**Recent Progress in Semiconductor Photocatalysis for Organic Fine Chemical Synthesis**

Suzan A. Khayyat, Rosilda Selvin and L. Selva Roselin

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/62220

#### **Abstract**

T1D rat. In addition, we developed the effective means to disperse light in water and at very

, Nurit Shalev2

and Dr. Avi Rotem2

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146 Applied Photosynthesis - New Progress

**Author details**

, Tali Goldman2

1 Greenonyx Technologies, Israel

2 Beta-O2 Technologies Ltd., Israel

Yoav Evron1

**References**

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Dimitry Azarov2

Photocatalytic process is a well-known reaction in photosynthesis by plants and algae. Artificial photosynthesis is a chemical process that mimics the natural plant photosyn‐ thesis to make important chemicals by using man-made materials. One of the most promising methods of artificial photosynthesis is synthesis of organic chemicals, including biodegradable plastics, pharmaceutical drugs, liquid fuels and intermediates for valuable chemicals, etc. In 1972, Fujishima and Honda discovered photocatalytic process using TiO2 semiconductor oxide electrodes to generate hydrogen from water. Researchers have achieved a single-step system that uses semiconductor particles for organic fine chemical synthesis under UV or visible radiation. This chapter summarizes the recent research trends on artificial photosynthesis by photocatalytic process for organic fine chemical synthesis on selected photocatalytic organic transformations, especially photocatalytic transformations by oxidation, carbon-carbon and carbon-heteroatom coupling, cyclization, etc.

**Keywords:** artificial photosynthesis, photocatalysis, organic synthesis, oxidation, cyc‐ lization, UV light, visible light, C-C bond formation

#### **1. Introduction**

The Earth receives energy of about 3 ×1024 joules in a year from sun, which is higher than the global energy consumption. Plants utilize the solar energy to fix atmospheric carbon dioxide and produce carbohydrates and oxygen by photosynthesis. Warburg and Negelein disclosed the photosynthesis, in which reaction occurs between CO2 and H2O in the presence of chloro‐ phyll and form O2 and carbohydrates [1]. It is worth to utilize the solar energy for various energyconsuming processes, since it is clean, sustainable and abundant resource. Artificial

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

photosynthesis is a process in which fundamental scientific principles of natural photosynthe‐ sis are applied to design a solar energy conversion to make important chemicals by using manmadematerials.Manyapproachesarereported.Oneofthesuccessfulreportsprovidesanoutline for solar energy storage in fuels [2]. Another important approach is finding a new route for the chemical production and synthesis by utilizing solar energy, which is an energy-decisive industrial process. The method to synthesize organic chemical by photochemical process was first reported by Giacomo Ciamician in 1912 [3]. Presently, photochemistry is a well-devel‐ oped field of chemistry and the majority of the experiments use direct excitation of molecules by UV light [4]. To activate the photoreaction under visible light, sensitizers are applied, which transfer energy or an electron from the excited state to the molecule to be converted. Various homogeneous sensitizers are successfully used for various organic transformations [5]. The homogeneous sensitizers are substituted by heterogeneous photosensitizers using photocata‐ lytic process and which are easily separable and therefore recycled. In 1972, Fujishima and HondareportedaphotocatalyticprocessusingTiO2 semiconductoroxidee1ectrodestogenerate hydrogen from water [6]. Semiconductors can act as photocatalysts for light-induced chemi‐ cal transformations because of their unique electronic structure, which is characterized by a filledvalencebandandanemptyconductionband.Whenaphotonwithanenergyofhνmatches or exceeds the band gap energy (Eg) of the semiconductor (SC), an electron in the valence band (VB) is promoted to the conduction band (CB), leaving a positive hole (h+ ) in VB. The photoexcitation can be written as [7]:

$$\text{SC} + h\nu \rightarrow \text{SC} \left( h^{+} \right)\_{\left( \text{v} b \right)} + \text{SC} \left( e^{-} \right)\_{\left( c b \right)} \tag{1}$$

Where SC is semiconductor, vb and cb represent the valance band and the conduction band, respectively. The reactive species, h+ and e<sup>−</sup> are powerful oxidizing and reducing agents, respectively. Subsequently, various oxidizing species such as •OH , O2 •− , various forms of active oxygen species, such as HO2, H2O2 and O, are produced [8,9].

The photo-excitation process over semiconductor photocatalyst is presented in **Figure 1**.

**Figure 1** Semiconductor photocatalysed reaction.

Different semiconductors (e.g., TiO2, ZnO, α-Fe2O3 and WO3) are considered for their potential use as photocatalysts. In early 1980s, great effort was placed on organic synthesis by semicon‐ ductor photocatalysis [10]. Photocatalysis in synthetic route has attracted many researchers, because this method presents a greener approach to organic synthesis [11,12]. Recent studies have revealed that highly selective redox reactions could be achieved by visible light irradia‐ tion. The studies employed in photocatalytic organic transformation includes, oxidation, reduction, carbon-carbon and carbon-hetero atom coupling, cyclization, isomerization, etc. This chapter deals with various studies performed in oxidation, carbon-carbon and carbonheteroatom coupling, cyclization by UV and visible light-induced photocatalysis.

In photocatalytic process, photo-oxidation is the most studied because the VB edge in most of the semiconductor catalysts have more positive than the oxidation potential of the functional group in the organic compounds. The oxidation reactions are mainly focused on the oxidation of alcohols, amines, cyclohexane and aromatic alkanes. The conversion and product selectivity could be controlled by tuning the reaction conditions, such as nature of solvent, excitation wavelength of the light, interface engineering such as surface modification to change the adsorption mode or electron transfer pathway.


**6.1. Ethical principles and prenatal counseling**

*Genetic counseling.* A clinical genetic consultation provided by a geneticist with practice in ART is required to the couples before starting PGD treatment. Its purpose is to confirm the genetic diagnosis, to evaluate the reproductive status of the couple, and to provide information about the disease, mode of inheritance, recurrence risk, genetic testing, and reproductive

Genetic counseling by a qualified geneticist or a certified genetic counselor is recommended to the couples to receive support and appropriate information in a nondirective manner and with no pressure, allowing them to make the best choice. Family history, reason for PGD, what is PGD, alternative reproductive options and side effects of treatment, the limitations of testing, success rates (about 30%), and possible outcome options should be discussed, includ-

Also, a multiple birth should be considered when ART is used. Thus, the couple should understand and consider the physical, psychological, and financial impact of treatment [31]. An important part of genetic counseling is to establish the reason for choosing PGD. In most cases, the couples choose PGD to avoid termination of pregnancy due to a genetic disease or to know earliest that the pregnancy is unaffected by a specific genetic abnormality [17]. Other reasons for PGD include a previously affected child or a loss of a child, recurrent abortions, or infertility. When parents are carriers for a recessive disorder, more embryos may be carriers for a mutant allele. The couple must be informed about the genetic status of the embryos and in the absence of a clinical feature in carriers, these can be considered for transfer to increase the number of available embryos. The issue of genetic testing of children for carrier status

should be discussed prior to offering prenatal diagnosis to confirm the PGD result.

risk of losing the pregnancy, and many of them may refuse the confirmatory test [29].

Sex selection is not allowed by law in many countries, while in others, it is allowed. Except some recessive X-linked disorders where females may have a mild phenotype, in these cases, the female embryos should be excluded for transfer, and the parents should be able to choose

After implantation, a new contact with a geneticist is required. Occasionally, when PGD is used, a misdiagnosis can occur; therefore, prenatal diagnosis should be offered. Prenatal diagnosis requires an invasive testing (chorionic villus sampling and amniocentesis) associated with the

The postnatal confirmatory diagnosis from blood is in contrast to recommendations for testing in childhood, which specify that unless there are clinical benefits to testing minors, testing for carrier or late disease conditions should be delayed until the child is old enough to understand the implications and be part of the decision making. In most cases, a successful PGD cycle will result in an ongoing pregnancy and a healthy live born infant. However, a

Biomedical ethics is based on applying various principles in order to create a framework of moral analysis that allows the practitioner to make an optimal decision in agreement with the

options, including PGD [38].

460 Congenital Anomalies - From the Embryo to the Neonate

ing an unsuccessful cycle [29, 30].

not to know the sex of their embryos.

follow-up after birth is recommended.

patients' wishes/needs and their point of view.

**6. Ethical considerations**

In order to improve medical practice in medical genetics and implicitly in prenatal genetic diagnosis, a set of essential ethical principles was developed to support a clinical decision [32, 35]:

Prenatal diagnosis (PD), and here we will only refer to invasive PD, involves a genetic test that allows the diagnosis of a fetus with a serious genetic disorder (and there is an issue of what "serious" means in the opinion of specialists), followed by communication of the data to parents. The purpose of prenatal genetic testing is exclusively medical and testing criteria should be clearly established [34].

When PD is recommended, the couple will be informed, regardless of their perspective on abortion because sometimes it can be useful for psychological and medical training for the birth of a child with a congenital anomaly [34]. However, PD is a voluntary decision of the couple who will decide if the suspected condition requires diagnosis testing or termination of the pregnancy.

In conclusion, ethical aspects surrounding PD are multiple and demanding for both the physician and parents, but using the qualified knowledge of a professional, exposed with much tact and patience, the couple will correctly understand the implications of the problem and their possible solutions/the lack of solutions and will take the best decision based on these

Prenatal Genetic Counseling in Congenital Anomalies http://dx.doi.org/10.5772/intechopen.74394 463

Mihaela Amelia Dobrescu\*, Florin Burada\*, Mihai Gabriel Cucu, Anca Lelia Riza,

\*Address all correspondence to<EMAIL_ADDRESS>and

of Medicine and Pharmacy of Craiova, Craiova, Romania

International. 2010;**107**(48):857-62

books for an open world

Biology. 2015;**868**:1-21

Gratiela Chelu, Razvan Mihail Plesea, Adela Cucu, Alina Liliana Cimpoeru and Mihai Ioana

Medical Genetics Regional Center (CRGM), Dolj, Human Genomics Laboratory, University

[1] Covic Mircea SD, Ionel S. Genetica Medicala. 2 ed. Romania, Iasi: Polirom; 2011.

[2] Fonda Allen J, Stoll K, Bernhardt BA. Pre- and post-test genetic counseling for chromosomal and Mendelian disorders. Seminars in Perinatology. 2016 Feb;**40**(1):44-55

[3] Handbook of Genetic Counseling/Trisomy 18—Wikibooks, open books for an open

[4] Wieacker P, Steinhard J. The Prenatal Diagnosis of Genetic Diseases. Deutsches Ärzteblatt

[5] Verma IC, Puri RD. Global burden of genetic disease and the role of genetic screening.

[6] Handbook of Genetic Counseling/Trisomy 13—Advanced Maternal Age—Occupational

[7] Handbook of Genetic Counseling/Down Syndrome—Trisomy 21-1—Wikibooks, open

[8] Ioannou D, Tempest HG. Meiotic nondisjunction: Insights into the origin and significance of aneuploidy in human spermatozoa. Advances in Experimental Medicine and

[9] Griffin DK. The incidence, origin, and etiology of aneuploidy. In: Jeon KW, editor.

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Exposures—Wikibooks, open books for an open world

aspects and according to their own convictions.

**Author details**

**References**

pp. 515-523

world

<EMAIL_ADDRESS>
The distinctiveness of PD consists in this one-sided decision of the pregnant woman whose sentence affects both herself and the unborn child; if a woman is able to make an independent and well-considered decision, she must have the necessary knowledge to act in the context that PD does not only give information about a potential termination of a pregnancy but also it provides information that will prepare the parents for the birth of an affected child.

For this purpose, pretesting counseling is vital, and it will determine not only the risk of the fetus being affected, but also the chances of it being normal, it will inform about the conditions that can be diagnosed and their consequences not only on the fetus but also on the care/ treatment options. Furthermore, it will also provide counseling regarding the limits of the test, the possibility of an irrelevant or unexpected result, and the couple's options after testing.

If a PD is established, the physician should discuss with the pregnant woman about all the possible aspects of the clinical features, including the heterogeneity of the clinical manifestations. The informed choice of the pregnant woman/couple in the diagnosis of a fetus with congenital malformations will be respected and protected without prejudice, giving importance and priority to the family and sociocultural background in which the couple and the future malformed child will spend their lives.

In the case of PD without medical indication, when the testing is only based on pregnancy/ couple's anxiety, it will be done but with a low priority in allocating resources compared to PD associated with medical reasons. The practice of PD testing with the intention of selecting the child's sex (except for X-linked diseases) is not permitted, as well as the testing of paternity (excepting the pregnancy after an incest or rape) [34].

Particularly, the evolution of technology with the implementation of NGS in PD complicates the ethical aspects because, although genetic diagnosis has been improved, the method has some limitations, some of them common with those of the usual methods of PD [35]:

In conclusion, ethical aspects surrounding PD are multiple and demanding for both the physician and parents, but using the qualified knowledge of a professional, exposed with much tact and patience, the couple will correctly understand the implications of the problem and their possible solutions/the lack of solutions and will take the best decision based on these aspects and according to their own convictions.