The synthesis of isosorbide aliphatic polyesters is demonstrated by the use of Novozym 435, a catalyst consisting of Candida antarctica lipase B immobilized on a macroporous support. Several experimental procedures were tested and azeotropic distillation was most effective in removing low mass byproduct. Furthermore, the use of diethyl ester derivatives of diacid comonomers gave isosorbide copolyesters with highest isolated yield and molecular weights. The length of the diacid aliphatic chain was less restrictive, but with a clear preference for longer aliphatic chains. The molecular mass values of the obtained products were equivalent or higher than those obtained by nonenzymatic polymerizations, a clear illustration of the potential of enzymatic over conventional catalysis. The ability of Novozym 435 to catalyze the synthesis of isosorbide polyester with weight-average molecular weights in excess of 40 000 Da was unexpected given that isosorbide has two chemically distinct secondary hydroxyl groups. This is the first example in which isosorbide polyesters were synthesized by enzyme catalysis, opening a large array of possibilities for this important class of biomass-derived building blocks. Because these polymers are potential biomaterials, the total absence of conventional Lewis acid catalyst residues represents a major improvement in the toxicity of the material.

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Here we report a continuous flow-based ionization method, capillary Vibrating Sharp-edge Spray Ionization (cVSSI), that nebulizes liquid sample directly at the outlet of a capillary without using high-speed nebulization gas or a high electrical field. cVSSI is built upon the recently reported VSSI principle which nebulizes bulk liquid using vibrating sharp-edges. By attaching a short piece of fused silica capillary on top of the vibrating glass slide in VSSI, liquid is nebulized at the outlet of the capillary as the result of the vibration. Utilizing standard 360 μm OD/100 μm ID capillary, cVSSI works with a wide range of flow rates from 1 μL/min to 1 mL/min. The power consumption is as low as 130 mW. ESI-like MS spectra are obtained for small molecules, peptides and proteins. 5 orders of magnitude linear response for acetaminophen solution is achieved with a limit of detection (LOD) of 3 nM. cVSSI is also demonstrated to be compatible with LC-MS analysis. Two LC-MS applications are demonstrated with cVSSI: 1) separation and detection of a mixture of small molecules; 2) bottom-up proteomics using a protein digest. A mixture of 9 common metabolites was appropriately separated and detected using LC-cVSSI-MS. In the bottom-up experiment, 78 peptides were detected using LC-cVSSI-MS/MS with a protein coverage of 100% for cytochrome c, which is comparable with the coverage obtained using LC-ESI-MS. cVSSI offers a means of interfacing LC or other continuous flow-based applications to mass spectrometers with the salient features of voltage-free, flexibility, small footprint and low power consumption.

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