Preparation and Evaluation of Taste Masked Famotidine Formulation Using Drug/β-cyclodextrin/Polymer Ternary Complexation Approach

The main aim of the present study was to evaluate potential of ternary complexation (comprising of drug, cyclodextrin and polymer) as an approach for taste masking. For this purpose famotidine with property of bitter taste was selected as a model drug. Improvement in taste masking capability of cyclodextrin towards famotidine was evaluated by formulating a ternary complex including hydrophilic polymer hydroxyl propyl methyl cellulose (HPMC 5 cps) as the third component. Phase solubility analysis at 25 °C was carried out for both the binary systems (viz. drug–cyclodextrin and drug–polymer) and the ternary system (drug–cyclodextrin–polymer). Ternary complex was prepared using solution method and was further characterized using XRD, DSC, FT-IR and microscopic studies. In vitro dissolution study was carried out to see the effect of ternary complexation on drug release. Taste perception study was carried out on human volunteers to evaluate the taste masking ability of ternary complexation. Results obtained from phase solubility analysis showed that the combined use of polymer and cyclodextrin effectively increased the stability constant of the complex [from 538 M⁻¹ for binary system to 15,096 M⁻¹ for ternary system]. Ternary system showed effective taste masking as compared to binary complex and at the same time showed no limiting effect on the drug release (D.E_15min = 90%). The effective taste masking was attributed to the enhanced complexation of famotidine in ternary system compared to binary system and the same was confirmed from the characterization studies. In conclusion, the study confirmed that ternary complexation can be utilized as an alternative approach for effective taste masking.     

γ-irradiation of PEGd,lPLA and PEG-PLGA Multiblock Copolymers: II. Effect of Oxygen and EPR Investigation

The purpose of this research was to evaluate how the presence of oxygen can affect irradiation-induced degradation reactions of PEGd,lPLA and PEG-PLGA multiblock copolymers submitted to gamma irradiation and to investigate the radiolytic behavior of the polymers. PEGd,lPLA, PEG-PLGA, PLA, and PLGA were irradiated by using a ⁶⁰Co irradiation source in air and under vacuum at 25 kGy total dose. Mw and Mn were evaluated by gel permeation chromatography. The stability study was carried out on three samples sets: (a) polymer samples irradiated and stored in air, (b) polymer samples irradiated and stored under vacuum, and (c) polymer samples irradiated under vacuum and stored in air. The thermal and radiolytic behavior was investigated by differential scanning calorimetry and electron paramagnetic resonance (EPR), respectively. Samples irradiated in air showed remarkable Mw and Mn reduction and Tg value reduction due to radiation-induced chain scission reactions. Higher stability was observed for samples irradiated and stored under vacuum. EPR spectra showed that the presence of PEG units in multiblock copolymer chains leads to: (a) decrease of the radiolytic yield of radicals and (b) decrease of the radical trapping efficiency and faster radical decay rates. It can be concluded that the presence of oxygen during the irradiation process and the storage phase significantly increases the entity of irradiation-induced damage.     

Coordination geometry induced control of channel morphology in divalent metal pyridinedicarboxylate coordination polymers containing a kinked tethering organodiimine

Hydrothermal synthesis has afforded two divalent metal coordination polymers incorporating tridentate 2,6-pyridinedicarboxylate (PDC) ligands and the kinked dipodal organodiimine 4,4′-dipyridylamine (dpa), {[Ni(PDC)(dpa)(H₂O)] · 2H₂O} (1) and {[Zn(PDC)(dpa)] · 3H₂O} (2), which were characterized by single crystal X-ray diffraction and spectral and thermogravimetric analyses. Although both 1 and 2 display one-dimensional (1-D) polymeric chain motifs, the different coordination environments (octahedral in 1, distorted square pyramidal in 2) provoke divergence in the structures and aggregations of the chain subunits. Compound 1 manifests both polycatenation and interdigitation of its 1-D polymeric chains, while 2 exhibits only interdigitation, resulting in widely disparate morphologies for water molecule-bearing channels within the extended structures. Compound 1 possesses three distinct channel types occupied by isolated water molecules. Compound 2 presents only one type of channel, larger than those in 1, filled with D(5) discrete-chain water molecule aggregations. In both cases the co-crystallized water molecules are anchored to the coordination polymer matrix by hydrogen bonding involving PDC carboxylate oxygen atoms and the central amine unit of the dpa ligands. These supramolecular interactions are crucial for stability, as 1 and 2 both undergo irreversible loss of crystallinity upon dehydration.     

Sonochemical synthesis of nano-sized metal-organic lead(II) polymer: A precursor for the preparation of nano-structured lead(II) iodide and lead(II) oxide

Nanoparticles of a new Pb^II metal-organic polymer, [Pb(μ-pyr)(μ-I)₂]_n (1), with a net-like morphology have been synthesized by the reaction of pyrazine with Pb(NO₃)₂ and NaI via sonochemical irradiation. Nano-structured PbI₂ and PbO were synthesized from compound 1 by calcination at argon and air atmospheres, respectively. The structure of 1 was determined by single crystal X-ray crystallography and the nano-structures were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The thermal stability of nano-sized and single crystalline samples of 1 were studied and compared.     

[Cu4(H2O)4(dmapox)2(btc)]n · 10nH2O: The first two-dimensional polymeric copper(II) complex with bridging μ-trans-oxamidate and μ4-1,2,4,5-benzentetracarboxylato ligands: Synthesis, crystal structure and DNA binding studies

A two-dimensional copper(II) polymer with formula of [Cu₄(H₂O)₄(dmapox)₂(btc)]_n · 10nH₂O, where dmapox is the dianion of N,N′-bis[3-(dimethylamino)propyl]oxamide and btc is the tetra-anion of 1,2,4,5-benzenetetracarboxylic acid, was synthesized and characterized by elemental analysis, conductivity measurement, IR and electronic spectral studies. The crystal structure of the complex has been determined by X-ray single-crystal diffraction. The structure consists of crystallized water molecules and neutral two-dimensional copper(II) coordination polymeric networks constructed both by the bis-tridentate μ-trans-dmapox and tetra-monodentate μ₄-btc bridging ligands. Each btc ligand links four trans-dmapox-bridged binuclear copper(II) building blocks [Cu₂(H₂O)₂(trans-dmapox)]²⁺ and each binuclear copper(II) building block attaches to two btc ligands forming an infinite 2D layer which consists of 4+4 grids with dimensions of 13.563(5) × 15.616(5) Å. The environment around the copper(II) atom can be described as a distorted square-pyramid and the Cu?Cu separations through μ-trans-dmapox and μ₄-btc bridging ligands are 5.225 Å (Cu1-Cu1ⁱ), 5.270 Å (Cu2-Cu2ⁱⁱ), 6.115 Å (Cu1-Cu2), 9.047 Å (Cu1-Cu2ⁱⁱⁱ) and 10.968 Å (Cu1-Cu1ⁱⁱⁱ), respectively. Abundant hydrogen bonds among the crystallized, the coordinated water molecules, and the uncoordinated carboxyl oxygen atoms cross-link the two-dimensional layers into an overall three-dimensional channel-like framework. The interaction of the copper(II) polymer with calf thymus DNA (CT-DNA) has been investigated by using absorption, emission spectral and electrochemical techniques. The results indicate that the copper(II) polymer interacts with DNA strongly (K_b = 4.8 × 10⁵ M⁻¹ and K_sv = 1.1 × 10⁴) and the interaction mode between the copper(II) polymer and DNA may be the groove binding. To the best of our knowledge, this is the first report about the crystal structure and DNA-binding studies of a two-dimensional copper(II) polymer bridged both by the trans-oxamidate and btc ligands.     

Organic-inorganic hybrid coordination polymers based on tetratopic pyridyl-bridging ligand: Syntheses, structures, and luminescent properties

Employing the symmetrical ligand 1,2,3,4-tetra-(4-pyridyl)-butane (TPB) as bridges, two novel Zn(II) coordination polymers were obtained and characterized by single crystal X-ray diffraction: [Zn(TPB)_0.5(NCS)₂] (1) and [Zn(TPB)(N₃)₂] (2). Polymer 1 features a 2D network with herringbone structural motif constructed by TPB, while polymer 2 shows a dense 3D network connected by TPB and μ_1,3-N₃- bridges. In the former, the TPB ligand acts as a four-connector, while in the latter it acts as four-connector and linear bridge. Both 1 and 2 exhibit strong fluorescent emissions in the solid state, which may be of significance in the field of photoactive materials.     

One-dimensional Zn(II) oligo(phenyleneethynylene)dicarboxylate coordination polymers: Synthesis, crystal structures, thermal and photoluminescent properties

The rigid, π-conjugated dicarboxylic acid 1,4-bis-[2-(4-carboxyphenyl)ethynyl]-2,5-dihexylbenzene {HO₂C[PEP(hexyl)₂EP]CO₂H} has been used to synthesise the new crystalline coordination polymers {Zn(O₂C[PEP(hexyl)₂EP]CO₂)(DMF)₂} (1) and {Zn(O₂C[PEP(hexyl)₂EP]CO₂)(DEF)₂} (2) in N,N-dimethylformamide (DMF) and N,N-diethylformamide (DEF), respectively, under mild conditions. Single-crystal X-ray crystallography revealed that 1 and 2 are isostructural and consist of uncharged zigzag coordination chains in which [Zn(formamide)₂]²⁺ fragments are bridged by (O₂C[PEP(hexyl)₂EP]CO₂)²⁻ ligands. The zigzag chains possess different intra-chain Zn?Zn?Zn angles due to the different volumes of the coordinating formamide molecules and subtle differences in the hydrophobic inter-chain interactions. Upon heating 1 and 2 to 200 °C, removal of the coordinating formamide molecules occurs, yielding the formamide-free compounds 1-DMF and 2-DEF of composition {Zn(O₂C[PEP(hexyl)₂EP]CO₂)}. According to powder X-ray diffraction and FT-IR spectroscopy studies, these materials are not crystalline but still possess partial ordering of intact, yet modified coordination chains in a structural arrangement which appears to be related to the respective parent compounds. Compounds 1, 2, 1-DMF and 2-DEF exhibit blue photoluminescence. The emission maxima of 1-DMF and 2-DEF are red-shifted by ca. 25 nm with respect to λ_max of 1 and 2, respectively.     

A 3-D (3,5)-connected Cd coordination framework with unique twofold interpenetrating (4·6)(4·6·8) network topology

Assembly of N,N′-bis(4-picolinoyl)hydrazine (H₂L) with cadmium nitrate in the presence of dicyanamide anion (dca) affords a new coordination polymer {[Cd(HL)(dca)] · (H₂O)_0.5}_n (1), in which the [Cd(HL)]_n layers are extended by dca bridges to result in a three-dimensional (3-D) coordination framework. The network structure of 1 has unusual (3,5)-connectivity and represents a new type of (4·6²)(4·6⁶·8³) topology. Two such identical and complementary networks are entangled to generate a twofold parallel interpenetrating supramolecular lattice.     

Synthesis, crystal structure, magnetic properties and EPR studies of Cu/Hg bimetallic thiocyanato-bridged coordination polymer

The new Cu/Hg bimetallic thiocyanato-bridged coordination polymer, [Cu(2-bzpy)Hg(SCN)₄]_n, has been synthesized and characterized by elemental analysis, magnetic measurements, EPR, and X-ray crystallography. X-ray diffraction analysis reveals that the title complex structure creates 3D network.     

A dicarboxylate with asymmetric coordination ability: Characterization of a two dimensional coordination polymer of copper(II) exhibiting spin canting

A copper(II) coordination polymer {[Cu₂(cpa)₂]}_n (1) (cpaH₂ = 4-carboxyphenoxyacetic acid) has been synthesized by hydrothermal technique. The X-ray structure of the compound shows that it is a 2D coordination polymer where Cu(II) ions are pentacoordinated in a square pyramidal fashion. The magnetic measurement of 1 in different magnetic fields suggest a weak ferromagnetic ordering taking place below 20 K, arising from spin canting phenomenon due to the non-coplanar basal planes of copper ions.