Acetyl Amino Research Articles

Extraction of Actinides and Lanthanides from Nitric Acid Solutions with Mixtures of 1,5-N,N'-Bis[(Diphenylphosphoryl)Acetyl(Hexyl)Amino]pentane and New Asymmetrical Phosphonium- and Imidazolium-Based Ionic Liquid

Extraction of Actinides and Lanthanides from Nitric Acid Solutions with Mixtures of 1,5-N,N'-Bis[(Diphenylphosphoryl)Acetyl(Hexyl)Amino]pentane and New Asymmetrical Phosphonium- and Imidazolium-Based Ionic Liquid

Characterization of isomeric acetyl amino acids and di-acetyl amino acids by LC/MS/MS.

Acetylation of amino acids is important in the molecular biology and biochemistry because they are part of several metabolic pathways. N-acetyl amino acids can form through degradation of N-acetyl proteins or direct acetylation of amino acids by specific enzymes. Acetylation of α-amino acids can be either on the alpha -NH2 or on the side-chain functional group, where both the acetyl products are isomeric and can show different biological roles. Theoretically, all proteinogenic α-amino acids are expected to undergo acetylation and they can be a part of metabolome. Thus, it is essential to detect and identify all the possible acetylated products of α-amino acids for untargeted metabolomics studies. In this study, it is aimed to synthesize and characterize all acetylated products of natural α-amino acids. A total of 20 Nα -acetyl amino acids (1-20), six side-chain acetyl amino acids (21-26), and six diacetyl amino acids (27-32) were synthesized and characterized by liquid chromatography-electrospray ionizationtandem mass spectrometry (LC-ESI-MS/MS). The [M + H]+ ions of all the acetyl amino acids were subjected to MS/MS experiments to obtain their structural information. Apart from the expected loss of (H2 O + CO) (immonium ions), most of the acetyl amino acids specifically showed loss of H2 O and loss of a ketene (C2 H2 O) from [M+H]+ ions. The side-chain acetyl amino acids showed a clear-cut structure specific fragment ions that enabled easy differentiation from their isomeric Nα -acetyl amino acids. The other isomeric/isobaric acetyl amino acids could also be easily distinguished by their MS/MS spectra. The MS/MS of immonium ions of the acetyl amino acids were also studied, and they included characteristic products reflecting the structures of parent Nα -acetyl and side-chain acetyl amino acids.

Modulating Catalytic Activity and Stability of Atomically Precise Gold Nanoclusters as Peroxidase Mimics via Ligand Engineering.

Metal nanoclusters (NCs), composed of a metal core and protecting ligands, show promising potentials as enzyme mimics for producing fuels, pharmaceuticals, and valuable chemicals, etc. Herein, we explore the critical role of ligands in modulating the peroxidase mimic activity and stability of Au NCs. A series of Au15(SR)13 NCs with various thiolate ligands [SR = N-acetyl-l-cysteine (NAC), 3-mercaptopropionic acid (MPA), or 3-mercapto-2-methylpropanoic acid (MMPA)] are utilized as model catalysts. It is found that Au15(NAC)13 shows higher structural stability than Au15(MMPA)13 and Au15(MPA)13 against external stimuli (e.g., pH, oxidants, and temperature) because of the intramolecular hydrogen bonds. More importantly, detailed enzymatic kinetics data show that the catalytic activity of Au15(NAC)13 is about 4.3 and 2.7 times higher than the catalytic activity of Au15(MMPA)13 and Au15(MPA)13, respectively. Density functional theory (DFT) calculations reveal that the Au atoms on the motif of Au NCs should be the active centers, whereas the superior peroxidase mimic activity of Au15(NAC)13 should originate from the emptier orbitals of Au atoms because of the electron-withdrawing effect of acetyl amino group in NAC. This work demonstrates the ligand-engineered electronic structure and functionality of atomically precise metal NCs, which afford molecular and atomic level insights for artificial enzyme design.

Evaluation of TyG index and TG/HDL-C ratio in HBeAg negative chronic hepatitis B infected patients.

Patients with hepatitis B e antigen (HBeAg) negative chronic HBV infection are regularly followed up. This study investigates the presence of insulin resistance and the relationship between hepatosteatosis and insulin resistance in patients with HBeAg negative chronic HBV infection using the TyG index and TG/HDL-C ratio. Patients with HBeAg negative chronic HBV infection who applied to the Infectious Diseases and Clinical Microbiology outpatient clinic between January 2019 and December 2020 were included in the study. Glucose, lipid panel, alanine amino transferase (ALT), acetyl amino transferase (AST), body mass index (BMI), TyG index, TG/HDL-C and hepatobiliary ultrasonography (USG) results were evaluated. The data were compared with the control group consisting of 308 HBsAg negative individuals. The study included 132 patients with a median age of 52 years. There was no significant difference between the patient and control groups regarding age, gender and BMI. Glucose, total cholesterol, TG, LDL, AST, ALT, TyG index and TG/HDL-C ratio were significantly higher in patient than in the control group. At the same time, the HDL value was significantly lower in the patients. There was a strong positive correlation between the TG and BMI, and a strong negative correlation between HDL levels and both TyG index and TG/HDL-C ratio. Our findings showed that the TyG index and TG/HDL-C ratio are helpful in the diagnosis of insulin resistance and hepatosteatosis in patients with HBeAg negative chronic HBV infection.

Feasibility of 1-Ethyl-4-butyl-1,2,4-triazolium Acetyl Amino Acid Ionic Liquids as Sustainable Heat-Transfer Fluids

Feasibility of 1-Ethyl-4-butyl-1,2,4-triazolium Acetyl Amino Acid Ionic Liquids as Sustainable Heat-Transfer Fluids

Thickness Analyses of 4-(Acetyl Amino)-2-Aminobenzoic Acid on ITO Thin Film Using Analytic Based of X-Ray Photoelectron Spectroscopy Method

In this study, the binding energies of 4-(acetyl amino)-2-aminobenzoic acid molecules that coated on the Indium Tin Oxide (ITO) surface with the self-assembled technique is measured by the XPS method. The thickness of the layer formed on the modified ITO surface is calculated by using XPS technique with an analytical approach. It is reported that the formation of commercially benzoic acid -based self-assembled monolayers (SAMs) is coated surely on ITO that is proved by this technique. According to this approach, the intensity of the substrate-originated photoemission peak from a semi-infinite substrate with a uniform over layer thickness, tXPS(SAM), is obtained from the SAM peak to In3d and Sn3d oxide (ITO) intensity peaks ratio (ISAM/IITO) that the Hill equation allows thin film thickness calculation from XPS data.

Effects of degree of deacetylation on hemostatic performance of partially deacetylated chitin sponges

Chitin/chitosan hemostatic materials have long been studied for uncontrolled hemorrhage, an urgent clinical problem due to severe blood-vessel damage or hemophilia. As one of the basic structural parameters of chitin, the degree of deacetylation (DD) significantly affects the material's physical, chemical, as well as biological properties. In this study, partially deacetylated chitins with a wide range of DD (23–81%) were prepared by homogeneous deacetylation, and sponges with these various chitins were fabricated by freeze-drying to study the effects of DD on their hemostatic properties. Among all sponge samples, the chitosan sponge with a DD of 48% showed the highest water absorption, whole blood adsorption, RBC adsorption rate, and the best hemostatic performance in an uncontrolled bleeding model of the rat femoral artery, demonstrating that a certain proportion of acetyl amino and amino groups could also activate the coagulation system and promote the adhesion of platelet and erythrocyte.

Facile synthesis and antimicrobial evaluations of some novel pyrazolo[3,4‐b]selenolo[3,2‐e]pyrazines and their related heterocycles

AbstractA new series of pyrazolopyrazinoselenolotriazolopyrimidines was synthesized by a facile method based on condensation of 5‐amino‐3‐methyl‐1‐phenyl‐1H‐pyrazolo[3,4‐b]selenolo[3,2‐e]pyrazine‐6‐carbonitrile (3) with triethyl orthoformate followed by intramolecular cyclization with hydrazine to afford 7‐amino‐8‐imino‐3‐methyl‐1‐phenyl‐1,8‐dihydro‐7H‐pyrazolo[3″,4″:5′,6′]pyrazino[2′,3′:4,5] selenolo[3,2‐d]pyrimidine (5). The latter compound was utilized as a multipurpose precursor for the construction of other new triazoles fused to the pyrazolopyrazino‐ selenolopyrimidine moiety. Alternatively, acetylation and chloro‐acetylation of compound 3 using acetic anhydride and chloroacetyl chloride yielded the acetyl amino 11 and chloroacetamido 12 derivatives, respectively. Compound 12 underwent nucleophilic substitution upon reaction with morpholine to provide the morpholinyl acetamide 13. Furthermore, the pyrazolopyridoselenolopyrazine ring system 14 was synthesized by the reaction of the o‐amino‐carbonitrile 3 with malononitrile. Assignment of the chemical structures for the new compounds was confirmed depending on elemental and spectral techniques. On the other hand, most of the synthesized compounds revealed promising results against various bacterial and fungal strains.

Chemical Composition and Bioactivity of Essential Oils from Cymbopogon nardus L. and Rosmarinus officinalis L. Against Ulomoides dermestoides (Fairmaire, 1893) (Coleoptera: Tenebrionidae)

Essential oils (EOs) represent valuable alternatives in handling pest insects in stored grains. The main objective of this study was to evaluate the chemical composition as well as the repellent, fumigant, and oviposition inhibition activities of the rosemary (Rosmarinus officinalis) and citronella (Cymbopogon nardus) EOs against Ulomoides dermestoides. Ethyl 3-[acetyl(butyl)amino] propanoate (IR3535), an active ingredient in repellent formulations was used as a positive control. The chemical compositions of the EOs were characterized by GC/MS. The EOs major compounds (>10 %) included 1,8-cineole (24.6 %), α-pinene (17.7 %), camphor (12.4 %), and camphene (11.3 %) for rosemary, whereas for citronella, the most abundant components were citronellal (25.3 %), citronellol (17.9 %) and geraniol (11.6 %). The biological action observed was dependent on the concentration used. Both EOs showed 100 %-repellency at the highest tested concentration (16 μL/mL) with RC50 values lower than 2.6 μL/mL after 4 h-exposure. Contact toxicity results showed that all treatments had mortality rates lower than 40 %, while fumigant action did not exceed 25 %. The exposure of adult insects to sublethal concentrations of the two EOs significantly inhibited oviposition at 2 and 4 μL/mL. These data suggest that citronella and rosemary EOs, employing different toxicity mechanisms, could be useful candidates for formulations utilized in the management and pest control in stored products.

Studies on Immunomodulatory Effect of Casein Phospho Peptide Isolated from Cultured Dairy Product

Bioactive peptides have been defined as specific protein fragments that have an impact on body functions or conditions and may ultimately influence health. Fermented milk is a dairy product which has abundance of bioactive peptides. In this study, Casein Phospho peptide (CPP) was isolated by enzymatic hydrolysis of fermented milk using trypsin. The molecular weight of the Casein Phospho peptide was 3.5 KDa. The anti-bacterial activity of Casein Phospho peptide was determined using four pathogens such as, Escherichia coli, Bacillus cereus, Staphylococcus aureus and Salmonella enterica. Casein phospho peptide formed a zone of inhibition against the pathogens. The bioactive peptides were characterized using Fourier Transform Infra-Red Spectroscopy (FT-IR), Casein Phospho peptide had aliphatic amine, acetyl amino I and acetyl amino II functional groups. The HPLC analysis of Casein Phospho peptide revealed that the major amino acid present was L- Glutamic acid and the amino acid present in lesser concentration was Leucine. Peripheral Blood Mononuclear Cells (PBMCs) were isolated from human blood and the cells were treated with Casein Phospho peptide to assess the immunomodulatory effect.
 Casein Phospho peptide was able to produce a higher concentration of IL-10 anti-inflammatory cytokines when treated with PBMCs.

Systemic characteristics of biomarkers and differential metabolites of raw and ripened pu-erh teas by chemical methods combined with a UPLC-QQQ-MS-based metabolomic approach

Pu-erh tea is one of the most popular beverages in China and Southeast Asia, however, influences from fermentation and storage on its chemical profile and quality are unclear. Thus, bioactivities and metabolomes of raw (17-raw) and ripened teas (17-rip through 06-rip) were assessed using chemical methods and a UPLC-QQQ-MS-based metabolomic approach. Results evidence that chemical components and antioxidant activities of 17-rip through 06-rip were similar but lower than those of 17-raw. Subsequently, 842 metabolites were identified from 17-raw, 17-rip and 06-rip, of which 20 and 19 metabolites were biomarkers for discerning 17-rip from 17-raw and 06-rip, respectively. Between 17-raw and 17-rip, 536 differential metabolites were identified, and 17-rip contained higher levels of gallic acid, acetyl amino acids, purine alkaloids, pyrimidine alkaloids and non-glycoside flavonoids and lower levels of sour compounds, quinic acid derivatives, amino acids, flavonoids glycosides, and flavan-3-ols; all of them were found to be positively but gallic acid and acetyl amino acids negatively correlated with two tested bioactivities. Between 17-rip and 06-rip, 175 differential metabolites were identified, among which alkaloids positively correlated to the two bioactivities. Overall, this study identified biomarkers distinguishing teas with different fermentation processes and storage times and different metabolites affecting their tastes and bioactivities.

Reduced effectiveness of repellents in a pyrethroid‐resistant strain of Aedes aegypti (Diptera: culicidae) and its correlation with olfactory sensitivity

The mosquito, Aedes aegypti (Diptera: Culicidae), is a vector of dengue fever, zika, chikungunya, and yellow fever viruses, and in many areas possesses significant levels of resistance to pyrethroids. Behavioral performance was assessed in 15, 30, and 60 min exposures in a high throughput vapor phase spatial repellency assay to three contact repellent standards: N,N-diethyl-3-methylbenzamide (DEET), ethyl 3-[acetyl(butyl)amino] propanoate (IR3535), and 2-undecanone, as well as pyrethrum extract, transfluthrin, and metofluthrin in susceptible (Orlando) and a pyrethroid-resistant Puerto Rico strain of Aedes aegypti. Additionally, electroantennographic studies were used to investigate the antennal sensitivities to these compounds in both strains. Resistance was found to all tested insect repellents in the Puerto Rico strain of Ae. aegypti. Resistance ratios at the different time points were about 2 for DEET, 3 for 2-undecanone, and 12 for IR3535. Resistance was also observed to pyrethrum extract (∼9-fold), transfluthrin (∼5-fold), and metofluthrin (∼48-fold) in repellent behavioral response. Electrophysiological analysis found decreased antennal sensitivity to all repellents tested, consistent with their behavioral effects. The reduced sensitivity to these repellents may represent a fitness cost arising from the kdr mutation present in Puerto Rico Aedes aegypti. This work highlights the need for understanding collateral effects from the evolution of pesticide resistance in mosquitoes, and the importance of finding alternative strategies to control resistance development. © 2019 Society of Chemical Industry.

Deltamethrin-resistant German Cockroaches Are Less Sensitive to the Insect Repellents DEET and IR3535 than Non-resistant Individuals.

The German cockroach, Blattella germanica (L.) (Blattodea: Blattellidae), is a serious worldwide pest with a considerable economical and sanitary impact. It is mainly controlled by the application of synthetic insecticides, but repeated use of these substances has promoted the appearance of resistance in cockroach populations throughout the world. The aim of this study was to compare the behavior of deltamethrin-susceptible (CIPEIN colony) and deltamethrin-resistant (JUBA and VGBA colonies) first instar nymphs exposed to the repellents N,N-diethyl-3-methylbenzamide (DEET) and ethyl 3-[acetyl(butyl)amino]propanoate (IR3535). Firstly, the behavior of the nymphs was assessed in an experimental arena in the absence of repellents. The parameters Distance Traveled, Velocity, Mobility Time, and Time Spent (in each half of the arena) were quantified using an image analyser, and showed that the behavior elicited by the three colonies was similar. After this, the behavior of the nymphs was quantified in an arena, half of which had been treated with repellent. The repellency of DEET increased as a linear function of log concentration for the three colonies. DEET elicited repellency as from a concentration of 97.49 µg/cm2 for the CIPEIN and JUBA colonies and 194.98 µg/cm2 for the VGBA colony. The repellency of IR3535 was weaker and started at a concentration of 389.96 µg/cm2 for the CIPEIN colony, 779.92 μg/cm2 for JUBA, and 1559.84 μg/cm2 for VGBA . Finally, nymphs were exposed to 3:1, 1:1, and 1:3 DEET:IR3535 mixtures, and a synergistic effect was observed only in the CIPEIN colony.

Molecular structure of human aortic valve by µSR- FTIR microscopy

Abstract Aortic valve is a part of the heart most frequently affected by pathological processes in humans what constitute a very serious health problem. Therefore, studies of morphology and molecular microstructure of the AV are needed. µSR- FTIR spectroscopy and microscopy represent unique tools to study chemical composition of the tissue and to identify spectroscopic markers characteristic for structural and functional features. Normal AV reveals a multi-layered structure and the compositional and structural changes within particular layers may trigger degenerative processes within the valve. Thus, deep insight into the structure of the valve to understand pathological processes occurring in AV is needed. In order to identify differences between three layers of human AV, tissue sections of macroscopically normal AV were studied using µSR- FTIR spectroscopy in combination with histological and histochemical stainings. Tissue sections deposited onto CaF2 substrates were mapped and representative set of IR spectra collected from fibrosa, spongiosa and ventricularis were analysed by Principal Component Analysis (PCA) in the spectral range between 1850–1000 cm−1 and 3050–2750 cm−1. PCA revealed a layered molecular structure of the valve and it was possible to identify IR bands associated to different tissue parts. Spongiosa layer was well differentiated from other two layers mainly based on IR bands characteristic for the distribution of glycosaminoglycans (GAGs) in the tissue – like 1170 cm−1 (υas(C-O-S)) and 1380 cm−1 (acetyl amino group). Additionally, it was distinguished from fibrosa and ventricularis based on 1085 cm−1 and 1240 cm−1 bands characteristic for GAGs and for carbohydrates- ν(C-O) and ν(C-O-C) respectively and nucleic acids -νsym(PO2−) and νasym(PO2−) respectively, which were less specific for this layer. The use of µSR- FTIR spectroscopy demonstrated co-localization of GAGs and lipids in spongiosa layer what may indicate their contribution in the very early phase of aortic valve calcific degeneration.

Facile Fabrication of Nanofibrillated Chitin/Ag2O Heterostructured Aerogels with High Iodine Capture Efficiency

Nanofibrillated chitin/Ag2O aerogels were fabricated for radioiodine removal. Chitin was first fabricated into nanofibers with abundant acetyl amino groups (–NHCOCH3) on the surface. Then, highly porous chitin nanofiber (ChNF) aerogels were obtained via freeze-drying. The ChNF aerogels exhibited a low bulk density of 2.19 mg/cm3 and a high specific surface area of 179.71 m2/g. Ag2O nanoparticles were evenly anchored on the surfaces of ChNF scaffolds via strong interactions with –NHCOCH3 groups, subsequently yielding Ag2O@ChNF heterostructured aerogels. The composites were used as efficient absorbents to remove radioiodine anions from water and capture a high amount of I2 vapor in the forms of AgI and iodine molecules. The adsorption capacity of the composite monoliths can reach up to 2.81 mmol/g of I− anions. The high adsorbability of the composite monolithic aerogel signifies its potential applications in radioactive waste disposal.

Comparative Evaluation of a Silicone Membrane as an Alternative to Skin for Testing Mosquito Repellents.

Repellents prevent mosquito bites and help reduce mosquito-borne disease, a global public health issue. Laboratory-based repellent bioassays predict the ability of compounds to deter mosquito feeding, but the variety of repellent bioassays and statistical analysis methods makes it difficult to compare results across methodologies. The most realistic data are collected when repellents are applied on the skin; however, this method exposes volunteers to chemicals and mosquito bites. Silicone membranes were investigated as an alternative to human skin in assays of repellent efficacy. Results from module system bioassays conducted in vitro with a silicone membrane were compared with in vivo bioassays conducted with N,N-diethyl-3-methylbenzamide (referred to as DEET), 1-piperidinecarboxylic acid 2-(2-hydroxyethyl)-1-methylpropylester (referred to as Picaridin), ethyl 3-[acetyl(butyl)amino]propanoate (referred to as IR3535), and para-menthane-3,8-diol (referred to as PMD) applied directly on the skin of the leg. No significant difference in mosquito feeding was found when comparing skin and volunteer-worn membrane controls using blood; however, feeding was significantly lower in unworn membrane controls using either 10% sucrose or blood, indicating that worn membranes are a possible surrogate for untreated human skin. Pooled data from six volunteers were used to generate dose-response curves of blood-feeding activity. Results from skin-applied repellents were modeled to determine if membranes could provide a predictive correlate for skin. Goodness-of-fit comparisons indicated that the nonlinear dose-response curves for the skin and membrane differed significantly for DEET and Picaridin, but did not differ significantly for IR3535 and PMD. With knowledge of the dose-response relationships and further modifications to this system, the membrane-based tests could be used for standardized repellent testing with infected vectors.

Structures of N-acetyl-DL-isoleucine, N-acetyl-DL-alloisoleucine and their ammonium salts; role of ammonium ions in crystal structure formation.

The crystal structures of N-acetyl-DL-isoleucine, N-acetyl-DL-alloisoleucine and their ammonium salts show that these four compounds exist as racemic compounds around room temperature. The two ammonium salts are arranged around a 21 screw axis, forming a helical column which consists of ammonium ions and single enantiomeric anions similar to the crystals of the ammonium salts of optically active N-acetyl-L-isoleucine and N-acetyl-D-alloisoleucine. The ammonium ion and the carboxylate ion in the helix are connected by three hydrogen bonds, the fourth hydrogen bond being formed between the ammonium ion and an external acetyl amino group of the neighboring helical column. The fourth hydrogen bond is formed between the ammonium ion and an external acetyl amino group of the neighboring 21 column. Ammonium N-acetyl-DL-alloisoleucinate was revealed to exist as an unstable racemic compound due to conformational similarity between the racemic and optically active compounds in the solid state and was optically resolved by fractional crystallization at 293 K.

A New Approach for the Synthesis of Chalcone, Acetyl Pyrazoline and Amino Pyrimidine Bearing 1,3,5- Triazine Nucleus as Potential Antimicrobial and Antitubercular Agent

In an attempt to find a new class of antimicrobial and antitubercular agent, a new series of chalcone, acetyl pyrazoline and amino pyrimidine bearing 1,3,5- triazine nucleus were synthesized with appropriate chemical reagent. Chalcones (D 1 -D 5 ) were synthesized by the classical Claisen-Schmidt condensation of substituted ketone (C) with variously substituted aldehydes via conventional method. Now treatment of chalcones with hydrazine hydrate/glacial acetic acid and guanidine hydrochloride/Alkali afforded the corresponding acetyl pyrazoline (E 1 -E 5 ) and amino pyrimidine (F 1 -F 5 ) derivatives respectively. The chemical structures of all newly synthesized compounds were established on the basis of their FTIR, 1H NMR, 13C NMR, LC-MS as well as elemental analysis. All the newly design compounds were assayed for their in vitro antimicrobial activity against selected pathogens by the Broth dilution method and in vitro antitubercular activity against Mycobacterium tuberculosis H 37 Rv using Lowenstein-Jensen MIC method. Most of the compounds showed appreciable antimicrobial activity against the all tested strains. Among the synthesized compounds D 1 , D 2 , D 3 , E1, E3, E4, F3 and F4 exhibited excellent antimicrobial activity and said to be the most proficient members of the series. Compound D 5 and F 5 exhibited promising antitubercular activity.

Desferrioxamine as an appropriate chelator for 90Nb: Comparison of its complexation properties for M-Df-Octreotide (M = Nb, Fe, Ga, Zr)

The niobium-90 radioisotope (90Nb) holds considerable promise for use in immuno-PET, due to its decay parameters (t½=14.6h, positron yield=53%, Eß+mean=0.35MeV and Eß+max = 1.5MeV). In particular, 90Nb appears well suited to detect in vivo the pharmacokinetics of large targeting vectors (50–150kDa). In order to be useful for immuno-PET chelators are required to both stabilize the radionuclide in terms of coordination chemistry and to facilitate the covalent attachment to the targeting vector. Different chelators were evaluated for this purpose in terms of radiolabelling efficiency and stability of the radiolabelled Nb(V) complex and in order to determine the most suitable candidate for conjugation to a biologically relevant targeting vector. For the purpose of studying the complexation properties the niobium radioisotope 95Nb was used as an analogue of 90Nb, by virtue of its longer half-life (35days) and lower cost (reactor-based production). Acyclic and cyclic chelators were investigated, with desferroxamine [Df: (N'-{5-[acetyl(hydroxy)amino]pentyl}-N-[5-({4-[(5-aminopentyl) (hydroxy)amino]-4-oxobutanoyl} amino)pentyl]-N-hydroxysuccinamide)] emerging as the best candidate. Greater than 99% radiolabelling was achieved at room temperature over a wide pH range. The 95Nb-Df complex is sufficiently stable for immuno-PET (<7% degradation over 7days in vitro). As a proof-of-principle, a Df conjugate featuring a well-established targeting vector, (D)-Phe1-octreotide, was evaluated. The fast labelling kinetics of the unconjugated chelator (Df) were retained for Df-succinyl-(D)Phe1-octreotide (Df-OC), with>90% labelling after 1h at room temperature over the pH range 5–7. Stability studies, performed in vitro in serum at physiological temperature (37°C), revealed that 87±2% of the radiolabelled molecule remained intact after 7days. Competition studies with relevant metal ions (zirconium(IV), gallium(III) and iron(III)) have been performed with Df-OC to gain insight to the relative stability [Nb-Df]-OC complex to transmetallation. At equimolar metal ion concentrations the [Nb-Df]-OC complex showed the greatest overall stability. The favourable radiolabelling characteristics of Df-OC and its stability indicate that Df is a potentially very useful chelator for the development of radiopharmaceuticals for 90Nb-PET.

Probing the non-native H helix translocation in apomyoglobin folding intermediates.

Apomyoglobin folds via sequential helical intermediates that are formed by rapid collapse of the A, B, G, and H helix regions. An equilibrium molten globule with a similar structure is formed near pH 4. Previous studies suggested that the folding intermediates are kinetically trapped states in which folding is impeded by non-native packing of the G and H helices. Fluorescence spectra of mutant proteins in which cysteine residues were introduced at several positions in the G and H helices show differential quenching of W14 fluorescence, providing direct evidence of translocation of the H helix relative to helices A and G in both the kinetic and equilibrium intermediates. Förster resonance energy transfer measurements show that a 5-({2-[(acetyl)amino]ethyl}amino)naphthalene-1-sulfonic acid acceptor coupled to K140C (helix H) is closer to Trp14 (helix A) in the equilibrium molten globule than in the native state, by a distance that is consistent with sliding of the H helix in an N-terminal direction by approximately one helical turn. Formation of an S108C–L135C disulfide prevents H helix translocation in the equilibrium molten globule by locking the G and H helices into their native register. By enforcing nativelike packing of the A, G, and H helices, the disulfide resolves local energetic frustration and facilitates transient docking of the E helix region onto the hydrophobic core but has only a small effect on the refolding rate. The apomyoglobin folding landscape is highly rugged, with several energetic bottlenecks that frustrate folding; relief of any one of the major identified bottlenecks is insufficient to speed progression to the transition state.