DP Values Research Articles

Collective effects in molecular motions in liquids

The collective effects in water were studied by investigating the spatial distribution of long-living hydrogen bonds and revealing correlations in molecular motions. The existence of extended clusters, whose molecules are linked by long-living bonds, suggests the existence of correlations between the motions of its molecules. The mean scalar products of the shift vectors of two molecules were calculated using the narrow ranges (DP) of intermolecular distances in the initial configuration. The average correlation coefficients (the cosines of angles between the shift vectors of two molecules) were also calculated. The DP and cosine values were averaged over all pairs with this intermolecular distance. The DP values increased with time and formed a plateau after a few hundred picoseconds. The plateau was attributed to the existence of molecular vortices that cover large (several nanometers) volumes of the liquid. The conclusion was drawn that hydrophobic species, for example, noble gas atoms incorporated in the water net could be involved in collective motions.

Analytical method for the determination of halogenated norbornene flame retardants in environmental and biota matrices by gas chromatography coupled to tandem mass spectrometry

A new methodology for the analysis of Dechlorane Plus and related compounds (DPMA, Dec 602, Dec 603 and Dec 604) by gas chromatography coupled to negative chemical ionization tandem mass spectrometry (GC–NCI–MS–MS) was developed for three different matrices, including environmental (sediment and sludge) and biota (fish) samples. Analytical parameters such as linearity, repeatability and reproducibility, recoveries, limits of detection and limits of quantification were evaluated, showing satisfactory values for the developed methodology. Moreover, a comparison with the analysis by GC–NCI–MS was carried out. Method limits of detection (MDLs), ranging between 0.12 and 1.26pg/gdw, 1.16–2.90pg/gdw and 2.30–21.1pg/glw for sediment, sludge and fish respectively, were much better than those obtained by GC–MS, with improvement factor up to 320. The applicability of the developed methodology was demonstrated by the analysis of real samples collected in a non-producing area, the Ebro river basin (Spain). DP values were up to 1.61ng/gdw, 18.8ng/gdw and 2.24ng/glw for sediment, sludge and fish samples, respectively.

High Hydrostatic Pressure Effect on Natural Microflora, Saccharomyces cerevisiae, Escherichia coli, and Listeria Innocua in Navel Orange Juice

An isostatic pressure system was used to treat fresh-squeezed orange juice inoculated with Saccharomyces cerevisiae, Escherichia coli, and Listeria innocua for selected times (come-up time, CUT, to 15 min plus CUT) and pressures (103 - 414 MPa). Specific agars, for each type of microorganism, were used for pour plating to count survivors after pressure treatment. Decimal reduction time values (Dp) were calculated from the first order kinetics modeling for S. cerevisiae (103-241 MPa), E. coli (103-241 MPa), and L. innocua (103-345 MPa) survivors in juice. Dp values of 6.1–52.1, 0.6–14.9, and 4.8–357.1 min were obtained for S. cerevisiae, E. coli, and L. innocua, respectively. zp values of 147.1, 92.6, and 59.2 MPa were calculated for these microorganisms, respectively. The come-up time (CUT, time required to reach the processing pressure), had an important effect on the microbial reduction. The initial counts of 5.3 x 105, 1.2 x 107, and 2.6 x 107 CFU/mL were reduced by 30, 88, and 27 percent for S. cerevisiae, E. coli, and L. innocua, respectively, at 241 MPa, after 1.2, 3.0 and 1.8 min of processing, respectively. However, no survivors were observed (<10 CFU>/mL) for the three types of microorganisms when processing at 241 MPa for times longer than 3 min or pressures higher than 241 MPa.

Hydrocarbonsadsorption on templated mesoporous materials: effect of the pore size, geometry and surface chemistry

Adsorption–desorption isotherms of aromatic (mesitylene and toluene) and aliphatic (methylcyclohexane, neopentane and n-pentane) hydrocarbons were measured on ordered mesoporous materials, including MCM-41, MCM-48, SBA-15, SBA-16 and MCF silicas, a periodic mesoporous organosilica and a CMK-3 carbon, in order to evaluate the effect of the adsorbent characteristics on the organic compounds adsorption behaviour. A clear separation between aliphatic and aromatic hydrocarbons is observed at low p/po for the materials having pores accessible by narrow openings. The presence of narrow pore openings causes an increase in the volume adsorbed of mesitylene, toluene, methylcyclohexane and n-pentane prior to capillary condensation that does not occur for neopentane. The increase of the hydrophobicity and change of the surface structure, resulting from the incorporation of chloromethyl groups on the silica walls, causes the p/po at which the aromatic hydrocarbons condense to increase while the introduction of aromatic rings into the pore walls has a less significant effect on the condensation pressures. However, at low p/po, all the hydrocarbons have higher affinity for the periodic mesoporous organosilica surface than for the pure silica or silica with chloromethyl groups surfaces, while these lower the affinity of the aromatic hydrocarbons. Good estimates of pore size (Dp) are obtained using the classical Kelvin equation from the mesitylene, toluene and methylcyclohexane adsorption data, for spheroidal pores of at least ∼20 nm. With n-pentane this occurs for pores of ∼30 nm while neopentane underestimates Dp values even for pores as large as these, although to a lesser extent than nitrogen.

Chain length dependence of the helix orientation in Langmuir–Blodgett monolayers of α-helical diblock copolypeptides

The effect of chain length on the helix orientation of α-helical diblock copolypeptides in Langmuir and Langmuir–Blodgett monolayers is reported for the first time. Amphiphilic diblock copolypeptides (PLGA-b-PMLGSLGs) of poly(α-L-glutamic acid) (PLGA) and poly(γ-methyl-L-glutamate-ran-γ-stearyl-L-glutamate) with 30 mol% of stearyl substituents (PMLGSLG) of various block lengths were studied. The tilt angle between the helices and the substrate-normal decreases upon increasing the transfer pressure coincident with “double brush” formation. The hydrophobic block length strongly affects the maximum surface chain density and thereby the helix orientation of the diblock copolypeptides. Increasing the degree of polymerization of the hydrophobic block (DPPMLGSLG) results in an increase in the helix tilt angle tentatively attributed to the off-axis interactions of the unscreened peptide dipoles between the parallel aligned α-helices. In those cases where the alkyl side chains surround the PMLGSLG helices, the smallest helix tilt angle of 29° for the PMLGSLG block and 67° for the PLGA block were obtained for the diblock copolymer of DPPLGA 37 and DPPMLGSLG 24. For smaller DP values of the hydrophobic block, in particular the diblock copolymer having DPPMLGSLG 11, the long alkyl side chains are partially expelled from the brush layer and the α-helices of the PMLGSLG block are oriented nearly perpendicular to the interface.

Redução da pressão arterial e do duplo produto de repouso após treinamento resistido em idosas hipertensas

Due to the existing controversies in literature about the potential benefits of resistance exercise training (RT) on arterial blood pressure (BP) at rest, and the lack of studies conducted with elderly hypertensive individuals, RT is seldom recommended as a non-pharmacological treatment for arterial hypertension. To verify the effect of progressive RT on BP, HR, and RPP in elderly women with controlled hypertension. 20 elderly women (66.8 +/- 5.6 years of age), with a sedentary lifestyle, monitored with anti-hypertensive medication, participated in a 12-week RT program (resistance training group - RTG). Twenty-six elderly women (65.3 +/- 3.4 years of age) with controlled hypertension did not engage in physical exercise during the study period, and composed the control group. After RT, there was a significant reduction in SBP, MBP, and DP values at rest. No significant drops in DBP and HR values at rest were observed after RT in both groups. The reduction in the RTG was 10.5 mmHg, 6.2 mmHg, and 2218.6 mmHg x bpm for SBP, MBP, and RPP, respectively. Progressive RT reduced SBP, MBP, and RPP values at rest of hypertensive elderly women who were on anti-hypertensive treatment.

Surface topography of zirconia implants does not alter action potentials of isolated rat sciatic nerves

The purpose of this study was to explore the effects of airborne-particle abrasion and selective infiltration etching of a yttrium-partially stabilized tetragonal zirconia polycrystal (Y-TZP) implant surfaces on nerve conduction. Particle-abraded Y-TZP (P/Y-TZP), selective infiltration etched Y-TZP (SIE/Y-TZP), and commercially pure titanium (CP-Ti) were used in the study (n = 5).The compound action potentials of the right and left sciatic nerves of eight sacrificed rats were quantified at the in vitro level. The implants were brought into intimate contact with the nerves and the time required for initiation of compound action potentials (TcAP), depolarization (Dp), repolarization (Rp), and amplitude of evoked compound action potentials (cAPs) were recorded before and after contact with the implants. The difference in cAPs between the basal response and after contact with CP-Ti implant was significant (p < 0.05). Time-dependent changes in cAPs of P/Y-TZP and SIE/Y-TZP groups and their basal nerve responses were similar (p > 0.05). Within- and between-subject comparisons revealed that TcAP, Dp, and Rp values for all groups were similar (p > 0.05). Particle-abraded and selective infiltration-etched zirconia implant surfaces do not alter nerve conduction beyond physiologic limits.

Rejection of pharmaceuticals and personal care products (PPCPs) and endocrine disrupting chemicals (EDCs) by low pressure reverse osmosis membranes

This paper aims to elucidate retention characteristics of some pharmaceuticals and personal care products (PPCPs), and endocrine disrupting chemicals (EDCs), by two polyamide low pressure reverse osmosis (LPRO) membranes. Feed solution pH did not have an influence on rejections of undissociated solutes, which was most likely governed by adsorption, size exclusion and diffusion simultaneously. Size exclusion was presumably dominant, especially with tight membranes (UTC-70U). Rejections of the solutes with low dipole moment (<1.0 debye) decreased with increasing octanol-water partition coefficient (K(ow)). The solutes with large K(ow) values were most likely adsorbed on membrane and subsequently passed through it resulting in larger diffusion coefficient (D(p)). The rejections decreased with increasing D(p) values irrespective of their dipole moments. Rejections of solutes with comparatively larger dipole moments might be dominated by diffusion and/or convection rather than their hydrophobicity. However, rejections of solutes with hydroxyl and carboxyl functional groups by UTC-60 increased with solution pH. More than 80% rejections were obtained for degree of dissociation (alpha)>0.5. Electrostatic repulsion played a key role for rejection of dissociated solutes, especially by loose LPRO membranes. Therefore, assessing the dissociation degree at desired pH values can be a key step to obtain an insight of rejection mechanisms by polyamide membranes.

Temperature-assisted high hydrostatic pressure inactivation of Staphylococcus aureus in a ham model system: evaluation in selective and nonselective medium

The purpose of this study was to investigate the inactivation kinetics of Staphylococcus aureus in a ham model system by high hydrostatic pressure at ambient (25 degrees C) and selected temperatures (45, 55 degrees C). Selective [Baird Parker (BP) agar] and nonselective [brain heart infusion (BHI) agar] growth media were used for enumeration in order to count viable and sublethally injured cells. The micro-organism was exposed to a range of pressures (450, 500, 550, 600 MPa) at ambient temperature (25 degrees C) for up to 45 min. Additionally, the behaviour of the micro-organism was evaluated at mild temperatures in combination with high pressure treatment, namely: (i) 350, 400 and 450 MPa at 45 degrees C; and (ii) 350 and 400 MPa at 55 degrees C, for up to 12 min. Inactivation kinetics were calculated in terms of D(p) and z(p) values. Survival curves of S. aureus at ambient temperature were mostly linear, whereas when temperature was applied, tailing was observed in most survival curves. The estimated D(p) values and therefore the number of surviving cells, were substantially higher on the selective BP agar in the whole range of pressures applied, indicating that S. aureus showed greater recovery in the selective BP agar than the nonselective BHI agar. Samples pressurized at ambient temperature needed higher pressures (over 500 MPa) to achieve a reduction of the population of the pathogen more than 5 log CFU ml(-1). The same level of inactivation was achieved at lower pressure levels when mild heating was simultaneously applied. Indeed, more than 6 log CFU ml(-1) reductions were obtained at 400 MPa and 55 degrees C within the first 7 min of the process in BHI medium. Elevated temperatures allowed lower pressure levels and shorter processing times of pathogen inactivation than at room temperature. Greater recovery of the pathogen was observed in the selective (BP agar) medium, regardless of pressure and temperature applied. The obtained kinetics could be employed by the industry in selecting optimum pressure/temperature processing conditions. Attention must be given to the selection of the enumeration medium, as the use of an inappropriate medium would lead to underestimation of the surviving cells, thus imposing a risk in the microbiological safety of the product.

A comparison of assisted reproductive technologies and outcomes between Europe and the United States

A comparison of assisted reproductive technologies and outcomes between Europe and the United States

Upgrading of paper-grade pulps to dissolving pulps by nitren extraction: properties of nitren extracted xylans in comparison to NaOH and KOH extracted xylans

Different paper-grade pulps were extracted with nitren, NaOH and KOH in order to produce dissolving pulps and polymeric xylan. The yield and structure of the isolated nitren and alkali xylans were investigated by carbohydrate analysis, HPSEC and 1H-NMR spectroscopy. In addition the effect of washing stages on the residual nickel content of the nitren xylans was investigated. By nitren extraction up to 98% of the xylan could be extracted out of the fully bleached eucalyptus and birch kraft pulps. The nitren extracted kraft xylans had DP values between 95 (birch) and 111 (eucalyptus). At most 5 mol% of the xylose units were substituted. In the case of pulps with low mannan content only marginally differences between the nitren and alkaline (KOH, NaOH) extractions occurred. The extraction of the relatively “mannnan rich” pulps of this study like softwood kraft and beech sulfite pulps revealed that the dissolution effect regarding mannans increased in the following order: nitren < KOH < NaOH. In general the nitren extractions required a lower chemical charge compared to the alkaline extractions, in order to yield similar amounts of xylans. On the other side the necessity of an effective nickel removal is a disadvantage of the nitren extractions.

Limitation observed in the application of the three dimensional solubility parameters to the coating formulation of poly (3-hydroxybutyrate-hydroxyvalerate) systems

Purpose: Poly (3-hydroxybutyrate-hydroxyvalerate) displayed high dipole-dipole interaction, a high hydrogen bonding but low polar interaction, and was therefore expected to be miscible with solvents/plasticizers that exhibit similar pattern of cohesive interaction. To determine the applicability, or otherwise of the theory of the three dimensional solubility parameters to the formulation of poly (3-hydroxybutyrate-hydroxyvalerate) polymeric coating system, and hence identify any limitation in the application of the theory. This aspect was investigated in the study. Method: The structural group contribution method was employed to compute the partial and total solubility parameters of the compounds – the biopol polymer, a series of organic solvents and plasticizers. The computed partial solubility parameters included: dipole-dipole (dd), polar (dp) and hydrogen bonding (dh). Following a standard procedure in the literatures, the dd and dp values were combined to form a composite solubility parameter, dv: where dv = &#8730 &#948d 2+&#948p 2. A plot of dh versus dv gave the energy maps, which depicted the energy levels of the various compounds and from which the miscibility of the compounds were predicted. The closer the position of the solvent or plasticizer to the polymer in the map, the greater, the probability of mixing. Cast films of the various polymeric formulations were made and examined for homogeneity by scanning electron microscopy. Results: It was possible to select suitable plasticizers that were miscible with the polymer by applying theory of solubility parameters. The prediction for the solvents was, however, erroneous and this may be attributable to the inability of the dv parameter to clearly reflect the differences between the dd and dp interactions of the polymer on the one hand and those of the various solvents in all situations on the other hand. This means that in certain instances, the dv values of the polymer and the solvents were similar even though their dd and dp interactions were dissimilar. Conclusion: The analysis of the data showed that the composite solubility parameter dv of compounds could be similar even though the actual energies of dd and dp interactions are different. This is a limitation in the application of the theory of the three dimensional solubility parameters. Keywords: keyword; keyword; keyword > Tropical Journal of Pharmaceutical Research Vol. 4 (1) 2005: pp. 355-362

Further study of the effect of particle size on slow particle clearance from the bronchial tree

The ICRP human respiratory tract model (HRTM) assumes that the 'slow-cleared fraction' fs in the bronchial (BB) and bronchiolar (bb) regions decreases with increasing particle geometric diameter dp. To test this assumption, five volunteers inhaled 8-microm aerodynamic diameter, dae, (111)In-polystyrene (PSL) and (198)Au particles simultaneously. The particles were administered at the end of each breath to maximise deposition in BB and bb. Because of the difference in densities (1.05 vs. 19.3 g cm(-3)), corresponding dp values are approximately 8 and 1.8 microm, and fs values are approximately 2 and 50%, respectively. However, lung retention was somewhat greater for PSL than for gold, contrary to the HRTM prediction. Other recent human experimental studies found no difference in retention for particles with the same dae but different dp values. It is concluded that the HRTM model of particle clearance from BB and bb needs revision.

Ab initio melting curve of molybdenum by the phase coexistence method

Ab initio calculations of the melting curve of molybdenum for the pressure range 0–400 GPa are reported. The calculations employ density functional theory (DFT) with the Perdew-Burke-Ernzerhof exchange-correlation functional in the projector augmented wave (PAW) implementation. Tests are presented showing that these techniques accurately reproduce experimental data on low-temperature body-centered cubic (bcc) Mo, and that PAW agrees closely with results from the full-potential linearized augmented plane-wave implementation. The work attempts to overcome the uncertainties inherent in earlier DFT calculations of the melting curve of Mo, by using the “reference coexistence” technique to determine the melting curve. In this technique, an empirical reference model (here, the embedded-atom model) is accurately fitted to DFT molecular dynamics data on the liquid and the high-temperature solid, the melting curve of the reference model is determined by simulations of coexisting solid and liquid, and the ab initio melting curve is obtained by applying free-energy corrections. The calculated melting curve agrees well with experiment at ambient pressure and is consistent with shock data at high pressure, but does not agree with the high-pressure melting curve deduced from static compression experiments. Calculated results for the radial distribution function show that the short-range atomic order of the liquid is very similar to that of the high-T solid, with a slight decrease of coordination number on passing from solid to liquid. The electronic densities of states in the two phases show only small differences. The results do not support a recent theory according to which very low dTm∕dP values are expected for bcc transition metals because of electron redistribution between s-p and d states.

Organic matter in degraded agricultural soils amended with composted and thermally-dried sewage sludges

The cumulative and residual effects of composted and thermally-dried sewage sludge (CSS and TSS, respectively) on soil organic matter and its humified fraction were evaluated in a field experiment under Mediterranean conditions. The experimental design included soil plots either unamended (control) or amended with mineral fertilizer, CSS and TSS at rates of 20 and 80 t ha(-)(1). After the first year of sewage sludge application, each plot was divided into two subplots. In one subplot group, no additional application of SS was made in the following 3 years, and the residual effect of the first applications was evaluated. In the second subplot group, the cumulative effect of sludge amendments was evaluated by applying CSS and TSS also in the following three consecutive years. Nine months after the yearly sludge and mineral fertilizer applications, surface soil samples from control and amended soils were collected and analyzed for total organic C (TOC), total extractable C (TEC), and humified C fractions, both humic acid C (HAC) and fulvic acid C (FAC) fractions. Compared with the control and mineral treatments, which showed similar results, the repeated application to soil of TSS, and specially CSS, induced an increase on the content of the organic fractions examined, as well as HA percentage (%HA=HAC/TOC) and degree of polymerisation (DP=HAC/FAC). In the residual experiment, the TOC, TEC, HAC and FAC content of soils amended once with CSS and TSS decreased slightly when increasing the time from the amendment, whereas the %HA and DP tended to increase. Further, three years after the sludge applications, with respect to the control soil, the soils amended once with CSS exhibited similar TOC, TEC, and FAC content, and slightly larger HAC content, %HA and DP; whereas those amended once with TSS, featured still larger TOC, TEC, HAC content, similar FAC content, and slightly larger %HA and DP values. As a whole, the results obtained suggested that both kind of sludges contribute to improved soil organic matter levels and humified fractions, although the CSS contribution can be considered as a more efficient organic amendment than the TSS, which may present problems of maturity and degradability.

Determination of thermodynamic and transport properties of solvents and non solvents in poly(L‐lactide‐co‐glycolide)

AbstractThermodynamic properties, partition coefficient, and diffusion coefficients of the various solvents (acetone, dichloromethane, trichloromethane, ethyl acetate, ethyl alcohol, tetrahydrofuran, and water) in poly(lactide‐co‐glycolide) (PLGA) at infinite dilution of the solvent have been determined by inverse gas chromatography (IGC). In IGC method, which is based on the characteristic equilibrium partitioning of a solute between a mobile phase and a stationary phase, a small pulse of solvent is introduced into the column and by the aid of retention volume of the solvent, several polymer solvent interaction properties, namely retention volume (Vg), infinitely dilute weight fraction activity coefficient (Ω), Flory–Huggins interaction parameter (χ), and solubility parameters of the polymer (δ) can be determined. The thermodynamic results indicated that trichloromethane and dichloromethane were the most suitable solvents among all the solvents studied for PLGA. The partition (K) and diffusion coefficients (Dp) of various solvents at infinite dilution of the solvent were calculated by using the model developed by Pawlisch et al. (Macromolecules 1987, 20, 1564). The optimum K and Dp values that best fit the data were found and the model predicted experimental data very well. So IGC method is a powerful tool for the determination of thermodynamic and diffusion properties of solvent in polymer at infinite dilution of the solvent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2426–2432, 2006

Influence of PEG Endgroup and Molecular Weight on Its Reactivity for Lipase-Catalyzed Polyester Synthesis

Polycondensations were performed at 70 degrees C in bulk using physically immobilized lipase B from Candida antarctica (CAL-B) as catalyst. Study of copolymerizations between sebacic acid and PEG diols of differing Mn values (200, 400, 600, 1000, 2000, and 10 000) showed that PEG 400 and 600 were most reactive (DP(avg) up to about 6). Increasing the PEG diol chain length from 600 to 1000, 2000, and 10 000 resulted in large decreases in copolymer DP(avg) values. PEG200 diacids (i.e., HOOC-(CH2)x-O-(CH2CH2O)n-(CH2)x-COOH) were successfully synthesized where x was 1, 4, 5, 7, 9, and 11. Study of copolymerizations of these diacids with 1,8-octanediol showed that, by introduction of a five-carbon methylene spacer (x = 5), remarkable increases in the reactivity of PEG200 diacids were achieved. In addition, introduction of this spacer was also effective for increasing the reactivity of PEG diacids of higher molecular weight (i.e., PEG400, 600, and 1000). This work verified the hypothesis that, by conversion of PEG chain ends to structures more closely resembling fatty acids, modified PEG building blocks are obtained that are better recognized as substrates by CAL-B during condensation reactions.

Block co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides as model compounds for methylcellulose and its dissolution/gelation behavior

A novel synthetic method for co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides was designed. These oligomers are of importance as model compounds for investigations on the dissolution behavior of commercial methylcelluloses. In this connection, insights into the chemical structure of ‘cross linking loci’ in the thermo reversible gelation of aqueous solution of methylcellulose are of particular significance. The synthetic procedure consists of glycosylation using glycosyl fluoride and oligomerization of sugar orthoester. Thus, phenyl 2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-1-thio-β-d-glucopyranoside (1) as a glycosyl acceptor was glycosylated with 4-O-acetyl-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-d-glucopyranosyl fluoride (2) as a glycosyl donor converted to give a cellotetraose derivative (3). Both reactants have been prepared from commercially available cellobiose. After deacetylation of 3, 3-O-benzyl-6-O-pivaloyl-α-d-glucopyranose 1,2,4-orthopivalate (5) was reacted with 4-hydroxyl group at non-reducing-end of cellotetraose derivative (4) to give the block co-oligomer (6). After the deprotection of compound 6, tri-O-methylated-block-unmodified cello-oligosaccharides (18 and 18′) (DP = 4 − 8, DS = 2.79 − 1.38) were obtained, monitored by MALDI-TOF MS spectra. Chloroform-soluble methylated cellotetraose derivatives (18 and 18′ (DP=4, n=0), DS=2.57, and 2.79, respectively) were also soluble in the water solution of tri-O-methylated-block-unmodified cello-oligosaccharides (DP=4−8, DS=2.79−1.50). This fact indicated that hydrophobic methylated cello-tetraose derivatives were encapsulated within a micelle of amphiphlic tri-O-methylated-block-unmodified cello-oligosaccharides. It was found that solubilities of 18 and 18′ (DP=4−8, DS=2.79−1.38) in water and chloroform were obviously different in the mixtures, depending on their DP and DS values. The substituent distribution of the tri-O-methylated-block-unmodified cello-oligosaccharides along one molecule and between molecules plays an important role in its solubility in water and chloroform.

Macromonomers and coordination polymerization

AbstractThe present work discusses the synthesis of well‐defined comb‐shaped polymers or graft copolymer structures based on coordination (co)polymerization of macromonomers. Polystyrene macromonomers with various polymerizable entities were synthesized first by induced deactivation reactions. The homopolymerization of these macromonomers in the presence of selected early or late transition metal catalysts was examined. Comb‐shaped polymers could be obtained over a large range of DP values. The results were compared to those obtained by anionic homopolymerization. Some results on the copolymerization of these PS macromonomers with ethylene in the presence of VERSIPOLTM type catalysts were presented.

Homogeneous Reduction of Haloacetonitriles by Electrogenerated Aromatic Radical Anions: Determination of the Reduction Potential of•CH2CN

The mechanism of homogeneous reduction of XCH2CN (X = Cl, Br, I) by organic radical anions (D•-) has been investigated in DMF. All three haloacetonitriles undergo a concerted dissociative electron transfer with formation of a fragment cluster in the solvent cage. The interaction energy Dp of the fragment cluster has been determined by applying the “sticky” dissociative electron-transfer model to the kinetic data obtained for the reaction between each XCH2CN and a series of donors. The interaction energies lie in the range from 0.19 to 1.67 kcal mol-1 and decrease from Cl to Br and to I. Both the smallness of Dp values and their dependence on the bulkiness of X- confirm the electrostatic character of these interactions. The intermediate radical stemming from the dissociative electron transfer to XCH2CN reacts with D•- either by radical coupling (kc) or by electron transfer (ket). Examination of the competition between these reactions, which can be expressed by a dimensionless parameter q = ket/(kc + ket), ...