Chemical Reaction Kinetics of the Pictet-Spengler Reaction

There is an extensive history of the use of alkaloids for medicinal purposes. Today, development of novel pharmaceutical alkaloids is imperative to developing effective drugs. The Pictet-Spengler reaction of dopamine with 4-hydroxyphenyl-acetaldehyde is the first step in the biosynthesis of thousands of known alkaloids. In this reaction, mechanisms have been proposed to explain the specificity of phosphate catalysis. However, the uniqueness of the phosphate ion in the Pictet-Spengler reaction is not explained. The Pictet-Spengler reaction of dopamine with propanal in phosphate buffer and in maleic acid buffer were evaluated and determined to be comparable. The reaction was found to be dependent on the base concentration in both buffers. When determining the rate limiting step, deuterated dopamine reacted at a slower rate than the natural abundance species and a large kinetic isotope effect was observed. This suggested that deprotonation is the rate-limiting step. In addition, an isomer of tetrahydroisoquinoline was observed, which we call isoTHI

ФОРМИРОВАНИЕ НАНОСТРУКТУР СЕРЕБРА МЕТОДОМ ИММЕРСИОННОГО ОСАЖДЕНИЯ НА ПОРИСТЫЙ КРЕМНИЙ И ИССЛЕДОВАНИЕ ИХ ОПТИЧЕСКИХ СВОЙСТВ

Nanostructures formed by immersion deposition of silver on porous silicon at different regimes for their application in surface enhanced Raman spectroscopy (SERS) has been presented. Porous silicon has been fabricated by anodization of monocrystalline silicon in water solution of isopropanol and hydrofluoric acid. Reflectance spectra of the obtained structures of silver/porous silicon have been studied. It has been revealed that the optimal regimes of SERS require using laser with wave length of 400-450 nm.Представлены результаты исследований наноструктур, изготовленных при различных режимах иммерсионного осаждения серебра на пористый кремний (ПК), для их применения в качестве активных субстратов в спектроскопии гигантского комбинационного рассеяния (ГКР). ПК был сформирован методом анодирования монокристаллического кремния в водно-спиртовом растворе фтористоводородной кислоты. Исследованы спектры отражения полученных наноструктур серебра на ПК. Выявлено, что для создания оптимальных условий ГКР-спектроскопии с использованием наноструктур серебра на ПК необходимо использовать возбуждающий лазер с длиной волны 400-450 нм

Experimental study of the sensitivity of a porous silicon ring resonator sensor using continuous in-flow measurements

A highly sensitive photonic sensor based on a porous silicon ring resonator was developed and experimentally characterized. The photonic sensing structure was fabricated by exploiting a porous silicon double layer, where the top layer of a low porosity was used to form photonic elements by e-beam lithography and the bottom layer of a high porosity was used to confine light in the vertical direction. The sensing performance of the ring resonator sensor based on porous silicon was compared for the different resonances within the analyzed wavelength range both for transverse-electric and transverse-magnetic polarizations. We determined that a sensitivity up to 439 nm/RIU for low refractive index changes can be achieved depending on the optical field distribution given by each resonance/polarization

ФОРМИРОВАНИЕ КРЕМНИЕВЫХ НАНОНИТЕЙ МЕТОДОМ МЕТАЛЛ-СТИМУЛИРОВАННОГО ХИМИЧЕСКОГО ТРАВЛЕНИЯ И ИССЛЕДОВАНИЕ ИХ ОПТИЧЕСКИХ СВОЙСТВ

The results of study and development of silicon nanowires (SiNWs) formation by metal-assisted chemical etching (MACE) are introduced. Linear dependence of SiNWs length from etching time is established. Total and mirror reflectance spectra, Raman scattering spectra of SiNWs and photoluminescence (PL) spectra are studied. Si band broadening and shifting to short-wave region in Raman spectra with increasing of etching time are revealed.Представлены результаты исследования особенностей формирования и оптических свойств кремниевых нанонитей (КН), формируемых методом металл-стимулированного химического травления (МСХТ) монокристаллического кремния дырочного и электронного типа проводимости. Установлено, что с увеличением времени химического травления длина КН линейно возрастает. Исследованы спектры полного и зеркального инфракрасного (ИК) отражения, спектры комбинационного рассеяния (КР) света сформированных КН, а также спектры фотолюминесценции (ФЛ). Выявлено, что полоса кремния в спектре КР с увеличением времени химического травления расширяется и сдвигается в коротковолновую область

СТРУКТУРНЫЕ СВОЙСТВА ЧАСТИЦ ПОРИСТОГО КРЕМНИЯ, ФОРМИРУЕМЫХ МЕТОДОМ МАГНИЙТЕРМИЧЕСКОГО ВОССТАНОВЛЕНИЯ ДИОКСИДА КРЕМНИЯ, ИЗГОТОВЛЕННОГО ИЗ КРЕМНИЙСОДЕРЖАЩИХ РАСТЕНИЙ

The study results of formation regularities, morphology and composition of porous silicon particles fabricated by the magnesiothermal reduction of different samples of biogenic silicon dioxide at 650 °С under an argon atmosphere are presented.Приведены результаты исследования закономерностей формирования и изучения морфологии и состава частиц пористого кремния полученных методом магнийтермического восстановления диоксида кремния, изготовленного из образцов различных видов кремнийсодержащего растительного сырья, при температуре 650 °С в атмосфере аргона

Surface Enhanced Raman Spectroscopy of Lactoferrin Adsorbed on Silvered Porous Silicon Covered with Graphene

We registered surface enhanced Raman scattering (SERS) spectra of the human lactoferrin molecules adsorbed on a silvered porous silicon (por-Si) from 106–1018 M solutions. It was found that the por-Si template causes a negative surface potential of silver particles and their chemical resistivity to oxidation. These properties provided to attract positively charged lactoferrin molecules and prevent their interaction with metallic particles upon 473 nm laser excitation. The SERS spectra of lactoferrin adsorbed from 106 M solution were rather weak but a decrease of the concentration to 10-10 M led to an enormous growth of the SERS signal. This effect took place as oligomers of lactoferrin were broken down to monomeric units while its concentration was reduced. Oligomers are too large for a uniform overlap with electromagnetic field from silver particles. They cannot provide an intensive SERS signal from the top part of the molecules in contrast to monomers that can be completely covered by the electromagnetic field. The SERS spectra of lactoferrin at the 10-14 and 10-16 M concentrations were less intensive and started to change due to increasing contribution from the laser burned molecules. To prevent overheating the analyte molecules on the silvered por-Si were protected with graphene, which allowed the detection of lactoferrin adsorbed from the 10-18 M solution

Formation of silver NANOSTRUCTURES by immersion deposition method onto POROUS SILICON and study of their optical properties

Nanostructures formed by immersion deposition of silver on porous silicon at different regimes for their application in surface enhanced Raman spectroscopy (SERS) has been presented. Porous silicon has been fabricated by anodization of monocrystalline silicon in water solution of isopropanol and hydrofluoric acid. Reflectance spectra of the obtained structures of silver/porous silicon have been studied. It has been revealed that the optimal regimes of SERS require using laser with wave length of 400-450 nm

FORMATION OF SILICON NANOWIRES BY METAL-ASSISTED CHEMICAL ETCHING AND STUDY OF ITS OPTICAL PROPERTIES

The results of study and development of silicon nanowires (SiNWs) formation by metal-assisted chemical etching (MACE) are introduced. Linear dependence of SiNWs length from etching time is established. Total and mirror reflectance spectra, Raman scattering spectra of SiNWs and photoluminescence (PL) spectra are studied. Si band broadening and shifting to short-wave region in Raman spectra with increasing of etching time are revealed