bluuebunny/crossref_metadata_2025 huggingface dataset:
Common-Lines and Passenger Assignment in Congested Transit Networks
Authors: Cominetti Roberto , Correa José
Published: December 2003

We analyze a Wardrop equilibrium model for passenger assignment in general transit networks, including the effects of congestion over the passengers' choices. The model is based on the common-line paradigm, which is applied to general networks using a dynamic programming approach. Congestion is treated by means of a simplified bulk queue model described in the appendix. We provide a complete characterization of the set of equilibria in the common-line setting, including the conditions for existence and uniqueness. This characterization reveals the existence of ranges of flow in which a Braess-like paradox appears, and in which a flow increase does not affect the system performance as measured by transit times. The congested common-line model is used to state an equilibrium model for general transit networks, and to establish the existence of a network equilibrium.
A Doubly Dynamic Schedule-based Assignment Model for Transit Networks
Authors: Nuzzolo Agostino , Russo Francesco , Crisalli Umberto
Published: December 2003

In order to improve the performances of transit modeling and in particular to assess the effects of the introduction of ITS technologies, which imply substantial changes in user behavior, in the last 10 years transit path choice and assignment models that use a schedule-based approach, instead of the traditional frequency-based one, have been developed. This paper presents a schedule-based path choice model for high-frequency transit networks, which allows us to consider the evolution in time of transit services, both within-day and day-to-day, as well as the day-to-day learning process of attributes by which users choose. On the basis of this path choice model a dynamic process assignment model, both within-day and day-to-day (from which the term “doubly dynamic” derives), was developed and tested on a realistically sized network to verify its applicability for operations planning.
Modeling Bus Stops in Transit Networks: A Survey and New Formulations
Authors: Bouzaïene-Ayari Belgacem , Gendreau Michel , Nguyen Sang
Published: December 2003

In this paper, we undertake a detailed study of the bus stop problem in congested transit networks. In the first part of the paper, we present and discuss the bus stop models existing in the literature. In the second part, we propose a new general model for which we prove a number of good properties and we give equivalent formulations. Then, we examine two special cases of the general model. In the first case, the line capacities are considered limited and therefore they can not be exceeded by the on-board passenger flows. In the second case, the strict capacity constraints are relaxed in order to obtain a stop model that can be easily integrated into an assignment model to predict the global passenger behavior in transit networks.
Dispatching Buses in Parking Depots
Authors: Gallo Giorgio , Miele Federico Di
Published: December 2003

Very often, space is a scarce resource in bus depots located in congested urban areas: Vehicles arriving at the end of their trips are packed together in a rather small space. This implies that when a vehicle has to leave to start a new trip, most often other vehicles have to be moved to clear the way. Here a new model, based on “Noncrossing Matching” and “Generalized Assignment,” is presented to allocate parking spaces to vehicles in a depot to minimize the shunting cost. The results obtained by applying this approach to a real-life case are discussed.
Multiobjective Metaheuristics for the Bus Driver Scheduling Problem
Authors: Lourenço Helena R. , Paixão José P. , Portugal Rita
Published: December 2003

We present new multiobjective metaheuristics for solving real-world crew scheduling problems in public bus transport companies. Since the crews of these companies are drivers, we will designate the problem as bus-driver scheduling. Crew scheduling problems are well known, and several mathematical programming-based techniques have been proposed to solve them, in particular, using the single-objective set-covering formulation. However, in practice, there exists the need to consider multiple objectives, some of them in conflict with each other; for example, the cost and service quality, implying also that alternative solution methods have to be developed. We propose multiobjective metaheuristics based on the tabu search and genetic algorithms. These metaheuristics also present some innovation features related with the structure of the crew scheduling problem that guide the search efficiently and enable them to find good solutions. Some of these new features can also be applied to the development of heuristics to other combinatorial optimization problems. A summary of computational results with real-data problems is presented. The methods have been successfully incorporated in the GIST Planning Transportation Systems and are actually used by several companies.
Benders Decomposition for Simultaneous Aircraft Routing and Crew Scheduling
Authors: Cordeau Jean-François , Stojković Goran , Soumis François , Desrosiers Jacques
Published: December 2003

Given a set of flight legs to be flown by a single type of aircraft, the simultaneous aircraft routing and crew scheduling problem consists of determining a minimum-cost set of aircraft routes and crew pairings such that each flight leg is covered by one aircraft and one crew, and side constraints are satisfied. While some side constraints such as maximum flight time and maintenance requirements involve only crews or aircraft, linking constraints impose minimum connection times for crews that depend on aircraft connections. To handle these linking constraints, a solution approach based on Benders decomposition is proposed. The solution process iterates between a master problem that solves the aircraft routing problem, and a subproblem that solves the crew pairing problem. Because of their particular structure, both of these problems are solved by column generation. A heuristic branch-and-bound method is used to compute integer solutions. On a set of test instances based on data provided by an airline, the integrated approach produced significant cost savings in comparison with the sequential planning process commonly used in practice. The largest instance solved contains more than 500 flight legs over a 3-day period.
An Efficient Algorithm for Dynamic Traffic Equilibrium Assignment with Queues
Authors: Akamatsu Takashi
Published: December 2003

This paper presents an efficient algorithm for solving the dynamic user equilibrium (DUE) traffic assignment with a one-to-many origin-destination (OD) pattern. To achieve the efficiency of the algorithm, we employ the following three strategies. First, we exploit the decomposition property of the DUE assignment with respect to the departure time from an origin; we consider the algorithm that solves each of the decomposed DUE assignments sequentially. Second, we represent the decomposed DUE assignment by an arc-node formulation, not by using path variables. Third, we take advantage of the fact that the decomposed DUE assignment reduces to (finite dimensional) nonlinear complementarity problems (NCPs); we develop the algorithm based on the globally convergent Newton's method for general NCPs. These strategies, together with graph theoretic devices, enable us to design a new algorithm which does not require path enumeration and is capable of dealing with very large-scale networks. Numerical experiments disclose that the proposed algorithm solves the DUE assignment very rapidly, even in large-scale networks with some thousands of links and nodes where conventional heuristic algorithms do not converge to the accurate equilibrium solution.
A Variable Neighborhood Descent Algorithm for the Undirected Capacitated Arc Routing Problem
Authors: Hertz Alain , Mittaz Michel
Published: December 2003

The undirected capacitated arc routing problem (CARP) arises naturally in several applications where streets require maintenance, or customers located along road must be serviced. Basic algorithmic procedures have recently been developed for the design of heuristics in an arc routing context. This article reports on the use of these basic tools in a variable neighborhood descent algorithm for the solution of the undirected CARP.
The Arc Routing and Scheduling Problem with Transshipment
Authors: De Rosa Barbara , Improta Gennaro , Ghiani Gianpaolo , Musmanno Roberto
Published: December 2003

This article introduces the Arc Routing and Scheduling Problem with Transshipment (ARPT), a particular Arc Routing Problem whose applications arise in garbage collection. In the ARPT,the demand is collected by specially equipped vehicles, taken to a transfer station, shredded or compacted and, finally, transported to a dump site by means of high-capacity trucks. A lower bound, based on a relaxation of an integer linear formulation of the problem, is developed for the ARPT. A tailored Tabu Search heuristic is also devised. Computational results on a set of benchmark instances are reported.
Airline Crew Scheduling with Time Windows and Plane-Count Constraints
Authors: Klabjan Diego , Johnson Ellis L. , Nemhauser George L. , Gelman Eric , Ramaswamy Srini
Published: December 2003

Airline planning consists of several problems that are currently solved separately. We address a partial integration of schedule planning, aircraft routing, and crew scheduling. In particular, we provide more flexibility for crew scheduling while maintaining the feasibility of aircraft routing by adding plane-count constraints to the crew-scheduling problem. In addition, we assume that the departure times of flights have not yet been fixed and we are allowed to move the departure time of a flight as long as it is within a given time window. We demonstrate that such a model yields solutions to the crew-scheduling problem with significantly lower costs than those obtained from the traditional model.
A Note on the Single Leg, Multifare Seat Allocation Problem
Authors: Li Michael Z. F. , Oum Tae H.
Published: December 2003

In this note, we attempt to prove the equivalence of the optimality conditions from three well-known existing models that deal with the seat allocation problem for a single leg, multifare flight with independent fare class demands.
Stochastic Vehicle Routing with Random Travel Times
Authors: Kenyon Astrid S. , Morton David P.
Published: December 2003

We consider stochastic vehicle routing problems on a network with random travel and service times. A fleet of one or more vehicles is available to be routed through the network to service each node. Two versions of the model are developed based on alternative objective functions. We provide bounds on optimal objective function values and conditions under which reductions to simpler models can be made. Our solution method embeds a branch-and-cut scheme within a Monte Carlo sampling-based procedure.
Detecting Dynamic Traffic Assignment Capacity Paradoxes in Saturated Networks
Authors: Akamatsu Takashi , Heydecker Benjamin
Published: December 2003

Creation of a new link or increase in capacity of an existing link can reduce the efficiency of a congested network as measured by the total travel cost. This phenomenon, of which an extreme example is given by Braess paradox, has been examined in conventional studies within the framework of static assignment. For dynamic traffic assignment, which makes account of the effect of congestion through explicit representation of queues, Akamatsu (2000) gave a simple example of the occurrence of this paradox. The present paper extends that result to a more general network. We first present a necessary and sufficient condition for the paradox to occur in a general network in which there is a queue on each link. We then give a graph-theoretic interpretation of the condition, which gives us a convenient method to test whether or not the paradox will occur by performing certain tests on information that describes the network structure. Finally, as an application of this theory, we examine several example networks and queueing patterns where occurrence of this paradox is inevitable.
An Improved Branch-and-Cut Algorithm for the Capacitated Vehicle Routing Problem
Authors: Achuthan N. R. , Caccetta L. , Hill S. P.
Published: December 2003

The capacitated vehicle routing problem (CVRP) deals with the distribution of a single commodity from a centralized depot to a number of specified customer locations with known demands. The CVRP considered in this paper assumes common vehicle capacity, fixed or variable number of vehicles, and an objective to minimize the total distance traveled by all the vehicles. This paper develops several new cutting planes for this problem, and uses them in an exact branch-and-cut algorithm. Two of the new cutting planes are based on a specified structure of an optimal solution and its existence. Computational results are reported for 1,650 simulated Euclidean problems as well as 24 standard literature test problems; solved problems range in size from 15–100 customers. A comparative analysis demonstrates the significant computational benefit of the proposed method.
A Variable Trip Time Model for Cyclic Railway Timetabling
Authors: Kroon Leo G. , Peeters Leon W. P.
Published: December 2003

In this paper we describe how variable trip times can be included into an existing cyclic railway timetabling model based on the well-known periodic event scheduling problem (PESP). Thereby we provide an extension of the existing model because in the existing model it is assumed that the trip times of all trains on all tracks of the railway network are known a priori. However, the latter may be too restrictive in practice. The solution space of the extended model that we present is larger because small deviations from the fixed trip times are allowed. This is especially useful when a feasible solution to the fixed trip time model does not exist. The solutions obtained from the extended model are proven to be correct under certain necessary and sufficient conditions. Furthermore, the extended model has the same general structure as the original model. Therefore, solution methods developed for the original fixed trip time model can be applied to the extended model as well.
Using Integer Programming to Solve the Train-Platforming Problem
Authors: Billionnet Alain
Published: December 2003

We consider the problem of assigning trains to the available tracks at a railway station, given the daily timetable and the structural and operational constraints. This trainplatforming problem is a key problem in railway station operations, and for a large station, many working days are required for an expert planner to construct the train-platforming. This problem was studied in De Luca Cardillo and Mione (1998), where it is formulated as a graph-coloring problem. These authors propose to solve it by an efficient heuristic algorithm combined with reduction techniques. In this paper, we show that integer programming is a very interesting tool to exactly solve the train-platforming problem as formulated in De Luca Cardillo and Mione (1998) by a graph-coloring problem. The fact of being able to solve it in an exact way by using an integer-programming solver obviously has many advantages. Some computational results are reported.
Erratum: A Stochastic Modeling Approach to Real-Time Prediction of Queue Overflows
Authors: Sheu Jiuh-Biing
Published: December 2003

Queue overflow is a critical issue in developing queue prediction technologies for applications in Advanced Transportation Management System (ATMS). Conventional queue prediction methods, however, are limited to incident-free queue length prediction where traffic arrivals can be readily obtained using detectors. Despite the problems posed by queue overflow, studies addressing queue-overflow issues, or for predicting queue overflows beyond detectors, appear inadequate. This paper describes an advanced methodology which uses a stochastic system modeling approach and random processes for predicting queue lengths beyond detectors in real time. Lane changing is taken into account in developing the queue-overflow prediction model because lane changing accompanies queue overflow in most cases. A discrete-time, nonlinear stochastic system is specified for modeling the queues and lane changes beyond detectors during queue-overflow occurrence. The noise terms of the recursive equations of the model account for the effects of queues and a variety of arriving volumes on vehicular lane-changing maneuvers during queue-overflow occurrence. The unknown traffic arrivals beyond detectors are predicted employing random processes. In addition, a recursive estimation algorithm for predicting real-time queue overflows is developed utilizing the extended Kalman filtering technique. Preliminary test results indicate that the proposed methodology is promising for real-time prediction of queue overflows. The predicted queue overflows can be used not only in understanding the phenomenon of lane traffic patterns during queue-overflow occurrence, but also in developing related advanced technologies such as real-time road traffic congestion control and management systems.
Revenue Management in a Dynamic Network Environment
Authors: Bertsimas Dimitris , Popescu Ioana
Published: December 2003

We investigate dynamic policies for allocating scarce inventory to stochastic demand for multiple fare classes, in a network environment so as to maximize total expected revenues. Typical applications include sequential reservations for an airline network, hotel, or car rental service. We propose and analyze a new algorithm based on approximate dynamic programming, both theoretically and computationally. This algorithm uses adaptive, nonadditive bid prices from a linear programming relaxation. We provide computational results that give insight into the performance of the new algorithm and the widely used bid-price control, for several networks and demand scenarios. We extend the proposed algorithm to handle cancellations and no-shows by incorporating oversales decisions in the underlying linear programming formulation. We report encouraging computational results that show that the new algorithm leads to higher revenues and more robust performance than bid-price control.
Time-Dependent, Label-Constrained Shortest Path Problems with Applications
Authors: Sherali Hanif D. , Hobeika Antoine G. , Kangwalklai Sasikul
Published: December 2003

In this paper, we consider a variant of shortest path problems where, in addition to congestion related time-dependent link travel times on a given transportation network, we also have specific labels for each arc denoting particular modes of travel. The problem then involves finding a time-dependent shortest path from an origin node to a destination node that also conforms with some admissible string of labels. This problem arises in theRoute Planner Moduleof Transportation Analysis Simulation System (TRANSIMS), which is developed by theLos Alamos National Laboratoryand is part of a multitrackTravel Model Improvement Programsponsored by the U.S. Department of Transportation (DOT) and the Environmental Protection Agency (EPA). We propose an effective algorithm for this problem by adapting efficient existing partitioned shortest path algorithmic schemes to handle time dependency along with the label constraints. We also develop several heuristics to curtail the search based on various route restrictions, indicators of progress, and projected travel times to complete the trip. The proposed methodology is applied to solve some real multimodal test problems related to the Portland, Oregon, transportation system. Computational results for both the exact method and the heuristic curtailing schemes are provided.
Solving a Practical Pickup and Delivery Problem
Authors: Xu Hang , Chen Zhi-Long , Rajagopal Srinivas , Arunapuram Sundar
Published: December 2003

We consider a pickup and delivery vehicle routing problem commonly encountered in real-world logistics operations. The problem involves a set of practical complications that have received little attention in the vehicle routing literature. In this problem, there are multiple carriers and multiple vehicle types available to cover a set of pickup and delivery orders, each of which has multiple pickup time windows and multiple delivery time windows. Orders and carrier/vehicle types must satisfy a set of compatibility constraints that specify which orders cannot be covered by which carrier/vehicle types and which orders cannot be shipped together. Order loading and unloading sequence must satisfy the nested precedence constraint that requires that an order cannot be unloaded until all the orders loaded into the truck later than this order are unloaded. Each vehicle trip must satisfy the driver's work rules prescribed by the Department of Transportation which specify legal working hours of a driver. The cost of a trip is determined by several factors including a fixed charge, total mileage, total waiting time, and total layover time of the driver. We propose column generation based solution approaches to this complex problem. The problem is formulated as a set partitioning type formulation containing an exponential number of columns. We apply the standard column generation procedure to solve the linear relaxation of this set partitioning type formulation in which the resulting master problem is a linear program and solved very efficiently by an LP solver, while the resulting subproblems are computationally intractable and solved by fast heuristics. An integer solution is obtained by using an IP solver to solve a restricted version of the original set partitioning type formulation that only contains the columns generated in solving the linear relaxation. The approaches are evaluated based on lower bounds obtained by solving the linear relaxation to optimality by using an exact dynamic programming algorithm to solve the subproblems exactly. It is shown that the approaches are capable of generating near-optimal solutions quickly for randomly generated instances with up to 200 orders. For larger randomly generated instances with up to 500 orders, it is shown that computational times required by these approaches are acceptable.
Rerouting Aircraft for Airline Recovery
Authors: Rosenberger Jay M. , Johnson Ellis L. , Nemhauser George L.
Published: December 2003

Disruptions in airline transportation systems can prevent airlines from executing their schedules as planned. Adverse weather conditions, congestion at airports, and mechanical failures often hinder a flight schedule. During such events, decision makers must reschedule flight legs, and reroute aircraft, pilots, and passengers. We present an optimization model that reschedules legs and reroutes aircraft by minimizing an objective function involving rerouting and cancellation costs. We develop a heuristic for selecting which aircraft are rerouted, and we provide proof of concept by evaluating our model using a simulation of airline operations. Finally, we revise the model to minimize crew and passenger disruptions.
Optimization-Based Analysis of Collaborative Airport Arrival Planning
Authors: Andersson Kari , Hall William , Atkins Stephen , Feron Eric
Published: December 2003

This paper describes, a novel optimization-based approach to benefits analysis that allows us to analyze new collaborative air traffic management tools. We apply this method to analysis of the Collaborative Arrival Planner (CAP), a concept under development by NASA as part of a suite of decision-support tools for improved air traffic management. Central to our benefits analysis is an integer program, the Arrival Sequencing Model (ASM), which minimizes cost through adjustments to the arrival sequence. We use the ASM to evaluate whether CAP-enabled airline control over and/or visibility into the airport arrival sequencing process could improve overall performance of the air transportation system.
An Airspace Planning and Collaborative Decision-Making Model: Part I—Probabilistic Conflicts, Workload, and Equity Considerations
Authors: Sherali Hanif D. , Staats Raymond W. , Trani Antonio A.
Published: December 2003

We present a large-scale, airspace planning and collaborative decision-making model (APCDM) to enhance the management of the U.S. National Airspace System (NAS). Given a set of flights that must be scheduled during some planning horizon, along with alternative surrogate trajectories for each flight as prompted by various airspace restriction scenarios imposed by dynamic severe weather systems or space launch special use airspaces (SUA), we develop a mixed-integer programming model to select a set of flight plans from among these alternatives, subject to flight safety, air traffic control workload, and airline equity constraints. The model includes a three-dimensional probabilistic conflict analysis, the derivation of valid inequalities, the development of air traffic control workload metrics, and the consideration of equity among airline carriers in absorbing costs related to rerouting, delays, and possible cancellations. The resulting APCDM model has potential use for both tactical and strategic applications, such as air traffic control in response to severe weather phenomena or spacecraft launches, FAA policy evaluation (separation standards, workload restrictions, sectorization strategies), Homeland Defense contingency planning, and military air campaign planning. The model can also serve a useful role in augmenting the FAA's National Playbook of standardized flight profiles in different disruption-prone regions of the national airspace. The present paper focuses on the theory and model development; Part II of this paper will address model parameter estimations and implementation test results.
The Biochemical Reactions of Organometallics with Enzymes and Proteins
Authors: Ryabov Alexander D.
Published: December 2003

Most specialists doing organometallic chemistry have little understanding of what modern biochemistry is. On the other hand, most biochemists believe that organometallic chemistry stands much apart from the problems they study. But the real distance, if any, between these magnificent pyramids of modern science is progressively decreasing. Their interaction has given birth to a new branch of science, organometallic biochemistry, the general aspects of which are discussed here.
Incarcerated Atoms and Reactive Molecules
Authors: Hopf Henning
Published: December 2003

The two most spectacular host‐guest complexes of recent times are reported here: 1. Cram et al. have successfully synthesized unsubstituted cyclobutadiene in a hemicarcerand at room temperature. This combines the chemists' desire for measurable amounts of highly reactive molecules with that of being able to investigate the molecule, disturbed as little as possible by chemical stabilization. 2. Schwarz et al. have been able to produce complexes of C‐ and C‐fullerene and helium mass spectrometrically; on the basis of several findings, the helium atom in these complexes must be located in the cage. This success could have an enormous stimulating influence on the endohedral chemistry of the fullerenes.
Reactivity of Cobalt Atoms towards 1,2,3,4,5‐Pentamethylcyclopentadienyl: Synthesis and Structure of Bis(η5‐pentamethylcyclopentadienyl)‐(μ2‐η5:η5‐pentamethylcyclopentadienyl)dicobalt and Bis(η5‐pentamethylcyclopentadienyl)dicobalt
Authors: Schneider Jörg J. , Goddard Richard , Werner Stefan , Krüger Carl
Published: December 2003

For corrigendum see DOI:10.1002/anie.199213921
On a Metathesis Reaction of Tetrathiafulvalene (TTF)
Authors: Hopf Henning , Kreutzer Martin , Jones Peter George
Published: December 2003

For corrigendum see DOI:10.1002/anie.199113862
Pressure‐Assisted Formation of a Cobalt–Carbon σ Bond: A High‐Pressure Pulse Radiolysis Study
Authors: van Eldik Rudi , Cohen Haim , Meyerstein Dan
Published: December 2003

A distinctly negative reaction volume (−16.4 ± 1.6 cm3 mol−1) characterizes reaction (a), which involves an almost pressure‐independent bond formation and a highly pressure‐decelerated bond breakage process. This indicates that pressure assists the formation of the cobalt–carbon σ‐bond by shifting the overall equilibrium to the right with increasing pressure. These results are discussed in terms of ligand substitution of CoII and homolysis of CoIII‐complexes, respectively (nta = nitrilotriacetate).
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Solvation Effects on Geometry and Chemical Shifts. An Ab Initio/IGLO Reconciliation of Apparent Experimental Inconsistencies on H3B · NH3
Authors: Bühl Michael , Steinke Thomas , von Ragué Schleyer Paul , Boese Roland
Published: December 2003

To what extent can the structural parameters of a molecule be altered by the surrounding medium? According to model calculations in a polar solvent continuum, the BN bond length in H3B. NH3 in aqueous solution is indicated to be shortened by ca. 0.1 Å over the value in the gas phase (1.672 Å, microwave), i.e. to nearly the BN separation in the solidstate (1.564 Å, X‐ray). Similar calculations with the solvent hexane gave a value of 1.62 Å.
The Two‐Electron Reduction of 1,1′‐Diphenylethene by Lithium or Sodium to Different 1,1,4,4‐Tetraphenylbutane‐1,4‐diide Salts via CC Bond Formation—A Monomeric Dilithium Contact Ion Triple and a Polymer String of “Hydrocarbon Oysters Containing Solvated Sodium Pearls”
Authors: Bock Hans , Ruppert Klaus , Havlas Zdenek , Bensch Wolfgang , Hönle Wolfgang , von Schnering Hans Georg
Published: December 2003

The reduction of 1,1‐diphenylethene with alkali metals to give 1,1,4,4‐tetraphenylbutane has model character for the course of anionic styrene copolymerization. It has been possible to grow single crystal of the air‐sensitive dianionic intermediates and to determine their structure. The structures of the butane‐1,4‐diide salts are decisively influenced by the radii of the counterions: in the momomeric dilithium contact ion triple, an anti‐periplanar ⊖CH2CCH2C⊖ chain is present. In comparison the polymer strand of the disodium salt consists of contact ion pair anions, which form intramolecular Na⊕ ‐diphenyl sand which units with synclinal butane conformation, and are coupled via further ether‐coordinated Na⊕ counterions.
Cycloalkadiynes—From Bent Triple Bonds to Strained Cage Compounds
Authors: Gleiter Rolf
Published: December 2003

The synthesis of Cycloalkadiynes with medium‐sized rings may be accomplished by a number of ring‐closing and elimination reactions. Information concerning the conformation of the rings as well as the extent of transannular interaction between the triple bonds is obtained by analysis of X‐ray crystallographic data and by photoelectron spectroscopy. The diacetylene complexes of Ag1 and Cu1 show hardly any structural change compared to the uncomplexed compounds while the bis(hexacarbonyldicobalt) complexes differ significantly in their structural parameters. Reaction of Cycloalkadiynes with dicarbonyl(η5‐cyclopentadienyl)cobalt yields inter‐ and intramolecular cyclobutadiene complexes. The superphane of cyclobutadiene formed by the intermolecular reaction can be transformed into a number of highly strained cage compounds in few steps. In addition, the variety of such cage compounds can be increased if the reaction of a cyclic diacetylene is carried out with dimethylacetylenedicarboxylate in the presence of aluminum chloride. The intermediate bridged Dewar benzenes eventually lead to propellaprismanes.
An Unusual Interplay Between Macromolecular and Supramolecular Helicity in Polyisocyanates Dissolved in a Chiral Liquid Crystal
Authors: Green Mark M. , Weng Dexi , Shang Wen , Labes M. M.
Published: December 2003

For corrigendum see DOI:10.1002/anie.199510321
Electrostatic Activation of Nucleofuges: Cationic Leaving Groups
Authors: Weiss Robert , Engel Stefan
Published: December 2003

The substitution of two chlorine atoms by dimethylaminopyridino groups in PCl3 (1), MeOPCl2 (2), and MeOP(O)Cl2 (3) yields phosphorus derivatives that are dicationic (1 and 2) or monocationic (3). These molecules are highly activated toward nucleophilic attack. For the first time, in nucleophilic reactions a cationic group is the leaving group. In fact, the nucleofuge derived from 3 is a better leaving group than the trifluoromethane sulfonate ion.
Ion‐Spray Mass Spectrometry of Lipopeptide Vaccines
Authors: Metzger Jörg W. , Beck Werner , Jung Günther
Published: December 2003

Its speed and accuracy and the extremely simple sample preparation required recommends ion‐spray mass spectrometry as a technique for studying highly lipophilic and amphiphilic molecules of high molecular mass and, in particular, for biomolecules (which have not previously been able to be characterized by mass spectrometry). Routine analyses detect molecular masses up to 6000 u with an accuracy of ± 1 u.
Sugars as Chiral Auxiliaries for the Synthesis of Enantiomerically Pure Compounds
Authors: Reissig Hans‐Ulrich
Published: December 2003

The large number of functional groups and stereogenic centers was the main reason why sugar and sugar derivatives were hardly ever employed as chiral auxiliaries in asymmetric syntheses. Recent publications on highly enantioselective reactions performed with sugar auxiliaries (alkylations, aldol additions, amino acid syntheses, cyclopropanations, and Diels–Alder reactions) show that this reticence was unjustified. What is more, these compounds are, as a rule, easily accessible and inexpensive. They are thus predestined for a much wider use in asymmetric synthesis.
Does the Naked Fluoride Ion Exist?
Authors: Seppelt Konrad
Published: December 2003

Of course in a chemical environment the F− ion cannot exist—this is the answer to the question in the title of this highlight. But in 1991 two reagents were described that make an almost naked fluoride ion available. K. O. Christl et al. synthesized for the first time pure Me4N+F−, from which complex fluoro anions with high coordination numbers can be prepared (for example, [XeF5]− and [IF8]−). R. Schwesinger et al. succeeded in preparing anhydrous [(Me2N)3PNP (NMe2)3]+ F−, which has an extremely large cation–anion distance and promises to be a useful reagent in organic synthesis.
The Beilstein Test: An Unintentional Dioxin Source in Analytical and Research Laboratories
Authors: Scholz‐Böttcher Barbara M. , Bahadir Müfit , Hopf Henning
Published: December 2003

Hazard: Beilstein test! Just one Beilstein test can expose the analyst to more than the acceptable daily limit of 2,3,7,8‐tetrachlorodibenzo‐l, 4‐dioxin, depending on the analyte. The conditions of this routine test for halogenated organic compounds are comparable to those of the Cu‐catalyzed formation of polychlorinated dibenzo‐p‐dioxins and ‐furans from organic substances and halogen donors in, for instance, the incineration of waste.
Molecules with Large Cavities in Supramolecular Chemistry
Authors: Seel Christian , Vögtle Fritz
Published: December 2003

Supramolecular chemistryis a new area of research that has rapidly developed from pure synthetic chemistry, and its novelty has led to interdisciplinary cooperation between organic and inorganic chemistry, biochemistry, physical and theoretical chemistry, and physics. Whereasmolecular chemistryessentially deals with the covalent bonding of atoms, Supramolecular chemistry is predominantly involved in the study of the weaker intermolecular interactions resulting in the association and self‐organization of several components to form larger aggregates (supramolecules). The first crown ether discovered by the subsequent Nobel prizewinner Pedersen was more the fortuitous reaction product of an impurity, but nowadays, some twenty‐five years later, chemists are able to tailor host molecules to special requirements. Host compounds having a cyclophane skeleton make an important contribution, since their aromatic structural units ensure the necessary rigidity of the molecular structures and thereby improve the preorganization of the coordination sites for the cooperative binding of the guests. During the course of the rapid development of Supramolecular chemistry such a large number of synthetic hosts has been developed and their interaction with guests studied in such depth that we must restrict ourselves here to a discussion of a particular group of host compounds, namely cavity‐supporting macrobicyclic and macrooligocyclic phanesu, which bear a similar relation to open‐chain and monocyclic hosts as the metal‐complexing cryptands to the podands and crown ethers. The molecular architecture of these three‐dimensionally bridged macrooligocycles is a challenge for synthetic chemistry. (Not only the size and shape of the intramolecular cavity, but also the provision of the latter with suitable coordination centers have to be included in the synthesis strategy.) The capacity for the envelopment of guests from all sides and the expedientendofunctionalization often also produce a particularly strong binding of host and guest, outstanding selectivities with regards to molecular recognition, and special properties of the Supramolecular complexes.
Distorted Molecules: Perturbation Design, Preparation and Structures
Authors: Bock Hans , Ruppert Klaus , Näther Christian , Havlas Zdenek , Herrmann Hans‐Friedrich , Arad Claudia , Göbel Ilka , John Andreas , Meuret Jochen , Nick Sabine , Rauschenbach Andreas , Seitz Wolfgang , Vaupel Torsten , Solouki Bahman
Published: December 2003

The structure of a molecule can change considerably as its energy and thus its electron distribution within the time‐domain of dynamic relaxation varies. Based on comparison of approriate measured data of related compounds and supported by quantum chemical calculations, therefore, charge‐perturbed and/or sterically overcrowded molecules can be designed. Their preparation, handling, and structural characterization, frequently under extreme and especially largely aprotic conditions, provides some surprises. New structural principles become evident and old‐fashioned ones are confirmed. Thus the contact‐ion aggregates that form on ultrasonically supported reduction of unsaturated hydrocarbons with sodium metal partly contain dibenzene sodium sandwiches. Vicinal dimethylamino substituents or isoelectronic isopropyl groups cause steric overcrowding and facilitate oxidation to molecular cations by energetically favorable delocalization of the generated positive charge. Molecules and molecular ions in which an even number of π electrons are distributed over a σ skeleton containing an odd number of centers preferentially form cyanine subunits. This is demonstrated by the novel ethene dication and dianion salts with central CC single bonds and molecular halves twisted relative to each other. Altogether in two years well over 50 structures have been determined. Much has been learned from them, especially about electron transfer and contact ion‐pair formation in aprotic solvents. Nevertheless, we had to realize that answers to many questions, above all “what crystallizes, how, and why”, are still out of reach.
Synthetic Bilayer Membranes: Molecular Design, Self‐Organization, and Application
Authors: Kunitake Toyoki
Published: December 2003

Lipid bilayers are a most central building block of the biological molecular organization. Their two‐dimensional self‐assembly is essential to the generation of biological shapes and sizes on the molecular level. The observation that a totally synthetic amphiphile in water is spontaneously assembled to a bilayer structure suggested that bilayer formation is a general physicochemical phenomenon that is not restricted to particular structures of biolipid molecules. Bilayer formation is now observed for a large variety of synthetic amphiphiles which contain one, two, three, or four alkyl tails. The flexible alkyl tail may be replaced by perfluoroalkyl chains. The supramolecular structures obtained therefrom can be related to the component's molecular structure in many cases. The structural variety and the ease of molecular design make the synthetic bilayer an attractive vehicle for organizing covalently bound functional units and guest molecules. In addition, stable monolayers on water, planar lipid membranes (BLM), and free‐standing cast films are obtainable because of the self‐assembling property of bilayer‐forming compounds. These molecular organizations display common supramolecular features. The use of the cast film as a molecular template provides exciting potential for the production of novel two‐dimensional materials.
Matrix‐Assisted Laser Desorption Mass Spectrometry of Lignins**
Authors: Metzger Jürgen O. , Bicke Christine , Faix Oskar , Tuszynski Wilfried , Angermann Raimond , Karas Michael , Strupat Kerstin
Published: December 2003

The matrix‐supported laser desorption technique proved to be quick, sensitive, and informative in the characterization of lignins. The technique yields the molecular weight distribution directly (for birch lignin up to about 16000 Da), while the well‐resolved fine structure of the spectrum confirms the existence of oligomers from trimers through to nonamers. The hyperfine structure reflects the complicated structure of lignin, constructed of monomeric units that are linked to one another through various types of bonds.
Protein Engineering: Modified Hemoglobin as a Blood Substitute
Authors: Jessen Timm‐H. , Hilgenfeld Rolf
Published: December 2003

Does the race for an efficient and safe blood substitute have a front‐runner? Since hemoglobin plays a crucial role in the transport of oxygen in the human body, most of the research into blood substitutes concentrates on this protein. However, because even hemoglobin in one's own body can induce extreme immune reactions, its administration is not without danger. Nagai et al. have now succeeded in modifying this protein by genetic engineering, and several of the problems so far encountered—decomposition of hemoglobin into dimers, prohibitively high oxygen affinity—have been solved. The experiments on rats and dogs with regard to the suitability of solutions of this modified hemoglobin as a blood substitute have been successful.
Material Properties and Purity of C60
Authors: Werner Harald , Bublak Daniela , Göbel Ulrich , Henschke Bettina , Bensch Wolfgang , Schlögl Robert
Published: December 2003

The fullerenes can be described as molecular analogues of activated charcoal with a large inner surface. Accordingly, in the solid state, C60 adsorbs organic molecules and oxygen from the air. The conditions of the production, purification, and storage therefore dictate the electronic and dynamic properties of the van der Waals crystals. Obtaining fullerene samples with defined and reproducible properties is more difficult than previously thought.
Novel Iron Carbonyl Telluride Clusters: Synthesis and Characterization of [Fe5Te4(CO)14]2− and [Fe8Te10(CO)20]2−
Authors: Roof Lisa C. , Pennington William T. , Kolis Joseph W.
Published: December 2003

A simple route to large FeTe clusters seems to have been found by the authors in the redox reaction between [Fe(CO)5] and (Ph4P)2Te4. Depending on the molar ratio of the reactants either (Ph4P)2‐1 or (Ph4P)2‐2 is isolated. In addition, 1 can be converted into 2 by elemental Te. Especially noteworthy in 2 is the Te2 ligand which links two hardly distorted Fe4Te4 cubanes.
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The Reaction of Unactivated Cobalt Powder with Iodophosphoranes. The Synthesis of [Co(PMe3)2I3] and the Isolation of the “Frozen Transition‐State” Complex [(nBu3PI)2(μ‐I)] [(nBu3PI)(μ‐I)CoI3]
Authors: McAuliffe Charles A. , Godfrey Stephen M. , Mackie Anthony G. , Pritchard Robin G.
Published: December 2003

The alkyl substituents at the iodophosphorane determine the nature of the product formed in reactions with cobalt powder. Whereas Co and Me3PI2 react to give the trigonal‐bipyramidal cobalt(III) complex 1, the reaction between Co and nBu3PI2 halts at the very unusual cobalt(II) compound 2. The structure of 2, which corresponds to a possible transition state in the formation of 1, provides an insight into the mechanistic pathway for the reaction of metal powders with dihalogen phosphoranes.
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On Quantifying Chirality
Authors: Buda Andrzej B. , der Heyde Thomas Auf , Mislow Kurt
Published: December 2003

Since Pasteur's epochal discoveries a century and a half ago, the concept of chirality has continued to play a central role in chemistry and biochemistry. Can chirality be measured? It has long been known that molecular chirality can be given a quantitative meaning through functions specifically parametrized to match the magnitude of pseudoscalar observables. However, chirality is a property that is independent of its physical and chemical manifestations : for a system to be chiral, all that is required is the absence of improper rotations in the symmetry group of the system. This being the case, how can chirality be measured if the “system” is an abstract geometric figure, for example, a scalene triangle in the plane or an asymmetric tetrahedron in three‐dimensional space? How does chirality vary as a function of pure shape? In this review we describe recent efforts designed to answer these and related questions.
Semiconductor‐Catalyzed Photoaddition of Cyclic Enol Ethers to 1, 2‐Diazenes
Authors: Künneth Ronald , Feldmer Christian , Kisch Horst
Published: December 2003

In contrast to the homogeneous reactions, in which the linear addition of aliphatic CH bonds to the NN group proceeds only with activated diazenes (R1 = R2 = CO2R), the heterogeneous ZnS‐ and CdS‐catalyzed photoaddition takes place also with nonactivated diaryl‐ and alkylaryl‐l,2‐diazenes [Eq. (a); e.g. R1 = R2 = Ph; R3H = 3,4‐dihydropyran].
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Novel Strategies for the Synthesis and Crystallization of Electrophilic Dinuclear Cations: Solution and Solid‐State Properties of [Re2(NCCH3)10][Mo6O19]2
Authors: Bernstein Stacey N. , Dunbar Kim R.
Published: December 2003

An attractive route to mixed‐valent metal oxideshas been developed from the observation that on slow heating1completely loses its acetonitrile ligands at temperatures below 350 °C and is transformed into an oxide containing MoVIand Re in two oxidation states. Salt1is prepared surprisingly simply according to Equation (a) and shows unexpected electron‐acceptor properties, which makes it a potential source of a naked Reion. The structural parameters of the cation of1point to a ReRe triple bond, although no strong α or π donors stabilize the system.equation image
Oxoniobates Containing Metal Clusters
Authors: Köhler Jürgen , Svensson Gunnar , Simon Arndt
Published: December 2003

Metal clusters, discrete or condensed, are characteristic of the structures of many compounds which contain transition metals in low oxidation states. The highly reduced oxoniobates support the concept of condensed clusters. They contain Nb6O12 clusters which are either isolated or linked at the apices of the Nb6 octahedra to form oligomeric chains or networks. The analysis of the bonding relationships allows the identification of different types of Nb atoms and thus the quantitative prediction of valence electron concentrations for finite or infinite structures composed of these condensed M6X12 clusters.
A New Approach to Bis(arene)titanium(0) and ‐titanium(–I) Complexes; Structure of Bis(arene)titanates(1–)
Authors: Blackburn David W. , Britton Doyle , Ellis John E.
Published: December 2003

The reduction of titanium tetrachloride with arene radical anions (such as biphenyl or 4,4′‐di‐tert‐butylbiphenyl potassium), as summarized in Equation (a), affords the corresponding bis(arene)titanates(l—) K[1] and K[2] in high yields, which were structurally characterized as K[2.2.2]cryptand complexes. The oxidation of K[1] and K[2] with I2 leads to the corresponding neutral bis(arene)titanium complexes. Such metallocenes were previously accessible only by metal atom–ligand cocondensation or sonochemical reactions.
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