CH Values Research Articles

Effect of substitution pattern on 1H, 13C NMR chemical shifts and 1JCH coupling constants in heparin derivatives

1H, 13C NMR chemical shifts and 1 J CH coupling constants were measured for derivatives of heparin containing various sulfation patterns. 1H and 13C chemical shifts varied considerably after introducing electronegative sulfate groups. Chemical shifts of protons linked to carbons changed by up to 1 ppm on substitution with O- and N-sulfate or acetyl groups. Differences up to 10 ppm were detected for 13C chemical shifts in substituted glucosamine, but a less clear dependence was found in iduronate. 1 J CH values formed two groups, corresponding to either sulfation or non-sulfation at positions 2 and 3 of glucosamine. O-sulfation caused increases up to 6 Hz in 1 J CH and N-sulfation decreases up to 4 Hz. N-acetylation gave similar 1 J CH values to N-sulfation. At positions 2 and 3 of iduronate the trend was less marked; 1 J CH for O-sulfated positions usually increasing. Introduction of sulfate groups influences chemical shift and 1 J CH values at the position of substitution, but also at more remote positions. 1 J CH at the glycosidic linkage positions varied between free-amino and N-sulfated compounds, by up to 9 Hz. These results and changes in chemical shift values suggest that iduronate residues and the glycosidic linkages are affected, indicating overall conformational change. This may have important implications for biological activities.

Structural characterization of stearic acid in the crystalline state by the cross polarization in solid state 13C NMR

13C cross polarization/magic angle spinning (CP/MAS) NMR spectra of stearic acid with the crystallographic form C, deuterated the methyl and methylene groups besides a proton in the carboxylic group, were measured as a function of the contact time, in order to obtain the cross relaxation rate (1/ T CH) between the methylene carbons and protons in the compound. From these experimental results, it was found that the 1/ T CH values for the methylene carbons are proportional to r av −6, which is the averaged atomic distance between any specified carbon and protons. This means that the CP experiment provides a geometrical information using the partially deuterated molecules.

Chemical Transfer Energetics of the −CH2− Group: A Possible Probe for the Solvent Effect on Hydrophobic Hydration and the 3D-Structuredness of Solvents

Transfer Gibbs energies ΔG°t, and entropies, ΔS°t, of −CH2− have been evolved in aqueous mixtures of methanol (MeOH), ethanol (EtOH), 2-propanol (2-PrOH), tert-butyl alcohol (t-BuOH), and acetonitrile (ACN) by determining the solubilities of Ag salts of acetate (OAc-), propionate (OPr-), n-butyrate (OBu-), as well as picrate (Pi-) ions from 15 to 35 °C by spectrophotometric measurements. The chemical contributions of these energetics of the ions (i), ΔG°t,ch(i) and TΔS°t,ch(i), at T = 298.15 K have been evolved by subtracting the cavity effect and Born-type and ion−dipole-type electrostatic interaction effects. ΔG°t,ch(i) values of carboxylates (RCOO-) are guided by solvent acidity induced hydrophilic hydration (HlH) of the COO- ion and cosolvent induced hydrophobic hydration (HbH) of the R group and the back-bonding interaction of d10 electrons in the case of Ag+ ion, while TΔS°t,ch(i) values are partly guided by structural effects as well. ΔG°t,ch and TΔS°t,ch values of (−CH2−) are found to be more or less same, indicating their additivity. The increase in ΔG°t,ch (−CH2−)−composition profiles and the “characteristic maximum” of TΔS°t,ch (−CH2−)− composition profiles indicate the effect of increasingly reduced HbH caused by increasing 3D-structure promotion of these alkanols. The decrease in ΔG°t,ch (−CH2−) and the broad minimum in ΔS°t,ch (−CH2−) in aqueous ACN indicate the effect of increased HbH caused by 3D structure breaking of ACN. Thus the chemical transfer energetics and especially entropies of −CH2− reflect not only the solvent effect on HbH but also the 3D-structuredness of aquo-organic cosolvents.

Measurement of interglycosidic 3JCH coupling constants of selectively 13C labeled oligosaccharides by 2D J-resolved 1H NMR spectroscopy

Tri-, tetra-, and penta-saccharide fragments of the O-specific polysaccharide of Shigella dysenteriae type 1 have been prepared in which a d-galactose residue of each oligosaccharide methyl glycoside derivative contains a 13C label at C-1. The interglycosidic coupling constants ( 3 J CH) of these 13C nuclei with the H-3 nuclei of the adjacent 2-acetamido-2-deoxy- d-glucose residues have been measured by two-dimensional, J-resolved 1H NMR spectroscopy. The magnitudes of these coupling constants indicate that the trisaccharide is conformationally different to the higher oligosaccharide homologs, in agreement with previous studies of 13C chemical shifts and 1 J CH values.

The significance of the strain path analysis in the interpretation of piezocone dissipation data

When a piezocone is driven into the ground, pore water pressures are set up as a result of the stress changes. The dissipation of these pore pressures occurs in the subsequent con-solidation process in a manner dependent on the initial stress distribution as well as on the coefficient of consolidation. The process of analysis therefore has two distinct components. The first is to identify the appropriate total stress distribution caused by driving the piezocone, which acts as the initial condition for the consolidation. The second is to solve the consolidation problem itself. This approach has been followed by Levadoux & Baligh (1986, J. Geotech. Engng, ASCE 112, No. 7, 707–726), Baligh & Levadoux (1986, J. Geotech. Engng, ASCE 112, No. 7, 727–745) and by Houlsby & Teh (1988, Penetration testing 1988 (ed. J. de Ruiter), Balkema, Amsterdam, Vol. 2, pp. 777–783). Each of the two sets of authors uses the same consolidation theory for the second stage of the analysis, and a strain path method to identify the initial stress conditions. However, different assumptions about soil behaviour and the relevant soil parameters are made in carrying out the strain path analyses. A real situation will differ from the theoretical one both by differences from the model assumed, and in the choice of numerical values of the relevant parameters. For the two approaches to the piezocone analysis. Houlsby & Teh (1988) used an elastic-plastic model, in which the value of the rigidity index, G/su, may be specified in the analysis, while Levadoux & Baligh's solution, with a similar theoretical basis, used parameters specifically appropriate for Boston Blue Clay. This paper discusses the question of an appropriate choice of numerical values of the soil parameters and reports a comparison between the two theoretical predictions and field measurements from two different piezocones deployed in Sarapui soft clay, Brazil. The values of the coefficient of consolidation ch calculated from the field data by the two methods are then compared with high quality laboratory tests on the Sarapui clay. It is shown that both theoretical predictions provide good agreement for the shape of the dissipation curve, but that the predicted ch values are different, and that thought should indeed be given to the use of an appropriate value of G/su.

J-Compensated Proton-Detected Heteronuclear Shift-Correlation Experiments

A new proton-detected heteronuclear shift-correlation experiment, J-HSMQC, is proposed for sensitivity enhancement for samples containing a wide range of 1 J CH values. This method, which incorporates only two additional τ periods and has the same number of RF pulses as the HSQC experiment, is found to give significant enhancements for CH fragments with 1 J CH values which deviate considerably from the coupling constant for which τ is optimal. The J-HSMQC maps also contain reasonably intense two-bond correlations for some CH fragments.

Complement deficiencies in channel catfish ( Ictalurus punctatus) associated with temperature and seasonal mortality

This study examined serum complement levels in channel catfish from two commercial ponds over a period extending from the winter through the summer months. The fish from one pond (6B) experienced significant fungal associated mortality in the month of January. In March, there was also notable mortality of fish in the same pond; moribund fish exhibited external fungal as well as systemic Aeromonas infections. In July, all fish collected were apparently healthy in that there was no observed mortality. In contrast, the fish from the second pond (16A) were apparently healthy at all sample times except March when there was amild incidence of fungal associated mortality. The results of analyses of haemolytic complement activity showed that representative fish from both ponds had severe complement deficiences during January and March. The haemolytic complement activity continued to be monitored from fish from these ponds into the summer months and the CH 50 values were found to increase to within the normal range. To determine if low water temperature alone induced complement deficiencies, labolatory-acclimated catfish were subjected to a rapid down-shift in water temperature from 23°-11° C during a 24-h period, and the serum CH 50 values were monitored over the following 5 weeks. The results showed that low temperature can significantly affect the ability of catfish to maintain normal levels of haemolytic complement activity; however, these results do not appear to solely explain the abnormally low levels of haemolytic complement found in the serum of catfish during January and March. These results suggest that other factors, in addition to low temperature may have contributed to low CH values observed in the catfish during the winter and spring months. These analyses, in conjunction with other studies, suggest that fungal associated winter mortality and perhaps the subsequent bacterial infections associated with channel catfish during the following spring, are likely manifestations of a severe multifaceted immunodeficiency syndrome wherein complement as well as the humoral and cell-mediated immune systems are compromised.

Capsaicin-sensitive nerves modulate reactive hyperemia in rat gut.

Reactive hyperemia (RH) is a local, vascular response that occurs following release from mechanical occlusion of an artery, with restoration of intra-arterial pressure. The mechanism of this postocclusion hyperemia in the gut has not been identified, although metabolic, myogenic, and neurogenic mediators of this response have been proposed. The present study was conducted to evaluate a possible modulatory role for sensory innervation of the intestinal vasculature in RH, using acute and chronic treatment with capsaicin applied in different ways. In anesthetized rats, the velocity of flowing blood in the gut was determined continuously with a pulsed Doppler velocimeter, and arterial pressure was determined with a transducer. The increase in calculated intestinal vascular conductance at the height of RH (Ch), the excess volume of blood accumulating during RH, and the duration of the hyperemia were also used to quantify RH after occluding the anterior mesenteric artery for 30, 60, and 120 sec. In the initial control group of rats, the maximal increases in the velocity of flowing blood during RH were 61 +/- 4%, 90 +/- 7%, and 129 +/- 10% of control, conductances were increased to 192 +/- 5%, 222 +/- 12%, and 267 +/- 15% of control, volumes were 3.5 +/- 0.6 ml, 7.2 +/- 0.4 ml, and 16.2 +/- 1.8 ml, and durations of hyperemia were 78 +/- 5 sec, 93 +/- 6 sec, and 178 +/- 7 sec, respectively, after each elapsed period of occlusion. Acute treatment with periarterial capsaicin significantly decreased peak conductances in RH by 15-35% for all occlusions tested and reduced both volume and duration values. Rats treated with capsaicin in neonatal life exhibited reduced Ch values, as did adult rats treated chronically with capsaicin. Both periarterial and intrajejunal treatment with capsaicin decreased the duration of RH. Hexamethonium increased both Ch and the duration of RH and tended to reverse reductions in these parameters caused by capsaicin. These results suggest that sensory innervation of the intestinal vasculature exerts a modulatory influence in the regulation of intestinal RH.

1H and 13C NMR study of substituted 3-OH pyridines

n J HH, n J CH and δ 13C values have been measured for a series of X substituted 3-hydroxypyridines (X = 2-NH 2, 2-NO 2, 5-Cl, 6-CH 3, 2-Cl, 2-Br, 2-I). The results show that the additivity of δ 13C provides a valuable criterion to differentiate the phenolic from the zwitterion structure. This conclusion is based on the fact that in the first case, for 2-NH 2-, 2-NO 2-, 5-Cl- and 6-CH 3-3-hydroxypyridines, there is agreement between the experimental and the additivity δ 13C values, while in the three halogen derivatives (2-Cl-, 2-Br- and 2-I-3-hydroxypyridines) the δ exp—add C3 values of −4.95, −7.25 and 9.05 are probably due to the negative charge present on the three position of the zwitterion. Since the additivity of 1 J CH values holds in all substances examined (unlike the case of the 2-pyridone derivatives) it is not possible to use that criterion to differentiate between the phenolic and dipolar structures. The above conclusions are in agreement with IR, p K, NQR, RX, kinetics experiments and quantum chemical calculations of other authors.

13C- and 1H-NMR spectra of 2-pyridone derivatives

13C- and 1H-NMR spectroscopy was used to obtain n jHH , n JCH and δ C-13 for a series of substituted 2-hydroxypyridines (3-hydroxy; 4-hydroxy; 5-chloro; 3-methyl-5-chloro; 6-chloro; 6-amino; 6-hydroxy). It is shown that the additivity of δ C-13 and 1 J CH values provides a valuable criterion for differentiating between quinoidal and aromatic structures and in defining conformations. The first conclusion is based on the fact that for 3-substituted compounds there is accordance between experimental values and the additivity 1 J CH and δ C-13 values calculated for 2-pyridone. In the 6-substituted compounds there is marked deviation from additivity in 1 J CH. On the other hand, it seems that the substituent effect on δ C-13 in the hypothetical 2-hydroxypyridine and the real 2-pyridone are markedly different for C6, since there is no accordance between additivity and experimental values for the chemical shifts of this carbon. These conclusions are in agreement with results obtained from IR and p K studies and quantum-chemical calculations which indicate that a substituent in position 3 favours a pyridone structure, while a pyridinol structure is favoured when the substituent is at ring-position 6.

A 11b and 13c nmr determination of the structures of borate complexes of pentoses and related sugars

A 11B NMR study demonstrated that the four pentoses, like hexoses, form concurrently 1:1 and 1:2 borate complexes in aqueous solution, contrary to earlier reports. It also showed that in both species, the borate ion was bound to a vicinal diol site. The corresponding stability constants were determined by a potentiometric method. The structures of most 1:2 complexes were precised by 13C NMR spectroscopy, since the carbon atoms which bear the chelating diol group were clearly deshielded and had increased 1J CH values. The results were rationalised by grouping the sugars in series of related configurations. All sugars were complexed in furanose form. Those of the arabino - galacto - fructo series and of the xylo - gluco - sorbo series gave the same type of complex involving the anomeric hydroxyl group and the nearest ring CHOH. The very stable 1:2 complex of D-ribose was shown to be a mixture of two species in constant ratio, borate being bound either at C-1, C-2 or at C-2, C-3. The same result was obtained with the sugars of the lyxo - manno - tagato series, which also possessed two cis CHOH groups.

The influence of concomitant experimental hypertension and glomerulonephritis

Utilizing the two kidney-one clip Goldblatt model (CH), we have examined the influence of hypertension upon the course of antiglomerular basement membrane antibody-induced glomerulonephritis (GN) over a period of 10 to 14 weeks after induction of CH and GN, utilizing evaluations in the awake rat by renal micropuncture of the unclipped kidney and morphologic analysis (control [C], GN, CH, and GN+CH). Metabolic studies revealed that GN and GN+CH rats developed proteinuria, elevations in serum creatinine and blood pressure (P less than 0.05). GN+CH resulted in significant reductions in two kidney glomerular filtration rate (GFR) below values in C, and GFR in the unclipped kidney was markedly reduced when compared to CH. The glomerular capillary hydrostatic pressure and the pressure gradient( (delta P) were elevated approximately 4 to 5 mm Hg in GN and CH rats and 6 mm Hg above GN and CH values in the GN+CH rats. The glomerular ultrafiltration coefficient (LpA) was reduced to approximately 40% of C in both GN and GN+CH in spite of further increases in delta P. Surface nephron filtration rate was similar in all groups, suggesting glomerular dysfunction was primarily in nephrons below the surface in GN+CH. Morphologic evaluation revealed that GN+CH exhibited a combination of diffuse and focally sclerotic lesions characteristic of GN and CH, respectively. Documented further increases in PG did not worsen glomerular morphology, but kidney GFR did decrease. Hypertension induced deterioration of glomerular function in nephrons below the surface was not associated with marked morphologic deterioration, but a combination of the characteristics of GN and CH.

Gas phase infrared contour simulation of isolated CH stretches in butane-d 9

n-Butane-d 9 was synthesized with the hydrogen atom located in one of the methyl groupings. Both CH stretches of the trans conformer and two of the three CH stretches of the gauche conformer were assigned to transitions observed in the gas phase infrared spectrum, using the harmonic rigid rotor approximation. The simulation lends support to the more recent literature values of the trans—gauche relative populations. The assignments agree with those obtained by other authors using different techniques, and, when compared to ν is CH values in propane, lead to γ substitution effects of methyl which are very small, except perhaps on the op * g (out-of-plane gauche) bond, where steric interaction is likely.

Vibrational spectra of cis and trans but-2-enes: assignments, isolated CH stretching frequencies and CH bond lengths

Infrared and Raman spectra have been obtained from 11 isotopomers of cis and trans but-2-enes in various phases ( c- and t-CH 3CHCHCH 3, CH 3CHCDCH 3, CD 3CHCHCD 3, CD 3CHCDCD 3, CD 3CDCDCD 3; c-CH 3CDCDCH 3). Nearly all the fundamentals are securely assigned. Isolated CH stretching frequencies ν is CH are observed or deduced from the spectra and used to predict CH bond lengths and dissociation energies. The olefinic CH and methyl CH s bonds are stronger in the cis compound than those in the trans, in keeping with substituent effects previously observed in propene, and with molecular mechanics predictions. Comparison of ν is CH values with local mode fifth overtone spectra for cis-CH 3CHCHCH 3 indicates that the part of the latter associated with the CH a bond cannot be readily interpreted.

Effect of solvent and internal rotation on 1JCH coupling in isopropylamine and isopropanol

The dependence of 1 J CH on the dielectric constant (ϵ) of the solvent has been studied in isopropylamine and isopropanol both by actual measurement and by calculation using the INDO-FPT-Solvaton method. In isopropylamine 1 J CH decreases with increasing ϵ, while in isopropanol it increases with ϵ, trends which are reproduced by the calculations. This difference is believed to relate to the fact that the calculated excitation energy increases with ϵ in the former compound but decreases as ϵ increases in the latter. Regarding the effects of internal rotation, it is deduced that a trans orientation of the lone pair on the nitrogen or oxygen atom relative to the CH bond in the isopropyl group, draws p electron density towards the CH bond, thus reducing the s character of the bond and consequently yielding smaller 1 J CH values.

Correlation of 13C- 1H spin-spin coupling constants and the sum of internuclear angle distortions in saturated hydrocarbons

An empirical relationship between one bond carbon-hydrogen spin-spin coupling constants, 1J CH and the sum of internuclear angle distortions, ΣΔθ has been found. The proposed formula gives 1J CH values with a 3.22 Hz average deviation from the experimental values (30 data points, s.d. = 2.74) and useable for both the methylene and methine carbons of saturated hydrocarbons.

Simple aromatic amines from justicia gendarussa. 13C NMR spectra of the bases and their analogues

Four simple 0-disubstituted aromatic amines have been isolated from the leaves of Justicia gendarussa Burm and characterized as 2-amino benzyl alcohol ( 3), 2-(2′-amino-benzylamino) benzyl alcohol ( 4) and their respective 0-methyl ethers 1 and 2 from 1H NMR and mass spectral analyses of the bases and their acetates. Structures 3 and 4 have also been confirmed by synthesis. Intramolecular hydrogen bonding (cf. 9, 13 and 14) has been envisaged to explain the unexpected shielding of -CH 2-OH carbon signals of 3 4 on acetylation and upfield displacement of -CH 2-N signal of 2a vs 4a in their 13C NMR spectra in CDCl 3 solution 1 J CH values have been found to be useful for the assignment of aromatic methine carbon signals in o-disubstituted compounds. Part 68 of the series Studies on Indian medicinal plants. For Part 67, see P. K. Dutta, D. Bagchi and S.C. Pakrashi, Indian J. Chem. in press.

A simple radioenzymatic procedure for the determination of choline and acetylcholine in brain regions of rats sacrificed by microwave irradiation.

A rapid and sensitive radioenzymatic method for analysis of choline (Ch) and acetylcholine (ACh) concentrations in rat brain regions is described. The ACh content is obtained as the difference in Ch concentration between a hydrolysed and an unhydrolysed tissue sample. The ACh content was 16+/-1.0 nmol/g in the cortex and 76+/-2.4 nmol/g in the striatum, and the corresponding Ch values were 23+/-2.5 and 33+/-1.2.

Isolated CH stretching frequencies, bond lengths and strengths in chloro-alkanes

Isolated CH stretching frequencies, v is CH, have been determined by infrared partial deuteration studies in CH 3CHCl 2, CH 3CCl 3 and (CH 3) 2CCl 2. New infrared data are also reported for CH 2ClCCl 3, CHCl 2CCl 3, and CHCl 2CHCl 2. These are used to predict CH bond lengths, dissociation energies and force constants. The present compounds together with those previously studied provide data for a complete series of ethanes in which chlorine and methyl groups are substituted for hydrogen, α and β substitution effects are described in terms of S α, S g and S t parameters which however are not additive. The effect of α-chlorine substitution is to raise v CH by progressively smaller amounts ( S Cl α) as the number of chlorines increases. The presence of a methyl group increases S Cl α, but CCl 3, decreases it. β-chlorine substitution raises a gauche CH frequency by progressively smaller amounts ( S Cl g). v is CH values are predicted for the conformers of CH 2ClCH 2Cl and CH 2ClCHCl 2. Assignments for the CH 3 species are discussed with reference to possible Fermi resonances.

An enzymatic method for measuring picomole quantities of acetylcholine and choline in CNS tissue

A rapid and sensitive enzymatic assay for measuring picomole quantities of both acetylcholine (ACh) and choline (Ch) in tissue extracts has been developed. After ACh and Ch were extracted into 15% 1 n formic acid/85% acetone by the procedure of Toru and Aprison, lipids were removed by a heptane-chloroform extraction. All quaternary ammonium compounds were isolated by precipitation with periodide. After the precipitate (including ACh and Ch) was dissolved in a known volume of water, aliquots were taken for both assays. In the ACh assay, endogenous Ch was removed after conversion to choline phosphate by choline kinase, whereas ACh was subsequently hydrolyzed by base. In the presence of [ 14C]acetyl-CoA and choline acetyltransferase, the choline moiety was converted into [ 14C]ACh. The labeled ACh was extracted into sodium tetraphenylboron/butenenitrile and then counted in a scintillation counter. In the Ch assay, the first enzyme reaction step is omitted and only the second is used. The lower limit of sensitivity in both assays is 20 pmoles. Once the tissue has been carried through the extraction step, over eighty determinations can be made in one day. In vivo levels of ACh and Ch in the cerebrum of rats are reported for totally frozen rats and for rats sacrificed by the near-freezing procedure of Takahashi and Aprison. Mean ACh values in the two groups statistically were the same (26.5 ± 2.2 and 25.3 ± 1.7 nmoles/g, respectively) whereas the mean Ch values were significantly different (25.7 ± 0.9 and 64.0 ± 3.6 nmoles/g, respectively). The difference in the Ch levels as well as the importance of specifying the conditions that effect the measurement of ACh and Ch are discussed.