Mechanism of Formation of Cadmium Oxalate Liesegang Rings

Qualitative and semiquantitative study of the Liesegang rings formed by the reaction of oxalic acid and cadmium chloride in the acidic range of pH in silica hydrogel is made. The behaviour of Jablczynski's space constant and Morce-Pierce's time constant at various temperatures, pH and concentration of outer electrolyte is studied. The possible mechanisms for the above observed behaviour are suggested. The deviations from Isemura's general obserations are interprerted by considering two particular aspects, viz., comparatively larger crystals constituting the rings and the irreversibility of inner and outer electrolytes.     

Soft matter dispersions with ordered inner structures, stabilized by ethoxylated phytosterols

This paper describes the formation and characterization of liquid crystalline dispersions based on the hexagonal phase of GMO/tricaprylin/water. As a stabilizer of the soft particles dispersed in the aqueous phase, a non-ionic, non-polymeric surfactant—ethoxylated phytosterol with 30 oxyethylene units (PhEO) was utilized. In contrast to Pluronic copolymers, normally utilized in the stabilization of liquid crystalline dispersions with ordered inner structure, use of such non-polymeric surfactant is not a common practice in this field. We revealed how properties of these particles, such as internal structure, size, and stability, can be rationally modified by the concentration of the stabilizing agent and processing conditions. The physical stability of the hexosomes was further examined by the LUMiFuge technique.Structural effect of PhEO solubilization on the properties of the bulk H_II mesophase system showed that phase behavior was greatly influenced following phase transitions: H_II → H_II + cubic → cubic + L_α → L_α. The decrease of hydrogen bonding of the hydroxyl and carbonyl groups of monoolein with water and simultaneous hydration of EO groups of PhEO appeared to be important for the observed behavior. The use of PhEO as a dispersant resulted in a soft matter multi-phase water dispersion with bimodal distribution of the particle population. Effective stabilization of hexosomes was obtained in an extremely narrow concentration range of PhEO (0.1–0.2 wt%), coexisting with small vesicles and disordered particles. At higher PhEO content, particles had disordered inner structure, and unilamellar and multilamellar vesicles, at the expense of hexosomes in consequence of incorporation of the dispersant into the hexosome structure. PhEO was found to induce lamellar phase formation, introducing disorder into the hexagonal LLC and reducing their domain size.Finally, hexosomes were evaluated as delivery vehicles for the therapeutic peptide desmopressin. Sustained release of this drug was observed during the first 10 h; however, permeation drastically increased in the 10–24 h range.     

A molecular keypad lock: a photochemical device capable of authorizing password entries

This paper describes a new concept in the way information can be protected at the molecular scale. By harnessing the principles of molecular Boolean logic, we have designed a molecular device that mimics the operation of an electronic keypad lock, e.g., a common security circuit used for numerous applications, in which access to an object or data is to be restricted to a limited number of persons. What distinguishes this lock from a simple molecular logic gate is the fact that its output signals are dependent not only on the proper combination of the inputs but also on the correct order by which these inputs are introduced. In other words, one needs to know the exact passwords that open this lock. The different password entries are coded by a combination of two chemical and one optical input signals, which can activate, separately, blue or green fluorescence output channels from pyrene or fluorescein fluorophores. The information in each channel is a single-bit light output signal that can be used to authorize a user, to verify authentication of a product, or to initiate a higher process. This development not only opens the way for a new class of molecular decision-making devices but also adds a new dimension of protection to existing defense technologies, such as cryptography and steganography, previously achieved with molecules.     

Biochemical evaluation of sulfur and nitrogen assimilation potential of mustard (Brassica juncea L. Czern. & Coss.) under application of slow-release sulfur fertilizer

Pot experiments were conducted to study the efficacy of a slow sulfur-releasing fertilizer, sulfur glass fritz (SGF 1), on growth, photosynthesis, and sulfur, and nitrogen assimilation potentials of brown mustard (Brassica juncea L. Czern. & Coss. cv. Pusa Jaikisan). Growth as indicated by biomass accumulation slowed down in response to the application of sulfur glass fritz. A similar trend was observed in the case of photosynthesis rate. The activity of two marker enzymes, ATP-sulfurylase and nitrate reductase, showed very low levels of activity, indicating poor assimilation of sulfur and nitrogen by the plant under sulfur glass fritz. It is therefore concluded that the release of sulfur by sulfur glass fritz is too slow and that the initial nonavailability of sulfur to the plants could lead to suboptimization of both sulfur- and nitrogen-assimilating enzymes. These factors may contribute to low rates of photosynthesis and poor growth.     

Microwave-Assisted Synthesis and Antimicrobial Activity of 3-(Arylsulfanyl)-4-hydroxy-2<Emphasis Type="Italic">H</Emphasis>-chromen-2-ones

An efficient microwave-assisted synthesis of 3-(arylsulfanyl)-4-hydroxy-2H-chromen-2-ones by condensation of arenesulfonohydrazides with 4-hydroxy-2H-chromen-2-one in the presence of iodine is described. The synthesized compounds were characterized by spectral data (IR, ¹H and ¹³C NMR, and mass spectra and elemental analyses) and were tested for their in vitro antimicrobial activity against bacterial and fungal organisms.     

Synthesis and evaluation of iron chelators with masked hydrophilic moieties

Synthetic iron chelators based on the natural siderophore ferrichrome have previously been shown to bind Fe(III) with high affinity (pKf > 27) and have shown no toxicity to mammalian cell cultures in vitro. A new class of lipophilic ferrichrome analogues carrying acetoxymethyl ester moieties has been synthesized. We have shown that these molecules penetrate rapidly through cell membranes and turn highly hydrophilic while inside the cells, upon esterase mediated hydrolysis of the lipophilic termini. The intracellular retention was visualized by labeling these analogues with a fluorescent naphthalic diimide probe. The prohydrophilic iron chelators have been shown to inhibit the metal-catalyzed intracellular formation of reactive oxygen species with high effectivity, and preliminary results suggest these molecules to be potent antimalarial agents.     

Molecular composites in thermosets

The synthesis of molecular composites where rigid polymer molecules are reinforcing elements in a thermoset bisimide matrix has been investigated. The approach has been designed to avoid phase separation by selecting systems where reaction of amine-terminated rigid and semiflexible oligomers with maleimide unsaturation occurs prior to crosslinking of the thermoset. This objective has been met for some compositions. The concentration and molecular weight of the rigid oligomers have been varied. The structure of the reinforcing polymer, the reactivity of the maleimide and the conditions for composite synthesis are variables of critical importance, and further work must determine the promise and limitations of this approach.     

Degradable polymer blends. I. Screening of miscible polymers

Blends of biodegradable polymers having properties distinct from the individual polymer components, and that are suitable for use as carriers of pharmaceutically active agents, were prepared from two or more polyanhydrides, polyesters, and mixtures of polyanhydrides and low molecular weight polyesters. The blends have different properties than the original polymers, providing a mean for altering the characteristics of the polymeric matrix without altering the chemical structure of the component polymers. Aliphatic, aromatic, and copolymers of polyanhydrides were miscible in each other and formed less crystalline compositions with a single melting point which was lower than the melting point of the starting polymers. The polyesters: poly(lactide-glycolide), poly(caprolactone), and poly(hydroxybutyric acid) presented some miscibility in each other. However, the polyanhydrides were immiscible with the polyesters resulting in a complete phase separation both in solution or in melt mixing. Only low molecular weight polyesters (in the range of 2000) of lactide and glycolide, mandelic acid, propylenefumarate, and caprolactone presented some miscibility with polyanhydrides. Similarly, poly(orthoester) and hydroxybutyric acid polymers formed a uniform mixture with the anhydride polymers which had the two melting points of the original polymers. Drug release from polymer blends composed of poly(hydroxybutyric acid) or low molecular weight poly(lactic acid) with poly(sebacic anhydride) (PSA) showed a constant release of drug for periods from 2 weeks to several months as a function of the PSA content in the blend. Increasing the content of PSA, a fast degrading polymer, increases the release rate from the blend. © 1993 John Wiley & Sons, Inc.     

Surface morphological and impedance spectroscopic studies on the interaction of polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) with mild steel in acid solutions

The inhibition of mild steel corrosion in aerated acid mixture of 0.5 N H₂SO₄ and 0.5 N HCl solution was investigated using potentiodynamic polarization studies, linear polarization studies, electrochemical impedance spectroscopy, adsorption, and surface morphological studies. The effect of inhibitor concentration on corrosion rate, degree of surface coverage, adsorption kinetics, and surface morphology is investigated. The inhibition efficiency increased markedly with increase in additive concentration. The presence of PEG and PVP decreases the double-layer capacitance and increases the charge-transfer resistance. The inhibitor molecules first adsorb on the metal surface following a Langmuir adsorption isotherm. Both PEG and PVP offer good inhibition properties for mild steel and act as mixed-type inhibitors. Surface analysis by scanning electron microscopy (SEM) and atomic force microscopy (AFM) shows that PVP offers better protection than PEG.