Detaching thiolates from copper and gold clusters: which bonds to break?

The interaction of alkanethiolates with small coinage metal clusters of copper and gold was studied based on density functional theory with a focus on the metal-thiolate junction. Calculation of fragmentation energies indicate that for Cu(n)-thiolate (n = 1,3,5,7, and 9) there is a progressive lowering in energy for the fragmentation of the S-C bond in the thiolate from a value of 2.9 eV for n = 1 to 1.4 eV for n = 9. The detailed electronic origins of this specific weakening are attributed to a polarization of electron density in the S-C bond as induced by bonding with the Cu(n) cluster. For the gold analogues, this effect is not observed and fragmentation at the S-C bond experiences only a slight 10% destabilization as n increases from 3 to 9. The relativistic origin of this difference between Cu and Au is discussed, and an analysis of bonding considerations is presented.     

Glycosidic bond formation in aqueous solution: on the oxocarbenium intermediate

The mechanism of specific acid-catalyzed glycosidic bond formation between methanol and alpha-d-glucopyranoside in aqueous solution at 300 K was studied using Car-Parrinello molecular dynamics. The reaction was found to proceed through a non-solvent equilibrated oxocarbenium cation intermediate characterized by the loss of a hydrogen-bonding interaction between the ring oxygen and solvating water. The mechanism, which was found to be D(N)A(N) in nature, is discussed in detail.     

Nonlinear model-predictive control with hysteresis compensation of an electro-pneumatic clutch for truck applications

This contribution presents two real-time capable nonlinear model-predictive control (NMPC) approaches for an electro-pneumatic clutch for heavy trucks: a centralized control approach and a cascaded one. A clutch is necessary at start-up or during gear shifts to connect or disconnect the combustion engine and the gear box. This automated actuator disburdens the driver and provides the necessary actuation force according to the large torque typically transmitted through the drive train. The force characteristic of the clutch, however, is subject to hysteresis, which is described by a generalized Bouc–Wen model and used for a feedforward hysteresis compensation in the control algorithm. The proposed NMPC-algorithm involves (i) a minimization of the difference between the desired and predicted state vector at the end of the prediction horizon and (ii) flatness-based techniques to compute desired trajectories for the complete state vector as well as the control input. The optimal control is given by an additional, minimum-norm control input that minimizes the difference between the predicted state vector and the desired one at the end of the prediction horizon. Thereby, the computation effort of the NMPC approaches can be kept relatively small, and a real-time evaluation becomes possible. A reduced-order observer estimates an effective pressure in the clutch that also accounts for an uncertain disturbance force. Thereby, a disturbance compensation and a high tracking accuracy is achievable for the piston position as controlled variable. The efficiency of the two proposed control structures is emphasized by experimental results from a dedicated test rig.     

Synthesis of diblock methylcellulose derivatives with regioselective functionalization patterns

This article describes a new synthesis strategy to prepare diblock copolymers as model compounds for industrially produced cellulose ethers exemplified with methylcellulose (MC). To elucidate a key structure for thermoreversible gelation of MC, five regioselectively methylated celluloses 1 – 5 (236, 23, 26, 3, and 6 MC), five corresponding methyl‐β‐D‐glucopyranosyl‐(1→4)‐cellulosides 6 – 10 , and five equiv methyl‐β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐cellulosides 11 – 15 were synthesized for the first time via combination of the glycosyl trichloroacetimidate method and the acid‐catalyzed methanolysis method. The structure of compounds 1 – 15 was confirmed by means of NMR spectroscopy and MALDI‐TOF MS. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

The unique minimality of an averaging projection

In this paper we will prove that an averaging projection P _a : K (H) → Y, given by the formula P_a(A)=\fracA+A^T2P_a(A)=\frac{A+A^T}{2} , is the only norm-one projection. Here, K (H) is a space of compact operators on a separable real Hilbert space H, and Y is the subspace of K(H) consisting of all symmetric operators.