bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrogen‐15 n.m.r. studies of 13C, 15N labeled arginine
Authors: London R. E. , Walker T. E. , Whaley T. W. , Matwiyoff N. A. 
Published: May 2005

Abstract15N n.m.r. spectra of [13C‐2, 3‐15N2‐guanidino]arginine and [13C, 15N2] urea were obtained in D2O and H2O at a variety of pH values both with and without proton decoupling. The effects of the proton exchange rate are readily observable in the proton coupled 15N spectra. When the guanidino group is deprotonated (pK = 12.5), the terminal nitrogens give a single resonance 6.6 ppm downfield of the protonated species, indicating a rapid tautomeric exchange. The observed NH and CN couplings are compared with calculated values, and good agreement is found for 1J(CN) using a Blizzard–Santry type calculation. The ramifications of the proton exchange on 15N n.m.r. spectra of amino acids and peptides are discussed.
INDOR study of 1H1H inter‐ring couplings in naphthalene derivatives
Authors: Attimonelli M. , Sciacovelli O. 
Published: May 2005

AbstractThe 1H n.m.r. spectra of two naphthalene derivatives have been completely analysed. The advantages of the INDOR technique have been illustrated in the determination, magnitudes and signs, of small couplings in complex spin systems. A splitting of 0.07 Hz has been resolved in the 100 MHz spectrum of 1,2‐dichloro‐3 nitronaphthalene. The signs of the inter‐ring coupling constants alternate with the number of intervening bonds.
Etude Stéréochimique par RMN 1H de Tetrahydropyrannes β‐Chlorés α‐Substitués
Authors: Delaunay Jacques , Lebouc Alain , Riobé Olivier 
Published: May 2005

AbstractL'étude RMN 1H des alkyl‐2 chloro‐3 tétrahydropyrannes, préparés par action des réactifs de Grignard sur le mélange des dichloro‐2,3 tétrahydropyrannes cis et trans, indique la présence de deux isomères cis et trans, dans lesquels les groupements alkyles sont en position équatoriale; le chloro‐3 phényl‐2 tétrahydropyranne n'existe que sous la forme trans (éq‐éq). L'étude RMN 1H des alcoxy (aryloxy)‐2 tétrahydropyranne n'existe que sous la forme trans (éq‐éq). L'étude RMN 1H des alcoxy (aryloy)‐2 chloro‐3 tétrahydropyrannes cis et trans, obtenus par action d'alcools et du phénol sur les měmes dérivés dichlorés, montre que le groupement alcoxyle (ou aryloxyle) est toujours en position axiale.
The stereochemical dependence of the vicinal 13C14N coupling constant as a constitutional probe
Authors: Valckx Ludo A. , Borremans Frans A. M. , Becu Chris E. , De Mar Robert H. K. , Anteunis Marc. J. O. 
Published: May 2005

AbstractThe magnitudes of 13C14N coupling constants have been measured in 12 rigid or anancomeric (biased) tetraalkylammonium iodides. The one‐bond coupling is typical for the degree of substitution of the carbon atom and the geminal coupling is very small. Vicinal couplings depend on the dihedral angle and other factors.
Self‐consistent Perturbation Theory of 13C magnetic resonance parameters in pyridines
Authors: Galasso Vinicio 
Published: May 2005

AbstractThe 13C chemical shifts for pyridine and 22 of its monosubstituted derivatives, the 13C19F couplings for fluoropyridines and the 13C15N couplings for pyridine, the pyridinium cation and pyridine‐N‐oxide have been calculated using the SCF‐INDO Finite Perturbation Theory. Experimental 13C chemical shifts show only modest correlation with calculated shieldings; trends and magnitudes are, however, reasonably reproduced in some cases. Theory yields a correct account of the magnitudes, signs and trends for the various couplings except for 2J(CF). Addition of an empirical correction of + 33.5 Hz to the Fermi contact term leads also to excellent reproduction of this coupling.
13C NMR spectra of non‐labelled and 15N‐mono‐labelled azo dyes
Authors: Lyčka Antonín , Šnobl Dobroslav , Macháček Vladimír , Večeřa Miroslav 
Published: May 2005

Abstract13C NMR spectra of four types of azo coupling products from benzenediazonium chloride have been measured and interpreted, viz. hydrazo compounds with an intramolecular hydrogen bond (3‐methyl‐1‐phenylpyrazole‐4,5‐dione 4‐phenylhydrazone), azo compounds without an intramolecular hydrogen bond (4‐hydroxyazobenzene), azo compounds with an intramolecular hydrogen bond (2‐hydroxy‐5‐tert‐butylazobenzene) and an equilibrium mixture of both the tautomers of 1‐phenylazo‐2‐naphthol. The absolute values of the J(15N13C) coupling constants have been determined by recording the spectra of the 15N isotopomers, and have been used, in some cases, for 13C signal assignment. A relationship has been found between the chemical shifts of the C‐1′ to C‐4′ carbons of the phenyl group (from the benzenediazonium ion) or the 1J(15N13C) coupling constant, and the composition of the tautomeric mixture.
Nuclear magnetic resonance spectra of psychotherapeutic agents. V*—conformational analysis of 1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepin‐2‐ones
Authors: Aversa M. C. , Giannetto P. , Romeo G. , Ficarra P. , Vigorita M. G. 
Published: May 2005

AbstractThe conformational analysis of biologically active lofendazam (7‐chloro‐5‐phenyl‐1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepin‐2‐one) is carried out by means of lanthanide shift reagent assisted 1H NMR spectroscopy: the lanthanide induced shift computer simulation suggests that in deuteriochloroform the heterocyclic ring of lofendazam assumes a cycloheptene‐like chair conformation, where 1‐N moves away from trigonal stereochemistry to a very flattened pyramidal structure. At room temperature the conformational equilibrium is markedly shifted (85%) towards the conformer showing pseudoaxial H‐1 and 5‐Ph. The remarkable influence of steric requirements in controlling conformation, and the importance of 3‐ and/or 4‐methyl groups in hindering the ring inversion at room temperature, have been verified by conformational analysis of suitable analogous 1,3,4,5‐tetraydro‐2H‐1,5‐benzodiazepin‐2‐ones.
Carbon–13 NMR studies of tautomerism in some 2‐substituted imidazoles and benzimidazoles
Authors: Papadopoulos E. Paul , Hollstein Ulrich 
Published: May 2005

AbstractThe 13C NMR spectra of several 2‐substituted imidazoles and benzimidazoles have been measured. The substituent was CH3, COOH and CONHR, where R = H, n‐Bu, p‐tolyl or m‐chlorophenyl. Carbons 4 and 5 in the imidazoles and the carbon pairs 8/9, 4/7 and 5/6 become equivalent by proton transfer from N‐1 to N‐3, possibly through intermolecular association. The rate of this proton exchange increases with concentration and temperature. It decreases with extension of the 2‐substituent (rate CH3≫CONH‐phenyl > CONH‐p‐tolyl ≃ CONH‐m‐chlorophenyl ≫ CONH‐n‐butyl) due to steric hindrance at the site of the (benz)imidazole nitrogen.
The NMR spectra of porphyrins 20—proton and 13C characterization of porphyrin atropisomers
Authors: Abraham Raymond J. , Plant James , Bedford Geoffrey R. 
Published: May 2005

AbstractThe preparation, isolation and characterization by proton and 13C NMR of the four possible atropisomers of meso‐tetra(2‐methoxy‐1‐naphthyl)porphyrin is described. Chemical shift differences due to atropisomerization effects are observed in the porphyrin and naphthyl rings. Comparison of the naphthyl chemical shifts with those of the model compound 1‐isopropenyl‐2‐methoxynaphthalene allows the shifts due to the porphyrin ring current to be isolated. The observed Δδ values of the naphthyl protons agree well with those calculated from the previously described porphyrin ring current model, and allow both the angle of tilt of the naphthyl ring and the dihedral angle of the 2‐methoxy substituent to be estimated. In contrast, the Δδ values for the naphthyl carbons bear no relationship to the calculated ring current shifts. Calculations of the total ring current contribution (porphyrin plus naphthyl rings) at the different naphthyl rings of the unsymmetric type III isomer show that at least part of the observed atropisomerism effects are due to the long‐range current shifts of the naphthyl rings. The results also provide a clear demonstration of the identity of the porphyrin ring current in the free base and porphyrin dication.
Conformations of side chains of somatostatin very high field proton NMR studies
Authors: Live David H. , Davis Donald G. , Agosta William C. , Cowburn David 
Published: May 2005

AbstractThe high field proton NMR spectra (500 and 600 MHz) of the peptide hormone somatostatin in D2O are reported. The results obtained are used to derive values of the couplings and chemical shifts related to the solution conformation of several of the side chains. This work resolves a discrepancy in the literature concerning the assignments of resonances in the spectrum. It also provides a means of testing the accuracy of obtaining values for these couplings and shifts in previous 2D NMR studies at lower field from strongly coupled multiplets in spectra of this complexity.
Isomerization and conjugation characteristics of the CN double bond. III—15N NMR studies of tautomerism in 2‐phenylamino‐2‐thiazoline and its thiazine analogue
Authors: Tóth Gábor , Almásy Attila 
Published: May 2005

Abstract15N NMR Spectroscopy shows, contrary to earlier suggestions, that 2‐phenylamino‐2‐thiazoline and its thiazine analogue are present in chloroform as an equilibrium of imino and amino tautomers in the ratio of 62:38 and 74:26, respectively.
Carbon‐13 NMR study of some isomeric n‐nitroindazole derivatives
Authors: Cohen‐Fernandes Pauline , Erkelens Cornelis , Habraken Clarisse L. 
Published: May 2005

AbstractThe 13C NMR spectra of 1,5‐ and 2,x‐dinitroindazoles “x=4‐7” and 3‐bromo‐1,x‐dinitroindazoles are recorded and discussed. The data on he 2,x‐dinitroindazoles confirm our previous structurea assignment based on 1H NMR spectroscopy. The 13C NMR spectra established that in the novel 3‐bromo‐1,x‐dinitroindazoles the N‐nitro group is attached at N‐1.
Structural assignment of monothiocarbonohydrazones by 1H NMR spectroscopy
Authors: Rajendran G. , Jain Sampat R. 
Published: May 2005

AbstractAnalysis of the 1H NMR spectra of several monothiocarbonohydrazones, some of them synthesized for the first time, shows that they exist as two structural isomers. Whereas, in general, the derivatives of aromatic aldehydes conform to a linear structure, the aliphatic carbonyl derivatives conform to heterocyclic or linear structures, depending on the size of the substituent groups. This dual behaviour is explained in terms of extended conjugation and steric hindrance.
Principal component analysis of the 13C NMR spectra of enamino ketones
Authors: Azzaro Marcel , Geribaldi Serge , Videau Bruno , Chastrette Maurice 
Published: May 2005

AbstractThe 13C NMR spectra of eleven 3‐N,N‐dialkylamino‐5,5‐dimethylcyclohex‐2‐en‐1‐ones have been determined. The chemical shifts of the three sp2 carbons and of the two methylene carbons on the cyclohexenone moiety have been subjected to factor analysis. Two factors are necessary and sufficient to account for more than 93% of the total variance. The more important axis (79%) corresponds to a factor closely related to the inductive and steric effects of the alkyl nitrogen substituents. The second parameter is more difficult to interpret and could correspond to the ‘ipso effects’ of amino groups.
A 1H and 13C NMR study of intramolecular rotations in syn‐ and anti‐o‐tolyl‐di‐tert‐butyl‐carbinols
Authors: Tiffon Bernard , Lomas John S. 
Published: May 2005

AbstractThe syn and anti rotamers of o‐tolyl‐di‐tert‐butylcarbinol, 2a and 2b, respectively, have been studied by 1H NMR at 200 MHz and by natural abundance 13C NMR at 50 MHz. 1H‐{1H} NOE enhancement factors are consistent with the known structures and the calculated geometries of these compounds. The relaxation time, T1, of the 2‐Me protons in 2b is unexpectedly higher than that for 2a. The 13C relaxation times of the 2‐Me and the quaternary carbon of the tert‐butyl group are also both higher in 2b than in 2a, suggesting that the rotation of these groups is faster in the less stable isomer. The activation energies for t‐Bu rotation, measured by 1H DNMR, agree with this conclusion. Further confirmation is provided by theoretical calculation of the 2‐Me and t‐Bu rotation barriers based on Allinger's MM2 force field. Comparison of measured ΔG‡ values from this work and from the literature with MM2‐calculated ΔH‡ values indicates that this force field systematically underestimates rotation barriers in open‐chain systems by a factor of approximately 0.64.
NMR spectra of carotenoporphyrins. Computer‐assisted conformational analysis
Authors: Chachaty Claude , Gust Devens , Moore Thomas A. , Nemeth Gregory A. , Liddell Paul A. , Moore Ana L. 
Published: May 2005

AbstractA computer‐assisted method of conformational analysis for porphyrin molecules bearing flexible side‐chains has been developed. The method utilizes the ring current‐induced chemical shift changes of the side‐chain protons which arise from the porphyrin macrocycle and any attached aryl rings. The treatment has been applied to a series of carotenoporphyrin molecules, which are important as models for a variety of photophysical processes in biological systems. Chemical shift data of sufficient accuracy for the conformational analysis were obtained from 500 MHz NMR experiments. The conformations of the carotenoporphyrins varied from extended ones with the carotenoid well away from the porphyrin ring to tightly folded species, depending on molecular constitution. The analytical method can be extended to other porphyrin‐based systems.
1H NMR investigation of ring mobility of 1,5‐benzodiazepine‐2,4‐diones
Authors: Chidichimo Giuseppe , Longeri Marcello , Menniti Giuseppina , Romeo Giovanni , Ferlazzo Alida 
Published: May 2005

AbstractThe ring mobility of some 1,5‐benzodiazepine‐2,4‐diones and 1,4‐benzodiazepin‐2‐one has been investigated by the temperature dependence of their 1H NMR spectra. The activation parameters have been obtained, and the influence of N‐1 substitution on the ring mobility is discussed, taking into account previously reported data for similar compounds.
Structure assignment by 1H and 13C NMR of two epimers derived from glycyrrhetic acid
Authors: Bongini Alessandro , Contento Michele , Orena Mario , Pifferi Giorgio , Erba Roberto 
Published: May 2005

AbstractA full assignment of the 13C signals of four pentacyclic triterpenes confirms the results obtained by 1H NMR analysis of steroidal methyls, resolving the stereochemistry of the oxidation product of 3‐β‐acetoxyolean‐12‐en‐30‐oic acid methyl ester.
The transport of proteins in Mauthner axon in fish as studied by autoradiography and interference microscopy
Authors: Jakoubek B. , Semiginovský B. , Bass A. , Scott D. 
Published: May 2005

AbstractUsing 1 C‐Leucine the rate of transport of proteins in single nerve fiber was investigated by quantitative autoradiography using the desheathed, hand‐free isolated Mauthner axons of fish.After different times of incubation of living fish in the radioactive medium a non‐uniform labelling of the isolated axons along their length was observed, which showed a characteristic pattern. The distribution of the label indicates: (a) a continuous supply of labelled proteins from the cell body to the axon, (b) accumulation of labelled proteins near the terminal end of the axon, (c) two different rates of the somato‐axonal transport of proteins (30–40 mm 24hr; 3.5 mm/24 hr).After the transection of the spinal cord no incorporation into the segments of the axon below the lesion was detectable.No changes of the dry mass between the proximal and distal parts of the Mauthner axon were detectable in interference microscope.The alternative explanations for the observed pattern of axonal labelling, i.e. local protein synthesis in axons and somato‐axonal flow of proteins, are discussed.
A statistical analysis of timing behavior
Authors: Suzuki Hisao , Saito Mizuo 
Published: May 2005

Abstract(1) When rabbits were trained on a differential reinforcement of low rate (DRL) 10 sec schedule, they successively made bar‐press response so that a sequence of inter‐response time (IRT) intervals were obtained for each training session. This sequence was subjected to the following statistical analysis. (2) The serial correlation coefficients of order 1 to 50 were calculated on each sequence. They were between –0.2 and +0.2, and seemed to be essentially zero. (3) The distribution of IRT intervals was found to be represented by a composite Weibull distribution function. (4) The relation between one of the Weibull parameters, shape parameter, and the hazard function of the bar‐pressing was discussed.
The effect of monocular deprivation on the synaptic contacts of the visual cortex
Authors: Fifková E. 
Published: May 2005

AbstractThe effect of visual deprivation on synaptic contacts in the visual cortex was studied with the electron microscope. The deprivation was achieved by unilateral lid suture in 14‐day old white rats before eye opening after which the animals were kept for 8 weeks. The density and the size of synaptic contacts in the upper part of the visual cortex (from the surface of layer II up to V) were estimated. The mean density of synapses of the visual cortex supplied by the deprived eye was 20% less than on the control side, the upper levels of the cortex being more affected. The mean size of synaptic contacts was larger (+7.5%) in the upper levels of the deprived cortex. No right left difference in density and size were found in control animals.
Calcium accumulation by isolated nerve ending particles from brain. I. The site of energy‐dependent accumulation
Authors: Lust W. David , Robinson Joseph D. 
Published: May 2005

AbstractSynaptosomes (isolated nerve ending particles) prepared from rat brain accumulated 45Ca in the presence of ATPd̊ and MgCl2. In order to localize the site of this energy‐dependent process the ability of synaptosomes to accumulate 45Ca was compared to that of a purified preparation of brain mitochondria, since mitochondria are contained within nerve endings. The purity of synaptosomal and mitochondrial fractions was monitored in terms of enzymatic markers and electron microscopy. The rate of accumulation by mitochondria was sufficient to account for the observed rate with synaptosomes, suggesting that the intra‐synaptosomal mitochondria were the site of accumulation in the nerve endings. Furthermore, subfractionation of synaptosomes that had accumulated 45Ca indicated that the bulk of the radioactivity was associated with the mitochondria recovered from the nerve ending. 45Ca accumulation was also supported by oxidizable substrates. This accumulation could not be blocked, either in synaptosomes or in mitochondria, by oligomycin. Since oligomycin blocked ATP‐energized accumulation, free ATP could therefore not be the energy source derived from these substrates, further implicating the intra‐synaptosomal mitochondria as the site of accumulation. Accumulation energized by oxidizable substrates was stimulated by Pi. No stimulation was apparent in the presence of ATP, probably due to the rapid release of Pi by ATPase activity, which was far greater than the rate of 45Ca accumulation. These findings suggest that mitochondria at the nerve ending may actively participate in regulating cytoplasmic Ca2+ levels, a vital role at that site.
Calcium accumulation by isolated nerve ending particles from brain. II. Factors influencing calcium movements
Authors: Lust W. David , Robinson Joseph D. 
Published: May 2005

AbstractA synaptosomal preparation from rat brain accumulated 45Ca by a temperature‐sensitive process requiring ATPd̊ and Mg++. The uptake of 45Ca was correlated with a net increase in total calcium, and after brief incubations the concentration of 45Ca in the particles was several hundred times that remaining in the medium. Calcium accumulation was associated with a corresponding stoichiometric accumulation of phosphate. Synaptosomes that had accumulated 45Ca during a prior incubation lost the radioactivity during a subsequent incubation in the absence of ATP. NaCl increased the efflux of accumulated 45Ca, a process distinguishable from the non‐specific inhibition of 45Ca accumulation by various solutes corresponding with their effects on intra‐synaptosomal volume. The Na+‐induced efflux of 45Ca was not affected by ouabain. Since the intrasynaptosomal mitochondria have been identified as the site of 45Ca accumulation in synaptosomes, the data suggest that these mitochondria may function as reservoirs of releasable Ca++ within the nerve ending, possibly participating in the Ca++‐dependent process of neurotransmitter release.
Activity patterns of catecholamine‐containing pontine neurons in the dorso‐lateral tegmentum of unrestrained cats
Authors: Chu Nai‐Shin , Bloom Floyd E. 
Published: May 2005

AbstractSingle catecholamine‐containing neurons in the dorso‐lateral pontine tegmentum were recorded in unanesthetized, freely behaving cats. Microscopic lesions were made on each recorded unit and subsequently identified for catecholamines by fluorescence histochemical analysis. The majority of the NE‐containing neurons exhibited low spontaneous discharge rates in quiet wakefulness and in slow wave sleep. In paradoxical sleep, the medially located NE‐containing neurons tend to exhibit ursting discharges which are closely related to individual PGO waves. The laterally or dorsally situated NE units fire more slowly and tend to derease their firing activity during paradoxical sleep. Tonically active, relatively fast NE‐containing units were also found. Often, those neurons showed greatly increased activity before the cat awoke from either slow wave sleep or paradoxical sleep, with activity persisting during the early moments of waking. The combination of histochemical and electrophysiologic methods proved essential for correlating neurochemistry and function within the heterogeneous NE‐containing nuclei of the cat pons.
Neurobiology of Stomotoca. II. Pacemakers and conduction pathways
Authors: Mackie G. O. 
Published: May 2005

AbstractEvidence is presented for separate conduction pathways for swimming and for tentacle coordination in the marginal nerves of the jellyfish Stomotoca. The effector muscles are fired through junctions sensitive to excess Mg++, probably represented by the neuromuscular synapses observed by electron microscopy. The swimming effector (striated muscle) fires one‐to‐one with nerve input signals and myoid conduction occurs. Tentacle responses (smooth muscle contractions) involve facilitation, presumably at the neuro‐effector junction; responses are graded and nonpropagating.Electrical correlates of two further conducting systems using the marginal nerves have been recorded. Their functions are unknown. One, the bridge system, extends up the four radii and encircles the peduncle; the other (ring system) is confined to the margin.A fifth conducting system is inferred in the case of the pointing response and its distribution is plotted. Signals have not been obtained from it. Pointing is accompanied by a burst of muscle potentials in the radial smooth muscles and is exhibited after a lengthy latency, indicating a local pacemaker.A sixth conducting pathway is the epithelial system, which mediates crumpling, a response involving the radial muscles without pacemaker intervention.Characteristic conduction velocities and wave forms are noted for the first four systems and for epithelial pulses. All systems, except perhaps the pointing conduction system, through‐conduct under excess Mg++.Spontaneous activity patterns are described for the swimming, tentacle pulse, and ring systems. Abrupt increases in light intensity inhibit spontaneous activity, sudden decreases augmenting it. In the absence of specialized photoreceptors, light is presumed to act directly on central neurons.Epithelial pulses inhibit swimming, apparently by blocking the generation or conduction of the primary nervous events. This observation, taken in conjunction with evidence of feedback inhibition of the primary swimming system by the cells it fires, is discussed in relation to possible mechanisms whereby the output of nerve cells might be altered by activity in the excitable epithelial cells which envelop them.