Emissive Synthetic Cofactors: A Highly Responsive NAD+ Analogue Reveals Biomolecular Recognition Features

Apart from its vital function as a redox cofactor, nicotinamide adenine dinucleotide ( NAD⁺ ) has emerged as a crucial substrate for NAD⁺ -consuming enzymes, including poly(ADP-ribosyl)transferase 1 (PARP1) and CD38/CD157. Their association with severe diseases, such as cancer, Alzheimer's disease, and depressions, necessitates the development of new analytical tools based on traceable NAD⁺ surrogates. Here, the synthesis, photophysics and biochemical utilization of an emissive, thieno[3,4-d]pyrimidine-based NAD⁺ surrogate, termed N^thAD⁺ , are described. Its preparation was accomplished by enzymatic conversion of synthetic ^th ATP by nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1). The new NAD⁺ analogue possesses useful photophysical features including redshifted absorption and emission maxima as well as a relatively high quantum yield. Serving as a versatile substrate, N^thAD⁺ was reduced by alcohol dehydrogenase (ADH) to N^thADH and afforded ^thADP-ribose ( ^th ADPr ) upon hydrolysis by NAD⁺ -nucleosidase (NADase). Furthermore, N^thAD⁺ was engaged in cholera toxin A (CTA)-catalyzed mono(^thADP-ribosyl)ation, but was found incapable in promoting PARP1-mediated poly(^thADP-ribosyl)ation. Due to its high photophysical responsiveness, N^thAD⁺ is suited for spectroscopic real-time monitoring. Intriguingly, and as an N7-lacking NAD⁺ surrogate, the thieno-based cofactor showed reduced compatibility (i.e., functional similarity compared to native NAD⁺ ) relative to its isothiazolo-based analogue. The distinct tolerance, displayed by diverse NAD⁺ producing and consuming enzymes, suggests unique biological recognition features and dependency on the purine N7 moiety, which is found to be of importance, if not essential, for PARP1-mediated reactions.     

Unexpected Fluorescence of Polyols and PEGylated Nanoparticles Derived from Carbon Dot Formation

Synthesis of nanoparticles in high‐boiling alcohols (so‐called polyol synthesis) and surface functionalization of nanoparticles with polyethylene glycol (so‐called PEGylation) in combination with certain heating are often accompanied with an intense fluorescence in the blue to green spectral range. Based on the polyol synthesis of Zn₃(PO₄)₂ nanoparticles and a critical consideration of the relevant experimental conditions—including the presence of nanoparticles, the role of dissolved metal salts (ZnCl₂, MgCl₂, KCl), the type of the polyol (DEG, GLY, PEG400), the temperature and time of heating (150–230 °C, 1–6 h)—we can correlate the observed fluorescence to the formation of carbon dots (C‐dots) stemming from thermal decomposition (i.e., dehydration and carbonization) of the polyol. Thus, the thermal decomposition of polyols results in C‐dots with a diameter of 3–5 nm at narrow size distribution. The formation of C‐dots is confirmed by transmission electron microscopy (TEM), high‐resolution TEM (HRTEM), X‐ray powder diffraction (XRD), Fourier‐transform infrared spectroscopy (FT‐IR), and fluorescence spectra.     

Two-color emission of Zn2SiO4:Mn from ionic liquid mediated synthesis

Yellow emitting β-Zn₂SiO₄:Mn²⁺ and green emitting α-Zn₂SiO₄:Mn²⁺ nanoparticles are synthesized by nucleation applying a zinc-containing ionic liquid. As-prepared material is non-agglomerated and very uniform with a mean diameter of 32 nm. According to X-ray diffraction (XRD) two crystallographic different modifications of Zn₂SiO₄ can be realized by annealing of as-prepared and non-crystalline nanomaterial at 750 and 1000 °C. Surprisingly, these crystalline materials are still nanosized, non-agglomerated and redispersible. Scanning electron microscopy (SEM) and dynamic light scattering (DLS) confirm particle diameters of 18 nm (β-Zn₂SiO₄:Mn²⁺) and 14 nm (α-Zn₂SiO₄:Mn²⁺). Photoluminescence indicates Mn²⁺-related emission at an average wavelength of 579 nm and 528 nm, and a quantum yield of 7% and 12% for β-Zn₂SiO₄:Mn²⁺ and α-Zn₂SiO₄:Mn²⁺, respectively.     

Differential non-destructive image current detection in a fourier transform quadrupole ion trap

Dual-detector differential non-destructive Fourier transform detection in a quadrupole ion trap is shown to improve signal intensity and reduce noise compared with spectra recorded using a single detector. A larger area detector in each end-cap electrode is machined to fit its hyperbolic shape and so minimize field imperfections on the z-axis. Argon, acetophenone and bromobenzene spectra were recorded to allow a comparison between single- and dual-detector (differential) modes of detection and to demonstrate the improvement achieved with differential detection. Copyright 1999 John Wiley & Sons, Ltd.     

Infrared photodetachment measurements near thresholds of C−

The relative cross section has been measured in the threshold regions of the following transitions: C^?(⁴S) + hv → C³P_0,1,2) + e^? and C^?(²D) + hv → C(¹D) + e^?. The electron affinity of carbon is determined EA(C) = 1.2629 ± = 0.0003 eV, and the binding energy of the metastable C^?(²D) state with respect to the C(³P₀) ground state is 0.033 ± 0.001 eV.