Effect of successive recycling and reuse of acid liquor for the synthesis of graphene oxides with higher oxygen-to-carbon ratios.

Graphene has recently drawn exponential attention due to its surprising physicochemical properties and diversified field of applications. Although graphene oxides (GOs), itself is an exclusive material, it is also an intermediate product for the production of reduced graphene oxides (rGOs), graphene and their derivatives, which are other more superficial materials. In this study, GOs with higher oxygen to carbon ratios were synthesized following the Tour method, where the excess feed acid liquor (FAL) of mixed concentrated sulfuric and orthophosphoric acids at a ratio of 90:10 was recovered from the reaction slurries by applying the centrifugation technique. About 80-90 % of the FAL was recycled and reused as feed for the subsequent batches. The changes in the properties of FAL for the five consecutive recycling and reuse were studied. The properties of recycled FALs were investigated by measuring density, moisture content, pH, and ion concentration. The consecutive recycling of FALs tends to increase the moisture content about 0.5% in each recycles. Ion-chromatography (IC) was used to measure the variation in SO42- and PO43- ions in the FALs. The H2SO4 reacts with KMnO4 and crystalized out from the recovered FAL faster than the phosphoric acid. So, sulfuric acid content in the makeover FALs must be greater than primary FAL. The product GOs were characterized using FT-IR, FT-Raman, UVVis, STA, SEM, XPS, Zeta-potential, and particle size analyzers. The variation of the properties of GOs with the changes in the reaction parameters such as temperature and time were investigated and correlated with the product yield. It was observed that the effect of temperature on the reaction rate was found to be negatively and positive with the reaction time. The oxygen-to-carbon atomic ratio from XPS analysis was found 66.7%, which supported the increase in product yields 66.9% in the experimental results. The effect of acid concentration, reaction temperature, and time on the GOs properties were satisfactory, correlated, and easily controllable with the reaction conditions. A higher extent of oxidation and enhanced product yields 65-70% were observed at 60-70 °C and 14-18 h. A mixture of nano- and macro-molecular GOs was obtained, and their compositions were easily controllable and separable by controlling the reaction conditions. A correlation was made among the properties of synthesized GOs, FAL, and recycled FAL and reaction conditions.

Calcined chicken eggshell-derived biomimetic nano-hydroxyapatite as a local drug-delivery aid for doxycycline hyclate: characterization, bio-activity, cytotoxicity, antibacterial activity and in vitro release study.

The integration of bioactive substances with antibiotics has been extensively pursued for the treatment of osteomyelitis. These materials, also known as biomaterials, can serve both as bone replacements and targeted drug delivery systems for antibiotics. In this study, biomimetic nano-hydroxyapatite (nHAp) was synthesized via the coprecipitation technique where waste chicken eggshell (WCE) was employed as the source of Ca. Heat treatment was performed at four different temperatures (100 °C, 300 °C, 600 °C and 900 °C). Subsequently, the samples were characterized using XRD, FTIR spectroscopy, Raman spectroscopy, FESEM, EDX, XPS, DLS hydrodynamic size and zeta potential analysis. Also, their biomedical effectiveness was evaluated in terms of cytotoxicity, hemolysis, antibacterial performance, and bioactivity. Doxycycline hyclate (DOXh) was loaded in the synthesized nHAp samples, and subsequently its in vitro release was studied under stirring in simulated body fluid (SBF). The DOXh release kinetics was evaluated, and it was found that the first-order model was the best fitted kinetic model describing the release of DOXh from the nHAp samples, except for nHAp100, which was best described by the Korsmeyer-Peppas model. The nHAp synthesized utilizing WCE showed excellent potential for biomedical application and can be used as a drug delivery agent for antibiotics, such as DOXh.

Architecting Ultrathin Graphitic C3N4 Nanosheets Incorporated PVA/Gelatin Bionanocomposite for Potential Biomedical Application: Effect on Drug Delivery, Release Kinetics, and Antibacterial Activity.

Planar (2D) nanomaterials are garnering broad recognition in diverse scientific areas because of their intrinsic features. Herein, bulk graphitic carbon nitride (g-C3N4) was prepared from melamine, which was exfoliated to produce g-C3N4 nanosheets. The prepared g-C3N4 nanosheets were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), photo luminescence (PL) spectroscopy, and dynamic light scattering (DLS). The stable dispersion of a g-C3N4 nanosheet was incorporated into a PVA/Gelatin matrix to explore its efficacy as a promising drug carrier. A remarkable 42% increase in tensile strength for 1% g-C3N4/PVA/Gelatin was attained compared with that of the PVA/Gelatin film. Thermal stability increased due to addition of g-C3N4 nanosheet in the PVA/Gelatin film, where the maximum thermal degradation temperature increased by 9.5 °C when the 1% nanosheet was added to the PVA/Gelatin film. Moreover, the g-C3N4 nanosheets and g-C3N4/PVA/Gelatin showed no cytotoxicity against HeLa and BHK-21 cells. To investigate the in vitro drug releasing efficacy, ciprofloxacin was incorporated into g-C3N4/PVA/Gelatin. Experimental results showed a 62% drug release within 120 min at physiological pH 7.4. The data was curve fitted by different kinetic models of drug release to understand the drug release mechanism. The experimental data was found to fit best with the Higuchi model and revealed the diffusion control mechanism of drug release. Additionally, antibacterial study confirmed the drug release potency from g-C3N4/PVA/Gelatin film on both Gram-positive and Gram-negative bacteria. The above-mentioned promising findings might lead to an opportunity of using g-C3N4 as a potential drug carrier.

Polyethylene glycol functionalized carbon nanotubes/gelatin-chitosan nanocomposite: An approach for significant drug release.

This research work blooms the new idea of developing a safe and controlled drug releasing matrix using multi-walled carbon nanotubes (MWCNTs). In aqueous solution, uniform and highly stable dispersion of MWCNTs was obtained after secondary functionalization with polyethylene glycol (PEG) which was studied by Fourier transmission infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Solution casting method was used to prepare MWCNTs/gelatin-chitosan nanocomposite films and the effect of MWCNTs on physico-mechanical, thermal and water uptake properties of the nanocomposites were evaluated. Incorporation of MWCNTs into the porous gelatin-chitosan matrix showed interesting stiffness and dampness along with developed microfibrillar structures within the pore walls intended at being used in tissue engineering of bone or cartilage. A common antibiotic drug, ciprofloxacin was incorporated into nanocomposite matrix. The evaluation of the effect of MWCNTs on drug release rate by dissolution test and antimicrobial susceptibility test was performed. Sharp release of the drug was found at early stages (∼1 h), but the rate was reduced afterwards, showing a sustained release. It was observed that for all microorganisms, the antibacterial activities of drug loaded MWCNTs/gelatin-chitosan nanocomposites were higher than that of drug loaded gelatin-chitosan composite films containing no MWCNTs. Comparative statistical studies by ANOVA techniques also showed remarkable difference between the antibacterial activities, exhibited by MWCNTs-incorporated and non-incorporated composite films.

Crystal structure of a photobiologically active brominated angular pyran-ocoumarin: bromo-hy-droxy-seselin.

The title compound, C14H13BrO3 [systematic name: rac-(9S,10R)-9-bromo-10-hy-droxy-8,8-dimethyl-9,10-di-hydro-2H,8H-pyrano[2,3-f]chromen-2-one], is a substituted pyran-ocoumarin, obtained by bromination of seselin [8,8-dimethyl-2H,8H-pyrano[2,3-f]chromen-2-one], which was isolated from the Indian herb Trachyspermum stictocarpum (Aajmod). The pyrano ring has a distorted half-chair conformation and its mean plane is inclined to the coumarin mean plane by 1.6 (2)°. In the crystal, mol-ecules are linked by pairs of O-H⋯O hydrogen bonds, forming inversion dimers with an R22(16) ring motif. The dimers stack along the a-axis direction and are linked by offset π-π inter-actions, forming columns [inter-centroid distance = 3.514 (4) Å].

Bis(tert-butylpyrene) nanotweezers and nanocalipers: enhanced extraction and recognition abilities for single-walled carbon nanotubes.

We developed a host-guest methodology for separation of single-walled carbon nanotubes (SWNTs) according to the handedness, diameter and metallicity by the use of diporphyrin nanotweezers and nanocalipers. Although the pyrene has been frequently used to replace porphyrin, due to a similar affinity to the surface of SWNTs and better availability, the extraction and recognition abilities of dipyrene nanotweezers were not so good as those of diporphyrin ones as we reported previously. However, introduction of a tert-butyl substituent at the 7'-position of 2-pyrene is found to enhance the extraction and recognition abilities of dipyrene nanotweezers and nanocalipers. That is, (6,5)-SWNTs were obtained in high purity by use of bis(tert-butylpyrene) nanotweezers with a phenanthrene spacer and metallic SWNTs were highly enriched by use of bis(tert-butylpyrene) nanocalipers with a carbazole-anthracene-carbazole spacer.

Enrichment of Large-Diameter Single-Walled Carbon Nanotubes (SWNTs) with Metallo-Octaethylporphyrins.

We report here a detailed experimental investigation on noncovalent functionalization of single-walled carbon nanotubes (SWNTs) with four different metallo-octaethylporphyrins (MOEPs). It has been found that the identity of the center metal of MOEP strongly influences the solubilization of SWNTs. MnOEPs and ZnOEPs successfully extracted SWNTs in methanol, as confirmed by absorption spectroscopy, while CoOEPs and CuOEPs were not able to extract SWNTs at all. Atomic force microscopy (AFM) studies revealed that large SWNTs bundles could be exfoliated into either individual SWNTs or very small bundles by complexation with ZnOEP molecules. As for enrichment of SWNTs, ZnOEPs and MnOEPs show similar diameter discrimination ability toward 76-CoMoCAT, providing the extracted SWNTs with relatively large diameters.

Improved selectivity in discriminating handedness and diameter of single-walled carbon nanotubes with N-substituted 3,6-carbazolylene-bridged chiral diporphyrin nanotweezers.

Chiral diporphyrin nanotweezers 1 consisting of two chiral porphyrins with N-substituted 3,6-carbazolylene in between have been studied for the separation of single-walled carbon nanotubes (SWNTs). As compared to the analogous nanotweezers 2 without an N-substitutent, nanotweezers 1 with the N-octylcarbazolylene spacer exhibit much higher extraction ability and better selectivity for SWNTs. A narrower diameter range of SWNTs, from 0.88 to 0.92 nm, was selectively extracted with nanotweezers 1. In addition, only (7,6)-SWNTs of 0.90 nm diameter were optically enriched through extraction with 1, while SWNTs extracted with 2 showed lower optical purity of (7,6)-SWNTs. These enhanced extraction and discrimination abilities of 1 can be attributed to the formation of a more stable SWNT complex of 1 than of 2 in methanol.

Simultaneous discrimination of handedness and diameter of single-walled carbon nanotubes (SWNTs) with chiral diporphyrin nanotweezers leading to enrichment of a single enantiomer of (6,5)-SWNTs.

Separation of single-walled carbon nanotubes (SWNTs) according to their handedness has been attracting growing interest. Our methodology to separate the enantiomers of SWNTs is based on molecular recognition with chiral diporphyrin nanotweezers. Herein, we report novel nanotweezers 1 consisting of two chiral porphyrins and phenanthrene in between. These nanotweezers 1 are rationally designed to discriminate diameter and handedness simultaneously by taking into account the relationship between the (n, m) selectivity and the structures of previously reported chiral nanotweezers. Owing to the relatively narrow cleft made by two porphyrins, the nanotweezers 1 showed high selectivity toward (6,5)-SWNTs possessing the smallest diameter among the major components of CoMoCAT-SWNTs. In addition, the chiral diporphyrin 1 discriminated the left- and right-handed structures of (6,5)-SWNTs, providing high enantiomeric excess (67% ee on the basis of the (6,5)-SWNTs with high optical purity recently reported by Weisman). In conclusion, only the single stereoisomer of (6,5)-SWNTs was highly enriched through the extraction of CoMoCAT-SWNTs with phenanthrene-bridged chiral diporphyrin nanotweezers 1.

Unexpectedly large binding constants of azulenes with fullerenes.

In spite of having small pi-conjugation systems, azulenes show large binding constants (10(4)-10(5)) to C(60) and C(70), which are larger than those of monoporphyrins and alternant aromatic hydrocarbons.

Inhibition of jack bean urease by organobismuth compounds.

Inhibitory activity of organobismuth compounds, triarylbismuthanes 1 and their dihalides 2 and 3, was examined against jack bean urease. Besides triarylbismuth dichlorides 2, triarylbismuth difluorides 3 and bismuthanes 1 exhibited the activity. Of all these compounds, triphenylbismuth difluoride 3a and tris(4-fluorophenyl)bismuth dichloride 2b showed the highest activity. These results indicate that generation of the inhibitory effect is not always governed by the Lewis acidity at the bismuth center. Such a tendency of inhibition by the organobismuth compounds is in good accord with that observed in the antibacterial activity against Helicobacter pylori, suggesting that H. pylori-produced urease may be a therapeutic target by bismuth-based drugs.