steel in a Sour (H2S) Environment by an Acryloyl-Based Polymer.

Corrosion poses safety and operational challenges in the oil and gas field, particularly in a sour environment. Corrosion inhibitors (CIs) are thus employed to protect the integrity of industrial assets. However, CIs have the potential to dramatically impair the effectiveness of other co-additives, such as kinetic hydrate inhibitors (KHIs). Here, we propose an acryloyl-based copolymer, previously used as a KHI, as an effective CI. The copolymer formulation provided a corrosion inhibition efficiency of up to 90% in a gas production environment, implying that it can reduce or even eliminate the need for an additional dedicated CI in the system. It also demonstrated a corrosion inhibition efficiency of up to 60% under field-simulated conditions for a wet sour crude processing environment. Molecular modeling suggests that the enhanced corrosion protection is imparted by the favorable interaction of the heteroatoms of the copolymer with the steel surface, potentially displacing adhered water molecules. All in all, we show that an acryloyl-based copolymer with dual functionalities can potentially overcome issues caused by incompatibilities in a sour environment, resulting in significant cost savings and operational ease.

Cost of high leverage in socially responsible firms in a linear dynamic panel model. Evidence from product market interactions.

Corporate Social responsibility is the major challenge for senior management of firms and they devoted the significant resources for CSR initiatives. Despite of significant comprehension of CSR, an ongoing debate is still under consideration about its economic repercussions in terms of "do well by doing good". Corporations are facing huge leverage cost with bad customer reputation in the product market. This study attempt to examine this phenomenon as the cost of high leverage in socially responsible firms and the product market interactions of those firms. The data is collected from 2009-2020 in linear dynamic setting for product market interaction, and two step system GMM estimation technique is applied for endogeneity concerns. The study identified that socially responsible firms are experiencing better growth in their sales in product market that maximize the financial benefits. However, the high leverage cost worsen their performance in product market because leverage is associated with some losses in market share due to unfavorable actions of competitors and customers. Socially responsible firms experience the low cost of high leverage which helps the firms to increase the performance in product market. Moreover, the corporate governance effectively devises the strategies to diminish the high leverage cost in the way towards better product market interactions. The results are conclusive across the financial crisis, firm's classifications and different channels of firms. The study enables the holistic and broader understanding of CSR in the reduction of high leverage cost with an intention to increase the firm's sustainability in product market. The study contributes with a view to ascertain the cost of high leverage in socially responsible firms for product market interactions of Pakistani firms in a linear dynamic panel.

Impact of Fluorine Substituents on π-Conjugated Polymer Main-Chain Conformations, Packing, and Electronic Couplings.

Taking the π-conjugated polymers PBDT[2X]T (X = H, F) as model systems, the effects of fluorine substitution on main-chain conformations, packing, and electronic couplings are examined. This combination of molecular dynamics simulations and solid-state NMR shows that a higher propensity for backbone planarity in PBDT[2F]T leads to more pronounced, yet staggered, chain stacking, which generally leads to higher electronic couplings and binding energy between neighboring chains.

Centerband-only-detection-of-exchange (31)P nuclear magnetic resonance and phospholipid lateral diffusion: theory, simulation and experiment.

Centerband-only-detection-of-exchange (CODEX) (31)P NMR lateral diffusion measurements were performed on dimyristoylphosphatidylcholine (DMPC) assembled into large unilamellar spherical vesicles. Optimization of sample and NMR acquisition conditions provided significant sensitivity enhancements relative to an earlier first report (Q. Saleem, A. Lai, H. Morales, and P. M. Macdonald, Chem. Phys. Lipids, 2012, 165, 721). An analytical description was developed that permitted the extraction of lateral diffusion coefficients from CODEX data, based on a Gaussian-diffusion-on-a-sphere model (A. Ghosh, J. Samuel, and S. Sinha, Europhys. Lett., 2012, 98, 30003-p1) as relevant to CODEX (31)P NMR measurements on a population of spherical unilamellar phospholipid bilayer vesicles displaying a distribution of vesicle radii.

Single lipid bilayer deposition on polymer surfaces using bicelles.

A lipid bilayer was deposited on a 3 µm diameter polystyrene (PS) bead via hydrophobic anchoring of bicelles containing oxyamine-bearing cholesteric moieties reacting with the aldehyde functionalized bead surface. Discoidal bicelles were formed by mixing dimyristoylphosphatidylcholine (DMPC), dihexanoylphosphatidylcholine (DHPC), dimyristoyltrimethylammonium propane (DMTAP), and the oxyamine-terminated cholesterol derivative, cholest-5-en-3ß-oxy-oct-3,6-oxa-an-8-oxyamine (CHOLOA), in the molar ratio DMPC/DHCP/DMTAP/CHOLOA (1/0.5/0.01/0.05) in water. Upon exposure to aldehyde-bearing PS beads, a stable single lipid bilayer coating rapidly formed at the bead surface. Fluorescence recovery after photobleaching demonstrated that the deposited lipids fused into an encapsulating lipid bilayer. Electrospray ionization mass spectrometry showed that the short chain lipid DHPC was entirely absent from the PS adherent lipid coating. Fluorescence quenching measurements proved that the coating was a single lipid bilayer. The bicelle coating method is thus simple and robust, can be modified to include membrane-associated species, and can be adapted to coat any number of different surfaces.

Thermal stabilization of bicelles by a bile-salt-derived detergent: a combined ³¹P and ²H nuclear magnetic resonance study.

The properties of bicelles composed of mixtures of long-chain lipids dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylglycerol (DMPG), stabilized by zwitterionic bile salt analogue 3-[(3-cholamidopropyl)dimethyl-d6-ammonio]-2-hydroxy-1-propanesulfonate (CHAPSO-d6), deuterated at both amino methyls, were investigated by a combination of (31)P and (2)H NMR, focusing on the behavior of CHAPSO as a function of temperature. For compositions of molar ratio q = [DMPC + DMPG]/[CHAPSO] = 3, R = [DMPG]/[DMPC + DMPG] = 0, 0.01 and 0.10 and lipid concentration CL = 25 wt % lipid at temperatures of between 30 and 60 °C, magnetic alignment was readily achieved as assessed via both (31)P NMR of the phospholipids and (2)H NMR of CHAPSO-d6. Increasing temperature yielded higher values for the chemical shift anisotropy of the former and the quadrupole splitting of the latter, consistent with the progressive migration of CHAPSO from edge regions into planar regions of the bicellar assemblies. However, relative to dihexadecyl phosphatidylcholine (DHPC), CHAPSO exhibited lower miscibility with DMPC, although the presence of DMPG enhanced this miscibility. At 65 °C, thermal instability became evident in the appearance of a separate isotropic component in both (31)P and (2)H NMR spectra. This isotropic phase was CHAPSO-enriched but less so as a function of increasing DMPG. These findings indicate that the enhanced thermal stability of CHAPSO- versus DHPC-containing bicelles arises from a combination of the larger surface area that edge CHAPSO is able to mask, mole for mole, and its relative preference for edge regions, plus, possibly, specific interactions with DMPG.

Liposome-coated hydrogel spheres: delivery vehicles with tandem release from distinct compartments.

We have fabricated unilamellar lipid bilayer VESicle-COated hydrogel spheres (VESCOgels) by carbodiimide-mediated coupling of liposomes bearing surface amines to core-shell hydrogel spheres bearing surface carboxyls. The amine-containing moiety, 3-O (2-aminoethoxyethyloxyethyl)carbamyl cholesterol (AECHO), was incorporated into large unilamellar vesicles (LUVs), diameter ∼100 nm, composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). The hydrogel, diameter ∼ 1 µm, consisted of a core of poly(N-isopropyl acrylamide) (pNIPAM) and a shell of p(NIPAM-co-acrylic acid (AA)). Activation of these surface-displayed carboxyls with N-hydroxysuccinimidyl (NHS) esters permitted amine coupling upon addition of AECHO-containing POPC LUVs. Bilayer integrity of the hydrogel-bound LUVs was maintained, and fusion of LUVs did not occur. Fluorescence assays of the release of cobalt-calcein trapped within hydrogel-bound LUVs and of sodium fluorescein trapped within the hydrogel itself showed that each compartment retained its distinct release attributes: fast release from the microgel and slow release from the LUVs. It is envisioned that VESCOgels will be useful, therefore, in applications requiring temporally controlled delivery of distinct drugs.

NMR methods for measuring lateral diffusion in membranes.

Lateral diffusion is a fundamental property of biological membrane components, important for a host of biomembrane functions. Although long studied, novel aspects of the relationship between the structure of membrane components and their lateral diffusion properties continue to emerge. NMR-based lateral diffusion measurements are complicated by the spectral broadening arising from the slow anisotropic motions in membranes. Nevertheless, both pulsed field gradient (PFG) and exchange spectroscopy (EXSY) methods can be adapted to permit NMR measurements of lateral diffusion in membranes. These variously will be described in overview, highlighting advantages and limitations of each, but with particular emphasis on results from our laboratory using (1)H PFG NMR measurements in magnetically aligned bicelles and (31)P CODEX (Centreband-Only-Detection-of-Exchange) measurements in spherical phospholipid vesicles.

Lateral diffusion of bilayer lipids measured via (31)P CODEX NMR.

We have employed (31)P CODEX (centre-band-only-detection-of-exchange) NMR to measure lateral diffusion coefficients of phospholipids in unilamellar lipid bilayer vesicles consisting of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC), alone or in mixtures with 30 mol% 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG) or cholesterol (CHOL). The lateral diffusion coefficients of POPC and POPG were extracted from experimental CODEX signal decays as a function of increasing mixing time, after accounting for the vesicle's size and size distribution, as determined via dynamic light scattering, and the viscosity of the vesicular suspension, as determined via (1)H pulsed field gradient NMR. Lateral diffusion coefficients for POPC and POPG determined in this fashion fell in the range 1.0-3.2 × 10(-12) m(2) s(-1) at 10 °C, depending on the vesicular composition, in good agreement with accepted values. Thus, two advantages of (31)P CODEX NMR for phospholipid lateral diffusion measurements are demonstrated: no labelling of the molecule of interest is necessary, and multiple lateral diffusion coefficients can be measured simultaneously. It is expected that this approach will prove particularly useful in diagnosing heterogeneities in lateral diffusion behaviours, such as might be expected for specific lipid-lipid or lipid-protein interactions, and thermotropic or electrostatically induced phase inhomogeneities.

Lipogels: single-lipid-bilayer-enclosed hydrogel spheres.

We have fabricated Lipogels consisting of a single POPC lipid bilayer supported by a micrometer-sized, thermoresponsive, hydrophobically modified (HM), hydrogel sphere. The hydrogel consists of a lightly cross-linked poly(N-isopropylacrylamide) (pNIPAM) core surrounded by a highly cross-linked acrylic acid (AA)-rich p(NIPAM-co-AA) shell. The lipid bilayer was assembled by binding liposomes to HM microgels, followed by several cycles of freeze-thaw. The pNIPAM volume phase transition (VPT) at ∼32 °C was present both before and after hydrophobic modification and after lipid bilayer coating. Fluorescence studies confirmed the fusion of liposomes into a continuous single bilayer. At a temperature above the VPT, it was found that the volume decrease in the hydrogel was coupled to the appearance of highly curved obtrusions of the uncompromised lipid bilayer into the surroundings. It is anticipated that these properties of Lipogels will prove to be useful in drug delivery applications and in fundamental biophysical studies of membranes.