Mechanism of sulfidation of small zinc oxide nanoparticles

ZnO has industrial utility as a solid sorbent for the removal of polluting sulfur compounds from petroleum-based fuels. Small ZnO nanoparticles may be more effective in terms of sorption capacity and ease of sulfidation as compared to bulk ZnO. Motivated by this promise, here, we study the sulfidation of ZnO NPs and uncover the solid-state mechanism of the process by crystallographic and optical absorbance characterization. The wurtzite-structure ZnO NPs undergo complete sulfidation to yield ZnS NPs with a drastically different zincblende structure. However, in the early stages, the ZnO NP lattice undergoes only substitutional doping by sulfur, while retaining its wurtzite structure. Above a threshold sulfur-doping level of 30 mol%, separate zincblende ZnS grains nucleate, which grow at the expense of the ZnO NPs, finally yielding ZnS NPs. Thus, the full oxide to sulfide transformation cannot be viewed simply as a topotactic place-exchange of anions. The product ZnS NPs formed by nucleation-growth share neither the crystallographic structure nor the size of the initial ZnO NPs. The reaction mechanism may inform the future design of nanostructured ZnO sorbents.

In the sulfidation of small ZnO nanoparticles, the nanoparticles first undergo sulfur doping followed by the nucleation-growth of ZnS domains.

Zinc oxide (ZnO) nanoparticles (NPs), due to their cost-effectiveness and biodegradability, have a multitude of applications^1–3 including coatings^4–8 and pigments,^9,10 catalysis,^11,12 energy storage,^13,14 and environmental remediation.^15–22 ZnO NPs have particular appeal as sorbents for scavenging polluting sulfur compounds such as mercaptans and hydrogen sulfide (H₂S) from petroleum-based fuels:^23–27 ZnO + H₂S → ZnS + H₂O. Lattice O²⁻ in the ZnO is replaced with S²⁻ scavenged from the pollutant. Bulk powders of ZnO have already been used for adsorptive removal of H₂S,^28,29 but NPs have specific advantages. With smaller grain sizes, mass transport limitations are lifted.²³ Whereas sulfidation is limited to the surface of bulk ZnO, with NPs, the entire mass of ZnO can undergo sulfidation, enabling high sorbent capacity.²³ Volume and morphology changes resulting from restructuring of the solid can also be more easily accommodated with NPs,²³ allowing regenerable use of the sorbent. Finally, the high specific surface area of NPs allows more enhanced kinetics of the sulfidation reaction, potentially facilitating much lower desulfurization temperatures as compared to the conventional operating temperatures of 650–800 °C.^23,29In this context, small few-nm size ZnO NPs can be expected to be particularly promising, but it is important to understand the manner in which these NPs undergo sulfidation. The structural mechanism of the sulfidation process³⁰ may have critical differences compared to bulk ZnO powders or even larger NPs of tens of nm in size²⁴ and may therefore influence sorbent design. In a seminal study, Park et al.³⁰ studied the sulfidation of hexagonal-shaped 14 nm ZnO nanocrystals (NCs) at high temperature (235 °C) using hexamethyldisilathiane. The reaction was found to involve the anion exchange of O²⁻ with S²⁻ in the NC lattice. The overall shape and crystallography of ZnS NCs was templated by the initial ZnO NCs. However, due to the faster outward diffusion of Zn²⁺ as compared to the inward diffusion of S²⁻, the exchange reaction was accompanied by a nanoscale Kirkendall phenomenon, as a result of which the ZnS NCs formed were hollow.Here, we track the step-wise sulfidation of smaller (ca. 5 nm) ZnO NPs using optical spectroscopy and X-ray crystallography. Prior to the onset of sulfidation, O²⁻ in wurtzite ZnO NPs undergoes substitutional doping with S²⁻ without any major change in its structure. Upon reaching a critical concentration of sulfur doping, separate zincblende ZnS grains form and grow into ZnS NPs. Thus, the sulfidation of these small ZnO NPs studied here is not simply a topotactic or templated place-exchange of anions; rather the nucleation and growth of a separate ZnS crystallite is involved in the latter stages.     

Vinylene and benzo[c][1,2,5]thiadiazole: effect of the π-spacer unit on the properties of bis(2-oxoindolin-3-ylidene)-benzodifuran-dione containing polymers for n-channel organic field-effect transistors

Two polymers based on (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo[1,2-b:4,5-b′]difuran-2,6(3H,7H)-dione (BIBDF) coupled with (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TVT) or dithienylbenzothiadiazole (TBT), namely PBIBDF-TVT and PBIBDF-TBT were synthesized via the Stille coupling reaction. The effect of benzothiadiazole or vinylene-π spacer of the copolymers on optical properties, energy levels, electronic device performance and microstructure were studied. It was found that PBIBDF-TBT based OFET devices, annealed at 180 °C, showed better performance with the highest electron mobility of 2.9 × 10⁻² cm² V s⁻¹ whereas PBIBDF-TVT polymer exhibited 5.0 × 10⁻⁴ cm² V s⁻¹. The two orders of magnitude higher electron mobility of PBIBDF-TBT over PBIBDT-TVT is a clear indicator of the better charge transport ability of this polymer semiconductor arising from its higher crystallinity and better donor–acceptor interaction.

Bottom-gate-top-contact OFET device structure using PBIBDF-TVT and PBIBDF-TBT based polymer semiconductors.     

Hydroxyapatite nanorods loaded with parathyroid hormone (PTH) synergistically enhance the net formative effect of PTH anabolic therapy

Parathyroid hormone (PTH) has been a major contributor to the anabolic therapy for osteoporosis, but its delivery to bone without losing activity and avoiding adverse local effects remain a challenge. Being the natural component of bone, use of hydroxyapatite for this purpose brings a major breakthrough in synergistic anabolism. This study focuses on synthesis, characterization and evaluation of in vitro and in vivo efficacy of PTH (1-34) adsorbed hydroxyapatite nanocarrier for synergistic enhancement in the anabolic activity of PTH for bone regeneration. The negative zeta potential of this nanocarrier facilitated its affinity to the Ca²⁺ rich bone tissue and solubilization at low pH enhanced specific delivery of PTH to the resorption pits in osteoporotic bone. In this process, PTH retained its anabolic effect and at the same time an increase in bone mineral content indicated enhancement of the net formative effect of the PTH anabolic therapy.     

Novel analogs of sulfasalazine as system xc− antiporter inhibitors: Insights from the molecular modeling studies

System x_c⁻ (Sx_c⁻), a cystine-glutamate antiporter, is established as an interesting target for the treatment of several pathologies including epileptic seizures, glioma, neurodegenerative diseases, and multiple sclerosis. Erastin, sorafenib, and sulfasalazine (SSZ) are a few of the established inhibitors of Sx_c⁻. However, its pharmacological inhibition with novel and potent agents is still very much required due to potential issues, for example, potency, bioavailability, and blood–brain barrier (BBB) permeability, with the current lead molecules such as SSZ. Therefore, in this study, we report the synthesis and structure–activity relationships (SAR) of SSZ derivatives along with molecular docking and dynamics simulations using the developed homology model of xCT chain of Sx_c⁻ antiporter. The generated homology model attempted to address the limitations of previously reported comparative protein models, thereby increasing the confidence in the computational modeling studies. The main objective of the present study was to derive a suitable lead structure from SSZ eliminating its potential issues for the treatment of glioblastoma multiforme (GBM), a deadly and malignant grade IV astrocytoma. The designed compounds with favorable Sx_c⁻ inhibitory activity following in vitro Sx_c⁻ inhibition studies, showed moderately potent cytotoxicity in patient-derived human glioblastoma cells, thereby generating potential interest in these compounds. The xCT-ligand model can be further optimized in search of potent lead molecules for novel drug discovery and development studies.     

Refining amyloid complete hematological response: Quantitative serum free light chains superior to ratio

Response assessment in light chain (AL) amyloidosis is based on serum and urine monoclonal protein studies. Newly diagnosed patients (n = 373) who achieved very good partial response or complete response (CR) to first line therapy were assessed for the survival impact of each of the monoclonal protein studies. At end of therapy (EOT), negative serum/urine immunofixation (IFE) was achieved in 61% of patients, 72% achieved normal serum free light chain ratio (sFLCR), and the median involved free light chain (iFLC) and difference between involved to uninvolved light chain (dFLC) were 17 mg/L and 5 mg/L, respectively. Overall, 46% of patients achieved a CR at EOT. At EOT, iFLC ≤20 mg/L and dFLC ≤10 mg/L were additive in survival discrimination to negative serum/urine IFE and were independent predictors of overall survival. In contrast, normalization of sFLCR did not add survival discrimination to serum/urine IFE and was not independent predictor of survival. We propose a new definition for hematological CR to include serum/urine IFE negativity plus iFLC ≤20 mg/L or dFLC ≤10 mg/L, instead of the current definition of serum/urine IFE negativity and normal sFLCR. Complete response using dFLC ≤10 mg/L had the best performance in those with significant renal dysfunction and by light chain isotype, making it the preferred partner to IFE. Validation of these results in a multicenter cohort is warranted.     

Cadaveric study of anatomical variations of the median nerve and persistent median artery at wrist

Background:

Awareness of anatomical variations of the median nerve at wrist is important in repair of traumatic injuries and treatments of compression syndrome because in these situations precise dissection of the nerve is mandatory and such variations are not infrequent.

Materials and Methods:

In this study, 52 hands of 52 fresh cadavers were dissected and median nerve anatomy along with the presence of persistent median artery (PMA) was noted.

Results:

A total of 26 hands (50%) had the deviation from the standard text book anatomy of the median nerve. There was early division of the median nerve into the medial and lateral branches in 11.53% hands. There was early branching of the 2^nd common digital nerve in 9.6% hands. The transligamentous motor branch to the thenar muscle was most prevalent (42.3% hands). The single motor branch to the thenar muscles was found in the majority of hands (84.6%). The PMA was present in 11.53% hands and it was associated with variations in the median nerve anatomy in all cases.

Conclusions:

This study shows a high percentage of deviation from standard anatomy as well as a high percentage of transligamentous thenar muscle motor branch. The presence of PMA was associated with variations in the median nerve anatomy in all cases. Therefore if PMA is present there are very high chances of associated median nerve anomalies.KEY WORDS: Anatomical variations, cadaveric study, median nerve, persistent median artery, wrist     

A potent enzybiotic against methicillin-resistant Staphylococcus aureus

Virus Genes - Staphylococcus aureus is one of the most dreadful infectious agents, responsible for high mortality and morbidity in both humans and animals. The increased prevalence of...