A novel 3D parallel mechanism for the passive motion simulation of the patella-femur-tibia complex

Parallel mechanisms have been exploited for the kinematic modelling of the passive motion, i.e. the motion under virtually unloaded conditions, of the patella-femur-tibia human joint. In particular, a new mechanism is devised in this paper: a 3D model of the patella-femur relative motion is presented which, combined with a previous simplified model of the femur-tibia relative motion, provides a suitable tool for the design of knee prostheses. Although less accurate than a previously presented model of the patella-femur-tibia joint, the new mechanism still replicates passive knee motion quite well and is simpler from a mechanical point of view. Experimental results validate the efficiency of the proposed model.     

Molybdenum-mediated synthesis of quinazolin-4(3H)-ones via cyclocarbonylation using microwave irradiation

A new, efficient and practical synthesis of quinazolin-4(3H)-ones is reported via molybdenum-mediated cyclocarbonylation using microwave irradiation. These methods allow access to a wide range of quinazolin-4(3H)-ones in reasonable yields without the need for gaseous carbon monoxide and palladium catalysts. A range of reactions illustrating the wide scope of this chemistry was carried out and all proceeded in reasonable yields.     

Gradient elution in counter-current chromatography: a new layout for an old path

Gradient elution in CCC is a powerful tool, which needs further systematic development to become robust and easy to use. The first attempt to build a correlation between gradient elution profile and distribution ratio (K(D)) values for model mixtures containing typical representatives of pharmaceutical compounds is presented in this paper. The three step estimation of the solvent system composition of a heptane-ethyl acetate-methanol-water (HEMWat) series is described. The estimation is based on simple measurements of initial and final stationary phase retention for gradient elution run, calculating gradient distribution ratio and correlating it with static K(D) against HEMWat number.     

Kinetic Resolution of (R,S)-2-Butanol Using Enzymatic Synthesis of Esters

Kinetic resolution of (R,S)-2-butanol using enzymatic synthesis of esters has been studied. (R,S)-2-Butanol is commonly found as a racemic mixture, and the products of its esterification are racemic mixtures too. This work is of great significance in the field of the enzymatic kinetic resolution due to the little information found in literature about the resolution of (R,S)-2-butanol as pure compound. So, this article is a contribution about the enzymatic resolution of (R,S)-2-butanol. The reaction here studied is the esterification/transesterification of (R,S)-2-butanol in organic media (n-hexane) using as biocatalyst the lipase Novozym 435?. The main target of this study is to analyze the influence of certain variables in this reaction. Some of these variables are acyl donor (acids and esters), concentration of substrates, enzyme/substrate ratio, and temperature. The main conclusions of this study are the positive effect of higher substrates concentration (1.5 M) and larger amount of enzyme (13.8 g mol(-1) substrate) on kinetic resolution rate but not a very noticeable effect on enantiomeric excesses. The longer the carboxylic acid chain is, the better results are obtained. Besides to achieve a satisfactory kinetic resolution, it is recommendable to select reaction times (180 min) at which the highest substrate enantiomeric excess is reached (~60%). The temperature has not an appreciable influence on the resolution in the range studied (40-60 °C). When an ester (vinyl acetate) is used as acyl donor, the resolution shows better results than when using a carboxylic acid as acyl donor (ee(s)?~90% at 90 min). Moreover, Michaelis-Menten parameters, v(max) and K(M), were determined, 0.04 mol l(-1) min(-1) and 0.41 mol l(-1), respectively.     

Measurement of one-bond 13Calpha-1Halpha residual dipolar coupling constants in proteins by selective manipulation of CalphaHalpha spins

We have developed new 2D and 3D experiments for the measurement of C(alpha)-H(alpha) residual dipolar coupling constants in (13)C and (15)N labelled proteins. Two experiments, 2D (HNCO)-(J-CA)NH and 3D (HN)CO-(J-CA)NH, sample the C(alpha)-H(alpha) splitting by means of C(alpha) magnetization, while 2D (J-HACACO)NH and 3D J-HA(CACO)NH use H(alpha) magnetization to achieve a similar result. In the 2D experiments the coupling evolution is superimposed on the evolution of the (15)N chemical shifts and the IPAP principle is used to obtain (1)H-(15)N HSQC-like spectra from which the splitting is determined. The use of a third dimension in 3D experiments reduces spectral overlap to the point where use of an IPAP scheme may not be necessary. The length of the sampling interval in the J-dimension of these experiments is dictated solely by the relaxation properties of C(alpha) or H(alpha) nuclei. This was made possible by the use of C(alpha) selective pulses in combination with either a DPFGSE or modified BIRD pulses. Inclusion of these pulse sequence elements in the J-evolution periods removes unwanted spin-spin interactions. This allows prolonged sampling periods ( approximately 25 ms) yielding higher precision C(alpha)-H(alpha) splitting determination than is achievable with existing frequency based methods.     

Evidence of structural strain in epitaxial graphene layers on 6H-SiC(0001)

The early stages of epitaxial graphene layer growth on the Si-terminated 6H-SiC (0001) are investigated by Auger electron spectroscopy (AES) and depolarized Raman spectroscopy. The selection of the depolarized component of the scattered light results in a significant increase in the C-C bond signal over the second order SiC Raman signal, which allows us to resolve submonolayer growth, including individual, localized C=C dimers in a diamondlike carbon matrix for AES C/Si ratio of approximately 3, and a strained graphene layer with delocalized electrons and Dirac single-band dispersion for AES C/Si ratio >6. The linear strain, measured at room temperature, is found to be compressive, which can be attributed to the large difference between the coefficients of thermal expansion of graphene and SiC. The magnitude of the compressive strain can be varied by adjusting the growth time at fixed annealing temperature.     

Green's formulation for robust phase unwrapping in digital holography

We present, for the first time to the best of our knowledge, a phase unwrapping method based on an algorithm which makes use of Green's first identity. This method aims at recovering the correct phase information encoded in a fringe pattern after digital holography (DH) numerical processing. DH provides a quantitative measurement of the three-dimensional surface profile of objects. The information about the profile can be obtained in principle from the phase-map. However, the measured phase-map provides the actual phase values wrapped mod.2π so that an unwrapping process is required in order to reconstruct the object profile.