scholarly journals The effect of host structure on the selectivity and mechanism of supramolecular catalysis of Prins cyclizations

2015 ◽  
Vol 6 (2) ◽  
pp. 1383-1393 ◽  
Author(s):  
William M. Hart-Cooper ◽  
Chen Zhao ◽  
Rebecca M. Triano ◽  
Parastou Yaghoubi ◽  
Haxel Lionel Ozores ◽  
...  
Keyword(s):  
Kinetic Studies ◽  
Product Selectivity ◽  
Supramolecular Catalysis ◽  
New Class ◽  
Substrate Modification ◽  
Host Structure ◽  
Terpenoid Cyclase ◽  
Prins Cyclizations

Catalyst and substrate modification, product selectivity and kinetic studies comprehensively describe a new class of terpenoid cyclase mimics.

Phosphorus ylides as a new class of compounds in CO2 activation: Thermodynamic and kinetic studies

2017 ◽  
Vol 21 ◽  
pp. 459-466 ◽  
Author(s):  
Hossein Sabet-Sarvestani ◽  
Mohammad Izadyar ◽  
Hossein Eshghi
Keyword(s):  
Kinetic Studies ◽  
Co2 Activation ◽  
Phosphorus Ylides ◽  
New Class

scholarly journals Mechanism-Based Design of Quinoline Potassium Acyltrifluoroborates (KATs) for Rapid Amide-Forming Ligations at Physiological pH

2021 ◽  
Author(s):  
Matthias Tanriver ◽  
Yi-Chung Dzeng ◽  
Erwin Lam ◽  
Jeffrey Bode
Keyword(s):  
Rate Constants ◽  
Kinetic Studies ◽  
X Ray Crystallography ◽  
Design And Synthesis ◽  
New Class ◽  
High Basicity ◽  
Acidic Conditions ◽  
Leaving Groups ◽  
Neutral Conditions

<div><div><div><p>Potassium acyltrifluoroborates (KATs) undergo chemoselective amide-forming ligations with hydroxylamines. Under aqueous, acidic conditions these ligations can proceed rapidly, with rate constants of ~20 M-1 s-1. The requirement for lower pH to obtain the fastest rates, however, limits their use with certain biomolecules and precludes in vivo applications. By mechanistic investigations into the KAT ligation, including kinetic studies, X-ray crystallography, and DFT calculations, we have identified a key role for a proton in accelerating the ligation. We applied this knowledge to the design and synthesis of 8-quinolyl acyltrifluoroborates, a new class of KATs that ligates with hydroxylamines at pH 7.4 with rate constants >4 M-1 s-1. We trace the enhanced rate at physiological pH to unexpectedly high basicity of the 8-quinoline-KATs, which leads to their protonation even under neutral conditions. This proton assists the formation of the key tetrahedral intermediate and activates the leaving groups on the hydroxylamine towards a concerted 1,2-BF3shift that leads to the amide product. We demonstrate that the fast ligations at pH 7.4 can be carried out with a protein substrate at micromolar concentrations.</p></div></div></div>

scholarly journals G6PD Nara: a new class 1 glucose-6-phosphate dehydrogenase variant with an eight amino acid deletion

Blood ◽  
1993 ◽  
Vol 82 (11) ◽  
pp. 3250-3252 ◽  
Author(s):  
A Hirono ◽  
H Fujii ◽  
M Shima ◽  
S Miwa
Keyword(s):  
Amino Acid ◽  
Kinetic Studies ◽  
Nucleotide Sequencing ◽  
Amino Acid Deletion ◽  
New Class ◽  
Class 1 ◽  
Measurable Activity ◽  
Exon 9 ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
G6pd Variant

Abstract In the course of molecular studies on Japanese glucose-6-phosphate dehydrogenase (G6PD) variants using single-strand conformation polymorphisms (SSCP) analysis, we found an unusual class 1 G6PD variant that had nucleotide deletion in exon 9. The patient showed chronic nonspherocytic hemolytic anemia associated with frequent episodes of severe hemolytic attack. The hemolysate exhibited no measurable activity. Although the partially purified enzyme had detectable activity, we could not perform kinetic studies because of its extreme instability. Nucleotide sequencing showed a unique 24 bp deletion at nucleotide 953–976 that predicts an eight amino acid deletion of TKGYLDDP at residue 319–326. While this is one of the most drastic structural alterations found in G6PD variants, the region with the amino acid deletion was distant from both the G6P and NADP+ binding sites and was located in a domain with low sequence homology among species. The comparatively low functional importance of the deleted region may have saved the patient from lethal tissue dysfunction.

scholarly journals Piperazine-Substituted Chalcones: A New Class of MAO-B, AChE, and BACE-1 Inhibitors for the Treatment of Neurologic Al Disorders

2021 ◽  
Author(s):  
Bijo Mathew ◽  
Jong Min Min Oh ◽  
Sarah Al-Rashed ◽  
Gaber El-Saber Batiha ◽  
Della Grace Thomas Parambi ◽  
...  
Keyword(s):  
Neurological Disorders ◽  
Kinetic Studies ◽  
Docking Simulations ◽  
Mao B ◽  
Lead Compounds ◽  
New Class ◽  
Competitive Inhibitors ◽  
Inhibitory Activities ◽  
New Treatments ◽  
Bace 1

Abstract Eleven piperazine-containing 1,3-diphenylprop-2-en-1-one derivatives (PC1-PC11) were evaluated for their inhibitory activities against monoamine oxidases (MAOs), cholinesterases (ChEs), and β-site amyloid precursor protein cleaving enzyme 1 (BACE-1) with a view toward developing new treatments for neurological disorders. Compounds PC10 and PC11 remarkably inhibited MAO-B inhibition with IC50 values of 0.65 and 0.71 µM, respectively. Ten of the eleven compounds weakly inhibited AChE and BChE with > 50% of residual activities at 10 µM, although PC4 inhibited AChE by 56.6% (IC50 = 8.77 µM). Compound PC3 effectively inhibited BACE-1 (IC50 = 6.72 µM), and PC10 and PC11 moderately inhibited BACE-1 (IC50 =14.9 and 15.3 µM, respectively). Reversibility and kinetic studies showed that PC10 and PC11 were reversible and competitive inhibitors of MAO-B with Ki values of 0.63 ± 0.13 and 0.53 ± 0.068 µM, respectively. ADME predictions for lead compounds revealed that PC10 and PC11 have central nervous system (CNS) drug-likeness. Molecular docking simulations showed that fluorine atom and trifluoromethyl group on PC10 and PC11, respectively, interacted with the substrate cavity of the MAO-B active site. Our results suggested that PC10 and PC11 be considered potential candidates for the treatment of neurological disorders such as Alzheimer’s disease and Parkinson’s disease.

scholarly journals G6PD Nara: a new class 1 glucose-6-phosphate dehydrogenase variant with an eight amino acid deletion

Blood ◽  
1993 ◽  
Vol 82 (11) ◽  
pp. 3250-3252
Author(s):  
A Hirono ◽  
H Fujii ◽  
M Shima ◽  
S Miwa
Keyword(s):  
Amino Acid ◽  
Kinetic Studies ◽  
Nucleotide Sequencing ◽  
Amino Acid Deletion ◽  
New Class ◽  
Class 1 ◽  
Measurable Activity ◽  
Exon 9 ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
G6pd Variant

In the course of molecular studies on Japanese glucose-6-phosphate dehydrogenase (G6PD) variants using single-strand conformation polymorphisms (SSCP) analysis, we found an unusual class 1 G6PD variant that had nucleotide deletion in exon 9. The patient showed chronic nonspherocytic hemolytic anemia associated with frequent episodes of severe hemolytic attack. The hemolysate exhibited no measurable activity. Although the partially purified enzyme had detectable activity, we could not perform kinetic studies because of its extreme instability. Nucleotide sequencing showed a unique 24 bp deletion at nucleotide 953–976 that predicts an eight amino acid deletion of TKGYLDDP at residue 319–326. While this is one of the most drastic structural alterations found in G6PD variants, the region with the amino acid deletion was distant from both the G6P and NADP+ binding sites and was located in a domain with low sequence homology among species. The comparatively low functional importance of the deleted region may have saved the patient from lethal tissue dysfunction.

scholarly journals Mechanism-Based Design of Quinoline Potassium Acyltrifluoroborates (KATs) for Rapid Amide-Forming Ligations at Physiological pH

2021 ◽  
Author(s):  
Matthias Tanriver ◽  
Yi-Chung Dzeng ◽  
Erwin Lam ◽  
Jeffrey Bode
Keyword(s):  
Rate Constants ◽  
Kinetic Studies ◽  
X Ray Crystallography ◽  
Design And Synthesis ◽  
New Class ◽  
High Basicity ◽  
Acidic Conditions ◽  
Leaving Groups ◽  
Neutral Conditions

<div><div><div><p>Potassium acyltrifluoroborates (KATs) undergo chemoselective amide-forming ligations with hydroxylamines. Under aqueous, acidic conditions these ligations can proceed rapidly, with rate constants of ~20 M-1 s-1. The requirement for lower pH to obtain the fastest rates, however, limits their use with certain biomolecules and precludes in vivo applications. By mechanistic investigations into the KAT ligation, including kinetic studies, X-ray crystallography, and DFT calculations, we have identified a key role for a proton in accelerating the ligation. We applied this knowledge to the design and synthesis of 8-quinolyl acyltrifluoroborates, a new class of KATs that ligates with hydroxylamines at pH 7.4 with rate constants >4 M-1 s-1. We trace the enhanced rate at physiological pH to unexpectedly high basicity of the 8-quinoline-KATs, which leads to their protonation even under neutral conditions. This proton assists the formation of the key tetrahedral intermediate and activates the leaving groups on the hydroxylamine towards a concerted 1,2-BF3shift that leads to the amide product. We demonstrate that the fast ligations at pH 7.4 can be carried out with a protein substrate at micromolar concentrations.</p></div></div></div>

In Situ microscopy of the anodic etching of silicon

1995 ◽  
Vol 53 ◽  
pp. 232-233
Author(s):  
Frances M. Ross ◽  
Peter C. Searson
Keyword(s):  
Composite Structures ◽  
High Surface ◽  
High Surface Area ◽  
Chemical Properties ◽  
Selective Etching ◽  
Silicon On Insulator ◽  
Second Phase ◽  
Porous Layers ◽  
New Class ◽  
Porous Semiconductors

Porous semiconductors represent a relatively new class of materials formed by the selective etching of a single or polycrystalline substrate. Although porous silicon has received considerable attention due to its novel optical properties1, porous layers can be formed in other semiconductors such as GaAs and GaP. These materials are characterised by very high surface area and by electrical, optical and chemical properties that may differ considerably from bulk. The properties depend on the pore morphology, which can be controlled by adjusting the processing conditions and the dopant concentration. A number of novel structures can be fabricated using selective etching. For example, self-supporting membranes can be made by growing pores through a wafer, films with modulated pore structure can be fabricated by varying the applied potential during growth, composite structures can be prepared by depositing a second phase into the pores and silicon-on-insulator structures can be formed by oxidising a buried porous layer. In all these applications the ability to grow nanostructures controllably is critical.

The microtubule associated protein (MAP) tau forms a new class of triple-stranded left-hand helical fibrous protein polymer

1992 ◽  
Vol 50 (1) ◽  
pp. 540-541
Author(s):  
G. C. Ruben ◽  
K. Iqbal ◽  
I. Grundke-Iqbal ◽  
H. Wisniewski ◽  
T. L. Ciardelli ◽  
...  
Keyword(s):  
Axial Ratio ◽  
Normal Structure ◽  
Paired Helical Filaments ◽  
Left Hand ◽  
New Class ◽  
Protein Polymer ◽  
Fibrous Protein ◽  
Protein Map ◽  
Neurotransmitter Transport ◽  
Alzheimer Neurofibrillary Tangles

In neurons, the microtubule associated protein, tau, is found in the axons. Tau stabilizes the microtubules required for neurotransmitter transport to the axonal terminal. Since tau has been found in both Alzheimer neurofibrillary tangles (NFT) and in paired helical filaments (PHF), the study of tau's normal structure had to preceed TEM studies of NFT and PHF. The structure of tau was first studied by ultracentrifugation. This work suggested that it was a rod shaped molecule with an axial ratio of 20:1. More recently, paraciystals of phosphorylated and nonphosphoiylated tau have been reported. Phosphorylated tau was 90-95 nm in length and 3-6 nm in diameter where as nonphosphorylated tau was 69-75 nm in length. A shorter length of 30 nm was reported for undamaged tau indicating that it is an extremely flexible molecule. Tau was also studied in relation to microtubules, and its length was found to be 56.1±14.1 nm.

Study of segregation in La1.8Sr0.2CuO4 superconductor by STEM-EDS microanalysis

1987 ◽  
Vol 45 ◽  
pp. 54-55
Author(s):  
T. F. Kelly ◽  
P. J. Lee ◽  
E. E. Hellstrom ◽  
D. C. Larbalestier
Keyword(s):  
Rare Earth ◽  
High Field ◽  
Transport Current ◽  
Total Thickness ◽  
New Class ◽  
Ceramic Superconductors ◽  
Current Densities ◽  
Group Ii ◽  
Eds Microanalysis

Recently there has been much excitement over a new class of high Tc (>30 K) ceramic superconductors of the form A1-xBxCuO4-x, where A is a rare earth and B is from Group II. Unfortunately these materials have only been able to support small transport current densities 1-10 A/cm2. It is very desirable to increase these values by 2 to 3 orders of magnitude for useful high field applications. The reason for these small transport currents is as yet unknown. Evidence has, however, been presented for superconducting clusters on a 50-100 nm scale and on a 1-3 μm scale. We therefore planned a detailed TEM and STEM microanalysis study in order to see whether any evidence for the clusters could be seen.A La1.8Sr0.2Cu04 pellet was cut into 1 mm thick slices from which 3 mm discs were cut. The discs were subsequently mechanically ground to 100 μm total thickness and dimpled to 20 μm thickness at the center.

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