A model for the etching of silicon in SF6/O2 plasmas

A model has been developed to describe the chemistry which occurs in SF₆/O₂ plasmas and the etching of silicon in these plasmas. Emphasis is placed nn the gas-phase free radical reactions, and the predictions n( the model are compared with experimental results. Forty-seven reactions are included, although a subset of 18 reactions describes the chemistry equally well. Agreement between the calculated and measured concentrations of stable products downstream of the plasma is better than a factor of 2. The need for additional kinetic data and fàr well-characterized diagnostic studies of SF₆/O₂ plasmas is discussed.     

Vacuum ultraviolet spark emission spectra of fluorine and some polyatomic fluorides in noble gases

Spark emission spectra in the vacuum ultraviolet are reported for several polyatomic fluorides in He + Ar mixtures, and for pure fluorine. These results are discussed in terms of the potential of a given fluorine compound for ArF formation. The 158 nm emission in fluorine is tentatively assigned to the ³Π_g → ³Π_u.     

Heteropoly acids in the determination of phosphorus by neutron activation analysis

Phosphorus is selectively extracted as molybdovanadophosphoric acid (MVPA) and determined indirectly using⁵²V. Silicon, germanium, arsenic, fluoride and tannic acid do not interfere. The sensitivity for phosphorus was 1421±13 counts⁵²V per ng P ml^–1 with a detection limit of 0.2 ng P ml^–1. The precision is ±10% over the range 0.7±70 ng P ml^–1. The sensitivity is four orders of magnitude greater than for conventional neutron activation analysis (NAA) using the³¹P(n, )²⁸ Al reaction and a SLOWPOKE II reactor. Greater selectivity for phosphorus is obtained than by direct measurement of³²P by beta ray spectroscopy.     

Synthesis of 1,5-disubstituted tetrazoles via Suzuki-Miyaura cross-coupling of 5-chloro-1-phenyltetrazole

Suzuki-Miyaura coupling reactions of 5-chloro-1-phenyl-tetrazole with various functionalized arylboronic acids were investigated. In the presence of catalytic amounts of SPhos/Pd(OAc)₂ or RuPhos/Pd(OAc)₂, the reaction proceeded smoothly to afford 1,5-diaryltetrazoles in good to excellent yields.     

Strategies in boosting photosensitization for biomedical applications

Science China Chemistry -     

A Universal DNA Aptamer that Recognizes Spike Proteins of Diverse SARS-CoV-2 Variants of Concern

We report on a unique DNA aptamer, denoted MSA52, that displays universally high affinity for the spike proteins of wildtype SARS-CoV-2 as well as the Alpha, Beta, Gamma, Epsilon, Kappa, Delta and Omicron variants. Using an aptamer pool produced from round 13 of selection against the S1 domain of the wildtype spike protein, we carried out one-round SELEX experiments using five different trimeric spike proteins from variants, followed by high-throughput sequencing and sequence alignment analysis of aptamers that formed complexes with all proteins. A previously unidentified aptamer, MSA52, showed K_d values ranging from 2 to 10 nM for all variant spike proteins, and also bound similarly to variants not present in the reselection experiments. This aptamer also recognized pseudotyped lentiviruses (PL) expressing eight different spike proteins of SARS-CoV-2 with K_d values between 20 and 50 pM, and was integrated into a simple colorimetric assay for detection of multiple PL variants. This discovery provides evidence that aptamers can be generated with high affinity to multiple variants of a single protein, including emerging variants, making it well-suited for molecular recognition of rapidly evolving targets such as those found in SARS-CoV-2.     

Configurational Lability at Tetrahedral Phosphorus: syn/anti-Isomerization of a P-Stereogenic Phosphiranium Cation by Intramolecular Epimerization at Phosphorus

Tetrahedral main-group compounds are normally configurationally stable, but P-epimerization of the chiral phosphiranium cations syn- or anti-[Mes*P(Me)CH₂CHPh][OTf] (Mes*=2,4,6-(t-Bu)₃C₆H₂) occurred under mild conditions at 60 °C in CD₂Cl₂, resulting in isomerization to give a syn-enriched equilibrium mixture. Ion exchange with excess [NBu₄][Δ-TRISPHAT] (Δ-TRISPHAT=Δ-P(o-C₆Cl₄O₂)₃) followed by chromatography on silica removed [NBu₄][OTf] and gave mixtures of syn- and anti-[Mes*P(Me)CH₂CHPh][Δ-TRISPHAT]?x[NBu₄][Δ-TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C. DFT calculations are consistent with a mechanism involving P-C cleavage to yield a hyperconjugation-stabilized carbocation, pyramidal inversion promoted by σ-interaction of the P lone pair with the neighboring β-carbocation, and ring closure with inversion of configuration at P.     

Siloxyaluminate and Siloxygallate Complexes as Models for Framework and Partially Hydrolyzed Framework Sites in Zeolites and Zeotypes

Anionic molecular models for nonhydrolyzed and partially hydrolyzed aluminum and gallium framework sites on silica, M[OSi(OtBu)₃]₄⁻ and HOM[OSi(OtBu)₃]₃⁻ (where M=Al or Ga), were synthesized from anionic chlorides Li{M[OSi(OtBu)₃]₃Cl} in salt metathesis reactions. Sequestration of lithium cations with [12]crown-4 afforded charge-separated ion pairs composed of monomeric anions M[OSi(OtBu)₃]₄⁻ with outer-sphere [([12]crown-4)₂Li]⁺ cations, and hydroxides {HOM[OSi(OtBu)₃]₃} with pendant [([12]crown-4)Li]⁺ cations. These molecular models were characterized by single-crystal X-ray diffraction, vibrational spectroscopy, mass spectrometry and NMR spectroscopy. Upon treatment of monomeric [([12]crown-4)Li]{HOM[OSi(OtBu)₃]₃} complexes with benzyl alcohol, benzyloxide complexes were formed, modeling a possible pathway for the formation of active sites for Meerwin–Ponndorf–Verley (MPV) transfer hydrogenations with Al/Ga-doped silica catalysts.     

Ultrasensitive single-cell proteomics workflow identifies >1000 protein groups per mammalian cell

We report on the combination of nanodroplet sample preparation, ultra-low-flow nanoLC, high-field asymmetric ion mobility spectrometry (FAIMS), and the latest-generation Orbitrap Eclipse Tribrid mass spectrometer for greatly improved single-cell proteome profiling. FAIMS effectively filtered out singly charged ions for more effective MS analysis of multiply charged peptides, resulting in an average of 1056 protein groups identified from single HeLa cells without MS1-level feature matching. This is 2.3 times more identifications than without FAIMS and a far greater level of proteome coverage for single mammalian cells than has been previously reported for a label-free study. Differential analysis of single microdissected motor neurons and interneurons from human spinal tissue indicated a similar level of proteome coverage, and the two subpopulations of cells were readily differentiated based on single-cell label-free quantification.

The combination of nanodroplet sample preparation, ultra-low-flow nanoLC, high-field asymmetric ion mobility spectrometry (FAIMS) and latest-generation mass spectrometry instrumentation provides dramatically improved single-cell proteome profiling.