On the quantum electrodynamics of moving bodies

A new synthesis of the principles of relativity and quantum mechanics is developed by replacing the Poincaré group for the de Sitter one. The new relativistic quantum mechanics is an indefinite-mass theory which is reduced to the standard theory on the mass shell. The charge conjugation acquires a geometrical meaning and the Stueckelberg interpretation for antiparticles naturally arises in the formalism. So the idea of the Dirac sea in the second-quantized formalism proves to be superfluous. The off-shell theory is free from ultraviolet divergences, which only appear in the process of mass-shell reduction.     

Photoinduced DNA Cleavage Reactions by Designed Analogues of Co(III)-Bleomycin: The Metalated Core Is the Primary Determinant of Sequence Specificity

A 2,4'-bithiazole group has been covalently attached to the Co(III) complex of a designed ligand PMAH that mimics the metal-binding locus of the antitumor drug bleomycin (BLM). The deprotonated PMA(-) ligand binds Co(III) via five nitrogens located in primary and secondary amines, a pyrimidine and an imidazole ring, and a peptide moiety. The 2,4'-bithiazole group is tethered to the [Co(PMA)](2+) unit via an imidazole that is connected to the bithiazole moiety with a (CH(2))(3) spacer. The structure of this hybrid analogue, namely, [Co(PMA)(Bit)]Cl(2) (7, Bit = 2'-methyl-2,4'-bithiazole-4-carboxamido-N'-(3-propyl)imidazole) has been established by spectroscopic techniques. 7 promotes photocleavage of DNA at micromolar concentrations. Unlike simpler analogues like [Co(PMA)(H(2)O)](2+) and [Co(PMA)Cl)](+) which induce random DNA cleavage upon UV illumination, 7 exhibits sequence specificity in the DNA photocleavage reaction. Intriguing is to note that 7 exhibits the same 5'GG-N3' sequence preference as another hybrid analogue [Co(PMA)(Int-A)]Cl(2) (6, Int-A = acridine-9-carboxamido-N'-(3-propyl)imidazole) that contains an acridine moiety as the DNA-binding group. The observed sequence specificity of 6 and 7 therefore does not reflect the sequence preferences of the DNA-binding groups (acridine and bithiazole). The results indicate that the metalated core of the hybrid analogues, i.e., the [Co(PMA)](2+) unit is the key factor in determining their sequence specificity.     

Alkene epoxidation catalyzed by cytochrome P450 BM-3 139-3

We recently reported conversion of cytochrome P450 BM-3, a medium-chain (C₁₂-C₁₈) fatty acid monooxygenase, into a highly efficient alkane hydroxylase by directed evolution [Nat. Biotechnol. 2002, 20, 1135]. P450 BM-3 mutant 139-3 exhibited high activity towards a variety of fatty acid and alkane substrates, including C₃-C₈ alkanes. We report here that mutant 139-3 is also active on benzene, styrene, cyclohexene, 1-hexene, and propylene. Benzene is converted to phenol, while styrene is converted to styrene oxide. Propylene oxidation generates only propylene oxide, but cyclohexene oxidation produces a mixture of cyclohexene oxide (85%) and 2-cyclohexene-1-ol (15%), and 1-hexene is converted to the allylic hydroxylation product, 1-hexene-3-ol. Initial rates of NADPH oxidation for 139-3 in the presence of the substrates greatly (17- to >100-fold) surpass the wild-type in all cases. However, NADPH consumption is only partially coupled to product formation (14-79%). This cytochrome P450 epoxidation catalyst is a suitable starting point for further evolution to improve coupling and activity.     

Thermal evolution of ceramic powders surrounding the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7–x</Subscript> composition

Organometallic-derived ceramic compositions surrounding YBa₂Cu₃O_7–x (123) were evaluated via DTA-TG runs and dilatometric densification. The compositions were either Y, Ba or Cu deficient respect to 123. For the Yttrium deficient compact the presence of liquids containing 0–1.3 mole %YO_1.5—capable of dissolving the 123 grains—can promote a rapid sintering behavior. For Copper deficient compact the main densification/contraction mechanisms were delayed till 985 °C. For both Barium and Copper deficient compacts a strong exudation of liquids was detected at 990 °C and 1020 °C, respectively.     

Fluorescence activated cell sorting for enzymatic activity

Directed evolution is a reliable method for protein engineering and as a tool for investigating structure/function relationships. A key for a successful directed evolution experiment is oftentimes the screen. Fluorescence activated cell sorting (FACS) is powerful high-throughput screening approach to isolate and identify mutants from large protein libraries. FACS has been successful in isolating proteins with improved or altered binding affinity. However, FACS screening for mutants with enhanced catalytic activity has been met with limited success. This review focuses on the FACS screening of protein libraries for enzymatic activity.     

Mid-infrared spectroscopy for detection of Huanglongbing (greening) in citrus leaves

In recent years, Huanglongbing (HLB) also known as citrus greening has greatly affected citrus orchards in Florida. This disease has caused significant economic and production losses costing about $750/acre for HLB management. Early and accurate detection of HLB is a critical management step to control the spread of this disease. This work focuses on the application of mid-infrared spectroscopy for the detection of HLB in citrus leaves. Leaf samples of healthy, nutrient-deficient, and HLB-infected trees were processed in two ways (process-1 and process-2) and analyzed using a rugged, portable mid-infrared spectrometer. Spectral absorbance data from the range of 5.15-10.72 μm (1942-933 cm⁻¹) were preprocessed (baseline correction, negative offset correction, and removal of water absorbance band) and used for data analysis. The first and second derivatives were calculated using the Savitzky-Golay method. The preprocessed raw dataset, first derivatives dataset, and second derivatives dataset were first analyzed by principal component analysis. Then, the selected principal component scores were classified using two classification algorithms, quadratic discriminant analysis (QDA) and k-nearest neighbor (kNN). When the spectral data from leaf samples processed using process-1 were used for data analysis, the kNN-based algorithm yielded higher classification accuracies (especially nutrient-deficient leaf class) than that of the other spectral data (process-2). The performance of the kNN-based algorithm (higher than 95%) was better than the QDA-based algorithm. Moreover, among different types of datasets, preprocessed raw dataset resulted in higher classification accuracies than first and second derivatives datasets. The spectral peak in the region of 9.0-10.5 μm (952-1112 cm⁻¹) was found to be distinctly different between the healthy and HLB-infected leaf samples. This carbohydrate peak could be attributed to the starch accumulation in the HLB-infected citrus leaves. Thus, this study demonstrates the applicability of mid-infrared spectroscopy for HLB detection in citrus.     

Solar Energy Conversion Using a Semiconductor Electrode Photosensitized by Tetraphenylporphyrin

The synthesis of meso-tetraphenylporphyrin (TPP) and its application in a solar- energy conversion device are described as an undergraduate laboratory experiment. In the first part of the exercise, a convenient procedure for the synthesis of TPP is presented. In the second section of the experiment, the construction of a high-efficiency photoelectrode that utilizes the light harvesting capacity of the porphyrin is presented. The spectral sensitization of a wide-band-gap semiconductor is achieved using TPP as an efficient photoreceptor, This mimics the role of the tetrapyrrolic macrocycle in natural photosynthesis.