Browsing by Subject "Amides"

Now showing 1 - 4 of 4

Open Access
Detecting secondary structure and surface orientation of helical peptide monolayers from resonant hybridization signals
(Nature Publishing Group, 2013) Alici, K. B.; Gallardo I.F.
Hybridization of dominant vibrational modes with meta-surface resonance allows detection of both structural changes and surface orientations of bound helical peptides. Depending on the resonance frequency of meta-molecules, a red- or blue- shift in peptide Amide-I frequency is observed. The underlying coupling mechanism is described by using a temporal coupled mode theory that is in very good agreement with the experimental results. This hybridization phenomenon constitutes the basis of many nanophotonic systems such as tunable coupled mode bio-sensors and dynamic peptide systems driven by infrared signals.
Open Access
Greasy cations bind to neutral macromolecules in aqueous solution
(American Chemical Society, 2024-06-05) Ertekin, Umay Eren; Okur, Halil İbrahim
Ions influence the solution properties of macromolecules. Although much is known about anions, cationic effects are considered mostly in terms of weak interactions or exclusion from neutral interfaces. Herein, we have systematically studied the effect of quaternary tetraalkylammonium cations ($NH_4+, NMe_4+, NEt_4+, NPr_4+, NBu_4+$) on the phase transition of poly(N-isopropylacrylamide) (PNIPAM) in aqueous solution. Solubility measurements were coupled to H-1 NMR and ATR-FTIR spectroscopic measurements. The solubility and NMR measurements revealed a direct binding between the greasiest cations and the isopropyl group of the macromolecule, evidenced from the nonlinear, Langmuir-type chemical shift response only at the isopropyl NMR signals with increasing salt concentrations. The ATR-FTIR measurements focusing on the amide oxygen showed that it is not the main direct-binding site. Additionally, the salting-out effects of the greasier cations correlate with their hydration entropies. These results demonstrate that the most weakly hydrated cations can bind to macromolecules as strongly as the weakly hydrated Hofmeister anions.
Open Access
Metal dicyanamides as efficient and robust water-oxidation catalysts
(Wiley Blackwell, 2017) Nune, S. V. K.; Basaran, A. T.; Ülker, E.; Mishra, R.; Karadas, F.
Non-oxide cobalt-based water-oxidation electrocatalysts have received attention recently for their relative ease of preparation, they are stable both in acidic and basic media, and they have higher turnover frequencies than cobalt oxides. Recent studies show that one of the main bottlenecks in the implementation of non-oxide systems to water splitting is the low number of active metal sites, which is in the order of nmol cm−2. Herein, a new series of non-oxide water-oxidation catalysts has been introduced to the field. Cobalt dicyanamides are observed to have around four times higher surface active sites and better catalytic performances than cyanide-based systems. Long-term catalytic studies (70 h) at an applied potential of 1.2 V and electrochemical studies performed in solutions in pH values of 3.0–12.0 indicate that the compounds are robust and retain their structures even under harsh conditions. Moreover, the addition of Ni impurities to cobalt dicyanamides is a feasible method to improve their catalytic activities.
Open Access
Synthesis and characterization of amino acid conjugates of oleanolic acid and their in vitro cytotoxic effect on HCC cell lines
(Pakistan Journal of Pharmaceutical Sciences, 2014) Mustufa, Muhammad Ayaz; Hashmi, I. A.; Manzoor, S.; Ahmed, A.; Ahmed, V.; Aslam, A.; Özen, Çiğdem; Naqvi, N.; Öztürk, Mehmet; Ali, F. I.
Oleanolic acid (3β-hydroxy-olean-12-en-28-oic acid; OA-01), a pentacyclic triterpene, exhibit a wide range of pharmacological and biological activities. We have isolated oleanolic acid from methanolic extract of Periploca aphylla, collected from surroundings of Karachi in the month of February. Furthermore, four known and two new C-28 amino acid conjugates of oleanolic acid were prepared to explore potential of these compounds on HCCs and one breast cancer cell line. Cytotoxic effects revealed that as compare to parent compound (OA-01), two derivatives OA-04 (p<0.0001) and OA-06 (p<0.01) showed significantly increased/higher inhibition rates.