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kJ
Kinds of kJ Terms modified by kJ Selected AbstractsVisual function in infants with brain lesions (1994)DEVELOPMENTAL MEDICINE & CHILD NEUROLOGY, Issue 11 2008Eugenio Mercuri Another in our series of commentaries on notable papers from the DMCN archives. The full paper is available at http://www.mackeith.co.uk Pike MG, Holmstrom G, de Vries LS, Pennock JM, Drew KJ, Sonksen PM, Dubowitz LM. Patterns of visual impairment associated with lesions of the preterm infant brain. Dev Med Child Neurol 1994; 36: 849,62. [source] Studies in Solution and the Solid State of Coordination Compounds Derived from LiBH4, NaBH4, and Bidentate Aromatic AminesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2010Milagros Aguilar-Martínez Abstract The mixture of 2,2,-bipyridylamine, 2,2,-bipyridine, 1,10-phenanthroline, 1,2-phenylendiamine, and 1,4-phenylendiamine each with LiBH4 and NaBH4 in a 1:1 molar ratio in THF yields seven new complexes of the type MBH4·L-THF and one complex of the type MBH4·L. These compounds were characterized by IR and NMR spectroscopy and X-ray single-crystal structure determinations. In the solid state, the [BH4], group is bidentate, as deduced from the stretching patterns observed in IR spectra and confirmed by X-ray single-crystal structure analysis. NMR spectroscopy showed that all amines act as bidentate ligands and are symmetrically coordinated to the metal cation. Complexes LiBH4 -2,2,-bipyridine-THF (1), NaBH4 -2,2,-bipyridine-THF (2), LiBH4 -1,10-phenanthroline-THF (3), and NaBH4 -1,10-phenanthroline-THF (4) have a discrete molecular structure, whereas the complexes LiBH4 -1,2-phenylendiamine-THF (5), NaBH4 -1,2-phenylendiamine-THF (6), LiBH4 -2,2,-dipyridilamine (7), and LiBH4 -1,4-phenylendiamine-THF (8) have polymeric structures in the solid state. N -borane-dipyridylamine adduct 9 was isolated from an aged solution of 7. IR spectroscopy of the new complexes showed that the structures of complexes 1, 3, 4, and 6 are maintained in the solid state and in solution. A rotational barrier for the [BH4], group of less than 38 KJ,mol,1 was estimated for some of the new complexes. [source] CK7 expression in primary cutaneous squamous cell carcinomaJOURNAL OF CUTANEOUS PATHOLOGY, Issue 9 2010Melissa Pulitzer Aim: To evaluate cytokeratin 7 (CK7) immunoreactivity in invasive primary cutaneous squamous cell carcinomas (SCCs). Methods: Twenty-seven primary cutaneous SCCs from 25 patients were evaluated for tumor grade using hematoxylin and eosin-stained slides and for percentage and intensity of immunoreactivity for CK7. All cases exhibited features of SCC with an in situ component. No glandular or tubular differentiation was present. Staining intensity was graded on a scale of 0,3, with 0 indicating no reaction. Of immunoreactive cases, percentage of tumor staining and distribution of immunoreactivity was documented. Results: Six of 27 SCCs (22%) exhibited immunostaining for CK7. Of those cases, three were poorly differentiated, exhibiting 2 to 3+ intensity in 5,15% of cells. Two were poorly differentiated, with 2 to 3+ intensity in 30,60% of cells. The remaining immunoreactive tumor was moderately differentiated, with 1+ intensity and 5% staining in an area of microinvasion. Conclusion: A subset of cutaneous SCCs, in particular, poorly differentiated tumors, may show focal-to-partial immunoreactivity for CK7. This is important to bear in mind when immunohistochemistry is used to distinguish SCC from simulants, such as porocarcinoma, or other adnexal carcinomas with squamous metaplasia. Pulitzer M, Desman G, Busam KJ. CK7 expression in primary cutaneous squamous cell carcinoma. [source] Distinction of conjunctival melanocytic nevi from melanomas by fluorescence in situ hybridizationJOURNAL OF CUTANEOUS PATHOLOGY, Issue 2 2010Klaus J. Busam A conjunctival melanocytic nevus may on occasion be difficult to distinguish from melanoma both clinically and histopathologically. An unambiguous correct diagnosis is critical because of major differences in management and prognosis. We evaluated a fluorescence in situ hybridization (FISH) assay, which has previously been shown to be of value for the diagnosis of melanocytic nevi and melanomas of the skin, using probes targeting 6p25 (RREB1), 6q23 (MYB), 11q13 (CCND1) and centromere 6 (CEP6), for its potential to assist in the distinction of conjunctival melanocytic nevi from melanomas. Four melanocytic nevi and eight melanomas of the conjunctiva were analyzed. Two of the melanomas were diagnostically problematic because of suboptimal histopathology. None of the conjunctival melanocytic nevi showed a level of chromosomal aberrations that met FISH criteria for a diagnosis of melanoma. All eight conjunctival melanomas (six unequivocal and two suspicious lesions) met FISH criteria for melanoma. Thus, results from FISH assay targeting 6p25, 6q23, 11q13 and centromere 6 correlated well with the histopathologic diagnoses and supported the histopathologic suspicion in two problem cases. The findings encourage further exploration of this technique as an ancillary method for the work-up of conjunctival melanocytic proliferations. Busam KJ, Fang Y, Jhanwar SC, Pulitzer MP, Marr B, Abramson DH. Distinction of conjunctival melanocytic nevi from melanomas by fluorescence in situ hybridization. [source] Fitness, fatness and activity as predictors of bone mineral density in older personsJOURNAL OF INTERNAL MEDICINE, Issue 5 2002K. J. Stewart Abstract. Stewart KJ, DeRegis JR, Turner KL, Bacher AC, Sung J, Hees PS, Tayback M, Ouyang P (Johns Hopkins Bayview Medical Center, Johns Hopkins University, School of Medicine, Baltimore, MD, USA). Fitness, fatness, and activity as predictors of bone mineral density in older persons. J Intern Med 2002; 252: 381,388. Objectives. To determine relationships of bone mineral density (BMD) with fitness, physical activity, and body composition and fat distribution. Design. Cross-sectional. Setting. General Clinical Research Center, Johns Hopkins Bayview Medical Center, Baltimore, Maryland. Subjects. Men (n = 38) and women (n = 46), aged 55,75 years with high normal blood pressure or mild hypertension but otherwise healthy. Methods. Aerobic fitness (oxygen uptake) on a treadmill, muscle strength by one-repetition maximum, activity by questionnaire, abdominal obesity by magnetic resonance imaging; anthropometrics, and body composition by dual energy X-ray absorptiometry (DXA) which measured total fat and lean mass, and BMD for the total skeleton, lumbar spine (L1,L4) and total hip. Results. Aerobic fitness did not correlate with BMD. Using multivariate analysis to ascertain independent contributions to the variance in BMD, in women, with adjustment for hormone replacement therapy (HRT), total skeleton BMD was independently related to muscle strength and abdominal total fat; total hip BMD to body weight; lumbar spine BMD to abdominal total fat. HRT also influenced BMD in the lumbar spine. In men, lumbar spine BMD was independently related to abdominal total fat physical activity and total hip BMD related to lower body strength. P < 0.05 for all of these correlations. Conclusions. Abdominal obesity and muscle strength emerge as predominant correlates of BMD in older persons with stronger relationships seen in women. Body weight and HRT also explained portions of the variance in BMD in women. Whether abdominal obesity is simply a marker for general obesity or has independent protective effects on bone is yet to be determined. [source] Chlamydia pneumoniae and luminal narrowing after coronary angioplastyJOURNAL OF INTERNAL MEDICINE, Issue 1 2001K. J. Mattila Mattila KJ, Juvonen JT, Kotamäki MK, Saikku PA (Helsinki University Hospital, Helsinki; Kainuu Central Hospital, Kajaani, and National Public Health Institute, Oulu, Finland). Chlamydia pneumoniae and luminal narrowing after coronary angioplasty. J Intern Med 2001; 250: 67,71. Objectives.,Numerous studies have linked Chlamydia pneumoniae with atherosclerotic vessel disease and a trend for an association of the bacteria with restenosis after percutaneous transluminae coronary angioplasty (PTCA) has also been observed. The aim of this study was to assess the role of Chlamydia pneumoniae in the luminal narrowing taking place after PTCA. Design.,A noninterventional 6-month follow-up study. Setting.,A university hospital. Subjects.,A total of 122 patients with angiographically proven coronary heart disease (CHD) referred for PTCA. Interventions.,None. Main outcome measures.,The degree of luminal narrowing in the coronary arteries following coronary angioplasty. Results.,The levels of C. pneumoniae antibodies (IgG, IgA and IgM classes) and immune complexes were not associated with luminal narrowing after PTCA in multivariate analyses whilst smoking, plasma endothelin levels and diabetes were. The serologic parameters did not change during the follow up either. Conclusions.,These results do not support a role for C. pneumoniae in luminal narrowing following PTCA. [source] Opposing roles of IL-17A and IL-25 in the regulation of TSLP production in human nasal epithelial cellsALLERGY, Issue 5 2010G. Xu To cite this article: Xu G, Zhang L, Wang DY, Xu R, Liu Z, Han DM, Wang XD, Zuo KJ, Li HB. Opposing roles of IL-17A and IL-25 in the regulation of TSLP production in human nasal epithelial cells. Allergy 2010; 65: 581,589. Abstract Background:, The importance of IL-17A, IL-17F, and IL-25 in allergic rhinitis (AR), as well as their possible role in regulation on thymic stromal lymphopoietin (TSLP) production in nasal epithelial cells, is not well understood. Objective:, To determine the possible regulation of IL-17A, IL-17F, and IL-25 on TSLP production in the initiation of allergic responses. Methods:, The levels of IL-17A, IL-17F, IL-25, and TSLP in nasal lavages of patients with AR were measured using an enzyme-linked immunosorbent assay (ELISA) and compared with that in normal controls. Then, primary human nasal epithelial cells (HNECs) were stimulated with dsRNA (0,75 ,g/ml), as well as IL-17A (100 ng/ml), IL-17F (100 ng/ml), and IL-25(100 ng/ml). The mRNA expression of IL-17A, IL-17F, IL-25, TSLP, as well as the chemokines CCL20, IL-8, and eotaxin was analyzed using quantitative real-time PCR, and their protein levels in the supernatants of cultured HNECs were determined by ELISA. Results:, Both TSLP and IL-17 cytokines are significantly elevated in patients with AR. dsRNA was found to increase the production of IL-17F, IL-25, TSLP, CCL20, and IL-8 in HNECs. Furthermore, IL-25 significantly enhanced dsRNA-induced TSLP production in primary HNECs and was dominant to the inhibitory effect of IL-17A on TSLP regulation. Conclusions:, Our study provides the first evidence that both IL-17F and IL-25 can be induced by dsRNA in HNECs. Despite of the opposing effects of IL-17A and IL-25 on TSLP regulation in HNECs, IL-25 was dominant to IL-17A, providing a plausible explanation for the simultaneous upregulation of IL-17 cytokines and TSLP in patients with AR. [source] A stochastic evaluation of the decision to specialize in orthodonticsORTHODONTICS & CRANIOFACIAL RESEARCH, Issue 1 2003SR Straja Structured Abstract Authors , Straja SR, Klatte KJ, Montgomery GL, Tuncay OC Objective , The objective of this paper is to identify under different scenarios, and from a financial point of view, the conditions required to successfully switch from the general dentistry practice to orthodontics. Study Design , A mail survey was used to collect the data from the practicing orthodontists. They estimated the income, at certain points, in the working life of an orthodontist. The general practitioner data were taken from the American Dental Association figures. Subsequently, a stochastic model was constructed. Results and Conclusion , Those who decide to buy an existing practice expect higher profits in the near future, and therefore the required minimum number of remaining years of practice is lower than for those deciding to start a new practice. For both scenarios, the 3-year residency will delay the profits compared with a 2-year residency. Thus, an increased number of remaining years of practice is required. There must be more than 10 working years left in the practitioner's life to make the switch profitable. [source] Variation of dust endotoxin concentrations by location and time within homes of young childrenPEDIATRIC ALLERGY AND IMMUNOLOGY, Issue 3 2010Dennis R. Ownby Ownby DR, Peterson EL, Williams LK, Zoratti EM, Wegienka GR, Woodcroft KJ, Joseph CLM, Johnson CC. Variation of dust endotoxin concentrations by location and time within homes of young children. Pediatr Allergy Immunol 2010: 21: 533,540. © 2010 John Wiley & Sons A/S Endotoxin may affect the development of allergic disease in childhood but little is known about endotoxin variation within homes. We sought to determine endotoxin concentration agreement within homes when five locations were each sampled twice 5 months apart. Endotoxin was measured using the recombinant Limulus factor C assay in dust samples from 585 homes of children enrolled in a prospective study and again in 335 homes 5 months later. The five locations sampled in each home were the child's bedroom floor, child's bed, mother's bedroom floor, mother's bed and living room floor. Concentrations of 4 allergens (Can f 1, Fel d 1, Der f 1 and Bla g 2) were also measured from the child's bedroom floor. In pair-wise comparisons, endotoxin concentrations in all locations within each home were significantly different from all other locations (p < 0.001) except for the child's and mother's bedroom floors (p = 0.272). Spearman correlations between endotoxin concentrations from the different locations were all statistically significant (p < 0.05) but of modest magnitude (r = 0.24,0.54). Similarly, correlations at each site over the 5 month observation interval were statistically significant but modest (r = 0.17,0.44). Pets and season of the year did not affect correlations, although correlations were lower if the floor was not carpeted. Endotoxin concentrations at all locations were minimally correlated with allergen concentrations in both negative and positive directions (r = ,0.12 to 0.12). We conclude that a single measurement of endotoxin from a home dust sample provides an imprecise estimate of dust endotoxin concentrations in other locations within the home and over a relatively short observation interval. [source] Target setting in intensive insulin management is associated with metabolic control: the Hvidoere Childhood Diabetes Study Group Centre Differences Study 2005PEDIATRIC DIABETES, Issue 4 2010PGF Swift Swift PGF, Skinner TC, de Beaufort CE, Cameron FJ, Åman J, Aanstoot H-J, Castaño L, Chiarelli F, Daneman D, Danne T, Dorchy H, Hoey H, Kaprio EA, Kaufman F, Kocova M, Mortensen HB, Njølstad PR, Phillip M, Robertson KJ, Schoenle EJ, Urakami T, Vanelli M, Ackermann RW, Skovlund SE for the Hvidoere Study Group on Childhood Diabetes. Target setting in intensive insulin management is associated with metabolic control: the Hvidoere Childhood Diabetes Study Group Centre Differences Study 2005. Objective: To evaluate glycaemic targets set by diabetes teams, their perception by adolescents and parents, and their influence on metabolic control. Methods: Clinical data and questionnaires were completed by adolescents, parents/carers and diabetes teams in 21 international centres. HbA1c was measured centrally. Results: A total of 2062 adolescents completed questionnaires (age 14.4 ± 2.3 yr; diabetes duration 6.1 ± 3.5 yr). Mean HbA 1c = 8.2 ± 1.4% with significant differences between centres (F = 12.3; p < 0.001) range from 7.4 to 9.1%. There was a significant correlation between parent (r = 0.20) and adolescent (r = 0.21) reports of their perceived ideal HbA1c and their actual HbA1c result (p < 0.001), and a stronger association between parents' (r = 0.39) and adolescents' (r = 0.4) reports of the HbA1c they would be happy with and their actual HbA1c result. There were significant differences between centres on parent and adolescent reports of ideal and happy with HbA1c (8.1 < F > 17.4;p < 0.001). A lower target HbA1c and greater consistency between members of teams within centres were associated with lower centre HbA1c (F = 16.0; df = 15; p < 0.001). Conclusions: Clear and consistent setting of glycaemic targets by diabetes teams is strongly associated with HbA1c outcome in adolescents. Target setting appears to play a significant role in explaining the differences in metabolic outcomes between centres. [source] A support theorem for quasianalytic functionalsMATHEMATISCHE NACHRICHTEN, Issue 4 2007Tobias Heinrich Abstract For a weight function , and an open set G in ,N denote by ,(,)(G) (resp. E{, }(G)) the , -ultradifferentiable functions of Beurling (resp. Roumieu) type on G. Using ideas of Hörmander it is shown that the functionals u in ,,(,)(G) and ,,{, }(G) can be embedded into the realanalytic functionals on ,N and that there is a smallest supporting set for u in the corresponding class which coincides with the realanalytic (hyperfunction) support of u. Moreover, if , is quasianalytic and if a compact subset K of G is the union of the compact sets K1 and K2 then each u , ,,{, }(G) which is supported by K can be decomposed as u = u1 + u2, where uj is supported by Kj for j = 1, 2. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A new look at the quantum mechanics of the harmonic oscillatorANNALEN DER PHYSIK, Issue 7-8 2007H.A. Kastrup Abstract In classical mechanics the harmonic oscillator (HO) provides the generic example for the use of angle and action variables and I > 0 which played a prominent role in the "old" Bohr-Sommerfeld quantum theory. However, already classically there is a problem which has essential implications for the quantum mechanics of the (,,I)-model for the HO: the transformation is only locally symplectic and singular for (q,p) = (0,0). Globally the phase space {(q,p)} has the topological structure of the plane ,2, whereas the phase space {(,,I)} corresponds globally to the punctured plane ,2 -(0,0) or to a simple cone with the tip deleted. From the properties of the symplectic transformations on that phase space one can derive the functions h0 = I, h1 = Icos , and h2 = - Isin , as the basic coordinates on {(,,I)}, where their Poisson brackets obey the Lie algebra of the symplectic group of the plane. This implies a qualitative difference as to the quantum theory of the phase space {(,,I)} compared to the usual one for {(q,p)}: In the quantum mechanics for the (,,I)-model of the HO the three hj correspond to the self-adjoint generators Kj, j = 0,1,2, of certain irreducible unitary representations of the symplectic group or one of its infinitely many covering groups, the representations being parametrized by a (Bargmann) index k > 0. This index k determines the ground state energy of the (,,I)-Hamiltonian . For an m -fold covering the lowest possible value for k is k = 1/m, which can be made arbitrarily small by choosing m accordingly! This is not in contradiction to the usual approach in terms of the operators Q and P which are now expressed as functions of the Kj, but keep their usual properties. The richer structure of the Kj quantum model of the HO is "erased" when passing to the simpler (Q,P)-model! This more refined approach to the quantum theory of the HO implies many experimental tests: Mulliken-type experiments for isotopic diatomic molecules, experiments with harmonic traps for atoms, ions and BE-condensates, with charged HOs in external electric fields and the (Landau) levels of charged particles in external magnetic fields, with the propagation of light in vacuum, passing through strong external electric or magnetic fields. Finally it may lead to a new theoretical estimate for the quantum vacuum energy of fields and its relation to the cosmological constant. [source] Microstructural, thermal, and electrical properties of Bi1.7V0.3Sr2Ca2Cu3Ox glass-ceramic superconductorCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2004T. S. Kayed Abstract A glass-ceramic Bi1.7V0.3Sr2Ca2Cu3Ox superconductor was prepared by the melt-quenching method. The compound was characterized by scanning electron microscopy, x-ray diffraction, differential thermal analysis, current-voltage characteristics, transport resistance measurements, and Hall effect measurements. Two main phases (BSCCO 2212 and 2223) were observed in the x-ray data and the values of the lattice parameters quite agree with the known values for 2212 and 2223 phases. The glass transition temperature was found to be 426 °C while the activation energy for crystallization of glass has been found to be Ea = 370.5 kJ / mol. This result indicates that the substitution of vanadium increased the activation energy for the BSCCO system. An offset Tc of 80 K was measured and the onset Tc was 100 K. The Hall resistivity ,H was found to be almost field-independent at the normal state. A negative Hall coefficient was observed and no sign reversal of ,H or RH could be noticed. The mobility and carrier density at different temperatures in the range 140-300 K under different applied magnetic fields up to 1.4 T were also measured and the results are discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Is postprandial hypertriglyceridaemia in relatives of type 2 diabetic subjects a consequence of insulin resistance?EUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 2 2005A. Kriketos Abstract Background, Higher postprandial triglyceride responses reported in first degree relatives of people with type 2 diabetes (REL) were postulated to be the result of an early, possibly intrinsic, defect in oral lipid handling. The postprandial triglyceride response to high fat meals (HFM) in normal subjects is reduced by the insulin response to dietary carbohydrate (CHO) in the meal. The aims of this study were to examine whether (1) insulin resistance is associated with an intrinsic defect in triglyceride handling in insulin-resistant REL and (2) insulin resistance is associated with altered triglyceride handling after HFM with high CHO content. Materials and methods, Postprandial responses to a HFM in normolipidaemic, normoglycaemic REL were compared with subjects without a family history of diabetes mellitus (CON). Over 6 h, the insulin, glucose, triglyceride and nonesterified fatty acid (NEFA) responses after a high fat (80 g fat), low CHO (HFM-LC; 20 g CHO, 4250 kJ) meal and a high fat, high CHO (HFM-HC; 100 g CHO, 5450 kJ) meal were examined. Results, The 10 (7F/3M) REL were significantly more insulin-resistant, determined by glucose infusion during a hyperinsulinaemic euglycaemic clamp than the 10 (5F/5M) CON (glucose infusion rate 44·6 ± 4·9 vs. 60·0 ± 4·8 µmol min,1 kg FFM,1, P = 0·037). Subjects were similar for age and body mass index (BMI). The triglyceride increments after the HFM-LC were similar in both, peaking at 180,240 min (,0·77 ± 0·11 mmol L,1), demonstrating no postprandial defect in REL, despite insulin resistance. There was a significantly lower postprandial triglyceride response in CON following the HFM-HC compared with the HFM-LC, but not in REL. In contrast, the higher insulin level during the HFM-HC was associated with significantly greater NEFA level suppression than in the HFM-LC (2·13 ± 0·51 vs. 0·70 ± 0·35 mmol L,1, P = 0·03), only in the REL. Conclusions, These results are inconsistent with a primary aetiological role for postprandial hypertriglyceridaemia in already insulin resistant type 2 diabetic REL, but raise the possibility that this potentially atherogenic manifestation is secondary to insulin resistance lessening VLDL production and/or release from the liver. [source] Nutritional supplements combined with dietary counselling diminish whole body protein catabolism in HIV-infected patientsEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 1 2000Berneis Background Weight loss and protein malnutrition are frequent complications in HIV-infected patients. The effect of an oral nutritional supplement combined with nutritional counselling on whole body protein metabolism was assessed. Materials and methods HIV-infected individuals with a body mass index < 21 kg m,2 or CD4-T cells < 500 , L,1 in stable clinical condition were randomly allocated to [ 1] receive either oral nutritional supplements (containing 2510 kJ, complete macro- and micronutrients) and dietary counselling (n = 8), or [ 2] identical monitoring but no supplements or specific nutritional advice (controls, n = 7). Whole body leucine kinetics and leucine oxidation rate were determined by [1,13C]-leucine infusions and lean and fat mass were measured before and 12 weeks after intervention. Results Leucine oxidation (protein catabolism) decreased in the group receiving nutritional intervention from 0.33 ± 0.02 to 0.26 ± 0.02 ,mol kg,1 min,1 after 12 weeks (P < 0.05; P < 0.05 vs. control group) but remained unchanged in the control group. Whole body leucine flux showed a tendency to decrease in the intervention group from 1.92 ± 0.19 to 1.73 ± 0.14 ,mol kg,1 min,1 (P = 0.07) and remained unchanged in the control group (2.21 ± 0.16 and 2.27 ± 0.14 ,mol kg,1 min,1, respectively). Lean body mass determined by bioelectrical impedance analysis increased in the nutritional intervention group from 84 ± 2 to 86 ± 2 per cent (P < 0.05) and fat mass decreased from 17 ± 2 to 14 ± 2 per cent (P < 0.05) of total body weight whereas neither mass changed in the control group. Nutritional intervention had no significant effect on lymphocyte CD4 counts, on plasma TNFR 55, TNFR 75 and ILR 2 concentrations and on quality of life. Conclusions The data demonstrate an anticatabolic effect of nutritional supplements combined with dietary counselling in HIV-infected subjects. They suggest that diminished whole body protein catabolism resulted in a change of body composition (increased lean mass, decreased fat mass). [source] Formation of Metastable Na2CrO4 -Type LiNiPO4 from a Phosphate,Formate PrecursorEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2010Violeta Koleva Abstract High-pressure modification of LiNiPO4 with a Na2CrO4 -type structure was obtained at ambient pressure and low temperature from a mixed LiNi,phosphate,formate precursor, LiNiPO4Hx(HCOO)x·yH2O (where x , 1.2 and y , 2.5). The structural and thermal characterization of the precursor and the LiNiPO4 compositions were carried out by powder XRD analysis, IR spectroscopy, and DSC analysis. Thermal treatment of LiNiPO4Hx(HCOO)x·yH2O precursors between 450 and 650 °C yields a mixture of the two structural modifications of LiNiPO4: the Na2CrO4 type and the olivine type. It was established that the obtained Na2CrO4 -type LiNiPO4 is a metastable phase, which completely transforms at 700 °C into the olivine-type phase. The enthalpy of the phase transition is ,H = ,43.40 kJ,mol,1. The mechanism of formation of the two forms of LiNiPO4 from the LiNi,phosphate,formate precursor is discussed. [source] Sulfur Dioxide and Water: Structures and Energies of the Hydrated Species SO2·nH2O, [HSO3],·nH2O, [SO3H],·nH2O, and H2SO3·nH2O (n = 0,8)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2009Ralf Steudel Abstract The structures of a large number of hydrates of sulfur dioxide (SO2·nH2O), of the sulfonate ion ([HSO3],·nH2O), of the tautomeric hydrogensulfite anion ([SO3H],·nH2O), and of sulfurous acid (H2SO3·nH2O) with up to eight water molecules attached to these species have been optimized at the B3LYP/6-31G(2df,p) level of theory (DFT). The calculated vibrational frequencies allow the definite assignment of certain characteristic modes, and in this way a convincing interpretation of published spectra of aqueous SO2 as well as of SO2 adsorbed on very cold ice crystals has been achieved for the first time. Single-point calculations at the G3X(MP2) level of theory were used to calculate the binding energies of the water molecules in SO2·nH2O as well as the relative stabilities of the isomeric anionic species [HSO3],·nH2O and [SO3H],·nH2O. Generally, the water molecules tend to stick together forming clusters, whereas the particular sulfur-containing molecule remains at the surface of the water cluster, but it is always strongly hydrogen-bonded. Only when there are more than six water molecules are the anions more or less completely surrounded by water molecules. DFT calculations erroneously predict that the gaseous hydrated sulfonate ions are more stable than the isomeric hydrogensulfite ions, even when hydrated with six water molecules. However, if these hydrated species are calculated as being embedded in a polar continuum simulating the aqueous phase, the hydrogensulfite ions are more stable than the sulfonate ions, in agreement with various spectroscopic observations on aqueous sulfite solutions. On the other hand, at the higher G3X(MP2) level, the gaseous hydrated hydrogensulfite anions are more stable than the corresponding sulfonate ions only if the number of water molecules is larger than four, whereas for the weakly hydrated anions the order of relative energies is reversed. The possible implications of these results for the enzymatic oxidation of "sulfite ions" ([HSO3], and [SO3H],) by sulfite oxidase are discussed. The conversion of SO2·6H2O into its isomer H2SO3·5H2O is predicted to be exothermic (,H°298 = ,56.1 kJ,mol,1) and exergonic (,G°298 = ,22.5 kJ,mol,1). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Dynamic Stereochemical Behaviour of Congested Ruthenium(II) Complexes Containing Asymmetric Thioether Ligands Based on Pyridine and PyrimidineEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 30 2008Giuseppe Tresoldi Abstract The asymmetric thioethers L [L = 2-pyridylmethyl 2,-pyrimidyl sulfide (pps) and 2-(4-methylpyrimidyl) 2,-pyridylmethyl sulfide (mps)] reacted with cis -[RuCl2(N,N -L,)2] [L, = di-2-pyridyl sulfide (dps); 2,2,-bis(4-methylpyridyl) sulfide (4mdps); 2,2,-bis(5-methylpyridyl) sulfide (5mdps)] to give the five-membered-ring chelate complexes [Ru(N,N -L,)2(Npyridine,S -L)]++ as the major products (92,95,%). Because the sulfur and ruthenium atoms are stereogenic centres, with (R) and (S) and , and , configurations, respectively, four isomers, including the enantiomers were obtained. At low temperature and in the methylene region of the 1H NMR spectra, two AB systems due to the enantiomer couples ,S ,R (a) and ,R ,S (b) were observed with abundances of 77,89 and 6,18,%, respectively. Furthermore, NMR spectroscopic investigations showed that the hybrid polydentate ligands L change their coordination mode. Thus, although a and b largely predominate, a mixture of species containing L and the Ru(N,N -L,)2 unit in the ratio 1:1 are present. The four-membered-ring chelate complexes [Ru(N,N -L,)2(Npyrimidine,S -L)]++ (c), as minor species (abundance 1,8,%), are always observed, whereas the dinuclear species [{Ru(N,N -L,)2}2(,-L)2]+4 (d, e) are observed when L, = dps or 5mdps. In these cases, four AB systems are assigned to dinuclear species d and e containing two bridging L that act as Npyridine,S- or Npyridine,Npyrimidine -donor ligands. The 1H NMR spectra are temperature dependent in that at low temperature the complexes undergo inversion of the chiral centre of the coordinated sulfur atom (a [rlhar2] b) and the dimer (d, e) and monomer (c) are in equilibrium; at higher temperatures the complexes undergo a structural dynamic rearrangement, which involves exchange between the coordinated and uncoordinated N atoms (b [rlhar2] c). One-dimensional band-shape analysis of the exchanging methylene and methyl proton signals showed that the energy barriers for inversion of the sulfur centre are in the 50,53 kJ,mol,1 range, whereas those for the higher-temperatures process are in the 62,68 kJ,mol,1 range. The possible mechanisms of the processes are discussed. NMR spectroscopic findings suggest that inversion at the sulfur centre occurs without any bond rupture, whereas the exchange, at higher temperatures (b [rlhar2] c), is a dissociative process involving the breaking of a Ru,Npyridine bond.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Cleavage of CO by Mo[N(R)Ar]3 ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2007Gemma Christian Abstract The reaction of MoL3 [L = NH2 and N(tBu)Ar] with CO was explored using DFT in order to rationalize why CO cleavage is not observed experimentally for this system in contrast to the corresponding N2 reaction which results in spontaneous cleavage of the N,N bond. The binding of CO to MoL3 was found to be both kinetically and thermodynamically favored over the binding of N2, with the formation of the encounter complex, L3Mo,CO, calculated to be without barrier and exothermic. While the overall reaction to form the C,MoL3 and O,MoL3 products was calculated to be energetically favorable, both the encounter complex and intermediate dimer, L3Mo,CO,MoL3, were found to be lower in energy than the products, with the final C,O cleavage step calculated to be endothermic by 169 kJ,mol,1 and 163 kJ,mol,1 for L = NH2 and N(tBu)Ar, respectively. The unfavorable CO cleavage step can be attributed to the fact that Mo does not possess the optimum d-electron configuration to sufficiently stabilise the carbide and oxide products relative to the CO-bridged intermediate dimer.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] The First Sandwich Complex with an Octa(thioether) Coordination Sphere: Bis(maleonitrile-tetrathia-12-crown-4)silver(I),EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2006Hans-Jürgen Holdt Abstract The new tetrathiacrown ethers maleonitrile-tetrathia-12-crown-4 (mn12S4) and maleonitrile-tetrathia-13-crown-4 (mn13S4) have been prepared and characterised by X-ray crystallographic analysis. These crown ethers form 2:1, 3:2 and 1:1 complexes with AgY (Y = BF4, PF6). The crystal structures of [Ag(mn12S4)2]BF4 (3a), [Ag(mn13S4)2]BF4 (4a) and [Ag2(mn13S4)3](PF6)2 (6b) have been determined. Compound 3a contains the centrosymmetric sandwich complex cation [Ag(mn12S4)2]+ where each mn12S4 ligand is coordinated to the Ag centre in an endo manner through all four S atoms. The 2:1 complex [Ag(mn12S4)2]+ is the first sandwich complex with a tetrathiacrown ether and the first complex with an octa(thioether) coordination sphere. The crystal structure of compound 4a also reveals a 2:1 complex. This complex, [Ag(mn13S4)2]+, exhibits a half-sandwich structure. One mn13S4 ligand coordinates to Ag+ by all four S donor atoms and the other 13S4 crown by only one S atom. Compound 6b contains a dinuclear Ag complex. The Ag complexes 3a,b,8a,b were also studied by electrospray ionisation mass spectrometry. Collision-induced dissociation (CID) was used to compare the relative stability of 2:1 complexes [AgL2]+ and 1:1 complexes [AgL]+ (L = mn12S4, mn13S4). The 13C NMR chemical shifts of 2:1 and 1:1 Ag complexes and their corresponding free ligands were also estimated and compared. The free energy of the barrier of ring inversion (,G,) for [Ag(mn12S4)2]+ was determined to be 64 kJ,mol,1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Theoretical Study on Hetero-Diels,Alder Reaction of Butadiene with Benzaldehyde Catalyzed by Chiral InIII ComplexesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2010Xiuli Cao Abstract The mechanism of the hetero-Diels,Alder reaction of butadiene with benzaldehyde catalyzed by chiral N,N, -dioxide/In(OTf)3 complexes was studied theoretically by using density functional theory (DFT) and model system. The computational results indicate that the catalyzed reaction proceeded through a concerted mechanism via a highly zwitterionic transition state. The lowest energy barrier was 11.8 kJ,mol,1, which is 63.0 kJ,mol,1 lower than that of the uncatalyzed reaction. The results indicate that the endo approach is advantageous over the exo approach, because exo transitions states suffer from more steric hindrance than the endo transitions states as a result of interactions among the substrates, the trifluoromethanesulfonic group and the R4 groups of the ligand. The (S) configuration was observed predominantly over the (R) form, because there is no distinguishable repulsion between butadiene and the exo amino side or the endo amino side of the ligand. Besides, the interactions between the terminal hydrogen atoms of butadiene and the oxygen atoms of the trifluoromethanesulfonic group make the structure more stable. Thus, the experimental results were explained well by calculation of the chiral N,N, -dioxide/In(OTf)3 complex catalyzed hetero-Diels,Alder reaction at the molecular level. [source] Boron-Based Diastereomerism and Enantiomerism in Imine Complexes , Determination of the Absolute Configuration at Boron by CD SpectroscopyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 31 2008Manfred Braun Abstract Boron turns out to be a stable stereogenic center in imine complexes of aryl and alkyl boronates. Diastereomerically pure complexes 7a,c are obtained from chiral imine ligands 5a,b that are derived from the amino alcohol (R)- 4. The configuration at the boron atom is determined by crystal structure analyses. Racemic boronates 10a,c, available from a condensation of aryl boronic acids 6 with the achiral imine ligand 9, can be separated into stable enantiomers by HPLC on a chiral column. The racemization barrier ,G, has been determined to amount to 105,115 kJ,mol,1. The comparison of calculated and measured CD spectra permits to assign unambiguously the absolute configuration to boron in the enantiomeric boronate-imine complex 10a.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Robustness of a 3 min all-out cycling test to manipulations of power profile and cadence in humansEXPERIMENTAL PHYSIOLOGY, Issue 3 2008Anni Vanhatalo The purpose of this study was to assess whether end-test power output (EP, synonymous with ,critical power') and the work done above EP (WEP) during a 3 min all-out cycling test against a fixed resistance were affected by the manipulation of cadence or pacing. Nine subjects performed a ramp test followed, in random order, by three cadence trials (in which flywheel resistance was manipulated to achieve end-test cadences which varied by ,20 r.p.m.) and two pacing trials (30 s at 100 or 130% of maximal ramp test power, followed by 2.5 min all-out effort against standard resistance). End-test power output was calculated as the mean power output over the final 30 s and the WEP as the power,time integral over 180 s for each trial. End-test power output was unaffected by reducing cadence below that of the ,standard test' but was reduced by ,10 W on the adoption of a higher cadence [244 ± 41 W for high cadence (at an end-test cadence of 95 ± 7 r.p.m.), 254 ± 40 W for the standard test (at 88 ± 6 r.p.m.) and 251 ± 38 W for low cadence (at 77 ± 5 r.p.m.)]. Pacing over the initial 30 s of the test had no effect on the EP or WEP estimates in comparison with the standard trial. The WEP was significantly higher in the low cadence trial (16.2 ± 4.4 kJ) and lower in the high cadence trial (12.9 ± 3.6 kJ) than in the standard test (14.2 ± 3.7 kJ). Thus, EP is robust to the manipulation of power profile but is reduced by adopting cadences higher than ,standard'. While the WEP is robust to initial pacing applied, it is sensitive to even relatively minor changes in cadence. [source] Metabolic Heat Production, Heat Loss and the Circadian Rhythm of Body Temperature in the RatEXPERIMENTAL PHYSIOLOGY, Issue 3 2003Roberto Refinetti Metabolic heat production (calculated from oxygen consumption), dry heat loss (measured in a calorimeter) and body temperature (measured by telemetry) were recorded simultaneously at 6 min intervals over five consecutive days in rats maintained in constant darkness. Robust circadian rhythmicity (confirmed by chi square periodogram analysis) was observed in all three variables. The rhythm of heat production was phase-advanced by about half an hour in relation to the body temperature rhythm, whereas the rhythm of heat loss was phase-delayed by about half an hour. The balance of heat production and heat loss exhibited a daily oscillation 180 deg out of phase with the oscillation in body temperature. Computations indicated that the amount of heat associated with the generation of the body temperature rhythm (1.6 kJ) corresponds to less than 1% of the total daily energy budget (172 kJ) in this species. Because of the small magnitude of the fraction of heat balance associated with the body temperature rhythm, it is likely that the daily oscillation in heat balance has a very slow effect on body temperature, thus accounting for the 180 deg phase difference between the rhythms of heat balance and body temperature. [source] The histidine-phosphocarrier protein of Streptomyces coelicolor folds by a partially folded species at low pHFEBS JOURNAL, Issue 10 2003Gregorio Fernández-Ballester The folding of a 93-residue protein, the histidine-phosphocarrier protein of Streptomyces coelicolor, HPr, has been studied using several biophysical techniques, namely fluorescence, 8-anilinonaphthalene-1-sulfate binding, circular dichroism, Fourier transform infrared spectroscopy, gel filtration chromatography and differential scanning calorimetry. The chemical-denaturation behaviour of HPr, followed by fluorescence, CD and gel filtration, at pH 7.5 and 25 °C, is described as a two-state process, which does not involve the accumulation of thermodynamically stable intermediates. Its conformational stability under those conditions is ,G = 4.0 ± 0.2 kcal·mol,1 (1 kcal = 4.18 kJ), which makes the HPr from S. coelicolor the most unstable member of the HPr family described so far. The stability of the protein does not change significantly from pH 7,9, as concluded from the differential scanning calorimetry and thermal CD experiments. Conformational studies at low pH (pH 2.5,4) suggest that, in the absence of cosmotropic agents, HPr does not unfold completely; rather, it accumulates partially folded species. The transition from those species to other states with native-like secondary and tertiary structure, occurs with a pKa = 3.3 ± 0.3, as measured by the averaged measurements obtained by CD and fluorescence. However, this transition does not agree either with: (a) that measured by burial of hydrophobic patches (8-anilinonaphthalene-1-sulfate binding experiments); or (b) that measured by acquisition of native-like compactness (gel-filtration studies). It seems that acquisition of native-like features occurs in a wide pH range and it cannot be ascribed to a unique side-chain titration. These series of intermediates have not been reported previously in any member of the HPr family. [source] A Quantum-Chemical Study on Understanding the Dehydrogenation Mechanisms of Metal (Na, K, or Mg) Cation Substitution in Lithium Amide NanoclustersADVANCED FUNCTIONAL MATERIALS, Issue 12 2010Lanlan Li Abstract The hydrogen-releasing activity of (LiNH2)6,LiH nanoclusters and metal (Na, K, or Mg)-cation substituted nanoclusters (denoted as (NaNH2)(LiNH2)5, (KNH2)(LiNH2)5, and (MgNH)(LiNH2)5) are studied using ab initio molecular orbital theory. Kinetics results show that the rate-determining step for the dehydrogenation of the (LiNH2)6,LiH nanocluster is the ammonia liberation from the amide with a high activation energy of 167.0,kJ,mol,1 (at B3LYP/6-31,+,G(d,p) level). However, metal (Na, K, Mg)-cation substitution in amide,hydride nanosystems reduces the activation energies for the rate-determining step to 156.8, 149.6, and 144.1,kJ,mol,1 (at B3LYP/6-31,+,G(d,p) level) for (NaNH2)(LiNH2)5, (KNH2)(LiNH2)5, and (MgNH)(LiNH2)5, respectively. Furthermore, only the ,NH2 group bound to the Na/K cation is destabilized after Na/K cation substitution, indicating that the improving effect from Na/K-cation substitution is due to a short-range interaction. On the other hand, Mg-cation substitution affects all ,NH2 groups in the nanocluster, resulting in weakened N,H covalent bonding together with stronger ionic interactions between Li and the ,NH2 group. The present results shed light on the dehydrogenation mechanisms of metal-cation substitution in lithium amide,hydride nanoclusters and the application of (MgNH)(LiNH2)5 nanoclusters as promising hydrogen-storage media. [source] Migratory Atlantic salmon as vectors for the transfer of energy and nutrients between freshwater and marine environmentsFRESHWATER BIOLOGY, Issue 1 2003Bror Jonsson SUMMARY 1.,Annual energy, carbon, nitrogen and phosphorus fluxes across the river mouth by Atlantic salmon were estimated for 18 years (1976,94) in the Norwegian River Imsa. The total energy content of the emigrating smolts in each year varied considerably with a mean value of 237 × 103 kJ. That of returning adults also varied between years with a mean value of 141 × 104 kJ. One-sea-winter salmon (grilse) made up 65% of the total energy content of the spawners in the river. Dead carcasses remaining in the river after spawning were estimated to have a mean annual energy content of 175 × 103 kJ. 2.,The net annual energy flux from the sea to the river varied between 48 × 103 kJ (1987) and 152 × 104 kJ (1989) with a mean of 616 × 103 kJ, and a coefficient of variation of 67%. Average net marine import of the returning adults was 83 × 104 kJ year,1 with a coefficient of variation of 52%. Mean annual export of C, N and P to sea by the smolts was 595, 131 and 22 kg, and by kelts 1535, 352 and 70 kg, respectively, whereas gross import via the adults was 3176 kg C, 735 kg N and 132 kg P. The annual flux across the river mouth was 1046 kg C, 253 kg N and 39 kg P. The net marine import were 1585 kg C, 371 kg N and 60 kg P. The net flux was estimated at 0.2% for nitrogen and 5% for phosphorus of the total river load. 3.,The energy flux caused by Atlantic salmon spawning in the River Imsa was relatively high because the general nutrient load in the river is low. Thus, even though most Atlantic salmon survive spawning, their contribution to the nutrient flux in the river is significant. [source] Evaluation of RuxWySez Catalyst as a Cathode Electrode in a Polymer Electrolyte Membrane Fuel CellFUEL CELLS, Issue 1 2010K. Suárez-Alcántara Abstract The oxygen reduction reaction (ORR) on RuxWySez is of great importance in the development of a novel cathode electrode in a polymer electrolyte membrane fuel cell (PEMFC) technology. The RuxWySez electrocatalyst was synthesised in an organic solvent for 3,h. The powder was characterised by transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). The electrocatalyst consisted of agglomerates of nanometric size (,50,150,nm) particles. In the electrochemical studies, rotating disc electrode (RDE) and rotating ring-disc electrode (RRDE) techniques were used to determine the oxygen reduction kinetics in 0.5,M H2SO4. The kinetic studies include the determination of Tafel slope (112,mV,dec,1), exchange current density at 25,°C (1.48,×,10,4,mA,cm,2) and the apparent activation energy of the oxygen reaction (52.1,,,0.4,kJ,mol,1). Analysis of the data shows a multi-electron charge transfer process to water formation, with 2% H2O2 production. A single PEMFC with the RuxWySez cathode catalysts generated a power density of 180,mW,cm,2. Performance achieved with a loading of 1.4,mg,cm,2 of a 40,wt% RuxWySez and 60,wt% carbon Vulcan (i.e. 0.56,mg,cm,2 of pure RuxWySez). Single PEMFC working was obtained with hydrogen and oxygen at 80,°C with 30,psi. [source] UV-vis-Induced Vitrification of a Molecular Crystal,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2007T. Naito Abstract A charge-transfer complex of 2,5-dimethyl- N,N,-dicyanoquinonediimine (DM) with silver (crystalline Ag(DM)2, defined as ,) is irreversibly transformed by UV-vis illumination. Depending on the illumination conditions, three new types of solids (defined as ,, ,, and ,) with different structural and physical properties are obtained and examined by a variety of analytical techniques, including solid-state, high-resolution, cross-polarization magic angle spinning (CP-MAS) 13C,NMR, elemental analysis (EA), mass spectrometry (MS), X-ray absorption fine structure (XAFS), and powder X-ray diffraction (XRD). The CP-MAS, EA, MS, and XAFS results indicate that compound , is a glass state of Ag(DM)2. The transformation from crystalline (,) to amorphous (,) solid Ag(DM)2 is an irreversible exothermic glass transition (glass-transition temperature 155.2,°C; ,H,=,,126.8,kJ,mol,1), which implies that the glass form is thermodynamically more stable than the crystalline form. Compound , (Ag(DM)1.5) consists of silver nanoparticles (diameter (7,±,2),nm ) dispersed in a glassy matrix of neutral DM molecules. The N,CN,Ag coordination bonds of the , form are not maintained in the , form. Decomposition of , by intense illumination results in a white solid (,), identified as being composed of silver nanoparticles (diameter (60,±,10),nm). Physical and spectroscopic (XAFS) measurements, together with XRD analysis, indicate that the silver nanoparticles in both , and , are crystalline with lattice parameters similar to bulk silver; however, the magnetic susceptibilities differ from bulk silver. [source] Rearrangements in Model Peptide-Type Radicals via Intramolecular Hydrogen-Atom TransferHELVETICA CHIMICA ACTA, Issue 10 2006Damian Moran Abstract Intramolecular H-atom transfer in model peptide-type radicals was investigated with high-level quantum-chemistry calculations. Examination of 1,2-, 1,3-, 1,5-, and 1,6[C,,,N]-H shifts, 1,4- and 1,7[C,,,C]-H shifts, and 1,4[N,,,N]-H shifts (Scheme,1), was carried out with a number of theoretical methods. In the first place, the performance of UB3-LYP (with the 6-31G(d), 6-31G(2df,p), and 6-311+G(d,p) basis sets) and UMP2 (with the 6-31G(d) basis set) was assessed for the determination of radical geometries. We found that there is only a small basis-set dependence for the UB3-LYP structures, and geometries optimized with UB3-LYP/6-31G(d) are generally sufficient for use in conjunction with high-level composite methods in the determination of improved H-transfer thermochemistry. Methods assessed in this regard include the high-level composite methods, G3(MP2)-RAD, CBS-QB3, and G3//B3-LYP, as well as the density-functional methods B3-LYP, MPWB1K, and BMK in association with the 6-31+G(d,p) and 6-311++G(3df,3pd) basis sets. The high-level methods give results that are close to one another, while the recently developed functionals MPWB1K and BMK provide cost-effective alternatives. For the systems considered, the transformation of an N-centered radical to a C-centered radical is always exothermic (by 25,kJ,,,mol,1 or more), and this can lead to quite modest barrier heights of less than 60,kJ,,,mol,1 (specifically for 1,5[C,,,N]-H and 1,6[C,,,N]-H shifts). H-Migration barriers appear to decrease as the ring size in the transition structure (TS) increases, with a lowering of the barrier being found, for example when moving from a rearrangement proceeding via a four-membered-ring TS (e.g., the 1,3[C,,,N]-H shift, CH3C(O)NH.,,,.CH2C(O)NH2) to a rearrangement proceeding via a six-membered-ring TS (e.g., the 1,5[C,,,N]-H shift, .NHCH2C(O)NHCH3,,,NH2CH2C(O)NHCH2.). [source] | |||||||||||||||||||||||||||||||||||||||||||