bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and polymerization of fluorinated acrylic monomers substituted in α‐position, 2. Synthesis and polymerization of 2‐perfluorohexylethyl α‐acetoxyacrylate
Authors: Bessiere Jean‐Marie , Boutevin Bernard , el Bachiri Abderrahim , el Harfi Ahmed
Published: April 2003

The synthesis of 2‐perfluorohexylethyl α‐acetoxyacrylate (b) H2CC(OAc)CO2C2H4C6F13 (1) was performed in two steps starting from pyruvic acid and 2‐perfluorohexylethanol (3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluoro‐1‐octanol) with an overall yield of about 50%. Esterification of pyruvic acid with the adequate fluorinated alcohol was followed by enol acetylation to give monomer 1. Homopolymerization and copolymerization of 1 are easily carried out. From the kinetic study of the homopolymerization and copolymerization of 1 with styrene, the numerical values of the ratio square of the rate constant of propagation over the rate constant of termination k/kt and of the copolymerization reactivity ratios r1 and r2 of the two monomers were determined.
Ion pairs, cations and anions in ternary solutions of bis(polystyryl)magnesium and magnesium bromide in tetrahydrofuran
Authors: Jappens‐Loosen Pascale , Beylen Marcel Van , Huyskens Pierre
Published: April 2003

A conductometric method is developed for the study of the ternary solutions in tetrahydrofuran of bis(polystyryl)magnesium (PStMgPSt) containing various proportions r of magnesium bromide. The concentration of bis(polystyryl)magnesium varies from 10−4 to 2.10−3 mol.dm−3, the ratio r from O to 17,4 and the temperature from +20°C down to −60°C. The addition of MgBr2 provokes the replacement of the ion pairs PStMgPSt by PStMgBr, the dismutation constant being at 20°C Kdism = 42 ± 2 with a molar enthalpy of − 5 ± 2 kJ.mol−1. The dismutation is chiefly ruled by a conjugated steric effect that lowers the stability of PStMgPSt. In this concentration range, aggregation of styryl ion pairs is negligible. Moreover for a given r the degree of dissociation of the polymer is independent of its concentration. This is due to the complete predominance in this concentration range of the triple anions Mg(PSt), MgBr(PSt) and MgBr2PSt−, approximately in the proportions of the ion pairs fpp, fbp and fbb as calculated from the dismutation constant. The triple anions MgBr are still completely negligible, as are also the triple cations. The single cations MgPSt+ and MgBr+ are approximately in the proportion fpp. Kdism/fbp, the latter are ones becoming predominant above r = 3.
Synthesis of poly(N‐tert‐butylaziridine)s with functional end‐groups
Authors: Christova Darina C. , Velichkova Rumiana S. , Panayotov Ivan M.
Published: April 2003

Poly(N‐tert‐butylaziridine) (poly(TBA)) with hydroxy, amino, HOC(O)CHCHC(O)and P(O)(OCH3)2 end‐groups were synthesized via termination reactions of living poly(TBA) with appropriate nucleophiles. 2‐Aminoethanol, sodium 2‐aminoethylate, maleic anhydride and dimethyl phosphonate were used. The functionally terminated oligomers were of uniform size and with a functionally near one.
Conductivity and photoconductivity of undoped and doped Langmuir‐Blodgett films of a polymer with hexaalkoxytriphenylene side‐groups
Authors: Catry Christian , Van der Auweraer Mark , De Schryver Frans C. , Bengs Holger , Häussling Lucas , Karthaus Olaf , Ringsdorf Helmut
Published: April 2003

Langmuir‐Blodgett films from a polymer with triphenylene moieties in the side groups deposited on a quartz substratum with aluminium and gold electrodes show a dark conductivity in the plane of the Langmuir‐Blodgett film. This dark conductivity is increased using gold electrodes as compared with aluminium electrodes. It depends in a superlinear way upon the applied electric field and is not enhanced by oxygen. The dark conductivity can be enhanced by doping the Langmuir‐Blodgett films with iodine but it is not influenced by doping the Langmuir‐Blodgett films with 2,4,7‐trinitro‐9‐fluorenone. Upon excitation in the absorption band of the triphenylene moiety an in‐plane photocurrent, which is enhanced by oxygen, could be observed. Also the photocurrent is enhanced by using gold electrodes. Doping the Langmuir‐Blodgett films with iodine or 2,4,7‐trinitro‐9‐fluorenone quenches the photocurrent. Up to 10 W/m2 the photocurrent depends linearly upon the intensity of the incident light.
Synthesis and physical properties of telechelic monodispersed diols 4. Monoaddition of 10‐undecenol to novel dithiols
Authors: Améduri Bruno , Berrada Khalid , Boutevin Bernard , Mélas Michel , Bowden Roy D.
Published: April 2003

The synthesis of novel telechelic monodispersed diols produced from the radical monoaddition of an excess of 10‐undecenol with novel α, ω‐dithiols, initiated by peroxides, is presented. The telechelic dithiols employed were prepared from nonconjugated dienes and a commercially available dithiol, or by esterification of adipic acid with 2‐mercaptoethanol. From these dithiols, the diols were selectively obtained in high yields. Such α, ω‐dihydroxylated compounds were characterized by both 1H and 13C NMR spectroscopy. The diol which exhibits the ester functions shows excellent solubility in common organic solvents contrarily to the other ones. The physical properties (Tg, Tm and decomposition temperatures) of these diols were compared and it is noted that the thermostability of these monodispersed telechelic diols is much better than those of the polydispersed commercially available ones such as poly(ethylene glycol)s or poly(tetramethylene glycol)s.
New poly(amide‐imide)s syntheses, 6. Preparation and properties of poly(amide‐imide)s derived from 2,7‐bis(4‐aminophenoxy)naphthalene, trimellitic anhydride and various aromatic diamines
Authors: Yang Chin…Ping , Chen Wen‐Tung
Published: April 2003

An imide ring‐containing dicarboxylic acid, 2,7‐bis[4‐(N‐trimellitoyl)phenoxy]naphthalene (1,1′,3,3′‐tetraoxo‐2,2′‐[2,7‐naphthylenedioxybis(1,4‐phenylene)]di‐1H, 3H‐isoindole‐5‐carboxylic acid (3)), was prepared by condensation of 2,7‐bis(4‐aminophenoxy)naphthalene (4,4′‐(2,7‐naphthylenedioxy)dianiline) and trimellitic anhydride (1,2,4‐benzenetricarboxylic acid 1,2‐anhydride). A series of new aromatic poly(amide‐imide)s 5 containing bis(phenoxy)naphthalene moieties having inherent viscosities of 0,8–1,57 dL/g were prepared by direct polycondensation of this diimide‐diacid 3 with various aromatic diamines using triphenyl phosphite and pyridine as condensing agents in 1‐methyl‐2‐pyrrolidone (NMP) in the presence of calcium dichloride. Polymers 5 show excellent solubility in polar solvents such as NMP, and most of them could be cast into transparent and tough films. Measurements of wide‐angle X‐ray diffraction revealed that those polymer containing p‐phenylene or oxyphenylene groups are partially crystalline. Amorphous members exhibit glass transition temperature in the range of 250–311°C. Thermal analyses indicated that these polymers are fairly stable, and the 10% weight loss temperature were recorded in the ranges of 526–575°C in nitrogen and 481–556°C in air.
A propos de quelques anomalies de la polymérisation radicalaire du vinyl‐1‐imidazole
Authors: Chapiro Adolphe , Randriamahefa Solo , Schmitt Nicole
Published: April 2003

The polymerization of 1‐vinylimidazole (VI) was initiated with benzoyl peroxide (POB) in bulk and in methanol solutions while gamma‐ray initiation was used for the reaction in a ternary mixture with methanol and hexane. These conditions were chosen in order to understand better some anomalies observed in the grafting of VI on radiation‐peroxidized polyethylene. It was found that POB induces an addition reaction onto VI giving rise to a polymer of low molecular weight. This reaction occurs at low temperature and could involve ionic species. VI not being miscible with hexane, its gamma‐ray initiated polymerization was investigated in a ternary mixture with methanol at 60°C. Under such conditions the reaction proceeds “normally”, except in the vicinity of a demixing point where a strong auto‐acceleration occurs. This effect presumably results from a phase separation into micro‐droplets in which the reaction proceeds similarly to an emulsion polymerization. It is concluded that the abnormal behaviour of VI in the grafting reaction onto peroxidized polyethylene observed earlier follows from the initiation process by peroxides and not from the hydrocarbon nature of polyethylene.
Phase transition of liquid‐crystalline polyesters with biphenyl mesogen under high pressures
Authors: Maeda Yoji , Toriumi Hirokazu
Published: April 2003

The structural and thermal behavior of liquid‐crystalline polyesters at hydrostatic pressure was investigated by using a high‐pressure DTA and a wide‐angle X‐ray scattering apparatus equipped with a high‐pressure sample vessel. The thermotropic polyesters (two homopolymers and the corresponding copolymer) are based upon 4,4′‐biphenyldiol as the mesogen and aliphatic dibasic acids containing 7 and 8 methylene groups as flexible spacer, which are labeled as PB‐7, PB‐8, and PB‐7,8 (30/70 mol‐%), respectively. The phase diagrams of the PB‐7, PB‐8 and PB‐7,8 samples were constructed for pressures up to 300 MPa. At room temperature both the PB‐7 and the PB‐8 crystals are compressed hydrostatically in the molecular chain and lateral packing directions. The d spacing of the low‐angle reflection of the PB‐8 crystal, corresponding to the layer spacing, decreases by about 2,6 ± 0,2 Å at the crystal (K)‐smectic H(SH) transition under all pressures, while the crystal reflections of PB‐7 disappear at the K‐nematic (N) transition. The d spacings of the wide‐angle reflections of both crystals, corresponding to the lateral packing in the crystals, expand gradually with increasing temperature up to the K‐mesophase transition. The increase in lateral spacing of the PB‐8 crystal at the K‐SH transition changes slightly from ca. 0,29 Å at 0,1 MPa to 0,22 Å at 300 MPa. It is concluded that the transition mechanisms of the K‐SH transition of PB‐8 and the K‐N transition of PB‐7 are maintained at pressures up to 300 MPa.
Chain transfer reaction to terminal olefins in the polymerization of 1‐phenyl‐1‐propyne with Nb and Ta catalysts
Authors: Kouzai Hiroaki , Masuda Toshio , Higashimura Toshinobu
Published: April 2003

Effects of various olefins as chain transfer agents were studied in the polymerization of 1‐phenyl‐1‐propyne catalyzed by NbCl5—Bu4Sn (1:2) (Bu: butyl) and TaCl5—Bu4Sn (1:2). In the Nb‐catalyzed polymerizations, Si‐containing terminal olefins, especially butyldimethylvinylsilane and dimethylphenylvinylsilane, proved to greatly lower the polymer molecular weight; e.g., the number‐average molecular weight (M̄n) of the polymer formed without an olefin was 2,0 · 105, whereas it decreased to 7 · 103 − 1 · 104, i.e., below 1/20 in the presence of the Si‐containing olefins (1/5 equivalent to the monomer). In the Ta‐catalyzed polymerization, in contrast, hydrocarbon terminal olefins like 1‐octene were effective; e.g., while the M̄n of the polymer reached 4,0 · 105 without an olefin, the M̄n was no more than 9 · 103 − 2 · 104, i.e., smaller than 1/25 in the presence of olefins. Poly(1‐phenyl‐1‐propyne) obtained using the Nb catalyst in the presence of butyldimethylvinylsilane possesses the terminal butyldimethylsilyl group derived from the added olefin. Thus, suitable olefins are useful to control the molecular weight of poly(1‐phenyl‐1‐propyne) by chain transfer, which verifies the metal‐carbene mechanism for the polymerization of 1‐phenyl‐1‐propyne by group 5 transition metal catalysts.
Immobilization of bioactive substances on poly(alkylene phosphate)s, 1. Immobilization of 2‐phenylethylamine
Authors: Tzevi Raina , Todorova Galina , Kossev Krassimir , Troev Koljo , Georgiev Emil M. , Roundhill D. Max
Published: April 2003

Poly(alkylene phosphate)s of low molecular weight were synthesized by polytransesterification of dialkyl phosphonates with poly(ethylene glycol)s (PEG). These poly(alkylene phosphonate)s were then converted into poly(alkylene phosphate)s by using the Atherton‐Todd reaction in methanol as a solvent. The compound 2‐phenylethylamine was immobilized on these polymers via ionic bonds. These immobilizations were achieved by both alkylation and dealkylation reactions. The final products from these reactions are the polyanions. The structures of these products were determined by a combination of 1H, 31P and 31C NMR spectroscopy.
Yolk proteolysis in rainbow trout oocytes after serum‐free culture: Evidence for a novel biochemical mechanism of atresia in oviparous vertebrates
Authors: Wood Antony W. , Kraak Glen Van Der
Published: April 2003

Our recent studies show little evidence for increased granulosa cell apoptosis during atresia in teleost follicles, in direct contrast to the mammalian model. Histological evidence suggests that atresia in many oviparous vertebrates involves proteolytic degradation of the energy‐rich yolk storage proteins within the oocyte. This study tests the hypothesis that physiological conditions that promote atresia (hormone withdrawal) lead to increased lysosomal protease activity in rainbow trout oocytes. We subjected rainbow trout ovarian follicles to conditions that promote atresia (serum‐free culture) for up to 72 hr, and measured the activity of lysosomal proteases using routine enzymatic assays. Furthermore, we used high performance liquid chromatography to quantify the increase in free amino acids resulting from proteolysis of yolk proteins. Concomitantly, we evaluated the extent of follicular apoptosis during prolonged serum‐free culture, using caspase‐3‐like activity and DNA fragmentation as indicators of apoptosis. Our results show a significant, time‐dependent increase in cathepsin L‐like, but not cathepsin D‐like, activity levels during culture in serum‐free medium; increased cathepsin L‐like activity is confirmed by a significant increase in oocyte free amino acid content after 72 hr culture. In contrast, we detected only a transient increase in apoptosis during prolonged serum‐free culture, as revealed through both radioactive 3′end‐labeling of oligonucleosomal DNA fragments, and caspase‐3‐like activity. The results of this study provide the first evidence for a novel mechanism of follicular atresia in teleosts involving cathepsin‐mediated yolk proteolysis. Mol. Reprod. Dev. 65: 219–227, 2003. © 2003 Wiley‐Liss, Inc.
Calcitonin acts as a first messenger to regulate adenylyl cyclase/cAMP and mammalian sperm function
Authors: Adeoya‐Osiguwa S.A. , Fraser L.R.
Published: April 2003

Calcitonin stimulates capacitation in uncapacitated mouse spermatozoa and then inhibits spontaneous acrosome loss in capacitated cells, responses similar to those elicited by fertilization promoting peptide (FPP), a peptide known to regulate the adenylyl cyclase/cAMP pathway. This study investigated the hypothesis that calcitonin also modulates this pathway. Calcitonin significantly stimulated cAMP production in uncapacitated spermatozoa and then inhibited it in capacitated cells; the magnitude of both stimulatory and inhibitory changes was similar to that obtained with FPP but the inhibitory responses to FPP preceded those of calcitonin. This possibly reflects the involvement of two different adenosine receptors in response to FPP compared with one calcitonin receptor. Calcitonin receptors were located on the acrosomal cap and the flagellum, the midpiece having a greater abundance than the principal piece. Although both calcitonin and adenosine receptors are found in the head and flagellum, there was no evidence for cross‐talk between them. Chlortetracycline investigations to determine the minimum extracellular Ca2+ requirement for responses to calcitonin revealed that calcitonin significantly stimulated capacitation in Ca2+‐deficient medium but FPP did not. Calcitonin also significantly stimulated cAMP production under these conditions, and similarly preincubated suspensions, when diluted into +Ca2+ medium, were significantly more fertile in vitro than untreated controls. These results indicate that calcitonin, like FPP, acts as a first messenger to regulate the production of cAMP and mammalian sperm function, but the differences in Ca2+ requirements suggest that calcitonin and FPP may regulate different isoforms of adenylyl cyclase. Mol. Reprod. Dev. 65: 228–236, 2003. © 2003 Wiley‐Liss, Inc.
Genomic structure and promoter activity of the testis haploid germ cell‐specific intronless genes, Tact1 and Tact2
Authors: Hisano Mizue , Yamada Shuichi , Tanaka Hiromitsu , Nishimune Yoshitake , Nozaki Masami
Published: April 2003

The Tact1 and Tact2 genes, each of which encodes an actin‐like protein, are exclusively expressed and translated in haploid germ cells in testis. To characterize the haploid germ cell‐specific gene structure, a mouse genomic library was screened with a Tact1 cDNA as a probe, and four independent phage clones containing the Tact1 gene were isolated. Southern hybridization and sequencing analyses revealed that Tact1 and Tact2 were single copy genes contained on a common fragment in a head‐to‐head orientation, and that the distance between these genes was less than 2 kb. Comparison of the nucleotide sequences of genomic DNA and cDNA demonstrated that Tact1 and Tact2 lack introns, although all known actin or actin‐related genes in mammals contain introns. Human Tact orthologues also lack introns and are located within 6.4 kb in a head‐to‐head orientation. These findings indicate that Tact1 and Tact2 or one of these genes arose by retroposition of a spliced mRNA transcribed from an actin progenitor gene prior to the divergence of rodents and primates. The Tact1 and Tact2 genes are unusual retroposons in that they have retained an open reading frame and are expressed in testicular germ cells, because almost all retroposons become pseudogenes. It was revealed that a 2kb sequence between the two genes bidirectionally controls haploid germ‐cell specific expression by analyzing transgenic mice. Comparison of the murine Tact genes with their human orthologues showed a high level of identity between the two species in the 5′‐upstream and non‐coding sequences as well as in the coding region, indicating that conserved elements in these regions may be involved in the regulation of haploid germ cell‐specific expression. The promoter region contains no TATA‐, CCAAT‐ or GC‐boxes, although there are potential cAMP response element (CRE)‐like motifs in the 5′‐upstream region and the 5′‐untranslated region in Tact1 and Tact2, respectively. Transient promoter analyses indicate that CREMτ may activate Tact1 and Tact2 expression in germ cells. Mol. Reprod. Dev. 65: 148–156, 2003. © 2003 Wiley‐Liss, Inc.
Hyperglycemia‐induced apoptosis affects sex ratio of bovine and murine preimplantation embryos
Authors: Jiménez Adela , Madrid‐Bury Ninoska , Fernández Raúl , Pérez‐Garnelo Sonia , Moreira Pedro , Pintado Belén , de la Fuente Julio , Gutiérrez‐Adán Alfonso
Published: April 2003

The effect of glucose in the medium used during in vitro culture on both cell death by apoptosis and the sex ratio of bovine blastocysts derived from in vitro‐matured and in vitro‐fertilized oocytes was evaluated. Oocytes were matured, inseminated, and cultured in vitro in mSOF medium with 10% FCS with or without glucose supplementation. Exposure to high concentrations of glucose (10, 20, and 30 mM) during bovine embryo development in vitro from zygote to blastocyst resulted in a decrease in the number of cells per embryo and an increase in the frequency of apoptotic cells. A significantly higher proportion of females was found among those embryos that developed under hyperglycemic conditions in vitro. Moreover, both murine and bovine blastocysts incubated for 6 hr in 20 mM glucose had a significantly higher number of apoptotic cells in comparison to control. In this study, we also determined whether blastocyst production of the X‐linked inhibitor of apoptosis protein (XIAP) differs between the sexes. Our results show that female bovine blastocysts produce significantly higher amounts of XIAP mRNA than males and this could be crucial in explaining the higher proportion of female blastocysts observed following in vitro culture under hyperglycemic conditions which induce apoptosis. Moreover, a higher proportion of female murine blastocysts cultured under hyperglycemic conditions were implanted in the uterus (65.3 of implantations from embryos cultured with 20 mM of glucose are females vs. 49% in control). This mechanism provides an explanation for the significant reduction of male children born to diabetic mothers. Mol. Reprod. Dev. 65: 180–187, 2003. © 2003 Wiley‐Liss, Inc.
Cloning and expression of a novel cDNA encoding shell coat protein, cp4, from the brushtail possum (Trichosurus vulpecula)
Authors: Cui Shuliang , Selwood Lynne
Published: April 2003

The marsupial conceptus is enclosed by several egg coats of evolutionary significance and unknown composition, of which the shell coat in mammals occurs only in marsupials and monotremes. Intact coats are vital to marsupial embryonic development. Towards a better understanding of the marsupial coat proteins, a cDNA sequence (cp4) encoding a shell coat protein was cloned from the brushtail possum. A cDNA library of a zygote stage uterus was screened using a deduced oligonucleotide sequence based on a partial amino acid sequence of the coat protein. This study has confirmed a single copy cp4 gene encoding a unique protein of 306 amino acids, although its N‐terminus shares high sequence identity with the C‐terminal half of the enzyme α‐enolase. Using Northern blots, the expression of cp4 in adult tissues showed that cp4 transcript is restricted predominantly to the uterus with two stages of expression occurring in the gravid uterus at early cleavage and bilaminar stages, suggesting an important developmental role for CP4. Using RT‐PCR, cp4‐specific expression as represented by the 3′‐end 400 bp was present in heart, liver, oviduct, and uterus. Uterine expression reflected the increase found with Northern blot except that expression was low at unilaminar and bilaminar stages. Mol. Reprod. Dev. 65: 141–147, 2003. © 2003 Wiley‐Liss, Inc.
Antisense oligodeoxynucleotide inhibits expression of recombinant porcine follicle‐stimulating hormone receptor
Authors: Zhu Changhong , Wang Yifang , Nixon Mark D. , La Barbera Andrew R.
Published: April 2003

Follicle‐stimulating hormone (FSH) regulates folliculogenesis in the ovary and spermatogenesis in the testis via specific, high affinity membrane‐bound receptors (FSHR). To assess the role of FSHR gene expression in regulating expression of FSHR protein in the plasma membrane, the effects of a porcine FSHR cDNA antisense oligodeoxynucleotide (ODN) on FSHR mRNA levels and 125I‐FSH binding were determined in Chinese hamster ovary cells stably expressing recombinant porcine FSHR (pFSHR‐CHO cells). An 18‐mer phosphorothioated antisense ODN corresponding to the region surrounding the translation initiation codon of the porcine FSHR cDNA was synthesized. An 18‐mer phosphorothioated nonsense sequence of identical nucleotide composition was synthesized for use as a control. pFSHR‐CHO cells were cultured in the absence or presence of 1–20 μM antisense or nonsense ODN for 24 hr and then assayed for porcine FSHR mRNA, using quantitative reverse transcription and competitive polymerase chain reaction, and for 125I‐FSH binding activity. Treatment with 10 μM antisense ODN caused a paradoxical increase in porcine FSHR mRNA. Nonsense ODN had no effect on porcine FSHR mRNA. Antisense, but not nonsense, ODN (10 μM) inhibited membrane binding of 125I‐FSH by 13.6 ± 0.8% (mean ± SEM, n = 3, P < 0.05) in 24 hr. Treatment of cells with antisense ODN (10 μM) for 48 hr resulted in a 76 ± 1.5% (P < 0.05) inhibition of 125I‐FSH binding. These results indicate that an FSHR antisense ODN effectively inhibits porcine FSHR synthesis and inhibition of receptor synthesis causes a decrease in functional membrane‐bound FSHR. Mol. Reprod. Dev. 65: 188–193, 2003. © 2003 Wiley‐Liss, Inc.
Differences in the BOLD fMRI response to direct and indirect cortical stimulation in the rat
Authors: Austin V.C. , Blamire A.M. , Grieve S.M. , O'Neill M.J. , Styles P. , Matthews P.M. , Sibson N.R.
Published: April 2003

Functional MRI (fMRI) exploits a relationship between neuronal activity, metabolism, and cerebral blood flow to functionally map the brain. We have developed a model of direct cortical stimulation in the rat that can be combined with fMRI and used to compare the hemodynamic responses to direct and indirect cortical stimulation. Unilateral electrical stimulation of the rat hindpaw motor cortex, via stereotaxically positioned carbon‐fiber electrodes, yielded blood oxygenation level‐dependent (BOLD) fMRI signal changes in both the stimulated and homotypic contralateral motor cortices. The maximal signal intensity change in both cortices was similar (stimulated = 3.7 ± 1.7%; contralateral = 3.2 ± 1.0%), although the response duration in the directly stimulated cortex was significantly longer (48.1 ± 5.7 sec vs. 19.0 ± 5.3 sec). Activation of the contralateral cortex is likely to occur via stimulation of corticocortical pathways, as distinct from direct electrical stimulation, and the response profile is similar to that observed in remote (e.g., forepaw) stimulation fMRI studies. Differences in the neuronal pool activated, or neurovascular mediators released, may account for the more prolonged BOLD response observed in the directly stimulated cortex. This work demonstrates the combination of direct cortical stimulation in the rat with fMRI and thus extends the scope of rodent fMRI into brain regions inaccessible to peripheral stimulation techniques. Magn Reson Med 49:838–847, 2003. © 2003 Wiley‐Liss, Inc.
Assessment of myocardial blood volume and water exchange: Theoretical considerations and in vivo results
Authors: Bjørnerud Atle , Bjerner Tomas , Johansson Lars O. , Ahlström Håkan K.
Published: April 2003

The measured signal response in contrast‐enhanced myocardial perfusion imaging has been shown to be affected by the rate of water exchange between the intravascular and extravascular compartments, the effect being particularly significant when intravascular contrast agents are used. In the present study, the T1 relaxation rates were measured in eight pigs in blood and myocardium using a Look‐Locker sequence after repeated injections of the intravascular contrast agent NC100150. The selection of myocardial region of interest was automated based on a minimum chi‐square method. The intra‐ and extravascular water exchange rates and the myocardial blood volume were calculated from the measured relaxation rates by applying a two‐compartment water exchange limited model that accounts for biexponential longitudinal relaxation. The following (mean ± SD) values were obtained for the exchange frequency (f), the extravascular residence time (τe), the intravascular residence time (τi) and blood volume (BV), respectively: f = 1.39 ± 0.52 s‐1, τe = 708 ± 264 ms, τi = 107 ± 63 ms, and BV = 11.2 ± 2.1 mL/100 g. The mean value of f was found to be about 15% higher if biexponential relaxation was not accounted for, supporting the hypothesis that significant biexponential relaxation in tissues with large blood volume can lead to an overestimation of water exchange rates unless corrected for. Magn Reson Med 49:828–837, 2003. © 2003 Wiley‐Liss, Inc.
Automatic segmentation of the brain and intracranial cerebrospinal fluid in T1‐weighted volume MRI scans of the head, and its application to serial cerebral and intracranial volumetry
Authors: Lemieux Louis , Hammers Alexander , Mackinnon Toby , Liu Rebecca S.N.
Published: April 2003

A new fully automatic algorithm for the segmentation of the brain and total intracranial cerebrospinal fluid (CSF) from T1‐weighted volume MRI scans of the head, called Exbrain v.2, is described. The algorithm was developed in the context of serial intracranial volumetry. A brain mask obtained using a previous version of the algorithm forms the basis of the CSF segmentation. Improved brain segmentation is then obtained by iterative tracking of the brain–CSF interface. Gray matter (GM), white matter (WM), and intracranial CSF volumes and probability maps are calculated based on a model of intensity probability distribution (IPD) that includes two partial volume classes: GM‐CSF and GM‐WM. Accuracy was assessed using the Montreal Neurological Institute's (MNI) digital phantom scan. Reproducibility was assessed using scan pairs from 24 controls and 10 patients with epilepsy. Segmentation overlap with the gold standard was 98% for the brain and 95%, 96%, and 97% for the GM, WM, and total intracranial contents, respectively; CSF overlap was 86%. In the controls, the Bland and Altman coefficient of reliability (CR) was 35.2 cm3 for the total brain volume (TBV) and 29.0 cm3 for the intracranial volume (ICV). Scan‐matching reduced CR to 25.2 cm3 and 17.1 cm3 for the TBV and ICV, respectively. For the patients, similar CR values were obtained for the ICV. Magn Reson Med 49:872–884, 2003. © 2003 Wiley‐Liss, Inc.
Arterial spin labeling perfusion fMRI with very low task frequency
Authors: Wang Jiongjiong , Aguirre Geoffrey K. , Kimberg Daniel Y. , Roc Anne C. , Li Lin , Detre John A.
Published: April 2003

Functional magnetic resonance imaging (fMRI) has become the most widely used modality for visualizing regional brain activation in response to sensorimotor or cognitive tasks. While the majority of fMRI studies have used blood oxygenation level‐dependent (BOLD) contrast as a marker for neural activation, baseline drift effects result in poor sensitivity for detecting slow variations in neural activity. By contrast, drift effects are minimized in arterial spin labeling (ASL) perfusion contrast, primarily as a result of successive pairwise subtraction between images acquired with and without labeling. Recent data suggest that ASL contrast shows stable noise characteristics over the entire frequency spectrum, which makes it suitable for studying low‐frequency events in brain function. The present study investigates the relative sensitivities of ASL and BOLD contrast in detecting changes in motor cortex activation over a spectrum of frequencies of experimental design, where the alternating period between the resting state and activation is varied from 30 s up to 24 hr. The results demonstrate that 1) ASL contrast can detect differences in motor cortex activation over periods of minutes, hours, and even days; 2) the functional sensitivity of ASL contrast becomes superior to that of BOLD contrast when the alternating period between the resting state and activation is greater than a few minutes; and 3) task activation measured by ASL tends to have less intersubject variability than BOLD contrast. The improved sensitivity of the ASL contrast for low task frequency and longitudinal studies, along with its superior power in group analysis, is expected to extend the range of experimental designs that can be studied using fMRI. Magn Reson Med 49:796–802, 2003. © 2003 Wiley‐Liss, Inc.
Quantitative proton short‐echo‐time LASER spectroscopy of normal human white matter and hippocampus at 4 Tesla incorporating macromolecule subtraction
Authors: Kassem Mohamed N.E. , Bartha Robert
Published: April 2003

Accurate quantification of in vivo short‐echo‐time (TE) 1H spectra must account for contributions from both mobile metabolites and less mobile macromolecules, which can fluctuate in disease. The purpose of this study was to develop an approach for the acquisition and processing of macromolecule information to optimize metabolite quantification accuracy and precision. Human parietal white matter (8‐cm3 voxel) and posterior hippocampus (1.7‐cm3 voxel) metabolite levels were quantified, following manomolecule subtraction, from short‐echo‐time spectra (TE = 46 ms) acquired at 4.0 Tesla with localization by adiabatic selective refocusing (LASER). Nineteen metabolites were fit using a time domain Levenberg‐Marquardt minimization that incorporated prior knowledge of metabolite lineshapes. The macromolecule contribution to the spectrum was reduced by 87% (P < 0.05) when the acquisition of single averages of the full spectrum and macromolecule spectrum were interleaved to reduce subtraction errors due to motion. Subtracting the Hankel Lanczos singular value decomposition (HLSVD) fit of the macromolecule spectrum, which contained no random noise, did not alter quantified metabolite levels but did not increase metabolite quantification precision. Several metabolites had higher concentrations in the posterior hippocampus compared to parietal white matter, which emphasizes the need to carefully control for partial volume contamination in hippocampal spectroscopy studies. Magn Reson Med 49:918–927, 2003. © 2003 Wiley‐Liss, Inc.
Fast U‐FLARE‐based correlation‐peak imaging with complete effective homonuclear decoupling
Authors: Mayer Dirk , Dreher Wolfgang , Leibfritz Dieter
Published: April 2003

A new fast correlation‐peak imaging technique is presented that combines 2D correlation spectroscopy with an ultrafast low‐angle rapid acquisition with relaxation enhancement (U‐FLARE) imaging module. Constant time chemical shift (CS) encoding is used in both time dimensions to achieve effective homonuclear decoupling in both frequency dimensions. The intervals between excitation and mixing (tc1) and between mixing and start of the MRI module (tc2) can be optimized to maximize the coherence transfer for a particular metabolite. Experiments were performed with evolution times tc1 and tc2 of 100 ms and 50 ms, respectively, which were determined by simulation of the spectroscopic part of the sequence for the spin systems of myo‐inositol (Ins) and taurine (Tau). The use of a circularly reduced CS‐encoding scheme shortened the minimum total measurement time to 35 min. The sequence was implemented on a 4.7 T imaging system and tested on a spherical phantom filled with a solution of Ins. The in vivo application of this method on healthy rat brain demonstrates its improved spectral resolution, as cross‐peak signals from both Ins and Tau can be separated clearly. Magn Reson Med 49:810–816, 2003. © 2003 Wiley‐Liss, Inc.
Quantitative evaluation of susceptibility and shielding effects of nitinol, platinum, cobalt‐alloy, and stainless steel stents
Authors: Wang Yi , Truong Thuy N. , Yen Cecil , Bilecen Deniz , Watts Richard , Trost David W. , Prince Martin R.
Published: April 2003

The purpose of this study is to quantitatively estimate the shielding and susceptibility effects of commonly used metallic stents on MR signal. Two experiments were performed using a 3D gradient echo sequence with short TE to image a stent phantom: 1) short TR and high flip angle (contrast enhanced MRA parameters), and 2) long TR (TR ≫ T1) and low flip angle. The factor characterizing susceptibility effects was estimated from the signal phase of the first experiment, and then the factor characterizing the shielding effects was derived from the second experiment. Susceptibility induced signal loss was negligible (<1%) for nonstainless‐steel (nitinol, platinum, and cobalt‐alloy) stents and totally destructive (100%) for the stainless steel stent. Signal loss due to RF shielding was 31–62% for nitinol stents, 14–50% for platinum stents, 50–77% for the cobalt‐alloy stents (undetermined for the stainless steel stent), varied with stent orientation, diameter, and wall geometry. In summary, stents made of nitinol, platinum, and cobalt‐alloy have negligible susceptibility effects but stents made of stainless steel may have complete dephasing. All stents have substantial shielding effects, which vary with composition, geometry, and orientation. Large platinum stents may have the smallest artifacts and are the best suited for postinterventional MR imaging. Magn Reson Med 49:972–976, 2003. © 2003 Wiley‐Liss, Inc.
Balanced phase‐contrast steady‐state free precession (PC‐SSFP): A novel technique for velocity encoding by gradient inversion
Authors: Markl M. , Alley M.T. , Pelc N.J.
Published: April 2003

A technique for measuring velocity is presented that combines cine phase contrast (PC) MRI and balanced steady‐state free precession (SSFP) imaging, and is thus termed PC‐SSFP. Flow encoding was performed without the introduction of additional velocity encoding gradients in order to keep the repetition time (TR) as short as in typical SSFP imaging sequences. Sensitivity to through‐plane velocities was instead established by inverting (i.e., negating) all gradients along the slice‐select direction. Velocity sensitivity (VENC) could be adjusted by altering the first moments of the slice‐select gradients. Disturbances of the SSFP steady state were avoided by acquiring different flow echoes in consecutively (i.e., sequentially) executed scans, each over several cardiac cycles, using separate steady‐state preparation periods. A comparison of phantom measurements with those from established 2D‐cine‐PC MRI demonstrated excellent correlation between both modalities. In examinations of volunteers, PC‐SSFP exhibited a higher intrinsic signal‐to‐noise ratio (SNR) and consequently low phase noise in measured velocities compared to conventional PC scans. An additional benefit of PC‐SSFP is that it relies less on in‐flow‐dependent signal enhancement, and thus yields more uniform SNRs and better depictions of vessel geometry throughout the whole cardiac cycle in structures with slow and/or pulsatile flow. Magn Reson Med 49:945–952, 2003. © 2003 Wiley‐Liss, Inc.
Increased brain white matter diffusivity in normal adult aging: Relationship to anisotropy and partial voluming
Authors: Pfefferbaum Adolf , Sullivan Edith V.
Published: April 2003

Diffusion tensor imaging (DTI) was used to examine 1) age‐related changes in genu, splenium, and centrum semiovale white matter diffusivity in 64 healthy men and women (age 23–85 years); 2) the relationship between diffusivity (trace) and fractional anisotropy (FA) across and within individuals; and 3) the role of macrostructural and microstructural partial voluming effects on the DTI metrics. Regional differences were greater in FA (∼43%) than in trace (∼16%). Depending on the region of interest, trace increased with age (r = 0.24 to 0.58) and FA decreased with age (r = −0.29 to −0.79). FA was inversely correlated with trace, even when controlling for age. Histogram analysis of trace and FA following systematic expansion and dilation of the white matter regions demonstrated greater susceptibility of FA than trace to error arising from macrostructural partial voluming, i.e., erroneous inclusion of primarily nonwhite‐matter voxels. Three‐phase ellipsoid shape analysis revealed that after morphometric erosion the spherical component remained greater in older than younger subjects in the splenium and centrum, suggesting that age‐related reduction in FA arises from intravoxel increased interstitial fluid. Reducing the size of the white matter samples to control for macrostructural partial voluming attenuated but did not negate effects, indicating that observed changes in white matter with aging can reflect real microstructural alterations rather than sampling artifact. Morphological dilation of white matter regions of interest resulting in purposeful inclusion of non‐white matter pixels significantly reduced mean FA, suggesting that reports of FA values below 0.25 in healthy adults may reflect partial voluming rather than actual changes in white matter coherence. Magn Reson Med 49:953–961, 2003. © 2003 Wiley‐Liss, Inc.
Physicochemical characterization of dispersed chicken feather keratin
Authors: Ward Wilfred H. , High Loretta M. , Lundgren Harold P.
Published: April 2003

Reduced chicken feather keratin forms a soluble complex in neutral aqueous sodium alkylbenzenesulfonate (average: dodecylbenzenesulfonate). The chemical composition, specific refractive increment, partial specific volume, electrophoretic mobility, osmotic pressure, diffusion constants, and ultracentrifugal sedimentation of the complex have been studied. The complex is heterogeneous but similar to egg albumin–sodium alkylbenzenesulfonate mixtures previously studied in general properties, including fiber‐forming properties, the average molecular weight of the dispersed protein units, and the relative symmetry of the dispersed units in dilute solution.
Characterization of cellulose derivatives by solution properties: Plasticizers as solvents
Authors: Spurlin H. M. , Martin A. F. , Tennent H. G.
Published: April 2003

The dimensional stability of molded thermoplastic articles is a function of the extent to which stresses are frozen into them on molding. The kind and amount of plasticizer included in the material to be molded may be varied to minimize the amount of these stresses. Methods of obtaining fundamental information about polymer–plasticizer systems from simple measurements of viscosity and osmotic pressure are suggested in this paper, and some results for cellulose derivatives are given.
Mechanism of vinyl polymerizations. IX. Some factors affecting copolymerization
Authors: Price Charles C.
Published: April 2003

The influence on polymerization and copolymerization of various structural factors, especially polarity at the double bond of the monomer, is discussed. The effect of substituents in donating or withdrawing electrons appears to be an important regulating factor in copolymerization.
Cellulose acetate esters containing amino nitrogen
Authors: Gardner Thomas S.
Published: April 2003

Nitrogen was introduced into cellulose acetate by the incorporation of amino acid groups. Some of the mixed esters were soluble in organic solvents. Cast films were examined for dyeing properties with wool‐type dyes. Many of the mixed esters containing above 1% nitrogen dyed well with xylene brilliant blue, a typical wool‐type dye, Mixed cellulose acetate esters were synthesized containing glycine, dl‐α‐alanine, β‐alanine, and α‐isoaminobutyric, d‐glutamic, and p‐aminobenzoic acids. The amino groups were protected by acetylation prior to use. The N‐acetyl amino acids were treated with cellulose diacetate in dioxane solution containing chloroacetic anhydride and magnesium perchlorate as impellor and catalyst, respectively. Cellulose acetate metanilate was prepared by use of the aminosulfo acid chloride. An attempt was made to prepare 6‐aminocellulose by the reaction of aqueous ammonia, and also sodamide in liquid ammonia on 6‐iodotosylcellulose acetate. Only traces of nitrogen were introduced by this procedure and the recovered products showed signs of extreme degradation.
Density of cellulose fibers. I. Introduction and experiments on the penetration of liquids into dry cellulose
Authors: Hermans P. H. , Vermaas D.
Published: April 2003

In this paper it is emphasized that density is a typically macroscopic concept which cannot be transferred to small particles or bodies with small pores. This fact has not been duly accounted for in earlier work on the density of cellulose fibers. The usual interpretation of density determinations in various media is criticized and the point of view that cellulose fibers should be considered as porous bodies is dropped. The pore system occurring in native fibers is coarse enough not to interfere with density determinations in indifferent organic liquids.

It is shown experimentally that even substances like water and glycerol penetrate very slowly into dry cellulose and that indifferent organic liquids do not penetrate at all. In the experiments with water vapor a new phenomenon, the heterogeneous course of absorption, is observed, giving rise to sharp microscopically visible boundary lines between the wet and the dry portion of the fiber.
Submicroscopic structure of cellulose gels
Authors: Frey‐Wyssling A. , Mühlethaler K.
Published: April 2003

In the following paper the crystallization of submicroscopic cellular strands from multimolecular, cellulose films is illustrated by electron micrographs.
Statistical behavior of the single chain molecule and its relation to the statistical behavior of assemblies consisting of many chain molecules
Authors: Kuhn Werner , Grün Franz
Published: April 2003

The molecules of high‐molecular substances, for instance, those present in rubber, can be treated statistically in two ways. On the one hand, these molecules are such complicated structures that it is possible to attribute a separate entropy and free energy to each giant molecule. On the other hand, solutions of high‐molecular substances represent systems in which the single chain molecule is the elementary particle, and to which statistical considerations and concepts such as entropy and free energy can be applied. Depending upon the parameter considered, the same chain molecule must sometimes be treated as a complicated system and at other times as an elementary particle. The problems originating from the simultaneous existence of two stages in the statistical treatment are examined. It is shown that the entropy of an assembly of many chain molecules is not simply equal to the sum of the entropies of the separate chain molecules. This becomes apparent particularly when determining the distribution function with respect to a particular parameter (e.g., distance between the two end points of a molecule) from a statistical consideration of the single molecule on the one hand, and from a consideration of an assembly of identical molecules on the other hand. The relations between entropy and free energy of the individual particle and the a priori probabilities on which the treatment of an assembly is to be based are explained. It is further shown that the same particle can give rise to a macroscopic phenomenon in two ways and to approximately the same extent: first, as a complicated system, and second, as an element in a large assembly of identical particles. This applies in particular to the elastic retractive force and to the strain birefringence in rubber and related substances.
Elastic deformation and molecular weight in polyisobutylene
Authors: Rehner John
Published: April 2003

A rapid procedure is described for estimating the average molecular weights of polyisobutylenes from deformation‐rate measurements.
Relation between molecular weight and intrinsic viscosity for polymethyl methacrylate
Authors: Baxendale J. H. , Bywater S. , Evans M. G.
Published: April 2003

The chain lengths of polymethyl methacrylates prepared with ferrous ion–hydrogen peroxide as the initiating system are consistent with the scheme advanced for the mechanism of the polymerization. The relation between intrinsic viscosity in benzene and molecular weight for fractionated polymethyl methacrylate has been determined and leads to the equation: n = 2.81 × 103 [η]C6H61.32. This equation agrees very well with the data of Schulz, provided that the correct method of extrapolating the osmotic pressures to zero concentration is used. Using the relationship between [η]C6H6 and [η]CHCl3 obtained experimentally, the relation between n and [η]CHCl3 (at 20°C.) is: n = 1.81 l3 × 103[η]CHCl31.22.
Modern views on the chemistry of vulcanization changes. I. Nature of the reaction between sulfur and olefins
Authors: Farmer E. Harold , Shipley F. W.
Published: April 2003

Whatever additional factors may be concerned in the production of good vulcanizates from natural rubber by the action of sulfur, there is no doubt that the action of sulfur on olefinic materials in general at the ordinary vulcanization temperature is a chemical one, the primary course of which is determined largely by the constitution of the olefin, and hence may be profitably studied by experimentation with olefins of different unsaturation patterns. Unaccelerated reaction between sulfur and simple monoolefins leads almost exclusively to cross linking of the separate olefin molecules, mostly in pairs, by groups of sulfur atoms. When, however, two or more olefinic units occur in the same molecule, as in the disoprenic hydrocarbons, intramolecular cross linking, i.e., cyclization, at once becomes possible, and the result of sulfur action consists partly in the cross linking of separate molecules as with the monoolefins, but largely in cyclization of the individual olefinic chains, thereby forming sulfur‐containing rings. These changes entail a certain loss of unsaturation, from which deductions can be made as to the mechanism of the reaction.