Reversed-phase high-performance liquid chromatographic separation of diastereomers of (R,S)-mexiletine prepared by microwave irradiation with four new chiral derivatizing reagents based on trichloro-s-triazine having amino acids as chiral auxiliaries and 10 others having amino acid amides

A new series of chiral derivatizing reagents (CDRs) consisting of four dichloro-s-triazine reagents was synthesized by nucleophilic substitution of one chlorine atom in trichloro-s-triazine with amino acids, namely L-Leu, D-Phg, L-Val and L-Ala as chiral auxiliaries. Two other sets of CDRs consisting of four dichloro-s-triazine (DCT) and six monochloro-s-triazine (MCT) reagents were also prepared by nucleophilic substitution of chlorine atom(s) with different amino acid amides as chiral auxiliaries in trichloro-s-triazine and its 6-methoxy derivative, respectively. These 14 CDRs were used for the synthesis of diastereomers of (R,S)-mexiletine under microwave irradiation (i.e. 60s and 90 s at 85% power (of 800 W) using DCT and MCT reagents, respectively), which were resolved by reversed-phase high-performance liquid chromatography using C18 column and gradient eluting mixtures of methanol with aqueous trifluoroacetic acid (TFA) with UV detection at 230 nm. The resolution (R(s)), difference between retention times of resolved diastereomers (Δt) and retention factors (k) obtained for the three sets of diastereomers were compared among themselves and among the three groups. Explanations have been offered for longer retention times and better resolution of diastereomers prepared with DCT reagents in comparison of their MCT counterparts and, for the influence of hydrophobicity of the side chain R of the amino acid in the CDRs on retention times and resolution. The newly synthesized CDRs were observed to be superior as compared to their amide counterparts in terms of providing better resolution and cost effectiveness. The method was validated for limit of detection, linearity, accuracy and precision.     

Nonlinear optical properties of novel tunable, one dimensional molecular superlattice polymers (heteroarylene methines) containing alternating aromatic and quinoid segments

We have investigated the spectral dispersion of second molecular hyperpolarizability ?? (?????; ??, ???, ??) of three derivatives of heteroarylene methine by antiresonant ring interferometric nonlinear spectroscopic technique using femtosecond modelocked Ti:sapphire laser in the spectral range of 725?C820?nm. The observed dispersion of ?? has been explained in the framework of three-essential states model involving the ground state, a one-photon excited state and a two-photon excited state. The spectral response of the hyperpolarizability has been correlated with the electronic and chemical structures of the three derivatives of heteroarylene methine. The estimated ?? values have been compared to the fundamental quantum mechanical limit. We have found for the first time that the heteroarylene methines approach this limit within a factor of 2 while even the best known molecule so far falls short of this limit by a factor of 30.     

Phosphonate self-assembled monolayers on aluminum surfaces

Substrates of aluminum (Al) deposited by physical vapor deposition onto Si substrates and then chemically reacted with perfluorodecylphosphonic acid (PFDPAlSi), decylphosphonic acid (DPAlSi), and octadecylphosphonic acid (ODPAlSi) were studied by x-ray photoelectron spectroscopy (XPS), contact angle measurements, atomic force microscopy (AFM), and friction force microscopy, a derivative of AFM, to characterize their surface chemical composition, roughness, and micro-/nanotribological properties. XPS analysis confirmed the presence of perfluorinated and nonperfluorinated alkylphosphonate molecules on the PFDPAlSi, DPAlSi, and ODPAlSi. The sessile drop static contact angle of pure water on PFDPAlSi was typically more than 130 degrees and on DPAlSi and ODPAlSi typically more than 125 degrees indicating that all phosphonic acid reacted AlSi samples were very hydrophobic. The surface roughness for PFDPAlSi, DPAlSi, ODPAlSi, and bare AlSi was approximately 35 nm as determined by AFM. The surface energy for PFDPAlSi was determined to be approximately 11 mNm by the Zisman plot method compared to 21 and 20 mNm for DPAlSi and ODPAlSi, respectively. Tribology involves the measure of lateral forces due to friction and adhesion between two surfaces. Friction, adhesion, and wear play important roles in the performance of micro-/nanoelectromechanical systems. PFDPAlSi gave the lowest adhesion and coefficient of friction values while bare AlSi gave the highest. The adhesion and coefficient of friction values for DPAlSi and ODPAlSi were comparable.     

Direct Resolution of Six Beta Blockers into their Enantiomers on Silica Plates Impregnated with l-Asp and l-Glu

JPC – Journal of Planar Chromatography – Modern TLC - Resolution of racemic metoprolol, propranolol, carvedilol, bisoprolol, salbutamol, and labetalol, commonly used ß-blockers,...     

12 Gsample/s wavelength division sampling analogue-to-digitalconverter

We have demonstrated a 12Gsample/s continuous time ADC system using wavelength division sampling. Three 4Gsample/s optical pulse trains operating at different wavelengths are interleaved in time to achieved a rate of 12Gsample/s. The interleaving and demultiplexing of the samples is performed using only passive optical filters. Three 4Gsample/s electronic ADCs are then used to digitise the data, the complete signal being reconstructed in the digital domain     

30 Gsample/s time-stretch analogue-to-digital converter

High speed analogue-to-digital conversion using a photonic time-stretch preprocessor followed by an electronic digitiser is demonstrated. The preprocessing increases the effective sampling rate and input bandwidth of the digitiser. The system exhibits 30 Gsample/s sampling rate with 26 dB signal-to-noise ratio over a 4 GHz bandwidth     

Large eddy simulation of turbulent channel flow using an algebraic model

In this paper an algebraic model from the constitutive equations of the subgrid stresses has been developed. This model has an additional term in comparison with the mixed model, which represents the backscatter of energy explicitly. The proposed model thus provides independent modelling of the different energy transfer mechanisms, thereby capturing the effect of subgrid scales more accurately. The model is also found to depict the flow anisotropy better than the linear and mixed models. The energy transfer capability of the model is analysed for the isotropic decay and the forced isotropic turbulence. The turbulent plane channel flow simulation is performed over three Reynolds numbers, Re_τ=180, 395 and 590, and the results are compared with that of the dynamic model, Smagorinsky model, and the DNS data. Both the algebraic and dynamic models are in good agreement with the DNS data for the mean flow quantities. However, the algebraic model is found to be more accurate for the turbulence intensities and the higher‐order statistics. The capability of the algebraic model to represent backscatter is also demonstrated. Copyright © 2005 John Wiley & Sons, Ltd.     

l-Amino Acids as Chiral Selectors for the Enantioseparation of (±)-Bupropion by Ligand Exchange Thin-Layer Chromatography Using Cu(II) Complex via Four Different Approaches

JPC – Journal of Planar Chromatography – Modern TLC - The present paper deals with direct enantioresolution of (±)-bupropion using thin-layer chromatography and different...     

Microwave Promoted One‐Pot Synthesis of Some Novel N‐Aryl Isoquinoline Derivatives

Homophthalic anhydride 1 reacts with different aromatic amines to produce N‐substituted homophthalimides 2 under microwave irradiation. A rapid microwave‐assisted chemical synthesis of condensed 4‐substituted furo[2,3‐c]isoquinoline‐1,5(2H,4H)‐diones 3 and 5‐substituted‐2,3‐dihydro‐1H‐pyrano[2,3‐c]isoquinoline‐1,6(5H)‐diones 4 involving the condensation of a variety of alkanoyl chlorides with 2‐arylisoquinoline‐1,3‐diones 2 in the presence of base and aprotic solvent is described for the first time. By contrast, the facile ring opening reaction of furo[2,3‐c]isoquinoline‐1,5(2H,4H)‐dione 3 with Vilsmeier–Haack reagent under microwave irradiation yielded the α‐β unsaturated carboxyaldehyde 5 . This novel and clean one‐pot methodology, which is characterized by very short reaction time and easy workup procedure, can be exploited to generate some novel condensed isoquinoline derivatives.