Structure of gum arabic in aqueous solution

Gum arabic, a natural polysaccharide derived from exudates of Acacia senegal and Acacia seyal trees, is a commonly used food hydrocolloid. The complex chemical structure of the gum has been widely studied revealing a multifraction material consisting mainly of a highly branched polysaccharide and a protein–polysaccharide complex (GAGP) as a minor component. This work investigates its mesoscopic structure in aqueous solution by small‐angle X‐ray and neutron scattering combined with cryotransmission electrons microscopy. Scattering measurements reveal an intricate shape composed of many spheroidal aggregates assigned to the polysaccharide with a small amount of larger coils. A scattering peak is observed at moderate to high concentrations, the spacing of which exhibits a c^?1/3 power law relation to polymer concentration (c). Upon addition of salt, this peak disappears, indicating its electrostatic nature. The large coils contribute a q^?2 power law at the low scattering vector (q) range. However, at low concentration in which the interaggregate peak is not observed, a q^?1 power law at the low q range indicates the possible existence of a fraction with a locally extended conformation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3265–3271, 2006     

Refinement of structures previously proposed for gum arabic and other acacia gum exudates

In the light of advances in structural gum-chemistry, the analytical data available from earlier analytical and structural studies of gum arabic (Acacia Senegal Willd.), and of the gum exudates from Acacia laeta, A. campylacantha and A. seyal, have been re-interpreted. The structures originally suggested were based on random arbitrary assignments of substituent sugars without an attempt to establish regular structures. Modelling considerations and recalculations show that the data can also be interpreted in terms of more ordered structures. These are consistent with almost all of the available experimental data and give a much clearer insight into the nature and extent of the structural differences shown by the two Acacia gums of commercial importance. Acacia senegal (gum arabic, gum hashab) and Acacia seyal (gum talha).     

Diffusivity of whey protein and gum arabic in their coacervates

Structural properties of whey protein (WP)/gum arabic (GA) coacervates were investigated by measuring the diffusivity of WP and GA in their coacervate phase as a function of pH by means of three different complementary techniques. The combination of these measurements revealed new insights into the structure of coacervates. Nuclear magnetic resonance (NMR) measured the self-diffusion coefficient of the GA in the coacervate phase prepared at various pH values. Fluorescence recovery after photobleaching (FRAP) was measured using a confocal scanning laser microscope. The WP and GA were covalently labeled with two different dyes. The time of fluorescence recovery, related to the inverse of the diffusion coefficient, was evaluated from the measurements, and the diffusivity of the WP and GA on a long time scale could be individually estimated at each pH value. Diffusing wave spectroscopy (DWS) combined with transmission measurement was carried out in the coacervate phase, and the diffusion coefficient, corresponding to the averaged diffusion of all particles that scattered in the system, was calculated as a function of pH. Independently of the technique used, the results showed that the diffusion of the WP and GA within the coacervate phase was reduced as compared to a diluted biopolymer mixture. NMR, DWS, and FRAP measurements gave similar results, indicating that the biopolymers moved the slowest in the coacervate matrix at pH 4.0-4.2. It is assumed that the diffusion of the WP and GA is reduced because of a higher electrostatic interaction between the biopolymers. Furthermore, FRAP results showed that in the coacervate phase WP molecules diffused 10 times faster than GA molecules. This result is very relevant because it shows that WP and GA move independently in the liquid coacervate phase. Finally, DWS measurements revealed that the coacervate phase rearranged with time, as evidenced by a decrease of the diffusion coefficient and a loss of the turbidity of the sample. A more homogeneous transparent coacervate phase was obtained after a few days/weeks. Faster rearrangement was obtained at pH 3.0 and 3.5 than at higher pH values.     

Role of thermoxidation and depolymerisation in the ageing of systems paper/gum arabic/historical ink

The aim of this study was to assess the role and proportional representation of depolymerisation and thermoxidation reaction paths in the systems paper/gum arabic (GA)/historical ink during various accelerated ageing methods. The historical inks under study are iron-gall, bistre, and sepia. The results indicate that thermoxidation represents only a minor reaction path in the ageing of paper/GA/ink systems except for the iron-gall ink and the light-thermal method of accelerated ageing. The iron-gall ink accelerates both reaction paths of ageing, i.e. thermoxidation and depolymerisation; in this case, thermoxidation might become the prevailing degradation reaction path. For the sepia ink, an anti-depolymerisation stabilising effect in thermal methods of ageing has been detected. Considering the thermoxidation reaction path, the results even suggest that a compound preventing thermoxidation is formed during the thermally accelerated ageing in air and in 100 mg L^?1 of NO₂. In the light-thermal ageing, the most stable sample is the Whatman paper (W)/GA/bistre ink.     

Palladium nanoparticles supported on gum arabic as a reusable catalyst for solvent-free Mizoroki-Heck reaction

Palladium nanoparticles (2–8 nm) supported on gum arabic has been prepared under green conditions in water. Gum arabic has been used as both support and reducing agent. These nanoparticles have been characterized by UV–Vis, XRD and EDX spectra as well as SEM and TEM images. The nanoparticles have been applied as the catalyst in Mizoroki-Heck reaction of different aryl halides (I, Br, Cl) with butyl acrylate in the presence of n-Pr₃N under solvent-free conditions at 140 °C. The reusability of the catalyst was also checked for five consecutive runs.     

Spectrophotometric determination of paraquat with BiI(-)(4) in the presence of gum arabic

A spectrophotometric method for determination of Paraquat, based on its reaction with BiI(-)(4) ion in the presence of gum arabic, is described. The apparent molar absorptivity of the product is 1.64 x 10(4) 1.mole(-1).cm(-1) at 515 nm. Results for the analysis of commercial herbicides are in good agreement with those obtained by the dithionite method.     

Structure and configuration of cauferinin

Summary From the roots ofFerula conocaula Korov. a terpenoid coumarin of the iresane series with three hydroxy groups has been isolated which has been called cauferinin.On the basis of the result of a study of its chemical and spectral characteristics and its conversion into cauferin, the structure and relative configuration (I) has been put forward for cauferinin.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Orginal article translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 151–154, March–April, 1979.     

Structure and configuration of tavimolidin

From the roots ofPeucedanum mogoltavicum Korov. have been isolated tadzhiferin, farnesiferol B, 5-methoxy-3,4-methylenedioxypropiophenone, and a new terpenoid coumarin — tavimolidin. The structure and absolute configuration of tavimolidin have been established on the basis of a study of its chemical and spectral characteristics. The passage from tavimolidin to feselol has confirmed the structure proposed previously for mogoltavinin, mogoltavin, and mogoltin and has established their absolute configurations.