bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variable selection in random calibration of near‐infrared instruments: ridge regression and partial least squares regression settings
Authors: Gusnanto Arief , Pawitan Yudi , Huang Jian , Lane Bill 
Published: March 2003

AbstractStandard methods for calibration of near‐infrared instruments, such as partial least‐squares (PLS) and ridge regression (RR), typically use the full set of wavelengths in the model. In this paper we investigate the effect of variable (wavelength) selection for these two methods on the model prediction. For RR the selection is optimized with respect to the ridge parameter, the number of variables and the configuration of the variables in the model. A fast iterative computational algorithm is developed for the purpose of this optimization. For PLS the selection is optimized with respect to the number of components, the number of variables and the configuration of the variables. We use three real data sets in this study: processed milk from the market, milk from a dairy farm and milk from the production line of a milk processing factory. The quantity of interest is the concentration of fat in the milk. The observations are randomly split into estimation and validation sets. Optimization is based on the mean square prediction error computed on the validation set. The results indicate that the wavelength selection will not always give better prediction than using all of the available wavelengths. Investigation of the information in the spectra is necessary to determine whether all of them are relevant to the objective of the model. Copyright © 2003 John Wiley & Sons, Ltd.
Macrocycles from Perhalogenated Heterocycles
Authors: Sandford Graham 
Published: March 2003

AbstractPerhalogenated heteroaromatic systems, such as trichloro‐s‐triazine and pentafluoropyridine, are multifunctional “building blocks” that react with a number of appropriate difunctional nucleophiles to provide access to a variety of macrocyclic and even cage‐like molecular architectures. Unusual structural and complexation characteristics of the systems reported so far, such as the recognition of anions, provide a further stimulus for the development of this area.
High‐Pressure Structural Trends of Group 15 Elements: Simple Packed Structures versus Complex Host–Guest Arrangements
Authors: Häussermann Ulrich 
Published: March 2003

AbstractThe Group 15 elements P, As, Sb, and Bi all have layered structures consisting of six‐membered rings under ambient conditions and attain the body‐centered cubic (bcc) structure at the highest pressures applied. In the intermediate pressure region, however, phosphorus and its heavier congeners behave profoundly differently. In this region P first attains the open packed simple cubic (sc) structure for a wide range of pressures and then transforms into the rarely observed simple hexagonal (sh) structure. For the heavier congeners complex, incommensurately modulated host–guest structures emerge as intermediate pressure structures. We investigated the high‐pressure behavior of P and As by ab initio density functional calculations in which pseudopotentials and a plane wave basis set were employed. The incommensurately modulated high‐pressure structure of As was approximated by a supercell. Our calculations reproduced the experimentally established pressure stability ranges of the sc and sh structures for P and the host–guest structure for As very well. We found that the sc and especially the sh structure are decisively stabilized by the admixture of d states in the occupied levels of the electronic structure. This admixture releases s–s antibonding states above the Fermi level (s–d mixing). With pressure, s–d mixing increases rapidly for P, whereas it remains at a low level for As. As a consequence, the band energy contribution to the total energy determines the structural stability for P in the intermediate pressure region, giving rise to simple packed structures. On the other hand, in the intermediate pressure region of the heavier Group 15 elements, a delicate interplay between the electrostatic Madelung energy and the band energy leads to the formation of complex structures.
A Novel Design Method of Ratiometric Fluorescent Probes Based on Fluorescence Resonance Energy Transfer Switching by Spectral Overlap Integral
Authors: Takakusa Hideo , Kikuchi Kazuya , Urano Yasuteru , Kojima Hirotatsu , Nagano Tetsuo 
Published: March 2003

AbstractA ratiometric measurement, namely, simultaneous recording of the fluorescence intensities at two wavelengths and calculation of their ratio, allows greater precision than measurements at a single wavelength, and is suitable for cellular imaging studies. Here we describe a novel method of designing probes for ratiometric measurement of hydrolytic enzyme activity based on switching of fluorescence resonance energy transfer (FRET). This method employs fluorescent probes with a 3′‐O,6′‐O‐protected fluorescein acceptor linked to a coumarin donor through a linker moiety. As there is no spectral overlap integral between the coumarin emission and fluorescein absorption, the fluorescein moiety cannot accept the excitation energy of the donor moiety and the donor fluorescence can be observed. After cleavage of the protective groups by hydrolytic enzymes, the fluorescein moiety shows a strong absorption in the coumarin emission region, and then acceptor fluorescence due to FRET is observed. Based on this mechanism, we have developed novel ratiometric fluorescent probes (1–3) for protein tyrosine phosphatase (PTP) activity. They exhibit a large shift in their emission wavelength after reaction with PTPs. The fluorescence quenching problem that usually occurs with FRET probes is overcome by using the coumarin–cyclohexane–fluorescein FRET cassette moiety, in which close contact of the two dyes is hindered. After study of their chemical and kinetic properties, we have concluded that compounds 1 and 2 bearing a rigid cyclohexane linker are practically useful for the ratiometric measurement of PTPs activity. The design concept described in this paper, using FRET switching by spectral overlap integral and a rigid link that prevents close contact of the two dyes, should also be applicable to other hydrolytic enzymes by introducing other appropriate enzyme‐cleavable groups into the fluorescein acceptor.
Cover Picture: Synthesis, Structure, and Properties of Novel Open‐Cage Fullerenes Having Heteroatom(s) on the Rim of the Orifice (Chem. Eur. J. 7/2003)
Authors: Murata Yasujiro , Murata Michihisa , Komatsu Koichi 
Published: March 2003

AbstractThe cover picture shows a newly developed synthetic route to an open‐cage fullerene derivative with a 13‐membered ring orifice and its X‐ray crystallographic structure. The open‐cage fullerene is a key compound for the organic synthesis of endohedral fullerene complexes. Heating a solution of C60 with 3‐(2‐pyridyl)‐5,6‐diphenyl‐1,2,4‐triazine afforded an open‐cage derivative of C60 with an eight‐membered ring orifice, in 85% yield. The orifice was enlarged to a 12‐membered ring by photo‐oxidative cleavage of a double bond at the rim, and further to a 13‐membered ring by insertion of a sulfur atom into the rim by heating with elemental sulfur in the presence of tetrakis(dimethylamino)ethylene (TDAE). An overall yield of the final product based on C60 was 40%. X‐ray crystallography indicated that the final product has a circlular‐shaped orifice, which would probably be the biggest hole opened on the fullerene cage so far. A detailed description of this study is reported by K. Komatsu et al. on p. 1600 ff.
Adjustment of Twist Angles in Pseudo‐Helical Lanthanide Complexes by the Size of Metal Ions
Authors: Mizukami Shin , Houjou Hirohiko , Kanesato Masatoshi , Hiratani Kazuhisa 
Published: March 2003

AbstractControl of self‐assembled nanostructures is a promising technique for nanotechnology. We have examined as to whether nanostructures could be controlled by the size of the central metal ion. Lanthanides are a natural choice for such a study as the size of their trivalent ions changes with atomic number gradually. For this investigation, a series of rare earth complexes ([LaL1], [CeL1], [SmL1], [TbL1], [YL1], and [LuL1]) with a tripodal heptadentate ligand L1 were synthesized, and their X‐ray crystallographic analysis was performed. Although the structures of the ligand (H3L1) and of the metal complex ([ML1]) were quite different, all complexes were almost isostructural pseudohelices. The result of the crystallographic studies demonstrated that the twist angles of helices in the complexes depend on the ionic size of the central metal. A detailed analysis helped determine which portion of the helical strand contributed to the total helicity, and the major cause for the difference in helicity among the lanthanides is discussed. Moreover, this result is the first example showing that LaIII and LuIII complexes with the same tripodal heptadentate ligand are isostractural.
Large Enhancement of the Nonlinear Optical Response of Reduced Fullerene Derivatives
Authors: Koudoumas Emmanuil , Konstantaki Maria , Mavromanolakis Antonis , Couris Stelios , Fanti Marianna , Zerbetto Francesco , Kordatos Konstantinos , Prato Maurizio 
Published: March 2003

AbstractThe third‐order nonlinear optical properties of fulleropyrrolidine and its salt as well as their reduced forms are investigated. Upon reduction, the response increases by up to, and sometimes more than, three orders of magnitude, giving values comparable to the largest ever reported. Calculations and experiments provide a coherent picture for the nonlinear optical properties of these new materials.
Photochemical Reaction of N,N‐Dimethyl‐4‐chloroaniline with Dienes: New Synthetic Paths via a Phenyl Cation
Authors: Guizzardi Benedetta , Mella Mariella , Fagnoni Maurizio , Albini Angelo 
Published: March 2003

AbstractThe irradiation of N,N‐dimethyl‐4‐chloroaniline in the presence of open‐chain dienes in acetonitrile leads to addition of the aminophenyl and chloro groups across one of the double bonds; transannular cyclization takes place with cyclic dienes, leading to an arylnortricyclene from norbornadiene and to 1‐arylbicyclo[3.3.0]octanes from 1,5‐cyclooctadiene. The reaction proceeds by photoheterolysis of the chloroaniline to yield the 4‐aminophenyl cation and addition to a CC double bond. The chemistry of the adduct cation depends on structure and medium, involving ion pairs in MeCN and solvated ions in CF3CH2OH. In the latter solvent, formation of ethers from open‐chain alkenes is accompanied by Wagner–Meerwein hydride shift. In acetonitrile, the cation from cyclooctadiene partitions between deprotonation and Ritter addition, while the one from norbornadiene is reduced; both cations undergo nucleophilic addition in trifluoroethanol. The relevance of these cationic reactions under unusually mild conditions is discussed.
Getting Closer to the Real Bacterial Cell Wall Target: Biomolecular Interactions of Water‐Soluble Lipid II with Glycopeptide Antibiotics
Authors: Vollmerhaus Pauline J. , Breukink Eefjan , Heck Albert J. R. 
Published: March 2003

AbstractA novel synthesized water‐soluble variant of lipid II (LII) was used to evaluate the noncovalent interactions between a number of glycopeptide antibiotics and their receptor by bioaffinity electrospray ionization mass spectrometry (ESI‐MS). The water‐soluble variant of lipid II is an improved design, compared to the traditionally used tripeptide N,N′‐diacetyl‐L‐lysyl‐D‐alanyl‐D‐alanine (KAA), of the target molecule on the bacterial cell wall. A representative group of glycopeptide antibiotics was selected for this study to evaluate the validity of the novel cell‐wall‐mimicking target LII. Structure–function relationships of various glycopeptide antibiotics were investigated by means of 1) bioaffinity mass spectrometry to evaluate solution‐phase molecular interactions with both LII and KAA, 2) fluorescence leakage experiments to study the interactions with the membrane‐embedded lipid II, and 3) minimum inhibitory concentrations against the indicator strain Micrococcus flavus. Our results with the novel LII molecule reveal that some antibiotics interact differently with KAA and LII. Additionally, our data cast doubt on the hypothesis that antibiotic selfdimerization assists in the in‐vivo efficacy. Finally, the water‐soluble lipid II proved to be a better model of the bacterial cell wall.
Highly Stereoselective Radical Cyclization of Haloacetals Controlled by the Acetal Center
Authors: Villar Félix , Kolly‐Kovac Tanja , Equey Olivier , Renaud Philippe 
Published: March 2003

AbstractA systematic investigation of radical haloacetal cyclizations (Ueno–Stork reaction) where the acetal center is the unique stereogenic element is reported. This highly diastereoselective reaction can be used for the preparation of polysubstituted tetrahydrofurans andγ‐lactones. We report herein the full experimental details of reactions where up to three new chiral centers are created. To demonstrate the potential of this approach, short syntheses of (+)‐eldanolide and of tricyclic acetals related to biologically active lignans have been achieved.
A Computational Study of Radical Haloacetal Cyclizations Controlled by the Acetal Center
Authors: Corminboeuf Olivier , Renaud Philippe , Schiesser Carl H. 
Published: March 2003

AbstractThe stereochemical outcome of the radical haloacetal cyclization reaction (Ueno–Stork reaction) has been examined by ab initio and other molecular orbital techniques. It was found that the stereochemistry of 5‐exo‐ and 6‐exo trig cyclizations can be accurately predicted from calculations using moderate levels of theory (UHF/6‐311G** or B3LYP/6‐311G**). A simplified computational procedure, easily run on a standard desktop computer, has been developed that provides excellent predictive ability for the stereochemical outcome for the reactions in question. Interestingly, a novel twist transition state has been identified for the first time in 5‐exo‐trig radical cyclization reactions.
Driving Force Dependence of Intermolecular Electron‐Transfer Reactions of Fullerenes
Authors: Fukuzumi Shunichi , Ohkubo Kei , Imahori Hiroshi , Guldi Dirk M. 
Published: March 2003

AbstractPulse‐radiolytic studies were performed to determine the rate constants of intermolecular electron transfer (ket) from fullerenes (C60, C76, and C78) to a series of arene radical cations in dichloromethane. The one‐electron oxidation potentials of the employed arenes—corresponding to the one‐electron reduction potentials of arene π‐radical cations—were determined in dichloromethane to evaluate the driving forces of electron‐transfer oxidation of fullerenes with arene π‐radical cations. The driving force dependence of log ket shows a pronounced decrease towards the highly exothermic region, representing the first definitive confirmation of the existence of the Marcus inverted region in a truly intermolecular electron transfer. Electron‐transfer reduction of fullerenes with anthracene radical anion was also examined by laser flash photolysis in benzonitrile. The anthracene radical anion was produced by photoinduced electron transfer from 10,10′‐dimethyl‐9,9′,10,10′‐tetrahydro‐9,9′‐biacridine [(AcrH)2] to the singlet excited state of anthracene in benzonitrile. The rate constants of electron transfer (ket) from anthracene radical anion to C60, C70, and a C60 derivative were determined from the decay of anthracene radical anion in the presence of various concentrations of the fullerene. Importantly, a significant decrease in the ket value was observed at large driving forces (1.50 eV) as compared to the diffusion‐limited value seen at smaller driving forces (0.96 eV). In conclusion, our study presents clear evidence for the Marcus inverted region in both the electron‐transfer reduction and oxidation of fullerenes.
A Quantum Chemical Study of Racemization Pathways in Substituted Chrysene Derivatives
Authors: Kind Carsten , Götz Andreas W. , Hess Bernd A. 
Published: March 2003

AbstractThe potential‐energy surfaces of 5,11‐disubstituted 6,12‐dimethoxychrysene and chrysene‐6,12‐dione derivatives were investigated by means of density functional calculations. We report relative energies of all conformers and an identification of the racemisation pathways of the chiral equilibrium structures. By analysis of homodesmotic reactions we were able to obtain an estimate for the strain energy of the substituted compounds. This strain energy can be used as a means of measuring the steric effects exerted by the substituents.
Sequence‐Selective Metalation of Double‐Helical Oligodeoxyribonucleotides with PtII, MnII, and ZnII Ions
Authors: Vinje J. , Parkinson J. A. , Sadler P. J. , Brown T. , Sletten E. 
Published: March 2003

AbstractReactions of [PtCl(dien)]+ (dien=diethylenetriamine), Mn2+ and Zn2+ ions with three different double‐helical oligodeoxyribonucleotides, which contain the central sequence GGXY (XY=AT, TA or CC) have been monitored by NMR spectroscopy. 2 D [1H, 15N] HSQC/HMQC NMR spectroscopy using 15N‐labeled Pt(dien) shows that the rate of formation of 3′‐G‐N 7 and 5′‐G‐N 7 platinated adducts is highly sequence dependent. The relative rates of platination of 5′‐G versus 3′‐G are largest for the sequence ‐GGCC‐, for which only a small fraction of the 3′‐G adduct is formed; for ‐GGTA‐, the rate of 5′‐G platination is about eight times that of 3′‐G, and for ‐GGAT‐ the ratio is 1.2. These values are in qualitative agreement with those obtained for G‐N 7/Mn2+ selectivity as determined by paramagnetic line broadening of the adjacent G‐H 8, and also G‐N 7/Zn2+ selectivity as determined by G‐H 8 chemical shift changes. Fluctuation in the nucleophilicity of G‐N 7 may be explained by variation of the π‐stacking interaction between base residues along the double helix. The reaction mixtures containing platinated 3′‐G and 5′‐G fractions were separated by HPLC. Since the duplexes are self‐complementary, the platinated single strands were readily annealed to duplexes with twofold symmetry and analyzed by 2 D [1H, 1H] NOESY NMR spectroscopy. Unexpectedly, the 5′‐G‐H 8 resonance signals of both 5′‐G and 3′‐G platinated duplexes showed large downfield shifts in the range δ=0.3–0.6 ppm, while the 3′‐G‐H 8 resonance signals in both cases exhibited no, or only slight, upfield shifts. Resonance signals for several other protons in the central region undergo large chemical shift variations induced by platination, indicating that monofunctional binding to DNA leads to appreciable conformational changes.
Photochemical and Thermal Transformations of 1‐Aryloxy‐2‐ and 4‐Azidoanthraquinones
Authors: Klimenko Lubov S. , Pritchina Elena A. , Gritsan Nina P. 
Published: March 2003

AbstractThe photolysis of 1‐aryloxy‐2‐azidoanthraquinones (3) in benzene is described herein which gave 1‐hydroxy‐2‐arylaminoanthraquinones (4) and two types of 5H‐naphtho[2,3‐c]phenoxazine‐8,13‐diones (5 and 6). Thermolysis of 3 yielded only one of phenoxazines 5 and small amount of 4. On the other hand thermolysis of 3 in the presence of phenols gave phenoxazine 6 as a major product. The mechanism of the photolysis and thermolysis of 2‐azido‐1‐aryloxyanthraquinones (3) is proposed and supported by the results from semiempirical calculations. A relative contribution of the primary photoreactions—azido group dissociation and aryl group migration was estimated to be 3:1. Photolysis and thermolysis of 4‐azido‐1‐(p‐tert‐butylphenoxy)‐9,10‐anthraquinone (8) gave 3‐(p‐tert‐butylphenoxy)‐anthra[1,9‐cd]‐izoxazole‐6‐one (9) as the only product.
Growth of Well‐Aligned γ‐MnO2 Monocrystalline Nanowires through a Coordination‐Polymer‐Precursor Route
Authors: Xiong Yujie , Xie Yi , Li Zhengquan , Wu Changzheng 
Published: March 2003

AbstractA new coordination‐polymer‐precursor route has been developed to synthesize nanowires under hydrothermal conditions. In the present work, well‐aligned γ‐MnO2 nanowires, growing along the [0 0 2] axis, have successfully been prepared by selecting an appropriate coordination polymer [{Mn(SO4)(4,4′‐bpy)(H2O)2}n] as precursor. In comparison with the experimental results from other coordination‐polymer precursors, it is found that only [{Mn(SO4)(4,4′‐bpy)(H2O)2}n] is appropriate for the formation of γ‐MnO2 crystal lattices during the process of oxidization. The IR absorption spectra of as‐obtained precipitates at different reaction intervals minutely describe the reaction process, due to the different coordination abilities of ligands in the coordination polymer. More evidence about the mechanism will be further explored in the future study. Further observations show the ordered alignment of nanowires' tops and such well‐aligned nanowires provide more possible applications in lithium batteries.
Epithelial lesions in prophylactic mastectomy specimens from women with BRCA mutations
Authors: Kauff Noah D. , Brogi Edi , Scheuer Lauren , Pathak Dorothy R. , Borgen Patrick I. , Hudis Clifford A. , Offit Kenneth , Robson Mark E. 
Published: March 2003

AbstractBACKGROUNDIt has been suggested that BRCA‐associated breast carcinoma may often lack a detectable preinvasive phase. To investigate this hypothesis, the authors compared the prevalence of histopathologic lesions in prophylactic mastectomy (PM) specimens from women with BRCA mutations and in mastectomy specimens obtained at autopsy from an age and race‐matched comparison group without a known cancer predisposition.METHODSAll specimens from women with a deleterious BRCA1 or BRCA2 mutation who participated in an ongoing follow‐up study and underwent PM at Memorial Sloan‐Kettering Cancer Center between November 1, 1987 and May 31, 2001 were reviewed. For each case, breast tissue from two age and race‐matched women without a known cancer predisposition was also reviewed. The prevalence of benign, premalignant, and cancerous lesions was compared.RESULTSMastectomy specimens from 24 cases and 48 comparison subjects were reviewed. Ductal carcinoma in situ (DCIS), atypical ductal hyperplasia (ADH), and atypical lobular hyperplasia (ALH) were all more common in PM specimens from women with BRCA mutations than in those from the comparison group. The odds ratio for the detection of any high‐risk lesion (DCIS, lobular carcinoma in situ, ADH, or ALH) in specimens from BRCA mutation carriers was 12.7 (95% confidence interval, 3.1–52.4; P < 0.001).CONCLUSIONSLesions associated with an increased risk of subsequent malignancy are more common in PM specimens from women with BRCA mutations than in breast tissue obtained at autopsy from unaffected women without a known predisposition. This finding suggests that hereditary breast carcinoma has a preinvasive phase that may be detectable with aggressive surveillance. Cancer 2003;97:1601–8. © 2003 American Cancer Society.DOI 10.1002/cncr.11225