Labile Groups Research Articles

Variation of intra‐aggregate organic carbon affects aggregate formation and stability during organic manure fertilization in a fluvo‐aquic soil

AbstractThe aggregate formation and stability are controlled by the dynamics of soil organic matters (SOM), but how it is related to SOM chemical composition within different‐sized aggregates is largely unknown during manure fertilization. In this study, the variations of intra‐aggregate organic carbon (OC), including intra‐particulate organic matter (iPOM) and mineral‐associated organic matter, were quantitatively and qualitatively analysed, and then, their effects on aggregate formation and stability were assessed under four treatments: control (CK), mineral fertilizer (NPK), reduced manure (30%M) and manure fertilizers (M). Manure application (M) significantly increased macroaggregate proportion, mean weight diameter (MWD), and OC contents within different‐sized aggregates compared to CK, NPK, and 30%M. The OC accumulation of macroaggregate in M was attributed to OC content increase in silt plus clay subfraction rather than iPOM with more labile organic groups; oppositely, in microaggregate it was located in the relatively stable fine iPOM. The macroaggregate formation and stability were controlled by the fine iPOM within macroaggregates, whose abundant polysaccharide‐C and aliphatic‐C after manure fertilization advanced the microbial growth except for Gram‐positive bacteria, which further promoted macroaggregate formation and stability. The free silt plus clay fraction also affected macroaggregate formation and stability, and its polysaccharide‐C derived from microorganisms or decomposing SOM was positively associated with MWD and macroaggregate proportion. Because polysaccharide‐C can be easily associated with mineral particles, further improving micro‐ or macroaggregation. We conclude that continuous manure fertilization could increase labile SOM accumulation within aggregates and then facilitate microbial growth, which collectively are responsible for aggregate formation and stabilization.

Divergent Synthesis of Natural Benzyl Salicylate and Benzyl Gentisate Glucosides.

Herein is reported the first total synthesis of benzyl salicylate and benzyl gentisate glucosides present in various plant species, in particular the Salix genus, such as Populus balsamifera and P. trichocarpa. The method permits the synthesis of several natural phenolic acid derivatives and their glucosides starting from salicylic or gentisic acid. The divergent approach afforded access to three different acetylated glucosides from a common synthetic intermediate. The key step in the total synthesis of naturally occurring glycosides-the selective deacetylation of the sugar moiety-was achieved in the presence of a labile benzyl ester group by employing mild deacetylation conditions. The protocol permitted synthesis of trichocarpine (4 steps, 40% overall yield), isotrichocarpine (3 steps, 51% overall yield), trichoside (6 steps, 40% overall yield), and deoxytrichocarpine (3 steps, 42% overall yield) for the first time (>95% purity). Also, the optimized mild deacetylation conditions allowed synthesis of 2-O-acetylated derivatives of all four glycosides (5-17% overall yield, 90-95% purity), which are rare plant metabolites.

Sensitivity of soil carbon dynamics to nitrogen and phosphorus enrichment in an alpine meadow

Anthropogenic activities and atmospheric deposition have increased the nitrogen (N) and phosphorus (P) inputs to terrestrial ecosystems, which can significantly alter ecosystem carbon cycling. To better understand the mechanisms of soil organic carbon (SOC) responding to nutrient fertilization, we measured physical fractions (by particle-size fractionation) and chemical composition (by solid-state 13C NMR spectroscopy) of SOC, plant biomass and nutrient concentration, soil chemistry, microbial biomass and community composition after 10 years of N and P addition in an alpine meadow on the Tibetan Plateau. Our results showed that total SOC and mineral-associated organic carbon (MAOC) contents were not affected by N and P addition. However, P addition promoted particulate organic carbon (POC), which was likely attributed to hampered decomposition by lower microbial biomass (particularly fungi). In contrast, N addition did not change POC, probably because more plant biomass inputs were offset by faster decomposition of higher-quality plant litter (lower C:N ratio). Moreover, N addition rather than P addition decreased the percentage of labile functional group of O-alkyl C, whereas slightly increased alkyl-aromatic C:O-alkyl C ratio. These changes in SOC chemical composition with N inputs were likely caused by enhanced labile OM decomposition and rhizodeposit inputs. Overall, our results suggest that long-term exogenous N input could potentially accelerate SOM decomposition indicated by the chemical composition, but P input could result in inhibition of SOM decomposition and accumulation of POC stock in the alpine meadow ecosystem.

Effects of ferric and manganese precursors on catalytic activity of Fe-Mn/TiO2 catalysts for selective reduction of NO with ammonia at low temperature.

Fe-Mn/TiO2 catalysts were prepared through the wet impregnation process to selective catalytic reduction of NO by NH3 at low temperature, and series of experiments were conducted to investigate the effects of key precursors on their SCR performance. Ferric nitrate, ferrous sulfate, and ferrous chloride were chosen as Fe precursors while manganese nitrate, manganese acetate, and manganese chloride as Mn precursors. These precursors had been commonly used to prepare Fe-Mn/TiO2 catalysts by numerous researchers. The results showed that there were distinct differences in NO conversion efficiencies at low temperature of catalysts prepared with different precursors. Catalysts prepared with ferric nitrate and manganese nitrate precursors exhibited the best catalytic performance at low temperature, while three kinds of catalysts prepared with manganese chloride precursors exhibited significantly low catalytic activity. All catalysts were characterized by XRD, SEM, H2-TPR, NH3-TPD, and XPS. The results indicated that when the catalysts were prepared with manganese nitrate or manganese acetate as precursors, Mn4+ contents and Oβ/(Oβ+ Oα) ratios decreased in an order of ferric nitrate > ferrous sulfate > ferrous chloride, which was consistent with the change of catalytic activities of the corresponding catalysts at low temperature. It can be found that the excellent catalytic performance of Fe(A)-Mn(a)/TiO2 was ascribed to high redox property and enrichment of Mn4+species and surface chemical labile oxygen groups.

Mechanistic Insights on Skin Sensitization to Linalool Hydroperoxides: EPR Evidence on Radical Intermediates Formation in Reconstructed Human Epidermis and 13C NMR Reactivity Studies with Thiol Residues

Linalool is one of the most commonly used fragrance terpenes in consumer products. While pure linalool is considered as non-allergenic because it has a very low skin sensitization potential, its autoxidation on air leads to allylic hydroperoxides that have been shown to be major skin sensitizers. These hydroperoxides have the potential to form antigens via radical mechanisms. In order to obtain in-depth insights of such reactivity, we first investigated the formation of free radicals derived from linalool hydroperoxides in situ in a model of human reconstructed epidermis by electron paramagnetic resonance combined with spin trapping. The formation of carbon- and oxygen-centered radical species derived from the hydroperoxides was especially evidenced in an epidermis model, mimicking human skin and thus closer to what may happen in vivo. To further investigate these results, we synthesized linalool hydroperoxides containing a 13C-substitution at positions precursor of carbon radicals to elucidate if one of these positions could react with cysteine, its thiol chemical function being one of the most labile groups prone to react through radical mechanisms. Reactions were followed by mono- and bidimensional 13C NMR. We validated that carbon radicals derived from allylic hydrogen abstraction by the initially formed alkoxyl radical and/or from its β-scission can alter directly the lateral chain of cysteine forming adducts via radical processes. Such results provide an original vision on the mechanisms likely involved in the reaction with thiol groups that might be present in the skin environment. Consequently, the present findings are a step ahead toward the understanding of protein binding processes to allergenic allylic hydroperoxides of linalool through the involvement of free radical species and thus of their sensitizing potential.

Improved Synthesis of Sulfur-Containing Glycosides by Suppressing Thioacetyl Migration.

Complex mixtures were often observed when we attempted to synthesize 4-thio- and 2,4-dithio-glycoside derivatives by double parallel and double serial inversion, thus leading to no or low yields of target products. The reason was later found to be that many unexpected side products were produced when a nucleophile substituted the leaving group on the substrate containing the thioacetate group. We hypothesized that thioacetyl migration is prone to occur due to the labile thioacetate group even under weak basic conditions caused by the nucleophile, leading to this result. Therefore, we managed to inhibit the generation of thiol groups from thioacetate groups by the addition of an appropriate amount of conjugate acid/anhydride, successfully improving the synthesis of 4-thio- and 2,4-dithio-glycoside derivatives. The target products which were previously difficult to synthesize, were herein obtained in relatively high yields. Finally, 4-deoxy- and 2,4-dideoxy-glycoside derivatives were efficiently synthesized through the removal of thioacetate groups under UV light, starting from 4-thio- and 2,4-dithio-glycoside derivatives.

Symposium review: One-carbon metabolism and methyl donor nutrition in the dairy cow

The present review focuses on methyl donor metabolism and nutrition in the periparturient and lactating dairy cow. Methyl donors are involved in one-carbon metabolism, which includes the folate and Met cycles. These cycles work in unison to support lipid, nucleotide, and protein synthesis, as well as methylation reactions and the maintenance of redox status. A key feature of one-carbon metabolism is the multi-step conversion of tetrahydrofolate to 5-methyltetrahyrofolate. Homocysteine and 5-methyltetrahyrofolate are utilized by vitamin B12-dependent Met synthase to couple the folate and Met cycles and generate Met. Methionine may also be remethylated from choline-derived betaine under the action of betaine hydroxymethyltransferase. Regardless, Met is converted within the Met cycle to S-adenosylmethionine, which is universally utilized in methyl-group transfer reactions including the synthesis of phosphatidylcholine. Homocysteine may also enter the transsulfuration pathway to generate glutathione or taurine for scavenging of reactive oxygen metabolites. In the transition cow, a high demand exists for compounds with a labile methyl group. Limited methyl group supply may contribute to inadequate hepatic phosphatidylcholine synthesis and hepatic triglyceride export, systemic oxidative stress, and compromised milk production. To minimize the perils associated with methyl donor deficiency, the peripartum cow relies on de novo methylneogenesis from tetrahydrofolate. In addition, dietary supplementation of rumen-protected folic acid, vitamin B12, Met, choline, and betaine are potential nutritional approaches to target one-carbon pools and improve methyl donor balance in transition cows. Such strategies have merit considering research demonstrating their ability to improve milk production efficiency, milk protein synthesis, hepatic health, and immune response. This review aims to summarize the current understanding of folic acid, vitamin B12, Met, choline, and betaine utilization in the dairy cow. Methyl donor co-supplementation, fatty acid feeding strategies that may optimize methyl donor supplementation efficacy, and potential epigenetic mechanisms are also considered.

Synthesis and Liver Microsomal Metabolic Stability Studies of a Fluorine-Substituted δ-Tocotrienol Derivative.

A fluoro-substituted δ-tocotrienol derivative, DT3-F2, was synthesized. This compound was designed to stabilize the metabolically labile terminal methyl groups of δ-tocotrienol by replacing one C-H bond on each of the two methyl groups with a C-F bond. However, in vitro metabolic stability studies using mouse liver microsomes revealed an unexpected rapid enzymatic C-F bond hydrolysis of DT3-F2. To the best of our knowledge, this is the first report of an unusual metabolic hydrolysis of allylic C-F bonds.

Tariquidar-related triazoles as potent, selective and stable inhibitors of ABCG2 (BCRP)

Tariquidar derivatives have been described as potent and selective ABCG2 inhibitors. However, their susceptibility to hydrolysis limits their applicability. The current study comprises the synthesis and characterization of novel tariquidar-related inhibitors, obtained by bioisosteric replacement of the labile moieties in our previous tariquidar analog UR-ME22-1 (9). CuAAC (“click” reaction) gave convenient access to a triazole core as a substitute for the labile amide group and the labile ester moiety was replaced by different acyl groups in a Sugasawa reaction. A stability assay proved the enhancement of the stability in blood plasma. Compounds UR-MB108 (57) and UR-MB136 (59) inhibited ABCG2 in a Hoechst 33342 transport assay with an IC50 value of about 80 nM and belong to the most potent ABCG2 inhibitors described so far. Compound 57 was highly selective, whereas its PEGylated analog 59 showed some potency at ABCB1. Both 57 and 59 produced an ABCG2 ATPase-depressing effect which is in agreement with our precedent cryo-EM study identifying 59 as an ATPase inhibitor that exerts its effect via locking the inward-facing conformation. Thermostabilization of ABCG2 by 57 and 59 can be taken as a hint to comparable binding to ABCG2. As reference substances, compounds 57 and 59 allow additional mechanistic studies on ABCG2 inhibition. Due to their stability in blood plasma, they are also applicable in vivo. The highly specific inhibitor 57 is suited for PET labeling, helping to further elucidate the (patho)physiological role of ABCG2, e.g. at the BBB.

Chemo-selective Rh-catalysed hydrogenation of azides into amines

Rh/Al2O3 can be used as an effective chemo-selective reductive catalyst that combines the mild conditions of catalytic hydrogenation with high selectivity for azide moieties in the presence of other hydrogenolysis labile groups such as benzyl and benzyloxycarbonyl functionalities. The practicality of this strategy is exemplified with a range of azide-containing carbohydrate and amino acid derivatives.

Covalent attachment of resveratrol to stainless steel toward the development of a resveratrol-releasing bare-metal stent.

Herein, we describe the covalent attachment of resveratrol, a naturally occurring antioxidant, to the surface of stainless-steel as a model for designing a novel bare-metal stent to treat coronary artery disease. Resveratrol has been shown to reduce oxidative stress in dysfunctional endothelial cells, and stimulate arterial healing. Resveratrol treatments, however, are limited by low water solubility, such that a localized delivery to the site of arterial narrowing via a coated stent presents a promising strategy for improving stent outcomes. Our attachment strategy utilizes zirconium vapor deposition to lay down a thin layer of zirconium oxide with labile hydrocarbon groups at the surface. Resveratrol can displace these hydrocarbons in aprotic solvent to afford a covalently attached layer of resveratrol. We evaluated the release of resveratrol under a range of pH levels, including physiological conditions (pH = 7.4 and 37 °C). Furthermore, we established that endothelial cells grown on a resveratrol-bound surface release elevated nitric oxide levels compared to controls, a key endothelial signaling molecule responsible for arterial health. These results are promising toward the development of a resveratrol-coated bare-metal stent to improve patient outcomes.

Hafnium(IV) Chloride Catalyzes Highly Efficient Acetalization of Carbonyl Compounds.

Hafnium(IV) tetrachloride efficiently catalyzes the protection of a variety of aldehydes and ketones, including benzophenone, acetophenone, and cyclohexanone, to the corresponding dimethyl acetals and 1,3-dioxolanes, under microwave heating. Substrates possessing acid-labile protecting groups (TBDPS and Boc) chemoselectively generated the corresponding acetal/ketal in excellent yields. In this study. the selective protection of aldehydes and ketones using a Hafnium(IV) chloride, which is a novel catalyst, under microwave heating was observed. Hence, it is imperative to find suitable conditions to promote the protection reaction in high yields and short reaction times. This study was undertaken not only to find a novel catalyst but also to perform the reaction with substrates bearing acid-labile protecting groups, and study the more challenging ketones as benzophenone. Using a microwave synthesis reactor Monowave 400 of Anton Paar, the protection reaction was performed on a raging temperature of 100°C ±1, a pressure of 2.9 bar, and an electric power of 50 W. More than 40 substrates have been screened and protected, not only the aldehydes were protected in high yields but also the more challenging ketones such as benzophenone were protected. All the products were purified by simple flash column chromatography, using silica gel and hexanes/ethyl acetate (90:10) as eluents. Finally, the protected substrates were characterized by NMR 1H, 13C and APCI-HRMS-QTOF. Preliminary screening allowed us to find that 5 mol % of the catalyst is enough to furnish the protected aldehyde or ketone in up to 99% yield. Also it was found that substrates with a variety of substitutions on the aromatic ring (aldehyde or ketone), that include electron-withdrawing and electrondonating group, can be protected using this methodology in high yields. The more challenging cyclic ketones were also protected in up to 86% yield. It was found that trimethyl orthoformate is a very good additive to obtain the protected acetophenone. Finally, the protection of aldehydes with sensitive functional groups was performed. Indeed, it was found that substrates bearing acid labile groups such as Boc and TBDPS, chemoselectively generated the corresponding acetal/ketal compound while keeping the protective groups intact in up to 73% yield. Hafnium(IV) chloride as a catalyst provides a simple, highly efficient, and general chemoselective methodology for the protection of a variety of structurally diverse aldehydes and ketones. The major advantages offered by this method are: high yields, low catalyst loading, air-stability, and non-toxicity.

Metamorphic transformations of nitrogen functionalities: Stabilization of organic nitrogen in anthracite and its effect on δ15N parameter

Abstract The coal metamorphism, as it evolves the microstructure of the coals, would also have significant influences on the structural transformations and isotopic discriminations of the primary chemical moieties. The present study aims to illustrate the nitrogen functionalities present within the chemical framework of the bituminous coal samples from the Raniganj and the Jharia Basins and anthracite A samples of the fold-thrust belts of the Sikkim Himalayas as well as to document the metamorphic transformations of these nitrogenous moieties with the advent in the degree of the coalification. The stable carbon (−24.08 to −21.67‰ for bituminous coal samples and −23.91 to −21.39‰ for anthracite A samples) and nitrogen isotopes (1.64–2.81‰ for the bituminous coal samples; 1.07–3.44‰ for the anthracite A samples) do not show any significant variation with the vitrinite reflectance and, therefore, correspond to the terrestrial higher plant sources of the organic matter. Further, the weak shifts of stable nitrogen isotope values in the anthracite A samples may be attributed to the preservation of the organic nitrogen in the thermally stable aromatic and heterocyclic structures. The total organic carbon to total nitrogen (TOC/TN) ratio may represent the vascular organic matter input into the mire in the case of bituminous coal samples (33.49–43.69), while for the anthracite A samples, this ratio may be an indication of the preservation of the organic nitrogen in the stable chemical framework within the microstructure. The primary alteration of the labile nitrogen-containing groups including the pyrrolic structures would have been initiated by the aqueous fluid entering into the reactive chemical framework during hydrothermal metamorphism. During these processes, most of the nitrogen atoms would have been quaternarized, which is evidenced by strong correlation (r = 0.96) between the relative area ratio of the graphitic to pyrrolic nitrogen and the mean random vitrinite reflectance. Moreover, the intensity and relative area ratio of the pyridinic to pyrrolic nitrogen are strongly correlated with the mean random vitrinite reflectance (r = 0.92 and 0.89, respectively) suggesting entanglement of the nitrogen atoms within the pyridinic forms as well with increasing metamorphic temperature. These structural rearrangements would have intensified the cyclazine structures and preserved the pyridinic forms in the anthracite A samples. Due to the increase in aromaticity and consequent increase in surface hydrophobicity and decrease in the interlayer spacing, the fluid would have lost its mobile phase and could not invade the relatively inert aromatic clusters. Thus, the organic nitrogen atoms were preserved within the thermochemically stable functionalities without showing any substantial isotopic variation. The scientific contribution of this present investigation, hence, lies in depicting the transformation of organic nitrogen among the pyrrolic, pyridinic and the cyclazine moieties with insignificant shifts in stable nitrogen isotope during coalification.

Biocompatibility and hemocompatibility of hydrothermally derived reduced graphene oxide using soluble starch as a reducing agent

Graphene-based nanomaterials (GBNs) have many applications as biomedical materials in tissue engineering and regenerative medicine. We report on the preparation of starch-(functionalized) reduced graphene oxide nanosheets (SRGO) using soluble starch as a reducing agent in a hydrothermal method, and their in vitro interactions with human skin fibroblasts and red blood cells (RBCs). Our results indicate that soluble SRGO nanosheets were prepared using graphene oxide (GO) as a raw material. SRGO-1 and -10, which were prepared using different concentrations of soluble starch after hydrothermal treatment, were characterized by ultraviolet-visible spectroscopy and showed a peak shift at 260 nm corresponding to the deoxygenation of GO and restoration of the conjugated aromatic structure. Dynamic light scattering and zeta potential measurements were used to determine Z-average sizes and surface charges of GO and SRGOs. X-ray diffractometry, attenuated total reflectance Fourier-transform infrared spectroscopy, and Raman spectroscopy revealed the progressive elimination of labile oxygen functional groups during hydrothermal treatment and restoration of the π-conjugated network. X-ray photoelectron spectroscopy showed de-oxidation of SRGOs, which had high carbon to oxygen ratios (C/O) as compared with GO. Interactions of SRGO-1 and -10 with skin fibroblasts showed excellent biocompatibility even at a concentration of 200 μg/ml with cell viabilities up to 88% and 90%, respectively, whereas notable cytotoxicity was observed for GO at 20 μg/ml. Similarly, SRGO-1 and -10 did not exhibit toxicity to RBCs compared to GO. Biofilm formation and metabolic activities of biofilm by the bacterium Staphylococcus aureus were also evaluated using a crystal violet and a tetrazolium reduction assay, respectively. The described hydrothermal method used to synthesize SRGO provides a cheap, facile, and environmentally friendly means of producing water-dispersible, biocompatible and hemocompatible reduced GOs for the fabrication of novel GBNs for various biomedical applications.

Sequencing Heparan Sulfate Using HILIC LC-NETD-MS/MS.

Heparan sulfate (HS) mediates a wide range of protein binding interactions key to normal and pathological physiology. Though liquid chromatography coupled with mass spectrometry (LC-MS) based disaccharide composition analysis is able to profile changes in HS composition, the heterogeneity of modifications and the labile sulfate group present major challenges for liquid chromatography tandem mass spectrometry (LC-MS/MS) sequencing of the HS oligosaccharides that represent protein binding determinants. Here, we report online LC-MS/MS sequencing of HS oligosaccharides using hydrophilic interaction liquid chromatography (HILIC) and negative electron transfer dissociation (NETD). A series of synthetic HS oligosaccharides varying in chain length (tetramers and hexamers), number of sulfate groups (3-7), sulfate patterns (sulfate positional isomers), and uronic acid epimerization (epimers) were separated and sequenced. The LC elution order of isomeric compounds was associated with their fine structure. The application of an online cation exchange device (ion suppressor) enhanced the precursor charge states, and the subsequent NETD produced abundant glycosidic fragments, allowing the characterization of both lowly sulfated and highly sulfated HS oligosaccharides. Furthermore, the diagnostic cross-ring ions differentiated the 6-O sulfation and 3-O sulfation, allowing unambiguous structural assignment. Collectively, this LC-NETD-MS/MS method is a powerful tool for sequencing of heterogeneous HS mixtures and is applicable for the differentiation of both isomers and epimers, for the characterization of saccharide mixtures with a varying extent of sulfation and even for the determination of both predominant and rare modification motifs. Thus, LC-NETD-MS/MS has great potential for further application to biological studies.

Host-Guest Feature of DPPP Bridged Arene-Ruthenium Clip Derived Molecular Rectangle.

The development of DPPP2- (H2DPPP = 2,5-dihydro-3,6-di-2-pyridylpyrrolo(3,4-c)pyrrole-1,4-dione) bridged (NN∩NN) diruthenium complexes [(Cym)(X)RuII(μ-dppp)RuII(X)(Cym)] (Cym = para-cymene and X = OTf- (1), SCN- (2), N3- (3), NO2-(4)) are considered as the probable molecular clips for the construction of metallarectangle. Crystal structures of 2-4 established anticonfiguration with respect to monodentate SCN-, N3- and NO2- groups, respectively. Though molecular clips 2-4 failed to provide the desired metallarectangle in combination with the 4,4'-bipyridine spacer, 1 with the labile OTf groups facilitated to achieve the metallarectangle 5. The crystal structure of 5 revealed that two twisted 4,4'-bipyridine spacers bridged between the two units of dimeric 1 in symmetric fashion, which in effect led to the newer class of molecular rectangle 5 with a hydrophobic cavity size of the cationic host of 8.32 × 11.11 Å2. Furthermore, the host-guest interaction potential of 5 with special reference to the guest molecule, pyrene, was explored. The crystal structure of the resultant molecule 6 ascertained the partial encapsulation of two pyrene molecules inside the hydrophobic cavity of 5, due to the twisted 4,4'-bipyridine spacer units between the two ruthenium clips. It also attributed a noncovalent CH-π interaction involving protons of pyrene and the π-electron cloud of 4,4'-bipyridine as well as a weak interaction between pyrene protons and the pendant C═O group of DPPP. Encapsulation of the guest molecule (pyrene) inside the cavity of the metallarectangle was also monitored by following the quenching of florescent intensity of pyrene on addition of 5.

Sugar alcohol provides imaging contrast in cancer detection

Clinical imaging is widely used to detect, characterize and stage cancers in addition to monitoring the therapeutic progress. Magnetic resonance imaging (MRI) aided by contrast agents utilizes the differential relaxivity property of water to distinguish between tumorous and normal tissue. Here, we describe an MRI contrast method for the detection of cancer using a sugar alcohol, maltitol, a common low caloric sugar substitute that exploits the chemical exchange saturation transfer (CEST) property of the labile hydroxyl group protons on maltitol (malCEST). In vitro studies pointed toward concentration and pH-dependent CEST effect peaking at 1 ppm downfield to the water resonance. Studies with control rats showed that intravenously injected maltitol does not cross the intact blood-brain barrier (BBB). In glioma carrying rats, administration of maltitol resulted in the elevation of CEST contrast in the tumor region only owing to permeable BBB. These preliminary results show that this method may lead to the development of maltitol and other sugar alcohol derivatives as MRI contrast agents for a variety of preclinical imaging applications.

Chemical reaction and diffusion kinetics during laser-induced submillisecond heating for lithographic applications

Reactions in solid-state chemistry are controlled by both underlying chemical reaction rates and temperature-dependent diffusion of reactants and products. Due to distinctly different activation energies, the relative rates of reaction and diffusion may shift dramatically with temperature. In this work, the acid catalyzed deprotection of acid labile groups of model chemically amplified photopolymers was studied to understand the effects of temperature on diffusion-coupled reactions. In these systems, strong acids form during exposure of photoacid generators (PAGs) to ultraviolet radiation and then diffuse and catalyze deprotection reactions. By using very short duration laser-induced heating for the postexposure bake step, the potential reaction temperature range is extended by several hundred degrees compared to traditional thermal processing temperatures. Thermal degradation at these temperatures is avoided by simultaneously reducing the heating time from minutes to submilliseconds. Both diffusion and reaction rates were measured in this high temperature region for three different photoresists combined with two different PAGs, with activation energies of the key processes determined. The interplay of diffusion and reaction rates was also examined by comparing results of high-resolution pattern formation. The best image formation at high temperature was achieved using photoresists with high deprotection rates combined with PAGs exhibiting low diffusivity.

Functionalization of Enzymatically Synthesized Rigid Poly(itaconate)s via Post‐Polymerization Aza‐Michael Addition of Primary Amines

AbstractThe bulky 1,4‐cyclohexanedimethanol was used as co‐monomer for introducing rigidity in lipase synthetized poly(itaconate)s. Poly(1,4‐cyclohexanedimethanol itaconate) was synthetized on a 14 g scale at 50 °C, under solvent‐free conditions and 70 mbar using only 135 Units of lipase B from Candida antarctica per gram of monomer. The mild conditions preserved the labile vinyl group of itaconic acid and avoided the decomposition of 1,4‐cyclohexanedimethanol, both observed in chemical polycondensations. Experimental and computational data show that the enzymatic polycondensation proceeds despite the low reactivity of C1 of itaconic acid. The rigid poly(1,4‐cyclohexanedimethanol itaconate) was investigated in the context of aza‐Michael addition of hexamethylenediamine and 2‐phenylethylamine to the vinyl moiety. The enzymatically synthesized linear poly(1,4‐butylene itaconate) was studied as a comparison. The two oligoesters (Molecular Weights ranging from 720 to 2859 g mol−1) reacted on a gram scale, at 40–50 °C, at atmospheric pressure and in solvent‐free conditions. The addition of primary amines led to amine‐functionalized oligoesters but also to chain degradation, and the reactivity of the poly(itaconate)s was influenced by the rigidity of the polymer chain. Upon the formation of the secondary amine adduct, the linear poly(1,4‐butylene itaconate) undergoes fast intramolecular cyclization and subsequent degradation via pyrrolidone formation, especially in the presence of hexamethylenediamine. On the contrary, the bulky 1,4‐cyclohexanedimethanol confers rigidity to poly(1,4‐cyclohexanedimethanol itaconate), which hampers the intramolecular cyclization. Also, the bulkiness of the amine and the use of solvent emerged as factors that affect the reactivity of poly(itaconate)s. Therefore, the possibility to insert discrete units of itaconic acid in oligoesters using biocatalysts under solvent‐free mild conditions opens new routes for the generation of bio‐based functional polymers or amine‐triggered degradable materials, as a function of the rigidity of the polyester chain.magnified image

Preferential Solvation of Mordant Black and Solochrome Dark Blue in Mixed Solvent Systems

In this study, the preferential solvation of Mordant Black and Solochrome Dark Blue were investigated in mixed solvent systems of aqueous methanol, ethanol, propan-1-ol, propan-2-ol, methanol: ethanol, methanol:propan-1-ol, methanol:propan-2-ol, ethanol:propan-1-ol, ethanol:propan-2-ol, propan-1-ol:propan-2-ol and carbon tetrachloride: dimethylformamide. Results showed a deviation of solvation data from ideality over the majority of composition ranges in all the solvent mixtures. The type and contribution of specific and non-specific solute-solvent interactions were analyzed in the framework of the linear solvation energy relationships. Statistical analysis of single, dual, and multiparametric equations revealed that in pure solvents, spectral behaviours of MB and SDB were affected by the polarity and basicity of the solvent milieu respectively. However in aqueous alcohols, polarity of the solvent milieu was the most significant determinant of spectral patterns with α and β parameters playing secondary contributory roles in the spectral changes of MB and SDB, respectively. Multiparametric equations generally yielded the best fitted model in mixed alcohol systems with polarity remaining the largest contributor, followed by β and α of the solvent milieu in that order. Spectral-structure relationships identified ion-dipole interactions involving the charged sulphonate and hydrazone moieties as well as proton-donor-acceptor interactions of the common labile hydroxyl groups as mechanisms for the observed solvation data.