A family of high-buffering capacity diamino sulfate isoelectric buffers for pH-biased isoelectric trapping separations

Abstract

pH-biased isoelectric trapping separations are hindered by the lack of suitable isoelectric buffers with pI values in the 5.8 < pI range. Two generic approaches are described here for the cost-effective synthesis of a family of diamino sulfate buffers that have high buffering capacities in their isoelectric state: the first approach relies on the sulfation of existing, commercially available diamino alcohol intermediates, the second approach calls for the synthesis of diamino alcohols from epichlorohydrin and widely available secondary amines, and subsequent sulfation of the new diamino alcohol. The diamino sulfate buffers are recovered in isoelectric state, in high purity. Four members of the family having pI values in the 5.8 < pI < 8.9 range have been synthesized, analytically characterized by capillary electrophoresis (CE), electrospray ionization-time of flight-mass spectrometry (ESI-TOF-MS), 1-D and 2-D nuclear magnetic resonance (NMR) spectroscopy, and X-ray crystallography. All four diamino sulfates have been successfully used as pH biasers in the receiving stream in preparative-scale pH-biased isoelectric trapping protein separations.

Isoelectric buffers, part 3: Determination of pKa and pI values of diamino sulfate carrier ampholytes by indirect UV‐detection capillary electrophoresis

“…, and 1,3-bis(1-piperidino)-2-Osulfo-propane (BPSP), were synthesized in our laboratory according to the procedures described in [41].…”

“…Since the diamino sulfates lack appropriate UV chromophores, initially only the pH ranges that bracket their pI values were determined by indirect UV-detection CE, not the actual pK a values [41]. However, recently, an indirect UV-detection CE method was developed for the determination of the pK a values of the UV-transparent quaternary ammonium dicarboxylic acid CAs [42], based on the results of three preceding papers that described ways to obtain thermodynamically correct pK a values [43][44][45].…”

“…Recently, two families of single-component, good CAs have been synthesized: diamino sulfates [41] with pI values greater than 5.7 and quaternary ammonium dicarboxylic acids with pI values lower than 4.3 [42]. The diamino sulfate CAs were obtained by reacting the pyridine complex of sulfur trioxide with a diamino alcohol intermediate (either commercially available or synthesized from two equivalents of a secondary amine and one equivalent of epichlorohydrin).…”

“…The diamino sulfate CAs were obtained by reacting the pyridine complex of sulfur trioxide with a diamino alcohol intermediate (either commercially available or synthesized from two equivalents of a secondary amine and one equivalent of epichlorohydrin). The diamino sulfates were then titrated to their corresponding pIs and recovered by crystallization as inner salts [41]. The quaternary ammonium dicarboxylic acid CAs were obtained by one of the two ways: (i) by reacting amino dicarboxylic acids with alkyl halides and (ii) by reacting secondary amines with an alkyl ester of a halocarboxylic acid, followed by hydrolysis of the esters by a strong base.…”

Capillary electrophoresis of proteins 2003–2005

“…Newly synthesized diamino sulfate isoelectric buffers with pI in the range of 5.8-8.9 have been used for pH-biased isoelectric trapping protein separations [86]. Another isoelectric buffer synthesized for CZE was bismorpholine derivative of pivalic with pI 6.5 [87].…”