Toward the synthesis and biological evaluation of hirsutide

Abstract  The present investigation deals with the synthesis of a N-methylated cyclotetrapeptide, hirsutide (2), by coupling of the dipeptide units Boc-l-phenylalanyl-l-N-methylphenylalanine-OH and l-valyl-l-N-methylphenylalanine-OMe followed by cyclization of the linear tetrapeptide fragment. The chemical structure was established on the basis of analytical as well as spectroscopic data. The newly synthesized cyclic peptide was subjected to pharmacological screening and found to be highly potent against the gram-negative bacteria Pseudomonas aeruginosa and Klebsiella pneumoniae at 6 μg cm⁻³. In addition, potent antihelmintic activity against the earthworms Megascoplex konkanensis and Pontoscotex corethruses at 1 and 2 mg cm⁻³, and potent cytotoxic activity against Dalton’s lymphoma ascites and Ehrlich’s ascites carcinoma cell lines with IC₅₀ values of 14 and 22 μM were also observed. Studies revealed that the pentafluorophenyl ester method employing a catalytic amount of N-methylmorpholine proved to be better for cyclization of the linear tetrapeptide unit. Graphical abstract        

Photostability of UV Absorber Systems in Sunscreens†

Sunscreens are used to protect the human skin against harmful UV radiation. Today there is a trend toward higher sun protection factors (SPF) and better UVA protection. Methods for the assessment of SPF and UVA protection involve irradiation of the product, and the photostability properties of the sunscreen have an influence on its performance. Sunscreens often contain more than one UV filter. Thus it is important to understand the photostability properties of the complete system. The filter combinations used may exhibit destabilizing, stabilizing or inert interactions. For that reason, besides assessment of the properties of the single filters, photostabilities of binary filter combinations are investigated. Destabilization occurs when two UV absorbers undergo a chemical reaction after absorption of UV radiation. Stabilization may be achieved when the optical density of the system is very high, giving rise to a self‐protection effect of the sunscreen film. Photounstable UV absorbers may be additionally stabilized by employing triplet quenchers. Being aware of these mechanisms and applying them for specific UV filter combinations can help in designing efficient sunscreens.     

Hydrothermal synthesis and structural characterization of novel α-Keggin unit-supported Cu(II)- and Mn(II)-bipyridine complexes from a <Emphasis Type="Italic">tri</Emphasis>-lacunary precursor

Blue [{Cu(2,2′-bipy)₂}₂{α-SiW₁₂O₄₀}] (bipy = bipyridyl) (1) and pale yellow [Mn(2,2′-bipy)₃]₂[α-SiW₁₂O₄₀] (2) have been synthesized hydrothermally and characterized by IR spectroscopy and single crystal X-ray structure analysis. In 1, the [α-SiW₁₂O₄₀]⁴⁻ ion acts as a bridge between the two [{Cu(2,2′-bipy)₂]²⁺ moieties via coordination through the terminal oxygen atoms, while in 2, the [Mn(2,2′-bipy)₃]²⁺ ion balances the charge on the polyoxo anion without forming any covalent bond. To the best of our knowledge, this is the first example of transition metal-mediated transformation of [α-SiW₉O₃₄]¹⁰⁻ to [α-SiW₁₂O₄₀]⁴⁻. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The Use of Iron-Enriched Yeast for the Production of Flatbread

The most common cause of iron deficiency is an improperly balanced diet, in which the body’s need for iron cannot be met by absorption of this element from food. Targeted iron supplementation and food fortification may be the main treatments for iron deficiency in the population. However, many iron-rich supplements and foods have low bioavailability of this element. In our study, we used yeast enriched with iron ions to produce flatbread. The yeast cells accumulated iron ions from the medium supplemented with Fe(NO₃)₃·9H₂O, additionally one of the cultures was treated with pulsed electric field in order to increase the accumulation. The potential bioavailability of iron from flatbread containing 385.8 ± 4.12 mg of iron in 100 g dry mass was 10.83 ± 0.94%. All the flatbreads had a moderate glycemic index. There were no significant differences in antioxidant activity against DPPH^• between flatbread with iron-enriched and non-iron-enriched yeast. Sensory evaluation showed that this product is acceptable to consumers since no metallic aftertaste was detected. Iron enriched flatbread can potentially be an alternative to dietary supplements in iron deficiency states.     

Linear Poly(methyl glycerol) and Linear Polyglycerol as Potent Protein and Cell Resistant Alternatives to Poly(ethylene glycol)

The nonspecific interaction of proteins with surfaces in contact with biofluids leads to adverse problems and is prevented by a biocompatible surface coating. The current benchmark material among such coatings is poly(ethylene glycol) (PEG). Herein, we report on the synthesis of linear polyglycerol derivatives as promising alternatives to PEG. Therefore, gold surfaces as a model system are functionalized with a self‐assembled monolayer (SAM) by a two‐step anhydride coupling and a direct thiol immobilization of linear poly(methyl glycerol) and polyglycerol. Surface plasmon resonance (SPR) spectroscopy reveals both types of functionalized surfaces to be as resistant as PEG towards the adsorption of the test proteins fibrinogen, pepsin, albumin, and lysozyme. Moreover, linear polyglycerols adsorb even less proteins from human plasma than a PEG‐modified surface. Additional cell adhesion experiments on linear poly(methyl glycerol) and polyglycerol‐modified surfaces show comparable cell resistance as for a PEG‐modified surface. Also, in the case of long‐term stability, high cell resistance is observed for all samples in medium. Additional in vitro cell‐toxicity tests add to the argument that linear poly(methyl glycerol) and polyglycerol are strong candidates for promising alternatives to PEG, which can easily be modified for biocompatible functionalization of other surfaces.     

Cellulose--model films and the fundamental approach

This critical review describes the recent arrival of ultrathin films of cellulose. The methodology of preparation as well as the applications of the films for fundamental research is fully covered. The review places cellulose in a wider scientific context where cellulose research is no longer a field of interest for specialised scientists only. Cellulose and cellulosic materials should interest communities such as biochemists, physical chemists, surface chemists, organic chemists, polymer chemists and also physicists working close the disciplines mentioned. (149 references.).     

Representation of Operators in the Time-Frequency Domain and Generalized Gabor Multipliers

Starting from a general operator representation in the time-frequency domain, this paper addresses the problem of approximating linear operators by operators that are diagonal or band-diagonal with respect to Gabor frames. A characterization of operators that can be realized as Gabor multipliers is given and necessary conditions for the existence of (Hilbert-Schmidt) optimal Gabor multiplier approximations are discussed and an efficient method for the calculation of an operator’s best approximation by a Gabor multiplier is derived. The spreading function of Gabor multipliers yields new error estimates for these approximations. Generalizations (multiple Gabor multipliers) are introduced for better approximation of overspread operators. The Riesz property of the projection operators involved in generalized Gabor multipliers is characterized, and a method for obtaining an operator’s best approximation by a multiple Gabor multiplier is suggested. Finally, it is shown that in certain situations, generalized Gabor multipliers reduce to a finite sum of regular Gabor multipliers with adapted windows.     

Fluid velocity based simulation of hydraulic fracture: a penny shaped model—part I: the numerical algorithm

In the first part of this paper, a universal fluid velocity based algorithm for simulating hydraulic fracture with leak-off, previously demonstrated for the PKN and KGD models, is extended to obtain solutions for a penny-shaped crack. The numerical scheme is capable of dealing with both the viscosity and toughness dominated regimes, with the fracture being driven by a power-law fluid. The computational approach utilizes two dependent variables; the fracture aperture and the reduced fluid velocity. The latter allows for the application of a local condition of the Stefan type (the speed equation) to trace the fracture front. The obtained numerical solutions are carefully tested using various methods, and are shown to achieve a high level of accuracy.