bluuebunny/crossref_metadata_2025 huggingface dataset:
Rational Strategies for Directed Evolution of Biocatalysts –Application to Candida antarctica lipase B (CALB)
Authors: Chodorge Matthieu , Fourage Laurent , Ullmann Christophe , Duvivier Vincent , Masson Jean‐Michel , Lefèvre Fabrice
Published: June 2005

Provided that the industrial constraints have been properly defined, the directed evolution technologies available today enable one to design tailor‐made enzymes and biocatalytic routes for chemical processes. Family shuffling has proved to be a successful strategy using traditional recombination protocols. However, when starting from a single gene, the first step is to create the appropriate population of parental genes to ensure an efficient recombination during gene shuffling. Our recent work focused on the determination of rational directed evolution strategies that can be applied for the creation of an improved biocatalyst within the requested industrial timelines. For this purpose, we have developed a rational approach that first explores the “protein plasticity” (ability of the protein to accept mutations with a limited loss of activity) of the enzyme, which enables us to estimate (i) the “optimal mutation load” (number of mutations introduced per gene that gives the highest frequency of improved variants) and (ii) the “ad minima size sample” (minimal number of clones to be screened) that can be used to rapidly improve this enzyme. We have then applied this approach to create in a few weeks variants of the well known lipase B with a seven fold improvement in thermostability.
Recent Advances in the Oligosaccharide Synthesis Promoted by Catalytically Engineered Glycosidases
Authors: Perugino Giuseppe , Cobucci‐Ponzano Beatrice , Rossi Mosè , Moracci Marco
Published: June 2005

In oligosaccharide synthesis the chemo‐enzymatic approach is often chosen to obtain the desired glycosidic bond by exploiting the exquisite substrate specificity and stereoselectivity of glycosidases and glycosyltransferases. In recent years the invention of new enzymatic activities, named glycosynthases, created a third route for the enzymatic synthesis of oligosaccharides. Glycosynthases are mutant glycosidases, devoid of hydrolytic activity, that produce oligosaccharides with yields >80%. The glycosynthase technology is now well established and was greatly improved recently. Several groups experimentally proved that this methodology can be applied to several glycosidases and that the activity of existing glycosynthases can be significantly enhanced. In this review we briefly describe the characteristics of these synthetic tools and show a survey of the most recent findings. Methods for the prediction of the glycosynthetic potential of known glycosidases are also discussed.
Recombinant Chlorobenzene Dioxygenase from Pseudomonas sp. P51: A Biocatalyst for Regioselective Oxidation of Aromatic Nitriles
Authors: Yildirim Selcuk , Franko Telma T. , Wohlgemuth Roland , Kohler Hans‐Peter E. , Witholt Bernard , Schmid Andreas
Published: June 2005

An efficient biocatalyst was developed for the cis‐dihydroxylation of aromatic nitriles. The chlorobenzene dioxygenase (CDO) genes of Pseudomonas sp. strain P51 were cloned under the strict control of the Palk promoter of Pseudomonas putida GPo1. Escherichia coli JM101 cells carrying the resulting plasmid pTEZ30 were used for the biotransformation of benzonitrile in a 2‐L stirred tank bioreactor. Use of a stable expression system resulted in an average specific activity and an average volumetric productivity of 1.47 U/g cdw and 120 mg of product/h/L, respectively. The values represent a three‐fold increase compared to the results of the similar biotransformations with E. coli JM101 (pTCB144) where the genes of CDO were expressed under the control of lac promoter. The productivity of the cis‐dihydroxylation process was limited by product toxicity. Removal of the products at toxic concentrations by means of an external charcoal column resulted in an additional increase in product concentration by 43%. E. coli JM101 (pTEZ30) was further used for the regio‐ and stereospecific dihydroxylations of various monosubstituted benzonitriles, benzyl cyanide, and cinnamonitrile. Biotransformations resulted in products with 42.9–97.1% enantiomeric excess. Initial enzymatic activities and isolated yields were obtained in the range of 1.7–4.7 U/g cdw and of 3–62%, respectively.
Analysis of mode transitions in biological networks
Authors: El‐Farra Nael H. , Gani Adiwinata , Christofides Panagiotis D.
Published: May 2005

This work presents a methodology for the analysis of mode transitions in biological networks. The proposed approach is predicated on the notion of orchestrating switching between the domains of attraction of the steady states of the constituent modes. Initially, the overall network is modeled as a switched nonlinear system that consists of multiple modes, each governed by a set of continuous‐time differential equations. The transitions between the continuous modes are triggered by discrete events (changes in model parameters that correspond to alterations in physiological conditions). Then, following the characterization of the steady‐state behavior of each mode, Lyapunov techniques are used to characterize the domains of attraction of the steady states. Finally, by analyzing how the domains of attraction of the various modes overlap with one other, a switching rule is derived to determine when, and if, a given mode transition at a given time results in the desired steady‐state behavior. The proposed method is demonstrated using models of biological networks that arise in cell cycle regulation and the bacteriophage λ‐switch system. © 2005 American Institute of Chemical Engineers AIChE J, 2005
Mirrorless optical bistability in molecular aggregates with dipole–dipole interaction
Authors: Gusev V. V.
Published: May 2005

The possibility of mirrorless optical bistability in molecular aggregates with dipole–dipole interaction was studied theoretically. Dimers and ordered layers of the Langmuir–Blodgett type or J‐aggregates consisting of identical polyatomic fluorescent molecules were chosen as molecular aggregate models. The investigation was carried out on the basis of the Bogolubov equation chain for the density matrix of molecular aggregates and its components. It is shown that the fluorescence intensity and absorption ability are described by bistable and hysteresislike behaviour when the parameters of the molecular aggregate and pumping radiation are chosen suitably. An analysis of the bistability mechanism in such aggregates is given. Possibilities of controlling one light beam by another and switching polychromatic light flow by using a bistable device based on molecular aggregates are discussed.
Scanning tunnelling microscopy investigations of self‐assembled monolayers of poly(3‐decyl‐thiophene) on graphite
Authors: Bonfiglio Annalisa , Paradiso Rita , Di Zitti Ermanno , Ricci Davide , Bolognesi Alberto , Porzio William
Published: May 2005

The self‐assembly technique experimented for the deposition of alkanes and alkyl derivatives on layered compounds at the liquid/solid interface has been successfully extended to the adsorption of poly(3‐decyl‐thiophene) on graphite. The molecular films so obtained have been investigated using scanning tunnelling microscopy (STM). Images taken in both the constant‐current and constant‐height modes show highly packed arrays of molecules characterised by an average length and an average spacing that are in good agreement with results obtained by X‐ray diffraction investigations. Constant‐current images allow one to observe domain formations in preferential directions coincident with the main axes of the graphite lattice, while constant‐height imaging, performed on small areas, allows one to resolve atomic structures within the polymer backbone. In particular, periodic, 0.71 nm spaced features have been identified along the side of the polymer backbone; they can be associated with the length of two monomer units and are attributable to imaging of sulphur atoms in the backbone.
Langmuir–Blodgett films of indandione‐1,3 pyridinium betaine. I: Preparation, electronic structure, optical properties
Authors: Rutkis M. A. , Gerca L. E. , Silinsh E. A. , Neilands O. Y. , Roze M. P. , Berzinsh E. L. , Klimkans A. B. , Larsson S.
Published: May 2005

The synthesis of a new polar amphiphilic derivative of indandione‐1,3 pyridinium betaine (IPB) with different lengths of the aliphatic tail, containing 11 (C11IPB) and 17 (C17IPB) carbon atoms respectively, is described. The electronic structure (charge distribution, energy spectra, dipole moments in ground and excited states) of the IPB molecule has been calculated in the framework of the MO CNDO methods. Studies of compression π‐A isotherms of these compounds show that C17IPB forms two stable phases of monolayer on the water surface, one in the 10–30 mN m−1 and the other in the 35–50 nM m−1 surface pressure region. The corresponding areas A0 per molecule are 37 and 33 Å2 respectively. Techniques for the preparation of Langmuir‐Blodgett (LB) multilayers of C17IPB in the high‐pressure region (π = 40 mN m−1) on glass, quartz or sapphire substrates are described. C17IPB forms LB multilayer films of Z‐type configuration with oriented dipole moments. Ellipsometric data, luminescence spectra and results of preliminary studies of second‐harmonic generation in these LB films are presented.
In situ optical monitoring of the movpe growth of ZnSe on GaAs
Authors: Hayashi Keiji , Yoshino Junji , Kukimoto Hiroshi
Published: May 2005

In situ optical reflection measurement was employed to study surface processes during the MOVPE growth of ZnSe films under an alternate supply of diethylzinc (DEZn) and dimethylselenide (DMSe) using H2 and/or N2 as carrier gases. We have found that the time‐dependent reflection signal exhibits a unique saw‐toothed pattern during the DEZn supply, which is attributed to the adsorption and structural change of the DEZn. In contrast, the influence of DMSe on the time‐dependent signal appears to be rather marginal. A growth mechanism is proposed based on these experimental results, through which the important role of ambient hydrogen is discussed.
Growth modes of solution‐grown CdS thin films
Authors: Sebastian P. J. , Hu Hailin , Fernández A. M.
Published: May 2005

The growth modes of CdS thin films on glass in a chemical bath were analysed using scanning electron microscopy and optical microscopy. The results of these studies show that the film growth occurs by ion‐by‐ion condensation and by colloidal particles of CdS adhering to the substrate. Both mechanisms are operative from the initial stages of film growth. The predominance of one or other of these two growth modes depends on the abundance of Cd and S ions present in the solution, which is determined by the amount of complexing and sulphurising agents and ammonia used for the controlled release of Cd and S ions into the solution. The growth mode influences the optical properties of the films.
Cerebral hypoperfusion and clinical onset of dementia: The Rotterdam study
Authors: Ruitenberg Annemieke , den Heijer Tom , Bakker Stef L. M. , van Swieten John C. , Koudstaal Peter J. , Hofman Albert , Breteler Monique M. B.
Published: May 2005

Cerebral blood flow (CBF) velocity is decreased in patients with Alzheimer's disease. It is being debated whether this reflects diminished demand because of advanced neurodegeneration or that cerebral hypoperfusion contributes to dementia. We examined the relation of CBF velocity as measured with transcranial Doppler with dementia and markers of incipient dementia (ie, cognitive decline and hippocampal and amygdalar atrophy on magnetic resonance imaging) in 1,730 participants of the Rotterdam Study aged 55 years and older. Cognitive decline in the 6.5 years preceding CBF velocity measurement was assessed with repeated Mini‐Mental State Examinations in nondemented subjects (n = 1,716). Hippocampal and amygdalar volumes were assessed in a subset of 170 nondemented subjects. Subjects with greater CBF velocity were less likely to have dementia. Furthermore, in nondemented subjects, greater CBF velocity was related to significantly less cognitive decline over the preceding period (odds ratio per standard deviation increase in mean CBF 0.74 [95% confidence interval, 0.58–0.98]) and larger hippocampal and amygdalar volumes. A low CBF is associated with dementia, but also with markers of incipient dementia. Although we cannot exclude that this is caused by preclinical neurodegeneration leading to hypoperfusion, it does suggest that cerebral hypoperfusion precedes and possibly contributes to onset of clinical dementia. Ann Neurol 2005;57:789–794
Introducing an active cluster‐based information retrieval paradigm
Authors: Loureiro Oscar , Siegelmann Hava
Published: June 2005

When a client interacts with an expert, e.g., a doctor, it falls upon the expert to ask questions that steer the process towards fulfilling the client's needs. This is most efficient given that the expert has more knowledge and a broader view of possible illnesses and treatments. On the other hand, when faced with an information retrieval (IR) task, most IR systems leave to the client the task of coming up with queries. We propose an information retrieval framework that assumes the responsibility of leading the users to the information, thus increasing efficiency and satisfaction.
User‐process model approach to improve user interface usability
Authors: Ju Boryung , Gluck Myke
Published: June 2005

Our purpose in this study is to inductively reorganize software interface menu items based on a user's process model. The proposed menu interface in this study used direct users' input, such as goals and strategies for solving their information needs, to reorganize and re‐label menus. To assess its effectiveness, efficiency, and user satisfaction with actual users, we implemented and compared this new menu version to the original interface that was based upon a traditional categorical menu organization. The significance of this study is that it incorporates user process modeling into the design of the user interface, providing insights into the impact of such modeling on the usability of an information system. Results from the usability testing do indicate that the proposed menu and the traditional menu are similarly effective for users in terms of task completion time and accuracy. User preferences and debriefing comments from usability testing also indicate users preferred the user‐process based arrangement of menu items as displayed. However, the types of tasks (different problem type) suggest significant differences for results in task completion time and in accuracy, sometimes favoring the new version. In other words, usable and effective menu organization depends more on the types of tasks and the domain of knowledge than mere menu organization, although menu organization is a factor in the process.
Use of the z‐transform to investigate nanopulse penetration of biological matter
Authors: Su S. , Dai Weizhong , Haynie Donald T. , Simicevic N.
Published: June 2005

Short duration, fast rise time electromagnetic ultra‐wideband (UWB) pulses (“nanopulses”) are generated by numerous electronic devices. Many new technologies involving nanopulses are under development and expected to become widely available soon. Study of nanopulse bioeffects therefore is needed to ensure human safety and to probe the useful range of nanopulses in possible biomedical and biotechnological applications. In this article, we present a new approximation of the Cole–Cole expression for the frequency dependence of the dielectric properties of tissues. The approximation is based on a z‐transformation of the electric displacement and a second‐order Taylor approximation of the Cole–Cole expression. The approach has been applied to investigating the penetration of nanopulses into biological matter as a function of the dielectric properties of tissue and pulse width. Solutions to Maxwell's equations are calculated using the finite difference time domain method (FDTD). Bioelectromagnetics 26:389–397, 2005. © 2005 Wiley‐Liss, Inc.
Antenna modeling considerations for accurate SAR calculations in human phantoms in close proximity to GSM cellular base station antennas
Authors: van Wyk Marnus J. , Bingle Marianne , Meyer Frans J.C.
Published: June 2005

International bodies such as International Commission on Non‐Ionizing Radiation Protection (ICNIRP) and the Institute for Electrical and Electronic Engineering (IEEE) make provision for human exposure assessment based on SAR calculations (or measurements) and basic restrictions. In the case of base station exposure this is mostly applicable to occupational exposure scenarios in the very near field of these antennas where the conservative reference level criteria could be unnecessarily restrictive. This study presents a variety of critical aspects that need to be considered when calculating SAR in a human body close to a mobile phone base station antenna. A hybrid FEM/MoM technique is proposed as a suitable numerical method to obtain accurate results. The verification of the FEM/MoM implementation has been presented in a previous publication; the focus of this study is an investigation into the detail that must be included in a numerical model of the antenna, to accurately represent the real‐world scenario. This is accomplished by comparing numerical results to measurements for a generic GSM base station antenna and appropriate, representative canonical and human phantoms. The results show that it is critical to take the disturbance effect of the human phantom (a large conductive body) on the base station antenna into account when the antenna‐phantom spacing is less than 300 mm. For these small spacings, the antenna structure must be modeled in detail. The conclusion is that it is feasible to calculate, using the proposed techniques and methodology, accurate occupational compliance zones around base station antennas based on a SAR profile and basic restriction guidelines. Bioelectromagnetics 26:502–509, 2005. © 2005 Wiley‐Liss, Inc.
Solution structure of χ‐conopeptide MrIA, a modulator of the human norepinephrine transporter
Authors: Nilsson K. Peter R. , Lovelace Erica S. , Caesar Christina E. , Tynngård Nahreen , Alewood Paul F. , Johansson Helena M. , Sharpe Iain A. , Lewis Richard J. , Daly Norelle L. , Craik David J.
Published: June 2005

The χ‐conopeptides MrIA and MrIB are 13‐residue peptides with two disulfide bonds that inhibit human and rat norepinephrine transporter systems and are of significant interest for the design of novel drugs involved in pain treatment. In the current study we have determined the solution structure of MrIA using NMR spectroscopy. The major element of secondary structure is a β‐hairpin with the two strands connected by an inverse γ‐turn. The residues primarily involved in activity have previously been shown to be located in the turn region (Sharpe, I. A.; Palant, E.; Schroder, C. I.; Kaye, D. M.; Adams, D. J.; Alewood, P. F.; Lewis, R. J. J Biol Chem 2003, 278, 40317–40323), which appears to be more flexible than the β‐strands based on disorder in the ensemble of calculated structures. Analogues of MrIA with N‐terminal truncations indicate that the N‐terminal residues play a role in defining a stable conformation and the native disulfide connectivity. In particular, noncovalent interactions between Val3 and Hyp12 are likely to be involved in maintaining a stable conformation. The N‐terminus also affects activity, as a single N‐terminal deletion introduced additional pharmacology at rat vas deferens, while deleting the first two amino acids reduced χ‐conopeptide potency. © 2005 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 80: 815–823, 2005

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Clinical significance of Ki-67 proliferation index in disease progression and prognosis of patients with resected colorectal carcinoma
Authors: Valera V , Yokoyama N , Walter B , Okamoto H , Suda T , Hatakeyama K
Published: June 2005

Background

The prognostic role of proliferation markers in patients with colorectal neoplasia is inconclusive. The aim of this study was to evaluate proliferation markers in patients with colorectal carcinoma, to relate these to standard clinicopathological findings and to investigate their potential role in the prediction of long-term survival.

Methods

Archived formalin-fixed, paraffin-embedded tissue samples from a cohort of 106 patients who underwent curative resection for colorectal carcinoma were analysed to determine a Ki-67 (MIB-1)-derived proliferation index (PI) using a double immunostaining technique. The relationship between PI and standard clinicopathological variables was assessed and its association with long-term survival evaluated.

Results

A significant association was found between PI and tumour (T) status (P = 0·001), lymph node (N) involvement (P = 0·0098), the presence of distant metastases (P < 0·010) and advanced stage of disease (P < 0·001). On multivariate analysis, PI was shown to be an independent prognostic factor for long-term survival (hazard ratio 2·1 (95 per cent confidence interval 1·1 to 4·1); P = 0·032).

Conclusion

Cell proliferation is significantly associated with tumour progression and may be used to identify patients with a predicted adverse outcome after resection of colorectal carcinoma.
Improvement in survival following surgery for colorectal cancer
Authors: McArdle C S , McKee R F , Finlay I G , Wotherspoon H , Hole D J
Published: June 2005

Background

Recent reports based on registry data have shown that survival after surgery for colorectal cancer is improving in the UK. It is not clear whether these improvements are due to earlier presentation or more effective treatment.

Methods

Outcome for 645 patients with colorectal cancer admitted to Glasgow Royal Infirmary between 1974 and 1979 was compared with that for 354 patients admitted between 1991 and 1994.

Results

More patients in the later period had Dukes' A or B tumours and fewer had evidence of metastatic spread (P < 0·001); more underwent potentially curative resection (57·6 versus 49·9 per cent; P < 0·001) and fewer underwent palliative diversion. The overall postoperative mortality rate fell from 14·1 to 8·5 per cent (P = 0·017). Overall and cancer-specific 5-year survival after potentially curative resection increased from 40·1 to 60·5 per cent and from 47·3 to 71·7 per cent respectively (both P < 0·001). Compared with the earlier period, the adjusted hazard ratio for cancer-specific survival following potentially curative resection was 0·452 (95 per cent confidence interval 0·329 to 0·622; P < 0·001).

Conclusion

The observed improvement in survival was mainly due to improvements in the quality of surgery and in perioperative care rather than earlier presentation.
Accuracy of computed tomography in the detection of blunt bowel and mesenteric injuries
Authors: Elton C , Riaz A A , Young N , Schamschula R , Papadopoulos B , Malka V
Published: June 2005

Background

There are conflicting views on the accuracy of computed tomography (CT) findings in patients with bowel and mesenteric injuries (BMIs) following blunt abdominal trauma. The aim of the present study was to assess the accuracy of the CT report during a trauma call.

Methods

Ninety-eight patients underwent preoperative abdominal spiral CT and subsequent laparotomy following blunt trauma between January 1996 and March 2001 at a level I trauma centre. The immediate results of the scans were reported by the on-call radiology registrar and written in the medical notes by the trauma team leader. Seventy of the 98 preoperative abdominal CT scans were retrieved from the radiology department and reported by two consultant radiologists with a special interest in trauma radiology.

Results

The sensitivity and specificity of the 70 expert CT reports were 80 (95 per cent confidence interval (c.i.) 66 to 94) and 78 (95 per cent c.i. 65 to 90) per cent respectively for diagnosing a BMI. The sensitivity and specificity of the immediate CT reports were 93 (95 per cent c.i. 84 to 100) and 71 (95 per cent c.i. 60 to 83) per cent respectively.

Conclusion

Spiral CT is highly sensitive for detecting a BMI following blunt abdominal trauma. This sensitivity is maintained when the scan is reported by a radiology registrar.
Incidence and management of pancreatic leakage after pancreatoduodenectomy
Authors: de Castro S M M , Busch O R C , van Gulik T M , Obertop H , Gouma D J
Published: June 2005

Background

Optimal management of severe pancreatic leakage after pancreatoduodenectomy can reduce morbidity and mortality. Completion pancreatectomy may be adequate but leads to endocrine insufficiency. This study evaluated an alternative management strategy for pancreatic leakage.

Methods

Outcome after disconnection of the jejunal limb, resection of the pancreatic body and preservation of a small pancreatic remnant, performed between 1997 and 2002, was compared with that after completion pancreatectomy performed between 1992 and 1996.

Results

Pancreatoduodenectomy was performed in 459 consecutive patients. Pancreatic leakage occurred in 41 patients (8·9 per cent); its incidence did not change over the study period. Non-surgical drainage procedures were performed in 14 patients, of whom one died, and surgical drainage in eight patients, of whom two died. Completion pancreatectomy was performed in nine patients with no deaths. A pancreatic remnant was preserved in ten patients, of whom three died. A remnant tail had to be resected in two patients and three patients still developed endocrine insufficiency (‘brittle’ diabetes).

Conclusion

The incidence of pancreatic leakage did not change over the study interval. Preservation of a small pancreatic tail was associated with higher morbidity and mortality rates than those of completion pancreatectomy.
Randomized clinical trial comparing regional and general anaesthesia in minimally invasive video-assisted parathyroidectomy
Authors: Miccoli P , Barellini L , Monchik J M , Rago R , Berti P F
Published: June 2005

Background

This randomized clinical trial was performed in a single institution to compare the results of minimally invasive video-assisted parathyroidectomy (MIVAP) conducted under regional anaesthesia (RA) or general anaesthesia (GA).

Methods

Fifty-one patients undergoing MIVAP for primary hyperparathyroidism were assigned randomly to either RA (26 patients) or GA (25). RA involved a bilateral deep cervical block, and local infiltration of the incision site with a mixture of 0·25 per cent lignocaine and 0·15 per cent bupivacaine. GA was induced by intravenous administration of propofol, remifentanil and rocuronium bromide.

Results

The two groups were matched for age, sex, adenoma size, and preoperative serum calcium and parathyroid hormone levels. The interval from skin incision to closure was similar in the two groups (27·6 and 25·8 min for RA and GA respectively), whereas the total operating time (from induction of anaesthesia to return to the ward) was significantly lower with RA (72·1 versus 90·2 min; P = 0·001). The postoperative requirement for pain medication, measured in terms of amount of ketorolac administered at the request of the patient, was significantly lower in the RA group (28·5 versus 80 mg/day; P < 0·001).

Conclusion

MIVAP performed under RA was associated with a shorter overall operating time and a reduced need for postoperative pain relief.
Electronic structure of Zn‐chlorin π‐anions studied by spectroscopic and quantum‐chemical methods
Authors: Shulga A. M. , Sinyakov G. N. , Filatov I. V. , Gurinovich G. P. , Dzilinski K.
Published: May 2005

Electronic structure of neutral Zn‐chlorin complexes and their π‐mono‐ and dianions has been considered. The π‐anions were obtained by reduction of neutral chlorins with a sodium mirror in tetrahydrofuran solution. Results of spectroscopic studies have been compared with semiempirical quantum‐chemical calculations. Characteristic bands in electronic absorption spectra of the uv, visible and near infrared regions are in good agreement with CNDO/S‐CI calculations. Partially resolved hyperfine structure in EPR spectra of π‐radical anions was observed. Parameters of the EPR spectra obtained by using the simulation technique were compared with spin densities calculated by the INDO method. The detailed interpretation of 1H and 13C NMR spectra of neutral and dianion Zn‐octaethylchlorins is presented. All the proton signals in π‐dianions are shifted upfield because of the influence of paramagnetic ring current. The upfield shifts in 13C NMR spectra of the species studied have been observed too, except for two carbon atoms of the pyrrole ring being placed opposite the hydrogenated one. The 13C peak positions correlate with the charge distribution on C atoms in neutral molecules as well as in π‐dianions. © 1995 John Wiley & Sons, Inc.
Water Cluster Growth in Hydrophobic Solid Nanospaces
Authors: Ohba Tomonori , Kanoh Hirofumi , Kaneko Katsumi
Published: June 2005

The growth mechanism of water clusters in carbon nanopores is clearly elucidated by in situ small‐angle X‐ray scattering (SAXS) studies and grand canonical Monte Carlo (GCMC) simulations at 293–313 K. Water molecules are isolated from each other in hydrophobic nanopores below relative pressures (P/P0) of 0.5. Water molecules associate with each other to form clusters of about 0.6 nm in size at P/P0=0.6, accompanied by a remarkable aggregation of these clusters. The complete filling of carbon nanopores finishes at about P/P0=0.8. The correlation length analysis of SAXS profiles leads to the proposal of a growth mechanism for these water clusters and the presence of the critical cluster size of 0.6 nm leads to extremely stable clusters of water molecules in hydrophobic nanopores. Once a cluster of the critical size is formed in hydrophobic nanopores, the predominant water adsorption begins to fill carbon nanopores.
Gadolinium(III)‐Loaded Nanoparticulate Zeolites as Potential High‐Field MRI Contrast Agents: Relationship Between Structure and Relaxivity
Authors: Csajbók Éva , Bányai István , Vander Elst Luce , Muller Robert N. , Zhou Wuzong , Peters Joop A.
Published: June 2005

The effects of dealumination, pore size, and calcination on the efficiency (as expressed in the relaxivity) of Gd3+‐loaded zeolites for potential application as magnetic resonance imaging (MRI) contrast agents were studied. Partial dealumination of zeolites NaY or NaA by treatment with (NH4)2SiF6 or diluted HCl resulted in materials that, upon loading with Gd3+, had a much higher relaxivity than the corresponding non‐dealuminated materials. Analysis of the 1H NMR dispersion profiles of the various zeolites showed that this can be mainly ascribed to an increase of the amount of water inside the zeolite cavities as a result of the destruction of walls between cavities. However, the average residence time of water inside the Gd3+‐loaded cavities did not change significantly, which suggests that the windows of the Gd3+‐loaded cavities are not affected by the dealumination. Upon calcination, the Gd3+ ions moved to the small sodalite cavities and became less accessible for water, resulting in a decrease in relaxivity. The important role of diffusion for the relaxivity was demonstrated by a comparison of the relaxivity of Gd3+‐loaded zeolite NaY and NaA samples. NaA had much lower relaxivities due to the smaller pore sizes. The transversal relaxivities of the Gd3+‐doped zeolites are comparable in magnitude to the longitudinal ones at low magnetic fields (<60 MHz). However at higher fields, the transversal relaxivities steeply increased, whereas the longitudinal relaxivities decreased as field strength increased. Therefore, these materials have potential as T1 MRI contrast agents at low field, and as T2 agents at higher fields.
Probing Molecular Wires: Synthesis, Structural, and Electronic Study of Donor–Acceptor Assemblies Exhibiting Long‐Range Electron Transfer
Authors: Giacalone Francesco , Segura José L. , Martín Nazario , Ramey Jeff , Guldi Dirk M.
Published: June 2005

A series of donor–acceptor arrays (C60–oligo‐PPV–exTTF; 16–20) incorporating π‐conjugated oligo(phenylenevinylene) wires (oligo‐PPV) of different length between π‐extended tetrathiafulvalene (exTTF) as electron donor and C60 as electron acceptor has been prepared by multistep convergent synthetic approaches. The electronic interactions between the three electroactive species present in 16–20 were investigated by UV‐visible spectroscopy and cyclic voltammetry (CV). Our studies clearly show that, although the C60 units are connected to the exTTF donors through a π‐conjugated oligo‐PPV framework, no significant electronic interactions are observed in the ground state. Interestingly, photoinduced electron‐transfer processes over distances of up to 50 Å afford highly stabilized radical ion pairs. The measured lifetimes for the photogenerated charge‐separated states are in the range of hundreds of nanoseconds (∼500 ns) in benzonitrile, regardless of the oligomer length (i.e., from the monomer to the pentamer). A different lifetime (4.35 μs) is observed for the heptamer‐containing array. This difference in lifetime has been accounted for by the loss of planarity of the oPPV moiety that increases with the wire length, as established by semi‐empirical (PM3) theoretical calculations carried out with 19 and 20. The charge recombination dynamics reveal a very low attenuation factor (β=0.01±0.005 Å−1). This β value, as well as the strong electron coupling (V∼5.5 cm−1) between the donor and the acceptor units, clearly reveals a nanowire behavior for the π‐conjugated oligomer, which paves the way for applications in nanotechnology.
Amino Acid Catalyzed Neogenesis of Carbohydrates: A Plausible Ancient Transformation
Authors: Córdova Armando , Ibrahem Ismail , Casas Jesús , Sundén Henrik , Engqvist Magnus , Reyes Efraim
Published: June 2005

Hexose sugars play a fundamental role in vital biochemical processes and their biosynthesis is achieved through enzyme‐catalyzed pathways. Herein we disclose the ability of amino acids to catalyze the asymmetric neogenesis of carbohydrates by sequential cross‐aldol reactions. The amino acids mediate the asymmetric de novo synthesis of natural L‐ and D‐hexoses and their analogues with excellent stereoselectivity in organic solvents. In some cases, the four new stereocenters are assembled with almost absolute stereocontrol. The unique feature of these results is that, when an amino acid is employed as the catalyst, a single reaction sequence can convert a protected glycol aldehyde into a hexose in one step. For example, proline and its derivatives catalyze the asymmetric neogenesis of allose with >99 % ee in one chemical manipulation. Furthermore, all amino acids tested catalyzed the asymmetric formation of natural sugars under prebiotic conditions, with alanine being the smallest catalyst. The inherent simplicity of this catalytic process suggests that a catalytic prebiotic “gluconeogenesis” may occur, in which amino acids transfer their stereochemical information to sugars. In addition, the amino acid catalyzed stereoselective sequential cross‐aldol reactions were performed as a two‐step procedure with different aldehydes as acceptors and nucleophiles. The employment of two different amino acids as catalysts for the iterative direct aldol reactions enabled the asymmetric synthesis of deoxysugars with >99 % ee. In addition, the direct amino acid catalyzed C2+C2+C2 methodology is a new entry for the short, highly enantioselective de novo synthesis of carbohydrate derivatives, isotope‐labeled sugars, and polyketide natural products. The one‐pot asymmetric de novo syntheses of deoxy and polyketide carbohydrates involved a novel dynamic kinetic asymmetric transformation (DYKAT) mediated by an amino acid.
Cooperative Recognition of C60–Ammonium Substrates by a Ditopic Oligophenylenevinylene/Crown Ether Host
Authors: Elhabiri Mourad , Trabolsi Ali , Cardinali François , Hahn Uwe , Albrecht‐Gary Anne‐Marie , Nierengarten Jean‐François
Published: June 2005

A new fullerene derivative with an ammonium subunit has been prepared. Its ability to form supramolecular complexes with oligophenylenevinylene derivatives bearing one or two crown ether moieties has been evidenced by electrospray mass spectrometry, and UV‐visible and luminescence spectroscopy experiments. Interestingly, the assembly of the C60–ammonium cation with the oligophenylenevinylene derivative bearing two crown ether moieties leads to the cooperative formation of the 2:1 complex owing to intramolecular fullerene–fullerene interactions.
Immunomodulation with interferon‐gamma and colony‐stimulating factors for refractory fungal infections in patients with leukemia
Authors: Dignani M. Cecilia , Rex John H. , Chan Ka‐Wah , Dow Gordon , deMagalhaes‐Silverman Margarida , Maddox AnneMarie , Walsh Thomas , Anaissie Elias
Published: June 2005

BACKGROUND

Invasive fungal infections (IFI) in immunocompromised patients are associated with significant morbidity and mortality, despite appropriate antifungal treatment and recovery from neutropenia. The outcome of these infections depends significantly on the overall state of immunosuppression, including mainly the phagocytic system (neutrophils and macrophages). Interferon‐gamma (IFN‐γ), granulocyte‐colony—stimulating factor (G‐CSF) and granulocyte‐macrophage—colony‐stimulating factor (GM‐CSF) are cytokines that enhance the activity of neutrophils and macrophages.

METHODS

The authors reported 4 patients with leukemia and refractory invasive candidiasis or trichosporonosis despite 1–13 months of appropriate antifungal treatment.

RESULTS

Cytokines were administered for 1.5–5 months without significant toxicity. For each patient, initiation of interferon‐gamma plus a colony‐stimulating factor resulted in a clinical response. The contribution of cytokines to control the fungal infection in these 4 patients was suggested by the strong inflammatory reaction observed in the 2 patients who had an immediate response (within 7 days of initiation of cytokine therapy) and by the good outcome in the 2 other patients in whom antifungal agents were discontinued at the start of cytokine therapy.

CONCLUSIONS

These data suggested a potential role for immunomodulation in patients with leukemia with refractory invasive fungal infections. Cancer 2005. Published 2005 by the American Cancer Society.
Bis(salicylaldiminato)titanium Complexes Containing Bulky Imine Substituents: Synthesis, Characterization and Ethene Polymerization Studies
Authors: Pärssinen Antti , Luhtanen Tommi , Klinga Martti , Pakkanen Tapani , Leskelä Markku , Repo Timo
Published: June 2005

A series of titanium complexes bearing two anionic [N, O–] bidentate salicylaldiminato ligands, namely bis[(N‐salicylidene)anilinato]titanium(IV) dichloride (1), bis[(N‐salicylidene)‐2,6‐dimethylanilinato]titanium(IV) dichloride (2), bis[(N‐salicylidene)‐2,6‐di‐i‐ propylanilinato]titanium(IV) dichloride (3), bis[(N‐salicylidene)‐(1‐naphthalenylimino)]titanium(IV) dichloride (4), bis[(N‐salicylidene)‐2,6‐difluoroanilinato]titanium(IV) dichloride (5), and bis[(N‐3‐fluorosalicylidene)‐2,6‐difluoroanilinato]titanium(IV) dichloride (6) have been synthesized with good yields by a two‐step procedure. The X‐ray structure analysis reveals that in complex 2, titanium has a distorted octahedral coordination sphere in which the oxygen atoms and the chloride ligands form the basal plane. Both the chloride and the phenoxy moieties have a cis orientation and the angle between the chloride ligands is 93.05°. The imine nitrogen atoms complete the octahedral coordination of the Ti center by occupying the axial positions. The newly synthesized (2 and 4–6) and already known complexes (1 and 3) were introduced in detailed ethene‐polymerization studies. The activities achieved were low to moderate depending on the size and nature of the imino substituents. The polyethenes (PEs) produced had high molar masses, and the modalities of the molecular weight distributions varyied with polymerization temperature. Based on the results of ab initio calculations and on the experimental data obtained, an explanation for uni‐ and bimodal polymerization behavior and the differences in catalytic activities are given. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Lanthanide(III) Chelates of DTPA Bis(amide) Glycoconjugates: Potential Imaging Agents Targeted at the Asyaloglycoprotein Receptor
Authors: Baía Paula , André João P. , Geraldes Carlos F. G. C. , Martins José A. , Merbach André E. , Tóth Éva
Published: June 2005

The synthesis and characterisation of a new class of DTPA bis(amide) linked glycoconjugates of different sugars [lactose (Lac) and galactose (Gal)] and valencies (di and tetra) and their LnIII complexes is reported. The 1H NMR spectra of the SmIII and EuIII complexes of DTPAGal2, DTPAGal4, and DTPALac2, obtained between 7 and 80 °C, indicate that several of the four possible diastereoisomeric pairs of structures resulting from the chirality of the three bound DTPA nitrogen atoms are present in solution, with different relative populations. The dynamic effects of racemisation of the central nitrogen atom in the NMR spectra show that this process is fast at 60 °C for the SmIII complexes and slow at 7 °C for the EuIII complexes. The in vitro r1 nuclear magnetic relaxation dispersion (NMRD) of the water protons of the GdIII–DTPA bis(amide) glycoconjugate containing two lactosyl moieties [GdIII–DTPALac2] was studied, yielding the molecular parameters that govern its relaxivity. Its r1 value, at 25 °C and 20 MHz, is 13 % higher than that reported for GdIII chelates of lower molecular weight DTPA bis(amides), such as DTPA‐BMA, consistent with a five times larger τR value. The water exchange rate, kex, and the electron spin relaxation parameters of the GdIII–DTPALac2 complex are within the usual range for similar GdIII–DTPA bis(amide) chelates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Crystallographic and Electrochemical Characteristics ofLa0.7Mg0.3Ni4.5–x(Al0.5Mo0.5)x (x = 0–0.8) Hydrogen Storage Alloys
Authors: Zhang Xin‐Bo , Sun Dan‐Zi , Yin Wen‐Ya , Chai Yu‐Jun , Zhao Min‐Shou
Published: June 2005

The structure, hydrogen storage property, and electrochemical characteristics of the La0.7Mg0.3Ni4.5–x(Al0.5Mo0.5)x (x = 0, 0.2, 0.4, 0.6, 0.8) hydrogen storage alloys have been investigated systematically. The X‐ray powder diffraction and Rietveld analysis results reveal that all the alloys mainly consist of the La(La, Mg)2Ni9 phase and the LaNi5 phase. The electrochemical measurements show that the maximum discharge capacity increases first from 246.3 (x = 0) to 345.4 mAh/g (x = 0.6) and then decreases to 317.6 mAh/g (x = 0.8), which is consistent with the variation of the hydrogen storage capacity indicated by the P‐C isotherms. For the discharge current density of 1200 mA/g, the high‐rate dischargeability of the alloy electrodes increases linearly from 47.2 % (x = 0) to 73.8 % (x = 0.8). Moreover, according to the linear polarization curves, the exchange current density of the alloy electrodes also increases monotonously with increasing x. The hydrogen diffusion coefficient increases with increasing Al and Mo content, and thus increases the low‐temperature dischargeability of the alloy electrodes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Electrochemical Synthesis and Structural Characterisation of Cadmium and Mercury Complexes Containing Pyrimidine‐2‐thionate Ligands
Authors: Rodríguez Antonio , Sousa‐Pedrares Antonio , García‐Vázquez José A. , Romero Jaime , Sousa Antonio
Published: June 2005

The electrochemical oxidation of anodic metal (cadmium or mercury) in a cell containing an acetonitrile solution of the appropriate pyrimidine‐2‐thione (RpymSH) affords complexes [M(RpymS)2] (M = Cd, Hg; R = 4‐CF3, 4,6‐CF3,Me and 4,6‐CF3,Ph). When 2,2'‐bipyridine (bipy) or 1,10‐phenanthroline (phen) was added to the electrolytic cell, adducts of cadmium and compounds with these coligands were obtained. All the compounds have been characterised by microanalysis, IR spectroscopy and, in the case of the compounds that were sufficiently soluble, by 1H, 13C and 199Hg NMR spectroscopy. The compounds [Cd(4‐CF3pymS)2] (1), [Cd(4,6‐CF3MepymS)2(bipy)] (4), [Cd(4,6‐CF3PhpymS)2(phen)] (6) and [Hg(4,6‐CF3MepymS)2] (8) were also characterised by X‐ray diffraction. Compound 1 presents a polymeric structure with the polymer chains interconnected by intermolecular C–H···N interactions. Compounds 4 and 6 adopt mononuclear structures, with weak inter‐ and intramolecular C–H···π interactions, as well as π–π stacking interactions for compound 6. Compound 8 also presents a mononuclear structure with intermolecular π–π interactions between the pyrimidine rings and additional weak Hg···Hg contacts (3.484 Å). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
A New Spherical Metallacryptate Compound [Na{Cu6(Thr)8(H2O)2(ClO4)4}]·ClO4·5 H2O: Magnetic Properties and DFT Calculations
Authors: Xiang Sheng‐Chang , Hu Sheng‐Min , Zhang Jian‐Jun , Wu Xin‐Tao , Li Jun‐Qian
Published: June 2005

The hexanuclear copper(II) complex with threoninato acid has been synthesized. Its structure can be described as an octahedron cage with D2h symmetry in which six copper ions are bound by eight threoninato acids with a [3.11223130] coordination mode and one Na+ cation being captured within the center of the cage. In contrast with other hexanuclear copper compounds containing amino acids, the title compound has a prolate Cu6 octahedron with the longest axial distance and a rectangle equatorial plane, as well as special coordinated perchlorate ions. Compared with classic cryptate, hexanuclear copper(II) compounds with amino acids can be regarded as a new topologic type of spherical macrotricyclic metallacryptates [2,2,2,2] whose cages have a high selectivity for sodium ions. The analysis of magnetic susceptibility data shows that the threoninato compound has a ground state with spin S = 3. The computing coupling constant between the equatorial Cu centers and the axial ones is 4.4 cm–1,calculated by using DFT methods for a model compound. This is close to three known experimental values of 1.39, 0.56 or 0.43 cm–1 for complexes with 4‐hydroxy‐L‐prolinato, L‐prolinato or L‐threoninato acid as ligands, respectively. The dominant ferromagnetic interactions for these complexes can be essentially attributed to the orthogonality between the magnetic orbitals, dxz or dyz orbitals for the equatorial CuII centers and d orbitals for the axial ones. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Surface Segregation in SnO2–Fe2O3 Nanopowders and Effects in Mössbauer Spectroscopy
Authors: Castro Ricardo H. R. , Hidalgo Pilar , Coaquira José A. H. , Bettini Jefferson , Zanchet Daniela , Gouvêa Douglas
Published: June 2005

SnO2–Fe2O3 nanopowders prepared by the polymeric precursor method were studied by combined conventional and high‐resolution techniques. The powders treated at 500 °C were analyzed by EDS local probe associated with HRTEM to directly detect surface segregation of Fe ions onto SnO2 nanoparticles over a broad range of concentrations. The segregation of these ions controls the system microstructure by changing the surface energies and acting as nucleation sites for the formation of a Fe oxide phase (magnetite) at high Fe concentrations. A technologically interesting core–shell‐type particle structure, with a magnetic shell and semiconductor core, was observed for the first time. The influence of the segregated Fe ions in Mössbauer spectra is also addressed as a new proposal for the interpretation of the effects of composition changes in both the bulk and at the interface of particles. In this proposal, the two observed sites in Mössbauer spectra would be independently related to bulk‐substituted and surface‐segregated Fe ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)