bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aminoglycoside–Quinacridine Conjugates: Towards Recognition of the P6.1 Element of Telomerase RNA
Authors: Kaiser Markus , Sainlos Matthieu , Lehn Jean‐Marie , Bombard Sophie , Teulade‐Fichou Marie‐Paule 
Published: January 2006

AbstractA modular synthesis has been developed which allows easy and rapid attachment of one or two aminoglycoside units to a quinacridine intercalator, thereby leading to monomeric and dimeric conjugates. Melting temperature (Tm) experiments show that the tobramycin dimeric conjugate TD1 exhibits strong binding to the P6.1 element of human telomerase RNA. By contrast, tobramycin alone is much less efficient and the monomeric compound TM1 elicits a poor binding ability. Monitoring of the interaction by an electrophoretic mobility shift assay shows a 1:1 stoichiometry for the binding of the dimeric compound to the hairpin structure and confirms the lower affinity for a control duplex. Protection experiments with RNase T1 indicate interaction of the drug both in the stem and in the loop of the hairpin. Taken together, the data suggest a binding of TD1 inside the hairpin at the stem‐loop junction. The same trends are observed with paromomycin and kanamycin analogues but with a lower affinity.
Mechanism of Nitrate Reduction by Desulfovibrio desulfuricans Nitrate Reductase—A Theoretical Investigation
Authors: Leopoldini Monica , Russo Nino , Toscano Marirosa , Dulak Marcin , Wesolowski Tomasz Adam 
Published: January 2006

AbstractThe oxidative half‐reaction of oxygen atom transfer from nitrate to an MoIV complex has been investigated at various levels of theory. Two models have been used to simulate the enzyme active site. In the second, more advanced model, additional amino acid residues capable of significantly affecting the catalytic efficiency of the enzyme were included. B3LYP/6–31+G*, ONIOM, and orbital‐free embedding approaches have been used to construct the potential energy profile and to qualitatively compare the results of a QM/MM study with those obtained by a full quantum mechanical strategy. The study has confirmed the utility of the orbital‐free embedding method in the description of enzymatic processes.
Complex Wurtzite ZnSe Microspheres with High Hierarchy and Their Optical Properties
Authors: Yao Weitang , Yu Shu‐Hong , Jiang Jun , Zhang Lin 
Published: January 2006

AbstractComplex wurtzite ZnSe microspheres with hierarchical fractal structure and showing strong quantum‐size effects can be prepared easily by a mild solvothermal reaction in a diethylenetriamine (DETA)–deionized water (DIW) binary solution. The ZnSe microspheres are made up of nanosheets, each formed by the face‐to‐face pairing of two individual nanosheets. In addition, high‐order, flowerlike hierarchical structures are formed by the attachment of flexible, uniform nanofibers to the exposed faces of each nanosheet pair. The surface morphology of the nanosheets changed as reaction time increased and the detailed phase‐transformation and shape‐evolution processes were studied. This approach could provide an effective strategy for tuning the electronic and optical properties of semiconductors, with special advantages over the traditional high‐temperature approach, and could be extended to access other semiconductor materials with unusual morphologies and structures.
Spatial Extent of the Singlet and Triplet Excitons in Luminescent Angular‐Shaped Transition‐Metal Diynes and Polyynes Comprising Non‐π‐Conjugated Group 16 Main Group Elements
Authors: Poon Suk‐Yue , Wong Wai‐Yeung , Cheah Kok‐Wai , Shi Jian‐Xin 
Published: January 2006

AbstractA novel approach based on conjugation interruption has been developed and is presented for a series of luminescent and thermally stable chalcogen‐bridged platinum(II) polyyne polymers trans‐[{Pt(PBu3)2CC(C6H4)E(C6H4)CC}n] (E=O, S, SO, SO2). Particular attention was focused on the photophysical properties of these Group 10 polymetallaynes and comparison was made to their binuclear model complexes trans‐[Pt(Ph)(PEt3)2CC(C6H4)E(C6H4)CCPt(Ph)(PEt3)2] and their closest Group 11 gold(I) and Group 12 mercury(II) neighbours, [MCC(C6H4)E(C6H4)CCM] (M=Au(PPh3), HgMe; E=O, S, SO, SO2). The regiochemical structures of these angular‐shaped molecules were studied by NMR spectroscopy and single‐crystal X‐ray structural analyses. Upon photoexcitation, each one has an intense purple‐blue fluorescence emission near 400 nm in dilute fluid solutions at room temperature. Harvesting of the organic triplet emissions harnessed through the strong heavy‐atom effects of Group 10–12 transition metals was studied in detail. These metal‐containing aryleneethynylenes spaced by chalcogen units were found to have large optical gaps and high‐energy triplet states. The influence of metal‐ and chalcogen‐based conjugation interrupters on the intersystem crossing rate and on the spatial extent of the lowest singlet and triplet excitons was fully elucidated. We discuss and compare the phosphorescence spectra of these transition‐metal diynes and polyynes in terms of the nature of the metal centre, conjugated chain length and Group 16 spacer unit. Our work here indicates that high‐energy triplet states in these materials intrinsically give rise to very efficient phosphorescence with fast radiative decays and one could readily observe room‐temperature phosphorescence for the platinum polyynes.
A Stacking Interaction between a Bridging Hydrogen Atom and Aromatic π Density in the n‐B18H22–Benzene System
Authors: Hamilton Ewan J. M. , Kultyshev Roman G. , Du Bin , Meyers Edward A. , Liu Shengming , Hadad Christopher M. , Shore Sheldon G. 
Published: January 2006

AbstractThe structures of n‐B18H22 and of n‐B18H22⋅C6H6 were determined by single‐crystal X‐ray analysis at −60 °C. The geometry of the boron cluster itself does not seem to be appreciably affected by solvation. There does, however, appear to be an unusual interaction of a polyborane bridging hydrogen atom with the benzene π system, giving rise to an extended stacked structure. The 1H{11B} spectrum of n‐B18H22 in [D6]benzene differs from that in [D12]cyclohexane most noticeably in the bridging proton region. Upon moving from the aliphatic to the aromatic solvent, the greatest increase in shielding was for the signal corresponding to the bridge hydrogen atom that interacts with the π system of benzene; the signal was shifted upfield by 0.49 ppm. Density functional theory calculations were performed on 1:1 and 2:1 complexes of the n‐B18H22 unit with benzene.
Kinetic Energy Release of C70+ and Its Endohedral Cation N@C70+: Activation Energy for N Extrusion
Authors: Cao Baopeng , Peres Tikva , Lifshitz Chava , Cross R. James , Saunders Martin 
Published: January 2006

AbstractUnimolecular decomposition of C70+ and its endohedral cation N@C70+ were studied by high‐resolution mass‐analyzed ion kinetic energy (MIKE) spectrometry. Information on the energetics and dynamics of these reactions was extracted. C70+ dissociates unimolecularly by loss of a C2 unit, whereas N@C70+ expels the endohedral N atom. Kinetic energy release distributions (KERDs) in these reactions were measured. By use of finite heat bath theory (FHBT), the binding energy for C2 emission from C70+ and the activation energy for N elimination from N@C70+ were deduced from KERDs in the light of a recent finding that fragmentation of fullerene cations proceeds via a very loose transition state. The activation energy measured for N extrusion from N@C70+ was found to be lower than that for C2 evaporation, higher than the value from its neutral molecule N@C70 obtained on the basis of thermal stability measurements, and coincident with the theoretical value. The results provide confirmation that the proposed extrusion mechanism in which the N atom escapes from the cage via formation of an aza‐bridged intermediate is correct.
Adiponectin, ghrelin, and leptin in cancer cachexia in breast and colon cancer patients
Authors: Wolf Ido , Sadetzki Seigal , Kanety Hannah , Kundel Yulia , Pariente Clara , Epstein Nava , Oberman Bernice , Catane Raphael , Kaufman Bella , Shimon Ilan 
Published: January 2006

AbstractBACKGROUNDThe hormone ghrelin and the adipocytokines leptin and adiponectin participate in body weight regulation. In response to weight loss, ghrelin and adiponectin levels increase and leptin decreases. Cancer cachexia is a complex metabolic state, characterized by loss of muscle mass and adipose tissue together with anorexia. The authors hypothesized that responses of these hormones may be attenuated in cancer cachexia.METHODSFasting plasma ghrelin, adiponectin, and leptin levels, as well as weight loss, were determined in 40 cancer patients: 18 of them suffered from cancer‐induced cachexia, and 22 served as a comparison group. Hormone levels were measured before administration of cancer therapy.RESULTSA similar distribution of age, gender, and diagnosis was observed in both study groups, but the cachectic patients had higher rates of metastatic disease and lower albumin levels. No significant correlation was observed between plasma adiponectin levels and weight loss. Mean plasma ghrelin levels were higher among cachectic compared with noncachectic patients. Notably, the association between ghrelin levels and weight loss was only modest, and in a third of the cachectic patients, ghrelin levels were equal to or lower than those in the noncachectic group. Plasma leptin levels showed gender‐dependent associations, and significantly lower levels were found among cachectic women but not among cachectic men.CONCLUSIONSResults suggested a gender‐dependent attenuation of expected physiologic responses to weight loss among cancer cachexia patients. Thus, impaired response of adiponectin, ghrelin, and leptin may play a role in the pathogenesis of cancer cachexia syndrome. Cancer 2006. © 2006 American Cancer Society.
Effective Controlled Release of Captopril by Silylation of Mesoporous MCM‐41
Authors: Qu Fengyu , Zhu Guangshan , Huang Shiying , Li Shougui , Qiu Shilun 
Published: January 2006

AbstractThe release of the water‐soluble drug Captopril is controlled by tailoring the surface properties of mesoporous silica via stepwise silylation. The degree of silylation is manipulated by adjusting the initial concentration of silylanizing reagent (trimethylchlorosilane, TMCS). The silylanized and drug‐loaded samples are characterized by powder X‐ray diffraction, Fourier transform IR spectroscopy, N2 adsorption and desorption,29Si cross‐polarization magic angle spinning NMR spectroscopy, and transmission electron microscopy. The drug‐loading amount is correlated to the Brunauer–Emmett–Teller surface area and surface hydrophilicity/hydrophobicity of the mesoporous silica material, while drug release profiles can be controlled by tailoring the surface properties and pore size.
Probing the Acidity of p‐Substituted Phenols in the Excited State: Electronic Spectroscopy of the p‐Cyanophenol–Water Cluster
Authors: Jacoby Christoph , Böhm Marcel , Vu Chau , Ratzer Christian , Schmitt Michael 
Published: January 2006

AbstractThe hydrogen bond structure of the p‐cyanophenol–water cluster has been determined in the ground and first excited electronic state by rotationally resolved UV spectroscopy. The water molecule is trans‐linearly bound to the hydroxy group of the p‐cyanophenol moiety, with hydrogen bond distances considerably shorter in both electronic states than in the similar phenol‐water cluster. The structure of the cluster has been elucidated by ab initio calculations at various levels of theory and compared to the experimental findings. The barriers to internal rotation of the water moiety were determined experimentally to be 275 and 183 cm−1for the ground and excited state, respectively. Hydrogen bond distances and the energy barrier to water torsion correlate with the pKavalues of different substituted phenols for both electronic states.
Chair, Boat and Twist Conformation of Dodecamethylcyclohexasilane and Undecamethylcyclohexasilane: A Combined DFT and Raman Spectroscopic Study
Authors: Tekautz Günter , Binter Alexandra , Hassler Karl , Flock Michaela 
Published: January 2006

AbstractThe conformations of dodecamethylcyclohexasilane Si6Me12 and undecamethylcyclohexasilane Si6Me11H have been investigated by ab initio calculations employing the B3LYP density functional with a 6‐31+G(d) basis set. Local minima as well as transition structures were calculated with imposed symmetry constraints. For Si6Me12, three unique minima, which correspond to the chair, twist and boat conformations were located with relative zero‐point‐vibration‐corrected energies of 0.0, 7.8 and 11.4 kJ mol−1. A half‐chair conformation with four coplanar silicon atoms connects the chair and twisted minima via an energy barrier of 16.0 and 8.2 kJ mol−1, respectively. A second transition structure with a barrier of 3.9/0.3 kJ mol−1connects the twist with the boat structure. Solution Raman spectra of Si6(CH3)12 and Si6(CD3)12 fully corroborate these results. Below −40 °C, the symmetric SiSi ring breathing vibration is a single line, which develops a shoulder (originating from the twist conformer) at longer wavelengths whose intensity increases with increasing temperature. From a Van′t Hoff plot, the chair/twist enthalpy difference is 6.6±1.5 kJ mol−1for Si6(CH3)12 and 6.0±1.5 kJ mol−1for Si6(CD3)12, which is in reasonable agreement with the ab initio results. Due to the low barrier, the boat conformation cannot be observed, because either the lowest torsional vibration level lies above it or a rapid interconversion between the twist and boat conformations occurs, resulting in averaged Raman spectra. For Si6Me11H, six local minima were located. The chair with the hydrogen atom in the axial position (axial chair) is the global minimum, followed by the equatorial chair (+1.9 kJ mol−1) and the three twist conformers (+5.3, +8.0 and +8.1 kJ mol−1). The highest local minimum (+11.9 kJ mol−1) is a Cssymmetric boat with the hydrogen atom in the equatorial position. Two possible pathways for the chair‐to‐chair interconversion with barriers of 13.9 and 14.5 kJ mol−1have been investigated. The solution Raman spectra in the SiSi ring breathing region clearly show that below −50 °C only the axial and equatorial chairs are present, with an experimental ΔH‐value of 0.46 kJ mol−1. With increasing temperature a shoulder develops which is attributed to the combined twist conformers. The experimental ΔH‐value is 6.9 kJ mol−1, in good agreement with the ab initio results. Due to the low interconversion barriers, the various twist conformers cannot be detected separately.
Determining Molecular Structures and Conformations Directly from Electron Diffraction using a Genetic Algorithm
Authors: Habershon Scott , Zewail Ahmed H. 
Published: January 2006

AbstractA global optimization strategy, based upon application of a genetic algorithm (GA), is demonstrated as an approach for determining the structures of molecules possessing significant conformational flexibility directly from gas‐phase electron diffraction data. In contrast to the common approach to molecular structure determination, based on trial‐and‐error assessment of structures available from quantum chemical calculations, the GA approach described here does not require expensive quantum mechanical calculations or manual searching of the potential energy surface of the sample molecule, relying instead upon simple comparison between the experimental and calculated diffraction pattern derived from a proposed trial molecular structure. Structures as complex as all‐trans retinal and p‐coumaric acid, both important chromophores in photosensing processes, may be determined by this approach. In the examples presented here, we find that the GA approach can determine the correct conformation of a flexible molecule described by 11 independent torsion angles. We also demonstrate applications to samples comprising a mixture of two distinct molecular conformations. With these results we conclude that applications of this approach are very promising in elucidating the structures of large molecules directly from electron diffraction data.
On parameter estimation of a simple real‐time flow aggregation model
Authors: Fu Huirong 
Published: January 2006

AbstractThere exists a clear need for a comprehensive framework for accurately analysing and realistically modelling the key traffic statistics that determine network performance. Recently, a novel traffic model, sinusoid with uniform noise (SUN), has been proposed, which outperforms other models in that it can simultaneously achieve tractability, parsimony, accuracy (in predicting network performance), and efficiency (in real‐time capability). In this paper, we design, evaluate and compare several estimation approaches, including variance‐based estimation (Var), minimum mean‐square‐error‐based estimation (MMSE), MMSE with the constraint of variance (Var+MMSE), MMSE of autocorrelation function with the constraint of variance (Var+AutoCor+MMSE), and variance of secondary demand‐based estimation (Secondary Variance), to determining the key parameters in the SUN model. Integrated with the SUN model, all the proposed methods are able to capture the basic behaviour of the aggregation reservation system and closely approximate the system performance. In addition, we find that: (1) the Var is very simple to operate and provides both upper and lower performance bounds. It can be integrated into other methods to provide very accurate approximation to the aggregation's performance and thus obtain an accurate solution; (2) Var+AutoCor+MMSE is superior to other proposed methods in the accuracy to determine system performance; and (3) Var+MMSE and Var+AutoCor+MMSE differ from the other three methods in that both adopt an experimental analysis method, which helps to improve the prediction accuracy while reducing computation complexity. Copyright © 2005 John Wiley & Sons, Ltd.
Hyperelliptic curves encryption combined with block codes for Gaussian channel
Authors: Jirón I. , Soto I. , Carrasco R. , Becerra N. 
Published: January 2006

AbstractIn this paper, a new cryptographic system is constructed using a combination of a hyperelliptic curve of genus g = 2 over the Galois field GF(2n) and a Reed–Solomon code (N, K) over the Galois field GF(2m) and this system uses a smaller key than the elliptic curves cryptosystem and the Rivest, Shamir, and Adleman cryptosystem. The design criterion for the combination can be expressed as the data compression condition and addressing capability of the code. In addition, the system performance is compared with other systems; extraordinary improvements of 8 and 16.5 dB can be obtained for a BER = 10−5, when compared with binary phase shift keying and differential chaos shift keying, respectively. This system has a polynomial complexity, which depends on data length and the number of operations in GF(2n). Copyright © 2005 John Wiley & Sons, Ltd.
Closed‐form expression for the BER of m‐QAM‐OFDM systems over time‐ and frequency‐selective wireless channels
Authors: Castells F. , Almenar V. 
Published: January 2006

AbstractThe broadcast DVB‐T system is an m‐QAM‐OFDM communication system that includes pilot‐symbol‐assisted modulation (PSAM) in order to enhance channel estimation at the receiver. This characteristic makes DVB‐T suitable for a mobile reception, over time‐ and frequency‐selective wireless channels. In this work, a closed‐form expression for the BER as a function of the transmission system, channel model and the channel estimation strategy employed at the receiver is derived. In addition, adjacent channel interference due to Doppler effects is also considered. The results are focused on the DVB‐T system under different scenarios. The channel estimation at the receiver has been shown to be very critical, and the impact of channel estimation errors on the BER is analysed in detail. Copyright © 2005 John Wiley & Sons, Ltd.
Improving fairness of PGMCC
Authors: Chen Hualiang , Liu Zhongxin , Chen Zengqiang , Yuan Zhuzhi 
Published: January 2006

AbstractPGM congestion control (pgmcc), a single‐rate multicast congestion control scheme, is one of the most promising schemes which aim to solve the problem of multicast fairness with TCP. However, by deep investigation, we find that there exist two inappropriate mechanisms in this scheme, which are the fixed slow start threshold (ssthresh) and the mechanism of changing a group representative (acker). Our experiments have revealed the fact that these mechanisms can lead to the unfairness of pgmcc under some network conditions. In this paper, two new mechanisms have been proposed to replace the original ones. One mechanism is to make the sender adapt the value of ssthresh to the network conditions to mimic the action of TCP, and in order to avoid being more aggressive than TCP, the other one is to make the sender reduce the congestion window by half when the acker changes. Our experiment results, parts of which are discussed in this paper, show that the modified pgmcc can achieve better performance than the original one. Copyright © 2005 John Wiley & Sons, Ltd.
An efficient MAC protocol for multi‐channel mobilead hocnetworks based on location information
Authors: Tseng Yu‐Chee , Wu Shih‐Lin , Chao Chih‐Min , Sheu Jang‐Ping 
Published: January 2006

AbstractThis paper considers thechannel assignmentproblem in a multi‐channel MANET environment. We propose a scheme calledGRID, by which a mobile host can easily determine which channel to use based on its current location. In fact, following the GSM style, our GRID spends no communication cost to allocate channels to mobile hosts since channel assignment is purely determined by hosts' physical locations. We show that this can improve thechannel reuseratio. We then propose a multi‐channel MAC protocol, which integrates GRID. Our protocol is characterized by the following features: (i) it follows an ‘on‐demand’ style to access the medium and thus a mobile host will occupy a channel only when necessary, (ii) the number of channels required is independent of the network topology, and (iii) no form of clock synchronization is required. On the other hand, most existing protocols assign channels to a host statically even if it has no intention to transmit [IEEE/ACM Trans. Networks1995;3(4):441–449; 1993;1(6): 668–677;IEEE J. Selected Areas Commun.1999;17(8):1345–1352], require a number of channels which is a function of the maximum connectivity [IEEE/ACM Trans. Networks1995;3(4):441–449; 1993;1(6): 668–677;Proceedings of IEEE MILCOM'97,November 1997;IEEE J. Selected Areas Commun.1999;17(8):1345–1352], or necessitate a clock synchronization among all hosts in the MANET [IEEE J. Selected Areas Commun.1999;17(8):1345–1352;Proceedings of IEEE INFOCOM'99, October 1999]. Through simulations, we demonstrate the advantages of our protocol. Copyright © 2005 John Wiley & Sons, Ltd.