A polarisation based approach to model strain dependent electrostatic pressure of dielectric elastomer actuators

A wide-spread lumped parameter model describing the electrostatic pressure is presented by Pelrine et. al. in 1998 [1]. In Pelrine's model, the electrostatic pressure is affected by the relative permittivity of the material, also known as dielectric constant. However, many researchers found that the dielectric constant of DEAs is not constant at all, but decreasing with increasing pre-stretch of the material. In this work, an alternative modelling approach is presented, explaining the stretch dependent actuation pressure. It is shown that this new model fits experimental data found in literature quite well. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical analysis of the internal rotation in aminoborane and borylphosphine

Using a recently proposed orbital deletion procedure and the block-localized wavefunction method, the rotational barriers in H₂BNH₂ and H₂BPH₂ are analyzed in terms of conjugation, hyperconjugation, steric effect and pyramidalization. With the zero-point energy corrections, the π-binding strengths in the planar H₂BNH₂ and H₂BPH₂ are both around 20 kcal/mol at the HF level using the 6-311+G** basis set. With the deactivation of the π atomic orbitals on the boron atom and the evolution from a planar structure to a 90°-twisted structure, the steric repulsion between the B‐H and the N‐H or P‐H is relieved and moreover, the negative hyperconjugation from the lone electron pair or pairs on the nitrogen or phosphorus atoms to the antibonding orbital ^χ* _B H ₂ of the BH₂ group stabilizes the twisted structure by 7.4(8.8) or 4.0(5.0) kcal/mol at the HF/6-31G*(6-311+G**) level. However, the repulsive interaction between the lone pair(s) and the two BH σ bonds is so prominent that the overall steric effect contributes 20.3(22.9) and 19.3(19.8) kcal/mol to the rotational barriers in H₂BNH₂ and H₂BPH₂ with the 6-31G*(6-311+G**) basis set. The present techniques and analyses may also give some clues to justify the parameterization in the empirical molecular mechanics methods. Received: 17 April 1998 / Accepted: 17 September 1998 / Published online: 1 February 1999     

8-Aza-2′-deoxyguanosine and Related 1,2,3-Triazolo[4,5-d]pyrimidine 2′-Deoxyribofuranosides

The synthesis of 8-azaguanine N⁹-, N⁸-, and N⁷-(2′-deoxyribonucleosides) 1–3 , related to 2′-deoxyguanosine ( 4 ), is described. Glycosylation of the anion of 5-amino-7-methoxy-3H-1,2,3-triazolo[4,5-d]pyrimidine ( 5 ) with 2-deoxy-3,5-di-O-(4-toluoyl)-α-D -erythro-pentofuranosyl chloride ( 6 ) afforded the regioisomeric glycosylation products 7a/7b, 8a/8b , and 9 (Scheme 1) which were detoluoylated to give 10a, 10b, 11a, 11b , and 12a . The anomeric configuration as well as the position of glycosylation were determined by combination of UV, ¹³C-NMR, and ¹H-NMR NOE-difference spectroscopy. The 2-amino-8-aza-2′-deoxyadenosine ( 13 ), obtained from 7a , was deaminated by adenosine deaminase to yield 8-aza-2′-deoxyguanosine ( 1 ), whereas the N⁷- and N⁸-regioisomers were no substrates of the enzyme. The N-glycosylic bond of compound 1 (0.1 N HCl) is ca. 10 times more stable than that of 2′-deoxyguanosine ( 4 ).     

New Types of Very Efficient Photolabile Protecting Groups Based upon the [2‐(2‐Nitrophenyl)propoxy]carbonyl (NPPOC) Moiety

Based upon the photolabile [2‐(2‐nitrophenyl)propoxy]carbonyl group (NPPOC), a large number of modified 2‐(2‐nitrophenyl)propanol derivatives substituted at the phenyl ring (see 23 – 34 and 57 – 76 ) as well as at the side‐chain (see 85 – 92 and 95 – 98 ) were synthesized to improve the photoreactivity of this new type of photolabile entity. The phenyl moiety was also exchanged by the naphthalenyl group (see 102, 103, 105, 108, 110, 113 , and 114 ), the thienyl substituent (see 115, 117, 118 , and 120 ), and the benzothienyl substituent (see 121 ). The 2‐(2‐nitroaryl‐ and heteroaryl)propanols were converted with diphosgene into the corresponding carbonochloridates, which reacted subsequently with thymidine to the thymidine 5′‐(protected carbonates) 123 – 178 as the main reaction products. In several cases, the corresponding 3′‐carbonates and 3′,5′‐dicarbonates 179 – 212 were also isolated and characterized. Photolysis studies under standardized conditions (see Table) indicated that the rate of photocleavage varies in a broad range depending on the substituents. So far, the thymidine 5′‐[2‐(5‐halo‐2‐nitrophenyl)propyl carbonates] 127 – 129 , 5′‐[2‐(nitro[1,1′‐biphenyl]3‐yl)propyl carbonates] 136 – 139 , 5′‐{2‐[2‐nitro‐5‐(thianthren‐1‐yl)phenyl]propyl carbonate} ( 140 ), 5′‐[2‐(5‐naphthalenyl‐2‐nitrophenyl)propyl carbonates] 141 and 142 , and 5′‐[2‐(2‐nitro‐5‐thienylphenyl)propyl carbonates] 143 and 144 showed the best properties regarding fast and uniform deprotection. Since the nucleobases of 213 – 215 do not influence the photocleavage features, in general, the new type of photolabile building blocks allows in form of their 3′‐phosphoramidites the photolithographic formation of high‐quality biochips.     

Robust calibrations on reduced sample sets for API content prediction in tablets: Definition of a cost-effective NIR model development strategy

Owing to spectral variations from other sources than the component of interest, large investments in the NIR model development may be required to obtain satisfactory and robust prediction performance. To make the NIR model development for routine active pharmaceutical ingredient (API) prediction in tablets more cost-effective, alternative modelling strategies were proposed. They used a massive amount of prior spectral information on intra- and inter-batch variation and the pure component spectra to define a clutter, i.e., the detrimental spectral information. This was subsequently used for artificial data augmentation and/or orthogonal projections. The model performance improved statistically significantly, with a 34–40% reduction in RMSEP while needing fewer model latent variables, by applying the following procedure before PLS regression: (1) augmentation of the calibration spectra with the spectral shapes from the clutter, and (2) net analyte pre-processing (NAP). The improved prediction performance was not compromised when reducing the variability in the calibration set, making exhaustive calibration unnecessary. Strong water content variations in the tablets caused frequency shifts of the API absorption signals that could not be included in the clutter. Updating the model for this kind of variation demonstrated that the completeness of the clutter is critical for the performance of these models and that the model will only be more robust for spectral variation that is not co-linear with the one from the property of interest.     

Quantitative determination of fluoxetine in human serum by high performance thin layer chromatography

A high performance thin layer chromatographic method was developed and validated for the quantification of fluoxetine in human serum. Fluoxetine was extracted by liquid–liquid extraction method with diethyl ether as extraction solvent. Imipramine was used as internal standard. The chromatographic separation was achieved on precoated silica gel F 254 high performance thin layer chromatographic plates using a mixture of toluene/acetic acid glacial (4:5 v/v) as mobile phase. 4‐Dimethylamino‐azobenzene‐4‐sulphonyl chloride was used as derivatization reagent. Densitometric detection was done at 272 nm. The method was linear between 12.5 and 87.5 ng/spot, corresponding to 0.05 and 0.35 ng/μL of fluoxetine in human serum after extraction process and applying 25 μL to the chromatographic plates. The method correlation coefficient was 0.999. The intra‐assay and inter‐assay precisions, expressed as the RSD, were in the range of 0.70–2.01% (n=3) and 0.81–3.90% (n=9), respectively. The LOD was 0.23 ng, and the LOQ was 0.70 ng. The method proved be accurate, with a recovery between 94.75 and 98.95%, with a RSD not higher than 3.61% and was selective for the active principle tested. This method was successfully applied to quantify fluoxetine in patient serum samples. In conclusion, the method is useful for quantitative determination of fluoxetine in human serum.     

Kinetic study of gamma-glutamyltransferase activity by electrophoretically mediated microanalysis combined with micellar electrokinetic capillary chromatography

The use of capillary electrophoresis for the determination of gamma-glutamyltransferase (GGT) activity with gamma-glutamyl-p-nitroanilide (Glu-p-NA) as a substrate was investigated. The reaction velocity was quantified spectrophotometrically by the corrected peak area of the product p-nitroaniline (pNA) at 380 nm. Micelles composed of sodium deoxycholic acid were used in the background electrolyte in order to obtain a baseline separation between the substrate and the product. The presence of the micelles did not influence the enzymatic reaction. The electrophoretic system was used, not only for the separation and quantitation of the different reaction compounds but also for the in-capillary mixing of the enzyme and substrate plugs. This methodology is known as electrophoretically mediated microanalysis (EMMA). With the developed in-capillary activity assay an average Michaelis constant (K(M)) for GGT was calculated to be 2.09 mM (RSD = 7.3%, n = 3), a value consistent with previously reported values.