Quantifying the relative contribution of hydrogen bonding and hydrophobic environments, and coordinating groups, in the zinc(II)-water acidity by synthetic modelling chemistry

Ligands derived from the tripodal N4 ligand tris(pyridylmethyl)amine ((pyCH2)3N, tpa) of general formula (6-RNHpyCH2)nN(CH2py)(3-n)(R = H, n= 1-3 L(1-3); R = neopentyl, n= 1-3 L'(1-3)) were used to elucidate and quantify the magnitude of the effects exerted by hydrogen bonding and hydrophobic environments in the zinc-water acidity of their complexes. The pKa of the zinc-bound water molecule of [(L(1-3))Zn(OH2)]2+ and [(L'(1-3))Zn(OH2)]2+ 1'-3' was determined by potentiometric pH titrations in water (1-3) or water-ethanol (1:1) (1'-3'). The zinc(II) water acidity gradually increases as the number of -NH2 hydrogen bonding groups adjacent to the water molecule increases. Thus, the zinc-bound water of [(L3)Zn(OH2)]2+ and [(tpa)Zn(OH2)]2+ deprotonate with pKa values of 6.0 and 8.0, respectively. The pKa of the water molecule, however, is only raised from 8.0 in [(tpa)Zn(OH2)]2+ to 9.1 in [(bpg)Zn(OH2)]+ (bpa =(pyCH2)2N(CH2COO-)). Moreover, the acidity of the zinc-bound water of several of the five-coordinate zinc(II) complexes with the hydrogen bonding groups is greater than that of four-coordinate [((12)aneN3)Zn(OH2)]2+ (pKa = 7.0). This result shows that the magnitude of the effect exerted by the hydrogen bonding groups can be larger than that induced by changing one neutral by one anionic ligand, and/or even by changing the coordination number of the zinc(II) centre. The X-ray structure of [(L'2)Zn(OH)]ClO4 2' and [(L'3)Zn(OH)]ClO4.CH3CN 3'.CH3CN is reported, and show the neopentylamino groups forming N-H...O hydrogen bonds with the zinc-bound hydroxide. Although, which have hydrogen bonding and hydrophobic groups, have a zinc-bound water more acidic than [(tpa)Zn(OH2)]2+, their pKa is not always lower than that of 1-3. This result suggests that a hydrogen bonding microenvironment may be more effective than a hydrophobic one to increase the zinc-water acidity.     

Hydroxypropyl chitosan bearing beta-cyclodextrin cavities: synthesis and slow release of its inclusion complex with a model hydrophobic drug

Hydroxypropyl chitosan-graft-carboxymethyl beta-cyclodextrin (HPCH-g-CM beta-CD) was synthesized by grafting CM beta-CD onto HPCH using water soluble 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) as the condensing agent. Due to the presence of hydrophobic beta-CD rings onto the HPCH backbone, this polymer can be used as a matrix for controlled drug release. The adsorption of a hydrophobic model drug, ketoprofen, by HPCH-g-CM beta-CD microparticles (using tripolyphosphate as an ionic crosslinking agent) fitted well in the Langmuir isotherm equation. The drug dissolution profile showed that HPCH-g-CM beta-CD microparticles provided a slower release of the entrapped ketoprofen than chitosan, and the release behavior was influenced by the pH value of the medium. These results suggest that beta-CD grafted with chitosan derivatives may become a potential biodegradable delivery system to control the release of hydrophobic drugs with pH-responsive capability.     

Synthesis and Characterization of Chitosan‐graft‐Poly(3‐(trimethoxysilyl)propyl methacrylate) Initiated by Ceric (IV) Ion

The grafting of 3‐(trimethoxysilyl)propyl methacrylate (TMSPM) onto chitosan by ceric ion initiation was studied under homogeneous conditions in 2% acetic acid solution. The grafted polymer was characterized by FT‐IR, ¹H‐NMR, TGA and XRD and swelling studies. TGA results showed that the incorporation of TMSPM to the chitosan chains decreased the thermal stability of the grafted chitosan. Due to the grafting of TMSPM, the crystallinity of chitosan derivatives was found to be destroyed. The solubility of the grafted chitosan in water was improved. The effects of reaction conditions such as initiator concentration, monomer concentration, reaction temperature and reaction time were studied by determining the grafting parameters such as grafting and grafting efficiency. Under optimum conditions, the grafting parameters were achieved as 1440 and 97%, respectively.     

Relative importance of hydrogen bonding and coordinating groups in modulating the zinc-water acidity

The presence of second-sphere -NH(2) groups in the proximity of a zinc(ii)-bound water molecule enhances its acidity by ca. 2 pK(a) units.     

Enhanced cycling properties of transition metal molybdates, Li x M2(MoO4)3 {0?≤ x

K. M. Begam  M. S. Michael  S. R. S. Prabaharan 《Ionics》2007,13(6):467-471

Evaluation of Methanogenic Activity of Biogas Plant Slurry for Monitoring Codigestion of Ossein Factory Wastes and Cyanobacterial Biomass

Overall measurement of methanogenic activity of sludge and or slurry is thought as a key for understanding the basic physiology of anaerobic consortia involved in anaerobic digestion process of an alternative biomass. In this study, the methanogenic activity of biogas plant slurry was used to evaluate the anaerobic digestion of ossein factory wastes such as sinews and primary clarified bone waste (PCBW) and cyanobacterial biomass in standard assay conditions. A maximum methanogenic activity was reported here when ossein factory wastes mixed with cyanobacterial biomass in specific proportions in which sinews and PCBW alone also favored to a significant methane yield. Cyanobacterial biomass alone did not give a desirable methanogenic activity. Approximately 48% of total solids were destroyed from these wastes after 30 days. This study gives information on the use of these wastes with suitable proportions for taking an effort in a large-scale anaerobic digestion in an effective way of ossein factory.     

Nanofibrous polyaniline thin film prepared by plasma‐induced polymerization technique for detection of NO2 gas

A nanofibrous polyaniline (PANI) thin film was fabricated using plasma‐induced polymerization method and explored its application in the fabrication of NO₂ gas sensor. The effects of substrate position, pressure, and the number of plasma pulses on the PANI film growth rate were monitored and an optimum condition for the PANI thin film preparation was established. The resulting PANI film was characterized with UV–visible spectrophotometer, FTIR, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The PANI thin film possessed nanofibers with a diameter ranging from 15 to 20 nm. The NO₂ gas sensing behavior was studied by measuring the change in electrical conductivity of PANI film with respect to NO₂ gas concentration and exposure time. The optimized sensor exhibited a sensitivity factor of 206 with a response time of 23 sec. The NO₂ gas sensor using nanofibrous PANI thin film as sensing probe showed a linear current response to the NO₂ gas concentration in the range of 10–100 ppm. Copyright © 2009 John Wiley & Sons, Ltd.     

New NASICON type oxyanion high capacity anode, Li2Co2(MoO4)3, for lithium-ion batteries: preliminary studies

We describe in this paper the lithium insertion/extraction behavior of a new NASICON type Li₂Co₂(MoO₄)₃ at a low potential and explored the possibility of considering this new oxyanion material as anode for lithium-ion batteries for the first time. Li₂Co₂(MoO₄)₃ was synthesized by a soft-combustion glycine-nitrate low temperature protocol. Test cells were assembled using composite Li₂Co₂(MoO₄)₃ as the negative electrode material and a thin lithium foil as the positive electrode material separated by a microporous polypropylene (Celgard® membrane) soaked in aprotic organic electrolyte (1 M LiPF₆ in EC/DMC). Electrochemical discharge down to 0.001 V from OCV (～3.5 V) revealed that about 35 Li⁺ could ^possibly be inserted into Li₂Co₂(MoO₄)₃ during the first discharge (reduction) corresponding to a specific capacity amounting to 1,500 mAh g^?1. This is roughly fourfold higher compared to that of frequently used graphite electrodes. However, about 24 Li⁺ could be extracted during the first charge. It is interesting to note that the same amount of Li⁺ could be inserted during the second Li⁺ insertion process (second cycle discharge) giving rise to a second discharge capacity of 1,070 mAh g^?1. It was also observed that a major portion of lithium intake occurs below 1.0 V vs Li/Li⁺, which is typical of anodes being used in lithium-ion batteries.     

Nanostructured lithium-free oxyanion cathode, Li x Co2(MoO4)3 [0≤ x <3] for 3 V class lithium batteries

A new nanostructured framework-type polyanion material, Li _x Co₂(MoO₄)₃ [0≤?x?<3], was studied as a positive electrode for use in 3-Volt class lithium-ion cells for the first time. The new material was synthesized in a lithium-free composition and examined its structure, morphology, and electrochemical characteristics. Co₂(MoO₄)₃ was found to crystallize in a monoclinic structure with lattice parameters: a?=?14.280(9) ?, b?=?3.382(8) ?, c?=?10.557(1) ?, and β?=?117.9728° (space group P2/m). The redox behavior of this new material was demonstrated in lithium-containing test cells. The material offered a discharge capacity of approximately 110 mAh g^?1 between 3.5 and 1.5 V during the first cycle and retained 50% capacity at the end of the 20th cycle. The poor capacity retention is obviously attributed to the poor electronic conductivity of Co₂(MoO₄)₃ owing to its open framework structure. To overcome the intrinsic low electronic conductivity of polyanion materials, we have adapted a nanocomposite approach by way of adding nanoporous carbon matrix (particle size approximately 10 nm) together with the conventional conductive additive (acetylene black) and demonstrated that the overall electronic conductivity could be improved significantly, yielding an initial discharge capacity of 121 mAh g^?1 using nanocomposite electrode in the potential range 3.5 V down to 2.0 V.