Secondary OH Research Articles

Gas-phase reaction products and yields of terpinolene with ozone and nitric oxide using a new derivatization agent.

The new derivatization agent, O-tert-butylhydroxylamine hydrochloride (TBOX) was used to investigate the carbonyl reaction products from terpinolene ozonolysis. With ozone (O3) as the limiting reagent, four carbonyl compounds were detected: methylglyoxal (MG), 4-methylcyclohex-3-en-1-one, (4MCH), 6-oxo-3-(propan-2-ylidene) heptanal (6OPH), and 3,6-dioxoheptanal (36DOH). The tricarbonyl 36DOH has not been previously observed. Using cyclohexane as a hydroxyl radical (OH•) scavenger, the yields of 6OPH and 36DOH were reduced indicating the influence secondary OH• radicals have on terpinolene ozonolysis products. However, the MG yield increased and the 4MCH yield was unchanged when OH•radicals were scavenged suggesting they are only made by the terpinolene + O3 reaction. The detection of 36DOH using TBOX highlights the advantages of a smaller molecular weight derivatization agent for the detection of multi-carbonyl compounds. The product yields from terpinolene ozonolysis experiments conducted in the presence of 20 ppb nitric oxide (NO) remained unchanged except for MG which decreased. However, in experiments where O3 was kept constant at 50 ppb and NO was varied (20, 50, 100 ppb) MG, 6OPH, 36DOH decreased with increasing NO while 4MCH increased with increasing NO. The use of TBOX derivatization if combined with other derivatization agents may address a recurring need to simply and accurately detect multi-functional oxygenated species in air.

Enlarging the substrate portfolio of the thermophilic esterase EST2 from Alicyclobacillus acidocaldarius.

The enzymatic regioselective hydrolysis of (a) acetylated mono- to tetrasaccharides of different nature, (b) of acetylated aryl glycosides and (c) of different acetylated nucleosides was studied enlarging the portfolio of substrates that can be employed by the thermophilic esterase EST2 from Alicyclobacillus acidocaldarius. The reactions were optimised to the extent that the amount of enzyme needed was lowered of two orders of magnitude with respect to the previously reported reactions, namely from 4000 to 40 U of enzyme per reaction. New additional solvents were screened and dramatic changes in regioselectivity were observed depending on the amount and type of solvent used. For example, in the presence of 10 % DMF, only two α-D-glucose products 6-OH and 4,6-OH (in a 76:24 ratio) were detected, whereas with 25 % DMF, at least four products of similar amount were observed. This versatility adds specific value to the biocatalyst making possible the design of biocatalytic reactions with different hydrophobic ester substrates. As an additional remarkable example, EST2 catalysed with a good yield and high regioselectivity the hydrolysis of p-nitrophenyl β-D-xylopyranoside triacetate producing only the monoacetylated derivative with acetyl group in 3-O-position, in 2 min. The results with nucleosides as substrates are particularly interesting. The peracetates of 3',5'-di-O-acetylthymidine are converted almost quantitatively (95 %) to the monoacetylated derivative possessing free secondary OH; this regioselectivity is complementary to hydrolysis/alcoholysis reactions catalysed by CAL-B lipase or to other microbial hydrolytic biocatalysts, generally giving products with free primary OH groups. A docking analysis was undertaken with all analysed substrates suggesting a structural interpretation of the results. In most of cases, the best pose of the selected substrate was in line with the observed regioselectivity.

Purification, structural characterization, and modification of organosolv wheat straw lignin.

Biolignin, a wheat straw lignin produced by acetic acid/formic acid/water hydrolysis, was characterized by (31)P and (13)C-(1)H 2D NMR spectroscopy and by size-exclusion chromatography. Biolignin is a mixture of low molar mass compounds (Mn = 1660 g/mol) made up of S, G, and H units and of coumaric and ferulic acid units. β-5 and β-O-4 interunit linkages are partially acylated in the γ-position by acetate and p-coumarate groups. Deacylated samples with a low content of contaminants were obtained by combining alkaline hydrolysis and solvent extraction. The high phenolic OH content found by (31)P NMR reflects the presence of condensed aromatic units, such as 5-5 units. Reaction of purified lignin with ethanol and ethane-1,2-diol yielded esterified lignins much more soluble than Biolignin in common organic solvents. During this reaction, the secondary OH of β-O-4 linkages was simultaneously etherified. Phenol hydroxyethylation by 2-chloroethanol yielded samples containing only aliphatic hydroxyl groups.

Regioselective Ring-Opening Polymerization of a Polyhydroxycarboxylic Acid for the Synthesis of a Nanoscale Carrier Material with pH-Dependent Stability and Sustained Drug Release.

Synthetic polyesters are usually composed of monohydroxycarboxylic acids to avoid the problem of regioselectivity during ring-opening polymerization. In contrast, the linear polyester BICpoly contains four secondary OH groups and is nevertheless esterified regioselectively at only one of these positions. Neither the synthesis of the tricyclic monomers nor the ring-opening polymerization requires protecting groups, making BICpoly an attractive novel and biocompatible polymer. BICpoly nanoparticles can be loaded with low-molecular weight drugs or coated onto surfaces as thin films. The release of loaded compounds makes BICpoly an attractive depot for drug release, as shown herein by loading BICpoly with dyes or the cytostatic drug doxorubicin. BICpoly is distinguishable from other polymers by its characteristic pH-dependent degradation.

Glycerolysis of methyl oleate on MgO: Experimental and theoretical study of the reaction selectivity

The liquid-phase MgO-promoted glycerolysis of methyl oleate, a fatty acid methyl ester (FAME), to give acylglycerol products was studied both, experimentally and by density functional theory (DFT). Catalytic results showed that strongly basic low coordination O2− surface sites participate in kinetically relevant steps of the glycerolysis reaction. Changes in the selectivity toward the different mono- and diglyceride isomers were investigated by varying the reaction conditions. The main product was always α-glyceryl monooleate (α-MG), a monoglyceride with the ester fragment at one of the terminal positions of the glycerol molecule; the β-MG isomer, with the ester substituted at position 2 was obtained in much lower amounts.The molecular modeling of glycerol (Gly) and FAME adsorptions as well as of the glycerolysis reaction was carried out using periodic DFT calculations and a model of stepped MgO surface. Results indicated that FAME was more weakly adsorbed than Gly; the latter adsorbs on a coordinatively unsaturated surface O2− site with OH bond breaking at position 2 of the Gly molecule, giving therefore a surface β-glyceroxide species. Calculations explained the apparent contradiction between the preferential formation of the α-MG isomer and the energetically favored dissociation of the secondary OH group of Gly that leads to the β-glyceroxide species. They predict that the β-glyceroxide species participates in the pathways conducting to both, α- and β-MG isomers. Synthesis of α-MG occurs by CO coupling of β-glyceroxide with FAME at one of the two primary OH groups of the β-glyceroxide species. Two transition states (TS) and a tetrahedral intermediate (TI) are involved in both, α-MG and β-MG isomer formation. However, the pathway toward β-MG is limited by the large sterical effects associated to the TI formation. Contrarily, the TI leading to α-MG is relatively easy to form.

Softwood kraft lignin for value-added applications: Fractionation and structural characterization

This study focuses on a systematic, structural characterization of lignin samples fractionated from softwood industrial black liquor (BL). In addition to the isolation efficiency, the impact of fractionation and pulping severity on lignin structure was studied. BL samples from different chemical pulping stages were collected and the lignin was fractionated by sequential precipitation. While the alteration in structure and properties of the samples recovered from different delignification stages was only marginal, the spectroscopic characterization of the isolated lignin revealed significant alteration in its structure and functionalities as a function of the pH. Lignin samples precipitated at pH 10.5 exhibited the highest purity, as indicated by them having the lowest content of polysaccharides. In contrast, the samples precipitated at a pH of 2.5 revealed the highest carbohydrate content, rising from 9.7% at the beginning of cooking, to 36.8% at the end. At the same time, these lignin samples had the lowest Mw and the highest number of phenolic hydroxyl groups. Based on spectroscopic analysis, low Mw kraft lignin displayed an unusually high carboxyl content and a low methoxyl group content. All of the kraft lignin samples showed a reduction in the number of primary and secondary OH groups, which continuously decreased over the course of pulping. An opposite trend was observed with decreasing precipitation pH.

Bismuth modified Au-Pt bimetallic catalysts for dihydroxyacetone production

Bi has been employed as a modifier for AuPt/AC alloy based catalysts for the base-free glycerol oxidation. The addition of Bi has a significant effect on the selectivity of the reaction. Indeed, in the absence of Bi, the oxidation of the primary alcohol function is favored with the production of glyceric acid as main product. On the contrary, the addition of Bi promotes the oxidation of the secondary OH function leading to the production of dihydroxyacetone (DHA) as the main product (selectivity of 63% at 80% conversion). Differently from the gold-free catalyst Bi-Pt/AC, which suffers from Bi leaching, the Au modified one, namely Bi-AuPt/AC, enhances the catalyst stability by limiting the Bi leaching thus resulting in a good selectivity to DHA even at high conversion.

A new agent for derivatizing carbonyl species used to investigate limonene ozonolysis

A new method for derivatizing carbonyl compounds is presented. The conversion of a series of dicarbonyls to oximes in aqueous solution and from gas-phase sampling was achieved using O-tert-butylhydroxylamine hydrochloride (TBOX). Some advantages of using this derivatization agent include: aqueous reactions, lower molecular weight oximes, and shortened oxime-formation reaction time. Additionally, the TBOX derivatization technique was used to investigate the carbonyl reaction products from limonene ozonolysis. With ozone (O3) as the limiting reagent, four carbonyl compounds were detected: 7-hydroxy-6-oxo-3-(prop-1-en-2-yl)heptanal; 3-Isopropenyl-6-oxoheptanal (IPOH), 3-acetyl-6-oxoheptanal (3A6O) and one carbonyl of unknown structure. Using cyclohexane as a hydroxyl (OH) radical scavenger, the relative yields (peak area) of the unknown carbonyl, IPOH, and 3A6O were reduced indicating the influence secondary OH radicals have on limonene ozonolysis products. The relative yield of the hydroxy-dicarbonyl based on the chromatogram was unchanged suggesting it is only made by the limonene + O3 reaction. The detection of 3A6O using TBOX highlights the advantages of a smaller molecular weight derivatization agent for the detection of multi-carbonyl compounds. The use of TBOX derivatization if combined with other derivatization agents may address a recurring need to simply and accurately detect multi-functional oxygenated species in air.

Evaluation of Combustion Mechanisms Using Global Uncertainty and Sensitivity Analyses: A Case Study for Low‐Temperature Dimethyl Ether Oxidation

ABSTRACTA global uncertainty analysis is performed for three current mechanisms describing the low‐temperature oxidation of dimethyl ether (Aramco Mech 1.3, Metcalfe et al., Int J Chem Kinet 2013, 45, 638–675; Zheng et al., Proc Combust Inst 2005, 30, 1101–1109; Liu et al., Combust Flame 2013, 160, 2654–2668) with application to simulations of species concentrations (CH2O, H2O2, CH3OCHO) corresponding to existing data from an atmospheric pressure flow reactor and high‐pressure ignition delays. When incorporating uncertainties in reaction rates within a global sampling approach, the distributions of predicted targets can span several orders of magnitude. The experimental profiles, however, fall within the predictive uncertainty limits. A variance‐based sensitivity analysis is then undertaken using high dimensional model representations. The main contributions to predictive uncertainties come from the CH3OCH2 + O2 system, with isomerization, propagation, chain‐branching, secondary OH formation, and peroxy–peroxy reactions all playing a role. The response surface describing the relationship between sampled reaction rates and predicted outputs is complex in all cases. Higher order interactions between parameters contribute significantly to output variance, and no single reaction channel dominates for any of the conditions studied. Sensitivity scatter plots illustrate that many different parameter combinations could lead to good agreement with specific sets of experimental data. The Aramco scheme is then updated based on data from a recent study by Eskola et al. (J Phys Chem A, in press), which presents quite different temperature and pressure dependencies for the rates of CH3OCH2O2 → CH2OCH2O2H and CH2OCH2O2H → OH+2CH2O compared with currently used values and includes well skipping channels. The updates from Eskola worsen the agreement with experiments when used in isolation. However, if the rate of the CH2OCH2O2H + O2 channel is subsequently reduced, very good agreement can be achieved. Owing to the complex nature of the response surface, the tuning of this channel remains speculative. Further detailed studies of the temperature and pressure dependence of the CH3OCH2O2 + O2, CH2OCH2O2H + O2 system are recommended to reduce uncertainties within current dimethyl ether mechanisms for low‐temperature conditions.

Chlorine as a primary radical: evaluation of methods to understand its role in initiation of oxidative cycles

Abstract. The role of chlorine atoms (Cl) in atmospheric oxidation has been traditionally thought to be limited to the marine boundary layer, where they are produced through heterogeneous reactions involving sea salt. However, recent observation of photolytic Cl precursors (ClNO2 and Cl2) formed from anthropogenic pollution has expanded the potential importance of Cl to include coastal and continental urban areas. Measurements of ClNO2 in Los Angeles during CalNex (California Nexus – Research at the Nexus of Air Quality and Climate Change) showed it to be an important primary (first generation) radical source. Evolution of ratios of volatile organic compounds (VOCs) has been proposed as a method to quantify Cl oxidation, but we find no evidence from this approach for a significant role of Cl oxidation in Los Angeles. We use a box model with the Master Chemical Mechanism (MCM v3.2) chemistry scheme, constrained by observations in Los Angeles, to examine the Cl sensitivity of commonly used VOC ratios as a function of NOx and secondary radical production. Model results indicate VOC tracer ratios could not detect the influence of Cl unless the ratio of [OH] to [Cl] was less than 200 for at least a day. However, the model results also show that secondary (second generation) OH production resulting from Cl oxidation of VOCs is strongly influenced by NOx, and that this effect obscures the importance of Cl as a primary oxidant. Calculated concentrations of Cl showed a maximum in mid-morning due to a photolytic source from ClNO2 and loss primarily to reactions with VOCs. The [OH] to [Cl] ratio was below 200 for approximately 3 h in the morning, but Cl oxidation was not evident from the measured ratios of VOCs. Instead, model simulations show that secondary OH production causes VOC ratio evolution to follow that expected for OH oxidation, despite the significant input of primary Cl from ClNO2 photolysis in the morning. Even though OH is by far the dominant oxidant in Los Angeles, Cl atoms do play an important role in photochemistry there, constituting 9% of the primary radical source. Furthermore, Cl–VOC reactivity differs from that of OH, being more than an order of magnitude larger and dominated by VOCs, such as alkanes, that are less reactive toward OH. Primary Cl is also slightly more effective as a radical source than primary OH due to its greater propensity to initiate radical propagation chains via VOC reactions relative to chain termination via reaction with nitrogen oxides.

Electrocatalytic selective oxidation of glycerol to tartronate on Au/C anode catalysts in anion exchange membrane fuel cells with electricity cogeneration

Sustainable cogeneration of tartronate (high yield of 61.8%) and electrical energy (1527J, 12h) has been achieved from direct electrocatalytic oxidation of glycerol on Au/C in a 5cm2 anion exchange membrane-direct glycerol fuel cells (AEM-DGFCs). The electrode structure and reaction conditions exhibited strong effects on the anode potential, which can be tuned to <0.45V in favor of oxidizing two primary OH groups of glycerol while minimizing over-oxidation of the secondary OH and CC bond cleavage, thereby promoting the tartronate production. The relatively low activity of partial oxidation products (glycerate, tartronate, mesoxalate) on Au/C revealed in half cell indicates that the tartronate generation in AEM-DGFCs is through direct adsorbed C3 intermediates oxidation. Mass transport of reactants and reaction intermediates governed by the operational conditions was also found to play a critical role in regulating reaction rate and the desired products selectivity. Furthermore, Au/C prepared via aqueous phase reduction method (Au/C-AQ) was compared with organic phase nanocapsule method (Au/C-NC), and it shows the residual surfactants have little effect on the tartronate yield.

Measuring Biogenic Volatile Organic Compounds (BVOCs) from Vegetation in Terms of Ozone Reactivity

A new system that uses the total reactivity with ozone (RO3) was developed for measuring biogenic volatile organic compounds (BVOCs) emitted from vegetation into the atmosphere. The decrease in ozone caused by the reaction with VOCs was monitored at the ppbv level by dual chemiluminescence detectors (CLDs) based on the NO-O3 reaction. Ozone was monitored by the dual CLDs before and after the reactor to correct for fluctuations in the ozone concentration. Such dual detectors can remove the interference caused by water vapor. A glass double-tube was adopted as the reactor. The loss rate of ozone to the wall was typically (6 ± 3) × 10–4 s–1. Gaseous cyclohexane was also added to the sample before it was introduced into the reactor to scavenge secondary OH radicals. From the characterization of the RO3 analyzer using the standard VOC sample, the dependence of ozone reduction on the reaction time and reactivity were shown to agree with theoretical predictions. A calibration procedure for determining the reaction time was also established. Consequently, the detection limit for RO3 in a 57-s reaction was determined to be 1.4 × 10–4 s–1 (S/N = 3), which corresponded to 27 ppbv of limonene. It was confirmed that the RO3 analyzer was capable of measuring BVOC levels. Finally, a practical trial was conducted in which BVOCs emitted from a real needle-leaf tree were monitored. BVOC emissions from the tree were detected and a significant increase in RO3 was observed when the tree was irradiated with light.

Gas-phase conversion of 1,3-butanediol on single acid–base and Cu-promoted oxides

The gas-phase conversion of 1,3-diols was studied on catalysts containing different active sites and using 1,3-butanediol as a model molecule. Transformation of the diol primary and/or secondary OH groups by dehydration and dehydrogenation reactions yields valuable oxygenates combining OH and CC, OH and CO or CC and CO functions, along with other compounds. A series of single oxides with different acid–base properties, copper–silica and copper-single oxide catalysts were prepared by several methods and characterized by TPR, XRD and N2O chemisorption.Acid–base oxides transform 1,3-butanediol at low rates. Oxide electronegativity determines the main reaction pathway: acidic oxides promote 1,3-butanediol dehydration toward unsaturated alcohols and olefins, whereas basic oxides dehydrogenate-dehydrate the diol toward the unsaturated ketone.The effect of Cu0 in monofunctional copper–silica, or bifunctional copper–acid or copper–base catalysts, is to increase the reaction rate and to shift the reaction pathway toward 1,3-butanediol dehydrogenation. The metal dispersion depends on the preparation method by impregnation, ion exchange or co-precipitation. Small Cu0 particles strongly adsorb reactant and products allowing consecutive reactions to take place after initial dehydrogenation. In bifunctional catalysts, the role of the acid or base sites is to promote consecutive dehydration-hydrogenation or CC bond cleavage reactions, respectively.

Conversion of diols by dehydrogenation and dehydration reactions on silica-supported copper catalysts

The gas-phase conversion of a 1,3-polyol (1,3-butanediol) containing primary and secondary OH functions was studied on a series of copper-silica catalysts, ZCuSiO2 (Z=1–25wt.% Cu), and thoroughly characterized by several techniques such as BET surface area, TPR, XRD, N2O chemisorption, and UV-vis-DRS. The physicochemical properties of the ZCuSiO2 catalysts depended on whether the metal loading was above or below the copper monolayer surface coverage (Z=13.5wt.% Cu). Copper species presenting different degrees of interaction with the silica support were detected. At low Z values Cu0 dispersion was high (D≈40%) due to a predominant contribution of nano-sized Cu species (3nm) which are difficult to reduce, but for Z>13.5wt.%, D abruptly dropped to 3–8% because of formation of larger tridimensional Cu clustered species (30nm) that reduced at lower temperatures because of a decreased copper-silica interaction.On ZCuSiO2 catalysts, dehydrogenation of the 1,3-butanediol secondary OH function prevailed over that of the primary one and therefore valuable ketones were the main reaction products. Consecutively to dehydrogenation, dehydration and hydrogenation reactions also took place. Products of the tandem reaction were the β-hydroxy ketone (4-hydroxy-2-butanone), the α,β-unsaturated ketone (methyl vinyl ketone) and the saturated ketone (methyl ethyl ketone). A direct 1,3-butanediol dehydration pathway toward methyl ethyl ketone was also found. Reaction pathways were strongly dependent on the Cu loading and therefore on the kind of Cu species (isolated or clustered). When compared at similar conversion levels, selectivity to the dehydrogenation product 4-hydroxy-2-butanone increased with Z suggesting that on large Cu0 particles 4-hydroxy-2-butanone was released to the gas phase before being converted in consecutive steps. On the contrary, on highly dispersed Cu0 crystals of low Cu loading catalysts, 1,3-butanediol was readily dehydrated giving the saturated ketone.Kinetically relevant reaction steps of 1,3-butanediol conversion by dehydrogenation and dehydration were promoted on Cu0 sites. Dehydration of the intermediate 4-hydroxy-2-butanone also occurred on Cu0 sites. Turnover rates were constant on Cu0 nano particles and slightly higher on clustered species.

Polymer Networks from Preformed Precursors Having Molecular Weight and Group Reactivity Distributions. Theory and Application

High-performance cross-linked polymeric materials are now prepared from preformed precursors typical by distributions of molecular weights, number and reactivities of functional groups, and specific architectures. This makes theoretical treatment of networks evolution and their final structure difficult. This paper describes kinetically controlled cross-linking of a precursor formed from polyfunctional cores by arm extension by which molecular weight distribution develops and new groups of different reactivity are formed. These precursors are then cross-linked with a polyfunctional cross-linker. If the precursor groups react independently, a random (binomial) distribution of reactive groups results and the gel point conversion and other network parameters are independent of the differences in reactivity the groups with the cross-linker. If the condition of random (binomial) distribution is not met (fixed numbers of groups or substitution effect in the precursor molecules), this independence does not exist. Relations for molecular weight averages prior to gelation and gel fraction and concentration of elastically active network chains in the postgel state are derived. This general treatment applies to precursors obtained by a wide variety of chain extension chemistries and any of the family of cross–linking reactions of A + B type. In the second part, the general form of the theory was adapted to describe polyether precursors prepared by addition of an epoxy ester (glycidyl pivalate) to multifunctional polyols and their curing with a tri-isocyanate. Some of the primary OH groups of the core are chain–extended to form a polyether chain terminated by a secondary OH group. The distributions are altered by additional reactions – transesterification and alcoholysis. The branching theory was modified and the results compared with experiments. Gel point conversions were affected by these additional reactions, but the concentration of elastically active network chains (EANCs) (calculated from equilibrium elastic modulus) did not change much. The fraction of formed bonds wasted in cycles amounted to 12–22%.

Performance, structure and mechanism of Pd–Ag alloy catalyst for selective oxidation of glycerol to dihydroxyacetone

The mechanism of the oxidation of glycerol to dihydroxyacetone over Pd–Ag catalysts was discussed. Characterization results suggest that the metal composition of the surface of the crystalline Pd–Ag alloy particles is almost the same as the bulk composition. The synergetic effects of Pd and Ag appear on the oxidation of the secondary OH group of vic-diols. The reaction order with respect to glycerol concentration over Pd–Ag/C was zero, suggesting the strong interaction between glycerol and the catalyst surface. The reaction order with respect to O2 pressure was 0.4, suggesting that the rate-determining step is the reaction involving oxygen species. These reaction trends and characterization results support the mechanism where the terminal OH group of glycerol is adsorbed on the Ag site and the neighboring secondary OH group (CH–OH) is attacked by the oxygen species dissociatively adsorbed on the Pd site.

Hydroxyl‐functional polyurethanes and polyesters: synthesis, properties and potential biomedical application

AbstractThis mini review gives an overview of the synthesis of polyurethanes and polyesters with pendant hydroxyl groups performed mainly in our group. Significant for the synthesis of most of these polymers with hydroxyl‐functional side groups is that no protection groups are needed. This is realised either by generating the OH group during polymer synthesis—demonstrated by the preparation of hydroxyl‐functional polyurethanes from dicarbonate monomers and diamines—or by using catalysts which discriminate between primary and secondary OH groups—demonstrated by the synthesis of hydroxyl‐functional polyesters based on malic acid using scandium triflate as catalyst. In addition, the potential of carbonate couplers for the synthesis of multifunctional polyurethane is presented. The application of such multifunctional polyurethanes as antimicrobial polymers and coatings is briefly discussed. Copyright © 2012 Society of Chemical Industry

Vibrational dynamics and hydrogen bond properties of β-CD nanosponges: an FTIR-ATR, Raman and solid-state NMR spectroscopic study

Cyclodextrin nanosponges (CDNS) are cross-linked polymers with remarkable inclusion/release properties. CDNS show swelling capability and a hydrophilicity/hydrophobicity balance that can be dramatically modified by the type and quantity of cross-linking agents. Here, we focus our attention on samples of β-cyclodextrin nanosponges (β-CDNS) obtained by reacting β-cyclodextrin (β-CD) with the cross-linking agent carbonyldiimidazole at different β-CD:cross-linking agent molar ratio. The vibrational properties of CDNS thus synthesized have been investigated by Fourier transform infrared spectroscopy in attenuated total reflectance geometry and Raman spectroscopy in the dry state at room temperature. The quantitative analysis of the O–H stretching region (3,000–3,800 cm−1) allowed us to obtain structural information on the role played by primary and secondary OH groups in the hydrogen bond network of the polymer. Also, the contribution of interstitial and intracavity crystallization water molecules is reported. Solid-state NMR spectroscopy is used to study the molecular mobility of the polymer by measuring the 1H spin–lattice relaxation time in the rotating frame (T1ρ). The T1ρ values obtained for the polymer β-CDNS are compared with free β-CD. The observed relaxation parameters point out that the ester formation occurs mainly at the primary OH groups of CDs, also supporting the interpretation of vibrational spectra.

High-Yield Synthesis of Dendrimers through Alternate Multiaddition Reactions with Commercially Available Reagents

Abstract An alternate multiaddition (AMA) process consisting of Michael addition and urethane formation is proposed to achieve the quantity synthesis of dendrimers without by-product formation and any weight loss by using commercially available compounds. α-Thioglycerol (TG) was added to pentaerythritol tetraacrylate (PETA) to give the corresponding octaol, but the subsequent reaction with 1,1-bis(acryloyloxymethyl)ethyl isocyanate (BEI) resulted in incomplete urethane formation because of the steric effect of the secondary OH groups. The replacement of BEI with 2-isocyanatoethyl acrylate (AOI) improved the efficiency of the addition of NCO to the secondary OH groups, but an excess amount of AOI was required. Subsequently, we employed the combination of PETA, 2-sulfanylethanol (SE), and BEI. The addition of SE to PETA produced readily the tetraol, which was reacted with BEI to afford dendritic octaacrylate (Ac8b). The repetition of the two addition reactions gave dendritic octaol and hexadecylacrylate (Ac16b), respectively, in large scales. The base-catalyzed Michael addition of 2-naphthalenethiol to acrylate residues of Ac8a and Ac16b gave naphthylthio-terminated dendrimers N8b and N16b, respectively, which were purified by column chromatography. GPC as well as UV-spectroscopic analysis of N8b and N16b revealed that N8b is reasonably monodispersed whereas the purity of N16b is slightly reduced.

Peptide Binding to β-Cyclodextrins: Structure, Dynamics, Energetics, and Electronic Effects

Peptide-cyclodextrin and protein-cyclodextrin host-guest complexes are becoming more and more important for industrial applications, in particular in the fields of pharmaceutical and food chemistry. They have already deserved many experimental investigations although the effect of complex formation in terms of peptide (or protein) structure is not well-known yet. Theoretical calculations represent a unique tool to analyze such effects, and with this aim we have carried out in the present investigation molecular dynamics simulations and combined quantum mechanics-molecular mechanics calculations. We have studied complexes formed between the model Ace-Phe-Nme peptide and the β-cyclodextrin (β-CD) macromolecule, and our analysis focuses on the following points: (1) how is the peptide structure modified in going from bulk water to CD environment (backbone torsion angles), (2) which are the main peptide-CD interactions, in particular in terms of hydrogen bonds, (3) which relative peptide-CD orientation is preferred and which are the structural and energetic differences between them, and (4) how the electronic properties of the peptide changes under complex formation. Overall, our calculations show that in the most stable configuration, the backbone chain lies in the narrow rim of the CD. Strong hydrogen bonds form between the H atoms of the peptidic NH groups and oxygen atoms of the secondary OH groups in the CD. These and other (weaker) hydrogen bonds formed by the carbonyl groups reduce considerably the flexibility of the peptide structure, compared to bulk water, and produce a marked increase of the local dipole moment by favoring configurations in which the two C═O bonds point toward the same direction. This effect might have important consequences in terms of the peptide secondary structure, although this hypothesis needs to be tested using larger peptide models.