bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamics of membrane lipid hydration
Authors: Wennerström H. , Sparr E.
Published: October 2007

Zwitterionic or polar lipids that form lamellar phases swell in the presence of water to take up between 10 and 30 water molecules per lipid. The degree of the water uptake depends both on the state of the alkyl chains, liquid or solid, and on the nature of the polar group. The swelling behavior has been extensively characterized on the free-energy level through measuring the relation between the chemical potential of the water and the degree of swelling. In spite of the extensive studies of this type, consensus is still lacking concerning the molecular mechanism causing the swelling. The two main ideas that explain the existence of the effectively repulsive force between two opposing bilayers are (i) a water structure effect and (ii) thermal excitations of the lipid molecules. The first is from a thermodynamic perspective caused by a negative partial molar enthalpy of the water, whereas for the second, the repulsion is caused by positive entropy.

A further insight into the swelling behavior is obtained by simultaneously measuring the partial molar free energy and the partial molar enthalpy using a twin double calorimeter. Such measurements show for binary lipid–water and for ternary lipid –cholesterol –water systems that the first four water molecules enter the bilayer driven by a favorable enthalpic interaction, whereas for higher water contents, the partial free energy and the partial enthalpy have opposite signs. In spite of the fact that the partial free energy varies with water content in a similar way, the partial enthalpies depend strongly on the nature of the lipid sample. Thus, it is obvious that a molecular interpretation of the enthalpy values has to involve the lipid degrees of freedom. This is a strong indication that the interpretation of the free energies should also include the same degrees of freedom. This gives experimental evidence in favor of an interpretation of the molecular mechanism causing the swelling that involves changes in the thermal excitation of the lipid degrees of freedom.
Quantum aspects of low-temperature properties of crystals: A calorimetric study in interaction with spectroscopy and diffraction
Authors: Matsuo T.
Published: October 2007

Some of the molecular and ionic crystals containing hydrogen undergo phase transitions only when they are deuterated. This indicates that not only the intermolecular potential energy, but also the kinetic energy of the nuclei are involved in an essential way in the mechanisms of the transitions. The quantum effects implied by these observations are discussed in terms of tunneling of protons and deuterons. Experimental evidence for deuteration-induced phase transitions and nuclear tunneling states accumulated by low temperature calorimetry, far infrared spectroscopy,and neutron diffraction is discussed.
Exploring the entire conformational space of proteins by high-pressure NMR
Authors: Akasaka Kazuyuki
Published: October 2007

A protein in solution is a thermodynamic entity, spanning, in principle, the entire allowed conformational space from the fully folded N to the fully unfolded U. Although some alternately or partially folded higher-energy conformers may coexist with N and U, they are seldom detected spectroscopically because their populations are usually quite low under physiological conditions. I describe here a new type of experiment, a combination of multidimensional NMR spectroscopy with pressure, that is capable of detecting and analyzing structures and thermodynamic stability of these higher-energy conformers. The idea is based on the finding that under physiological conditions the conformational order of a globular protein normally decreases in parallel with its partial molar volume (negative δV), so that under equilibrium conditions, the population is shifted to a less and-less-ordered conformer with increasing pressure. In principle, with the high space resolution of the multidimensional NMR, the method enables one to explore protein structure and stability in atomic detail in a wide conformational space from N to U with pressure and temperature as variables. The method will provide us with a strong basis for understanding the fundamental phenomena of proteins:function, folding, and aggregation.
Significance of impurities in the safety evaluation of crop protection products (IUPAC Technical Report)
Authors: Ambrus Á. , Hamilton D. J. , Kuiper H. A. , Racke K. D.
Published: October 2007

There may be substantial differences in the chemical composition of technical-grade products of the same active ingredient manufactured under different conditions, from different raw materials, or by different routes of synthesis. Resulting differences in impurity content may significantly affect the toxicological properties of pesticide products. Relevant impurities are those that may exhibit pronounced toxic effects compared to the active ingredient, affect phytotoxicity or physical properties of formulations, result in undesirable residues in food,or cause environmental contamination. The first safety assessment of an active ingredient by a regulatory body considers toxicological data developed on a representative batch of technical products, with the assumption that the material produced commercially by the original or generic manufacturers has an equal or higher content of active ingredient and contains the same or fewer impurities at equal or lower concentrations as the fully characterized technical product used in the toxicological tests. Three steps are essential for ensuring the safety of commercial technical- grade pesticide products, whether produced by the original manufacturer or by generic manufacturers. First, the identity and chemical structure of the impurities must be elucidated.This should include positive identification of major (=1 %) and all toxicologically or environmentally relevant impurities, and characterization of minor impurities (>0.1 %). Second, in addition to recognition of a minimum active ingredient content, official specifications should also list relevant impurities and their maximum permissible concentrations.Implementation of these specifications should be aided by a decision-making scheme for establishing similarity of subsequently evaluated technical products. Third, appropriate analytical methods for the detection and quantification of impurity levels should be developed and employed in a quality-monitoring program associated with the manufacturing and formulation process.
Critical assessment: Use of supersonic jet spectrometry for complex mixture analysis (IUPAC Technical Report)
Authors: Imasaka Totaro , Moore D. S. , Vo-Dinh T.
Published: October 2007

When cooled to a temperature of a few K using supersonic jet expansion into a vacuum, a molecule exists in the lowest vibrational level of the ground electronic state and is isolated at collision-free conditions. The absorption or excitation/fluorescence spectrum is then greatly simplified, when transitions occur from this single vibrational level to a limited number of vibrational levels in the excited electronic state. This method, called supersonic jet spectrometry, is a powerful analytical technique because of its high selectivity, since the chemical species can be accurately identified and selectively quantified using the sharp spectral features even for large molecules. Supersonic jet spectrometry has distinct advantages over other low-temperature spectrometries,in that it can be combined with gas-phase separation and detection techniques such as chromatography or mass spectrometry. Therefore, this spectrometric technique can be used as a versatile analytical means, not only for basic research on pure substances, but also for practical trace analysis of chemical species in multicomponent samples (e.g., in biological monitoring or in environmental monitoring).
σ Bonds: Electronic structure, photophysics, and photochemistry of oligosilanes
Authors: Fogarty H. A. , Casher D. L. , Imhof Roman , Schepers T. , Rooklin D. W. , Michl J.
Published: October 2007

The making and breaking of σ bonds is an integral part of almost all photochemical reactions. Yet, the electronic states of σ electrons are not nearly as well understood as the states of π-electron systems. Efforts in our laboratory to enhance the current state of their understanding are described, using the specific example of oligosilanes. We address the intrinsically cyclic nature of σ delocalization and its dependence on chain length and conformation, both in terms of theory and spectroscopic experiments, from the simplest disilane chromophore to the spectral properties of the individual conformers of permethylated heptasilane. We also describe a new low-energy luminescence from certain conformers of permethylated oligosilanes.
Photochemical processes in photosynthesis studied by advanced electron paramagnetic resonance techniques
Authors: Lubitz Wolfgang
Published: October 2007

Various continuous-wave and pulse electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) experiments performed on the radical species occurring in photosynthetic reaction centers of plants and bacteria during light-induced charge separation are reviewed here. Emphasis is placed on time-resolved experiments performed on short-lived intermediate states such as radical pairs and triplet states for which also hyperfine information can be obtained from pulse ENDOR spectroscopy. Detailed insight into the electronic structure of these intermediates and their interaction with the protein environment is now becoming available.
Electron-transfer reactions studied by laser-induced optoacoustics: Learning about chromophore-medium (protein) interactions
Authors: Braslavsky S. E.
Published: October 2007

The ability of time-resolving enthalpy (ΔH) and structural volume (ΔV) changes in the nano- to µs time range offered by laser-induced optoacoustic spectroscopy (LIOAS) opens the possibility of a stepwise thermodynamic analysis of chromophore-medium interactions upon photoinduced reactions in biological systems. We applied LIOAS to biological photoreceptors, as well as to model systems, with the purpose of understanding the origin of ΔV in electron-transfer (ET) reactions in those systems. The linear correlation between the counterion-dependent volume changes and ΔH for the free-radical formation upon ET quenching of erythrosin dianion triplet, 3Er2-, by Mo(CN)84- and of Ru(bpy)32+ by MV2+ is interpreted in terms of an enthalpy–entropy compensation owing to the strong influence of the counterions on the water hydrogen-bond network in which the reactants are embedded. The relatively large entropic term determined for radical formation thus originates in water rearrangements during the process. The increasing contraction in acetonitrile, propionitrile, butyronitrile, and valeronitrile for the ET quenching of 3Zn-tetraphenylporphin by 1,4-benzoquinone is understood by considering the increasing interaction strength between the electron-pair donor nitriles and ZnTPP+. Thus, in polar environments, specific chromophore-medium (solvent or proteins) interactions, in addition to electrostriction, should be considered to explain the time-resolved ΔV and ΔH values.
Triplet carbenes: From fleeting existence to attractive molecular units
Authors: Tomioka H.
Published: October 2007

Attempts to stabilize the triplet state of carbenes to the extent that they can survive under normal conditions were made, in which triplet carbenes having a half-life of 19 min are realized. A way to use the resulting persistent carbene as a unit to construct photosensitive magnetic materials is also discussed.
Regio- and stereoselective functionalization of electron-deficient alkenes by organosilicon compounds via photoinduced electron transfer
Authors: Mizuno K. , Hayamizu T. , Maeda Hajime
Published: October 2007

Regio- and stereoselective photoallylation of electron-deficient alkenes by use of allylic silanes via photoinduced electron transfer has been described. Similar photoinduced  functionalization reactions such as arylmethylation, alkylation, and silylation can be achieved by using a variety of organosilicon compounds. These photoreactions proceed via radical cations of organosilicon compounds and radical anions of electron-deficient alkenes as reactive intermediates. The key step of the photoreactions is the attack of carbon radicals, which are generated from the radical cations of organosilicon compounds, on the radical anions of alkenes. The mechanism of the regio- and stereoselective photofunctionalization is discussed.
Photoinduced dynamics in hydrogen-bonded rotaxanes
Authors: Brouwer Albert M. , Fazio Sandro M. , Frochot Céline , Gatti Francesco G. , Leigh David A. , Wong Jenny K. Y. , Wurpel George W. H.
Published: October 2007

Two classes of rotaxanes are described in which photoinduced processes modulate a large-amplitude motion. In the first type, E–Z-isomerization of a fumaric diamide unit to a maleic diamide leads to a substantial weakening of the hydrogen bonds between the diamide and the macrocyclic ring that surrounds it. As a result, the rate of the pirouetting motion is increased approximately by six orders of magnitude. In the second type, intermolecular photoinduced electron transfer is used to induce a reversible shuttling motion on a time scale of microseconds. Medium effects on the rate of shuttling are presented.
Electron and excitation transfer in hetero-supramolecular assemblies and at molecule­nanoparticle interfaces
Authors: Piotrowiak Piotr , Deshayes Kurt , Romanova Zinaida S. , Pagba Cynthia , Hore Sarmimala , Zordan Giovanni , Place Ileana , Farrán Agnes
Published: October 2007

Encapsulation of chromophores within Cram-type hemicarcerands allowed the investigation of fundamental photophysical phenomena, such as long-range triplet energy transfer, electron transfer, and the remote heavy atom effect. Furthermore, novel water-soluble hemicarcerands are being used to develop unique hybrid materials composed of semiconductor nanoparticles and host–guest assemblies. Photoinduced charge injection from the “incarcerated” guest into the conduction band of the semiconductor has been demonstrated.
Molecular porphyrin­fullerene architectures
Authors: Guldi D. M.
Published: October 2007

This article describes the utilization of porphyrin and fullerene architectures—yielding artificial light-harvesting antenna and reaction center mimics—to tune the electronic coupling element between electron donor and electron acceptor and ultimately to affect the total reorganization energy. Most importantly, the effects that these parameters have on the rate, yield, and lifetime of the energetic charge-separated states are discussed.
Cation-dependent photochromic properties of novel ditopic receptors
Authors: Fedorova O. A. , Fedorov Y. V. , Andrjukhina E. N. , Gromov S. P. , Alfimov M. V.
Published: October 2007

Novel crown-containing 2-styrylbenzothiazoles were prepared to obtain optical ditopic receptors that can bind alkaline-earth metal cations by a crown ether fragment and could serve as host for the heavy metal cations and proton owing to the presence of the heterocyclic part. Photochemical transformations of the ditopic receptors depend on the type of metal cations present in solution. They include trans–cis-isomerization, [2+2]-cycloaddition, and electrocyclic reaction.
Photoresponsive porous organosilicas
Authors: García Hermenegildo
Published: October 2007

Novel structured functional hybrid materials can be obtained by incorporating photoresponsive organic components into the silicate walls of periodic mesoporous silicates. Two such materials are described, containing either viologens or stilbene analogs. Thermal or photochemical activation of viologen units generates the corresponding radical cations, whose lifetime can vary from months to milliseconds, depending on the surfactant content of the solid. In a second example, the porosity and tortuosity of the silicate can be modulated by irradiation of an organosilica containing a stilbene-like moiety.
Critically evaluated propagation rate coefficients in free-radical polymerizations: Part III. Methacrylates with cyclic ester groups (IUPAC Technical Report)
Authors: Beuermann Sabine
Published: October 2007

Propagation rate coefficients, kp, as a function of temperature, are reported for bulk free-radical homopolymerizations of oxiranylmethyl, cyclohexyl, and benzyl methacrylate at ambient pressure and low conversion. The data were obtained from experiments combining pulsed-laser initiated polymerization and size-exclusion chromatography. The data determined from experiments carried out in independent laboratories obey the consistency criteria established for this technique. The rate coefficients for the three monomers are well represented by a single Arrhenius relation.
Minimum requirements for reporting analytical data for environmental samples (IUPAC Technical Report)
Authors: Egli Hans , Dassenakis Manos , Garelick Hemda , van Grieken René , Peijnenburg W. J. G. M. , Klasinc Leo , Kördel Werner , Priest Nick , Tavares Tania
Published: October 2007

In view of the significance of environmental analytical data, it is essential that the quality of both sampling strategy and analysis be assured and that procedures used, as well as all relevant additional information, are reported. There is a minimum level of information required in order to guarantee the fitness-for-use of the data. Emanating from discussions on the fundamental problems of the analysis of environmental samples for chemical or biological contaminants, a general guidance is given regarding the minimum information that should be provided to adequately describe the sampling strategy, method of sampling, sample properties, handling between sampling and analysis (including storage conditions, pretreatments, homogenization, subsampling), and the analytical methodology (including calculation and validation procedures). Special attention and specific guidance are given for the environmental compartments soil, pore water, groundwater, inland surface water, sediment, seawater, precipitation water, and air.
Atomic weights of the elements 2001 (IUPAC Technical Report)
Authors: Loss R. D.
Published: October 2007

The biennial review of atomic-weight, Ar(E), determinations and other cognate data have resulted in changes for the standard atomic weights of the following elements:  FromToZinc65.39 ± 0.0265.409 ± 0.004Krypton83.80 ± 0.0183.798 ± 0.002Molybdenum95.94 ± 0.01 95.94 ± 0.02Dysprosium162.50 ± 0.03162.500 ± 0.001

Presented are updated tables of the standard atomic weights and their uncertainties estimated by combining experimental uncertainties and terrestrial variabilities. In addition, this report again contains an updated table of relative atomicmass values and half-lives of selected radioisotopes. Changes in the evaluated isotope abundance values from those published in 1997 are relatively minor and will be published in a major review of each element in 2003. Many elements have a different isotopic composition in some nonterrestrial materials. Some recent data on parent nuclides that might affect isotope abundances or atomic-weight values are included in this report for the information of the interested scientific community.
New discoveries at the interface of boron and carbon chemistries
Authors: Hawthorne M. Frederick
Published: October 2007

The continued growth of polyhedral borane chemistry is illustrated by the successful synthesis of [closo-B12(OH)12]2 –by the H2O2 oxidation of [closo-B12H12,]2. The hydroxylated species reacts with common organic reagents to produce 12-fold degenerately substituted carboxylate esters, ethers, and carbamate esters. The ether derivatives undergo facile and reversible redox reactions in which the B12 scaffold serves as a one-or two-electron donor giving stable oxidation states described by [closo -or hypercloso-B12OR)12]n with n = −2,−1,and 0. The loss of polyhedral electrons is compensated by back-bonding from the attached ether oxygen substituents. Structural comparisons are presented along with representative reaction chemistry. Derivatives that bear functional groups on the termini of the 12-fold set of substituents provide a vast array of potential applications. To distinguish these new polyfunctional icosahedral species from dendrimers,they have been designated as closomers.
Reactions of boranes and metallaboranes with phosphines
Authors: Barton Lawrence , Volkov Oleg , Hata Mitsuhiro , McQuade Paul , Rath Nigam P.
Published: October 2007

This paper reports extensions of the well-established field of phosphine–borane chemistry. Linked clusters, for example, {[(PPh3)2(CO)OsB4H7-3-BH2-PPh2]2 [(Fe(C5H4)2]}, are formed in reactions of rigid backboned bidentate phosphines with {2,2,2-(PPh3)2(CO)-nido-2-OsB5H9]. Reaction of bidentate phosphines with the unsaturated clusters [8,8-PPh3)2-nido-8,7-RhSB9H10] and [9,9-(PPh3)2-nido-9,7,8-RhC2B8 H11] leads to the isolation of novel species such as {1-(PPh3)[1,3-(µ-dppm)]-closo -1,2-RhSB9H8},with a dppm molecule bridging adjacent metal and boron vertices in the cage, [1,1-(ç2-dppe)-3-(ç1-dppm)-closo-1,2-RhSB 9H8], a mixed ligand system, and {9,9-ç2-[(ç2-BH3)PPh2PCH2 PPh2]-nido- 9,7,8-RhC2B8H11} which contains a bidentate dppm BH3 moiety. The formation of bidentate phosphine-linked main group transition-metal moieties such as [BH3PPh2(CH)nPPh2IrCp*Cl2] is also described as is an example of a bidentate phosphine-polyhedral borane adduct [NR4][B11H12(dppm)] in which the borane cage is isoelectronic with [B11H14]–. Finally, a novel oxidative coupling reaction promoted by Cp2ZrCl2/n-BuLi to form the new nonaborane cage system, arachno -B9H11(PPh3)2, an unusual homolog of the well-known species B10H12(PPh3)2, is reported.
Two-electron aromatics containing three and four adjacent boron atoms
Authors: Präsang C. , Mlodzianowska A. , Geiseler G. , Massa W. , Hofmann M. , Berndt A.
Published: October 2007

A two-electron aromatic bis (tris-trimethylsilylmethylene)-substituted tetraborane(4) was found to be a useful precursor for the synthesis of two-electron aromatic tetraboranes(6), triboracyclopropanates,as well as tetraboranes(6) distorted toward triboracyclopropanates with boryl bridges. Bishomo two-electron aromatics with a borata bridge and a protonated borata bridge, respectively, are also presented.
Role of B(C6F5)3 in catalyst activation, anion formation, and as C6F5 transfer agent
Authors: Bochmann Manfred , Lancaster Simon J. , Hannant Mark D. , Rodriguez Antonio , Schormann Mark , Walker Dennis A. , Woodman Timothy J.
Published: October 2007

The versatile reactivity of B(C6F5)3 in alkene polymerization reactions is summarized. Adduct formation with basic anions such as CN– and NH2– gives extremely weakly co- ordinating diborates, which are the basis of some of the most active polymerization catalysts known to date. By contrast, the reaction of B(C6F5)3 with zirconium half-sandwich complexes leads to extensive C6F5 transfer, including the surprising formation of borole-bridged triple decker complexes. Main group alkyls undergo such C6F5 exchange reactions very readily unless donor ligands are present. Borate salts of new three-coordinate zinc alkyl cations proved to be highly effective catalysts for the ring-opening polymerization of epoxides and lactones.
Boron clusters for medicinal drug design: Selective estrogen receptor modulators bearing carborane
Authors: Endo Yasuyuki , Yoshimi Tomohiro , Miyaura Chisato
Published: October 2007

The molecular shape and hydrophobicity of dicarba-closo -dodecaboranes may allow a new medical application as biologically active molecules. Recently, we have developed potent estrogen receptor (ER) agonists bearing carborane cage. The most potent compound (BE120) exhibited activity at least several times greater than that of 17 beta-estradiol in luciferase reporter gene assay and ER alpha binding. We also designed and synthesized estrogen antagonists on the basis of the structure of BE120, and we noticed the characteristic features of compound (BE360) having carborane cage and two phenols. The ER binding affinity of BE360 is comparable to that of estradiol. To examine in vivo estrogenic activity of the compound in bone, ovariectomized (OVX) mice were given BE360 or estradiol subcutaneously for 4 weeks. Treatment with BE360 at 1–30 µg/day dose-dependently restored bone loss in OVX mice to sham level without estrogenic action in uterus. These results suggest its possible application to osteoporosis as a new type of selective ER modulator.
Rearrangements in the nona-and azanonaborane clusters
Authors: El-Zaria M. , Dörfler U. , Gabel D.
Published: October 2007

In the conversion of nonaboranes B9H13SMe2 to azanonaboranes B8NH11-NHR, one boron atom is lost. This boron atom was identified, and a pathway for the rearrangement of the cluster is proposed, based on the fate of covalently labeled boron atoms.
Synthesis and properties of linear, branched, and cyclic metallacarborane oligomers
Authors: Grimes Russell N.
Published: October 2007

A rapidly developing area of organometallic chemistry centers on polynuclear metal coordination compounds having specified, highly symmetric geometries such as squares, triangles, rectangles, or rigid rods. Interest in such molecules arises in part from their unusual, aesthetically appealing structures, and on the possibilities for assembling them into extended systems having useful electronic, optical, magnetic, catalytic, or other properties. Given their characteristic thermal and oxidative stability, chemical versatility, and relatively low-bulk, metallocene-like steric requirements, small metallacarboranes are attractive candidates as building blocks for such structures. Recent work in our laboratory on the controlled substitution and linkage of these clusters has opened the way to some new metallacarborane “designer ”chemistry that is described in this article.
Recent advances in the chemistry of carboranes and metallacarboranes
Authors: Hosmane Narayan S.
Published: October 2007

An overview of the syntheses, structures, and reactivity of the compounds formed by the incorporation of a number of d- and f-block metals into C2B4- and C2B9-carborane cages have been presented. In addition,the development of a safe, bench-scale preparation of the toxic and commercially unavailable polyhedral borane synthon, namely pentaborane(9), has also been described. Thus, this report discusses the latest developments leading to a sys- tematic synthetic approach to a number of carborane precursors and the subsequent reaction chemistry in the formation of a number of “carbons-apart ”metallacarboranes.
Use of organoboron halides in organic synthesis
Authors: Kabalka G. W. , Wu Z. , Ju Y.
Published: October 2007

Several new organic transformations have been achieved utilizing boron halide reagents. Aryl aldehydes are conveniently converted to gem-dichloromethylbenzenes using boron trichloride. Aryl aldehydes are alkylated by alkylboron chlorides in a Grignard-like fashion to generate the corresponding arylalkanols or alkylboron chlorides. Aryl aldehydes react with divinylboron halides (generated via the haloboration of alkynes) to produce 1,5-di-halo-1,4-dienes in excellent yields.
Polyhedral boron-containing cluster chemistry: Aspects of architecture beyond the icosahedron
Authors: Shea Suzanne L. , Bould Jonathan , Londesborough Michael G. S. , Perera Sarath D. , Franken Andreas , Ormsby Daniel L. , Jelínek Tomás , Stíbr Bohumil , Holub Josef , Kilner Colin A. , Thornton-Pett Mark , Kennedy John D.
Published: October 2007

For the structural extent of the polyhedral molecular chemistry of boron to rival that of the organic chemistry of the carbon hydrides, (a) the individual boron-containing polyhedra need to be fused together to make larger contiguous covalent assemblies, and (b) an intermolecular chemistry needs to be developed. Contemporary examples are given that illustrate novel chemistry in both these areas and that may point the way to some future developments.
New asymmetric syntheses with boronic esters and fluoroboranes
Authors: Matteson Donald S.
Published: October 2007

Efficient cleavage of sterically hindered boronic esters of asymmetric diols to recover both the diol and a more reactive borane derivative has been a challenging problem. A remarkable borosilicate glass-catalyzed cleavage with thionyl chloride and imidazole proved less useful than hoped for. Potassium bifluoride converts boronic esters to diols and alkyltrifluoroborates. These with chlorosilanes yield alkyldifluoroboranes, which with alkyl azides form secondary amines in high enantiopurity.
Mechanism of the opening of the closo-NB11 clusters by bases
Authors: Paetzold Peter , Müller Jens , Meyer Franc , Lomme Petra
Published: October 2007

The icosahedral aza-closo-dodecaboranes RNB11H11(R = H, Me, Ph) are opened by neutral bases L or anionic bases X– to give the nido-species RNB11H11L or [RNB11H11X]–, respectively, with a nonplanar pentagonal aperture; the N atom and a BHB hydrogen bridge are situated at opposite sides of the aperture. The BL or the BX vertex is found in the aperture either adjacent to the hydrogen bridge (type 1; C1) or adjacent to nitrogen (type 2;C1) or off the aperture adjacent to nitrogen on a mirror plane (type 3;Cs). At any rate, the isomer of type 1 is the primary product, which may rearrange to yield an isomer of type 3 via an isomer of type 2. Working in deuteromethanol shows that the bridging H atom originates from the primarily attacked BH vertex. The process from RNB11H11 to its base adduct of type 3 includes the opening and the closure of skeletal BN bonds and the jumping of the extra-H atom from endo into bridging positions and vice versa, whereas the base does not alter its position. The application of the opening process to a series of aza-closo-dodecaboranes with non-hydrogen boron ligands confirms that only atoms of the ortho-belt of the starting material are involved in structural changes. The elementary steps from the closo -species to the three isomers are identified as a [3c, 1c] collocation and subsequent [3c, 2c] translocations in the picture of molecular orbitals localized over three or two centers or to one center (lone pair).
Tandem allylboration-ring-closing metathesis reactions for the preparation of biologically active molecules
Authors: Ramachandran P. Veeraraghavan , Reddy M. Venkat Ram , Brown Herbert C.
Published: October 2007

The development of asymmetric synthesis during the past two decades aided organic chemists considerably in the synthesis of complex natural products. Organoborane chemistry continues to play an important role in asymmetric synthesis. One of the important reactions that has become very common in the arsenal of synthetic chemists is allylboration and related reactions. Another important reaction that has recently attained enormous importance in organic chemistry is the ring-closing metathesis (RCM) reaction. Indeed, a combination of allylboration and RCM reactions provides an excellent route to cyclic ethers, lactones, lactams, etc. Herein, we describe a sequential asymmetric allylboration and RCM reaction protocol that has been utilized for the synthesis of several alpha-pyrone-containing natural products,particularly biologically active molecules.
Small boranes, carboranes, and heterocarboranes
Authors: Siebert W. , Maier C.-J. , Maier A. , Greiwe P. , Bayer M. J. , Hofmann M. , Pritzkow H.
Published: October 2007

Dehalogenation of 1,2-dichloro-diborane(4) derivatives with Na/K alloy does not lead to planar cyclo-tetraboranes but to the blue puckered diisopropylamino compound and to the yellow 2,2,6,6-tetramethylpiperidino-tetraboratetrahedrane derivative, respectively. With smaller dialkylamino substituents, the formation of orange-red cyclo-hexaborane (BNMe2)6 and the green closo -hexaborane (BNEt2)6 is observed. When a 1:1 mixture of Me2NBCl2 and [Me2N(Cl)B]2 is dehalogenated, a small amount of colorless crystals of the planar diamond-shaped tetrabora-bicyclo-butane [(Me2N)2BB -BNMe2]2 is obtained. Its MO analysis reveals that eight framework electrons are used to form two 3c,2e sigma bonds, one 4c,2e pi bond, and one 4c,2e sigma bond along the edges.

A new approach to reactive closo-dicarbapentaboranes involves the hydroboration of dichloroboryl-tbutylacetylene with HBCl2 leading to Me3CCH2C(BCl2)3. On heating, it is transformed into the closo-dicarbapentaborane (Me3CCH2C)2(BCl)3, in which the chlorine atoms may be substituted to give new derivatives.

By reacting B2Cl4 with C5Me5-SiMe3 the nido-1-borane-2,3,4,5,6-pentacarbahexa- borane(6)is stabilized by the Lewis acid BCl3 to give (MeC)5B-BCl3.

Hydroboration of 3,4-bis(isopropylidene)-1,3-diborolanes leads to the formation of nido-2,3,5-tricarbahexaboranes(7),which may be deprotonated to give the corresponding anions isolobal with C5H5
-. Heterotricarbahexaboranes are obtained when a 3,4-bis(dichloroboryl)-2,5-hexadiene derivative is reacted with heptamethyldisilazane and hexamethyl-disilthiane to give the corresponding 1,2,5-azadiborolane and thiadiborolane. Their hydroboration leads to the aza-and thia-nido-dicarbahexaboranes, respectively.
Molecular and polymeric precursors to boron carbide nanofibers, nanocylinders, and nanoporous ceramics
Authors: Pender Mark J. , Forsthoefel Kersten M. , Sneddon Larry G.
Published: October 2007

New decaborane-based, single-source molecular and polymeric precursors to boron carbide have been developed that enable the formation of boron carbide in processed forms, including nanofibers, nanocylinders, and nanoporous materials.
New carboranes and phosphaboranes
Authors: Stíbr Bohumil
Published: October 2007

A review is presented on the new routes to the synthesis of the monocarbaboranes [arachno-6-CB9H14]–, arachno-4-CB8H14, and nido-1-CB8H12, that now have become excellent starting materials for the preparation of a family of seven-, eight-, and nine-vertex closo-monocarbaborane anions [2-CB6H7]–, [1-CB7H8]–, and [4-CB8H9]–. These anions exhibit high stability and have a good chance to become new candidates for weakly coordinated anion chemistry. Discussed are also reactions leading new families of phosphacarboranes that contain one, two, and three phosphorus atoms in the cage. These compounds, namely closo- 2,1-PCB8H9, closo-6,1-PCB8H9, nido -7,8,9-PC2B8H11, nido-7,8,11-PC 2B8H11, and nido- 7,8,9,10-P3CB7H8 ,are structural analogs of the corresponding carboranes and are likely to exhibit similar chemical behavior.
Boron clusters: Do they receive the deserved interest?
Authors: Teixidor Francesc , Viñas Clara , Demonceau Albert , Nuñez Rosario
Published: October 2007

New applications in which the carborane and metallacarborane species play a crucial role have been recently developed. In these applications, clusters display many particular characteristics that do not find parallel in their organic counterparts. The o-carborane can modulate the C···C distances depending on the substituents bonded to the cluster carbon atom and can lead to the formation of uncommon halogenophosphane charge-transfer “spoke ” complexes with iodine due to their electron-withdrawing capacity. Besides, metallacarboranes have been used as doping agents in organic conducting polymers and as catalysts in Kharasch reactions.
Evolving patterns in boron cluster chemistry
Authors: Fox Mark A. , Wade Ken
Published: October 2007

This paper outlines the development of our knowledge and understanding of the structures and bonding of boron cluster compounds, with particular reference to the evolving complementary roles localized bonding and molecular orbital treatments have played in providing simple rationalizations of their polyhedral molecules.
Supraicosahedral (metalla) carboranes
Authors: Boyd Alan S. F. , Burke Anthony , Ellis David , Ferrer Daniel , Giles Barry T. , Laguna Miguel A. , McIntosh Ruaraidh , Macgregor Stuart A. , Ormsby Daniel L. , Rosair Georgina M. , Schmidt Frank , Wilson Neil M. M. , Welch Alan J.
Published: October 2007

Although supraicosahedral (hetero) boranes have long been of interest to theoreticians, the area is under-developed from a synthetic viewpoint. The synthesis of supraicosahedral carboranes by reduction then capitation (RedCap) of C2B10 species is attractive, but unsuccessful as long as the cage carbon atoms are free to separate in the reduction step. Studies on 4,1,6-MC2B10 13-vertex metallacarboranes have shown that the partial degradation of such species can be a facile process, in spite of the fact that the binding energy of the metal atom to the carborane framework can be at least as high as that of a {BH}fragment. These findings support the general concept of the kinetic instability of 1,6-C2B11 species, explaining why a supraicosahedral carborane could not be made from 1,2-C2B10H12. However, tethering together the two cage C atoms with a C6H4(CH2)2 strap ultimately allowed the synthesis of the first supraicosahedral carborane. This species has a henicosahedral geometry, and there is evidence that a facile rearrangement from kinetic to thermodynamic isomer has occurred. The RedCap synthesis of this unprecedented cluster has the potential to be applied successively, yielding 14-,15-,16-, etc. vertex carboranes, the larger of which may be sufficiently kinetically stable to exist without a C,C tether.
Controlled synthesis of carbons-adjacent and-apart nido -and arachno-carborane anions and their metal complexes
Authors: Xie Zuowei
Published: October 2007

The controlled synthesis of carborane anions is a difficult challenge and is of great interest to synthetic chemists. By varying the bridge length of cage carbons-linked o-carboranes, the two cage carbon atoms are locked in place during the reactions, leading to the controlled synthesis of ortho-, meta- and para-isomer of nido-carborane dianions. The isomers of arachno-carborane tetraanions can also be prepared in the controlled manner via chang- ing the electronic configuration of the transition-metal ions or the bridge length. This article provides an overview of our recent work on this subject.
Boron-gadolinium binary system as a magnetic resonance imaging boron carrier
Authors: Yamamoto Yoshinori
Published: October 2007

The evaluation of the Gd-carborane DTPA complex as a magnetic resonance imaging (MRI) and boron carrier agent was carried out in vivo. The MRI revealed that the Gd-carborane DTPA was metabolized slower in the body in comparison with Gd-DTPA.
Enolboration of conjugated ketones and synthesis of beta-amino alcohols and boronated alpha-amino acids
Authors: Zaidlewicz M. , Sokól W. , Wolan A. , Cytarska J. , Tafelska-Kaczmarek A. , Dzielendziak A. , Prewysz-Kwinto A.
Published: October 2007

Enolization–aldolization of conjugated ketones, enantioselective synthesis of benzofuryl beta-amino alcohols, and synthesis of p-dihydroxyborylphenylalanine (BPA) and its analogs are described. Aldolization of benzaldehyde with lithium dienolates derived from unhindered conjugated cyclohexenones favored anti- selectivity, whereas syn selectivity was favored for hindered cyclohexenones. Anti-aldols were preferentially formed from dienolborinates derived from conjugated cyklohexenones, however,competing aldolization at the 2-position was observed for hindered ketones. Benzofuryl beta-amino alcohols were prepared using as a key step the enantioselective reduction of the corresponding alpha-bromoacetylbenzofurans with (–)-B- -chlorodiisopinocampheylborane. Ionic liquids were used as solvents for the synthesis of BPA by the Suzuki cross-coupling reaction. The reaction time is short, and a solution of the catalyst in the ionic liquid can be recycled.
Mission and challenges of polymer science and technology
Authors: Stepto R. , Horie K. , Kitayama T. , Abe Akihiro
Published: October 2007

Following the first IUPAC Polymer Conference on the Mission and Challenges of Polymer Science and Technology (IUPAC PC2002), this article highlights and summarizes the historical development of polymer science and technology and the recent advances that have occurred and are occurring in the subject. It highlights the mission and challenges for the future, particularly as reflected in the papers presented at the conference and in the con- ference’s concluding panel discussion. The important role of IUPAC in defining and leading developments in polymer science and technology is also described. The central role of polymer science and technology and its close interactions with chemical, physical, and biological sciences are defined and discussed. The 21st century is shown to be the Age of Polymers.
Molecular structure and dynamics of proteins in solution: Insights derived from high-resolution NMR approaches
Authors: Torchia D. A. , Ishima Rieko
Published: October 2007

This article reviews heteronuclear NMR techniques that are used to characterize the 3D structures and internal molecular dynamics of proteins in solution. Applications to several proteins that have been studied in our laboratory are presented. Topics discussed include sequential assignments, the use of nuclear Overhauser enhancement spectroscopy (NOESY) and residual dipolar coupling restraints to determine protein structure, and the use of relaxation measurements to obtain information about protein internal motions. Also discussed are recent computational approaches directed at increasing the efficiency of structure determination, as well as new methods for studying large proteins.
Rotaxanes and catenanes as prototypes of molecular machines and motors
Authors: Dietrich-Buchecker C. O. , Jimenez-Molero M. C. , Sartor V. , Sauvage J.-P.
Published: October 2007

In the course of the last 20 years, our view on rotaxanes and catenanes has completely changed. Copper(I)-templated strategies, in particular, have allowed us to prepare catenanes on a real preparative scale, in a few chemical steps from commercially available compounds. A particularly significant improvement was the introduction of the recently developed ring-closing metathesis reaction, using Grubbs catalyst. The dynamic properties of rotaxanes and catenanes has been exploited to construct molecular systems for which one component can be set in motion under the action of an external signal, while the other components can be considered as motionless (artificial molecular “machines ”and “motors ”). A particularly representative example is that of a rotaxane dimer, whose overall length can be controlled chemically: A metal exchange reaction (CuI/ZnII) triggers a reversible contraction/stretching process of the same molecular assembly, in a way reminiscent of the functioning of biological muscles.
Challenge in polymer physics
Authors: Doi Masao
Published: October 2007

One of the challenges in polymer physics is to predict the structure and properties of polymeric materials from their microstructures and processing conditions by integrating various theories and simulation methods. We have been involved in such a challenge through a governmental project involving computational modeling of polymeric materials. This article discusses how we tackled the challenge and describes the system we developed.
Nitropyridines: Synthesis and reactions
Authors: Bakke J. M.
Published: October 2007

Reaction of pyridine and substituted pyridines with N2O5 in an organic solvent gives the N-nitropyridinium ion. When this is reacted with SO2/HSO3– in water, 3-nitropyridine is obtained (77 % yield). With substituted pyridines, the method gives good yields for 4-substituted and moderate yields for 3-substituted pyridines. The reaction mechanism is not an electrophilic aromatic substitution, but one in which the nitro group migrates from the 1-position to the 3-position by a [1,5 ] sigmatropic shift. From 4-aminopyridine, imi- dazo [4,5-c ] pyridines have been synthesized. From 3-nitropyridine, 5-nitropyridine-2-sulfonic acid is formed in a two-step reaction. From this, a series of 2-substituted-5-nitro-pyridines has been synthesized. 3-Nitropyridine and 4-substituted-3-nitropyridines have been substituted with ammonia and amines by the vicarious substitution method and by the oxidative substitution method in the position para to the nitro group. High regioselectivities and yields have been obtained in both cases to afford a series of 4-substituted-2-alkylamino-5-nitropyridines.
Novel chemistry of indole in the synthesis of heterocycles
Authors: Gribble G. W.
Published: October 2007

Indoles that are substituted at the 2- or 3-position with electron-withdrawing groups (nitro, phenylsulfonyl) undergo nucleophilic addition, 1,3-dipolar cycloaddition, and Diels–Alder reactions to give a variety of indoles, pyrroloindoles, and carbazoles. New methods for the synthesis of furo[3,4-b]indoles and the novel ring system furo[3,4-b]pyrrole are described for the first time. Diels–Alder reactions of furo[3,4-b]pyrroles afford indoles after dehydration of the primary cycloadducts. Efficient syntheses of both 2- and 3-nitroindoles from indole are reported, and the first generation and successful electrophilic trapping of a 2,3-dilithioindole has been achieved.
Use of 3-halo-1-azaallylic anions in heterocyclic chemistry
Authors: Giubellina Nicola , Aelterman Wim , De Kimpe Norbert
Published: October 2007

The synthetic potential of lithio 3-halo-1-azaallylic anions as building blocks in organic chemistry and especially in heterocyclic chemistry will be highlighted by the synthesis of functionalized imines, obtained after reaction of 3-halo-1-azaallylic anions with het- eroatom-substituted electrophiles. Thus, the latter generated functionalized imines are suitable building blocks for the synthesis of a whole range of heterocycles and physiologically active compounds, including agrochemicals and pharmaceuticals. 3-Halo-1-azaallylic anions were used in the synthesis of N-alkyl-3,3-dichloroazetidines, 2,3-disubstituted pyrroles, piperidines, 2-substituted pyridines, 2-alkoxytetrahydrofurans,etc., from which a large range of useful and interesting chemicals can be produced, e.g., 2-azetines and 9-alkyl- 2-phenyl-3a-beta,4,6,7,8,9,9a-beta,9b-beta-octahydro-1H-pyrrolo [3,4,h]quinoline-1,3-diones. The utility of the present methodology is demonstrated by the synthesis of the pheromone (S)-manicone, the sulfur-containing flavor compound 2-[(methylthio)methyl ]-2-butenal, and some agrochemical and pharmaceutical compounds.
Birch reduction and its application in the total synthesis of natural products
Authors: Rao G. S. R. Subba
Published: October 2007

The unique availability of substituted cyclohexa-1,4- and 1,3-dienes, notably enol ethers, from Birch reduction of anisoles, permits many novel synthetic reactions of general utility. The total synthesis of several natural products derived from polyketides have been accomplished using a Diels–Alder and Alder–Rickert process. The strategies of the synthesis are discussed.
Ring opening of heterocycles by an arene-catalyzed lithiation
Authors: Yus Miguel
Published: October 2007

The ring opening of different three-, four-, five-and six-membered oxygen-, nitrogen- and sulfur-containing saturated heterocycles using lithium and a catalytic amount of an arene (naphthalene or DTBB) yields a series of functionalized organolithium compounds, which, by reaction with different electrophiles, allow the preparation of polyfunctionalized molecules in only one synthetic operation.
Properties and Units in the Clinical Laboratory Sciences. Part XIX. Properties and Units for Transfusion Medicine and Immunohematology (IUPAC Technical Report)
Authors: Varming K. , Forsum U. , Bruunshuus Ivan , Olesen H.
Published: October 2007

This document is part of an ongoing effort to standardize transmission of laboratory data across cultural and linguistic domains, without attempting to standardize the routine language used by clinicians and laboratory practitioners. It comprises a general introduction and an alphabetic list of properties. The list is based on the syntax for properties recommended by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) and the International Union of Pure and Applied Chemistry (IUPAC). The nomenclature is primarily from the Working Party on Terminology of the International Society of Blood Transfusion (ISBT).