bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term morphometric and immunohistochemical findings in human free microvascular muscle flaps
Authors: Kauhanen M. Susanna C. , Lorenzetti Fulvio , Leivo Ilmo V.V. , Tukiainen Erkki , Asko‐Seljavaara Sirpa L.
Published: January 2004

Reinnervation, muscle regeneration, density of microvessels, and muscle‐type specific atrophy were studied 3–4 years after surgery in surgically nonreinnervated free microvascular muscle flaps to 13 patients transplanted to the upper or lower extremities. Routine histology and immunohistochemistry for PGP 9.5 and S‐100 (neuronal markers), Ki‐67 (cell proliferation), myosin (muscle fiber types), and CD‐31 (endothelium) were carried out, and results were analyzed morphometrically. Three to 4 years after surgery, severe atrophy of predominantly slow‐type fibers was seen in 9 cases. In 4 cases, muscle‐fiber diameter and fiber‐type distribution were close to normal. Long intraoperative muscle ischemia and postoperative immobilization were associated with poor muscle bulk in flaps. The density of microvessels in flaps did not differ from control muscles. PGP 9.5 and S‐100 immunopositive nerve fibers were detected in 7 patients. Reinnervation was associated with good muscle bulk. In 4 patients, activation of satellite cells was evident. The results suggest that in some cases, spontaneous reinnervation may occur in free muscle flaps, and that several years after microvascular free flap transfer, the muscle still attempts to regenerate. © 2004 Wiley‐Liss, Inc.
VEGF‐promoted surgical angiogenesis in necrotic bone
Authors: Suzuki Osami , Bishop Allen T. , Sunagawa Toru , Katsube Kosuke , Friedrich Patricia F.
Published: January 2004

The ability of vascular endothelial growth factor (VEGF) to accelerate neoangiogenesis from implanted arterovenous (AV) bundles in necrotic bone was evaluated. A saphenous AV bundle was placed in a necrotic segment of rabbit ilium. In group II, VEGF (100 ng/h x 3 days) was administered by continuous infusion. Bone blood flow was measured with radioactive‐labeled microspheres, and capillary density was determined by microangiography combined with Spälteholtz bone clearing at 1, 2, and 4 weeks. Neovascularization was observed along the implanted vascular bundle in both groups. One week after surgery, bone blood flow and vessel area were significantly higher in VEGF‐treated animals (P < 0.05). No significant difference was observed at later times. Direct VEGF administration increased surgical angiogenesis and improved blood flow and neovascularization in necrotic bone 1 week after AV bundle implantation. Thereafter, a robust angiogenic response from the AV bundle was seen in both groups. © 2004 Wiley‐Liss, Inc.
Recent advances in the reconstruction of complex Achilles tendon defects
Authors: Ronel Daniel N. , Newman Martin I. , Gayle Lloyd B. , Hoffman Lloyd A.
Published: January 2004

Large, complex lower‐extremity defects in the region of the Achilles tendon occur when tendon loss or disruption is complicated by damage to surrounding structures, including soft tissue, vessels, or bone. The surgical approach to these complex defects has evolved from simple amputation to the recognition that satisfactory reconstruction has three components: functional reconstruction of the tendon, importation of vascularized soft tissue, and skin coverage. Many techniques have been developed to address these difficult reconstructive goals, which often require multiple procedures or complicated single‐stage operations. Microsurgical advances have begun to reduce the complexity of Achilles tendon region reconstruction, and excellent results can be obtained which restore function, form, and cosmesis with minimal morbidity. © 2003 Wiley‐Liss, Inc.
Salutary effects of radiopaque contrast media on the survival of random‐pattern skin flaps in the rat: An experimental study
Authors: Askar Ibrahim , Bozkurt Mehmet , Oktay M. Faruk , Gürlek Ali , Keles Celalettin
Published: January 2004

The radiopaque contrast medium diatrizoate, has a vasodilator effect so that it is used in sudden‐deafness secondary ischemic injury. However, ischemic problems are encountered, especially when longer flaps are elevated. A longer flap also has ischemic and relatively ischemic tissue, and may obtain some benefit from contrast media. Forty male Sprague‐Dawley rats, weighing about 350–400 g, were used, and randomly divided into four groups (n = 10 rats each group): group 1 was the control, group 2 the diatrizoate, group 3 the iopamidol, and group 4 the iothalamate group. A rectangular 3 x 10 cm caudally based dorsal skin flap was elevated, and sutured back to its original place. In the control group, no pharmacologic agent was administered. Sodium‐meglumine‐diatrizoate 10 mg/kg/day was administered parenterally in the first experimental group (diatrizoate group); iopamidol 10 mg/kg/day in the second experimental group (iopamidol group); and iothalamate sodium 10 mg/kg/day in the third experimental group (iothalamate group) for 7 postoperative days. On postoperative day 7, all flaps were photographed, and the area of flap survival was measured by using a polar planimeter. The results were statistically evaluated with the Kruskal‐Wallis test and Mann‐Whitney U‐test (P = 0.05). The mean flap survival ranged from 79% in the iopamidol group to 83% in the diatrizoate group, and was significantly greater in all experimental groups (P < 0.05) compared to the control group (59%). There was no significant difference between experimental groups (P < 0.05). We believe that radiopaque contrast media have a beneficial effect in improving skin flap viability when distal flap necrosis is a potential complication of longer flaps. © 2003 Wiley‐Liss, Inc.
Free anteromedial thigh flap: Clinical application and review of literature
Authors: Schoeller Thomas , Huemer Georg M. , Shafighi Maziar , Gurunluoglu Raffi , Wechselberger Gottfried , Piza‐Katzer Hildegunde
Published: January 2004

The anteromedial thigh (AMT) flap is reviewed in terms of its vascular anatomy and previous clinical reports in the literature. Our own series of 5 patients treated with this flap for defects in the head and neck region and lower extremity is presented. Although several authors controversially discussed vasculature, we constantly found the pedicle as an emerging septocutaneous perforator at a point where the medial border of the rectus femoris muscle is crossed by the sartorius muscle. In all 5 patients, the AMT flap provided stable coverage with no flap loss. Based on our findings, we conclude that the anteromedial thigh flap offers all the advantages of fasciocutaneous flaps. Therefore, we recommend this flap as an alternative for defects requiring coverages of thin to moderate skin thickness. However, it should be remembered that variations in vascular anatomy are possible. © 2003 Wiley‐Liss, Inc.
Arterialization of the portal stump by right renal artery after portocaval shunt in the rat
Authors: Li Destri Giovanni , La Greca Gaetano , Greco Luigi , Greco Raffaele , Licitra Edelweiss , Lanteri Raffaele , Di Cataldo Antonio
Published: January 2004

Portosystemic shunts cause severe secondary effects, so that arterializations of the portal stump are planned to increase the blood supply to the liver. The aim of this study was to verify the technical feasibility of arterialization of the portal stump with the right renal artery in order to obtain a valid experimental model to study the pathophysiology of arterial revascularization of the liver. Twenty rats underwent end‐to‐side portocaval shunt + end‐to‐end anastomosis between the right renal artery and portal stump; another 20 rats were subjected to the same surgical procedure, but the portal stump underwent a reduction in size. In our study, both techniques gave good results, but the use of an operating microscope and good microsurgical training were essential in achieving a good patency rate (78.3%).Le derivazioni portosistemiche causano severi effetti collaterali per cui è stata ideata l'arterializzazione del moncone portale allo scopo di aumentare l'apporto ematico al fegato. Scopo di questo lavoro è stato quello di verificare la fattibilità tecnica dell'arterializzazione del moncone portale con l'arteria renale destra allo scopo di mettere a punto un valido modello sperimentale per studiare gli aspetti fisiopatologici della rivascolarizzazione arteriosa del fegato. Venti ratti sono stati sottoposti ad anastomosi porta‐cava termino‐laterale + anastomosi termino‐terminale tra arteria renale destra e moncone portale, altri venti ratti sono stati sottoposti allo stesso intervento chirurgico con la variante della riduzione del diametro del moncone portale. Nel nostro studio entrambe le tecniche hanno fornito buoni risultati ma a nostro parere l'uso del microscopio operatore ed un efficace training microchirurgico sono stati essenziali per ottenere una soddisfacente percentuale di pervietà (78.3%). © 2003 Wiley‐Liss, Inc.
Hyperbaric oxygen for the treatment of early‐phase Dupuytren's contracture
Authors: Yıldız Şenol , Karacaoğlu Ercan , Pehlivan Özcan
Published: January 2004

Dupuytren's disease (DD) is a proliferative disorder of autosomal‐dominant inheritance, with variable penetrance of gene expression. The treatment of DD is challenging. Both operative and nonoperative approaches were reported for treatment of the disease, but no perfect approach has gained popularity as the best choice of treatment. Most of the emphasis has been placed on surgical techniques, but outcomes were reported to be dependent on some variables such as case selection, timing of surgery, and the surgeon's training and experience. In this paper, we report on a hyperbaric oxygen (HBO) treatment for early‐phase DD. HBO treatment was applied to a female aged 23 years who had a mild form of DD. Physical findings and complaints before and after HBO treatment were compared. Total relief of symptoms as well as physical findings were obtained with HBO treatment. HBO for the treatment of DD is a novel concept. Having treated only one case is not enough to conclude that HBO is the only effective mode of treatment for DD. HBO should also be tried to treat early‐phase or mild contractures of DD. Unfortunately, HBO has a disadvantage, i.e., cost. But HBO is not invasive, and because of the nature of HBO treatment, most of the complications seen after surgeries, e.g., wound‐healing problems, damage to the digital nerves and vessels, buttonholing of the skin, and tendon sheath opening, are not seen. © 2003 Wiley‐Liss, Inc.
On sampling and sampling errors in histomorphometry of peripheral nerve fibers
Authors: Geuna Stefano , Gigo‐Benato Davilene , De Castro Rodrigues Antonio
Published: January 2004

Histomorphometrical assessment of regenerated peripheral nerves is a very common goal of many studies in experimental microsurgery. In this paper, the main critical issues in nerve fiber sampling for quantitative morphological assessment are addressed. The equal opportunity rule, i.e., the basic paradigm of random sampling, is described, together with an explanation of how sampling errors, in the selection of histologic fields and of the nerve fibers inside them, can produce a bias in quantitative estimates. Finally, some practical suggestions on how to cope with the most common sampling errors are provided, in order to help researchers obtain reliable histomorphometrical data on peripheral nerve fibers. © 2003 Wiley‐Liss, Inc.
Large recurrent plexiform neurofibroma of the foot and ankle
Authors: Pu Lee L.Q. , Vasconez Henry C.
Published: January 2004

Plexiform neurofibroma often causes significant pain, deformity, and functional problems in the affected part of the body. Surgical management of the condition can be challenging, and local recurrence is common because of inadequate resection of the tumor. One patient with a large recurrent plexiform neurofibroma of the foot and ankle was treated successfully with a complete resection of the tumor, followed by a free latissimus dorsi muscle transfer with a skin graft for soft‐tissue reconstruction. The patient has regained good contour of the foot and ankle, and has been symptom‐free with no evidence of local recurrence in the affected area for 18 months. The authors believe that thorough preoperative planning and state‐of‐the‐art reconstructions, as described here, are the keys to their success. © 2003 Wiley‐Liss, Inc.
Combined free‐tissue transfer for primary reconstruction of radial part of the hand
Authors: Rui Yongjun , Shou Kuishui , Zhang Quanrong , Xu Yajun , Sun Zhenzhong , Xu Lei
Published: January 2004

This paper presents 14 cases of primary reconstruction of radial‐part hand defect by combined free‐tissue transfer. The thumb was reconstructed by wraparound flap or second‐toe transfer, while a lateral upper‐arm flap or anterolateral thigh flap was transferred to cover the soft‐tissue defect of the radial part of the hand. The arteries of the toe and flap were anastomosed and cascaded with the radial artery in an anatomical “snuffbox.” Fourteen toes and 13 flaps survived in 14 cases. Only one flap was lost. Two‐point discrimination of thumb tips was between 4–8 mm. The results suggest that combined free‐tissue transfer appears to be a promising way of reconstructing a defect of the radial part of the hand. © 2004 Wiley‐Liss, Inc.
Insights into the interactions between a drug and a membrane protein target by fluorine cross‐polarization magic angle spinning NMR
Authors: Boland Martin P. , Middleton David A.
Published: January 2004

The fluorinated anti‐psychotic drug trifluoperazine (TFP) has been shown to be a K+‐competitive inhibitor of gastric H+/K+‐ATPase, a membrane‐embedded therapeutic target for peptic ulcer disease. This paper describes how variable contact time 19F cross‐polarization magic angle spinning (VCT‐CP/MAS) NMR has been used to probe the inhibitory interactions between TFP and H+/K+‐ATPase in native gastric membranes. The 19F CP/MAS spectra for TFP in H+/K+‐ATPase enriched (GI) gastric membranes and in control membranes containing less than 5 nmol of the protein indicated that the drug associates with the membranes independently of the presence of H+/K+‐ATPase. The 19F peak intensities in the VCT‐CP/MAS experiment confirmed that TFP undergoes slow dissociation (koff < 100 s−1) from binding sites in GI membranes, and more rapid dissociation (koff < 100 s−1) from control membranes. The spectra showed that up to 40% of bound TFP was displaced from GI membranes by 100 mM K+ and by the K+‐competitive inhibitor TMPIP, but TFP was not displaced from the control membranes. Hence the spectra of TFP in GI membranes represent the drug bound to the K+‐competitive inhibitory site of H+/K+‐ATPase and to other non‐specific sites. The affinity of TFP for the K+‐competitive site (KD = 4 mM) was determined from a binding curve of 19F peak intensity versus TFP concentration after correction for non‐specific binding. The KD was much higher than the IC50 for ATPase inhibition (8 µM), which suggests that the substantial non‐specific binding of TFP to the membranes contributes to ATPase inhibition. This novel approach to probing ligand binding can be applied to a wide range of membrane‐embedded pharmaceutical targets, such as G‐protein coupled receptors and ion channels, regardless of the size of the protein or strength of binding. Copyright © 2004 John Wiley & Sons, Ltd.
Peptide‐related alterations of membrane‐associated water: deuterium solid‐state NMR investigations of phosphatidylcholine membranes at different hydration levels
Authors: Mendonça Moraes Cléria , Bechinger Burkhard
Published: January 2004

Deuterated water associated with oriented POPC bilayers was investigated before and after the addition of 2 mol% peptide. Membranes in the presences of antimicrobial‐(LAH4), pore‐forming‐ (the segments M2 of influenza A and S4 of the domain I of rat brain sodium channels) or lysine‐containing model peptides (LAK1 and LAK3) were investigated by 2H and proton‐decoupled 31P solid‐state NMR. The NMR spectra were recorded as a function of hydration in the range between 15 and 93% relative humidity and of sample composition. In the presence of peptides an increased association of water is observed. A quantitative analysis suggests that the peptide‐induced changes in the lipid bilayer packing have a significant effect on membrane–water association. The quadrupolar splittings of 2H2O at a given degree of hydration indicate that the changes of the water deuterium order parameter are specific for the peptide sequence and the lipid composition. Copyright © 2004 John Wiley & Sons, Ltd.
Solid‐state 2H NMR studies of the effects of cholesterol on the acyl chain dynamics of magnetically aligned phospholipid bilayers
Authors: Tiburu Elvis K. , Dave Paresh C. , Lorigan Gary A.
Published: January 2004

We report the utilization of magnetically aligned phospholipid bilayers (bicelles) to study the effects of cholesterol in phospholipid bilayers for both chain perdeuterated DMPC and partially deuterated α‐[2,2,3,4,4,6‐d6]‐cholesterol using 2H solid‐state NMR spectroscopy. The quadrupolar splittings at 40°C were 25.5 and 37.7 kHz, respectively, for the 2,4‐2Heq and 2,4‐2Hax deuterons when the bilayer normal of the discs was aligned perpendicular to the static magnetic field. The quadrupolar splittings were doubled when Yb3+ ions were added to flip the bicelles 90° such that the bilayer normal was colinear with the magnetic field. The results suggest that cholesterol is incorporated into the bicelle discs. For chain perdeuterated DMPC‐d54, incorporated into DMPC–DHPC bicelle discs, the individual quadrupolar splittings of the methylene and methyl groups doubled on going from the perpendicular to the parallel alignment. Also, the presence of cholesterol increased the overall ordering of the acyl chains of the phospholipids. SCDi calculations were extracted directly from the 2H quadrupolar splittings of the chain perdeuterated DMPC. The order parameter, SCDi, calculations clearly indicated an overall degree of ordering of the acyl chains in the presence of cholesterol. We also noted a disordering effect at higher temperatures. This study demonstrates the ease with which 2H order parameters can be calculated utilizing magnetically aligned phospholipid bilayers when compared with randomly dispersed membrane samples. Copyright © 2004 John Wiley & Sons, Ltd.
Site‐directed 13C solid‐state NMR studies on membrane proteins: strategy and goals toward revealing conformation and dynamics as illustrated for bacteriorhodopsin labeled with [1‐13C]amino acid residues
Authors: Saitô Hazime , Mikami Jun , Yamaguchi Satoru , Tanio Michikazu , Kira Atushi , Arakawa Tadashi , Yamamoto Kazutoshi , Tuzi Satoru
Published: January 2004

We have so far demonstrated that well‐resolved and site‐specifically assigned 13C peaks as recorded by site‐directed NMR study on 13C‐labeled membrane proteins can serve as a convenient probe to reveal their local conformation and dynamics. We attempted here to clarify the extent to which 13C NMR spectra of 13C‐labeled fully hydrated bacteriorhodopsin (bR) as a typical membrane protein are visible or well resolved in the presence of inherent fluctuation motions with frequency of 102–108 Hz, especially at the membrane surfaces. Accordingly, we estimated the relative proportion of 13C NMR signals from the surface areas with and without peak suppression by the accelerated transverse relaxation effect by surface‐bound Mn2+ ions, which could be effective for residues within 8.7 Å of the membrane surface. It turned out that the experimental findings are consistent with the predicted amount of amino acid residues under consideration located within 8.7 Å of the surface for [1‐13C]Val‐ and Ile‐labeled bR and also [3‐13C]Ala‐bR. In contrast, 13C NMR peaks from such surfaces area are almost completely or partially suppressed for [1‐13C]Gly‐, Ala‐, Leu‐, Phe‐ and Trp‐labeled bR, as a result of plausible interference of the fluctuation frequency with frequency of magic angle spinning (104 Hz). We further assigned several 13C NMR signals of [1‐13C] Val‐, Trp‐ and Ile‐labeled bR on the basis of a variety of site‐directed mutants with reference to those of the wild type. Further, we recorded the 13C NMR of bR in lipid bilayers to search for the optimal conditions to be able to obtain signals with the highest peak intensities and spectral resolution. Backbone dynamics turn out to be essential for recording 13C NMR spectra so as to escape from motional frequencies of the order of 104–105 Hz, either in the direction of accelerated fluctuation or slowed motions in the direction of forming the 2D array. Copyright © 2004 John Wiley & Sons, Ltd.
The αM1 transmembrane segment of the nicotinic acetylcholine receptor interacts strongly with model membranes
Authors: de Planque Maurits R. R. , Rijkers Dirk T. S. , Liskamp Rob M. J. , Separovic Frances
Published: January 2004

The transmembrane domain of the nicotinic acetylcholine receptor (nAChR) plays a role in the regulation of the activity of this important ligand‐gated ion channel. The lipid composition of the host membrane affects conformational equilibria of the nAChR and several classes of inhibitors, most notably anaesthetics, interact directly or indirectly with the four transmembrane M‐segments, M1–M4, of the nAChR subunits. It has proven difficult to gain insight into structure–function relationships of the M‐segments in the context of the entire receptor and the biomembrane environment. However, model membrane systems are well suited to obtain detailed information about protein–lipid interactions. In this solid‐state NMR study, we characterized interactions between a synthetic αM1 segment of the T. californica nAChR and model membranes of different phosphatidylcholine (PC) lipids. The results indicate that αM1 interacts strongly with PC bilayers: the peptide orders the lipid acyl chains and induces the formation of small vesicles, possibly through modification of the lateral pressure profile in the bilayer. The multilamellar vesicle morphology was stabilized by the presence of cholesterol, implying that either the rigidity or the bilayer thickness is a relevant parameter for αM1–membrane interactions, which also has been suggested for the entire nAChR. Our results suggest that the model systems are to a certain extent sensitive to peptide–bilayer hydrophobic matching requirements, but that the lipid response to hydrophobic mismatch alone is not the explanation. The effect of αM1 on different PC bilayers may indicate that the peptide is conformationally flexible, which in turn would support a membrane‐mediated modulation of the conformation of transmembrane segments of the nAChR. Copyright © 2004 John Wiley & Sons, Ltd.
Effects of antidepressants on the conformation of phospholipid headgroups studied by solid‐state NMR
Authors: Santos Jose S. , Lee Dong‐Kuk , Ramamoorthy Ayyalusamy
Published: January 2004

The effect of tricyclic antidepressants (TCA) on phospholipid bilayer structure and dynamics was studied to provide insight into the mechanism of TCA‐induced intracellular accumulation of lipids (known as lipidosis). Specifically we asked if the lipid–TCA interaction was TCA or lipid specific and if such physical interactions could contribute to lipidosis. These interactions were probed in multilamellar vesicles and mechanically oriented bilayers of mixed phosphatidylcholine–phosphatidylglycerol (PC–PG) phospholipids using 31P and 14N solid‐state NMR techniques. Changes in bilayer architecture in the presence of TCAs were observed to be dependent on the TCA's effective charge and steric constraints. The results further show that desipramine and imipramine evoke distinguishable changes on the membrane surface, particularly on the headgroup order, conformation and dynamics of phospholipids. Desipramine increases the disorder of the choline site at the phosphatidylcholine headgroup while leaving the conformation and dynamics of the phosphate region largely unchanged. Incorporation of imipramine changes both lipid headgroup conformation and dynamics. Our results suggest that a correlation between TCA‐induced changes in bilayer architecture and the ability of these compounds to induce lipidosis is, however, not straightforward as imipramine was shown to induce more dramatic changes in bilayer conformation and dynamics than desipramine. The use of 14N as a probe was instrumental in arriving at the presented conclusions. Copyright © 2004 John Wiley & Sons, Ltd.
Precision 1H–1H distance measurement via 13C NMR signals: utilization of 1H–1H double‐quantum dipolar interactions recoupled under magic angle spinning conditions
Authors: Matsuki Yoh , Akutsu Hideo , Fujiwara Toshimichi
Published: January 2004

We applied the POST‐C7 DQ‐dipolar recoupling pulse sequence to the measurement of 1H–1H distances with high precision. The spectral resolution is enhanced by detecting the 1H magnetization via 13C signals. A least‐squares fitting of the build‐up curve of the transferred magnetization to the exact numerical simulations yielded a 1Hα–1Hβ distance of 248 ± 4 pm for fully 13C‐labeled L‐valine. This distance agrees with the neutron diffraction study. The negative transferred magnetization clearly indicates that the direct DQ 1H–1H dipolar couplings have the largest effect. The signal for the magnetization transfer builds up rapidly by the direct 1H–1H dipolar coupling, and decreases to zero at longer mixing time when the relayed magnetization transfer becomes significant. This large intensity change of the signal leads to the high precision in the distance measurement. We inspected factors that limit the effective bandwidth of the POST‐C7 recoupling for the 1H and 13C homonuclear spin systems. The spin interactions at times shorter than the cycle time of the C7 sequence were also evaluated to measure the distances. The carbon‐detected 2D 1H DQ mixing experiment was demonstrated for the measurement of multiple 1H–1H distances. Copyright © 2004 John Wiley & Sons, Ltd.
Multi‐dimensional pulsed field gradient magic angle spinning NMR experiments on membranes
Authors: Gaede Holly C. , Gawrisch Klaus
Published: January 2004

The benefits of gradient techniques in the study of lipid membranes are demonstrated on a sample of 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3 phosphocholine (POPC) liposomes embedded with ibuprofen. Most techniques from gradient NMR spectroscopy on solution samples are directly applicable to membrane samples subjected to magic angle spinning (MAS). Gradient‐enhanced homo‐ and heteronuclear chemical shift correlation techniques were used to make resonance assignments. Gradient NOESY experiments provide insight into the location and dynamics of lipids, ibuprofen and water. Application of gradients not only reduces experiment time but also the t1 noise in the multi‐dimensional spectra. Diffusion measurements with pulsed field gradients characterize lateral movements of lipid and drug molecules in membranes. The theoretical framework for data analysis of MAS diffusion experiments on randomly oriented multilamellar liposomes is presented. Published in 2004 by John Wiley & Sons, Ltd.
A solid‐state NMR study of the fast and slow dynamics of collagen fibrils at varying hydration levels
Authors: Reichert Detlef , Pascui Ovidiu , deAzevedo Eduardo R. , Bonagamba Tito J. , Arnold Klaus , Huster Daniel
Published: January 2004

We report solid‐state NMR investigations of the effect of temperature and hydration on the molecular mobility of collagen isolated from bovine achilles tendon. 13C cross‐polarization magic angle spinning (MAS) experiments were performed on samples at natural abundance, using NMR methods that detect motionally averaged dipolar interactions and chemical shift anisotropies and also slow reorientational processes. Fast motions with correlation times much shorter than 40 µs scale dipolar couplings and chemical shift anisotropies of the carbon sites in collagen. These motionally averaged anisotropic interactions provide a measure of the amplitudes of the segmental motions expressed by a molecular order parameter. The data reveal that increasing hydration has a much stronger effect on the amplitude of the molecular processes than increasing temperature. In particular, the Cγ carbons of the hydroxyproline residues exhibit a strong dependence of the amplitude of motion on the hydration level. This could be correlated with the effect of hydration on the hydrogen bonding structure in collagen, for which this residue is known to play a crucial role. The applicability of 1D MAS exchange experiments to investigate motions on the millisecond time‐scale is discussed and first results are presented. Slow motions with correlation times of the order of milliseconds have also been detected for hydrated collagen. Copyright © 2004 John Wiley & Sons, Ltd.
NMR methods for studying the structure and dynamics of oncogenic and antihistaminic peptides in biomembranes
Authors: Sizun Christina , Aussenac Fabien , Grelard Axelle , Dufourc Erick J.
Published: January 2004

We present several applications of both wide‐line and magic angle spinning (MAS) solid‐state NMR of bicelles in which are embedded fragments of a tyrosine kinase receptor or enkephalins. The magnetically orientable bicelle membranes are shown to be of particular interest for studying the functional properties of lipids and proteins in a state that is very close to their natural environment. Quadrupolar, dipolar and chemical shielding interactions can be used to determine minute alterations of internal membrane dynamics and the orientation of peptides with respect to the membrane plane. MAS of bicelles can in turn lead to high‐resolution proton spectra of hydrated membranes. Using deuterium–proton contrast methods one can then obtain pseudo‐high‐resolution proton spectra of peptides or proteins embedded in deuterated membranes and determine their atomic 3D structure using quasi‐conventional liquid‐state NMR methods. Copyright © 2004 John Wiley & Sons, Ltd.
Structural role of tyrosine in Bombyx mori silk fibroin, studied by solid‐state NMR and molecular mechanics on a model peptide prepared as silk I and II
Authors: Asakura Tetsuo , Suita Kohei , Kameda Tsunenori , Afonin Sergii , Ulrich Anne S.
Published: January 2004

The influence of the bulky and H‐bonding Tyr side‐chain on its Ala‐ and Gly‐rich environment in Bombyx mori silk fibroin was examined by 13C cross‐polarization magic angle spinning (CP/MAS), static 2H and 19F NMR and molecular mechanics calculations. Model peptides of the type (AG)15 were synthesized with Tyr in a number of different positions, precipitated under conditions favoring either of the two characteristic protein conformations, and the resulting structures were assigned from their 13C chemical shifts. Dialysis of native fibroin or the simple (AG)15 peptide from a 9 M LiBr solution against water produces silk I (the structure of silk before spinning), whereas drying from formic acid yields silk II (fibrous structure after spinning). We found that the introduction one or more Tyr into (AG)15 can have a dramatic effect not only on the local backbone conformation but also on the long‐range intermolecular chain packing in the samples. The antiparallel β‐sheet conformation of silk II is able readily to accommodate a single Tyr residue. Interestingly, the β‐turn conformation of silk I only remains stable when Tyr is positioned near the chain terminus in (AG)12YG(AG)2, but the conformation is driven towards silk II when Tyr is located in the central region of (AG)7YG(AG)7. The role of H‐bonding was tested by replacing Tyr with Phe or 4F‐Phe, which are no longer compatible with silk I and fully induced a silk II conformation. In the presence of several Tyr residues a mixture of distorted β‐sheet and β‐turn conformations was obtained, regardless of the precipitation conditions. Static 2H NMR of ring‐deuterated [3′,5′‐2H2]Tyr located in the central region of (AG)7YG(AG)7 showed that the side‐chain is immobilized in both silk I and II, which was also observed by static 19F NMR of the 4F‐Phe analogue. To visualize the local packing around the Tyr side‐chain, molecular mechanics calculations were performed on a mixture of (AG)4 and AGAGYGAG, starting from either the β‐turn type II or the antiparallel β‐sheet structure. The resulting structures show that the intermolecular chain arrangement is significantly affected by Tyr, thus explaining the long‐range packing effects in the semi‐crystalline regions of silk fibers compared with the crystalline regions that are devoid of Tyr. Copyright © 2004 John Wiley & Sons, Ltd.
Improved pulse sequences for pure exchange solid‐state NMR spectroscopy
Authors: Vosegaard Thomas , Nielsen Niels C.
Published: January 2004

Spin‐exchange experiments are useful for improving the resolution and establishment of sequential assignments in solid‐state NMR spectra of uniformly 15N‐labeled proteins oriented macroscopically in phospholipid bilayers. To exploit this advantage fully, it is crucial that the diagonal peaks in the two‐dimensional exchange spectra are suppressed. This may be accomplished using the recent pure‐exchange (PUREX) experiments, which, however, suffer from up to a threefold reduction of the cross‐peak intensity relative to experiments without diagonal‐peak suppression. This loss in sensitivity may severely hamper the applicability for the study of membrane proteins. In this paper, we present a two‐dimensional exchange experiment (iPUREX) which improves the PUREX sensitivity by 50%. The performance of iPUREX is demonstrated experimentally by proton‐mediated 15N–15N spin‐exchange experiments for a 15N‐labeled N‐acetyl‐L‐valyl‐L‐leucine dipeptide. The relevance of exchange experiments with diagonal‐peak suppression for large, uniformly 15N‐labeled membrane proteins in oriented phospholipid bilayers is demonstrated numerically for the G‐protein coupled receptor rhodopsin. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis of polybutadiene‐based particles via dispersion ring‐opening metathesis polymerization
Authors: Chemtob Abraham , Héroguez Valérie , Gnanou Yves
Published: January 2004

Latex particles based on 1,4‐polybutadiene were synthesized via dispersion ring‐opening metathesis copolymerization of 1,5‐cyclooctadiene with a α‐norbornenyl poly(ethylene oxide) macromonomer. Stable but polydisperse colloidal dispersions in the 50 nm to 10 μm size range were obtained. In this work, particular attention was paid to the effects of the kinetics of copolymerization on the structure of the graft copolymers formed and on the onset of turbidity. Strategies to prepare monodisperse polybutadiene particles were also designed through the growth of a polybutadiene shell from a well‐defined polynorbornene seed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1154–1163, 2004
Synthesis of ultra‐high‐molecular‐weight poly(α‐olefin)s by thiobis(phenoxy)titanium/modified methylaluminoxane system
Authors: Fujita Masayuki , Seki Yoshinori , Miyatake Tatsuya
Published: January 2004

Polymerization of 1‐butene with thiobis(phenoxy)titanium dichloride (TBPTiCl2) with modified methylaluminoxane (MMAO) yielded atactic and regioirregular poly(1‐butene) with low molecular weight. However, productivity was increased and the yielded polymer structure was changed when water‐modified MMAO (WM‐MMAO) was used as a cocatalyst. The molecular weight of obtained polymer with TBPTiCl2/WM‐MMAO was dramatically increased and reached over 9 million g/mol. Poly(1‐butene) produced by this catalytic system was almost regioregular and slightly isotactic. 1‐Hexene and 1‐octene were also polymerized by this catalytic system. In all cases, the ultra‐high‐molecular‐weight polymers were obtained. These results showed that the modified structure of the MMAO cluster by water affects the productivity, molecular weight, regioregularity, and stereoregularity of yielded polyolefins. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1107–1111, 2004
The effect of compositions and combinations of the reactants upon the copolycondensation of isophthalic acid/terephthalic acid with a combination of hydroquinones and bisphenols by tosyl chloride/dimethylformamide/pyridine
Authors: Higashi Fukuji , Koyanagi Sakura
Published: January 2004

Copolycondensation of isophthalic acid (IPA)/terephthalic acid (TPA) with various combinations of 2,2‐bis(4‐hydroxyphenyl)propane (BPA) and hydroquinones (HQs) or bisphenols (BPs) was conducted to study the effects of the compositions of IPA/TPA and of BPA/HQs or BPA/BPs upon the reaction. Different from homopolycondensation of each of diol components examined where most of the reaction was facilitated by lower contents of IPA at about 70 mol %, the copolycondensation was influenced by a combination of diol components. With chlorohydroquinone (ClHQ) or bis(4‐hydroxyphenyl)sulfone (BPS) having a polar chlorine or sulfonyl substituent, the reaction proceeded most satisfactorily at IPA/TPA = 30/70, whereas it was IPA/TPA = 50/50 for the reaction with nonpolar methyl substituted methylhydroquinone (MeHQ). The reaction with 2,2‐bis(3,5‐dichloro‐4‐hydroxyphenyl)propane (TC‐BPA), despite having polar chlorine substituents in TC‐BPA, was not affected by IPA/TPA compositions. Alternatively, from the viewpoint of the compositions of diol components, the reactions containing 30–50 mol % of HQs or BPS yielded better results except for the reaction of IPA/TPA = 70/30, in which higher contents of MeHQ was more favorable. On the basis of sequence distributions of diol components in the resultant copolymers determined by NMR, compositions of IPA/TPA or diol components and combinations of the diols producing random copolymers yielded better results in copolycondensation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1100–1106, 2004
Effects of tris(pentafluorophenyl)borane on the activation of a metal alkyl‐free Ni‐based catalyst in the polymerization of 1,3‐butadiene
Authors: Jang Youngchan , Choi Dai Seung , Han Shin
Published: January 2004

The activation of a metal alkyl‐free Ni‐based catalyst with B(C6F5)3 was investigated in the polymerization of 1,3‐butadiene. A catalyst of bis(1,5‐cyclooctadiene)nickel (Ni(COD)2)/B(C6F5)3 was found to have high catalytic activity and 1,4‐cis stereoregularity. The catalyst was also found to provide polybutadiene having a molecular weight (Mw) of up to 117,000, even in the absence of AlR3 and MAO. Variations in the mol ratio of B(C6F5)3 to Ni affected catalytic activity, 1,4‐cis stereoregularity, and the Mw of polybutadiene, while the molecular weight distribution (MWD) of polybutadiene showed little correlation with the mol ratio of B(C6F5)3 to Ni. The use of other borane compounds such as B(C6H5)3, BEt3, and BF3 etherate in place of B(C6F5)3 clearly showed the two main functions of B(C6F5)3 in the present catalyst. The high Lewis acidity of B(C6F5)3 enabled it to activate catalytic complexes, thus inducing the polymerization. The steric bulkiness of B(C6F5)3 suppressed chain transfer reactions, contributing to the production of polybutadiene with a high Mw. Kinetic studies showed that the catalyst had an induction period, possibly due to the time needed for the formation of catalytic complexes starting from Ni(COD)2. A plot of −ln (1−X), where X is the fractional conversion, as a function of time resulted in a linear relationship, showing that the present catalyst system followed first‐order kinetics with respect to monomer concentration. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1164–1173, 2004
Amphiphilic block copolymers of high‐molecular‐weight poly(ethylene oxide) and either ε‐caprolactone or γ‐methyl‐ε‐caprolactone: Synthesis and characterization
Authors: Vangeyte P. , Jérôme R.
Published: January 2004

Ethylene oxide (EO) has been block‐polymerized with both ε‐caprolactone (ε‐CL) and γ‐methyl‐ε‐caprolactone (MCL) through the combination of the anionic polymerization of EO and the ring‐opening polymerization (ROP) of ε‐CL and MCL. ω‐Hydroxyl poly(ethylene oxide) has been reacted with triethylaluminum (OH/Al = 1) and converted into a macroinitiator for ROP of ε‐CL and MCL. In toluene at room temperature, this polymerization leads to a bimodal molecular weight distribution as a result of monomer insertion in only some of the aluminum alkoxide bonds. However, in a more polar solvent (methylene chloride) added with 1 equiv of a Lewis base (pyridine), the expected diblock is formed selectively, and this indicates that aggregation of the active species in toluene is responsible for a macroinitiator efficiency of less than 1. A series of amphiphilic diblock copolymers with poly(ε‐caprolactone) (semicrystalline) and poly(γ‐methyl‐ε‐caprolactone) (amorphous) as the hydrophobic blocks have been prepared and characterized with size exclusion chromatography,1H NMR, IR, and wide‐angle X‐ray scattering. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1132–1142, 2004
Properties of double‐hydrophilic graft copolymers with a polyacetal backbone
Authors: Baśko Małgorzata , Kubisa Przemysław
Published: January 2004

Graft copolymers consisting of the polyacetal backbone substituted with COO− groups and poly(oxyethylene) (POE) side chains in different proportions were synthesized, and their efficiency as modifiers of the processes occurring at the interphase between inorganic particles and the surrounding aqueous phase was studied. The series of double hydrophilic graft copolymers (DHGC) was obtained differing in the length of the main chain, the number of carboxylate groups, and the number of POE side chains in the macromolecule. Studies of the effect of DHGC on the stability of aqueous calcium carbonate (CaCO3) suspensions and on the shape and size of the CaCO3 crystals formed in the presence of DHGC allowed us to draw some conclusions concerning the effect of the structure of DHGC on their efficiency as modifiers of the processes occurring at the interphase between inorganic particles and the surrounding aqueous phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1189–1197, 2004
Silicone‐based impact modifiers for poly(vinyl chloride), engineering resins, and blends
Authors: Yanagase Akira , Ito Masakazu
Published: January 2004

Silicone‐based impact modifiers were prepared in a previous study. The modifiers were composed of silicone/acrylic rubber cores and grafted acrylic shells. They improved the toughness of poly(vinyl chloride) (PVC) and poly(methyl methacrylate). The silicone emulsion that was used to produce the silicone‐based impact modifiers was prepared via two routes: emulsion polymerization and bulk polymerization of octamethyltetracyclosiloxane. Many silicone‐based impact modifiers were produced that had different silicone/acrylic rubber characteristics. Through a toughness examination of modified PVC, the best composition of the silicone‐based impact modifiers was obtained, and the silicone content in the rubber composition was 25 wt %. The morphology of the silicone‐based impact modifiers, determined by transmission electron microscopy, was as follows: core and second shell polymers were mainly poly(butyl acrylate), and the first shell polymer was silicone. The silicone‐based impact modifiers were blended with engineering resins such as PVC, polycarbonate (PC), poly(butylene terephthalate) (PBT), and PC/PBT mixtures. The impact strength under standard conditions and after weathering test conditions for blends of the silicone‐based impact modifiers were investigated with respect to two commercially available acrylic and methyl methacrylate/butadiene/styrene impact modifiers. The results showed good weatherability and good toughness under low‐temperature conditions for the silicone‐based impact modifiers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1112–1119, 2004
Effect of the crosslink density on the morphology and properties of reaction‐injection‐molding poly(urethane urea) elastomers
Authors: Li Zaifeng , Yang Guanghua , Xu Chunming
Published: January 2004

The effect of the crosslink density on the morphology and properties of reaction‐injection‐molding poly(urethane urea) (PUU) elastomers was investigated. Fourier transform infrared spectroscopy data showed that the linear and crosslinked PUU had entirely different hard‐domain sizes and hard‐segment ordering. A study of the morphology indicated that an increase in the crosslink density increased microphase mixing. Differential scanning calorimetry studies indicated that the hard‐segment initial glass‐transition temperature was independent of the crosslink density. The glass‐transition temperature of the soft segment was highest when the network was perfect. The tensile‐strength behavior showed that the mechanical properties of PUU reached a maximum when the network was perfect. The increase in the resilience of the crosslinked PUU elastomer was higher than that of the linear PUU elastomer with an increase in temperature, and the reduction of the hardness of the former was also higher than that of the latter. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1126–1131, 2004
Performance of various activators in ethylene polymerization based on an iron(II) catalyst system
Authors: Wang Qi , Yang Huaxiang , Fan Zhiqiang , Xu Hong
Published: January 2004

Ethylisobutylaluminoxane (EBAO) and its analogues were synthesized by a reaction between an triethylaluminum (Et3Al)/triisobutylaluminum (i‐Bu3Al) mixture and 4‐fluorobenzeneboronic acid, phenylboronic acid, or n‐butaneboronic acid and subsequent hydrolysis with water. They were used as cocatalysts in ethylene polymerization catalyzed by an iron complex {[(ArNC(Me))2C5H3N]FeCl2, where Ar is 2,6‐diisopropylphenyl}. Polyethylene with a high molecular weight and a narrow molecular weight distribution was prepared with modified EBAOs, and the performance of the iron complex at high polymerization temperatures was greatly improved. The activators for the iron complex also affected the polymerization activity and the molecular weight of the resultant polyethylene. It was suggested that the stereo and electronic effects of the substitute groups of aluminoxane contributed to the improved performance of the new activators. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1093–1099, 2004
New blue electroluminescent n‐type polyfluorene copolymers with a 1,3,4‐oxadiazole unit in the main chain
Authors: Yang Nam Choul , Lee Sang Min , Yoo Young Man , Kim Jai Kyeong , Suh Dong Hack
Published: January 2004

Novel polyfluorene copolymers alternately having an 1,3,4‐oxadiazole unit in the main chain were prepared by both one‐step and two‐step methods for polyoxadiazole synthesis. They displayed highly efficient blue photoluminescence, the properties of which were affected by the extent of conjugation and the changes in the electron density by a side chain. An electrochemical analysis of the polymers using cyclic voltammetry suggested that they could be used as electron‐transport/hole‐blocking materials as well as blue emission materials for polymer light‐emitting diodes. A simple double‐layer device consisting of poly(N‐vinylcarbazole) as a hole‐transport layer and poly[(9,9′‐didodecylfluorene‐2,7‐diyl)‐alt‐((1,4‐bis(1,3,4‐oxadiazole)‐2,5‐di(2‐ethylhexyloxy)phenylene)‐5,5′‐diyl)] as an emission layer exhibited narrow blue electroluminescence with a maximum at 430 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1058–1068, 2004