Israel Journal of Chemistry

Các hằng số tốc độ dập tắt huỳnh quang, k_q, nằm trong khoảng từ 10⁶ đến 2 × 10¹⁰ M⁻¹ giây⁻¹, của hơn 60 hệ thống cho-nhận electron điển hình đã được đo trong acetonitrile tách oxy và cho thấy có mối quan hệ với sự thay đổi thế năng tự do, ΔG₂₃, liên quan đến quá trình chuyển electron thực tế

Hình ảnh phóng to

trong phức hợp gặp gỡ và thay đổi trong khoảng từ +5 đến −60 kcal/mol. Mối quan hệ này dựa trên cơ chế chuyển electron ngoại-đường dãn cơ adiabatic yêu cầu ΔG^≠₂₃, thế năng tự do kích hoạt của quá trình này, là một hàm đơn điệu của ΔG₂₃ và cho phép tính toán các hằng số tốc độ dập tắt chuyển electron từ dữ liệu quang phổ và điện hóa.

Một nghiên cứu chi tiết về một số hệ thống mà các hằng số dập tắt tính toán khác biệt với các hằng số thí nghiệm đến vài bậc quy mô đã tiết lộ rằng cơ chế dập tắt hoạt động trong những trường hợp này là chuyển nguyên tử hydro thay vì chuyển electron.

Các điều kiện mà các cơ chế khác nhau này áp dụng và hậu quả của chúng được thảo luận.

Over the past few decades, crystalline silicon solar cells have been extensively studied due to their high efficiency, high reliability, and low cost. In addition, these types of cells lead the industry and account for more than half of the market. For the foreseeable future, Si will still be a critical material for photovoltaic devices in the solar cell industry. In this paper, we discuss key issues, cell concepts, and the status of recent high‐efficiency crystalline silicon solar cells.

New species, detected by ⁷⁷Se NMR, are formed on mixing α‐selenoalkyllithium compounds and CuI/SMe₂. These species decompose at −40° to olefins 8 but can be allylated in high yield at −100°. Similar reactions are observed with thio‐analogues.

Nucleotide‐based therapeutics have the potential to treat many inherited and acquired diseases. However, for this form of therapy to become clinically successful, safe and efficient delivery vehicles need to be developed. In this article, we review the synthesis, properties, and use of poly(ß‐amino ester)s as vectors for gene delivery. High‐throughput synthesis and screening studies have identified poly(ß‐amino ester)s that can complex DNA and mediate transfection with efficiencies that are superior to the best commercially available polymer‐ and lipid‐based transfection reagents. Structure‐function studies show that high‐molecular‐weight (>10 kDa) amine‐terminated polymers with primary alcohol side chains are the most efficient vectors to date. In vivo, the most effective polymer, C32, delivers plasmid DNA at high levels following intra‐tumor injection, with excellent biocompatibility. Interestingly, C32 inhibits transfection to surrounding muscle tissue, making it a good candidate for local gene therapy. In addition to simple polymer/DNA complexes insoluble microparticles can be formed using poly(ß‐amino ester)s to physically encapsulate DNA and with sizes appropriate for phagocytosis by antigen‐presenting cells. Uptake of these particles by macrophages results in protein expression levels up to 5 orders of magnitude higher than traditional poly(lactic‐co‐glycolic acid) microparticles containing DNA and can be potent stimulators of antigen presenting cells. Furthermore, in vivo delivery of poly(ß‐amino ester) microparticle genetic vaccines leads to an antigen‐specific, immune‐mediated rejection of a lethal tumor dosage. Taken together, these results show that poly(ß‐amino ester)s have broad potential as delivery systems for drug and gene therapies.

The energy transfer from an oxacyanine to a thiacyanine dye was investigated in monolayer assemblies. No temperature‐dependence of the efficiency was observed between 300 K and 20 K in arrangements where the donor molecules were isolated. However, in arrangements where the donor was organized into a large aggregate and the acceptor was highly diluted in the adjacent monolayer, the efficiency of the energy transfer was proportional to the absolute temperature; the spectral distributions of the fluorescence of the donor and the absorption of the acceptor were equally well matched at low and high temperatures. A simple model is discussed based on the idea that the energetic match needed for energy and electron transfer occurs occasionally due to thermal fluctuations and that this match will not be achieved below a certain temperature. A mechanism based on exciton hopping in the aggregate followed by energy transfer from a molecule in the vicinity of the acceptor to the acceptor does not explain the observed temperature‐dependence. However, the present experimental data can be rationalized by assuming that the excitation extends over a certain domain (consisting of about 10 donor dye molecules at room temperature and about 150 molecules at 20 K) which moves over the aggregate, occasionally reaching the vicinity of an acceptor molecule.

Equilibrium constants for the reaction of aryl thiol anions with hydroxyethyl disulfide have been measured which, along with literature data, demonstrate a slope of 1.21 for a plot of log K^S− (R'S‐ + RSSR ⇌ R'SSR + ‐SR) vs pKa. Rate constants were measured also for these endothermic reactions of aryl thiol anions with hydroxyethyl disulfide and also for the exothermic reactions of alkyl thiol anions with the mixed disulfide of mercaptoethanol and 4‐nitro‐2,3,5,6‐tetrafluorothiophenol. These kinetic data, obtained over a range of K^S− of 10²¹, show the gradual curvature expected for Hammond postulate type behavior. A quantitative measure of this curvature in terms of the Marcus formalism was carried out for these two data sets along with four others having more moderate values of ΔG. The data were fit with a value for the intrinsic barrier, λ/4 = 11.6 kcal, and a value for the work term W_r = 4.0 kcal. A comparison is made of these values with the similar values found for alkyl, proton and acyl transfer reactions. The importance of using a variety of substrates with a series of bases or nucleophiles, rather than a single substrate, is discussed, as are the cause for curvature other than Hammond postulate behavior.

With rising levels of CO₂ in our atmosphere, technologies capable of converting CO₂ into useful products have become more valuable. The field of electrochemical CO₂ reduction is reviewed here, with sections on mechanism, formate (formic acid) production, carbon monoxide production, reduction to higher products (methanol, methane, etc.), use of flow cells, high pressure approaches, molecular catalysts, non‐aqueous electrolytes, and solid oxide electrolysis cells. These diverse approaches to electrochemical CO₂ reduction are compared and contrasted, emphasizing potential processes that would be feasible for large‐scale use. Although the focus is on recent reports, highlights of older reports are also included due to their important contributions to the field, particularly for high‐rate electrolysis.

We review in part our computational, design, synthesis, and biological studies on a remarkable class of compounds and their designed analogs that have led to preclinical candidates for the treatment of cancer, a first‐in‐class approach to Alzheimer’s disease, and a promising strategy to eradicate HIV/AIDS. Because these leads target, in part, protein kinase C (PKC) isozymes, they have therapeutic potential even beyond this striking set of therapeutic indications. This program has given rise to new synthetic methodology and represents an increasingly important direction of synthesis focused on achieving function through synthesis‐informed design (function‐oriented synthesis).

We report the measurement of the room‐temperature optical properties of antenna chlorophyll proteins (prepared with sodium dodecyl sulfate membrane solubilization) from six plant species of five different orders: pea (Pisum sativum), soy (Glycine max), barley (Hordeum vulgare), spinach (Spinacea oleracea), yew (Taxus canadensis), and fern (Onoclea sensibilis). All six species' antenna protein preparations exhibit optical spectra which are similar in great detail, implying similar internal chromophore arrangements from species to species. Features of the spectra thought due to chromophore interactions disappear upon heat denaturation. A model proposed by Van Metter for spinach chlorophyll protein has been revised and is consistent with all the data presented here.

Fluoroxy reagents are versatile and useful electrophilic fluorinating reagents. Having wide applicability in a variety of solvents they display great potential for the synthesis of specifically fluorinated analogs of bioactive molecules.