bluuebunny/crossref_metadata_2025 huggingface dataset:
A CT‐based analytical dose calculation method for HDR brachytherapy
Authors: Poon Emily , Verhaegen Frank
Published: August 2009

Purpose:

This article presents an analytical dose calculation method for high‐dose‐rate brachytherapy, taking into account the effects of inhomogeneities and reduced photon backscatter near the skin. The adequacy of the Task Group 43 (TG‐43) two‐dimensional formalism for treatment planning is also assessed.

Methods:

The proposed method uses material composition and density data derived from computed tomography images. The primary and scatter dose distributions for each dwell position are calculated first as if the patient is an infinite water phantom. This is done using either TG‐43 or a database of Monte Carlo (MC) dose distributions. The latter can be used to account for the effects of shielding in water. Subsequently, corrections for photon attenuation, scatter, and spectral variations along medium‐ or low‐ inhomogeneities are made according to the radiological paths determined by ray tracing. The scatter dose is then scaled by a correction factor that depends on the distances between the point of interest, the body contour, and the source position. Dose calculations are done for phantoms with tissue and lead inserts, as well as patient plans for head‐and‐neck, esophagus, and MammoSite balloon breast brachytherapy treatments. Gamma indices are evaluated using a dose‐difference criterion of 3% and a distance‐to‐agreement criterion of 2 mm. PTRAN_CT MC calculations are used as the reference dose distributions.

Results:

For the phantom with tissue and lead inserts, the percentages of the voxels of interest passing the gamma criteria are 100% for the analytical calculation and 91% for TG‐43. For the breast patient plan, TG‐43 overestimates the target volume receiving the prescribed dose by 4% and the dose to the hottest of the skin by 9%, whereas the analytical and MC results agree within 0.4%. are 100% and 48% for the analytical and TG‐43 calculations, respectively. For the head‐and‐neck and esophagus patient plans, are for both calculation methods.

Conclusions:

A correction‐based dose calculation method has been validated for HDR brachytherapy. Its high calculation efficiency makes it feasible for use in treatment planning. Because tissue inhomogeneity effects are small and primary dose predominates in the near‐source region, TG‐43 is adequate for target dose estimation provided shielding and contrast solution are not used.
A comparison of HDR brachytherapy and IMRT techniques for dose escalation in prostate cancer: A radiobiological modeling study
Authors: Fatyga M. , Williamson J. F. , Dogan N. , Todor D. , Siebers J. V. , George R. , Barani I. , Hagan M.
Published: August 2009

A course of one to three large fractions of high dose rate (HDR) interstitial brachytherapy is an attractive alternative to intensity modulated radiation therapy (IMRT) for delivering boost doses to the prostate in combination with additional external beam irradiation for intermediate risk disease. The purpose of this work is to quantitatively compare single‐fraction HDR boosts to biologically equivalent fractionated IMRT boosts, assuming idealized image guided delivery (igIMRT) and conventional delivery (cIMRT). For nine prostate patients, both seven‐field IMRT and HDR boosts were planned. The linear‐quadratic model was used to compute biologically equivalent dose prescriptions. The cIMRT plan was evaluated as a static plan and with simulated random and setup errors. The authors conclude that HDR delivery produces a therapeutic ratio which is significantly better than the conventional IMRT and comparable to or better than the igIMRT delivery. For the HDR, the rectal gBEUD analysis is strongly influenced by high dose DVH tails. A saturation BED, beyond which no further injury can occur, must be assumed. Modeling of organ motion uncertainties yields mean outcomes similar to static plan outcomes.
Dual resolution cone beam breast CT: A feasibility study
Authors: Chen Lingyun , Shen Youtao , Lai Chao‐Jen , Han Tao , Zhong Yuncheng , Ge Shuaiping , Liu Xinming , Wang Tianpeng , Yang Wei T. , Whitman Gary J. , Shaw Chris C.
Published: August 2009

Purpose:

In this study, the authors investigated the feasibility of a dual resolution volume‐of‐interest (VOI) cone beam breast CT technique and compared two implementation approaches in terms of dose saving and scatter reduction.

Methods:

With this technique, a lead VOI mask with an opening is inserted between the x‐ray source and the breast to deliver x‐ray exposure to the VOI while blocking x rays outside the VOI. A CCD detector is used to collect the high resolution projection data of the VOI. Low resolution cone beam CT (CBCT) images of the entire breast, acquired with a flat panel (FP) detector, were used to calculate the projection data outside the VOI with the ray‐tracing reprojection method. The Feldkamp–Davis–Kress filtered backprojection algorithm was used to reconstruct the dual resolution 3D images. Breast phantoms with and smaller microcalcifications (MCs) were imaged with both FP and FP‐CCD dual resolution CBCT systems, respectively. Two approaches of implementing the dual resolution technique, breast‐centered approach and VOI‐centered approach, were investigated and evaluated for dose saving and scatter reduction with Monte Carlo simulation using a GEANT4 package.

Results:

The results showed that the breast‐centered approach saved more breast absorbed dose than did VOI‐centered approach with similar scatter reduction. The MCs in fatty breast phantom, which were invisible with FP CBCT scan, became visible with the FP‐CCD dual resolution CBCT scan.

Conclusions:

These results indicate potential improvement of the image quality inside the VOI with reduced breast dose both inside and outside the VOI.
From the limits of the classical model of sensitometric curves to a realistic model based on the percolation theory for GafChromic™ EBT films
Authors: del Moral F. , Vázquez J. A. , Ferrero J. J. , Willisch P. , Ramírez R. D. , Teijeiro A. , Medina A. López , Andrade B. , Vázquez J. , Salvador F. , Medal D. , Salgado M. , Muñoz V.
Published: August 2009

Purpose:

Modern radiotherapy uses complex treatments that necessitate more complex quality assurance procedures. As a continuous medium, GafChromic EBT films offer suitable features for such verification. However, its sensitometric curve is not fully understood in terms of classical theoretical models. In fact, measured optical densities and those predicted by the classical models differ significantly. This difference increases systematically with wider dose ranges. Thus, achieving the accuracy required for intensity‐modulated radiotherapy (IMRT) by classical methods is not possible, plecluding their use. As a result, experimental parametrizations, such as polynomial fits, are replacing phenomenological expressions in modern investigations. This article focuses on identifying new theoretical ways to describe sensitometric curves and on evaluating the quality of fit for experimental data based on four proposed models.

Methods:

A whole mathematical formalism starting with a geometrical version of the classical theory is used to develop new expressions for the sensitometric curves. General results from the percolation theory are also used. A flat‐bed‐scanner‐based method was chosen for the film analysis. Different tests were performed, such as consistency of the numeric results for the proposed model and double examination using data from independent researchers.

Results:

Results show that the percolation‐theory‐based model provides the best theoretical explanation for the sensitometric behavior of GafChromic films. The different sizes of active centers or monomer crystals of the film are the basis of this model, allowing acquisition of information about the internal structure of the films. Values for the mean size of the active centers were obtained in accordance with technical specifications. In this model, the dynamics of the interaction between the active centers of GafChromic film and radiation is also characterized by means of its interaction cross‐section value.

Conclusions:

The percolation model fulfills the accuracy requirements for quality‐control procedures when large ranges of doses are used and offers a physical explanation for the film response.
Matching extended‐SSD electron beams to multileaf collimated photon beams in the treatment of head and neck cancer
Authors: Steel Jared , Stewart Allan , Satory Philip
Published: August 2009

Purpose:

Matching the penumbra of a electron beam to the penumbra of a photon beam is a dose optimization challenge, especially when the electron beam is applied from an extended source‐to‐surface distance (SSD), as in the case of some head and neck treatments. Traditionally low melting point alloy blocks have been used to define the photon beam shielding over the spinal cord region. However, these are inherently time consuming to construct and employ in the clinical situation. Multileaf collimators (MLCs) provide a fast and reproducible shielding option but generate geometrically nonconformal approximations to the desired beam edge definition. The effects of substituting Cerrobend® for the MLC shielding mode in the context of beam matching with extended‐SSD electron beams are the subject of this investigation.

Methods:

Relative dose beam data from a Varian EX 2100 linear accelerator were acquired in a water tank under the electron beam at both standard and extended‐SSD and under the photon beam defined by Cerrobend® and a number of MLC stepping regimes. The effect of increasing the electron beam SSD on the beam penumbra was assessed. MLC stepping was also assessed in terms of the effects on both the mean photon beam penumbra and the intraleaf dose‐profile nonuniformity relative to the MLC midleaf. Computational techniques were used to combine the beam data so as to simulate composite relative dosimetry in the water tank, allowing fine control of beam abutment gap variation. Idealized volumetric dosimetry was generated based on the percentage depth‐dose data for the beam modes and the abutment geometries involved. Comparison was made between each composite dosimetry dataset and the relevant ideal dosimetry dataset by way of subtraction.

Results:

Weighted dose‐difference volume histograms (DDVHs) were produced, and these, in turn, summed to provide an overall dosimetry score for each abutment and shielding type/angle combination. Increasing the electron beam SSD increased the penumbra width (defined as the lateral distance of the 80% and 20% isodose contours) by at the depths of . Mean photon beam penumbra width increased with increased MLC stepping, and the mean MLC penumbra was times greater than that across the corresponding Cerrobend® shielding. Intraleaf dose discrepancy in the direction orthogonal to the beam edge also increased with MLC stepping.

Conclusions:

The weighted DDVH comparison techniques allowed the composite dosimetry resulting from the interplay of the abovementioned variables to be ranked. The MLC dosimetry ranked as good or better than that resulting from beam matching with Cerrobend® for all except large field overlaps ( gap). The results for the linear‐weighted DDVH comparison suggest that optimal MLC abutment dosimetry results from an optical surface gap of around . Furthermore, this appears reasonably lenient to abutment gap variation, such as that arising from uncertainty in beam markup or other setup errors.
Accelerated ray tracing for radiotherapy dose calculations on a GPU
Authors: de Greef M. , Crezee J. , van Eijk J. C. , Pool R. , Bel A.
Published: August 2009

Purpose:

The graphical processing unit (GPU) on modern graphics cards offers the possibility of accelerating arithmetically intensive tasks. By splitting the work into a large number of independent jobs, order‐of‐magnitude speedups are reported. In this article, the possible speedup of PLATO's ray tracing algorithm for dose calculations using a GPU is investigated.

Methods:

A GPU version of the ray tracing algorithm was implemented using NVIDIA's CUDA, which extends the standard C language with functionality to program graphics cards. The developed algorithm was compared based on the accuracy and speed to a multithreaded version of the PLATO ray tracing algorithm. This comparison was performed for three test geometries, a phantom and two radiotherapy planning CT datasets (a pelvic and a head‐and‐neck case). For each geometry, four different source positions were evaluated. In addition to this, for the head‐and‐neck case also a vertex field was evaluated.

Results:

The GPU algorithm was proven to be more accurate than the PLATO algorithm by elimination of the look‐up table for indices that introduces discretization errors in the reference algorithm. Speedups for ray tracing were found to be in the range of 2.1–10.1, relative to the multithreaded PLATO algorithm running four threads. For dose calculations the speedup measured was in the range of 1.5–6.2. For the speedup of both the ray tracing and the dose calculation, a strong dependency on the tested geometry was found. This dependency is related to the fraction of air within the patient's bounding box resulting in idle threads.

Conclusions:

With the use of a GPU, ray tracing for dose calculations can be performed accurately in considerably less time. Ray tracing was accelerated, on average, with a factor of 6 for the evaluated cases. Dose calculation for a single beam can typically be carried out in for clinically realistic datasets. These findings can be used in conventional planning to enable (nearly) real‐time dose calculations. Also the importance for treatment optimization techniques is evident.
Effect of prolonged stimulation on cerebral hemodynamic: A time‐resolved fNIRS study
Authors: Butti Michele , Contini Davide , Molteni Erika , Caffini Matteo , Spinelli Lorenzo , Baselli Giuseppe , Bianchi Anna Maria , Cerutti Sergio , Cubeddu Rinaldo , Torricelli Alessandro
Published: August 2009

Purpose:

Sustained attention is one of the most important cognitive abilities for the management of everyday life, but it is often studied only at the behavioral level, while functional correlates are scarcely investigated. In this article, the authors address the topic of characterizing the dynamics of cerebral metabolism in the prefrontal cortex during a task of prolonged attention.

Method:

By means of multichannel time‐resolved functional near‐infrared spectroscopy and generalized linear model based data processing, the authors measured the hemodynamic response of the prefrontal cortex from 19 healthy subjects to a shortened version of a sustained attention task (Conners’ Continuous Performance Test), lasting for.

Results:

The task elicited significant brain activation, which did not remain constant for the entire task, but showed a drop not correlated with performance decay after the beginning of the task. Furthermore, oxygenated hemoglobin showed an increasing trend also during the first phase of the recovery, just after the end of the task.

Conclusion:

The results indicate a nontrivial dynamics of neural activation, habituation processes, and hemodynamic/metabolic coupling. These results encourage further studies about continuous stimulation of cognitive functions on both healthy and pathological subjects.
‐band EPR imaging as a tool for gradient dose reconstruction in irradiated bones
Authors: Levêque Philippe , Godechal Quentin , Bol Anne , Trompier François , Gallez Bernard
Published: August 2009

Purpose:

Various tools are currently available for dose reconstruction in individuals after accidental exposure to ionizing radiation. Among the available biological analyses, Monte Carlo simulations, and biophysical methods, such as electron paramagnetic resonance (EPR), the latter has proved its usefulness for retrospective dosimetry. Although EPR spectroscopy is probably the most sensitive technique, it does not provide spatial dosimetric data. This information is, however, highly desirable when steep dose gradient irradiations are involved. The purpose of this work was to explore the possibilities of EPR imaging (EPRI) for spatial dose reconstruction in irradiated biological material.

Methods:

‐band EPRI was used to reconstruct ex vivo the relative dose distribution in human bone samples and hydroxyapatite phantoms after irradiation with brachytherapy seeds or x rays. Three situations were investigated: Homogeneous, stepwise gradient, and continuous gradient irradiation.

Results:

EPRI gave a faithful relative spin density distribution in bone samples and in hydroxyapatite phantoms. Measured dose ratios were in close agreement with the actual delivered dose ratios. EPRI was able to distinguish the dose gradients induced by two different sources ( and ). However, the measured spatial resolution of the system was 1.9 mm and this appeared to be a limiting factor. The method could be improved by using new signal postprocessing strategies.

Conclusions:

This study demonstrates that EPRI can be used to assess the regional relative dose distribution in irradiated bone samples. The method is currently applicable toex vivo measurements of small size samples with low variation in tissue density but is likely to be adapted for in vivo application using ‐band EPRI.
A real‐time prostate cancer detection technique using needle insertion force and patient‐specific criteria during percutaneous intervention
Authors: Yan K. , Podder T. , Li L. , Joseph J. , Rubens D. R. , Messing E. M. , Liao L. , Yu Y.
Published: August 2009

In this article, the authors present a novel real‐time cancer detection technique by using needle insertion forces in conjunction with patient‐specific criteria during percutaneous interventions. Needle insertion experiments and pathological analysis were performed for developing a computer‐aided detection (CAD) model. Backward stepwise regression method was performed to identify the statistically significant patient‐specific factors. A baseline force model was then developed using these significant factors. The threshold force model that estimated the lower bound of the cancerous tissue forces was formulated by adding an adjustable classifier to the baseline force model. Trade‐off between sensitivity and specificity was obtained by varying the threshold value of the classifier, from which the receiver‐operating characteristic (ROC) curve was generated. Sequential quadratic programming was used to optimize the CAD model by maximizing the area under the ROC curve (AUC) using a set of model‐training patient data. When the CAD model was evaluated using an independent set of model‐validation patient data, an AUC of 0.90 was achieved. The feasibility of cancer detection in real time during percutaneous interventions was established.
Coat Variation in the Domestic Dog Is Governed by Variants in Three Genes
Authors: Cadieu Edouard , Neff Mark W. , Quignon Pascale , Walsh Kari , Chase Kevin , Parker Heidi G. , VonHoldt Bridgett M. , Rhue Alison , Boyko Adam , Byers Alexandra , Wong Aaron , Mosher Dana S. , Elkahloun Abdel G. , Spady Tyrone C. , André Catherine , Lark K. Gordon , Cargill Michelle , Bustamante Carlos D. , Wayne Robert K. , Ostrander Elaine A.
Published: August 2009

Dog Coats Shed Genetic Secrets

The coats of domestic dogs show great variation—long, short, straight, wavy, curly, wiry, or smooth. To investigate how this variation arises,

Cadieu
et al.

(p.
150
, published online 27 August) performed genome-wide association studies on 80 different dog breeds. The coat phenotype could be dissected into three simple traits of length, curl, and growth pattern or texture with each trait controlled by one major gene,
FGF5
(fibroblast growth factor-5),
KRT71
(keratin-71), and
RSPO2
(R-spondin-2), respectively. In combination, variants in these three genes alone account for the vast majority of the coat phenotypes in purebred dogs in the United States. Thus, a small number of simply inherited traits can be remixed to create extraordinary phenotypic variation.
Potential-time response for several types of programmed current at most usual electrodes. Theoretical study of CE and EC mechanisms
Authors: Molina Ángela , López-Tenés Manuela
Published: August 2009

The theoretical study of the potential-time response corresponding to the CE and EC mechanisms at the DME by using non linear perturbation functions with the general form I(t) = I0tuewt and I(t) = I0(t1 + t)v is presented. Equations for the potential-time curves and for the transition times have been derived by taking into account the sphericity of the electrode. Methods for determining heterogeneous and homogeneous kinetic parameters are proposed. The expressions corresponding to an null blank period, to an expanding plane electrode and to spherical and plane stationary electrodes, can be deduced as particular cases of the equations obtained in this work.
Polarizability and nonpolarizability of oil-water interfaces with relevance to a.c. impendance measurements
Authors: Kakiuchi Takashi , Senda Mitsugi
Published: August 2009

We have estimated the degree of polarizability of a polarized oil-water interface used as a working interface and that of the nonpolarizability of a nonpolarized interface used as a reference oil-water interface from the numerical calculation of dc and ac current vs potential behavior at both interfaces. Theoretical equations of dc and ac currents for simultaneous cation and anion transfer of supporting electrolytes have been derived for the planar stationary interface for reversible and quasi-reversible cases. In the derivation, the migration effect and the coupling of the cation and anion transfer have been incorporated. The transfer of ions constituting a supporting electrolyte contributes to the total admittance of the interface even in the region where the interface may be considered as polarized in dc sense, as pointed out first by Samec et al. (J. Electroanal. Chem. 126, 121 (1981)). Moreover, the reference oil-water interface is not ideally reversible, so that the contribution from this interface to the measured admittance cannot be negligible, unless the area of the reference oil-water interface is much larger than that of the working oil-water interface. The effect of non-ideality of the reference oil-water interface on the determination of double layer capacitances and kinetic parameters of charge transfer at the working oil-water interface has been estimated.
Reduction of the Ni(II) ion at the dropping mercury electrode from amoxicillin water solution
Authors: Erceg Milenko R. , Kapetanović Vera P. , Sužnjević Desanka Ž.
Published: August 2009

The nature of polarographic precurrents of Ni(II) ion in the presence of amoxicillin as well as the behaviour of amoxicillin in the electrical double layer has been investigated. It has been established the formation of the mono complex of Ni(II) ion with amoxicillin adsorbed at the mercury. The reduction mechanism of the complex has been proposed. Taking into account the effect of the double layer on the kinetics, the rate constant of the heterogenous reaction of the complex formation has been found to be 5.8 · 103 l mol-1 s -1.
The effect of thiazine dyes on polarographic determination of tellurium
Authors: Kiriyak Ludmila
Published: August 2009

The effect of thionine, azure I and methylene blue on the electroreduction of tellurium(IV) has been studied in the solutions of oxalic, tartaric and trihydroxyglutaric acids. It has been shown that the electrode process is complicated by adsorption of all components of the electrochemical reaction. This causes an increase of the tellurium analytical signal. The determinations is not hampered by great excesses of various elements. Optimal conditions were found according to which determinations were carried out of tellurium in binary mixtures Pb-Te, Cd-Te, Fe-Te, Bi-Te and of tellurium admixtures in bismuth of high purity, doped by tellurium.
Secondary lithium cell: Separators compatible with electrolyte solution based on cyclic esters
Authors: Manev Vesselin , Nassalevska Anna , Momchilov Anton , Pistoia Gianfranco , Pasquali Mauro
Published: August 2009

To overcome the incompatibility between microporous polypropylene separator and electrolyte solutions based on cyclic esters, three methods of preliminary impregnation of the separator with electrolyte solution, without using surface active agents, are investigated. Values of the specific resistance of the separator, measured in 1M solutions of lithium salts in propylene carbonate, depending on the method of preliminary treatment, are obtained. Experimental data from the tests of secondary lithium button cells supplied with pretreated separators are presented. It is concluded that the pretreatment methods discussed can be used successfully. The best results are obtained by thermal pretreatment with the basic solvent.
Anodic dissolution of zinc in aqueous-methanolic trichloroacetic acid solutions
Authors: Hefny Mohamed H. , Babaqi Abdullah S. , El-Basiouny Mohamed S. , Abdullah Ragab M.
Published: August 2009

Steady state current-potential curves for the anodic dissolution of zinc in aqueous-methanolic 0.25M trichloracetic acid solutions were constructed for wide ranges of the solution composition and temperature. Analysis of the results reveal that the increase of the water content and rise of temperature of the solution increases the corrosion rate. The most plausible role of the solvent lies within the stabilization of the anodic dissolution reaction products by water molecules. The changes in the properties of the solution due to the presence of methanol which give rise to hindrance of the anodic dissolution reaction are adsorption of methanol, change of viscosity and pH of the solution. These factors seem to be of secondary importance.
Geometrical descriptors of molecules
Authors: Tvarůžek Pavel , Komenda Jaro
Published: August 2009

Individual molecules and/or their conformers are unequivocally described by the geometrical descriptors derived from the proper values of the square matrix belonging to the K graph. This graph is constructed on the basis of the bonds existing in the molecule, their relative lenghts, and dihedral angles (if the latter assume the values of 0, 90, 180, and 270°).
Alkoxide-to-hydroxide ion activity ratios in water-ethylene glycol and water-1-propanol systems
Authors: Mollin Jiří , Karásková Eva
Published: August 2009

The dissociation constants of water and alcohol, their ionic products as well the ionic product of the mixture, equilibrium constants of the OH- + ROH ⇆ RO- + H2O equilibrium, and the alkoxide-to-hydroxide ion activity ratios were determined in water-ethylene glycol and water-1-propanol systems. The conditions of validity of Rochester’s equation are discussed.
Generation of hydrogen peroxide by reduction of oxygen in semihydrophobic trickle electrodes
Authors: Špalek Otomar , Balogh Karel
Published: August 2009

The reduction of oxygen to hydrogen peroxide was studied in semihydrophobic trickle electrodes prepared from crushed graphite and teflonized carbon black. The potential of these electrodes was found markedly more positive and the peroxide current yields appreciably higher than for electrodes made of used crushed graphite. The reason for this is the higher surface area of the electrodes containing carbon black and occurrence of a three-phase interface in them. The relevant properties, i.e. electric resistance, electrolyte holdup, polarization curves for the oxygen reduction and pexide current yields, were also studied for trickle electrodes containing graphite felt. The electrochemical activity of electrodes made from untreated felt was found rather low but it increased several times when felt pretreated by oxidation was used.
Study of the sorption of selected pesticides on nonpolar sorbents
Authors: Svoboda Ladislav , Jandera Pavel , Churáček Jaroslav
Published: August 2009

The break-through curves of aqueous solutions of selected pesticides were evaluated to determine the suitability of a number of nonpolar sorbents based on active carbon, synthetic polymers and modified silica gel for enrichment dilute aqueous solution of these compounds. The best results were obtained using the styrene-divinylbenzene sorbents Aquapak 440A and Amberlite XAD-2, the styrene-ethylenedimethacrylate copolymer Separon SE and octadecyl silica gel materials. The effect of some experimental conditions on the sorption process, i.e. the flow rate of the sample through the column, the pesticide concentration in solution, the pH of the sorption medium, etc., was also studied. The results obtained are immediately applicable to the concentration of trace amounts of pesticides in water samples in sorption columns and also to chromatographic analysis by the HPLC method.
Synthesis of four new V1 antagonists of arginine-vasopressin (AVP) containing new thioacids at position 1 and their vasoconstrictor activity towards isolated mesenteric arterial vessels of rats
Authors: Lammek Bernard , Derdowska Izabela , Wierzba Tomasz M. , Juzwa Witold
Published: August 2009

In an attempt to determine some of the structural features in position 1 that account for V1 antagonism, four new analogues of arginine-vasopressin were synthesized and the effect of the modifications on the vasoconstrictor activity was checked using isolated mesenteric arterial vessels of rats. The protected precursors required for these analogues were synthesized by a solid phase method of peptide synthesis. One of the reported analogues, namely [1-(4-mercapto-4-tetrahydrothiopyraneacetic acid)., 2-O-methyltyrosine, 8-arginine]vasopressin appears to be a potent competitive antagonist of the vasoconstrictor effect by AVP.
Immobilized Oospora lactis lipase preparations and their properties
Authors: Davranov Kakhramon , Sattarov Abdimurod , Diyorov Jamil
Published: August 2009

It has been shown that adsorption on microcrystalline and AE-cellulose partially modified by the palmitoyl residue is an effective method of immobilizing the lipases of fungus Oospora lactis. The kinetics of the lipases are characterized by substrate inhibition. Immobilization considerably increases the heat stability of the lipases.
1,3-dipolar cycloadditions of heterocyclic nitrile oxides to substituted N-phenylmaleinimides
Authors: Jedlovská Eva , Fišera Lubor , Goljer Igor , Konopíková Mária , Belenkii Leonid I.
Published: August 2009

Cycloadditions of 2-furannitrile oxide (Ia), 5-nitro-2-furannitrile oxide (Ib), 5-(3-nitrophenyl)-2-furannitrile oxide (Ic), 5-(4-nitrophenyl)-2-furannitrile oxide (Id), and 2,5-dimethyl-3-dimethl-3-furannitrile oxide (Ie) with 4- or 2,6-disubstituted N-phenylmaleinimide are described. Investigated were also cycloadditions of 2,5-dimethyl-3-thiophenenitrile oxide (IVa), 2,4,5-trimethyl-3-thiophenenitrile oxide (IVb), 2,3-dimethyl-4-ethyl-3-thiophenenitrile oxide (IVc), 2,5-dimethyl-4-(1-methylethyl)-3-thiophenenitrile oxide (IVd), and 3,5-di(1,1-dimethylethyl)-2-thiophenenitrile oxide (V) with N-(2,6-dimethylphenyl)maleinimide. The steric course of these reactions is discussed.
Reactions of isothiocyanates and isocyanates with some silylated nitrogen-containing nucleophiles
Authors: Gonda Jozef , Antalová Zuzana
Published: August 2009

Aryl isothiocyanates and arylisocyanates react with N,O-bis(trimethylsilyl)acetamide to give N-methyl-N’-arylthioureas and ureas. Also nucleophilic additions of other aprotic nucleophiles (e.g. N-trimethylsilylimidazole, N-trimethylsilylpiperidine and N-trimethylsilylmorpholine) to the N=C=X (X = O, S) group were investigated.
Synthesis of some new 7-substituted aminomethyl-6-chloroquinoline-5,8-quinone
Authors: Yanni Amal S. , Khalil Zarif H.
Published: August 2009

Some new 7-substituted aminomethyl-6-chloroquinoline-5,8-quinone (II-IV) have been obtained by the Mannich reaction on 6-chloroquinoline-5,8-dione and biologically evaluated.
Excess molar volumes of binary mixtures of acetic acid and propionic acid with some members of homologous series of alkanes
Authors: Drábek Ondřej , Cibulka Ivan
Published: August 2009

Excess molar volumes of binary liquid mixtures of (acetic or propionic acid = hexane) at 25 and 35°C, and (acetic or propionic acid + heptane or octane) and (acetic acid + dodecane) at 25°C, measured with a tilting dilution dilatometer, are reported. The excess volumes are positive over the entire concentration range for all mixtures and increase with increasing length of an alkane molecule, decrease with increasing of the alkyl chain in a molecule of carboxylic acid, and increase with increasing temperature.
Ionic product of water in the nitrobenzene phase of the two-phase water-nitrobenzene extraction system
Authors: Makrlík Emanuel
Published: August 2009

General relations among thermodynamic parameters, which characterize the transfer of the ions H+ and OH- from the aqueous into nitrobenzene phase of the two-phase water-nitrobenzene extraction system and dissociation equilibria of H2O in both phases of this system, have been derived. Further, using the known parameters ionic product of water in nitrobenzene saturated with water has been evaluated for a temperature of 25°C: PnbH2O = 10-29.2 mol2 dm-6.
On the bed expansion in aggregative fluidization
Authors: Hartman Miloslav , Veselý Václav , Svoboda Karel
Published: August 2009

Prediction of two hydrodynamic models and four entirely empirical correlations for the expansion of freely bubbling fluidized beds are compared with four sets of the experimental data. The results provide answers to some practical questions regarding the applicability of the recently proposed relationship for predicting the expansion in the fluidized beds with larger particles.
An ESR study of the peroxidase reaction catalyzed by human methaemoglobin and methaemoglobin-haptoglobin complex
Authors: Stejskalová Jana , Stopka Pavel , Pavlíček Zdeněk
Published: August 2009

The ESR spectra of peroxidase systems of methaemoglobin-ascorbic acid-hydrogen peroxide and methaemoglobin-haptoglobin complex-ascorbic acid-hydrogen peroxide have been measured in the acetate buffer of pH 4.5. For the system with methaemoglobin an asymmetrical signal with g ~ 2 has been observed which is interpreted as the perpendicular region of anisotropic spectrum of superoxide radical. On the other hand, for the system with methaemoglobin-haptoglobin complex the observed signal with g ~ 2 is symmetrical and is interpreted as a signal of delocalized electron. After realization of three repeatedly induced peroxidase processes the ESR signal of the perpendicular part of anisotropic spectrum of superoxide radical is distinctly diminished, whereas the signal of delocalized electron remains practically unchanged. An amino acid analysis of methaemoglobin along with results of the ESR measurements make it possible to derive a hypothesis about the role of haptoglobin in increasing of the peroxidase activity of methaemoglobin.
A-homo-B,19-dinorandrostanes from 6β-methanesulfonyloxy-5-methyl-19-nor-5β-androst-9-ene derivatives
Authors: Kasal Alexander , Podlaha Jaroslav , Zajíček Jaroslav
Published: August 2009

6β-Methanesulfonyloxy derivatives of 5-methyl-19-nor-5β-androst-9-enes with different oxygen functionalities in positions 3β and 17 ( compounds IX and XVII) were converted to 4a-methyleno-A-homo-B,19-dinor-5β-androst-9-ene derivatives (compounds X, XX and XXI) which were hydrogenated to give derivatives of 4aα-methyl-A-homo-5,19-dinor-5β,10α-androstane (XXII, XXIII) and 4aα-methyl-A-homo-B,19-dinor-5α,9β-androstane (XXIV, XXV). The structure of the latter compounds has been confirmed by X-ray diffraction of diketone XXVII which has been shown, in accordance with calculations by the MM2 method, to exist in a boat conformation of the ring C. The 17β-hydroxy-3-ketone XXX exhibits in vivo antiandrogenic activity.
Isolation, stereochemistry, and biosynthesis of Šormosterol, a novel cyclopropane-containing sponge sterol
Authors: Silva Christopher J. , Djerassi Carl
Published: August 2009

Šormosterol ((24R)-24,25-methylenecholesterol, XVIII, a product of the novo sterol biosynthesis in the marine sponge Lissodendoryx topsenti, was shown, trough the use of suitably labeled precursors, to be a new alternative product of the initial S-adenosylmethionine (SAM) methylation of the 24,25 double bond in the sterol side chain. Additional labeling experiments demonstrated that the cyclopropane ring is not further modifies in vivo by the sponge.
Structural analysis of biological macromolecular assemblies by electron microscopic techniques
Authors: Boublik Miloslav , Mandiyan Valsan , Tumminia Santa J.
Published: August 2009

The development of high resolution electron microscopic techniques and the introduction of quantitative image analysis has provided a direct basis for studying the structure of biological macromolecules. Apart from the determination of overall morphology, including 3-D image reconstruction, these techniques provide information on the internal architecture of biological macromolecular assemblies, the topography of functional sites, the interactions of their components and elemental microanalysis in situ. Thus, from a mere photographic recording system of the past, electron microscopy has evolved into a high resolution quantitative spectroscopic analytical method.
Horseradish peroxidase-mediated preparation of dimers from eugenol and isoeugenol
Authors: Krawczyk Andrzej R. , Lipkowska Ewa , Wróbel Jerzy T.
Published: August 2009

Coupling of eugenol (I) and isoeugenol (II) by means of horseradish peroxidase and hydrogen peroxide resulted in ~20% yield of dimeric compounds: 5,5’-diallyl-2,2’-dihydroxy-3,3’-dimethoxy-biphenyl (III) and 2-(4’-hydroxy-3’-methoxy)phenyl-7-methoxy-3-methyl-5-propenyl-2,3-dihydrobenzofurane (IV), respectively.
Determination of limiting molar conductivities of weak organic acids in aqueous solutions
Authors: García Begoña , Domingo Inmaculada , Domingo Pedro L. , Leal José M.
Published: August 2009

Conductance, potentiometric, and spectrophotometric measurements have been made at 25°C of aqueous solution containing sulfanilic, hippuric, mandelic, and 3,5-dinitrosalicylic acids at different concentrations. Conductance data were analyzed using the methods of Fuoss-Kraus, Kraus-Parker, and Shedlovsky for conductivity of the free ions. Using the calculated limiting conductances, activity coefficients, and degrees of dissociation, the dissociation constants of the weak acids were determined. From plots Δ vs c1/2, reliable values for Δ0 were estimated, using a computer program, and by means of an iterative method the proper value of Δ0 was determined, independently of that initially introduced. Values of pK were also obtained from potentiometric and spectrophotometric measurements. Evidence for the existence of univalent and divalent ions in aqueous solutions of 3,5-dinitrosalicylic acid was obtained spectrophotometrically, this fact justifying the poorer results provided by conductance measurements.
Study of the film formation process in liquid-liquid extraction flow injection analysis
Authors: Kubáň Vlastimil
Published: August 2009

The behaviour of a thin film of an organic solvent on the walls of the extraction coil in a continuous liquid-liquid extraction flow system was studied using a computer-controlled fast-recording on-tube photometric detection system (approx. 3 ms time resolution). A single-loop injector was employed to introduce precise, reproducible volumes (Sr < 2%) of one phase into the continuous stream of the other as a segmented volume standard. The film thickness Df, ranging from 1 to 20 μm for a 0.7 mm teflon tube, was calculated from the segment lengthening at a different chloroform flow rates and was found to obey a polynominal dependence on the linear flow rate, df = f(uα), where α < 1.
Hydrophobic partitioning of proteins in a two-phase aqueous system of poly(oxyethylene)-dextran alternatively derivatized by 2-hydroxy-3-phenoxypropyl group
Authors: Gemeiner Peter , Kochjarová Helena , Horváthová Marta , Breier Albert
Published: August 2009

We have observed that in a two-phase aqueous system composed of poly(oxyethylene) and dextran, trypsin, ovalbumin, serum albumin and immunoglobulin G are preferentially partitioned into the dextran phase. The accumulation of proteins in this more hydrophilic phase increased with the increasing concentration of the polymers in both phases. This trend remained essentially unchanged even after the hydrophobization of the poly(oxyethylene) (POE) phase by 2-hydroxy-3-phenoxypropyl (HPP). The affinity of all four proteins for the dextran phase decreased after the hydrophobization of the dextran phase by the HPP ligand. The affinity decrease was uniform with all four proteins. The hydrophobic partitioning of all four proteins in the systems composed of (HPP-POE) and dextran and of POE and (HPP-dextran) was probably governed by an identical mechanism. The size and charge of the globular protein played an important role in this mechanism.
Structural effects in the oxidation of ketones by acid iodate
Authors: Manikyamba Prerepa
Published: August 2009

The kinetics of oxidation of aliphatic, alicyclic and aryl alkyl ketones by acid iodate has been studied in aqueous methanol medium. The reaction exhibits first order dependence each on [iodate] and [ketone]. The reaction is acid catalysed and a medium of low dielectric constant is favourable for the oxidation process. The oxidation rates are slower than the enolisation rates of the ketones. The mechanism proposed involves rate limiting attack of IO+2 on the enol form of the ketone leading to the formation of an intermediate carbonium ion which undergoes solvolysis, ultimately leading to the formation of a methoxy derivative. The order of reactivity of these structurally different ketones is discussed in terms of stability of the enol formed from the ketone and of the stability of the carbonium ion formed due to attack of the oxidant species in the slow step.
Synthesis and 13C NMR spectra of disaccharides related to glucoxylans and xyloglucans
Authors: Petráková Eva , Krupová Ivana , Schraml Jan , Hirsch Ján
Published: August 2009

β-(1 → 2), (1 → 3) and (1 → 4) linked D-glucopyranosyl-D-xylopyranoses were obtained in high yields via condensation of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide with the appropriate benzyl di-O-benzyl-β-D-xylopyranosides under conditions of modified Koenigs-Knorr reaction and deprotection of the acetyl and benzyl groups. 4-O-β-D-Xylopyranosyl-D-glucopyranose was synthesized similarly starting from 2,3,4-tri-O-acetyl-α-D-xylopyranosyl bromide and 1,2,3,6-tetra-O-acetyl-β-D-glucopyranose; it served as a xyloglucan model substance. The 13C NMR spectra of final disaccharides and their intermediates are presented.
Preparation of solid superacid catalysts by chemical modification of oxides. I.
Authors: Hochmann Tomáš , Setínek Karel
Published: August 2009

Properties of solid acid catalysts prepared by modification of oxides have been examined. The oxides Al2O3, SiO2, TiO2, SnO2, Sb2O3, ZrO2 and ZrSiO4 were impregnated by aqueous solutions of H2SO4, H3PO4, NH4F and NH4Cl, respectively, and calcined at 500, 650 and 800°C. For the so prepared catalysts, the strength and number of their acid centres and their activity for hydrocarbon reactions were determined.
Mushroom tyrosinase-modified carbon paste electrode as an amperometric biosensor for phenols
Authors: Skládal Petr
Published: August 2009

A biosensor for a variety of substances could be readily prepared by the adsorption of partially purified mushroom tyrosinase at a carbon paste electrode, producing an enzyme layer which was protected with a dialysis membrane. The electrode poised at – 100mV (vs an Ag/AgCl reference electrode) functions on the basis of a reversible electrochemical reduction of the o-quinones formed from phenols in the tyrosinase reaction. The response times were 40 s for o-diphenols and 2 min for monophenols; the reproducibility for 10 consecutive assays of 3 μmol l-1 phenol solution was better than 4%. The detection limit was 10 nmol l-1 (catechol as substrate) and the steady state responses were linear up to a concentration of 200 μmol l-1. The optimum pH values were 6.0 for phenol and 6.5 for catechol. The shapes of the pH-response curves indicated the presence of at least two tyrosinase isoenzymes with different pH optima.
Crystal structure of dicadmium(II) ethylenediphosphinetetraacetate octahydrate
Authors: Podlaha Jaroslav , Podlahová Jana
Published: August 2009

The crystal structure of the title compound containing a phosphorus analogue of EDTA as the ligand was determined from single-crystal X-ray diffraction data and refined to R = 0.028 for 1 920 observed reflections. The crystals are monocyclic, space group P21/c,a = 8.6169(8), b = 16.0539(9), c = 8.2504(6)Å, β = 103.458(7)° and Z = 2. The structure is completely different from that of the nitrogen prototype, [CdEDTA]2-. It consists of double-stranded polymeric layers which are composed of metal coordination polyhedra linked by μ6-hexadentate ligands; the layers lie parallel to the bc plane and are joined along the a axis through hydrogen bonding donated by water molecules. Because of steric requirements of phosphorus, the coordination polyhedron around Cd is greatly distorted and can best be described as a 5 + 3 type. One P atom, two oxygen atoms from two monodentate carboxylate groups and two water molecules form an approximate trigonal bipyramid and further three more remote carboxylate oxygens complete the arrangement, resulting in an O7P distorted bicapped trigonal prism.
Infrared spectroscopic study of the products of thermal degradation of polyamides in inert atmosphere
Authors: Svoboda Miroslav , Schneider Bohdan , Štokr Jan
Published: August 2009

Infrared spectra were measured of condensates generated by heating polyamide-6, polyamide-12, polyamide-11, polyamide-8 and polyamide-6,6 in inert atmosphere at 300, 350, 400, 500, and 600°C for various time. The products of thermal degradation were characterized by infrared spectroscopy. It was found that the thermal history of polyamide degradation can be detected from infrared spectra.
Bis(monoazacrown ether)s: Effects of bridge length and ring size on stability and selectivity in alkali ion sandwich complex formation
Authors: Holý Petr , Koudelka Juraj , Bělohradský Martin , Stibor Ivan , Závada Jiří
Published: August 2009

Sodium, potassium, rubidium and caesium ion complex formation was investigated in two homologous series of bis(azacrown ether)s Ia-Ic and IIa-IIc. Three complementary bis(azacrown ether)s series IIIa-IIIc, IVa-IVc and Va-Vc were employed for a more detailed study of sodium complexation. Very pronounced effects of bridge length as well as macroring size were found in the investigated series and interpreted mainly in terms of various proclivity of individual ligands and alkali ions to sandwich complex formation. Remarkably high selectivities in alkali ion formation were noted for the shortest bridge ligands Ia and Ib, the former preferring strongly sodium and the latter potassium complex formation.
Synthesis of some new sulfonamide derivatives of 7-chloroquinoline-5,8-dione and pyridocarbazolediones
Authors: Yanni Amal S. , Khalil Zarif H. , Timmawy Ahmed A.
Published: August 2009

Interaction of 6-chloroquinoline-5,8-dione hydrochloride (I) or 6,7-dichloroquinoline-5,8-dione (II) with sulfa drug in ethanol containing diethylaniline afforded 7-substituted sulfonamide-10H-pyrido[3,2-b]carbazole-5,11-dione (III), and sulfonamide derivatives of 7-chloroquinoline-5,8-diones (IV). Moreover the reaction of II with arylamine in pyridine afforded substituted 6H-pyrido[2,3-b]carbazole-5,11-dione (V). The structure of the compounds was determined by elemental and spectral analysis, and by chemical reaction.
A 15N, 13C, and 1H NMR study of reaction products from arylguanidines and chloroformate esters
Authors: Lyčka Antonín , Palát Karel
Published: August 2009

The 15N, 13C, and 1H NMR spectra of the reaction products from arylguanidines with two mols of chloroformate esters have been measured. With application of the corresponding 15N isotopomer it has been proved that the reaction products have the structures IIIa-IIIc.