Quantitative insights into tightly and loosely bound water in hydration shells of amino acids.

The hydration of amino acids closely correlates the hydration of peptides and proteins and is critical to their biological functions. However, complete and quantitative understanding about the hydration of amino acids is lacking. Here, tightly and loosely bound water of 20 zwitterionic amino acids are quantitatively distinguished and determined by Raman spectroscopy with multivariate curve resolution (Raman-MCR) and differential scanning calorimetry (DSC). The total hydration water obtained from Raman-MCR and the tightly bound water determined by DSC have certain relevance, but they do not exactly correspond. In particular, Pro, Arg and Lys exhibit larger number of tightly bound water molecules (4.02-6.59), showing a significant influence on the onset transition temperature and the melting enthalpy values of water molecules, which provides direct evidence for their unique functions associated with biological water. Asn, Ser, Thr, Met, His and Glu have a smaller number of tightly bound water molecules (0.30-1.31), whilst the other remaining 11 amino acids only contain loosely bound water molecules. Four exceptional amino acids Ile, Leu, Phe and Val show fewer tightly bound water molecules but a higher number of loosely bound water molecules. As for the hydration shell structure, most amino acids except Pro and Trp enhance tetrahedral water structure and H-bonds relative to pure water and at least 1.9% of the hydration water molecules associated with the amino acids show non-hydrogen-bonded OH defects. This work combines two effective experimental techniques to reveal the hydration water structure and quantitatively analyze two kinds of bound water molecules of 20 amino acids.

Interactions of isoorientin and its Semi-synthetic analogs with human serum albumin.

Isoorientin is a C-glycosyl flavone with a wide range of health beneficial effects and inhibits glycogen synthase kinase 3ß (GSK-3ß) potentially against Alzheimer's disease. Its semi-synthetic derivatives have greater potency than isoorientin. The present study was aimed to determine the mechanism of interactions of isoorientin and its derivatives with human serum albumin (HSA) using multi-spectroscopic, microscale thermophoresis (MST) and computational studies. Spectra of steady-state fluorescence, UV-Vis, and time-resolved fluorescence indicated that isoorientin and its derivatives quenched the intrinsic fluorescence of HSA through a static quenching process. Isoorientin and its derivatives had a moderate affinity with HSA (Ka 7.7-14.9 × 104 M-1). The binding process was accompanied by an exothermic phenomenon, ΔG° of HSA-isoorientin and its derivatives systems were calculated as from -29.51 kJ mol-1 to -27.87 kJ mol-1. Displacement experiments with site-specific markers revealed that isoorientin and its derivatives bind to HSA at site II (subdomain IIIA) only. A reduction in the α-helical content of HSA-isoorientin and its derivatives complex was observed, because the conformational changes was structurally perturbed by the hydrophilic groups of the compounds. Further molecular modeling studies confirmed that the binding of isoorientin and its derivatives to the site II via hydrophobic interaction. The MST results confirmed the interactions between HSA and the compounds of interest. The esterase-like assay studies indicated that isoorientin and its derivatives shared the same binding site in HSA, and their induced structural changes of HSA may have been caused by partial unfolding of HSA. This work helps to understand transport, distribution, bioactivity, and design of flavonoid-based GSK-3ß inhibitors.

Fabrication of b-Oriented MFI Zeolite Membranes by a Printing-Transfer Seed Layer Procedure.

Highly b-oriented MFI zeolite (abbreviated as BOMZ) membranes are attractive due to less grain boundary defects and straight channels normal to the substrate, enhancing selectivity and flux in membrane separation. Herein, we demonstrate a novel, effective and easily-amplified printing-transfer oriented-seed-layer technique to manufacture uniform BOMZ seed monolayer on porous supports. Furthermore, a facile and effective approach for the synthesis of highly BOMZ membranes by introducing poly(hexamethylene biguanide) hydrochloride as a twin crystal inhibitor during seeded growth is demonstrated. Well-intergrown BOMZ membranes (∼650 nm thick) obtained on porous Al2 O3 supports show a flux of 2.8 kg m-2 h-1 with a separation factor as high as 71 for pervaporation in the 60 °C feed of EtOH/H2 O (5 wt%), which is much higher than those of random membranes. The developed seed assembly technique on porous supports underlines great potential for facile preparation of oriented seed layers on porous supports.

The binding process of BmKTX and BmKTX-D33H toward to Kv1.3 channel: a molecular dynamics simulation study.

The potassium channel Kv1.3 is an important pharmacological target and the Kaliotoxin-type toxins (α-KTX-3 family) are its specific blockers. Here, we study the binding process of two kinds of Kaliotoxin-type toxins:BmKTX and its mutant (BmKTX-D33H) toward to Kv1.3 channel using MD simulation and umbrella sampling simulation, respectively. The calculated binding free energies are -27 kcal/mol and -34 kcal/mol for BmKTX and BmKTX-D33H, respectively, which are consistent with experimental results. The further analysis indicate that the characteristic of electrostatic potential of the α-KTX-3 have important effect on their binding modes with Kv1.3 channel; the residue 33 in BmKTX or BmKTX-D33H plays a key role in determine their binding orientations toward to Kv1.3 channel; when residue 33 (or 34) has negative electrostatic potential, the anti-parallel ß-sheet domain of α-KTX-3 toxin peptide will keep away from the filter region of Kv1.3 channel, as BmKTX; when residue 33(or 34) has positive electrostatic potential, the anti-parallel ß-sheet domain of α-KTX-3 toxin peptide will interact with the filter region of Kv1.3 channel, as BmKTX-D33H. Above all, electrostatic potential differences on toxin surfaces and correlations motions within the toxins will determine the toxin-potassium channel interaction model. In addition, the hydrogen bond interaction is the pivotal factor for the Kv1.3-Kaliotoxin association. Understanding the binding mechanism of toxin-potassium channel will facilitate the rational development of new toxin analogue.Communicated by Ramaswamy H. Sarma.

Methane Dry Reforming by Ni-Cu Nanoalloys Anchored on Periclase-Phase MgAlOx Nanosheets for Enhanced Syngas Production.

Stable and efficient syngas production via methane dry reforming is highly desirable as it utilizes two greenhouse gases simultaneously. In this work, active Ni-Cu nanoalloys stably anchored on periclase-phase MgAlOx nanosheets were successfully synthesized by a hydrothermal method. These highly dispersed small Ni-Cu alloys strongly interacted with the periclase-phase MgAlOx nanosheets, on which abundant base sites were accessible. On the optimal catalyst (6Ni6CuMgAl-S), methane and carbon dioxide conversion always reached 85 and 90% at 700 °C under a gas hour speed velocity of 40,000 mL/gcat h for more than 70 h. The hydrogen production rate was maintained at 1.8 mmol/min, and the ratio of H2/CO was kept at approximately 0.96 under a CH4 and CO2 flow rate of 25 mL/min. Coke deposition and Ni sintering were effectively suppressed by the formation of a Ni-Cu alloy, the laminar structure, and the periclase phase of the MgAlOx support. Moreover, the alloy nanoparticles were reconstructed into a segregated Ni-Cu alloy structure in response to the reaction environment, and this structure was more stable and still active. Density functional theory calculations showed that carbon adsorption was inhibited on the segregated Ni-Cu alloy. Furthermore, the experimental thermogravimetric and O2-TPO results confirmed the significant decrease in carbon deposition on the Ni-Cu alloy catalysts.