Development of a Scalable, Chromatography-Free Synthesis of t-Bu-SMS-Phos and Application to the Synthesis of an Important Chiral CF3-Alcohol Derivative with High Enantioselectivity Using Rh-Catalyzed Asymmetric Hydrogenation.

A chromatography-free, asymmetric synthesis of the C2-symmetric P-chiral diphosphine t-Bu-SMS-Phos was developed using a chiral auxiliary-based approach in five steps from the chiral auxiliary in 36% overall yield. Separtion and recovery of the auxiliary were achieved with good yield (97%) to enable recycling of the chiral auxiliary. An air-stable crystalline form of the final ligand was identified to enable isolation of the final ligand by crystallization to avoid chromatography. This synthetic route was applied to prepare up to 4 kg of the final ligand. The utility of this material was demonstrated in the asymmetric hydrogenation of trifluoromethyl vinyl acetate at 0.1 mol % Rh loading to access a surrogate for the pharmaceutically relavent chiral trifluoroisopropanol fragment in excellent yield and enantiomeric excess (98.6%).

High throughput, high resolution enzymatic lithography process: effect of crystallite size, moisture, and enzyme concentration.

By bringing enzymes into contact with predefined regions of a surface, a polymer film can be selectively degraded to form desired patterns that find a variety of applications in biotechnology and electronics. This so-called "enzymatic lithography" is an environmentally friendly process as it does not require actinic radiation or synthetic chemicals to develop the patterns. A significant challenge to using enzymatic lithography has been the need to restrict the mobility of the enzyme in order to maintain control of feature sizes. Previous approaches have resulted in low throughput and were limited to polymer films only a few nanometers thick. In this paper, we demonstrate an enzymatic lithography system based on Candida antartica lipase B (CALB) and poly(ε-caprolactone) (PCL) that can resolve fine-scale features, (<1 µm across) in thick (0.1-2.0 µm) polymer films. A Polymer Pen Lithography (PPL) tool was developed to deposit an aqueous solution of CALB onto a spin-cast PCL film. Immobilization of the enzyme on the polymer surface was monitored using fluorescence microscopy by labeling CALB with FITC. The crystallite size in the PCL films was systematically varied; small crystallites resulted in significantly faster etch rates (20 nm/min) and the ability to resolve smaller features (as fine as 1 µm). The effect of printing conditions and relative humidity during incubation is also presented. Patterns formed in the PCL film were transferred to an underlying copper foil demonstrating a "Green" approach to the fabrication of printed circuit boards.

Patterned enzymatic degradation of poly(ε-caprolactone) by high-affinity microcontact printing and polymer pen lithography.

This paper reports deposition of Candida antarctica Lipase B (CALB) on relatively thick poly(ε-caprolactone) (PCL) films (300-500 nm) to create well-defined patterns using two different writing techniques: high-affinity microcontact (HA-µCL) and polymer pen (PPL) lithography. For both, an aqueous CALB ink is absorbed onto a polydimethylsiloxane (PDMS) writing implement (PDMS stamp or a PDMS pen tip), which is transferred to a spun-cast PCL film. HA-µCL experiments demonstrated the importance of applied pressure to obtain high-resolution patterns since uniform contact is needed between raised 20 µm parallel line regions of the PDMS stamp and the surface. AFM imaging shows pattern formation evolves gradually over incubation time only in areas stamped with CALB cutting through spherulites without apparent influence by grain boundaries. Strong binding of CALB to PCL is postulated as the mechanism by which lateral diffusion is limited. PPL enables formation of an arbitrary image by appropriate programming of the robot. The PDMS pen tips were coated with an aqueous CALB solution and then brought into contact with the PCL film to transfer CALB onto the surface. By repeating the ink transfer step multiple times where pen tips are brought into contact with the PCL film at a different locations, a pattern of dots is formed. After printing, patterns were developed at 37 °C and 95% RH. Over a 7-day period, CALB progressively etched the PCL down to the silicon wafer on which it was spun (350 nm) giving round holes with diameters about 10 µm. AFM images show the formation of steep PCL walls indicating CALB degraded the PCL film in areas to which it was applied. This work demonstrates that high-resolution patterns can be achieved without immobilizing the enzyme on the surface of polymeric stamps that limits the depth of features obtained as well as the throughput of the process.

Isolation and biophysical study of fruit cuticles.

The cuticle, a hydrophobic protective layer on the aerial parts of terrestrial plants, functions as a versatile defensive barrier to various biotic and abiotic stresses and also regulates water flow from the external environment. A biopolyester (cutin) and long-chain fatty acids (waxes) form the principal structural framework of the cuticle; the functional integrity of the cuticular layer depends on the outer 'epicuticular' layer as well as the blend consisting of the cutin biopolymer and 'intracuticular' waxes. Herein, we describe a comprehensive protocol to extract waxes exhaustively from commercial tomato (Solanum lycopersicum) fruit cuticles or to remove epicuticular and intracuticular waxes sequentially and selectively from the cuticle composite. The method of Jetter and Schäffer (2001) was adapted for the stepwise extraction of epicuticular and intracuticular waxes from the fruit cuticle. To monitor the process of sequential wax removal, solid-state cross-polarization magic-angle-spinning (CPMAS) (13)C NMR spectroscopy was used in parallel with atomic force microscopy (AFM), providing molecular-level structural profiles of the bulk materials complemented by information on the microscale topography and roughness of the cuticular surfaces. To evaluate the cross-linking capabilities of dewaxed cuticles from cultivated wild-type and single-gene mutant tomato fruits, MAS (13)C NMR was used to compare the relative proportions of oxygenated aliphatic (CHO and CH(2)O) chemical moieties. Exhaustive dewaxing by stepwise Soxhlet extraction with a panel of solvents of varying polarity provides an effective means to isolate wax moieties based on the hydrophobic characteristics of their aliphatic and aromatic constituents, while preserving the chemical structure of the cutin biopolyester. The mechanical extraction of epicuticular waxes and selective removal of intracuticular waxes, when monitored by complementary physical methodologies, provides an unprecedented means to investigate the cuticle assembly: this approach reveals the supramolecular organization and structural integration of various types of waxes, the architecture of the cutin-wax matrix, and the chemical composition of each constituent. In addition, solid-state (13)C NMR reveals differences in the relative numbers of CHO and CH(2)O chemical moieties for wild-type and mutant red ripe tomato fruits. The NMR techniques offer exceptional tools to fingerprint the molecular structure of cuticular materials that are insoluble, amorphous, and chemically heterogeneous. As a noninvasive surface-selective imaging technique, AFM furnishes an effective and direct means to probe the structural organization of the cuticular assembly on the nm-µm length scale.