Carbonyl Resonances Research Articles

Production and optimization of bioplastic (Polyhydroxybutyrate) from Bacillus cereus strain SH-02 using response surface methodology

BackgroundPolyhydroxybutyrate (PHB) is a biopolymer formed by some microbes in response to excess carbon sources or essential nutrient depletion. PHBs are entirely biodegradable into CO2 and H2O under aerobic and anaerobic conditions. It has several applications in various fields such as medicine, pharmacy, agriculture, and food packaging due to its biocompatibility and nontoxicity nature.ResultIn the present study, PHB-producing bacterium was isolated from the Dirout channel at Assiut Governorate. This isolate was characterized phenotypically and genetically as Bacillus cereus SH-02 (OM992297). According to one-way ANOVA test, the maximum PHB content was observed after 72 h of incubation at 35 °C using glucose and peptone as carbon and nitrogen source. Response surface methodology (RSM) was used to study the interactive effects of glucose concentration, peptone concentration, and pH on PHB production. This result proved that all variables have a significant effect on PHB production either independently or in the interaction with each other. The optimized medium conditions with the constraint to maximize PHB content and concentration were 22.315 g/L glucose, and 15.625 g/L peptone at pH 7.048. The maximum PHB content and concentration were 3100.799 mg/L and 28.799% which was close to the actual value (3051 mg/l and 28.7%). The polymer was identified as PHB using FTIR, NMR, and mass spectrometry. FT-IR analysis showed a strong band at 1724 cm− 1 which attributed to the ester group’s carbonyl while NMR analysis has different peaks at 169.15, 67.6, 40.77, and 19.75 ppm that were corresponding to carbonyl, methine, methylene, and methyl resonance. Mass spectroscopy exhibited molecular weight for methyl 3- hydroxybutyric acid.ConclusionPHB–producing strain was identified as Bacillus cereus SH-02 (OM992297). Under optimum conditions from RSM analysis, the maximum PHB content and concentration of this strain can reach (3100.799 mg/L and 28.799%); respectively. FTIR, NMR, and Mass spectrometry were used to confirm the polymer as PHB. Our results demonstrated that optimization using RSM is one of the strategies used for reducing the production cost. RSM can determine the optimal factors to produce the polymer in a better way and in a larger quantity without consuming time.

Copolymerisation of β‐butyrolactone and γ‐butyrolactone using yttrium amine bis(phenolate) catalysts

AbstractThe synthesis of poly(3‐hydroxbutyrate‐co‐4‐hydroxybutyrate) is reported with a family of yttrium amine bis(phenolate) catalysts via ring‐opening polymerisation of β‐butyrolactone and γ‐butyrolactone. Poly(3‐hydroxybutyrate), poly(4‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) were prepared at −40 °C with a 10 mol L−1 monomer concentration using a range of amine bis(phenolate) catalysts. It was found that poly(3‐hydroxybutyrate) synthesis is inferior under these conditions to that attainable at room temperature. In contrast, poly(4‐hydroxybutyrate) synthesis achieved up to 33% conversion under these conditions. Poly(3‐hydroxybutyrate) polymers containing up to 63% 4‐hydroxybutyrate inclusion were obtained when β‐butyrolactone and γ‐butyrolactone were copolymerised, with γ‐butyrolactone in excess in the monomer feed. The carbonyl resonances between 169 and 174 ppm in the 13C NMR spectra of this copolymer were assigned. Gel permeation chromatography of the copolymers showed that the number‐average molecular weights are consistently greater than the calculated values, and the dispersities are generally greater than 1.4, demonstrating limited control by the catalysts. Despite this restricted control, these catalysts were able to convert appreciable amounts of monomers into polymers either individually or within a copolymerisation. © 2022 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Isomer-specific influences on ignition and intermediates of two C5 ketones in an RCM

Ketones have been considered as potential biofuels and main components of blend stock for internal engines. To better understand the chemical kinetics of ketones, ignition delay times of 2-pentanone (propyl methyl ketone, PMK) and 3-pentanone (diethyl ketone, DEK) were measured at temperatures of 895–1128 K under 10 and 20 bar, at equivalence ratios (ϕ) of 0.5 and 1.0 in a rapid compression machine (RCM). To explore the impact of carbonyl functionality and resonance stabilized structures of fuel radicals on their combustion kinetics, high-temperature pyrolysis at 1130 K and relatively low-temperature oxidation at 950 K studies were performed in an RCM, and the time-resolved species concentration profiles under these two conditions were quantified using a fast sampling system and gas chromatography (GC). A new kinetic model containing low-temperature reactions was built aiming at predicting the pyrolysis and oxidation behaviors of both ketones. The consumption pathways of the resonance stabilization fuel radicals through oxygen addition and following reactions are promoted since the decomposition rates of these radicals are about 4 orders magnitudes lower than regular fuel radicals. The occurrences of the so-called “addition-dissociation reactions”, i.e., ketones reacting with a hydrogen yielding aldehyde or reacting with a methyl radical yielding shorter-chain-length ketones, are verified in pyrolysis experiments. Based on experiments and model analysis, the carbonyl functionality in both ketones is preserved during the process of β-scissions of fuel radicals and α-scissions of fuel-related acyl radicals, resulting in the direct formation of CO and ketene. However, the position of carbonyl functionality has a significant impact on the species pools.

Assessment of milk fat content in fat blends by 13C NMR spectroscopy analysis of butyrate

Butyric acid (butyrate) is a candidate marker of milk fat in complex fat blends, since it is exclusive of milk triacylglycerols (TAGs) from different ruminant species. In this work, we determined the amount of milk fat used for the preparation of fat blends by 13C Nuclear Magnetic Resonance (13C NMR) spectroscopy-based quantification of butyrate. When tested on fat samples spiked with known amounts of reference bovine milk fat (BCR-519 certified material), the relative composition of the mixtures was reliably assessed through the integration of the diagnostic 13C NMR carbonyl (C1) or α-carbonyl methylene (C2) resonances of butyrate. NMR data exhibited strict correlation with high resolution-gas chromatography (GC) of fatty acid methyl esters (R2 = 0.99), which was used as an independent and well-established method for the determination of butyrate. Thus, 13C NMR can be used for the direct assessment of milk fat content in fat mixtures, at a limit of detection lower than 5%, with clear advantages over the traditional GC methods in terms of speed, robustness and minimal sample handling. The natural variability of butyrate in milk has been taken into account to estimate the uncertainty associated with the milk fat content in unknown fat blends.

Assignment of solid-state 13C and 1H NMR spectra of paramagnetic Ni(II) acetylacetonate complexes aided by first-principles computations

Recent advances in computational methodology allowed for first-principles calculations of the nuclear shielding tensor for a series of paramagnetic nickel(II) acetylacetonate complexes, [Ni(acac)2L2] with L = H2O, D2O, NH3, ND3, and PMe2Ph have provided detailed insight into the origin of the paramagnetic contributions to the total shift tensor. This was employed for the assignment of the solid-state 1,2H and 13C MAS NMR spectra of these compounds. The two major contributions to the isotropic shifts are by orbital (diamagnetic-like) and contact mechanism. The orbital shielding, contact, as well as dipolar terms all contribute to the anisotropic component. The calculations suggest reassignment of the 13C methyl and carbonyl resonances in the acac ligand [Inorg. Chem.53, 2014, 399] leading to isotropic paramagnetic shifts of δ(13C) ≈ 800–1100 ppm and ≈180–300 ppm for 13C for the methyl and carbonyl carbons located three and two bonds away from the paramagnetic Ni(II) ion, respectively. Assignment using three different empirical correlations, i.e., paramagnetic shifts, shift anisotropy, and relaxation (T1) were ambiguous, however the latter two support the computational results. Thus, solid-state NMR spectroscopy in combination with modern quantum-chemical calculations of paramagnetic shifts constitutes a promising tool for structural investigations of metal complexes and materials.

Following Metabolism in Living Microorganisms by Hyperpolarized (1)H NMR.

Dissolution dynamic nuclear polarization (dDNP) is used to enhance the sensitivity of nuclear magnetic resonance (NMR), enabling monitoring of metabolism and specific enzymatic reactions in vivo. dDNP involves rapid sample dissolution and transfer to a spectrometer/scanner for subsequent signal detection. So far, most biologically oriented dDNP studies have relied on hyperpolarizing long-lived nuclear spin species such as (13)C in small molecules. While advantages could also arise from observing hyperpolarized (1)H, short relaxation times limit the utility of prepolarizing this sensitive but fast relaxing nucleus. Recently, it has been reported that (1)H NMR peaks in solution-phase experiments could be hyperpolarized by spontaneous magnetization transfers from bound (13)C nuclei following dDNP. This work demonstrates the potential of this sensitivity-enhancing approach to probe the enzymatic process that could not be suitably resolved by (13)C dDNP MR. Here we measured, in microorganisms, the action of pyruvate decarboxylase (PDC) and pyruvate formate lyase (PFL)-enzymes that catalyze the decarboxylation of pyruvate to form acetaldehyde and formate, respectively. While (13)C NMR did not possess the resolution to distinguish the starting pyruvate precursor from the carbonyl resonances in the resulting products, these processes could be monitored by (1)H NMR at 500 MHz. These observations were possible in both yeast and bacteria in minute-long kinetic measurements where the hyperpolarized (13)C enhanced, via (13)C → (1)H cross-relaxation, the signals of protons binding to the (13)C over the course of enzymatic reactions. In addition to these spontaneous heteronuclear enhancement experiments, single-shot acquisitions based on J-driven (13)C → (1)H polarization transfers were also carried out. These resulted in higher signal enhancements of the (1)H resonances but were not suitable for multishot kinetic studies. The potential of these (1)H-based approaches for measurements in vivo is briefly discussed.

Observation of potentially troublesome (2) JCC correlations in 1,1-ADEQUATE spectra.

Despite the tremendous usage of HMBC to establish long-range (1) H-(13) C and (1) H-(15) N heteronuclear correlations, an inherent drawback of the experiment is the indeterminate nature of the (n) JXH correlations afforded by the experiment. A priori there is no reliable way of determining whether a given (n) JCH correlation is, for example, via two-, three-, or sometimes even four-bonds. This limitation of the HMBC experiment spurred the development of the ADEQUATE family of NMR experiments that rely on, in the case of 1,1-ADEQUATE, an out-and-back transfer of magnetization via the (1) JCC homonuclear coupling constant, which is significantly larger than (n) JCC (where n = 2-4) couplings in most cases. Hence, the 1,1-ADEQUATE experiment has generally been assumed to unequivocally provide the equivalent of (2) JCH correlations. The recent development of the 1,1- and 1,n-HD-ADEQUATE experiments that can provide homodecoupling for certain (1) JCC and (n) JCC correlations has increased the sensitivity of the ADEQUATE experiments significantly and can allow acquisition of these data in a fraction of the time required for the original iterations of this pulse sequence. With these gains in sensitivity, however, there occasionally come unanticipated consequences. We have observed that the collapse of proton multiplets, in addition to providing better s/n for the desired (1) JCC correlations can facilitate the observation of typically weaker (2) JCC correlations across intervening carbonyl resonances in 1,1-HD-ADEQUATE spectra. Several examples are shown, with the results supported by the measurement of the (2) JCC coupling constants in question using J-modulated-HD-ADEQUATE and DFT calculations. Copyright © 2016 John Wiley & Sons, Ltd.

Chemical Adhesion of Polyalkenoate-based Adhesives to Hydroxyapatite.

To evaluate the chemical interaction between synthetic hydroxyapatite (HAp) and polyalkenoic acid copolymer- based (also known as Vitrebond copolymer [VCP]) adhesives. Six dentin adhesive formulations were used: 1) Adper Single Bond Plus (SB); 2) SB formulation without VCP (SBnoVCP); 3) Adper Easy Bond (EB); 4) EB formulation without VCP (EBnoVCP); 5) Scotchbond Universal adhesive (SBU); 6) SBU formulation without VCP (SBUnoVCP). Each adhesive was mixed with HAp, polymerized, and analyzed using FTIR and 13C/31P NMR spectroscopy. The FTIR spectra of SB+HAp indicated that the carbonyl group changed absorption wavenumber compared to that of SBnoVCP+HAp. 13C NMR analysis showed that the presence of methacrylated phosphoric esters in the EB and SBU formulations led to similar carbonyl resonance with or without VCP. 31P NMR revealed a resonance shift at 0.5 ppm for SB+HAp, EB+HAp and SBU+HAp spectra. In comparison with EB+HAp and SBU+HAp, a slight fade-out of the same resonance shift for EBnoVCP+HAp and SBUnoVCP+HAp was observed without completely disappearing, respectively, meaning that VCP might induce a modification of phosphorus moieties in addition to the ionic interaction between phosphate ester groups and HAp. Our data suggests that a chemical interaction occurred between VCP-containing adhesives and synthetic HAp.

¹³Cα decoupling during direct observation of carbonyl resonances in solution NMR of isotopically enriched proteins.

Direct detection of (13)C can be advantageous when studying uniformly enriched proteins, in particular for paramagnetic proteins or when hydrogen exchange with solvent is fast. A scheme recently introduced for long-observation-window band-selective homonuclear decoupling in solid state NMR, LOW-BASHD (Struppe et al. in J Magn Reson 236:89-94, 2013) is shown to be effective for (13)C(α) decoupling during direct (13)C' observation in solution NMR experiments too. For this purpose, adjustment of the decoupling pulse parameters and delays is demonstrated to be important for increasing spectral resolution, to reduce three-spin effects, and to decrease the intensity of decoupling side-bands. LOW-BASHD then yields (13)C' line widths comparable to those obtained with the popular IPAP method, while enhancing sensitivity by ca 35%. As a practical application of LOW-BASHD decoupling, requiring quantitative intensity measurement over a wide dynamic range, the impact of lipid binding on the (13)C'-detected NCO spectrum of the intrinsically disordered protein α-synuclein is compared with that on the (1)H-detected (1)H-(15)N HSQC spectrum. Results confirm that synuclein's "dark state" behavior is not caused by paramagnetic relaxation or rapid hydrogen exchange.

Thermal Stability of Larger Carbonyl Compounds: 2‐Methylbutyraldehyde

ABSTRACTWe have decomposed 2‐methylbutyraldehye in single pulse shock tube experiments, at temperatures between 1075 K to 1250 K and pressures of 1.5 and 6 atm. Five reaction channels have been identified from the unimolecular products that have been detected. The products involve CC bond cleavage together with a retro‐ene reaction. Particularly remarkable is the detection of small amount of butane; the first time that an alkane has been detected in these high‐temperature experiments. The formation of butane represents evidence of the roaming radical reaction or more generally the high‐temperature radical disproportionation reaction. Ethylene is present in large yields, and this is traced to a 1,2 H‐transfer reaction involving the highly exothermic transfer of a carbonyl hydrogen to an alkyl site. The results are consistent with earlier single pulse shock tube experiments on the 2‐ketones. In particular, they confirm the earlier observation that substituting a methyl and hydrogen atom with a doubly bonded oxygen atom have very little effect on the rate constant of the adjoining CC bond. The yields of ethylene are consistent with a very low value of the carbonyl resonance energy.

High resolution 13CNMR detection of short‐ and medium‐chain synthetic triacylglycerols used in butterfat adulteration

Recently in European countries, control laboratories have revealed real cases of deceptive practices in which synthetic triacylglycerols (TAGs) were used for adulterating butterfat. The complex fat blends are difficult to detect with the classical methods of analysis, especially when the adulterating TAGs contain fatty acids (FAs) in the proportions similar to that of genuine butter. Nevertheless, because butyric acid (C4) exclusively occurs at the sn‐3 position in milk fat TAGs, the determination of its distribution on the glycerol backbone provides a diagnostic indicator to differentiate genuine butter from mixtures with synthetic TAGs. Herein, we have demonstrated the straightforward application of mono‐dimensional 13C NMR spectroscopy for detecting synthetic TAGs in mixtures with authentic butterfat. The method is based on the 13C NMR determination of the regioisomeric distribution of C4 between the sn‐1,3‐ and sn‐2‐positions and boasts several analytical advantages, such as specificity, robustness and minimal sample handling. The limit of detection (LOD) and limit of quantification (LOQ) of the synthetic fats, estimated to be 1 and 2.5% w/w, respectively, easily surpass the limit of 10% at which a fraudulent practice might be economically attractive.Practical applications We have developed a robust and efficient method, based on high resolution 13C NMR spectroscopy, for detecting the adulteration of butterfat with synthetic low‐ and medium‐carbon number TAG mixtures. In milk fat TAGs, butyric acid is esterified exclusively at the sn‐3 position of the glycerol backbone. Thus, the method relies on 13C NMR monitoring of the carbonyl resonance of butyric acid at the sn‐2 glycerol position, which is diagnostic of synthetic or interesterified TAGs. The 13C NMR‐based analysis overcomes the pitfalls of traditional pattern recognition methodologies for the assessment of butter authenticity, which can be ineffective when butter is adulterated with synthetic TAGs obtained from FA in proportions similar to those of natural milk fat. The method achieves reliable quantification up to 2.5% w/w of adulterating fats (LOQ) and can detect quantities as low as 1% w/w of synthetic TAGs blended with butter (LOD).

Three-dimensional triple-resonance NMR Spectroscopy of isotopically enriched proteins

Four new and complementary three-dimensional triple-resonance experiments are described for obtaining complete backbone 1H, 13C, and 15N resonance assignments of proteins uniformly enriched with 13C and 15N. The new methods all rely on 1H detection and use multiple magnetization transfers through well-resolved one-bond J couplings. Therefore, the 3D experiments are sensitive and permit relatively rapid recording of 3D spectra (l–2 days) for protein concentrations on the order of 1 mM. One experiment (HNCO) correlates the amide 1H and 15N shifts with the 13C shift of the carbonyl resonance of the preceding amino acid. A second experiment (HNCA) correlates the intraresidue amide 1H and 15N shifts with the C α chemical shift. This experiment often also provides a weak correlation between the amide NH and 15N resonances of one amino acid and the Ca resonance of the preceding amino acid. A third experiment (HCACO) correlates the H α and C α shifts with the intraresidue carbonyl shift. Finally, a 3D relay experiment, HCA(CO)N, correlates Ha and Cal resonances of one residue with the 15N frequency of the succeeding residue. The principles of these experiments are described in terms of the operator formalism. To optimize spectral resolution, special attention is paid to removal of undesired J splittings in the 3D spectra. Technical details regarding the implementation of these triple-resonance experiments on a commercial spectrometer are also provided. The experiments are demonstrated for the protein calmodulin (16.7 kDa).

Transient hydrogen bonding in uniformly 13C,15N‐Labeled Carbohydrates in Water

We report NMR studies of transient hydrogen bonding in a polysaccharide (PS) dissolved in water without cosolvent at ambient temperature. The PS portion of the Escherichia coli O142 lipopolysaccharide is comprised of repeating pentasaccharide units of GalNAc (N-acetyl galactosamine), GlcNAc (N-acetyl glucosamine), and rhamnose in a 3:1:1 ratio, respectively. A 105-ns molecular dynamics (MD) simulation on one pentasaccharide repeat unit predicts transient inter-residue hydrogen bonds from the GalNAc NH groups in the PS. To investigate these predictions experimentally, the PS was uniformly ¹³C,¹⁵N enriched and the NH, carbonyl, C2, C4, and methyl resonances of the GalNAc and GlcNAc residues assigned using through-bond triple-resonance NMR experiments. Temperature dependence of amide NH chemical shifts and one-bond NH J couplings support that NH groups on two of the GalNAc residues are donors in transient hydrogen bonds. The remaining GalNAc and GlcNAc NHs do not appear to be donors from either temperature-dependent chemical shifts or one-bond NH J couplings. These results substantiate the presence of weak or partial hydrogen bonds in carbohydrates, and that MD simulations of repeating units in PSs provide insight into overall PS structure and dynamics.

Morphology and molecular dynamics of hard α-keratin under pressure by 1H and 13C solid-state NMR

The effect of uniaxial pressure on phase composition, aminoacid side-chain and backbone dynamics, as well as rigid domain sizes of hard α-keratin from human fingernail clippings was investigated by 1H solid-state and 13C cross-polarization MAS NMR spectroscopy. Proton spin–diffusion NMR experiments revealed that the rigid-domain sizes increased upon compression. The 13C carbonyl resonance components were shown to be very sensitive to the transition of α-helices to β-sheets induced by uniaxial compression. Carbon-13 longitudinal relaxation in the rotating frame showed dynamic heterogeneity of aminoacid residues especially during the α-helix to β-sheet transition.

Radical copolymerization of vinylidene cyanide with 2,2,2-trifluoroethyl methacrylate: Structure and characterization

A novel copolymer of vinylidene cyanide (VCN) and 2,2,2-trifluoroethyl methacrylate (MATRIF) was synthesized by bulk free radical process in a 52% yield from an equimolar comonomer feed. The copolymer's composition and microstruc- ture were analyzed by FTIR, 1 H- and 13 C-NMR spectroscopy, SEC, and elemental analysis. The reactivity ratios calculated from both the Q-e Alfrey-Price parameters and the Jenkins' Patterns Scheme indicate a tendency to alternation in the copolymerization, the latter method suggesting that MATRIF homopropagation be slightly favoured (rV ¼ r12 ¼ 0.1, rM ¼ r21 ¼ 0.3). The molar incorporation of VCN in the copolymer was only 42 mol % according to the 9.0 wt % nitrogen content deter- mined by elemental analysis, in good agreement with the value obtained by 1 H-NMR. High-resolution 1 Ha nd 13 C-NMR spectra were used to study the microstructure of the copolymer. As an example, the three well-resolved carbonyl resonances in the 13 C- NMR spectrum were assigned to the MATRIF-centered triads VMV, VMM, and MMM, respectively, (V and M stand for VCN and MATRIF, respectively). The presence of VCN dyads (e.g., in VVM and VVV sequences) was shown to be marginal or absent alto- gether. Thermogravimetric analysis of poly(VCN-co-MATRIF) co- polymer showed good thermal stability, and its main pyrolytic degradation taking place only above 368 � C. A 4% weight loss at about 222 � C suggested the presence of a few VCN homodyads, possibly inducing thermal depolymerization. V C 2010 Wiley Periodi- cals, Inc. J Polym Sci Part A: Polym Chem 48: 4900-4908, 2010

Bound fractions of methacrylate polymers adsorbed on silica using FTIR

AbstractThe H‐bonding of carbonyl groups on a series of methacrylate polymers with silanols on fumed silica was studied with transmission FTIR. The set included poly(alkyl methacrylates) with alkyl groups, (n‐CnH2n+1) of n = 1, 2, 4, and 12 and poly(benzyl methacrylate). Shifts in the vibrational frequencies for bound carbonyl groups (of ∼20 cm−1 lower than those found in the bulk) were observed in the adsorbed polymer samples. A series of samples with different adsorbed amounts (varying from 0.5 to 2.0 mg m−2) of each polymer was prepared to determine the effect of the side chain on the H‐bonding. The fractions of bound carbonyls, p, for each of the methacrylate polymers studied, were calculated from a model based on the ratios of the absorption coefficients of the bound to free carbonyl resonances, X (= αb/αf). The X values were determined from linear regressions of the ratios of the free to bound carbonyl intensities as a function of the amounts of adsorbed polymer, Mt. The bound fractions, p, were observed to decrease with increase in adsorbed amounts and with increase in the lengths of the side chains of the methacrylate polymers, except for poly(lauryl methacrylate) (PLMA). PLMA has a very low glass transition temperature (Tg) and is likely rubbery on the surface, whereas the other polymers are likely glassy at ambient temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1911–1918, 2010

CarbonK-edge spectra of carbonate minerals

Carbon K-edge X-ray spectroscopy has been applied to the study of a wide range of organic samples, from polymers and coals to interstellar dust particles. Identification of carbonaceous materials within these samples is accomplished by the pattern of resonances in the 280-320 eV energy region. Carbonate minerals are often encountered in the study of natural samples, and have been identified by a distinctive resonance at 290.3 eV. Here C K-edge and Ca L-edge spectra from a range of carbonate minerals are presented. Although all carbonates exhibit a sharp 290 eV resonance, both the precise position of this resonance and the positions of other resonances vary among minerals. The relative strengths of the different carbonate resonances also vary with crystal orientation to the linearly polarized X-ray beam. Intriguingly, several carbonate minerals also exhibit a strong 288.6 eV resonance, consistent with the position of a carbonyl resonance rather than carbonate. Calcite and aragonite, although indistinguishable spectrally at the C K-edge, exhibited significantly different spectra at the Ca L-edge. The distinctive spectral fingerprints of carbonates provide an identification tool, allowing for the examination of such processes as carbon sequestration in minerals, Mn substitution in marine calcium carbonates (dolomitization) and serpentinization of basalts.

Narrow carbonyl resonances in proton-diluted proteins facilitate NMR assignments in the solid-state

HNCO/HNCACO type correlation experiments are an alternative for assignment of backbone resonances in extensively deuterated proteins in the solid-state, given the fact that line widths on the order of 14-17 Hz are achieved in the carbonyl dimension without the need of high power decoupling. The achieved resolution demonstrates that MAS solid-state NMR on extensively deuterated proteins is able to compete with solution-state NMR spectroscopy if proteins are investigated with correlation times tau(c) that exceed 25 ns.

Microstructure determination of poly(acrylonitrile-co-methyl methacrylate-co-methyl acrylate) terpolymers by 2D HMBC

A compositional and configurational sequence analysis from two-dimensional heteronuclear multiple bond correlation (HMBC) spectra of acrylonitrile/methyl methacrylate/methyl acrylate (A/B/M) terpolymer is being reported here. The methylene and methine carbon resonances assigned from 2D HSQC spectra were established by analyzing two and three bond order couplings with methyl, methylene and methine protons. α-Methyl carbon resonance of B-unit and methine carbon resonances of A- and M-unit were assigned up to triad compositional and configurational sequences while methylene carbon resonances were assigned up to tetrad compositional and configurational sequences. The assignments of carbonyl carbon resonances based on analysis of three bond couplings with methyl and methylene protons are reported. Quaternary carbon resonance of B-unit was assigned completely with the help of two bond order couplings with methyl and methylene protons. Both carbonyl and quaternary carbon resonances were found to be sensitive up to triad compositional and configurational sequences. Complete spectral assignment of quaternary and carbonyl carbon resonances showing the critical contribution of 2D HMBC spectra is indirect analysis of carbon resonances.

New Hyperpolarized Contrast Agents for 13C-MRI from Para-Hydrogenation of Oligooxyethylenic Alkynes

Two alkyne derivatives, which contain one and two oligooxyethylenic chains respectively, showed to be good substrates for para-hydrogenation reactions, yielding the corresponding hyperpolarized alkenes in good yields. A suitable theory has been developed to account for the observed results, fully explaining the different para-H 2 induced effects observed upon the para-hydrogenation of symmetrically and asymmetrically substituted alkynes in ALTADENA and PASADENA modes. The oligooxyethylenic substituent provides good water solubility to the para-hydrogenated symmetrical derivative. (13)C-MR in vitro images of the latter derivative were obtained both in acetone and in water solutions (130 mM), using the ALTADENA procedure and after application of the field cycling procedure which allows acquisition of an in-phase (13)C carbonyl resonance. The finding that the hydrogenated product is water-soluble in contrast to the parent alkyne which is not allows for the pursuit of a fast phase-transfer separation from the organic solvent, the unreacted substrate, and the catalyst to obtain a "ready-to-use" water solution suitable for further in vivo MRI applications.