Gábor Dibó

Microwave-assisted conversion of carbohydrates to levulinic acid: an essential step in biomass conversion

Degradation of non-edible carbohydrates to levulinic acid (4-oxopentanoic acid) was studied by using dielectric heating with microwave energy. Levulinic acid and its reduced and dehydrated derivative, γ-valerolactone (GVL), can be used for the production of small-molecule, functionalized hydrocarbons, which might be potential platform molecules for the chemical industry. First, simple model compounds (fructose, glucose, saccharose and cellobiose) were hydrolyzed in order to find the optimum reaction conditions (e.g. reagent, reaction temperature, acid concentration, time) for the degradation and transformation of polysaccharides (cellulose, chitin, chitosan) by using controlled microwave irradiation. Cellulose, a non-edible biopolymer of plant origin, was successfully converted to levulinic acid under the optimized conditions (2 M H2SO4, 170 °C, 50 min) with a yield of 34.2% in a mono-mode Multisynth microwave reactor. The reactions proceeded with hydrochloric acid catalysis as well, and a slightly better yield was achieved, however, using HCl (a chlorine containing catalyst) raises serious environmental concerns. The hydrolysis of glucosamine-based glycans (D-glucosamine, N-Ac-D-glucosamine, LMw-chitosan, MMw-chitosan, chitin) was also studied and optimized with sulfuric acid as a catalyst in a mono-mode Multisynth microwave reactor. The highest yield of levulinic acid was obtained with 2 M H2SO4 at 190 °C for 30 min. N-Ac-D-glucosamine, D-glucosamine, LMw-chitosan and MMw-chitosan resulted in levulinic acid with yields between 20.6% and 32.7%, the larger molecular weight chitin was degraded to levulinic acid with a yield of 37.8%.

Chemical Synthesis of Peptide Libraries

Abstract The efficiency of the “portioning-mixing” method is demonstrated by the synthesis of more than one million hexapeptides in 5 days. An example is described to illustrate the possibility of completion of partial peptide libraries. Our method is also shown to be suitable to carry out binary peptide synthesis. In addition, a new screening method is outlined based on specific interaction of peptides with living cells.

An improved catalytic system for the reduction of levulinic acid to γ-valerolactone

An improved bidentate phosphine-modified recyclable catalytic system was developed for the selective conversion of biomass-derived levulinic acid into γ-valerolactone with a TOF of 21 233 h−1 in solvent-, chlorine- and additive-free reaction environments.

Synthesis of γ-valerolactone using a continuous-flow reactor

This study describes the heterogeneous catalysed continuous synthesis of γ-valerolactone (GVL) using a continuous-flow reactor, H-Cube® and H-Cube Pro™, equipped with 5% Ru/C, 10% Pd/C and RANEY® Ni CatCart®. The highest yield of GVL was achieved by using 5% Ru/C in the presence of 0.015 mol L−1 Bu-P(C6H4-m-SO3Na)2 ligand under 100 bar H2 at 100 °C.

Direct asymmetric reduction of levulinic acid to gamma-valerolactone: synthesis of a chiral platform molecule

Levulinic acid was directly converted to optically active (S)-gamma-valerolactone, a proposed biomass-based chiral platform molecule. By using a SEGPHOS ligand-modified ruthenium catalyst in methanol as a co-solvent, eventually, 100% chemoselectivity, and 82% enantioselectivity were achieved. The effect of the catalyst composition and reaction parameters on the activity and selectivity was investigated in detail. The conversion of a “real” biomass derived levulinic acid to optically active GVL without decreasing the enantioselectivity was also demonstrated.

Rhodium-catalyzed hydrogenation of olefins in γ-valerolactone-based ionic liquids

γ-Valerolactone-based ionic liquids were successfully used as the catalyst phase for [Rh(cod)2][BF4]/RP(C6H4-m-SO3Na)2 (R = Me, Pr, Bu, Cp) catalyzed hydrogenation of different olefins. Compared to broadly used ionic liquids e.g. 1-butyl-3-methylimidazolium chloride [bmim][Cl], the turnover frequencies were significantly higher and the reaction was selective for the CC double bonds in the presence of carbonyl, cyano, and phenyl groups. The catalyst was recycled for ten consecutive runs under regular or biphasic conditions without loss of activity. The vapour pressure and viscosity of γ-valerolactone-based ionic liquids were determined as well.

Production of platform molecules from sweet sorghum

This study proves that the non-food dedicated sweet sorghum (Sorghum bicolor) can be a possible source and/or raw material of platform molecules such as levulinic acid (LA) and 5-hydroxymethyl-2-furaldehyde (5-HMF). The high sugar-containing juice derived from sweet sorghum can be efficiently converted to LA and 5-HMF by using microwave dielectric heating. Centrifugal separation was proposed as a first step of the technology to remove the insoluble materials (fibers, starch, and sand) to obtain high sugar containing feedstock for acid-catalyzed dehydration. The effects of pretreatment by centrifugal separation and reaction conditions (irradiation time, acid concentration and reaction temperature) on the formation of levulinic acid were studied. The conversions were monitored by in situ NMR spectroscopy. It was shown that maximum yield (31.4%) of LA was achieved in the presence of 2 M sulfuric acid by applying 30 min irradiation at 160 °C to the sorghum sample treated for 20 min in a centrifuge at a rotational force of 5870. It was also revealed that 5-HMF can be produced from the sweet sorghum juice in the presence of 0.05 M sulfuric acid at 120 °C.

Catalytic transfer hydrogenation in γ-valerolactone-based ionic liquids

The combination of transfer hydrogenation reaction with the advantages of γ-valerolactone-based ionic liquids could result in an environmentally benign method for the reduction of organic substrates. Ionic liquids containing 4-hydroxyvalerate anion were applied as alternative solvents for the reduction of acetophenone, its substituted forms and different alkenes using transition metal based catalysts. The optimal conditions (e.g. type of catalyst precursor and hydrogen donor) for the transformation were also specified.

An improved method for isolation of the C-terminal fragment of proteins

An efficient and easily realizable method for the isolation of the C-terminal fragment is described. Proteins are esterified by methanolic HCl and subsequently digested with pepsin. The peptide mixture is submitted to paper electrophoresis in pH 2.1 buffer. The identification of the C-terminal peptide is performed by preparing a guide peptide map, using pH 5.5 buffer in the second dimension. The C-terminal fragment appears as an on-diagonal spot. It can be isolated by a pH 5.5 run of the corresponding band from the first (pH 2.1) electrophoretogram. Since the C-terminal peptide is the fastest moving component, there is no need for its further purification. The expected yield is about 40%.

Position of the Peptide Linkage in Glutamyl‐Taurine from Calf Brain Synaptic Vesicles

Abstract: To elucidate the position of the peptide bond in glutamyl‐taurine this dipeptide was extracted from calf brain synaptic vesicles and subjected to paper electrophore‐sis. It was analyzed further in an automatic amino acid analyzer prior and subsequent to acid hydrolysis. Both á‐ and γ‐forms were found to be present in approximately equal amounts.