Dextran-coated CdSe quantum dots for the optical detection of monosaccharides by resonance light-scattering technique

A resonance light-scattering (RLS) detection method for saccharides was developed using dextran-coated CdSe quantum dots (dextran-CdSe-QDs) optical probes. The dextran-CdSe-QDs can be aggregated with concanavalin A (Con A), and the change in RLS intensity is used to monitor the extent of aggregation. The presence of glucose competitively binds with Con A, dissociating the Con A/dextran-CdSe-QDs complexes, affording the RLS intensity change and hence determining glucose concentrations in the range from a few to about 90 mM. Transmission electron microscopy was used to investigate the competitive interaction between glucose and dextran-CdSe-QDs with Con A. The competitive strategy could also be used to detect similar types of saccharides and the affinities of various monosaccharides for Con A increased in the order galactose?glucose < fructose < mannose. The proposed method was successfully applied to determine glucose in the human serum.

A resonance light-scattering (RLS) detection method for saccharides was developed using dextran-coated CdSe quantum dots (dextran-CdSe-QDs) optical probes. The dextran-CdSe-QDs were coupled to concanavalin A (Con A) to facilitate the aggregation of nanoparticles. The presence of glucose competitively binds with Con A, dissociating the Con A/dextran-CdSe-QDs complexes affording the RLS intensity change and hence determining glucose in the range from a few millimolar to about 90 mM. The proposed method was applied to the determination of glucose in human serum samples with satisfactory results.

     

Photopolymerization of methyl methacrylate and some other vinyl monomers with the use of chlorine as photoinitiator

Low concentrations (0.001–0.03M) of chlorine easily induce photopolymerization of MMA at 40°C. Kinetic data indicate that polymerization follows a radical mechanism involving complexation of monomer by the initiator and initiation takes place through radical generation during photodecomposition of the initiator-monomer complex. Termination appears to take place bimolecularly. The k_p²/k_t value for MMA polymerization at 40°C was found to be 0.83 × 10^?2. Rates of chlorine-initiated photopolymerization were found to decrease in the order MMA, EMA ? VA, Sty > MA.     

STUDY OF THE PHOTOINITIATED CATIONIC POLYMERIZATION OF 3,4-EPOXY-1-BUTENE

The photopolymerization of 3,4-epoxy-1-butene (1) was investigated using Fourier transform real-time infrared spectroscopy (FT-RTIR). The effects of photoinitiator structure and concentration and light intensity on the photopolymerization were investigated. Compared to related epoxide monomers, 1 was shown to be more reactive and this was ascribed to stabilization of the growing cationic chain end by the double bond during the ring-opening polymerization. Epoxide 1 was also shown to be useful as a reactive diluent in the photopolymerization of multifunctional epoxides and was observed to accelerate the polymerization of less reactive epoxy monomers.     

Photopolymerization of methyl methacrylate with the use of iodine as the photoinitiator

Kinetics of photopolymerization of MMA at 40°C with the use of iodine as the photoinitiator was studied. At low range of iodine concentration (< 0.0004M), the rate of polymerization was proportional to square root of iodine concentration and the monomer exponent was 2.5, while at a higher range of iodine concentration, (0.0005–0.002M) the initiator exponent and monomer exponent were zero and 3.6–3.8 (i.e., close to 4), respectively. The chain-transfer constant of iodine at 40°C was found to be 6.0. Polymerization was found to be largely inhibited in the presence of relatively high concentrations of iodine (> 0.005M) and also in presence of hydroquinone. Kinetic and other data indicate a radical mechanism of polymerization involving complexation of monomer molecules with iodine prior to radical generation, and termination is believed to take place bimolecularly at low iodine concentrations and unimolecularly, involving reaction with iodine, at high iodine concentrations (initiator termination).     

Structure of cholesteric gels and their electrically induced light scattering and colour changes

Abstract

Networks with a helical structure containing large amounts of low mass liquid crystal molecules (gels) were produced by photopolymerization of a nematic diacrylate in the presence of low mass cholesteric mixtures. Prior to polymerization the systems selectively reflected a band of circularly polarized light. Upon polymerization, the gels obtained gave rise to two reflection peaks which were subsequently associated with polymer rich and polymer poor phases. At high network concentrations (>40 per cent w/w) one of the peaks did not appear, indicating that the behaviour of the molecules which were not chemically attached to the network was totally dominated by the network. From the gap required for the suppression of the rotation of the director, it was estimated that the molecules, which were not crosslinked, were confined in layers thinner than 85 nm. The gels were very transparent and did not give rise to excess light scattering as compared with the monomeric state. Upon application of an electric field, colour changes as well as light scattering were induced. These efffects were found to be highly dependent on the state of the polarization of the light as well as the kind of field applied. The response times were very short and they depended strongly on the structure of the network.     

An extremely sensitive monoboronic acid based fluorescent sensor for glucose

An extremely sensitive monoboronic acid based fluorescent sensor for glucose was developed. This was carried out by assembling a fluorescent monoboronic acid, 3-aminophenylboronic acid (PBA) indirectly onto gold surface via its electrostatic interaction with cysteine (Cys) that was directly assembled on the gold surface. The formation of self-assembled bilayers (SAB) was confirmed and primarily characterized by cyclic voltammetry and X-ray photoelectron spectra (XPS). The SAB containing PBA was found fluorescent and its fluorescence showed an extremely high sensitivity to the presence of glucose and other monosaccharides such as galactose and fructose with quenching constants at 10⁸ M⁻¹ order of magnitude compared to those at 10² M⁻¹ in bulk solutions. The quenching constants were found to vary in the order of that is different from that in bulk solution which shows the highest binding affinity toward d-fructose and very low sensitivity toward glucose. The reported monoboronic acid based SAB fluorescent sensor showed the highest sensitivity towards glucose with the capacity of detecting saccharides of concentration down to nanomolar level. It was also demonstrated that the fluorescence from PBA/Cys/Au can be easily recovered after each measurement event and therefore also represents a new reusable method for immobilizing reagent in fabricating chemosensors.     

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.     

RADICAL POLYMERIZATION OF METHYL METHACRYLATE WITH DIPHENYL DISELENIDE UNDER THERMAL OR PHOTOIRRADIATIONAL CONDITIONS

Polymerization of methyl methacrylate (MMA) with diphenyl diselenide (DPDSE) in the presence of AIBN at 60°C was investigated. DPDSE was worked as a chain transfer agent (CTA). The chain transfer constant (C_tr) of DPDSE for MMA was estimated to be 1.43. On the other hand, DPDSE was functioned as a photoiniferter for the photopolymerization of MMA. In a limited range of conversion, both the polymer yield and number average of molecular weight ([Mbar]_n) increased with the reaction time, and the [Mbar]_n linearly increased with the yield. The terminal structure of poly(MMA) was investigated by the ⁷⁷Se NMR spectrum based on Methyl α-phenylseleno isobutylate (MSEPI) as model compound of the ω-chain end of poly(MMA). Further, photopolymerization of poly (MMA) containing phenylseleno group at ω-chain end as a polymeric photoiniferter with MMA effectively afforded a poly (MMA) having higher molecular weight.     

Combined Liquid Chromatography-Mas Spectrometry for Microscale Structural Studies of Carbohydrates

Abstract

Combined HPLC-thermospray was spectrometry of mono-and disaccharides, 1-0-methylglycosides and 0-permethy mono - through tetrasaccharicdes has been studied to asess the potential role of thermospray ionization for microscale structural studies of saccharides and glycoconjugates, and for high sensitivity detection of liquid chromatographic effluents. Using NH₄CO₂H as evaluant for reversed-phase HPLC, abundant MNH₄ ⁴ ions are formed form monosaccharides and mono-and per-methylated saccharides, and are suitable formonitoring sub-nanogram constituents in HPLC effluents. Detection of 100 pg (0.5pmole) of 1-0-methylhexopy-ranosides with signal/noise> 10 is demonstrated.     

Development and Optimisation of HILIC-LC-MS Method for Determination of Carbohydrates in Fermentation Samples

Saccharides are the most common carbon source for Streptococcus thermophilus, which is a widely used bacterium in the production of fermented dairy products. The performance of the strain is influenced by the consumption of different saccharides during fermentation. Therefore, a precise measurement of the concentrations of saccharides in the fermentation media is essential. An 18-min long method with limits of quantitation in the range of 0.159–0.704 mg/L and with ¹³C labelled internal standards employing hydrophilic interaction chromatography coupled to mass spectrometric detection-(HILIC-LC-MS) allowed for simultaneous quantification of five saccharides: fructose, glucose, galactose, sucrose, and lactose in the fermentation samples. The method included a four-step sample preparation protocol, which could be easily applied to high-throughput analysis. The developed method was validated and applied to the fermentation samples produced by Streptococcus thermophilus.     

Synthesis and Photoinitiated Cationic Polymerization of Epoxidized Castor Oil and Its Derivatives

ABSTRACT

In this communication we describe the synthesis of epoxidized castor oil (ECO) as an interesting and inexpensive biorenewable monomer by an efficient and low cost epoxidation process. Also described are studies of the photoinitiated cationic polymerization of ECO using diaryliodonium salt photoinitiators. The influence of the structure and the concentration of the photoinitiator on the polymerization are reported. The ability of photosensitizers to accelerate the photopolymerization was also studied. Studies comparing the photopolymerization behavior of ECO with other commercially available epoxidized linseed and soybean oils and with other types of synthetic epoxy monomers were conducted. The excellent reactivity of ECO can be ascribed to the presence of both epoxy and hydroxyl groups in the molecule which permits this material to polymerize mainly by an activated monomer mechanism.

     

Photopolymerization of methyl methacrylate and other vinyl monomers with the use of N-bromosuccinimide as photoinitiator

Polymerization of MMA was done in the presence of visible light (440 nm) with the use of N-bromosuccinimide (NBS) as the photoinitiator. The initiator exponent and intensity exponent were 0.5, and the monomer exponent was found to be unity. The polymerization was inhibited in the presence of hydroquinone. The average k_p²/k_t for this photopolymerization system was found to be 0.296 × 10^?2 and the activation energy of photopolymerization was 4.67 kcal/mole. Kinetic and other evidence indicate that the overall polymerization takes place by a radical mechanism. With NBS as the photoinitiator, the order of polymerizability at 40°C was MMA, EMA ? MA ? VA, and styrene could not be polymerized under similar conditions.     

Comparative studies of the effects of dimethylaniline,methylaniline and aniline in the benzophenonesensitized photopolymerization of methyl methacrylate in bulk and in solution

Comparative studies of the photopolymerization of methyl methacrylate (MMA) at 35 using benzophenone (BP) as sensitizer in combination with dimethylaniline (DMA), methylaniline (MA) or aniline (A) are reported. In each case the initiator exponent is appreciably less than 0.5. Considering rates of polymerization, inhibition periods and apparent activation energy, the relative effectiveness of the amines in photopolymerization is DMA > MA > A. Solvent effects are also different in the 3 amine systems. In each case photoreduction of BP by the amine, through formation of the BP'-amine exciplex, leads to generation of an amine radical and the semipinacol radical, the former acting as an initiator and the latter as a terminator (primary radical termination). Kinetic analysis indicates that the rate constants of initiation, k_c for the amine radicals lie in the order DMA radical > MA radical > A radical.     

Thermolysis of furoxans annulated with five-membered carbocycles in the presence of dipolarophiles

The conditions for the thermolysis of furoxans annulated with differently strained five-membered carbocycles (cyclopentafuroxan 1, norbornenofuroxan 2, and acenaphthofuroxan 3) to bis(nitrile oxides) in the presence of various dipolarophiles (diethyl acetylenedicarboxylate, benzoylformonitrile, and ethoxycarbonylformonitrile) were optimized. It was found that the reactivities of the above furoxans as sources of bis(nitrile oxides) decrease in the order 2 > 1 > 3. Among the furoxans studied, only norbornenofuroxan 2 can be recommended as a possible cross-linking reagent for polymers. The formation of di-N-oxides of 3,4-bis(cyanopropyl)-, 3,4-bis(cyanocyclopentyl)-, and 3,4-bis(cyanonaphthyl)furoxans was detected. They resulted from intermolecular cyclodimerization of bis(nitrile oxides) initially formed in the thermolysis of furoxans 1–3. Dedicated to Academician V. A. Tartakovsky on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1521–1528, August, 2007.     

Abilities of 1‐(9‐anthrylmethyloxy)‐2‐pyridone and related compounds to initiate radical and cationic photopolymerizations

This study explored the abilities of 1‐(9‐anthrylmethyloxy)‐2‐pyridone and related compounds, which absorb long‐wavelength light (>350 nm), to photochemically initiate radical and cationic polymerizations. It was found that the irradiation of the title compounds initiates the radical polymerization of styrene whereas the cationic polymerization of oxetane proceeds in the presence of these photoinitiators to a negligible extent. The behavior of 9‐anthrylmethyloxyl and amidyl radicals in the photopolymerization process of styrene was discussed based on ¹H NMR, UV, and fluorescence spectral data. In addition, the photoinitiation ability of the anthrylmethyloxyl end group was also investigated by using its model compound. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2859–2865, 2004     

New supramolecular ferrocenyl amides: synthesis,characterization, and preliminary DNA-binding studies

Three ferrocenyl amides have been synthesized and characterized by analytical techniques. Based on single-crystal X-ray analysis, a supramolecular structure was attributed to 1 owing to the presence of intermolecular non-covalent interactions. UV-Visible spectroscopy, viscometry, and dynamic laser light scattering was used to assess the mode of interaction and binding of these complexes with DNA, which varied in the sequence 1?>?2?>?3. The binding is presumably due to the ability of these complexes to form secondary non-covalent interactions with DNA bases. Complex-DNA adduct formation depends on the nature of R of the amide.     

Regiospecific Anomerisation of Acylated Glycosyl Azides and Benzoylated Disaccharides by Using TiCl4

Chelation induced anomerisation is promoted when Lewis acids, such as TiCl₄ or SnCl₄, coordinate to the pyranose ring oxygen atom and another site, giving rise to endocyclic cleavage and isomerisation to the more stable anomer. In this research regiospecific site‐directed anomerisation is demonstrated. TiCl₄ (2.5 equiv) was employed to induce anomerisation of 15 glycosyl azide and disaccharide substrates of low reactivity, and high yields (>75 %) and stereoselectivies (α/β>9:1) were achieved. The examples included glucopyranuronate, galactopyranuronate and mannopyranuronate as well as N‐acetylated glucopyranuronate and galactopyranuronate derivatives. A disaccharide with the α1→4 linkage found in polygalacturonan was included. The use of benzoylated saccharides was found to be important in disaccharide anomerisation as attempts to isomerise related acetyl protected and 2,3‐carbonate protected derivatives were not successful.     

Characterization of Pectins Isolated from Mongolian Plants

Abstract

Pectic polysaccharides (HP, RP) were extracted from Mongolia hawthorn berries and from rhubarb stalks by hot aqueous oxalic acid treatment. Both polysaccharides contained approximately 78% of galacturonate. HP displayed a low degree of esterification (DE) and arabinose/galactose molar ratio 1.7:1. RP was higher in DE and contained these sugars in a molar ratio 0.5:1. Rhamnose, fucose, xylose, glucose, mannose, 2-O-methylxylose, and 2-O-methylfucose were found in lower amounts. Results from ¹³C NMR spectroscopy and methylation analysis indicated the presence of branched arabinans, (1?>4)-and (1?>3,6)-linked galactans and hemicelluloses of the xylan and glucan types. The pectins differed in theirmolecular properties. HP exhibited a low molecular weight (M _W = 45,000), whereas RP had a broad M _W-distribution with M _W= 360,000. Independently of these differences, the binding capacity of both pectins towards divalent cations was influenced by the DE only and increased in the order: Ca²⁺ < Cd²⁺ < Pb²⁺ < Cu²⁺.     

A Rapid Determination of Sucrose and Fructose in Biological Samples by Video Densitometry

Abstract

Simple, rapid methods which have been developed for the separation and quantification of sucrose and fructose in biological materials are presented. The method uses thin layer chromatography. The saccharides are stained with thymol-reagent on the chromatograms. The quantitative determination of red spots of saccharides are performed with a Telechrom video densitometer. The density of the spots are directly proportional to the concentration of the saccharides in a certain range. The saccharides content of the sample may be determined with a standard curve on the same chromatograms. The reproducibility of the methods are characterized by a cofficient of variation of about 4–5%     

Vinyl polymerization. 275. Polymerization of vinyl monomers photosensitized by tetramethyltetrazene

A study of the photopolymerization of vinyl monomers in the presence of tetramethyltetrazene (TMT) was made. TMT was found to act as an effective sensitizer. In the photopolymerization of vinyl monomers such as methyl methacrylate or styrene the rate of polymerization was expressed by the equation: R_p = k[TMT]^1/2[monomer]. The chain-transfer constant of TMT under ultraviolet irradiation was estimated to be 3.8 × 10^?2 for the above monomers. A linear correlation was found to exist between the reactivity of dimethylamino radical toward the vinyl monomers and e values for the corresponding monomers.