Mid Chain Research Articles

Vegetation History in a Peat Succession Over the Past 8,000 years in the ISM-Controlled Kedarnath Region, Garhwal Himalaya: Reconstruction Using Molecular Fossils

The Holocene epoch has witnessed several natural climate variations and these are well encoded in various geological archives. The present biomarker investigation in conjunction with previously published multi-proxy records was applied to reconstruct organic matter (OM) sources forming the peat succession spanning the last 8000 cal yr BP and shift in hydrological conditions from the Kedarnath region, Garhwal Himalaya. Intensified monsoon prevailed from ∼7515 until ∼2300 cal yr BP but with reversal to transient arid period particularly between ∼5200 and ∼3600 cal yr BP as revealed by the variability in n-C23/n-C31, ACL (average chain length of n-alkanes) and Paq (P-aqueous) values. A prolonged arid phase is recognizable during the interval between ∼2200 and ∼370 cal yr BP suggested by the n-alkane proxies. Regional scale heterogeneity in the monsoonal pattern is known in the studied temporal range of mid to late Holocene across the Indian subcontinent that is probably a result of complex climate dynamics, sensitivity of proxies and impact of teleconnections. The biomarker signatures deduced from gas chromatography mass spectrometry (GCMS) analysis are suggestive of a mixed biotic input that includes prokaryotes, Sphagnum spp. and gymnosperm flora. The mid chain alkanes viz. n-C23 and n-C25 denote the presence of typical peat forming Sphagnum moss that preferentially grows in humid and waterlogged conditions. Diterpane marker such as ent-kaurane indicates contribution of gymnosperms, whereas the hopanes are signatures of microbial input. The preservation of organic matter is attributed to little microbial degradation in a largely suboxic depositional environment. Our study strengthens the applicability of organic geochemical proxies for the reconstruction of past climate history and indicates their suitability for use on longer timescales given the high preservation potential of the molecular remains.

A Structural Investigation on Polystyrene with Cyclohexene Mid-Chain Group: Thermal Stability and Self-Assembly Kinetics in Nonpolar and Polar Aprotic Solutions

This study was focused on cyclohexene (CH) mid-chain functional polymer of polystyrene (PSt-CH-PSt) because of its potential application in nanotechnology and its possible usage in hierarchical structures.
 Molecular and nano scale structural characterizations and thermal behavior of the powder form PSt-CH-PSt functional polymer were carried out by FTIR, SAXS, XRD and DSC methods. Solutions of PSt-CH-PSt in tetrahydrofuran and chloroform were also investigated by SAXS and FTIR.
 The stable one type nano particles which have oblate core-shell shape were determined in powder form and in solution of PSt-CH-PSt. The self-assembly kinetics of the polymer indicate that the mid chain part location in oblate core shell aggregations may be controlled by polar aprotic THF and nonpolar CLF solvent effects. Exponential decreasing in oblate shell volumes of PSt-CH-PSt nano globules in THF as a function of temperature was also determined by SAXS.

CLINICAL CASE OF CONGENITAL SPONTANEOUS BILATERAL CHYLOTHORAX

Chylothorax is a pathological condition associated with the accumulation of lymphatic fluid in the pleural cavity. This pathology occurs quite rarely, but it is a complex and often life threatening disease that results in deep respiratory, metabolic and immunological disorders. Occurs in any age group, including the neonatal period. Currently, there are few reports of congenital chylothorax, no practical recommendations for the clinical management of this category of patients, mortality is from 20 % to 60 %. At present, there is no single point of view regarding the pathogenesis of the occurrence of chylothorax. In the modern literature, the following etiopathogenetic factors are indicated: iatrogenic causes (cardiothoracic surgical interventions, puncture of the central veins from the system of vena cava superior, trauma during labor), increased pressure in the system of the upper vena cava (thrombosis, congenital malformations of the heart), diaphragmatic hernia, congenital defects of lymphatic system (hypoplasia of vessels or vascular walls), lymphangiomatosis, genetic defects (Down syndrome, Noonan, monosomy X, etc.), congenital cytomegalovirus infection, inflammatory process. Infants in whom chylothorax has been diagnosed with up to 35 weeks of gestation and initiated prenatal treatment have improved postnatal results. In the postnatal period, the initial steps of the treatment include drainage of the pleural cavity, adequate ventilation, parenteral nutrition, specific enteral nutrition (a formula with high protein content, reduced lipid content, and, instead, should contain mid chain triglycerides - MCT), correction of albumin content, electrolytes (typical hyperkaliemia, hyponatremia) and drug therapy (octreotide). The clinical case of a premature baby with congenital bilateral chylothorax is an example of successful conservative treatment.

A modelling approach to assess the environmental/radiological impact of C-14 release from radioactive waste repositories

Assessments of the environmental impact of C-14 disposal often assume that C-14 is converted into gases that are able to migrate to the surface, where they pose a radiological risk. However, uncertainties, associated with the long-term release of C-14 from graphite and the evolution in the post-closure environment of a geological disposal facility (GDF), exist. In this paper, an integrated modelling framework has been developed to investigate these uncertainties. The modelling framework consists of a biogeochemical near field model which interfaces with a geosphere/biosphere model and it is verified by comparing the results to those obtained from other models. A sensitivity analysis discloses that a faster mid chain scission rate of stopped cellulose about four orders of magnitude assesses a twice higher effective dose. In another scenario, which is related to the control of microbial activity by pH and the availability of carbon dioxide to microbes, the effective dose is two orders of magnitude higher compared with a reference scenario. This modelling work illustrates also the importance of far field parameters, such as the rock permeability and the release area of gas pathway, to the assessment of effective dose.

Hydroxylation of EPDM as a means for ambient temperature vulcanisation via urethane chemistry

This paper describes a single-step, quantitative method for hydroxylation of unsaturated rubbers like EPDM. The resultant polyhydroxy elastomer was vulcanised using a diisocyanate under relatively milder conditions. The vulcanised product showed increased modulus in contrast to the sulfur- or peroxide-crosslinked systems. The enhanced cohesion originates from the urethane linkages which can be controlled either by regulating the concentration of the oxidant during hydroxylation or through the isocyanate –to- hydroxyl ratio (NCO/OH) during vulcanisation. This is the first ever report on the mid chain hydroxylation of unsaturated polymers and their polyurethane networks.

Modeling Framework for Biogenic Methane Formation from Coal

In situ biodegradation of coal to methane offers an innovative and attractive alternative to the prevailing methods of harnessing the energy potential of coal. This alternative approach employs a community of microorganisms to biologically generate methane from unmined coal and has the promise of causing less pollution, reducing the environmental impact of mining, and being potentially less expensive.(9,10,15−18) The goal of our work is to develop a novel, comprehensive, and quantitative mathematical modeling framework to better understand the process of biogenic methane formation from coal. Intermediate chemical species and metabolic pathways are identified using existing literature information and are incorporated into a lumped kinetic model, referred to as the Coal to Methane (C2M) Kinetic Model. Several intermediate compounds have been lumped into polyaromatics (PACs), long chain fatty acids (LCFAs), and mid chain fatty acids (MCFAs), etc. The simulations of the model and sensitivity analysis along wi...

Effect of benign and tumor parenchyma metabolomic profiles on compensatory renal growth in renal cell carcinoma surgical patients.

446 Background: Pre-operative kidney volume is an independent predictor of glomerular filtration rate in renal cell carcinoma patients. Compensatory renal growth (CRG) can ensue prior to nephrectomy in parallel to tumor growth and benign parenchyma loss. We aimed to test whether renal metabolite abundances significantly associate with CRG, suggesting a causative relationship. Methods: Tissue metabolomics data from 49 patients, with a median age of 60 years, were previously collected and the pre-operative fold-change of their contra to ipsi-lateral benign kidney volume served as a surrogate for their CRG. Contra-lateral kidney volume fold-change within a 3.3 +/- 2.1 years follow-up interval was used as a surrogate for long-term CRG. Using a multivariable statistical model we identified metabolites whose abundances significantly associate with CRG. Results: We identified 13 metabolites in the benign (e.g. L-urobilin) and 163 metabolites in the malignant (e.g. 3-indoxyl-sulfate) tissues to significantly associate with CRG. Benign/tumor fold change in metabolite abundances revealed three additional metabolites with a significant positive association with CRG (e.g. p-cresol sulfate). At the pathway level, we show that fatty-acid oxidation is highly enriched with metabolites whose benign tissue abundances strongly positively associate with CRG, whereas in the tumor tissue significant enrichment of dipeptides (positive association) and benzoate, glycolysis/gluconeogenesis, lysolipid and nucleotide sugar pentose (negative associations) sub-pathways were observed. The effect of metabolite abundances in the benign tissue on long term CRG provided further support for positive association of fatty-acid metabolism sub-pathway enrichment, where sphingolipid, monoacylglycerol, long chain fatty acids, and mid chain fatty acids were enriched for a negative association. Conclusions: These data suggest that specific biological processes in the benign as well as in the tumor parenchyma strongly influence compensatory renal growth.

Organic compound-mineral interactions: Using flash pyrolysis to monitor the adsorption of fatty acids on calcite

Fatty acids are near ubiquitous organic compounds in living organisms in the Earth’s biosphere. Following death of an organism in the marine environment its fatty acids may survive descent to the sea bed where they can be juxtaposed with minerals. The aim of this study was to investigate the interaction of fatty acids with the common marine mineral calcite. Adsorption of tetradecanoic acid (C14) on calcite results in a sigmoidal or “s” isotherm. Flash pyrolysis experiments were conducted on samples of fatty acid adsorbed onto calcite and were compared with similar experiments on pure fatty acid and on salts of a fatty acid. Flash pyrolysis of pure tetradecanoic acid generated unsaturated and saturated hydrocarbons and a series of unsaturated and saturated low molecular weight fatty acids. Flash pyrolysis of free tetradecanoic acid salt produced saturated and unsaturated hydrocarbons, an aldehyde and a homologous series of saturated and unsaturated ketones, one of which was a symmetrical mid chain ketone (14-heptacosanone). Flash pyrolysis data from adsorbed tetradecanoic acid samples suggested that adsorption is analogous to the formation of the calcium salt of tetradecanoic acid. A key characteristic of the flash pyrolysis products of adsorbed fatty acids and fatty acid salts was the production of ketones with higher molecular weights than the starting fatty acids. Ketonisation was not observed from the flash pyrolysis of pure acid which implied the catalytic significance of the calcite mineral surface. The abundance of hydrocarbons relative to ketones in the pyrolysates negatively correlated with the proportion of fatty acids adsorbed to the surface of calcite. The ability to use flash pyrolysis to diagnose the nature of fatty acid interactions with mineral surfaces provides a valuable tool for monitoring the fate of these important lipids at the Earth’s surface as they pass into the geosphere and are subjected to diagenetic processes.

Surface chemistry of the interactions of cationic nanoemulsions with human meibum films

PurposeIkervis® (IKV) cationic nanoemulsions (CNE) were demonstrated to enhance tear film stability in vivo possibly via effect on tear film lipid layer (TFLL). Therefore the interactions of IKV and of binary and ternary mixtures of its constituents were studied with human meibum (MGS) films. The binary mixtures consisted of 2% mid chain triglycerides (MCT) blended with 0.005% cetalkonium chloride (CKC) and 0.3% Tyloxapol (e.g. MCT/CKC and MCT/Tylo respectively). The ternary mixture contained MCT/CKC/Tylo (2%/0.005%/0.3%). The impact of 0.1 μM bovine submaxillary mucin (BSM) on CNE/MGS interactions was also evaluated.MethodsMGS and CNE oils were spread at the air/water interface of a Langmuir surface balance in range of 2D ratios (20/1, 10/1, 5/1, 3/1, 2/1 and 1/1) at two measurement regimes: with (i) MGS or (ii) total lipid amount kept constant. The films capability to reorganize during dynamic area cycling was evaluated. The layers dilatational rheology was probed via the step/relaxation method. Films structure was monitored with Brewster Angle microscopy.ResultsThe binary mixtures showed limited spreading and miscibility with MGS resulting in poor mechanical properties. The ternary mixture and IKV spread and mixed well with MGS. At fixed MGS amount, the inclusion of CNEs enhanced the structure, properties and elasticity of the layers. At fixed total lipid, the films remained primarily elastic, but at high (≤3/1) CNE content the elasticity slightly decreased and heterogeneities in layers structure were observed. BSM enhanced the ternary mixture (IKV)/ MGS interactions.ConclusionsAt physiologically relevant MGS/CNE ratios MCT/CKC/Tylo and IKV interact favorably with MGS films. The positive effect of BSM suggests that polyanionic polysaccharides can enhance CNE/TFLL interactions in vivo.Support: Collaborative study grant by Santen SAS, Evry, France.

Chain dynamics in foamed polysiloxane materials: Influence of the tin catalyst phase on material properties

We report on our underpinning science activities investigating the through life performance properties of foamed polysiloxanes. These materials are manufactured through tin octanoate based condensation cure chemistry. The tin catalyst plays an important role, not only in determining crosslink density and microstructure, but also potentially influencing properties (compression set and load retention) important to through life performance. In this study, Mossbauer Spectroscopy and X-ray fluorescence has been used to assess the nature and distribution of the tin species and show evidence for highly localized catalyst regions, including a mobile tin phase. In addition, testing was carried out using a NMR MOUSE (Mobile Unit for Surface Exploration) together with a CPMG (Carr Purcell Meiboom Gill) spin echo sequence to probe chain dynamics through the measurement of spin-spin or transverse relaxation (T2) responses. We have used model polysiloxanes to demonstrate that the NMR MOUSE capability is relatively sensitive to crosslink density. In general, the more resticted the environment around a given chain structure, the more rapidly it is likely to relax, and potential chain confinement effects of the tin phase may be assessed through the measurement of T2 parameters. Our work shows that the tin catalyst has a binding action and affects the dynamics of the relatively more rigid environments (such as crosslinks) as well as the mobility of chain ends and mid chain components (long T2). Load retention properties are reduced with increased tin catalyst loading, and this ties in with the influence of the tin particles on chain dynamics. The observations reported here support our initiative to develop predictive models representative of the through life performance of foamed polysiloxanes.

Biome-scale characterisation and differentiation of semi-arid and arid zone soil organic matter compositions using pyrolysis–GC/MS analysis

Soil organic matter (SOM) is a major pool within the global carbon cycle and understanding its composition (and compositional variability) is critical for predicting its response to future climatic change. Arid and semi-arid regions are typified by relatively low soil organic matter concentrations, but their vast area means that they still represent an important component of the global soil carbon pool. Recent studies have demonstrated the potential of pyrolysis–gas chromatography/mass spectrometry (py–GC/MS) to elucidate basic inter-biome differences in SOM composition. This study provides a first systematic application of py–GC/MS to the analysis of macromolecular SOM across a semi-arid/arid environment; specifically the Fynbos and Succulent Karoo Biomes of South Africa.Data from 27 sites across the region reveal considerable plot-scale variability in SOM quantity and quality, but also demonstrate distinct inter-biome differences in SOM composition. Overall, the pyrolysis data suggest that SOM in the Fynbos Biome contains a higher abundance of minimally/unaltered plant-derived structures, such as lignin and cellulose, in contrast with the more variable, more microbially-altered SOM of the Succulent Karoo. Pyrolysis of soils in the latter biome generally produces higher proportions of simple aromatic and certain nitrogen-bearing pyrolysis products. The majority of soils associated with lowest total organic carbon contents tend to produce a much more limited number of aromatic pyrolysis products. Principal component analyses (PCA) suggest that the overall extent of organic matter degradation is the primary driver of compositional variability across the study area and regardless of biome/ecoregion, the pathways of degradation are essentially similar. Additional affects are also observed, notably in the Succulent Karoo where some soils are relatively enriched in short to mid chain length aliphatic pyrolysis products. Across the whole study area, the extent of degradation, which is broadly represented by the PCA axis 1 scores, is correlated with mean annual rainfall, although the relationship is relatively weak, highlighting the potential significance of other factors, such as local edaphic conditions, soil mineralogy and other mechanisms of dryland SOM degradation such as photo-degradation. Overall, the study demonstrates that despite some known limitations, the systematic application of py–GC/MS can yield insights into large/landscape-scale variability in SOM quality and quantity.

<I>Aedes aegypti</I> (Diptera: Culicidae) Biting Deterrence: Structure-Activity Relationship of Saturated and Unsaturated Fatty Acids

In this study we evaluated the biting deterrent effects of a series of saturated and unsaturated fatty acids against Aedes aegypti (L), yellow fever mosquito (Diptera: Culicidae) using the K & Dbioassay module system. Saturated (C6:0 to C16:0 and C18:0) and unsaturated fatty acids (C11:1 to C14:1, C16:1, C18:1, and C18:2) showed biting deterrence index (BDI) values significantly greater than ethanol, the negative control. Among the saturated fatty acids, mid chain length acids (C10:0 to C13:0) showed higher biting deterrence than short (C6:0 to C9:0) and long chain length acids (C14:0 to C18:0), except for C8:0 and C16:0 that were more active than the other short and long chain acids. The BDI values of mid chain length acids (C10:0 to C13:0) were not significantly less than N, N-diethyl-meta-toluamide (DEET), the positive control. Among the unsaturated fatty acids, C11:1 showed the highest activity (BDI = 1.05) and C18:2 had the lowest activity (BDI = 0.7). In C11:1, C12:1, and C14:1 BDI values were not significantly less than DEET. After the preliminary observations, residual activity bioassays were performed on C11:0, C12:0, C11:1, and C12:1 over a 24-h period. All the fatty acids (C11:0, C12:0, C11:1, and C12:1) and DEET showed significantly higher activity at all test intervals than the solvent control. At treatment and 1-h posttreatment, all fatty acids showed proportion not biting (PNB) values not significantly less than DEET. At 3-, 6-, and 12-h posttreatment, all fatty acids showed PNB values significantly greater than DEET. At 24-h posttreatment, only the PNB value for C12:0 was significantly higher than DEET. The dose-responses of C12:0 and DEET were determined at concentrations of 5-25 nmol/cm2. As in the residual activity bioassays, the PNB values for C12:0 and DEET at 25 nmol/cm(2) were not significantly different. However, at lower concentrations, the PNB values for C12:0 were significantly greater than DEET. These results clearly indicate that mid chain length fatty acids not only have levels of biting deterrence similar to DEET at 25 nmnol/cm(2) in our test system, but also appeared to be more persistent than DEET. In contrast, in vivo cloth patch assay system showed that the mid-chain length fatty acids, C11:0, C11:1, C12:0, and C12:1 had minimum effective dose (MED) values greater than DEET against Ae. aegypti and their relative repellency varied according to species tested. The MED values of 120 (C11:0), 145 (C12:0) and 116 (C11:1) nmol/cm(2) against Anopheles quadrimaculatus Say, indicated that these acids were not as potent as DEET with a MED of 54 nmol/cm(2). The MED ratio of the C11:0 and C11:1 for all three mosquito species indicated the C11 saturated and unsaturated acids as more repellent than their corresponding C12:0 and C12:1 homologues.

Comparative biochemical characterization and in silico analysis of novel lipases Lip11 and Lip12 with Lip2 from Yarrowia lipolytica

Novel lipases lip11 and lip12 from Yarrowia lipolytica MSR80 were cloned and expressed in E. coli HB101 pEZZ18 system along with lip2. These enzymes were constitutively expressed as extracellular proteins with IgG tag. The enzymes were purified by affinity chromatography and analyzed by SDS-PAGE with specific activity of 314, 352 and 198 U/mg for Lip2, Lip11 and Lip12, respectively on olive oil. Biochemical characterization showed that all were active over broad range of pH 4.0-9.0 and temperature 20-80 °C with optima at pH 7 and 40 °C. All the three lipases were thermostable up to 80 °C with varying t(½). Activity on various substrates revealed that they were most active on oils > triacylglycerides > p-np-esters. Relatively Lip2 and Lip11 showed specificity for mid to long chain fatty acids, while Lip12 was mid chain specific. GC analysis of triolein hydrolysis by these lipases revealed that Lip2 and Lip11 are regioselective, while Lip12 is not. Effect of metal ions showed that Lip2 and Lip12 were activated by Ca²⁺ whereas Lip11 by Mg²⁺. All were thiol activated and inhibited by PMSF and N-bromosuccinimide. All were activated by non polar solvents and inhibited by polar solvents. Detailed sequence analysis and structural predictions revealed Lip11 and Lip12 shared 61 and 62 % homology with Lip2 (3O0D) and three dimensional superimposition revealed Lip2 was closer to Lip11 than to Lip12 as was observed during biochemical characterization. Finally, thermostability and substrate specificity has been explained on the basis of detailed amino acid analysis.

The physicochemical and tribological properties of oleic acid based triester biolubricants

Currently, increasing pollutants in the environment lead to an increase in the use of plant oil based biolubricants. These products could lead to a significant reduction in environmental pollution and thus contribute to the discovery of a replacement for petroleum-based lubricants. Plant oils are advantageous because they are rapidly biodegradable, renewable, excellent lubricants and inexpensive to produce. However, these oils show poor stability to oxidation and unfavorable properties at low temperatures. Thus, this work outlines modifications in the epoxidation, oxirane ring opening, esterification and acylation reactions used to produce oleic acid based triester derivatives. These products have improved physicochemical and tribological properties that make them good biolubricant base stock candidates. Octyl 9-(lauroyloxy)-10-(behenoxy)octadecanoate 22 has the lowest pour point (−45 °C) while octyl 9-(lauroyloxy)-10-(octyloxy)octadecanoate 16 has the highest onset temperature. Based on the results, an increase in mid chain substituent length improves the pour point and anti-wear properties but conversely lowers the onset temperature.

Synthetic biolubricant basestocks based on environmentally friendly raw materials

This work outlines modifications in the epoxidation, oxirane ring opening, estrification and acylation reactions to produce oleic acid based triester derivatives. Measuring of pour point (PP), flash point (FP), viscosity index (VI), oxidation onset temperature (OT) and signal maximum temperature (SMT) was carried out for each compound. The resulting product structures were confirmed by NMR and FTIR spectroscopic analysis. The results showed that butyl 9-(decanoyloxy)-10-(behenoxy)octadecanoate with bulky ester behenyl mid chain exhibited the most favorable low-temperature performance (PP −47°C). On the other hand, butyl 9-(decanoyloxy)-10-(octyloxy)octadecanoate exhibited higher oxidation stability (OT 173°C) than the other synthetic esters. In conclusion, an increase in mid chain substituent length improves the PP and conversely lowers the OT.

Relevance of backbiting and beta‐scission reactions in the free radical polymerization of Acrylonitrile

AbstractSummary: In this work, backbiting and beta‐scission reactions are investigated through Quantum Chemistry methods by adopting the Becke 3 parameters and Lee Yang Parr functional (B3LYP) and 6‐31G(d,p) basis set. Namely, the 1:3, 1:5 and 1:7 backbiting reactions are studied for acrylonitrile polymerization. It was found that the backbiting 1:5 is the most favorited because this kinetic event leads to the formation of a 6 membered transition state, while the backbiting 1:3 requires high activation energy due to the formation of a highly strained 4 membered ring. 7:3 backbiting reaction was also examined, since it is an alternative pathway that can explain the formation of defects generated by radicals in the third position. Simulations showed that this kinetic step is characterized by high rate constant because of its low activation energy.The right and left beta‐scission reactions from the mid chain radicals formed by the considered backbiting reactions are also studied. Computational analysis demonstrated that all beta‐scission reactions are endothermic and both the right and left beta‐scission reactions have the same activation energy, which seems to be more influenced by the position of the mid chain radical.

Facile conversion of RAFT polymers into hydroxyl functional polymers: a detailed investigation of variable monomer and RAFT agent combinations

We report the systematic investigation of a recently introduced one-pot radical transformation of methacrylate and acrylate-type polymers prepared via reversible addition fragmentation chain transfer (RAFT) polymerization into hydroxyl functional polymers. The simple reaction procedure involves stirring a solution of the RAFT functional polymer and an azo-initiator in tetrahydrofuran at elevated temperatures (T = 60 °C) in the presence of ambient air. Subsequent reduction of the formed hydroperoxide functional polymers to hydroxyl functional polymers is achieved in a one-pot procedure using triphenylphosphine. Polymers investigated in the current study are poly(methyl acrylate) (pMA), poly(butyl acrylate) (pBA), poly(isobornyl acrylate) (piBoA) and poly(tert-butyl acrylate) (ptBA) carrying a dithiobenzoate or phenyldithioacetate end terminius as well as a symmetrical trithiocarbonate mid chain function. Quantitative conversion into the hydroperoxyl and hydroxyl terminated product is observed when trithiocarbonate functional polymers are employed. In the case of dithiobenzoate and phenyldithioacetate functional acrylic polymers, some minor side products due to the oxidation of the RAFT end-group are generated. Size exclusion chromatography (SEC) and size exclusion chromatography–electrospray mass spectrometry (SEC-ESI-MS) were employed to monitor the progress of the reaction and to investigate the proposed reaction mechanism for the model polymers. When trithiocarbonate functional polymers are employed in the transformation reaction, the SEC analysis shows a bisection of the initial Mn. Collision induced dissociation (CID) MS experiments of the intermediate reaction products were conducted to gain in-depth information about the chemical structure. The new backbone linked hydroxyl group provides a versatile anchor for chemical end-group conversions and conjugation reactions with RAFT prepared polymers, alleviating problems with the rather limited ability of the dithioester end-group to undergo non-radical transformations.

Free radical polymerization of cyclohexyl acrylate involving interconversion between propagating and mid-chain radicals

The ESR spectrum of the propagating radical of cyclohexyl acrylate (CHA) overlapping with a three-line spectrum of a mid-chain radical was recorded in benzene as a non-polar solvent. The hyperfine coupling constants for the α- and β-hydrogens of the propagating radical of CHA were assigned based on the spectrum of the polymer radical of CHA-α-d. The polymerization of CHA was found to proceed in the presence of two types of radical species with different reactivities, the propagating radical and the mid-chain radical. The content of the mid-chain radical produced by abstraction of the α-hydrogen of the monomeric unit of the polymer was found to increase up to 25% with increasing conversion. The content of branching in the polymers arising from the hydrogen abstraction, 1.2–3.5%, determined by 13C NMR spectroscopy was also found to increase with progress of the polymerization. The rate of the intramolecular formation of the mid-chain radical relative to propagation was estimated from the branching content at an infinitely low conversion, which was obtained by extrapolation, to be 0.65% at 1 mol/l of CHA. The absolute rate coefficients for the propagation ( k p) and termination ( k t) of CHA were determined using kinetic data obtained by FT-near infrared spectroscopy and the concentration of the propagating radical extrapolated to 0% conversion to minimize the influence of the mid-chain radicals: k p =1224 l/mol s and k t =5.7×10 5 l/mol s at 60°C. These seemed to be apparent values because the propagating radical is repeatedly converted to the less reactive mid-chain radical by the intramolecular hydrogen abstraction during the lifetime of each radical. Slow initiation by the mid chain radical would result in the propagating radical which propagates further and accompanies the conversion to the mid-chain radical.

Flame and thermal resistance of phosphorus-functionalized poly(methyl methacrylate) and polystyrene

A series of phosphorus functionalized poly(methyl methacrylate) (PMMA) and polystyrene (PS) samples where the phosphorus functions are located at the chain ends, as pendant groups and as blocks in the middle of the polymer chain were evaluated for their flame and thermal resistance. The limiting oxygen index values (LOI) of the polymers revealed that the flame retardant efficiency of the phosphorus was dependent on its nature and position in the polymer chain and the type of polymer rather than on its absolute concentration. On a comparative scale, polymers with phosphorus at chain ends and in the middle of the chain exhibited better flame retardant properties. The polymers were subjected to thermogravimetric analysis (TGA) in air and N 2 under dynamic conditions and the trends in thermal behaviour with change in structure and composition have been examined and compared with that of the homopolymers. Except when located at chain ends, the phosphorus functionalization adversely affected the initial thermal characteristics of the PMMA samples, but with an improvement at elevated temperatures. For PS, phosphorus functionalization as pendant groups reduced their thermal resistance whereas chain-end and mid chain functionalization either did not affect or slightly improved their overall thermal resistance. All phosphorus-containing polymers left some char residue at higher temperatures. The activation energies for the major step of thermal decomposition were calculated from the thermograms. As the phosphorus content increased, the activation energy for a given degradation step was found to decrease except when the degradation was principally due to the phosphorus containing polymer block where a reverse trend was observed. The flame resistance of the polymers could be correlated to some extent with their thermal behaviour.

Biochemistry of human milk in early lactation.

With the analysis of more than 550 human milk samples we showed that triglycerides (accounting for 96-99% of the total lipids) increased from 2 to 3.5 g/100 ml mainly during the first week postpartum and remained constant thereafter. In contrast, both cholesterol and vitamin E concentrations decreased from 35 to 20 mg/100 ml and from 1.7 to 0.30 mg/100 ml, respectively. The phospholipids remained constant (40 mg/100 ml). Also the fatty acid composition of total lipids changed. Mid chain fatty acids (C10, C12, C14) increased, whereas the long chain polyunsaturated fatty acids decreased. The P/S-ratio of 0.32 remained constant throughout lactation. The mean protein content of human milk decreased from approximately 2 g/100 ml at day 2 to approximately 1 g/100 ml at day 36 of lactation. The content of each individual amino acid decreased likewise. However, when we expressed the amino acid values in relation to the protein value--that is as g amino acid per g protein--some decreased, some remained constant and some increased indicating a changing protein pattern. From these data we computer-calculated a sharp decrease in IgA content, a moderate decrease for lactoferrin and constant values for casein and a-Lactalbumin. Throughout the whole period of investigation, non protein nitrogen accounted for about 20% of total nitrogen. Although the absolute values decreased according to total nitrogen, the sum of free amino acids, as well as the amount of taurine, remained constant. Lactose increased from about 4 g/100 ml to 6 g/100 ml during the first days of lactation. The calcium content increased from a mean value of 25 mg/100 ml at day 1 to 32 mg/100 ml at day 5 and remained constant at 30 mg/100 ml up to day 36. Phosphorus content increased from 10 mg/100 ml at day 1 to 17 mg/100 ml at day 8 and then continuously decreased to 13 mg/100 ml at day 36. The protein-bound part of the calcium remained constant during the period investigation, the fat-associated part increased from 11% to 26%. Protein-bound phosphorus decreased from 45% in colostral milk to 29% in transitional and 23% in mature milk.