One of the more impressive features of the living organism is the degree of control it is able to exercise over its chemistry.

A set of molecules in a given environment will react predictably according to the laws of chemistry. Quite often, as the synthetic organic chemist is ruefully aware, these laws allow more than one reaction to take place, and a multitude of products to be synthesized. The set of molecules that makes up the living organism is also governed by the laws of chemistry. The organism is able to, however, limit reactivity to a single product. In many cases this is a necessity; multiple reactions can often lead to unacceptable inefficiency or death.

Those involved in the synthesis of new, nonbiological materials with enhanced properties could benefit from this level of control. In the simple case, production of only the single desired product in high yields would be a great economic boon. On another level, this control could lead to the production of materials that are otherwise inaccessible. An obvious example is the modification of a polymer. Only with precise reaction control can all the monomers be modified in the same way.

Organisms achieve their required degree of control of chemical reactions through a mechanism of positive regulation. Under the conditions found in an organism, virtually no reaction will take place at a rate that is sufficient to sustain the life processes. Those that do occur take place only in the presence of a catalyst. To allow a reaction to occur, the organism simply synthesizes the catalyst that is specific for that reaction and does so only at the appropriate time and place and to the required extent. Should that reaction no longer be needed, the catalyst is destroyed or inactivated.

Intense efforts have been directed at the stabilization of proteins because of their potential uses in organic synthesis, diagnostics, and the pharmaceutical industry. These efforts have resulted in a number of methods to stabilize enzymes including adsorbtion on inert supports or ion exchange resins, entrapment within a gel (with or without crosslinking of the gel or protein), covalent attachment to beads or polymeric supports, inclusion in micelles, chemical derivatization of the protein and mutagenesis. However, these methods do not provide a general approach to solving the problem of protein stability. We believed that the multi-site attachment of a carbohydrate-based macromolecule to the surface of a protein would provide structural stability and a water-like microenvironment for the protein under harsh reaction conditions.

The use of enzymes in organic solvents has enabled two distinct polymer syntheses to be performed. The first is the enzyme-catalyzed polycondensation of sucrose with an adipic acid derivative in pyridine. Taking advantage of the extremely high regioselectivity of proleather, an alkaline protease, sucrose has been polymerized with 6 and 1' ester linkages. The result is a highly water-soluble product with sucrose an integral part of the polymer backbone. The polyester is degraded by the proleather in aqueous solution, thereby suggesting that the polymer is biodegradable. The second polymer synthesis is the free-radical polymerization of phenols using horseradish peroxidase in dioxane-water mixtures. Molecular weights in excess of 25,000 have been produced. The scope of polymerization can be predicted based on enzyme kinetics in organic media and using a Monte Carlo simulation. Astonishingly accurate simulations have been run that suggest that the high degree of control afforded by enzymatic catalysis over conventional chemical catalysts can be usedpredictively in polymer synthesis. This is of great importance in process control of polymer syntheses.

The discovery of catalysts that can selectively couple unprotected peptide fragments would revolutionize protein chemistry by allowing convergent polypeptide synthesis. Proteolytic enzymes have the capability to perform this chemistry because the protein can specifically recognize and bind to C-terminal and N-terminal peptide sequences, activate the C-terminal peptide sequence by forming an acyl-enzyme intermediate, and couple the two peptide fragments together. However, barriers that limit the use of proteases as catalysts for convergent peptide synthesis include (i) the stability of proteolytic enzymes in organic solvent systems; (ii) a simple and effective C-erminal and N-terminal protecting group strategy; and (iii) the isolation of the polypeptide product from the reaction mixture. In the previous paper we reported the stabilization of enzymes by the covalent attachment of proteins through their ο-lysine residues to a series of carbohydrate-based macromolecules. In this paper we report the use of carbohydrate protein conjugates of proteases [CPC(proteases)] as catalysts for peptide bond synthesis and a general strategy for convergent oligopeptide synthesis.

Enzyme-catalyzed preparation of polymers offers several potentially valuable advantages over the usual polymerization procedures. This paper summarizes our successful use of lipase-catalyzed polycondensations to prepare both a series of achiral [AA-BB]x polyesters from bis(2,2,2- trichloroethyl) alkanedioates and diols and of an optically active, epoxy-substituted polyester having a stereochemical purity estimated to be greater than 96%, from racemic bis(2,2,2-trichloroethyl) trans-3,4-epoxyhexanedioate and 1,4-butanediol. All of the reactions were carried out at ambient temperature in anhydrous, low to intermediate polarity, organic solvents such as ether, THF, 2-ethoxyethyl ether, dibenzyl ether, o-dichlorobenzene, or methylene choride, using porcine pancreatic lipase (PPL) as the catalyst. The molecular weight achieved by the polycondensation is limited by accumulation of the trihaloethanol that forms as the reaction progresses, probably because it frees enzyme-bound water permitting hydrolysis of the polymer to occur. This problem has been alleviated by using a high boiling solvent and removing the alcohol by placing the re'action mixture under vacuum.

Chicken egg-white lysozyme (CEWL) is used as a model to attempt to engineer proteins for enhanced thermostability. Site-directed mutagenesis is employed for selective amino acid substitution to probe the contribution of an individual amino acid in a given sequence to thermostability. A linear correlation is found between the side-chain volume of a triplet of amino acid residues located at the interior core of the protein and its thermostability. Additional mutant constructs at the core position reveal that hyperpacking can disrupt other intramolecular contacts and offset the hydrophobic stabilization due to denser packing. Multiple substitutions at different loci of the protein are combined to analyze the additivity of thermostability mutations.

The most fundamental goal of the synthetic chemist is control of molecular architecture. With respect to small molecules (i.e., those of molecular weight less than a few thousand), this means absolute control of chemical connectivity and stereochemistry – complete specification of molecular structure. But in macromolecular chemistry, controlled architecture has meant something quite different. Because polymerizations are in general statistical processes, conventional polymeric materials are characterized by substantial heterogeneity in chain length, sequence and stereochemistry [1]. Control is exercised in a statistical sense only, and considerable skill is required to control even the average properties of the chain population and the dispersity in those properties.

Synthetic poly-α-amino acids spread at the air-water interface can form monomolecular films. These polymers may assume several conformations, namely the α-helix, β-pleated sheets or random coils. The stabilizing forces can be inter- or intramolecular and are mainly hydrogen bonding and hydrophobic interactions. The area/residue values for helical polymers differ significantly from those of β-sheets.

Poly-α-amino acids can form both cholesteric and nematic structures. Synthetic polypeptides of amphiphilic character, of both α and β conformers, can by synthesized and are very surface active. These polymers associate with cell membranes or lipoproteins. Many biologically active polypeptides, such as hormones, form amphiphilic α-helices and these ligands bind to receptor sites on cell surfaces.

These polypeptides offer a source of materials whose properties can be varied as desired, providing opportunities for rationale drug design.

The adsorption of poly(l-lysine) (PLL) from aqueous solution to poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) is investigated. Adsorption is controlled by choice of solvent (and PLL solution conformation) or by FEP surface chemistry. PLL adsorbs from pH 11 buffer solution to FEP: PLL adsorption is concomitant with the liberation of water molecules from the FEP-water interface resulting in a decreased interfacial free energy between organic and aqueous phases. PLL does not adsorb from an aqueous pH 7 solution to FEP unless the FEP surface is carboxylic acid-functionalized (FEPCO2H):an ionic interaction between FEP-carboxylate and PLL-ammonium enhances adsorption.

The surface modifications are charaterized by attenuated total reflectance infrared spectroscopy (ATR IR), ultraviolet-visible spectrophotometry (UV-vis), contact angle, and quantitatively by x-ray photoelectron spectroscopy (XPS). The adsorbed amount of PLL to FEP (from pH 11) is proportional to molecular weight whereas the adsorbed amount of PLL to FEP-CO2H (pH 7) is independent of molecular weight and likely proportional to surface charge density. The modified film samples (relative to the unmodified film samples) show improved characteristics in terms of wettability, chemical reactivity, adhesion, cell growth.

A selection of microscopic pores is being made by genetic manipulation of a bacterial channel protein, α-hemolysin (α-HL). It will include: pores with different internal diameters, with differential selectivity for the passage of classes of molecules, and with different gating properties. The pores will be made into monolayers and incorporated into materials such as thin films to confer novel permeability properties upon them. Such products will have several technological applications, for example as molecular filters in sensors or as components of optically gated devices in electronics.

The processes by which microorganisms, particularly bacteria, produce inorganic mineral particles are reviewed.

Iron sulfide production by bacteria can be classified as extracellular or intracellular. Extracellular iron sulfide production is mediated by anaerobic, dissimilatory sulfate-reducing bacteria which produce sulfide as a product of their respiration. Released sulfide reacts with iron (and other metals) in the extracellular environment producing a variety of iron sulfide minerals including “amorphous iron sulfide”, mackinawite, greigite, pyrrhotite, marcasite, and pyrite. The type of minerals formed is dependent upon pH, Eh, and other physical and chemical factors. Extracellular production of these minerals are examples of biologically-induced mineralization in which mineral formation occurs from chemical and/or physical changes in the surrounding environment by the organism.

Several species of aquatic bacteria are known to exploit the earth's geomagnetic field as a means of directing their motion towards suitable habitats. A feature common to these bacteria is the presence of discrete intracellular magnetic inclusions, magnetosomes, aligned in chains along the long axis of the organism. The size and orientation of the individual magnetic particles imparts a permanent magnetic dipole moment to the cell which is, in turn, responsible for the magnetotactic response. In all species examined to date the magnetic particles have been found to be well-ordered, single domain, membrane-bounded crystals with reproducible, species-specific morphologies. Until recently, however, only crystals of the mixed valence iron oxide, magnetite (Fe3O4), were identified in these magnetotactic bacteria. We have now identified three species of bacteria from sulphidic environments which contain crystals of the mixed valence ferrimagnetic iron sulphide, greigite (Fe3S4). High resolution electron microscopical studies of the biogenic greigite crystals showed that they also exhibit the narrow size range (50–90nm) and unique crystallographic habits (e.g. cubo-octahedral, rectangular prismatic) which characterized and distinguished the inclusions in other magnetotactic species. Thus, it would appear that the bio-precipitation of iron sulphides in magnetotactic bacteria is a highly regulated process which is directed and controlled at the molecular level. These findings are not only important to our understanding of biomineralization in unicellular organisms but may also be significant to studies of paleomagnetism. Furthermore, the controlled synthesis of greigite presents an interesting challenge to material scientists and solid state chemists.

In 1975, Blakemore discovered the freshwater magnetotactic bacterium Aquaspirillum magnetotacticum which navigates along the magnetic-field direction. Electron microscopic work showed that the magnetotactic bacteria contain magnetosomes which are intracytoplasmic membrane-bound particles of magnetite, Fe3 O4. The magnetosomes are within the single-domain size range (∼500 Å) of Fe3O4. The magnetosomes within cells are often arranged in one or more chains with the chain axis more or less parallel to the axis of motility of the cell. A detailed study of the magnetic properties of magnetotactic bacteria can be found in the paper by Moskowitz.

Because of their unique properties of self-assembly and selective ion permeability across the lipid bilayers, phospholipid vesicles were used as reaction vessels for the synthesis of ultrafine, multicomponent ceramic particles containing Y, Ba, Cu, and Ag. Chemical inhomogeneities in the system were limited to the individual particle size (< 50 nun), which was a considerable improvement over particles prepared using bulk precipitation routes. The consistent barium deficiency was a serious problem that arose when attempting to control the stoichiometry of the multicomponent system. Our experimental evidence suggests that chemical interactions between the barium cations and the vesicleforming phospholipid may inhibit the precipitation of barium salts. In a parallel study, we performed consolidation studies on vesicle-precipitated Ag2O particles before and after the removal of the phospholipid molecules. Particle packing was greatly improved in the surfactant coated particles. This demonstrates the multifunctionality of this biomimetic system in which the vesicle membrane simultaneously acts as: (i) a reaction cell for particle precipitation, (ii) an ion selective membrane that affects precipitation kinetics, (iii) a barrier to prevent spontaneous agglomeration of the ultrafine particles, and (iv) a lubricant/dispersantth atfacilitatesp article rearrangementd uring consolidation.

Some acidic biopolymers serve as dispersants for colloidal processing of ceramics. One biopolymer we tested was alginate, a heteropolysaccharide containing two carboxylic sugar acids, D-mannuronic and D-guluronic. Kelp alginate was a suitable dispersant, provided that its viscosity was reduced by partial acid hydrolysis. Low molecular weight polymers rich in guluronic acid proved to be better dispersants than those rich in mannuronic acid, perhaps due to their greater charge density caused by their buckled molecular configuration. In situ processing of ceramic materials was tested by growing the alginate-producing bacterium, Azotobacter vinelandii, in the presence of alumina particles. Growth occurred at 15 vol% alumina in medium. Alumina particles which were exposed to such treatment showed a high packing density comparable to that with purified polymer. We also tested polypeptide polymers of the dicarboxylic amino acids, glutamate and aspartate, which also served as excellent dispersants for small alumina particles.

The photorefractive and photodiffractive properties of a 2 × 10−3 M, 30μim thin film of bacteriorhodopsin at - 40°C are analyzed by using optical absorption spectroscopy, the Kramers- Kronig transformation and coupled wave theory. Conversion of M to bR generates a dispersion in the refractive index that has a broad negative band from 450 to 540 nm [Δn500nm - -0.0016] and a broad positive band from 590 to 700 nm [Δn605nm - 0.0016]. The large change in refractive index for moderate solute concentration is due to the formation of the protonated Schiff base chromophore in bR which generates a large red shift in the absorption spectrum as well as a large increase in oscillator strength. The integrated diffraction efficiency from 300 - 800nm is dominated by refractive index contributions (ηphase) which are maximum in regions of minimal bR and M absorption. The maximum in the refractive (phase) component occurs at 451 nm (ηphase - 9.7%) whereas the maximum in the absorption component occurs at 575 nm (ηabs - 2.2%). The maximum efficiency of diffraction is observed at ∼440 nm (ηtotal - 10.7%). Adequate diffractive performance for most applications is predicted for write wavelengths in the regions 380 - 420 & 500 - 650 nm and for read wavelengths from 380 to 740 nm.

The photosynthetic reaction centers of plants and bacteria are photovoltaic devices on the molecular scale which convert light energy into chemical potential energy in the form of long-lived, energetic charge separated states. It is now possible to prepare synthetic multicomponent molecules which mimic important aspects of this process. For example, one of the keys to reaction center function is a multistep electron transfer strategy. In this paper, two general types of multistep electron transfer, sequential and parallel, are described and illustrated with several synthetic triad and pentad molecules.

Artificial membranes possessing physicochemical properties similar to biological membranes have been synthesized by immobilization of synthetic amphiphiles in layered ceramics. The intercalated bilayer-forming amphiphiles exhibit a gallery height of about 39 Å. Retention of bilayer-forming characteristics is further confirmed by the presence of a crystal to liquid-crystal phase transition. A dramatic increase in the membrane capacitance at the tansition temperature is attributed to an increase in membrane fluidity.

Studies involving the specific and non-specific surface recognition of biotin on biotinylated LB lipid monolayers by streptavidin and avidin conjugated phycoerythrin are presented. Both streptavidin and avidin conjugates were injected under the monolayer and found to preferentially adsorb to the biotinylated monolayers at the air-water interface. Pressure-area isotherms displayed a biotin-streptavidin/avidin complex dependent increase in surface pressure at expanded areas indicating protein adsorption. The binding of protein was confirmed by transferring the monolayer films to solid supports and measuring the characteristic intense phycoerythrin fluorescence at 576 nm. The effect of protein charge, monolayer packing density and structure, and activation of the tetramer proteins towards specific and non-specific binding are discussed. These results suggest a novel and general methodology for the two-dimensional ordering of protein monolayers with potential bioelectronic, optical and protein structure research applications.