Piv‐Proψ[CH2–NH–O]Gly–NHiPr

The pseudodipeptide, (S)‐N‐iso­propyl {[N‐(pivaloyl)­pyrrol­idin‐2‐yl]­methyl­amino­oxy}acet­amide, C₁₅H₂₉N₃O₃, adopts a global extended conformation with the hydroxy­l­amine group in the g⁺/g^? structure. The C‐terminal amide NH interacts intramolecularly with the hydroxy­lamine O atom. Both NH bonds of each mol­ecule are hydrogen bonded to the C‐­terminal amide carbonyl of a neighbouring mol­ecule.     

Thermosensitive gel formation of novel polypeptides containing a collagen‐derived Pro‐Hyp‐Gly sequence and an elastin‐derived Val‐Pro‐Gly‐Val‐Gly sequence

A triple‐helix‐forming collagen model peptide, (prolyl‐trans‐4‐hydroxyprolyl‐glycyl)₁₀ [(Pro‐Hyp‐Gly)₁₀], and a thermosensitive elastin‐derived pentapeptide, valyl‐prolyl‐glycyl‐valyl‐glycyl (Val‐Pro‐Gly‐Val‐Gly), were copolymerized in various mole ratios using 1‐ethyl‐3‐(3‐dimethylaminopropyl)‐carbodiimide hydrochloride and 1‐hydroxybenzotriazole in dimethyl sulfoxide at 20 °C. All of the obtained polypeptides have molecular weight higher than 10³ and contain a triple‐helical structure, and showed an inverse phase transition from transparent solution to turbid suspension in response to a rise in temperature. The lower critical solution temperature of the polypeptide solution decreased upon increasing the content of Val‐Pro‐Gly‐Val‐Gly. Furthermore, polypeptides containing 82–86 mol % of Val‐Pro‐Gly‐Val‐Gly in composition showed reversible gel formation, suggesting that (Pro‐Hyp‐Gly)₁₀ acts as a hydrated unit and Val‐Pro‐Gly‐Val‐Gly acts as a thermosensitive crosslinking point. These biodegradable thermosensitive polypeptides may be useful for biomedical applications, including, as a scaffold for tissue regeneration. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6048–6056, 2005     

1H and 13C NMR study of phosphopeptides: 2—Ac–PSer–Gly,Ala–PSer–Gly and Gly–PSer–Phe

¹H and ¹³C NMR spectra of AC–PSer–Gly, Ala–PSer–Gly and Gly–PSer–Phe have been measured and analysed as a function of pD. The NMR parameters of the PSeryl side chain are a function of the sequence. The second titration step of the phosphate group (pK₂ = 5.7) is much more difficult to detect in Ac–PSer–Gly and Ala–PSer–Gly than in Gly–PSer–Phe. The conformation in which H-α? C-α? C-β? O? P forms a planar W-type arrangement predominates only for Ala–PSer–Gly. In the other two phosphopeptides the gauche conformations contribute increasingly, in particular for Gly–PSer–Phe.     

Energetic switch of the proline effect in collision‐induced dissociation of singly and doubly protonated peptide Ala‐Ala‐Arg‐Pro‐Ala‐Ala

Suppression of the selective cleavage at N‐terminal of proline is observed in the peptide cleavage by proteolytic enzyme trypsin and in the fragment ion mass spectra of peptides containing Arg‐Pro sequence. An insight into the fragmentation mechanism of the influence of arginine residue on the proline effect can help in prediction of mass spectra and in protein structure analysis. In this work, collision‐induced dissociation spectra of singly and doubly charged peptide AARPAA were studied by ESI MS/MS and theoretical calculation methods. The proline effect was evaluated by comparing the experimental ratio of fragments originated from cleavage of different amide bonds. The results revealed that the backbone amide bond cleavage was selected by the energy barrier height of the fragmentation pathway although the strong proton affinity of the Arg side chain affected the stereostructure of the peptide and the dissociation mechanism. The thermodynamic stability of the fragment ions played a secondary role in the abundance ratio of fragments generated via different pathways. Fragmentation studies of protonated peptide AACitPAA supported the energy‐dependent hypothesis. The results provide an explanation to the long‐term arguments between the steric conflict and the proton mobility mechanisms of proline effect.     

A linear free-energy correlation in the low-energy tandem mass spectra of protonated tripeptides Gly–Gly–Xxx

The backbone cleavages of protonated tripeptide ions of the series Gly—Gly—Xxx, where Xxx ? Gly, Ala, Val, d-Leu, l-Leu, Ile, Phe, Tyr, Trp, Pro, Met and Glu, were studied in a hybrid tandem mass spectrometer. C-Terminal y-type ions and N-terminal a- and b-type ions were noted. A linear relationship between log (y₁/b₂) and the proton affinity of the C-terminal amino acid substituents was found: as the proton affinity of the C-terminal residue increases, the fraction of y₁ ion formation increases. When the C-terminal substituent was more basic than Trp, the b₂ ion was not observed. It is likely that the site of protonation changes from peptide bond to side-chain for just these residues, Lys, His and Arg.     

A pipecolic acid (Pip)‐containing dipeptide,Boc‐d‐Ala‐l‐Pip‐NHiPr

The title dipeptide, 1‐(tert‐butoxy­carbonyl‐d ‐alanyl)‐N‐iso­propyl‐l ‐pipecol­amide or Boc‐d ‐Ala‐l ‐Pip‐NHⁱPr (H‐Pip‐OH is pipecolic acid or piperidine‐2‐carboxylic acid), C₁₇H₃₁N₃­O₄, with a d –l heterochiral sequence, adopts a type II′β‐­turn conformation, with all‐trans amide functions, where the C‐terminal amide NH group interacts with the Boc carbonyl O atom to form a classical i+3 i intramolecular hydrogen bond. The C^α substituent takes an axial position [H^α (Pip) equatorial] and the trans pipecolamide function is nearly planar.     

Toward direct determination of conformations of protein building units from multidimensional NMR experiments I. A theoretical case study of For‐Gly‐NH2 and For‐L‐Ala‐NH2

NMR chemical shielding anisotropy tensors have been computed, employing several basis sets and the GIAO‐RHF and GIAO‐MP2 formalisms of electronic structure theory, for all the atoms of the five and nine typical backbone conformers of For‐Gly‐NH₂ and For‐L ‐Ala‐NH₂, respectively. Multidimensional chemical shift plots, as a function of the respective backbone fold, have been generated for both peptide models. On the 2D ¹H^NH‐¹⁵N^NH and ¹⁵N^NH‐¹³C^α plots the most notable feature is that at all levels of theory studied the backbone conformers cluster in different regions. Computed chemical shifts, as well as their averages, have been compared to relevant experimental values taken from the BioMagnetic Resonance Bank (BMRB). At the highest levels of theory, for all nuclei but the amide protons, deviations between statistically averaged theoretical and experimental shifts are as low as 1–3%. These results indicate that chemical shift information from selected multiple‐pulse NMR experiments (e.g., 2D‐HSQC and 3D‐HNCA) could directly be employed to extract folding information for polypeptides and proteins. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 882–900, 2000     

Cyano–cyano and chloro–cyano interactions in two imidazole derivatives

In two closely related 1‐aryl‐2‐methyl‐4‐nitro‐5‐cyano­imid­azoles, namely 2‐methyl‐4‐nitro‐1‐phenyl‐1H‐imidazole‐5‐carbo­nitrile, C₁₁H₈N₄O₂, and 1‐(4‐chloro­phenyl)‐2‐methyl‐4‐nitro‐1H‐imidazole‐5‐carbo­nitrile, C₁₁H₇ClN₄O₂, different weak intermolecular interactions determine the crystal packing. In the 1‐phenyl derivative, dipole–dipole interactions between antiparallel cyano groups connect mol­ecules into centrosymmetric dimers, while in the 1‐(4‐chloro­phenyl) derivative, the dimers are connected by C≡N⋯Cl—C halogen bonds. These interactions, together with weak C—H⋯O(N) hydrogen bonds, connect mol­ecules related by subsequent centres of inversion into infinite tapes.     

A Nanosized Gly‐Decorated Praseodymium‐Stabilized Selenotungstate Cluster: Synthesis,Structure, and Oxidation Catalysis

A flexible one‐pot strategy with pyramidal Se^IV heteroatoms was employed for the assembly of the praseodymium‐containing gly‐decorated polyoxotungstate [{Pr₃(H₂O)₁₀[Se₂W₂₂O₇₆(gly)₂]}₂(Se₂W₇O₃₀H₂)]¹⁸⁻ ( 1 a ), which is constructed from one {Se₂W₇O₃₀H₂} unit and two identical {Pr₃(H₂O)₁₀[Se₂W₂₂O₇₆(gly)₂]} units. Furthermore, the catalytic performance of Cs₂Na₄H₁₂[{Pr₃(H₂O)₁₀[Se₂W₂₂O₇₆(gly)₂]}₂(Se₂W₇O₃₀H₂)] ⋅ 25 H₂O ( 1 ) for alkene epoxidation with hydrogen peroxide was investigated under mild reaction conditions, and the experimental results suggested that compound 1 exhibits good catalytic performance for the epoxidation of cyclooctene.     

Eight Schiff bases derived from various salicylaldehydes: phenol–imine and keto–amine forms,conformational disorder,and supramolecular assembly in one and two dimensions

Structures are reported for eight Schiff bases derived from various salicylaldehydes: five are newly synthesized and re‐investigations are reported for three previously reported structures, leading, in each case, to some revision of previous conclusions. In (E)‐N‐(3,4‐dimethylisoxazol‐5‐yl)‐4‐[(2‐hydroxybenzylidene)amino]benzenesulfonamide, C₁₈H₁₇N₃O₄S, (I), and (E)‐4‐[(5‐bromo‐2‐hydroxy‐3‐methoxybenzylidene)amino]‐N‐(3,4‐dimethylisoxazol‐5‐yl)benzenesulfonamide. C₁₉H₁₈BrN₃O₅S, (II), the isoxazole rings adopt different orientations relative to the rest of the molecules, despite the additional substituents in (II) being in the aryl ring remote from the isoxazole unit. The molecules of both (E)‐4‐bromo‐2‐[(2‐hydroxyphenylimino)methyl]‐6‐methoxyphenol, C₁₄H₁₂BrNO₃, (III), and (E)‐4‐bromo‐2‐methoxy‐6‐[(2‐methoxyphenylimino)methyl]phenol, C₁₅H₁₄BrNO₃, (IV), are both effectively planar; while (III) adopts the phenol–imine constitution, (IV) adopts the keto–amine constitution. (E)‐2‐Methoxy‐6‐[(2‐methoxyphenylimino)methyl]phenol, C₁₅H₁₅NO₃, (V), which was determined previously using powder X‐ray data assuming the phenol–imine constitution, has now been refined from single‐crystal X‐ray data, confirming the phenol–imine constitution. In (E)‐3‐benzoyl‐2‐[(5‐fluoro‐2‐hydroxybenzylidene)amino]‐4,5,6,7‐tetrahydrobenzo[b]thiophene, C₂₂H₁₈FNO₂S, (VI), the fused carbocyclic ring exhibits conformational disorder; both disorder components, having populations of 0.705 (4) and 0.295 (4), adopt half‐chair conformations. The isostructural (E)‐3‐benzoyl‐2‐[(2‐hydroxybenzylidene)amino)]‐4,5,6,7‐tetrahydrobenzo[b]thiophene, C₂₂H₁₉NO₂S, (VII), which was originally reported as having a fully ordered structure [Kaur et al. (2014). Acta Cryst. E 70 , o476–o477], has been rerefined using the original data set and found to exhibit the same type of disorder as found in (VI), with disordered populations having occupancies of 0.851 (3) and 0.149 (3). The triclinic polymorph of (E)‐[(2‐hydroxyphenylimino)methyl]phenol, C₁₃H₁₁NO₂, (VIII), which crystallizes with Z′ = 2 in the space group P, has been described variously as occurring as the keto–amine tautomer [Maciejewska et al. (1999). J. Phys. Org. Chem. 12 , 875–880] and as the phenol–imine tautomer [Tunç et al. (2009). J. Chem. Crystallogr. 39 , 672–676]. Rerefinement of this structure using one of the original data sets shows that both of the independent molecules exist in the keto–amine form. In the structures of compounds (I), (VI), (VII) and (VIII), hydrogen bonds generate simple chains, while a chain of rings is formed in (V). Sheets are formed by hydrogen bonds in both (II) and (III), while in (IV), the sheet structure is built from aromatic π–π stacking interactions.     

Synthesis,structure characterization,photoluminescence properties and TD–DFT calculations for two new borates

Due to their rich structural chemistry and wide variety of applications, borate materials have provided a rich area of research. In a continuation of this research, diethylammonium bis(2‐oxidobenzoato‐κ²O¹,O²)borate, C₄H₁₂N⁺·BO₄(C₇H₄O)₂⁻, (1), and propylammonium bis(2‐oxidobenzoato‐κ²O¹,O²)borate, C₃H₁₀N⁺·BO₄(C₇H₄O)₂⁻, (2), have been synthesized by the reaction of boric acid with salicylic acid under ambient conditions. In both structures, the B atom exhibits a slightly distorted tetrahedral environment formed by the bidentate coordination of two salicylate anions via the O atoms of the central carboxylate and oxide groups. In the crystals of salts (1) and (2), mixed cation–anion layers lying parallel to the (101) plane are formed through N—H…O, C—H…O and C—H…π/N—H…O hydrogen‐bonding interactions, resulting, in each case, in a two‐dimensional supramolecular architecture in the solid state. The photoluminescence properties of the salts were studied using the as‐synthesized samples and reveal that salts (1) and (2) both display a strong blue‐light emission, with maxima at 489 and 491 nm, respectively. In DFT/TD–DFT (time‐dependent density functional theory) studies, the blue emission appears to be derived from an intramolecular charge transfer (ICT) excited state. In addition, IR and UV–Vis spectroscopies were used to investigate the title salts.     

One donor–two acceptor (D–A1)‐(D–A2) random terpolymers containing perylene diimide,naphthalene diimide,and carbazole units

A series of one donor–two acceptor (D–A₁)‐(D–A₂) random terpolymers containing a 2,7‐carbazole donor and varying compositions of perylene diimide (PDI) and naphthalene diimide (NDI) acceptors was synthesized via Suzuki coupling polymerization. The optical properties of the terpolymers are weighted sums of the constituent parent copolymers and all show strong absorption over the 400 to 700 nm range with optical bandgaps ranging from 1.77 to 1.87 eV, depending on acceptor composition. The copolymers were tested as acceptor materials in bulk heterojunction all‐polymer solar cells using poly[(4,8‐bis‐(2‐ethylhexyloxy)‐benzo[1,2‐b;4,5‐b′]dithiophene)‐2,6‐diyl‐alt‐(4‐(2‐ethylhexanoyl)‐thieno[3,4‐b]thiophene)‐2,6‐diyl] (PBDTTT‐C) as the donor material. In contrast to the optoelectronic properties, the measured device parameters are not composition dependent, and rather depend solely on the presence of the NDI unit, where the devices containing any amount of NDI perform half as well as those using the parent polymer containing only carbazole and PDI. Overall this is the first example of a one donor–two acceptor random terpolymer system containing perylene diimide (PDI) and naphthalene diimide (NDI) acceptor units, and demonstrates a facile method of tuning polymer optoelectronic properties while minimizing the need for complicated synthetic and purification steps. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3337–3345     

Synthesis,Crystal Structure,and Ultraviolet–Visible Spectrum of 8–Substituted–10,10–Dimethyl–10H–pyrido[1,2–a]indolium Perchlorates–Containing Thienyl Moiety

Two novel compounds, 8–[2–(2–thienyl)vinyl]–10,10–dimethyl–10H–pyrido[1,2–a] indolium perchlorate ( 3a ) and 8–[2–(5–phenyl–2–thienyl)vinyl]–10,10–dimethyl–10H–pyrido[1,2–a]indolium perchlorate ( 3b ) were synthesized and characterized by IR, ¹H–NMR, elemental analyses, and X–ray diffraction. Crystal structural analysis suggested that either 3a or 3b exhibited good coplanarity and rings and vinyl in the target molecule could make up a large conjugated system. Ultraviolet–visible absorption analysis indicated both 3a and 3b possessed large maximum absorptions, and 3b underwent a significant redshift (43.0 nm) in comparison with 3a .     

Gold‐Catalyzed Cycloisomerization and Diels–Alder Reaction of 1,4,9‐Dienyne Esters to 3 a,6‐Methanoisoindole Esters with Pro‐Inflammatory Cytokine Antagonist Activity

A synthetic method to prepare 3a,6‐methanoisoindole esters efficiently by gold(I)‐catalyzed tandem 1,2‐acyloxy migration/Nazarov cyclization followed by Diels–Alder reaction of 1,4,9‐dienyne esters is described. We also report the ability of one example to inhibit binding of tumor necrosis factor‐α (TNF‐α) to the tumor necrosis factor receptor 1 (TNFR1) site and TNF‐α‐induced nuclear factor κ‐light‐chain‐enhancer of activated B cells (NF‐κB) activation in cell at a half‐maximal inhibitory concentration (IC₅₀) value of 6.6 μM . Along with this is a study showing the isoindolyl derivative to exhibit low toxicity toward human hepatocellular liver carcinoma (HepG2) cells and its possible mode of activity based on molecular modeling analysis.     

Crystallographic evidence of Gly‐d,l‐Met oxidation to its sulfoxide in the presence of gold(III): solid solution of the racemic mixture of two diastereoisomers

Crystallographic analysis of a solid solution of two diastereoisomers, i.e. ({(1S,R)‐1‐carboxy‐3‐[(R,S)‐methylsulfinyl]propyl}aminocarbonyl)methanaminium tetrachloridoaurate(III) and ({(1S,R)‐1‐carboxy‐3‐[(S,R)‐methylsulfinyl]propyl}aminocarbonyl)methanaminium tetrachloridoaurate(III), (C₇H₁₅N₂O₄S)[AuCl₄], has shown that in the presence of gold(III), the methionine part of the Gly‐d ,l ‐Met dipeptide is oxidized to sulfoxide, and no coordination to the Au^III cation through the S atom of the sulfoxide is observed. In view of our observation, literature reports that methionine acts as an N,S‐bidentate donor ligand forming stable gold(III) complexes require verification. Moreover, it has been demonstrated that crystallization of the oxidation product leads to a substantial 77:23 excess of both S‐methionine/R‐sulfoxide and R‐methionine/S‐sulfoxide over S‐methionine/S‐sulfoxide and R‐methionine/R‐sulfoxide. The presence of two different diastereoisomers at the same crystallographic site is a source of static disorder at this site.