Heterobimetallic Complexes of Rhenium and Zinc: Potential Catalysts for Homogeneous Syngas Conversion

6-(Diphenylphosphino)-2,2′-bipyridine (PNN) coordinates to rhenium carbonyls in both κ^1(P) and κ^2(N,N) modes; in the former, the free bpy moiety readily binds to zinc alkyls and halides. [Re(κ^1(P)-PNN)(CO)_5][OTf] reacts with dialkylzinc reagents to form [Re(κ^1(P)-PNN·ZnR)(CO)_4(μ_(2-)C(O)R)][OTf] (R = Me, Et, Bn), in which an alkyl group has been transferred to a carbonyl carbon and the resulting monoalkyl Zn is bound both to the bpy nitrogens and the acyl oxygen. ZnCl_2 binds readily to the bpy group in Re(κ^1(P)-PNN)(CO)_4Me, and the resulting adduct undergoes facile migratory insertion, assisted by the Lewis acidic pendent Zn, to yield Re(κ^1(P)-PNN·ZnCl)(μ_(2-)Cl)(CO)_3(μ_(2-)C(O)Me), in which one of the chlorides occupies the sixth coordination site on Re. Migratory insertion is inhibited by THF or other ethers that can coordinate to ZnCl_2. Migratory insertion is also observed for Re(κ1(P)-PNN)(CO)_4(CH_2Ph) but not for Re(κ^1(P)-PNN)(CO)_4(CH_2OCH_3); coordination of the methoxy oxygen to Zn appears to block its ability to coordinate to the carbonyl oxygen and facilitate migratory insertion. Intramolecular Lewis acid promoted hydride transfer from [(dmpe)_2PtH][PF_6] to a carbonyl in [Re(κ^1(P)-PNN)(CO)_5][OTf] results in formation of a Re–formyl species; additional hydride transfer leads to a novel Re–Zn-bonded product along with some formal dehyde

Developmental Networks and Interpersonal Support of Beginning Counselors

As beginning counselors leave the structured support of graduate school and enter the workplace, they often experience a turbulent transition (Ronnestad & Skovholt, 2003). Professional and personal relationships play a significant role in counselors’ developmental experiences during this transitional period (Skovholt & Trotter-Mathison, 2011). However, few existing research studies examine the experiences of beginning counselors, and studies focusing on developmentally-focused relationships of beginning counselors are even more sparse. The purpose of this study was to investigate and describe the experiences of beginning counselors as they engage in and seek interpersonal supports, including their expressed needs and goals, the makeup of their developmental networks, and their perspective of the professional-social environmental factors influencing their development. I utilized a qualitative content analysis to examine the experiences, garnered using semi-structured interviews, of 12 beginning counselors regarding their developmental networks and interpersonal support. I identified five major themes: Context of Personal-Professional Identity; Adjustment/Transition; Growth Orientation; Network organization; and Connective Tissue. Findings generally supported conceptualizations of beginning counselors in Ronnestad and Skovholt’s (2003) counselor development theory and offered mixed support for constructs within Higgins and Kram’s (2001) developmental network model. Implications include recommended methods for counselor educators to promote effective developmental relationships in and outside of the classroom and suggestions for established clinical professionals to foster welcoming workplace environments that ease new counselors’ transition from training to practice. I conclude with suggestions for future research

Encoder-Decoder Networks for Self-Supervised Pretraining and Downstream Signal Bandwidth Regression on Digital Antenna Arrays

This work presents the first applications of self-supervised learning applied to data from digital antenna arrays. Encoder-decoder networks are pretrained on digital array data to perform a self-supervised noisy-reconstruction task called channel in-painting, in which the network infers the contents of array data that has been masked with zeros. The self-supervised step requires no human-labeled data. The encoder architecture and weights from pretraining are then transferred to a new network with a task-specific decoder, and the new network is trained on a small volume of labeled data. We show that pretraining on the unlabeled data allows the new network to perform the task of bandwidth regression on the digital array data better than an equivalent network that is trained on the same labeled data from random initialization

A W-String Realization of the Bosonic String

It has recently been shown that the ordinary bosonic string can be represented by a special background of N=1 or N=2 strings. In this paper, it will be shown that the bosonic string can also be represented by a special background of $W$-strings.Comment: 8 pages plain Tex, KCL-TH-93-1

Transformations of Group 7 Carbonyl Complexes: Possible Intermediates in a Homogeneous Syngas Conversion Scheme

A variety of C−H and C−C bond forming reactions of group 7 carbonyl complexes have been studied as potential steps in a homogeneously catalyzed conversion of syngas to C_(2+) compounds. The metal formyl complexes M(CO)_3(PPh_3)_2(CHO) (M = Mn, Re) are substantially stabilized by coordination of boranes BX_3 (X = F, C_6F_5) in the form of novel boroxycarbene complexes M(CO)_3(PPh_3)_2(CHOBX_3), but these boron-stabilized carbenes do not react with hydride sources to undergo further reduction to metal alkyls. The related manganese methoxycarbene cations [Mn(CO)_(5−x)(PPh_3)_x(CHOMe)]+ (x = 1 or 2), obtained by methylation of the formyls, do react with hydrides to form methoxymethyl complexes, which undergo further migratory insertion under an atmosphere of CO. The resulting acyls, cis- and trans-Mn(PPh_3)(CO)_4(C(O)CH_2OMe), can be alkylated to form the cationic carbene complex [Mn(PPh_3)(CO)_4(C(OR)CH_2OMe)]^+, which undergoes a 1,2 hydride shift to form 1,2-dialkoxyethylene, which is displaced from the metal, releasing triflate or diethyl ether adducts of [Mn(PPh_3)(CO)_4]^+. The acyl can also be protonated with HOTf to form a hydroxycarbene complex, which rearranges to Mn(PPh_3)(CO)_4(CH_2COOMe) and is protonolyzed to yield methyl acetate and [Mn(PPh_3)(CO)_4]^+; addition of L (L = PPh_3, CO) to the manganese cation regenerates [Mn(PPh_3)(CO)_4(L)]^+. Since the original formyl complex can be obtained by the reaction of [Mn(PPh_3)(CO)_5]^+ with [PtH(dmpe)_2]^+, which in turn can be generated from H_2, this set of transformations amounts to a stoichiometric cycle for selectively converting H_2 and CO into a C_2 compound under mild conditions

Phased Dithered Watermarking for Physical Layer Authentication

Wireless protocols can have authentication added at the physical layer without breaking the protocol for unaware clients. This study develops closed form expressions for the probability of bit errors when a technique called phase-dithered watermarking is used to add such an authentication message. The probability of bit errors is found for both message and authentication signals using phase-dithered watermarking on BPSK, QPSK, QAM, and DBPSK. When applicable results are compared to similar studies and confirmed with computer simulations.Electrical Engineerin

Soybean Cyst Nematode Hatching Behavior

The ability of soybean cyst nematodes (SCN. Heterodera glycines) to lay dormant as eggs within a cyst for up to 11 years, has made this parasite a principal target for soybean crop pest management. Research on SCN hatching will improve understanding of SCN biology will uncover new mechanisms for their control. This poster summarizes three experiments using hatching stimulants, soybean root exudate (SRE) zinc chloride, testing whether it affects post hatch development

Development of a Tunable Mammalian Protein Expression System and an Investigation of Promoter Interference in Three Promoters Often Utilized in the Production of Biopharmaceuticals

Cell line engineering strategies for improved biopharmaceutical production in mammalian cells often involve the expression of one/multiple genes to try and improve the cellular processes involved in recombinant protein production. Most strategies are relatively simple, involving the use of a strong constitutive promoter for expression of one or more proteins to help increase production. Results often vary and can be cell line and product specific and mean a generic strategy is unlikely to be found. There is a need for more sophisticated expression systems which can express multiple genes but in a controlled fashion and tuned to meet the needs of a specific product. This thesis can be split into two distinct parts but both concern the expression of multiple genes in mammalian cells and recombinant protein production. A tunable mammalian expression system for multi-gene engineering composed of elements of the mammalian unfolded protein response has been developed. ATF6 (activating transcription factor 6) and its binding element (ERSE – ER stress response element) were used to control the expression of the reporter proteins SEAP (secreted alkaline phosphatase) and GFP (green fluorescent protein). By expressing different amounts of ATF6 and by inserting different numbers of ERSEs upstream of a SV40 (Simian virus 40) promoter, driving SEAP/GFP gene transcription, the level of reporter protein expression could be manipulated in a controlled fashion. The system was capable of controlled/tunable expression of both reporter proteins when expressed alone and when they were co-expressed. This a novel use for ATF6 and ERSE and the first step towards the development of a tunable mammalian expression system for multi-gene engineering. This system could also be easily modified to include or use different transcription factors and binding sites as well as having the potential to use completely synthetic components. This work also showed that the presence of ‘promoter interference’ (the negative influence of one promoter on another) could be used to our advantage to increase the range of expression. The SV40 early, human CMV (cytomegalovirus) major immediate-early and human EF1α (elongation factor 1 alpha) are constitutive promoters frequently used in recombinant protein production. The former being used mainly for expression of selection genes and the latter two for strong expression of recombinant proteins. The differences in the strengths of the promoters was demonstrated in CHO (Chinese hamster ovary) cells (CMV > EF1α > SV40) and also their abilities to negatively affect the expression from a co-expressed promoter. The negative influence of one promoter on another is termed ‘promoter interference’. The CMV promoter was shown to have the greatest negative effect on expression from another promoter, decreasing both SEAP mRNA and protein expression, while the SV40 had the least. SEAP expression from the SV40 was reduced the most by the presence of a competing promoter. The level of interference inflicted by a competing promoter (CMV > EF1α > SV40) seemed to be relative to its strength. This is the first time these three important promoters have been compared in a way which not only demonstrates their relative strengths but also their ability to interfere with another promoter when present in the same transient expression system. This also has implications for their use in multi-gene engineering strategies if there is a need for controlled/tunable expression of multiple genes. The work with ATF6 and ERSE showed how ‘promoter interference’ could be used to our advantage and not necessarily be just a negative occurrence. One hypothesis for why promoter interference occurs is there is competition between promoters for shared transcription factors (TFs). The promoters were analysed for potential transcription factor binding sites (TFBSs) using the programs MatInspector and ModelInspector. The analysis showed that the SV40 promoter had the least number and variety of potential TFBSs. Both the CMV and EF1α had greater numbers and variety of potential TFBSs. All three promoters had common potential TFBSs but the SV40 promoter shared a greater proportion of its sites with the other two promoters. The number of potential TFBSs and the proportion which were shared reflected both the strength and the ability of a promoter to interfere with another. All three contained TFBSs for the SP1 (specificity protein 1) family of TFs and over-expression of SP1 counter-acted the effects of promoter interference showing that it can affect the expression of all three promoters. However, promoter interference will involve more than just a single TF and also more than just competition for transcriptional activators. This is the first time these three promoters have been compared in terms of the potential TFBSs they contain. The TFBS analysis highlighted the complexity in the control of these promoters and with the effects of promoter interference means that they will be ill suited for the controlled expression of multiple genes without modification. The work in this thesis was directed towards the controlled expression of multiple genes in mammalian cells for recombinant protein production. We have presented one novel way of controlling the expression of one/two genes with the rest of the thesis looking at the phenomenon of ‘promoter interference’ between three commonly used promoters. This thesis tries to highlight the importance of multi-gene expression systems as well showing that these three promoters may not be suitable without further modification and also the importance of considering promoter interactions when more than one is present in the same system. The switch to completely synthetic multi-gene control systems is something we envisage happening in the future as the complexities and capabilities of these systems grow