bluuebunny/crossref_metadata_2025_split huggingface dataset:
Exploring the Border between Concerted and Two‐Step Pathways of 1,3‐Dipolar Cycloadditions of Organic Azides to Cyclic Ketene N,X‐Acetals. – Synthesis and 15N‐NMR Spectra of Zwitterions and Spirocyclic Cycloadducts
Authors: Quast Helmut , Ach Manfred , Balthasar Jürgen , Hergenröther Thomas , Regnat Dieter , Lehmann Jens , Banert Klaus 
Published: June 2005

AbstractCyclic ketene N,X‐acetals 1 are electron‐rich dipolarophiles that undergo 1,3‐dipolar cycloaddition reactions with organic azides 2 ranging from alkyl to strongly electron‐deficient azides, e.g., picryl azide (2L; R1=2,4,6‐(NO2)3C6H2) and sulfonyl azides 2M–O (R1=XSO2; cf. Scheme 1). Reactions of the latter with the most‐nucleophilic ketene N,N‐acetals 1A provided the first examples for two‐step HOMO(dipolarophile)–LUMO(1,3‐dipole)‐controlled 1,3‐dipolar cycloadditions via intermediate zwitterions 3. To set the stage for an exploration of the frontier between concerted and two‐step 1,3‐dipolar cycloadditions of this type, we first describe the scope and limitations of concerted cycloadditions of 2 to 1 and delineate a number of zwitterions 3. Alkyl azides 2A–C add exclusively to ketene N,N‐acetals that are derived from 1H‐tetrazole (see 1A) and 1H‐imidazole (see 1B,C), while almost all aryl azides yield cycloadducts 4 with the ketene N,X‐acetals (X=NR, O, S) employed, except for the case of extreme steric hindrance of the 1,3‐dipole (see 2E; R1=2,4,6‐(tBu)3C6H2). The most electron‐deficient paradigm, 2L, affords zwitterions 16D,E in the reactions with 1A, while ketene N,O‐ and N,S‐acetals furnish products of unstable intermediate cycloadducts. By tuning the electronic and steric demands of aryl azides to those of ketene N,N‐acetals 1A, we discovered new borderlines between concerted and two‐step 1,3‐dipolar cycloadditions that involve similar pairs of dipoles and dipolarophiles: 4‐Nitrophenyl azide (2G) and the 2,2‐dimethylpropylidene dipolarophile 1A (R, R=H, tBu) gave a cycloadduct 13 H, while 2‐nitrophenyl azide (2 H) and the same dipolarophile afforded a zwitterion 16A. Isopropylidene dipolarophile 1A (R=Me) reacted with both 2G and 2 H to afford cycloadducts 13G,J) but furnished a zwitterion 16B with 2,4‐dinitrophenyl azide (2I). Likewise, 1A (R=Me) reacted with the isomeric encumbered nitrophenyl azides 2J and 2K to yield a cycloadduct 13L and a zwitterion 16C, respectively. These examples suggest that, in principle, a host of such borderlines exist which can be crossed by means of small structural variations of the reactants. Eventually, we use 15N‐NMR spectroscopy for the first time to characterize spirocyclic cycloadducts 10–14 and 17 (Table 6), and zwitterions 16 (Table 7).
A path from Ih to C1 symmetry for C20 cage molecule
Authors: Wang Zhigang , Lian Keyan , Pan Shoufu , Fan Xianhong 
Published: June 2005

AbstractThe symmetry of the C20 cage is studied based on the intrinsical relationship among point groups (Bradley, C. J.; Cracknell, A. P. The Mathematical Theory of Symmetry in Solids; Claredon Press: Oxford, 1972). The structure of the C20 cage with Ih symmetry is constructed, as are eight other structures with subgroup symmetry. A path from Ih symmetry to C1 symmetry is obtained for the closed‐shell electronic state, and the structure with D2h symmetry is the most stable on this path. Using the D2h structure the correlation energy correction is studied on the condition of restricted excitation space at the CCSD(T) level. We obtain curves on the relation between the orbital numbers and the total energy at the CCSD(T), CCSD, and MP2 level, respectively. The results of these curves obtained from MP2 and CCSD(T) methods have the same tendency, while the results of CCSD gradually diverge with an increase in orbital numbers. When the orbitals used in the calculation reach 460, the total energy is −759.644 hartree at MP2 level and is −759.721 hartree by the CCSD(T) method. From the calculation results, we find that a large basis set can improve the reliability of the MP2 method, and to restrict excitation space is necessary when using the CCSD(T) method. © 2005 Wiley Periodicals, Inc. J Comput Chem 12: 1279–1283, 2005
Effects of temperature and water on critical oxygen tension of turtle embryos
Authors: Kam Yeong‐Choy , Lillywhite Harvey B. 
Published: June 2005

AbstractThe influences of temperature and water on the ability of turtle embryos to tolerate hypoxia were investigated by measuring critical oxygen tension, Pc, at different levels of temperature (22, 27, and 32°C) and hydric conditions (3 and 13% gravimetric water content). Eggs were half‐buried in sand with 3 or 13% gravimetric water content and incubated at a constant 30°C. Using a closed metabolic chamber, oxygen consumption, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} $\end{document}, was measured at decreasing oxygen tensions. Embryonic \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} $\end{document} varied as a function of incubation day and temperature, whereas the Pc differed among temperatures but not among incubation days. At a given incubation day, the Pc increased in direct proportion to temperature. Eggs incubated in sand with 13% gravimetric water content achieved greater mass at days 30 and 39 than did those in sand with 3% gravimetric water content. However, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} $\end{document}, Pc, and masses of yolk‐free hatchlings were similar in the two hydric conditions, indicating that hypoxic tolerance of turtle eggs is not curtailed by excessive water absorption. The similarity in Pc is likely attributable to the small \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm V}\limits^{\rm .} $\end{document}/surface area ratio of turtle eggs. Within the range of parameters studied, temperature, but not water, can modify the Pc of turtle embryos. © 1994 Wiley‐Liss, Inc.
Serial repetition of cilia pairs along the tail surface of an ascidian larva
Authors: Crowther Robert J. , Whittaker J. R. 
Published: June 2005

AbstractRegularly spaced cilia pairs were found in two rows immediately opposite to each other mid‐dorsally and mid‐ventrally along the larval tail surface of the ascidian protochordate Ciona intestinalis. There were approximately ten such equidistantly placed dorsal‐ventral sets embedded in the matrix of the extracellular larval test which forms the flattened vertical tail fin. These immotile cilia originate from pairs of cell bodies in mid‐dorsal and mid‐ventral peripheral nerves running beneath the tail epidermis. The cilia and neural cell bodies were visualized by immunocytochemical staining with anti‐tubulin antibodies; their nature was confirmed by ultrastructural examination. This pattern of cilia and neural cell body placement is conceivably related to the segmentation found in vertebrates. © 1994 Wiley‐Liss, Inc.
Effect of exogenous estradiol applied at different embryonic stages on sex determination, growth, and mortality in the leopard gecko (Eublepharis macularius)
Authors: Tousignant Alan , Crews David 
Published: June 2005

AbstractTemperature‐dependent sex determination (TSD) occurs in three orders of reptiles. Several studies have examined the ability of estradiol to produce female hatchlings incubated at a male‐producing temperature. The results of these experiments support the idea that estradiol could be used as a powerful tool in the conservation of endangered species with TSD by manipulating hatchling sex ratios. However, these experiments have concentrated on the mechanism of determination. This experiment was designed to test the efficacy of various dosages of estradiol applied at two different stages to alter the hatchling sex ratio as well as determining the potential use of such manipulation for conservation efforts by monitoring egg mortality and hatchling growth. The leopard gecko (Eublepharis macularius) exhibits TSD and reaches reproductive maturity in less than one year, making it an excellent model for evaluating the long‐term effects of estradiol. The results demonstrate that estradiol has a dose‐dependent effect on the hatchling sex ratio while only high dosages applied at the later stage of development showed increased mortality. Estrogen‐determined females grew at the same rate as temperature‐determined females and have produced viable hatchlings. Estradiol treatment of eggs from endangered species may provide a method of insuring female offspring when the TSD pattern is unknown or equipment for controlled incubation is unavailable. © 1994 Wiley‐Liss, Inc.
Development of in vitro organ culture techniques for differentiation and growth of cartilages and bones from teleost fish and comparisons with in vivo skeletal development
Authors: Miyake Tsutomu , Hall Brian K. 
Published: June 2005

AbstractTo examine molecular and cellular mechanisms of fish skeletogenesis, an in vitro organ culture system was developed to achieve effective maintenance, growth, and/or differentiation of embryonic skeletal tissues from Oryzias latipes (Japanese ricefish) and Brachydanio rerio (zebra‐fish). In vivo and in vitro skeletogenesis were compared. The techniques developed here open the way for descriptive and experimental in vitro analyses of fish skeletogenesis. The present study found that submerged organ culture using medium 199 or Leibovitz's L‐15, supplemented with fetal bovine serum and ascorbic acid, was most suitable. Supplementation with antibiotic‐antimycotics prevented microbial contamination, especially during explant preparation. Two types of inorganic membrane substrates did not produce different results from culture on plastic Falcon dishes; all sustained healthy embryonic skeletal explants. The present system sustained maintenance, growth, or de novo differentiation of embryonic skeletal tissues, when compared with in vivo formation and growth of the embryonic cranial skeletons in the two species. Already formed bones (parasphenoid, opercule and/or branchiostegal rays) and cartilages were successfully maintained and/or grew in culture. Both perichondral bone (around gill arches, hyosymplecticum, hyoid arch, Meckel's cartilage) and membrane bone (dentary) differentiated de novo, but did not mineralize. De novo hypertrophy of chondrocytes was observed in some cartilages as occurs in normal development. Although already formed teeth were maintained, de novo differentiation of teeth was not observed in vitro, suggesting that mandibular and gill perichondral bones may form independently of tooth formation.
Estradiol‐17β associated with the sex reversal in protandrous black porgy, Acanthopagrus schlegeli
Authors: Chang Ching‐Fong , Lee Mong‐Fong , Chen Guan‐Ru 
Published: June 2005

AbstractThe objectives of this study were to investigate the seasonal changes of steroid profiles, estradiol‐17β (E2), testosterone (T), and 17α‐hydroxyprogesterone (17α‐OH P), among female, male, and reversing female black porgy, Acanthopagrus schlegeli. The experimental induction of sex reversal in juvenile black porgy by exogenous E2 was also studied. Three‐year‐old male (n = 8) and four‐year‐old female (n = 7) black porgy were selected for the experiment of seasonal changes of steroid profiles. Blood samples were collected from each fish at 2 week intervals for 8 months. Plasma samples in three‐year‐old males were further classified to those of males (n = 4) and reversing females (n = 4) based on the sexual stage of the gonad at the end of the experiment. Plasma E2 profiles in males were significantly different from those in the reversing females. Peak levels of plasma E2 in the females and reversing females occurring during the early prespawning season were similar. Lower levels of plasma E2 were, however, observed in the males. Plasma T did not differ significantly in females, males or reversing females. Low and constant levels of plasma 17α‐OH P were observed in each group of fish. In the experimental induction of sex reversal, oral administration of E2 (4 mg per kg of feed) for 5 months suppressed the spermiation and inhibited gonadal growth but successfully induced the precocious sex change at the prespawning stage in one‐year‐old black porgy. Ovarian tissue with primary oocytes was predominant in the gonads of E2‐fed fishes. Our data suggest that high levels of plasma E2 in the prespawning and spawning season are likely correlated with the natural sex reversal of black porgy. E2 likely plays an important role in sex reversal of protandrous black porgy. © 1994 Wiley‐Liss, Inc.
Plasma levels of eggshell zr‐proteins, estradiol‐17β, and gonadotropins during an annual reproductive cycle of Atlantic salmon (Salmo salar)
Authors: Oppen‐Berntsen D. O. , Olsen S. O. , Rong C. J. , Taranger G. L. , Swanson P. , Walther B. T. 
Published: June 2005

AbstractEggshell zona radiata proteins (zr‐proteins) were found to occur normally in plasma of sexually mature female (but not male) Atlantic salmon (Salmon salar). In order to ascertain the physiological relevance of these findings, we developed a specific enzyme‐linked immunoassay for zr‐proteins and screened plasma from sexually maturing Atlantic salmon females throughout an annual reproductive cycle. While zr‐proteins were detectable at low levels in female adult salmon plasma prior to sexual maturation, zr‐protein levels increased dramatically as sexual maturation proceeded. The strong correlation between gonado‐somatic index (GSI) and plasma zr‐proteins indicates a reproductive role for blood borne zr‐proteins. During the vitellogenic phase, levels of plasma zr‐proteins were positively correlated with GSI and with plasma levels of gonadotropin I (GtH I) and estradiol‐17β, as determined by radioimmuno‐assays. However, during final sexual maturation, only the plasma level of gonadotropin II (GtH II) was positively correlated to GSI. In contrast, zr‐proteins and estradiol‐17β were both negatively correlated to plasma level of GtH II during this period. In view of estradiol‐17β‐induced hepatic synthesis and secretion of zr‐proteins (Oppen‐Berntsen et al.: Journal of Endocrinology 135:293–302, 1992a) and the established role of gonadotropins in regulating ovarian estradiol synthesis, we interpret the observed correlations among plasma levels of GtH I, estradiol‐17β and zr‐proteins in Atlantic salmon to signify that GtH I regulates ovarian estradiol‐17β synthesis, which in turn regulates hepatic synthesis and secretion of both vitellogenin and zr‐proteins during oogenesis. © 1994 Wiley‐Liss, Inc.
Effects of spatial and temporal resolution for MR image‐guided thermal ablation of prostate with transurethral ultrasound
Authors: Pisani Laura J. , Ross Anthony B. , Diederich Chris J. , Nau William H. , Sommer F. Graham , Glover Gary H. , Butts Kim 
Published: June 2005

AbstractPurposeTo describe approaches for determining optimal spatial and temporal resolutions for the proton resonance frequency shift method of quantitative magnetic resonance temperature imaging (MRTI) guidance of transurethral ultrasonic prostate ablation.Materials and MethodsTemperature distributions of two transurethral ultrasound applicators (90° sectored tubular and planar arrays) for canine prostate ablation were measured via MRTI during in vivo sonication, and agree well with two‐dimensional finite difference model simulations at various spatial resolutions. Measured temperature distributions establish the relevant signal‐to‐noise ratio (SNR) range for thermometry in an interventional MR scanner, and are reconstructed at different resolutions to compare resultant temperature measurements. Various temporal resolutions are calculated by averaging MRTI frames.ResultsWhen noise is added to simulated temperature distributions for tubular and planar applicators, the minimum root mean squared (RMS) error is achieved by reconstructing to pixel sizes of 1.9 and 1.7 mm, respectively. In in vivo measurements, low spatial resolution MRTI data are shown to reduce the noise without significantly affecting thermal dose calculations. Temporal resolution of 0.66 frames/minute leads to measurement errors of more than 12°C during rapid heating.ConclusionOptimizing MRTI pixel size entails balancing large pixel SNR gain with accuracy in representing underlying temperature distributions. J. Magn. Reson. Imaging 2005;22:109–118. © 2005 Wiley‐Liss, Inc.
Importance of bone‐conducted sound transmission on patient hearing in the MR scanner
Authors: Moelker Adriaan , Maas Ronald A.J.J. , Vogel Mika W. , Ouhlous Mohamed , Pattynama Peter M.T. 
Published: June 2005

AbstractPurposeto evaluate the influence of bone‐conduction in the MR environment compared to a standardized acoustic environment.Materials and MethodsAcoustic noise is an unwanted side effect of MRI that is commonly tackled with passive hearing protection. In an MR scanner, however, with the patient completely surrounded by the MR sounds and in close contact with the vibrating MR table and gantry, bone‐conduction may increase subjective sound levels, restricting the efficacy of passive protection that reduces air‐conducted noise only. A total of 10 volunteers were subjected to pure MR tones, covering the frequency range relevant for hearing and at 60 dB, generated through the MR system's gradient coils. Bone‐conduction was determined for various passive damping conditions in an MR scanner and was compared to that acquired in an acoustically‐calibrated environment. The contribution of mechanical vibrations to bone‐conduction was determined. Also, with a microphone in the ear canal, the objective efficacy of the passive protection was measured.ResultsWe found no difference between the bone‐conduction experiments executed inside the imager and in the acoustically‐controlled environment. The overall insertion loss of the passive hearing protectors was over 20 dB with strongest effects at 0.4 and 2.5 kHz.ConclusionAs bone‐conduction is not more pronounced inside the MR scanner than outside, the previous reports on the subjective evaluation of protection devices in MRI hold their validity. J. Magn. Reson. Imaging 2005;22:163–169. © 2005 Wiley‐Liss, Inc.
Apparent diffusion coefficient measurements with diffusion‐weighted magnetic resonance imaging for evaluation of hepatic fibrosis
Authors: Koinuma Miwa , Ohashi Isamu , Hanafusa Kaoru , Shibuya Hitoshi 
Published: June 2005

AbstractPurposeTo evaluate the use of apparent diffusion coefficient (ADC) measurements based on diffusion‐weighted MRI (DWI) to assess stage of liver disease.Materials and MethodsA total of 31 patients who underwent both a liver biopsy and DWI and 132 patients who only underwent DWI were enrolled. Biopsy specimens were scored for fibrosis and necroinflammation according to the Knodell histology activity index (HAI). The 31 patients consisted of 21 patients with chronic hepatitis and 10 with cirrhosis (Child‐Pugh stage A in nine and stage B in one), and the 132 patients consisted of 56 patients with cirrhosis (Child‐Pugh stage A in 41, stage B in 10, and stage C in five), 42 with chronic hepatitis, and 34 with normal liver function. The ADCs in the liver parenchyma were measured using DWI with relatively low b factors (b = 0.01 and 128.01 seconds/mm2) and were compared among the HAI scores and among patients with cirrhosis, chronic hepatitis, and normal liver function.ResultsThe ADCs decreased as the fibrosis score in the HAI increased, and the correlation was statistically significant (P < 0.0001). No relationship between the ADCs and the necroinflammation scores in the HAI was found. The ADCs decreased as the stage of liver disease progressed or as the Child‐Pugh stage progressed, and these relationships were statistically significant (P < 0.0001).ConclusionADC measurements are potentially useful for the evaluation of fibrosis staging in the liver. J. Magn. Reson. Imaging 2005;22:80–85. © 2005 Wiley‐Liss, Inc.
Local staging of rectal carcinoma and assessment of the circumferential resection margin with high‐resolution MRI using an integrated parallel acquisition technique
Authors: Oberholzer Katja , Junginger Theodor , Kreitner Karl‐F. , Krummenauer Frank , Simiantonaki Nektaria , Trouet Susan , Thelen Manfred 
Published: June 2005

AbstractPurposeTo assess the diagnostic accuracy of integrated parallel acquisition technique (iPAT) in local staging of rectal carcinoma in comparison to conventional high‐resolution MRI.Materials and MethodsA total of 28 patients with a neoplasm of the rectum and 15 control patients underwent MRI of the pelvis. High‐resolution images were acquired conventionally and with iPAT using a modified sensitivity encoding (mSENSE). Image quality, signal‐to‐noise and contrast‐to‐noise ratios (SNR, CNR), tumor extent, nodal status, and delineation of the circumferential resection margin (CRM) were compared. In 19 patients with a carcinoma, MR findings were correlated with the histopathological diagnosis. Tumor distance to the CRM was matched with resection specimen in 12 cases.ResultsThe comparison of both MR techniques revealed no clinically relevant differences in tumor staging and delineation of the CRM, though SNR and CNR were significantly lower in mSENSE images. Tumor stage was concordant in 17 of 19 cases compared to histopathology. In four of nine patients with T3 and T4 carcinomas, the histopathological resection margin was ≤2 mm, in five cases MRI predicted a margin of ≤2 mm.ConclusionThe application of iPAT in local staging of rectal carcinoma is time‐saving and does not degrade diagnostic accuracy. Tumor stage, nodal status, and the CRM can be assessed equally compared to conventional acquisition techniques. J. Magn. Reson. Imaging 2005;22:101–108. © 2005 Wiley‐Liss, Inc.
MRI in Crohn's disease
Authors: Horsthuis Karin , Lavini Cristina , Stoker Jaap 
Published: June 2005

AbstractTechnological developments have extended the role of MRI in the evaluation of the gastrointestinal tract. The potential of MRI to evaluate disease activity in Crohn's disease has been investigated extensively, as MRI has intrinsic advantages over other techniques, including noninvasiveness and the absence of ionizing radiation. For perianal fistulizing disease MRI has become a mainstay in evaluation of disease, as localization and extent of disease can be very well appreciated using both T2‐weighted and T1‐weighted sequences, fat suppression, and intravenous contrast medium. Imaging of the small bowel and colon in Crohn's disease is more complicated due to bowel peristalsis and respiratory movement. However, using fast breathhold sequences and intravenous spasmolytic medication, images of good diagnostic quality can be acquired. To obtain sufficiently distended bowel, which in our estimation is a prerequisite for evaluation of the bowel, MR enteroclysis can be performed. However, applicability of different oral contrast media has been studied, as a noninvasive method for bowel distension would be preferable. Abdominal MRI is a valuable imaging technique for evaluation of luminal, transmural, and extraintestinal manifestations of Crohn's disease as degree of disease activity, presence of luminal pathology (e.g., stenoses), and extraintestinal manifestations of disease (e.g., abscesses, fistulas) can be accurately assessed. J. Magn. Reson. Imaging 2005;22:1–12. © 2005 Wiley‐Liss, Inc.