Antonello Santini

The longest, regular polypeptide 310 helix at atomic resolution

A synthetic, terminally blocked homodecapeptide from the C alpha, alpha-dimethylated glycyl residue alpha-aminoisobutyric acid has been analyzed by single-crystal X-ray diffraction and the structure refined to R = 0.073. The compound crystallizes as a perfect 3(10) helix, stabilized by eight consecutive intramolecular N-H . . . O = C hydrogen bonds. This is the first observation at atomic resolution of a regular polypeptide 3(10) helix as long as three complete turns.

Characterization of High Purity Lycopene from Tomato Wastes Using a New Pressurized Extraction Approach

In this paper, a method for the extraction of high purity lycopene from tomato wastes is presented. The method is based on a pressurized extraction that uses the Extractor Naviglio, and it is performed in the 0.7-0.9 MPa range. Tomato skin, the byproduct deriving from manufacturing of tomato, in a water dispersion, are used as starting material. Lycopene is transferred, for the effect of the high pressure used, in the form of molecular aggregates into the water as a dispersion, while apolar compounds remain in the matrix. The aggregates are easily purified in a single subsequent step by using methanol, thus, obtaining lycopene at 98% chromatographic purity or higher. A new stationary phase, phenyl-hexyl silicone, and a simple water/acetonitrile gradient were used for HPLC analysis of lycopene. The extract was characterized by UV-Vis spectrophotometry, (1)H NMR, (13)C NMR, and electrospray ionization mass spectrometry. An average recovery of 2.8 mg lycopene/kg tomato waste can be obtained after 4 hours of extraction and using tap water as the extracting liquid. The recovery percentage was of about 10%. The exhausted tomato byproduct can be easily dried and used in agriculture or as feeding for animals.

Preferred conformation of peptides rich in alicyclic Cα,α-disubstituted glycines

The conformational preferences of the alicyclic Cα,α‐disubstituted glycines Acnc (1‐amino‐1‐cycloalkane‐carboxylic acid; n = 4, 7, 9, 12) were assessed in selected model compounds, including homopeptides and Ala (or Aib, α‐aminoisobutyric acid)/Acnc peptides containing a small total number of residues, by Fourier transform ir absorption, 1H‐nmr, and x‐ray diffraction analyses. The results obtained indicate that β‐turn and 310‐helical structures are preferentially adopted by short peptides rich in these cycloaliphatic α‐amino acids.

Structural versatility of peptides from Cα,α-dialkylated glycines: a conformational energy calculation and X-ray diffraction study of homopeptides from 1-aminocyclopentane-1-carboxylic acid☆

Abstract Coformational energy calculations on the 1-aminocyclopentane-1-carboxylic acid monopeptide Ac-Acc 5 -NHMe indicate that this C α,α -dialkylated, cyclic α-amino acid residue is conformationally restricted and that its minimum energy conformation falls in the α/3 10 -helical region. The results of the theoretical analysis are in agreement with the crystal-state structural tendency of p BrBz(Acc 5 ) 4 O t Bu·2 MeOH , p BrBz(Acc 5 ) 5 O t Bu· MeOH , and Z(Acc 5 ) 6 O t Bu, determined by X-ray diffraction and also described in this work (formation of 3 10 -helices). The implications for the use of Acc 5 residues in designing conformationally constrained analogues of bioactive peptides are briefly discussed.

Conformational Characterization of the 1-Aminocyclobutane-1-carboxylic Acid Residue in Model Peptides

A series of N‐ and C‐protected, monodispersed homo‐oligopeptides (to the dodecamer level) from the small‐ring alicyclic Cα,α‐dialkylated glycine 1‐aminocyclobutane‐1‐carboxylic acid (Ac4c) and two Ala/Ac4c tripeptides were synthesized by solution methods and fully characterized. The conformational preferences of all the model peptides were determined in deuterochloroform solution by FT‐IR absorption and 1H‐NMR. The molecular structures of the amino acid derivatives Z‐Ac4c‐OH and Z2‐Ac4c‐OH, the tripeptides Z‐(Ac4c)3‐OtBu, Z‐Ac4c‐(L‐Ala)2‐OMe and Z‐L‐Ala‐Ac4c‐L‐Ala‐OMe, and the tetrapeptide Z‐(Ac4c)4‐OtBu were determined in the crystal state by X‐ray diffraction. The average geometry of the cyclobutyl moiety of the Ac4c residue was assessed and the τ(N–Cα–C′) bond angle was found to be significantly expanded from the regular tetrahedral value. The conformational data are strongly in favour of the conclusion that the Ac4c residue is an effective β‐turn and helix former. A comparison with the structural propensities of α‐aminoisobutyric acid, the prototype of Cα,α‐dialkylated glycines, and the other extensively investigated members of the family of 1‐aminocycloalkane‐1‐carboxylic acids (Acnc, with n=3, 5–8) is made and the implications for the use of the Ac4c residue in conformationally constrained peptide analogues are briefly examined.

Linear oligopeptides. Part 227. X-Ray crystal and molecular structures of two α-helix-forming (Aib-L-Ala)sequential oligopeptides, pBrBz-(Aib-L-Ala)5-OMe and pBrBz-(Aib-L-Ala)6-OMe

A crystal-state structutal analysis of pBrBz-(Aib-LAla)5-OMe tetrahydrate and pBrBz-(Aib-L-Ala)6-OMe dihydrate has been performed by X-ray diffraction. The decapeptide and dodecapeptide molecules are both basically α-helical with five and seven 1 â†� 5 intramolecular H-bonds, respectively. A similarity between the two structures is also seen near the C-terminus, where regularity of the α-helix is disrupted in favour of formation of intramolecular H-bonds of the 1 â†� 4 and 1 â†� 6 types. A brief comparison with parameters and interactions characteristic of the helices present in globular proteins has been made.

Structural versatility of peptides containing Cα,α-dialkylated glycines. An X-ray diffraction study of six 1-aminocyclopropane-1-carboxylic acid rich peptides☆

The molecular and crystal structures of six fully blocked, Ac3c-rich peptides to the tetramer level were determined by X-ray diffraction. The peptides are Fmoc-(Ac3c)2-OMe·CH3OH, Ac-(Ac3c)2-OMe, t-Boc-Ac3c-l-Phe-OMe, pBrBz-(Ac3c)3-OMe·H2O, Z-Gly-Ac3c-Gly-OTmb·(CH32CO, andt-Boc-(Ac3c)4-OMe·2H2O. Type-I (I′) β-bends and distorted 310-helices were found to be typical of the tri- and tetrapeptides, respectively. In the dipeptides, too short to form β-bend conformations, other less common structural features may be observed. The average geometry of the cyclopropyl moiety of the Ac3c residue is asymmetric and the N-Cα-C′ bond angle is significantly expanded from the regular tetrahedral value. A comparison with the structural preferences of other extensively investigated Cα,α-dialkylated α-amino acids is made and the implications for the use of the Ac3c residue in conformational design are examined.

Nutraceuticals: A paradigm of proactive medicine

&NA; Nutraceuticals define a new category which shades the frontier between drugs and food. As per its definition, a nutraceutical is “a food or part of a food that provides benefits health in addition to its nutritional content”. Active substances either way extracted from plants (phytocomplexes) or of animal origin, when extracted, concentrated and administered in a suitable pharmaceutical form, can create a very promising toolbox useful to prevent and/or support the therapy of some pathologic conditions given their proven clinical efficacy. It is worldwide recognized that diet and lifestyle are essential to promote and maintain well‐being and nice‐being condition, other than help to prevent diseases possible onset. Both non‐correct dietary habits and lifestyle can in fact determine pathological conditions. The metabolic syndrome, a worldwide epidemic threat, can be named an outstanding example. This syndrome is characterized by a cascade of cardio metabolic risk factors which include obesity, insulin resistance, hypertension, and dyslipidemia. Prevention is the key strategy for an effective proactive medicine, in which efforts are addressed to prevention and, consequently, to lower the risk connected to some lifestyle related diseases reducing, at the same time, any National Health Systems cost needed to guarantee the proper therapeutic approach based on pharmaceuticals. Nutraceuticals use in prevention is a proactive reverse approach tool to pre‐clinical health conditions. They can be effectively used, by including in the daily diet, in an area which shades in the range “beyond the diet, before drugs”, since they combine both nutritional and beneficial healthy properties of food extracts with the healing properties of natural active compounds. Graphical abstract Figure. No caption available.

Helical screw sense of peptide molecules: The pentapeptide system (Aib)4/L-Val[L-(αMe)Val] in the crystal state

The crystal-state preferred conformations of six Nα-blocked pentapeptide esters, each containing four helicogenic, achiral α-aminoisobutyric acid (Aib) residues followed by one chiral L-valine (L-Val) or Cα-methyl-L-valine [(αMe)Val] residue at the C-terminus, have been assessed by x-ray diffraction analysis. In all of the compounds the (Aib)4 sequence is folded in a regular 310-helical conformation. In the four pentapeptides characterized by the L-(αMe)Val residue two conformationally distinct molecules occur in the asymmetric unit. Conversely, only one molecule is observed in the asymmetric unit of two pentapeptides with the C-terminal L-Val residue. In the L-Val based peptides the helical screw sense of the (Aib)4 sequence is right-handed, whereas in the L(αMe)Val analogues both right- and left-handed helical screw senses concomitantly occur in the two crystallographically independent molecules.

Aflatoxin M1 in raw, UHT milk and dairy products in Sicily (Italy)

A survey on 73 milk samples from different animal breeds and 24 dairy products samples from Sicily, Italy, was carried out for the presence of aflatoxin M1 (AFM1) by LC-fluorescence detection after immunoaffinity cleanup. AFM1 was detected in 48% and 42% of the milk and dairy samples at concentration ranges between <5.0–16.0 and <5.0–18.0 ng L−1, respectively. Within the raw milk samples, 92% had an AFM1 content below 5.0 ng L−1, in 7% of the cases it was in the range 5.0–10.0 ng L−1 and 1% was contaminated between 10.0 and 20.0 ng L−1. For the dairy products, ultra-high-temperature treated (UHT) milk, milk cream and cheese, the incidence was 42%, of which 83% contained less than 5.0 ng L−1 and 17% contained 10.0–20.0 ng L−1 AFM1. The levels of contamination found justify continuous monitoring for public health and to reduce consumer exposure.