Effects of cyclodextrins and saccharides on dual fluorescence of N,N-dimethyl-4-aminophenylboronic acid in water

N,N-Dimethyl-4-aminophenylboronic acid (DMAPB) showed pH-dependent dual fluorescence at 360 and 462 nm originating from locally excited (LE) and twisted intramolecular charge transfer (TICT) states, respectively, in aqueous solutions. Upon complexation with α-CD, LE fluorescence was markedly increased while TICT fluorescence was decreased. In contrast, both LE and TICT fluorescence were increased when DMAPB was complexed with β-CD. The fluorescence variations enabled us to determine the 1:1 and 1:2 binding constants of the DMAPB/α-CD complex to be 10 and 40 M⁻¹, respectively, and the 1:1 binding constant of the DMAPB/β-CD complex to be 635 M⁻¹. The dual fluorescence of DMAPB alone was found to be a good indicator of saccharide sensing. Under weakly alkaline conditions, saccharides suppressed TICT fluorescence while increasing LE fluorescence. Among the saccharides investigated, d-fructose induced the largest fluorescence change, followed by d-ribose and d-glucose. This order is consistent with the stability of the boronate esters of DMAPB with saccharides. In the presence of β-CD, saccharide selectivity was unchanged, while fluorescence was amplified. These results demonstrate the superiority of the supramolecular DMAPB/β-CD complex to DMAPB alone as a ratiometric fluorescence sensor for saccharides in water.     

Ground and excited state proton transfer reaction of salicylidine-3,4,7-methyl amine in micelles

The effect of neutral, cationic and anionic micellar environments on the ground and excited state proton transfer reactions of salicylidine-3,4,7-methyl amine (SMA) in water has been studied by steady state and time resolved fluorescence spectroscopy. In the ground state, the formation of the primary form of SMA is enhanced at the expense of the zwitterionic species due to micellization. In the excited state, anion formation decreases both in the presence of Triton-X and cetyl trimethyl ammonium bromide (CTAB). However, in the presence of sodium dodecyl sulphate (SDS), the anionic emission increases after reaching a certain micellar concentration. The lifetime of the anion is significantly reduced in CTAB compared to that in the bulk water and also in the presence of Triton-X. It is proposed that the destabilization and modification of SMA anion occurs due to the different electrostatic environments produced by micellization.     

Elucidating the Anomalous Binding Enhancement of Isoquinoline Boronic Acid for Sialic Acid Under Acidic Conditions: Expanding Biorecognition Beyond Vicinal Diols

A zwitterionic heterocyclic boronic acid based on 4-isoquinolineboronic acid (IQBA) exhibits the highest reported binding affinity for sialic acid or N-acetylneuraminic acid (Neu5Ac, K=5390±190 m ⁻¹) through the formation of a cyclic boronate ester complex under acidic conditions (pH 3). This anomalous pH-dependent binding enhancement does not occur with common neutral saccharides (e.g., glucose, fructose, sorbitiol), because it is mediated via selective complexation to a α-hydroxycarboxylate moiety forming a stable ion pair and ternary complex with Neu5Ac in phosphate buffer. IQBA expands biorecognition beyond classical vicinal diols under neutral or alkaline buffer conditions, which enables the direct analysis of Neu5Ac by native fluorescence with sub-micromolar detection limits.     

The design of boronic acid spectroscopic reporter compounds by taking advantage of the pK(a)-lowering effect of diol binding: nitrophenol-based color reporters for diols

The complex that forms between a boronic acid and a diol is often much more acidic than the starting boronic acid. In conditions where the solution pH is between the two pK(a) values, the boron atom will convert from a neutral trigonal form to an anionic tetrahedral form upon complexation. Such a change is likely to dramatically alter the electron density of neighboring groups. Utilizing this effect, we have designed and synthesized two nitrophenol-based boronic acid reporter compounds that change ionization states and therefore spectroscopic properties upon diol binding. Both compounds show significant UV changes upon addition of saccharides. For example, a blue shift of the absorption max from 373 to 332 nm was observed with the addition of D-fructose to 2-hydroxy-5-nitrophenylboronic acid at neutral pH. Such a reporter compound can be used as a recognition and signaling unit for the construction of polyboronic acid sensors for the selective and specific recognitions of saccharides of biological significance.     

新型含苯硼酸和萘双亲化合物的合成与囊泡荧光传感器的制备

合成了含有识别基团苯硼酸和荧光基团萘的新型对-[(5-十二烷氧基-1-氧基)萘]甲基苯硼酸{p-[(5-dodecyloxy-1-oxy) naphthalene] methyl-phenylboronic acid, DNMPBA}双亲化合物; 该化合物在THF/水选择性溶剂中自组织成囊泡, 囊泡的相变温度为56.8 ℃; 当向囊泡体系加糖时, DNMPBA囊泡中的萘生色基在345 nm的荧光峰强度急剧增强; 荧光强度随添加不同糖的变化趋势为果糖>葡萄糖>麦芽糖>乙二醇. 荧光强度增强可能归因于所形成的硼酸酯减弱了DNMPBA双亲化合物中一个氧原子孤对电子对萘生色基的猝灭作用而使荧光强度重新恢复. DNMPBA囊泡与糖的相互作用导致体系荧光强度变化, 使该体系有可能应用于检测生物物质如糖的化学传感器.     

Effects of denaturation on soy protein-xanthan interactions: comparison of a whipping-rheological and a bubbling method

The effect of xanthan on foam formation and on physical mechanisms of destabilization involved in the breakdown of foams made from native and denatured soy protein at neutral pH was studied by a bubbling and a whipping-rheological method. Parameters describing foam formation and destabilization by liquid drainage and disproportionation obtained by the two methods showed that the addition of xanthan was accompanied by delayed rates of drainage and disproportionation and reduced foam height decay (collapse). Drainage showed the largest reduction, mainly because of the increased bulk viscosity. In the absence of xanthan, protein denaturation enhanced foam formation and stability against drainage and disproportionation, but increased the collapse of foams. In the presence of xanthan, differences in foam formation and drainage/disproportionation stability between native and denatured soy protein were greatly reduced. However, differences in foam collapse were greatly enhanced. The increased stability of foams in the presence of xanthan could not be explained purely in terms of increased aqueous phase viscosity. More specific interactions of xanthan and soy proteins at the air-water interface influencing the surface rheology, and the protein composition and aggregation, are involved.     

Photo‐ and pH‐Tunable Multicolor Fluorescent Nanoparticle‐Based Spiropyran‐ and BODIPY‐Conjugated Polymer with Graphene Oxide

We report a stimuli‐responsive fluorescent nanomaterial, based on graphene oxide coupled with a polymer conjugated with photochromic spiropyran (SP) dye and hydrophobic boron dipyrromethane (BODIPY) dye, for application in triggered target multicolor bioimaging. Graphene oxide (GO) was reduced by catechol‐conjugated polymers under mildly alkaline conditions, which enabled to formation of functionalized multicolor graphene nanoparticles that can be induced by irradiation with UV light and by changing the pH from acidic to neutral. Investigation of these nanoparticles by using AFM, fluorescence emission, and in vitro cell and in vivo imaging revealed that they show different tunable colors in bioimaging applications and, more specifically, in cancer‐cell detection. The stability, biocompatibility, and quenching efficacy of this nanocomposite open a different perspective for cell imaging in different independent colors, sequentially and simultaneously.     

荧光衍生中性糖的高效液相色谱分析

在HypersilODS2色谱柱上,利用新型荧光试剂1,2-苯并-3,4-二氢咔唑-9-乙基肼基甲酸酯(BCEC)作柱前衍生化试剂,采用梯度洗脱对5种中性糖荧光衍生物进行了优化分离.65℃下在乙腈溶剂中以冰乙酸作催化剂,衍生反应6.5h后获得稳定的荧光产物,衍生反应完全.激发和发射波长分别为λex=333nm,λem=390nm.线性回归系数均在0.999以上,检测限为24.3～62.1fmol.     

Determination of saccharides in biological materials by high-performance anion-exchange chromatography with pulsed amperometric detection

High-performance anion-exchange chromatography (HPAEC) coupled with pulsed amperometric detection (PAD) under alkaline conditions (pH 9-13) separates aminosaccharides, neutral saccharides and glycuronic acids based upon their molecular size, saccharide composition and glycosidic linkages. Carbohydrates were extracted by utilizing 0.5 M H2SO4 (neutral monosaccharides), 0.25 M H2SO4 coupled with enzyme catalysis (glycuronic acids) and 3 M H2SO4 (aminosaccharides). Solid-phase extraction with strong cation and strong anion resins was used to partition the cationic aminosaccharides and anionic glycuronic acids and to deionize acid extracts for neutral saccharides. Separation was conducted on a medium-capacity anion-exchange column (36 mequiv.) utilizing sodium hydroxide (5-200 mM and sodium acetate (0-250 mM) as the mobile phase. The saccharides were detected by oxidation at a gold working electrode with triple-pulsed amperometry. HPAEC-PAD was found superior to high-performance liquid chromatography with refractive index (RI) detection for neutral monosaccharides and aminosaccharides and to low-wavelength UV detection for glycuronic acids in terms of resolution and sensitivity. HPAEC-PAD was not subject to interferences as was the case for low UV detection (210 nm) or RI analyses and was highly selective for mono- and aminosaccharides and glycuronic acids. The use of HPAEC-PAD was applied for the determination of the saccharide composition of organic materials (plant residues, animal wastes and sewage sludge), microbial polymers and soil.     

The hydrogen bonding properties of cytosine: a computational study of cytosine complexed with hydrogen fluoride, water, and ammonia

Density functional theory is used to study the hydrogen bonding pattern in cytosine, which does not contain alternating proton donor and acceptor sites and therefore is unique compared with the other pyrimidines. Complexes between various small molecules (HF, H(2)O, and NH(3)) and four main binding sites in (neutral and (N1) anionic) cytosine are considered. Two complexes (O2(N1) and N3(N4)) involve neighboring cytosine proton acceptor and donor sites, which leads to cooperative interactions and bidendate hydrogen bonds. The third (less stable) complex (N4) involves a single cytosine donor. The final (O2-N3) complex involves two cytosine proton acceptors, which leads to an anticooperative hydrogen bonding pattern for H(2)O and NH(3). On the neutral surface, the anticooperative O2-N3 complex is less stable than those involving bidentate hydrogen bonds, and the H(2)O complex cannot be characterized when diffuse functions are included in the (6-31G(d,p)) basis set. On the contrary, the anionic O2-N3 structure is the most stable complex, while the HF and H(2)O N3(N4) complexes cannot be characterized with diffuse functions. B3LYP and MP2 potential energy surface scans are used to consider the relationship between the water N3(N4) and O2-N3 complexes. These calculations reveal that diffuse functions reduce the conversion barrier between the two complexes on both the neutral and anionic surfaces, where the reduction leads to a (O2-N3) energy plateau on the neutral surface and complete (N3(N4)) complex destabilization on the anionic surface. From these complexes, the effects of hydrogen bonds on the (N1) acidity of cytosine are determined, and it is found that the trends in the effects of hydrogen bonds on the (N1) acidity are similar for all pyrimidines.     

Polyamide grafted with polypyrrole: formation, properties, and stability

Conducting textiles of polyamide (PA) fabrics and polypyrrole (PPy) were prepared by in situ oxidative chemical polymerisation of pyrrole (Py) on the surface of PA textiles using FeCl₃ as oxidant. The anionic surfactant, dodecylbenzenesulphonic acid, was used as co-dopant during Py polymerisation on the textile surface. The influence of the monomer amount and polymerisation conditions on formation of the conducting PPy layer, conductivity, morphology, and stability of the prepared PA/PPy was studied. The conductivity of modified textiles decreased rapidly after the washing process, so a special Py-functionalised silane (1-(3-(triethoxysilyl)propylamino)-3-(1-H-pyrrole-1-yl)propan-2-ol; SP) was synthesised and applied to the PA surface prior to PPy formation. The presence of SP on the PA surface after completion of the sol-gel process was verified by Fourier transform infrared spectroscopy with an attenuated total reflectance. Pyrrole polymerisation was subsequently applied to the SP pre-treated textile surface. The influence of SP concentration on both the fastness of the conducting layer after the washing process and stability of the electrical conductivity of the prepared PA/PPy samples was investigated. Surface conductivity of the samples treated and untreated by the sol-gel process of SP was measured both prior to and after washing of the prepared textiles. It was found that an application of 0.6 mass % of SP significantly improved the fastness of the PPy layers. Examination of the modified PA surface using scanning electron microscopy disclosed the differences in the formation of PPy on PA textiles when using SP and also showed differences on the PPy modified textile surface prior to and after washing. The method of X-ray photoelectron spectroscopy was used for a detailed study of the surface composition. It was confirmed that the pre-treatment with Py-functionalised triethoxysilane significantly influenced the chemical composition of the PA surface modified with PPy.     

Complexation of Al(III) by 8-Hydroxyquinoline and Drastic Fluorescence Enhancement in Reverse Micelles

Complexation of Al^IIIby 8-hydroxyquinoline and fluorescence behavior of the quinolinate(s) were studied in reverse micellar systems at low water content, and compared to aqueous media. Two surfactants were used: one was cationic (CTAC: cetyltrimethylammonium chloride) and the other was anionic (AOT: sodium bis(2-ethylhexyl)sulfosuccinate). The results obtained in the CTAC/dichloromethane system (W= [H₂O]/[surfactant] = 0.9) showed that complexation occurred very likely in the oil phase and no micellar effect was observed. On the contrary, in the presence of AOT, specific micellar effects were observed due to the presence of the anionic polar heads: stabilization of the positively charged 1:1 and 1:2 chelates, at the expense of the neutral water-insoluble 1:3 chelate which is formed in aqueous solutions under similar conditions;drastic fluorescence enhancement factorsof 120 and 100 in AOT/heptane (W= 1.5) and AOT/dichloromethane (W= 1.6), respectively. Such factors have never been reported so far in either hydroorganic or direct micellar systems. In return, the length of time for the production of the complex(es) is increased because of the microheterogeneity of the medium and the small sizes of the water pools.     

Characterization of the singlet and triplet excited states of 3-chloro-4-methylumbelliferone

An extensive photophysical characterization of 3-chloro-4-methylumbelliferone (3Cl4MU) in the ground-state, S(0), first excited singlet state, S(1), and lowest triplet state, T(1), was undertaken in water, neutral ethanol, acidified ethanol, and basified ethanol. Quantitative measurements of quantum yields (fluorescence, phosphorescence, intersystem crossing, internal conversion, and singlet oxygen formation) together with lifetimes were obtained at room and low temperature in water, dioxane/water mixtures, and alcohols. The different transient species were assigned and a general kinetic scheme is presented, summarizing the excited-state multiequilibria of 3Cl4MU. In water, the equilibrium is restricted to neutral (N*) and anionic (A*) species, both in the ground (pK(a) = 7.2) and first excited singlet states (pK(a)* = 0.5). In dioxane/water mixtures (pH ca. 6), substantial changes of the kinetics of the S(1) state were observed with the appearance of an additional tautomeric T* species. In low water content mixtures (mixture 9:1 v:v), only the neutral (N*) and tautomeric (T*) forms of 3Cl4MU are observed, whereas at higher water content mixtures (water mole fraction superior to 0.45), all three species N*, T*, and A* coexist in the excited state. In the triplet state, in the nonprotic and nonpolar solvent dioxane, the observed transient signals were assigned as the triplet-triplet transition of the neutral form, N*(T(1)) → N*(T(n)). In water, two transient species were observed and are assigned as the triplets of the neutral N*(T(1)) and the anionic form, A*(T(1)) (also obtained in basified ethanol). The phosphorescence spectra and decays of 3Cl4MU, in neutral, acidified, and basified solutions, demonstrate that only these two species N*(T(1)) and A*(T(1)) exist in the lowest lying triplet state, T(1). The radiative channel was found dominant for the deactivation of the anionic species, whereas with the neutral the S(1) ? S(0) internal conversion competes with fluorescence. For both N* and A* the intersystem crossing yield represents a minor deactivation channel for S(1).     

Evaluation of the role of multiple hydrogen bonding in offering stability to negative ion adducts in electrospray mass spectrometry

An experimental approach, electrospray mass spectrometry (ES-MS), and a theoretical approach employing computer modeling, have been used to characterize the interaction between small inorganic anions and neutral analyte molecules that form anionic adduct species in negative mode ES mass spectrometry. Certain anionic adducts of small saccharides (e.g., alpha-D-glucose, sucrose) have shown exceptional stability in ES mass spectra even when internal energies are raised at high "cone" voltages. Computer modeling studies reveal that multiple hydrogen bonding strengthens the interaction between these neutral molecules and the attaching anion. The equilibrium structures and stabilization energies of these anionic adducts have been evaluated by semi-empirical, ab initio, and density functional theory (DFT) methods. Chloride anion is found to be capable of forming "bridging" hydrogen bonds between monosaccharide rings of polysaccharides resulting in the stabilization of chloride adducts, thus reducing the tendency for the glycosidic bond to decompose. Moreover, the tendency for various hydroxyl hydrogens on saccharide molecules to dissociate in the form of HA (A-, anion) during decomposition of anionic adducts, thereby forming [M - H]-, has also been evaluated by computer modeling.     

Photophysics of xanthene dyes in surfactant solution

The spectral (both absorption and fluorescence) and photoelectrochemical studies of some anionic xanthene dyes namely erythrosine B, rose bengal and eosin have been carried out in micellar solution of cationic cetyl trimethyl ammonium bromide (CTAB), anionic sodium dodecyl sulphate (SDS) and neutral triton X-100 (TX-100). The results show that all these dyes form 1:1 electron-donor-acceptor (EDA) or charge-transfer (CT) complexes with TX-100, which acts as an electron donor. There is no interaction of these dyes with SDS, whereas the interaction with CTAB is mainly electrostatic in nature. In presence of TX-100, these dyes show enhancement of fluorescence intensity with a red shift and develop photovoltage in a photoelectrochemical cell. A good correlation has been found among the photovoltage generation in the systems consisting of these dyes and TX-100, spectral shift due to complex formation and thermodynamic properties of these complexes.     

The effect of an anionic surfactant on the rheology and stability of high volume fraction O/W emulsion stabilized by PVA

The effect of the addition of an anionic surfactant (sodium dodecyl benzene sulphonate) on the rheology and storage stability of concentrated O/W emulsions stabilized by poly (vinyl alcohol) is reported. It was found that the surfactant markedly reduced the magnitudes of the storage modulii of the emulsions. This could be attributed to a reduction in the interfacial tension resulting from the formation of polyelectrolyte type complexes between the PVA and NaDBS at the O/W interface. The results were compared to the equation (given by Princen) relating concentrated emulsion rheology to the interfacial tension and droplet size. Reasonable agreement was found, though there was a small difference in the constants in the equation given by Princen and those found here. The agreement suggested that the emulsions were deforming above a critical volume fraction and that the rheological properties were dominated by the dilation of the interface during shear. Microelectrophoresis measurements showed that the addition of the surfactant conferred a charge onto the PVA stabilized droplets as a result of the formation of the polyelectrolyte complex. The NaDBS was found to reduce the long-term stability of the emulsions compared to emulsions containing PVA alone.     

New fluorescence method for the determination of the critical micelle concentration by photosensitive monoazacryptand derivatives

A novel fluorescence method for the determination of the critical micelle concentration (cmc) is reported. The cmc values of nonionic and anionic surfactants were evaluated utilizing a photosensitive monoazacryptand-Ba2+ complex, whose fluorescence intensity is sensitively changed by environmental conditions based on the photoinduced electron transfer (PET) mechanism as a fluorescent probe (PET method). Based on a comparison of the cmc values obtained by the PET method versus those obtained by conventional fluorescence-based methods as well as the values reported in the literature, one can conclude that the PET method is useful for the cmc determination. In particular, the PET method was more effective for the cmc determination of nonionic surfactants with very low cmc values (< 10(-5) M) than any other fluorescence-based method. In the cases of anionic surfactants, the PET method revealed the formation of the premicellar aggregates comprised of surfactant molecules and fluorescent probes below the cmc. Moreover, the hydrophobicity around the monoazacryptand-Ba2+ complex incorporated into various nonionic surfactant micelles was evaluated by this PET method.     

High-nuclearity Pt-Tl-Fe complexes: structural, electrochemistry, and spectroelectrochemistry studies

A series of heteropolynuclear Pt-Tl-Fe complexes have been synthesized and structurally characterized. The final structures strongly depend on the geometry of the precursor and the Pt/Tl ratio used. Thus, the anionic heteroleptic cis-configured [cis-Pt(C(6)F(5))(2)(C≡CFc)(2)](2-) and [Pt(bzq)(C≡CFc)(2)](-) (Fc = ferrocenyl) complexes react with Tl(+) to form discrete octanuclear (PPh(3)Me)(2)[{trans,cis,cis-PtTl(C(6)F(5))(2)(C≡CFc)(2)}(2)] (1), [PtTl(bzq)(C≡CFc)(2)](2) (5; bzq = benzoquinolate), and decanuclear [trans,cis,cis-PtTl(2)(C(6)F(5))(2)(C≡CFc)(2)](2) (3) derivatives, stabilized by both Pt(II)···Tl(I) and Tl(I)···η(2)(alkynyl) bonds. By contrast, Q(2)[trans-Pt(C(6)F(5))(2)(C≡CFc)(2)] (Q = NBu(4)) reacts with Tl(+) to give the one-dimensional (1-D) anionic [(NBu(4)){trans,trans,trans-PtTl(C(6)F(5))(2)(C≡CFc)(2)}](n) (2) and neutral [trans,trans,trans-PtTl(2)(C(6)F(5))(2)(C≡CFc)(2)](n) (4) polymeric chains based on [PtFc(2)](2-) platinate fragments and Tl(+) (2) or [Tl···Tl](2+) (4) units, respectively, connected by Pt(II)···Tl(I) and secondary weak κ-η(1) (2) or η(2) (4) alkynyl···Tl(I) bonding. The formation of 1-4 is reversible, and thus treatment of neutral 3 and 4 with PPh(3)MeBr causes the precipitation of TlBr, returning toward the formation of the anionic 1 and 2' (Q = PPh(3)Me). Two slightly different pseudopolymorphs were found for 2', depending on the crystallization solvent. Finally, the reaction of the homoleptic [Pt(C≡CFc)(4)](2-) with 2 equiv of Tl(+) affords the tetradecanuclear sandwich type complex [Pt(2)Tl(4)(C≡CFc)(8)] (6). Electrochemical, spectroelectrochemical, and theoretical studies have been carried out to elucidate the effect produced by the interaction of the Tl(+) with the Pt-C≡CFc fragments. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) of 1-5 reveal that, in general, neutralization of the anionic fragments increases the stability of the fully oxidized species and gives higher E(1/2) (Fc) values than those observed in their precursors, increasing with the number of Pt-Tl bonding interactions. However, the electronic communication between Fc groups is reduced or even lost upon Tl(+) coordination, as confirmed by electrochemical (CVs and DPVs voltammograms, 1-5) and spectroelectrochemical (UV-vis-NIR, 2-4) studies. Complexes 2 and 4 still display some electronic interaction between the Fc groups, supported by the presence of an IVCT band in their UV-vis-NIR spectra of oxidized species and additional comparative DFT calculations with the precursor [trans-Pt(C(6)F(5))(2)(C≡CFc)(2)](2-) and complex 3.     

MALDI linear-field reflectron TOF post-source decay analysis of underivatized oligosaccharides: Determination of glycosidic linkages and anomeric configurations using anion attachment

Six different anionic species (fluoride, chloride, bromide, iodide, nitrate, and acetate) are tested for their abilities to form anionic adducts with neutral oligosaccharides that are detectable by MALDI-TOF mass spectrometry. Fluoride and acetate cannot form anionic adducts with the oligosaccharides in significant yields. However, bromide, iodide, and nitrate anionic adducts consistently appear in higher abundances relative to [M - H](-), just like the highly stable chloride adducts. Post-source decay (PSD) decompositions of Br(-), I(-), and NO(3)(-) adducts of oligosaccharides provide no structural information, i.e., they yield the respective anions as the main product ions. However, determination of linkage types is achieved by analysis of structurally-informative diagnostic peaks offered by negative ion PSD spectra of chloride adducts of oligosaccharides, whereas the relative peak intensities of pairs of diagnostic fragment ions allow differentiation of anomeric configurations of glycosidic bonds. Thus, simultaneous identification of the linkage types and anomeric configurations of glycosidic bonds is achieved. Our data indicate that negative ion PSD fragmentation patterns of chloride adducts of oligosaccharides are mainly determined by the linkage types. Correlation may exist between the linkage positions and fragmentation mechanisms and/or steric requirements for both cross-ring and glycosidic bond fragmentations. PSD of the chloride adducts of saccharides containing a terminal Glcalpha1-2Fru linkage also yields chlorine-containing fragment ions which appear to be specifically diagnostic for a fructose linked at the 2-position on the reducing end. This also allows differentiation from saccharides with a 1-1 linked pyranose on the same position.     

Application of the zeta potential measurements to explanation of colloidal Cr2O3 stability mechanism in the presence of the ionic polyamino acids

In the presented paper, the influence of the molecular weight and the type of polyamino acid functional groups on the electrokinetic properties and the stability of chromium (III) oxide suspension were examined. Analysis of the data obtained from the adsorption, potentiometric titration, zeta potential, and stability measurements allows to propose stabilization or destabilization mechanism of the studied systems. In the studies, there were used polyamino acids with different ionic characters: anionic polyaspartic acid and cationic polylysine. The measurements showed that the zeta potential depends on the concentration and molecular weight of the applied polymer. Stability of the chromium (III) oxide suspensions in the presence of ionic polyamino acids increases compared to the results obtained in the absence of polymers. The exception is LYS 4,900 at pH?=?10. Under these conditions, the decrease in stability is observed due to formation of polymer bridges between the polymer chains adsorbed on different colloidal particles. Determination of the stabilization/destabilization mechanism of the polyamino acid/chromium (III) oxide system and examination of the effects of polymer molecular weight on the stabilization properties can contribute to a wider use of this group of compounds as potential stabilizers or flocculants in many industrial suspensions.