Proton-decoupled 13C NMR Research Articles

Ionic Lignin Polymers for Controlled CO2 Capture, Release, and Conversion into High-Value Chemicals.

In this study, an innovative and cost-effective ionic polymer for CO2 capture and utilization for the first time, using abundant and nonfood-based biomass lignin is reported. The modified ionic polymer synthesizes through the reaction of glycidyltrimethylammonium chloride with lignin under alkaline conditions to yield quaternary ammonium ionic functionality. Subsequently, the hydroxide-based pure ionic lignin polymer is employed for CO2 capture from both direct air and concentrated CO2 sources at room temperature and atmospheric pressure. Structural characterization of the polymers is accomplished through 1H, 13C, and 2D-heteronuclear single quantum coherence (HSQC)NMR, and FT-IR spectroscopy. The CO2 capture process is established through the formation of bicarbonate ions alongside the presence of CO2. The captured CO2 is precisely quantified by using inverse-gated proton decoupled 13C NMR with an internal standard (trioxane). Remarkably, the captured-CO2 amounts of ionic lignin polymer are 1.06mmol g-1 (47mg g-1) from concentrated-CO2 source and 0.60mmol g-1 (26mg g-1) from direct-air. The captured-CO2 in ionic lignin polymer is released in controlled manner and utilized in the synthesis of cyclic carbonate, showcasing the productive application of the captured carbon. Moreover, the fully controlled recovering of ionic lignin polymer achieves via repeated CO2 release ↔ CO2 capture.

Hydrazone-flavonol based oxidovanadium(V) complexes: Synthesis, characterization and antihyperglycemic activity of chloro derivative in vivo

Wet synthesis approach afforded four new heteroleptic mononuclear neutral diamagnetic oxidovanadium(V) complexes, comprising salicylaldehyde-based 2-furoic acid hydrazones and a flavonol coligand of the general composition [VO(fla)(L-ONO)]. The complexes were comprehensively characterized, including chemical analysis, conductometry, infrared, electronic, and mass spectroscopy, as well as 1D 1H and proton-decoupled 13C(1H) NMR spectroscopy, alongside extensive 2D 1H1H COSY, 1H13C HMQC, and 1H13C HMBC NMR analyses. Additionally, the quantum chemical properties of the complexes were studied using Gaussian at the B3LYP, HF, and M062X levels on the 6–31++g(d,p) basis sets. The interaction of these hydrolytically inert vanadium complexes and the BSA was investigated through spectrofluorimetric titration, synchronous fluorimetry, and FRET analysis in a temperature-dependent manner, providing valuable thermodynamic insights into van der Waals interactions and hydrogen bonding. Molecular docking was conducted to gain further understanding of the specific binding sites of the complexes to BSA. Complex 2, featuring a 5-chloro-substituted salicylaldehyde component of the hydrazone, was extensively examined for its biological activity in vivo. The effects of complex administration on biochemical and hematological parameters were evaluated in both healthy and diabetic Wistar rats, revealing antihyperglycemic activity at millimolar concentration. Furthermore, histopathological analysis and bioaccumulation studies of the complex in the brain, kidneys, and livers of healthy and diabetic rats revealed the potential for further development of vanadium(V) hydrazone complexes as antidiabetic and insulin-mimetic agents.

Rhenium(I)-tetrazolato functional luminescent polymers: Organic-inorganic hybrids via RAFT and post-polymerization modification

A series of well-defined tetrazole-functionalized (co)polymers based on the styrenic structural motif that are able to serve as macromolecular ligands for the coordination of a luminescent rhenium(I) complex are presented. Copolymers of styrene with 4-cyanostyrene containing different ratios of cyano appended groups have been synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Post-polymerization modification of the cyano groups via reaction with NaN3 yielded the corresponding tetrazole functionalized copolymers. These tetrazole functional materials are able to serve as macromolecular ligands for the coordination of metal complexes: a rhenium(I) species has been incorporated into the polymeric structure by coordination to the tetrazole groups on the copolymers. The parent (co)polymers have been characterised by size exclusion chromatography (SEC), while inverse-gated proton decoupled 13C NMR spectroscopy and infrared spectroscopy confirmed the formation of the tetrazole functional group and subsequent metal coordination. The photophysical properties of the copolymer-rhenium(I) hybrid luminescent materials have been fully investigated. Absorption and emission profiles confirmed coordination between the tetrazole functionality appended to the polymer material and the rhenium(I) precursor complex. Lifetime measurements and quantum yields confirmed that the presence of the polymeric scaffold does not interfere with the luminescent properties of the rhenium(I) complex.

13C NMR Spectroscopy: A Tool for Study of Conformational Analysis of 2-Aryl-trans-decahydroquinolin-4-ols

In this investigation, proton decoupled 13C NMR Spectroscopy was used as a tool for the study of conformations of differently substituted 2-aryl-trans-decahydroquinolin-4-ols. The fusion of the rings in 2-aryl-trans-decahydroquinolin-4-ols was conclusively proved to be trans-, from a comparison of the experimental and calculated values. The signal assignments were made on the basis of the model system and in this case trans-decahydroquinoline was taken as model system. Substituent parameters for methyl, hydroxyl, and phenyl groups were derived from analogous systems and incorporated in the model system to obtain the calculated values. An examination of the 13C chemical shift values indicated that the configuration of the hydroxyl group was equatorial in all the α-forms of 2-aryl-trans-decahydroquinolin-4-ols and that of β-form’s was axial. In 3-Methyl-2-aryl-trans-decahydroquinolin-4-ols the chemical shifts suggested equatorial configuration to methyl and phenyl groups. Further, for 1-Methyl-2-aryl-trans-decahydroquinolin-4-ol and 1,3-dimethyl-2-aryl-trans-decahydroquinolin-4-ols the 1-or N-methyl group was found to has a greater preference to the equatorial position.

The rate of lactate production from glucose in hearts is not altered by per-deuteration of glucose

This study was designed to determine whether perdeuterated glucose experiences a kinetic isotope effect (KIE) as glucose passes through glycolysis and is further oxidized in the tricarboxylic acid (TCA) cycle. Metabolism of deuterated glucose was investigated in two groups of perfused rat hearts. The control group was supplied with a 1:1 mixture of [U-13C6]glucose and [1,6-13C2]glucose, while the experimental group received [U-13C6,U-2H7]glucose and [1,6-13C2]glucose. Tissue extracts were analyzed by 1H, 2H and proton-decoupled 13C NMR spectroscopy. Extensive 2H-13C scalar coupling plus chemical shift isotope effects were observed in the proton-decoupled 13C NMR spectra of lactate, alanine and glutamate. A small but measureable (∼8%) difference in the rate of conversion of [U-13C6]glucose vs. [1,6-13C2]glucose to lactate, likely reflecting rates of CC bond breakage in the aldolase reaction, but conversion of [U-13C6]glucose versus [U-13C6,U-2H7]glucose to lactate did not differ. This shows that the presence of deuterium in glucose does not alter glycolytic flux. However, there were two distinct effects of deuteration on metabolism of glucose to alanine and oxidation of glucose in the TCA. First, alanine undergoes extensive exchange of methyl deuterons with solvent protons in the alanine amino transferase reaction. Second, there is a substantial kinetic isotope effect in metabolism of [U-13C6,U-2H7]glucose to alanine and glutamate. In the presence of [U-13C6,U-2H7]glucose, alanine and lactate are not in rapid exchange with the same pool of pyruvate. These studies indicate that the appearance of hyperpolarized 13C-lactate from hyperpolarized [U-13C6,U-2H7]glucose is not substantially influenced by a deuterium kinetic isotope effect.

Butyrate-rich Colonic Microenvironment Is a Relevant Selection Factor for Metabolically Adapted Tumor Cells

The short chain fatty acid (SCFA) butyrate is a product of colonic fermentation of dietary fibers. It is the main source of energy for normal colonocytes, but cannot be metabolized by most tumor cells. Butyrate also functions as a histone deacetylase (HDAC) inhibitor to control cell proliferation and apoptosis. In consequence, butyrate and its derived drugs are used in cancer therapy. Here we show that aggressive tumor cells that retain the capacity of metabolizing butyrate are positively selected in their microenvironment. In the mouse xenograft model, butyrate-preselected human colon cancer cells gave rise to subcutaneous tumors that grew faster and were more angiogenic than those derived from untreated cells. Similarly, butyrate-preselected cells demonstrated a significant increase in rates of homing to the lung after intravenous injection. Our data showed that butyrate regulates the expression of VEGF and its receptor KDR at the transcriptional level potentially through FoxM1, resulting in the generation of a functional VEGF:KDR autocrine growth loop. Cells selected by chronic exposure to butyrate express higher levels of MMP2, MMP9, α2 and α3 integrins, and lower levels of E-cadherin, a marker for epithelial to mesenchymal transition. The orthotopic model of colon cancer showed that cells preselected by butyrate are able to colonize the animals locally and at distant organs, whereas control cells can only generate a local tumor in the cecum. Together our data shows that a butyrate-rich microenvironment may select for tumor cells that are able to metabolize butyrate, which are also phenotypically more aggressive.

Characterisation of the 1H and 13C NMR spectra of methylcitric acid

Methylcitric acid (MCA) was synthesised in Reformatsky reaction (2 RS, 3 RS stereoisomers) and in the nucleophilic addition (2 RS, 3 SR stereoisomers). The stereoselectivity of these reactions was analysed. 1H and 13C NMR spectra of diastereoisomers of methylcitric acid were recorded and interpreted. The values of 1H chemical shifts and 1H– 1H coupling constants were analysed. Proton-decoupled high-resolution 13C NMR spectra of MCA diastereoisomers were measured in a series of dilute water solutions of various acidities. These data may provide a basis for unequivocal determination of the presence of MCA in the urine samples of patients’ suffering from propionic acidemia, methylmalonic aciduria, or holocarboxylase synthetase deficiency. NMR spectroscopy enables determination of MCA diastereoisomers in body fluids and can be a complementary and useful diagnostic tool.

Media phosphate and iron(II) supplementation affect Penicillium cell wall polymer structure

Our investigations focus on the effect of media nutrients, specifically phosphate and iron(II) on the composition of Penicillium fellutanum cell wall-derived polymers. In these studies we use four different media: high phosphate standard growth (HPSG), high phosphate high iron standard growth (HPSG Fe), low phosphate standard growth (LPSG), and low phosphate high iron standard growth (LPSG Fe). Mycelia obtained from these media are autoclaved in water to obtain heat-solubilized, cell wall-derived glycopeptides. Structures of heat-solubilized large (>14 kD) and small (<14 kD) mycelial glycopeptides have been characterized by GC/MS, NMR, and carbohydrate, phosphate, and protein analyses. We report that the phosphodiester composition in these polymers is a function of media phosphate and ferrous ion. Proton-decoupled 13C NMR spectra indicate that the large autoclaved mycelial polymers or LAMs resemble the 65 kD extracellular peptidophosphogalactomannans (pPGMs) in structure, however, they are very different from the small mycelial polymers or SAMs that consist primarily of glucose and peptides. Supported by NIH/NIGMS MBRS Grant# 2S06 GM008197.

Quantitative estimation of the degree of derivatization: an alternative methodology using 1-D and 2-D NMR experiments.

The precise estimation of the degree of derivatization of functional groups in polymers is important for determining their macroscopic properties. In this work, the quantitative estimation of the extent of esterification of novolac copolymers with di-tert-butyl dicarbonate was studied. Although the extent of esterification has been calculated previously by quantifying the signals from FT-IR and UV-Vis spectroscopy, these were restricted to monitoring the progress of the derivatization process. The 13C NMR signal intensities from the inverse-gated 1H-decoupled NMR spectrum have been used recently for the quantitative estimation of the degree of esterification of polymers. An alternative methodology has been suggested by us based on the fully relaxed 1H chemical shift intensities. However, since the proton signals of novolac resins are generally broad and overlapping, the proton decoupled 13C NMR spectrum was used to identify the 1H NMR signals using the 2-D HSQC technique. A TOCSY experiment was also performed to confirm further the 1H NMR signal assignments and, finally, the deconvoluted 1H NMR spectrum was used for the calculation of the extent of derivatization.

A multinuclear ( 1H, 13C, 15N) NMR study of cis-halonitrosylbis(dithiocarbamato)iron(II) complexes: effect of replacement of S by Se

The 1H and proton-decoupled 13C NMR spectra of several cis-Fe(NO)(E 2CNR 2) 2X complexes (where R is an organic substituent, E=S and/or Se, and X=Cl −, Br − or I −) have been measured at room temperature in CDCl 3, as well as the 15N NMR spectrum (natural abundance) of cis-Fe(NO)(S 2CN(C 2H 5) 2) 2I. The two CE 2 signals observed between 190 and 206 ppm in the { 1H} 13C NMR spectra of these cis-Fe(NO)(E 2CNR 2) 2X complexes provide an indication of the structural rigidity of these compounds in solution. The multiple 13C NMR peaks observed for the four E 2CN( CH 2R) 2 α-carbons further support this rigidity. The 13C NMR signal of the α-C atoms of the ligand is dependent on the proximate chalcogen, the second chalcogen of the ligand and the ligand atoms to which each of these is trans. The 13C NMR spectra of the cis-Fe(NO)(E 2CNR 2) 2X complexes are comparable to the spectra of the structurally similar cis-Fe(S 2CNRR ′) 2(CO) 2 complexes and give insight into the interpretation of the 13C NMR spectra of the Co(SSeCNR 2) 3 series. The { 1H} 13C NMR spectrum of cis-Fe(SSeCN(C 2H 5) 2) 2(CO) 2 is included for comparison. The 1H NMR spectra are complex; the diethyl derivative exhibits a complex multiplet which is interpreted as four overlapping ABX 3 systems for the NC H 2(C H 3) protons. The 15N NMR spectrum of cis-Fe(NO)(S 2CN(C 2H 5) 2) 2I exhibits three peaks: 210.92, 209.09 and 29.28 ppm. This is interpreted as each dithiocarbamate ligand experiencing a different magnetic environment and the NO ligand. The 15N NMR spectrum is compared to tetraethylthiuram disulfide, Co(S 2CN(C 2H 5) 2) 3 and cis-Fe(S 2CN(C 2H 5) 2) 2(CO) 2 and is interpreted as indicating similar S 2C-NRR ′ rotational barriers.

A study of long range dipolar coupling constants in 4′-pentyloxy-4-biphenylcarbonitrile (5OCB)

It was shown previously that long range 2H-13 C dipolar coupling constants in liquid crystals could be obtained from the proton-decoupled 13C NMR spectrum of monodeuterated compounds. This approach has now been applied to the study of 4′-(1-deuteropentyloxy)-4-biphenylcarbonitrile (5OCB-d1). The 113C spectrum of this compound gives nine 2H- 13C dipolar coupling constants for carbon ranging from one to six bonds away from the dueterium nucleus. The 2 H NMR and 5OCB-d1 gives the deuterium quadrupole coupling constant and the 1H- 2H dipolar coupling constant for the α -CHD group. In addition, eleven 2-bond and two 3-bond 1H- 13C dipolar coupling constants have been obtained for 4′-pentyloxy-4-biphenylcarbonitrile (non-deuterated 5OCB) by using the 2D 13C method of proton-encoded local field spectroscopy.

Oxidation of acetate in rabbit skeletal muscle: detection by 13C NMR spectroscopy in vivo.

The results of a proton-decoupled and Overhauser-enhanced 13C NMR study of acetate metabolism in skeletal muscle are reported. [2-13C]Acetate was infused intravenously over 2 h into anesthetized rabbits, and skeletal muscle in the lateral thigh was monitored by 13C NMR spectroscopy at 4.7 T. Stable 13C enrichment in carbons 2, 3, and 4 of glutamate was observed at the end of the infusion, and the half-time for enrichment was 17 min for glutamate C4 and 50 min for glutamate C2 and C3. The contribution of exogenous acetate to acetylcoenzyme A was nearly equal in skeletal muscle and heart in vivo (83-87%, measured in tissue extracts), comparable with earlier perfused heart studies in which acetate was the sole available substrate. Although relative flux through the combined anaplerotic pathways (relative to citric acid cycle flux) was higher in quiescent skeletal muscle (28%) compared with hearts (3%) from the same animals, actual anaplerotic flux was estimated to be substantially higher in heart than in skeletal muscle after correcting for differences in citric acid cycle flux in the two tissues.

In vivo hepatic glucose and glycogen metabolism in meal fed rats.

Short term starvation is associated with a depletion in hepatic glycogen stores which are quickly replenished within 6-7 hours [ 11 upon refeeding. Glucose levels during short term starvation are maintained primarily from glycogenolysis (75%) and to a lesser extent from gluconeogenesis (25%) [2] using lactate, alanine and glycerol as the major precursors for this process. When rats are meal-fed, carbohydrate and lipid metabolism undergo some profound changes contrary to normal short term starvation patterns. Pallardo and Williamson [3] showed that when rats are placed on a routine meal feeding regime for 10 days hepatic lipid synthesis rates were vastly increased. However, similar hepatic glycogen deposition rates to ad libitum fed rats prevailed. We have been investigating the use of I3C-NMR spectroscopy to study the disposal of l-13C glucose in the liver. 13C-NMR spectroscopy has been used to study glycogen synthesis in muscle and liver and also to gain information on gluconeogenic rates in rats and man [4]. Using proton-decoupled 13C-NMR spectroscopy it is possible to observe in vivo changes in l-13C glucose levels and 13C-l incorporation into the glycogen macromolecule. We have investigated the hepatic carbohydrate status of 4 week meal-fed rats prior and post feeding after a bolus infusion of glucose. Ten age-matched female Wistar rats (1 85-2000) were housed in a reverse light/dark room [light off 10:00fight on 22:00] and allowed access to a standard chow diet for 2 hours per day for 4 weeks [10:00 to 12:00]. The experiments were c d e d out over a period of 5 days where two rats per day were experimented on for pre (23 hour starved) and post meal (1 hour after the end of feeding) hepatic glucose/glycogen metabolism. The rats were anaesthetised with 60mglmVkg sodium pentobarbital and a blood sample removed from the jugular vein. The hepatic portal vein was cannulated and attached to a line containing D-glu~osel -~~C (99atom % I3C) [2oOmg/ml; 250mglkgl. A dual-tunedproton/carbon surface coil was positioned directly onto the liver and the animal placed in the bore of the magnet. Proton-decoupled carbon13 spectra were obtained at 50.309MHz using a 4.7 Tesla, 33cm horizontal bore system, an acquisition time of 0.205s, a relaxation time of O.ls, a pulse width of 70ps and a spectral width of 12kHz. Twenty-five array elements consisting of 512 averages over a period of 65 mins were collected (ie 1 spectra=2.6 mins. to acquire). Two base-line spectra were collected prior to the infusion of the 13C-glucose [75mg;20mg/min]. Subsequent to infusion of the C-glucose,the spectra obtained were referenced to C-l,O glucose at 96.60ppm and C-1 glycogen appearance observed at 100.48ppm. Quantification of the glucose and glycogen involved the integration of the respective resonances in each spectrum and standardised to the -CH#CH, integrated region [5]. Figure I shows typical carbon spectra prior to glucose infusion and 30 mins. post infusion, with the evolution of glycogen clearly visible at 100.48ppm. It can also be seen that the hepatic 13Cglucose disposal in the two groups are very similar, however, the post meal decay is faster. Glycogen 13C incorporation rate in the pre-meal group is shown to rise linearly for 30 minutes post glucose infusion. The rate was considerably faster than that in rats either fed ad libitum or starved [5 and unpublished]. The post meal group shows little net incorporation of 13C-glucose into glycogen implying that either maximal glycogen levels had been reached or synthesis was occumng preferentially from the unlabelled pool of 3 and 4 carbon precursors generated during refeeding. With food FIG 1

Biosynthesis of erythromycin: origin of the methyl protons.

13C-Nuclear magnetic resonance (13C-NMR) spectroscopy has been used to locate deuterium atoms incorporated biosynthetically into erythromycin from [3-13CD3]- and [3-13C]sodium propionate and L-[13CD3]- and L-[13C]methionine in Saccharopolyspora erythraea JCM 4748. The alpha-shifts of deuterated methyl groups were clearly observed in broad-band deuterium and proton-decoupled 13C-NMR spectra. The seven propionate-derived methyl groups and the four methionine-derived methyl groups were shown to undergo no exchange of methyl protons during the biosynthesis of erythromycin.

Comparative high resolution NMR studies of n- and p-type doped polyacetylene films

High resolution NMR provides unique abilities to study either properties of the polymer chains or behavior of the doping agent in the conducting polymers. Magic angle spinning proton decoupled 13C NMR was applied to n-type sodium doped, (CHNa y) x (y ≤ 0.3), and p-type iodine doped, [CH(I 3) y] x (y ≤ 0.19), polyacetylene films prepared by Shirakawa's method. Also 2-dimensional nutation spectra of half-integer spin ( I = 3 2 ) quadrupolar 23Na nuclei were measured. All the spectra were studied as a function of the dopant content, y, determined by weight uptake after doping. The films were controlled by measurement of the conductivity which was about 10 and 50 Ω −1 cm −1 for heavily iodine and sodium doped material, respectively. We discuss our results on: (i) formation of the extended polycarbonium ions (charged solitons), (ii) doping induced cis/trans isomerization, (iii) partial compensation of (CHNa) x films by oxygen and moisture, (iv) intersite electron-electron correlations on the polymer chain, and (v) ordering of the sodium ions and occurrence of at least two different crystal phases of the polyacetylene-sodium system.

13C- and 31P-NMR studies of human colon cancer in-vitro and in-vivo

We report comparative 31P-NMR studies in-vivo and in-vitro of the human adenocarcinoma cell line HCT-116 in a high-density, perfused microcarrier culture and as a tumour from the same cell line grown in three different immune-suppressed animal models (NIH triple deficient, Nude, SCID). The phosphate metabolite ratios, pH nmr and intracellular free magnesium, derived from the 31P-NMR spectra, were compared for the in-vivo and in-vitro systems. Results obtained with HCT-116 cells on microcarrier beads are quantitatively similar to that of small (122 mm 3), tumours in-vivo derived from the same cell line in any of the immune-suppressed animal systems studied. This suggests that in-vitro microcarrier cell culture serves as a useful model system for deriving information about metabolism of small, tumours in-vivo. It offers the additional advantages of allowing for precise control of substrate milieu, perfusion and oxygenation. The microcarrier system was also used to measure flux through glycolysis and the pentose cycle. In particular, we measured glucose utilization and the production of lactate, alanine, glutamine and glycogen in proton-decoupled 13C-NMR experiments following administration of [1- 13C] glucose. We found that (63% ± 6%) of the glucose utilized was released as [3- 13C] lactate in the presence of oxygen, indicating that the HCT-116 cells have a high level of aerobic glycolysis. Serial labelling experiments with [1- 13C] glucose and [6- 13C] glucose reveal that at least (11.6% ± 1.3%) of the glucose utilized enters the pentose cycle. We determined that (6.9% ± 1.2%) of the glucose utilized is recycled to glucose via the pentose cycle while (4.7% ± 1.4%) of the glucose utilized enters the pentose cycle to form lactate. The high rate of recycling via the pentose cycle suggests that a significant fraction of cellular NADPH is generated by the pentose cycle as opposed to generation by the malate-pyruvate shuttle.

Multinuclear NMR spectroscopy of the cellular slime mold Polysphondylium pallidum. Monitoring of the encystment and excystment processes.

Polysphondylium pallidum microcysts and amoebae have been investigated by 31P- and natural-abundance proton-decoupled 13C-NMR spectroscopy. Microcysts have been found to contain as prominent metabolites a phosphomonoester, inositol hexakisphosphate (1.4 mM), two phosphodiesters [glycerophosphocholine (5.5 mM) and glycerophosphoethanolamine (2.6 mM)], as well as nucleoside triphosphates (3 mM) and polyphosphates (greater than 10 mM), the polyamines 1,3-diamino-propane (3.5 mM), putrescine (16 mM) and spermidine (3 mM) and the sugar trehalose (31 mM). In vivo 31P-NMR has shown that the level of nucleoside triphosphates in microcysts was maintained metabolically and that the pH of their cytosol, deduced from the chemical shift of cytosolic Pi was 7.2. The absence of trehalose, glycerophosphocholine and glycerophosphoethanolamine in P. pallidum amoebae was the most remarkable difference from microcysts. Microcyst germination (excystment), induced by reduction of the ionic strength of the microcyst bathing medium, was monitored non-invasively by 31P- and 13C-NMR spectroscopy. The major modifications observed during excystment were the progressive disappearance of trehalose used as energy source, of glycerophosphocholine and glycerophosphoethanolamine used as membrane phospholipid precursors, and, finally, the appearance of NMR-visible polyphosphates and of cellobiose. As a mirror situation, P. pallidum amoebae responded to a high-ionic-strength stress by production of trehalose, glycerophosphocholine, and glycerophosphoethanolamine, and induction of an encystment process.

Carbon-13 NMR for the assessment of human brain glucose metabolism in vivo

Proton-decoupled 13C NMR spectra of the human head were obtained during hyperglycemic glucose clamping using intravenous infusions of [1-13C]glucose in normal volunteers. In addition to 13C signals of mobile lipids, a variety of new metabolite resonances could be resolved for the first time in the human brain. At an enrichment level of 20% [1-13C]glucose, the signals of alpha- and beta-glucose at 92.7 and 96.6 ppm, respectively, could be detected in the human brain after only an infusion period of 15 min. The spatial localization of the different regions of interest was confirmed by 13C NMR spectroscopic imaging with a time resolution of 9 min. Increasing the enrichment level to 99% [1-13C]glucose not only improved the time resolution but allowed the detection of metabolic breakdown products of [1-13C]glucose. The time course of 13C label incorporation into the C2, C3, and C4 resonances of glutamate/glutamine and into lactate could be recorded in the human brain. These results suggest the possibility of obtaining time-resolved, spatially selective, and chemically specific information on the human body.

Multinuclear ( 1H, 13C, 59Co, 77Se) NMR studies of thioseleno- and diselenocarbamato complexes of cobalt(III) and indium(III) in CDCl 3 solution

The proton decoupled 13C NMR spectra of several Co(Se 2CNR 2) 3, Co(SSeCNR 2) 3, In(Se 2CNR 2) 3 and In(SSeCNR 2) 3 complexes(where R=organic substituent) have been measured in CDCl 3 solution (23–64 mM). Each of the diselenocarbamate complexes exhibits a single peak for the NCSe 2 carbon at 188–197 ppm for Co(III) and at 186–198 ppm for In(III) complexes. The alkyl carbons in the position alpha to the amine N also appear as a single peak. The In(SSeCNR 2) 3 complexes exhibit single peaks for the NCSSe carbons (192–202 ppm), but the alkyl carbons in the position alpha to the amine N appear as two distinct singlets, indicating hindered rotation about the SSeCNR 2 bond. The Co(SSeCNR 2) 3 complexes exhibit four peaks of approximately equal intensity for the NCSSe carbon which is interpreted as evidence for the stereochemical rigidity of the facial and meridional isomers. The alkyl carbons in the position alpha to the amine N appear as six peaks (except for occasional accidental degeneracy) which is interpreted as evidence for hindered rotation about the SSeCNR 2 bond in these two isomers. The 1H NMR spectra of these complexes have been measured in CDCl 3 solution (30–63 mM). The 1H spectra of Co(Se 2CNR 2) 3 are similar to those reported for Co(S 2CNR 2) 3, but those for the Co(SSeCNR 2) 3 complexes are further split by hindered rotation about the SSeCNR 2 bond rendering each R non-equivalent. The 1H spectra for the various derivatives of In(SSeCNR 2) 3 and In(Se 2CNR 2) 3 are similar and indicate ra pid D⇄cL interconversion and evidence (in the case of In(SSeCNR 2) 3) for hindered rotation about the CN bond. The 59Co NMR spectra of the Co(Se 2CNR 2) 3 complexes exhibit signals (6690–7260 ppm) in close agreement with results reported in the literature. The 59Co NMR signals of Co(SSeCNR 2) 3 are approximately identical to those of the corresponding Co(S 2CNR 2) 3 complexes but are generally at lower field than for the corresponding Co(Se 2CNR 2) 3 complexes. Similar to the dithiocarbamate complexes, there is evidence for a correlation between the 59Co chemical shifts and μ eff 2 for the corresponding Fe(SSeCNR 2) 3. The 77Se NMR spectra of these complexes have been measured in saturated CDCl 3 solution. The 77Se spectra of the diselenocarbamates exhibits single peaks with In exhibiting a higher chemical shift (approx. 400 ppm) than the corresponding Co complex. This trend is seen in the corresponding thiosclenocarbamates, but the Co derivatives generally exhibit two peaks of approximately equal intensity, indicating the stereochemical rigidity of the fac and mer isomers.

Kinetics of self-exchange of bis(1,4,7-trithiacyclononane)iron(III)/(II) in acetonitrile and in acidic aqueous solution

The rate constant kex of the [Formula: see text] self-exchange reaction cannot be measured in most common solvents because of spontaneous reduction of the [Formula: see text] ion, which is also sensitive to photolysis by visible light. However, in CD3CN at −41 to −19 °C, reproducible proton-decoupled 13C NMR line broadening measurements are possible, and give kex = (5.3 ± 0.3) × 104 kg mol−1s−1 at 0 °C, ΔH* = 10.3 ± 1.8 kJ mol−1, and ΔS* = −116 ± 7 J K−1 mol−1, at ionic strength I = 0.1 mol kg−1. Proton NMR line broadening experiments are marginally practicable in very acidic water (2.0 mol kg−1 D2SO4/D2O) near 0 °C, and give kex = 3.2 × 106 kg mol−1 s−1 at 1 °C. The relative kex values of these and other low-spin/low-spin FeIII/II self-exchange reactions follow the predictions of the Marcus–Hush theory at least qualitatively. The effect of ionic strength, however, is less than predicted, probably because of the formation of less reactive anion–cation pairs. Keywords: electron transfer kinetics, crown thioether complexes.