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The trinuclear complex [Cu3PHI]6+, derived from a ligand containing two chiral L-histidine residues, performs the catalytic oxidation of L- and D-Dopa with remarkable enantio-differentiation; this depends on the anchoring effect provided by the copper center which is not participating in the catalytic reaction and recognizes the chirality of the substrate.
Crystallisation of calcium carbonate in the presence of the polycarboxylate 1,3-diamino-2-hydroxypropane-N,N,N',N'-tetraacetate results in the formation of "microtrumpets" composed of nanocrystalline calcite.
Starting from a protected L-tryptophan derivative the pyrrolobenzoxazine core unit of paeciloxazine can be synthesized in two oxidation steps.
This article highlights areas of research at the interface of nanotechnology, the physical sciences, and biology that are related to energy conversion: specifically, those related to photovoltaic applications. Although much ongoing work is seeking to understand basic processes of photosynthesis and chemical conversion, such as light harvesting, electron transfer, and ion transport, application of this knowledge to the development of fully synthetic and/or hybrid devices is still in its infancy. To develop systems that produce energy in an efficient manner, it is important both to understand the biological mechanisms of energy flow for optimization of primary structure and to appreciate the roles of architecture and assembly. Whether devices are completely synthetic and mimic biological processes or devices use natural biomolecules, much of the research for future power systems will happen at the intersection of disciplines.
Two neutral macrobicyclic anion receptors 4 and 6, containing a calix[4]arene in the cone conformation, two l-alanine units, and a 2,6-diacylpyridine or a phthaloyl bridge, are described. The x-ray crystal structure of the acetone complexes of the pyridine containing macrocycle 6 shows the four amide NH groups to be in close proximity to the chiral pocket delimited by the pyridine and one aromatic nucleus of the calix[4]arene. This conformation is also the most stable in acetone-d6 solution, as proven by one- and two-dimensional NMR spectral measurements. Electrospray ionization-MS and (1)H NMR experiments reveal that the two ligands strongly bind carboxylate anions in acetone solution. H-bonding interactions between the carboxylate anions and the amide NH groups, together with pi/pi stacking, are invoked to explain the efficiency and the selectivity of these anion receptors.
The design of polymers and oligomers that mimic the complex structures and remarkable biological properties of proteins is an important endeavor with both fundamental and practical implications. Recently, a number of nonnatural peptides with designed sequences have been elaborated to provide biologically active structures; in particular, facially amphiphilic peptides built from beta-amino acids have been shown to mimic both the structures as well as the biological function of natural antimicrobial peptides such as magainins and cecropins. However, these natural peptides as well as their beta-peptide analogues are expensive to prepare and difficult to produce on a large scale, limiting their potential use to certain pharmaceutical applications. We therefore have designed a series of facially amphiphilic arylamide polymers that capture the physical and biological properties of this class of antimicrobial peptides, but are easy to prepare from inexpensive monomers. The design process was aided by molecular calculations with density functional theory-computed torsional potentials. This new class of amphiphilic polymers may be applied in situations where inexpensive antimicrobial agents are required.
The synthesis of a covalent dimer of chlorophyll a which possesses properties strikingly similar to those exhibited by P700 special pair chlorophyll in vivo is described. The covalent dimer is characterized by several spectroscopic techniques. Hydrogen bonding nucleophiles, such as water, primary alcohols, and primary thiols, are effective in generating a species from solutions of 10 muM covalent dimer in hydrophobic solvents which absorbs light near 700 nm. Formation of this in vitro special pair is a rapid, spontaneous process at room temperature. The range of nucleophiles which promote this process suggests that amino acid residues may function in a similar fashion to form P700 in chlorophyll-protein complexes. The photochemical properties of this in vitro special pair mimic those of in vivo P700 species. The 697 nm absorption of the in vitro special pair undergoes photo-bleaching rapidly in the presence of iodine that results in the production of a cation radical which exhibits an electron spin resonance signal similar to that of oxidized P700 observed in Chlorella vulgaris.
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Stable nitroxide radicals have found wide applications in chemistry and biology and they have some potential applications in medicine due to their antioxidant properties. Nitrocellulose filters impregnated with lipid-like substances are used as an imitation of biomembranes and could be used as a controlled drug release vehicle, while experiments with hollow fibres can be useful in the modelling of a drug delivery via blood vessels. This paper describes mechanisms of the nitroxide transport in four different model systems, i.e. a) exit of nitroxide into aqueous solution from porous nitrocellulose filters, impregnated with organic solvents, b) transport of nitroxides through the impregnated membrane from one into another aqueous solution, c) transport of nitroxides from bulk phase of organic solvents through the impregnated membrane into aqueous phase with ascorbic acid, and d) transport of nitroxides from liquid organic phase into aqueous solution through porous hollow fibres. The results are analysed in terms of mass transfer resistance of a membrane, organic and aqueous phase, based on nitroxide diffusion and distribution coefficients. Ascorbic acid reduced nitroxides in water and enhanced the rate of their transfer due to the decrease of transport resistance of unstirred aqueous layers. It is demonstrated that in the case of biomembranes the rate limiting step could be the transport through unstirred aqueous layers and membrane/water interface.
This paper discusses the rationale for the development of tissue engineering and associated therapies and provides observations on the emerging developments in these areas.
The aminoglycosidic antibiotic, neomycin B, is an inhibitor of the binding of Rev to RRE. This paper reports on the synthesis of analogs of neomycin B as potential anti-HIV compounds designed to function as inhibitors of Rev/RRE binding.
Several polyamine derivatives (I-V) conjugated with or without an intercalative moiety were prepared as ribonuclease mimics. Although no DNA-cleaving activity was observed for all compounds tested, mimics I, III, and V bearing an intercalative moiety along with the primary amine and/or imidazole moieties exhibited potent RNA-cleaving activity at near physiological pH. The RNA-cleaving reactions of the compounds show characteristic bell-shaped pH dependency, and the optimal pH values for III and V were well correlated to the pKa values of their active sites, primary amine, and imidazole moieties.
Abiomimetic motility assay is used to analyze the mechanism of force production by site-directed polymerization of actin. Polystyrene microspheres, functionalized in a controlled fashion by the N-WASP protein, the ubiquitous activator of Arp2/3 complex, undergo actin-based propulsion in a medium that consists of five pure proteins. We have analyzed the dependence of velocity on N-WASP surface density, on the concentration of capping protein, and on external force. Movement was not slowed down by increasing the diameter of the beads (0.2 to 3 microm) nor by increasing the viscosity of the medium by 10(5)-fold. This important result shows that forces due to actin polymerization are balanced by internal forces due to transient attachment of filament ends at the surface. These forces are greater than the viscous drag. Using Alexa488-labeled Arp2/3, we show that Arp2/3 is incorporated in the actin tail like G-actin by barbed end branching of filaments at the bead surface, not by side branching, and that filaments are more densely branched upon increasing gelsolin concentration. These data support models in which the rates of filament branching and capping control velocity, and autocatalytic branching of filament ends, rather than filament nucleation, occurs at the particle surface.
Skin tumor promotion induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) was inhibited by a concurrent and topical application of phthalic acid mono-n-butyl ester cupric salt (PAMBCu) in CD-1 mice initiated with 7,12-dimethylbenz[a]anthracene. PAMBCu inhibited TPA-caused epidermal ornithine decarboxylase (ODC) induction and ear edema formation, i.e. skin inflammation. However, neither PAMBCu nor superoxide dismutase (SOD) inhibited TPA-caused ODC induction in primary cultured mouse epidermal cells. 7-Bromomethylbenz[a]anthracene (BrMBA) is known to be a non-TPA type of tumor promoting agent. Epidermal ODC induction and inflammation caused by BrMBA were not inhibited by a concurrent application of PAMBCu. When mice were topically treated twice with PAMBCu, i.e. concurrently with and 7 h after BrMBA treatment, BrMBA-caused ODC induction was markedly suppressed. The same dose regimen of PAMBCu, however, failed to inhibit tumor promotion and inflammation caused by BrMBA. PAMBCu showed SOD-mimetic activity in superoxide generating systems, i.e. xanthine-xanthine oxidase reaction and TPA-stimulated polymorphonuclear leukocytes (PMN). Mono-n-butyl phthalate, which lacks SOD-mimetic activity, failed to inhibit TPA-caused ODC induction and skin inflammation. Therefore, inhibition by PAMBCu of TPA-caused tumor promotion, epidermal ODC induction and inflammation may be attributable to its SOD-mimetic activity. The results also support the contention that a superoxide anion of non-epidermal cell origin, such as PMN and macrophages, plays a role (probably some enhancing role) in in vivo ODC induction and tumor promotion caused by TPA. Failure of PAMBCu to inhibit BrMBA-caused tumor promotion suggests that superoxide anion generation is not involved in the tumor promoting action of this agent and that the anti-tumor promoting action of PAMBCu is dependent on the nature of the tumor promoting agents.
A novel controller for a multifinger hand prosthesis was developed and tested to measure its accuracy and performance in transducing volitional signals for individual "phantom" fingers. Pneumatic sensors were fabricated from open-cell polymeric foam, and were interposed between the prosthetic socket and superficial extrinsic tendons associated with individual finger flexion. Test subjects were prompted to move individual fingers or combinations thereof to execute either taps or grasps. Sensor outputs were processed by a computer that controlled motions of individual fingers on a mechanical prosthesis. Trials on three upper-limb amputees showed that after brief training sessions, the TAP controller was effective at producing voluntary flexions of individual fingers and grasping motions. Signal energies were between 5 and 25 dB relative to noise from all sources, including adjacent sensors, indicating high degrees of both sensitivity and specificity for tendon-associated transduction. Finger flexions at up to three repetitions per second, and rhythmic tapping of sequential fingers were readily transduced. One amputee subject was able to play a short piano piece with three fingers, at approximately one-quarter normal tempo. TAP sensors responded linearly to graded forces from individual fingers, indicating proportional force control. Our results demonstrate the feasibility of restoring some degree of finger dexterity by noninvasive sensing of extrinsic tendons.
Cimetidine sulfoxide, N-desmethylcimetidine, N-desmethylcimetidine sulfoxide, cimetidine guanylurea, and the 5-hydroxymethylimidazole derivative of cimetidine sulfoxide were isolated from the reaction of cimetidine with Fenton reagent. The product distribution from the reaction of cimetidine with Fenton reagent clearly simulates the metabolism of cimetidine by the mixed-function oxidase.
The conformation of [Leu5]enkephalin has been studied by 1H-NMR spectroscopy in media more like the actual environment in which the agonist-receptor interaction takes place than water, i.e. in three cryoprotective mixtures (dimethylformamide/water, methanol/water and ethylene glycol/water), in aqueous SDS and in two neat solvents, dimethylformamide and acetonitrile, whose dielectric constants (36.7 and 37.5) are intermediate between that of water and that of the lipid phase. In all cases examined, contrary to the studies in water or dimethylsulfoxide, we were able to detect numerous nuclear Overhauser effects, indicating that the media employed favour well-defined structures and/or reduce the internal motions of the peptide. Data from both organic solvents and cryoprotective mixtures suggest a 4----1 beta turn as the most probable structure of [Leu5]enkephalin in solution, whereas in SDS/H2O micelles the structural picture appears completely different, suggesting the presence of a 5----2 beta turn. The existence of two different preferred conformations of enkephalins may possibly be related to their ability to be effective towards both mu and delta opioid receptors.
In order to develop an adequate scaffold for skin tissue engineering, a bilayered gelatin-chondroitin 6 sulfate-hyaluronic acid membrane with a different pore size on either side was prepared. A rete ridges-like topographic microporous structure, which provided the paracrine crosstalk in the epithelial-mesenchymal interactions, was formed. Chondroitin-6-sulfate and hyaluronic acid were incorporated within the gelatin membrane to mimic skin composition and create an appropriate microenvironment for cell proliferation, differentiation, and migration. In the study, the lower layer of the membrane (pore size: 150 microm) was seeded with dermal fibroblasts and acted as the feeder layer for keratinocyte inoculation. Meanwhile, the upper layer (pore size: 20-50 microm) was seeded with keratinocytes for epidermalization. The dermal fibroblasts were dynamically seeded in a self-designed spinner flask for more even cell distribution. The keratinocytes were cultured in submerged conditions for 5 days and then in an air-liquid interface condition for further differentiation. After being cultured for 21 days, the upper layer, seeded with keratinocytes, developed into an epidermis-like structure while the lower part, which was seeded with dermal fibroblasts developed into a dermis-like structure. A histological examination and immunostain were used to prove that keratinocytes maintain their phenotype and stratified epidermis layers were formed within 21 days. In brief, the bilayered skin substitute with biological dermal analog and epidermal structure was successfully fabricated. From this study, we can suggest that the culture model is suitable for autologous skin equivalent preparation.