Silver Cluster Interactions with Tyrosine: Towards Amino Acid Detection

Tyrosine (Tyr) is involved in the synthesis of neurotransmitters, catecholamines, thyroid hormones, etc. Multiple pathologies are associated with impaired Tyr metabolism. Silver nanoclusters (Ag NCs) can be applied for colorimetric, fluorescent, and surface-enhanced Raman spectroscopy (SERS) detection of Tyr. However, one should understand the theoretical basics of interactions between Tyr and Ag NCs. Thereby, we calculated the binding energy (Eb) between Tyr and Agnq (n = 1–8; q = 0–2) NCs using the density functional theory (DFT) to find the most stable complexes. Since Ag NCs are synthesized on Tyr in an aqueous solution at pH 12.5, we studied Tyr−1, semiquinone (SemiQ−1), and Tyr−2. Ag32+ and Ag5+ had the highest Eb. The absorption spectrum of Tyr−2 significantly red-shifts with the attachment of Ag32+, which is prospective for colorimetric Tyr detection. Ag32+ interacts with all functional groups of SemiQ−1 (phenolate, amino group, and carboxylate), which makes detection of Tyr possible due to band emergence at 1324 cm−1 in the vibrational spectrum. The ground state charge transfer between Ag and carboxylate determines the band emergence at 1661 cm−1 in the Raman spectrum of the SemiQ−1–Ag32+ complex. Thus, the prospects of Tyr detection using silver nanoclusters were demonstrated.

Оценка влияния икосаэдрических "магических" чисел на термическую стабильность малых нанокластеров серебра

A comparative analysis of thermally induced structural transitions in silver nanoclusters, the number of atoms of which corresponded to the “magic” numbers of the icosahedral (Ih) structure with variation of their initial morphology, was carried out by the molecular dynamics method using the modified tight-binding potential TB-SMA. It is shown that, in the case of the initial fcc phase, the formation of the Ih modification, depending on the particle size, occurred either at the stage of preliminary thermal relaxation or during further heating. At the initial amorphous morphology, the nature of the structural transitions underwent significant changes. Thus, even in the case of Ag55 clusters, the icosahedral structure was formed only in 50-60% of the experiments performed. Based on the data obtained, it was concluded that to create a stable Ih structure, it is necessary to use the thermal cycling procedure.

Tunable luminescence of silver-exchanged SOD zeolite thermally treated under mild conditions

Silver nanoclusters confined zeolite scaffolds have been considered as a promising luminescent material. Herein, luminescent silver nanoclusters were synthesized by incorporating Ag+ and Cs+ ions into the as-synthesized SOD zeolites...

Surface Environment Complication Makes Ag29 Nanoclusters More Robust and Their Unique Packing in the Supracrystal Lattice

Silver nanoclusters have received unprecedented attention in the cluster science owing to their promising functionalities and intriguing physical/chemical properties. However, the essential instability significantly impedes their extensive applications. We herein...

STRUCTURAL STABILITY OF Ag AND Ag NANOCLUSTERS WITH A CHANGE IN THE INITIAL MORPHOLOGY

В статье методом молекулярной динамики с использованием модифицированного потенциала сильной связи TB-SMA (second moment approximation of tight-binding) проводится сравнительный анализ характера термически индуцированных структурных переходов в нанокластерах серебра, число атомов в которых соответствует «магическим» числам икосаэдрической структуры, при вариации их начальной морфологии. Показано, что в случае начальной ГЦК конфигурации формирование Ih модификации происходит либо на этапе предварительной термической релаксации, либо в ходе дальнейшего нагрева. При начальной аморфной морфологии характер структурных переходов претерпевает значительные изменения. Так, например, формирующаяся Ih модификация обладает большей стабильностью в области высоких температур и точка плавления нанокластеров смещается на величину более 100 К. Такой эффект обусловлен более плавным изменением удельной потенциальной энергии нанокластера в сравнении со случаем, когда устойчивая Ih конфигурация формируется при низких температурах. Полученные данные могут быть использованы при процессах создания нанокластеров серебра с требуемым внутренним строением. This article provides a comparative analysis of thermally induced structural transitions in silver nanoclusters with a change in their initial morphology. The study was executed by the molecular dynamics method using the modified TB-SMA (second moment approximation of tight-binding) tight binding potential. The number of atoms in nanoclusters corresponds to the icosahedral structure «magic» numbers. It is shown that for nanoclusters with the initial FCC configuration, the Ih modification is formed either at the stage of preliminary thermal relaxation or during further heating. For nanoclusters with an initial amorphous morphology, the nature of structural transitions undergoes significant changes. For example, the formed Ih modification is more stable at high temperatures and the melting point of nanoclusters shifts by more than 100 K. This effect is due to a smoother change in the specific potential energy of the nanocluster in comparison with the case when a stable Ih configuration is formed at low temperatures. The data obtained can be used in processes to create silver nanoclusters with the required internal structure.

Fluorescent AgNCs Formed on Bifunctional DNA Template for Potassium Ion Detection

In this study, we examined properties of silver nanoclusters, which are AgNCs stabilized by DNA oligonucleotide scaffold containing G-quadruplex-forming sequences: human telomeric (Tel22) or thrombin-binding aptamer (TBA). Thus, we obtained two fluorescent probes abbreviated as Tel22C12-AgNCs and TBAC12-AgNCs, which were characterized using absorption, circular dichroism and fluorescence spectroscopy. Both probes emit green and red fluorescence. The presence of silver nanoclusters did not destabilize the formed G-quadruplexes. The structural changes of probes upon binding K+ or Na+ ions cause quenching in their red emission. Green emission was slightly quenched only in the case of Tel22C12-AgNCs; on the contrary, for TBAC12-AgNC’s green emission, we observed an increasing fluorescence signal. Moreover, the Tel22C12-AgNCs system shows not only a higher binding preference for K+ over Na+, but it was able to monitor small changes in K+ concentrations in the buffer mimicking extracellular conditions (high content of Na+ ions). These results suggest that Tel22C12-AgNCs exhibit the potential to monitor transmembrane potassium transport.